The Posterior Interosseous Flap

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The Posterior Interosseous FlapB Youssef1, A Dancey, 1 V P Sumathi2, F C Peart1.

1.Regional Department of Burns and Plastic Surgery, University Hospital Birmingham, Selly Oak Hospital, Birmingham, United Kingdom. 2.Department of Musculoskeletal Pathology, The Royal Orthopaedic Hospital, Birmingham, United Kingdom.

Case report

A 57 year-old gentleman presented to his General Practitioner with a swelling on the dorsal aspect of his left hand. The swelling had gradually increased in size over the last 12 months. It was not painful, associated with any neurological symptoms or functional loss. There was no history of trauma or infection.

There was no significant past medical history of note and he does not take any regular medication. He works in a slaughterhouse, he does not smoke and drinks socially.

On examination he had a five by seven cm swelling on the dorsal aspect of his left hand. It was soft, smooth, mobile and it did not appear to involve the extensor tendons. The patient was able to make a composite fist, he had full extension at the metacarpal-phalangeal joint and at the proximal and distal inter-phalangeal joints. There was no associated lymphadenopathy or neurovascular deficit.

An MRI (Figure 1 and 2) and incision biopsy were performed. Histology confirmed the presence of a desmoplastic fibroblastoma (collagenous fibroma). This is a rare benign soft tissue tumour of fibroblastic origin. In keeping with the current literature on collagenous fibroma they present as firm, well-circumscribed subcutaneous, or intramuscular, painless masses typically long standing in duration. Complete surgical excision is the recommended course of action (1). And this was the proposed plan with immediate reconstruction of the defect after discussion at the soft tissue tumour multi-disciplinary meeting.

Figure 1: transverse section through the hand revealing the soft tissue tumour above the 4th and 5th metacarpals.

Figure 2: Coronal section through the left hand, demonstrating the soft tissue mass.

Procedure

A doppler examination of the vessel and the perforating branches of the interosseous vessels was performed.

The surface marking of the posterior interosseous artery was drawn along a line joining the lateral epicondyle of the humerus and the ulnar styloid. A point nine cm distal to the lateral epicondyle of the humerus marks the centre of the fasciocutaneous element of the flap (Figure 3).

A tourniquet was inflated to 230mmHg prior to dissection to create a bloodless field. The tumour extended down to the periosteum of the metacarpals, it involved extensor digiti minimi (EDM), extensor digitorum communis (EDC) to the ring finger and the paratenon from EDC to the middle finger. The skin and tumour was excised taking these structures en bloc with the underlying periosteum and the fascia from the interosseous muscles (Figure 4,5).

Extensor indicis proprius was harvested and split into two tails and transferred to EDC at the level of the MCPJ via a 900 weave through the tendon using a 3.0 braided polyester suture (Ticron, Tycon) (Figure 6).

The vessels lie orientated in the sagital plane in the fascial septum between extensor carpi ulnaris and extensor digiti minimi muscles. The artery is superficial in the distal half and in the proximal half it lies underneath extensor digiti minimi. Therefore the flap was raised distal to proximal. The pivot point is 2 cm distal to the radio-carpal joint, it is at this point that the posterior interosseous artery anastomoses with the anterior interosseous artery. The flap was then tunnelled to the dorsum of the hand from its pivot point. The superficial veins were preserved and haemostasis was achieved (Figure 7,8,9).

The flap was inset and the donor site covered with meshed SSG. The skin bridge was divided and a split skin graft was placed over the pedicle. One 10 French suction drain was placed under the flap (Figure 10). The tourniquet was released and excellent blood flow was observed to the flap.

Figure 3: pre-operative marking. Flap designed according to the size of the tumour. Length and position of the pedicle marked.

Figure 4: Initial dissection of the soft tissue tumour on the dorsum of left hand.

Figure 5: The excised soft tissue tumour. excised

Figure 6: Extensor Digitorum Communis (EDC) to the small and ring finger was excised en bloc with the tumour and an Extensor Indicis Proprius transfer to EDC performed.

Figure 7: Elevation of the flap the posterior interosseous artery and its venae commitantes are displayed.

Figure 8 & 9: Fascio-cutaneous flap and pedicle completely elevated.

Figure 10:Image of the flap in its final position and the donor site covered with a split skin graft.

Figure 11:Two weeks post operatively, the flap and skin graft have taken well.

Pathology

The results of the histo-pathological examination of the specimen were discussed at the multi-disciplinary meeting, which confirmed that this was a desmoplastic fibroblastoma.

Figure 12: Macroscopic picture: cut surface shows a well circumscribed, greyish white tumour measuring 5x4x2.7 cm.

Figure 13: Microscopic image (x40): shows a paucicellular lesion composed of spindled and stellate shaped fibroblasts set in a collagenous stroma.

The excision margins were clear of tumour and no further treatment is required at this stage. He will be followed up at regular intervals as an outpatient.

Anatomy of the posterior interosseous flap

The posterior interosseous flap is a type B fascio-cutaneous flap. The flap is developed in a plane between the fascia and muscle. Here exists a layer of loose connective tissue and fat containing cutaneous veins, nerves and a rich network of arteries.

The perforating vessels of the posterior interosseous artery penetrate the fascia to run longitudinally with numerous transverse anastomoses in the subcutaneous tissue. The fascia envelops the muscle tissue and thickens to form a septum between individual muscle bellies. The posterior interosseous artery arises from the common interosseous artery, passes posteriorly above the interosseous membrane and then runs between supinator superficially and abductor polllicis longus deeply with the posterior interosseous nerve to descend and supply the extensors muscles of the forearm. It forms an anastomosis with the distal branches of the anterior interosseous artery and the dorsal carpal arch. The artery gives of perforators along its entire length. The septocutaneous perforators anastomose in the superficial layer of the deep fascia and form rich vascular arcades. Near the wrist joint, three types of anastomoses have been identified. The first one with the anterior interosseous artery is located just proximal to the distal radio-ulnar joint. The second one with the dorsal carpal arch, and the third includes several branches that surround the ulnar head on both sides and anastomoses with the ulnar artery. This rich vascular supply means that the flap can be raised even when one of the anastomoses is injured. .

Course and distribution of the posterior interosseous artery

Cross section through the middle third of the forearm.

Venous drainage is from both the superficial and the deep systems, and there are multiple anastomoses between these venous channels. There is venous drainage through the superficial veins and the venae commitantes within pedicle to ensure flap survival (2).

Discussion

Reconstruction of the soft tissue on the dorsum of the hand can be a challenging problem. Free flaps can be time consuming, require specialised equipment and labour intensive post-operative care. Distant flaps may require multiple stage reconstruction and prolonged periods of immobilisation.

Local fascio-cutaneous flaps, although limited in mobility and quantity, offer simple and effective wound coverage. The donor sites do not often require reconstruction and can be closed directly or using a split skin graft.

Fasciocutaneous flaps Fasciocutaneous flaps are tissue flaps that include skin, subcutaneous tissue, and the underlying fascia.

When moving skin alone, the distance it can travel is limited by its length to breadth ratio. Including the deep fascia with its prefascial and subfascial plexuses enhances the circulation of these flaps, but also frees these limb flaps from the length and breadth limitations they were previously subjected to. They are simple to elevate, quick, and fairly reliable in healthy patients. They provide ideal resurfacing where a thin flap of tissue is required. No functional loss results from the area they are raised as no muscle is taken.

Fasciocutaneous flaps can be used to provide cover over areas of bare tendon and bone. The procedure can be pre-planned, as described in our case report, based on the direction and orientation of the fascial plexus or fasciocutaneous perforators. These flaps provide a donor sites in areas where random axial flaps are not feasable. There are disadvantages; they are not as resistant to infection as muscle flaps and predicting failure can be difficult (2,3).

Cormack and Lamberty classification of fasciocutaneous flaps (4,5).

Type A has multiple fascio-cutaneous perforators. They enter at the base of the flap and extend through the full length of the flap. The flap can be based proximally, distally, or as an island.

Type B has a single moderately sized fasciocutaneous perforator. This can be used as a free flap or as an island.

Type C has multiple small perforators running along the fascial septum. The supplying artery is included with the flap. It can be based proximally, distally, or as a free flap.

Type D is an osteomyocutaneous flap. It