Tunnel neuropathies
In addition to direct wounds, tunnel neuropathies play a huge role in the pathology of the peripheral nervous system. These are specific lesions that occur at sites of natural anatomical narrowings, the so-called "tunnels".
The anatomical substrates for the formation of such tunnels include:
- Rigid osteofibrous canals.
- Fibromuscular spaces.
- Aponeurotic slits.
- Openings in the ligamentous apparatus.
Pathogenesis and etiology It is precisely in these narrow anatomical zones that ideal conditions are created for the development of local compression (squeezing) and subsequent ischemia of the nerve trunk.
Tunnel syndromes are of paramount clinical significance because they are the leading cause of "spontaneous" mononeuropathies, that is, lesions that develop without prior acute trauma or injury. The decisive triggering factor in their formation is prolonged microtraumatization. It may be associated with professional activity, regular sports training, or even routine daily loads.
Surgical repair: microsurgical suture
If a nerve trunk transection has occurred, its surgical suturing is required. The most advanced technique is considered to be the microsurgical (intrafascicular) suture.
Features of the technique: The surgery is performed under mandatory optical magnification using the finest atraumatic suture material. The main advantage of this approach is its low invasiveness and the ability to accurately align a large number of individual nerve bundles (in contrast to the simpler epineural suture). However, the technique requires high qualification of the operating surgeon and specialized equipment.
Stages of suture placement:
- Passing the sutures intended for the continuous intrafascicular suture.
- Suturing the bundles located on the anterior semicircle of the nerve. The knots are tied at the upper and lower poles, after which the nerve trunk is rotated by exactly 180°.
- Final suturing of all remaining bundles with the placement of a third fixing knot.
- Placement of reinforcing outer epineural sutures.
Neurolysis and delayed injuries
Neurolysis is a surgery aimed at freeing the nerve trunk from the scar tissue compressing it.
This intervention is indicated in cases where the anatomical integrity of the nerve itself is preserved, but its normal function is lost due to a severe scarring process around or inside it. During the surgery, the nerve is freed both externally and internally. It is important to remember that the internal stage (intraneural neurolysis) must not be performed blindly—it requires the use of operating optics and microinstruments.
Tactics for delayed complete nerve transection If a long time has passed since the complete anatomical transection, surgical tactics are built according to a strict algorithm:
- First, a thorough neurolysis of the nerve ends is performed.
- Then, the formed neuromas (pathological thickenings at the ends of the ruptured nerve) are resected.
- At the final stage, the surgeon assesses the magnitude of the diastase (separation of the nerve ends after scar excision).
The choice of connection method depends on the defect size:
- If the diastase is no more than 2 cm, placement of a direct epineural suture is possible.
- If the diastase is significant or there is a true tissue defect (more than 2 cm), direct suturing is impossible. In such situations, autoplasty is used. To replace the defect, a section of a less functionally significant nerve is used. The classical and most successful donor for such transplantation is traditionally the sural nerve (n. suralis).
Briefly: answers to topical questions
Which forearm muscles are innervated by the ulnar nerve?
In the forearm, the ulnar nerve innervates two muscles responsible for flexing the hand and the distal phalanges of the fingers.
- Flexor carpi ulnaris (m. flexor carpi ulnaris) — provides flexion and adduction of the hand.
- Deep flexor of fingers (ulnar part) (m. flexor digitorum profundus) — provides flexion of the distal phalanges of digits IV and V.
Which hand muscles are innervated by the ulnar nerve?
In the hand, the deep branch of the ulnar nerve innervates the muscles of the hypothenar eminence, the central group, and part of the thenar eminence muscles.
- Hypothenar muscles (m. abductor digiti minimi, m. opponens digiti minimi, m. flexor digiti minimi brevis) — muscles of the little finger.
- Lumbrical muscles (mm. lumbricales) — III and IV muscles.
- Interosseous muscles (mm. interossei palmares et dorsales) — all palmar and dorsal.
- Adductor pollicis (m. adductor pollicis).
- Flexor pollicis brevis (m. flexor pollicis brevis) — deep head only.
Which skin zones are innervated by the ulnar nerve in the hand?
The ulnar nerve provides sensory innervation to the medial (ulnar) half of the hand.
- Palmar surface: skin of the medial part of the palm, entirely digit V and the ulnar (medial) side of digit IV (1.5 digits in total).
- Dorsal surface: skin of the medial part of the hand dorsum, entirely digits V and IV, as well as the ulnar (medial) side of digit III (2.5 digits in total).
The boundary of the innervation zones with the median nerve on the palm runs strictly along the axis of digit IV.
What typical hand deformity occurs with ulnar nerve injury?
Ulnar nerve injury leads to a specific "claw hand" (or "bird hand") deformity. It occurs due to paralysis of the interosseous and lumbrical muscles. Visually, the deformity manifests as sharp hyperextension of the fingers at the metacarpophalangeal joints and their pronounced flexion at the interphalangeal joints. This pathological posture is most pronounced for digits IV and V of the hand.
In which anatomical canals does ulnar nerve compression most frequently occur?
Ulnar nerve compression most frequently occurs in anatomical narrowings at the level of the elbow and wrist joints.
- Retroepicondylar groove — the most common site of compression at the elbow level (about 75% of cases).
- Cubital tunnel — the second most frequent compression site at the elbow level (about 25% of cases).
- Guyon's canal — the anatomical canal at the level of the wrist joint and hand where the tunnel syndrome of the same name develops.
Which clinical tests are used to diagnose ulnar nerve injury?
Motor tests and percussion tests are used for the clinical diagnosis of ulnar nerve injury.
- Froment's sign — detection of weakness of the 1st interosseous muscle.
- “Key pinch” test — detection of weakness of the adductor pollicis muscle.
- Tinel's sign — the appearance of painful paresthesias in the nerve innervation zone upon percussion at the suspected compression site.
- Testing the inability to scratch the table with the nail of the little finger.
Muscle strength is also assessed using the MRC scale.
2-centimeter rule: if the nerve defect is up to 2 cm, an epineurial suture is applied; if greater than 2 cm, autografting is required (using a graft).
Class and exam questions
What is the core of a neurolysis procedure?
This is the surgical release of an anatomically intact nerve from compression by scar tissue both externally and within the nerve trunk itself.
Which nerve is most commonly used as a donor in autografting?
The sural nerve (n. suralis) is considered the most suitable donor for transplantation because it is less functionally significant.
Why is a microsurgical suture preferable to an epineurial one?
The intrafascicular (microsurgical) suture is less traumatic and allows the surgeon to accurately align a much greater number of nerve bundles, improving the recovery prognosis.
What else to study on this topic
- Technique of neuroma resection in chronic peripheral nerve injuries
- Biomechanics of nerve trunk rotation in microsurgical repair
- Pathophysiological mechanisms of ischemia in entrapment syndromes
- Comparative characteristics of epineurial and intrafascicular sutures
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