12th August 2024

Mononeuropathies

Carpal tunnel syndrome

Compression of the median nerve at the wrist causes thenar wasting, weakness of ‘LOAF’ muscles (lateral lumbricals, opponens pollicis, abductor pollicis brevis and flexor pollicis brevis), and sensory loss over the palm and lateral three and a half fingers.

Other median nerve injuries

Damage at the elbow gives similar symptoms to those of carpal tunnel syndrome, with the addition of weakness of forearm pronation and wrist flexion.

Damage to the anterior interosseous branch nerve causes weakness of forearm pronation and flexion of the thumb and index finger. It most commonly occurs in the context of forearm trauma or neuralgic amyotrophy (a brachial plexopathy characterised by severe pain and weakness in the distribution of the upper brachial plexus).

Ulnar nerve injury

This generally occurs due to elbow trauma at the medial condyle or in Guyon’s canal in the wrist. It causes weakness of wrist flexors, interossei, medial two lumbricals, and hypothenar wasting. There is sensory loss over the ulnar border of the palm and medial 1.5 fingers.

Radial nerve injury

This is most commonly caused by humeral fracture or compression of the radial nerve in the spiral groove. Signs include weakness of wrist and finger extension and sensory loss over the dorsum of the hand.

Common peroneal nerve injury

Causes of common peroneal nerve injury include fibula fractures, leg crossing or stretching and leg casts. Signs on examination include weak dorsiflexion and eversion of the ankle and sensory loss to the dorsum of the foot. Inversion is innervated by the tibial nerve so is not affected, which helps to differentiate this from an L5 radiculopathy.

Posterior tibial nerve injury

Generally, this is injured in the ankle (tarsal tunnel) due to fractures of the talus, calcaneus or medial malleolus or rheumatoid disease. Signs include weak intrinsic foot muscles (e.g. inability to stand on tiptoes) and sensory loss over the sole of the foot.

Sciatic nerve injury

Injury in the gluteal region can damage the sciatic nerve, and this generally occurs secondary to hip dislocation or fracture, or hip surgery. Other causes include pelvic masses and piriformis syndrome. It presents with weakness of the hamstrings and muscles below the knee, sensory loss to the lower leg sparing the medial calf and foot arch and loss of the ankle reflex (with preserved patellar reflex).

Mid-femoral region injury can occur with femoral fracture or ischaemia. Signs are similar to the above but generally without hamstring involvement.

Femoral nerve injury

This has similar causes to gluteal-region sciatic injury. Typical signs are quadriceps weakness, sensory loss over the anterior and medial thigh, medial shin and arch, and a diminished patellar reflex with normal ankle jerk.

Lateral femoral cutaneous nerve

Meralgia paresthetica is a pure sensory syndrome caused by compression of the lateral femoral cutaneous nerve, characterised by anterior and lateral thigh pain. Risk factors include obesity, tight fitting clothes or belts, hip injuries or repetitive motion of the hip.

Morton’s neuroma

This describes nerve thickening between the 3ʳᵈ and 4ᵗʰ metatarsophalangeal joints, which can cause a burning pain.

Neuralgic amyotrophy

Also known as Parsonage-Turner syndrome, neuralgic amyotrphy is an inflammatory brachial plexopathy characterised by severe pain with later development of patchy weakness in the distribution of the upper brachial plexus.