Biomechanical performance of variable and fixed angle locked volar plates for the dorsally comminuted distal radius.

BACKGROUND: The ideal treatment strategy for the dorsally comminuted distal radius fracture continues to evolve. Newer plate designs allow for variable axis screw placement while maintaining the advantages of locked technology. The purpose of this study is to compare the biomechanical properties of one variable axis plate with two traditional locked constructs. METHODS: Simulated fractures were created via a distal 1 cm dorsal wedge osteotomy in radius bone analogs. The analogs were of low stiffness and rigidity to create a worst-case strength condition for the subject radius plates. This fracture-gap model was fixated using one of three different locked volar distal radius plates: a variable axis plate (Stryker VariAx) or fixed axis (DePuy DVR, Smith & Nephew Peri-Loc) designs. The constructs were then tested at physiologic loading levels in axial compression and bending (dorsal and volar) modes. Construct stiffness was assessed by fracture gap motion during the different loading conditions. As a within-study control, intact bone analogs were similarly tested. RESULTS: All plated constructs were significantly less stiff than the intact control bone models in all loading modes (p<0.040). Amongst the plated constructs, the VariAx was stiffest axially (p=0.032) and the Peri-Loc was stiffest in bending (p<0.024). CONCLUSION: In this analog bone fracture gap model, the variable axis locking technology was stiffer in axial compression than other plates, though less stiff in bending.

Anatomic placement of the Herbert-Whipple screw in scaphoid fractures: a cadaver study.

An anthropometric cadaver study was performed to determine the optimal placement of a Herbert-Whipple screw in the scaphoid. Twenty pairs of cadaver wrists were examined and anthropometric analysis of the scaphoids using plain radiography, computed tomography, and en bloc resection was performed. Scaphoid vascularity was evaluated using India ink injection. Radiographic and actual measurements of height and width confirmed symmetry in paired scaphoids. Anatomic evaluation defined a safe zone for screw placement. K-wire placement defined the extent of this zone. The entry point of this zone was found by moving dorsally and distally 15% of the lateral radiographic length of the contralateral scaphoid from the volar aspect of the scaphoid tuberosity. Moving 10% of this same length from the membranous central portion of the scapholunate ligament defined the target site. Computed tomography confirmed proper position of the screw to maximize bony purchase and avoid articular penetration while maintaining dorsal vascular integrity.

Patella-tibial transfixation for posterior cruciate ligament repair and reconstruction: a biomechanical analysis.

The posterior cruciate ligament (PCL) restricts posterior translation of the tibia on the femur. Because flexion of the knee increases tension on the PCL, the knee is usually immobilized in extension after PCL repair or reconstruction. Patella-tibial transfixation (olecranization), however, has been proposed to reduce the tension on the PCL without requiring immobilization of the knee. The objective of this study was: (1) to evaluate the distribution of strain in the anterolateral and posterior oblique fiber bundles of the PCLs in eight cadaveric knees before and after olecranization and (2) to measure the patellofemoral contact pressures at various degrees of knee flexion. Olecranization significantly (P < 0.05) reduced the strain on the anterolateral fiber bundles of the PCL at 15 degrees -45 degrees of flexion. No significant strain reduction was observed in the posterior oblique fiber bundles. Patellofemoral contact pressures measured from digitized Fuji sensitive film indicated significantly increased contact pressures (P < 0.05) following olecranization from 0 degrees -60 degrees of knee flexion. Increased parapatellar soft tissue tightness limited knee flexion to 90 degrees and patella lift-off occurred at 75 degrees. Although olecranization of the patella does reduce strain on the intact PCL within a selected range of motion, the beneficial effect of allowing early motion may be negated by the potentially harmful effects imposed upon the patellofemoral articular cartilage by increased contact pressures.