Introduction

The Delta Motion device (developed by Finsbury Orthopaedics, Leatherhead, United Kingdom, now manufactured by DePuy, Leeds, United Kingdom) is a pre-assembled factory fitted cup. It has been introduced to overcome some of the concerns relating to intra-operative assembly with improper seating of the liner and chipping. This device has a thinner shell and liner in comparison with other cups, allowing the use of larger sized heads which should help reduce the risk of impingement and dislocation. A drawback of the pre-assembled design is the inability to use supplementary screws to achieve stability and the difficulty in obtaining primary stability compared with a thin titanium shell. To date we are not aware of any publications reviewing the outcomes of these devices.

Sagittal stability of the knee is believed to be of significant importance following a total knee arthroplasty. We examine three different knee designs at a minimum of twenty-four months postoperatively. Sagittal stability was measured at four degrees of flexion; 0°, 30°, 60° and 90° to examine the effect of design on mid-flexion stability.

The knee designs included the rotating platform LCS design, the cruciate sparing Triathlon system and the medial rotating knee design, MRK.

Following ethical approval 50 cases were enrolled into the study, 15 male and 35 female. Eighteen LCS, 18 MRK and 14 Triathlon knee designs were analysed. Sagittal stability was measured using the KT1000 device. Active range of movement was measured using a hand held goniometer and recorded as was Oxford knee score, WOMAC knee score, SF12 and Kujala patellofemoral knee score.

Mean follow-up was 37 months postoperative with a mean age of 73 years. Mean weight was 82.7 kgs and height 164 cms. There was no significant difference in preoperative demographics between the groups. Mean active post-operative range of motion of the knee was from 2–113° with no significant difference between groups.

Sagittal stability was similar in all three groups in full extension; however the MRK design showed improved stability in the mid-range of flexion (30–90°). Patient satisfaction also showed a similar trend with MRK achieving slightly better patient reported outcomes than that of the LCS and Triathlon systems, although this was not statistically significant.

All three knee designs demonstrated good post-operative range of movement with comparative improvement of patient scores to other reported studies. The MRK knee design showed an improved mid-flexion sagittal stability.

The purpose of this study was to prospectively measure serum cobalt and chromium ion levels in patients who had MITCH Resurfacing (Stryker) and to correlate these with acetabular component orientation (anteversion and inclination).

Twenty-seven patients were enrolled in the study. Serum ion levels were measured pre-operatively, six weeks, six months, twelve months and twenty-four months post-operatively. Axial CT scans of the pelvis were used to measure cup anteversion and plain radiographs used to measure cup inclination.

The median serum cobalt and chromium levels at one year were 14.5 nmol/l (range, 6 nmol/l to 59 nmol/l) and 36 nmol/l (range, 17nmol/l to 63 nmol/l) respectively. The median serum cobalt and chromium levels at two years were 16.5 nmol/l (range, 6 nmol/l to 75 nmol/l) and 37.5 nmol/l (range, 13 nmol/l to 109 nmol/l) respectively. The mean cup inclination was 43° (range, 30° to 60°). The mean cup anteversion was 19° (range, 1° to 47°). There was no clear correlation with cup position and serum ion levels. There was one outlier with slightly elevated chromium (109 nmol/l) in a female with a small head size.

All patients at all time points showed serum cobalt and chromium levels below the level indicating a high-risk implant (7 parts per billion or chromium >134 nmol/l and cobalt > 119 nmol/l). Our results show no clear relationship between cup position and serum metal ions in this group of patients with relatively well-positioned components

Introduction

Modularity is being increasingly used throughout the world for both primary and revision total hip arthroplasty. Recently there have been concerns of increased corrosion and fretting at the modular junctions. In the SROM® modular hip system, two modular junctions are the head-neck taper junction and the stem-sleeve taper junction. The aim of this study was to investigate corrosion at these junctions with the use of different bearing materials.