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COMPLEX HAND NEURAL INNERVATION ISSUES& UNDERSTANDING 'TRUE' HAND OF BENEDICTION.15 October at 16:28 from atlas
COMPLEX HAND NEURAL INNERVATION ISSUES& UNDERSTANDING 'TRUE' HAND OF BENEDICTION.Share15 October at 16:25 from atlas
The so-called Hand of Benediction(HOB) is the result of a significant and chronic lesion of the median nerve (MN) at the level of the elbow or upper arm.
The ability to flex II & III at the MCP joints AND to flex and extend them at the PIP and DIP joints are LOST because of loss of innervation of the LATERAL 2 LUMBRICALES and the LATERAL HALF OF FDP: which I have stated in earlier articles are supplied by the MEDIAN NERVE.Flexion at PIP of IV & V is weakened , but flexion at the MCP and DIP joints of IV & V remains INTACT (ulnar nerve).The extensor digitorum is left unopposed and the MCP joints of II & III remain EXTENDED WHILE ATTEMPTING TO MAKE A FIST.The HOB ( so called 'Pope's hand') in summary is inability to flex II & III at PIP and thenar atrophy on ATTEMPTING to make a fist.
Some hand specialists incorrectly use the term of "HOB" to include the above median nerve mediated sign (on ATTEMPTING to make a fist), but also with ULNAR CLAWING(UC).
The HOB more correctly refers to only damage to the median nerve and is only seen with ATTEMPTED FIST MAKING(flexion of all the digits),leaving the 2nd & 3rd digits extended. ULNAR CLAWING refers exclusively to ulnar nerve damage with ATTEMPTED EXTENSION of all the digits (NOT FLEXION)- leaving digits IV & V FLEXED.
ESSENITAL PRACTICAL SUMMARY : (i)Median nerve: 1st & 2nd lumbricales, 3 thenar muscles(APB,FPB & opponens pollicis).. meian nerve to flex I & II at PIP on attempting to make a (all finger flexed) fist and thenar atrophy. 'LOAF'=Lumbricales 1&2,Opponens pollicis,Abductor pollicis brevis and Flexor pollicis brevis.( of thenar eminence!).;
(ii) Ulnar nerve:3rd & 4th lumbricales, 3 hypothenar muscles, the palmar& dorsal interossei-PaD DaB !), palmaris brevis and the adductor pollicis.Ulnar damage- 3rd & 4th lumbricales are UNABLE to extend the PIP & DIP of IV & V and there may be hypothenar atrophy.
CAUSES OF ULNAR NEUROPATHY
(i) At the elbow:
Perioperative compression, elbow fractures with resultant cubitus valgus(aka 'tarduy ulnar palsy'),direct blunt/sharp trauma,deformity(e.g R.A.),metabolic(diabetes mellitus), transient operative brachial artery occlusion,subdermal hormonal implant,venipuncture,Haemophilia /haematomas,malnutrition causing to peri-elbow fat loss, smoking, bands, scarring etc.
(ii) At the wrist
Ganglionic cysts, tumours,non-fracture blunt trauma,aberrant artery and idiopathic.
MEDIAN NERVE RARITIES
(i) The median nerve typically bifurcates AFTER the median nerve EXITS the (approximate 21 mm carpal tunnel and 1.5 mm thick TVCL- David Fuller:Assistant Professor Surgery, David Cooper (New Jersey ,USA)Hospital,21/10/2009))-In 5-10% of cases the median nerve bifurcates more proximal in the carpal tunnel,wrist or forearm.I have seen all of these variations. I have operated on a median nerve , operated on initially bib a colleague (after typical CTS & NCS via standard palmar modified incision), who had a BIFID median nerve in 2 separate compartments.(Also published by T.P Wolter , U.Kleiner, E.M . Noah & N.Pallua in Eur Plast Surg(2003) 26;26; 102-104:Persistent CTS after both endoscopic and open release: a rare case of a bifid median nerve in two separate compartments.These authors describe the Lanz 4 patterns of branching of the median nerve in the carpal tunnel:I:one trunk, with various motor branch patterns(46%); II:Accessory branches originating in the carpal tunnel(7.5%); III :Proximal branching of the nerve =?- persistent median artery or accessory lumbricale muscle (2.9%); and IV: branching proximally to the TVCL re-uniting distally or piercing the ligament( 2.9%).Surgeons SHOULD be aware of variations , especially the high risk Lanz type III ( Tountas CP et al.J Hand Surg(am).1987 Sep;12(5 Pt1):708-12) - these operations are often deemed low risk...be aware! open surgery must minimise the risk to thenar motor branch(sub and trans-ligamentous-appearance in respect of the TVCL).
(ii) during gestation a median artery that serves the hand retracts-however it can persist -and cause CTS.
(iii)Martin-Gruber Anastamosis:median nerve branches cross over in the FA and merge with the ulnar nerve to innervate parts of the forehand.
(iv) Riche-Cannieu anastamosis: connection between the recurrent branch of the median nerve and deep branch of the ulnar nerve in the hand-unusual deficits may be DIFFICULT to explain with reference to 'typical' anatomy. MRI and NCS-a wise clinician should be aware of the traps!
(v) HAND SENSORY INNERVATION SUMMARY ( TYPICAL):
(a) Median nerve: palmar thenar eminence and adjacent palm of II, II and 1/4 III AND thumb(I), index(II), middle(III) and adjacent 1/2 ring(IV) ANDdorsal distal thumb(i), index(ii) and middle (III) , inc nails.
(b) Ulnar nerve: palmarV & adjacent 1/2 IV and adjacent palm AND dorsal similar as palmar PLUS entire IV and proximal adjacentIII AND on DORSAL side medial palmar sensation extends in a triangle into distal medial FA (unlike palmar where ulnar nerve ONLY supplies hypothenar palm to wrist line crease).
(c) Radial nerve:Palmar-negligible: lateral proximal thumb margin. DORSAL:Triangle on thenar side of distal FA and adjacent dorsal radial hand and proximal thumb(i),index(II) and adjacent 1/2 middle(III) finger but NOT the distal thumb, index or middle(median nerve).
Peripheral nerve neuro-anatomy is complex but MUST be known and examined by a Neurosurgeon EVERY day. Neurologists, NCS/EMB/MRI WILL give assistance BUT the Neurosurgeon MUST know the detailed variations , particularly as the surgeon DECIDES on surgery, then PERFORMS IT.
DR MICHAEL CORONEOS CIME MASE
NATIOANAL RACS EXAMINER
MEDICAL STUDENT EXAMINER
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