Negative muscle pennation angle as a sign of massive musculotendinous retraction after tendon tear: paradoxical function of the vastus lateralis muscle.

In the presented case, an isolated vastus lateralis tendon tear resulted in a negative pennation angle of the distal muscle fibers acting paradoxical to the physiological direction of the proximal muscle fibers. This observation makes the value of an in situ repair of a far retracted tendon tear with interposition of a graft questionable and emphasizes early over late anatomic surgical restoration of the muscle architecture after tendon tears.