Objectives:
Multi-ligamentous knee injuries (MLKI) can be debilitating and result in persistent functional limitations. These severe injuries are seen with increasing frequency in patients with elevated body mass index (BMI). The impact of elevated BMI on mid- to long-term outcomes after MLKI is not clear. We hypothesize that patients with elevated BMI demonstrate worse patient-reported outcome scores at mid- to long-term follow-up after surgical treatment of MLKI.

Methods

Records were reviewed to identify patients treated surgically for MLKI at a single institution between July 2005 and June 2018. Chart review was performed and patient demographics, injury information, and surgical data were collected. Patients were subsequently contacted and asked to complete a patient-reported outcomes assessment including the Tegner activity scale and Knee Injury and Osteoarthritis Outcome Score (KOOS). Patients were categorized by BMI into three categories based on Centers for Disease Control and Prevention (CDC) guidelines: normal/overweight (BMI < 30 kg/m2), obese (BMI from 30 to 39.9 kg/m2), and morbidly obese (BMI = 40 kg/m2). Patient-reported outcomes were compared among the three groups using ANOVA testing. Multiple linear regression analysis was used determine whether obesity or morbid obesity were associated with poorer patient-reported outcome scores compared to the BMI < 30 group, controlling for age at injury and mechanism of injury.

Results

A total 58 patients with 62 MLKI completed patient-reported outcomes scores at a mean follow-up of 8.1 years from surgery (range: 2.6 to 14.9 years). Mean age at the time of injury was 30.2 years (range: 17 to 63 years) and mean BMI at the time of injury was 30.3 kg/m2 (range 18.5 to 78.8 kg/m2). Overall patient reported outcome scores at follow-up were: Tegner: 4.8 ± 2.1, KOOS symptoms: 76.8 ± 17.3, KOOS pain: 82.3 ± 16.7, KOOS ADL: 87.7± 15.6, KOOS Sport 63.8 ± 30.2, and KOOS Knee QOL: 58.6 ± 25.6. Morbidly obese patients (BMI = 40 kg/m2) were noted to have lower KOOS scores than those with BMI < 30 kg/m2 (p < 0.05). Significantly lower Tegner score were noted in the morbidly obese group (2.1 ± 1.2) compared to the obese (5.1 ± 2.0) and BMI < 30 kg/m2 (5.2 ± 2.0) groups (p < 0.05). No significant differences in KOOS or Tegner scores were noted between obese patients (BMI from 30 to 39.9 kg/m2) and those with BMI < 30 kg/m2. Multiple linear regression demonstrated poorer patient-reported outcomes in the morbidly obese group compared to the BMI < 30 kg/m2 group (all p < 0.05), but no significant differences were noted between the obese group and the BMI < 30 kg/m2 group, controlling for patient age and mechanism of injury.

Conclusion

Morbid obesity is associated with poorer mid- to long-term patient-reported outcomes following surgical treatment of MKLI compared to patients with BMI < 30 kg/m2, controlling for age and mechanism of injury. Patients with BMI between 30 and 40 did not have poorer outcomes compared to patients with BMI < 30.