BMI Change Associated with Waiting Times for Primary Lower Limb Arthroplasty


Raised BMI (Body Mass Index) gives worse outcomes, higher revision risks and increased complications in lower limb arthroplasty. Lengthy NHS (National Health Service) waiting lists allow patients an opportunity to increase BMI by time of surgery, thus affecting outcomes. This study assesses association of BMI change with waiting time for lower limb arthroplasty.


This is a retrospective analysis of prospective primary THAs (Total Hip Arthroplasty) and TKAs (Total Knee Arthroplasty) performed between August 2018 to May 2019, collecting patient demographics, ASA (American Society of Anaesthetists) grade, BMI at pre- operative assessment and day of surgery and time interval between these. Descriptive analysis of demographics and ASA grade was performed, unpaired T-test used to examine significance of weight change and Pearson’s coefficient used to assess the association between BMI change and time.


There were 213 patients; 107 THA and 106 TKA, average age 70.3 (30-95), median ASA 2. 40% of patients had a BMI increase (average 2.5), 44% remained unchanged and 16% had a BMI decrease (average 1.5). 28% of patients put on >5kg whereas 14% lost >5kg (p>0.0001). As a whole, there was no correlation between weight change and waiting time (Pearson coefficient -0.2, P=0.0007) (Graph 1). However, patients who did increase weight showed significant positive correlation with waiting time: 22% (46) patients put on >5kg (average waiting time 59.3 days, median BMI increase 3.5; Pearson coefficient 0.98, p>0.0001), 15% (32) patients put on >1 stone/6.3kg (average waiting time 67.5 days, median BMI increase 3.7; Pearson coefficient 0.98, p>0.0001) and 6.1% (13) patients put on >10kg (average waiting time 43.8 days, median BMI increase 4.4; Pearson coefficient 0.99, p>0.0001).


We recommend repeat pre-op assessment no more than 6 weeks before surgery to ensure BMI has not unduly changed to give patients the best potential post-op outcomes.

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