Infraspinatus and deltoid length and patient height: implications for lateralization and distalization in reverse total shoulder arthroplasty

Predictive factors for postoperative outcomes after reverse shoulder arthroplasty: a systematic review

BACKGROUND

The use of reverse total shoulder arthroplasty (RTSA) has increased at a greater rate than other shoulder procedures. In general, clinical and functional outcomes after RTSA have been favorable regardless of indication. However, little evidence exists regarding patient specific factors associated with clinical improvement after RTSA. Predicting postoperative outcomes after RTSA may support patients and physicians to establish more accurate patient expectations and contribute in treatment decisions. The aim of this study was to determine predictive factors for postoperative outcomes after RTSA for patients with degenerative shoulder disorders.

METHODS

EMBASE, PubMed, Cochrane Library and PEDro were searched to identify cohort studies reporting on predictive factors for postoperative outcomes after RTSA. Authors independently screened publications on eligibility. Risk of bias for each publication was assessed using the QUIPS tool. A qualitative description of the results was given. The GRADE framework was used to establish the quality of evidence.

RESULTS

A total of 1986 references were found of which 11 relevant articles were included in the analysis. Risk of bias was assessed as low (N = 7, 63.6%) or moderate (N = 4, 36.4%). According to the evidence synthesis there was moderate-quality evidence indicating that greater height predicts better postoperative shoulder function, and greater preoperative range of motion (ROM) predicts increased postoperative ROM following.

CONCLUSION

Preoperative predictive factors that may predict postoperative outcomes are: patient height and preoperative range of motion. These factors should be considered in the preoperative decision making for a RTSA, and can potentially be used to aid in preoperative decision making.

LEVEL OF EVIDENCE

Level I; Systematic review.

Impact of reverse shoulder arthroplasty design and patient shoulder size on moment arms and muscle fiber lengths in shoulder abductors

BACKGROUND

Reverse shoulder arthroplasty (RSA) increases the moment arm of the deltoid; however, there is limited knowledge on the accompanying changes in muscle architecture that play a role in muscle force production. The purpose of this study was to use a geometric shoulder model to evaluate the anterior deltoid, middle deltoid, and supraspinatus regarding (1) the differences in moment arms and muscle-tendon lengths in small, medium, and large native shoulders and (2) the impact of 3 RSA designs on moment arms, muscle fiber lengths, and force-length (F-L) curves.

METHODS

A geometric model of the native glenohumeral joint was developed, validated, and adjusted to represent small, medium, and large shoulders. Moment arms, muscle-tendon lengths, and normalized muscle fiber lengths were assessed for the supraspinatus, anterior deltoid, and middle deltoid from 0° to 90° of abduction. RSA designs were modeled and virtually implanted, including a lateralized glenosphere with an inlay 135° humeral component (lateral glenoid-medial humerus [LGMH]), a medialized glenosphere with an onlay 145° humeral component (medial glenoid-lateral humerus [MGLH]), and a medialized glenosphere with an inlay 155° humeral component (medial glenoid-medial humerus [MGMH]). Descriptive statistics were used to compare moment arms and normalized muscle fiber lengths.

RESULTS

As shoulder size increased, the moment arms and muscle-tendon lengths for the anterior deltoid, middle deltoid, and supraspinatus increased. All RSA designs achieved greater moment arms for the anterior and middle deltoid, with the MGLH design achieving the largest increase. The resting normalized muscle fiber length of the anterior and middle deltoid was substantially increased in the MGLH (1.29) and MGMH (1.24) designs, shifting the operating ranges of these muscles to the descending portions of their F-L curves, whereas the LGMH design maintained a resting deltoid fiber length (1.14) and operating range similar to the native shoulder. All RSA designs demonstrated a decrease in the native supraspinatus moment arm in early abduction, with the largest decrease in the MGLH design (-59%) and minimal decrease in the LGMH design (-14%). The supraspinatus operated on the ascending limb of its F-L curve in the native shoulder and remained on this portion of the F-L curve for all RSA designs.

CONCLUSION

Although the MGLH design maximizes the abduction moment arm for the anterior and middle deltoid, overlengthening of the muscle may compromise deltoid muscle force production by forcing the muscle to operate on the descending portion of its F-L curve. In contrast, the LGMH design increases the abduction moment arm for the anterior and middle deltoid more modestly while allowing the muscle to operate near the plateau of its F-L curve and maximizing its force-producing potential.

The internal structure of the infraspinatus muscle: a magnetic resonance study

Purpose

This study aimed to describe the internal structure of the infraspinatus muscle. A secondary aim was to explore differences in internal structure between genders, sides, and correlations to demographic data.

Methods

In total, 106 shoulder MRI examinations of patients between 18 and 30 years of age seeking care in 2012–2020 at The Sahlgrenska University Hospital in Gothenburg, Sweden were re-reviewed.

Results

The number of intramuscular tendons centrally in the infraspinatus muscle varied between 3 and 8 (median = 5). Laterally, the number of intramuscular tendons varied between 1 and 5 (median = 2). There was no difference in the median between the genders or sides. No correlations between the number of intramuscular tendons and demographic data were found. The muscle volume varied between 63 and 249 ml with a median of 188 ml for males and 122 ml for females. There was no significant difference in volume between the sides. The muscle volume correlated with body weight (Pearson’s correlation coefficient, r = 0.72, p < 0.001) and height (r = 0.61, p < 0.001).

Conclusion

The anatomical variations of the infraspinatus muscle are widespread. In the medial part of the muscle belly, the number of intramuscular tendons varied between 3 and 8, while the number of intramuscular tendons laterally varied between 1 and 5. Results of our study may help to understand the internal structure of the infraspinatus muscle and its function in shoulder stabilization.

Early restoration of shoulder function in patients with the Grammont prosthesis compared to lateralized humeral design in reverse shoulder arthroplasty

BACKGROUND

This study aimed to compare the clinical outcomes and radiographic parameters of patients after reverse shoulder arthroplasty (RSA) between the Grammont prosthesis and lateralized humeral design prosthesis.

METHODS

A total of 114 patients who underwent RSA with a lateralized humeral design (group L; 71 shoulders) and medialized humeral design (group M; 43 shoulders) prosthesis for cuff tear arthropathy or irreparable rotator cuff tear were enrolled. Clinical outcomes including visual analog scale (VAS), American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES), and Constant scores and range of motion (ROM) were serially followed up at postoperative 3, 6, 12, and 24 months. Radiographic parameters were measured to evaluate preoperative and postoperative status.

RESULTS

Both prostheses demonstrated similar clinical outcomes and shoulder function preoperatively and at postoperative 2 years (P >.05). However, patients in group M had significantly better postoperative active forward flexion (postoperative 3 months, 115° ± 12° vs. 101° ± 14°; P <.001; 6 months, 125° ± 13° vs. 118° ± 13°; P <.013) and abduction (3 months, 105° ± 12° vs. 98° ± 12°; P = .002); VAS (3 months, 3.1 ± 1.2 vs. 3.7 ± 1.4; P = .031; 6 months, 2.3 ± 1.1 vs. 2.8 ± 1.3; P = .038); ASES (3 months, 64.2 ± 7.0 vs. 60.4 ± 9.2; P = .022; 6 months, 70.6 ± 6.0 vs. 66.6 ± 8.1; P = .007); and Constant scores (6 months, 59.6 ± 6.9 vs. 55.7 ± 9.3; P = .020). Group L showed a significantly lower rate of scapular notching than group M (15.5% vs. 41.8%; P < .001). The position of the proximal humerus in group L was more lateralized and less distalized than in group M after RSA.

CONCLUSIONS

RSA with both the Grammont and lateralized humeral design prostheses provided similar shoulder ROM restoration and functional improvements at a minimum of 2 years. However, patients with a humeral lateralized prosthesis showed slower recovery of shoulder function and ROM up to postoperative 6 months despite a lower incidence of scapular notching.