Unicompartmental Osteoarthritis of the Knee: Diagnosis and Treatment of Malalignment

Osteoarthritis (OA) of the knee is a common medical condition that is often seen in general practice and causes considerable pain and immobility. In the United States, approximately 6% of the population aged 30 years and older and 12% of the population aged 65 years and older suffer from knee osteoarthritis.1 In addition to the consequences for the patient, osteoarthritis forms a considerable burden for society because of its chronic course and the high costs of interventions.2 In the Netherlands 1% of the total medical costs is spent on osteoarthritis.3 Osteoarthritis of the entire knee is distinguished from osteoarthritis of one compartment, which is generally caused by a mechanical problem.4 The mechanical axis of a straight leg is defined as a line passing from the centre of the hip, through the centre of the knee to the centre of the ankle.5 Patients with osteoarthritis of the medial compartment often have varus alignment, and the mechanical axis and load bearing pass through the medial compartment (=genu varum arthroticum). Patients with osteoarthritis of the lateral compartment often have a valgus alignment, and the mechanical axis and load bearing pass through the lateral compartment (genu valgum arthroticum). Axial malalignment (varus or valgus alignment) increases the risk for progression of knee osteoarthritis and predicts a decline in physical function.6 Besides the usual treatment for osteoarthritis, specific interventions for unicompartmental knee osteoarthritis include conservative interventions e.g. (knee braces and foot/ ankle orthoses) as well as surgical treatments (e.g. a correction osteotomy to reduce load of the osteoarthritic compartment of the knee).7-15 The anterior-posterior whole leg radiograph (WLR) is considered the gold standard for determining axial alignment and serves as the basis for planning a knee osteotomy in patients with osteoarthritis. In many studies the WLR has been made in standing position, whereas others have preferred the supine position.13,14,16,17