Failure rate of a rotating hinge knee design due to yoke fracture of the hinged tibial insert: a retrospective data analysis and review of the literature

Abstract

Purpose: Rotating hinge knee prostheses are known to provide inherent stability. Yoke fractures of the hinged tibial insert of modern generation rotating hinge devices are a matter of continued concern. The aim of this study was to describe incidence and management of yoke fracture of the LPS™ hinged tibial insert.

Methods: Retrospective data analysis of two institutions identified 40 patients with a LPS™ total knee arthroplasty. Implant survival and prosthetic complications was calculated according to Kaplan-Meier.

Results: Out of the group of 40 patients, four fractures of the metal yoke occurred in four cases (failure rate: 10%). Furthermore, a second fracture occurred in two patients. The overall revision-free prosthetic survival was 57% at 38 months, while prosthetic survival until yoke fracture was 86% at 38 months.

Conclusion: Handling yoke fractures as mechanical complication includes replacing the hinged insert, stabilization of the joint and joint line height preservation in order to decrease the cantilever effect at the insert-base plate interface.

Fig. 1

Design of the LPS™ hinged tibial inserts. The central rotational stem of the LPS™ knee system is part cylindrical at the tip and part conical at the base of the polyethylene tray

Fig. 2

a, b Case 1: anteroposterior and lateral radiographs of a dislocated LPS™ prostheses due to a fractured metal yoke 38 months after implantation. c The fractured and explanted metal yoke of the 14-mm LPS™ insert, 38 months following implantation

Fig. 3

a Kaplan–Meier curves of implant survival according to the classification system of Henderson et al. [9]. b Kaplan–Meier curve for yoke fractures and the overall revision-free survival, for which the calculated implant survival was 86% and 57% at 38 months of follow-up, respectively

Fig. 4

a Graphic delineation demonstrating the yokes’ fracture due to high axial load during flexion combined with several millimeters of distraction and posterior dislocating forces. b Graphic delineation showing the non-rotatory motion and the cantilever effect at the insert–base plate interface of a rotating hinge device, supposed to be responsible for the failure of the hinged insert as published in the study of Schwarzkopf et al. [20]