Background

A first generation once annealed highly crosslinked polyethylene (HXLPE) was introduced in 1998. At 8 years it was reported to have a 78% reduction in wear compared with conventional polyethylene and no osteolysis. However, concerns regarding the long-term performance and oxidative resistance of this annealed material exist because of the presence of free radicals.

Introduction

Technological advances in the processing of polyethylene have led to improved survivorship of total hip arthroplasty. The purpose of this study was to determine if a second generation highly cross-linked polyethylene could improve upon wear rates compared to conventional and first generation cross-linked polyethylene in patients undergoing primary total hip arthroplasty.

The aim of this study was to investigate the use of large diameter head THR to treat fractured neck of femur, and to demonstrate if this conferred greater stability.

Forty-six (46) independent, mentally alert patients with displaced intracapsular fractures underwent THR. Mean age was 72.1 years. Outcome measures were dislocation, reoperation/ revision rate, Oxford hip score (OHS), Euroqol (EQ-5D) and residential status. Data was collected prospectively, with review being carried out at 3 months and 1 year.

At mean follow-up (12.5 months) there were no dislocations. Reoperation, revision and infection rate were all 0%. Two patients died (4.3%). Mean pre-injury and postoperative OHS were 12.1 and 17.9 respectively. Mean pre-injury and postoperative EQ-5D index scores were 0.97 and 0.83 respectively. Mean postoperative walking distance was 2.5 miles. There were no changes in residential status.

This is the first published series utilizing 36-mm diameter metal-on-metal THR for the treatment of fractured neck of femur. We have demonstrated that it affords patients excellent stability with no recorded dislocations.

In patients with significant bone loss and a nonfunctioning extensor mechanism, the approach to revision is complicated. We describe a unique approach to solve this complex problem to help restore clinically satisfactory results. Our technique involves the use of a donor allograft that consists of proximal tibia along with the attached extensor mechanism (patellar tendon-patella-quadriceps tendon).

Five reconstructions utilizing bone allografts and extensor mechanisms were performed by two surgeons. Each has extensive surgical history on the affected knee and presented with gross instability, considerable bone loss, and significant extensor lag or total loss of extension. The implants used were press-fit stems with the tibial baseplate cemented into the allograft prior to implantation. In this series, either hinged or total stabilized prostheses were used.

The follow up ranged from 1 to 5 years. The only complication to date was reported in one patient who required irrigation and debridement with surgical wound closure after partial dehiscence. However the patency of the allograft was not disrupted.

All prostheses have been noted to be stable with no signs of loosening.

This procedure presented should be considered a salvage procedure for bone stock and extensor mechanism deficiency in revision total knee arthroplasty. The advantage to our allograft is the inherent stability of the proximal tibia with the tibial tubercle and associated extensor mechanism. For patients with this complex deficiency, there has been no effective method of treatment and we advocate the use of this procedure to restore function and relieve pain to an otherwise grossly unstable and functionally limited joint.

Introduction: Wear simulator studies have predicted that highly cross-linked polyethylenes can reduce linear wear by 50–90% when compared to traditional polyethylene (gamma sterilized in air). Clinical experience with a highly cross-linked polyethylene which was irradiated to 10 megarads and cold anneled but not remelted (Crossfire) began in October 1998.

Methods: 72 Crossfire implants (69 patients) were implanted and have a minimum 3 year follow-up (mean 3.85 years). 31 of these implants (29 patients) have a minimum 4 year follow-up (mean 4.64 years). Linear wear utilizing a validated computerized technique was measured and compared to 38 hips (37 patients) implanted with a non-cross-linked polyethylene (gamma irradiated – N2 vac) with a mean follow-up of 4.96 years.

Results: The mean wear in millimeters per year for the highly cross-linked Crossfire polyethylene with minimum 3 year follow-up was 0.054 (sd=0.032). At minimum 4 year follow-up wear was 0.057 mm/yr (sd=0.036). The wear for the N2 vac non-cross-linked polyethylene was 0.138 mm/yr (sd=0.066). Using a standard t-test the difference in wear was highly significant at p=< 0.001.

Discussion & Conclusion: Cross-linking is the only material characteristic shown to improve wear performance of polyethylene. Our clinical experience demonstrates a 50% reduction in wear over N2 vac irradiated polyethylene during the first three years with no significant change out to a mean of 4.64 years. Cross-linked polyethylenes hold great hopes for significant reduction in wear and osteolysis and prolonged life of hip arthroplasty in patients of all ages.