Periarticular raft constructs and fracture stability in split-depression tibial plateau fractures

Abstract

Objectives

To evaluate relative fracture stability yielded by screws placed above a lateral plate, as well as locking and non-locking screws placed through a plate in a split depression tibia plateau fracture model.

Methods

Cadaver tibia specimens (mean age 74.1 years) were randomised across 3 groups: Groups 1: raft-construct outside the plate, 2: non-locking raft screws through the plate, and 3: locking raft screws through the plate. Displacement of the depressed fragment was recorded with force values from 400 N to 1600 N in increasing 400 N increments. The force required to elicit lateral plateau fragment displacement of 5 mm, 10 mm, and 15 mm was also recorded.

Results

None of the mechanical testing results demonstrated statistical significance with p-values of <0.05. Cyclic testing of Groups 1, 2, and 3 at 400 N revealed displacements of 0.54 mm, 0.64 mm, and 0.48 mm, respectively. At 800 N, displacements were 1.36 mm, 1.4 mm, and 1.4 mm, respectively. At 1200 N, displacements were 2.4 mm, 1.9 mm, and 2.1 mm, respectively. At 1600 N, displacements were 2.8 mm, 2.5 mm, and 2 mm, respectively. Resistance to displacement data demonstrated the mean force required to displace the fracture 5 mm in Groups 1, 2, and 3 were 250 N, 330 N, and 318 N, respectively. For 10 mm of displacement, forces required were 394 N, 515 N, and 556 N, respectively. For 15 mm of displacement, forces required were 681 N, 853 N, and 963 N, respectively. Compared to combined groups using screws through the plate, Group 1 demonstrated lower displacement ≤800 N, but demonstrated greater displacement >800 N. Group 2 demonstrated greatest resistance to plateau displacement of 5 mm compared to Group 1 or 3, while Group 3 was most resistant to greater displacement. The combined group using screws through the plate (Groups 2 + 3) was consistently more resistant than Group 1 at all levels of displacement.

Conclusions

Designs utilising screws through the plate trended towards statistically significant improved stability against plateau displacement relative to utilising screws outside the plate. Our study also suggests that there is no significant benefit of locking screws over non-locking screws in this unicondylar tibia plateau fracture model.

Introduction

Lateral tibial plateau fracture fixation has been investigated previously using a variety of fixation constructs.1, 2, 3, 4, 5, 6, 7, 8 Kirschner wire fixation, “raft” screw constructs, and lag screws have been employed as a method to resist the depression and loss of reduction inherent to this fracture pattern.2, 5, 7 Using the Schatzker classification, tibial plateau types I, II, and III involve only the lateral condyle and suggest a different treatment regimen than the medial or bicondylar variants (Schatzker IV–VI) typically associated with higher energy mechanisms.9, 10 Debate surrounds the question of what is ideal internal fixation for preventing depression of articular fragments with respect to preventing subsequent loss of reduction during the postoperative course of rehabilitation. The raft construct has recently been tested biomechanically and was shown to be more resistant to local depression loads than for both large fragment constructs without bone graft and buttress plate constructs with bone graft.⁴ Small fragment 3.5 mm diameter screws have been shown to provide acceptable stability, challenging former choices of large fragment screws for use directly under articular fragments.1, 3, 7, 11

To the best of our knowledge, there have not been any studies answering the relative importance of placing raft screws above versus through lateral plates used to fix the lateral plateau. The purpose of this study is to determine which of 3 raft construct designs demonstrates the greatest resistance to plateau displacement in a (AO/OTA 41-B3) tibial plateau fracture model, and secondarily whether a subarticular raft construct placed through a plate demonstrates greater resistance to plateau displacement than when placed independently outside the plate. Our hypothesis, derived from previous data on fixed angle construct stability,12, 13 was that the load required to cause raft construct failure would be greatest in the locked raft construct placed through the plate, followed by the non-locked raft construct, followed by the raft of screws placed independently of the plate.