Superior Dislocation of Patella Without Osteophytes – A Rare Case

A 66-year-old woman sustained a “sprain” of her right knee while walking inside a supermarket. She complained of sudden knee pain and was unable to walk or move her right knee. She attended Accident and Emergency Department and was admitted into Orthopaedic ward with a diagnosis of “patella tendon rupture”. Physical examination on admission showed swelling, bruise and local tenderness just below the inferior pole of upward migrated patella bone. The extensor mechanism was loss. Passive knee motion was 0-20 degree only, limited by pain. Plain radiographs showed superior migrated patella. Beside ultrasound showed intact patella tendon. Closed reduction without anaesthesia was done successfully with an immediate regain of knee motion to 0-80 degree. Post-reduction x ray showed reduced patella with no fracture. Follow-up at 6 weeks showed normal active motion knee motion with full quadriceps power. Superior patellar dislocation is a rare condition. At 2016, only 23 cases were reported in English literature. It should be considered as a differential diagnosis of patella tendon rupture or locked knee. Pathognomonic radiographic features include proximal displaced patella with superior pole tilted away from femur and a dimple in skin. Ultrasonography may be used to exclude patella tendon rupture, which is a more common diagnosis in elderly. Most superior dislocations are due to interlocking patella and trochlear osteophyte. This may the second reported case of superior dislocation of patella without osteophytes. Closed reduction may be done without general anaesthesia. After reduction of superior patella dislocation, the functional recovery is rapid.