Lipoma of the Teres Minor in Rotator Cuff Arthropathy-A Case Report

Although lipomas are the most common mesenchymal tumors, the intramuscular type is rare. We report the case of a patient with rotator cuff arthropathy with a lipoma in the teres minor. Wide surgical excision and total shoulder arthroplasty with reverse prosthesis was performed and 18 months of follow up showed excellent results with any recurrence. The teres minor is extremely important for the proper function of a reverse prosthesis, and lipoma growth in the muscular belly can compromise the functionality of the prosthesis. To the best of our knowledge, this is the first case report of a rotator cuff arthropathy with a lipoma in the teres minor.

Myxoid pleomorphic liposarcoma in the teres minor muscle: A case report

RATIONALE

Myxoid pleomorphic liposarcoma (MPL) is a rare aggressive adipocytic tumor that mainly presents in children and adolescents. It is most frequently observed in the mediastinum and rarely in the head and neck, perineal region, or back. Herein, we report the first published case of MPL of the teres minor muscle.

PATIENT CONCERNS

A 24-years-old woman presented with a painless palpable mass in her right shoulder.

DIAGNOSES

Magnetic resonance imaging identified a 9.0 × 7.0 × 4.0 cm mass suspected to be a sarcoma in the teres minor muscle. Positron emission tomography/computed tomography revealed no evidence of distant metastasis. Histopathological examination revealed the mass to be an MPL, which was assigned a histologic grade of 3 according to the French Federation of Cancer Centers Sarcoma Group system. No tumor cells were observed along the resected margins.

INTERVENTIONS

Under general anesthesia, the right teres minor muscle containing the mass was excised en bloc and frozen biopsy confirmed that the tumor cells did not invade the surrounding tissues.

OUTCOMES

The patient underwent radiotherapy and was followed up for 6 months without complications.

LESSONS

Although MPL in the teres minor muscle is rare, it should be considered in the differential diagnosis in patients with a mass in the teres minor muscle due to its poor prognosis.

Teres minor muscle hypertrophy is a negative predictor of outcomes after reverse total shoulder arthroplasty: an evaluation of preoperative magnetic resonance imaging and postoperative implant position

BACKGROUND

Predictors of outcomes after reverse total shoulder arthroplasty (rTSA) remain unclear. The purpose of this study was to analyze the impact of preoperative muscle quality and postoperative implant positioning on patient-reported outcomes following rTSA.

METHODS

We evaluated 88 shoulders treated with rTSA in which preoperative magnetic resonance imaging was available. Preoperative muscle quality was evaluated, including fatty infiltration, rotator cuff muscle volume, and total tear size. Postoperative implant position was determined radiographically. The correlation between imaging parameters and the 2-year postoperative American Shoulder and Elbow Surgeons (ASES) score was examined. Multivariate analyses were performed to adjust for confounding factors including patient demographic characteristics and implant position.

RESULTS

Univariate analysis showed that the ASES score was significantly lower in patients with teres minor muscle hypertrophy relative to those with normal muscle (73.3 ± 22.8 vs. 84.2 ± 16.9, P = .02). The functional subscore was significantly lower in patients with grade 2 fatty infiltration of the deltoid muscle relative to those with grade 0 fatty infiltration (26.1 ± 14.6 vs. 34.8 ± 11.6, P = .03). Older age was associated with a higher pain subscore (ρ = 0.32, P = .002). Multivariate analysis demonstrated that teres minor muscle hypertrophy remained a significant independent predictor of the ASES score (β coefficient = 91.3, P = .03).

CONCLUSION

Teres minor muscle hypertrophy is an independent negative predictor of patient-reported outcomes after rTSA.

Quadrilateral space syndrome induced by a large degenerative osteophyte

A 41-year-old gentleman presented with decreased range of motion. Initial radiographs demonstrated extensive osteoarthritic changes involving the glenohumeral joint with a large inferior oriented osteophyte. Subsequent MRI of the shoulder was obtained which demonstrated isolated fatty atrophy of the teres minor and, to a lesser extent, deltoid muscles. The axillary nerve was visualized entering the quadrilateral space which, although, was severely narrowed secondary to the large osteophyte. The patient's clinical symptoms and MRI findings were consistent with quadrilateral space syndrome. The patient wanted to attempt conservative therapy first; and therefore, subsequently underwent physical therapy with improvement of shoulder strength and range of motion.

Latissimus dorsi tendon transfer in reverse shoulder arthroplasty: transfer location affects strength

Background

The optimal insertion location of a latissimus dorsi tendon transfer to restore external rotation after reverse shoulder arthroplasty (RSA) is not well established. The aim of this biomechanical study was to determine the effect of tendon transfer location on external rotation torque, in conjunction with varying RSA humeral component lateralization. We hypothesized that proximal tendon transfers, along with increasing humeral lateralization, would maximize external rotation torque.

Methods

Eight fresh-frozen cadaveric shoulders underwent RSA and were tested on an in vitro shoulder simulator. A latissimus dorsi tendon transfer was tested at three insertion locations (lateral greater tuberosity [Lat-GT]; teres minor footprint [Tm-FP]; lateral shaft [Lat-Shft]), and external rotation torque was measured. Additional test conditions included varying humeral component lateralization (-5, 0, +5, +10, +15 mm), abduction angle (0°, 45°, 90°), and internal/external rotation (-60°, -30°, 0°, 30°, 60°).

Results

The Lat-GT and Tm-FP insertions of the latissimus dorsi transfer both generated significantly greater torques (P < .001) than the Lat-Shft. When comparing Lat-GT to Tm-FP, there were no significant differences (P = .362). At 60˚ of external rotation, RSA humeral component lateralization from -5 to +15 mm significantly increased the external rotation torque of Lat-GT by 67% (P = .035), Tm-FP by 43% (P = .001), and of Lat-Shft by 42% (P = .002).

Conclusion

Latissimus dorsi tendon transfer to the proximal lateral aspect of the greater tuberosity and to the insertion site of the teres minor generated significantly more external rotation torque than transfer to the lateral humeral shaft. In addition, the use of a humeral component with greater offset also substantially increases the torque generated by the tendon transfer.

Short-term outcomes of arthroscopic partial repair vs. latissimus dorsi tendon transfer in patients with massive and partially repairable rotator cuff tears

BACKGROUND

There is limited evidence on clinical outcomes of arthroscopic partial repair (APR) and latissimus dorsi tendon transfer (LDTT) for posterosuperior massive rotator cuff tears (mRCTs). We aimed to compare clinical outcomes of APR and LDTT for partially repairable posterosuperior mRCTs and to determine whether outcomes differ among tears that involve the teres minor.

METHODS

We retrieved the records of 112 consecutive patients with mRCTs deemed partially repairable due to fatty infiltration (FI) stage ≥3 in one or more rotator cuff muscles. Of the tears, 12 involved the subscapularis, 32 were managed conservatively, 14 were treated by reverse shoulder arthroplasty, and 7 were treated by stand-alone biceps tenotomy. Of the remaining 47 shoulders, 26 underwent APR and 21 underwent LDTT. At a minimum of 12 months, we recorded complications, active forward elevation, external rotation, the Constant-Murley score, American Shoulder and Elbow Surgeons (ASES) score, Subjective Shoulder Value (SSV), and Simple Shoulder Test (SST) score.

RESULTS

No significant differences between the APR and LDTT groups were found in terms of follow-up (23.4 ± 3.5 months vs. 22.1 ± 4.1 months, P = .242), Constant-Murley score (64.8 ± 13.7 vs. 58.9 ± 20.0, P = .622), ASES score (78.3 ± 19.3 vs. 74.4 ± 14.5, P = .128), active forward elevation (158.1° ± 19.4° vs. 142.8° ± 49.1°, P = .698), or external rotation (33.3° ± 17.4° vs. 32.2° ± 20.9°, P = .752). By contrast, the APR group had a higher SSV (73.3 ± 17.5 vs. 59.5 ± 20.0, P = .010), and SST score (8.3 ± 2.4 vs. 6.4 ± 3.0, P = .024). Univariable analysis revealed that advanced FI of the teres minor compromised Constant-Murley scores (β = -25.8, P = .001) and tended to compromise ASES scores (β = -15.2, P = .062). Multivariable analysis corroborated that advanced FI of the teres minor compromised Constant-Murley scores (β = -26.9, P = .001) and tended to compromise ASES scores (β = -16.5, P = .058).

CONCLUSION

Both APR and LDTT granted similar early clinical outcomes for partially repairable posterosuperior mRCTs, regardless whether the teres minor was intact or torn. Advanced FI of the teres minor was the only independent factor associated with outcomes, as it significantly compromised Constant-Murley scores and tended to compromise ASES scores.

Preoperative Fatty Infiltration of the Teres Minor Negatively Affects Postoperative Outcomes in Patients With Rotator Cuff Pathology

Background

The teres minor is a critical component of the rotator cuff and serves as one of the few external rotators of the humerus. Information is lacking regarding the effect of teres minor atrophy in isolation and in the setting of concomitant full-thickness rotator cuff tears on outcomes in patients undergoing rotator cuff surgery.

Purpose

To investigate the effect of preoperative teres minor fatty infiltration on postoperative clinical outcomes in patients with and without full-thickness rotator cuff pathology.

Study Design

Cohort study; Level of evidence, 3.

Methods

A retrospective review of patients undergoing primary arthroscopic shoulder surgery between 2014 and 2016 was performed. Preoperative magnetic resonance imaging was used to determine fatty infiltration for each rotator cuff muscle using the modified Goutallier classification. American Shoulder and Elbow Surgeons (ASES) as well as the shortened version of Disabilities of the Arm, Shoulder and Hand (QuickDASH) scores were obtained preoperatively and during follow-up. Exclusion criteria included prior surgery on the ipsilateral shoulder or a diagnosis of inflammatory arthropathy. For analysis, patients were dichotomized to grade 0 or grade 1-4 atrophy of the teres minor as well as to full-thickness or partial-thickness rotator cuff pathology.

Results

A total of 36 of 47 (76.6%) patients (mean age, 63 years; range, 45-76 years) were available for postoperative follow-up at a mean of 40 months (range, 30-48 months). Postoperative ASES score was significantly higher and QuickDASH score was significantly lower among all patients in the grade 0 group compared with the grade 1-4 group. Postoperative ASES and QuickDASH scores were not significantly different in patients with partial-thickness rotator cuff tears at any time point. However, the postoperative ASES score was significantly higher and QuickDASH score was significantly lower in the grade 0 versus grade 1-4 group for patients with full-thickness rotator cuff pathology.

Conclusion

Preoperative teres minor atrophy in patients undergoing surgery for rotator cuff pathology may impair postoperative clinical outcomes, especially in patients with full-thickness tears.

The Application of Double Elastic Band Exercise in the 90/90 Arm Position for Overhead Athletes

BACKGROUND

Traditional exercises performed with the shoulder in the position of 90° abduction and external rotation with elbow flexion (90/90) while using a single elastic band showed moderate activity of both the lower trapezius (LT) and infraspinatus (IS) muscle. The purpose of this study was to investigate activity of the teres minor (TMi) and the LT muscles during standing external rotation exercise with the shoulder in the 90/90 position with 2 elastic bands in both the frontal and the scapular plane.

HYPOTHESIS

TMi, IS, and LT muscle activities will vary depending on whether the shoulder is positioned in the frontal or scapular plane with the application of 2 elastic bands. Also, the serratus anterior (SA) and teres major (TMa) muscles will produce different muscular activity patterns during exercises performed with 2 elastic bands in the frontal plane compared with the TMi and LT muscles.

STUDY DESIGN

Controlled laboratory study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 21 collegiate baseball players volunteered to participate. The electromyography (EMG) activities of the TMi, IS, LT, SA, TMa, middle deltoid (MD), posterior deltoid, and upper trapezius (UT) muscles were measured with the 90/90 arm position during both isometric and oscillation resistance exercises with 2 elastic bands oriented in the frontal and scapular planes.

RESULTS

A significant difference was observed in EMG activity of both the TMi and the LT muscles between single and double elastic band applications in the frontal plane (P < 0.05). In contrast, EMG activity of the IS, SA, and TMa muscles was significantly increased in the scapular plane compared with the frontal plane (P < 0.05).

CONCLUSION

The standing 90/90 position effectively increased both TMi and LT muscle EMG activity with the double elastic band in the frontal plane while minimizing UT and MD muscle activity. EMG activity of the IS, SA, and TMa muscles increased with exercise in the scapular plane as compared with the frontal plane.

CLINICAL RELEVANCE

Oscillation movement under double elastic band application differentiated external rotator muscle and scapular muscle activities between the frontal and scapular plane during the 90/90 exercise in the frontal plane compared with the scapular plane. Clinicians can utilize each of the scapular and frontal positions based on their desired focus for muscular activation.

Posterior shoulder tightness can be a risk factor of scapular malposition: a cadaveric biomechanical study

BACKGROUND

Scapular malposition and posterior shoulder tightness are key pathologic processes in the shoulder of throwing athletes. The objective of this study was to investigate the effects of posterior capsule tightness, posterior rotator cuff muscle tightness, or both on scapular position.

METHODS

Ten shoulders from 5 fresh frozen cadaveric male torsos were tested in maximum internal, neutral, and maximum external shoulder rotations at 0°, 45°, and 90° of shoulder abduction. Scapular rotation-namely, upward and downward rotation, internal and external rotation, and anterior and posterior tilt-and the scapula-spine distance were measured by using a MicroScribe digitizer (Revware, Raleigh, NC, USA). Each shoulder underwent 4 experimental stages: intact; isolated posterior rotator cuff muscle (infraspinatus and teres minor) tightness; both posterior rotator cuff muscle and capsule tightness; and isolated posterior capsule tightness.

RESULTS

Posterior muscle tightness significantly decreased upward rotation (P< .05) only in maximum shoulder internal rotation at 45° or 90° of shoulder abduction, whereas posterior capsule tightness did not affect upward rotation (P= .09 to .96). Posterior capsule tightness significantly increased scapular internal rotation (P< .01), but posterior muscle tightness did not change scapular internal rotation (P= .62 to .89). Posterior capsule tightness significantly increased both the superior and inferior scapula-spine distance (ie, caused scapular protraction) in maximum shoulder external rotation at 90° of abduction (P< .01).

CONCLUSION

Posterior shoulder tightness resulted in scapular malposition. However, the muscular and capsular components of that tightness affected the scapular position differently. For the treatment of scapula malposition, stretching of the posterior shoulder capsule and muscles is recommended.

Electromyographic analysis of selected shoulder muscles during rehabilitation exercises

BACKGROUND

Overhead work-activities and repetitive use of arm in occupational tasks are known risk factors to cause shoulder injury that often develops to functional disability. Rehabilitation exercises (REs) are capable of slowing this development.

OBJECTIVE

The main objective of the present work is to experiment with common REs and to identify those which produce significant integrated electromyography (iEMG) activation of selected shoulder muscles namely, posterior deltoid, infraspinatus, teres minor, upper trapezius, middle trapezius and lower trapezius.

METHODS

  Ten healthy male occupational workers, exposed to the risk of shoulder injury, performed six REs while iEMG activities of concerning muscles are recorded using Biopac MP 150 system. REs are cross-examined statistically to select those which yield higher iEMG activations.

RESULTS

Results indicate that upper trapezius presents the highest iEMG activity in exercise 6 (standing ER at 90∘ abduction and 90∘ elbow flexion). Middle trapezius and lower trapezius show highest activation in exercise 1 (prone horizontal abduction at 90∘ with full external rotation with thumb right up). Also, posterior deltoid, infraspinatus, and teres minor have the highest iEMG activity in this exercise.

CONCLUSIONS

Results provide basic information to select appropriate rehabilitation programs for occupational workers exposed to the risk of shoulder injury.

Hypertrophic teres minor restores shoulder strength and range of external rotation in posterosuperior rotator cuff tears

BACKGROUND

In posterosuperior rotator cuff tears (PS-RCT), the progression of infraspinatus (ISP) muscle atrophy seems to induce compensatory hypertrophy of the teres minor (TM) muscles. However, the effect of these changes on shoulder strength and range of external rotation (ER) remains unclear. This study determined the strength and range of ER in patients with PS-RCT with atrophic ISP and hypertrophic TM and compared this with patients with PS-RCT and normal or deficient TM.

METHODS

We investigated 35 patients with PS-RCT and atrophic ISP. TM muscles were classified as hypertrophic (type A) in 17, normal (type B) in 10, or deficient (type C) in 8. The strength ratio of the affected shoulder to the healthy contralateral shoulder was calculated, and the active range of motion was measured for both shoulders.

RESULTS

The strength ratios of ER in types A, B, and C were 60%, 33%, and 7% (P < .01) with the patient's arm at the side and were 60%, 35%, and 5% (P < .001) at 90° abduction, respectively. The average ranges of ER in types A, B, and C were 22.6°, 15.0°, and -12.5° (P < .001) with the patient's arm at the side and were 71.6°, 44.5°, and 21.9° at 90° abduction (P < .01), respectively. The differences between shoulder types in other measures of strength or ER range were not significant.

CONCLUSIONS

In patients with PS-RCT and atrophic ISP, shoulders with compensatory hypertrophy of the TM had greater strength and range of ER than shoulders with normal or atrophic TM.

Effects of two stretching methods on shoulder range of motion and muscle stiffness in baseball players with posterior shoulder tightness: a randomized controlled trial

BACKGROUND

The cross-body stretch and sleeper stretch are widely used for improving flexibility of the posterior shoulder. These stretching methods were modified by Wilk. However, few quantitative data are available on the new, modified stretching methods. A recent study reported the immediate effects of stretching and soft tissue mobilization on the shoulder range of motion (ROM) and muscle stiffness in subjects with posterior shoulder tightness. However, the long-term effect of stretching for muscle stiffness is unknown. The objective of this study was to examine the effects of 2 stretching methods, the modified cross-body stretch (MCS) and the modified sleeper stretch (MSS), on shoulder ROM and muscle stiffness in baseball players with posterior shoulder tightness.

METHODS

Twenty-four college baseball players with ROM limitations in shoulder internal rotation were randomly assigned to the MCS or MSS group. We measured shoulder internal rotation and horizontal adduction ROM and assessed posterior shoulder muscle stiffness with ultrasonic shear wave elastography before and after a 4-week intervention. Subjects were asked to perform 3 repetitions of the stretching exercises every day, for 30 seconds, with their dominant shoulder.

RESULTS

In both groups, shoulder internal rotation and horizontal adduction ROM were significantly increased after the 4-week intervention. Muscle stiffness of the teres minor decreased in the MCS group, and that of the infraspinatus decreased in the MSS group.

CONCLUSIONS

The MCS and MSS are effective for increasing shoulder internal rotation and horizontal adduction ROM and decreasing muscle stiffness of the infraspinatus or teres minor.

Arthroscopic Partial Repair of Irreparable Rotator Cuff Tears: Preoperative Factors Associated With Outcome Deterioration Over 2 Years

BACKGROUND

Arthroscopic partial repair is a treatment option in irreparable large-to-massive rotator cuff tears without arthritic changes. However, there are indications that arthroscopic partial repair does not yield satisfactory outcomes.

PURPOSE

To report the clinical and radiographic results of arthroscopic partial repairs in patients with irreparable large-to-massive cuff tears. In addition, an analysis was performed regarding preoperative factors that may influence patient outcomes and patient-rated satisfaction over time.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

From 2005 to 2011, a total of 31 patients who underwent arthroscopic partial repair for irreparable large-to-massive cuff tears were retrospectively evaluated. Partial repair was defined as posterior cuff tissue repair with or without subscapularis tendon repair to restore the transverse force couple of the cuff. Pain visual analog scale (PVAS), questionnaire results (American Shoulder and Elbow Surgeons [ASES] and Simple Shoulder Test [SST]), and radiographic changes (acromiohumeral distance and degenerative change) were assessed preoperatively, at first follow-up (roughly 1 year postoperatively), and at final follow-up (>2 years postoperatively). Patients rated their satisfaction level at each postoperative follow-up as well. Preoperative factors that might influence outcomes, such as patient demographics, tear size, and fatty infiltration, were investigated.

RESULTS

The preoperative, first follow-up, and final follow-up results for mean PVAS (5.13, 2.13, and 3.16, respectively) and questionnaires (ASES: 41.97, 76.37, and 73.78; SST: 3.61, 6.33, and 6.07, respectively) improved significantly (all P < .05). Radiographic evaluation showed no difference compared with preoperative status. Nevertheless, patient-rated satisfaction at final evaluation was inferior: 16 good responses ("very satisfied" and "satisfied") and 15 poor responses ("rather the same" and "dissatisfied"). Despite initial improvements in both groups (P < .05), patients with poor satisfaction demonstrated statistically significant deterioration in mean PVAS (from 2.07 to 4.67), questionnaire scores (ASES: from 74.56 to 59.80; SST: from 5.11 to 3.81), and acromiohumeral distance (from 7.19 to 5.06 mm) between the first and final follow-up (all P < .05). Patients with good satisfaction showed no significant difference or they improved (P > .05) from the first to the final follow-up. Among preoperative factors, fatty infiltration of the teres minor was identified as the only statistically significant factor affecting patient-rated satisfaction (P = .007).

CONCLUSION

This study showed that arthroscopic partial repair may produce initial improvement in selected outcomes at 2-year follow-up. However, about half of the patients in the study were not satisfied with their outcomes, which had deteriorated over time. Preoperative fatty infiltration of the teres minor was the only factor that correlated with worse final outcomes and poor satisfaction after arthroscopic partial repair.

The effect of humeral version on teres minor muscle moment arm, length, and impingement in reverse shoulder arthroplasty during activities of daily living

BACKGROUND

External rotation can be compromised after reverse total shoulder arthroplasty (RTSA). A functional teres minor (TM) is relatively common in patients with posterosuperior tears of the rotator cuff, and its function should be enhanced for better postoperative results. The aim of this study was to investigate how the version of humeral fixation can affect the TM rotational moment arm and muscle length as well as impingement after RTSA.

METHODS

A 3-dimensional shoulder model was used to describe RTSA. Four humeral fixation versions were tested: +20°, 0°, -20°, and -40° (+, anteverted; -, retroverted). TM rotational moment arm and length as well as impingement-free range of motion were calculated for a set of 3 simple clinical motions: (1) scapula plane abduction (0°-150°); (2) internal/external rotation with the arm in adduction; and (3) internal/external rotation with the arm in abduction. Six common activities of daily living were also evaluated.

RESULTS

An anteverted fixation maximized TM moment arms, but it also resulted in very short muscle length (compared with normal) and increased inferior impingement. In contrast, 40° humeral retroversion resulted in the longest TM muscle length, but it also showed the smallest moment arms and increased anterior impingement in some of the activities of daily living.

CONCLUSIONS

Even if TM external rotation moment arm is higher in RTSA than in a normal shoulder, the decreased length could impair its force generation. The 0° and 20° retroversion was the optimum compromise between sufficient TM length and moment arm with minimum impingement.

Muscle activity pattern of the shoulder external rotators differs in adduction and abduction: an analysis using positron emission tomography

BACKGROUND

The muscle activity pattern during shoulder external rotation has not been fully clarified. This study aimed to determine the activities involved in external rotation in the adducted and abducted positions using positron emission tomography (PET).

METHODS

Seven healthy volunteers underwent PET examinations after performing external rotation using an elastic band at both 0° and 90° of shoulder abduction in the frontal plane. External rotation exercise was performed before and after injection of fluorine 18 fluorodeoxyglucose, which was followed by PET examination. The protocols for external rotation exercise were identical between the 2 shoulder positions. To obtain control data, PET examination was also performed under resting conditions. The order of these 3 PET examinations was randomized, and they were performed at intervals of 1 week or greater. Each PET image was fused to the corresponding magnetic resonance image to identify each shoulder muscle. After this, the standardized uptake value was calculated in each muscle and was compared between the 2 shoulder positions.

RESULTS

The infraspinatus showed the greatest muscle activity during external rotation at 0° of abduction, whereas the teres minor showed the greatest activity at 90° of abduction. The teres minor-infraspinatus ratio at 90° of abduction (mean ± SD, 1.21 ± 0.23) was significantly higher than that at 0° of abduction (0.84 ± 0.15) (P < .01).

CONCLUSION

The infraspinatus and teres minor are the main shoulder external rotators. The teres minor is more important as an external rotator in abduction than in adduction.

Variation in external rotation moment arms among subregions of supraspinatus, infraspinatus, and teres minor muscles

A rotator cuff tear causes morphologic changes in rotator cuff muscles and tendons and reduced shoulder strength. The mechanisms by which these changes affect joint strength are not understood. This study's purpose was to empirically determine rotation moment arms for subregions of supraspinatus, infraspinatus, and for teres minor, and to test the hypothesis that subregions of the cuff tendons increase their effective moment arms through connections to other subregions. Tendon excursions were measured for full ranges of rotation on 10 independent glenohumeral specimens with the humerus abducted in the scapular plane at 10 and 60 degrees . Supraspinatus and infraspinatus tendons were divided into equal width subregions. Two conditions were tested: tendon divided to the musculotendinous junction, and tendon divided to the insertion on the humerus. Moment arms were determined from tendon excursion via the principle of virtual work. Moment arms for the infraspinatus (p < 0.001) and supraspinatus (p < 0.001) were significantly greater when the tendon was only divided to the musculotendinous junction versus division to the humeral head. Moment arms across subregions of infraspinatus (p < 0.001) and supraspinatus (p < 0.001) were significantly different. A difference in teres minor moment arm was not found for the two cuff tendon conditions. Moment arm differences between muscle subregions and for tendon division conditions have clinical implications. Interaction between cuff regions could explain why some subjects retain strength after a small cuff tear. This finding helps explain why a partial cuff repair may be beneficial when a complete repair is not possible. Data presented here can help differentiate between cuff tear cases that would benefit from cuff repair and cases for which cuff repair might not be as favorable.