Cemented THR, Uncemented THR and Birmingham Hip Replacement outcomes compared for death rate and revision rate BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e3319 (Published 14 June 2012) Cite this as: BMJ 2012;344:e3319 D J W McMinn, consultant orthopaedic surgeon1, K I E Snell, PhD student2, J Daniel, director of research1, R B C Treacy, consultant orthopaedic surgeon3, P B Pynsent, director of research and teaching centre3, R D Riley, reader in biostatistics4 http://www.bmj.com/content/344/bmj.e3319 Objectives: To examine mortality and revision rates among patients with osteoarthritis undergoing hip arthroplasty and to compare these rates between patients undergoing cemented or uncemented procedures and to compare outcomes between men undergoing stemmed total hip replacements and Birmingham hip resurfacing. Population: About 275 000 patient records. Main outcome measures: Hip arthroplasty procedures were linked to the time to any subsequent mortality or revision (implant failure). Flexible parametric survival analysis methods were used to analyse time to mortality and also time to revision. Comparisons between procedure groups were adjusted for age, sex, American Society of Anesthesiologists (ASA) grade, and complexity. Conclusions: There is a small but significant increased risk of revision with uncemented rather than cemented total hip replacement, and a small but significant increased risk of death with cemented procedures. It is not known whether these are causal relations or caused by residual confounding. Compared with uncemented and cemented total hip replacements, Birmingham hip resurfacing has a significantly lower risk of death in men of all ages. Previously, only adjusted analyses of hip implant revision rates have been used to recommend and justify use of cheaper cemented total hip implants. Our investigations additionally consider mortality rates and suggest a potentially higher mortality rate with cemented total hip replacements, which merits further investigation. The evidence in this analysis suggests there are differences between the outcomes of cemented and uncemented total hip replacements in terms of both revision and mortality rates. On average across the population, our model predicts that performing a cemented instead of an uncemented total hip replacement results in an extra death once in every 77 (95% confidence interval 53 to 143) procedures every eight years for patients who do not undergo revision before this time; conversely, the disadvantage of uncemented total hip replacement is that an extra revision is predicted within eight years for every 67 (58 to 84) procedures for patients alive at this time. Secondary analyses in men showed that the lowest death rate is associated with Birmingham hip resurfacing. By performing a cemented total hip replacement instead of resurfacing, our analysis predicts an extra death occurs within six years for every 23 (17 to 35) operations. Although the hazard ratios and differences in survival probabilities for mortality between procedure types are small, a large number of people currently undergo hip arthroplasty and the number is increasing year on year. Therefore even small differences, if they are genuine, indicate potentially large numbers of avoidable deaths. For example, an estimated 1.2 million hip arthroplasties56 were performed worldwide in 2011 alone. If hypothetically 1.2 million planned cemented procedures were changed to uncemented procedures then, based on our model estimates, there would be a predicted 15 584 (8392 to 22 641) fewer deaths by eight years for patients who had not undergone revision by this time. As the baby-boomer generation ages the number of arthroplasties has been progressively increasing and therefore the number of potential avoidable deaths could also progressively increase if cemented hips continue to be used widely. If 40% of these 1.2 million are assumed to be men then, based on our estimates, switching 0.48 million cemented procedures to Birmingham hip resurfacing would lead to a predicted 20 869 fewer deaths (13 714 to 28 235) at six years for who had not undergone revision before this time… …Over six years’ follow-up, Birmingham hip resurfacing had a significantly lower mortality rate than uncemented and cemented total hip replacement in men of all ages, but a higher revision rate than cemented total hip replacement.

Epidemiological magnitude of the problem

Although polymethylmethacrylate (PMMA) bone cement is biocompatible, adverse cardiopulmonary effects57 58 59 60 61 62 have been widely documented during and after the cementation period. Modern cement techniques,63 including pressurisation, which were developed to improve cement penetration and fixation can exacerbate these events.64 During the reaming and pressurisation processes fat, marrow, air, particles of bone, cement, and aggregates of platelets and fibrin are driven into the systemic circulation57 with the potential for intraoperative and postoperative embolic events and adult respiratory distress syndrome. Embolic events have been found to correlate with haemodynamic changes suggesting pulmonary embolism65 and have been observed in over 90% of cases66 by transoesophageal echocardiography. Furthermore about 10% of normal patients have right to left shunt, giving the possibility of systemic embolisation with unknown long term effects.67 68 69 In comparison, the relative rarity of overt postoperative adult respiratory distress syndrome in patients suggests that the embolic insult is usually insufficient to cause important clinical symptoms immediately. The persistence of increased mortality over eight years, however, raises the question of whether the embolisation has the potential to reduce the normal respiratory reserve, making the patient prone to succumb to minor respiratory diseases in the longer term. A long term detrimental effect on other organ systems from systemic embolisation could also explain the continuing increased mortality. We have had the opportunity of studying embolisation intraoperatively after cemented total hip replacement and Birmingham hip resurfacing using transoesophageal echocardiography.70 The embolisation of echogenic material into the right heart and lungs is markedly different with the two different procedures. With Birmingham hip resurfacing, there is momentary transient embolisation or no embolisation, whereas with cemented total hip replacement there is profound embolisation, which can persist for up to 20 minutes. Furthermore, the potential long term detrimental effects from prolonged exposure to nephrotoxic agents such as gentamicin from the bone cement cannot be ruled out, and this matter is being actively investigated.

What is already known on this topic

• Unadjusted and adjusted survival analyses suggest cemented total hip replacements are associated with better implant survival (improved revision rates) than uncemented total hip replacement and hip resurfacings.
• NICE indicate there are no data to support the use of generally more costly uncemented total hip replacement, though adjusted comparisons of mortality rates have previously been lacking

What this study adds

• In the National Joint Register, there are large baseline differences in characteristics of patients undergoing cemented, uncemented, or resurfacing procedures, which makes unadjusted comparisons inappropriate
• Over eight years’ follow-up uncemented total hip replacement was associated with a small but significant increased revision rate compared with cemented total hip replacement at any time for patients alive and unrevised at that time, and cemented total hip replacement was associated with a small but significant increased mortality rate compared with uncemented total hip replacement at any time for patients without a revision at that time
• Over six years’ follow-up, Birmingham hip resurfacing had a significantly lower mortality rate than uncemented and cemented total hip replacement in men of all ages, but a higher revision rate than cemented total hip replacement