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Case Reports in Orthopedics
Volume 2015, Article ID 328386, 4 pages
Case Report

Patella Dislocation with Vertical Axis Rotation: The “Dorsal Fin” Patella

1Trauma and Orthopaedic Department, Addenbrooke’s Hospital, Cambridge University Hospitals NHS Foundation Trust, Hill Road, Cambridge CB2 0QQ, UK
2University of Cambridge School of Clinical Medicine, UK

Received 6 January 2015; Revised 9 March 2015; Accepted 16 March 2015

Academic Editor: John Nyland

Copyright © 2015 David Gamble et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A 44-year-old woman presented following minor trauma to her right knee. While dancing she externally rotated around a planted foot and felt sudden pain in her right knee. She presented with her knee locked in extension with a “dorsal fin” appearance of the soft tissues tented over the patella. This was diagnosed as a rare case of an intraarticular patella dislocation, which was rotated 90 degrees about the vertical axis. Closed reduction in the emergency room was unsuccessful but was achieved in theatre under general anaesthetic with muscle relaxation. Postreduction arthroscopy demonstrated that no osteochondral or soft tissue damage to the knee had been sustained. In patients presenting with a knee locked in extension with tenting of skin over the patella (the “dorsal fin” appearance), intra-articular patella dislocation should be suspected. Attempts to reduce vertical patella dislocations under sedation with excessive force or repeatedly without success should be avoided to prevent unnecessary damage to the patellofemoral joint. In this clinical situation we recommend closed reduction under general anaesthetic followed by immediate knee arthroscopy under the same anaesthetic to ensure that there is no chondral damage to the patella or femoral trochlea and to rule out an osteochondral fracture.