There are many complex causes for the so-called 'claw hand' (CH).
CH is also known as the 'intrinsic minus' hand.This is characterised by hypertension at the MP joints and flexion at the PIP and DIP joints.The intrinsic tendons of the fingers-lumbricales and interrossei span the MP joints PALMAR to their axis of rotation and function to FLEX these joints.The lumbricales act more powerfully than the interossei because they attach more DISTALLY and have more moment of force.Beyond the MP joints these tendons continue on the LATERAL bands of the extensor tendons linking with the extensor mechanism and pass dorsal to the axis of the PIP and DIP joints thus EXTENDING these joints.The interossei also insert into the bases of the proximal phalaanbnges, such that the dorsal interossei aBduct the fingers from each other while the palmar interossei aDduct. Loss of function of the intrinsics leads to an imbalance of the tensions between the long extrinsic (extensors AND flexors) and the short intrinsic muscles.The resting tone of the intrinsics is LOST leading to unopposed long EXTENSORS across the MP joints and unopposed long FLEXORS across the IP joints leading to the characteristic 'claw' hand deformity.
CAUSES OF CLAW HAND
(i) ULNAR NERVE PALSY:ALL THE INTEROSSEI are paralysed(none sullied by median nerve) as well as the ULNAR SIDED LUMRICALES (RADIAL ARE MEDIAN NERVE= index and middle finger). As a result the clawing is CONFINED to the ring and little fingers(4 & 5) and the thumb (1).Ulnar nerve compression at the elbow will cause ulnar claw and ulnar sensory loss.A wrist laceration is the commonest cause of ulnar nerve palsy, and at this level the proximally innervated long flexors th the ring and little fingers are INTACT, compared to the high ulnar nerve injuries where the long flexors are paralysed, making finger flexion and the claw deformity less obvious.
(ii) PARALYSIS DUE TO MEDIAN & ULNAR NERVE INJURY:
This produces a full claw hand.Also can arise from lesions from C8 and T1 roots/inferior plexus.Leprosy world wide remains the commonest cause for a claw hand.
(i)Volkmann's Contracture(deep flexor compartment syndrome),(ii) Intrinsic muscle contacture(Bunnell Test),(iii)Dupuytren's contracture(palpate the palm and the contracted fingrers cannot be passively extended),(iv)Campylodactyly(congenital flexion contractors-congential), (v)Spastic hand(wrist flexed and clasping of thumb in the palm and inability to passively extend flexor tendons). (vi)Neuropathies.
Pope's Hand (Hand of Benediction):
The median nerve controls the 1st and 2nd lumbricales, 3 thenar muscle, FPB and via a distal branch the opponens pollicis.The HOB is seen with median nerve lesions leading to thenar atrophy and inability to flex the 1st & 2nd fingers at PIP.
Some clinicians use the term 'HOB" to include the pure median nerve description above and ulnar clawing.But the term 'HOB' more frequently refers to median nerve damage and results on attempted flexion of ALL the digits (leaving the 2nd and 3rd extended) , while 'ulnar claw' refers to exclusive damage to the ulnar nerve and is seen with attempted EXTENSION of ALL the digits (leaving digits 4 & 5 FLEXED).
This is all complex -neuroanatomy is important- don't just order NCS- there are less Neurologists nowadays!
DR MICHAEL CORONEOS CIME MASE
NATIONAL RACS EXAMINER
MASE & EXAM/SURGICALLY CURRENT CIME
CIME MASE FRCSI FRCS(EDIN)SN FACS FRACS MB BS(1ST CLASS HONOURS) MNSA MNSQ MAPS MANZSOM