Small patella syndrome (SPS) is a very rare benign bone dysplasia affecting skeletal structures of the lower limb and the pelvis.

A very rare benign bone dysplasia affecting skeletal structures of the lower limb and the pelvis. Less than 50 patients have been reported worldwide. The main clinical features include patellar aplasia or hypoplasia, associated with absent, delayed or irregular ossification of the ischiopubic junctions and/or the infra-acetabular axe-cut notches. Additional features found in the majority of reported patients include femur and foot anomalies. Craniofacial anomalies have been reported occasionally. Inherited in an autosomal dominant manner and is caused by mutations in the human TBX4 gene (chromosome 17q22). TBX4 mutations account for familial cases with a distinctive facial appearance and those without facial features.