When considering foot deformities, there are two pathologies that we most commonly encounter: bunions and hammertoes. We have discussed in past blogs that a bunion is not just a bunion, and there is more to it. Hammertoes are just as involved.
So what makes a hammertoe tick? Let’s break it down. In actuality there are three types:1,2
• A true hammertoe involves extension contracture at the metatarsophalangeal joint (MPJ). There is also a flexion contracture at the proximal interphalangeal joint (PIPJ) and an extension contracture at the distal interphalangeal joint (DIPJ).
• Claw toe is similar to true hammertoe with the exception of a flexion contracture at the distal interphalangeal joint.
• With mallet toes,the only deformity comes at the distal interphalangeal joint, which is in flexion.
So what causes the digit to conform to such contractures? To understand this, we need to dive into the deeper end of anatomy for a few moments. There are several things physicians need to take into account.1,2
1. What helps the dorsiflex is the extensor digitorum longus (EDL) muscle, which originates from the lower leg and inserts into the second through fifth digits. This muscle is more active during the swing and heel contact phases of gait to help clear the toes so patients do not drag them. The extensor digitorum longus and brevis muscles also help stabilize the proximal phalanx against the head of the metatarsal during propulsion.
2. What helps the toes plantarflex are the flexor digitorumlongus (FDL) and flexor digitorum brevis(FDB) muscles. These apply the counterforce to the extensor tendons on the top of the foot.
3. The extensor hood/apparatus is a fibrous structure that surrounds the MPJs. It is made up of two components, the wing and sling. It extends from the extensor tendon to the digit and wraps around the MPJ where, in essence, the proximal phalanx kind of sits in. When the extensor muscle contracts, it pulls up on the proximal phalanx and causes dorsiflexion at the MPJ.
These muscles are the main deforming forces when it comes to hammertoe problems. How do these normal muscles and associated tendons act abnormally?
Pain occurs when the top of the digit rubs against the shoe and creates a callus or an ulcer. Patients may even experience pain under the ball of the foot as the dorsally contracted digit actually pushes down on the metatarsal head, creating a more prominent callus or ulcer on the bottom of the foot.
There are several other muscles involved with digit deformities. These are the lumbricales, interossei and quadratus plantae.1,2
The lumbricales are four muscles that insert into the proximal phalanx and extensor hood. These muscles are extremely good at flexing the MPJ and extending the proximal interphalangeal joint and the distal interphalangeal joint.3
The interossei are a group of muscles with main function of stabilizing the digits in the transverse plane. These muscles function during the stance phase of gait and keep the proximal phalanx from being plantarflexed through the ground.
The quadratus plantae provides proximal stability to the lumbricales and the flexor digitorum longus muscles. It also functions to straighten the pull of the flexor digitorum longus.
All right. Now that we have established an idea of the structures involved in creating digital deformities, let us address the three main types of a hammertoe deformity.1,2
Flexor stabilization. This is the most common cause, occurring in a pronated foot type when the flexor digitorum longusor flexor digitorum brevis gains a mechanical advantage over the interossei muscles. Due to the decreased action of the interossei, whether from overpronationor some neuropathic process, the flexors contract earlier and longer to try to stabilize the digit. There is often an associated adductovarus deformity to the fourth and fifth digits because the quadratus plantae loses its straightening pull over the flexor digitorum longus.
Flexor substitution. This is the least common cause. It occurs in a supinated foot type. Again, the flexors gain an advantage over the interossei. There is no adductovarus deformity of the fourth or fifth digits. This situation usually occurs when the Achilles tendon is weak and the other flexors compensate by contracting earlier and longer.
Extensor substitution. This occurs in the swing phase of gait rather than the stance phase like the other two scenarios. The EDL gains an advantage over the lumbricales. Typically, this occurs in a cavus type of foot deformity.
If you had not noticed, the interossei and lumbricales are easily taken advantage of.
Actual causes of the aforementioned types of hammertoe deformities may include: post-traumatic, inflammatory, neurologic, congenital, post-surgical and unknown etiologies.3
I will not go into great detail of the types of surgical procedures that one can perform. This blog installment was not meant to discuss the types of procedures but mainly to describe the pathology behind the deformity.
The main purpose of surgical correction is to reduce the contracted digit. Surgeons can do this by removing portions of bone, releasing capsular structures, releasing certain tendons or transferring one tendon to another location.
Questions or comments please direct to Dr. Jeff Bowman via www.houstonfootspecialists.com  .
1. Banks AS, Downey MS, Martin DE, et al. McGlamry's Comprehensive Textbook of Foot and Ankle Surgery, third edition, volume 1. Lippincott, Williams, Philadelphia, 2001.
2. Coughlin MJ, Mann RA, Saltzman C (eds.) Surgery of the Foot and Ankle. Eighth edition. Mosby, St. Louis, 2011.
3. Easley ME, Wiesel SW (eds.) Operative Techniques in Foot and Ankle Surgery, Lippincott, Williams & Wilkins, Philadelphia, 2011.