Late Cocking Phase Of Throwing Research Articles

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.

Dominant-Sided First-Rib Stress Fracture in a Collegiate Baseball Pitcher: A Case Report.

The incidence of asymptomatic fatigue fractures of the first rib in the young, active male population is very low; these fractures were observed in only 0.001% of retrospectively reviewed chest radiographs in one series1. First-rib fractures have been postulated to result from several primary mechanisms: high-energy direct impact such as a motor vehicle collision2, indirect trauma such as a fall on an outstretched arm3, fatigue fractures from repeated muscular contracture4, or sudden, violent muscular forces resulting in stress fractures5. Although the exact incidence of first-rib stress fracture caused by sudden muscular contracture is not known, many repetitive activities, including gymnastics, tennis, basketball, weightlifting, and even coughing or sneezing, have been associated with this mechanism6. We present the case of a first-rib stress fracture in a collegiate baseball pitcher and discuss the relevant literature. The patient was informed that data concerning the case would be submitted for publication, and he provided consent. A nineteen-year-old right-hand-dominant male collegiate baseball pitcher presented to the office with the symptom of right shoulder pain. He denied any history of trauma but stated that he had felt a popping sensation in the shoulder while pitching several days prior to presentation, and he had had pain since that time with both pitching and activities of daily living. He denied any change in the pitching mechanics or increase in the number of pitches in the preceding several weeks. He had no prior history of trauma to the spine or thorax. The pain was aggravated by the late-cocking phase of throwing. He also admitted to difficulty with deep inspiration because of the pain at the base of the neck, but had no dyspnea at rest. On examination, he was 6′8″ (203.2 cm) tall and weighed 193 lb …

Ligamentous restraints to external rotation of the humerus in the late-cocking phase of throwing. A cadaveric biomechanical investigation.

The late-cocking phase of throwing is characterized by extreme external rotation of the abducted arm; repeated stress in this position is a potential source of glenohumeral joint laxity. To determine the ligamentous restraints for external rotation in this position, 20 cadaver shoulders (mean age, 65 +/- 16 years) were dissected, leaving the rotator cuff tendons, coracoacromial ligament, glenohumeral capsule and ligaments, and coracohumeral ligament intact. The combined superior and middle glenohumeral ligaments, anterior band of the inferior glenohumeral ligament, and the entire inferior glenohumeral ligament were marked with sutures during arthroscopy. Specimens were mounted in a testing apparatus to simulate the late-cocking position. Forces of 22 N were applied to each of the rotator cuff tendons. An external rotation torque (0.06 N x m/sec to a peak of 3.4 N x m) was applied to the humerus of each specimen with the capsule intact and again after a single randomly chosen ligament was cut (N = 5 in each group). Cutting the entire inferior glenohumeral ligament resulted in the greatest increase in external rotation (10.2 degrees +/- 4.9 degrees). This was not significantly different from sectioning the coracohumeral ligament (8.6 degrees +/- 7.3 degrees). The anterior band of the inferior glenohumeral ligament (2.7 degrees +/- 1.5 degrees) and the superior and middle glenohumeral ligaments (0.7 degrees +/- 0.3 degrees) were significantly less important in limiting external rotation.