Loss of forearm rotation into the palm up position called supination is common after repair of a distal bicep rupture. But it’s not normal in the sense that you don’t have full motion or strength when you need it.
Surgeons aren’t sure why this happens. When they look at all the various procedures and analyze each variable, they come up with no reason for this loss of strength. It doesn’t happen to everyone, so there may be an anatomical or biomechanical explanation. It seems to occur whether the surgeon uses a one-incision versus a two-incision approach. So it’s not likely caused by that factor.
There was some question about whether or not it occurs because the tendon doesn’t always get reattached at the same place where it pulls away from the bone. That spot is called the footprint. But arthroscopic surgery from the posterior approach (coming in from behind the elbow) allows for complete restoration of the footprint, so that’s not it.
Anything that disrupts the surgical site (e.g., using the arm too much too soon) should affect motion created by the tendon in all directions If forearm supination is affected, then other motions controlled by the biceps tendon (such as elbow flexion) should also be compromised. But that doesn’t seem to be the case.
More study is needed to get to the bottom of this mystery. For now, when this happens, patients are encouraged to see a physical therapist who can help you get your full motion, strength, and function back. It shouldn’t take too long. In addition to some hands on approaches to restore motion, the therapist can give you a home program to round out the rest.