gms | German Medical Science

Objective: High tibial osteotomy (HTO) is commonly used to treat moderate osteoarthritis (OA) of the medial compartment of the knee. Published techniques for medial opening wedge HTO recommend leaving the lateral cortex intact, so as to provide rotational stability for the construct. However, intraoperative lateral cortex fractures can occur, and the stability of the construct might be compromised. The aim of this study was to determine how rotational malalignment of the tibial segment distal to the osteotomy site would affect intraarticular contact pressure distribution in the knee and ankle joints.

Method: A medial, L-shaped opening wedge high tibial osteotomy was performed on eight human lower body specimens. A previously developed stainless-steel device with integrated load cell was used to axially load the leg. Pressure-sensitive sensors were used to measure intraarticular contact pressures. Intraoperative changes in alignment were monitored in real time using computer navigation. Baseline measurements were taken for each leg in its native alignment. An axial loading force was applied to the leg in the caudal-craneal direction and gradually ramped up from 0 to 550 N. Intraarticular contact pressure (kg) and contact area (mm²) data were collected.

Multiple linear regression models were constructed to estimate changes in contact pressure and contact surface area in the medial and lateral compartments of the knee and in the ankle, in response to 15º malrotation of the distal tibial fragment after 10º and 15º medial opening wedge HTO.

Results and conclusion: Moderate-to-large alignment changes after medial opening wedge HTO resulted in a significant shift in intraarticular contact pressures from the medial compartment of the knee towards the lateral compartment (P<0.05). However, fixation of the distal tibial segment at 15º of internal rotation neutralized this intended beneficial effect (P<0.05). In the ankle, internal rotation of the distal tibia caused a significant reduction in contact pressures and tibiotalar contact area (P<0.05).

This study sheds light on a potential and important complication of HTO procedures. Should a cortical hinge fracture occur, the surgeon may lack the ability of controlling the rotation of the bone fragments. As our results show, malrotation of the distal tibial fragment negates the intended effect of offloading the diseased compartment of the knee, as the contact pressures remained similar to the native knee. Furthermore, malrotation led to abnormal ankle contact pressures, which could help explain postoperative ankle symptoms.