Collegiate baseball pitchers demonstrate a relationship between ball velocity and elbow varus torque, both within and across pitchers.

High elbow varus torque during baseball pitching has been identified as a potential cause of ulnar collateral ligament injury in baseball pitchers. In general, elbow varus torque increases as ball velocity increases across pitchers. However, studies incorporating within-subject analyses report that not all professional pitchers have a positive relationship between elbow varus torque and ball velocity (T-V relationship). It remains unknown whether collegiate pitchers show the same trend as professionals in their T-V relationships. The current study investigated the T-V relationship of collegiate pitchers focusing on both across and within pitchers. Division 1 collegiate pitchers (n = 81) were assessed for elbow torque and ball velocity during pitching. Both across- and within-pitcher T-V relationships were significant (p < 0.05) using linear regression. However, more variance in elbow varus torque was explained using the within-pitcher relationship (R2 = 0.29) than the across-pitcher relationship (R2 = 0.05). Of the 81 pitchers, nearly half (n = 39) had significant T-V relationships, while the other half (n = 42) did not. Our findings indicate that the T-V relationship should be assessed on an individual basis as T-V is pitcher-specific.

Direct 3-dimensional measurement of scapular kinematics during dynamic movements in vivo.

The purpose of this study was to describe 3-dimensional scapular motion patterns during dynamic shoulder movements with the use of a direct technique. Direct measurement of active scapular motion was accomplished by insertion of 2 1.6-mm bone pins into the spine of the scapula in 8 healthy volunteers (5 men, 3 women). A small, 3-dimensional motion sensor was rigidly fixed to the scapular pins. Sensors were also attached to the thoracic spine (T3) with tape and to the humerus with a specially designed cuff. During active scapular plane elevation, the scapula upwardly rotated (mean [SD] = 50 degrees [4.8 degrees ]), tilted posteriorly around a medial-lateral axis (30 degrees [13.0 degrees ]), and externally rotated around a vertical axis (24 degrees [12.8 degrees ]). Lowering of the arm resulted in a reversal of these motions in a slightly different pattern. The mean ratio of glenohumeral to scapulothoracic motion was 1.7:1. Normal scapular motion consists of substantial rotations around 3 axes, not simply upward rotation. Understanding normal scapular motion may assist in the identification of abnormal motion associated with various shoulder disorders.

Dynamic measurements of three-dimensional scapular kinematics: a validation study.

The validation of two noninvasive methods for measuring the dynamic three-dimensional kinematics of the human scapula with a magnetic tracking device is presented. One method consists of simply fixing a sensor directly to the acromion and the other consists of mounting a sensor to an adjustable plastic jig that fits over the scapular spine and acromion. The concurrent validity of both methods was assessed separately by comparison with data collected simultaneously from an invasive approach in which pins were drilled directly into the scapula. The differences between bone and skin based measurements represents an estimation of skin motion artifact. The average motion pattern of each surface method was similar to that measured by the invasive technique, especially below 120 degrees of elevation. These results indicate that with careful consideration, both methods may offer reasonably accurate representations of scapular motion that may be used to study shoulder pathologies and help develop computational models.

A review of self-report scales for the assessment of functional limitation and disability of the shoulder.

A shoulder disorder affects a patient's overall quality of life. Self-report outcome measures can be used to assess the effects of shoulder dysfunction in terms of patients' functional limitations and disabilities. Selection of a shoulder-specific scale from the numerous scales available can be overwhelming. The purpose of this study was to review the self-report scales in current use for assessing the shoulder joint. A MEDLINE literature search was performed to locate scales appropriate to the assessment of function and disability of the shoulder. Only scales with established measurement properties were selected for review. Eleven scales were reviewed. Methodological and practical criteria were established to evaluate each scale. All scales met the minimal criteria, but not all scales were equal with regard to the criteria established for analysis.

Scapular kinematics: effects of altering the Euler angle sequence of rotations.

An analysis of Euler angle sequences is presented for the scapula. In vivo kinematics were collected with a magnetic tracking device on eight healthy volunteers. To ensure accurate representation of scapular motion, pins were rigidly drilled into the scapular spine. Three rotations of the scapula with respect to the thorax were recorded during humeral elevation in the scapular plane: posterior (or backward) tilting, upward (or lateral) rotation and external rotation (or retraction). Rotations using all six possible Euler angle sequences were calculated for which each angle was represented only once. The sequence proposed by an International Society of Biomechanics subcommittee on shoulder motion (external rotation, upward rotation, posterior tilting) is consistent with both research- and clinical-based two-dimensional representations of scapular motion. Results from the present study indicate that changing sequence results in significant alterations in the description of motion, with differences up to 50 degrees noted for some angles. Therefore, in order to compare results across different laboratories, it is recommended that the proposed standard sequence be adopted.