Hello - It seems that the primary injury is to the buttock, which means gluteal inhibition. This makes it difficult to cant (lift) the hemi-pelvis on the uninjured side in order to lift the good leg and so allow it to swing through. It is likely that your patient is therefore leaning his trunk towards the injured side to "passively" lift the pelvis. If this is done repetatively when walking mid-back pain could follow. Try using a walking stick on the uninjured side. Driver-Jowitt