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 4 conditions: (1) intact shoulder; (2) simulated massive rotator cuff tear, (3) 3-mm acromiograft condition, and (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 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/external rotation angles (P < .05). The 3-mm acromiograft also decreased superior translation of the humeral head compared with 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 < .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 in the treatment of massive cuff tears. Because grafting the acromion's undersurface is new with limited clinical outcomes, further observation is crucial. Using a Teflon instead of an acellular dermal matrix allograft for bursal acromial resurfacing could yield different results, requiring careful interpretation.

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.

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.

Internal brace augmentation improves the biomechanical properties of trapeziometacarpal joint dorsoradial ligament repair.

This study investigated whether dorsoradial ligament repair with internal brace augmentation provided more immediate stability in the trapeziometacarpal joint than dorsoradial ligament repair alone. Seven matched pairs of cadaveric hands were used. One specimen from each pair was assigned to the repair-only group and the other to the repair + internal brace augmentation group. Trapeziometacarpal joint range of motion and translation were quantified under different conditions for both groups: (1) intact, (2) transected dorsoradial ligament, and (3) repaired dorsoradial ligament or repaired dorsoradial ligament plus internal brace augmentation. Load-to-failure tests were performed after repair. Range of motion and translation were increased by dorsoradial ligament transection and were decreased by dorsoradial ligament repair; however, compared to the intact condition, the repair-only group demonstrated greater flexion/extension range, while the repair + internal brace group showed no significant difference in range of motion. Mean loads at 2- and 3-mm displacements were greater in the repair + internal brace group than in the repair-only group (18.0 ± 1.8 N vs. 10.8 ± 1.3 N for 2 mm displacement and 35.3 ± 3.7 N vs. 23.1 ± 2.9 N for 3 mm displacement, respectively). Internal brace augmentation improved the load-to-failure characteristics of dorsoradial ligament repair without compromising range of motion. LEVEL OF EVIDENCE: IV.

A Biological Spacer to Treat Irreparable Rotator Cuff Tears: A Biomechanical Study Utilizing a Secured Versus Unsecured Tensor Fascia Lata Graft.

BACKGROUND: Designed to help treat pain and loss of function after rotator cuff repair, allograft spacer procedures utilize a graft to act as a spacer in the subacromial space, decreasing pain from impingement of the greater tuberosity on the acromion at the extremes of overhead motion. PURPOSE: To evaluate the biomechanical characteristics of secured versus unsecured tensor fascia lata allografts used in an allograft spacer procedure. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 8 fresh-frozen cadaveric shoulder specimens were used. There were 4 conditions tested: (1) intact rotator cuff, (2) stage III rotator cuff tear (complete supraspinatus tendon and superior one-half of the infraspinatus tendon), (3) unsecured tensor fascia lata graft, and (4) secured tensor fascia lata graft. Both superior and posterior translation of the humeral head were calculated in each condition. A 4-cm × 5-cm × 6-mm tensor fascia lata graft was used in the subacromial space to act as a spacer. Grafts were secured at the lateral edge of the native rotator cuff footprint with 2 knotless anchors. RESULTS: With unbalanced loading, both secured and unsecured grafts varied in their ability to limit superior and posterior translation at various rotation angles back to levels seen with intact rotator cuffs at 0° and 20° of abduction. During balanced loading, both unsecured and secured grafts limited superior and posterior translation more than those seen in the rotator cuff-deficient condition (P < .01) and similar to those seen in the intact condition (P > .05). The secured and unsecured grafts allowed similar amounts of translation at every position with both unbalanced and balanced loading (P > .05). Finally, total graft motion was <7 mm in all positions. CONCLUSION: Unsecured tensor fascia lata grafts were biomechanically equivalent to secured grafts when used during allograft spacer procedures. CLINICAL RELEVANCE: While both grafts were successful at limiting superior and posterior translation of the humeral head during early range of motion, the unsecured graft represents a cheaper, easier option to utilize during allograft spacer procedures.

Biomechanical Comparison of FiberLock Suspensionplasty and Flexor Carpi Radialis Ligament Reconstruction for Treatment of Thumb Carpometacarpal Osteoarthritis.

BACKGROUND: The purpose of this study was to compare the cyclic and load to failure characteristics of post-trapeziectomy suspensionplasty with the FiberLock Suspension System (FLSS; Arthrex Inc., Naples, Florida) to flexor carpi radialis ligament reconstruction (FCRLR). We hypothesized that the FLSS will have increased stiffness, yield, and ultimate load compared with FCRLR. METHODS: Ten matched pairs of cadaveric hands were used. One side of each pair was randomly assigned to receive the FCRLR or FLSS and the contralateral side received the other suspensionplasty. A complete trapeziectomy was performed followed by FLSS or FCRLR. Cyclic and load to failure characteristics were measured with loading in the distal to proximal direction. A preload of 1 N with 30 cycles of 1 N to 10 N was applied, followed by load to failure. A paired t test was used for statistical analysis (P < .05). RESULTS: The FLSS had significantly decreased nonrecoverable deformation and deformation at peak load during cyclic loading (P < .04). The FLSS also had significantly increased stiffness, yield load, ultimate load, and load and energy absorbed at 10 mm displacement compared with FCRLR (P < .04). All 10 FCRLR specimens failed with suture tearing through the tendon. Nine FLSS specimens failed due to suture slipping from the SwiveLock anchor (Arthrex Inc., Naples, Florida) and 1 failed due to the FiberTak anchor (Arthrex Inc., Naples, Florida) pulling through the index metacarpal. CONCLUSION: Suspensionplasty with the FLSS demonstrated greater structural integrity compared with FCRLR following trapeziectomy. The FLSS procedure may result in decreased thumb subsidence and decreased construct failure.

Load-Dependent Characteristics of Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasty: A Biomechanical Study.

Background: Increased load bearing across the patellofemoral and tibiofemoral articulations has been associated with total knee arthroplasty (TKA) complications. Therefore, the purpose of this study was to quantify the biomechanical characteristics of the patellofemoral and tibiofemoral joints and simulate varying weight-bearing demands after posterior cruciate ligament-retaining (CR) and posterior-stabilized (PS) TKAs. Methods: Eight fresh-frozen cadaveric knees (average age, 68.4 years; range, 40-86 years) were tested using a custom knee system with muscle-loading capabilities. The TKA knees were tested with a CR and then a PS TKA implant and were loaded at 6 different flexion angles from 15° to 90° with progressively increasing loads. The independent variables were the implant types (CR and PS TKA), progressively increased loading, and knee flexion angle (KFA). The dependent variables were the patellofemoral and tibiofemoral kinematics and contact characteristics. Results: The results showed that at higher KFAs, the position of the femur translated significantly more posterior in CR implants than in PS implants (36.6 ± 5.2 mm and 32.5 ± 5.7 mm, respectively). The patellofemoral contact force and contact area were significantly greater in PS than in CR implants at higher KFAs and loads (102.4 ± 12.5 N and 88.1 ± 10.9 N, respectively). Lastly, the tibiofemoral contact force was significantly greater in the CR than the PS implant at flexion angles of 45°, 60°, 75°, and 90° KFA, the average at these flexion angles for all loads tested being 246.1 ± 42.1 N and 192.8 ± 54.8 N for CR and PS implants, respectively. Conclusions: In this biomechanical study, CR TKAs showed less patellofemoral contact force, but more tibiofemoral contact force than PS TKAs. For higher loads across the joint and at increased flexion angles, there was significantly more posterior femur translation in the CR design with a preserved posterior cruciate ligament and therefore significantly less patellofemoral contact area and force than in the PS design. The different effects of loading on implants are an important consideration for physicians as patients with higher load demands should consider the significantly greater patellofemoral contact force and area of the PS over the CR design.

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.

Acellular Human Dermal Allograft Tuberoplasty Improved the Biomechanics in Mid-Range and Higher Abduction Angles in a Cadaveric Model of Massive Irreparable Rotator Cuff Tears.

Purpose: To evaluate the biomechanical effects of acellular human dermal allograft tuberoplasty (AHDAT) in a cadaveric model of an irreparable supraspinatus + anterior one-half infraspinatus (stage III) rotator cuff tear. Methods: Eight cadaveric shoulders were tested at 20°, 40°, and 60° of glenohumeral abduction (AB) and 0°, 30°, 60°, and 90° of external rotation (ER). Superior humeral translation, acromiohumeral distance, and subacromial contact were quantified for 4 conditions: (1) intact, (2) stage III tear (entire supraspinatus and anterior one-half infraspinatus), (3) single-layer AHDAT, and (4) double-layer AHDAT. Results: Stage III tear significantly increased superior translation at 20° and 40° AB and all ER angles and at 60° AB/60° ER (P ≤ .045 vs intact). Compared to the stage III tear, the single-layer AHDAT significantly decreased superior translation at 60° AB/60° ER (P = .003), whereas the double-layer AHDAT significantly decreased superior translation at 40° and 60° AB at all ER angles except 60° AB/0° ER (P ≤ .028). The stage III tear significantly decreased acromiohumeral distance at 20° AB (P ≤ .003); both grafts increased acromiohumeral distance to intact levels (P ≥ .055 vs intact). Stage III tear increased subacromial contact pressure at 20° and 40° AB/0° and 30° ER and at 60° AB/30° and 60° ER (P ≤ .034). Both AHDAT groups decreased contact pressure at 40° AB/30° and 60° ER back to intact, whereas the double-layer AHDAT also decreased contact pressure at 20° AB/0° and 60° ER and 60° AB/30° ER (P ≥ .051 vs intact). Conclusions: Both single- and double-layer grafts for AHDAT improved superior translation, subacromial contact characteristics, and acromiohumeral distance after a stage III rotator cuff tear, with varying effectiveness due to the position-dependent nature of greater tuberosity to acromial contact with abduction. Clinical Relevance: The best treatment for massive or irreparable rotator cuff tears is a matter of concern. The results of this study will help determine whether an acellular human dermal allograft tuberoplasty is a potential treatment option worthy of further investigation.

Effect of Glenoid Bone Loss and Shoulder Position on Axillary Nerve Anatomy During the Latarjet Procedure.

BACKGROUND: The Latarjet procedure is increasingly being utilized for the treatment of glenoid bone loss and has a relatively high neurological complication rate. Understanding the position-dependent anatomy of the axillary nerve (AN) is crucial to preventing injuries. PURPOSE: To quantify the effects of changes in the shoulder position and degree of glenoid bone loss during the Latarjet procedure on the position of the AN. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 10 cadaveric shoulders were dissected, leaving the tendons of the rotator cuff and deltoid for muscle loading. The 3-dimensional position of the AN was quantified relative to the inferior glenoid under 3 conditions: (1) intact shoulder, (2) Latarjet procedure with 15% bone loss, and (3) Latarjet procedure with 30% bone loss. Measurements were obtained at 0°, 30°, and 60° of glenohumeral abduction (equivalent to 0°, 45°, and 90° of shoulder abduction) and at 0°, 45°, and 90° of humeral external rotation (ER). RESULTS: Abduction of the shoulder to 60° resulted in a posterior (9.5 ± 1.1 mm; P < .001), superior (3.0 ± 1.2 mm; P = .013), and lateral (19.1 ± 2.3 mm; P < .001) shift of the AN, and ER to 90° resulted in anterior translation (10.0 ± 1.2 mm; P < .001). Overall, ER increased the minimum AN-glenoid distance at 30° of abduction (14.9 ± 1.3 mm [0° of ER] vs 17.3 ± 1.5 mm [90° of ER]; P = .045). The Latarjet procedure with both 15 and 30% glenoid bone loss resulted in a superior and medial shift of the AN relative to the intact state. A decreased minimum AN-glenoid distance was seen after the Latarjet procedure with 30% bone loss at 60° abduction and 90° ER (17.7 ± 1.6 mm [intact] vs 13.9 ± 1.6 mm [30% bone loss]; P = .007), but no significant differences were seen after the Latarjet procedure with 15% bone loss. CONCLUSION: Abduction of the shoulder induced a superior, lateral, and posterior shift of the AN, and ER caused anterior translation. Interestingly, the Latarjet procedure, when performed on shoulders with extensive glenoid bone loss, significantly reduced the minimum AN-glenoid distance during shoulder abduction and ER. These novel findings imply that patients with substantial glenoid bone loss may be at a higher risk of AN injuries during critical portions of the procedure. Consequently, it is imperative that surgeons account for alterations in nerve anatomy during revision procedures. CLINICAL RELEVANCE: This study attempts to improve understanding of the position-dependent effect of shoulder position and glenoid bone loss after the Latarjet procedure on AN anatomy. Improved knowledge of AN anatomy is crucial to preventing potentially devastating AN injuries during the Latarjet procedure.