The phantom osteotomy is here: an algorithm for managing the joint line convergence angle in osteotomies around the...

Realignment osteotomy around the knee is currently experiencing significant growth in the UK and further afield. Osteotomy can be utilised to treat a wide range of conditions, but is most often considered in patients presenting with unicompartmental knee arthritis with coronal plane mechanical malalignment, who have failed conservative treatment. This article reviews management strategies to improve accuracy in knee osteotomy surgery, with a specific focus on handling an elevated joint line convergence angle (JLCA). Increased JLCA has historically resulted in less predictable correction outcomes after coronal plane realignment osteotomy, and this has been referred to as the 'soft tissue lottery' after such surgery. A fresh approach is presented to understanding and classifying knee varus, and how this influences joint loading and consequent implications to the JLCA. The valgus knee is similarly considered. Myths regarding the 'tipping point' (with respect to the weight bearing axis of the knee) are dispelled, and an algorithm is presented for handling an elevated JLCA, predicated on adjusting osteotomy targets for the portion of the elevation caused by joint space opening, rather than from joint space loss, with clinical examples. The theory and practice of using 'phantom' corrections within the joint to partially correct the JLCA when preoperatively planning using digitally acquired longleg radiographs is presented. Guidelines are also provided for parameters to safeguard outcomes in osteotomy surgery with respect to correction targets and philosophies around surgical planning and execution.