Instructions for Somsak Nerve transfer

N to long head of triceps to anterior division of

the axillary nerveCompiled by Dr S Selvaganesh

Hand Surgery Fellow KTPH

Cadaveric dissection

First Nerve transfer workshop,KTPH, Singapore

Practical 4

Incision

• Specimen in prone position

• Make a 10cm longitudinal curvilinear incision on the posterior arm.

• From the level of the quadrilateral space following the posterior order of deltoid and continuing distally along the midpoint of triceps.

Superficial dissection

• Lift up the skin flaps - look for the upper lateral cutaneous nerve of the arm (ULCNA) – will guide to the posterior division

• This branch can be confirmed by gentle traction, which dimples the skin

Deep dissection• Split the fascia at the point where the ULCNA pierces - trace this back

to the posterior division of the axillary nerve - loop

• Follow the posterior division deep until the anterior division is identified - trace distally to the deltoid muscle

• (The anatomy in the space may be difficult to define and axillary vessels may cross the nerve branches)

Upper Lateral Cutaneous Nerve of Arm

Deep dissection• If ULCNA unidentified, identify the anterior division• Anterior division – passes deep to the posterior border of the deltoid

muscle - 5cm distal to the postero-lateral corner of the acromion• There are usually two main branches and lifting the deltoid using a

retractor placed more proximally facilitates this exposure without risking damage to the nerve branches• Use a rubber surgical loop to tag the anterior and posterior divisions

of the axillary nerve

Posterior branch

Deep dissection – between long & lateral heads of triceps

• Identify a fat streak on the triceps• Develop the plane between the long and lateral heads of triceps -

gentle finger dissection• Carefully place a self-retaining retractor in this interval – avoid

damage to the triceps branches• The white tendon of latissimus dorsi – between quadranqular (axillary

nerve) & triangular spaces (RN & Branches)• Tag each nerve with surgical loops

Recipient Division• Divide the axillary nerve as proximally as possible – gentle loop

surgical traction• Separation of the anterior and posterior divisions by endoneurolysis• (Avoid injury to the axillary artery or vein branches in the

quadrilateral space)• Select a donor muscle branch from triceps long head (Somsak) or

medial head branch

Donor Division• The posterior cutaneous nerve of the arm lies on top of the main

radial nerve – can confuse• Trace the branch distally to see where the motor branch enters the

muscle & confirm with the faculty• Divide donor distally – external neurolysis using gentle surgical loop

retraction

Coaptation• Coapt using 9’0 nylon 2 - 3 sutures - use microscope• (May be supported with Tisseel fibrin glue)• Ensure tension free and remain tension free throughout a full passive

range of shoulder motion

Thank you