This is the second of a series of reviews of registries. This review looks specifically at worldwide registry data that have been collected on knee arthroplasty, what we have learned from their reports, and what the limitations are as to what we currently know.

Objectives

Wear debris released from bearing surfaces has been shown to provoke negative immune responses in the recipient. Excessive wear has been linked to early failure of prostheses. Analysis using coordinate measuring machines (CMMs) can provide estimates of total volumetric material loss of explanted prostheses and can help to understand device failure. The accuracy of volumetric testing has been debated, with some investigators stating that only protocols involving hundreds of thousands of measurement points are sufficient. We looked to examine this assumption and to apply the findings to the clinical arena.

As many as 25% to 40% of unicompartmental knee replacement (UKR) revisions are performed for pain, a possible cause of which is proximal tibial strain. The aim of this study was to examine the effect of UKR implant design and material on cortical and cancellous proximal tibial strain in a synthetic bone model. Composite Sawbone tibiae were implanted with cemented UKR components of different designs, either all-polyethylene or metal-backed. The tibiae were subsequently loaded in 500 N increments to 2500 N, unloading between increments. Cortical surface strain was measured using a digital image correlation technique. Cancellous damage was measured using acoustic emission, an engineering technique that detects sonic waves (‘hits’) produced when damage occurs in material.

Anteromedial cortical surface strain showed significant differences between implants at 1500 N and 2500 N in the proximal 10 mm only (p < 0.001), with relative strain shielding in metal-backed implants. Acoustic emission showed significant differences in cancellous bone damage between implants at all loads (p = 0.001). All-polyethylene implants displayed 16.6 times the total number of cumulative acoustic emission hits as controls. All-polyethylene implants also displayed more hits than controls at all loads (p < 0.001), more than metal-backed implants at loads ≥ 1500 N (p < 0.001), and greater acoustic emission activity on unloading than controls (p = 0.01), reflecting a lack of implant stiffness. All-polyethylene implants were associated with a significant increase in damage at the microscopic level compared with metal-backed implants, even at low loads. All-polyethylene implants should be used with caution in patients who are likely to impose large loads across their knee joint.

Cite this article: Bone Joint J 2013;95-B:1339–47.

In this paper, we will consider the current role of metal-on-metal bearings by looking at three subtypes of MoM hip arthroplasty separately: Hip resurfacing, large head (> 36 mm) MoM THA and MoM THA with traditional femoral head sizes.

Following the recall of modular neck hip stems in July 2012, research into femoral modularity will intensify over the next few years. This review aims to provide surgeons with an up-to-date summary of the clinically relevant evidence. The development of femoral modularity, and a classification system, is described. The theoretical rationale for modularity is summarised and the clinical outcomes are explored. The review also examines the clinically relevant problems reported following the use of femoral stems with a modular neck.

Joint replacement registries in the United Kingdom and Australia have provided data on the failure rates of modular devices but cannot identify the mechanism of failure. This information is needed to determine whether modular neck femoral stems will be used in the future, and how we should monitor patients who already have them implanted.

Cite this article: Bone Joint J 2013;95-B:1011–21.

We obtained information from the Elective Orthopaedic Centre on 1523 patients with baseline and six-month Oxford hip scores (OHS) after undergoing primary hip replacement (THR) and 1784 patients with Oxford knee scores (OKS) for primary knee replacement (TKR) who completed a six-month satisfaction questionnaire.

Receiver operating characteristic curves identified an absolute change in OHS of 14 points or more as the point that discriminates best between patients’ satisfaction levels and an 11-point change for the OKS. Satisfaction is highest (97.6%) in patients with an absolute change in OHS of 14 points or more, compared with lower levels of satisfaction (81.8%) below this threshold. Similarly, an 11-point absolute change in OKS was associated with 95.4% satisfaction compared with 76.5% below this threshold. For the six-month OHS a score of 35 points or more distinguished patients with the highest satisfaction level, and for the six-month OKS 30 points or more identified the highest level of satisfaction. The thresholds varied according to patients’ pre-operative score, where those with severe pre-operative pain/function required a lower six-month score to achieve the highest levels of satisfaction.

Our data suggest that the choice of a six-month follow-up to assess patient-reported outcomes of THR/TKR is acceptable. The thresholds help to differentiate between patients with different levels of satisfaction, but external validation will be required prior to general implementation in clinical practice.

The National Institute for Clinical Excellence (NICE) produces recommendations on appropriate treatment within the National Health Service (NHS) in England and Wales. The NICE guidelines on prophylaxis for venous thromboembolism in orthopaedic surgery recommend that all patients be offered a low molecular weight heparin (LMWH). The linked hospital episode statistics of 219 602 patients were examined to determine the rates of complications following lower limb arthroplasty for the 12-month periods prior to and following the publication of these guidelines. These were compared with data from the National Joint Registry (England and Wales) regarding the use of LMWH during the same periods. There was a significant increase in the reported use of LMWH (59.5% to 67.6%, p < 0.001) following the publication of the guidelines. However, the 90-day venous thromboembolism events actually increased slightly following total hip replacement (THR, 1.69% to 1.84%, p = 0.06) and remained unchanged following total knee replacement (TKR, 1.99% to 2.04%). Return to theatre in the first 30 days for infection did not show significant changes. There was an increase in the number of patients diagnosed with thrombocytopenia, which was significant following THR (0.11% to 0.16%, p = 0.04). The recommendations from NICE are based on predicted reductions in venous thromboembolism events, reducing morbidity, mortality and costs to the NHS.

The early results in orthopaedic patients do not support these predictions, but do show an increase in complications.