Accuracy of three dimensional-planned patient-specific instrumentation in femoral and tibial rotational osteotomy for patellofemoral instability

PURPOSE
Patellofemoral instability can be caused by tibial or femoral torsional deformity. Established surgical treatment options are rotational osteotomies, but the transfer from pre-operative planning to surgical execution can be challenging. Patient-specific instruments (PSI) are proofed to be helpful tools in realignment surgery. However, accuracy of PSI in femoral and tibial rotational osteotomies remains still unknown. Goal of the present study was to evaluate the accuracy of PSI in femoral and tibial rotational osteotomies in a patient population suffering from patellofemoral instability.

METHODS
All patients that underwent femoral or tibial rotational osteotomy using PSI in case of patellofemoral instability from October 2015 until April 2019 in our clinic were included. Twelve knees with twelve supracondylar femoral and seven supratuberositary tibial rotational osteotomies could be included. Accuracy of the correction was assessed using pre- and post-operative CT scans based on conventional measurements and, in 3D, based on 3D bone models of the respective patients.

RESULTS
CT measurements revealed an absolute difference between planned and achieved rotation of 4.8° ± 3.1° for femoral and 7.9° ± 3.7° for tibial rotational osteotomies without significant difference (p = 0.069). Regarding 3D assessment, a significant difference could be observed for the residual error between femoral and tibial rotational osteotomies in the 3D angle (p = 0.014) with a higher accuracy for the femoral side.