How To Address Sesamoids in Hallux Valgus Surgery
The surgical correction of hallux valgus (aka bunion) is one of the most common operations a foot and ankle surgeon will face. With over 130 procedures described to date, no one procedure has proven to be the definitive solution for every bunion situation. However, the common denominators for success remain osseous realignment and soft tissue balancing. The location of the sesamoid complex in relationship to the first metatarsal plays an integral part in determining whether one has achieved this realignment and balancing act.
The exact etiology of hallux valgus still remains rather controversial. Research has determined that both intrinsic and extrinsic factors have been implicated in the development of bunions. Intrinsic etiologies may include pes plano valgus, hypermobility, metatarsus primus varus, rheumatoid arthritis, collagen and neuromuscular disorders as well as hereditary predispositions. Coughlin and Roger reported the presence of hallux valgus in 29 of 31 mothers (94 percent) whose children were also affected.1 A similar study by Hardy and Clapham found that 57 of 91 patients (63 percent) in their series had a parent with hallux valgus.2
Although pronation, heredity and other intrinsic factors play a key role in the development of hallux valgus, extrinsic factors such as shoegear may prove to be equally as important. Hallux valgus has proven to occur predominantly in shoe-wearing populations. Fashionable footwear worn by many women is more constraining than those worn by men and many authors feel these shoes are a leading factor behind hallux valgus development. This may explain the 4:1 ratio of females to males who present with bunion deformities. Coughlin and Thompson reported a higher incidence of hallux valgus in females between their 30s and 50s. They suggested that constricting footwear was the causative agent.3
Likewise, Sim-Fook and Hodgson found a 33.9 percent incidence of hallux valgus among shoe-wearing populations in comparison to a 1.9 percent incidence in non-shoe-wearing populations.4 However, when it comes to juvenile hallux valgus, researchers showed that constricting footwear played a leading role in hallux valgus development in only 24 percent of the patients they evaluated.5
A combination of intrinsic and extrinsic factors is probably the most logical explanation of hallux valgus development. The combination ultimately leads to a progressive deformity with an increase in the first intermetatarsal angle (IM) and lateral deviation of the hallux. As the deformity progresses, soft tissue imbalance perpetuates the hallux valgus development, creating a retrograde buckling effect at the level of the metatarsophalangeal joint. Incidentally, as the metatarsal shifts medially, the sesamoid complex becomes degenerative as these structures are subluxed from their respective grooves formed by the plantar crista.
This “lateral transposition” of the sesamoid complex renders a distinct mechanical advantage, lending itself to be one of the primary deforming forces in hallux valgus development. It is important to realize that this subluxation process is the direct effect of the medial migration of the first metatarsal rather than movement by the sesamoids themselves. This concept is particularly important when it comes to addressing the hallux valgus via surgical intervention.
Keys To Evaluating Hallux Valgus Deformities
Accurate evaluation of the hallux valgus deformity prior to surgery helps to ensure proper procedure selection for the best possible outcome. Physicians should utilize clinical and radiographic parameters in this decision process. Clinically, it is critical to evaluate the patient in a weightbearing and non-weightbearing manner. Often, the hallux valgus deformity will be accentuated by the faulty mechanics one possesses upon weightbearing. Notably, the treating physician should observe the hallux position, apparent intermetatarsal angle and the presence of EHL contracture.6 An increase in the hallux valgus angle and splaying of the metatarsals may indicate a higher degree of hypermobility than the physician would previously see in a non-weightbearing exam.6