Search

Background: Optimizing the function of muscles that cross the glenohumeral articulation in reverse total shoulder arthroplasty (RTSA) is controversial. The current study used a geometric model of the shoulder to systematically examine surgical placement and implant-design parameters to determine which RTSA configuration most closely reproduces native muscle-tendon lengths of the deltoid and rotator cuff. Methods: A geometric model of the glenohumeral joint was developed and adjusted to represent small, medium, and large shoulders. Muscle-tendon lengths were assessed for the anterior deltoid, middle deltoid, posterior deltoid, and supraspinatus from 0 to 90° of scaption; for the subscapularis from 0° to 60° of internal rotation (IR) and 0° to 60° of scaption; for the infraspinatus from 0° to 60° of external rotation (ER) and 0° to 60° of scaption; and for the teres minor from 0° to 60° of ER at 90° of scaption. RTSA designs were virtually implanted using the following parameters: (1) surgical placement with a centered or inferior glenosphere position and a humeral offset of 0, 5, or 10mmrelative to the anatomic neck plane, (2) implant design involving a glenosphere size of 30, 36, or 42 mm, glenosphere lateralization of 0, 5, or 10 mm, and humeral neck-shaft angle of 135°, 145°, or 155°. Thus, 486 RTSA-shoulder size combinations were analyzed. Linear regression assessed the strength of association between parameters and the change in each muscletendon length from the native length. Results: The configuration that most closely restored anatomic muscle-tendon lengths in a small shoulder was a 30-mm glenosphere with a centered position, 5 mm of glenoid lateralization, 0 mm of humeral offset, and a 135° neck-shaft angle. For a medium shoulder, the corresponding combination was 36mm, centered, 5mm, 0mm, and 135°. For a large shoulder, it was 30mm, centered, 10mm, 0mm, and 135°. The most important implant-design parameter associated with restoration of native muscle-tendon lengths was the neck-shaft angle, with a 135° neck-shaft angle being favored (b = 0.568 to 0.657, p < 0.001). Themost important surgical parameter associated with restoration of nativemuscle-tendon lengths was humeral offset, with a humeral socket placed at the anatomic neck plane being favored (b = 0.441 to 0.535, p < 0.001). Conclusions: A combination of a smaller, lateralized glenosphere, a humeral socket placed at the anatomic neck plane, and an anatomic 135° neck-shaft angle best restored native deltoid and rotator cuff muscle-tendon lengths in RTSA. Clinical Relevance: This study of surgical and implant factors in RTSA highlighted optimal configurations for restoration of native muscle-tendon lengths of the deltoid and rotator cuff, which has direct implications for surgical technique and implant selection. Additionally, it demonstrated the most influential surgical and implant factors with respect to muscletendon lengths, which can be used to aid intraoperative decision-making. [ABSTRACT FROM AUTHOR]

This paper presents the methodology and results of teaching an entire engineering course using challenge-based instruction. The challenges consisted of eight biomechanics multimedia learning modules developed by the authors as part of a broader NSF educational coalition. The biomechanics modules were presented in an undergraduate mechanical engineering course titled "Biomechanics of Human Movement." The class (N = 18) was divided into three-member teams. Each team performed the eight computer-based assignments in intervals of one-two weeks per challenge during the semester. Pre-tests, post-tests, affect surveys, a biomechanics topics matrix, and student outcomes surveys were conducted during the course to determine the success of this approach. This paper outlines the challenge-based approaches used and presents assessment methods for a full, semester-long course. Thus, it is directed at faculty who may wish to use this interesting approach in their own engineering courses.

The aim of this randomized controlled trial was to measure and compare six‐degree‐of‐freedom (6‐DOF) knee joint motion of three total knee arthroplasty (TKA) implant designs across a range of daily activities. Seventy‐five TKA patients were recruited to this study and randomly assigned a posterior‐stabilized (PS), cruciate‐retaining (CR), or medial‐stabilized (MS) implant. Six months after surgery, patients performed five activities of daily living: level walking, step‐up, step‐down, sit‐to‐stand, and stand‐to‐sit. Mobile biplane X‐ray imaging was used to measure 6‐DOF knee kinematics and the center of rotation of the knee in the transverse plane for each activity. Mean 6‐DOF knee kinematics were consistently similar for PS and CR, whereas MS was more externally rotated and abducted, and lateral shift was lower across all activities. Peak‐to‐peak anterior drawer for MS was also significantly lower during walking, step‐up, and step‐down (p < 0.017). The center of rotation of the knee in the transverse plane was located on the medial side for MS, whereas PS and CR rotated about the lateral compartment or close to the tibial origin. The kinematic function of MS was more similar to that of the healthy knee than PS and CR based on reduced paradoxical anterior translation at low flexion angles and a transverse center of rotation located in the medial compartment. Overall, 6‐DOF knee joint motion for PS and CR were similar across all daily activities, whereas that measured for MS was appreciably different. The kinematic patterns observed for MS reflects a highly conforming medial articulation in the MS design. [ABSTRACT FROM AUTHOR]