Unlocking a locked knee by ultrasound guided anesthetic injection

Twenty-three-year old male patient with a background of mild cerebral palsy (with limited effect on mobility) presented with 36 hours history of pain on the lateral aspect of his left knee. On examination his knee was locked and there was no associated history of trauma. A detailed MRI scan required in extension and unlocked leg to elucidate the cause. This was achieved by administration of local anesthetic under ultrasound guidance to the lateral aspect of the knee with successful results. This case is important as it looks at minimally invasive management of the acutely locked knee prior to more detailed imaging. Pseudolocking of the knee is a well-known cause of knee locking. Performing a magnetic resonance imaging (MRI) scan to diagnose cases of pseudolocking can prevent unnecessary intervention such as arthroscopy. In our case, the orthopedic team was reluctant to take the patient to theatre without more detailed imaging, given his medical history. There are very few case reports in the literature which address this issue and there is no case in the literature using this technique in cerebral palsy with muscle spasm.