The mechanical alignment (MA) technique has been described as a ‘systematic’ technique, that standardises the approach to every TKR surgery, without considering the native knee alignment or individual differences in anatomy1. It is biomechanically sound because it reduces the potential for unbalanced loads on the prosthesis, and so reduces the risk of accelerated wear and loosening1.
MA was introduced at the dawn of knee arthroplasty, when poor quality polyethylene, and rudimentary cementing techniques and instrumentation, made it necessary to achieve acceptable implant survivorship1.
Since then much has changed: the introduction of more anatomic implant designs, improved polyethylene, enhanced instrumentation and surgery-assisting technologies, and modern cement/cementing techniques allow precise and reproducible implantation and improved fixation1.
Despite these improvements, and the excellent survivorship provided by MA, clinical results have been relatively poor when compared with those of THR1. Rates of dissatisfaction and residual symptoms like pain, instability or stiffness have been reported at approximately 15% and 50%, respectively1. Patients rarely perceive their MA TKR feels ‘normal’, and forgotten joints scores are low compared to THR/PKR2,3.
The observation that advancements in knee design and surgical precision have not completely resolved these issues, has shone a light on the inherent technical limitations with the MA philosophy, which creates a non-physiological implant position by altering the native anatomy, physiological ligament balance and kinematics1.
The solution could be a patient-specific and personalised surgical technique that aims to create a more physiological prosthetic knee by restoring the individual native anatomy, physiological soft-tissue balance, and kinematics1. This technique, composed of a series of well-defined steps, is a true resurfacing, where the bone cuts are anatomical rather than mechanical, and soft-tissue release is largely avoided1.
So far, the results for this technique have been promising, with early reports of low complication rates, and high function and patient satisfaction1. Patients also appear to be at less risk of developing anterior knee pain, and are three times more likely to rate their TKR as feeling ‘normal’1,4.
According to the authors, the next challenge is to verify the suitability of this technique for all patient anatomies/determine which anatomies or biomechanics should not be ‘fully restored’ with this technique1.
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