Research highlights – 9 December 2011

Research questions” “Research highlights” is a weekly round-up of research papers appearing in the print BMJ. We start off with this week’s research questions, before providing more detail on some individual research papers and accompanying articles.

It has become clear over the past year that the regulation and approval of new medical devices falls far short of that for new drugs, posing serious risks to patients (for a comprehensive primer on the topic see this page) The “metal on metal” hip replacement has caused particular concern.

In these devices, both parts – the prosthetic head of femur and the cup – are made of hardened alloy. This seemed a good design, as it allowed the femoral head to be bigger and less likely to dislocate. But last year the UK Medicines and Healthcare Products Regulatory Agency (MHRA) issued an alert about severe cases of metallosis related to the release of ions from these implants, and recommended that patients should be followed up at least annually for five years postoperatively, and more frequently in the presence of symptoms.

A few months later Johnson and Johnson recalled for safety reasons more than 93 000 metal on metal hip resurfacing devices.

The US Food and Drug Administration (FDA) has been monitoring reports of such failures and, in November 2009, it commissioned and funded a formal systematic review to determine the comparative safety and effectiveness of different hip implants. Art Sedrakyan, from Cornell University, and colleagues from the FDA and from Harvard Medical School and School of Public Health now report the findings of that review. They found reports of only 3139 patients and 3404 hips enrolled in 18 studies from 1995 to 2011, but also reviewed reports of more than 830,000 hip implant operations in national registries. Overall, metal on metal or ceramic on ceramic implants had no advantage over traditional polyethylene based bearings, and metal on metal bearings seemed associated with a substantially higher occurrence of revision surgery. The reporting of the comparative trials was often “less than adequate,” and the authors highlight the difficulties of obtaining strong evidence in orthopaedics, saying that we need international collaborations to advance reporting and harmonise the methods of evaluating devices.

The FDA is on the case. On 2-3 December it hosted a public workshop where experts from the FDA (including Sedrakyan and colleagues), MHRA, academia, surgeons, patients, and journal editors (including from the BMJ) discussed ways to improve the development, approval, and postmarketing surveillance of medical and surgical devices and procedures ( The workshop focused particularly on how the IDEAL framework for surgical innovation might be used to improve evidence generation and evaluation ( This is definitely a story to watch.

Meanwhile, what should doctors do when patients come with concerns or symptoms related to their metal on metal hip implants? Camdon Fary and colleagues advise on the assessment and management of any such patient who presents with potential joint failure

The authors recommend referring for an expert ultrasound examination followed by magnetic resonance imaging if a lesion is detected, and warning the patient that another hip replacement is on the cards.

Rapid or standard intravenous rehydration for dehydrated children?

Because of its potential benefits (quickly reducing a child’s agitation and clinical signs of dehydration and improving alertness and appetite), rapid intravenous rehydration has become part of clinical practice, despite a lack of evidence of efficacy. So Stephen Freedman and colleagues conducted a pragmatic controlled trial in a paediatric emergency department in Toronto, Canada. They compared rapid (60 mL/kg) and standard (20 mL/kg) rehydration with saline over an hour in 226 children with dehydration from gastroenteritis who had not responded to oral rehydration and had been prescribed intravenous rehydration. 

They found no difference between the groups in the proportions who were rehydrated at two hours or who required prolonged treatment, nor in the dehydration scores over the four hour study period. Indeed, the median time to discharge was longer in the rapid rehydration group.  The authors unsurprisingly conclude that rapid intravenous rehydration had no clinical benefits in children with mild to moderate dehydration and that, given its potential side effects, it should not be used routinely.

Rapid responses to the full article on and the linked editorial, by Alan Nager, make several criticisms of the paper, largely relating to the pragmatic nature of the trial reflecting current clinical practice.  In particular, they don’t like the inclusion of mild to moderately dehydrated children rather than limiting the study to those with severe dehydration (which is uncommon in Western countries) and the suboptimal measurement of dehydration. However, none argue with the general conclusion that, in the absence of large rigorous clinical trials to establish its efficacy, rapid intravenous rehydration should not be adopted unquestioningly.

Research online

Association between bisphosphonate use and implant survival after primary total arthroplasty of the knee or hip

In a UK cohort study using data for over 40 000 patients undergoing primary hip or knee arthroplasty, bisphosphonate users had a lower rate of revision at five years and a longer time to revision than non-users, Daniel Prieto-Alhambra and colleagues report. The findings require confirmation in experimental studies (doi:10.1136/bmj.d7222).