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Clinical lead, Mr Chris Gooding
New developments in hip surgery

At the open meeting of the American Hip Society in Chicago in March 2013, Don Garbuz1 presented a seminal paper on the diagnostic accuracy of MRI versus ultrasound for detecting pseudotumours in asymptomatic patients who had previously had a metal-on-metal total hip replacement. The authors demonstrated that ultrasound had a sensitivity of 100% and a specificity of 96% compared with a sensitivity of 92% and specificity of 100% for MRI in detecting pseudotumours. As ultrasound is 100% sensitive, the authors concluded that a negative ultrasound scan excludes a pseudotumour in asymptomatic patients and recommended its use as the initial screening tool. Ultrasound is a useful screening tool as it is inexpensive, easy to administer and is well tolerated by patients. It is also a valid, reliable and reproducible diagnostic test in the right hands. With the MRI resources of most hospitals under enormous pressure, an ultrasound scan should perhaps be the first line investigation of choice when it comes to excluding the possibility of a pseudotumour in patients with a painful metal-on-metal hip replacement. This is an important paper and a worthy winner of the John Charnley award.

With the advent of increasing transparency regarding surgeons’ outcomes, Schairer 2 presented an interesting paper on the causes and frequency of unplanned hospital re-admission after total hip replacement. They demonstrated in their institution that at 90 days primary THR had an unplanned re-admission rate of 5% compared with 10% for revision THR and 18% for antibiotic-spacer staged revision THR. Although medical diagnoses accounted for a quarter of unplanned re-admissions, over a half were as a result of dislocation, surgical site infection and post-operative haematoma. Risk factors for re-admission included type of procedure, hospital stay greater than 5 days, cardiac valve disease, diabetes with endorgan complications and substance abuse. The authors highlighted that healthcare quality measures that include re-admission rates as a guide for the quality of healthcare need to distinguish between primary and revision procedures. Otherwise tertiary referral centres in particular who undertake the majority of the revision workload will be unfairly reflected in outcome data. In addition, for the public and the profession as a whole to have confidence in the data that is put out in the public domain we need a robust mechanism for collecting the data but also the right tools for the job. For this to be done properly it needs to be adequately resourced and co-ordinated, which is no mean feat in the current economic climate!

Finally, another paper which was also presented at the American Hip Society meeting discussed the complication rate following hip and knee replacement in the morbidly obese patient.3 The authors reviewed a cohort of 12,355 patients and found no significant differences for patients with a BMI > 40 Kg/m2 compared with other BMI groups in the first 6-8 weeks after operation for symptomatic DVT, asymptomatic DVT or symptomatic PE. The authors did identify one study published previously that had shown that obesity (BMI 30 kg/m2) was a risk factor for post-operative DVT/PE within 30 days of knee or hip replacement4 but came to the interesting conclusion that this may be because this study used different anticoagulation (mainly warfarin) rather than rivaroxaban or enoxaparin which the authors had used in their study. Possibly the type of anticoagulation used as prophylaxis in obese patients is a potential risk factor for a post-operative venous thrombo-embolism and this may be different to other BMI groups. With obesity particularly in the western world rapidly becoming an epidemic this is  an increasingly relevant and important question to answer. In this level 3 study the authors did report that there was an increased risk of erythema, peripheral oedema, diarrhoea, gastrointestinal or abdominal pain, wound inflammation or infection, extrasurgical site infections and respiratory tract or lung infections in the morbidly obese patient. As well as finding no increased venous thromboembolism risk there was also no increased risk of bleeding in this patient group. With the increasing number of obese patients requiring hip and knee replacement this important paper helps both surgeons and patients understand the potential complications which should be discussed as part of the informed consent process and allow adequate discussion of these risks.

Chris Gooding, Locum Consultant Orthopaedic Surgeon, Addenbrooke’s Hospital, Cambrige, UK
January 2014

References:

1. Garbuz, DS, Hargreaves, BA, Duncan, CP, et al.  The John Charnley Award: Diagnostic accuracy of MRI versus ultrasound for detecting pseudotumors in asymptomatic metal-on-metal THA. Clin Orthop Relat Res 2013;Jul 19. [Epub ahead of print].
2. Schairer, WW, Sing, DC, Vail, TP, et al. Causes and frequency of unplanned hospital readmission after total hip arthroplasty. Clin Orthop Relat Res 2013;June 26. [Epub ahead of print].
3. Friedman, RJ, Hess  S, Berkowitz, SD, et al.  Complication rates after hip or knee arthroplasty in morbidly obese patients. Clin Orthop Relat Res 2013;471:3358-66.
4. Mantilla CB, Horlocker TT, Schroeder DR, et al. Risk factors for clinically relevant pulmonary embolism and deep venous thrombosis in patients undergoing primary hip or knee arthroplasty. Anesthesiology 2003;99:552–60.


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