Abstract
Background: The Oxford unicompartmental knee replacement (UKR) use in the lateral compartment has been associated with a reduced flexion range, increased medial compartment pain and a higher dislocation rate than seen with its medial counterpart due to the inadequacy of a flat tibial tray replacing the domed anatomy of the lateral tibia. A new design incorporating a domed tibial component and a biconcave meniscal bearing has been developed to overcome these problems. This current study was designed to establish whether this modi-fied ‘domed’ implant has maintained the established normal kinematic profile of the Oxford UKR.
Methods: The study population consisted of 60 participants from three equal groups; Group 1- Normal volunteer knees (n = 20), Group 2 – Flat Oxford Lateral UKR’s (n = 20) and Group 3 – Domed Oxford Lateral UKR’s (n = 20). The sagittal plane kinematics of each involved knee was assessed continuously using videofluoroscopic analysis. A standardised protocol of step-up and deep lunge was used to assess loadbearing range of motion during which the patella tendon angle (PTA) was measured as a function of the knee flexion angle (KFA).
Results: PTA/KFA values compared at 10 degree KFA increments from maximal extension to maximal flexion for all 3 groups did not demonstrate any statistically significant difference in PTA values between any group as measured by a 3-way ANOVA. The Domed implant achieved higher maximal active flexion during the lunge exercise than those with a Flat implant. Only 33% of the Flat UKR’s achieved KFA of 130 degrees or more under load whilst performing a lunge, compared with 75% of domed UKR’s and 90% of normal knees. No Flat UKR achieved a KFA of 140 degrees or more, yet 50% of all domed UKR’s did, as also did 60% of all normal knees.
Conclusions: There is no significant difference in the sagittal plane kinematics of the domed and flat Oxford UKR’s. Both implant designs have a favourable kinematic profile closely resembling the normal knee. The domed knees though do have a greater range of motion under load as compared to the flats, approaching levels seen with the normal knee.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
