In a cross sectional cohort study three different metal on metal total hip systems were assessed. Two monoblock acetabular designs; the Durom socket (Zimmer, Warsaw, In) and the Birmingham socket (Smith and Nephew, Memphis, TN), and one modular metal on metal total hip system (Pinnacle, Depuy Orthopaedics, Warsaw, In) in patients who have received these implants in the our region. 56 patients were recruited in total. All patients were assessed clinically, radiologically and biochemically. Whole blood Cobalt, Chromium and titanium levels were tested.

The median head size used in the Birmingham group was 52mm (Range 44mm to 56mm), and in the Durom group, 48mm (Range 42 to 54mm). The median head size used in the modular Pinnacle group was 40mm (Range 36–44mm).

The blood metal ions levels in the larger non modular acetabular sockets were significantly raised compared to the Pinnacle group. For Co 1.95 µg/l and 2.70 µg/l in the Durom and Birmingham groups respectively compared to only 0.52 µg/l in the Pinnacle group (P< 0.001). Mean Cr levels were the same for the two monoblock systems, 1.9 µg/l compared to the Pinnacle sockets 1.2 µg/l (P< 0.001).

Our study clearly demonstrates that there is a significant difference in metal ion levels in patients following a monobloc large head arthroplasty system compared to a smaller modular metal on metal hip arthroplasty. The smaller head size appears to produce less metal ions whilst at the same time a 36mm–44mm head size is large enough to increase hip stability and range of movement as well as decreasing the risk of impingement. In our practice we are no longer using this design and the safest strategy, when considering metal on metal bearings, is to use a modular, smaller head system such as the Pinnacle.

Introduction

We discuss the use of the SMILES (Stanmore Modular Individualised Lower Extremity System) in salvage revision knee surgery and review the medium-long term results of 42 cases.

Recent interest has focused on minimally invasive hip surgery, with less attention being directed to maximising the potential benefits of this type of surgery. We have developed a new multidisciplinary programme for patients undergoing total hip replacement in order to facilitate an overnight hip replacement service.

The programme involves a pre-operative regimen of education and physiotherapy, a modified anaesthetic technique, a minimally invasive surgical approach and a portable local anaesthetic pump infusion for post-operative pain control. Strict inclusion and exclusion criteria were developed based on age, medical status and social circumstances. Patients were mobilised on the day of their operation and discharged home with an ‘outreach team’ support network. No patient complained that their discharge was early. Independent evaluation was performed using the Oxford Hip Questionnaire, the Merle d'Aubigné clinical rating system and Visual Analogue Pain Scores. Thirty seven patients underwent total hip replacement using the new protocol.

The average length of stay was 1.2 days. The mean pain score on discharge was 1.3/10. The Oxford Hip Questionnaire and Merle d'Aubigné scores were comparable to patients who underwent surgery prior to the introduction of the new protocol. Minimising in-patient stay for total hip replacement benefits the patient by reducing exposure to nosocomial infection and expediting the return to a normal environment for faster rehabilitation. This new programme allows patients undergoing total hip replacement to be discharged after 1 night post-operatively without compromising safety or quality of care.

Minimally invasive surgery with a suitable infrastructure can be used to dramatically reduce the length of stay in suitable patients. This can be achieved reliably, safely and with high patient satisfaction. In order to gain the benefit of Minimally Invasive Surgery we recommend introducing this type of comprehensive programme.