Masaki Akeda

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 Effect of Capsular Shift in the Treatment of Hip Microinstability. Creation and Testing of a Novel Hip Instability Model

Objectives: The objective of the study was 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. Methods: Eight fresh frozen cadaveric hips, average age 58.5, were tested with a custom hip jig. To create the hip laxity model, the capsule was stretched in extension under 35Nm of torque for 1 hour in neutral rotation. Specimens went through a series of six testing conditions: intact, vented, stretched, capsulotomy, side to side repair, and capsular shift. Specimens were tested in internal (IR) and external (ER) rotational range of motion under 1.5 Nm of torque at 5 positions: 5° extension, 0°, 15°, 30° and 45° flexion. Maximum extension was measured at 5Nm torque, and femoral distraction under 40N and 80N of force. Following creation of the instability model, capsulotomy was performed just distal to and in line with the labrum from 12 o’clock to 4 o’clock through the entire substance of the iliofemoral ligament. Capsulotomies underwent two repairs, including a 1 cm capsular shift technique and side to side repair using #2 vicryl. Statistical analysis was performed using repeated measures ANOVA with TUKEY post-hoc analysis. Results: Analysis of the “stretched” state showed significantly increased IR at 5° ext, 0° flex, 15° flex, and 30° flex and increased distraction at 40N and 80N as compared to intact (Figure 1)(Table 1). Max extension increased by 6.6° between intact and stretched, however this was not statistically significant. Capsulotomy condition significantly increased ER and IR from intact at all flexion-extension positions. Furthermore, capsulotomy increased distraction at 40N and 80N, as well as max extension, as compared to intact. The repair restored IR back to the stretched state but not to the intact state at 5° ext and 0° flex (19.6° vs 24.5° and 21.8° vs 26.4°, respectively). The capsular shift significantly decreased IR compared to stretched state at 5° ext, 0°, and 15° flex, and at 5° ext and 0° compared to the vented state. Capsular shift restricted IR significantly more than repair at 5° ext, 0° flex, and 15° flex. Capsule shift and repair had similar effects on ER. Distraction distance at 40N and 80N was greater in the repair compared to the shift but this was not statistically significant. The capsular shift decreased distraction as compared to the stretched state but the repair did not. Maximum extension was significantly reduced back to the intact/vented state from the laxity state in the capsular shift but not in the repair. Conclusion: The instability model (stretched) was shown to have significantly greater range of motion, extension, and distraction than the intact condition. The greatest effects of capsular shift are seen with internal rotation, extension, and distraction with minimal effect on external rotation. The biomechanical effects of the capsular shift procedure in hip laxity patients show that its use can safely treat pathologic hip capsular laxity.

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.

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.

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 throwers 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.

The Effects of Posterior Rotator Cuff Cable Tears on Glenohumeral Biomechanics in a Cadaveric Model of the Throwing Shoulder

Objectives: The rotator cuff cable has been postulated to be the primary load bearing substructure of the superior part of the rotator cuff. Tears of the posterior rotator cable are frequently seen in overhead throwing athletes. Although the biomechanical significance of the anterior rotator cable has been well described, our current understanding of the relevance of the posterior cable is limited. The purpose of this study was to examine how partial-thickness tears and full-thickness tears of the posterior rotator cable would alter glenohumeral biomechanics and kinematics in cadaveric shoulder models. Methods: Eight fresh-frozen cadaveric shoulder specimens were prepared and tested. To simulate the sequence of glenohumeral positions during the throwing motion, specimens were mounted on a custom shoulder testing system with the humerus positioned at 90° of abduction (30° scapular upward rotation, 60° glenohumeral abduction) and tested at 30, 60, 90, and 120 degrees of external rotation. After a circumferential capsulotomy was performed, rotator cuff muscles were loaded based on physiologic cross-sectional area ratios, and testing for each specimen was performed on each the following three conditions: intact posterior cable, partial-thickness (50%) articular-sided posterior cable tear, and full-thickness posterior cable tear. Primary outcome measures tested for each condition under the various degrees of glenohumeral rotation were: 1) anterior and total glenohumeral translation after application of a 30N anterior force; 2) path of glenohumeral articulation; 3) glenohumeral joint force. Results: With a 30N anterior force at 120° of external rotation, there was a significant increase in anterior glenohumeral translation between intact and full-thickness tear specimens (7.28±2.00mm and 17.49±3.75mm, respectively; p<0.05). Similarly, total joint translation at 120° of external rotation significantly increased between intact and full-thickness tear specimens (10.37±3.18mm and 23.37±5.05mm, respectively; p<0.05). No significant differences were apparent at other degrees of rotation (30, 60, 90 degrees), or with partial-thickness tears. Changes in the path of glenohumeral articulation were likewise most evident at 120° of external rotation, with a progressively anterior, inferior, and lateral shift in articulation with sequential sectioning of the posterior cable. Lastly, with regards to alterations in glenohumeral joint force, no significant changes were seen in any of the conditions. Conclusion: In this cadaveric shoulder model of the throwing shoulder, tears of the posterior rotator cuff cable lead to altered glenohumeral biomechanics and kinematics. These changes were most profound at 120° of external rotation, suggesting the importance of an intact posterior cable as a potential stabilizer during the late-cocking phase of throwing.

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.