Introduction: Patient-specific instruments (PSI) have been shown to be a good solution in getting accurate bone cuts in total knee arthroplasty (TKA) in many studies. However, the need for an extra CT/MRI makes the existing PSI method costly and unsafe. X-ray-based PSI can solve these problems, if proven to be accurate. The purpose of this study was to introduce a novel method to measure the performance of X-ray to 3D-based PSI (X3DPSI ® ) in achieving planned bone cuts by comparing with conventional instruments (CI).
Materials and methods: This was a prospective study of a total of ten patients undergoing TKA surgery. Preoperative full length lower limb scanogram was done with specialized calibration strap-on marker to develop X3DPSI ® which was used intraoperatively for the placement of guiding pins for the cutting jig. Similarly, intraoperative guide pins were placed using CI also. Calibrated intraoperative X-ray images, in AP and LAT view, were taken while the cutting-block guiding pins were placed on the distal femur and proximal tibia. These X-ray images were used to calculate the cutting plane alignments for femur and tibia and to simulate the postoperative hip-knee-ankle (HKA) angle and MAD (mechanical axis deviation), in a virtual Tabplan3D environment for both the methods.
Results: The results showed that there was a significant difference between the two methods in terms of femoral cutting plane angles and in terms of the HKA angles and MAD. There was no significant difference in the tibial cutting plane angles in the coronal plane.
Conclusion: The mechanical axis alignment achieved based on the virtual cuts made using the X3DPSI ® was significantly better than the alignment achieved based on the cuts made using the CI, in terms of both HKA and MAD. This novel method of X-ray-based PSI is a low-cost alternative to CT/MRI-based PSI if found to be accurate in future planned studies.
Keywords: PSI; TKR; X-ray based PSI; Xray-based 3D reconstruction.
© Indian Orthopaedics Association 2022.