title: Radiological characteristics of the knee joint in nail patella syndrome.
abstract: OBJECTIVE
  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.
  
  
  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%).
  
  
  CONCLUSIONS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Canisius-Wilhelmina Ziekenhuis, Department of Orthopaedic Surgery, P.O. Box 9015, 6500 GS Nijmegen, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Tigchelaar
authors.affiliation: Radboud University Medical Center, Department of Radiology P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: J de
authors.initials: Jd
authors.lastname: Rooy
authors.affiliation: Radboud University Medical Center, Department of Radiology P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Hannink
authors.affiliation: Canisius-Wilhelmina Ziekenhuis, Department of Orthopaedic Surgery, P.O. Box 9015, 6500 GS Nijmegen, The Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Koëter
authors.affiliation: Radboud University Medical Center, Department of Radiology P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: van Kampen
authors.affiliation: Radboud University Medical Center, Department of Radiology P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Bongers
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001175:Arthrography / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009261:Nail-Patella Syndrome / Q000000981:diagnostic imaging*; D010329:Patella / Q000000981:diagnostic imaging; D011446:Prospective Studies; D012720:Severity of Illness Index; D055815:Young Adult
keywords: Nail patella syndrome; characteristics; knee; patella; radiology