Risk factors of throwing injuries related to pitching mechanics in young baseball players: a longitudinal cohort study

BACKGROUND

Risk factors for throwing injuries related to pitching mechanics are unknown. Insufficient pelvic rotation during pitching may be a risk factor for shoulder and elbow injury. This cohort study aimed to identify biomechanics risk factors for throwing injuries in young baseball players. We hypothesized that excessive mechanical load and motion errors would be risk factors for throwing injuries.

METHODS

Young baseball pitchers (aged 8-9 years) were recruited from regional baseball leagues between December 2016 and December 2019. Pitching measurements were performed before the start of each season and after the end of the last season in December 2019. The trunk tilt angular displacement, pelvic rotation angular displacement, and forearm rotation angle were calculated using a markerless motion capture system. We also measured elbow varus torque using an accelerometer. After the initial test session, each participant was followed up for 3 years to determine the occurrence of throwing injuries. Players with throwing shoulder and elbow injuries were categorized into the throwing injury group, and those without shoulder and elbow pain for 3 years were categorized into the noninjured group.

RESULTS

In this study, 97 baseball pitchers completed a 3-year follow-up. Among those participants, 66 (68.0%) had throwing injuries. A significant difference was observed between the throwing injury and noninjured groups, whereby the injured players had less pelvic rotation angular displacement.

CONCLUSION

Insufficient pelvic rotation during pitching is a newly discovered risk factor related to throwing injuries.

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.

Risk factors for throwing elbow injuries during pitching analyzed by simulation using human musculoskeletal model in youth baseball pitchers

BACKGROUND

Pitching mechanics are believed to be risk factors for throwing elbow injury. Thus, a prospective study of abnormal mechanics in youth baseball players is needed. This study aimed to analyze the ulnar collateral ligament during normal pitching using SIMM (Software for Interactive Musculoskeletal Modeling) for analysis and investigate the risk parameters of throwing elbow injuries in youth baseball players. We hypothesized that excessive ulnar collateral ligament force during pitching would be a risk factor for throwing elbow injuries in this population.

METHODS

In this cohort study, youth baseball pitchers (aged 9-11 years) were instructed to throw a ball into a netted target. Using a SIMM musculoskeletal model, we analyzed the force of the anterior band of the anterior oblique ligament, posterior band of the anterior oblique ligament (AOL_PB), and elbow varus moment during pitching (foot contact to ball release). We calculated the integral of each force of the anterior band of the anterior oblique ligament and AOL_PB during pitching and summarized these data to establish an impulse at the medial epicondyle. Each participant was followed up for 12 months to assess the occurrence of throwing elbow injury.

RESULTS

During the 12-month follow-up period, 18 pitchers (28.1%) reported throwing elbow injuries in the throwing arm. The results of this study showed that the maximum AOL_PB force and the impulse at the medial epicondyle were risk factors for throwing elbow injuries. The maximum AOL_PB force was significantly higher in the throwing elbow injury group than in the uninjured group (59.4 ± 17.8 N vs. 47.1 ± 17.5 N, P = .014). The impulse at the medial epicondyle was also significantly different (11.1 ± 4.0 N ･ s in the throwing elbow injury group vs. 8.3 ± 4.4 N ･ s in the uninjured group, P = .025).

CONCLUSIONS

Increasing the AOL_PB force or the impulse at the medial epicondyle may increase the risk of throwing elbow injuries in youth baseball pitchers. It may be possible to reduce injury risk by focusing on ways to decrease AOL_PB load and cumulative stress on the medial epicondyle throughout the throwing motion while still maintaining high levels of ball velocity.

Return-to-play outcomes in high school baseball players after ulnar collateral ligament injuries: dynamic contributions of flexor digitorum superficialis function

BACKGROUND

Ulnar collateral ligament (UCL) injuries are common in baseball pitchers. The purpose of this study was to evaluate changes to medial elbow joint laxity under valgus stress, as well as under valgus stress with flexor digitorum superficialis (FDS) contraction, and its ability to predict rehabilitation outcomes.

METHODS

Sixty-one UCL injuries were diagnosed. All patients were high school students who initially received rehabilitation treatment. Rates of return to play and return to the same level of play or higher (RTSP) were calculated and correlated with joint gapping under the following conditions: elbow gravity valgus stress and intra-articular ring-down artifact (RDA) at rest, elbow gravity valgus stress, and elbow gravity valgus stress with maximum FDS contraction.

RESULTS

The overall RTSP rate in patients receiving nonoperative treatment was 83.6% (51 of 61 patients). The RDA at rest significantly differed between the RTSP and non-RTSP groups, with an odds ratio of 17.5. This result indicated that the RDA could be a predictor of rehabilitation outcomes. Moreover, there were significant differences in the RDA under gravity valgus stress conditions with FDS contraction between the 2 groups, with an odds ratio of 98.0. Multivariate logistic regression analysis identified 1 variable (RDA under valgus stress with FDS contraction) as the most significant predictive factor for successful treatment of UCL elbow injury.

CONCLUSIONS

UCL injuries in high school baseball players can be successfully treated nonoperatively in most cases. Stress ultrasound with FDS muscle contraction can help predict the potential for RTSP.

Superior Capsule Reconstruction Using Fascia Lata Allograft Compared With Double- and Single-Layer Dermal Allograft: A Biomechanical Study

PURPOSE

To biomechanically characterize superior capsule reconstruction (SCR) using fascia lata allograft, double-layer dermal allograft, and single-layer dermal allograft for a clinically relevant massive irreparable rotator cuff tear involving the entire supraspinatus and 50% of the infraspinatus tendons.

METHODS

Eight cadaveric specimens were tested in 0°, 30°, and 60° abduction for (1) intact, (2) massive rotator cuff tear, (3) SCR using fascia lata, (4) SCR using double-layer dermis, and (5) SCR using single-layer dermis. Superior translation and subacromial contact pressure were measured. Statistical analysis was conducted using repeated measures ANOVA or paired t test with P < .05.

RESULTS

Massive rotator cuff tear significantly increased superior translation of the humeral head at all abduction angles (P < .05). At 0° abduction, all SCR conditions significantly decreased superior translation compared with the massive tear but did not restore translation (P < .05) to intact. Fascia lata and double-layer dermis SCR restored superior translation to intact at 30° and 60° of abduction, but single-layer dermis did not. Subacromial contact pressure at 0° of abduction significantly decreased with SCR with fascia lata and double-layer dermis compared with tear. At 30°, all SCR conditions significantly decreased subacromial contact pressure. Single-layer dermis graft thickness significantly decreased more than fascia lata during testing (P = .02).

CONCLUSION

For SCR tensioned at 20° glenohumeral abduction, all 3 graft types may restore superior translation and subacromial contact pressure depending on the glenohumeral abduction angle; fascia lata and double-layer dermis may be more effective than single-layer dermis.

CLINICAL RELEVANCE

If a dermal graft is to be used for SCR, consideration should be given to doubling the graft for increased thickness and better restorative biomechanical properties, which may improve clinical outcomes following SCR.

Predictors of Failure of Return to Play in Youth Baseball Players After Capitellar Osteochondritis Dissecans: Focus on Elbow Valgus Laxity and Radiocapitellar Congruity

BACKGROUND

Osteochondritis dissecans of the humeral capitellum (capitellar OCD) is a common injury among youth baseball players, but there are only a few studies that report on return to play with nonoperative treatment.

PURPOSE

To evaluate the medial elbow joint laxity under valgus stress and radiocapitellar congruity in patients with capitellar OCD and evaluate their relationship to predicting rehabilitation outcome.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Capitellar OCD was diagnosed in 81 patients included in our study. All patients were elementary school students who initially received rehabilitation treatment after injury. The rates of return to the same level of play or higher (RTSP) were calculated and correlated with the joint gap difference between the dominant and nondominant elbows using ultrasound and radiocapitellar congruity (proximal, lateral, and anterior radial translation length), which was assessed using plain radiographs of the dominant elbow.

RESULTS

The overall RTSP rates of patients with nonoperative treatment was 70.4% (57/81). The multivariate logistic regression analysis identified OCD classification (stage I, odds ratio [OR], 4.076; 95% CI, 1.171-14.190) and 1 continuous variable (proximal radial translation length on anteroposterior view, OR, 0.661; 95% CI, 0.479-0.911) as the significant predictive factors for outcome after nonoperative treatment.

CONCLUSION

The early stage of capitellar OCD in youth baseball players can be successfully treated nonoperatively in the majority of cases. The presence of proximal radial translation can predict the outcome of nonoperative management of capitellar OCD.

Posterior shoulder tightness can be a risk factor of scapular malposition: a cadaveric biomechanical study

BACKGROUND

Scapular malposition and posterior shoulder tightness are key pathologic processes in the shoulder of throwing athletes. The objective of this study was to investigate the effects of posterior capsule tightness, posterior rotator cuff muscle tightness, or both on scapular position.

METHODS

Ten shoulders from 5 fresh frozen cadaveric male torsos were tested in maximum internal, neutral, and maximum external shoulder rotations at 0°, 45°, and 90° of shoulder abduction. Scapular rotation-namely, upward and downward rotation, internal and external rotation, and anterior and posterior tilt-and the scapula-spine distance were measured by using a MicroScribe digitizer (Revware, Raleigh, NC, USA). Each shoulder underwent 4 experimental stages: intact; isolated posterior rotator cuff muscle (infraspinatus and teres minor) tightness; both posterior rotator cuff muscle and capsule tightness; and isolated posterior capsule tightness.

RESULTS

Posterior muscle tightness significantly decreased upward rotation (P< .05) only in maximum shoulder internal rotation at 45° or 90° of shoulder abduction, whereas posterior capsule tightness did not affect upward rotation (P= .09 to .96). Posterior capsule tightness significantly increased scapular internal rotation (P< .01), but posterior muscle tightness did not change scapular internal rotation (P= .62 to .89). Posterior capsule tightness significantly increased both the superior and inferior scapula-spine distance (ie, caused scapular protraction) in maximum shoulder external rotation at 90° of abduction (P< .01).

CONCLUSION

Posterior shoulder tightness resulted in scapular malposition. However, the muscular and capsular components of that tightness affected the scapular position differently. For the treatment of scapula malposition, stretching of the posterior shoulder capsule and muscles is recommended.

Ulnar collateral ligament insufficiency affects cubital tunnel syndrome during throwing motion: a cadaveric biomechanical study

BACKGROUND

In throwing athletes, cubital tunnel syndrome and insufficiency of the ulnar collateral ligament (UCL) are common pathologic processes of the elbow. The objective of this study was to investigate the effect of UCL tears on ulnar nerve elongation in the simulated throwing position.

METHODS

Eight fresh frozen cadaveric upper limbs were tested at the simulated late cocking to acceleration phase in the throwing motion using an elbow testing system. Elbow valgus laxity and ulnar nerve length and strain under 2 Nm of applied valgus torque (maximum torque in cadaveric elbow) were evaluated. Paired t-tests were used to compare all data between intact UCLs and UCLs after complete transection of the anterior oblique ligament. Linear regression analysis was used to investigate relationships between elbow valgus laxity and ulnar nerve strain.

RESULTS

Elbow valgus laxity significantly increased after transection of the UCL. Ulnar nerve length after UCL transection was significantly greater than that in the intact condition at 60° (P = .006) and 90° of elbow flexion (P < .0001). In addition, ulnar nerve strain was positive (increased) at 60° and 90° of elbow flexion. Maximum ulnar nerve strain at 90° of elbow flexion was 3.9% ± 0.9% when the UCL was intact and 6.8% ± 0.7% after transection. UCL transection yielded significant positive correlation between elbow valgus laxity and ulnar nerve strain (P = .006; r = .4714).

CONCLUSION

Increased elbow valgus laxity due to UCL insufficiency may cause elongation of the ulnar nerve and exacerbate cubital tunnel syndrome during the throwing motion.

Throwing Injuries in Youth Baseball Players: Can a Prevention Program Help? A Randomized Controlled Trial

BACKGROUND

Throwing injuries of the shoulder and elbow are common among youth baseball players.

HYPOTHESIS

A prevention program will reduce the incidence of throwing injuries of the shoulder and elbow by 50% among youth baseball players.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

The authors block randomized 16 youth baseball teams consisting of 237 players aged 9 to 11 years into an intervention group (8 teams, 117 players) and a control group (8 teams, 120 players). The intervention program consisted of 5 stretching, 2 dynamic mobility, and 2 balance training exercises performed during warm-up. Both groups were followed up for 12 months, during which the incidence of shoulder and elbow injuries was recorded. In addition, ball speed during pitching as a performance-related factor and variables of physical function (passive range of motion of the elbow, shoulder and hip, dynamic balance, and thoracic kyphosis angle) were assessed during the pre- and postintervention periods.

RESULTS

The incidence of shoulder and elbow injuries in the intervention group (1.7 per 1000 athlete-exposures) was significantly lower than that in the control group (3.1 per 1000 athlete-exposures) (hazard ratio, 1.940; 95% CI, 1.175-3.205; P = .010). The factors related to pitching performance, as assessed by ball speed, tended to increase in the intervention group as compared with the control group (P = .010). The program also improved shoulder horizontal adduction deficits on the dominant side, hip internal rotation on the nondominant side, and the thoracic kyphosis angle.

CONCLUSION

A prevention program decreases throwing injuries of the shoulder and elbow and enhances the parameter of pitching performance in youth baseball players.

Additional Dorsal Fibrocartilage Repair in a Combined Radial Collateral Ligament and Dorsal Fibrocartilage Injury of the Thumb Metacarpophalangeal Joint

The purpose of this study was to evaluate the necessity of an additional dorsal fibrocartilage (DFC) repair in combined radial collateral ligament (RCL) and DFC injuries of the thumb metacarpophalangeal joint (MPJ). Eight cadaveric thumbs were used. Ulnar/radial deviation, prosupination, and volar/dorsal laxity were measured. Serial sectioning was performed of the RCL and the DFC. The RCL followed by the DFC were then reattached sequentially. Measurements were performed for intact, RCL cut, RCL+DFC cut, RCL repair alone, and RCL+DFC repair. The neutral position shifted ulnarly, pronated, and subluxed volarly after RCL+DFC cut. Volar subluxation was reduced with RCL+DFC repair compared with RCL repair alone. With external loading, ulnar deviation, pronation, and volar laxity increased significantly after RCL+DFC cut. Ulnar deviation reduced significantly with RCL+DFC repair (12.4°, 10.8°, and 10.9°) compared with RCL repair alone (14.4°, 14.3°, and 18.9°) at 0°, 30°, and 60°, respectively. Pronation reduced significantly with RCL+DFC repair (7.1° and 9.4°) compared with RCL repair alone (10.2° and 12.6°) at 0° and 30°, respectively. Volar subluxation reduced significantly with RCL+DFC repair (0.9 mm and 1.2 mm) compared with RCL repair alone (2.1 mm and 1.8 mm) at 30°and 60°, respectively. Radial collateral ligament repair alone does not restore anatomic dorsoradial stability of the thumb MPJ in a combined RCL and DFC injury. Combined repair of the RCL and the DFC is recommended to reduce the MPJ to its native position and minimize postoperative laxity. [Orthopedics. 2019; 42(2):e268-e272.].

Lower shoulder abduction during throwing motion may cause forceful internal impingement and decreased anterior stability

BACKGROUND

Internal impingement and decreased anterior stability, which result from shoulder capsular loosening, are common shoulder pathologies in throwing athletes. The purpose of this study was to assess the effect of shoulder abduction angle on shoulder internal impingement and anterior shoulder stability during the simulated throwing motion.

METHODS

Eight cadaveric shoulders were tested by simulating the late-cocking and acceleration phases of the throwing motion for intact and thrower's shoulder conditions. The maximal glenohumeral external rotation, anterior translation, location of the rotator cuff insertion with respect to the glenoid, length and site of internal impingement, and glenohumeral contact pressure were measured. All data were compared between shoulder abduction angles of 80°, 90°, and 100°.

RESULTS

Decreasing shoulder abduction in the simulated late-cocking phase shifted the humeral head posteriorly (P < .03) and superiorly (P < .001), decreasing the total internal impingement area between the greater tuberosity and glenoid (P = .04) and increasing the glenohumeral contact pressure during internal impingement (P = .02). In the simulated acceleration phase, anterior glenohumeral translation significantly increased as the shoulder abduction angle decreased (P < .001).

CONCLUSION

Decreasing shoulder abduction significantly increased the contact pressure during internal impingement in the simulated late-cocking phase of the throwing motion. During the simulated acceleration phase of the throwing motion, anterior glenohumeral translation significantly increased as shoulder abduction decreased.

A biomechanical cadaveric study comparing superior capsule reconstruction using fascia lata allograft with human dermal allograft for irreparable rotator cuff tear

BACKGROUND

Biomechanical and clinical success of the superior capsule reconstruction (SCR) using fascia lata (FL) grafts has been reported. In the United States, human dermal (HD) allograft has been used successfully for SCRs; however, the biomechanical characteristics have not been reported.

METHODS

Eight cadaveric shoulders were tested in 5 conditions: (1) intact; (2) irreparable supraspinatus tear; (3) SCR using FL allograft with anterior and posterior suturing; (4) SCR using HD allograft with anterior and posterior suturing; and (5) SCR using HD allograft with posterior suturing. Rotational range of motion, superior translation, glenohumeral joint force, and subacromial contact were measured at 0°, 30°, and 60° of glenohumeral abduction in the scapular plane. Graft dimensions before and after testing were also recorded. Biomechanical parameters were compared using a repeated-measures analysis of variance with Tukey post hoc test, and graft dimensions were compared using a Student t-test (P < .05).

RESULTS

Irreparable supraspinatus tear significantly increased superior translation, superior glenohumeral joint force, and subacromial contact pressure, which were completely restored with the SCR FL allografts. Both SCR HD allograft repairs partially restored superior translation and completely restored subacromial contact and superior glenohumeral joint force. The HD allografts significantly elongated by 15% during testing, whereas the FL allograft lengths were unchanged.

CONCLUSIONS

Single-layered HD SCR allografts partially restored superior glenohumeral stability, whereas FL allograft SCR completely restored the superior glenohumeral stability. This may be due to the greater flexibility of the HD allograft, and the SCR procedure used was developed on the basis of FL grafts.

Dorsoradial Instability of the Thumb Metacarpophalangeal Joint: A Biomechanical Investigation

PURPOSE

To define the role of the dorsal capsule and associated dorsal fibrocartilage (DFC) and their interactions with the radial collateral ligament (RCL) as a thumb metacarpophalangeal (MCP) joint stabilizer.

METHODS

Eight cadaveric thumbs were mounted onto a custom jig with 20 N of muscle load applied. The thumb position in space was digitized to measure ulnar-radial, pronation-supination, and volar-dorsal laxity at 0°, 30°, and 60° MCP joint flexion. Serial sectioning was performed and measurements were repeated for the intact state, proper RCL insufficiency, proper and accessory (complete) RCL insufficiency, complete RCL with 50% DFC (radial) insufficiency, and complete RCL with complete DFC insufficiency.

RESULTS

Ulnar-radial deviation, pronation-supination, and volar-dorsal translation significantly changed at 30° and 60° MCP joint flexion when comparing complete RCL insufficiency with complete RCL with 50% DFC insufficiency. At 30° flexion, significant increases were found in ulnar deviation, pronation, and volar translation, and there was a decrease in supination. At 60° flexion, ulnar deviation, pronation, and volar translation increased and radial deviation decreased significantly. At 30° flexion, the resting position significantly pronated and translated volarly. At 60° flexion, the resting position significantly shifted ulnarly, pronated, and translated volarly.

CONCLUSIONS

The DFC acts as a secondary stabilizer of the thumb MCP joint, working in tandem with the RCL. It acts by stabilizing the MCP joint dorsoradially when external forces are applied across the joint. This cadaveric study shows that RCL insufficiency with a concomitant DFC injury is less likely to be stable than RCL injuries alone, and that this effect is more pronounced with MCP joint flexion.

CLINICAL RELEVANCE

Increasing incompetence of the secondary stabilizers of the RCL, such as the DFC, will likely result in increased clinical instability upon physical examination. The results of this study also suggest the need to consider repair of the DFC at the time of RCL repair.

Partial-thickness tears involving the rotator cable lead to abnormal glenohumeral kinematics

HYPOTHESIS

The objective of this study was to determine the biomechanical function of the rotator cable when a partial-thickness (>50%) tear is present. We compared intact specimens with partial tears of the anterior cable followed by partial anterior and posterior tears in regard to glenohumeral kinematics and translation. The hypothesis was that partial-thickness tears will lead to abnormal glenohumeral biomechanics, including glenohumeral translation and path of glenohumeral articulation.

METHODS

Five fresh frozen cadaveric shoulders with intact labrum, rotator cuff, and humerus were tested using a custom shoulder testing system in the scapular plane. Glenohumeral translation was measured after applying an anterior load of 30 N at different angles of external rotation. The path of glenohumeral articulation was measured by calculating the humeral head center with respect to the glenoid articular surface at 30°, 60°, 90°, and 120° of external rotation.

RESULTS

With an anterior force of 30 N, there was a significant increase in anterior and total translation at 30° of external rotation after the anterior cable was cut (P < .05). When the tear was extended to the posterior cable, there was a significant increase in anterior, inferior, and total translation at 30° and 120° of external rotation (P < .05). With respect to the path of glenohumeral articulation , the humeral head apex was shifted superiorly at 90° and 120° of external rotation after the posterior cable was cut (P < .05).

CONCLUSION

Partial-thickness articular-sided rotator cuff tears with a thickness >50% involving the rotator cable increased glenohumeral translation and changed kinematics in our cadaveric biomechanical model.

Remplissage of an Off-track Hill-Sachs Lesion Is Necessary to Restore Biomechanical Glenohumeral Joint Stability in a Bipolar Bone Loss Model

PURPOSE

To validate the glenoid track concept in a cadaveric bipolar bone loss model and to test whether "on-track" and "off-track" lesions can be stabilized with Bankart repair (BR) with or without Hill-Sachs remplissage (HSR).

METHODS

Eight fresh-frozen cadaveric shoulders were tested in a custom apparatus with passive axial rotation and then progressive translational loading (10 to 40 N) at mid-range (60°) and end-range external rotation (90°). Injury conditions included glenoid bone loss of 15% with on-track (15%) and off-track (30%) Hill-Sachs lesions. Repair conditions included BR with HSR and BR without HSR.

RESULTS

For on-track lesions, engagement occurred with translation testing in one shoulder (12.5%) at end-range rotation. After BR, engagement was prevented for this shoulder. For off-track lesions, engagement with translation testing occurred in 8 shoulders (100%) at end-range rotation and in 6 (75%) at mid-range rotation. After BR, engagement was prevented in 4 of 6 engaging shoulders (67%) at mid-range rotation but was prevented in zero of 8 (0%) at end-range rotation. Adding HSR prevented engagement in all 14 engaging shoulders with off-track lesions (100%). BR with HSR resulted in supraphysiological stiffness for off-track lesions at mid- and end-range rotation (13.3 N/m vs 7.0 N/m and 10.0 N/m vs 5.0 N/m, P = .0002) and for on-track lesions at end-range rotation (10.1 N/m vs 5.0 N/m, P = .0002). Stiffness of BR with HSR was not different from the intact shoulder for on-track lesions at mid-range rotation (7.2 N/m vs 7.0 N/m, P > .99).

CONCLUSIONS

The patterns of engagement of Hill-Sachs lesions with a 15% glenoid defect in this model give support to the glenoid track concept. BR plus remplissage resulted in supraphysiological shoulder stiffness but was necessary to prevent engagement of off-track bipolar bone lesions.

CLINICAL RELEVANCE

This biomechanical study provides evidence to aid in surgical decision making by examining the effects of bipolar bone loss and soft-tissue reconstruction on shoulder stability.

What Is the Critical Value of Glenoid Bone Loss at Which Soft Tissue Bankart Repair Does Not Restore Glenohumeral Translation, Restricts Range of Motion, and Leads to Abnormal Humeral Head Position?

BACKGROUND

A general consensus has been formed that glenoid bone loss greater than 20% to 25% is the critical amount at which bony augmentation procedures are needed; however, recent clinical results suggest that the critical levels must be reconsidered to lower values.

PURPOSE

This study aimed to find the critical value of anterior glenoid bone loss when a soft tissue repair is not adequate to restore anterior-inferior glenohumeral translation, rotational range of motion, or humeral head position using a biomechanical anterior shoulder instability model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight cadaveric shoulders were tested with a customized shoulder testing system. Range of motion, translation, and humeral head position were measured at 60° of glenohumeral abduction in the scapular plane under a total of 40-N rotator cuff muscle loading in the following 11 conditions: intact; soft tissue Bankart lesion and repair; Bankart lesion with 10%, 15%, 20%, and 25% glenoid bone defects based on the largest anteroposterior width of the glenoid; and soft tissue Bankart repair for each respective glenoid defect. Serial osteotomies for each percentage of bone loss were made parallel to the long axis of the glenoid.

RESULTS

There was significantly decreased external rotation (121.2° ± 2.8° to 113.5° ± 3.3°; P = .004), increased anteroinferior translation with an externally applied load (3.0 ± 1.2 mm to 7.5 ± 1.1 mm at 20 N; P = .008), and increased posterior (0.2 ± 0.6 mm to 2.7 ± 0.8 mm; P = .049) and inferior shift (2.9 ± 0.7 mm to 6.6 ± 1.1 mm; P = .018) of the humeral head apex in the position of maximum external rotation after soft tissue Bankart repair of a 15% glenoid defect compared with the repair of a Bankart lesion without a glenoid defect, respectively.

CONCLUSION

Glenoid defects of 15% or more of the largest anteroposterior glenoid width should be considered the critical bone loss amount at which soft tissue repair cannot restore glenohumeral translation, restricts rotational range of motion, and leads to abnormal humeral head position.

CLINICAL RELEVANCE

The critical level of anterior glenoid bone loss at which bony restorations should be considered is closer to 15% of the largest anteroposterior width of glenoid for defects perpendicular to the superoinferior glenoid axis, which is lower than the commonly accepted threshold of 20% to 25%.

Biomechanical Effects of Capsular Shift in the Treatment of Hip Microinstability: Creation and Testing of a Novel Hip Instability Model

BACKGROUND

A capsular shift procedure has been described for the treatment of hip instability; however, the biomechanical effects of such a shift are unknown.

PURPOSE

To create a cadaveric model of hip capsule laxity and evaluate the biomechanical effects of a capsular shift used to treat hip instability on this model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight cadaveric hips with an average age of 58.5 years were tested with a custom hip testing system in 6 conditions: intact, vented, instability, capsulotomy, side-to-side repair, and capsular shift. To create the hip model, the capsule was stretched in extension under 35 N·m of torque for 1 hour in neutral rotation. Measurements included internal and external rotation with 1.5 N·m of torque at 5 positions: 5° of extension and 0°, 15°, 30°, and 45° of flexion for each of the above conditions. The degree of maximum extension with 5 N·m of torque and the amount of femoral distraction with 40 N and 80 N of force were measured. Statistical analysis was performed by use of repeated-measures analysis of variance with Tukey post hoc analysis.

RESULTS

The instability state significantly increased internal rotation at all flexion angles and increased distraction compared with the intact state. The capsulotomy condition resulted in significantly increased external rotation and internal rotation at all positions, increased distraction, and maximum extension compared with the intact state. The side-to-side repair condition restored internal rotation back to the instability state but not to the intact state at 5° of extension and 0° of flexion. The capsular shift state significantly decreased internal rotation compared with the instability state at 5° of extension and 0° and 15° of flexion. The capsular shift and side-to-side repair conditions had similar effects on external rotation at all flexion-extension positions. The capsular shift state decreased distraction and maximum extension compared with the instability state, but the side-to-side repair state did not.

CONCLUSION

The hip capsular instability model was shown to have significantly greater total range of motion, external rotation, and extension compared with the intact condition. The greatest effects of capsular shift are seen with internal rotation, maximum extension, and distraction, with minimal effect on external rotation compared with the side-to side repair state.

CLINICAL RELEVANCE

The biomechanical effects of the capsular shift procedure indicate that it can be used to treat hip capsular laxity by decreasing extension and distraction with minimal effect on external rotation.