Locked knee from superior dislocation of the patella-diagnosis and management of a rare injury

Abstract

Knee locking is often caused by a torn meniscus or loose body. A rare cause of knee locking is a superior dislocation of the patella following trauma with less than 20 reported cases in the English literature. An unusual case of a locked knee secondary to interlocking osteophytes between the medial femoral condyle and the inferior pole of the patella without any history of trauma is presented.

A rare patella anatomical abnormality causing locking in an adolescent girl

“…The patella has been implicated in causing locking when superiorly dislocated, of which there have been less than 20 reported cases since 1956 [9]. Min et al also described patellar dislocation caused by a large lateral gutter lipoma in a 19-year-old male [8].…”

Superior Patellar Dislocation Misdiagnosed as Patellar Tendon Rupture: The Value of Ultrasonography

“…Most patients with this condition had preexisting degenerative joint [1–23]. Osteophytes at the inferior aspect of patella and at the anterior aspect of medial condyle of femur are the identified cause of the locked knee in extension [7, 8, 12, 18, 19, 23]. The usual mechanism of injury is forceful contraction of quadriceps tendon with or without a posteriorly directed force [9].…”

“…A key advantage of ultrasound over MRI is the ability to image tendons and bones dynamically and being useful for evaluating the reduction immediately in emergency department [4, 18]. Furthermore, in some cases, imaging is needed to look for any associated intra-articular damage such as osteophytes, osteochondral injury, or ligament tears.…”

Locked Superior Patellar Dislocation

“…Superior patellar dislocations are extremely rare causes of knee locking, with fewer than 20 cases reported in the English literature. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The causes of these locked dislocations have varied, from traumatic 6 to atraumatic. 1,4,5,8 For patients who dislocate and lock atraumatically, the postulated mechanisms have ranged from hyperextention 8 to eccentric muscle contraction 13 to knee subluxation associated with vastus tear.…”