Introduction

A metal ion study was undertaken in patients who had received an articular surface replacement. The design of these components is optimised in line with lubrication theory and produces low levels of wear in hip joint simulators.

Introduction: The DePuy ASRTM hip resurfacing system has been in clinical use since 2003. Its design features include a diametral clearance of 100–150 microns for optimal wear, and thinner components for improved bone preservation. Three of the six designer surgeons have pooled their clinical experience from three countries.

Methods: 1030 consecutive cases have been studied prospectively at annual intervals,. There were 379 females (average age 56.8 years, 16–71 years) and 579 males (average age 56.9 years, 21–75 years). 86% of patients had a primary diagnosis of Osteoarthritis. Follow up data has been collected by patient questionnaire, radiographs and clinical review. All retrieved specimens have been analysed

Results: The size of implants used varied from 46mm outside diameter acetabular component to 70mm

The Harris Hip Score improved from a pre-operative mean of 56.99 to 97.12 at the latest follow up, and 60% of patients were scored at 100. At the latest follow up, 91% of patients scored 6 or above on the UCLA activity score; indicating at least regular participation in moderate exercise.

There were no dislocations and no clinically evident DVT’s or PE’s

There have been 11 revisions for fracture (1.06%). Five of these were intra-operative fractures, and six of these took place in patients aged over 50years. Fractures occurred in 3.1% of patients 65 years or more and in 0.5% of patients under 65 years(P< 0.05). In addition there were three revisions for cup loosening (0.29%) all in women over 60 years, three for unexplained pain (0.29%), one for impingement and subluxation, and one for infection(0.1%) Five patients have died with the resurfacing in situ (0.51%), for unrelated causes.

The 3-year cumulative survival rate for all patients and all components was 97.4%. For 425 patients under 55 years the cumulative survival rate was 99.4%, aged under 65 years was 98.3%, and aged over 65 yrs was 94.8 %.

Discussion: Clinical results of this all-inclusive cohort of patients using a new resurfacing implant have been typical of other resurfacing systems and confirm excellent relief of pain and rapid return to an active lifestyle. The failures were evident within the first year after implantation, with no revisions occurring after 2 years. Cup loosening has been a rare complication associated with older females and only 0.29% of patients have undergone revision surgery for pain which could not be attributed to implant loosening or infection.

Introduction: Over 20,000 DePuy ASRTM hip resurfacing procedures have been performed since 2003, the implant design applying modern engineering and tribological principles to minimise metal-on-metal bearing wear. Enhanced fixation of both components, high-carbon cobalt-chromium alloy, reduced material thickness and small diametral clearance 100–150 microns are all supported by non-clinical testing. There are published reports of very low wear on hip joint simulators (Dowson D, et al. 2004 Dec;19(8 Suppl 3):124–30.), low wear on retrieval analysis (Morlock MM et al 1: Proc Inst Mech Eng [H]. 2006 Feb;220(2):333–44.) and excellent clinical results (Siebel T et al, Proc Inst Mech Eng [H]. 2006 Feb;220(2):345–53. We recently reported median whole blood chromium and cobalt ion levels of 1.56 ppb and 1.65 ppb at 24 months (Cobb AG et al, British Orthopaedic Association Congress 2007)

Methods: 1030 consecutive cases carried out by 3 of the surgeon-designers between July 2003 and May 2007 have been studied prospectively at annual intervals. 2 to 4 years follow-up data is available on 293 hips.

Results: There have been 11 revisions for fracture (1.06%), 6 in patients aged over 65 years(3.4%), 5 in patients aged up to 65 years (0.6%) (P< 0.001).

There have been 3 revisions for cup loosening (0.29%) and 3 for pain (0.29%). 5 patients have died (0.51%). There was one revision for infection and one for impingement.

Average Harris Hip Score rose from 57.0 to 97.1, and 60% of patients scored 100.

UCLA activity score was 6 or over in 91%, and the median score was 7.5.

All failures were evident by 12 months

The Cumulative Survival Rate at 3 years was 97.4%,, 99.5% for 55 years and under, 98.3% for under 65 years, and 94.2 % 65 years and over.

Discussion: The 2 to 4 year clinical follow-up of the latest generation of surface hip implants is satisfactory. Technical errors during implantation or patient selection accounted for most of the failures. The risk of failure between 12 months and 4 years is low.

The aim of this study was to assess the results of bilateral total knee replacement (TKR) staged one week apart during one hospital admission and compare these results with those of bilateral sequential TKRs and bilateral TKRs performed in 2 separate admissions by a single surgeon using a single prosthesis. Between 5th November 1997 and 10th August 2004, 104 patients underwent bilateral LCS TKRs using the Anteroposterior glide (APG) tibial component. The patients were analysed in 3 groups. The patients in Group 1 underwent bilateral sequential TKR under the same anaesthetic. The patients in Group 2 underwent bilateral TKRs under 2 separate anaesthetics, 7 days apart, during the same admission. The patients in Group 3 underwent bilateral TKR under 2 separate admissions, essentially 2 unilateral TKRs. The patients in Group 1 had shorter operations (p< 0.0001) and shorter hospital stays (p< 0.0001). Patients in Group 2 had less blood loss (p=0.004) but were not transfused any less than the other groups. The complication rate was low and comparable in all groups. There were no in hospital or 30 day deaths in any of the groups. Those patients in Group 3 had worse AKS function scores (p=0.02) and those patients in Group 2 had a significantly better HSS score (p=0.02). There was no significant difference between the groups in terms of range of motion or the AKS Knee score. This study has confirmed a shorter operation and hospital stay when the bilateral TKRs are carried out under the same anaesthetic. These patients also bled the most postoperatively. There was little difference in terms of complications and clinical outcome at a mean follow up of 4 years. With appropriate patient selection, both same anaesthetic and same admission bilateral TKR are safe methods to treat bilateral arthritis.

Introduction and aims: The aim of this study was to determine the relationship between pre-operative Single Photon Emission Tomography (SPECT) scan findings and intra-operative assessments of patello-femoral and tibio-femoral OA, in patients undergoing tibio-femoral uni-compartmental knee arthroplasty (UKA).

Method: Over a six-month period 36 knees in 30 patients, undergoing UKA, were investigated pre-operatively with a SPECT scan to confirm single compartment disease. The male to female ratio of patients was 18:12, with an average age of 63 years (range 44–78). A single radiologist reported all cases, and graded uptake in each compartment. At surgery, the degree of OA encountered in each compartment was assessed by size and grade by the two senior authors, and assigned an OA score. The data was analysed statistically for an association between the SPECT scan score and OA score, using Kendall’s Tau-b.

Results: A statistically significant relationship was demonstrated between positive uptake in a compartment and the presence of OA (p < 0.05), and this was consistent for all compartments. When analysed specifically, the associations were strongest in the medial femoral condyle (0.58) and the medial tibial plateau (0.67), and weakest in the patella (0.35) and trochlea (0.46), and lateral tibial plateau (0.34).

Conclusion: We conclude that SPECT scans can provide useful information regarding the degree of OA in knee compartments when planning UKA, particularly with medial compartment disease. The lower degree of association between scan findings and OA encountered in the patello-femoral compartment, and lateral tibial plateau, indicates greater vigilance should be applied when making intra-operative assessments of these areas.

Aim: To determine the intra operative biomechanical properties of a semitendinosus graft used in ACL reconstruction.

Introduction: ACL reconstruction has become a commonly performed operation with 1,139 of these procedures being performed in South Australia in 1997 (SA Health Commission)

The majority of the scientific literature is based on data obtained from elderly cadaveric material. Little is known about the biomechanical properties of the soft tissue grafts currently used prior to implantation. The correct preconditioning and intraoperative tensioning of the soft tissue grafts has also not been investigated.

The initial graft biomechanical properties are important. Inadequate tension will lead to continuing instability whilst excessive tension may cause accelerated joint arthrosis. The tension in the graft may decrease by 30% if it has not been cyclically pretensioned.

Methods: A machine has been designed that will allow the intraoperative biomechanical testing of soft tissue grafts immediately prior to their implantation into the patient during ACL reconstruction. Data will be available on creep, stress relaxation, and tensile testing.

This device will also allow the accurate preconditioning of the graft, providing objective data that can then be compared to the subsequent clinical progress of the patient.

All testing will be accomplished during the time it takes to prepare the tunnels for insertion of the graft, and as such will not prolong unnecessarily the operative time.

Procedure: Once the graft has been prepared prior to fixation, it will be placed between two clamps. One is fixed to a load cell whilst the other is coupled to a linear actuator. The linear actuator will be driven by a computer controlled stepper motor under close-loop control. Custom software will cyclically load the autograft between two definable load points. A linear variable differential transformer (LVDT) will be used to monitor displacement of the autograft and load will be monitored with a load cell of capacity 125Kg.

This set-up will be immersed in a saline water bath maintained at body temperature during testing. The load cell will be hermetically sealed, with clamps and water bath being autoclavable. With the facilities for draping, the test area will remain sterile. The auto graft clamps will be designed to allow fixation of various graft materials (eg semitendinosus, gracilis, bone-patella tendon-bone) and adjustable for graft lengths. The water bath will house a thermocouple, heating mat and controller to maintain the saline temperature to within 1°C.

The testing system will be mounted on a stainless steel trolley for mobility in the operating room with an underlying shelf to house the associated electronics and a retractable side draw for storage of the laptop computer.

The autograft will be preconditioned between two known loads for 20 cycles recording load and displacement simultaneously on a laptop computer. Once preconditioned, the autograft will then be used for the ACL reconstruction in the standard way.

Summary: Objective data on preconditioning of ACL grafts, has never before been available intra-operatively. We outline the experimental set-up which has been designed and is undergoing testing prior to its use in a prospective study.