Digital deformities and abnormal biomechanical issues associated with central toe ulceration include hammertoe contracture, transverse plane toe deformity, hallux valgus, hallux limitus, overlapping toes, bone spurs, arthritis, excessive toe length, and ankle equinus. Deformity alone is typically not sufficient to cause ulceration, whereas the dyad of neuropathy and deformity is almost always present. Hammertoe deformity predisposes to abnormal pressure on the dorsal aspect of the proximal interphalangeal joint (PIPJ) or distal interphalangeal joint (DIPJ) as well as the distal tip of the toe near the toenail (Fig. 16.2). Dorsal ulceration is amenable to extra-depth toe box shoe therapy, while the tip of toe ulceration associated with hammertoe contracture is less easily rectified with simple shoe or insert measures. Patients with neuropathic wounds oftentimes present with chronic wounds that already have deep-seated osteomyelitis at which point conservative measures are no longer a viable option. Hammertoe contracture also creates a retrograde buckling force on the metatarsal head, which results in abnormal pressure on the plantar aspect of the metatarsophalangeal joint (MPJ). Interdigital ulceration is associated with transverse plane deformity (medial or lateral drift), hallux valgus, and overlapping toes. Arthritic interphalangeal joints (IPJs) can also become enlarged and prominent with resultant soft tissue breakdown which may ultimately lead to osteomyelitis. Isolated elongation of a central toe (commonly the second) is associated with nonhealing and recurrent tip of toe ulceration which is highly prone to osteomyelitis of the distal phalanx. An uncomplicated wound on a long toe can be rectified with proper fitting shoes, but the longest toe is commonly contracted at the tip which exacerbates the problem.

Conservative therapy of digital ulcerations typically focuses on reducing pressure and off-loading the problematic area, as well as appropriate local wound care. Offloading is often in the form of orthotic inserts, shoes with an extra-depth toe box to allow room for the contracted toe (s), or digital pads to protect against dorsal, plantar, or interdigital pressure. These measures are especially useful for pre-ulcerative or superficial ulcerative lesions. If these conservative measures fail to aid in timely wound healing, osteomyelitis is a frequent sequelae.

Conservative off-loading measures may not be effective if the wound is caused by digital deformity more so than ill-fitting shoes. Tip of toe ulceration associated with mallet toe deformity does not respond to longer shoes, and interdigital wounds may not resolve with wider shoes if the problem is caused by hallux valgus or an overlapping second toe. Understanding the biomechanics of neuropathic forefoot ulceration is therefore important and has significant impact when deciding on the ideal treatment plan including surgical procedure selection.

Osteomyelitis of a central toe is most commonly associated with a chronic wound that has failed to heal. Early surgical intervention allows prophylactic treatment of recurrent or nonhealing ulcerations with the intent to avoid progression to contiguous spread osteomyelitis and/or acute infection requiring amputation. The central toes are very amenable to reconstructive podiatric procedures which are designed to correct structural deformity and reduce bone prominence yet maintain a functional or at least cosmetically appealing toe.

Phalangeal osteomyelitis associated with gangrene typically develops late in the course of digital gangrene. Noninfected dry gangrene of the lesser toes is primarily treated with vascular intervention, while the affected toe is initially left alone to allow demarcation. Dry gangrene can be monitored for months while waiting to see if autoamputation is likely to occur. This process can be successful depending on restoration of digital perfusion and extent of tissue necrosis. Autoamputation ideally occurs distal to the tip of the distal phalanx which allows natural healing. Autoamputation through the IPJs results in bone and cartilage exposure which is less amenable to secondary healing. Some patients are able to granulate over the end of the bone, but osteomyelitis may eventually develop if bone remains exposed for an extended period of time. Conversion to a clean surgical site is often preferred and may simply require cutting the bone short enough that the soft tissue can finally heal over the bone.

Dry gangrene may eventually turn to infected wet gangrene as the nonviable tissue becomes necrotic and infected. Infected gangrene is commonly associated with osteomyelitis since full-thickness necrosis includes necrosis of the periosteum and joint capsule. The wait and watch approach is no longer an option once infection develops and surgical treatment is typically necessary. A surgical cure of phalangeal osteomyelitis associated with gangrene is likely to be achieved with toe, ray, or transmetatarsal amputation (TMA), but healing may be compromised in comparison to patients undergoing amputation for neuropathic conditions.

Central digital gangrene can also occur due to an embolic event which is less likely to become infected or need amputation. Embolic lesions tend to be smaller and may impact multiple toes which should prompt work up to identify a cause. These lesions are more amenable to the wait and watch approach to allow demarcation and eventual healing.

The diagnosis of central digital osteomyelitis requires consideration of the entire clinical picture since standard X-rays have a poor diagnostic track record. Advanced imaging is less practical for the small phalangeal bones of the central toes. Special X-ray techniques are helpful to isolate the area of concern since imaging of the involved toe may be compromised by overshadowing from adjacent toes and digital contracture (Fig. 16.6). The probe-to-bone test is particularly useful with toe ulcerations since bone is fairly close to the skin surface, though the positive predictive valve has been controversial [2, 3]. A nonhealing digital wound with deep depth or sinus tract concerning for bone or joint exposure plus clinical evidence of soft tissue infection should raise suspicion for osteomyelitis. Plain radiographs and laboratory workup combined with clinical findings are the mainstay of diagnosis at this stage, and we rarely pursue advanced imaging for central toe wounds. Bone biopsy is the next logical step which can be obtained in the process of bone debridement, IPJ arthroplasty, tip of toe amputation, or removal of the entire toe. The decision to remove the entire toe has more to do with compromised soft tissue or severe deformity that is not amenable to reconstructive procedures which are determined by clinical exam rather than MRI or bone scan. Needle biopsy of a central toe is possible but can be challenging due to the small nature of the phalanges and close proximity of wounds to the IPJs, toenail, and vascular structures. Needle biopsy does not address digital deformity or bone prominence, and therefore open bone resection may be the most prudent method to obtain bone specimen for biopsy.