The tibial spine sign does not indicate cartilage damage in the central area of the distal lateral femoral condyle

Purpose

A radiographic overlap of the lateral femoral condyle and the lateral tibial spine (‘tibial spine sign’) might indicate lateral compartment cartilage damage and might be considered a contraindication for unicompartmental knee arthroplasty (UKA). Therefore, the following research questions were asked: (1) does the presence of a ‘tibial spine sign’ on radiographs correlate with cartilage lesions on the medial aspect of the lateral femoral condyle on corresponding MRIs?; (2) do cartilage lesions on the medial aspect of the lateral femoral condyle indicate cartilage damage in the central area of the distal lateral femur?; and 3) is the ‘tibial spine sign’ impacted by the degree of varus deformity, the amount of coronal tibiofemoral subluxation or the functional status of the ACL?

Methods

One hundred consecutive knees with varus OA in 84 patients were prospectively included. The relationship of the lateral femoral condyle and the tibial spine was graded from 0 to 2 based on the degree of overlap on AP standing knee radiographs. On MRI, cartilage on the medial aspect of the lateral femoral condyle was assessed. Cartilage in the weight-bearing area of the distal lateral femur was analysed according to the OARSI system.

Results

The ‘tibial spine sign’ assessment correlated well with the degree of cartilage damage on the medial aspect of the lateral condyle (r_s = 0.7, p < 0.001) but did not impact histological OARSI grades in the central weight bearing area of the lateral condyle (n.s.). Mechanical varus and tibiofemoral subluxation were not associated (n.s.) with a positive tibial spine sign. Knees with suggestive ACL insufficiency on MRI had more often a positive tibial spine sign; however, this difference was not statistically significant (n.s.).

Conclusion

A positive tibial spine sign does not indicate histologic cartilage damage in the central area of the distal lateral femur and may not be considered a contraindication for medial UKA.

Level of evidence

Level III, diagnostic study.