Subluxation of metatarsals following partial amputation in cases of diabetic osteomyelitis
Diabetic wounds and the bone infections (osteomyelitis) that can often result from diabetic wounds are always challenging to treat. In my years of practice, I’ve found no better teacher than experience in treating these complicated cases. Diabetic wounds of the skin often infect the underlying bones. These bone infections are treated by IV antibiotics, surgical amputations or a combination of both. In this blog post, I want to bring to light an unusual post operative complication in two cases of partial metatarsal amputation for osteomyelitis. But first, let’s talk a little bit about metatarsal anatomy.
Functional anatomy of the metatarsal
A metatarsal bone and it’s associated toe bones are referred to as a ray. The first ray consists of the 1st metatarsal along with the proximal and distal phalanges of the great toe. The 5th ray consists of the 5th metatarsal along with the proximal, middle and distal phalanges of the 5th toe. The 1st ray and the 5th ray work in conjunction with the other metatarsals and toes to deliver force from the calf to the ball-of-the-foot, to provide push off during gait. Each of the rays of the foot share a tight, yet adaptable connection to the midfoot to adapt to changes in the surface of the ground such as slope, uphill, uneven surface, etc.
Partial amputation of the metatarsal and complications
Partial amputation of the 1st or the 5th ray may have a significant impact on the biomechanical properties of the ray and remaining metatarsal bone. In most cases, following the resection of a portion of the metatarsal, the remaining ray stays in a static position, anchored by the ligaments attached to the remaining bone. In other cases, when the biomechanics of the ray are altered by amputation, the remaining ray and metatarsal bone can change position. This change of position of the bone is called subluxation. Subluxation can lead to ulceration of the skin. If the goal of a diabetic amputation is go obtain a functional outcome, re-ulceration is considered a poor outcome and can be a contributing factor to limb loss.
Case #1 – 1st metatarsal subluxation following 1st metatarsal head resection for osteomyelitis.
JR is a 46 y/o male with a 15+ year history of poorly controlled insulin dependent diabetes. JR presented to my clinic with a history of recurrent wounds of the plantar aspect of the great toe of the left foot. X-rays showed radiolucency of the great toe and 1st metatarsal head consistent with osteomyelitis. Surgery and 6 weeks of IV antibiotics were successful in resolving the infection. The patient was lost to follow up.
A year later, the patient presented to my office with a new wound on the plantar aspect of the 1st metatarsal, left foot. New x-rays found significant plantar subluxation of the 1st ray. JR is currently responding to custom diabetic insoles.
Case #2 – 5th metatarsal subluxation following 5th metatarsal head resection
LL is a 56 y/o male with multi-year history of poorly controlled diabetes. LL worked as a UPS driver, on his feet for greater than 8 hours a day. LL presented with recurrent ulcerations beneath the 5th metatarsal head that refused to respond to off-loading and rx insoles. 5th metatarsal head resection was performed and resolved the issue of recurrent ulcerations allowing LL to return to work. 1.5 years later, LL presented again to clinic with significant subluxation of the 5th metatarsal, abducting from the foot. The subluxed 5th metatarsal resulted in a new wound and a new case of osteomyelitis.
Two additional surgeries were necessary to resolve LL’s wounds and bone infections. The first procedure was used to shorten the 5th metatarsal. The remaining styloid process of the 5th metatarsal became infected after 6months and also had to be excised.
Discussion-
Subluxation of the 1st or the 5th metatarsal is uncommon following partial ray resection. But in some cases, as we see from the two cases above, complications from partial ray resection do occur and can lead to significant problems for these diabetic patients.
Removing a portion of the 1st or 5th ray may result in buckling of the ray and subluxation of the metatarsal. In a healthy foot, the rigidity of the foot created by multiple bones and their associated ligaments results in a foot that is at the same time rigid to deliver load yet flexible to adapt to the ever changing uneven ground. Partial resection of the 1st or 5th ray may result in buckling of the ray and subsequent subluxation of the metatarsal.
Jeff
Medical Advisor
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