The anatomical safe zone for medial opening oblique wedge high tibial osteotomy.

INTRODUCTION The end of medial opening oblique wedge high tibial osteotomy (HTO) points into a narrow area between the articular cartilage of the posterolateral proximal tibia and proximal tibiofibular joint (PTFJ) at the tibial site, which is an anatomical safe zone (ASZ) for osteotomy. We studied the ASZ and its relation to the fibular tip, including the level of posterior cruciate ligament (PCL) insertion, to avoid penetration into the knee and PTFJ, and PCL injury by osteotomy. METHODS Ten pairs of embalmed cadaveric legs were disarticulated at the knee joint and then examined. Soft tissues at the proximal tibia were removed. The posterior capsule of the PTFJ was incised to identify the articular cartilage of the PTFJ at the tibial site. The height of the fibular tip and the thickness of the ASZ were measured and calculated to determine the relationship between the ASZ and fibular tip. The level of PCL insertion was measured from the posterior articular surface of the proximal tibia to the distal attachment of the PCL. RESULTS The average height of the fibular tip and the thickness of the ASZ were 5.43 ± 1.53 mm and 4.12 ± 1.60 mm, respectively. On average, the fibular tip was 1.31 ± 1.28 mm higher than the ASZ, and the level of PCL insertion was 10.10 ± 1.88 mm. CONCLUSION To ensure safety during medial opening oblique wedge HTO, the end of osteotomy should point accurately into the ASZ at a level just below the fibular tip as reference. Proximal osteotomy thickness should not be less than 10 mm at the level of PCL insertion.