Radial nerve paralysis or avulsion of the nerves in the brachial plexus, or possibly a nerve root problem at the spinal cord level considering the possible severity of the forces involved in the injury. Usually most of the progress is made towards recovery in the first 6 weeks or so following injury so it seems unlikely to me that you have much hope of increased nerve function at this point.

Another complicating factor in these cases is muscle fibrosis. When a muscle does not get signals from the nerves it doesn't flex. After awhile, it can't flex anymore and just gets fibrosed in one position. Once this happens the leg is not functional even if the nerve function does return.