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Compressive Ulnar Neuropathies at the Elbow (eg Cubital Tunnel Syndrome)

Introduction

Second most common upper extremity nerve entrapment after carpal tunnel syndrome.

Anatomy

There are five potential sites of entrapment beginning 10cm proximal to the elbow and end 5cm distal to the elbow:

  1. Intermuscular septum - Includes an area extending from the Arcade of Struthers to the medial epicondyle. The Arcade of Struthers is a musculofascial band present in 70% of extremities and located approximately 8cm proximal to the medial epicondyle. This arcade is not to be confused with the ligament of Struthers, which is involved with compression of the median nerve. In the absence of an arcade of Struthers, the nerve may be compressed as it passes through the medial intermuscular septum after anterior dislocation of the nerve or iatrogenically after ulnar nerve transposition when the septum is left intact. Other causes include impingement against a hypertrophied medial head of triceps  or a friction neuritis secondary to the medial head of triceps snapping over the medial epicondyle.
  2. Medial epicondyle - Tardy ulnar nerve palsy resulting from impingement over medial epicondyle due to a valgus defomity resulting  from an old epiphyseal injury of lateral condyle or suprcondylar fracture malunion.
  3. Epicondylar groove - Boundaries include the medial epicondyle, olecranon, and a fibroapneurotic band covering. Other contents of this canal include superior and inferior ulnar collateral arteries and the ulnar recurrent artery. Lesions within the groove include fracture fragments, degenerative osteophytes, soft-tissue tumrs, ganglia, synovitis, hematoma, and osteochondromas. External sources include an anomalous anconeus muscle,  improper surgical positioning or resting ones arm on objects such as the window frame while driving. Symptoms may also be due to nerve dislocation or subluxation over the medial epicondyle as a result of congenital laxity  of the fibroaponeurotic covering of the epicondylar groove, hypoplasia of the trochlea, or posttraumatic deformity of the epicondyle. Be aware that asymptomic  hypermobility of the nerve is present in approximately 20% of the population, usually bilaterally. This is a predisposing condition for friction neuritis and injury secondary to casting and injections.
  4. Cubital tunnel - A tunnel between the humeral and ulnar heads of the flexor carpi ulnaris muscle. Floor: medial collateral ligament; Roof: Osborne's ligament (continuation of fibroapneurotic covering of epicondylar groove); This tunnel decreases in cross-sectional area with elbow flexion and results in 7- to 20-fold increases in tunnel pressure.
  5. Flexor-pronator aponeurosis - Fascia located at point of exit from flexor carpi ulnaris - Nerve is intramuscular for 5m prior to its exit.

Anomalies in the nervous structures in the forearm may result in all of the intrinsic hand muscles being innervated by only one nerve or, more commonly, result in muscles with dual innervations.

  • The Martin-Gruber communication in proximal forearm carries motor fibers from the median nerve to the ulnar nerve. Typically located 3-10 cm distal to medial epicodyle. A similar, more rare communication may also exist in the distal forearm.
  • Riche-Cannieu connection is a communication between the motor branch of the ulnar nerve and the recurrent branch of the median nerve

Pathogenesis

Describe the biologic basis of the disorder or the mechanism of injury

Natural History

Describe the natural history,epidemiology and prognosis

Patient History and Physical Findings

History:

  • Symptoms include numbness paresthesias in an ulnar nerve distribution, pain radiating both proximal and/or distal, difficulty performing certain tasks, and early hand fatigue with repetitive activities.

Physical Findings:

  • C-spine exam to rule out radiculopathy (ROM, axial load)
  • Elbow carrying angle, ROM
  • Palpate nerve along it's path looking for tenderness, enlargements and dislocation with elbow flexion
  • Look for Tinel's sign along course of nerve
  • Elbow flexion test - Positive when symptoms are reproduced after keeping elbow in full flexion for up to one minute; (Similar in principle to Phalen's test for carpal tunnel syndrome.)
  • Numbness in ulnar nerve distribution
    • If numbness is only at the volar aspect of the ulnar nerve distribution, consider the diagnosis of ulnar tunnel syndrome (compression at Guyon's canal).
    • Test vibratory perception and light touch with Semmes-Weinstein monofilaments
  • Wartenberg sign - inability to adduct the little finger
  • intrinsic muscle wasting is indicative of chronic compression
  • Severe weakness will reveal:
    • Clawing of the ring and little fingers
    • Positive Froment's sign - thumb IP flexion required to hold sheet of paper between second ray and thumb
    • Positive Jeanne's sign - hyperextension of the thumb MCP joint

Imaging and Diagnostic Studies

Radiography:

X-ray: AP, oblique, lateral, epicondylar groove profile

MRI has little role at present.

Electrodiagnostic studies

Important when clinical findings are equivocal, site of compression is uncertain, site of compression is thought to involve multiple levels, or polyneuropathy is suspected. Tests should be carried out with the elbow flexed.

Differential Diagnosis

  • C8-T1 radiculopathy
  • medial cord pathology
    • thoracic outlet syndrom
    • Pancoast tumor
  • Double crush syndrome - when the nerve is compromised at one level (e.g. cervical nerve roots) it is more susceptible to damage at another
  • diabetes
  • hypothyroidism
  • alcoholism
  • malignancy
  • vitamin deficiency

Classification

McGowan Classification:

  • Grade I: Minimal; parasthesias and numbness present, but no weakness
  • Grade II: intermediate; wasting of interosseous muscles
  • Grade III: Severe; complete intrinsic paralysis

Treatment

Medical therapy:

Nonoperative treatment:

  • Consider in the pregnant patient

Operative treatment:

  • This neuropathy will only get worse in the vast majority of cases and does not respond well to conservative therapy. Therefore surgical decompression is recommended. Surgical options include:
    • Simple decompression without transposition
      • The ulnar nerve may sublux in up to 90% of patients postoperatively and become symptomatic
      • However, a meta analysis of randomized controlled trials found no difference in motor nerve-conduction velocities or clinical outcome scores between simple decompression and subcutaneous or submuscular transposition in patients with no history of prior trauma or surgery
    • Subcutaneous transposition
    • Submuscular transposition
      • Surgical results are similar to subcutaneous transposition.

Pearls and Pitfalls

  • During surgical decompression, excise the distal medial intermuscular septum; if this is not excised it acts as a fulcrum over which the nerve must pass. 
  • Be aware of the medial collateral ligament during your dissection; Iatrogenic injury will lead to elbow instability.

Postoperative Care

Include immediate postoperative care and rehabilitation

Outcome

Include functional and prosthetic survivorship data as applicable

Complications

Include overview of complications

References

JAAOS Articles

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