Inferior Patella Dislocation due to Impaction in the Femoral
Acute inferior dislocation of the patella, also known as central intra-articular dislocation, is a rare presentation in orthopedics which having been first reported by Midelfart in 1887. The patella is stabilized passively by ligaments and bony structures and dynamically by the extensor mechanism. There are 2 types of inferior patella dislocation, type I which occurs in young patients, and type II which affects the elderly population. This case demonstrates a rare subtype of an inferior patellar dislocation in the femoral trochlea with an intact extensor mechanism, in which osteophyte fracture had aided a closed reduction.

A 92-year-old lady with a background of dementia tripped and fell in her nursing home landing directly on her left flexed knee. She struggled to move her knee and presented after 1 day. On examination, the left knee was held in 85° of flexion with an abnormal knee contour. The knee was swollen, there was bruising over the inferior pole of the patella, and the patellar tendon had a lax feel. Radiographs demonstrated that the upper pole of the patella was impacted in the femoral trochlea with a fracture of a superior pole osteophyte. There was no rotational malalignment of the patella in any plane. Rupture of the extensor mechanism was suspected but there was no palpable gap in the quadriceps tendon. A computer tomography scan confirmed the diagnosis of inferior patella dislocation with no associated fracture. Following opioid analgesia, the patella was reduced with hyperflexion of the knee and superior pressure on the superior pole of the patella. Patella reduction was confirmed clinically and with plain radiographs which also showed evidence of patella-femoral degenerative disease. Ultrasound examination showed an intact extensor mechanism. The knee was rested in a removable extension splint, and full weight-bearing was allowed after 24 h when the pain is controlled. The splint was retained for 3 weeks, and at 6 weeks, the patient had regained her baseline range of knee movement.