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

Muscle Compensation Strategies to Maintain Glenohumeral Joint Stability in Rotator Cuff Tears: A Cadaveric Study

BACKGROUND

Superior translation of the humeral head is often identified in large and massive rotator cuff (RC) tears. However, the ability of the remaining RC muscles to compensate for the forces causing such superior translation in RC tears remains unclear. The purpose of this study was to investigate the impact of compensatory forces exerted by the remaining RC muscles on humeral head translation using a progressive RC tear model.

METHODS

Eight fresh-frozen cadaveric shoulders (mean donor age, 57 years) were tested using a custom shoulder testing system. In addition to an intact RC model, 3 RC tear models were created: a supraspinatus tear (Tear I); combined supraspinatus and infraspinatus tears (Tear II); and combined tears of the supraspinatus, infraspinatus, and superior one-third of the subscapularis (Tear III). Compensatory conditions were simulated by increasing the loading of the remaining RC muscles in each RC tear model. Humeral head translation was measured at different abduction and neutral rotation angles in each condition with normal and high deltoid muscle loading.

RESULTS

Significant superior translation of the humeral head was observed in Tears II and III (but not Tear I), compared with the intact state, under high loading of the deltoid during abduction and during rotation. In Tear II, compensatory conditions involving increased loading of the teres minor and subscapularis muscles effectively reduced superior translation, so that no significant differences were observed compared with the intact state, even under high deltoid muscle loading. However, in Tear III, significant superior translation was still observed, regardless of the compensatory conditions.

CONCLUSIONS

ompensation by the remaining RC muscles, particularly the teres minor and subscapularis, effectively reduced superior translation of the humeral head in the posterosuperior RC tear model, whereas this compensatory strategy was insufficient if tears also involved the superior one-third of the subscapularis.

CLINICAL RELEVANCE

Patients with posterosuperior RC tears may find conservative treatment focusing on strengthening the remaining RC muscles, especially the subscapularis and teres minor, to be beneficial. Conversely, patients with repairable massive RC tears also involving the subscapularis tendon may benefit from surgical interventions aimed at primarily repairing the subscapularis tendon to restore the transverse force couple. Massive tears deemed not to be repairable should be evaluated for arthroplasty or other procedures.

Mid-term outcomes of arthroscopically assisted lower trapezius tendon transfer using Achilles allograft in treatment of posterior-superior irreparable rotator cuff tear

BACKGROUND

Arthroscopically assisted lower trapezius tendon (aLTT) transfer is one of the treatment options for posterior-superior irreparable rotator cuff tears (PSIRCTs). Although short-term clinical outcomes have shown promising results, there are currently no reported clinical outcomes over a longer follow-up period. This study evaluated the mid-term outcomes of aLTT transfer in patients with a diagnosis of PSIRCT.

METHODS

This retrospective case-series study included patients who underwent aLTT transfer between May 2017 and May 2019. The clinical outcome assessment included the visual analog scale (VAS) pain score, Constant score, American Shoulder and Elbow Surgeons score, University of California-Los Angeles score, Activities of Daily Living Requiring Active External Rotation (ADLER) score, active range of motion, Single Assessment Numeric Evaluation score, and return-to-work rate. The radiographic analysis included the acromiohumeral distance, Hamada grade, and integrity of the transferred tendon at final follow-up. Subgroup analyses were performed based on the integrity of the transferred tendon and the trophicity of the teres minor (Tm).

RESULTS

This study enrolled 36 patients with a mean age of 63.4 years who met the inclusion criteria and were followed up for a mean of 58.2 ± 5.3 months. At final follow-up, the patients showed significant improvement in mean VAS score, Constant score, American Shoulder and Elbow Surgeons score, University of California-Los Angeles score, ADLER score, and active range of motion in all directions except internal rotation. A decrease in the acromiohumeral distance and an increase in the Hamada grade were observed at final follow-up (P = .040 and P = .006, respectively). Retears of the transferred tendon occurred in 7 patients, and postoperative infections developed in 2 individuals. An interesting finding was that the retear group still demonstrated improvement in the VAS score but did not show improvement in external rotation at the side by the final follow-up. Compared with the Tm non-hypertrophy group, the Tm hypertrophy group showed significantly better improvement in external rotation at 90° of abduction and at the side, as well as the ADLER score. Of the study patients, 30 (83.3%) were able to successfully resume their previous work.

CONCLUSION

In this study, aLTT transfer in patients with PSIRCTs demonstrated significant improvements in clinical and radiologic outcomes by the final follow-up. These findings provide support for the mid-term safety and effectiveness of aLTT transfer as a viable joint-preserving treatment option for PSIRCTs. However, larger and longer-term studies are still needed to further validate these findings.

Clinical results of arthroscopically-assisted lower trapezius transfer using fascia lata autograft for posterior superior irreparable rotator cuff tear

Background

Different interpositional grafts have been proposed to connect between the lower trapezius tendon (LTT) to the humerus during LTT transfer. While studies often mention the successful use of Achilles tendon allograft, there is currently no literature reporting the clinical outcomes of utilizing fascia lata autograft (FLA) in LTT transfer. Therefore, the current study aims to evaluate the clinical and radiologic results of LTT using FLA for posterior superior irreparable rotator cuff tears (PSIRCTs) without arthritis.

Patient and methods

The present study constitutes a retrospective case series involving 22 patients, with a mean follow-up of 35.9 ± 15.9 months. Pain levels were gauged using the Visual Analog Scale (VAS), while shoulder function was comprehensively assessed through the Constant and ASES (American Shoulder and Elbow Society) scores. The evaluation of shoulder activities in daily living employed the ADLER (Activities of Daily Living Requiring Active External Rotation) score. Active ROM (Range of Motion) of all directions were obtained, radiologic assessments included key parameters such as AHD (Acromion Humeral Distance) and the Hamada grade. Finally, the integrity of the transferred LTT was evaluated, and a subgroup analysis was undertaken based on Tm trophicity.

Results

By the final follow-up period, VAS, Constant, ASES, and ALDER demonstrated significant improvement. Active ROM significantly improved in (FE) forward elevation to 155° ± 29°, abduction (Abd) to 140° ± 32°, external rotation (ER) at 90° Abd to 68° ± 19°, and ER at the side to 39° ± 17°. AHD and Hamada grade showed no significant arthritic progression. Tm hypertrophy group experienced superior improvements in ER compared to that of the non-hypertrophy group. Complications included re-tear (n = 2), infection (n = 1) and donor-site morbidity (n = 1).

Conclusion

The study highlighted promising clinical outcomes of LTT transfer using FLA, with no significant complications. Along with Achilles tendon allograft, FLA can be a safe and viable alternative interpositional graft choice.

Lower trapezius and latissimus dorsi transfer relieve teres minor activity into the physiological range in Collin D irreparable posterosuperior massive rotator cuff tears: a biomechanical analysis

BACKGROUND

Tendon transfers are established techniques to regain external rotation mobility in patients with an irreparable, posterosuperior massive rotator cuff tear (MRCT). Posterosuperior MRCT with intact teres minor (type D MRCT) can lead to excessive teres minor loading to maintain external rotation. We hypothesize that tendon transfers are effective in relieving teres minor loading in type D MRCTs. Our aim was to biomechanically assess muscle synergism with latissimus dorsi (LD transfer) and lower trapezius (LT transfer) tendon transfer during external rotation at different abduction heights.

METHODS

Using musculoskeletal modeling, we analyzed and compared the moment arm, muscle torque, and muscle activity between a healthy and type D MRCT pathologic model with and without the LD- or LT transfer at infraspinatus and teres minor insertion sites. Output measures were analyzed during external rotation at different abduction angles and 10-50 N resistance against external rotation. We assessed its impact on teres minor loading in a type D MRCT. Morphologic variations were parameterized using the critical shoulder angle and the acromiohumeral distance to address variations among patients.

RESULTS

Both transfer types reduced teres minor torque and activity significantly, reaching physiological state at 40 N external resistance (P < .001), with insertion to infraspinatus site being more effective than teres minor site (P < .001). External rotation moment arms of LD transfer were larger than LT transfer at 90° abduction (25.1 ± 0.8 mm vs. 21.2 ± 0.6 mm, P < .001) and vice versa at 0° abduction (17.4 ± 0.5 mm vs. 24.0 ± 0.2 mm, P < .001). Although the healthy infraspinatus was the main external rotator in all abduction angles (50%-70% torque), a type D MRCT resulted in a 70%-90% increase of teres minor torque and an up to 7-fold increase in its activity leading to excessive loadings beyond 10 N resistance against external rotation. Varying the critical shoulder angle and the acromiohumeral distance led to minor variations in muscle moment arm and muscle activity.

CONCLUSION

We identified biomechanical efficacy of both tendon transfers in type D MRCT regarding teres minor load relief and superior performance of the transfers at the infraspinatus insertion site.

When and how much does the muscle strength recover after arthroscopic superior capsular reconstruction?

BACKGROUND

Recently, arthroscopic superior capsular reconstruction (SCR) has been performed for irreparable large to massive rotator cuff tears and excellent clinical results have been reported. Although the muscle strength is reported to recover, it has not yet been clarified when and how much it recovers. The purpose of this study was to determine the recovery pattern of muscle strength after SCR.

METHODS

We retrospectively reviewed 35 patients (mean age, 65 years) who met the following inclusion criteria: (1) patients with large to massive irreparable tears of the rotator cuff including the supraspinatus and infraspinatus tendons; (2) those with severe muscle atrophy and fatty change; (3) those who underwent assessment of muscle quality and strength by magnetic resonance imaging and dynamometry at 6 months, 1 year, and 2 years; (4) those with a minimum follow-up period of 2 years; and (5) those without severe osteoarthritis. The isometric muscle strength of scaption (ie, scapular-plane elevation), internal rotation, and external rotation in adduction was measured twice for each motion by a dynamometer.

RESULTS

Relative to the muscle strength on the uninvolved side, the involved side showed 61% ± 21% in scaption, 63% ± 20% in external rotation, and 103% ± 29% in internal rotation at 2 years after surgery. Whereas no significant differences were observed between the 1-year and 2-year follow-up assessments, a significant difference in muscle strength of scaption was found between 6 months and 1 year (P = .0174). Graft retear was seen in 5 cases (14%). There was a trend that the muscle strength of scaption and external rotation in the no-retear group was greater than that in the retear group despite no significant difference (P = .0717 and P = .0824, respectively).

CONCLUSION

The recovery of the muscle strength after SCR was observed until 1 year after surgery, and the muscle strength of scaption and external rotation returned to 60% of that on the uninvolved side at 2 years.

The Posterosuperior Tetralogy Scoring System as a Practical Tool to Predict Shoulder Function After Posterosuperior Large-to-Massive Rotator Cuff Repairs

Background

Fatty infiltration (FI) or atrophy alone has been found to be inaccurate in predicting shoulder function after repair of large-to-massive rotator cuff tears (L/MRCTs), especially when a diverse extent of FI and atrophy presents in multiple rotator cuff muscles.

Purpose/Hypothesis

The Posterosuperior Tetralogy Scoring System (PS-Tetra Score), which integrates FI and atrophy, was proposed to predict shoulder function after surgery. It was hypothesized was that a PS-Tetra Score ≥3 would be a risk factor for poor shoulder function after repair of posterosuperior L/MRCTs and would possess greater diagnostic value than using isolated FI or atrophy of the supraspinatus (SSP) or infraspinatus (ISP).

Study Design

Case-control study; Level of evidence, 3.

Methods

A total of 187 arthroscopic repairs of posterosuperior L/MRCTs were reviewed. Magnetic resonance imaging evaluations were performed of FI and atrophy of the SSP and ISP, teres minor hypertrophy, tendon retraction, and acromiohumeral distance. A postoperative American Shoulder and Elbow Surgeons (ASES) score of 70 was used to subgroup patients according to shoulder function. Univariate and multivariate analyses were performed to determine the risk factors of poor shoulder function (ASES ≤70). The diagnostic values of different indicators for predicting shoulder function were evaluated.

Results

In univariate analysis, female sex, higher Goutallier grade of the SSP and ISP, positive SSP tangent sign, and PS-Tetra Score ≥3 was significantly associated with ASES score ≤70, whereas in binary logistic regression analysis, a PS-Tetra Score ≥3 was the only significant risk factor for poor shoulder function. The occurrence rate of poor function in shoulders with a PS-Tetra Score of 0, 1, 2, 3, and 4 was 0% (0/52), 0% (0/52), 19.57% (9/46), 58.06% (18/31), and 83.33% (5/6), respectively. PS-Tetra Score ≥3 possessed higher crude agreement (87.70%), specificity (90.97%), positive predictive value (62.16%), and area under the receiver operating characteristic curve (0.814) than the other 3 indicators, with relatively high negative predictive value (94.00%) and moderate sensitivity (71.88%).

Conclusion

PS-Tetra Score ≥3 was a risk factor of poor shoulder function after repair of posterosuperior L/MRCTs and possessed greater diagnostic value than using isolated FI or atrophy of SSP or ISP alone for predicting shoulder function.

The remaining teres minor and subscapularis may contribute to preventing superior migration of the humeral head and progression of osteoarthritic change in rotator cuff tears

Background

Superior migration of the humeral head is common in large and massive rotator cuff tears (RCTs). Humeral heads migrate superiorly according to an increase in the RCT size; however, the relevance of the remaining cuff has not been elucidated. This study investigated the relation between superior migration of the humeral head and the remaining rotator cuff, especially the teres minor (TM) and subscapularis (SSC), in RCTs involving tears and atrophy of the infraspinatus (ISP).

Methods

Plain anteroposterior radiographic and magnetic resonance imaging examinations were performed on 1345 patients between January 2013 and March 2018. A total of 188 shoulders with tears of the supraspinatus and ISP with atrophic ISP were evaluated. Gradings of superior migration of the humeral head and osteoarthritic change were evaluated using the acromiohumeral interval, Oizumi classification, and Hamada classification on plain anteroposterior radiographs. The cross-sectional area of the remaining rotator cuff muscles was evaluated using oblique sagittal magnetic resonance imaging. The TM was classified as hypertrophic (H) and normal and atrophic (NA). The SSC was classified as nonatrophic (N) and atrophic (A). All shoulders were classified as groups A (H-N), B (NA-N), C (H-A), and D (NA-A). Age- and sex-matched patients with no cuff tears were also enrolled (control).

Results

The acromiohumeral intervals of the control group and groups A-D were 11.4 ± 2.4, 9.5 ± 3.8, 7.8 ± 4.1, 7.2 ± 4.0, and 5.4 ± 3.5 mm (84, 74, 64, 21, and 29 shoulders, respectively), with significant differences between groups A and D (P < .001) and groups B and D (P = .016). Grade 3 of the Oizumi classification and grades 3, 4, and 5 of the Hamada classification were significantly higher in group D than in others (P < .001).

Conclusion

The group showing hypertrophic TM and nonatrophic SSC prevented significantly migration of the humeral head and cuff tear osteoarthritis compared to the group showing atrophic TM and SSC in posterosuperior RCTs. The findings indicate that the remaining TM and SSC may prevent superior migration of the humeral head and progression of osteoarthritic change in RCTs. In treating patients with large and massive posterosuperior RCTs, the status of the remaining TM and SSC muscles should be assessed.

Latissimus dorsi transfer vs. lower trapezius transfer for posterosuperior irreparable rotator cuff tears

BACKGROUND

Latissimus dorsi transfer (LDT) and lower trapezius transfer (LTT) are effective treatment options for posterosuperior irreparable rotator cuff tears (IRCTs) in relatively young patients and elderly high-demand patients without arthritic changes. However, the optimal treatment option for patients with posterosuperior IRCT remains a subject of ongoing debate. This study aimed to compare clinical and radiologic short-term outcomes between arthroscopic-assisted LDT (aLDT) and arthroscopic-assisted LTT (aLTT) in patients with posterosuperior IRCT.

METHODS

This retrospective crossover study included patients who underwent aLDT or aLTT for posterosuperior IRCT and who had a minimum clinical follow-up time of 2 years after undergoing surgical procedures between January 2012 and June 2019. A total of 90 patients with posterosuperior IRCT were divided into 2 groups according to the surgical procedure: group D underwent aLDT (n = 48) and group T underwent aLTT (n = 42). Clinical outcomes comprised the visual analog scale score for pain, active shoulder range of motion (ROM), American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) score, and activities of daily living that require active external rotation (ADLER) score. Radiologic outcomes included acromiohumeral distance (AHD). The progression of arthritis was evaluated using Hamada grade. Graft integrity was assessed using postoperative magnetic resonance imaging.

RESULTS

Significant improvements in clinical outcomes were observed in both groups. Active shoulder external rotation (P < .001), postoperative ASES score (P < .001), and ADLER score (P < .001) were significantly higher in group T than in group D. AHD at 2-year follow-up was significantly higher in group T than in group D (P < .001). The rate of progression of arthritis was significantly higher in group D (31.3%) than in group T (7.1%) (P = .031).

CONCLUSIONS

Although both LDT and LTT improved the overall clinical outcomes of patients with posterosuperior IRCT, LTT was superior to LDT in terms of shoulder ROM, functional improvement, and progression of arthritis. Our findings indicate that LTT may be the preferred treatment option for posterosuperior IRCT in relatively active and young patients.

Agreement in rotator cuff muscles measurement between ultrasonography and magnetic resonance imaging

Background/objective

It is important to assess the atrophy of the rotator cuff to better understand shoulder function and pain. Previously, magnetic resonance imaging has been used for the evaluation of atrophy of rotator cuff muscles, which is time consuming. Therefore, a measurement tool requiring little time and easy accessibility is clinically desirable to be used frequently in rehabilitation. Recently, rotator cuff muscles have been evaluated using ultrasonography. However, little is known about the agreement of evaluation in rotator cuff muscles between magnetic resonance imaging and ultrasonography. The purpose of this study was to demonstrate the agreement between the muscle thickness measurements of supraspinatus, infraspinatus, and teres minor muscles by ultrasonography and the cross-sectional area measured by magnetic resonance imaging in the patient with rotator cuff tears.

Methods

A total of 47 patients with rotator cuff tears were enrolled. There were the 37 small tears, four medium tears, and six large tears, and the involved rotator cuff muscles were the supraspinatus in 37 shoulders, and the supraspinatus and infraspinatus in 10 shoulders. The measuring variables were muscle thickness and cross-sectional area of supraspinatus, infraspinatus, and teres minor muscles by using magnetic resonance imaging. Further, the muscle thickness of the rotator cuff were assessed using ultrasonography. A single regression model was used for demonstrating the agreement between the cross-sectional area measurement by magnetic resonance imaging and the muscle thickness measured using ultrasonography and magnetic resonance imaging of rotator cuff muscles. Additionally, the Bland-Altman plots between magnetic resonance imaging and ultrasonography was analyzed.

Results

The cross-sectional area were correlated with the muscle thickness measurement of rotator cuff muscles by magnetic resonance imaging, significantly (supraspinatus: r = 0.84, infraspinatus: ρ = 0.63, teres minor: ρ = 0.61, all p < 0.001). There were significant agreements between the cross-sectional area measured by magnetic resonance imaging and muscle thickness measured by ultrasonography (supraspinatus: r = 0.80, infraspinatus: ρ = 0.78, teres minor: ρ = 0.74, all p < 0.001). Bland-Altman plots revealed significant correlations between the average and the difference of the two measurements in supraspinatus (r = 0.36, p = 0.012), infraspinatus (r = 0.38, p < 0.001), and teres minor (r = 0.42, p < 0.001). These results clarified the proportional bias between MRI and US.

Conclusion

This study showed that, similar to magnetic resonance imaging, ultrasonography is a useful tool for assessing muscle atrophy of supraspinatus, infraspinatus, and teres minor muscles.

Quantitative magnetic resonance imaging assessment of the infraspinatus and teres minor in massive rotator cuff tear and its significance in clinical outcome after rotator cuff repair

BACKGROUND

Teres minor (TM) muscle hypertrophy in large to massive rotator cuff tears (RCTs) has been considered a compensatory change to atrophy of the infraspinatus (ISP). However, few reports have assessed its relation to the prognosis after rotator cuff repair.

METHODS

A total of 139 patients who underwent arthroscopic repair of large to massive RCTs involving the ISP between January 2013 and December 2015 were retrospectively investigated. Occupational ratios of the ISP (OR_ISP) and TM (OR_TM) were measured by sagittal magnetic resonance imaging (MRI). Rotator cuff healing was evaluated by MRI 1 year postoperatively, and functional outcomes using the Simple Shoulder Test (SST) and Constant score and external rotator (ER) strength by isokinetic muscle performance test (IMPT) were measured.

RESULTS

A total of 116 patients completed the MRI and IMPT at 1 year postoperatively, and functional scores were measured at least 2 years postoperatively. Of these, the repaired tendon had not healed in 34 patients (29%). There was a highly negative correlation between OR_ISP and OR_TM both pre- and postoperatively (Pearson correlation = -0.52 and -0.54, respectively). Preoperative OR_ISP was significantly higher in the healed than in the healing failure group (0.47 ± 0.10 vs. 0.41 ± 0.12, P = .02); however, postoperative OR_ISP and pre- and postoperative OR_TM were not. The preoperative OR_ISP cutoff value for healing was 0.46. For functional outcomes, only postoperative OR_ISP showed a statistical correlation with SST, Constant score (P = .04 and .03, respectively), and ER strength (P = .02).

CONCLUSION

TM muscle hypertrophy in large to massive RCT appears to be a compensatory change in the progression of atrophy of the ISP muscle and was not a significant indicator of either better healing of the repaired rotator cuff tendon or better function. Only preoperative OR_ISP was an independent prognostic factor affecting rotator cuff healing after repair of large to massive RCTs.

Superior capsular reconstruction - A systematic review and meta-analysis

BACKGROUND

Since Mihata's 2012 proposal to arthroscopically reconstruct the superior capsule of patients with massive irreparable cuff tears, many studies have reported the clinical results of this technique using different types of grafts (fascia lata autograft, dermal allograft, porcine dermal xenograft or long head of biceps autograft).

PURPOSE

The objective of this meta-analysis was to report the clinical and radiological results of these superior capsule reconstructions.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-Analyzes (PRISMA) recommendations were used to conduct this systematic review. A bibliographic search was performed of the electronic databases MEDLINE, Scopus, Embase and the Cochrane Library. The quality of the studies was assessed according to the MINORS criterion (Methodological Index for Nonrandomized Studies). The inclusion criteria were studies in English evaluating superior capsular reconstruction.

RESULTS

No level I or II studies met the inclusion criteria. Eighteen studies were selected from the 97 identified, including 637 shoulders (64% male) with a mean age of 62 years [95% CI: 60.3-63.5]. At the mean follow-up of 24.3 months (12-60), the range of motion was significantly increased from 82.6° [60.0-105.2] to 141.9° [109.9-173.8] in abduction, from 113.1° [98.3-127.9] to 153.3° [147.4-159.2] in elevation, from 35.5° [30.9-40.2] 43.4° [35.4-51.3] in external rotation and from 7.2 [5.4-9] to 9.9 [8.9-10.9] in internal rotation. Functional scores were significantly improved from 5.4 [4.8-5.9] to 1.3 [0.9-1.7] points for VAS, from 42.5 [15.7-69.3] to 59.3 [30.1-88.6] points for Constant, from 39.0% [38.1-39.8] to 79.8% [76.4-83.3] for the SSV, and from 48.2 [45.2-51.1] to 81.2 [77.2-85.1] points for the ASES. The healing rate was 76.1% [64.4-84.9]. The complication rate was 5.6% [1.8-16.3] and the reverse shoulder arthroplasty revision rate was 7.1% [3.8-12.8].

CONCLUSION

Superior capsule reconstructions allow satisfactory clinical and radiological results to be obtained at 2 years of follow-up. Due to the small number of high quality comparative studies available, its true place in the therapeutic arsenal cannot be fully confirmed. However, it seems that the best indication for this technique is isolated irreparable rupture of the supraspinatus, in cases of medical treatment failure.

LEVEL OF EVIDENCE

III; meta-analysis of heterogeneous studies.

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.

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.

Surface-based modeling of muscles: Functional simulation of the shoulder

Musculoskeletal simulations are an essential tool for studying functional implications of pathologies and of potential surgical outcomes, e.g., for the complex shoulder anatomy. Most shoulder models rely on line-segment approximation of muscles with potential limitations. Comprehensive shoulder models based on continuum-mechanics are scarce due to their complexity in both modeling and computation. In this paper, we present a surface-based modeling approach for muscles, which simplifies the modeling process and is efficient for computation. We propose to use surface geometries for modeling muscles, and devise an automatic approach to generate such models, given the locations of the origin and insertion of tendons. The surfaces are expressed as higher-order tensor B-splines, which ensure smoothness of the geometrical representation. They are simulated as membrane elements within a finite element simulation. This is demonstrated on a comprehensive model of the upper limb, where muscle activations needed to perform desired motions are obtained by using inverse dynamics. In synthetic examples, we demonstrate our proposed surface elements both to be easy to customize (e.g., with spatially varying material properties) and to be substantially (up to 12 times) faster in simulation compared to their volumetric counterpart. With our presented automatic approach of muscle wrapping around bones, the humeral head is exemplified to be wrapped physiologically consistently with surface elements. Our functional simulation is shown to successfully replicate a tracked shoulder motion during activities of daily living. We demonstrate surface-based models to be a numerically stable and computationally efficient compromise between line-segment and volumetric models, enabling anatomical correctness, subject-specific customization, and fast simulations, for a comprehensive simulation of musculoskeletal motion.

Effect of preoperative teres minor hypertrophy on reverse total shoulder arthroplasty

BACKGROUND

The preoperative status of the teres minor (Tm) can affect the outcome of reverse total shoulder arthroplasty (RTSA). The effect of preoperative Tm hypertrophy on the outcome of RTSA is unclear.

METHODS

A total of 86 shoulders that underwent RTSA were retrospectively enrolled. Of these, 48 cases with a Tm occupation ratio (OR) of >0.288 in the preoperative magnetic resonance image were assigned to the hypertrophic group, and 38 cases to the control group. The two groups were compared with respect to preoperative rotator cuff tear involvement, fatty infiltration, pre- and postoperative rotator cuff ORs, pain scores, functional scores, range of motion, and muscle strength. Postoperative Tm ORs in 1-year follow-up multidetector computed tomography were compared with preoperative Tm ORs.

RESULTS

Preoperatively, integrities of infraspinatus (ISP) and supraspinatus were significantly different between the 2 groups (P = .001, 0.009, each). Preoperative ISP ORs were significantly related to preoperative Tm ORs (r = -0.534, P < .001). The mean pre- to postoperative change of Tm ORs in the hypertrophic group decreased (-0.029 ± 0.068), whereas that of the control group increased (+0.047 ± 0.092). Postoperative pain scores, functional scores, range of motion, and muscle strength were not different between groups.

CONCLUSIONS

In cases of advanced rotator cuff tear requiring RTSA, Tm hypertrophy is found to be related to tear and atrophy of the ISP, suggesting that Tm hypertrophy is a compensatory change for ISP dysfunction. However, Tm hypertrophy was observed to diminish after RTSA. Preoperative Tm hypertrophy appears to have no beneficial effect on the outcomes of RTSA.

Factors associated with pain in nonsurgically treated rotator cuff tears -A study with magnetic resonance imaging

BACKGROUND

In rotator cuff tears, some cases become asymptomatic with nonsurgical treatment, others remain symptomatic. The purpose of this study was to identify factors associated with pain in nonsurgically treated rotator cuff tears using magnetic resonance imaging (MRI).

METHODS

In total, 108 shoulders diagnosed with supraspinatus (SSP) tendon tears using MRI were nonsurgically treated, and MRI was repeated after more than a year. The patients were divided into pain or improvement group according to whether the pain persisted or disappeared. Bursal fluid accumulation; SSP tendon retraction; subscapularis (SSC) tendon tears; infraspinatus (ISP) tendon tears; and Goutallier classification into SSC, SSP, and ISP were included as evaluation factors. Predictive factors for persistent pain on initial MRI and factors associated with persisting pain after nonsurgical treatment on repeat MRI were statistically analyzed using multivariate logistic regression analysis.

RESULTS

The improvement group showed a significant decrease in bursal fluid accumulation compared with the pain group (p < 0.01). SSC tendon tears (OR, 4.42; 95% CI, 1.16-16.9; P = 0.03) on initial MRI were significantly associated with persistent pain. Bursal fluid accumulation (OR, 2.44; 95% CI, 1.18-5.07; P = 0.02) and SSC tendon tears (OR, 2.25; 95% CI, 1.15-4.39; P = 0.02) on repeat MRI were significantly associated with persistent pain.

CONCLUSIONS

Bursal fluid accumulation decreased when pain improved. The involvement of SSC tendon tears can serve as a predictive factor for persistent pain. Pain may persist although patients with rotator cuff tears including SSC tendon tears are nonsurgically treated.

LEVEL OF EVIDENCE

Level IV case-control study.

The pattern of idiopathic isolated teres minor atrophy with regard to its two-bundle anatomy

OBJECTIVE

We aimed to analyze the pattern of teres minor atrophy with regard to its two-bundle anatomy and to assess its association with clinical factors.

MATERIALS AND METHODS

Shoulder MRIs performed between January and December 2016 were retrospectively reviewed. Images were evaluated for the presence and pattern of isolated teres minor atrophy. Isolated teres minor atrophy was categorized into complete or partial pattern, and partial pattern was further classified according to the portion of the muscle that was predominantly affected. The medical records were reviewed to identify clinical factors associated with teres minor atrophy.

RESULTS

Seventy-eight shoulders out of 1,264 (6.2%) showed isolated teres minor atrophy; complete pattern in 41.0%, and partial pattern in 59.0%. Most cases of partial pattern had predominant involvement of the medial-dorsal component (82.6%). There was no significant association between teres minor atrophy and previous trauma, shoulder instability, osteoarthritis, and previous operation. The history of shoulder instability was more frequently found in patients with isolated teres minor atrophy (6.4%), compared with the control group (2.6%), although the difference was not statistically significant.

CONCLUSION

Isolated teres minor atrophy may be either complete or partial, and the partial pattern may involve either the medial-dorsal or the lateral-ventral component of the muscle. The imaging findings of partial pattern teres minor atrophy indicate that the two muscle components may have separate innervation.

A new anatomical insight into the aetiology of lateral trunk of suprascapular nerve neuropathy: isolated infraspinatus atrophy

Introduction

Although the pathomechanism of isolated infraspinatus atrophy (ISA) in throwing sports is known to be traction, it is unclear why only some players are affected. One likely explanation is that the infraspinatus pulling force exerted by its contracture generate the compressive resultant component force (Fn) compressing the lateral trunk of the suprascapular nerve (LTSN) against the edge of scapular spine. This paper makes two key assumptions (1) the course of LTSN in relation to the scapular spine, defined as the suprascapular-scapular spine angle (SSSA) is the key individual anatomical feature influencing the Fn magnitude, and thus potentially ISA development (2) SSSA is correlated with scapular notch type.

Materials and methods

The bone landmarks of the LTSN course were identified in 18 formalin-fixed cadaveric shoulders, and the SSSA was measured in 101 dry scapulae. The correlation between the SSSA and suprascapular notch type was evaluated. The Fn value was simulated mathematically based on the values of the SSSA of 101 dry scapulae and the prevalence of ISA in chosen throwing sports, as given in the literature: i.e., beach volleyball − 34% (group A1 − 34%; group A2—remaining 66% of scapulae) and tennis − 52% (group B1 − 52%; group B2—remaining 48% of scapulae).

Results

The mean SSSA value was 44.57° (± 7.9) and Fn 79 N (± 13.1). No statistically significant correlation was revealed between suprascapular notch type and SSSA. Groups A1 and B1 possessed significantly lower SSSA values (p < 0.000) and significantly higher Fn magnitude (p < 0.000) than groups A2 and B2 respectively. The average difference of Fn was 28.1% between group A1 and A2 and 31% between group B1 and B2.

Conclusions

The SSSA has a wide range of values depending on the individual: the angle influencing the magnitude of the compressive resultant force Fn on the LTSN at the lateral edge of the scapular spine via contraction of the infraspinatus muscle. The prevalence of ISA in throwing sports may be correlated with the SSSA of the LTSN. However, further combined clinical, MRI or/and CT studies are needed to confirm this.