Cubital Tunnel Syndrome
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Direct answer
Cubital tunnel syndrome is compression of the ulnar nerve behind the medial epicondyle at the elbow, producing numbness of the ring and little fingers and weakness of the intrinsic hand muscles. Froment's sign and Wartenberg's sign are the classic clinical tests of ulnar motor weakness. Anterior transposition is a common surgical option when weakness or wasting is present or conservative measures fail.
What you must remember
- Anatomy: the cubital tunnel lies behind the medial epicondyle, roofed by the Osborne ligament, which is the fascia spanning the two heads of flexor carpi ulnaris.
- Symptoms: numbness and tingling in the ring and little fingers, worse with elbow flexion and at night, with clumsiness and, in later disease, clawing of the ring and little fingers (often less marked in high lesions, the ulnar paradox).
- Froment's sign: on pinching paper between the thumb and index finger, the patient flexes the thumb interphalangeal joint, using flexor pollicis longus to compensate for weak adductor pollicis.
- Wartenberg's sign: the little finger abducts at rest because the extensor digiti minimi is unopposed by weak ulnar-supplied interossei.
- Dorsum of the hand: the dorsal ulnar cutaneous nerve branches in the forearm, proximal to the wrist, so an elbow lesion can cause dorsal hand numbness, which a distal wrist lesion spares.
- Wasting: the first dorsal interosseous and hypothenar muscles waste in established disease.
- Treatment: activity modification and night elbow padding first, then surgery for weakness, wasting or failed conservative care.
A stepwise approach to diagnosis and treatment
Cubital tunnel syndrome is localised by combining the sensory pattern, the motor signs and the nerve conduction study. The steps below follow the order in which a clinician confirms the level and decides on surgery.
- Take the history: ask about night numbness, clumsiness, and leaning on the elbow or sustaining prolonged elbow flexion.
- Map the sensation: the ring and little fingers are affected, and dorsal hand numbness also fits an elbow lesion, since the dorsal ulnar cutaneous branch arises in the forearm, below the elbow.
- Test the motor pattern: check grip and pinch, Froment's and Wartenberg's signs, and wasting of the first dorsal interosseous and hypothenar muscles.
- Provoke the symptoms: a Tinel test over the tunnel and a sustained elbow flexion test reproduce the tingling when the nerve is compressed.
- Confirm with nerve conduction: slowed ulnar conduction across the elbow confirms the level and grades the severity.
- Choose the treatment: protective measures come first, and surgery such as in situ decompression, medial epicondylectomy or anterior transposition is chosen when weakness or wasting is present or symptoms persist.
Where the exam tries to catch you
Cubital tunnel questions are usually decided by separating the elbow lesion from the wrist lesion and by reading the motor signs correctly.
- Trap: expecting the dorsum of the hand to be spared in an elbow lesion. Correct: the dorsal ulnar cutaneous branch arises in the forearm above the wrist, so cubital tunnel lesions can cause dorsal numbness, while a distal Guyon lesion spares it.
- Trap: attributing Froment's sign to the median nerve. Correct: the thumb flexion is compensation for weak adductor pollicis from ulnar nerve palsy, with flexor pollicis longus doing the work.
- Trap: operating on every patient with numbness. Correct: mild disease without weakness is managed conservatively, and surgery is reserved for weakness, wasting or failed treatment.
Frequently asked questions
What is Froment's sign in cubital tunnel syndrome?
Froment's sign is a clinical test in which the patient pinches a piece of paper between the thumb and index finger. Thumb interphalangeal flexion is used to compensate for weak adductor pollicis in ulnar nerve palsy. The sign indicates ulnar motor weakness at the elbow or wrist.
Why does the little finger abduct in Wartenberg's sign?
The little finger abducts in Wartenberg's sign because the extensor digiti minimi, supplied by the radial nerve, is unopposed by the weakened ulnar-supplied interossei. This imbalance is a sign of ulnar nerve compression. It is best observed with the hand relaxed.
Which surgery is commonly performed for cubital tunnel syndrome?
Anterior transposition is a common surgical option for cubital tunnel syndrome, moving the ulnar nerve to the front of the medial epicondyle. In situ decompression and medial epicondylectomy are alternatives. The choice depends on severity and the surgeon's judgement.
How does cubital tunnel syndrome differ from carpal tunnel syndrome in sensation?
Cubital tunnel syndrome affects the ring and little fingers and can also involve the dorsal and palmar ulnar hand, while carpal tunnel syndrome affects the thumb, index and middle fingers and spares the thenar eminence. The palmar cutaneous branch leaves before the carpal tunnel, which explains thenar sparing. The sensory pattern therefore helps localise the level.