Female, age 34, 126 lbs.
History and Chief Complaint
For the past seven years, the patient’s feet have become progressively more uncomfortable. At first she developed calluses under her 2nd and 5th metatarsal heads, and she experienced generalized fatigue in her feet and legs after ordinary activity and work.
Recently, rather large bumps have developed on the outside of both feet in the area of the 5th metatarsal head and base. She has difficulty in finding comfortable shoes in any style.
Clinical Exam and Observations
The patient has normal ranges of motion in her subtalar, midtarsal and ankle joints, bilaterally. There is no indication of any type of equinus influence or deformity. Off weight bearing, her arch is medium height, which becomes low on weight bearing. However, her calcaneus does not appear to evert in static stance. The range of motion in her 1st MPJ is at least 75 degrees, bilaterally. However, her 5th metatarsal rays seem to have a limited range of dorsiflexion, bilaterally.
The patient’s feet demonstrate a large protrusion at the base of the 5th metatarsal bilaterally, as well as a classic Tailor bunionette over the lateral aspect of the 5th metatarsal head with mild swelling, bilaterally. There is a dense callus under the 2nd and 5th metatarsal heads and a lesser callus plantar to the 5th metatarsal base, bilaterally.
Bilateral congenital plantarflexed 5th ray with concomitant Tailor bunionette and sub 2nd and 5th intractable plantar keratoma (IPK).
While she does not demonstrate any major rearfoot or forefoot deformities, she does pronate abnormally throughout the midstance and early propulsive phases of gait.
Under these circumstances, the 1st and 5th metatarsal rays tend to be unstable and the ground reactive force will have the ability to move them “up and out of the way”. Bilaterally, the shearing IPK sub 2nd metatarsal head clearly suggests that the 1st ray responds in that manner. It moves up and out of the way, thereby exposing the 2nd metatarsal head to undue stress and shearing because of the 2nd met IPK. But what happened to cause the 5th metatarsal problems?
By definition, a congenital plantarflexed 5th ray is one whose plantarflexion is so great that when a dorsiflectory force is applied, it either will remain below the transverse plane of the lesser metatarsal or will just reach that plane but not move above it when it is fully pronated to its highest dorsal excursion.
In this case we are observing the classic scenario for this deformity. When the foot is abnormally pronated, ground reaction forces against the congenital plantarflexed 5th ray quickly become excessive and the congential plantarflexed 5th ray will pronate and dorsiflex because of its instability. Since pronation is a complex motion taking place around a tri-plane axis, as the 5th ray dorsiflexes it also must rotate on its side in the frontal plane (evert) and move away from the 4th in the transverse place (abduct). Over time the 5th metatarsal bone subluxes dorsally at its case and this allows for even greater eversion and abduction of the 5th ray.
Clinically, the protrusion of the base of the 5th metatarsal bone and the callus beneath it suggest that the 5th ray is totally subluxed and unstable. The “bowing” of the 5th metatarsal shaft reinforces this inference since the subluxed 5th ray is actually lying on its side, and we are observing the sagittal plane curve of the metatarsal bone lying in the transverse plane. Also, because of the extreme mobility and shearing motion of the 5th metatarsal bone, the plantar condyles of the head are literally pushing out and digging into the soft tissue that is fixed by the lateral side of the shoe because of the Tailor bunionette and bursitis.
Finally, in an adult patient it is often difficult to recognize the extent of a congenital 5th ray plantarflexion that might have existed at a younger age. In this patient it must have been considerable because the amount of pronation/subluxation of the 5th ray that occurred was still not adequate enough to move the 5th metatarsal head “up and out of the way”. Thus, a shearing callus and IPK resulted.
Therapeutic management of this patient may involve two approaches, either concurrent or staged. From a conservative perspective, fully controlling custom-made foot orthotics are appropriate. A rearfoot varus post and 1st and 5th cut out will allow the rays to plantarflex and stabilize below the heel of the other lesser metatarsal bones, thereby reducing the shear forces of the 2nd and 5th metatarsal heads and Tailor bunionette. If this approach fails or the results are equivocal, it is appropriate to consider a mild dorsiflectory osteotomy of the 5th metatarsal bone as a second stage.