A 56-year-old woman presents to the emergency department with acute pain in her left knee. The unbearable pain arose acutely when she, lying on a couch, received a massage of her legs. Since then she has been unable to move or put weight on the knee. The patient is not known to have knee complaints. On physical examination, we saw a patient in great pain. We observed swelling on the craniolateral side of the left knee, without hydrops or haemarthrosis. Movement examination of the knee was not possible because of the severe pain.
An X-ray was taken that showed a striking picture: there was a patellar disposition, in which the patella was hooked behind the upper edge of the trochlea. The mechanism behind this most likely relies on osteophyte formation at both the patella and the trochlea (most pronounced in Figure 1c). Hyperextension of the knee in combination with manipulation of the patella in the patient, who was very relaxed due to the massage, probably resulted in the hooking.
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