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Correct Positioning of the Medial Patellofemoral Ligament: Troubleshooting in the Operating Room
Take-Home Points
- Use fluoroscopy, isometry, or both to double-check the femoral attachment point. Failure to do so can lead to an overtensioned or undertensioned graft caused by anisometric graft placement.
- To minimize the risk of fracture, avoid drilling transverse tunnels across the patella.
- Do not “pre-tension” the medial patellofemoral ligament graft. There should be little or no tension in the graft when the patella is centered in the groove, regardless of the angle of knee flexion.
- The angle of knee flexion during securing of the graft may be important for inaccurate femoral tunnel placement. Before final fixation of the graft, always range the knee fully to make sure full passive motion will be possible once the graft is secured.
- Understanding the anatomy of the MPFL is key before considering reconstructing: That is, fluoroscopy only suggests a “cloud” to begin assessment of the femoral attachment site and is secondary to anatomic references and check of length changes between the attachment point through range of motion. New studies demonstrate the patellar attachment is broad and extends proximally from the historical patellar attachment site to an equal distance along the distal quadriceps.
The medial patellofemoral ligament (MPFL), which is essential in preventing lateral patellar instability, becomes torn in almost 100% of dislocation events.1 Therefore, in cases of failed nonoperative management, this important constraint should be reconstructed. Reconstruction is technically challenging, precision is needed to avoid postoperative complications, and a thorough understanding of the native MPFL anatomy is paramount.
As a thickening of the medial patellar retinaculum, the MPFL connects the medial patella to the medial femur. The femoral insertion has been described a few ways. In a cadaveric study, LaPrade and colleagues2 noted that it inserts 1.9 mm anterior and 3.2 mm distal to the adductor tubercle. Radiographically, the attachment has been described by Schöttle and colleagues3 and Stephen and colleagues.4 These techniques are discussed in more detail later.
The MPFL is a static restraint to lateral patellar translation—it acts only as a checkrein. It functions mainly in 0° to 30° of knee flexion because once the patella engages the trochlear groove, the bony articulation guides the patella during the rest of knee flexion.5 Most authors agree that the native MPFL is mostly isometric, and the re-created ligament should replicate it.6,7 Using cadaveric specimens, Steensen and colleagues6 found that, from 0° to 90° of knee flexion, the distance from the inferior patellar attachment to the superior femoral attachment changed only 1.1 mm.
Biomechanical studies have shown that a MPFL graft with excessive tension predisposes to postoperative abnormal patellofemoral contact pressures, which cause anterior knee pain, loss of knee flexion, and patellofemoral chondrosis.8-10 Furthermore, an overtensioned graft can cause iatrogenic medial patellar subluxation, and an undertensioned graft may still allow for pathologic lateral patellar translation.
Anatomical Bony Insertions
Femoral Insertion
Precise localization of the proper anatomical femoral attachment of the MPFL is a crucial step in reconstruction.11 Small errors in femoral location have resulted in significant loss of graft isometry, increased patellofemoral contact pressures in cadaveric models,4,7 and increased rates of failure after both MPFL repair12 and reconstruction.13 Several methods for confirming proper femoral location during surgery have been described; these methods help obviate the need for large formal dissection of the medial knee.
In a cadaveric study, Schöttle and colleagues3 described a reproducible radiographic point that precisely identifies the appropriate femoral location for MPFL graft placement. The point is located on a standard true lateral radiograph of the distal femur. First, a line is drawn extending the posterior cortex of the femur distally. Next, 2 lines are drawn perpendicular to the first: one intersecting the posterior point of the Blumensaat line, the other intersecting the transition between the posterior femoral condyle and the posterior femoral cortex3 (Figure 1). 
Another radiographic method for intraoperatively identifying the anatomical MPFL femoral attachment was described by Stephen and colleagues.4 They used a cadaveric model to confirm radiographic findings and found that the femoral attachment point, taking the anterior-to-posterior medial femoral condyle distance to be 100%, was identified 40% from the posterior border of the medial femoral condyle, 50% from the distal border, and 60% from the anterior border. This simple “40%–50%–60%” normalizing rule for radiographically defining the femoral attachment point is another helpful intraoperative adjunct for templating the appropriate location for graft placement, but calculation in a sterile operative environment can be difficult.
Both of these techniques depend on a perfect lateral radiograph of the knee, as even minor variations in a radiograph can have a dramatic effect on the appearance of the starting point.
Palpation of bony landmarks is another method for preliminarily identifying the appropriate location for femoral pin placement. If done properly, palpation helps obviate the need for corrections when confirming location using isometry or radiography. The center of the femoral attachment of the MPFL can be located in a groove midway between the medial epicondyle and the adductor tubercle.4 Fujino and colleagues15 conducted a cadaveric study of 31 knees in an effort to relate osseous landmarks with the femoral attachment of the MPFL. In all knees, the adductor tubercle was a reliable osseous landmark. The anatomical MPFL attachment was 10.6 mm distal to the apex of the adductor tubercle and was consistent between knees.
Although all these options offer the best available and most reproducible methods for establishing an anatomical femoral graft insertion site, it is important to note that they are based on cadaveric specimens without recurrent patellar instability. Most knees with chronic patellar instability have associated anatomical abnormalities that are not present in nondysplastic cadaveric specimens, which may alter the relationship of osseous landmarks such as the medial epicondyle and adductor tubercle.16 In a recent study of 30 patients with chronic lateral patellar instability, Sanchis-Alfonso and colleagues16 used 3-dimensional computed tomography with these radiographic landmarks and simulated femoral graft attachment sites. They found that the methods of Schöttle and colleagues3 and Stephen and colleagues4 did not provide precise anatomical femoral placement. Ziegler and colleagues14 correlated the anatomical femoral location of the MPFL with the Schöttle point and found the radiographic site to be 4 mm, on average, off the anatomical location. The location of an appropriate anatomical femoral attachment should be confirmed using multiple methods, including palpation of known osseous landmarks, intraoperative fluoroscopy, and, most important, assessment of graft isometry through full range of motion (ROM).
Patellar Insertion
The patellar attachment of the MPFL has received considerably less attention than the femoral attachment.11 Anatomical studies have shown that the MPFL inserts on the superomedial half to third of the patella, in addition to a portion inserting on the undersurface of the vastus medialis.17
Troubleshooting
It is essential to check graft tension through full knee ROM and observe how the graft behaves in order to prevent iatrogenic complications11 (Figures 6A, 6B).
If the graft is secured in high degrees of knee flexion, and the femoral location is not anatomical, a different phenomenon occurs when the knee is brought back into extension. For proximal femoral tunnels, the graft loosens in knee extension and may lead to continued lateral patellar instability. On the other hand, a distal femoral tunnel may result in iatrogenic medial patellar subluxation as the graft becomes too tight in extension.
Correct Amount of Graft Tension
Overtightening the MPFL during fixation is an easy but avoidable mistake. Unlike the anterior cruciate ligament, the MPFL should not be secured while applying maximum tension. Stephen and colleagues7 and Beck and colleagues8 found that tension of only 2 N (~0.5 lb) is needed to accurately re-create the biomechanics of the native graft.
The amount of tension may inadvertently be increased by an interference screw, which tends to pull the graft into the femoral tunnel during insertion. Attention should be given to watching and palpating the graft as the screw is inserted, especially during the last few turns. Turning the screw half a turn backwards after full insertion can release this increased tension and help avoid overtensioning.
Correct Amount of Knee Flexion
This is probably the least studied aspect of MPFL reconstruction. Recommendations range from 0° to 90° of knee flexion during fixation.7,25-30 Most recommendations are surgeon preference, or are based on a sound rationale that lacks supporting research. Tensioning in full extension has been advocated for assessing for the appropriate amount of lateral patellar translation.27 Authors who endorse deeper knee flexion (60°-90°) think that, because the patella engages a deeper trochlear groove in increased flexion, the bony articulation can be used to establish graft length.30,31
Our cadaveric study showed that lower degrees of knee flexion are safest for minimizing the effect of a malpositioned femoral tunnel.26 If femoral tunnel location is not exactly anatomical, any errors are magnified (with even worse graft mechanics) the deeper in flexion the graft is fixed. Once the patella engages the trochlear groove, at about 30° of knee flexion, this can assist in establishing correct graft length. Therefore, we recommend fixation of the graft in 30° to 45° of knee flexion. Our study results also showed that, if femoral tunnel location is anatomical, the graft will be mostly isometric through knee ROM, and, therefore, amount of initial knee flexion does not affect graft behavior.
Regardless of knee flexion chosen, it is imperative to take the knee through full ROM after fixation to ensure the graft does not excessively loosen or tighten in flexion or extension.
Conclusion
MPFL reconstruction is fraught with errors and technical nuances that may be underappreciated. Accurately locating the femoral insertion is crucial to a biomechanically sound graft, and this location should be scrutinized during surgery with accurate radiographs or bony landmarks and verified with knee ROM. Although there is no clear gold standard for fixation and graft options, the graft should be secured while pulling very little tension (2 N) and with the knee in 30° to 45° of flexion to minimize the effect of any inaccuracies in femoral location. Overall, most patients do well after MPFL reconstruction, and attention to surgical technical detail helps maximize the chances of a satisfactory outcome.
Am J Orthop. 2017;46(2):76-81. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
1. Sallay PI, Poggi J, Speer KP, Garrett WE. Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med. 1996;24(1):52-60.
2. LaPrade RF, Engebretsen AH, Ly TV, Johansen S, Wentorf FA, Engebretsen L. The anatomy of the medial part of the knee. J Bone Joint Surg Am. 2007;89(9):2000-2010.
3. Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35(5):801-804.
4. Stephen JM, Lumpaopong P, Deehan DJ, Kader D, Amis AA. The medial patellofemoral ligament: location of femoral attachment and length change patterns resulting from anatomic and nonanatomic attachments. Am J Sports Med. 2012;40(8):1871-1879.
5. Amis AA, Firer P, Mountney J, Senavongse W, Thomas NP. Anatomy and biomechanics of the medial patellofemoral ligament. Knee. 2003;10(3):215-220.
6. Steensen RN, Dopirak RM, McDonald WG 3rd. The anatomy and isometry of the medial patellofemoral ligament: implications for reconstruction. Am J Sports Med. 2004;32(6):1509-1513.
7. Stephen JM, Kaider D, Lumpaopong P, Deehan DJ, Amis AA. The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction. Am J Sports Med. 2014;42(2):364-372.
8. Beck P, Brown NA, Greis PE, Burks RT. Patellofemoral contact pressures and lateral patellar translation after medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35(9):1557-1563.
9. Bollier M, Fulkerson J, Cosgarea A, Tanaka M. Technical failure of medial patellofemoral ligament reconstruction. Arthroscopy. 2011;27(8):1153-1159.
10. Elias JJ, Cosgarea AJ. Technical errors during medial patellofemoral ligament reconstruction could overload medial patellofemoral cartilage: a computational analysis. Am J Sports Med. 2006;34(9):1478-1485.
11. Sanchis-Alfonso V. Guidelines for medial patellofemoral ligament reconstruction in chronic lateral patellar instability. J Am Acad Orthop Surg. 2014;22(3):175-182.
12. Camp CL, Krych AJ, Dahm DL, Levy BA, Stuart MJ. Medial patellofemoral ligament repair for recurrent patellar dislocation. Am J Sports Med. 2010;38(11):2248-2254.
13. Hopper GP, Leach WJ, Rooney BP, Walker CR, Blyth MJ. Does degree of trochlear dysplasia and position of femoral tunnel influence outcome after medial patellofemoral ligament reconstruction? Am J Sports Med. 2014;42(3):716-722.
14. Ziegler CG, Fulkerson JP, Edgar C. Radiographic reference points are inaccurate with and without a true lateral radiograph: the importance of anatomy in medial patellofemoral ligament reconstruction. Am J Sports Med. 2016;44(1):133-142.
15. Fujino K, Tajima G, Yan J, et al. Morphology of the femoral insertion site of the medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc. 2015;23(4):998-1003.
16. Sanchis-Alfonso V, Ramirez-Fuentes C, Montesinos-Berry E, Aparisi-Rodriguez F, Martí-Bonmatí L. Does radiographic location ensure precise anatomic location of the femoral fixation site in medial patellofemoral ligament surgery? Knee Surg Sports Traumatol Arthrosc. 2016;24(9):2838-2844.
17. Smirk C, Morris H. The anatomy and reconstruction of the medial patellofemoral ligament. Knee. 2003;10(3):221-227.
18. Tateishi T, Tsuchiya M, Motosugi N, et al. Graft length change and radiographic assessment of femoral drill hole position for medial patellofemoral ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2011;19(3):400-407.
19. Mariani PP, Liguori L, Cerullo G, Iannella G, Floris L. Arthroscopic patellar reinsertion of the MPFL in acute patellar dislocations. Knee Surg Sports Traumatol Arthrosc. 2011;19(4):628-633.
20. Schöttle PB, Hensler D, Imhoff AB. Anatomical double-bundle MPFL reconstruction with an aperture fixation. Knee Surg Sports Traumatol Arthrosc. 2010;18(2):147-151.
21. Siebold R, Chikale S, Sartory N, Hariri N, Feil S, Pässler HH. Hamstring graft fixation in MPFL reconstruction at the patella using a transosseous suture technique. Knee Surg Sports Traumatol Arthrosc. 2010;18(11):1542-1544.
22. Song SY, Kim IS, Chang HG, Shin JH, Kim HJ, Seo YJ. Anatomic medial patellofemoral ligament reconstruction using patellar suture anchor fixation for recurrent patellar instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2431-2437.
23. Burrus MT, Werner BC, Conte EJ, Diduch DR. Troubleshooting the femoral attachment during medial patellofemoral ligament reconstruction: location, location, location. Orthop J Sports Med. 2015;3(1):2325967115569198.
24. Thaunat M, Erasmus PJ. Management of overtight medial patellofemoral ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2009;17(5):480-483.
25. Arendt EA, Moeller A, Agel J. Clinical outcomes of medial patellofemoral ligament repair in recurrent (chronic) lateral patella dislocations. Knee Surg Sports Traumatol Arthrosc. 2011;19(11):1909-1914.
26. Burrus MT, Werner BC, Cancienne JM, Gwathmey FW, Diduch DR. MPFL graft fixation in low degrees of knee flexion minimizes errors made in the femoral location [published online April 16, 2016]. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-016-4111-4.
27. Feller JA, Richmond AK, Wasiak J. Medial patellofemoral ligament reconstruction as an isolated or combined procedure for recurrent patellar instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2470-2476.
28. Lippacher S, Dreyhaupt J, Williams SR, Reichel H, Nelitz M. Reconstruction of the medial patellofemoral ligament: clinical outcomes and return to sports. Am J Sports Med. 2014;42(7):1661-1668.
29. Nelitz M, Dreyhaupt J, Reichel H, Woelfle J, Lippacher S. Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: surgical technique and clinical outcome. Am J Sports Med. 2013;41(1):58-63.
30. Nomura E, Horiuchi Y, Kihara M. A mid-term follow-up of medial patellofemoral ligament reconstruction using an artificial ligament for recurrent patellar dislocation. Knee. 2000;7(4):211-215.
31. Steiner TM, Torga-Spak R, Teitge RA. Medial patellofemoral ligament reconstruction in patients with lateral patellar instability and trochlear dysplasia. Am J Sports Med. 2006;34(8):1254-1261.
Take-Home Points
- Use fluoroscopy, isometry, or both to double-check the femoral attachment point. Failure to do so can lead to an overtensioned or undertensioned graft caused by anisometric graft placement.
- To minimize the risk of fracture, avoid drilling transverse tunnels across the patella.
- Do not “pre-tension” the medial patellofemoral ligament graft. There should be little or no tension in the graft when the patella is centered in the groove, regardless of the angle of knee flexion.
- The angle of knee flexion during securing of the graft may be important for inaccurate femoral tunnel placement. Before final fixation of the graft, always range the knee fully to make sure full passive motion will be possible once the graft is secured.
- Understanding the anatomy of the MPFL is key before considering reconstructing: That is, fluoroscopy only suggests a “cloud” to begin assessment of the femoral attachment site and is secondary to anatomic references and check of length changes between the attachment point through range of motion. New studies demonstrate the patellar attachment is broad and extends proximally from the historical patellar attachment site to an equal distance along the distal quadriceps.
The medial patellofemoral ligament (MPFL), which is essential in preventing lateral patellar instability, becomes torn in almost 100% of dislocation events.1 Therefore, in cases of failed nonoperative management, this important constraint should be reconstructed. Reconstruction is technically challenging, precision is needed to avoid postoperative complications, and a thorough understanding of the native MPFL anatomy is paramount.
As a thickening of the medial patellar retinaculum, the MPFL connects the medial patella to the medial femur. The femoral insertion has been described a few ways. In a cadaveric study, LaPrade and colleagues2 noted that it inserts 1.9 mm anterior and 3.2 mm distal to the adductor tubercle. Radiographically, the attachment has been described by Schöttle and colleagues3 and Stephen and colleagues.4 These techniques are discussed in more detail later.
The MPFL is a static restraint to lateral patellar translation—it acts only as a checkrein. It functions mainly in 0° to 30° of knee flexion because once the patella engages the trochlear groove, the bony articulation guides the patella during the rest of knee flexion.5 Most authors agree that the native MPFL is mostly isometric, and the re-created ligament should replicate it.6,7 Using cadaveric specimens, Steensen and colleagues6 found that, from 0° to 90° of knee flexion, the distance from the inferior patellar attachment to the superior femoral attachment changed only 1.1 mm.
Biomechanical studies have shown that a MPFL graft with excessive tension predisposes to postoperative abnormal patellofemoral contact pressures, which cause anterior knee pain, loss of knee flexion, and patellofemoral chondrosis.8-10 Furthermore, an overtensioned graft can cause iatrogenic medial patellar subluxation, and an undertensioned graft may still allow for pathologic lateral patellar translation.
Anatomical Bony Insertions
Femoral Insertion
Precise localization of the proper anatomical femoral attachment of the MPFL is a crucial step in reconstruction.11 Small errors in femoral location have resulted in significant loss of graft isometry, increased patellofemoral contact pressures in cadaveric models,4,7 and increased rates of failure after both MPFL repair12 and reconstruction.13 Several methods for confirming proper femoral location during surgery have been described; these methods help obviate the need for large formal dissection of the medial knee.
In a cadaveric study, Schöttle and colleagues3 described a reproducible radiographic point that precisely identifies the appropriate femoral location for MPFL graft placement. The point is located on a standard true lateral radiograph of the distal femur. First, a line is drawn extending the posterior cortex of the femur distally. Next, 2 lines are drawn perpendicular to the first: one intersecting the posterior point of the Blumensaat line, the other intersecting the transition between the posterior femoral condyle and the posterior femoral cortex3 (Figure 1).
Another radiographic method for intraoperatively identifying the anatomical MPFL femoral attachment was described by Stephen and colleagues.4 They used a cadaveric model to confirm radiographic findings and found that the femoral attachment point, taking the anterior-to-posterior medial femoral condyle distance to be 100%, was identified 40% from the posterior border of the medial femoral condyle, 50% from the distal border, and 60% from the anterior border. This simple “40%–50%–60%” normalizing rule for radiographically defining the femoral attachment point is another helpful intraoperative adjunct for templating the appropriate location for graft placement, but calculation in a sterile operative environment can be difficult.
Both of these techniques depend on a perfect lateral radiograph of the knee, as even minor variations in a radiograph can have a dramatic effect on the appearance of the starting point.
Palpation of bony landmarks is another method for preliminarily identifying the appropriate location for femoral pin placement. If done properly, palpation helps obviate the need for corrections when confirming location using isometry or radiography. The center of the femoral attachment of the MPFL can be located in a groove midway between the medial epicondyle and the adductor tubercle.4 Fujino and colleagues15 conducted a cadaveric study of 31 knees in an effort to relate osseous landmarks with the femoral attachment of the MPFL. In all knees, the adductor tubercle was a reliable osseous landmark. The anatomical MPFL attachment was 10.6 mm distal to the apex of the adductor tubercle and was consistent between knees.
Although all these options offer the best available and most reproducible methods for establishing an anatomical femoral graft insertion site, it is important to note that they are based on cadaveric specimens without recurrent patellar instability. Most knees with chronic patellar instability have associated anatomical abnormalities that are not present in nondysplastic cadaveric specimens, which may alter the relationship of osseous landmarks such as the medial epicondyle and adductor tubercle.16 In a recent study of 30 patients with chronic lateral patellar instability, Sanchis-Alfonso and colleagues16 used 3-dimensional computed tomography with these radiographic landmarks and simulated femoral graft attachment sites. They found that the methods of Schöttle and colleagues3 and Stephen and colleagues4 did not provide precise anatomical femoral placement. Ziegler and colleagues14 correlated the anatomical femoral location of the MPFL with the Schöttle point and found the radiographic site to be 4 mm, on average, off the anatomical location. The location of an appropriate anatomical femoral attachment should be confirmed using multiple methods, including palpation of known osseous landmarks, intraoperative fluoroscopy, and, most important, assessment of graft isometry through full range of motion (ROM).
Patellar Insertion
The patellar attachment of the MPFL has received considerably less attention than the femoral attachment.11 Anatomical studies have shown that the MPFL inserts on the superomedial half to third of the patella, in addition to a portion inserting on the undersurface of the vastus medialis.17
Troubleshooting
It is essential to check graft tension through full knee ROM and observe how the graft behaves in order to prevent iatrogenic complications11 (Figures 6A, 6B).
If the graft is secured in high degrees of knee flexion, and the femoral location is not anatomical, a different phenomenon occurs when the knee is brought back into extension. For proximal femoral tunnels, the graft loosens in knee extension and may lead to continued lateral patellar instability. On the other hand, a distal femoral tunnel may result in iatrogenic medial patellar subluxation as the graft becomes too tight in extension.
Correct Amount of Graft Tension
Overtightening the MPFL during fixation is an easy but avoidable mistake. Unlike the anterior cruciate ligament, the MPFL should not be secured while applying maximum tension. Stephen and colleagues7 and Beck and colleagues8 found that tension of only 2 N (~0.5 lb) is needed to accurately re-create the biomechanics of the native graft.
The amount of tension may inadvertently be increased by an interference screw, which tends to pull the graft into the femoral tunnel during insertion. Attention should be given to watching and palpating the graft as the screw is inserted, especially during the last few turns. Turning the screw half a turn backwards after full insertion can release this increased tension and help avoid overtensioning.
Correct Amount of Knee Flexion
This is probably the least studied aspect of MPFL reconstruction. Recommendations range from 0° to 90° of knee flexion during fixation.7,25-30 Most recommendations are surgeon preference, or are based on a sound rationale that lacks supporting research. Tensioning in full extension has been advocated for assessing for the appropriate amount of lateral patellar translation.27 Authors who endorse deeper knee flexion (60°-90°) think that, because the patella engages a deeper trochlear groove in increased flexion, the bony articulation can be used to establish graft length.30,31
Our cadaveric study showed that lower degrees of knee flexion are safest for minimizing the effect of a malpositioned femoral tunnel.26 If femoral tunnel location is not exactly anatomical, any errors are magnified (with even worse graft mechanics) the deeper in flexion the graft is fixed. Once the patella engages the trochlear groove, at about 30° of knee flexion, this can assist in establishing correct graft length. Therefore, we recommend fixation of the graft in 30° to 45° of knee flexion. Our study results also showed that, if femoral tunnel location is anatomical, the graft will be mostly isometric through knee ROM, and, therefore, amount of initial knee flexion does not affect graft behavior.
Regardless of knee flexion chosen, it is imperative to take the knee through full ROM after fixation to ensure the graft does not excessively loosen or tighten in flexion or extension.
Conclusion
MPFL reconstruction is fraught with errors and technical nuances that may be underappreciated. Accurately locating the femoral insertion is crucial to a biomechanically sound graft, and this location should be scrutinized during surgery with accurate radiographs or bony landmarks and verified with knee ROM. Although there is no clear gold standard for fixation and graft options, the graft should be secured while pulling very little tension (2 N) and with the knee in 30° to 45° of flexion to minimize the effect of any inaccuracies in femoral location. Overall, most patients do well after MPFL reconstruction, and attention to surgical technical detail helps maximize the chances of a satisfactory outcome.
Am J Orthop. 2017;46(2):76-81. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
Take-Home Points
- Use fluoroscopy, isometry, or both to double-check the femoral attachment point. Failure to do so can lead to an overtensioned or undertensioned graft caused by anisometric graft placement.
- To minimize the risk of fracture, avoid drilling transverse tunnels across the patella.
- Do not “pre-tension” the medial patellofemoral ligament graft. There should be little or no tension in the graft when the patella is centered in the groove, regardless of the angle of knee flexion.
- The angle of knee flexion during securing of the graft may be important for inaccurate femoral tunnel placement. Before final fixation of the graft, always range the knee fully to make sure full passive motion will be possible once the graft is secured.
- Understanding the anatomy of the MPFL is key before considering reconstructing: That is, fluoroscopy only suggests a “cloud” to begin assessment of the femoral attachment site and is secondary to anatomic references and check of length changes between the attachment point through range of motion. New studies demonstrate the patellar attachment is broad and extends proximally from the historical patellar attachment site to an equal distance along the distal quadriceps.
The medial patellofemoral ligament (MPFL), which is essential in preventing lateral patellar instability, becomes torn in almost 100% of dislocation events.1 Therefore, in cases of failed nonoperative management, this important constraint should be reconstructed. Reconstruction is technically challenging, precision is needed to avoid postoperative complications, and a thorough understanding of the native MPFL anatomy is paramount.
As a thickening of the medial patellar retinaculum, the MPFL connects the medial patella to the medial femur. The femoral insertion has been described a few ways. In a cadaveric study, LaPrade and colleagues2 noted that it inserts 1.9 mm anterior and 3.2 mm distal to the adductor tubercle. Radiographically, the attachment has been described by Schöttle and colleagues3 and Stephen and colleagues.4 These techniques are discussed in more detail later.
The MPFL is a static restraint to lateral patellar translation—it acts only as a checkrein. It functions mainly in 0° to 30° of knee flexion because once the patella engages the trochlear groove, the bony articulation guides the patella during the rest of knee flexion.5 Most authors agree that the native MPFL is mostly isometric, and the re-created ligament should replicate it.6,7 Using cadaveric specimens, Steensen and colleagues6 found that, from 0° to 90° of knee flexion, the distance from the inferior patellar attachment to the superior femoral attachment changed only 1.1 mm.
Biomechanical studies have shown that a MPFL graft with excessive tension predisposes to postoperative abnormal patellofemoral contact pressures, which cause anterior knee pain, loss of knee flexion, and patellofemoral chondrosis.8-10 Furthermore, an overtensioned graft can cause iatrogenic medial patellar subluxation, and an undertensioned graft may still allow for pathologic lateral patellar translation.
Anatomical Bony Insertions
Femoral Insertion
Precise localization of the proper anatomical femoral attachment of the MPFL is a crucial step in reconstruction.11 Small errors in femoral location have resulted in significant loss of graft isometry, increased patellofemoral contact pressures in cadaveric models,4,7 and increased rates of failure after both MPFL repair12 and reconstruction.13 Several methods for confirming proper femoral location during surgery have been described; these methods help obviate the need for large formal dissection of the medial knee.
In a cadaveric study, Schöttle and colleagues3 described a reproducible radiographic point that precisely identifies the appropriate femoral location for MPFL graft placement. The point is located on a standard true lateral radiograph of the distal femur. First, a line is drawn extending the posterior cortex of the femur distally. Next, 2 lines are drawn perpendicular to the first: one intersecting the posterior point of the Blumensaat line, the other intersecting the transition between the posterior femoral condyle and the posterior femoral cortex3 (Figure 1).
Another radiographic method for intraoperatively identifying the anatomical MPFL femoral attachment was described by Stephen and colleagues.4 They used a cadaveric model to confirm radiographic findings and found that the femoral attachment point, taking the anterior-to-posterior medial femoral condyle distance to be 100%, was identified 40% from the posterior border of the medial femoral condyle, 50% from the distal border, and 60% from the anterior border. This simple “40%–50%–60%” normalizing rule for radiographically defining the femoral attachment point is another helpful intraoperative adjunct for templating the appropriate location for graft placement, but calculation in a sterile operative environment can be difficult.
Both of these techniques depend on a perfect lateral radiograph of the knee, as even minor variations in a radiograph can have a dramatic effect on the appearance of the starting point.
Palpation of bony landmarks is another method for preliminarily identifying the appropriate location for femoral pin placement. If done properly, palpation helps obviate the need for corrections when confirming location using isometry or radiography. The center of the femoral attachment of the MPFL can be located in a groove midway between the medial epicondyle and the adductor tubercle.4 Fujino and colleagues15 conducted a cadaveric study of 31 knees in an effort to relate osseous landmarks with the femoral attachment of the MPFL. In all knees, the adductor tubercle was a reliable osseous landmark. The anatomical MPFL attachment was 10.6 mm distal to the apex of the adductor tubercle and was consistent between knees.
Although all these options offer the best available and most reproducible methods for establishing an anatomical femoral graft insertion site, it is important to note that they are based on cadaveric specimens without recurrent patellar instability. Most knees with chronic patellar instability have associated anatomical abnormalities that are not present in nondysplastic cadaveric specimens, which may alter the relationship of osseous landmarks such as the medial epicondyle and adductor tubercle.16 In a recent study of 30 patients with chronic lateral patellar instability, Sanchis-Alfonso and colleagues16 used 3-dimensional computed tomography with these radiographic landmarks and simulated femoral graft attachment sites. They found that the methods of Schöttle and colleagues3 and Stephen and colleagues4 did not provide precise anatomical femoral placement. Ziegler and colleagues14 correlated the anatomical femoral location of the MPFL with the Schöttle point and found the radiographic site to be 4 mm, on average, off the anatomical location. The location of an appropriate anatomical femoral attachment should be confirmed using multiple methods, including palpation of known osseous landmarks, intraoperative fluoroscopy, and, most important, assessment of graft isometry through full range of motion (ROM).
Patellar Insertion
The patellar attachment of the MPFL has received considerably less attention than the femoral attachment.11 Anatomical studies have shown that the MPFL inserts on the superomedial half to third of the patella, in addition to a portion inserting on the undersurface of the vastus medialis.17
Troubleshooting
It is essential to check graft tension through full knee ROM and observe how the graft behaves in order to prevent iatrogenic complications11 (Figures 6A, 6B).
If the graft is secured in high degrees of knee flexion, and the femoral location is not anatomical, a different phenomenon occurs when the knee is brought back into extension. For proximal femoral tunnels, the graft loosens in knee extension and may lead to continued lateral patellar instability. On the other hand, a distal femoral tunnel may result in iatrogenic medial patellar subluxation as the graft becomes too tight in extension.
Correct Amount of Graft Tension
Overtightening the MPFL during fixation is an easy but avoidable mistake. Unlike the anterior cruciate ligament, the MPFL should not be secured while applying maximum tension. Stephen and colleagues7 and Beck and colleagues8 found that tension of only 2 N (~0.5 lb) is needed to accurately re-create the biomechanics of the native graft.
The amount of tension may inadvertently be increased by an interference screw, which tends to pull the graft into the femoral tunnel during insertion. Attention should be given to watching and palpating the graft as the screw is inserted, especially during the last few turns. Turning the screw half a turn backwards after full insertion can release this increased tension and help avoid overtensioning.
Correct Amount of Knee Flexion
This is probably the least studied aspect of MPFL reconstruction. Recommendations range from 0° to 90° of knee flexion during fixation.7,25-30 Most recommendations are surgeon preference, or are based on a sound rationale that lacks supporting research. Tensioning in full extension has been advocated for assessing for the appropriate amount of lateral patellar translation.27 Authors who endorse deeper knee flexion (60°-90°) think that, because the patella engages a deeper trochlear groove in increased flexion, the bony articulation can be used to establish graft length.30,31
Our cadaveric study showed that lower degrees of knee flexion are safest for minimizing the effect of a malpositioned femoral tunnel.26 If femoral tunnel location is not exactly anatomical, any errors are magnified (with even worse graft mechanics) the deeper in flexion the graft is fixed. Once the patella engages the trochlear groove, at about 30° of knee flexion, this can assist in establishing correct graft length. Therefore, we recommend fixation of the graft in 30° to 45° of knee flexion. Our study results also showed that, if femoral tunnel location is anatomical, the graft will be mostly isometric through knee ROM, and, therefore, amount of initial knee flexion does not affect graft behavior.
Regardless of knee flexion chosen, it is imperative to take the knee through full ROM after fixation to ensure the graft does not excessively loosen or tighten in flexion or extension.
Conclusion
MPFL reconstruction is fraught with errors and technical nuances that may be underappreciated. Accurately locating the femoral insertion is crucial to a biomechanically sound graft, and this location should be scrutinized during surgery with accurate radiographs or bony landmarks and verified with knee ROM. Although there is no clear gold standard for fixation and graft options, the graft should be secured while pulling very little tension (2 N) and with the knee in 30° to 45° of flexion to minimize the effect of any inaccuracies in femoral location. Overall, most patients do well after MPFL reconstruction, and attention to surgical technical detail helps maximize the chances of a satisfactory outcome.
Am J Orthop. 2017;46(2):76-81. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.
1. Sallay PI, Poggi J, Speer KP, Garrett WE. Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med. 1996;24(1):52-60.
2. LaPrade RF, Engebretsen AH, Ly TV, Johansen S, Wentorf FA, Engebretsen L. The anatomy of the medial part of the knee. J Bone Joint Surg Am. 2007;89(9):2000-2010.
3. Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35(5):801-804.
4. Stephen JM, Lumpaopong P, Deehan DJ, Kader D, Amis AA. The medial patellofemoral ligament: location of femoral attachment and length change patterns resulting from anatomic and nonanatomic attachments. Am J Sports Med. 2012;40(8):1871-1879.
5. Amis AA, Firer P, Mountney J, Senavongse W, Thomas NP. Anatomy and biomechanics of the medial patellofemoral ligament. Knee. 2003;10(3):215-220.
6. Steensen RN, Dopirak RM, McDonald WG 3rd. The anatomy and isometry of the medial patellofemoral ligament: implications for reconstruction. Am J Sports Med. 2004;32(6):1509-1513.
7. Stephen JM, Kaider D, Lumpaopong P, Deehan DJ, Amis AA. The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction. Am J Sports Med. 2014;42(2):364-372.
8. Beck P, Brown NA, Greis PE, Burks RT. Patellofemoral contact pressures and lateral patellar translation after medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35(9):1557-1563.
9. Bollier M, Fulkerson J, Cosgarea A, Tanaka M. Technical failure of medial patellofemoral ligament reconstruction. Arthroscopy. 2011;27(8):1153-1159.
10. Elias JJ, Cosgarea AJ. Technical errors during medial patellofemoral ligament reconstruction could overload medial patellofemoral cartilage: a computational analysis. Am J Sports Med. 2006;34(9):1478-1485.
11. Sanchis-Alfonso V. Guidelines for medial patellofemoral ligament reconstruction in chronic lateral patellar instability. J Am Acad Orthop Surg. 2014;22(3):175-182.
12. Camp CL, Krych AJ, Dahm DL, Levy BA, Stuart MJ. Medial patellofemoral ligament repair for recurrent patellar dislocation. Am J Sports Med. 2010;38(11):2248-2254.
13. Hopper GP, Leach WJ, Rooney BP, Walker CR, Blyth MJ. Does degree of trochlear dysplasia and position of femoral tunnel influence outcome after medial patellofemoral ligament reconstruction? Am J Sports Med. 2014;42(3):716-722.
14. Ziegler CG, Fulkerson JP, Edgar C. Radiographic reference points are inaccurate with and without a true lateral radiograph: the importance of anatomy in medial patellofemoral ligament reconstruction. Am J Sports Med. 2016;44(1):133-142.
15. Fujino K, Tajima G, Yan J, et al. Morphology of the femoral insertion site of the medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc. 2015;23(4):998-1003.
16. Sanchis-Alfonso V, Ramirez-Fuentes C, Montesinos-Berry E, Aparisi-Rodriguez F, Martí-Bonmatí L. Does radiographic location ensure precise anatomic location of the femoral fixation site in medial patellofemoral ligament surgery? Knee Surg Sports Traumatol Arthrosc. 2016;24(9):2838-2844.
17. Smirk C, Morris H. The anatomy and reconstruction of the medial patellofemoral ligament. Knee. 2003;10(3):221-227.
18. Tateishi T, Tsuchiya M, Motosugi N, et al. Graft length change and radiographic assessment of femoral drill hole position for medial patellofemoral ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2011;19(3):400-407.
19. Mariani PP, Liguori L, Cerullo G, Iannella G, Floris L. Arthroscopic patellar reinsertion of the MPFL in acute patellar dislocations. Knee Surg Sports Traumatol Arthrosc. 2011;19(4):628-633.
20. Schöttle PB, Hensler D, Imhoff AB. Anatomical double-bundle MPFL reconstruction with an aperture fixation. Knee Surg Sports Traumatol Arthrosc. 2010;18(2):147-151.
21. Siebold R, Chikale S, Sartory N, Hariri N, Feil S, Pässler HH. Hamstring graft fixation in MPFL reconstruction at the patella using a transosseous suture technique. Knee Surg Sports Traumatol Arthrosc. 2010;18(11):1542-1544.
22. Song SY, Kim IS, Chang HG, Shin JH, Kim HJ, Seo YJ. Anatomic medial patellofemoral ligament reconstruction using patellar suture anchor fixation for recurrent patellar instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2431-2437.
23. Burrus MT, Werner BC, Conte EJ, Diduch DR. Troubleshooting the femoral attachment during medial patellofemoral ligament reconstruction: location, location, location. Orthop J Sports Med. 2015;3(1):2325967115569198.
24. Thaunat M, Erasmus PJ. Management of overtight medial patellofemoral ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2009;17(5):480-483.
25. Arendt EA, Moeller A, Agel J. Clinical outcomes of medial patellofemoral ligament repair in recurrent (chronic) lateral patella dislocations. Knee Surg Sports Traumatol Arthrosc. 2011;19(11):1909-1914.
26. Burrus MT, Werner BC, Cancienne JM, Gwathmey FW, Diduch DR. MPFL graft fixation in low degrees of knee flexion minimizes errors made in the femoral location [published online April 16, 2016]. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-016-4111-4.
27. Feller JA, Richmond AK, Wasiak J. Medial patellofemoral ligament reconstruction as an isolated or combined procedure for recurrent patellar instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2470-2476.
28. Lippacher S, Dreyhaupt J, Williams SR, Reichel H, Nelitz M. Reconstruction of the medial patellofemoral ligament: clinical outcomes and return to sports. Am J Sports Med. 2014;42(7):1661-1668.
29. Nelitz M, Dreyhaupt J, Reichel H, Woelfle J, Lippacher S. Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: surgical technique and clinical outcome. Am J Sports Med. 2013;41(1):58-63.
30. Nomura E, Horiuchi Y, Kihara M. A mid-term follow-up of medial patellofemoral ligament reconstruction using an artificial ligament for recurrent patellar dislocation. Knee. 2000;7(4):211-215.
31. Steiner TM, Torga-Spak R, Teitge RA. Medial patellofemoral ligament reconstruction in patients with lateral patellar instability and trochlear dysplasia. Am J Sports Med. 2006;34(8):1254-1261.
1. Sallay PI, Poggi J, Speer KP, Garrett WE. Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med. 1996;24(1):52-60.
2. LaPrade RF, Engebretsen AH, Ly TV, Johansen S, Wentorf FA, Engebretsen L. The anatomy of the medial part of the knee. J Bone Joint Surg Am. 2007;89(9):2000-2010.
3. Schöttle PB, Schmeling A, Rosenstiel N, Weiler A. Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35(5):801-804.
4. Stephen JM, Lumpaopong P, Deehan DJ, Kader D, Amis AA. The medial patellofemoral ligament: location of femoral attachment and length change patterns resulting from anatomic and nonanatomic attachments. Am J Sports Med. 2012;40(8):1871-1879.
5. Amis AA, Firer P, Mountney J, Senavongse W, Thomas NP. Anatomy and biomechanics of the medial patellofemoral ligament. Knee. 2003;10(3):215-220.
6. Steensen RN, Dopirak RM, McDonald WG 3rd. The anatomy and isometry of the medial patellofemoral ligament: implications for reconstruction. Am J Sports Med. 2004;32(6):1509-1513.
7. Stephen JM, Kaider D, Lumpaopong P, Deehan DJ, Amis AA. The effect of femoral tunnel position and graft tension on patellar contact mechanics and kinematics after medial patellofemoral ligament reconstruction. Am J Sports Med. 2014;42(2):364-372.
8. Beck P, Brown NA, Greis PE, Burks RT. Patellofemoral contact pressures and lateral patellar translation after medial patellofemoral ligament reconstruction. Am J Sports Med. 2007;35(9):1557-1563.
9. Bollier M, Fulkerson J, Cosgarea A, Tanaka M. Technical failure of medial patellofemoral ligament reconstruction. Arthroscopy. 2011;27(8):1153-1159.
10. Elias JJ, Cosgarea AJ. Technical errors during medial patellofemoral ligament reconstruction could overload medial patellofemoral cartilage: a computational analysis. Am J Sports Med. 2006;34(9):1478-1485.
11. Sanchis-Alfonso V. Guidelines for medial patellofemoral ligament reconstruction in chronic lateral patellar instability. J Am Acad Orthop Surg. 2014;22(3):175-182.
12. Camp CL, Krych AJ, Dahm DL, Levy BA, Stuart MJ. Medial patellofemoral ligament repair for recurrent patellar dislocation. Am J Sports Med. 2010;38(11):2248-2254.
13. Hopper GP, Leach WJ, Rooney BP, Walker CR, Blyth MJ. Does degree of trochlear dysplasia and position of femoral tunnel influence outcome after medial patellofemoral ligament reconstruction? Am J Sports Med. 2014;42(3):716-722.
14. Ziegler CG, Fulkerson JP, Edgar C. Radiographic reference points are inaccurate with and without a true lateral radiograph: the importance of anatomy in medial patellofemoral ligament reconstruction. Am J Sports Med. 2016;44(1):133-142.
15. Fujino K, Tajima G, Yan J, et al. Morphology of the femoral insertion site of the medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc. 2015;23(4):998-1003.
16. Sanchis-Alfonso V, Ramirez-Fuentes C, Montesinos-Berry E, Aparisi-Rodriguez F, Martí-Bonmatí L. Does radiographic location ensure precise anatomic location of the femoral fixation site in medial patellofemoral ligament surgery? Knee Surg Sports Traumatol Arthrosc. 2016;24(9):2838-2844.
17. Smirk C, Morris H. The anatomy and reconstruction of the medial patellofemoral ligament. Knee. 2003;10(3):221-227.
18. Tateishi T, Tsuchiya M, Motosugi N, et al. Graft length change and radiographic assessment of femoral drill hole position for medial patellofemoral ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2011;19(3):400-407.
19. Mariani PP, Liguori L, Cerullo G, Iannella G, Floris L. Arthroscopic patellar reinsertion of the MPFL in acute patellar dislocations. Knee Surg Sports Traumatol Arthrosc. 2011;19(4):628-633.
20. Schöttle PB, Hensler D, Imhoff AB. Anatomical double-bundle MPFL reconstruction with an aperture fixation. Knee Surg Sports Traumatol Arthrosc. 2010;18(2):147-151.
21. Siebold R, Chikale S, Sartory N, Hariri N, Feil S, Pässler HH. Hamstring graft fixation in MPFL reconstruction at the patella using a transosseous suture technique. Knee Surg Sports Traumatol Arthrosc. 2010;18(11):1542-1544.
22. Song SY, Kim IS, Chang HG, Shin JH, Kim HJ, Seo YJ. Anatomic medial patellofemoral ligament reconstruction using patellar suture anchor fixation for recurrent patellar instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2431-2437.
23. Burrus MT, Werner BC, Conte EJ, Diduch DR. Troubleshooting the femoral attachment during medial patellofemoral ligament reconstruction: location, location, location. Orthop J Sports Med. 2015;3(1):2325967115569198.
24. Thaunat M, Erasmus PJ. Management of overtight medial patellofemoral ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2009;17(5):480-483.
25. Arendt EA, Moeller A, Agel J. Clinical outcomes of medial patellofemoral ligament repair in recurrent (chronic) lateral patella dislocations. Knee Surg Sports Traumatol Arthrosc. 2011;19(11):1909-1914.
26. Burrus MT, Werner BC, Cancienne JM, Gwathmey FW, Diduch DR. MPFL graft fixation in low degrees of knee flexion minimizes errors made in the femoral location [published online April 16, 2016]. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-016-4111-4.
27. Feller JA, Richmond AK, Wasiak J. Medial patellofemoral ligament reconstruction as an isolated or combined procedure for recurrent patellar instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2470-2476.
28. Lippacher S, Dreyhaupt J, Williams SR, Reichel H, Nelitz M. Reconstruction of the medial patellofemoral ligament: clinical outcomes and return to sports. Am J Sports Med. 2014;42(7):1661-1668.
29. Nelitz M, Dreyhaupt J, Reichel H, Woelfle J, Lippacher S. Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: surgical technique and clinical outcome. Am J Sports Med. 2013;41(1):58-63.
30. Nomura E, Horiuchi Y, Kihara M. A mid-term follow-up of medial patellofemoral ligament reconstruction using an artificial ligament for recurrent patellar dislocation. Knee. 2000;7(4):211-215.
31. Steiner TM, Torga-Spak R, Teitge RA. Medial patellofemoral ligament reconstruction in patients with lateral patellar instability and trochlear dysplasia. Am J Sports Med. 2006;34(8):1254-1261.
