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BMI Thresholds for Hip Replacement 'Widen Inequalities'

NHS policies on patients' weight and access to hip replacement surgery are inappropriate and should be reconsidered, experts have urged.

The authors of an observational study, published in the journal BMC Medicine, pointed out that "with one in 10 people likely to need a joint replacement in their lifetime, many thousands of patients are directly affected by these policies", which were "worsening health inequalities", they said.

Rules implemented by NHS clinical commissioning groups (CCGs) across England to change the access to hip and knee replacement surgery for patients who were overweight or obese had been in effect for over 10 years, explained the authors. However, despite their widespread use, the impact of weight and body mass index (BMI) policies introduced by the groups on access to elective surgery was "not clear", the authors underlined, and added that policy use "varied by locality".

Dr Joanna McLaughlin from the Musculoskeletal Research Unit at the University of Bristol, and lead author, commented: "NHS policy on whether people can immediately access referral for hip replacement surgery if they are overweight or obese varies depends on where you live in England."

Regional differences meant that some areas had "no such policy", while in other areas patients were denied access to a hip replacement operation until their BMI was below a certain threshold or until they had waited extra time.

Health Inequalities Uncovered

The researchers from the University of Bristol set out to assess the impact of policies for BMI on access to hip replacement surgery in England, and to investigate if there was any evidence of worsening health inequalities.

They evaluated the impact of the introduction of CCG health optimisation policies on trends before and after the implementation of the intervention, and used data related to commissioning by CCGs prior to the transition of CCGs to Integrated Care Boards (ICBs).

For the study the researchers analysed the rates of primary hip replacement surgery of 480,364 patients – mean age 68.9 years, mean BMI 28.6, 60.6% female, primary reason for surgery being osteoarthritis – between January 2009 and December 2019 using data from the National Joint Registry (NJR). They then compared regions with and without a BMI policy. The main outcome measures were rate of surgery and patient demographics – BMI, index of multiple deprivation, independently funded surgery – over time.

The overall rates of surgery increased from 41.6 per 100,000 population aged 40+ per quarter year in 2009, to a peak of 72.6 in 2018, before declining to 59.5 in 2019 – a pattern that was consistent across intervention and control CCG localities. Most (86.5%) operations were publicly funded and 4.9% of patients who received operations were from the 10% of most deprived areas.

The researchers found commissioning localities that introduced a policy had higher surgery rates, and more affluent populations, at baseline than those which did not introduce policies. "It is possible that these factors may have been drivers for policy introduction," the authors postulated, since after policy introduction the rates of surgery fell, whereas in localities with no policy the rates increased. 

'Strict' policies mandating a BMI threshold for access to surgery were associated with the sharpest fall in rates (trend change) of 1.39 operations per 100,000 population aged 40+ per quarter-year, with this change "sustained over time".

"Changes in the rate of surgery were less pronounced for mild or moderate BMI policies," highlighted the authors, "and opposite to that seen in control CCGs with no policy."

An increase in the proportion of independently funded surgery was associated with the introduction of a strict policy and with the proportion of more affluent patients receiving surgery, the researchers found.

"These findings raise the concern that the use of BMI policies for hip replacement surgery risks widening health inequalities by increasing the link between access to surgery and socioeconomic circumstance," the authors cautioned.

Counterproductive Measures

Policies enforcing extra waiting time before surgery were associated with worsening mean pre-operative symptom scores and rising obesity, stressed the authors, who warned that these extra waiting time rules may be "counterproductive".

"NICE guidance on arthritis was updated in October 2022, and it clearly states that BMI should not be used to exclude people from referral to surgery, but restrictive policies are still in use in some regions," emphasised Dr McLaughlin.

The authors cautioned that BMI policies that prevented access to surgery for patients who were unable to lose weight may have meant these patients missed out on the quality of life benefits a hip replacement would have given them. "These policies have concerning associations with a sharp drop in the rate of joint replacements, worsening symptom scores, and worsening health inequalities," Dr McLaughlin said.

The research team urged commissioners and policy decision-makers to urgently reconsider restrictive policies that affected access to elective surgery.

Commissioners and policymakers should be aware of the "counterproductive effects" of BMI policies on patient outcomes and inequalities, they said, and recommended that BMI policies involving extra waiting time or mandatory BMI thresholds were "no longer used" to reduce access to hip replacement surgery.