Assessment of tibiofemoral position in total knee arthroplasty using the active flexion lateral radiograph

This study is a retrospective comparative cohort radiographic analysis of 114 consecutive patients who underwent posterior cruciate retaining (PCR) total knee arthroplasty (TKA), medial and patellofemoral compartment bicruciate retaining arthroplasty (BCR), or bicruciate substituting (BCS) TKA. In an effort to obtain a quantitative measurement of both anteroposterior (AP) tibiofemoral position and active knee flexion we have routinely taken post-operative lateral radiographs in a position of maximal active flexion. Passive range of motion (PRoM) after TKA was significantly greater than pre-operative passive range of motion for each cohort ( p < 0.001). When comparing post-operative active range of motion (ARoM) to PRoM, there was a statistically significant difference within the PCR and BCR cohorts ( p < 0.001 and p < 0.005, respectively), while none was detected in the BCS group ( p = 0.09). The mean rollback of PCR was − 1.2 mm, BCR was − 3.3 mm and BCS was − 12.0 mm. The mean rollback of all three groups was similar to measurements reported from previous fluoroscopic historical control data. Our findings indicate that tibiofemoral AP translation during knee flexion can be assessed on an active flexion lateral knee radiograph and provide additional information that is not available from a routine lateral radiograph.