FRACTURE LOAD FOR PERIPROSTHETIC TIBIAL FRACTURES IN UNICOMPARTMENTAL KNEE ARTHROPLASTY AND THE EFFECT OF SAWING DEFECTS: AN EXPERIMENTAL CADAVER STUDY

Abstract

Background and Purpose: Periprosthetic tibial plateau fractures are a rare but serious complication of UKA. Since they usually appear perioperatively they can be associated with sawing defects during implantation. The aim of the study was to evaluate fracture loads and fracture patterns under particular consideration whether extended vertical saw cuts reduce the stability of the tibial plateau and increase the risk of periprosthetic tibial plateau fractures.

Material and Methods: In 6 matched paired fresh frozen tibiae (donor data: f/m = 2/4, mean age 81.2 years, mean weight 61.7kg) tibial implantation of the cemented Oxford Uni was performed in group A and with an extended vertical saw cut of 10° in group B in a randomized fashion. Before fracturing the tibiae with a maximum load of 10.0kN under standard conditions, DEXA bone density measurement and standard X-Ray were accomplished. After load induction fracture patterns and maximum fracture loads were analyzed and correlated to BMD, BMI, bodyweight (BW), age and surface area of the tibial implant.

Results: In group A a maximum load of Fmax = 3.912 (2.346–8.500) kN lead to fractures, whereas in group B all tibiae fractured with a mean load of Fmax = 2.622 (1.085–5.036) kN. The difference was statistically different with p=0.028. The induced fractures were similar to those observed in clinical practice.

Between BMI and the maximum fracture loads inducing tibial plateau fractures a significant correlation could be proven for all tibiae (r=0.643).

Discussion: The observed fracture pattern showed metaphyseal fractures similar to those observed in clinical practise. Extended vertical saw cuts weaken the bone structure and therefore raise the risk of medial tibial plateau fractures. In our study extended vertical saw cuts of 10° reduce maximum fracture loads about 30%.

We recommend special training and modified instruments for inexperienced surgeons to minimize the incidence of extended vertical saw cuts and to reduce the risk of periprosthetic fractures.