Key Pearls For Performing Bunion Surgery
Structural hallux abductus occurs when the proximal articular set angle and the distal articular set angle are above normal. Even a mild hallux abductus can become more significant by moving the metatarsal head laterally and not addressing the articular set angles (i.e. iatrogenic hallux abductus).5 When the first metatarsal head moves laterally, the hallux abductus angle may become more relevant as the hallux may now abut the second digit. One may need to address this new iatrogenic hallux abductus surgically in order to realign the hallux parallel to the second digit. In this case, the surgeon can again apply the theory of similar triangles.
There are many different geometric considerations when performing bunion surgery. Often, the intermetatarsal angle is a major consideration when determining the best procedure. With a closing base wedge osteotomy, one can see how the size of the wedge correlates to the intermetatarsal angle and how the orientation of the axis can influence shortening and elevation of the first metatarsal.
Also of importance with any osteotomy is how the width of the blade and declination of the first metatarsal can cause shortening and subsequent elevation. While realigning the bony architecture of the first ray is critical, one must consider the surrounding soft tissues, particularly the extensor hallucis longus. The bowstring effect of the extensor hallucis longus on longstanding bunion deformities can be powerful and restoring its effective length can help limit digital deformities.
Lastly, do not forget the hallux abductus angle and associated articular set angles. Realigning the hallux for functional and aesthetic purposes often means paralleling the second toe/ray. As with the proximal closing base wedge, one can use the theory of similar triangles to determine the degree of wedge for a distal procedure.
We have discussed the geometric importance of intermetatarsal angle, metatarsal declination, the importance of the axis of an osteotomy and the hallux abductus angle. Additional biomechanical and geometric concerns include how much pronation has occurred in the foot, hypermobility of the first ray, the length of the first metatarsal and possible contractures of the soft tissue. The best outcomes result from combining the art of bunion surgery and the above geometric principles.
Dr. Mozena is in private practice at the Town Center Foot Clinic in Portland, Ore. He is a Fellow of the American College of Foot and Ankle Surgeons and is board certified in foot and ankle surgery. He is an associate of Western Health Sciences University Podiatric and Surgery Department.
Dr. Arndt is in private practice at the Town Center Foot Clinic in Portland, Ore.
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