A proposed modification to the Kellgren and Lawrence classification for knee osteoarthritis using a compartment-specific approach.

PURPOSE: Since Kellgren and Lawrence (KL) originally classified knee osteoarthritis, several authors have reported varying levels of reliability and a lack of uniformity in the use of this classification system. We propose several modifications to the KL classification including the use of a compartment-specific approach that we hypothesize will lead to a better understanding of knee OA while maintaining an adequate interobserver and intraobserver reliability.

METHODS: We propose the addition of the lateral and skyline-view radiographs to the standard anteroposterior (AP) and lateral projections in the evaluation. Also suggest a more precise definition of the evaluated parameters; the addition of the subchondral cancellous bone as parameter of evaluation; and the assessment of medial tibiofemoral compartment (MTFC), lateral tibiofemoral compartment (LTFC) and patellofemoral compartment (PFC) separately resulting in a compartment-specific KL staging score rather than a single overall KL score. Six evaluators (two knee surgeons, two radiologists and two knee fellows) used the modified KL classification to classify 230 randomly selected knees on two separate occasions. Reliabilities were assessed by calculating Krippendorff's ⍺ coefficients.

RESULTS: Two hundred and ten knees were included for final evaluation and analyses (53% left knees; 65% females; mean age 56 years old). Average interobserver reliability was moderate for all compartments (0.51 for the MTFC; 0.51 for the LTFC; and 0.56 for the PFC). Average intraobserver reliability was substantial for all compartments (0.63 for the MTFC; 0.65 for the LTFC; and 0.7 for the PFC). Experienced evaluators showed a higher intraobserver reliability than less-experienced evaluators.

CONCLUSIONS: A modified compartment-specific KL classification enables a practical and detailed description of knee OA involvement and demonstrates acceptable interobserver and intraobserver reliability. Level of Evidence: Level III.