Jason K. Green

Medial buttress versus lateral locked plating in a cadaver medial tibial plateau fracture model

Objective: To compare the mechanical stability of a medial tibial plateau fracture model secured with a lateral locking periarticular plate versus a medial buttress plate in cyclic testing and load to failure. Methods: Medial tibial plateau fractures were created in 6 matched pairs of fresh cadaveric tibias. In each pair of tibias, 1 side was randomly selected to be fixed with a lateral locking plate on 1 side and the contralateral limb to be fixed with a medial buttress plate. The fixated tibias then underwent cyclic testing followed by single-cycle failure compressive loading. Displacement of the medial tibial plateau was measured in both cyclic and failure testing. Results: Statistical analyses revealed relevant trends in fixation strength during cyclic testing, but neither the mean maximum displacement during nor mean residual displacement after cyclic testing were statistically different between the 2 fixation techniques. Statistically significant differences were observed for the mean forces to failure however. The medial buttress plate construct provided greater fixation strength with its failure force of 4136 ± 1469 N compared with the lateral locking plate mean failure force of 2895 ± 1237 N (P < 0.05). Conclusion: In the setting of a vertically oriented fracture in a medial tibial plateau without comminution, the medial buttress plate provides significantly greater stability in static loading, and a trend toward improved stability with cyclic loading. Clinical correlation is necessary to substantiate these findings.

Capsuloligamentous restraints to dorsal and palmar carpal translation.

PURPOSE The purpose of this study was to determine biomechanically the relative contributions of the dorsal and palmar capsuloligamentous structures to dorsal and palmar carpal stability. METHODS Seven fresh-frozen cadaver specimens were tested using a testing machine (MTS, Eden Prairie, MN) with low loads applied perpendicular to the axis of the radial diaphysis. We determined the loads required to achieve dorsal and palmar translation of the carpus on the radius as palmar and dorsal ligaments and capsule were sectioned sequentially. The relative contributions of the dorsal and palmar capsuloligamentous structures to dorsal and palmar stability were determined. RESULTS The palmar structures provided a statistically significantly greater restraint (61%) to dorsal translation of the carpus than did the dorsal structures (2%). The palmar structures also provided a statistically greater restraint (48%) to palmar translation of the carpus than did the dorsal structures (6%). CONCLUSIONS The palmar capsuloligamentous structures provided greater restraint to both dorsal and palmar translation of the carpus. We suggest that surgeons consider repair or reconstruction of traumatic injuries to these structures.

Contained femoral defects: biomechanical analysis of pin augmentation in cement.

Although in the proximal tibia the need for pin augmentation of cemented giant cell tumor defects depends on whether the defect is contained, there is controversy regarding the role for pins in the distal femur. The current study investigated whether Steinmann pin augmentation offers biomechanical advantages in cement reconstruction of contained defects of the lateral femoral condyle. Twelve pairs of human femurs were used. They were tested either with the bone intact, with a standardized contained defect in the lateral condyle, with a defect repaired with cement alone, and with a defect repaired with pins in the cement. Intact specimens had significantly higher load to failure than specimens with a defect. In the repaired specimens there were no significant differences in stiffness, peak load to failure, and energy to failure between the specimens repaired with just cement or augmented with pins. This study did not show any significant biomechanical advantage of this configuration of Steinmann pin reinforcement in cement for contained defects of the lateral femoral condyle.