Transverse patella fracture fixation: A cadaveric biomechanical comparison of cannulated screws and anterior tension band versus low-profile, multiplanar mesh plating

Abstract

Introduction: Multiplanar mesh plating of patella fractures has become more popular in recent years. It was the goal of this study to compare the biomechanical stability of cannulated screw with anterior tension band to multiplanar mesh plating for fixation of transverse patella fractures in cadaver specimens.

Materials and methods: Eight matched pairs of fresh frozen cadaveric knees were obtained and soft tissues dissected leaving the extensor mechanism, joint capsule, and retinaculum intact. Transverse fractures were created at the mid-portion of the patella. For each pair, one specimen was repaired using cannulated screws with anterior tension band, and the second was repaired using multiplanar mesh plating. Each specimen underwent cyclic extension loading with loads increasing by 1.1 kg after every 50 cycles. Interfragmentary displacement was measured at the end of each interval at both 5° and 45° of knee flexion angle, with fixation failure defined by >2 mm displacement.

Results: The specimens fixed with multiplanar mesh plating survived more cycles and higher loads than the specimens fixed with cannulated screws with anterior tension band (p = 0.011 comparing survival plots). After 150 cycles of extension loading, 3 of 8 of the specimens fixed with screws/tension band had failed, whereas none of the mesh plated specimens had failed. After 400 cycles, 7 of 8 of the screws/tension band had failed, whereas half of the mesh plated specimens had failed.

Conclusions: While a more technically challenging and expensive technique, mesh plating for patella fractures appears to offer greater durability than traditional cannulated screw with tension banding.

Keywords: Mesh plating; Patella fracture; Tension band.

Figure 1:

Anterior tension band repair specimen with anterior screws used for displacement measurement.

Figure 2:

Mesh plate repair specimen with anterior screws placed for fracture displacement measurement (A). Two views of contoured mesh plate with numeric labels for order of screw placement (B-C).

Figure 3:

Testing/loading apparatus and setup with metallic bar for weight application.

Figure 4:

Kaplan–Meier type plot showing mesh plate and cannulated screw specimen survival after cyclic loading with increasing load. The survival curves are statistically different by log-rank test (p = 0.011)

Figure 5:

Plots of interfragmentary displacement at fracture site for each individual specimen, for the two repair types at 5° of flexion. Failure criteria is shown at 2 mm displacement. (Amount of loading corresponding to each cycle count is shown in Fig. 4.)