Finding the Optimal Aim of Correction in Opening Wedge High Tibial Osteotomy Using 3D Printed Patient-specific Instrumentation (PSI). An RCT Comparing Correction Aimed at 62% Versus 55%.

HTO should play a major role in modern treatment algorithms for knee overload and osteoarthritis. By transferring load from the failing/osteoarthritic compartment of the knee to a healthier compartment, HTO can delay or stop the progression of osteoarthritis at an early stage. This can remove pain and increase knee function, making return to work, activities and sport possible. HTO may delay or avoid the need for total knee replacement for >10 years for at least 80% of patients.

The optimal target for the postoperative mechanical axis of the leg is not yet clarified. Both under- and overcorrection can lead to unfavourable results. The classical Fusjisawa´s point of 62%, or approximately 3 deg. of valgus, is still often used as the optimal target, and studies show good clinical results and longevity. With an often accepted accuracy of +/- 3 deg. with conventional methods, the accepted postoperative range of valgus will be from 0 deg. to 6 deg. But the optimal range is possibly much narrower. Recent studies suggest a narrower range and less overcorrection.

3D-printed patient specific instrumentation (PSI) is based on CT of the individual patient´s knee, data simulation of the planned correction and subsequent 3D printed guides for each patient. The PSI design varies, but involves a positioning guide fitting only in position one the proximal tibia, a cutting guidance and a wedge opening guide. PSI seem to improve accuracy to the level of approximately +/- 1 deg. from the preplanned correction and leads to fewer unacceptable outliers compared to the conventional methods available. Improved accuracy has not shown to yield better clinical results.

In the future the target axis should possibly be individualized, based on the pathology treated, gait analyses and data simulations.

Modern gait analysis using wearable accelerator sensors, often referred to as inertial measurement units (IMUs) is rapidly evolving. By coupling individualized and accurate osteotomy with gait analysis using wearable sensors, one could better predict and understand how to normalise each individual patients´ gait pattern and possibly improve patient satisfaction and function after surgery.