Congenital dislocation of the knee (CDK) is rare, and clinical semiology at birth is not always suitably analyzed. Existing classifications fail to guide treatment. The aim of the present study was to develop a CDK classification for the neonatal period.

A classification based on neonatal severity of clinical signs is easy to implement on simple criteria.

Fifty-one CDKs (40 patients) seen neonatally were included. Three types could be distinguished in terms of reduction and stability: type I, easily reducible CDK, with reduction snap when the femoral condyles pass in flexion, remaining stable in flexion; type II, “recalcitrant” dislocation, reducible by posteroanterior “piston” but unstable, with iterative dislocation once posteroanterior pressure on the condyles is relaxed; and type III, irreducible. The number of anterior skin grooves, global range of motion, flexion deficit and reduction stability were noted for each type.

Mean age at first consultation was 5.6 days (range: 0–30). CDK was type I, II and III in respectively 28, 16 and 7 cases. Number of skin grooves, flexion and baseline range of motion were greater in type I than types II and III.

The present neonatal clinical classification is original, logical and simple. It may be useful for prognosis and guiding treatment.

IV, single-center retrospective series.