Radiological characteristics of the knee joint in nail patella syndrome
2016
Aim Nail patella syndrome (NPS) is a skeletal dysplasia with patellofemoral
dysfunction as a key symptom. We present the first in-depth radiological
evaluation of the knee in a large series of NPS patients and describe
the typical malformations. Patients and Methods Conventional radiological examination of 95 skeletally mature
patients with NPS was performed. Patellar morphology was classified
according to the Wiberg classification as modified by Baumgartl
and Ficat criteria, and trochlear shape was classified according
to the Dejour classification. Results Patellar aplasia was present in 4/90 (4%), and patellar hypoplasia
in 77/90 (86%) of patients. The prevailing patellar shapes were
type III, type IV and Hunter’s cap. No patellar shape genotype-phenotype
association could be found. The malformations of the distal femur
comprised shortening of the lateral femoral condyle in 46 out of
84 patients (55%), with a prominent anterior surface of the lateral
femoral condyle in 47 out of 84 patients (56%) and a flat anterior
surface of the medial femoral condyle in 78 out of 85 patients (92%).
The trochlea was type A1 according to the Dejour classification
in 79 out of 85 patients (93%). Conclusion An easily recognisable characteristic quartet of malformations
consisting of patellar aplasiaor hypoplasia and the malformations
of the distal femur was found in 22 out of 81 patients (27%), with
the majority displaying at least three malformations. Take home message: The distinct malformations of the knee in
nail patella syndrome are easily recognisable on conventional radiographs
and lead to the correct interpretation of the aberrant morphology
which is essential in the treatment of these patellofemoral disorders. Cite this article: Bone Joint J 2016;98-B:483–9.
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