The Deep Fascia of the Forearm and the Ulnar Nerve: An Anatomical Study

Introduction A reoperation for a cubital tunnel syndrome is not uncommon. Patients often complain of sensorimotor symptoms in the ulnar nerve distribution after their primary surgery. The documented etiologies for such a phenomenon include a "new" kinking of the distal ulnar nerve and a "new" compression of the ulnar nerve by the fascial septum in between or tendinous bands over the muscles of the forearm. The deep fascial plane along which the ulnar nerve travels in the forearm has had scant attention. We present an anatomical study to provide a better understanding of such etiologies to aid physicians in performing successful primary ulnar nerve release that does not lead to risky reoperations and ultimately yields improved patient satisfaction. Materials and methods The forearms of 12 fresh frozen cadavers (24 arms) underwent dissection, during which the fascial relationships between the ulnar nerve and muscles of the anterior compartment were explored with a blunt technique. The relationship between the fascial planes and the ulnar nerve was quantitatively and qualitatively documented. The ranges of motion of the elbow were also observed for any potential compression points on the nerve during the movement. Results In all specimens (n = 24), the ulnar nerve entered the forearm between the humeral and ulnar heads of the flexor carpi ulnaris, after which it routed deep to a deep fascia between the anterior surface of the flexor carpi ulnaris and the posterior surface of the flexor digitorum superficialis. Ulnar nerve branches to the flexor carpi ulnaris pierced this fascial septum while en route to the posterior surface of the muscle. Medially, the branches to the flexor digitorum profundus also pierced this fascial plane. In most arms, the fascia became thinner near the junction between the proximal two-thirds and distal one-third of the forearm. On no side was the ulnar nerve found to be grossly compressed by this deep fascia. However, with the extension of the elbow, a degree of angulation of the proximal ulnar nerve was observed due to its compact connection with the deep fascia. Conclusion Our study revealed that there is an intimate relationship between the ulnar nerve and the deep fascia of the forearm. Since the ulnar branches to the overlying flexor carpi ulnaris pierce this deep structure, a care should be given to its anatomical course during surgery in this region to prevent denervation of the muscle.