DORSAL ULNAR SENSORY NERVE LACERATION

The complete transection of the dorsal ulnar sensory nerve remains a challenging problem for hand surgeons and their patients, and outcomes are typically worse than those seen after other upper extremity peripheral nerve lacerations. Despite advances in microsurgical nerve repair, repairs often leave patients with dorsal sensory deficits and painful neuromas, especially in adults.^1-5

Pathophysiology

• When a nerve is transected, the distal segment of the nerve undergoes Wallerian degeneration.
  • Distal axons degenerate secondary to calcium-activated calpain enzymes;^6,7 degenerating myelin is phagocytized by Schwann cells and macrophages. In the proximal stump, degeneration also occurs in a proximal direction for a distance of ≥1 nodes of Ranvier. In the distal segment, Schwann cells proliferate forming the bands of Bunger after nerve transection.
  • In the proximal segment, the axon cone develops and grows distally at a rate of 1-2mm/day (1 inch/mo) after the cut ends of the nerve have been approximated and realigned by microsurgical repair.
• Dorsal ulnar sensory nerve lacerations are usually classified as complete or partial; however, partial lacerations of this same nerve are uncommon.
• Axonotomesis: nerve is subjected to severe crush, stretch, or blast injury; axon can be severed with distal degeneration, while the Schwann cell basil lamina remains intact
• Neuropraxia: nerve is stretched and stops conducting impulses while the neural anatomy remains intact; there is no Wallerian degeneration after this type of stretch injury, and they usually recover without surgical intervention.⁷
• The most likely mechanism causing a dorsal ulnar sensory nerve deficit is a laceration, followed by stretch injuries and contusions.⁸
• Various surgical interventions may also cause a dorsal ulnar sensory nerve laceration through iatrogenic damage, such as arthroscopic repair of the triangular fibrocartilage complex or percutaneous pinning of the ulnar styloid, lunotriquetral joint, or little metacarpal base.^9,10  Performing a mini-dissection while identifying and protecting the involved nerve(s) can mitigate the risk for injury during percutaneous pinning.⁹
• The dorsal ulnar sensory nerve is also at risk during fasciectomies of an abductor digiti mini Dupuytren's cord.

Related Anatomy

• The ulnar nerve is the terminal branch of the medial cord of the brachial plexus. It traverses the axilla with the neurovascular bundle deep to the pectoralis major and minor, and consists of four major branches in the forearm: 1) the motor branch to the flexor digitorum profundus (FDP) for the ring and small fingers, 2) the volar cutaneous branch, 3) the dorsal cutaneous branch, and 4) the nerve of Henle.⁵
• In the hand, the ulnar nerve divides within the Guyon’s canal into the superficial sensory branch and the deep motor branch, creating three distinct topographical zones. Zone I is proximal to the bifurcation of the nerve and contains both motor and sensory fibers, Zone II contains the deep motor branch, and Zone III contains the superficial sensory branch.
  • The superficial sensory branch courses distally in the subcutaneous tissues to branch into a proper digital nerve to the ulnar border of the little finger and a common digital nerve to supply the fourth web space.^5,8
• The dorsal ulnar sensory nerve is composed of nerve fibers and axons covered by connective tissue called epineurium.
• The axon has a cell membrane (axolemma) surrounding a tube of neural cytoplasm (axoplasm).⁷Axons are encased by the endoneurium.
• Axons are grouped in fascicles that are surrounded by the perineurium.¹¹  Perineurium provides a diffusion and conduction barrier between the fascicles.⁷
• In the dorsal ulnar sensory nerve, groups of fascicles are arranged in fascicular groups, defined by the connective tissue called the internal epineurium.  At the level of the fifth MP joint the dorsal ulnar sensory nerve typically contains two fascicular groups while the ulnar digital nerve has three fascicular groups.
• In the distal part of the nerve, there are few connections between the fascicular groups; thus, the internal epineurium provides a surgical plane that can be dissected with microsurgical techniques.¹¹
• The two fascicular groups together compose the dorsal ulnar sensory nerve; external surface of the dorsal ulnar sensory nerve is covered by the external epineurium.
• When the dorsal ulnar sensory nerve is cut, the nerve ends separate producing a functional gap due to fascicular group inherent elasticity.
• There is no loss of nerve tissue, ie, no true defect; therefore, these ends can be repaired without excessive tension even if a few millimeters of neuroma are resected.¹¹
• If there is a long delay between laceration and nerve repair, the functional elastic gap may become more of a true defect because of scarring.
• End-to-end nerve repair is indicated to minimize the sensory deficit and potential neuroma pain.  If there is a true defect, then nerve grafting may be indicated.^12,13
• The dorsal ulnar sensory nerve originates approximately 5 to 6.5 cm proximal to the articular surface of the ulnar head or 8.3 cm proximal to the pisiform. It travels under flexor carpi ulnaris (FCU) muscle and enters the subcutaneous tissue approximately 1.5 cm proximal to the ulnar head. Two to three branches are typically present distal to the wrist and are at risk during wrist arthroscopy.²³

Incidence

• Peripheral nerve injury remains a common injury in civilian life.
• In one report, an estimated 20 million Americans suffer peripheral nerve injuries annually.¹⁴
• Between 1993-2006, there were 3,996 admissions for ulnar nerve lacerations, making them the most common major upper extremity peripheral nerve injury when compared with medial, radial, and brachial plexus injuries; 76.4% of these patients were male, and 59% were in the 18-44 age group.⁴
• Another report showed that 13.4% of wartime nerve injuries were lacerations of the ulnar nerve.¹⁵

Differential Diagnosis

• Complete nerve laceration
• Partial nerve laceration
• Neuropraxia (stretch or crush injury)
• Neuroma-in-continuity

A 32-year-old male amateur hockey player was practicing with his team when he dropped one of his gloves and attempted to pick it up. As he placed his hand on the ice, another player was skating backwards to receive a pass, and since he couldn’t see where he was going, skated over the man’s right hand. The skate left a clean cut across the top of the palm near the head of the metacarpals, and the wound began to severely bleed onto the ice. The man was subsequently taken to the ED, where they examined the injury and noticed that he had lost some sensation in his little finger and fourth web space and difficulty extending his fifth finger. The wound was anesthetized with 1% local, and the wound exploration showed a lacerated dorsal ulnar sensory nerve and a lacerated extensor digiti minimi tendon. The wound was irrigated, debrided, the skin sutured and a dressing and splint applied. The patient saw a hand surgeon who did a microsurgical dorsal ulnar sensory nerve repair and extensor tendon repair in the local ambulatory surgery center the following week.

• Loss of sensory function
• Persistent pain and/or paresthesias
• Dysesthesia 
• Neuroma-in-continuity
• Infection
• Complex regional pain syndrome

• Permanent sensory deficits after nerve repair remain a problem, especially for adults.¹
• Other factors that affect the outcome of dorsal ulnar sensory nerve repair include the age of patient (young patients do better); the level of the laceration (distal lacerations do better); the delay between injury and repair (earlier repairs do better); and the cause of the ulnar nerve laceration (sharp clean cuts do better).^1,7  One study identified patient age as the most important prognostic factor, with younger patients achieving significantly better results than adults.⁵

• The most important reason for identifying and preventing injury to the dorsal ulnar sensory nerve is the avoidance of neuroma for motion and subsequent pain.

New and Cited Articles

1. Pederson, WC. Median nerve injury and repair.J Hand Surg Am 2014;39(6):1216-22. PMID: 24862118
2. Galanakos, SP, Zoubos, AB, Ignatiadis, I, et al. Repair of complete nerve lacerations at the forearm: an outcome study using Rosen-Lundborg protocol. Microsurgery 2011;31(4):253-62.PMID: 21557303
3. Chemnitz, A, Bjorkman, A, Dahlin, LB, et al. Functional outcome thirty years after median and ulnar nerve repair in childhood and adolescence. J Bone Joint Surg Am 2013;95(4):329-37. PMID: 23426767
4. Lad, SP, Nathan, JK, Schubert, RD, et al. Trends in median, ulnar, radial, and brachioplexus nerve injuries in the United States. Neurosurgery 2010;66(5):953-60.PMID: 20414978
5. Pfaeffle, HJ, Waitayawinyu, T and Trumble, TE. Ulnar nerve laceration and repair. Hand Clin 2007;23(3):291-9. PMID: 17765581
6. Fernandez, L, Komatsu, DE, Gurevich, M, et al. Emerging Strategies on Adjuvant Therapies for Nerve Recovery. J Hand Surg Am 2018;43(4):368-373. PMID: 29618417
7. Birch R. Nerve Repair. In: Green’s Operative Hand Surgery, Wolfe SW, Hotchkiss RN, Pederson WC, Kozin SH (eds), Philadelphia, Elsevier Churchill Livingstone, 2011, pp. 1035-1092.
8. Woo, A, Bakri, K and Moran, SL. Management of ulnar nerve injuries. J Hand Surg Am 2015;40(1):173-81.PMID: 25442770
9. Naik, AA, Hinds, RM, Paksima, N, et al. Risk of Injury to the Dorsal Sensory Branch of the Ulnar Nerve With Percutaneous Pinning of Ulnar-Sided Structures. J Hand Surg Am 2016;41(7):e159-63. PMID: 27137081
10. Tsu-Hsin Chen, E, Wei, JD and Huang, VW. Injury of the dorsal sensory branch of the ulnar nerve as a complication of arthroscopic repair of the triangular fibrocartilage. J Hand Surg Br 2006;31(5):530-2. PMID: 16777280
11. Hurst, LC, Dowd, A, Sampson, SP, et al. Partial lacerations of median and ulnar nerves. J Hand Surg Am 1991;16(2):207-10. PMID: 2022827
12. Millesi, H. The nerve gap. Theory and clinical practice. Hand Clin 1986;2(4):651-63.PMID: 3539948
13. Terzis, J, Faibisoff, B and Williams, B. The nerve gap: suture under tension vs. graft. Plast Reconstr Surg 1975;56(2):166-70. PMID: 1096197
14. Taylor, CA, Braza, D, Rice, JB, et al. The incidence of peripheral nerve injury in extremity trauma. Am J Phys Med Rehabil 2008;87(5):381-5. PMID: 18334923
15. Birch, R, Misra, P, Stewart, MP, et al. Nerve injuries sustained during warfare: part II: Outcomes. J Bone Joint Surg Br 2012;94(4):529-35. PMID: 22434471
16. Kim, KH, Lee, SJ, Park, BK, et al. Sonoanatomy of sensory branches of the ulnar nerve below the elbow in healthy subjects. Muscle Nerve 2018;57(4):569-573. PMID: 28877548
17. Ruchelsman, DE, Price, AE, Valencia, H, et al. Sensory restoration by lateral antebrachial cutaneous to ulnar nerve transfer in children with global brachial plexus injuries. Hand (N Y) 2010;5(4):370-3. PMID: 22131917
18. Schenck, TL, Lin, S, Stewart, JK, et al. Sensory reanimation of the hand by transfer of the superficial branch of the radial nerve to the median and ulnar nerve. Brain Behav 2016;6(12). PMID: 28032001
19. Seddon HJ. Surgical Disorders of the Peripheral Nerves, ed 7. Edinburgh, Churchill-Livingstone, 1975, pp. 276-280.17.
20. Seddon HJ (ed): Peripheral Nerve Injuries, Medical Research Council Special Report Series No. 282, London, Her Majesty’s Stationery Office, 1954.
21. Kim, DH, Han, K, Tiel, RL, et al. Surgical outcomes of 654 ulnar nerve lesions. J Neurosurg 2003;98(5):993-1004. PMID: 12744359
22. Atiyya, AN and Nassar, WA. Ulnar Nerve Repair With Simultaneous Metacarpophalangeal Joint Capsulorrhaphy and Pulley Advancement. J Hand Surg Am 2015;40(9):1818-23.PMID: 26100986
23. Botte MJ, Cohen MS, Lavernia CJ, von Schroeder HP, Gellman H, Zinberg EM. The dorsal branch of the ulnar nerve: an anatomic study. J Hand Surg Am. 1990;15(4):603-607. 

Reviews

1. Pfaeffle, HJ, Waitayawinyu, T and Trumble, TE. Ulnar nerve laceration and repair. Hand Clin 2007;23(3):291-9. PMID: 17765581
2. Woo A, Bakri K, and Moran SL. Management of ulnar nerve injuries. J Hand Surg Am2015;40(1):173-81. PMID: 25442770

Classics

1. Puzey C. Case of Progressive Paralysis of the Ulnar Nerve, Consequent upon Injury: Operation: Successful Result. Br Med J1885;1(1272):979-80. PMID: 20751259
2. Woodward C. Injury to the Deep Branch of the Ulnar Nerve. Proc R Soc Med1914;7:151. PMID: 19978290