Wear patterns in anteromedial osteoarthritis of the knee evaluated with CT-arthrography

To analyze the value of CT-arthrography imaging in the diagnosis of knee osteoarthritis and to facilitate the selection of partial versus total knee replacement.

A retrospective study of 100 patients that had either medial unicompartmental knee replacement (UKR) (N=50) or total knee replacement (TKR) (N=50). One observer measured lower limb mechanical alignment and osteoarthritis patterns of the knee in each compartment with radiographs, CT-arthrography and full leg standing radiographs.

All patients had Kellgren-Lawrence grade IV osteoarthritis of the medial femorotibial joint with a mean (SD) varus alignment of the lower limb (172° (3.5°) HKA-angle). Zone mechanical axis distribution showed strong correlation with HKA-axis. Arthritis patterns were different for patients selected for UKR or TKR. UKR patients had anteromedial osteoarthritis and wear of the medial facet of the patella in contrast to TKR patients who had medial osteoarthritis associated with diffuse or lateral patellofemoral wear and wear of the central or posterior zones of the lateral compartment. Medial facet wear of the patella is related to more important varus alignment of the lower limb (Kennedy zone 0 and 1).

CT-arthrography imaging can show lesions that are not visible on plain or stress radiographs because of central or posterior localization with surrounding intact cartilage. Patients who develop tri-compartmental osteoarthritis despite varus alignment have probably other risk factors than their mechanical alignment and should be considered candidates for TKR.