Lesser Metatarsalgia: Are Lesser Metatarsal Osteotomies Necessary?
Iatrogentic metatarsalgia. Iatrogenic metatarsalgia may arise from malalignment of a previous metatarsal osteotomy or from metatarsal head resection. In addition, inherent surgical problems like nonunion, delayed union, failed hallux abducto valgus surgery and inappropriate procedure selection for the correction of hallux abducto valgus can lead to the transfer of ground reactive forces and overload shift of the adjacent metatarsals. One of the most common causes is the iatrogenic shortening of second metatarsal osteotomies. Elevation of the second ray may lead to third rocker metatarsalgia while shortening the second ray may lead to second rocker metatarsalgia. Finally, hallux valgus surgery that results in elevation of the first ray can also cause a lateral shift of plantar pressures to the lesser metatarsal bones.5
Understanding The Dynamics Of First Ray Mobility
For the purpose of this article, we will focus our discussion on primary metatarsalgia and concentrate on exploring the biomechanical etiologies contributing to this deformity, starting with the first ray function. Duchene was the first to consider the existence of first ray instability and Morton later theorized that this insufficiency contributes to further pedal pathologies, including lesser metatarsalgia.6
By definition, the first ray includes the medial joints of the first metatarsocuneiform and the naviculocuneiform. The first ray and medial column act as a rigid lever during the heel rise phase of the gait cycle. Once the gastroc-soleus complex contracts, the foot plantarflexes and rotates around the center of the talar body. Accordingly, the forces of weightbearing and Achilles tendon tension transmit to the ground through the medial column and first ray in order to propel the body forward.5
Approximately 60 percent of normal weightbearing forces pass through the first ray from heel strike to toe-off.7 Once the first ray fails to support the load, the medial column collapses, which leads to a lateral load shift to the lesser metatarsals. Morton proposed that the unstable first ray is an inherent cause of second metatarsal pathology.6 Greisberg and co-workers reported similar findings as patients with second MPJ synovitis and metatarsalgia noted greater first ray mobility.4
Furthermore, the instability of the first ray may also be visible at the frontal plane level as medial angulation of the first metatarsal through the first metatarsocuneiform joint contributing to the hallux valgus deformity. In fact, some studies have demonstrated increased sagittal plane mobility in patients with hallux valgus, thereby contributing to transfer metatarsalgia.4
Keys To Addressing Lesser Metatarsalgia
From our experience, we believe that the most predictable approach to lesser metatarsalgia is addressing the primary biomechanical pathologies that contribute to the presenting deformities. The initial step involves addressing the tight posterior muscle groups in patients with a confirmed equinus deformity via the Silfverskiold test. This occurs through tendo-Achilles lengthening in the case of gastroc-soleus equinus or through the endoscopic/open gastrocnemius recession approach in cases of gastrocnemius equinus. In doing so, the compensatory excess motion in the first ray decreases, thus lowering the load on the lesser metatarsals.