Pensy RA

Fracture of the distal radius is the wrist injury most often encountered by orthopedic and hand surgeons.¹ The number of fractures of the distal radius in the United States was estimated to be 640,000 in 2001, and the incidence is increasing.^2,3 Recent evidence has shown a substantial increase in treating these fractures with internal rather than closed fixation, even in the elderly.⁴

Treatment of complex intra-articular fractures of the distal radius requires an accurate diagnosis of the fracture pattern and a thoughtful approach to fixation. Although a majority of the fractures that meet the operative criteria are now treated with various anterior locked-plating techniques with good results, a subset requires more technically demanding fixation approaches, including fragment-specific approaches, dorsal and palmar plating, and combined internal and external fixation.

The sustentaculum lunatum, as we have named the palmar lunate facet, deserves specific attention because of its importance in load transmission across the radiocarpal joint and its key role in restoring the anatomy of the palmar distal radial metaphysis during internal fixation. This fragment in comminuted fractures was first ascribed special importance by Melone⁵ in his description of common fracture patterns. In the present article, we describe the anatomical characteristics of the sustentaculum lunatum and the clinical relevance of this fragment to management of fractures of the distal radius.

Classification

A variety of classification systems have been proposed to characterize and guide treatment of fractures of the distal radius. The earliest descriptions of fracture patterns were presented by Castaing⁶ and Frykman⁷ in the 1960s. The Frykman classification historically has been popular but is limited in accuracy in its characterization of fragments and their displacement and is limited in its ability to guide treatment. The classification system proposed by Melone and colleagues^5,8-10 was the first to truly describe fracture of the distal radius fragments in a relevant manner, including their characteristic “4 parts” (Figure 1). The authors emphasized the importance of the “medial complex” as the cornerstone of the radiocarpal and radioulnar joints.

The classification system developed by Müller and colleagues,¹¹ which was adopted by the AO (Arbeitsgemeinschaft für Osteosynthesefragen), might be the most descriptive and informative system, and it is widely used to conduct research and direct treatment. This system classifies fractures into A (extra-articular), B (partial articular), and C (complete articular) types and subclassifies them according to fracture location and comminution. These classifications, along with a conceptualization of the distal forearm as a 3-column structure involving the radial, ulnar, and intermediate columns (including the lunate facet), as proposed by Peine and colleagues,¹² gave us a framework for approaching fixation of fractures of the distal radius.

Etymology and Definition

Sustentaculum, from the Latin sustinere, “to support, check, or put off,” and taculum, “receptacle or holding space,” is a fitting description of the most distal portion of the palmar lunate facet, as it supports and holds the carpus, and specifically the lunate, on the radial articular surface. This portion is analogous to the sustentaculum tali, the named portion of the calcaneus that supports and articulates with the middle calcaneal articular surface of the talus¹³ and provides a reliable fragment for internal fixation of the calcaneus.

Anatomical and Biomechanical Considerations

The distal radial articular surface is composed of distinct scaphoid and lunate facets that articulate with their respective carpal bones. Several studies have characterized the anatomy of the distal radius.^14-17 Linscheid¹⁴ found that the lunate and scaphoid facets account for 46% and 43% of the contact area across the radiocarpal joint, respectively; this has been corroborated by others.¹⁵ A biomechanical study by Genda and Horii¹⁸ showed that the majority of stress across the wrist joint was concentrated at the palmar side of the distal radius in the neutral position. Although it is recognized that the scaphoid facet bears most of the load across the wrist in the neutral wrist position, most activities of daily living place the wrist in a slightly extended and ulnarly deviated position. This position results in a shift of the majority of load to the radiolunar articulation, constituting 53% of total force transmission.¹⁸ Subchondral bone density analyses have supported this lunate-predominant loading pattern across the radiocarpal articulation in most people.¹⁹ This loading pattern is also supported by the observation that failure of fixation and carpal subluxation generally occurs at the radiolunate articulation.

The palmar lip of the distal radius traditionally has been depicted and conceptualized as a flat extension of the metaphysis, leading to the development of implants that are not ideally designed for capturing this area in the fracture setting. A 3-dimensional (3-D) computed tomography (CT) study of the distal radii of healthy volunteers, conducted by Andermahr and colleagues,²⁰ showed that the contour of the palmar lunate facet projects from the palmar cortex of the radius by 3 mm on average and is about 19 mm in width (radial to ulnar dimension) (Figures 2A-2C). In the axial plane, the anterior cortex of the distal radius slopes in a palmar direction, from radial to ulnar. This presents a challenge in attempts to support the entire surface (scaphoid and lunate facets) with a single palmar implant.^20-25

A study conducted by Harness and colleagues²⁴ showed that the majority of palmar shear fractures are composed of multiple fragments of the lunar articular facet. Anatomical studies of the distal radiocarpal articulation have also described the ligamentous attachments to the sustentaculum lunatum.²⁶ The short radiolunate ligament, which originates from this fragment and inserts onto the lunate, provides stability to the carpus and, if not adequately fixed, leads to an incompetent restraint to palmar carpal translation. Isolated injuries of the short radiolunate ligament or fractures of the palmar lunate facet have been shown to result in palmar carpal translation.^27,28 In addition, attachments of the palmar radioulnar ligament and other more ulnar radiocarpal ligaments act as deforming forces on the palmar lunate facet.^24,26

Fracture Pattern Recognition

Although the AO type B palmar shear fracture pattern, also known as the Barton fracture, has classically been recognized as the fracture involving the palmar lunate facet and requiring special attention, many complete articular fractures feature involvement and fragmentation of this portion of the distal radius (Figures 3A-3F).²⁹ In highly comminuted complete articular and palmar shear fracture patterns, the morphology of the sustentaculum lunatum should be appreciated, and its adequate fixation to the radial metaphysis ensured, to prevent loss of reduction.

Visualization of the palmar lunate facet as a distinct fragment might be difficult in cases of highly comminuted fracture patterns. Standard CT or more recently described 3-D CT techniques with subtraction of the carpus might facilitate appreciation of this fragment for preoperative planning of approach and fixation.^29,30 Our institutional protocol involves obtaining preoperative traction radiographs of every fracture of the distal radius. These radiographs have reduced the need for CT in understanding the fracture pattern and aid in decision making.³¹

Besides appreciating the existence of the sustentaculum lunatum fragment, we should recognize that some injury patterns that split the lunate facet into unstable dorsal and palmar fragments might necessitate a separate dorsal approach to reduce and fix the dorsal lunate fragment. Traction radiographs can be especially useful in recognizing these patterns (a V sign is present) (Figures 4A, 4B).

Open Fractures

Highly comminuted fractures of the distal radius presenting with displaced lunate facet fragments can have high-energy mechanisms of injury. Although open fractures of the distal radius are associated with lower risk for infection (compared with open fractures of other long bones), they deserve special attention because of associated tendon and neurovascular injuries. Few studies have specifically assessed open fractures of the distal radius.^32-35 Only the study by Rozental and Blazar³⁴ listed associated injuries at the wrist level. The authors identified 4 patients (out of 18) with concomitant flexor tendon or neurovascular injuries that included radial or ulnar artery injury. In our experience, many open fractures of the distal radius are caused by an inside-out mechanism and present with an open wound either over the ulnar styloid or in the area of the ulnar side of the palmar radial metaphysis corresponding to the metaphyseal spike that mates with the sustentaculum lunatum (Figures 5A, 5B). Given these findings, we approach this intermediate column with particular care in cases of open fracture, paying attention to important structures (flexors, neurovascular) and looking for contamination from the environment into the fracture.

Fixation Techniques

The approach to fixation of partial articular palmar shear fractures is fairly straightforward. Buttress plate fixation has been well described and has had reliably good results.³⁶ However, in very distal fracture patterns and in cases in which the palmar lunate facet is fragmented as part of a complete articular fracture, a fragment-specific approach to fixation with or without spanning external fixation often is necessary.³⁷ The unrecognized sustentaculum lunatum fragment in comminuted complete articular fractures can lead to inadequate fixation constructs, resulting in loss of reduction and carpal subluxation in a palmar direction.^24,34,38

Our surgical approach uses the standard anterior interval between the radial artery and the flexor carpi radialis, as described by Henry.³⁹ The flexor pollicis longus is retracted ulnarly, revealing the pronator quadratus. We then reflect the pronator quadratus from the distal radial metaphysis until the most proximal and ulnar extent of the fracture is easily visualized. The palmar ulnar metaphyseal cortex that mates with the displaced sustentaculum lunatum is, in our experience, often the least comminuted portion of the metaphysis, thus providing a cortical key for restoration of height and alignment (Figures 5A, 5B). At our institution, fixation typically is achieved by contouring miniplates (1.3 or 1.5 mm) to capture and buttress the sustentaculum lunatum (Figures 6A, 6B). In our experience, the screw lengths in the most distal fixed-angle constructs at the palmar lip are limited to 6 mm or less to avoid penetration of the articular surface, though this has not been previously reported in the literature. After restoring the length and tilt of this intermediate column of the distal radius, we proceed with “rebuilding” the remainder of the fragments to our stabilized initial construct.

Various authors^40-43 have described alternative fixation methods for the palmar lunate facet fragment. Jupiter and Marent-Huber⁴² described 2.4-mm locked-plate fixation with either a standard palmar plate or T- or L-plates for cases in which the palmar lip fragment is very distal and small. In fact, some newer anatomical distal radius implants include features designed to target these fragments (Figures 7A, 7B). An alternative fixation method involves use of a 26-gauge stainless steel wire passed through drill holes in the metaphysis 1 cm proximal to the fracture and then passed through the palmar capsule just distal to the fragment and secured in figure-8 fashion while the fragment is manually held reduced.⁴¹ Still others have recommended limited internal fixation of the sustentaculum lunatum through an ulna-sided palmar approach to the distal radius (between the ulnar neurovascular bundle and the flexor tendons) combined with external fixation to restore length and palmar tilt in highly comminuted fractures.^40,43

A method involving arthroscopically assisted reduction and fixation of the lunate facet has also been described, though this procedure is technically demanding and has limited indications.⁴⁴ It uses a Freer elevator passed through the standard 3-4 portal after initial visualization and evacuation of hematoma. The Freer elevator is used to disimpact the sustentaculum lunatum and to elevate it from its depressed position. With the dorsal lunate facet left displaced to facilitate access to the palmar fragment, a nerve hook retractor is used to reduce the palmar facet to the radial styloid, and Kirschner wires are used to achieve interfragmentary fixation. The dorsal lunate fragment is then pieced back to the articular segment, and the entire construct is fixed to the radial metaphysis with additional Kirschner wires.

Discussion

Given the increasing incidence of fractures of the distal radius, internal fixation of these injuries will continue to be relevant. American Academy of Orthopaedic Surgeons guidelines recommend operative fixation for fractures with postreduction radial shortening of more than 3 mm, dorsal tilt of more than 10°, or intra-articular displacement or step-off of more than 2 mm.⁴⁵ Dr. Eglseder and Dr. Pensy indicate operative treatment of any incongruity of more than 2 mm in a young, active adult with a fracture of the distal radius. For the multifragmentary distal radius being treated operatively, attempts are made to achieve reduction more accurate than this, but formal dorsal exposure or direct visualization of the joint surface via dorsal capsulotomy is carefully chosen based on age, activity level, and bone quality. Recent high-level evidence⁴⁶ showed that closed treatment of unstable fractures of the distal radius results in good outcomes in the elderly. However, it is important to note that fractures displaced in a palmar direction and palmar shear patterns were excluded from that work. It is widely accepted that palmar carpal translation should be addressed with internal fixation, and specific attention must therefore be paid to the lunate facet as the cornerstone of the distal radius. Furthermore, high-energy comminuted fractures in young patients still necessitate internal fixation of fragments to restore alignment and articular congruity.

Conclusion

The importance of the palmar lunate facet in providing support and restraint to palmar carpal translation and the key role of this facet in restoring the anatomy of the distal radius have been known. This fragment deserves special attention because failure to adequately stabilize it results in loss of fixation and carpal subluxation. Various approaches and fixation techniques have been recommended, including the method we prefer and have described here. Our newly proposed term, sustentaculum lunatum, our review of its structure and function, and our descriptions of fixation techniques are intended to promote awareness of this fragment in the treatment of fractures of the distal radius.

Fracture of the distal radius is the wrist injury most often encountered by orthopedic and hand surgeons.¹ The number of fractures of the distal radius in the United States was estimated to be 640,000 in 2001, and the incidence is increasing.^2,3 Recent evidence has shown a substantial increase in treating these fractures with internal rather than closed fixation, even in the elderly.⁴

Treatment of complex intra-articular fractures of the distal radius requires an accurate diagnosis of the fracture pattern and a thoughtful approach to fixation. Although a majority of the fractures that meet the operative criteria are now treated with various anterior locked-plating techniques with good results, a subset requires more technically demanding fixation approaches, including fragment-specific approaches, dorsal and palmar plating, and combined internal and external fixation.

The sustentaculum lunatum, as we have named the palmar lunate facet, deserves specific attention because of its importance in load transmission across the radiocarpal joint and its key role in restoring the anatomy of the palmar distal radial metaphysis during internal fixation. This fragment in comminuted fractures was first ascribed special importance by Melone⁵ in his description of common fracture patterns. In the present article, we describe the anatomical characteristics of the sustentaculum lunatum and the clinical relevance of this fragment to management of fractures of the distal radius.

Classification

A variety of classification systems have been proposed to characterize and guide treatment of fractures of the distal radius. The earliest descriptions of fracture patterns were presented by Castaing⁶ and Frykman⁷ in the 1960s. The Frykman classification historically has been popular but is limited in accuracy in its characterization of fragments and their displacement and is limited in its ability to guide treatment. The classification system proposed by Melone and colleagues^5,8-10 was the first to truly describe fracture of the distal radius fragments in a relevant manner, including their characteristic “4 parts” (Figure 1). The authors emphasized the importance of the “medial complex” as the cornerstone of the radiocarpal and radioulnar joints.

The classification system developed by Müller and colleagues,¹¹ which was adopted by the AO (Arbeitsgemeinschaft für Osteosynthesefragen), might be the most descriptive and informative system, and it is widely used to conduct research and direct treatment. This system classifies fractures into A (extra-articular), B (partial articular), and C (complete articular) types and subclassifies them according to fracture location and comminution. These classifications, along with a conceptualization of the distal forearm as a 3-column structure involving the radial, ulnar, and intermediate columns (including the lunate facet), as proposed by Peine and colleagues,¹² gave us a framework for approaching fixation of fractures of the distal radius.

Etymology and Definition

Sustentaculum, from the Latin sustinere, “to support, check, or put off,” and taculum, “receptacle or holding space,” is a fitting description of the most distal portion of the palmar lunate facet, as it supports and holds the carpus, and specifically the lunate, on the radial articular surface. This portion is analogous to the sustentaculum tali, the named portion of the calcaneus that supports and articulates with the middle calcaneal articular surface of the talus¹³ and provides a reliable fragment for internal fixation of the calcaneus.

Anatomical and Biomechanical Considerations

The distal radial articular surface is composed of distinct scaphoid and lunate facets that articulate with their respective carpal bones. Several studies have characterized the anatomy of the distal radius.^14-17 Linscheid¹⁴ found that the lunate and scaphoid facets account for 46% and 43% of the contact area across the radiocarpal joint, respectively; this has been corroborated by others.¹⁵ A biomechanical study by Genda and Horii¹⁸ showed that the majority of stress across the wrist joint was concentrated at the palmar side of the distal radius in the neutral position. Although it is recognized that the scaphoid facet bears most of the load across the wrist in the neutral wrist position, most activities of daily living place the wrist in a slightly extended and ulnarly deviated position. This position results in a shift of the majority of load to the radiolunar articulation, constituting 53% of total force transmission.¹⁸ Subchondral bone density analyses have supported this lunate-predominant loading pattern across the radiocarpal articulation in most people.¹⁹ This loading pattern is also supported by the observation that failure of fixation and carpal subluxation generally occurs at the radiolunate articulation.

The palmar lip of the distal radius traditionally has been depicted and conceptualized as a flat extension of the metaphysis, leading to the development of implants that are not ideally designed for capturing this area in the fracture setting. A 3-dimensional (3-D) computed tomography (CT) study of the distal radii of healthy volunteers, conducted by Andermahr and colleagues,²⁰ showed that the contour of the palmar lunate facet projects from the palmar cortex of the radius by 3 mm on average and is about 19 mm in width (radial to ulnar dimension) (Figures 2A-2C). In the axial plane, the anterior cortex of the distal radius slopes in a palmar direction, from radial to ulnar. This presents a challenge in attempts to support the entire surface (scaphoid and lunate facets) with a single palmar implant.^20-25

A study conducted by Harness and colleagues²⁴ showed that the majority of palmar shear fractures are composed of multiple fragments of the lunar articular facet. Anatomical studies of the distal radiocarpal articulation have also described the ligamentous attachments to the sustentaculum lunatum.²⁶ The short radiolunate ligament, which originates from this fragment and inserts onto the lunate, provides stability to the carpus and, if not adequately fixed, leads to an incompetent restraint to palmar carpal translation. Isolated injuries of the short radiolunate ligament or fractures of the palmar lunate facet have been shown to result in palmar carpal translation.^27,28 In addition, attachments of the palmar radioulnar ligament and other more ulnar radiocarpal ligaments act as deforming forces on the palmar lunate facet.^24,26

Fracture Pattern Recognition

Although the AO type B palmar shear fracture pattern, also known as the Barton fracture, has classically been recognized as the fracture involving the palmar lunate facet and requiring special attention, many complete articular fractures feature involvement and fragmentation of this portion of the distal radius (Figures 3A-3F).²⁹ In highly comminuted complete articular and palmar shear fracture patterns, the morphology of the sustentaculum lunatum should be appreciated, and its adequate fixation to the radial metaphysis ensured, to prevent loss of reduction.

Visualization of the palmar lunate facet as a distinct fragment might be difficult in cases of highly comminuted fracture patterns. Standard CT or more recently described 3-D CT techniques with subtraction of the carpus might facilitate appreciation of this fragment for preoperative planning of approach and fixation.^29,30 Our institutional protocol involves obtaining preoperative traction radiographs of every fracture of the distal radius. These radiographs have reduced the need for CT in understanding the fracture pattern and aid in decision making.³¹

Besides appreciating the existence of the sustentaculum lunatum fragment, we should recognize that some injury patterns that split the lunate facet into unstable dorsal and palmar fragments might necessitate a separate dorsal approach to reduce and fix the dorsal lunate fragment. Traction radiographs can be especially useful in recognizing these patterns (a V sign is present) (Figures 4A, 4B).

Open Fractures

Highly comminuted fractures of the distal radius presenting with displaced lunate facet fragments can have high-energy mechanisms of injury. Although open fractures of the distal radius are associated with lower risk for infection (compared with open fractures of other long bones), they deserve special attention because of associated tendon and neurovascular injuries. Few studies have specifically assessed open fractures of the distal radius.^32-35 Only the study by Rozental and Blazar³⁴ listed associated injuries at the wrist level. The authors identified 4 patients (out of 18) with concomitant flexor tendon or neurovascular injuries that included radial or ulnar artery injury. In our experience, many open fractures of the distal radius are caused by an inside-out mechanism and present with an open wound either over the ulnar styloid or in the area of the ulnar side of the palmar radial metaphysis corresponding to the metaphyseal spike that mates with the sustentaculum lunatum (Figures 5A, 5B). Given these findings, we approach this intermediate column with particular care in cases of open fracture, paying attention to important structures (flexors, neurovascular) and looking for contamination from the environment into the fracture.

Fixation Techniques

The approach to fixation of partial articular palmar shear fractures is fairly straightforward. Buttress plate fixation has been well described and has had reliably good results.³⁶ However, in very distal fracture patterns and in cases in which the palmar lunate facet is fragmented as part of a complete articular fracture, a fragment-specific approach to fixation with or without spanning external fixation often is necessary.³⁷ The unrecognized sustentaculum lunatum fragment in comminuted complete articular fractures can lead to inadequate fixation constructs, resulting in loss of reduction and carpal subluxation in a palmar direction.^24,34,38

Our surgical approach uses the standard anterior interval between the radial artery and the flexor carpi radialis, as described by Henry.³⁹ The flexor pollicis longus is retracted ulnarly, revealing the pronator quadratus. We then reflect the pronator quadratus from the distal radial metaphysis until the most proximal and ulnar extent of the fracture is easily visualized. The palmar ulnar metaphyseal cortex that mates with the displaced sustentaculum lunatum is, in our experience, often the least comminuted portion of the metaphysis, thus providing a cortical key for restoration of height and alignment (Figures 5A, 5B). At our institution, fixation typically is achieved by contouring miniplates (1.3 or 1.5 mm) to capture and buttress the sustentaculum lunatum (Figures 6A, 6B). In our experience, the screw lengths in the most distal fixed-angle constructs at the palmar lip are limited to 6 mm or less to avoid penetration of the articular surface, though this has not been previously reported in the literature. After restoring the length and tilt of this intermediate column of the distal radius, we proceed with “rebuilding” the remainder of the fragments to our stabilized initial construct.

Various authors^40-43 have described alternative fixation methods for the palmar lunate facet fragment. Jupiter and Marent-Huber⁴² described 2.4-mm locked-plate fixation with either a standard palmar plate or T- or L-plates for cases in which the palmar lip fragment is very distal and small. In fact, some newer anatomical distal radius implants include features designed to target these fragments (Figures 7A, 7B). An alternative fixation method involves use of a 26-gauge stainless steel wire passed through drill holes in the metaphysis 1 cm proximal to the fracture and then passed through the palmar capsule just distal to the fragment and secured in figure-8 fashion while the fragment is manually held reduced.⁴¹ Still others have recommended limited internal fixation of the sustentaculum lunatum through an ulna-sided palmar approach to the distal radius (between the ulnar neurovascular bundle and the flexor tendons) combined with external fixation to restore length and palmar tilt in highly comminuted fractures.^40,43

A method involving arthroscopically assisted reduction and fixation of the lunate facet has also been described, though this procedure is technically demanding and has limited indications.⁴⁴ It uses a Freer elevator passed through the standard 3-4 portal after initial visualization and evacuation of hematoma. The Freer elevator is used to disimpact the sustentaculum lunatum and to elevate it from its depressed position. With the dorsal lunate facet left displaced to facilitate access to the palmar fragment, a nerve hook retractor is used to reduce the palmar facet to the radial styloid, and Kirschner wires are used to achieve interfragmentary fixation. The dorsal lunate fragment is then pieced back to the articular segment, and the entire construct is fixed to the radial metaphysis with additional Kirschner wires.

Discussion

Given the increasing incidence of fractures of the distal radius, internal fixation of these injuries will continue to be relevant. American Academy of Orthopaedic Surgeons guidelines recommend operative fixation for fractures with postreduction radial shortening of more than 3 mm, dorsal tilt of more than 10°, or intra-articular displacement or step-off of more than 2 mm.⁴⁵ Dr. Eglseder and Dr. Pensy indicate operative treatment of any incongruity of more than 2 mm in a young, active adult with a fracture of the distal radius. For the multifragmentary distal radius being treated operatively, attempts are made to achieve reduction more accurate than this, but formal dorsal exposure or direct visualization of the joint surface via dorsal capsulotomy is carefully chosen based on age, activity level, and bone quality. Recent high-level evidence⁴⁶ showed that closed treatment of unstable fractures of the distal radius results in good outcomes in the elderly. However, it is important to note that fractures displaced in a palmar direction and palmar shear patterns were excluded from that work. It is widely accepted that palmar carpal translation should be addressed with internal fixation, and specific attention must therefore be paid to the lunate facet as the cornerstone of the distal radius. Furthermore, high-energy comminuted fractures in young patients still necessitate internal fixation of fragments to restore alignment and articular congruity.

Conclusion

The importance of the palmar lunate facet in providing support and restraint to palmar carpal translation and the key role of this facet in restoring the anatomy of the distal radius have been known. This fragment deserves special attention because failure to adequately stabilize it results in loss of fixation and carpal subluxation. Various approaches and fixation techniques have been recommended, including the method we prefer and have described here. Our newly proposed term, sustentaculum lunatum, our review of its structure and function, and our descriptions of fixation techniques are intended to promote awareness of this fragment in the treatment of fractures of the distal radius.

Fracture of the distal radius is the wrist injury most often encountered by orthopedic and hand surgeons.¹ The number of fractures of the distal radius in the United States was estimated to be 640,000 in 2001, and the incidence is increasing.^2,3 Recent evidence has shown a substantial increase in treating these fractures with internal rather than closed fixation, even in the elderly.⁴

Treatment of complex intra-articular fractures of the distal radius requires an accurate diagnosis of the fracture pattern and a thoughtful approach to fixation. Although a majority of the fractures that meet the operative criteria are now treated with various anterior locked-plating techniques with good results, a subset requires more technically demanding fixation approaches, including fragment-specific approaches, dorsal and palmar plating, and combined internal and external fixation.

The sustentaculum lunatum, as we have named the palmar lunate facet, deserves specific attention because of its importance in load transmission across the radiocarpal joint and its key role in restoring the anatomy of the palmar distal radial metaphysis during internal fixation. This fragment in comminuted fractures was first ascribed special importance by Melone⁵ in his description of common fracture patterns. In the present article, we describe the anatomical characteristics of the sustentaculum lunatum and the clinical relevance of this fragment to management of fractures of the distal radius.

Classification

A variety of classification systems have been proposed to characterize and guide treatment of fractures of the distal radius. The earliest descriptions of fracture patterns were presented by Castaing⁶ and Frykman⁷ in the 1960s. The Frykman classification historically has been popular but is limited in accuracy in its characterization of fragments and their displacement and is limited in its ability to guide treatment. The classification system proposed by Melone and colleagues^5,8-10 was the first to truly describe fracture of the distal radius fragments in a relevant manner, including their characteristic “4 parts” (Figure 1). The authors emphasized the importance of the “medial complex” as the cornerstone of the radiocarpal and radioulnar joints.

The classification system developed by Müller and colleagues,¹¹ which was adopted by the AO (Arbeitsgemeinschaft für Osteosynthesefragen), might be the most descriptive and informative system, and it is widely used to conduct research and direct treatment. This system classifies fractures into A (extra-articular), B (partial articular), and C (complete articular) types and subclassifies them according to fracture location and comminution. These classifications, along with a conceptualization of the distal forearm as a 3-column structure involving the radial, ulnar, and intermediate columns (including the lunate facet), as proposed by Peine and colleagues,¹² gave us a framework for approaching fixation of fractures of the distal radius.

Etymology and Definition

Sustentaculum, from the Latin sustinere, “to support, check, or put off,” and taculum, “receptacle or holding space,” is a fitting description of the most distal portion of the palmar lunate facet, as it supports and holds the carpus, and specifically the lunate, on the radial articular surface. This portion is analogous to the sustentaculum tali, the named portion of the calcaneus that supports and articulates with the middle calcaneal articular surface of the talus¹³ and provides a reliable fragment for internal fixation of the calcaneus.

Anatomical and Biomechanical Considerations

The distal radial articular surface is composed of distinct scaphoid and lunate facets that articulate with their respective carpal bones. Several studies have characterized the anatomy of the distal radius.^14-17 Linscheid¹⁴ found that the lunate and scaphoid facets account for 46% and 43% of the contact area across the radiocarpal joint, respectively; this has been corroborated by others.¹⁵ A biomechanical study by Genda and Horii¹⁸ showed that the majority of stress across the wrist joint was concentrated at the palmar side of the distal radius in the neutral position. Although it is recognized that the scaphoid facet bears most of the load across the wrist in the neutral wrist position, most activities of daily living place the wrist in a slightly extended and ulnarly deviated position. This position results in a shift of the majority of load to the radiolunar articulation, constituting 53% of total force transmission.¹⁸ Subchondral bone density analyses have supported this lunate-predominant loading pattern across the radiocarpal articulation in most people.¹⁹ This loading pattern is also supported by the observation that failure of fixation and carpal subluxation generally occurs at the radiolunate articulation.

The palmar lip of the distal radius traditionally has been depicted and conceptualized as a flat extension of the metaphysis, leading to the development of implants that are not ideally designed for capturing this area in the fracture setting. A 3-dimensional (3-D) computed tomography (CT) study of the distal radii of healthy volunteers, conducted by Andermahr and colleagues,²⁰ showed that the contour of the palmar lunate facet projects from the palmar cortex of the radius by 3 mm on average and is about 19 mm in width (radial to ulnar dimension) (Figures 2A-2C). In the axial plane, the anterior cortex of the distal radius slopes in a palmar direction, from radial to ulnar. This presents a challenge in attempts to support the entire surface (scaphoid and lunate facets) with a single palmar implant.^20-25

A study conducted by Harness and colleagues²⁴ showed that the majority of palmar shear fractures are composed of multiple fragments of the lunar articular facet. Anatomical studies of the distal radiocarpal articulation have also described the ligamentous attachments to the sustentaculum lunatum.²⁶ The short radiolunate ligament, which originates from this fragment and inserts onto the lunate, provides stability to the carpus and, if not adequately fixed, leads to an incompetent restraint to palmar carpal translation. Isolated injuries of the short radiolunate ligament or fractures of the palmar lunate facet have been shown to result in palmar carpal translation.^27,28 In addition, attachments of the palmar radioulnar ligament and other more ulnar radiocarpal ligaments act as deforming forces on the palmar lunate facet.^24,26

Fracture Pattern Recognition

Although the AO type B palmar shear fracture pattern, also known as the Barton fracture, has classically been recognized as the fracture involving the palmar lunate facet and requiring special attention, many complete articular fractures feature involvement and fragmentation of this portion of the distal radius (Figures 3A-3F).²⁹ In highly comminuted complete articular and palmar shear fracture patterns, the morphology of the sustentaculum lunatum should be appreciated, and its adequate fixation to the radial metaphysis ensured, to prevent loss of reduction.

Visualization of the palmar lunate facet as a distinct fragment might be difficult in cases of highly comminuted fracture patterns. Standard CT or more recently described 3-D CT techniques with subtraction of the carpus might facilitate appreciation of this fragment for preoperative planning of approach and fixation.^29,30 Our institutional protocol involves obtaining preoperative traction radiographs of every fracture of the distal radius. These radiographs have reduced the need for CT in understanding the fracture pattern and aid in decision making.³¹

Besides appreciating the existence of the sustentaculum lunatum fragment, we should recognize that some injury patterns that split the lunate facet into unstable dorsal and palmar fragments might necessitate a separate dorsal approach to reduce and fix the dorsal lunate fragment. Traction radiographs can be especially useful in recognizing these patterns (a V sign is present) (Figures 4A, 4B).

Open Fractures

Highly comminuted fractures of the distal radius presenting with displaced lunate facet fragments can have high-energy mechanisms of injury. Although open fractures of the distal radius are associated with lower risk for infection (compared with open fractures of other long bones), they deserve special attention because of associated tendon and neurovascular injuries. Few studies have specifically assessed open fractures of the distal radius.^32-35 Only the study by Rozental and Blazar³⁴ listed associated injuries at the wrist level. The authors identified 4 patients (out of 18) with concomitant flexor tendon or neurovascular injuries that included radial or ulnar artery injury. In our experience, many open fractures of the distal radius are caused by an inside-out mechanism and present with an open wound either over the ulnar styloid or in the area of the ulnar side of the palmar radial metaphysis corresponding to the metaphyseal spike that mates with the sustentaculum lunatum (Figures 5A, 5B). Given these findings, we approach this intermediate column with particular care in cases of open fracture, paying attention to important structures (flexors, neurovascular) and looking for contamination from the environment into the fracture.

Fixation Techniques

The approach to fixation of partial articular palmar shear fractures is fairly straightforward. Buttress plate fixation has been well described and has had reliably good results.³⁶ However, in very distal fracture patterns and in cases in which the palmar lunate facet is fragmented as part of a complete articular fracture, a fragment-specific approach to fixation with or without spanning external fixation often is necessary.³⁷ The unrecognized sustentaculum lunatum fragment in comminuted complete articular fractures can lead to inadequate fixation constructs, resulting in loss of reduction and carpal subluxation in a palmar direction.^24,34,38

Our surgical approach uses the standard anterior interval between the radial artery and the flexor carpi radialis, as described by Henry.³⁹ The flexor pollicis longus is retracted ulnarly, revealing the pronator quadratus. We then reflect the pronator quadratus from the distal radial metaphysis until the most proximal and ulnar extent of the fracture is easily visualized. The palmar ulnar metaphyseal cortex that mates with the displaced sustentaculum lunatum is, in our experience, often the least comminuted portion of the metaphysis, thus providing a cortical key for restoration of height and alignment (Figures 5A, 5B). At our institution, fixation typically is achieved by contouring miniplates (1.3 or 1.5 mm) to capture and buttress the sustentaculum lunatum (Figures 6A, 6B). In our experience, the screw lengths in the most distal fixed-angle constructs at the palmar lip are limited to 6 mm or less to avoid penetration of the articular surface, though this has not been previously reported in the literature. After restoring the length and tilt of this intermediate column of the distal radius, we proceed with “rebuilding” the remainder of the fragments to our stabilized initial construct.

Various authors^40-43 have described alternative fixation methods for the palmar lunate facet fragment. Jupiter and Marent-Huber⁴² described 2.4-mm locked-plate fixation with either a standard palmar plate or T- or L-plates for cases in which the palmar lip fragment is very distal and small. In fact, some newer anatomical distal radius implants include features designed to target these fragments (Figures 7A, 7B). An alternative fixation method involves use of a 26-gauge stainless steel wire passed through drill holes in the metaphysis 1 cm proximal to the fracture and then passed through the palmar capsule just distal to the fragment and secured in figure-8 fashion while the fragment is manually held reduced.⁴¹ Still others have recommended limited internal fixation of the sustentaculum lunatum through an ulna-sided palmar approach to the distal radius (between the ulnar neurovascular bundle and the flexor tendons) combined with external fixation to restore length and palmar tilt in highly comminuted fractures.^40,43

A method involving arthroscopically assisted reduction and fixation of the lunate facet has also been described, though this procedure is technically demanding and has limited indications.⁴⁴ It uses a Freer elevator passed through the standard 3-4 portal after initial visualization and evacuation of hematoma. The Freer elevator is used to disimpact the sustentaculum lunatum and to elevate it from its depressed position. With the dorsal lunate facet left displaced to facilitate access to the palmar fragment, a nerve hook retractor is used to reduce the palmar facet to the radial styloid, and Kirschner wires are used to achieve interfragmentary fixation. The dorsal lunate fragment is then pieced back to the articular segment, and the entire construct is fixed to the radial metaphysis with additional Kirschner wires.

Discussion

Given the increasing incidence of fractures of the distal radius, internal fixation of these injuries will continue to be relevant. American Academy of Orthopaedic Surgeons guidelines recommend operative fixation for fractures with postreduction radial shortening of more than 3 mm, dorsal tilt of more than 10°, or intra-articular displacement or step-off of more than 2 mm.⁴⁵ Dr. Eglseder and Dr. Pensy indicate operative treatment of any incongruity of more than 2 mm in a young, active adult with a fracture of the distal radius. For the multifragmentary distal radius being treated operatively, attempts are made to achieve reduction more accurate than this, but formal dorsal exposure or direct visualization of the joint surface via dorsal capsulotomy is carefully chosen based on age, activity level, and bone quality. Recent high-level evidence⁴⁶ showed that closed treatment of unstable fractures of the distal radius results in good outcomes in the elderly. However, it is important to note that fractures displaced in a palmar direction and palmar shear patterns were excluded from that work. It is widely accepted that palmar carpal translation should be addressed with internal fixation, and specific attention must therefore be paid to the lunate facet as the cornerstone of the distal radius. Furthermore, high-energy comminuted fractures in young patients still necessitate internal fixation of fragments to restore alignment and articular congruity.

Conclusion

The importance of the palmar lunate facet in providing support and restraint to palmar carpal translation and the key role of this facet in restoring the anatomy of the distal radius have been known. This fragment deserves special attention because failure to adequately stabilize it results in loss of fixation and carpal subluxation. Various approaches and fixation techniques have been recommended, including the method we prefer and have described here. Our newly proposed term, sustentaculum lunatum, our review of its structure and function, and our descriptions of fixation techniques are intended to promote awareness of this fragment in the treatment of fractures of the distal radius.

A few days after an incidental cat bite, a patient presented to the emergency department for treatment of poison sumac exposure. He was discharged with oral methylprednisolone for the dermatitis and returned 1 week later with symptoms, examination findings, and laboratory results consistent with sepsis and bilateral upper extremity necrotizing soft-tissue infections. After administering multiple irrigation and débridement procedures, hyperbaric oxygen treatments, and an antibiotic regimen, the patient’s status greatly improved. However, the patient returned 1 month later with a new sternoclavicular joint prominence that was associated with painful crepitus. Additionally, he noted that his wrists were gradually becoming more swollen and painful. Imaging studies showed a lytic destruction of the sternoclavicular joint and erosive changes throughout the carpus and radiocarpal joint bilaterally, consistent with osteomyelitis. The patient was treated with ertapenem for 6 weeks, and his polyarthropathy resolved. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 73-year-old, right-hand–dominant man with no notable medical history presented to the emergency department for treatment of poison sumac exposure, incidentally, a few days after being bitten by a cat on the bilateral distal upper extremities. He was prescribed a course of oral methylprednisolone for dermatitis. A week later, the patient returned to the emergency department with altered mental status, fevers, diaphoresis, lethargy, and polyarthralgia. At the time of presentation, the patient’s vital signs were labile, and he was found to have extensive bilateral upper extremity erythema, blistering, petechiae, purpuric lesions, and exquisite pain with passive range of motion of his fingers and wrists. His leukocyte count was 25.1 × 10⁹/L, and he had elevated C-reactive protein level and erythrocyte sedimentation rate of 150 mg/L and 120 mm/h, respectively. He was admitted for management of sepsis and presumed bilateral upper extremity necrotizing soft-tissue infection.

Broad-spectrum intravenous (IV) antibiotics (vancomycin, piperacillin, tazobactam) were initiated after blood cultures were obtained, and the patient was taken emergently to the operating theatre for irrigation and débridement of his hands and wrists bilaterally. Arthrotomy of the wrist and débridement of the distal extensor compartment and its tenosynovium were performed on the right forearm, in addition to a decompressive fasciotomy of the left forearm. Postoperatively, the patient’s mental status improved and his vital signs gradually normalized. He received multiple hyperbaric oxygen treatments and underwent several additional operative débridement procedures with eventual closure of his wounds. At initial presentation, the differential diagnosis for the severe soft-tissue infection included necrotizing fasciitis or myositis caused by any of a variety of bacterial pathogens. Most notably, it was important to elicit the history of a cat bite to include and consider Pasteurella multocida as a potential pathogen. Initial cultures supported the diagnosis of acute P multocida necrotizing skin and soft-tissue infection, in addition to septic arthritis. The patient’s blood and intraoperative wound cultures grew P multocida. The antibiotic treatment was tailored initially to ampicillin and sulbactam and then to a final regimen of orally administered ciprofloxacin (750 mg twice a day), once susceptibility testing was performed on the cultures. On hospital day 10, the patient was discharged home, receiving a 6-week course of ciprofloxacin to complete the 8-week course of treatment.

At follow-up, approximately 1 month after discharge, the patient noted that he had developed a new right sternoclavicular joint prominence that was associated with painful crepitus. He also noted that his wrists were gradually becoming more swollen and painful bilaterally. Computed tomography scans of the chest were obtained to evaluate the sternoclavicular joint (Figure 1). Repeat radiographs of the wrists were also obtained (Figure 2). Imaging showed lytic destruction of the sternoclavicular joint and erosive changes throughout the carpus and radiocarpal joint, consistent with osteomyelitis. The C-reactive protein level and erythrocyte sedimentation rate at this time were 34 mg/L and 124 mm/h, respectively.

The patient returned to the operating room for débridement and biopsy of the right sternoclavicular joint and left wrist. This patient’s delayed presentation was characterized by a subacute worsening of isolated musculoskeletal complaints. The differential diagnosis then included infection with the same bacterial pathogen versus reactive or inflammatory arthritis. Several intraoperative cultures failed to grow any bacteria, including P multocida, although P multocida was the presumptive cause of the erosive polyarthropathy, considering that symptoms eventually resolved with a repeated course of IV-administered ertapenem for 6 weeks. The patient experienced complete resolution of his joint pain and swelling. He was able to resume his activities of daily living and had no further recurrence of symptoms at follow-up 3 months later.

Discussion

Cat bites often are the source of Pasteurella species infections because the bacteria are carried by more than 90% of cats.¹ These types of infections can cause septic arthritis, osteomyelitis, and deep subcutaneous and myofascial infections because of the sharp and narrow morphology of cat teeth. The infections can progress to necrotizing fasciitis and myositis if not recognized early, as was the case with our patient. Prophylactic antibiotic administration for animal bites is controversial and is not a universal practice.^1,2Pasteurella bacteremia is an atypical progression that occurs more often in patients with pneumonia, septic arthritis, or meningitis. Cases of Pasteurella sepsis, necrotizing fasciitis, and septic arthritis have been reported.^3-7 However, associated progressive septic arthritis and osteomyelitis, despite initial clinical improvement, have not been reported. Severe infection (ie, sepsis and septic shock) can occur in infants, pregnant women, and other immunocompromised patients.⁷ Immune suppression of our patient with steroid medication for poison sumac dermatitis likely contributed to the progression and systemic spread of an initially benign cat bite. Before prescribing steroids, it is imperative to ask about exposures and encourage patients to seek prompt medical attention with worsening or new symptoms. Healthy individuals rarely develop bacteremia; however, in these cases, mortality remains high at approximately 25%.^4,6

The clinical course of this case emphasizes the need for vigilance and thoroughness in obtaining histories from patients presenting with seemingly benign complaints, especially in vulnerable populations, such as infants, pregnant women, and immunocompromised adults. In this case, the progression of symptoms might have been avoided if the patient’s dermatitis had been treated conservatively or with topical rather than systemic steroids.

A few days after an incidental cat bite, a patient presented to the emergency department for treatment of poison sumac exposure. He was discharged with oral methylprednisolone for the dermatitis and returned 1 week later with symptoms, examination findings, and laboratory results consistent with sepsis and bilateral upper extremity necrotizing soft-tissue infections. After administering multiple irrigation and débridement procedures, hyperbaric oxygen treatments, and an antibiotic regimen, the patient’s status greatly improved. However, the patient returned 1 month later with a new sternoclavicular joint prominence that was associated with painful crepitus. Additionally, he noted that his wrists were gradually becoming more swollen and painful. Imaging studies showed a lytic destruction of the sternoclavicular joint and erosive changes throughout the carpus and radiocarpal joint bilaterally, consistent with osteomyelitis. The patient was treated with ertapenem for 6 weeks, and his polyarthropathy resolved. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 73-year-old, right-hand–dominant man with no notable medical history presented to the emergency department for treatment of poison sumac exposure, incidentally, a few days after being bitten by a cat on the bilateral distal upper extremities. He was prescribed a course of oral methylprednisolone for dermatitis. A week later, the patient returned to the emergency department with altered mental status, fevers, diaphoresis, lethargy, and polyarthralgia. At the time of presentation, the patient’s vital signs were labile, and he was found to have extensive bilateral upper extremity erythema, blistering, petechiae, purpuric lesions, and exquisite pain with passive range of motion of his fingers and wrists. His leukocyte count was 25.1 × 10⁹/L, and he had elevated C-reactive protein level and erythrocyte sedimentation rate of 150 mg/L and 120 mm/h, respectively. He was admitted for management of sepsis and presumed bilateral upper extremity necrotizing soft-tissue infection.

Broad-spectrum intravenous (IV) antibiotics (vancomycin, piperacillin, tazobactam) were initiated after blood cultures were obtained, and the patient was taken emergently to the operating theatre for irrigation and débridement of his hands and wrists bilaterally. Arthrotomy of the wrist and débridement of the distal extensor compartment and its tenosynovium were performed on the right forearm, in addition to a decompressive fasciotomy of the left forearm. Postoperatively, the patient’s mental status improved and his vital signs gradually normalized. He received multiple hyperbaric oxygen treatments and underwent several additional operative débridement procedures with eventual closure of his wounds. At initial presentation, the differential diagnosis for the severe soft-tissue infection included necrotizing fasciitis or myositis caused by any of a variety of bacterial pathogens. Most notably, it was important to elicit the history of a cat bite to include and consider Pasteurella multocida as a potential pathogen. Initial cultures supported the diagnosis of acute P multocida necrotizing skin and soft-tissue infection, in addition to septic arthritis. The patient’s blood and intraoperative wound cultures grew P multocida. The antibiotic treatment was tailored initially to ampicillin and sulbactam and then to a final regimen of orally administered ciprofloxacin (750 mg twice a day), once susceptibility testing was performed on the cultures. On hospital day 10, the patient was discharged home, receiving a 6-week course of ciprofloxacin to complete the 8-week course of treatment.

At follow-up, approximately 1 month after discharge, the patient noted that he had developed a new right sternoclavicular joint prominence that was associated with painful crepitus. He also noted that his wrists were gradually becoming more swollen and painful bilaterally. Computed tomography scans of the chest were obtained to evaluate the sternoclavicular joint (Figure 1). Repeat radiographs of the wrists were also obtained (Figure 2). Imaging showed lytic destruction of the sternoclavicular joint and erosive changes throughout the carpus and radiocarpal joint, consistent with osteomyelitis. The C-reactive protein level and erythrocyte sedimentation rate at this time were 34 mg/L and 124 mm/h, respectively.

The patient returned to the operating room for débridement and biopsy of the right sternoclavicular joint and left wrist. This patient’s delayed presentation was characterized by a subacute worsening of isolated musculoskeletal complaints. The differential diagnosis then included infection with the same bacterial pathogen versus reactive or inflammatory arthritis. Several intraoperative cultures failed to grow any bacteria, including P multocida, although P multocida was the presumptive cause of the erosive polyarthropathy, considering that symptoms eventually resolved with a repeated course of IV-administered ertapenem for 6 weeks. The patient experienced complete resolution of his joint pain and swelling. He was able to resume his activities of daily living and had no further recurrence of symptoms at follow-up 3 months later.

Discussion

Cat bites often are the source of Pasteurella species infections because the bacteria are carried by more than 90% of cats.¹ These types of infections can cause septic arthritis, osteomyelitis, and deep subcutaneous and myofascial infections because of the sharp and narrow morphology of cat teeth. The infections can progress to necrotizing fasciitis and myositis if not recognized early, as was the case with our patient. Prophylactic antibiotic administration for animal bites is controversial and is not a universal practice.^1,2Pasteurella bacteremia is an atypical progression that occurs more often in patients with pneumonia, septic arthritis, or meningitis. Cases of Pasteurella sepsis, necrotizing fasciitis, and septic arthritis have been reported.^3-7 However, associated progressive septic arthritis and osteomyelitis, despite initial clinical improvement, have not been reported. Severe infection (ie, sepsis and septic shock) can occur in infants, pregnant women, and other immunocompromised patients.⁷ Immune suppression of our patient with steroid medication for poison sumac dermatitis likely contributed to the progression and systemic spread of an initially benign cat bite. Before prescribing steroids, it is imperative to ask about exposures and encourage patients to seek prompt medical attention with worsening or new symptoms. Healthy individuals rarely develop bacteremia; however, in these cases, mortality remains high at approximately 25%.^4,6

The clinical course of this case emphasizes the need for vigilance and thoroughness in obtaining histories from patients presenting with seemingly benign complaints, especially in vulnerable populations, such as infants, pregnant women, and immunocompromised adults. In this case, the progression of symptoms might have been avoided if the patient’s dermatitis had been treated conservatively or with topical rather than systemic steroids.

A few days after an incidental cat bite, a patient presented to the emergency department for treatment of poison sumac exposure. He was discharged with oral methylprednisolone for the dermatitis and returned 1 week later with symptoms, examination findings, and laboratory results consistent with sepsis and bilateral upper extremity necrotizing soft-tissue infections. After administering multiple irrigation and débridement procedures, hyperbaric oxygen treatments, and an antibiotic regimen, the patient’s status greatly improved. However, the patient returned 1 month later with a new sternoclavicular joint prominence that was associated with painful crepitus. Additionally, he noted that his wrists were gradually becoming more swollen and painful. Imaging studies showed a lytic destruction of the sternoclavicular joint and erosive changes throughout the carpus and radiocarpal joint bilaterally, consistent with osteomyelitis. The patient was treated with ertapenem for 6 weeks, and his polyarthropathy resolved. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 73-year-old, right-hand–dominant man with no notable medical history presented to the emergency department for treatment of poison sumac exposure, incidentally, a few days after being bitten by a cat on the bilateral distal upper extremities. He was prescribed a course of oral methylprednisolone for dermatitis. A week later, the patient returned to the emergency department with altered mental status, fevers, diaphoresis, lethargy, and polyarthralgia. At the time of presentation, the patient’s vital signs were labile, and he was found to have extensive bilateral upper extremity erythema, blistering, petechiae, purpuric lesions, and exquisite pain with passive range of motion of his fingers and wrists. His leukocyte count was 25.1 × 10⁹/L, and he had elevated C-reactive protein level and erythrocyte sedimentation rate of 150 mg/L and 120 mm/h, respectively. He was admitted for management of sepsis and presumed bilateral upper extremity necrotizing soft-tissue infection.

Broad-spectrum intravenous (IV) antibiotics (vancomycin, piperacillin, tazobactam) were initiated after blood cultures were obtained, and the patient was taken emergently to the operating theatre for irrigation and débridement of his hands and wrists bilaterally. Arthrotomy of the wrist and débridement of the distal extensor compartment and its tenosynovium were performed on the right forearm, in addition to a decompressive fasciotomy of the left forearm. Postoperatively, the patient’s mental status improved and his vital signs gradually normalized. He received multiple hyperbaric oxygen treatments and underwent several additional operative débridement procedures with eventual closure of his wounds. At initial presentation, the differential diagnosis for the severe soft-tissue infection included necrotizing fasciitis or myositis caused by any of a variety of bacterial pathogens. Most notably, it was important to elicit the history of a cat bite to include and consider Pasteurella multocida as a potential pathogen. Initial cultures supported the diagnosis of acute P multocida necrotizing skin and soft-tissue infection, in addition to septic arthritis. The patient’s blood and intraoperative wound cultures grew P multocida. The antibiotic treatment was tailored initially to ampicillin and sulbactam and then to a final regimen of orally administered ciprofloxacin (750 mg twice a day), once susceptibility testing was performed on the cultures. On hospital day 10, the patient was discharged home, receiving a 6-week course of ciprofloxacin to complete the 8-week course of treatment.

At follow-up, approximately 1 month after discharge, the patient noted that he had developed a new right sternoclavicular joint prominence that was associated with painful crepitus. He also noted that his wrists were gradually becoming more swollen and painful bilaterally. Computed tomography scans of the chest were obtained to evaluate the sternoclavicular joint (Figure 1). Repeat radiographs of the wrists were also obtained (Figure 2). Imaging showed lytic destruction of the sternoclavicular joint and erosive changes throughout the carpus and radiocarpal joint, consistent with osteomyelitis. The C-reactive protein level and erythrocyte sedimentation rate at this time were 34 mg/L and 124 mm/h, respectively.

The patient returned to the operating room for débridement and biopsy of the right sternoclavicular joint and left wrist. This patient’s delayed presentation was characterized by a subacute worsening of isolated musculoskeletal complaints. The differential diagnosis then included infection with the same bacterial pathogen versus reactive or inflammatory arthritis. Several intraoperative cultures failed to grow any bacteria, including P multocida, although P multocida was the presumptive cause of the erosive polyarthropathy, considering that symptoms eventually resolved with a repeated course of IV-administered ertapenem for 6 weeks. The patient experienced complete resolution of his joint pain and swelling. He was able to resume his activities of daily living and had no further recurrence of symptoms at follow-up 3 months later.

Discussion

Cat bites often are the source of Pasteurella species infections because the bacteria are carried by more than 90% of cats.¹ These types of infections can cause septic arthritis, osteomyelitis, and deep subcutaneous and myofascial infections because of the sharp and narrow morphology of cat teeth. The infections can progress to necrotizing fasciitis and myositis if not recognized early, as was the case with our patient. Prophylactic antibiotic administration for animal bites is controversial and is not a universal practice.^1,2Pasteurella bacteremia is an atypical progression that occurs more often in patients with pneumonia, septic arthritis, or meningitis. Cases of Pasteurella sepsis, necrotizing fasciitis, and septic arthritis have been reported.^3-7 However, associated progressive septic arthritis and osteomyelitis, despite initial clinical improvement, have not been reported. Severe infection (ie, sepsis and septic shock) can occur in infants, pregnant women, and other immunocompromised patients.⁷ Immune suppression of our patient with steroid medication for poison sumac dermatitis likely contributed to the progression and systemic spread of an initially benign cat bite. Before prescribing steroids, it is imperative to ask about exposures and encourage patients to seek prompt medical attention with worsening or new symptoms. Healthy individuals rarely develop bacteremia; however, in these cases, mortality remains high at approximately 25%.^4,6

The clinical course of this case emphasizes the need for vigilance and thoroughness in obtaining histories from patients presenting with seemingly benign complaints, especially in vulnerable populations, such as infants, pregnant women, and immunocompromised adults. In this case, the progression of symptoms might have been avoided if the patient’s dermatitis had been treated conservatively or with topical rather than systemic steroids.