Study: BMI has no effect on outcomes, survivorship of modern cementless TKA
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Published results found no association between BMI and functional outcomes, survivorship, or all-cause and aseptic revisions in patients undergoing modern cementless total knee arthroplasty.
Using institutional registry data from July 1, 2013, to May 31, 2019, Graham S. Goh, MD, and colleagues analyzed outcomes of 1,408 modern cementless TKAs [Triathlon total knee system, Stryker]. Among the cohort, 136 patients were classified as having normal BMI; 476 patients were overweight; 423 patients were obese class I; 258 were obese class II; and 115 were obese class III. According to the study, outcome measures included Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, SF-12 physical and SF-12 mental scores, survivorship, all-cause revision and aseptic revision.
Overall, 34 knees (2.4%) were revised, 14 (1%) of which were for aseptic failure. Mean time to revision was 1.2 years, and this was consistent across all five BMI categories. At a mean 4-year follow-up, survivorship free from all-cause revision was 97.1%, while survivorship free from aseptic revision was 99%.
From preoperative measure to 2-year follow-up, Goh and colleagues found no significant differences in improvements of KOOS JR or SF-12 scores among all five BMI groups. Researchers noted mean KOOS JR and SF-12 physical scores were worse in the obesity groups at 2-year follow-up; however, the mean differences did not exceed the respective minimal clinically important differences.
After Cox regression analysis, Goh and colleagues found no association between BMI and functional or survivorship outcomes of modern cementless TKA, “possibly due to improved biological fixation at the bone-implant interface,” the researchers wrote in the study.
Perspective
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Christopher J. Wall, MBBS, BMedSc, FRACS, FAOrthA
Obesity is an important issue for the modern arthroplasty surgeon. The global prevalence of obesity is increasing, and this trend is likely contributing to a growing burden of knee osteoarthritis and subsequent total knee arthroplasty. In Australia, 58.4% of patients undergoing TKA are obese and 10.5% are class 3 obese.
A recent study from the Australian Orthopaedic Association National Joint Replacement Registry demonstrated a higher risk of revision for loosening in class 3 obese patients compared with non-obese patients. Reducing the risk of aseptic loosening in obese patients is an important consideration, particularly on the tibial side.
In the present study, Goh and colleagues investigated the influence of BMI on implant survivorship and patient-reported outcome measures (PROMs) in a cohort of 1,408 patients who underwent TKA using a modern cementless prosthesis, with minimum 2-year follow-up. They found that BMI was not associated with all-cause or aseptic revision risk, or preoperative to postoperative change in PROMs. Based on their findings, the authors remarked that “modern cementless designs may confer consistent durability across a wide range of body loads.”
While the findings of this study are promising, further research is needed to determine whether modern cementless implants reduce the risk of aseptic loosening in obese patients. Utilizing national registry data would allow longer-term follow-up in larger patient cohorts, with different implant designs.
References:
Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Hip, Knee & Shoulder Arthroplasty: 2021 Annual Report. https://aoanjrr.sahmri.com/annual-reports-2021.
Wall CJ, et al. J Bone Joint Surg Am. 2022;doi:10.2106/JBJS.21.01491.
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