Introduction: A departmental audit meeting identified a problem with mis-seating of the ceramic liner for the Trident Acetabular System.

Methods: We reviewed the initial postoperative radiographs of all patients who had undergone primary THR using the Trident Acetabulum. Independent review was performed by 3 experienced hip surgeons.

Results: One hundred and seventeen hips (113 patients) were identified. Nineteen had incomplete seating of the liner as judged by plain anteroposterior and lateral radiographs, (prevalence 16.3%). Pre-operative diagnosis was not a risk factor for mis-seating of the liner. One case of complete liner dissociation necessitating revision was identified; another mis-seated liner was also revised in the early postoperative period and two that were initially incompletely seated were noted on follow up radiograph to have spontaneously re-seated. Out of 15 surgeons who had used this system, 10 had at least one case where the liner was incompletely seated.

Discussion: There may be technical issues with regard to implanting this prosthesis of which surgeons should be aware. The Trident Ceramic Acetabular System has a unique design that features a titanium sleeve encapsulating the ceramic that is elevated at the periphery. This sleeve may prevent complete circumferential inspection of the liner when attempting to assess intra-operative seating. We also believe that the Trident shell can deform upon implantation, preventing complete seating of the liner. This theory is supported by the observation that two originally mis-seated liners were noted to have spontaneously re-seated on subsequent radiographs. This phenomenon can be explained by the viscoelasticity of bone and elastic recoil of the shell. The cases of persistent liner mis-seating may be explained if the hoop stresses upon implantation are large enough for plastic deformation to occur. Potential problems include metallosis, implant loosening and fatigue fracture of either the shell or liner as a result of fretting.

Introduction: Intra-articular injection of steroid to the hip prior to joint arthroplasty has been suggested in some studies to carry a risk of infection up to 30% and subsequent revision surgery required in up to 12.5%.

Methods: We undertook a review of all intra-articular hip injections performed at the Queen Alexandra Hospital, Portsmouth and the Royal Haslar Hospital, Ports-mouth between January 2000 and April 2006. Hospital notes including operation notes, anaesthetic preoperative assessments and clinic letters were used to collect the following data. Name, age, sex, and premorbid conditions in particular diabetes, medication, date of injection, substance injected, date of arthroplasty and post operative complications.

Results: 370 intra-articular hip injections were performed of which 55 subsequently had total hip arthroplasty. 1 required washout post operatively but components remained and to date have not required revision. 1 required excision arthroplasty to eradicate deep infection and is still awaiting revision arthroplasty. This shows an infection risk of 3.6% and revision rate of 1.8%.

Discussion: Our review does not show a high rate of infection following intra-articular injection. We conclude that the therapeutic and diagnostic benefits of intra-articular injection may be considered prior to total joint arthroplasty without the increased risk of subsequent infection

We reviewed the initial post-operative radiographs of the Trident acetabulum and identified a problem with seating of the metal-backed ceramic liner. We identified 117 hips in 113 patients who had undergone primary total hip replacement using the Trident shell with a metal-backed alumina liner. Of these, 19 (16.4%) were noted to have incomplete seating of the liner, as judged by plain anteroposterior and lateral radiographs. One case of complete liner dissociation necessitating early revision was not included in the prevalence figures. One mis-seated liner was revised in the early post-operative period and two that were initially incompletely seated were found on follow-up radiographs to have become correctly seated. There may be technical issues with regard to the implanting of this prosthesis of which surgeons should be aware. However, there is the distinct possibility that the Trident shell deforms upon implantation, thereby preventing complete seating of the liner.

We used laser Doppler flowmetry (LDF) to measure flux in cortical bone fragments as a method of determining their vascular status and viability. In an experimental tibial osteotomy measurements of flux were made from specific cortical sites both before and after osteotomy. Flux levels fell rapidly in non-vascularised fragments and remained significantly reduced throughout the experiment. By contrast, those in vascularised fragments were significantly reduced one and two hours after the osteotomy but then increased. From three hours after the osteotomy there was no significant difference in flux levels between the vascularised fragments and proximal bone stock.

We conclude that measurement of bone flux by LDF may have a role in the objective evaluation of the viability of bone fragments, but that further studies are required to validate the technique before its adoption in the management of the injured patient.