Patients with recurrent anterior shoulder instability exhibit altered glenohumeral and scapulothoracic joint kinematics during upper limb movement: A prospective comparative study.

BACKGROUND: Altered shoulder kinematics in patients with recurrent anterior shoulder instability remains poorly understood. This prospective study aimed to quantify in vivo glenohumeral and scapulothoracic joint kinematics and joint-contact positions in patients with shoulder instability and healthy controls. METHODS: Twenty patients with recurrent anterior shoulder instability (mean 28 years) and five patients without shoulder pathology (mean 39 years) were scanned using open CT in six static upper limb positions including 90° of abduction, combined abduction and external rotation, 90° of flexion, lift-off position (i.e. reaching behind the back) and the neutral shoulder with external rotation. Image datasets were digitally reconstructed to quantify shoulder joint kinematics and glenohumeral translation. FINDINGS: At 90° of abduction, instability patients demonstrated significantly less glenohumeral abduction and a reciprocal increase in upward scapulothoracic rotation compared to controls (mean difference: 13.3°, p = 0.038). With the shoulder in combined abduction and external rotation, instability patients showed a significant increase in glenohumeral rotation and a reciprocal decrease in scapulothoracic rotation compared to controls (mean difference: 5.0°, p = 0.042). There were no significant differences in humeral head translation in the sagittal plane (anterior-posterior axis) for all motions tested (p > 0.05). INTERPRETATION: Scapulothoracic and glenohumeral kinematics are significantly different between patients with recurrent anterior shoulder instability and those with a healthy shoulder. Instability patients compensate for reduced glenohumeral function during abduction by increasing scapular rotation. With the shoulder in combined abduction and external rotation position, greater glenohumeral joint angles without significantly increased humeral head translation suggest altered neuromuscular control in the unstable shoulder.

Validation of a Novel Patient Specific CT-Morphometric Technique for Quantifying Bone Graft Resorption Following the Latarjet Procedure.

Bone graft resorption following the Latarjet procedure has received considerable concern. Current methods quantifying bone graft resorption rely on two-dimensional (2D) CT-scans or three-dimensional (3D) techniques, which do not represent the whole graft volume/resorption (i.e., 2D assessment) or expose patients to additional radiation (i.e., 3D assessment) as this technique relies on early postoperative CT-scans. The aim of the present study was to develop and validate a patient-specific, CT-morphometric technique combining image registration with 3D CT-reconstruction to quantify bone graft resorption following the Latarjet procedure for recurrent anterior shoulder instability. Pre-operative and final follow-up CT-scans were segmented to digitally reconstruct 3D scapula geometries. A virtual Latarjet procedure was then conducted to model the timepoint-0 graft volume, which was compared with the final follow-up graft volume. Graft resorption at final follow-up was highly correlated to the 2D gold standard-technique by Zhu (Kendall tau coefficient = 0.73; p < 0.001). The new technique was also found to have excellent inter- and intra-rater reliability (ICC values, 0.931 and 0.991; both p < 0.001). The main finding of this study is that the technique presented is a valid and reliable method that provides the advantage of 3D-assessment of graft resorption at long-term follow-up without the need of an early postoperative CT-scan.

The moment arms and leverage of the human finger muscles.

The moment arm of a muscle's force represents the muscle's leverage or mechanical advantage in producing a joint moment. It is indicative of the muscle's potential to contribute to actuation of a joint in a particular joint motion direction and defines the role of the muscle, for example, as a joint flexor or abductor. The aims of this study were, firstly, to measure the moment arms of the flexor and extensor muscles of the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints, and the moment arms of the major abductor and adductor muscles of the metacarpophalangeal (MCP) joint of each finger in the hand; secondly, to assess the effect of change in joint angle on these moment arms; and thirdly, to determine if there are differences in a given flexor or extensor's muscle moment arms between the joints it spans on a given finger, and across its tendon slips to multiple fingers. The tendon-excursion method was used to measure instantaneous muscle moment arms in nine fresh-frozen entire forearm cadaver specimens. Joint flexion angle was found to have significant effects on the moment arms of the extensor muscles at the MCP and PIP joints (p < 0.05). In contrast, the digital flexor muscles maintained relatively constant moment arms through the range of joint flexion. The moment arms of the digital flexors and extensors spanning multiple joints in a finger were largest at the MCP joints and smallest at the DIP joints. The findings demonstrate greater torque generating capacity for tasks such as grasping at the proximal interphalangeal joints, and smaller torque capacity for finer movement control at the distal interphalangeal joints. The dataset generated in this study may be useful in the development and validation of computational models used in surgical planning, and rehabilitation.