1 Introduction

Isolated irreparable supraspinatus tears (IISTs) represent an uncommon but clinically challenging subset of rotator cuff pathology.¹ Conventional repair strategies are often not feasible because the torn supraspinatus tendon may demonstrate substantial retraction, poor tissue quality, or advanced fatty degeneration.^2,3 Middle trapezius tendon (MTT) transfer has recently emerged as a promising surgical alternative. Biomechanically, the middle trapezius exhibits a line of pull that closely resembles that of the supraspinatus, thereby facilitating the restoration of a more physiological force vector.^4–6 Recent clinical reports have shown encouraging results, including improvements in pain, patient-reported outcomes measures (PROM), range of motion (ROM), and strength.^7–11 Despite these promising findings, the influence of preoperative concomitant subscapularis pathology on postoperative outcomes following MTT transfer remains poorly understood. As the subscapularis plays a critical role in anterior shoulder stability and in maintaining the anterior–posterior force couple of the glenohumeral joint,^12,13 the tears or dysfunction of the subscapularis may compromise shoulder biomechanics, potentially limiting the functional benefits achievable with MTT transfer.

The purpose of this study was to compare the clinical and radiologic outcomes of MTT transfer in patients with IISTs between those with an intact subscapularis and those with concomitant subscapularis tears. It was hypothesized that MTT transfer would lead to significant improvements in pain, PROM, and ROM in both groups.

2 Materials and methods

2.1

2.1 Patient Selection

This retrospective study included patients who underwent arthroscopically assisted MTT transfer for IIST between December 2019 and October 2023. IISTs were defined based on the following criteria: (1) torn supraspinatus with retraction to the level of the glenoid, corresponding to Patte¹⁴ classification stage III; (2) high-grade fatty infiltration of the supraspinatus muscle, graded as Goutallier¹⁵ stage ≥3 on preoperative MRI; and (3) intraoperative inability to mobilize the tendon to its anatomic footprint. Surgical indications included persistent pain and functional impairment despite conservative management, confirmation of an IISTs, preserved glenohumeral joint space (Hamada¹⁶ grade ≤2), and either an intact or reparable subscapularis tendon. Patients were excluded if they had incomplete follow-up data or were lost to follow-up. Patients were stratified into two groups according to preoperative subscapularis integrity: (1) subscapularis-intact group and (2) subscapularis-tear group. Intraoperative subscapularis tears were classified according to the Lafosse¹⁷ classification: type I (partial tear of the superior third), type II (complete tear of the superior third), and type III (complete tear of the superior two-thirds) [Fig. 1].

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Fig. 1 Patient Selection MTT, middle trapezius tendon; IIST, isolated irreparable supraspinatus tear; N/A, not available; f/u, follow-up; MRI, magnetic resonance imaging.

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2.2

2.2 Surgical technique

All procedures were performed by a single surgeon (C.H.B.) using a standardized MTT transfer technique described in the literature.^8,18 Patients were positioned in the lateral decubitus position under general anesthesia. Diagnostic arthroscopy was first conducted to confirm the irreparability of the supraspinatus tendon. A supraspinatus tear was deemed irreparable when the tendon could not be mobilized to its native footprint and could not be repaired. In such cases, arthroscopically assisted MTT transfer was performed.

Before proceeding with the MTT transfer, any subscapularis tears identified during arthroscopy (Lafosse type I, n = 3; type II, n = 8; type III, n = 2) were addressed. Type I tears were managed with arthroscopic debridement, whereas type II and III tears were repaired in the subacromial space using a double-row suture-bridge technique with one triple-loaded medial-row suture anchor and two knotless lateral-row anchors [Fig. 2A]. Biceps tenodesis (Subscapularis-intact group, n = 3; Subscapularis-tear group, n = 0) or tenotomy (Subscapularis-intact group, n = 4; Subscapularis-tear group, n = 3) was performed when more than 50 % of the long head of the biceps tendon was compromised.

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Fig. 2 Surgical Procedure (A) Arthroscopic view from the lateral viewing portal showing the repaired subscapularis tendon (green asterisk) in the subacromial space using a double-row suture-bridge configuration. (B) Harvested middle trapezius tendon (white asterisk) secured with a traction suture. (C) Arthroscopic view from the lateral viewing portal showing the interpositional graft (blue asterisk) secured to the supraspinatus footprint. (D) Final construct demonstrating the interpositional graft (blue asterisk) secured to the harvested middle trapezius tendon (white asterisk).

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The MTT was harvested through a 5-cm incision superior to the scapular spine, with care taken to preserve the posterior acromioclavicular ligament. The lateral portion of the MTT was carefully dissected from the acromion and supraspinatus fascia and prepared with a traction suture at its distal end [Fig. 2B]. To establish continuity between the MTT and the humerus, an interpositional graft—either an Achilles tendon allograft or a fascia lata autograft—was used. Achilles tendon allografts (Subscapularis-intact group, n = 30; Subscapularis tear-group, n = 11) were prepared by removing the calcaneal bone and securing the graft end with two nonabsorbable sutures. Fascia lata autografts (Subscapularis-intact group, n = 18; Subscapularis-tear group, n = 2) were harvested as 5 × 15-cm strips, folded to achieve the desired thickness, and prepared in the same manner.

The supraspinatus footprint was arthroscopically debrided and decorticated to promote tendon-to-bone healing. Two triple-loaded suture anchors were placed medially at the supraspinatus footprint, and the interpositional graft was passed through the supraspinatus outlet and secured to the footprint using a double-row suture-bridge configuration with three knotless lateral-row anchors [Fig. 2C]. With the arm positioned in 45–60° of abduction, the interpositional graft was attached to the harvested MTT using a Krackow stitch with 3–5 cm of overlap [Fig. 2D]. Arthroscopic visualization was maintained throughout the procedure to confirm appropriate firm and appropriate fixation.

3 Results

After excluding 5 patients due to incomplete data and loss to follow-up, a total of 61 patients were included, comprising 48 patients with an intact subscapularis and 13 patients with a concomitant subscapularis tear. There were no significant demographic differences between the groups. The most common chief complaints were night pain and painful active ROM, particularly during forward elevation and abduction [Table 1]. In the overall cohort, significant postoperative improvements were observed in VAS and PROMs. Active ROM improved significantly in forward elevation and abduction. Strength measurements also demonstrated significant gains in forward elevation and abduction strength, whereas external rotation ROM and strength showed no significant changes [Table 2].

Both the subscapularis-intact and subscapularis-tear groups demonstrated significant postoperative improvements in pain, PROMs, ROM, and strength (p < 0.001), with no significant differences between the groups on direct comparison. Forward elevation and abduction tended to be lower postoperatively in the subscapularis-tear group, although these differences were not statistically significant. Preoperative ROM and strength of internal rotation were inferior in the subscapularis-tear group, but postoperative values were comparable between the groups [Table 3]. Achievement rates of the MCID for VAS, Constant, and ASES scores were high in both groups, exceeding 90 % [Table 4]. Complication rates were similar between groups. Partial tendon retear occurred in one patient in each group, both of whom were managed conservatively as their symptoms improved relative to the preoperative state. One patient in the subscapularis-tear group developed an early postoperative infection, which was successfully treated with arthroscopic irrigation and debridement followed by intravenous antibiotics. Another patient demonstrated minor progression of glenohumeral arthritis (Hamada +1). No patients developed advanced arthritis (Hamada ≥3) [Table 5].

4 Discussion

This study demonstrated that MTT transfer results in significant improvements in pain, PROMs, and ROM—specifically forward elevation and abduction—in patients with IISTs, irrespective of subscapularis integrity. Both the subscapularis-intact group and subscapularis-tear group showed significant improvements in VAS, PROMs, with no significant differences between the groups. Although preoperative ROM and strength for internal rotation were lower in the subscapularis-tear group, postoperative recovery restored these measures to levels comparable to those of the subscapularis-intact group. Furthermore, the rates of achieving the MCID were high in both groups. These findings suggest that, when appropriately managed during surgery, concomitant subscapularis tears do not substantially diminish the overall clinical effectiveness of MTT transfer.

The current study demonstrates that MTT transfer provides consistently favorable outcomes for IISTs, irrespective of subscapularis integrity. These promising clinical results can be attributed to the fundamental biomechanical and anatomical properties of the procedure, as MTT transfer functions independently of the preoperative status of other rotator cuff structures.^9,10 Biomechanical studies have shown that the tendon's length, excursion, and force vector are sufficient to safely replicate supraspinatus function, although scapular protraction may limit the transfer's reach.^4,5 Additional evidence indicates that MTT transfer restores superior humeral head stability, reduces subacromial contact pressure, and preserves overall shoulder ROM.⁵ Clinically, previous studies have reported significant improvements in pain, functional scores, and active forward elevation and abduction following MTT transfer, with minimal tendon retear or progression of cuff tear arthropathy, and augmentation of rotator cuff repair with MTT transfer has been shown to achieve greater functional gains compared with partial repair alone.^7–11 In line with these findings, the present study demonstrated substantial improvements in pain, PROMs, and forward elevation and abduction in both subscapularis-intact and subscapularis-tear groups. These results suggest that MTT transfer provides effective restoration of shoulder function even in the presence of concomitant subscapularis pathology, highlighting the procedure's versatility and reliability as a dynamic reconstructive option for IISTs.

The influence of subscapularis integrity on postoperative outcomes following reconstructive surgery for irreparable rotator cuff tears has been widely debated. Several studies have suggested that subscapularis deficiency may compromise surgical success. For example, Takayama et al.^20,21 reported that irreparable subscapularis tears in patients undergoing superior capsular reconstruction for pseudoparalytic shoulders with irreparable posterosuperior rotator cuff tears were associated with significantly poorer postoperative outcomes, including reduced shoulder elevation and abduction and failure to recover from pseudoparalysis, underscoring the critical role of subscapularis integrity in functional recovery. Similarly, Gerber et al.²² demonstrated that subscapularis insufficiency resulted in inferior long-term outcomes following latissimus dorsi transfer for irreparable posterosuperior rotator cuff tears, suggesting that subscapularis deficiency may negatively influence tendon transfer efficacy. In contrast, other studies indicate that meaningful improvement can still be achieved even in the presence of subscapularis pathology; for instance, Cunningham et al.²³ reported favorable outcomes and high patient satisfaction after latissimus dorsi transfer for irreparable posterosuperior rotator cuff tears despite untreated subscapularis insufficiency. Similarly, Akpinar et al.²⁴ demonstrated that patients undergoing lower trapezius tendon transfer for irreparable posterosuperior rotator cuff tears—with or without subscapularis tears requiring repair—achieved excellent short-term clinical outcomes, accompanied by improvement on physical examination. Consistent with this, the present study showed that patients with subscapularis tears achieved substantial postoperative improvements in VAS, Constant, and ASES scores, as well as in forward elevation and abduction, comparable to those observed in patients with intact subscapularis tendons. Although the subscapularis-tear group had slightly lower postoperative ASES scores and internal rotation strength, rates of achieving the MCID were high in both groups, indicating clinically meaningful improvements. These findings suggest that MTT transfer can effectively restore shoulder function even in the presence of subscapularis tears, and therefore subscapularis deficiency should not be considered an absolute contraindication for this procedure in patients with IISTs. Nonetheless, other factors, such as preoperative acromiohumeral interval, high-grade fatty infiltration of the rotator cuff, and a history of prior shoulder surgery, have been associated with poorer postoperative outcomes, underscoring the importance of evaluating overall shoulder pathology when predicting surgical success.^25–29

This study has several limitations. First, its retrospective design and the relatively small sample size of the subscapularis-tear group may have increased the risk of type II error. Second, the follow-up period was limited, preventing assessment of long-term clinical outcomes. Third, there is potential for examiner bias, as the Lafosse classification of subscapularis tears was determined intraoperatively by a single surgeon. Additionally, the small number of patients in the subscapularis-tear group restricted the ability to perform detailed subgroup analyses. Finally, the absence of multivariate analysis limits the identification of independent predictors of clinical outcomes.

5 Conclusion

MTT transfer provides significant improvements in pain, PROMs, forward elevation, and abduction in patients with IISTs, regardless of subscapularis integrity. Both subscapularis-intact and subscapularis-tear groups demonstrated significant improvements in VAS, Constant, and ASES scores, with no significant differences between groups. Although preoperative ROM and strength for internal rotation were lower in the subscapularis-tear group, postoperative recovery restored these measures to levels comparable with those of the subscapularis-intact group.

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

Ethical statement

This study was conducted in accordance with the Code of Ethics of the World Medical.

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.