Rapid subscapularis degeneration after retear following reverse shoulder arthroplasty managed with secondary pectoralis major tendon transfer: a case report

Reverse total shoulder arthroplasty (rTSA) has been widely used to treat cuff tear arthropathy (CTA) or massive irreparable rotator cuff tears.⁸ However, subscapularis (SSC) repair during rTSA remains controversial.³ The necessity of SSC repair may ultimately depend on the prosthesis design.⁹ In medialized prosthesis types, SSC repair is generally recommended to enhance postoperative stability.⁶ In contrast, for lateralized prostheses, several studies have reported no significant impact of SSC repair on postoperative dislocation rates.⁹ Nevertheless, other studies suggest that SSC repair in lateralized prostheses can lead to improved clinical outcomes and better internal rotation (IR) function.⁷ It has also been reported that even when SSC repair is performed in lateralized prostheses, retears occur in approximately 33% to 53% of cases, which are associated with reduced IR range and strength.^1,4,5 Overall, there is still no clear consensus regarding the necessity of SSC tendon repair following rTSA prosthesis implantation.

The ongoing debate largely stems from the difficulty in accurately assessing the quality of the repaired SSC, and in establishing a clear association between the quality of the repaired SSC and clinical outcomes. Even when the SSC is repaired, it remains challenging to precisely determine the relationship between muscle quality of repaired SSC and functional recovery. To better evaluate the role of the repaired SSC in clinical outcomes following rTSA, it is essential to assess the degree of SSC musculature. In this case report, we present 2 patients who demonstrated rapid progression of SSC muscle atrophy following retear of repaired SSC after rTSA, as confirmed by magnetic resonance imaging (MRI).

Cases

Two right-hand dominant male patients (aged 64 and 67 years) presented with chronic pain and weakness in the right shoulder. One of the patients had a history of rotator cuff repair surgery performed at another hospital approximately 2 years prior to visiting our institution. On physical examination, forward elevation was 80° and 90°, and external rotation was 10° and 15°, respectively. IR of both patients reached the L3 vertebral level behind the back. Both patients showed a positive external rotation lag sign, while the belly press test was negative. CTA was diagnosed based on plain radiographs showing Hamada grade 4 arthritic changes and MRI findings of severe fatty degeneration of the supraspinatus and infraspinatus (Fig. 1). Accordingly, both patients underwent reverse total shoulder arthroplasty using the Equinoxe Shoulder System (Exactech, Gainesville, FL, USA), which incorporates a medialized glenoid design with a lateralized humeral component. A standard 36-mm and 38-mm glenosphere was implanted using a 25.4 × 33.8-mm oval baseplate. The humeral component was positioned at 20° of retroversion with a neck–shaft angle of 132.5°, and both the humeral tray and polyethylene liner were implanted with a neutral offset (+0 and + 2.5 mm). The SSC tendon was carefully detached using the peel technique and subsequently repaired to its native footprint on the lesser tuberosity at the time of the index procedure (Fig. 2).

Figure 1.

Preoperative plain radiographs and magnetic resonance image of right shoulder. (A and C) Plain radiographs show cuff tear arthropathy consistent with Hamada grade 4 arthritic changes. (B and D) MRI reveals severe fatty degeneration of the supraspinatus and infraspinatus, while the subscapularis remains intact. (Figure (A) and (B) of patient 1, (C) and (D) of patient 2). MRI, magnetic resonance imaging.

Figure 2.

Intraoperative photography and postoperative plain radiograph of primary rTSA of right shoulder. (A and C) Intraoperative photography shows the subscapularis is repaired after implanting rTSA. (B and D) Postoperative plain radiograph shows a well-positioned and stable rTSA. (Figure (A) and (B) of patient 1, (C) and (D) of patient 2). rTSA, reverse total shoulder arthroplasty.

Initially, both patients were satisfied with the postoperative clinical outcomes. However, both patients began to complain of IR limitation and weakness at 10 months and 1 year after surgery, respectively. Sonography confirmed the retear of the repaired SSC. MRI performed at 1 year postoperatively demonstrated severe fatty infiltration of the SSC muscle, corresponding to Goutallier grade 4, which indicates almost complete fatty replacement of the muscle tissue (Fig. 3). In addition to the advanced fatty degeneration, there was marked atrophy of the SSC musculature, as evidenced by a substantial decrease in muscle volume and thinning of the muscle belly. This pattern of degeneration strongly suggested a loss of functional contractile elements within the SSC. The imaging findings confirmed that despite initial surgical repair, the SSC muscle had undergone rapid and extensive degenerative changes within a relatively short postoperative period if a retear of the repaired SSC occurs.

Figure 3.

Serial MRI of 2 patients of right shoulder. (A and D) Preoperative MRI shows an intact subscapularis. (B and E) MRI at 1 year postoperatively demonstrates severe fatty infiltration of the subscapularis muscle, corresponding to Goutallier grade 4, indicating near-complete fatty replacement. (C and F) MRI at 2 years postoperatively shows further progression of fatty infiltration and more pronounced muscle atrophy compared to the 1-year postoperative imaging. (Figure (A), (B) and (C) of patient 1, (D), (E) and (D) of patient 2). MRI, magnetic resonance imaging.

Despite 1 year of conservative treatment, including a strengthening exercise program, IR weakness persisted, particularly causing difficulties during toileting activities. Follow-up MRI performed at 2 years postoperatively demonstrated a further progression of fatty infiltration and more pronounced muscle atrophy compared to the 1-year postoperative imaging. The degree of degeneration had clearly worsened over time, indicating a continuous and rapid deterioration of the SSC muscle following the retear (Fig. 3). Functional assessments at that time indicated unsatisfactory outcomes. The pain visual analog scale score was 5. The Constant scores were 38 and 42 out of 100, and the American Shoulder and Elbow Surgeons (ASES) scores were 41 and 43 out of 100, respectively. IR at back was limited to the buttock level, and the measured IR strength was 14.6 N and 15.4 N, respectively (Fig. 4) (Table I).

Figure 4.

Clinical photographs taken at 2 years postoperatively of Right shoulder. (A and B) Internal rotation behind the back was limited to the buttock level in both patients. (Figure (A) of patient 1, (B) of patient 2).

Table I.

Clinical scores before and after secondary pectoralis major tendon transfer.

Variables	Age	Sex	Clinical score before secondary PM tendon transfer					Clinical score after secondary PM tendon transfer
			VAS	Constant	ASES	IR	IR strength	VAS	Constant	ASES	IR	IR strength
Patient 1	64	Male	5	38	41	Buttock	14.6 N	1	75	77	L3	28.7
Patient 2	67	Male	5	42	43	Buttock	15.4 N	1	78	80	L3	29.1

PM, pectoralis major; VAS, visual analog scale (for pain); ASES, American Shoulder and Elbow Surgeons; IR, internal rotation; N, newton.

After thorough discussion with the patients, secondary pectoralis major (PM) tendon transfers were performed. All revision surgeries were carried out under general anesthesia with the patient in the beach-chair position using a conventional deltopectoral approach. Intraoperative assessment confirmed insufficiency of the SSC, and any nonviable tissue was thoroughly débrided. For PM tendon harvest, the muscle was circumferentially released by freeing both its superior and inferior margins from adjacent soft tissues. The tendon was then detached as a single unit from its humeral insertion, without division of the clavicular and sternal heads. Two No. 2 sutures with needles were placed in a continuous locking configuration along the superior and inferior edges of the tendon. These sutures incorporated the deep tendinous surface near the insertion site to enhance fixation strength and minimize the risk of tendon failure. The mobilized tendon was subsequently transferred beneath the conjoined tendon to re-establish anterior shoulder stability. On the humeral side, preparation involved drawing a reference line extending from the bicipital groove to the upper margin of the teres minor insertion, followed by a second line placed 1.5 cm inferior to the first. Two transosseous tunnels were then created along these trajectories using a 2.0-mm Kirschner wire. Nonabsorbable No. 2 sutures were passed through each tunnel in a looped configuration and secured with sliding locking knots to maintain stable fixation and prevent suture displacement. The PM tendon was secured to the humerus with the arm positioned in full IR. Additional horizontal continuous locking sutures were placed along the superior and inferior borders of the tendon, carefully avoiding the muscular portion, to further reinforce the tendon-to-bone interface. In selected cases presenting with recurrent anterior instability, upsizing of the polyethylene insert was performed as an adjunctive procedure, while the PM transfer served as the principal stabilizing intervention (Fig. 5). Following surgery, all patients were immobilized in an abduction brace for a period of 4 to 6 weeks. Passive range-of-motion exercises were initiated after immobilization, followed by active-assisted movements at approximately 8 to 10 weeks postoperatively. Strengthening exercises targeting IR were commended at 3 months under the supervision of a physiotherapist.

Figure 5.

Intraoperative photography of secondary pectoralis major tendon transfer of Right shoulder. (A and C) Initial intraoperative photography shows a retear of the previously repaired subscapularis from the primary reverse total shoulder arthroplasty. (B and D) Final intraoperative photography shows the secondary pectoralis major tendon transfer (white asterisk) to the greater tuberosity of the humerus.

One year after surgery, both patients experienced significant pain relief, with visual analog scale scores decreasing to 1. Functional recovery was also favorable, with Constant scores improving to 75 and 78, and ASES scores improving to 77 and 80, respectively. IR improved from the buttock level to the L3 vertebral level, and IR strength increased to 28.7 N and 29.1 N, respectively (Fig. 6) (Table I).

Figure 6.

Clinical photographs after secondary pectoralis major tendon transfer of Right shoulder. (A and B) Internal rotation improved from the buttock level to the L3 vertebral level after secondary pectoralis major tendon transfer in both patients. (Figure (A) of patient 1, (B) of patient 2).

Discussion

This case report presents 2 patients who developed rapid and extensive SSC muscle degeneration and atrophy following an SSC retear after rTSA with SSC repair. Both patients initially showed satisfactory clinical outcomes after rTSA. However, they experienced IR weakness and functional limitations within one year postoperatively, which progressively worsened despite conservative management. Ultrasonography evaluation confirmed an SSC retear, and subsequent MRI demonstrated a rapid progression of fatty degeneration and muscle atrophy over a relatively short period. The clinical significance of these cases lies in the observation that when a repaired SSC fails after rTSA, the SSC muscle may undergo accelerated degeneration, leading to persistent IR dysfunction and a decline in overall shoulder function. This deterioration can substantially impair activities of daily living, particularly toileting, which heavily relies on adequate IR strength. These cases highlight the importance of vigilant postoperative monitoring of SSC integrity and suggest that timely intervention, such as PM tendon transfer, may provide meaningful functional recovery in cases where rapid SSC degeneration occurs after retear.

The precise contribution of the SSC in rTSA continues to be a subject of debate.³ Its functional importance seems to depend on the type of prosthesis.⁹ Recent studies have indicated that SSC repair may still play an important role in optimizing IR, even when lateralized prosthetic designs are employed.⁷ Nevertheless, the reported healing rates after SSC repair vary widely, typically ranging from 33% to 53%.^1,4,5 Baek et al demonstrated that patients with a healed SSC achieved significantly better IR active range of motion and IR strength compared to those with an unhealed or unrepaired SSC.¹ Similarly, this case report found that failure of SSC healing was linked to poorer postoperative outcomes, including reduced Constant scores, ASES scores, ADLIR scores, limited IR behind the back, and weakened IR strength. These results underscore the importance of SSC integrity in the recovery of functional IR and support the need for careful evaluation of the quality of repaired SSC during follow-up.

Evaluation of the repaired SSC tendon healing and muscle quality after rTSA can be challenging because of the presence of metal artifacts. There are several studies that have demonstrated the integrity of the repaired SSC after rTSA through ultrasonographic evaluation.^4,5 In these studies, ultrasonography was utilized to detect whether the repaired SSC tendon at the lesser tuberosity remained intact or was disrupted.^4,5 However, it is challenging to accurately assess the SSC musculature using ultrasonography because SSC is located deeper and more medially. Computed tomography has limitations in assessing the SSC tendon and musculature because of metal artifacts. However, MRI provides a reliable assessment of SSC musculature degeneration and atrophy, with relatively less variation in interpretation between observers despite the presence of metal artifacts. Although metal artifacts are present on MRI, as demonstrated in this case report, T1-weighted sagittal oblique views provided sufficient visualization to assess the Goutallier grade and muscular atrophy of the SSC.

Several clinical studies have investigated tendon transfer procedures to improve IR function after rTSA. Valenti et al reported that combining PM tendon transfer with lateralized rTSA in irreparable SSC cases significantly improved Constant-Murley scores, active IR, and abduction strength, enhancing overall shoulder function.¹⁰ Baek et al also reported that PM tendon transfer combined with rTSA significantly improved clinical outcomes in patients with CTA and massive irreparable rotator cuff tears with loss of active IR.² Consistent with these findings, the present case report also demonstrated that secondary PM tendon transfer after rTSA resulted in superior improvements in pain relief and clinical outcome including clinical score, IR active range of motion, and IR strength. These favorable outcomes may be attributed to the biomechanical benefits of PM tendon transfer. In a cadaveric study, Werthel et al showed that among various tendon transfer options, PM tendon transfer provided the largest IR moment arm. Moreover, they reported that PM tendon transfer may serve as a strong alternative to restore active IR when combined with a lateralized glenosphere in cases of irreparable SSC tears.¹¹ Based on this evidence, secondary PM tendon transfer may be considered a reasonable treatment option in cases of SSC retear following rTSA.

This study has several limitations. First, the findings are based on only 2 cases, which limits generalizability. Second, the follow-up period after secondary PM tendon transfer was less than two years, which may be insufficient to fully evaluate long-term outcomes and durability of the procedure. Third, assessment of SSC muscle degeneration using MRI may have been influenced by metal artifacts from the reverse shoulder arthroplasty implant. Finally, the absence of a control group precludes comparative analysis with other treatment options. Despite these limitations, this case report provides clinically meaningful insights into the rapid degeneration of the SSC after retear following rTSA and suggests that secondary PM tendon transfer may represent a valuable treatment option in selected patients.

Conclusion

This case report demonstrated the rapid progression of fatty degeneration and muscle atrophy following SSC retear after rTSA. Therefore, vigilant postoperative monitoring of SSC integrity is essential, particularly in symptomatic patients presenting with active IR deficiency. Timely interventions, such as PM tendon transfer, may provide meaningful functional recovery in cases of SSC retear after rTSA.

Disclaimers:

Funding: No funding was disclosed by the authors.

Conflict of interest: The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

Patient consent: Obtained.