Analysis of abduction moment arms after rotator cuff tear and acellular dermal matrix allograft reconstruction.

BACKGROUND: Biomechanical testing of abduction moment arms presents a useful method to assess the contributions of individual rotator cuff muscles to glenohumeral function. This study aimed to investigate the changes in abduction moment arms after the treatment of supraspinatus tears with superior capsular reconstruction (SCR), bursal acromial reconstruction (BAR), and a combined SCR-BAR procedure, all with human dermal allograft. METHODS: We tested 7 fresh-frozen cadaveric specimens under 6 conditions: (1) intact, (2) 50% supraspinatus tear (partial tear), (3) 100% supraspinatus tear, (4) SCR, (5) SCR combined with BAR, and (6) BAR. In each condition, the moment arms for the individual muscles of the teres minor, subscapularis, and infraspinatus were calculated throughout 90° of abduction using a motion capture system. Analysis of variance and post hoc Tukey testing were performed to determine significance. RESULTS: In the teres minor, the moment arms in the SCR (11.9 mm), BAR (10.1 mm), and SCR-BAR (11.9 mm) conditions were greater than those in the intact (8.5 mm; P = .001, P = .001, and P = .001, respectively), partial tear (9.1 mm; P = .001, P = .128, and P = .001, respectively), and complete tear (8.8 mm; P = .001, P = .011, and P = .001, respectively) conditions. Similarly, in the subscapularis, the moment arms in the SCR (13.4 mm), BAR (13.8 mm), and SCR-BAR (13.5 mm) conditions were greater than those in the intact (10.6 mm; P = .006, P = .001, and P = .003, respectively) and partial tear (10.4 mm; P = .006, P = .001, and P = .003, respectively) conditions. In the teres minor, the SCR (11.9 mm) and SCR-BAR (11.9 mm) conditions were also found to have significantly increased moment arms compared with the BAR condition (10.1 mm; P = .001 and P = .001, respectively). In the infraspinatus, the BAR condition (13.8 mm) was found to have a significantly decreased moment arm compared with the partial tear condition (15.8 mm, P = .026), with no other significant findings between conditions. CONCLUSION: Our results suggest that the moment arm contributions of the individual muscles comprising the rotator cuff can change after reconstruction to compensate for tears. SCR and SCR-BAR increase the moment arms in the teres minor and subscapularis, potentially allowing for increased abduction ability.

A Biomechanical Analysis of Shoulder Muscle Excursions During Abduction, After the Treatment of Massive Irreparable Rotator Cuff Tears Using Superior Capsular Reconstruction (SCR), Bursal Acromial Reconstruction (BAR), and SCR with BAR.

Introduction: Current understanding of the biomechanical effects of treatment options for irreparable rotator cuff (RC) tears is lacking. This study examines how shoulder muscle lengths and excursions are affected by superior capsular reconstruction (SCR), bursal acromial reconstruction (BAR), and SCR with BAR, following a complete supraspinatus tear. Method: Six fresh-frozen cadaveric shoulders were examined. Deltoid and RC muscle lengths were measured at 0, 30, 45, 60, and 90° of shoulder abduction under six conditions: (1) intact, (2) partially torn supraspinatus, (3) completely torn supraspinatus, (4) SCR, (5) SCR with BAR, and (6) BAR. Muscle excursions from 0-90° of abduction were then calculated. Results: Subscapularis muscle lengths after SCR, BAR, and SCR with BAR were significantly greater (post-hoc Tukey HSD test; p < .01) compared to the other conditions. Supraspinatus, infraspinatus, teres minor, and deltoid lengths were not significantly different (ANOVA test; p > .01) between the conditions. All muscle excursions remained statistically similar between the conditions (ANOVA test; p > .01). Conclusion: These findings demonstrate that the use of SCR, BAR, or SCR with BAR for a complete supraspinatus tear, may increase subscapularis muscle length while maintaining other shoulder muscle lengths. An increase in subscapularis length can allow for more effective subscapularis muscle strengthening and increased compensatory function in the long term. Additionally, all shoulder muscle excursions are preserved after partial or complete supraspinatus tears and after SCR, BAR, or SCR with BAR. Therefore, these surgical treatments can initially normalize shoulder muscle function during 0-90° of abduction, after an irreparable supraspinatus tear.

Evaluation of rotator cuff abduction moment arms for superior capsular reconstruction and reverse total shoulder arthroplasty.

PURPOSE: The rotator cuff (RC) muscles contribute to dynamic stability and rotational actions of the glenohumeral joint. Moment arm can be used to demonstrate the potential work a muscle contributes to a musculoskeletal joint rotation. This study aimed to understand the moment arm contributions of the RC muscles and explore changes following a complete supraspinatus tear treated with either superior capsular reconstruction (SCR) or reverse total shoulder arthroplasty (rTSA). METHODS: Five fresh-frozen cadaveric specimens were prepared and mounted in an apparatus where each intact RC muscle was held in tension with a line of action toward its origin on the scapula. Mean moment arms for each muscle were determined experimentally based on Optotrak data collected during cadaveric shoulder arm abduction. RESULTS: Using ANOVA testing, our analysis demonstrated significant differences (p < 0.001) in infraspinatus and teres minor moment arms after rTSA compared to the intact shoulder model. After SCR, significant differences (p < 0.001) were seen in teres minor, with these differences being statistically similar to the changes seen in teres minor after rTSA. Subscapularis showed no significant difference in moment arm values between the models (p = 0.148). CONCLUSION: Our results illustrate that mean moment arms were preserved in the RC muscles after complete supraspinatus tear. This study also shows evidence that subscapularis function may be maintained after SCR or rTSA. After SCR, infraspinatus may maintain similar abduction ability compared to the anatomical shoulder, while teres minor ability may increase. Infraspinatus may have decreased abduction ability after rTSA while teres minor may have increased ability.

Effects of implant rotational malposition on contact surface area after implantation of the augmented glenoid baseplate in the setting of glenoid bone loss.

AIM OF THE STUDY: Augmented glenoid baseplates are utilized in reverse total shoulder arthroplasty in the setting of glenoid bone loss. These implants permit lateralization of the joint line and correction of bony version abnormalities. To allow bone preservation in the setting of abnormal bony version or deficiency, the backside of the augmented glenoid baseplate is not perpendicular to the axis of the central post/screw. Thus, if the baseplate is implanted with any rotational malposition, this could affect the backside contact area available for ingrowth. The purpose of this study was to assess if rotational malpositioning of a full-wedge augmented baseplate alongside the axis of the central screw significantly affects the glenoid implant backside contact area. METHODS: Seven synthetic scapulas (Sawbones, Vashon, WA) were used to implant a 15° full-wedge glenoid baseplate (Wright Medical, Memphis, TN) according to the manufacturer's technique. The contact pressure between the baseplate and the glenoid surface at rotational positions 5°, 10°, and 15° clockwise (CW) and counterclockwise (CCW) from the central axis was measured with Extreme Low Fujifilm Prescale (Tekscan, Boston, MA). The data was analyzed digitally to obtain a percentage of contact surface area. To evaluate gross contact, a computed tomography (CT) scan was performed and manual measurements of contact between the glenoid and the baseplate were conducted using a standardized axial CT slice. RESULTS: The average contact area at zero degrees of malrotation was 37.26 ± 3.27%. Average contact areas for the simulated malposition cases were 13.99 ± 9.39% at 15° CCW, 24.89 ± 5.11% at 10° CW, and 19.32 ± 3.13% at 15° CW. Each of these results was significant (p < 0.003). On computed tomography, at 15° CCW, the contact area decreased by 39%; at 15° CW, the contact area decreased by 38%. DISCUSSION: The use of augmented glenoid baseplates presents a technical challenge. It is difficult to avoid implant malrotation along the axis of the central peg/screw, because the final rotation of the baseplate must be chosen while the implant is several centimeters away from the bone. This study found that 10° and 15° malrotation about the glenoid baseplate's central axis leads to significant decreases in the implant-bone contact area. CONCLUSIONS: When implanting an augmented baseplate for total shoulder arthroplasty, it is important to minimize baseplate malrotation to decrease the risk of baseplate loosening.

Is There an Association Between Authors' Conflicts of Interest and Outcomes in Clinical Studies Involving Autologous Chondrocyte Implantation?

BACKGROUND: Autologous chondrocyte implantation (ACI) is an increasingly popular technique for the treatment of articular cartilage defects. Because several companies have financial interests in ACI, it is important to consider possible conflicts of interest when evaluating studies reporting outcomes of ACI. PURPOSE: To determine whether there is an association between authors' financial conflicts of interest and the outcomes of ACI studies. STUDY DESIGN: Cross-sectional study. METHODS: A search of PubMed and MEDLINE databases for "autologous chondrocyte implantation" was performed. Clinical studies published after 2012 through May 15, 2019, and in English were included. Studies were determined to have financial conflicts of interest if any contributing author had relevant conflicts, either self-reported in the published study's disclosures section or reported online in the American Academy of Orthopaedic Surgeons Disclosure database or the Centers for Medicare & Medicaid Services Open Payments database. The outcomes of each study were rated as favorable, equivocal, or unfavorable based on predefined criteria and then tested for association with conflicts of interest through use of the Fisher exact test. RESULTS: A total of 79 studies met the inclusion criteria. Nearly all studies were of level 3 or 4 evidence. Conflicts of interest were established in 51.90% of studies (n = 41). Conflicts that were not self-reported by the authors were discovered in 18% of studies. The level of evidence was not associated with conflict of interest. No statistically significant difference was found in the rate of favorable outcomes between studies with conflicts (92.68%) and those with no conflicts (81.58%) (P = .126). Publications by US authors were more likely to have financial conflicts of interest (P = .003). CONCLUSION: Favorable results were reported in a majority of studies involving ACI. No statistical association was found between the frequency of favorable outcomes and the presence of financial conflicts of interest, country of authorship, or level of evidence. There was a trend toward more favorable outcomes in studies with conflicts of interest. Additionally, nearly 20% of publications had possible conflicts found online that were not self-reported. It is critical for orthopaedic surgeons to judiciously evaluate published studies and consider financial conflicts of interest before performing ACI techniques on patients.

Biomechanics in an Incomplete Versus Complete Supraspinatus Tear: A Cadaveric Study.

BACKGROUND: Degenerative and traumatic changes to the rotator cuff can result in massive and irreparable rotator cuff tears (RCTs). PURPOSE/HYPOTHESIS: The study objective was to conduct a biomechanical comparison between a small, incomplete RCT and a large, complete RCT. We hypothesized that the incomplete supraspinatus (SS) tear would lead to an incremental loss of abduction force and preserve vertical position of the humeral head, while a complete SS tear would cause superior humeral migration, decrease functional deltoid abduction force, and increase passive range of motion (ROM). STUDY DESIGN: Controlled laboratory study. METHODS: Six cadaveric shoulders were evaluated using a custom testing apparatus. Each shoulder was subjected to 3 conditions: (1) intact/control, (2) 50%, full-thickness, incomplete SS tear, and (3) 100%, complete SS tear. Deltoid abduction force, superior humeral head migration, and passive ROM were measured in static conditions at 0°, 30°, and 60° of glenohumeral abduction, respectively. RESULTS: The intact SS resulted in a mean deltoid abduction force of 2.5, 3.3, and 3.8 N at 0°, 30°, and 60° of abduction, respectively. Compared with the intact shoulder, there was no significant difference in mean abduction force seen in the incomplete tear, while the force was significantly decreased by 52% at 30° of abduction in the complete tear (P = .009). Compared with the incomplete tear, there were significant decreases in abduction force seen in the complete tear, by 33% and 48% (0.9 N and 1.1 N) at 0° and 30° of abduction, respectively (P = .04 and .004). The intact configuration experienced a mean superior humeral head migration of 1.5, 1.4, and 1.1 mm at 0°, 30°, and 60° of abduction, respectively. The complete tear resulted in a superior migration of 3.0 and 4.4 mm greater than the intact configuration at 0° and 30° of abduction, respectively (P = .001). There was a 5° and 10° increase in abduction ROM with 50% and 100% tears, respectively (P = .003 and .03). CONCLUSION: An incomplete SS tear does not significantly alter the biomechanics of the shoulder, while a large, complete SS tear leads to a significant superior humeral migration, a decreased deltoid abduction force, and a mild increase in passive ROM. CLINICAL RELEVANCE: Our findings demonstrate the effects of large SS tears on key biomechanical parameters, as they progress from partial tears.

Biomechanical effects of superior capsular reconstruction in a rotator cuff-deficient shoulder: a cadaveric study.

BACKGROUND: Superior capsular reconstruction (SCR) has been gaining popularity as a treatment for irreparable rotator cuff tears (RCTs), especially in younger patients. This biomechanical study aimed to investigate how SCR affects functional abduction force, humeral head migration, and passive range of motion following an irreparable RCT. We hypothesized that SCR will restore these parameters to nearly intact shoulder levels. METHODS: Six fresh-frozen cadaveric shoulders were evaluated using a custom biomechanical testing apparatus. Each shoulder was taken through 3 conditions: (1) intact (control); (2) irreparable, complete supraspinatus (SS) tear; and (3) SCR. Functional abduction force, superior humeral head migration, and passive range of motion, including axial shoulder rotation, were measured in static condition at 0°, 30°, and 60° of glenohumeral abduction. Data were analyzed using the paired Student t test or Wilcoxon signed rank test, depending on the results of normality testing. RESULTS: The irreparable SS tear resulted in significantly lower functional abduction force at 30° of abduction (P = .01) and a trend toward a decrease (P = .17) at 60° compared with the intact configuration. SCR shoulders produced greater functional force at 0° compared with the tear configuration (P = .046). Humeral head migration was significantly increased by 4.4 and 3.0 mm at 0° and 30° of abduction, respectively, when comparing the intact vs. SS tear configurations (P = .001). SCR decreased superior migration down to levels of intact shoulders at 0° and 30° of abduction (P = .008 and P = .013, respectively) and was not significantly different from the intact configuration at any angle. SCR decreased passive shoulder extension compared with the tear configuration and increased abduction compared with the intact configuration (P = .007 and P = .03, respectively). The overall arc of axial rotation was not significantly different between SCR and the intact configuration at any angle. CONCLUSIONS: In the setting of an irreparable SS tear, SCR restores key biomechanical parameters of the shoulder to intact levels. SCR should be considered for qualifying patients with irreparable RCTs.

The biomechanics of the supraspinatus-deficient shoulder treated with superior capsular reconstruction vs. reverse total shoulder arthroplasty-experimental study.

AIM OF THE STUDY: Our objective was to compare biomechanical effects of superior capsular reconstruction (SCR) and reverse total shoulder arthroplasty (rTSA) on shoulder motion, in the setting of an irreparable supraspinatus (SS) tear. We hypothesized that rTSA would produce greater improvement in abduction force and shift the humerus inferiorly, while SCR would produce greater range of motion (ROM) and prevent superior migration of the humerus during abduction. METHODS: Six cadaveric shoulders were evaluated using a custom biomechanical apparatus. Each shoulder underwent four experimental conditions: (1) intact/control, (2) irreparable SS tear, (3) SCR using dermal allograft, and (4) rTSA without SCR. Deltoid abduction force, superior humeral head translation, and passive range of motion were measured in static tendon loading condition at 0, 30, and 60° of glenohumeral abduction. RESULTS: Both rTSA and SCR restored abduction force to intact levels at all abduction angles. rTSA significantly increased abduction force compared with the SS-deficient shoulder at 0, 30, 60° (p = 0.04), while SCR produced a significant increase at 0° (p = 0.05) abduction. rTSA inferiorly shifted the humeral head by 27 mm (p = 0.002). SCR restored superior humeral head translation to intact SS levels. Compared with SCR, rTSA resulted in 25° less passive abduction (p = 0.001) without significant differences in forward flexion/extension. Compared with SCR, rTSA achieved 10° less passive internal rotation at 0° abduction (p = 0.03) and 26° and 17° greater external rotation at 30° and 60° abduction, respectively (p = 0.03, p = 0.04). DISCUSSION: Our investigation found that abduction force was restored to intact cuff levels by both procedures, without significant differences between the two techniques. SCR restored superior humeral head migration and rTSA translated the humerus inferiorly. rTSA resulted in decreased passive abduction ROM and increased external rotation, compared with SCR. CONCLUSION: Both SCR and rTSA restore key biomechanical parameters following an irreparable SS tear, although SCR offers superior passive abduction ROM.

Segmental acetabular rim defects, bone loss, oversizing, and press fit cup in total hip arthroplasty evaluated with a probabilistic finite element analysis.

PURPOSE: Management of segmental rim defects and bone mineral density (BMD) loss in the elderly prior to total hip replacement is unclear within classification systems for acetabular bone loss. In this study, our objectives were (1) to understand how a reduction in BMD in the elderly affects the oversizing of a press-fit cup for primary fixation and (2) to evaluate whether the location of the segmental defect affected cup fixation. METHODS: A finite element (FE) model was used to simulate and evaluate cup insertion and fixation in the context of segmental rim defects. We focused on the distribution of patients over age 70 and used BMD (estimated from CT) as a proxy for aging's implications on THR and used probabilistic FE analysis to understand how BMD loss affects oversizing of a press-fit cup. RESULTS: A cup oversized by 1.10 ± 0.28 mm provides sufficient fixation and lower stresses at the cup-bone interface for elderly patients. Defects in the anterior column and posterior column both required the same mean insertion force for cup seating of 84% (taken as an average of 2 anterior column and 2 posterior column defects) compared to the control configuration, which was 5% greater than the insertion force for a superior rim defect and 12% greater than the insertion force for an inferior rim defect. CONCLUSIONS: A defect along the superior or inferior rim had a minimal effect on cup fixation, while a defect in the columns created cup instability and increased stress at the defect location.