The perforating system of the ulnar forearm flap passes from the ulnar vessels to the investing layer of fascia in the septum between flexor carpi ulnaris and flexor digitorum superficialis. The flap is generally sited towards the ulnar side of the forearm, but in other respects the techniques involved in its transfer are similar to those of the radial forearm flap in its fasciocutan-eous form.
The two flaps have a largely similar range of potential usage, but the radial form is more often used in clinical practice.
LATERALUPPER ARM FLAP
This fasciocutaneous flap is raised on the lateral aspect of the upper arm, just above the lateral epicondyle of the humerus, using as its vascular basis the posterior branch of the radial collateral artery and its venae comitantes. It can also be transferred as an osteofasciocutaneous flap by including a segment of the underlying humeral shaft. The parent vessel of the perfusion system is the profunda brachii artery.
This vessel runs alongside the radial nerve, deep to triceps, in the spiral groove, and reaches the lateral intermus-cular septum between triceps and the insertion of deltoid. There it divides into two branches, anterior and posterior. The anterior branch, small and not always present, accompanies the radial nerve as it passes distally in the groove between brachialis and brachioradialis.
The posterior branch, with an external diameter of 1.5-2 mm, is consistently present, with associated venae comitantes, running distally in the intermuscular septum between triceps and the brachialis-brachioradialis muscle group. In the intermuscular septum it gives off branches which reach the investing layer of deep fascia and the overlying skin.
Additional multiple small vessels pass from it into the surrounding muscles, and also reach the humeral periosteum to which the intermuscular septum is attached. The lower lateral cutaneous nerve of the arm supplies sensation to the skin area and is aviable for suture in the recipient area if a sensate flap is desired. Division of the nerve, and of the posterior cutaneous nerve of the fore-arm which arises in common with it, leaves an anaesthetic area distal to the flap site.