2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


The Radiographic Decision Aid Does Not Work in High-BMI Patients for Unicompartmental Knee Replacement: A Retrospective Matched-Control Study

Naman Wahal, MBBS, MS Orthopaedics, Bikaner, Rajasthan INDIA
RAJESH MALHOTRA, MS Orthopaedics, FIMSA, FRCS, FACS, New Delhi INDIA

Indraprastha Apollo Hospital, DELHI, Delhi, INDIA

FDA Status Cleared

Summary

The study found that the radiographic decision aid for unicompartmental knee replacement (UKR) fails in high-BMI patients (BMI ≥ 35) by missing focal lateral cartilage damage, leading to a 25.8% intraoperative conversion to total knee replacement (TKR), increased operating time and highlighting the need for advanced imaging like MRI.

Abstract

Title:
The Radiographic Decision Aid Does Not Work in High-BMI Patients for Unicompartmental Knee Replacement: A Retrospective Matched-Control Study

Background

Osteoarthritis (OA) in high-BMI individuals (BMI ≥ 35) is influenced by both mechanical overload and inflammatory factors, which contribute to tricompartmental OA. While radiographic decision aids are commonly used to select patients for unicompartmental knee replacement (UKR), they frequently fail to detect focal cartilage loss in the lateral compartment in high-BMI patients. This leads to intraoperative conversion to total knee replacement (TKR) due to unexpected cartilage damage, resulting in increased operating time and higher costs. This study aims to evaluate the accuracy of the radiographic decision aid in high-BMI patients and compare outcomes between those who required conversion to TKR and those who successfully underwent UKR.

Methods

We conducted a retrospective analysis of 120 patients scheduled for UKR between August 2023 and July 2024. Among them, 31 patients (25.8%) required intraoperative conversion to TKR due to undetected issues: 24 conversions (77.4%) were due to focal full-thickness lateral cartilage loss, and 7 (22.6%) were due to ACL deficiency. All 24 patients with lateral cartilage loss had a BMI ≥ 35, with an average BMI of 36.8 (range: 35.2–41.4). The converted group was compared with a matched control group of 89 patients who successfully underwent UKR without conversion, matched for age, gender, and initial radiographic findings.

Results

In the converted group, all patients with lateral cartilage damage had a BMI ≥ 35. The radiographic decision aid failed to detect lateral compartment cartilage damage in 24 patients with high BMI, resulting in a sensitivity of 39.6% in detecting lateral defects. The average BMI in the conversion group was 36.8, significantly higher than the control group's average BMI of 32.1. Intraoperative conversion to TKR led to an average of 12 minutes of additional operating time without increasing cost. No significant lateral compartment damage was found intraoperatively in the control group.

Conclusion

The radiographic decision aid for UKR is ineffective in high-BMI patients (BMI ≥ 35), particularly in detecting focal cartilage damage in the lateral compartment. This results in a high rate of intraoperative conversion to TKR, causing increased operating time and surgical costs. The findings underscore the need for advanced imaging techniques, such as MRI, in the preoperative assessment of high-BMI patients to improve diagnostic accuracy and surgical planning. These also highlight the need for including clinical assessment in the decision aid.