Teruhisa Mihata

Functional and Structural Outcomes of Single-Row Versus Double-Row Versus Combined Double-Row and Suture-Bridge Repair for Rotator Cuff Tears

Background: Although previous biomechanical research has demonstrated the superiority of the suture-bridge rotator cuff repair over double-row repair from a mechanical point of view, no articles have described the structural and functional outcomes of this type of procedure. Hypothesis: The structural and functional outcomes after arthroscopic rotator cuff repair may be different between the single-row, double-row, and combined double-row and suture-bridge (compression double-row) techniques. Study Design: Cohort study; Level of evidence, 3. Methods: There were 206 shoulders in 201 patients with full-thickness rotator cuff tears that underwent arthroscopic rotator cuff repair. Eleven patients were lost to follow-up. Sixty-five shoulders were repaired using the single-row, 23 shoulders using the double-row, and 107 shoulders using the compression double-row techniques. Clinical outcomes were evaluated at an average of 38.5 months (range, 24-74 months) after rotator cuff repair. Postoperative cuff integrity was determined using Sugaya’s classification of magnetic resonance imaging (MRI). Results: The retear rates after arthroscopic rotator cuff repair were 10.8%, 26.1%, and 4.7%, respectively, for the single-row, double-row, and compression double-row techniques. In the subcategory of large and massive rotator cuff tears, the retear rate in the compression double-row group (3 of 40 shoulders, 7.5%) was significantly less than those in the single-row group (5 of 8 shoulders, 62.5%, P < .001) and the double-row group (5 of 12 shoulders, 41.7%, P < .01). Postoperative clinical outcomes in patients with a retear were significantly lower than those in patients without a retear for all 3 techniques. Conclusion: The additional suture bridges decreased the retear rate for large and massive tears. The combination of the double-row and suture-bridge techniques, which had the lowest rate of postoperative retear, is an effective option for arthroscopic repair of the rotator cuff tendons because the postoperative functional outcome in patients with a retear is inferior to that without retear.

Excessive Humeral External Rotation Results in Increased Shoulder Laxity

Background The quantitative relationship between increased anterior shoulder laxity and increased humeral external rotation observed in throwers remains unclear. Hypothesis An elongated anterior capsule, especially the anterior band of the inferior glenohumeral ligament, produced by excessive humeral external rotation will result in increased anterior shoulder laxity and increased humeral external rotation. Study Design Controlled laboratory study. Methods Seven cadaveric shoulders were tested to measure the humeral rotational range of motion, glenohumeral translations, and length of the anterior band of the inferior glenohumeral ligament. Data were collected for the intact shoulders and after nondestructive stretching of 10%, 20%, and 30% beyond maximum humeral external rotation. Results Nondestructive excessive external rotational stretching resulted in a significant increase in superior (30%, 3.3 mm) and inferior (30%, 2.3 mm) length of the anterior band of the inferior glenohumeral ligament, external rotation (30%, 35°), and anterior (30%, 2.4 mm), inferior (30%, 2.2 mm), and anterior-posterior (30%, 5.1 mm) translations. There were significant positive linear correlations between the length of the anterior band of the inferior glenohumeral ligament, external rotation, and anterior translation. Conclusions Excessive humeral external rotation results in an elongation of the anterior band of the inferior glenohumeral ligament and an increase in anterior and inferior glenohumeral translations and humeral external rotation. Clinical Relevance Repetitive excessive humeral external rotation observed in throwers may be one of the biomechanical causes for increased shoulder laxity and increased humeral external rotation.

Superior Capsule Reconstruction to Restore Superior Stability in Irreparable Rotator Cuff Tears A Biomechanical Cadaveric Study

Background: There have been many clinical reports of patch graft surgery for irreparable rotator cuff tears. However, the retear rate of the patch graft is relatively high because of the lack of superior stability, causing subacromial abrasions. Purpose: To compare superior stability among 3 types of patch grafting for simulated irreparable rotator cuff tears. Study Design: Controlled laboratory study. Methods: Eight cadaveric shoulders were tested in a custom shoulder testing system. Superior translation of the humerus, subacromial contact pressure, and glenohumeral joint force were quantified in the following 5 conditions: (1) when the rotator cuff was intact, (2) after cutting the supraspinatus tendon, (3) after the patch graft to reconstruct the supraspinatus tendon, (4) after the patch graft to reconstruct the superior capsule, and (5) after the patch graft to reconstruct both the supraspinatus tendon and superior capsule. While the graft was sutured to the torn tendon in condition 3, the graft was attached to the superior glenoid in condition 4. Results: Compared with values for intact rotator cuffs, cutting the supraspinatus tendon significantly increased superior translation (P < .05), significantly increased subacromial contact pressure (P < .05), and significantly decreased glenohumeral compression force (P < .05). Superior translation was restored partially after the supraspinatus tendon patch graft and restored fully after the superior capsule patch graft and after both patch grafts. All patch grafts fully restored the subacromial contact pressure (P < .05) but did not alter the glenohumeral joint force. Conclusion: When patch graft surgery is chosen for irreparable rotator cuff tears, the graft should be attached medially to the superior glenoid and laterally to the greater tuberosity to restore superior stability of the humeral head. Clinical Relevance: The superior capsule patch graft completely restored superior stability of the glenohumeral joint, while patch grafting to the supraspinatus tendon partially restored superior translation.

Excessive Glenohumeral Horizontal Abduction as Occurs During the Late Cocking Phase of the Throwing Motion Can Be Critical for Internal Impingement

Background The objective of this study was to determine the effects of increased horizontal abduction with maximum external rotation, as occurs during the late cocking phase of throwing motion, on shoulder internal impingement. Hypothesis An increase in glenohumeral horizontal abduction will cause overlap of the rotator cuff insertion with respect to the glenoid and increase pressure between the supraspinatus and infraspinatus tendon insertions on the greater tuberosity and the glenoid. Study Design Controlled laboratory study. Methods Eight cadaveric shoulders were tested with a custom shoulder testing system with the specimens in 60° of glenohumeral abduction and maximum external rotation. The amount of internal impingement was evaluated by assessing the location of the supraspinatus and infraspinatus articular insertions on the greater tuberosity relative to the glenoid using a MicroScribe 3DLX. Pressure in the posterior-superior quadrant of the glenoid was measured using Fuji prescale film. Data were obtained with the humerus in the scapular plane and 15°, 30°, and 45° of horizontal abduction from the scapular plane. Results At 30° and 45° of horizontal abduction, the articular margin of the supraspinatus and infraspinatus tendons was anterior to the posterior edge of the glenoid and less than 2 mm from the glenoid rim in the lateral direction; the contact pressure was also greater than that found in the scapular plane and 15° of horizontal abduction. Conclusion Horizontal abduction beyond the coronal plane increased the amount of overlap and contact pressure between the supraspinatus and infraspinatus tendons and glenoid. Clinical Relevance Excessive glenohumeral horizontal abduction beyond the coronal plane may cause internal impingement, which may lead to rotator cuff tears and superior labral anterior to posterior (SLAP) lesions.

Effects of Capsular Plication and Rotator Interval Closure in Simulated Multidirectional Shoulder Instability

BACKGROUND Arthroscopic treatment of multidirectional shoulder instability with use of capsular plication and rotator interval closure has been shown to be effective in several clinical studies; however, the biomechanical effects of these procedures have not been elucidated. The purpose of this study was to assess biomechanically the effect of arthroscopic capsular plication combined with rotator interval closure on rotational range of motion, humeral head position throughout rotation, and glenohumeral translation. METHODS Seven cadaveric shoulders were stretched to 10% beyond the maximum range of motion in 60 degrees and 0 degrees of glenohumeral abduction. Testing was performed for the intact and stretched conditions and following three sequential capsular repairs: anterior plication, posterior plication, and rotator interval closure. Rotational range of motion, humeral head position throughout the range of motion, and glenohumeral translations were measured in both positions. RESULTS Stretching increased the total rotational range of motion in 60 degrees and 0 degrees of abduction. After anterior plication alone, total rotation decreased significantly (p < 0.05) in both positions and was restored to the intact state. Total translation with a 20-N load increased significantly in the 60 degrees of abduction position after stretching (p = 0.03). Anterior-posterior translation decreased significantly compared with the stretched state only after all components of the repair were completed in 60 degrees of abduction (p = 0.0003 with a 15-N load and p = 0.0001 with a 20-N load). This decrease was also found to be significantly less than the intact condition (p = 0.008 with a 15-N load and p = 0.001 with a 20-N load). A similar trend in results was found with superior-inferior translations in the 0 degrees of abduction position. CONCLUSIONS Capsular plication alone reduces range of motion to the intact state. Reductions in translation, however, may require the addition of rotator interval closure. Changes in translation and rotation after repair are dependent on arm position. In some positions, the addition of rotator interval closure may also result in overtightening.

Biomechanical Assessment of Type II Superior Labral Anterior-Posterior (SLAP) Lesions Associated With Anterior Shoulder Capsular Laxity as Seen in Throwers A Cadaveric Study

Background Type II superior labral anterior-posterior lesions in throwers are often associated with anterior shoulder capsular laxity. Hypothesis Shoulder instability in patients with type II superior labral anterior-posterior lesions may result from the associated shoulder capsular laxity rather than the superior labral anterior-posterior lesion alone. Study Design Controlled laboratory study. Methods Six cadaveric shoulders were externally rotated to 20% beyond the maximum humeral external rotation at 60° of glenohumeral abduction, which simulated 90° of shoulder abduction, to detach the superior labrum and elongate the anterior shoulder capsular ligaments. The detached labrum was then repaired to isolate the effect of the detached superior labrum and that of the capsular laxity. Rotational range of motion was measured at 60° of glenohumeral abduction. Anterior-posterior glenohumeral translation was measured at 30° and 60° of glenohumeral abduction. Superior-inferior glenohumeral translation was measured at 0° and 60° of glenohumeral abduction. Results The experimentally created type II superior labral anterior-posterior lesion and capsular laxity significantly increased anterior translation at 30° (mean difference, 1.0 ± 0.8 mm; P < .05) and 60° (mean difference, 2.2 ± 2.0 mm; P < .05) of glenohumeral abduction. Subsequent superior labral anterior-posterior repair restored the anterior translation but only at 30° of glenohumeral abduction (mean difference, 0.9 ± 0.6 mm; P < .05). Conclusion Because of the anterior capsular laxity associated with type II superior labral anterior-posterior lesions, superior labral anterior-posterior repair of the peeled-back superior labrum may not restore anterior glenohumeral translation at 90° of shoulder abduction. Clinical Relevance Anterior shoulder capsular laxity associated with type II superior labral anterior-posterior lesions may cause anterior shoulder instability at 90° of shoulder abduction in throwers even after superior labral anterior-posterior lesion repair.

Biomechanical Role of Capsular Continuity in Superior Capsule Reconstruction for Irreparable Tears of the Supraspinatus Tendon

Background: Patients with irreparable rotator cuff tears have a defect of the superior capsule, which creates discontinuity of the shoulder capsule in the transverse direction (anterior-posterior direction). This effect is one of the causes underlying shoulder instability after rotator cuff tears. Purpose/Hypothesis: The purpose of this study was to assess the effects of anterior and posterior continuity on shoulder biomechanics after superior capsule reconstruction (SCR). The hypothesis was that capsular continuity in the transverse direction would improve glenohumeral stability after SCR. Study Design: Controlled laboratory study. Methods: Seven fresh-frozen cadaveric shoulders were tested by using a custom shoulder testing system. Subacromial peak contact pressure, glenohumeral superior translation, glenohumeral compression force, and glenohumeral range of motion (ROM) were compared among 5 conditions: (1) intact shoulder, (2) simulated irreparable supraspinatus tendon tear, (3) SCR without side-to-side suturing, (4) SCR with posterior side-to-side suturing, and (5) SCR with both anterior and posterior side-to-side suturing. Results: The creation of an irreparable supraspinatus tear significantly increased glenohumeral superior translation (0° of abduction: 254% of intact [P = .04]; 30° of abduction: 200% of intact [P = .04]) and subacromial peak contact pressure (0° of abduction: 302% of intact [P = .0001]; 30° of abduction: 239% of intact [P = .0006]), decreased glenohumeral compression force (0° of abduction: 85% of intact [P = .004]; 30° of abduction: 87% of intact [P = .0002]; 60° of abduction: 88% of intact [P = .0001]), and increased total ROM (0° of abduction: 16° increase [P = .008]). SCR without side-to-side suturing significantly decreased subacromial peak contact pressure (0° of abduction: 79% of intact [P = .0001]; 30° of abduction: 91% of intact [P = .001]; 60° of abduction: 55% of intact [P = .04]) but did not inhibit glenohumeral superior translation. By adding posterior side-to-side sutures, both glenohumeral superior translation (0° of abduction: 93% of intact [P = .02]; 30° of abduction: 110% of intact [P = .04]) and subacromial peak contact pressure decreased significantly (0° of abduction: 56% of intact [P = .0001]; 30° of abduction: 83% of intact [P = .0003]; 60° of abduction: 46% of intact [P = .04]). Neither SCR with nor SCR without side-to-side suturing ameliorated the tear-associated decrease in glenohumeral compression force and increase in total ROM. Adding anterior side-to-side sutures did not change any measurements compared with SCR with posterior side-to-side suturing. Conclusion: SCR with side-to-side suturing completely restored the superior stability of the shoulder joint by establishing posterior continuity between the graft, residual infraspinatus tendon, and underlying shoulder capsule. Clinical Relevance: Side-to-side suturing between the graft, residual infraspinatus tendon, and underlying shoulder capsule is recommended for SCR in patients with irreparable supraspinatus tendon tears to restore superior stability after surgery.

Role of the superior shoulder capsule in passive stability of the glenohumeral joint

BACKGROUND The shoulder capsule is the main static stabilizer of the glenohumeral joint. However, few studies specifically address the function of the superior shoulder capsule, which is usually damaged in patients with complete rotator cuff tears. Therefore, the purpose of this study was to determine the biomechanical contribution of the superior shoulder capsule to passive stability of the glenohumeral joint. METHODS Seven cadaveric shoulders were tested with a custom testing system. Glenohumeral translations, subacromial contact pressure, and glenohumeral external and internal rotations were quantified at 5°, 30°, and 60° of glenohumeral abduction. Data were compared among 3 conditions: (1) intact superior capsule, (2) after detaching the superior capsule from the greater tuberosity (tear model), and (3) after complete removal of the superior capsule from the greater tuberosity to the superior glenoid (defect model). RESULTS A tear of the superior capsule significantly (P < .05) increased anterior and inferior translations compared with those in the intact capsule. Creation of a superior capsular defect significantly (P < .05) increased glenohumeral translation in all directions, subacromial contact pressure at 30° of glenohumeral abduction, and external and internal rotations compared with those of the intact capsule. CONCLUSION The superior shoulder capsule plays an important role in passive stability of the glenohumeral joint. A tear in the superior capsule at the greater tuberosity, which may be seen with partial rotator cuff tears, increased anterior and inferior translations. A defect in the superior capsule, seen in massive cuff tears, increased glenohumeral translations in all directions.

Effect of Scapular Orientation on Shoulder Internal Impingement in a Cadaveric Model of the Cocking Phase of Throwing

BACKGROUND Although deviations in scapular orientation are thought to predispose to shoulder injuries in throwing athletes, the biomechanical mechanism underlying shoulder injuries in throwing athletes with an altered scapular orientation remains unclear. METHODS Seven fresh-frozen cadaveric shoulders were evaluated at 90° of abduction, with the humerus externally rotated from 90° to the maximum angle, to simulate the late cocking phase of the throwing motion. Loads were applied to the deltoid, pectoralis major, latissimus dorsi, teres major, and all rotator cuff muscles. Contact pressure in the glenohumeral joint was measured with use of a pressure sensor. The area of internal impingement was calculated on the basis of three-dimensional position data. Glenohumeral contact pressure and the area of impingement were compared between 20°, 30°, and 40° of internal scapular rotation; between 20°, 30°, and 40° of upward scapular rotation; and between 0° and 10° of anterior scapular tilt. Data were analyzed with use of repeated-measures analysis of variance with the Tukey post hoc test. RESULTS Contact pressure was at its maximum in the posterior aspect of the glenohumeral joint. The glenohumeral contact pressure and internal impingement area increased with increasing internal scapular rotation. The glenohumeral contact pressure at 40° of internal scapular rotation was significantly (43.4%) greater than that at 20° of internal scapular rotation (p < 0.01), and the impingement area at 40° of internal scapular rotation was significantly (43.1%) greater than that at 20° of internal scapular rotation (p < 0.05). Decreasing upward scapular rotation resulted in an increase in internal impingement area. The internal impingement area at 40° of upward motion was 38.1% less than that at 20° of upward rotation (p < 0.001) and 28.9% less than that at 30° of upward rotation (p < 0.01). CONCLUSIONS Increasing internal scapular rotation and decreasing upward scapular rotation significantly increase glenohumeral contact pressure and the area of impingement of the rotator cuff tendon between the greater tuberosity and glenoid during simulated throwing motion.

Effect of Rotator Cuff Muscle Imbalance on Forceful Internal Impingement and Peel-Back of the Superior Labrum A Cadaveric Study

Background Throwing athletes with shoulder pain have been shown to have decreased rotator cuff muscle strength. Shoulder internal impingement and labral peel-back mechanism, as may occur during the late cocking phase of throwing motion, are thought to cause rotator cuff injury and type II superior labrum anterior and posterior lesions. Therefore, the objective of this study was to assess the effect of rotator cuff muscle force on internal impingement and the peel-back of the superior labrum by quantifying maximum external rotation, glenohumeral contact pressure, and position of the cuff insertion relative to the glenoid. Hypothesis A change in rotator cuff muscle force will lead to increased external rotation, glenohumeral contact pressure, and overlap of the cuff insertion relative to the glenoid. Study Design Controlled laboratory study. Methods Eight fresh-frozen cadaveric shoulders were tested at the simulated late cocking position. Glenohumeral contact pressure, location of the cuff insertion relative to the glenoid, and maximum humeral external rotation angle were measured. The forces of the supraspinatus, subscapularis, and infraspinatus muscles were determined based on published clinical electromyographic data. To assess the effect of cuff muscle imbalance, each muscle force was varied. Horizontal abduction positions of 20°, 30°, and 40° with respect to the scapular plane were tested. Results Decreased subscapularis strength resulted in a significant increase in maximum external rotation (P <.001) and increased glenohumeral contact pressure (P <.01). The cuff insertion overlapped the edge of the glenoid at 30° and 40° of horizontal abduction for all muscle loading conditions. Conclusion Decreased subscapularis muscle strength in the position simulating the late cocking phase of throwing motion results in increased maximum external rotation and also increased glenohumeral contact pressure. Clinical Relevance Athletes with decreased subscapularis muscle strength, such as fatigue with repetitive throwing, may be more susceptible to rotator cuff tears and type II superior labrum anterior and posterior lesions. Subscapularis muscle strengthening exercises may be beneficial for preventing these injuries.