Research

Acetabular orientation: component and arthritis

x-ref Hip

The kerfuffle surrounding metal-on-metal hip arthroplasty has caused a re-evaluation of many accepted orthopaedic facts, including, for one, the best orientation of components to improve results and longevity. There is now, more than ever before, an emphasis on appropriate component alignment to minimise wear and improve longevity and clinical results. With a range of intra-operative methods for determining acetabular orientation (including use of the transverse acetabular ligament, computer guidance, the Lewinnek safe zone and alignment jigs), many rely on intra-operative landmarks which themselves may be altered by the disease process. A research team from Glasgow (UK) set out to establish what the ‘normal’ acetabular orientation is, in terms of inclination and anteversion, in patients presenting with osteoarthritic hips.⁵ Their study involved 65 patients with symptomatic osteoarthritic hips requiring total hip arthroplasty. The geometry of the acetabulum was measured using a computer navigation system in order to determine inclination and anteversion. There were some significant sex differences, with mean inclinations of 50.5° (standard deviation (sd) 7.8) in men and 52.1° (sd 6.7) in women, and mean anteversions of 8.3° (sd 8.7) in men and 14.4° (sd 11.6) in women. Many surgeons rely on the ‘safe zone’ described by Lewinnek of anteversion between 5º and 25º and inclination of 30º to 50º. However, 75% of the hips in this study were outside of this zone in at least one of these measures. There is no complete consensus on the ideal placement of the acetabular component, although biomechanical and other studies would advocate a more closed and less anteverted position than has been considered normal in the past – many still rely on the ‘safe zone’ to guide their cup placement. Whatever the surgeon is aiming for, it is important to know that natural acetabular orientation varies considerably between men and women and that the natural orientation may not be in a desirable position.

Analgesia after knee arthroplasty

x-ref Knee

One of the key factors that affects outcomes following surgery is post-operative pain control. Patient perceptions of outcome, engagement with physiotherapy and discharge timings have all been demonstrated to be, to a certain extent, determined by analgesia. Researchers from Dunedin (New Zealand) have set out to establish which of two competing analgesia regimes, continuous femoral nerve infusion or a single-shot femoral nerve block, was most effective.⁶ The research team designed a prospective randomised placebo-controlled trial with infusion of either bupivacaine or normal saline following a shot femoral nerve block after total knee arthroplasty. All patients underwent spinal anaesthesia with intrathecal morphine in addition to the nerve block. Outcomes were assessed over 72 hours following surgery with Visual Analogue Scale pain scores as the primary outcome measure. A range of secondary outcome measures including ‘top up’ analgesia requirements, side-effect profile and length of hospital stay were assessed. The study was adequately powered, with 86 patients included and randomised to one of the two treatment groups. Amazingly, there were no differences between the single-shot and infusion groups in any primary or secondary outcome measure within 72 hours of surgery. A negative randomised controlled trial is not necessarily a negative outcome. This study, without a shadow of doubt, has a clinically relevant message. The added costs, risks and time involved in setting up a continuous nerve infusion do not pay dividends in terms of better outcomes.

Bisphosphonate-associated femoral fractures

x-ref Trauma

The healthcare benefits at a population level are significant from the introduction of bisphosphonates, having been shown in large studies (including population studies in Italy) to reduce fracture risk and also to significantly improve mortality. However, the bisphosphonate story is not all roses. The side-effect profile is significant, including GI upset and osteonecrosis, and more recently bisphosphonate-associated fractures have been recognised and associated with the extended use of bisphosphonates. These, typically subtrochanteric, fractures are challenging to treat, with high complication rates and poor union rates. There are, however, little more than case series describing the incidence and natural history of such fractures. Researchers in Linköping (Sweden) set out with a population-based study of 5342 Swedes presenting with femoral fractures over a two-year period.⁷ This massive study represents a 97% inclusion rate of the available population. The research team identified 172 patients with atypical femoral fractures (93% of them in women). This was the basis of a nationwide cohort study and comparison was performed with 952 case controls with typical femoral fractures. For obvious reasons, this was not a case-matched series as the intention was to establish the differences in demographics between the two groups. The research team identified a number of factors associated with bisphosphonate fractures. The first was an age-adjusted relative risk of 55 for bisphosphonate use, and a threefold increased risk in women. In addition, the type of bisphosphonate was significant, with alendronate having a twofold relative risk compared with risedronate and a compound risk (with a relative risk of 126 with four years of bisphosphonate use). Absolute risk levels, however, remained low, with an incidence of 11 per 10 000 person-years of use. The authors were also able to quantify the risk following cessation of use, with a drop in risk by around 70% per year after stopping bisphosphonate use. Although the anecdotal evidence in the literature has suggested all of the findings of this study before, we really do commend the authors of this study for their tenacity. To study an entire population of femoral fractures is really the only way one can draw such conclusions. Quantification of the risk (and particularly the identification of differential risk) associated with different fracture patterns allows for proper healthcare planning. An excellent paper all round.