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 Characteristics of Glenosphere Orientation Based on Tilting Angle and Overhang Changes in Reverse Shoulder Arthroplasty.

Background: Glenoid position and inclination are important factors in protecting against scapular notching, which is the most common complication that directly affects the longevity of reverse shoulder arthroplasty (RSA). This study aimed to investigate the biomechanical characteristics of glenosphere orientation, comparing neutral tilt, inferior overhang with an eccentric glenosphere at the same placement of baseplate, and inferior tilt after 10° inferior reaming in the lower part of the glenoid in RSA. Methods: Nine cadaveric shoulders were tested with 5 combinations of customized glenoid components: a centric glenosphere was combined with a standard baseplate (group A); an eccentric glenosphere to provide 4-mm inferior overhang than the centric glenosphere was combined with a standard baseplate (group B); a centric glenosphere was combined with a wedge-shaped baseplate tilted inferiorly by 10° with the same center of rotation (group C); an eccentric glenosphere was attached to a wedge-shaped baseplate (group D); and 10° inferior reaming was performed on the lower part of the glenoid to apply 10° inferior tilt, with a centric glenosphere secured to the standard baseplate for simulation of clinical tilt (group E). Impingement-free angles for adduction, abduction, forward flexion, external rotation, and internal rotation were measured. The capability of the deltoid moment arm for abduction and forward flexion, deltoid length, and geometric analysis for adduction engagement were evaluated. Results: Compared with neutral tilt, inferior tilt at the same position showed no significant difference in impingement-free angle, moment arm capability, and deltoid length. However, group D resulted in better biomechanical properties than a central position, regardless of inferior tilt. Group E demonstrated a greater range of adduction, internal and external rotation, and higher abduction and forward flexion capability with distalization, compared to corresponding parameters for inferior tilt with a customized wedge-shaped baseplate. Conclusions: A 10° inferior tilt of the glenosphere, without changing the position of the baseplate, had no benefit in terms of the impingement-free angle and deltoid moment arm. However, an eccentric glenosphere had a significant advantage, regardless of inferior tilt. Inferior tilt through 10° inferior reaming showed better biomechanical results than neutral tilt due to the distalization effect.

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.

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.

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.

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.

Biomechanical comparison of open Bankart repair vs. conjoint tendon transfer in a 10% anterior glenoid bone loss shoulder instability model.

BACKGROUND: The treatment of shoulder instability in patients with subcritical glenoid bone loss poses a difficult problem for surgeons as new evidence supports a higher failure rate when a standard arthroscopic Bankart repair is used. The purpose of this study was to compare a conjoint tendon transfer (soft-tissue Bristow) to an open Bankart repair in a cadaveric instability model of 10% glenoid bone loss. METHODS: Eight cadaveric shoulders were tested using a custom testing system that allows for a 6-degree-of-freedom positioning of the glenohumeral joint. The rotator cuff muscles were loaded to simulate physiologic muscle conditions. Four conditions were tested: (1) intact, (2) Bankart lesion with 10% bone loss, (3) conjoint tendon transfer, and (4) open Bankart repair. Range of motion, glenohumeral kinematics, and anterior-inferior translation at 60° of external rotation with 20 N, 30 N, and 40 N were measured in the scapular and coronal planes. Glenohumeral joint translational stiffness was calculated as the linear fit of the translational force-displacement curve. Force to anterior-inferior dislocation was also measured in the coronal plane. Repeated measures analysis of variance with a Bonferroni correction was used for statistical analysis. RESULTS: A Bankart lesion with 10% bone loss increased the range of motion in both the scapular (P = .001) and coronal planes (P = .001). The conjoint tendon transfer had a minimal effect on the range of motion (vs. intact P = .019, .002), but the Bankart repair decreased the range of motion to intact (P = .9, .4). There was a significant decrease in glenohumeral joint translational stiffness for the Bankart lesion compared with intact in the coronal plane (P = .021). The conjoint tendon transfer significantly increased stiffness in the scapular plane (P = .034), and the Bankart repair increased stiffness in the coronal plane (P = .037) compared with the Bankart lesion. The conjoint tendon transfer shifted the humeral head posteriorly at 60° and 90° of external rotation in the scapular plane. The Bankart repair shifted the head posteriorly in maximum external rotation in the coronal plane. There was no significant difference in force to dislocation between the Bankart repair (75.8 ± 6.6 N) and the conjoint tendon transfer (66.5 ± 4.4 N) (P = .151). CONCLUSION: In the setting of subcritical bone loss, both the open Bankart repair and conjoint tendon transfer are biomechanically viable options for the treatment of anterior shoulder instability; further studies are needed to extrapolate these data to the clinical setting.

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.

Cadaveric Biomechanical Study of Partial Glenoid Arthroplasty Versus the Latarjet Procedure for Anterior Glenoid Bone Loss.

BACKGROUND: For severe anterior glenoid bone loss due to recurrent shoulder instability, the Latarjet procedure offers a dynamic sling effect in addition to bone augmentation. Yet, it heavily alters the surrounding anatomy, while fixation and graft union issues are also common. PURPOSE/HYPOTHESIS: The purpose of this study was to compare a novel printed 3-dimensional (3D) partial glenoid arthroplasty (PGA) implant with the classic Latarjet procedure. It was hypothesized that by replicating the original glenoid geometry and preserving soft tissue anatomy, PGA may better reproduce normal joint kinematics. In addition, the locking screw construct may offer stronger fixation. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 14 matched cadaveric shoulders were tested. The PGA implant was 3D printed in titanium based on preoperative computed tomography. The intact, 25% anterior glenoid bone loss, and postoperative states were tested in the scapular and coronal planes. The following parameters were measured: articular surface area and stepoff, rotational range of motion and the humeral head apex position during rotation, and load and linear stiffness at 25% anterior translation and at 2-mm construct displacement. RESULTS: The baseline dimensions of the glenoid articular surface were comparable between the groups. The articular surface area after PGA was significantly larger (P = .006) with less articular stepoff (P = .030). PGA better approximated the intact state's external (P = .006) and total (P = .019) rotational range of motion in the scapular plane. The course of the humeral head apex after PGA better followed that of the intact state (P < .001). Resistance against anterior translation after PGA was not significantly different compared with after the Latarjet procedure. Greater linear stiffness (P = .031) and loading (P = .002) at 2-mm construct displacement were demonstrated in the PGA group. CONCLUSION: In addressing anterior glenoid bone loss, PGA better approximated intact glenohumeral joint kinematics compared with the Latarjet procedure with less articular stepoff in a cadaveric model. PGA was comparable in resisting anterior translation while being significantly stronger against loading at 2-mm construct displacement. Further clinical studies are warranted to validate this novel procedure. CLINICAL RELEVANCE: A 3D-printed PGA implant may offer an alternative treatment option for severe glenoid bone loss due to shoulder instability, overcoming the previous drawbacks of the Latarjet procedure, including altered kinematics, fixation failure, and hardware issues.

The Gluteus Medius Experiences Significant Excursion With Hip Flexion.

Purpose: To evaluate the effect of hip flexion and rotation on excursion of the gluteus medius (Gmed) and minimus (Gmin) myotendinous unit. Methods: Seven hips from 4 cadaveric specimens (males, 68.5 ± 18.3 years old) were dissected to isolate the Gmed posterior and lateral insertions and the Gmin proximal and distal insertions. Sutures were placed from tendon insertions through origins created in the iliac fossa to simulate the myotendinous unit. A load of 10N was applied. Myotendinous excursion was measured at 10° hip extension and 0°, 45°, and 90° of hip flexion in neutral rotation, and from maximum internal and external rotation in 90° flexion. The amount of abduction and rotation was also measured at each flexion position with 20N applied to each tendon. Repeated-measures analysis of variance with Tukey post hoc was used for statistics. Results: Gmed-lateral excursion ranged from 2.4 ± 0.4 mm in 10° of hip extension to 23.0 ± 1.5 mm in 90° of flexion (P < .001), and Gmed-posterior excursion ranged from 0.92 ± 0.5 mm in 10° of extension to 38.1 ± 1.1 mm in 90° of flexion (P < .001). Gmin excursion shortened with hip flexion from 4.2 ± 0.3 mm in 10° of extension to -0.2 ± 1.5 mm in 90° of flexion (Gmin-prox: P = .525, Gmin-distal: P < .001). At 90° flexion from maximum internal to maximum external rotation, Gmin-distal and proximal demonstrated a 92.6% and 51.3% increase in excursion, respectively (P < .001). Gmed-lateral and Gmed-posterior demonstrated 49.4% and 23.1% increase in excursion with external rotation, respectively (P < .001). Conclusions: The Gmed myotendinous unit undergoes significant excursion with hip flexion, whereas both Gmed and Gmin had significant excursion with femoral external rotation in 90° flexion. Clinical Relevance: It is important to understand whether active or passive hip flexion or rotation in the early postoperative period causes excessive strain to an abductor tendon repair. We found that consideration should be given to limit flexion after Gmed repair and external rotation after Gmed or Gmin repairs.

Do Magnets Have the Potential to Serve as a Stabilizer for the Shoulder Joint in Massive Rotator Cuff Tears?: A Biomechanical Cadaveric Study.

Background: Disruption of the rotator cuff muscles compromises concavity compression force, which leads to superior migration of the humeral head and loss of stability. A novel idea of using the magnetic force to achieve shoulder stabilization in massive rotator cuff tears (MRCTs) was considered because the magnets can stabilize two separate entities with an attraction force. This study aimed to investigate the biomechanical effect of the magnetic force on shoulder stabilization in MRCTs. Methods: Seven fresh frozen cadaveric specimens were used with a customized shoulder testing system. Three testing conditions were set up: condition 1, intact rotator cuff without magnets; condition 2, an MRCT without magnets; condition 3, an MRCT with magnets. For each condition, anterior-posterior translation, superior translation, superior migration, and subacromial contact pressure were measured at 0°, 30°, and 60° of abduction. The abduction capability of condition 2 was compared with that of condition 3. Results: The anterior-posterior and superior translations increased in condition 2; however, they decreased compared to condition 2 when the magnets were applied (condition 3) in multiple test positions and loadings (p < 0.05). Abduction capability improved significantly in condition 3 compared with that in condition 2, even for less deltoid loading (p < 0.05). Conclusions: The magnet biomechanically played a positive role in stabilizing the shoulder joint and enabled abduction with less deltoid force in MRCTs. However, to ensure that the magnet is clinically applicable as a stabilizer for the shoulder joint, it is necessary to thoroughly verify its safety in the human body and to conduct further research on technical challenges.

Biomechanical characteristics of a new looping stitch versus the classic Krackow stitch for distal biceps fixation.

Background: The purpose of this study was to quantify the biomechanical characteristics of a new looping stitch, developed with the concepts of a looping, locking stitch that decreases needle penetrations of the tendon, and compare it to a classic Krackow stitch for distal biceps suture-tendon fixation. Methods: The Krackow stitch with No. 2 braided suture and the looping stitch with a No. 2 braided suture loop attached to a 25-mm-length by 1.3-mm-width polyblend suture tape were compared. The Looping stitch was performed with single strand locking loops and wrapping suture around the tendon, resulting in half the needle penetrations through the graft compared to the Krackow stitch. Ten matched pairs of human distal biceps tendons were used. One side of each pair was randomly assigned to either the Krackow or the looping stitch, and the contralateral side was used for the other stitch. For biomechanical testing, each construct was preloaded to 5 N for 60 seconds, followed by cyclic loading to 20 N, 40 N, and 60 N for 10 cycles each, and then loaded to failure. The deformation of the suture-tendon construct, stiffness, yield load, and ultimate load were quantified. Comparisons between the Krackow and looping stitches were performed with a paired t-test using P < .05 as statistically significant. Results: The Krackow stitch and looping stitch had no significant difference in stiffness, peak deformation, or nonrecoverable deformation after 10 cycles of loading to 20 N, 40 N, and 60 N. There was no difference between the Krackow stitch and looping stitch in load applied to displacement of 1 mm, 2 mm, and 3 mm. The ultimate load showed that the looping stitch was significantly stronger compared to the Krackow stitch (Krackow stitch: 223.7 ± 50.3 N; looping stitch: 312.7 ± 53.8 N) (P = .002). The failure modes were either suture breakage or tendon cut through. For the Krakow stitch, there was 1 suture breakage and 9 tendons cut through. For the looping stitch, there were five suture breakages, and five tendons cut through. Conclusions: With fewer needle penetrations, incorporation of 100% of the tendon diameter, and a higher ultimate load to failure compared to the Krackow stitch, the Looping stitch may be a viable option to reduce deformation, failure, and cut-out of the suture-tendon construct.

The biomechanical effects of acromial fracture angulation in reverse total shoulder arthroplasty.

BACKGROUND: The biomechanical changes and treatment guidelines on acromial fracture after reverse shoulder arthroplasty (RSA) are still not well understood. The purpose of our study was to analyze the biomechanical changes with respect to acromial fracture angulation in RSA. METHODS: RSA was performed on 9 fresh-frozen cadaveric shoulders. An acromial osteotomy was performed on the plane extending from the glenoid surface to simulate an acromion fracture. Four conditions of acromial fracture inferior angulation were evaluated (0°, 10°, 20°, and 30° angulation). The middle deltoid muscle loading origin position was adjusted based on the position of each acromial fracture. The impingement-free angle and capability of the deltoid to produce movement in the abduction and forward flexion planes were measured. The length of the anterior, middle, and posterior deltoid was also analyzed for each acromial fracture angulation. RESULTS: There was no significant difference in the abduction impingement angle between 0° (61.8° ± 2.9°) and 10° angulation (55.9° ± 2.8°); however, the abduction impingement angle of 20° (49.3° ± 2.9°) significantly decreased from 0° and 30° angulation (44.2° ± 4.6°), and 30° angulation significantly differed from 0° and 10° (P < .01). On forward flexion, 10° (75.6° ± 2.7°), 20° (67.9° ± 3.2°), and 30° angulation (59.8° ± 4.0°) had a significantly decreased impingement-free angle than 0° (84.2° ± 4.3°; P < .01), and 30° angulation had a significantly decreased impingement-free angle than 10°. On analysis of glenohumeral abduction capability, 0° significantly differed (at 12.5, 15.0, 17.5, and 20.0N) from 20° and 30°. For forward flexion capability, 30° angulation showed a significantly smaller value than 0° (15N vs. 20N). As acromial fracture angulation increased, the middle and posterior deltoid muscles of 10°, 20°, and 30° became shorter than those of 0°; however, no significant change was found in the anterior deltoid length. CONCLUSIONS: In acromial fractures at the plane of glenoid surface, 10° inferior angulation of the acromion did not interfere with abduction and abduction capability. However, 20° and 30° of inferior angulation caused prominent impingement in abduction and forward flexion and reduced abduction capability. In addition, there was a significant difference between 20° and 30°, suggesting that not only the location of the acromion fracture after RSA but also the degree of angulation are important factors for shoulder biomechanics.

Biomechanical Characterization of a New Locking Loop Stitch for Graft Fixation versus Krackow Stitch.

Background: The purpose of this study was to quantify and compare the biomechanical characteristics of a new locking loop stitch (LLS), developed utilizing the concepts of both running locking stitch and needleless stitch, to the traditional Krackow stitch. Methods: The Krackow stitch with No.2 braided suture and the LLS with 1.3-mm augmented polyblend suture tape were compared biomechanically. The LLS was performed with single strand locking loops and wrapping suture around the tendon, resulting in half the needle penetrations through the graft compared to the Krackow stitch. Twenty bovine extensor tendons were divided randomly into two groups. The tendons were prepared to match equal thickness and cross-sectional area. Each suture-tendon was stitched and preloaded to 5 N for 60 seconds, cyclically loaded to 20 N, 40 N, and 60 N for 10 cycles each, and then loaded to failure. The deformation of the suture-tendon construct, stiffness, yield load, and ultimate load were measured. Results: The LLS had significantly less deformation of the suture-tendon construct at 100 N, 200 N, 300 N, and at ultimate load compared to the Krackow stitch (Krackow stitch and LLS at 100 N: 1.3 ± 0.1 mm and 1.0 ± 0.2 mm, p < 0.001; 200 N: 3.0 ± 0.3 mm and 1.9 ± 0.2 mm, p < 0.001; 300 N: 5.1 ± 0.6 mm and 2.9 ± 0.4 mm, p < 0.001; ultimate load: 12.8 ± 2.8 mm and 5.0 ± 1.2 mm, p < 0.001). The LLS had significantly greater stiffness (Krackow stitch and LLS: 97.5 ± 6.9 N/mm and 117.2 ± 13.9 N/mm, p < 0.001) and yield load (Krackow stitch and LLS: 66.2 ± 15.9 N and 237.9 ± 93.6 N, p < 0.001) compared to the Krackow stitch. There was no significant difference in ultimate load (Krackow stitch: 450.2 ± 49.4 N; LLS: 472.6 ± 59.8 N; p = 0.290). Conclusions: The LLS had significantly smaller deformation of the suture-tendon construct compared to the Krackow stitch. The LLS may be a viable surgical alternative to the Krackow stitch for graft fixation when secure fixation is necessary.

Biomechanical Evaluation of TensionLoc Versus the Double Spike Plate for ACL Graft Tibial Fixation.

Background: The optimal tibial fixation of anterior cruciate ligament (ACL) reconstruction (ACLR) grafts remains controversial. Purpose/Hypothesis: The purpose of this study was to compare the biomechanical characteristics of the TensionLoc (TL) cortical fixation device with the Double Spike Plate (DSP) fixation device for ACL tibial fixation using both bone-patellar tendon-bone (BTB) and quadriceps grafts. It was hypothesized that there would be no differences in biomechanical characteristics between the fixation devices regardless of graft type. Study Design: Controlled laboratory study. Methods: ACLR was performed on 14 matched-pair cadaveric knee specimens-7 pairs using quadriceps grafts (n = 3 male cadaveric knee specimens; n = 4 female cadaveric knee specimens; age, 51 ± 8 years) and 7 pairs using BTB grafts (n = 3 male cadaveric knee specimens; n = 4 female cadaveric knee specimens; age, 50 ± 7 years). One side of each pair was randomized to receive DSP fixation, and the contralateral side received TL fixation. Specimens underwent cyclic ramp loading (10 cycles each at 50-100 N, 50-250 N, and 50-400 N), followed by load-to-failure testing, with the tensile force in line with the tibial tunnel. Results between the 2 fixation types were compared with a paired t test. Results: For the quadriceps graft, there were no significant differences in cyclic loading or load-to-failure characteristics between fixation types (P≥ .092 for all parameters). For the BTB graft, TL fixation resulted in higher stiffness than DSP at all cyclic testing cycles except for cycle 1 during 100-N loading and had lower displacement at 250-N loading (3.4 ± 0.1 vs 5.4 ± 0.3 mm; P = .045). For load to failure, TL fixation resulted in higher stiffness than DSP fixation (232 ± 3.1 vs 188.4 ± 6.4 N/mm; P = .046); however, all other load-to-failure parameters were not statistically different (P≥ .135 for all parameters). Conclusion: With the quadriceps tendon graft, there were no significant differences in biomechanical characteristics between TL and DSP ACL tibial fixations; however, with BTB grafts, the TL tibial fixation demonstrated greater biomechanical integrity than the DSP tibial fixation. Clinical Relevance: The TL fixation device may provide an alternative ACL tibial fixation option for BTB and soft tissue grafts.

Biomechanical consequences of glenoid and humeral lateralization in reverse total shoulder arthroplasty.

BACKGROUND: The objective of our study was to quantify the biomechanical effectiveness of lateralization in RTSA with respect to glenoid and humeral component configurations. METHODS: Eight cadaveric shoulders were tested in a custom shoulder testing system. Three parameters, including the glenosphere thickness, humeral tray offset, and insert thickness, were assessed by implanting 8 configurations on each specimen. Humeral position, maximum internal rotation, and maximum external rotation (ER) before impingement were quantified at 0° and 30° glenohumeral abduction. The adduction angle at which the humeral component contacted the inferior scapular neck and the abduction angle where acromial notching occurred were also measured. The simulated active range of motion, including ER and abduction capability, was tested by increasing the load applied to the remaining posterior cuff and middle deltoid, respectively. Stability was evaluated by the forces that induced anterior dislocation at 30° abduction. RESULTS: The thicker glenosphere affected only lateralization, whereas the centric humeral tray and thicker insert significantly affected humeral lateralization and distalization simultaneously. Greater adduction and ER angles were found in more lateralized humerus. A significant positive correlation between humeral lateralization and ER capability was observed; however, lateralization did not significantly improve implant stability in this cadaveric testing system. CONCLUSION: Lateralization is achievable at both the glenoid and humeral sides but has different effects; therefore, lateralized implant options should be selected according to patients' needs. Lateralization is an effective strategy for reducing adduction notching while increasing ER capability. Thicker glenospheres only affected humeral lateralization. The centric humeral tray would be selected for less distalization to avoid overlengthening, whereas an eccentric humeral tray is the most effective for distalization and medialization in reducing abduction notching to the acromion and for patients with pseudoparalysis.

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.

Effect of PARP-1 Inhibition on Rotator Cuff Healing: A Feasibility Study Using Veliparib in a Rat Model of Acute Rotator Cuff Repair.

BACKGROUND: PARP-1 (poly[ADP-ribose]) was shown to influence the inflammatory response after rotator cuff tear, leading to fibrosis, muscular atrophy, and fatty infiltration in mouse rotator cuff degeneration. So far, it is not known how PARP-1 influences enthesis healing after rotator cuff tear repair. HYPOTHESIS/PURPOSE: This study aimed to examine the feasibility of oral PARP-1 inhibition and investigate its influence on rat supraspinatus enthesis and muscle healing after rotator cuff repair. The hypothesis was that oral PARP-1 inhibition would improve enthesis healing after acute rotator cuff repair in a rat model. STUDY DESIGN: Controlled laboratory study. METHODS: In 24 Sprague-Dawley rats, the supraspinatus tendon was sharply detached and immediately repaired with a single transosseous suture. The rats were randomly allocated into 2 groups, with the rats in the inhibitor group receiving veliparib with a target dose of 12.5 mg/kg/d via drinking water during the postoperative recovery period. The animals were sacrificed 8 weeks after surgery. For the analysis, macroscopic, biomechanical, and histologic methods were used. RESULTS: Oral veliparib was safe for the rats, with no adverse effects observed. In total, the inhibitor group had a significantly better histologic grading of the enthesis with less scar tissue formation. The macroscopic cross-sectional area of the supraspinatus muscles was 10.5% higher (P = .034) in the inhibitor group, which was in agreement with an 8.7% higher microscopic muscle fiber diameter on histologic sections (P < .0001). There were no statistically significant differences in the biomechanical properties between the groups. CONCLUSION: This study is the first to investigate the influence of PARP-1 inhibition on healing enthesis. On the basis of these findings, we conclude that oral veliparib, which was previously shown to inhibit PARP-1 effectively, is safe to apply and has beneficial effects on morphologic enthesis healing and muscle fiber size. CLINICAL RELEVANCE: Modulating the inflammatory response through PARP-1 inhibition during the postoperative healing period is a promising approach to improve enthesis healing and reduce rotator cuff retearing. With substances already approved by the Food and Drug Administration, PARP-1 inhibition bears high potential for future translation into clinical application.

2022 Bernard Morrey Award: the elbow ulnar collateral ligament complex demonstrates region specific stretching and recovery characteristics with valgus loading.

BACKGROUND: The objective of this study was to quantify the valgus laxity and strain of the elbow ulnar collateral ligament (UCL) complex after repeated valgus stretching and subsequent recovery. Understanding these changes may have important implications in improving strategies for injury prevention and treatment. The hypothesis was that the UCL complex will demonstrate a permanent increase in valgus laxity and region-specific increase in strain as well as region-specific recovery characteristics. METHODS: Ten cadaveric elbows (7M, 3F, 61.7 ± 2.7 years) were used. Valgus angle and strain of the anterior and posterior bands of the anterior bundle and the posterior bundle were measured at 1 Nm, 2.5 Nm, 5 Nm, 7.5 Nm, and 10 Nm of valgus torque at 70° of flexion for: (1) intact UCL, (2) stretched UCL, and (3) rested UCL. To stretch the UCL, elbows were cycled with increasing valgus torque at 70° of flexion (10 Nm-20 Nm in 1 Nm increments) until the valgus angle increased 8° from the intact valgus angle measured at 1Nm. This position was held for 30 minutes. Specimens were then unloaded and rested for 2 hours. Linear mixed effects model with Tukey's post hoc test was used for statistical analysis. RESULTS: Stretching significantly increased valgus angle compared to the intact condition 3.2° ± 0.2° (P < .001). Strains of both the anterior and posterior bands of the anterior bundle were significantly increased from intact by 2.8% ± 0.9% (P = .015) and 3.1% ± 0.9% (P = .018), respectively at 10 Nm. Strain in the distal segment of the anterior band was significantly higher than the proximal segment with loads of 5 Nm and higher (P < .030). After resting, the valgus angle significantly decreased from the stretched condition by 1.0° ± 0.1° (P < .001) but failed to recover to intact levels (P < .004). After resting, the posterior band had a significantly increased strain compared to the intact state of 2.6% ± 1.4% (P = .049) while the anterior band was not significantly different from intact. CONCLUSION: After repeated valgus loading and subsequent resting, the UCL complex demonstrated permanent stretching with some recovery but not to intact levels. The anterior band demonstrated increased strain in the distal segment compared to the proximal segment with valgus loading. The anterior band was able to recover to strain levels similar to intact after resting, while the posterior band did not.