Total Knee Arthroplasty in Severe Valgus Deformity in a Patient with Achondroplasia

The authors present the results of total knee replacement in a 66-year-old woman with achondroplasia. The condition was diagnosed on the basis of clinical and radiographic findings; molecular genetic examination confirmed that the patient was heterozygous for the G1138A mutation responsible for substitution of an arginine for a glycine residue at position 380 (G380R). The patient presented with an unusual finding of severe fixed 20-degree valgus deformity, so far not published, which did not conform with the clinical features of achondroplasia. The authors presumed that the deformity had developed due to asymmetric growth of the distal femoral diaphysis resulting in a hypoplastic lateral femoral condyle and, consequently, valgus deformity. They put emphasis on thorough pre-operative radiography in order to define the size of components according to the templates, and on measurement of the valgus angle and femoral mechanical axis. They also drew attention to the problem of an extra-articular tibial alignment guide and recommended the use of its alternative or computer navigation. The surgery restored the mechanical axis, range of motion and stability of the knee, relieved pain and improved walking, which afforded a better quality of life for the patient.