Effects of hip joint transverse plane range of motion with a modeled effusion and capsular tear: A cadaveric study.

BACKGROUND: Multiple factors contribute to range of motion of the hip joint in the transverse plane: bony anatomy, hip capsule, corresponding ligaments, articular labrum, ligamentum teres, and negative intra-articular pressure. We hypothesized that violation of the negative pressure of the hip and simulation of an effusion would increase range of motion in the transverse plane in a cadaver model. METHODS: Ten hip specimens were obtained and dissected with the femur and iliac wing mounted in a custom joint-testing rig in neutral position. Specimens were tested at 0 and at 90° of flexion with 1.5Nm internal and external rotational torque. Three conditions were assessed: (1) intact specimen, (2) an effusion modeled by a 10ml saline infusion, and (3) a capsular tear. FINDINGS: The modeled effusion decreased rotational range of motion limits in both 0 and 90° of flexion, with a greater effect on the specimens at 0° flexion in external rotation with 4.1° less external rotation (p=0.009). A modeled capsular tear increased rotational motion limits in 0° of flexion in both internal and external rotation and in 90° flexion in internal rotation only (p<0.025). INTERPRETATION: An effusion may decrease the rotation of the hip, and a capsular tear may increase its rotation. This should be considered in hips with traumatic capsular tears or arthroscopic portals.

Optimal baseplate rotational alignment for locking-screw fixation in reverse total shoulder arthroplasty: a three-dimensional computer-aided design study.

BACKGROUND: Baseplate loosening in reverse total shoulder arthroplasty (RTSA) remains a concern. Placing peripheral screws into the 3 pillars of the densest scapular bone is believed to optimize baseplate fixation. Using a 3-dimensional computer-aided design (3D CAD) program, we investigated the optimal rotational baseplate alignment to maximize peripheral locking-screw purchase. METHODS: Seventy-three arthritic scapulae were reconstructed from computed tomography images and imported into a 3D CAD software program along with representations of an RTSA baseplate that uses 4 fixed-angle peripheral locking screws. The baseplate position was standardized, and the baseplate was rotated to maximize individual and combined peripheral locking-screw purchase in each of the 3 scapular pillars. RESULTS: The mean ± standard error of the mean positions for optimal individual peripheral locking-screw placement (referenced in internal rotation) were 6° ± 2° for the coracoid pillar, 198° ± 2° for the inferior pillar, and 295° ± 3° for the scapular spine pillar. Of note, 78% (57 of 73) of the screws attempting to obtain purchase in the scapular spine pillar could not be placed without an in-out-in configuration. In contrast, 100% of coracoid and 99% of inferior pillar screws achieved full purchase. The position of combined maximal fixation was 11° ± 1°. CONCLUSIONS: These results suggest that approximately 11° of internal rotation is the ideal baseplate position for maximal peripheral locking-screw fixation in RTSA. In addition, these results highlight the difficulty in obtaining optimal purchase in the scapular spine.

Biomechanical validation of medial pie-crusting for soft-tissue balancing in knee arthroplasty.

Balancing a varus knee is traditionally accomplished by releasing the medial soft-tissue sleeve off the tibia. Recently, "pie-crusting" (PC) medial structures has been described. In a biomechanical cadaver study we compared PC to traditional release (TR) to determine their effects on flexion and extension gaps. PC was done in five specimens along the anterior half of the medial soft-tissue sleeve and five along the posterior half, followed by a traditional release. In 90° flexion, valgus laxity after TR was significantly greater than after PC alone. PC of the anterior or posterior aspect of the medial soft-tissue sleeve can effect changes more in flexion than in extension, respectively. Complete TR did not provide more gap opening than PC in extension, but produced more effect in flexion.