Kaveh Sajadi, MD
Whether ‘tis nobler in the mind to bear the slings and arrows of our colleagues…
The role of the subscapularis in reverse total shoulder arthroplasty (rTSA) continues to be debated. Reverse TSA is most commonly performed via a deltopectoral approach, which often requires takedown of an intact, though possibly degenerated or atrophic, subscapularis tendon. Surgeons debate the importance of its repair at the conclusion of the surgery. This debate centers on the importance and role of the subscapularis in stability of the prosthesis, range of motion (both internal and external rotation), and outcomes. Those in favor of repair cite studies indicating lower dislocation rates with repair and better internal rotation; those opposed express concern about it potentially limiting external rotation and possibly opposing the deltoid in elevating the arm.1 This meta-analysis and systematic review sought to compare the dislocation rates and outcomes in rTSA with and without subscapularis tendon repair using the highest level of data available.
This meta-analysis and systematic review sought to compare the dislocation rates and outcomes in rTSA with and without subscapularis tendon repair using the highest level of data available.
It is important to clarify some descriptions used in the study. Since the introduction of the original Grammont style reverse prosthesis in the late 1980s and early 1990s, many different design modifications have been introduced.2 The primary differentiating characteristic between implant designs is the location of the center of rotation (COR) of the new glenohumeral articulation. By their very nature, all reverse designs medialize the COR compared with the native shoulder. However, systems with the COR at the glenoid face, as the original Grammont design, are considered medialized and those with the COR lateral to the glenoid are referred to in this paper as lateralized designs. Furthermore, the implant can have a medialized humerus (Grammont) or a lateralized humerus. Routman HD, et al, proposed a classification to standardize the nomenclature, dividing implants into the medial glenoid/medial humerus (Grammont), lateral glenoid/medial humerus, and medial glenoid/lateral humerus.2,3 Some of the implants in this study, classified as lateralized glenoids by the authors, are classified as medial glenoid/lateral humerus by Routman.
The authors performed a search of the available literature, returning 1,008 studies. Seven studies met the inclusion criteria and were analyzed in the systematic review. Five Level III studies were included in the meta-analysis. The meta-analysis involved 1,306 patients, with 723 undergoing subscapularis repair and 583 unrepaired. Rationale and decision-making were not included in the studies. Overall, there were statistically significantly more dislocations in the non-repair group than the repair group. While this seems to support subscapularis repair, this pooled data included both medialized and lateralized COR designs. When the data was separated by COR design, the findings were different. In the study using a medialized COR, as in the overall data, subscapularis repair decreased the dislocation rate. However, when looking only at prostheses with a lateralized COR, there was NO difference in the dislocation rate with or without subscapularis repair. Furthermore, the lateralized COR showed fewer dislocations than the medialized design, overall, when the subscapularis was repaired and when it wasn’t.
Another feature that was examined in this analysis was inlay versus onlay humeral design. In an onlay design, the humeral socket sits at the level of the humeral osteotomy; whereas with an inlay design, the humeral socket is recessed within the proximal humeral metaphysis. This feature, along with the neck-shaft angle, contributes to determining whether the humerus is considered medialized or lateralized. When this was analyzed, the onlay design had a significantly lower risk of dislocation compared with inlay. This may partially be due to improved deltoid wrapping with the lateralized humerus design.3 Deltoid wrapping refers to the wrapping of the middle deltoid around the greater tuberosity, resulting in increased humeral compression into the glenoid. Deltoid wrapping theoretically decreases the deltoid force needed to abduct the arm.2
In the systematic review, they attempted to look at the effect of subscapularis repair on outcomes. In the Werner BC, et al, study, the only difference identified was a worse improvement in ASES scores when the subscapularis was repaired versus not repaired in a lateralized design.4 Friedman RJ, et al, did not find a difference in ASES improvement based on subscapularis repair in lateralized design, though they did find that Constant score, active external rotation, and internal rotation score favored subscapularis repair.5
So, although the meta-analysis at first suggests decreased risk of dislocation with subscapularis repair, this is somewhat misleading. It is becoming clearer that the real answer to whether or not subscapularis repair has a role in instability is dependent on the design of the implant. With a traditional Grammont prosthesis, a medial glenoid and medial humerus design, the subscapularis is important for stability.4,6 With prostheses that lateralize either the glenoid or the humerus, subscapularis repair appears to not be as critical for stability.4-6 These design differences should be taken into consideration when the subscapularis is either chronically torn or irreparable.
So, although the meta-analysis at first suggests decreased risk of dislocation with subscapularis repair, this is somewhat misleading. It is becoming clearer that the real answer to whether or not subscapularis repair has a role in instability is dependent on the design of the implant.
As the authors of this study conclude, “The functional outcomes of reverse total shoulder arthroplasty with or without subscapularis repair largely appear to be equivalent…” Combine this with the study by de Boer FA, et al, that showed that up to 40% of subscapularis repairs had failed after rTSA, and you have a strong argument for using a lateralized design (medial glenoid/lateral humerus, or lateral glenoid/lateral humerus) to maximize stability.7
- Routman HD. The Role of Subscapularis Repair in Reverse Total Shoulder Arthroplasty. Bulletin of the Hospital for Joint Diseases 2013;71(Suppl 2):S108-12.
- Hansen ML, et al. The biomechanics of current reverse shoulder replacement options. Ann Joint 2019;4:17.
- Routman HD, et al. Reverse Shoulder Arthroplasty Design Classification System. Bulletin of the Hospital for Joint Diseases. 2015; 73(Supp 1; 25-14).
- Werner BC, et al. Clinical outcomes after reverse shoulder arthroplasty with and without subscapularis repair: the importance of considering glenosphere lateralization. J Am Acad Orthop Surg 2018; 26:e114.
- Friedman RJ, et al. Comparison of reverse total shoulder arthroplasty outcomes with and without subscapularis repair. J Shoulder Elbow Surg 2017; 26: 662-8.
- Matthewson G, et al. The effect of subscapularis repair on dislocation rates in reverse shoulder arthroplasty: a meta-analysis and systematic review. J Shoulder Elbow Surg (2019) Article in Press. 1-9.
- De Boer FA, et al. The influence of subscapularis tendon reattachment on range of motion in reversed shoulder arthroplasty: a clinical study. Musculoskelet Surg 2016; 100: 121-6.
Kaveh Sajadi, MD, practices orthopaedics with Kentucky Bone and Joint Surgeons and is an instructor in the University of Kentucky’s residency program. He completed his residency at the Campbell Clinic and his fellowship at the NYU Langone Hospital for Joint Diseases. Dr. Sajadi is a frequent instructor at Exactech domestic and international shoulder courses.