Osteomyelitis of the Forefoot: Is Amputation Necessary?
Diabetic foot osteomyelitis (DFO) typically arises as a complication of long-term diabetes. It is often linked to advanced peripheral neuropathy, peripheral arterial disease, foot deformities, and inadequate adherence to foot care practices. One severe complication of DFO is major lower extremity amputation, such as below-knee or above-knee amputation.
According to the World Health Organization (WHO), the risk for lower limb amputation is 10 times increased in patients dealing with diabetes.1 Furthermore, the risk of amputation is 4 times greater in diabetic foot wounds that include osteomyelitis.2 Above-knee amputation and below-knee amputation carry a grim 5-year survivability rate of approximately 47.9% and 31.5% respectively, surpassing that of many cancers.3 Osteomyelitis develops in up to 15% of patients with diabetic foot wounds and can be misdiagnosed up to 68% of the time.4 Survivability for diabetic foot osteomyelitis remains low with up to 37.6% all-cause mortality at approximately 3 years.5
Diagnosing Osteomyelitis
Diagnosis of osteomyelitis for hospitalized patients typically consists of clinical examination, lab work, imaging, and histopathological analysis via bone biopsy. Clinical examination often involves utilizing the probe-to-bone test, which has varied accuracy throughout literature. This test may be better utilized to rule out osteomyelitis than to diagnose osteomyelitis.6 Common lab work performed to aid in the diagnosis of osteomyelitis includes white blood cell count (WBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). A meta-analysis compiled by Sharma and colleagues found the average WBC count to diagnose osteomyelitis to be 10,630 per microliter, CRP to be 8839.3 mg/L (although the authors did note that this average was based on a very wide range of values and suggested a need for further research) and ESR to be 39.4 mm/hr. The pooled sensitivity and specificity included; WBC 65.1% and 65.8%, CRP 68.5% and 70.6%, and ESR 72.6% and 79.5%.7
Imaging is also commonly utilized to aid in diagnosing osteomyelitis in the inpatient setting. A meta-analysis by Llewellyn and team evaluated radiographs and magnetic resonance imaging (MRI) in diagnosing osteomyelitis in the diabetic foot.8 Radiographs in this analysis had a sensitivity and specificity of 61.9% and 78.3% and MRI 96.4% and 83.8%.8 Limited literature is available at present on the sensitivity or specificity of computed tomography. Additionally, in our institution, we have found nuclear imaging/bone scans to be even less reliable in diagnosing diabetic foot osteomyelitis.
The gold standard for definitive diagnosis of osteomyelitis remains bone culture, often combined with histopathological evaluation. Even with these results, diagnosis can be difficult. In a study by Meyr and coworkers, diagnosis differed widely between different pathologists. The study reported only a 33.3% total agreement on a diagnosis of “osteomyelitis,” “cannot exclude osteomyelitis,” or “no osteomyelitis” when evaluating the same specimen between 4 different pathologists.9 As one can ascertain from the above statistics, any one modality is far from perfect. Taking this into account, a surgeon cannot make a diagnosis of osteomyelitis in the diabetic foot without full knowledge of the clinical picture, labwork, imaging, and histopathologic analysis results.
Treatment Options and Current Considerations
Treatment options for diabetic foot osteomyelitis in the literature can vary from antibiotic management to surgical treatment. Surgically, one can take a conservative or more aggressive approach.10 In our institution, we have found success in treating osteomyelitis by by steering clear of amputation as a first-line option.
Amputations in the lower extremity, although perhaps the most direct of the surgical approaches to eradicate the pathology, comes at the cost of a multitude of potential complications including operation revision, dehiscence, phantom limb sensation, delayed healing, and recurrent infection, among other complications.11 Not only do postoperative complications have to be considered when electing amputation in the lower extremity, but discussing mortality outcomes is a serious conversation. In a previous meta-analysis, the mortality rates after receiving a minor amputation in the lower extremity were as follows: 3.5% at 1 month, 20% at 1 year, 28% at 3 years, 44.1% at 5 years, 51.3% at 6 to 7 years, and 58.5% at 8 to 9 years.12 In considering the above statistics and degree of severity of these infections, different surgical approaches may offer better solutions. Henke and colleagues, in a large scale study found that surgical debridement/minimal amputation improves wound healing.13 Patients who underwent local debridement or ostectomy procedures also had improved rates of limb salvage.13 In confirmation, a study by Van and team found conservative surgical management of osteomyelitis without amputation to be superior compared to antibiotics alone.14
Additionally, there are other procedures in the lower extremity that target biomechanical pathologies that may contribute to improving outcomes in various infectious and potentially life-threatening processes in the lower extremity. For example, a study completed by Kim and colleagues investigated the effectiveness of plantar fascial releases in an effort to address nonhealing diabetic plantar ulcerations. Fifty-six percent of ulcers healed within six weeks of release, which included plantar toe ulcerations and metatarsophalangeal joint ulcerations.15 Additionally, a previous study compiled by Rasmussen and team assessed the effectiveness of flexor tenotomies to prevent and heal neuropathic ulcerations on the distal aspect of toes in hammertoe deformities in individuals with diabetes. Results illustrated that all patients who
underwent preventive tenotomies had experienced no future ulcerations and nearly 93% of all patients with previous toe ulcerations healed in a mean of 21 days.16
Alternatively, a case series conducted by Walsh and coworkers addressed how to avoid major amputation due to underlying calcaneal osteomyelitis by undergoing calcanectomies.17 Results demonstrated that in a group of 7 patients with diabetic calcaneal ulcerations, 5 patients healed completely who underwent prophylactic calcanectomies as a means to offload and distribute weight-bearing forces. These same individuals did not require future transtibial amputation.17 These studies illustrate that by addressing biomechanical deformities with concomitant limb-threatening pathology, surgeons can potentially significantly diminish or eliminate the need for amputation and lessen the overall potential risk for patients.
In this article, we discuss the technique for and cases of conservative surgical treatment of osteomyelitis and, during the same operation, address the underlying biomechanical etiology. This includes percutaneous fixation to address either a significant hammertoe deformity or significant metatarsophalangeal joint contracture. To the author’s knowledge, there is no available literature evaluating this topic.
A Potential Approach to Avoid Amputation
Once determining that osteomyelitis is likely, and is concomitant with metatarsophalangeal joint (MTPJ) or digital contractures, a comprehensive preoperative discussion with the patient is mandatory in our practice. We always give the patient a choice of the different treatment options for osteomyelitis. This typically includes amputation, salvage efforts, or local wound care with antibiotics, depending on the clinical scenario. If the patient elects to proceed with an attempt at salvage, we discuss the possibility of pin placement. The decision to use either percutaneous fixation includes whether a significant hammertoe contracture is noted preoperatively or metatarsophalangeal joint contracture is noted following intraoperative resection of infected soft tissue and bone.
Our clinical exam evaluates the digital contracture, such as assessing extension at the metatarsophalangeal joint, flexion at the proximal interphalangeal joint (PIPJ) and extension at the distal interphalangeal joint (DIPJ) for hammertoe deformities. Evaluation of extension at metatarsophalangeal joint, flexion at the proximal interphalangeal joint and distal interphalangeal joint for claw toes, and flexion contracture at the distal interphalangeal joint for mallet toes also comes into play. We typically order X-rays and a CT scan/MRI, along with vascular studies.
If a significant hammertoe contracture is noted preoperatively, we perform excision of infected soft tissue and bone to healthy margins, with irrigation and vancomycin powder packed into the wound. We find that the ulcers are typically at the dorsal proximal interphalangeal joint for those with hammertoe contracture or the distal tip of the toe for claw/mallet toes. For metatarsophalangeal joint instability the ulcers are typically plantar or lateral of the joint.
We typically close the wound with nylon suture. This in essence acts as a surgical cure of the bone infection with only healthy bone and tissue remaining. We follow this with flexor tenotomy and 2.0 mm Kirschner wire fixation across the contracted joints through and into healthy and stable bone.
If we note additional contracture across the metatarsophalangeal joint following excision of infected soft tissue and bone, we irrigate the surgical site, pack vancomycin powder into the wound, typically closing with nylon suture. Again, this acts as a surgical cure of the bone infection. 2.0 mm K-wire fixation is then placed through the toe and across the unstable joint into healthy and stable bone. This wire usually also traverses through the proximal cortical bone of the metatarsal to assure maximal stability.
Case Examples to Consider
Our first patient had diabetes and osteomyelitis of the head of the proximal phalanx (Figure 1a). After full discussion of risks and benefits of all options, the patient elected to proceed with salvage attempt and hammertoe correction. After undergoing this procedure, the patient experienced an unremarkable postop course (Figure 1b). Longer term, at 98 days, the patient presented with complete healing and maintenance of correction noted (Figure 1c).
Another patient suffered from osteomyelitis of the fifth metatarsophalangeal joint and was had instability following intraoperative resection of infected soft tissue and bone (Figure 2a (page 16)and Figure 2b online). Again, after full preop informed consent discussion, the patient elected for a salvage procedure and biomechanical correction. Postoperatively the patient went on to complete healing and maintained correction by 83 days out (Figure 2c online).
Concluding Thoughts
Osteomyelitis is often associated with amputation in the diabetic foot. Morbidity and mortality are quite high when a patient undergoes an amputation. Mortality rates are as high as 58.5 percent at 9 years for even minor amputations.12 Patients with diabetes are also predisposed to biomechanical faults that can cause ulcerations and eventually osteomyelitis. Some common biomechanical abnormalities that are common throughout the literature and in our own institution include equinus, hallux valgus, metatarsophalangeal joint contracture, and hammertoe deformities.18 By pursuing a surgical cure (removing all infected bone and soft tissue); we describe a technique with temporary hardware placement to address the causative biomechanical fault. This not only creates a stable wound healing environment, but also effectively combines 2 surgeries into one. This not only has potential economic benefits but may also prophylactically reduce recurrence of the ulceration and bone infection.
By adding temporary fixation across the affected joints, we believe that this alleviates tension on skin edges and provides biomechanical stability to allow for proper healing. Although our personal experience is positive, further prospective studies are necessary to further evaluate percutaneous fixation or external fixation across areas of resected osteomyelitis in the foot and ankle and the effects this has on wound healing and amputation avoidance.
Dr. King is an Associate of the American College of Foot and Ankle Surgeons and practices at the NOMS Foot and Ankle Center in Boardman, OH.
Dr. Perez is a resident at East Liverpool City Hospital in Liverpool, OH
Dr. DiDomenico is a Fellow of the American College of Foot and Ankle Surgeons and practices at the NOMS Foot and Ankle Center in Boardman, OH.
References
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