A 17-year-old left-handed girl was referred to our institution with an inability to extend the fingers and thumb and weakness of wrist extension. This problem developed immediately after an elbow arthroscopy for loose body removal done 4 months earlier at an outside facility. She was otherwise healthy. Examination of the left upper extremity revealed 5/5 strength of the brachioradialis and the extensor carpi radialis longus muscles. The following muscles had 0/5 strength: extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum communis, extensor pollicis longus, extensor indicis proprius, abductor pollicis longus, extensor digiti minimi, and extensor pollicis brevis.