Osteocutaneous Posterior Interosseous Artery Flap
The posterior interosseous artery (PIA) flap was first described by Penteado et al in 1986.1 Costa et al subsequently added the ulna segment and described the osteocutaneous posterior interosseous artery flap in 1988.2
It is a distally based osteocutaneous pedicled flap, useful as a reconstructive option for bone and soft-tissue defects in the hand, without sacrificing a major artery to the hand or needing microsurgery.
The flap can comfortably reach the web spaces and proximal phalanges of the fingers.
On rare occasions, where defects are more distal, various techniques for extending the reach of the flap can be performed. This will be further described “Flap Variations.”
Injury in the region of the distal radioulnar joint (DRUJ) with damage to the PIA pedicle and the communicating branches with the anterior interosseous artery (AIA) results in loss of the distal blood supply to the flap. As such, patients with previous surgery or injury to the DRUJ may not be suitable candidates for this flap. Vascular studies, such as angiograms, need to be performed to exclude such injuries before the flap procedure can be done.
Smoking, diabetes, and underlying atherosclerosis increase the risk of failure, and persons with these conditions may be unsuitable candidates for this procedure.
Poor cosmesis of the donor site in an exposed and highly visible part of the forearm makes it unsuitable for some patients, and this needs to be discussed with the patient before surgery.
Although rare, the absence of the communicating branch of the AIA to the PIA may also make the latter less suitable as a pedicled flap.
The PIA originates from the common interosseous artery and, occasionally, directly from the ulnar artery in the proximal part of the forearm. The common interosseous artery arises from the ulnar artery at the level of the radial tuberosity and divides into the posterior and anterior interosseous arteries. The PIA runs deep to the supinator and enters the posterior compartment of the forearm.
The artery is accompanied by the posterior interosseous nerve (PIN) as well as small venae comitantes. The latter accompany the artery as far distally as the wrist. The branches of the PIN to the extensor carpi ulnaris (ECU) cross over the PIA at the junction of the middle and proximal third of the forearm.
The pedicle enters the septum between the extensor digiti minimi (EDM) and the ECU.
Along this course, the PIA gives off several cutaneous arteries, averaging 7 to 10. Angrigiani et al3 performed cadaveric and clinical dissections and found the presence of a large cutaneous branch, the proximal cutaneous branch, that courses the proximal segment. This branch is consistently present but has a variable origin.
At the distal forearm or wrist, the artery anastomoses with the communicating (recurrent) branch of the AIA, the dorsal carpal arch, and the vascular plexus surrounding the ulnar head ( Fig. 34.2 ).
Both the extensor pollicis longus (EPL) and extensor indicis proprius (EIP) muscles appear to have sufficient attachment to sustain a length of ulna via a periosteal supply. The EPL is attached more proximally and is more suitable for use in a distally based flap.
The territory of the flap that can be perfused by the PIA pedicle includes the middle and proximal third of the forearm, up to the lateral epicondyle. The width of the flap can be taken up to the width of the forearm.
The continuity of the PIA was absent at the level of the middle of the forearm in 1 out of 80 specimens in Angrigiani′s study.3 This may necessitate conversion to a free flap.
The frequent narrowing of the anastomosis between the communicating branch and the PIA with the occasional absence of continuity suggests the presence of a choke anastomosis.
The surface marking of the pedicle is drawn with the forearm in full pronation ( Fig. 34.3 ).
The humeral lateral epicondyle is connected to the midpoint of the DRUJ.
The midpoint of this line approximately marks the middle cutaneous perforator of the PIA. The communicating branch of the AIA is marked 2 cm proximal to the distal part of the DRUJ. The nerve to the ECU is marked at the junction of the proximal and middle third of this line.
Doppler examination along this line is usually performed to confirm the presence of the pedicle and the communication between the PIA and AIA, as well as to mark the positions of the main cutaneous perforators.
The cutaneous perforators can be differentiated from the axial pedicle by the disappearance of the Doppler signal as the probe is moved away in all directions.
To avoid confusion in the following steps, the terms “proximal” and “distal” refer to the flap in relation to the position in the forearm, and not according to the direction of blood flow.
Under general anesthesia, the patient is cleaned and draped, and positioned supine.
With the forearm in full pronation, the surface markings indicated above are drawn ( Fig. 34.3 ). The defect is marked out on a piece of paper template and transferred onto the forearm, for the design of the flap ( Fig. 34.4a–c ).
The procedure is performed with a tourniquet applied at the mid arm level.
The proximal limit of the flap can extend as far proximal as the elbow or just beyond the elbow joint.
The incision is initiated directly over the DRUJ, extending proximally up to the distal tip of the flap design. Skin is raised to expose the forearm fascia.
The ECU and EDM tendons are identified through the fascia. Incisions are made on the fascia over the ECU and EDM tendons, preserving the intervening cuff of forearm fascia, which will lead to the intermuscular septum containing the pedicle vessels. The former is retracted toward the ulna and dissected away from the septum. The latter is then retracted radially, exposing the PIA. The presence of the communicating branch from the AIA is then confirmed ( Fig. 34.2 ).
The skin incision is then carried proximally over the dorsoradial aspect of the flap and deepened through the forearm fascia, dissecting the forearm muscles from the fascia, gradually working toward the inter-muscular septum of interest. Note that there are other septa that need to be incised before reaching the septum containing the pedicle. Care should be taken not to injure the fine perforators on the septum.
The dorsoulnar aspect of the flap is then incised from distal to proximal forearm, deepened through the fascia. As with the dorsoradial aspect, the skin and fascia are dissected subfascially toward the pedicle, incising other septa along the way. Care should again be taken not to injure the perforators on the septum. Some of these perforators share branches to the muscles, and these branches need to be cauterized or clipped and divided with care so as not to injure the septal perforators to the skin ( Fig. 34.5a–c ).
The nerve to the ECU may be encountered in the junction between the proximal and middle third of the forearm during this part of the dissection ( Fig. 34.6 ). If perforators more proximal to this nerve need to be included within the flap, then the nerve should be divided and reanastomosed later. If this is not necessary, the proximal part of the flap can be mobilized by cutting the fascia just superficial to the nerve to ECU and carrying the incision on the fascia toward the lateral epicondyle.
The flap is now attached to the dorsal aspect of the ulna through the septum containing the pedicle vessels, with the proximal part mobilized.
The flap is then raised together with the deep fascia, from distal to proximal, up to the distal border of the supinator.
Any significantly sized cutaneous draining vein is preserved, for later anastomosis to the recipient site to help reduce the risk of venous congestion.
The extensor pollicis longus (EPL) muscle is then identified on the dorsoradial aspect of the flap, and the corresponding part of the ulna shaft on the dorsoulnar aspect is noted and marked ( Fig. 34.7a,b ).
The dissection is deepened to include a cuff of the EPL, down to the interosseous border of the ulna.
The interosseous membrane along the required length of ulna bone to be harvested is then incised. We recommend that the maximum width of ulna bone harvested should not exceed one-third the width to ensure integrity of the remnant donor bone.
The main trunk of the PIA is only 1.5 mm in diameter. Such a small-caliber vessel makes dissection delicate, and patient selection must screen out those with possible microcirculatory disorders.
Branches of the nerve to the ECU run superficial to this pedicle and sometimes need to be divided to deliver the flap. The authors routinely reanastomose these branches if initially divided.
Tunneling increases risk of pedicle compression and failure due to congestion.
Additional care of the pedicle to avoid kinking during the insetting process is crucial.
Postoperative wound swelling may compromise the circulation to the flap, resulting in congestion. Care should be exercised to ensure that the dressing is not compressive and to lighten dressing early if necessary.
Partial STO may be performed when necessary if flap swelling is significant.