Ulnar Nerve Entrapment

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Clinically Relevant Anatomy

• Clinically Relevant Anatomy 1,2,3
      o Ulnar nerve entrapment typically occurs at two main sites: the cubital tunnel and guyon’s canal. Guyon’s canal                syndrome, also known as, ulnar tunnel syndrome is much less common than cubital tunnel syndrome.
      o The ulnar nerve can also be disrupted at other sites if a fracture of the humerus, radius, or ulna is sustained. Rarely,          vascular pathology can lead to compression at atypical sites as well.
      o Function of the nerve can be compromised distal to the site of the lesion.
      o Course of the Ulnar nerve:
            - Originates from the C8-T1 nerve roots.
                  • There is a possible minor involvement of the C7 nerve root as well.

                                        File:Brachial Plexus.jpg
            - The ulnar nerve branches off the medial cord of the brachial plexus.
            - The ulnar nerve runs just medial to the axillary artery, and continues down the humerus.
            - About halfway down the humerus, the ulnar nerve pierces the medial intermuscular septum, and passes back                   over the medial head of the triceps.
            - The nerve continues around the posterior aspect of the medial epicondyle and goes through the ulnar groove.
            - It then courses underneath the tendonous arch also known as the cubital tunnel (humeral-ulnar aponeurosis),                   which is formed by the two heads of the flexor carpi ulnaris, and enters into the anterior compartment of the                     forearm.
            - In the forearm the nerve branches off into:
                  • Muscular branches of the ulnar nerve
                        o Innervates
                              - Flexor carpi ulnaris
                                    • flexion and adduction of wrist
                              - Ulnar portion of the Flexor digitorum profundus
                                    • Flexes distal phalanges at distal interphalangeal joints of digits 2-5 and assists with flexion of                                         hand
                  • Dorsal cutaneous sensory branch
                        o Supplies sensation to the dorsal aspect of the fifth finger and the dorsal medial portion of the 4th finger.
                  • Palmar cutaneous branch of the ulnar nerve
                        o Supplies sensation to the palmar aspect of the fifth finger and the palmar medial portion of the 4th                                    finger.
            - The ulnar nerve continues down the forearm medially and enters into the hand though the Guyon’s canal.
                  • Guyon’s canal
                        o Proximal wall
                              - Pisiform bone
                        o Distal wall
                              - Hook of the hamate
                        o Floor:
                              - Combination of the thick transverse carpal ligament, the hamate and triquetrum bones
                        o Roof
                              - Narrowed by a ligament running from pisiform to hamate.
            - In the hand the ulnar nerve branches off into:
                  • Superficial branch of ulnar nerve
                        o Supplies the Palmaris brevis
                              - steadies and corrugates skin of palm to help with grip
                  • Deep branch of ulnar nerve
                        o Supplies the interossei, third and fourth lumbricals, the adductor pollicis, and part of the flexor pollicis                              brevis.

Mechanism of Injury / Pathological Process

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Clinical Presentation

• Clinical Presentation 6,7,8,9,10,11
      o Symptoms of ulnar nerve entrapment depend on the diagnosis, or location of the lesion.
            - Cubital Tunnel Syndrome 6,7,8,9,10,11
                  • Is considered a repetitive stress injury where the ulnar nerve becomes entrapped with the cubital tunnel which is formed by the medial epicondyle, flexor carpi ulnaris and ligaments of the olecranon process of the ulna.
                  • Primarily affects anyone whose motions incorporate repetitive or prolonged elbow flexion such as leaning on the elbows.
                  • Cubital Tunnel Syndrome can present in different grades of severity:
                        o Grade I: Mild symptoms
                              - Intermittent paresthesia
                              - Minor hypoesthesia of the dorsal and palmar surfaces of the fifth and medial aspect of fourth digits
                              - No motor changes
                        o Grade II: Moderate and persistent symptoms
                              - Paresthesia
                              - Hypoesthesia of the dorsal and palmar surfaces of the fifth and medial aspect of fourth digits
                              - Mild weakness of ulnar innervated muscles
                              - Early signs of muscular atrophy
                        o Grade III: Severe symptoms
                              - Paresthesia
                              - Obvious loss of sensation of the dorsal and palmar surfaces of the fifth and medial aspect of fourth digits.
                              - Significant functional and motor impairment
                              - Muscle atrophy of the hand intrinsics
                              - Possible digital clawing of fourth and fifth digits (Sign of Benediction)
            - Guyon’s canal syndrome 6,7,8,9
                  • The ulnar nerve becomes entrapped between the hook of the hamate and the transverse carpal ligament which makes up the Guyon’s canal.
                  • Guyon’s canal syndrome is considered an overuse injury which is commonly caused by direct pressure on a handlebar (ie. Bicyle handlebar, weight lifting, construction equipment) and therefore, is sometimes referred to as “handle barpalsy”. It can also result from excessive gripping, twisting, or repeated wrist and hand motions. Also, entrapment may develop if the hand is flexed and ulnar deviated for prolonged periods of time.
                  • Symptoms caused by this syndrome consist of:
                        o Muscular atrophy
                              - Primarily the hypothenar muscles and interossei
                                    • Weakened finger abduction and adduction (interossei)
                                    • Weakened thumb adductor (adductor pollicis)
                              - Muscle sparing of the thenar group
                        o Sensory loss and pain
                              - May involve the palmar surface of the fifth digit and medial aspect of the fourth digit.
                              - Dorsum of medial aspect of the fourth finger and the dorsum of the fifth finger don’t have sensory loss.
                        o Ulnar Claw may present (sign of Benediction)
                              - Ulnar nerve compression due to trauma 11
                                    • The incidence of trauma leading to ulnar nerve compression is unknown; however ulnar neuropathy has been documented after distal humeral fractures and in up to 10% of elbow dislocations, and may also develop from any complex elbow or wrist trauma.

Diagnostic Procedures

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Outcome Measures

• Outcome Measures ¹³
      o Disabilities of the Arm, Shoulder, and Hand (DASH)
            - A 30 item questionnaire, targeted towards measuring the physical function and symptoms of patient
      o Patient Specific Functional Scale (PSFS)
            - A questionnaire that is utilized to quantify activity limitations and measure functional outcomes of patients
      o Quick DASH
            - A questionnaire that measures a patient’s functional ability and severity of their symptoms
      o Upper Extremity Functional Index (UEFI)
            - A questionnaire consisting of 20 items regarding severity of difficulty performing activities throughout the day

Management / Interventions

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Differential Diagnosis

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Key Evidence

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Resources

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Case Studies

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References

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