Reverse shoulder arthroplasty (RSA) is a treatment option for a spectrum of diseases in shoulders with rotator cuff deficiency. There are distinct morphologic changes in the scapular and glenoid anatomy in patients with chronic rotator cuff tears.1 A muscular imbalance that occurs in the joint as a result of rotator cuff deficiency leads to morphologic changes that eliminate the compressive forces that hold the humeral head against the glenoid.2 RSA effectively stabilizes the glenohumeral joint in shoulders with deficient rotator cuffs.3,4 In early work, Grammont proposed that the glenosphere center of rotation should be medialized (concentric to the central axis of the metaglene or baseplate) and lowered.5 Although the medialized center of rotation in Grammont prostheses decreases shear forces and improves the deltoid lever arm, it also tends to result in mechanical impingement between the superomedial aspect of the humeral polyethylene insert and the scapular neck—so-called inferior scapular notching.6-9
Notching, which has been reported in 50% to 96% of patients who receive a Delta III prosthesis, typically appears within the first few months after surgery but may be seen as late as 14 months after surgery.5,10-12 Postmortem studies have shown that notching corresponds with erosion of the inferior pole of the glenoid and scapular neck, thought to be caused by the polyethylene cup of the implant.13 Although some studies have found that notching stabilizes after 1 year, others have shown notching progressing for up to 4 years after surgery.11,12,14 The clinical relevance of notching continues to be controversial, but notching has been associated with poorer clinical outcomes, polyethylene wear, and local osteolysis. Component loosening has also been reported with notching of grade 3 or more.8,10 Ultimately, there is concern that scapular notching could progress, ultimately leading to late glenoid loosening and potentially catastrophic failure.
Scapular anatomy has become an area of increased focus in rotator cuff disorders and in effects on RSA biomechanics.9 Recent reports have described important scapular morphology variations that suggest more individualized adjustments are needed during RSA.9,15 In addition, some investigators have reported that development of notching appears to depend on the height and inclination of the implanted glenoid component, where an inferior position of the glenosphere leads to less impingement and better range of motion.8,16 Simovitch and colleagues8 found the angle between the glenosphere and scapular neck and the craniocaudal position of the glenosphere to be highly correlated with inferior notching. They combined these 2 parameters into a predictive algorithm that provides a guideline (notching index, <35) for prevention of notching.
We conducted a study to evaluate the scapular notching index as a predictive tool and to consider other factors that may be associated with scapular notching occurring with use of Grammont reverse replacement systems. We hypothesized that patients with a notching index of less than 35 would not develop notching and that patients with an index of more than 35 would have increased incidence and severity of notching.
Materials and Methods
Patients treated with RSA for painful cuff tear arthropathy or irreparable rotator cuff tear with pseudoparesis (inability to actively elevate shoulder >90° in presence of free passive anterior elevation) were included in this retrospective review. All patients were treated between 2006 and 2010 by 1 of 2 established senior shoulder subspecialty surgeons. Patients treated with a Delta (DePuy Orthopaedics, Warsaw, Indiana) or an Aequalis (Tornier, Edina, Minnesota) reverse shoulder implant were included in the study. A standard polyethylene liner was used for all patients. These prostheses have the same neck shaft angle, 155º, as they have similar geometric designs, both based on the Grammont design—semiconstrained inverted with a fixed, lowered, medialized center of rotation. Standard instrumentation was used for all procedures. Patients were excluded if any nonstandard techniques or components were used (constrained or high-mobility liner, glenoid bone grafting). Patients who underwent revision for a previous reverse total arthroplasty, a total shoulder arthroplasty, or a hemiarthroplasty, or for treatment of acute fracture, posttraumatic deformity, or posttraumatic arthritis, were also excluded from our analyses. Minimum follow-up for study inclusion was 24 months.
All procedures were performed with the patient in the semi-beach-chair position and with use of a deltopectoral approach. The glenoid was prepared such that minimal reaming was needed to preserve the subchondral plate. The glenoid baseplate was positioned in the recommended inferior position to minimize notching and optimize functional outcomes.13 After surgery, all patients were managed with a simple soft immobilizer with or without a pillow with the arm at the patient’s side in internal rotation. Immediate passive mobilization was begun under the direction of physical therapists. Passive and active-assisted exercises were continued with gradual progression to independent activities of daily living at 6 weeks. Clinical evaluations were performed before and after surgery by the operating surgeon or independent research nurse. Active forward flexion, passive external rotation, strength, and visual analog scale (VAS) pain scores were reviewed and recorded. Case-specific complications were also reviewed.