Bursal acromial resurfacing improves shoulder biomechanics in a cadaveric model of massive rotator cuff tear.

PURPOSE: To investigate the effectiveness of bursal acromial resurfacing (acromiograft) on acromiohumeral distance, subacromial contact area, and pressure in a cadaveric model of massive rotator cuff tear. METHODS: Eight fresh-frozen cadaveric shoulders were tested using a customized shoulder testing system. Humeral head translation, subacromial contact pressure, and the subacromial contact area were evaluated across four conditions: (1) intact shoulder; (2) simulated massive rotator cuff tear; (3) 3-mm acromiograft condition; (4) 6-mm acromiograft condition. The acromiografts were simulated using Teflon and a reported technique. The values were measured at 0°, 20°, and 40° abduction and 0°, 30°, 60°, and 90° external rotation (ER) for each abduction status. RESULTS: Compared with a massive cuff tear, the 6-mm acromiograft significantly reduced the superior translation of the humeral head at all abduction/ER angles (P<0.05). The 3-mm acromiograft also decreased superior translation of the humeral head compared to massive cuff tear, but not all differences were significant. The 3- and 6-mm acromiografts significantly decreased the subacromial contact pressure and increased the subacromial contact area in almost all positions (P<0.05). The 3-mm acromiograft maintained biomechanical properties similar to the intact condition, whereas the 6-mm acromiograft increased the contact area. CONCLUSIONS: This biomechanical study demonstrated that both 3- and 6- mm acromiografts using Teflon in a cadaveric model of a massive cuff tear resulted in recentering of the superiorly migrated humeral head, increased the subacromial contact area, and decreased the subacromial contact pressure. The 3- mm graft was sufficient for achieving the intended therapeutic effects. CLINICAL RELEVANCE: The acromiograft can normalize altered biomechanics and may aid the treatment of massive cuff tears. As grafting the acromion's undersurface is new with limited clinical outcomes, further observation is crucial. Using Teflon instead of ADM allograft for bursal acromial resurfacing could yield different results, requiring careful interpretation.

Biomechanical Comparison Between Superior Capsular Reconstruction and Lower Trapezius Tendon Transfer in Irreparable Posterosuperior Rotator Cuff Tears.

BACKGROUND: Superior capsular reconstruction (SCR) and lower trapezius tendon transfer (LTT) have recently been used to manage irreparable posterosuperior rotator cuff tears (PSRCTs). There has been a paucity of comparative biomechanical considerations between the 2 procedures. PURPOSE: To compare the glenohumeral stability and biomechanical properties between SCR and LTT in PSRCTs involving the entire infraspinatus tendon region. STUDY DESIGN: Controlled laboratory study. METHODS: Eight fresh-frozen cadaveric shoulders were tested at 0°, 20°, and 40° of shoulder abduction. Maximum internal, external, and total humeral range of motion (ROM), superior translation of the humeral head, and subacromial contact characteristics were compared among 4 conditions: (1) intact rotator cuff, (2) PSRCTs involving the entire infraspinatus tendon region, (3) LTT using Achilles allograft (12 N and 24 N of loading), and (4) SCR using fascia lata allograft. RESULTS: Although a decrease in total ROM was noted in LTT with 12 N compared with the tear condition, LTT with both 12 N and 24 N as well as SCR did not restrict total rotational ROM compared with the intact condition. LTT had decreased total ROM compared with tear condition at 20° of abduction (P = .042), while no significant decrease was confirmed at all abduction angles after SCR. SCR and LTT with 24 N decreased superior translation compared with the PSRCT condition at 0° and 20° of abduction (P < .037) but not significantly at 40° of abduction, whereas LTT with a 24-N load decreased glenohumeral superior translation at all abduction angles (P < .039). Both SCR and LTT decreased subacromial contact pressure compared with the tear condition (P < .014) at all abduction angles. SCR decreased subacromial contact pressure at 0° and 40° of abduction (P = .019 and P = .048, respectively) compared with LTT with 12 N of loading, while there was no difference between SCR and LTT with 24 N of loading in all abduction angles. SCR increased the contact area compared with the PSRCT condition at all abduction angles (P < .023), whereas LTT did not increase the contact area. CONCLUSION: SCR and LTT decreased glenohumeral superior translation and contact pressure compared with PSRCT conditions. The LTT was superior to SCR in terms of superior translation of the humeral head at a higher shoulder abduction angle, whereas the SCR showed more advantageous subacromial contact characteristics compared with LTT. CLINICAL RELEVANCE: These biomechanical findings provide insights into these 2 fundamentally different procedures for the treatment of young and active patients with PSRCTs involving the entire infraspinatus tendon region.

Varus-valgus alignment of humeral short stem in reverse total shoulder arthroplasty: does it really matter?

BACKGROUND: The utilization of short humeral stems in reverse total shoulder arthroplasty has gained attention in recent times. However, concerns regarding the risk of misalignment during implant insertion are associated with their use. METHODS: Eight fresh-frozen cadaveric shoulders were prepared for dissection and biomechanical testing. A bespoke humeral implant was fabricated to facilitate assessment of neutral, varus, and valgus alignments using a single stem, and 10° was established as the maximum permissible angle for misalignments. Shift in humerus position and changes in deltoid length attributable to misalignments relative to the neutral position were evaluated using a Microscribe 3DLx system. The impingement-free range of motion, encompassing abduction, adduction, internal rotation, and external rotation (ER), was gauged using a digital goniometer. The capacity for abduction was evaluated at maximal abduction angles under successive loading on the middle deltoid. A specialized traction system coupled with a force transducer was employed to measure anterior dislocation forces. RESULTS: Relative to the neutral alignment, valgus alignment resulted in a more distal (10.5 ± 2.4 mm) and medial (8.3 ± 2.2 mm) translation of the humeral component, whereas the varus alignment resulted in the humerus shifting more superiorly (11.2 ± 1.3 mm) and laterally (9.9 ± 0.9 mm) at 0° abduction. The valgus alignment exhibited the highest abduction angle than neutral alignment (86.2°, P < .001). Conversely, the varus alignment demonstrated significantly higher adduction (18.4 ± 7.4°, P < .001), internal rotation (68.9 ± 15.0°, P = .014), and ER (45.2 ± 10.5°, P = .002) at 0° abduction compared to the neutral alignments. Anterior dislocation forces were considerably lower (23.8 N) in the varus group compared to the neutral group at 0°ER (P = .047). Additionally, abduction capability was markedly higher in varus alignment at low deltoid loads than the neutral alignment (5N, P = .009; 7.5 N, P = .007). CONCLUSIONS: The varus position enhances rotational range of motion (ROM) but increases instability, while the valgus position does not significantly impact ROM or instability compared to the neutral position.

Middle trapezius tendon transfer using Achilles allograft for irreparable isolated supraspinatus tendon tears effectively restores the superior stability of the humeral head without restricting range of motion: a biomechanical study.

BACKGROUND: Middle trapezius tendon (MTT) transfer has been suggested for promising treatment of irreparable isolated supraspinatus tendon tears (IISTTs). However, there have been no attempts to assess the biomechanical efficacy of MTT transfer. This study aims to evaluate the biomechanical efficacy of MTT transfer in the setting of IISTTs. METHODS: Eight fresh frozen cadaveric shoulders were tested in 3 conditions: (1) intact rotator cuff, (2) IISTT, and (3) MTT transfer using Achilles allograft for IISTTs. Total humeral rotational range of motion (ROM), superior translation of the humeral head, and subacromial contact characteristics were measured at 0°, 20°, and 40° glenohumeral abduction (representing 0°, 30°, and 60° shoulder abduction). Superior translation and subacromial contact pressures were measured at 0°, 30°, 60°, and 90° external rotation (ER). Two different MTT muscle loading conditions were investigated. A linear mixed effects model and Tukey post hoc test were used for statistical analysis. RESULTS: Total ROM was significantly increased after IISTT at 20° abduction (P = .037). There were no changes in total ROM following MTT transfer compared to the IISTT condition (P > .625 for all comparisons). The IISTT condition significantly increased superior translation compared to the intact rotator cuff condition in 0° and 20° abduction with all ER angles (P < .001), 40° abduction-30° ER (P = .016), and 40° abduction-60° ER (P = .002). MTT transfer significantly decreased superior translation of the humeral head at all abduction angles compared to the IISTT condition (P < .026). MTT transfer significantly decreased peak contact pressure by 638.7 kPa (normal loading) and 726.8 kPa (double loading) at 0° abduction-30° ER compared to the IISTT condition (P < .001). Mean contact pressure was decreased by 102.8 kPa (normal loading) and 118.0 kPa (double loading) at 0° abduction-30° ER (P < .001) and 101.0 kPa (normal loading) and 99.2 kPa (double loading) at 0° abduction-60° ER (P < .001). MTT transfer at 20° abduction-30° ER with 24 N loading significantly decreased contact pressure by 91.2 kPa (P = .035). CONCLUSIONS: The MTT transfer biomechanically restored the superior humeral head translation and reduced the subacromial contact pressure in a cadaveric model of IISTT, while not restricting total ROM. These findings suggest that MTT transfer may have potential as a surgical treatment for IISTTs.

Latissimus Dorsi and Teres major tendon transfer increases internal rotation torque following lateralized reverse shoulder arthroplasty with subscapularis insufficiency.

INTRODUCTION: Limitation of active Internal Rotation (IR) following Reverse Shoulder Arthroplasty (RSA) in patients with massive Rotator Cuff Tears (mRCTs) with subscapularis insufficiency remains a challenge. Recently, RSA with Latissimus dorsi and Teres major (LDTM) transfer in patients with limited active IR has been demonstrated as a reliable treatment option. The purpose of this study was to biomechanically compare the IR torque following LDTM transfer with RSA in mRCT with subscapularis insufficiency to RSA without tendon transfer. METHODS: Eight cadaveric shoulders were tested (mean age: 64.5 ± 1.9 years) using a custom shoulder testing system that permits loading conditions of mRCT with subscapularis insufficiency. Two conditions were tested and compared. The first condition was RSA alone and the second condition was RSA with LDTM transfer. RSA with a medialized glenoid and lateralized humerus design was used for all specimens. The specimens were tested at 0°, 20° and 40° abduction at three different muscle loads: baseline, double, and triple, while the Teres minor and deltoid loads were kept constant. IR torque was measured with a torque wrench at 0°, 20°, and 40° abduction and 60° and 45° IR positions. Force required for anterior dislocation was measured at 20° abduction and 10° IR position. RESULTS: RSA with LDTM transfer had significantly higher IR torque at all abductions and muscle loading compared with RSA without transfer (average at all positions; RSA without transfer: 0.80 ± 0.02 Nm, LDTM transfer for all loads: 1.43 ± 0.10 Nm). RSA with LDTM transfer (91.4 ± 3.9 N) needed higher force for anterior dislocation compared to RSA alone (89.4 ± 4.1 N), but there was no significant difference. CONCLUSION: LDTM transfer with RSA increases IR torque compared to RSA without tendon transfer in a cadaveric model. LDTM transfer with RSA may be a reliable treatment option for patients with mRCT and subscapularis insufficiency who are expected to have limited active IR following RSA.

Latissimus dorsi and teres major tendon transfer for irreparable anterosuperior rotator cuff tear improves kinematics and internal rotation compared to latissimus dorsi tendon transfer.

INTRODUCTION: Latissimus dorsi and teres major (LDTM) tendon transfer has demonstrated better clinical outcomes compared to Latissimus dorsi (LD) transfer for irreparable anterosuperior cuff (subscapularis/supraspinatus) tears; however, the biomechanical effects of these procedures are unknown. Therefore, the objective of this study was to compare kinematics and internal rotation of LDTM transfer to LD transfer for anterosuperior cuff tear. METHODS: Eight cadaveric shoulders were tested in four conditions; (1) intact, (2) anterosuperior rotator cuff tear, (3) LDTM transfer, and (4) LD transfer. Glenohumeral kinematics and internal rotation at 0°, 30°, and 60° of glenohumeral abduction in the scapular plane were measured. Muscle loading was applied based on physiological cross-sectional area ratios with three muscle loading conditions to simulate potentially increased tension due to the advanced insertion site of the transferred tendons. RESULTS: The anterosuperior rotator cuff tear leads to a significant superior shift of the humeral head compared to intact at 0° and 30° abduction (p < 0.039). Both the LDTM (p < 0.047) and LD transfers (p < 0.032) significantly shifted the humeral head inferiorly compared to the tear condition.; however, the LDTM transfer shifted the head in the anteroinferior direction compared to the LD transfer at 60° abduction and 30° ER (p < 0.045). Both LDTM and LD transfer significantly increased internal resting rotation (p < 0.008) and maximum internal rotation (p < 0.008) compared to anterosuperior rotator cuff tear and intact at 30° and 60° abduction. LDTM transfer resulted in a significant internal resting rotation compared with the LD transfer at 30° abduction with double muscle loading (p = 0.02). At 0° abduction, the LDTM transfer (p < 0.027) significantly increased maximum internal rotation compared to anterosuperior rotator cuff tear and intact. CONCLUSION: Although both LDTM and LD tendon transfer improved the abnormal humeral head apex position and internal rotation compared with the tear condition, the LDTM transfer was biomechanically superior to the LD transfer in a cadaveric model.

Biomechanical comparison of combined latissimus dorsi and teres major tendon transfer vs. latissimus dorsi tendon transfer in shoulders with irreparable anterosuperior rotator cuff tears.

BACKGROUND: Irreparable anterosuperior rotator cuff tears (IASRCTs) can result in a gradual loss of active elevation and internal rotation, superior and anterior translation of the humeral head, and cuff tear arthropathy. Joint-preserving treatment options for IASRCTs in young and high-demand elderly patients remain a subject of ongoing debate. The aim of the study was to evaluate the biomechanical efficacy of the combined latissimus dorsi and teres major tendon (LDTM) transfer and compare it to an isolated latissimus dorsi (LD) transfer in a cadaveric IASRCT model. METHODS: Eight cadaveric shoulders (mean age, 68.3 ± 5.2 years; range 58-71) were tested with a custom shoulder testing system. All specimens were tested at 0°, 30°, and 60° of glenohumeral abduction in the scapular plane under 4 conditions: (1) intact, (2) IASRCT, (3) combined LDTM transfer, and (4) isolated LD transfer. The superior and anteroinferior translation and subacromial contact pressure were measured. The effects of 3 different LD and LDTM muscle loading conditions were investigated to determine the effectiveness of the muscle transfer conditions. A linear mixed effect model was used for statistical analysis, followed by a Tukey post hoc test. RESULTS: IASRCTs significantly increased superior translation, anteroinferior translation, and subacromial peak contact pressure. Combined LDTM transfer significantly decreased superior and anteroinferior translation compared with IASRCTs in all positions and muscle loadings. Isolated LD transfer did not significantly decrease superior (P > .115) and anteroinferior translation (P > .151) compared to IASRCT at any abduction and muscle loads except superior translation at 60° abduction and 90° of external rotation (ER) (P < .036). LDTM transfer also significantly decreased peak contact pressure from the IASRCT condition at every abduction angle (P < .046). However, isolated LD transfer significantly decreased subacromial peak contact pressure only at 30° abduction and 0° and 30° of ER with triple loading (P < .048), as well as at 60° abduction and 90° of ER (P < .003). CONCLUSIONS: Combined LDTM transfer decreased superior translation, anteroinferior translation, and subacromial contact pressure compared with the IASRCT condition. Isolated LD transfer did not improve glenohumeral translation and subacromial contact pressure. Combined LDTM transfer may be a more reliable treatment option than isolated LD transfer in patients with an IASRCT.

Outcomes of combined anterior latissimus dorsi and teres major tendon transfer for irreparable anterosuperior rotator cuff tears.

BACKGROUND: Irreparable anterosuperior rotator cuff tears (IASRCTs) can result in loss of active elevation, loss of internal rotation, and pseudoparalysis. Joint-preserving treatment options for IASRCTs in young and high-demand elderly patients are limited. The purpose of this study was to evaluate the clinical and radiologic outcomes of combined anterior latissimus dorsi and teres major (aLDTM) tendon transfer in patients with IASRCTs without reconstruction of the superior rotator cuff and capsular portion. METHODS: This retrospective study was conducted between 2015 and 2018. We included patients who underwent combined aLDTM tendon transfer for IASRCTs. Clinical outcomes included visual analog scale for pain, Constant score, American Shoulder and Elbow Surgeons score, University of California Los Angeles shoulder scores, activities of daily living requiring active internal rotation score, active range of motion, subscapularis-specific physical examination, and rate of return to work. Radiographic analyses included the assessment of acromiohumeral distance, Hamada grade for cuff tear arthropathy, rate of anterior glenohumeral subluxation reduction, and transferred tendon integrity at 2 years postoperatively. RESULTS: The mean follow-up period was 38.1 ± 13.7 (range: 24-63) months. Of the patients, 30 (mean age: 64.1 years) met the study criteria. Postoperatively, mean Constant, American Shoulder and Elbow Surgeons, University of California Los Angeles, and activities of daily living requiring active internal rotation scores improved from 47.4 to 69.9 (P < .001), 44.9 to 79.2 (P < .001), 20.0 to 28.7 (P < .001), and 13.2 to 26.9 (P < .001), respectively. The mean active range of motion was significantly increased postoperatively for both forward elevation (P < .001) and internal rotation at the back (P < .001). Of the patients, 24 (83%) returned to their previous work. No significant progression of cuff tear arthropathy was observed at final follow-up (Hamada grade: preoperative 1.3 ± 0.5 to postoperative 1.5 ± 0.7; p=0.155). Fifteen of 30 patients (50%) restored the anterior glenohumeral subluxation that was apparent preoperatively. One patient presented with transient axillary nerve palsy after surgery. Two patients presented with partial nonretracted tears of the transferred tendon. CONCLUSION: This minimum 2-year follow-up study demonstrated that combined aLDTM tendon transfer without reconstruction of the superior rotator cuff and capsular portion was a viable treatment option with favorable clinical and radiologic outcomes for patients with IASRCTs.

Restoration of active internal rotation following reverse shoulder arthroplasty: anterior latissimus dorsi and teres major combined transfer.

BACKGROUND: Reverse shoulder arthroplasty (RSA) for irreparable massive rotator cuff tear (mRCT) and cuff tear arthropathy (CTA) demonstrates satisfactory clinical outcomes. However, many studies have reported no significant improvements in internal and external rotation. To our knowledge, there have been no studies on new attempts to restore active internal rotation following RSA. The purpose of this study was to compare RSA alone and RSA with anterior latissimus dorsi and teres major (aLDTM) tendon transfer in patients with CTA and mRCT with combined loss of active elevation and internal rotation (CLEIR). METHODS: This retrospective cohort study included patients who underwent RSA with a lateralized design and had CLEIR between October 2014 and January 2019. Two groups were classified: patients who underwent RSA alone (group R, n = 36) and patients who underwent RSA with aLDTM tendon transfer (group T, n = 24). Clinical outcomes, including the visual analog scale score, Constant score, American Shoulder and Elbow Surgeons score, active range of motion, score for activities of daily living requiring active internal rotation (ADLIR), and ability to perform toileting activity, were compared. Moreover, radiologic outcomes and complications were compared. RESULTS: The mean follow-up period was 36.8 ± 11.6 months (range, 24-67 months). Both group R and group T showed significant improvements in clinical scores and active range of motion preoperatively and postoperatively. In group T, the Constant score (65.2 ± 7.5 vs. 58.1 ± 12.3, P = .008), ADLIR score (26.1 ± 3.1 vs. 20.3 ± 5.0, P < .001), internal rotation level with the arm behind the back (P < .001), and subscapularis-specific physical examination findings (P < .001) were significantly better than in group R. However, no significant difference in the American Shoulder and Elbow Surgeons score, forward flexion, and external rotation at 0° and 90° of abduction were found at final follow-up. Transient axillary nerve palsy was found in 2 patients in group T. However, there were no significant differences in complication rates between 2 groups. CONCLUSION: Lateralized RSA with aLDTM tendon transfer for patients with CTA and mRCT with CLEIR restored shoulder function and improved clinical outcomes, especially the ability to perform ADLIR and toileting activity.

Does Preservation of Coracoacromial Ligament Reduce the Acromial Stress Pathology Following Reverse Total Shoulder Arthroplasty?

INTRODUCTION: Acromial pathologies (AP), such as acromial stress reaction (ASR), acromial stress occult fracture (ASOF), and acromial stress fracture (ASF), are known as complications that deteriorate the clinical score and patient satisfaction after reverse total shoulder arthroplasty (RSA). Several factors that increase stress on the acromion have been reported as risk factors for AP, but this is also unclear. Thecoracoacromial ligament (CAL) is a structure that distributes the stress loading on such an acromion, although its importance has been mentioned, there is a lack of research. Therefore, we investigated the incidence of AP according to the preservation of the CAL and whether it is a risk factor. METHODS: The study was retrospectively conducted on patients who underwent RSA from 2016 and 2018. Patients with CAL transection was classified into group 1 and CAL preservation was classified into group 2. ASR and ASOF were identified through symptoms and ultrasound, and ASF identified through simple radiograph or computed tomography. The incidence of AP in each group was checked and compared. RESULTS: Of the total of 265 patients. Among 197 cases of group 1, 21 cases of ASR(10.7%), 28 cases of ASOF (14.2%),10 cases of ASF (5.1%), and 59 cases of total AP (29.4%). Among 68 cases in group 2, 2 cases (2.9%) of ASR, 6 cases of ASOF(8.8%), 1 case of ASF (1.5%), and 9 cases of total AP (13.2%). It was confirmed that ASR and ASOP were significantly decreased in the group preserving CAL. (P = .008). CONCLUSION: In the case of preservation of CAL during surgery, it was confirmed that the incidence of ASR, ASOF was reduced. Therefore, preservation of CAL can be regarded as a modifiable risk factor that can reduce the risk of AP by distributing the stress applied to acromion after RSA surgery.