Ulnar nerve palsy

Anatomy

  • Ulnar nerve is a branch of medial cord of brachial plexus which arises from C8 and T1 ventral rami.
  • It lies between the axillary artery and vein.
  • It lies posteromedial to the brachial artery.
  • In the arm at the level of coracobrachialis insertion, it pierces the medial intermuscular septum to enter the extensor compartment where it lies anterior to the medial head of triceps.
  • At the elbow it lies in the retrocondylar groove behind the medial epicondyle.
  • It enters the cubital tunnel between the 2 heads of flexor carpi ulnaris to reach the flexor compartment where it lies on the anterior surface of flexor digitorum profundus. It supplies the FCU and the medial half of FDP.
  • 7 cm proximal to the wrist it gives off the dorsal branch which supplies sensation to the ulnar part of dorsum f hand up to the proximal interphalangeal joints.
  • 5 cm above the wrist it gives off the palmar branch which supply the ulnar side of palm.
  • Nerve passes superficial to the flexor retinaculum, medial to the ulnar artery and radial to the FCU through the Guyon’s canal which lies between the pisiform medially and the hook of hamate laterally.
  • In the Guyon’s canal it divides into superficial and deep branches.
  • Superficial branch supplies the palmaris brevis and provides sensation to medial one and a half fingers.
  • Deep branch passes along with the deep branch of ulnar artery between the FDM and ADM. It pierces the ODM to reach the deep surface of flexor tendons.
  • Along with deep palmar arch it passes transversely.
  • Deep branch supplies hypothenar muscles, interossei, medial two lumbricals and ends by supplying adductor pollicis, deep head of flexor pollicis brevis and first dorsal interossei.
  • Ulnar nerves supplies
    • FCU
    • Medial half of FDP
    • Hypothenar muscles
    • Interossei
    • Medial 2 lumbricals
    • Adductor pollicis
    • Deep head of flexor pollicis brevis

Pathoanatomy

  • Martin-Gruber anastomosis
    • Seen in 15%
    • Between ulnar and either median or AIN in the forearm.
    • Carry motor fibres from median to ulnar for intrinsic muscles.
    • May result in intact intrinsic function in proximal ulnar lesions.
    • 4 Patterns
      • Type I 60%- Motor from median to ulnar to supply median innervated muscles
      • Type II 35%- Motor branch from median to supply ulnar
      • Type III 3%- Motor from ulnar to median to supply ulnar innervated muscles
      • Type IV- Motor from ulnar to median to supply median innervated muscles
  • RichieCannieu anastomosis
    • Between deep branch of ulnar and recurrent branch of median nerve.
    • Ulnar to median
    • May result in intact thenar muscle function in presence of median nerve injury.
  • Sites of nerve entrapment
    • At the elbow
      • Arcade of Struthers- Myofascial band extending from medial intermuscular septum to the medial head of triceps, 8 cm above medial epicondyle
      • Medial intermuscular septum where it pierces
      • Medial head of triceps
      • Medial epicondyle
      • Epicondylar groove
      • Cubital tunnel between 2 heads of FCU which are connected by aponeurotic Osborne’s ligament
      • Flexor pronator aponeurosis between FDP and FDS.
    • At the Guyon’s canal
      • Zone I- Proximal to bifurcation
      • Zone II- Distal to bifurcation. Contains deep branch.
      • Zone III- Contains the superficial branch
  • Functional losses in ulnar nerve injury
    • Loss of key pinch due to paralysis of adductor pollicis and first dorsal Interossei.
    • Clawing due to paralysis of Interossei and lumbricals in presence of functioning extrinsic extensors leading to MCPJ hyperextension and functioning long flexors leading to flexion of IPJ.
    • Loss of forward flexion of mobile fourth and fifth carpometacarpal joints lead to loss of transverse palmar arch manifested as inability to cup the hand to hold water.
    • Loss of normal integrated MCPJ and IPJ flexion. Normal finger flexion starts at MCPJ followed by IPJ. In ulnar nerve palsy IPJ flexes first followed by MCPJ. This rolling motion will lead to inability to grasp objects.
    • Loss of FDP function of medial 2 digits in high ulnar nerve palsy leads to diminished grip strength.

Clinical Features

  • Duchenne sign- Clawing
  • Cross finger test- Inability to cross index and middle finger over each other.
  • Pitres Testut sign- Inability to abduct middle finger to either side.
  • Wartenberg sign- Abduction of little finger.
  • Loss of normal sequence of finger flexion- Normally MCPJ flexes then the IPJ flexes. In ulnar nerve palsy MCPJ flexes last.
  • Loss of key pinch
  • Jeannes sign- MCPJ of thumb hyperextended during key pinch.
  • Masse sign- Loss of hypothenar eminence and flattened palmar metacarpal arch.
  • Pollock sign- Inability to flex DIPJ of little and ring fingers.
  • Froments sign- Substitution of adductor pollicis by FPL during key pinch.
  • Bouvier manoeuvre- Correct the hyperextension of MCPJ and ask the patient to extend IPJ. If IPJ extension is improved then Bouvier test is positive and claw and is termed simple claw hand. If IPJ extension doesn’t improve then test is negative and clawing is called complex claw hand.
  • Associated sensory loss over medial aspect of arm and forearm indicate medial cord lesion.
  • Systemic conditions mimicking ulnar palsy
    • Charcot Marie Tooth disease
    • Syringomyelia
    • Leprosy
    • Klumpke’s paralysis
    • Pancoast tumour
    • Cervical IVDP

To continue

https://learningorthopaedics.com/ulnar-nerve-palsy/

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