How To Address Avascular Necrosis
When surgeons perform distal first metatarsal osteotomies, avascular necrosis (AVN) is a relatively common complication. Accordingly, these authors emphasize having a strong understanding of the involved vascular anatomy, share intraoperative pearls for minimizing the risk and offer treatment insights when AVN does occur.
Although it is a relatively rare problem, avascular necrosis (AVN) of the first metatarsal head is a condition that we should be aware of and understand. This condition started getting attention when surgeons offered the first descriptions of distal metatarsal osteotomies for the correction of hallux valgus (HAV) deformities.1 These procedures have become a staple for the correction of mild to moderate HAV deformities and generally have a high success rate.
Avascular necrosis may occur in multiple bones throughout the body. In the foot, it most commonly affects the talus, first and second metatarsals, and the navicular and sesamoid bones. For the purposes of this article, we will offer a closer look at the development of AVN in the first metatarsal head and discuss proactive methods to minimize the risk of this complication.
Avascular necrosis is bone death secondary to ischemia. When blood supply to the bone is disrupted, it deprives the cells of oxygen and leads to osteonecrosis. This typically progresses as a series of events that begin with an initial insult and eventually leads to a loss of the blood supply.
The body attempts to repair the damaged bone via revascularization, resorption of necrotic bone and reossification. In the process, mechanical failure may occur at the repair interface, leading to subchondral fracturing and possible joint collapse. In this case, cartilaginous destruction takes place, leading to arthrosis and pain. 2
There are a variety of possible etiologies for AVN. These etiologies include: systemic and injectable corticosteroid use, hemoglobinopathies, Cushing’s disease, alcoholism, complications of trauma, and iatrogenic causes. The most commonly described cases of AVN occur after hallux valgus corrections by way of distal metatarsal osteotomies with or without the use of a lateral soft tissue release.
Keys To Understanding The Vascular Anatomy
A distal osteotomy disrupts the intraosseous blood supply to the metatarsal head. Given this reality, physicians expressed concern that the surgery may create AVN, especially when one combines the surgery with a lateral capsular release. There have been reports to support this concern. 3 However, better comprehension of the vascular anatomy illuminates safe zones that allow us to perform the surgery with a relatively low rate of complication.
A thorough understanding of the vascular network is an important first step toward a successful surgery. There are three main arteries that supply the first metatarsal. 4 The first dorsal metatarsal artery is a direct extension of the dorsalis pedis artery and passes dorsal to the first interosseous muscle. Its first branch is the nutrient artery, which enters the proximal one-third of the first metatarsal on the lateral aspect. The first dorsal metatarsal artery continues distally, forming a significant extracapsular anastomosis that supplies approximately two-thirds of the metatarsal head.
Be advised that careless use of a saw can put this structure at risk when one is making a distal osteotomy. A common mistake is to let the saw blade plunge into the intermetatarsal space as it penetrates the lateral cortex.