What is the Correlation between Coronal Plane Alignment Measured on Preoperative and Postoperative Weightbearing Radiographs and Intraoperative Navigation when stress is applied to the knee?

This study examines the correlation between the weight-bearing (WB) long leg radiograph (LLR) derived hip-knee-ankle angle (HKAA) and intra-operative supine computer-assisted surgery (CAS) derived HKAA measurements at the beginning and end of total knee arthroplasty (TKA). The primary aim of the study was to determine if weight-bearing alignment could be mimicked or inferred based on intra-operative alignment findings. We conducted a prospective analysis from a cohort of 129 TKAs undergoing a CAS TKA at a single centre by a single surgeon. The HKAA was recorded using the CAS navigation system immediately post registration of navigation data and after implantation of the prosthesis. The intra-operative HKAA was recorded in both the supine 'resting' position of the knee and also whilst the knee was manipulated in an effort to replicate the patient's weight-bearing alignment. These measurements were compared to the HKAA recorded on pre- and post-operative WB LLRs. There was a strong correlation between the pre-operative WB LLR HKAA and the intra-operative pre-implant CAS derived stressed HKAA (R= 0.946). However, there was no correlation between the post-operative WB LLR HKAA and the post-implant insertion HKAA as measured intra-operatively via CAS for either a 'resting' or 'stressed' position of the operated knee (R = 0.165 and R = 0.041, respectively). Thus, the interpretation of intra-operative alignment data is potentially problematic. Despite technological advances in the development and utilization of computer navigation and robotics in arthroplasty to help obtain the optimal alignment, it would seem apparent from our study this alignment does not correlate to upright stance post-operatively. Surgeons should apply caution to the strength of assumptions they place on intra-operative coronal plane alignment findings.