Effect of articular step-off and meniscectomy on joint alignment and contact pressures for fractures of the lateral tibial plateau

Objectives: To determine the effects of intraarticular step-off and lateral meniscectomy on the alignment of the articular axis, contact area, and pre ssures for lateral tibial plateau fractures. Design: Biomechanical cadaver study. Intervention: Six fresh cadaveric knees were used. A simulated split fractu re of the lateral tibial plateau was reproducibly created by osteotomies, a nd articular step-offs of zero, one, two, four, and six millimeters were ac hieved by using support shims. The knee was loaded with 500 newtons in 0 de grees and 350 newtons in 30 degrees of flexion. A digital camera determined changes in the alignment of the articular axis, and F-Scan sensors were in serted into the medial and lateral joint compartments to determine the pres sures and pressure distributions. Main Outcome Measurement: Each specimen was tested at step-offs of zero, on e, two, four, and six millimeters, with the presence or absence of the late ral meniscus. The changes in alignment of the articular axis, the contact a rea, and the average and maximum contact pressures for each condyle were ob tained. Results: Increased articular step-off heights progressively increased valgu s angulation and average and maximum contact pressures and progressively de creased contact areas in lateral compartment. At a six-millimeter step-off with 0 degrees of flexion, the valgus angle increased an average of 7.6 deg rees, and average contact pressures and maximum contact pressures increased an average of 208 percent and 97 percent, respectively, and contact area d ecreased an average of 33 percent (p < 0.05). Meniscectomy increased valgus angles by an average of 38 percent and contact pressures by an average of 45 percent and decreased contact areas by 26 percent in the lateral compart ment at the same articular step-off heights (p < 0.05). Conclusion: The results of this study show the importance of decreasing art icular step-off heights in treating lateral tibial plateau split fractures, particularly if a meniscectomy is performed.