1 Introduction

Irreparable posterosuperior rotator cuff tears (PSRCTs) represent a challenging clinical condition and are frequently associated with persistent pain, weakness, and functional limitations of the shoulder.^1,2 Loss of active external rotation is one of the most disabling consequences of PSRCTs, as it significantly impairs daily activities such as reaching overhead, combing hair, and performing tasks requiring shoulder elevation and rotation.^3–5 Among joint-preserving surgical options, posterior latissimus dorsi (LD) tendon transfer has been widely used to restore shoulder function in patients with irreparable PSRCTs, particularly in active individuals without advanced glenohumeral arthritis.^6–10 By transferring the LD tendon to the greater tuberosity, the procedure aims to restore external rotation and improve shoulder biomechanics through reconstitution of the posterior rotator cuff force couple.^11,12 Previous clinical studies have demonstrated that LD transfer can significantly improve pain, shoulder function, and range of motion (ROM) in the patients with irreparable PSRCTs.^{3,7–10,13–16}.

The teres minor (Tm) muscle is an important external rotator of the shoulder and plays a critical role in maintaining posterior shoulder stability. ^17–20 In the setting of infraspinatus dysfunction, the Tm may function as a compensatory external rotator.¹⁷ Previous studies have suggested that structural changes in the Tm, including hypertrophy, atrophy, or fatty infiltration, may influence shoulder function and the outcomes of surgical procedures for PSRCTs.^21–25 However, the influence of Tm trophicity on clinical outcomes after posterior LD transfer remains poorly understood. Therefore, this study is to evaluate the impact of Tm trophicity on clinical outcomes following arthroscopically assisted posterior LD transfer in patients with irreparable PSRCTs. It is hypothesized that posterior LD transfer would provide favorable clinical outcomes regardless of Tm trophicity; however, patients with hypertrophic Tm may demonstrate greater improvement in postoperative external rotation and external rotation strength compared with those with normal or hypotrophic Tm.

2 Methods

2.1

2.1 Study design and patient selection

This study is a retrospective single-center case series. The study protocol was approved by the Institutional Review Board (No. P01-202501-01-004). The requirement for informed consent was waived due to the retrospective nature of the study and the absence of additional risk to the patients. The study included patients who underwent arthroscopically assisted posterior LD tendon transfer for irreparable PSRCTs between April 2012 and June 2020 at a single institution. The surgical indications were as follows: (1) persistent shoulder pain and functional limitation despite conservative management for more than 6 months; (2) severely retracted supraspinatus and infraspinatus to the glenoid level on preoperative magnetic resonance imaging (MRI), corresponding to Patte²⁶ stage 3; (3) advanced fatty infiltration of the supraspinatus and infraspinatus muscles (Goutallier²⁷ grade ≥3); (4) intraoperative confirmation that the supraspinatus and infraspinatus tendons could not be mobilized to their anatomic footprint despite adequate release and mobilization; (5) an intact or reparable subscapularis tendon (Lafosse²⁸ classification ≤ III); and (6) absence or minimal glenohumeral arthritis (Hamada²⁹ grade ≤2). Contraindications included (1) advanced glenohumeral arthritis (Hamada²⁹ grade ≥3) and (2) an irreparable subscapularis tear (Lafosse²⁸ classification ≥ IV). Patients were excluded if they were lost to follow-up or lacked postoperative clinical or radiologic data [Fig. 1]. Tm integrity was not used as a surgical indication for posterior LD transfer, meaning patients with either intact Tm tendons or torn Tm involvement were included. All patients classified in the hypertrophic and normal groups demonstrated intact Tm tendons, whereas all patients in the hypotrophic group showed Tm tear.

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Fig. 1 Patient Selection Flow Chart LD, latissimus dorsi; PSRCTs, posterior superior rotator cuff tears; MRI, magnetic resonance imaging; f/u, follow-up; Tm, teres minor.

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2.4

2.4 Clinical and radiologic assessment

All clinical outcomes were assessed preoperatively and at the final follow-up. Pain was evaluated using the Visual Analog Scale (VAS). Functional outcomes were assessed using the American Shoulder and Elbow Surgeons (ASES) score and the Constant score. Shoulder ROM was measured using a goniometer and included forward elevation, abduction, external rotation at the side, external rotation at 90° of abduction, and internal rotation behind the back. Internal rotation was recorded according to the highest vertebral level reached by the thumb and subsequently converted to a numerical value for statistical analysis. Shoulder muscle strength was measured using a handheld dynamometer. Strength testing included forward elevation, abduction, external rotation at the side, and internal rotation at the side.

All radiography and MRI evaluations were assessed preoperatively and at the final follow-up. Radiographic assessment included measurement of the acromiohumeral distance (AHD) on standardized anteroposterior shoulder radiographs. The degree of cuff tear arthropathy was evaluated using the Hamada²⁹ classification. Preoperative MRI was reviewed to assess fatty infiltration of the rotator cuff muscles, including the supraspinatus, infraspinatus, subscapularis, and Tm, according to the Goutallier²⁷ classification, and MRI obtained at final follow-up was used to evaluate the postoperative integrity of the transferred tendon. The trophicity of the Tm muscle was assessed using preoperative MRI. On the oblique sagittal image where the scapular spine contacted the scapular body, the cross-sectional area of the Tm muscle was measured and divided by the total cross-sectional area of the external rotator muscles to calculate the Tm hypertrophy ratio.¹⁷ Based on this ratio, patients were categorized into three groups: hypertrophic, normal, and hypotrophic Tm. A ratio ≥0.288 was defined as Tm hypertrophy, a ratio between 0.112 and 0.288 was considered normal, and a ratio <0.112 indicated Tm hypotrophy.¹⁷ [Fig. 2] The hypertrophy ratio reflects the relative contribution of the Tm muscle to the total cross-sectional area of the external rotator muscles. A higher ratio indicates relative hypertrophy of the Tm compared with the other external rotator muscles, whereas a lower ratio indicates relative hypotrophy. The proportion of patients achieving the minimal clinically important difference (MCID) for the VAS, ASES, and Constant scores was calculated using the 0.5 standard deviation distribution method.³⁰ Postoperative complications, including retear of the transferred tendon, infection, stiffness, nerve injury, hematoma, and progression of glenohumeral arthritis, were recorded during the follow-up period.

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Fig. 2 Teres minor (Tm) Muscle Classification In the oblique sagittal MRI slice where the scapular spine contacts the scapular body, the cross-sectional area of the teres minor (Tm) muscle (blue dotted line) is measured and divided by the total area of the external rotator muscles (red dotted line) to obtain the Tm ratio. A ratio ≥0.288 is classified as hypertrophy, values between 0.112 and 0.288 are considered normal, and a ratio <0.112 indicates Tm hypotrophy.

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3 Results

After exclusion of 14 patients due to lost to follow-up, or incomplete or missing data, 83 patients were included in the final analysis. Based on the Tm hypertrophy ratio, patients were classified into the hypertrophic (n = 12), normal (n = 56), and hypotrophic (n = 15) groups. Baseline demographic characteristics were comparable among groups, with no significant differences in age, sex, BMI, follow-up duration, symptom duration, comorbidities, or fatty infiltration of the rotator cuff muscles. However, significant differences were observed in the fatty infiltration grades of the Tm among groups [Table I].

All groups demonstrated significant improvements in VAS, Constant score, and ASES score at final follow-up compared with preoperative values (p < 0.001 for all). Forward elevation and abduction improved significantly in all groups, with no significant differences between groups. External rotation at the side and at 90° of abduction also improved in all groups, yet the hypertrophic Tm group showed greater gains in both external rotation at side and at 90° of abduction [Table II]. Strength in forward elevation, abduction, and external rotation improved significantly in all groups, and it did not differ significantly between groups. Radiologic evaluation revealed smaller postoperative AHD and higher Hamada grades in the hypotrophic Tm group at the final follow-up [Table III]. The majority of patients achieved the MCID for VAS, Constant, and ASES scores, with no significant differences between groups [Table IV]. Complication rates, including retear, infection, stiffness, nerve injury, hematoma, and progression of glenohumeral arthritis, were comparable among groups. Retear occurred in 1 patient (8.3%) in the hypertrophic group, 11 patients (19.6%) in the normal group, and 3 patients (20.0%) in the hypotrophic group, without statistically significant differences [Table V].

4 Discussion

The main finding of this study is that arthroscopically assisted posterior LD transfer provides significant improvements in pain, shoulder function, and ROM in patients with irreparable PSRCTs, regardless of preoperative Tm trophicity. All groups demonstrated significant improvements in patient-reported outcome measures and shoulder ROM at final follow-up. However, patients with hypertrophic Tm demonstrated greater postoperative external rotation and external rotation strength compared with those with normal or hypotrophic Tm. Radiologic evaluation revealed smaller AHD and higher Hamada grades in the hypotrophic Tm group. Despite these differences, overall clinical improvement and the rates of achieving the MCID were comparable among groups.

The Tm is a key component of the posterior rotator cuff and plays an important role in shoulder external rotation and glenohumeral stability. ^17–20 In the presence of infraspinatus deficiency, the Tm often functions as a compensatory external rotator.^17,18 Previous studies have reported that hypertrophy of the Tm can develop as an adaptive response to chronic infraspinatus deficiency, potentially allowing preservation of external rotation strength and ROM in patients with PSRCTs.^17,18 Kikukawa et al.¹⁷ demonstrated that patients with hypertrophic Tm exhibited significantly greater external rotation strength compared with those with deficient Tm in the setting of PSRCTs. Biomechanical studies further support this compensatory mechanism, indicating that the Tm may experience substantially increased loading when the infraspinatus is dysfunctional.^19,31,32 Musculoskeletal modeling has shown that in massive PSRCTs, Tm torque and muscle activity may increase markedly in order to maintain external rotation, highlighting the important role of the Tm in preserving shoulder rotational function.²⁵ The findings of the present study are partially consistent with these previous reports. Patients with hypertrophic Tm demonstrated greater postoperative external rotation at side and at 90° abduction, suggesting that a well-compensated hypertrophic Tm may enhance external rotation function following posterior LD transfer.

The clinical relevance of Tm integrity has been emphasized in LD transfer procedures. Costouros et al.³³ reported that patients undergoing LD tendon transfer for irreparable PSRCTs achieved superior functional outcomes and greater external rotation when fatty infiltration of the Tm was minimal. Also, patients with preserved Tm integrity demonstrated significantly higher postoperative Constant scores and improved external rotation compared with those with advanced fatty infiltration.³³ Despite differences in external rotation ROM, overall clinical outcomes, including pain relief and functional scores, were similar among groups. These results suggest that posterior LD transfer itself may play a primary role in restoring shoulder biomechanics, whereas the native Tm contributes additional rotational strength rather than serving as the sole determinant of postoperative function. The transferred LD tendon functions as a dynamic stabilizer and helps re-establish the posterior force couple of glenohumeral joint, which may reduce dependence on the residual rotator cuff muscles. Biomechanical studies have further demonstrated that LD transfer procedures can redistribute muscle forces and reduce excessive loading on the remaining rotator cuff muscles. Menze et al.³² reported that LD transfers significantly decreased Tm torque and muscle activity in models of PSRCTs, restoring muscle loading toward physiologic levels. These findings suggest that LD transfer procedure may reduce the biomechanical demand placed on the Tm while simultaneously restoring balanced shoulder mechanics. This mechanism may explain why satisfactory clinical outcomes were achieved even in patients with hypotrophic Tm in the present study. Consistent with the results of the current study, several long-term clinical studies have demonstrated favorable outcomes following LD transfer. Gerber et al.³⁴ reported substantial improvements in shoulder function and pain relief at long-term follow-up after LD tendon transfer. Similarly, Kany et al.¹⁶ demonstrated sustained functional improvement at a minimum of ten years after surgery. El-Azab et al.³⁵ also reported durable pain relief and functional gains following LD transfer with mean follow-up of 9.3 years, particularly in younger and more active patients. The improvements observed in the present study are consistent with these prior reports and further support posterior LD transfer as an effective joint-preserving treatment option for irreparable PSRCTs. The radiologic findings of the present study were also comparable to those previously reported in the literature.^9,34,35 Although a slight decrease in AHD and progression of Hamada grade were observed at final follow-up, these radiographic changes did not appear to significantly influence clinical outcomes.

This study has several limitations. First, the retrospective design introduces potential selection bias. Second, although the overall cohort represents a relatively large series for this procedure, the number of patients in the hypertrophic and hypotrophic Tm groups was relatively small, which may have limited the statistical power for subgroup comparisons and the ability to detect subtle differences among groups. Third, postoperative dynamic analyses of muscle activation, such as electromyography (EMG), were not performed. Such evaluations could provide additional insight into the functional interaction between the transferred tendon and the native rotator cuff muscles. Fourth, concomitant procedures performed at the index surgery, including biceps-related procedures and subscapularis repair when indicated, may have acted as additional confounding factors. Fifth, the present study did not analyze the correlation between the degree of Tm fatty infiltration and other variables such as Tm cross-sectional area, shoulder muscle strength, ROM, or clinical outcome measures, as the primary focus of this study was to compare outcomes according to Tm trophicity groups. Future studies may further investigate these relationships to better clarify the functional role of the Tm muscle. Finally, all procedures were performed by a single experienced surgeon at a single institution, which may limit the generalizability of the findings.

5 Conclusion

Arthroscopically assisted posterior LD transfer provides significant pain relief and functional improvement in patients with irreparable PSRCTs regardless of preoperative Tm trophicity. Although hypertrophic Tm was associated with greater postoperative external rotation, overall clinical improvement and MCID achievement were similar among groups. Despite smaller postoperative AHD and higher Hamada grades in the hypotrophic group, clinical outcomes were comparable.

Ethical statement

This study was conducted in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki).

Guardian/Patient's consent

Regarding the manuscript “Middle Trapezius Tendon Transfer for Isolated Irreparable Supraspinatus Tears Shows Favorable Outcomes Despite Subscapularis Tear” as submitted to the Journal of Orthopedics, collectively declares that the requirement for informed consent was waived owing to the retrospective design of the study and the lack of additional harm to the patients.

Credit author statement

Chang Hee Baek: conceptualization, investigation, methodology, validation, project administration, resources, supervision, validation.

Bo Taek Kim: conceptualization, data curation, formal analysis, investigation, validation, methodology, validation, writing original draft, review/editing final draft.

Jung Gon Kim: conceptualization, formal analysis, investigation, methodology, validation.

Chaemoon Lim: conceptualization, formal analysis, investigation, methodology, validation.

Seung Jin Kim: data curation, formal analysis, investigation, methodology.

Funding

The authors did not receive support from any organization for the submitted work.

No funding was received to assist with the preparation of this manuscript.

No funding was received for conducting this study.

No funds, grants, or other support was received.

Funding source

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.