The Association of Tibia:Femur Ratio and Anterior Cruciate Ligament Injury.

BACKGROUND

The tibia:femur ratio (TFR) is an anatomic proportion describing the length of the tibia relative to the femur, with an established normative mean of 0.78 in skeletally mature individuals. Variation in TFR affects lower extremity biomechanics, and there is an association between elevated TFR and hip/knee osteoarthritis and patellar instability.

HYPOTHESIS

TFR variation may also be associated with anterior cruciate ligament (ACL) injury; thus, the purpose of this study is to determine if the mean TFR in patients with ACL injury is different from the mean normative TFR in the general population.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A total of 50 patients with magnetic resonance imaging-confirmed ACL injury underwent full-length lower extremity scanograms. Femoral length was measured from the most superior point of the femoral head to the center point of the medial femoral condyle. Tibial length was measured from the center point of the medial tibial plateau to the center point of the tibial plafond. The TFR was calculated by dividing the tibial length by the femoral length. The mean TFR of the study group was compared with the previously published mean TFR for normative controls with a 2-tailed test.

RESULTS

The mean TFR for the entire cohort of patients with ACL injury was 0.759 (SD, 0.029), which was significantly lower than the mean normative TFR of 0.781 ( = .0001). There were 29 (58.0%) male and 21 (42.0%) female patients. The mean TFR was similar for male (0.760) and female (0.757) patients ( = .77).

CONCLUSION

Patients with ACL injury demonstrated a significantly lower TFR than the previously published TFR for normative controls, which suggests that an association between TFR and ACL injury may exist. It is possible that decreasing tibial length relative to femoral length alters lower extremity biomechanics in such a manner that places the ACL at risk for injury.