Hip & Pelvis

Hip arthroscopy then arthroplasty?

As greater numbers are being diagnosed with femoroacetabular impingement, more patients are undergoing hip arthroscopy. Despite its increasing popularity, the results are far from clear. Patients are undergoing bone removal and labral repairs. When successful this is clearly positive, but what about when it is time for an arthroplasty? Is there an increased risk of infection? Does the hip arthroscopy affect the long- and short-term outcomes of the arthroplasty? The honest truth is, we don’t know. The team from Chicago, Illinois (USA) set out to establish if indeed there is an effect on the outcomes of the second procedure.¹ Although a small series, the authors were able to report on 42 patients who underwent subsequent hip arthroplasty following a hip arthroscopy, and matched them 2:1 by age, sex and BMI to primary total hips. Outcomes were assessed with the Harris hip score (HHS), complication rates and revision rates. Bearing in mind that this is a small study and so is likely to be significantly underpowered, it is the first to compare complication rates and revisions, and found them to be similar to primary total hip arthroplasty (THA) patients. Additionally, HHS improved in all patients, regardless of prior surgery. Thus, hip arthroscopy does not compromise subsequent THA, and patients should still be considered for THA after previous hip arthroscopy.

Another outcome score?

Cement-in-cement revision in the hip

Revising a cemented stem can be one of the most challenging aspects of revision hip arthroplasty. The advent of a cement-in-cement technique with the insertion of a smaller, shorter stem into the old cement mantle has already been reported in the literature with considerable success. However, this relies on a complete femoral canal and stable cement mantle. If a small-sized stem is already in situ and there is no smaller stem available, then the only alternative is to remove the cement mantle in the traditional way. The authors of this paper from Edinburgh (UK) are the first to publish the ‘in-cement’ revision technique.³ This technique involves the introduction of a stem of the same size as the original implant into the original cement mantle, without additional cement or downsizing. Potential benefits of this technique include a better view of the acetabulum, ability to use the same-sized stem with the same offset and neck length, and it is quicker! The paper reports 23 patients with a mean age of 65 years. Indications for revision were recurrent dislocation, aseptic loosening and infection. Mean follow-up was 67 months (12 to 128). The overall survivorship was 91.3%, with none of the patients requiring further revision for stem loosening or mechanical failure, though two patients required further revision for infection. The authors outline three key aspects to success: assessment of the cement mantle for stability and version once the old stem is removed; protection of the cement mantle while revising the acetabular component with a damp swab in the canal; and finally the re-insertion of the same-sized stem, without a centraliser. Clearly this is a small series of patients and, as the authors suggest, it warrants further investigation in a larger series with additional outcome measures, in particular radiographic outcomes. Although obviously only suitable in patients where an identical stem can be obtained, this very simple technique potentially avoids the added burden of having to remove the cement mantle in patients who may not otherwise be eligible for a cement-in-cement revision. Detractors would argue that this is really only an exchange, and that patients suitable for this procedure really didn’t need a femoral revision in the first place.

The determinants of poor outcomes in metallosis revision

Infection in arthroplasty

Tantalum acetabulum

The vogue for tantalum acetabular and femoral components is mostly due to the ability to form a firm bond with the bone and avoid the issues of delamination or failure, as the bone is able to fully osseointegrate with the prosthesis. The ability to augment bony defects with a biocompatible metal has dramatically changed the management of (amongst other things) acetabular defects. Despite dramatic uptake within the orthopaedic community, there isn’t really much evidence to support this approach. The porous coated tantalum acetabular shells when applied to acetabular defects are the focus of this paper from Vancouver, British Columbia (Canada). The authors report the outcomes of 46 patients, all recruited with a failed acetabular component and Paprosky grade II or III bone defect addressed with a hemispherical, tantalum acetabular component, supplementary screws and a cemented polyethylene liner.⁶ The authors report a minimum of ten years’ follow-up and they primarily focused on acetabular component survival, although clinical scores are also reported. The authors demonstrated excellent clinical results with the use of porous tantalum uncemented acetabular reconstruction in revision total hip arthroplasty, with an acetabular survival rate of 96% and overall joint survival of 92%. Clinical scores were also good with a mean Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) 92.6 pain score.

Silver-coated acetabular components

We are always interested in preventative methods for infection. As antimicrobials become more and more infective, the use of surface coatings to reduce infection is becoming more of a ‘go to’ position. An interesting and unique series of just 20 patients is reported by investigators in Saga (Japan). All the patients underwent implantation of an acetabular component thermal-sprayed with an silver oxide-containing hydroxyapatite-coated acetabular and femoral component.⁷ The authors report no adverse reactions attributed to the silver coating at one year after surgery. Silver is helpful in that it has a strongly cytotoxic effect and is active against bacterium. There are some concerns about toxicity; it is known to cause ‘silver skin’ at higher concentrations and can cause DNA damage in excessively high amounts. We are delighted to see this paper describing an effort to prevent and minimise the peri-operative risk of infection. These implants appear to be safe without compromising patient function and may become increasingly relevant. The key to establishing their safety is to carefully introduce new technology backed up by appropriate animal safety studies. Orthopaedic surgeons are all too familiar with the ongoing issues associated with metal-on-metal reactions and accumulated metal debris. Silver has a long track record of safe use in humans (in applications as diverse as the silver Negus tracheostomy tubes), however, clearly any new metallurgy involved in an articulating surface should be evacuated very carefully, given recent history.

High rates of failure with modular neck designs

Increased modularity adds the attractive option of a more ‘anatomical’ fit for many implants, with the advantage of increased restoration of normal anatomy and therefore function. However, there are some potential disadvantages to this approach and, with the phenomenon of trunnionosis already a problem, adding further junctional tapers (often with oblique loading) has the potential to worsen the situation. Some early clinical reports have suggested high failure rates from these implants. Researchers from Houston, Texas (USA) have set out to establish the potential problems with these systems, and have gone back to review their own modular total hip arthroplasty (THA) experience with 73 arthroplasties.⁸ The headline figures are that at a mean follow-up of 4.2 years after THA performed with a specific modular-neck femoral stem (Rejuvenate; Stryker, Kalamazoo, Michigan), the authors demonstrated an 86% clinical failure rate with 78% of the stems having undergone revision. A truly shocking outcome. The authors assign this to a corrosion-related failure rate. It is clear that continued close monitoring of this stem design is prudent and early revision after identification of stem failure is recommended. It does beg the question: how in the modern era can implants that have such a high failure rate be permitted for public release?