Revisional Surgery of Foot and Ankle Osteomyelitis

Crystal L. Ramanujam, John J. Stapleton, Thomas Zgonis

Osteomyelitis is considered one of the oldest diseases in history, dating back to 2500 to 3000 BC with the first written description of a case in humans from an Egyptian surgical treatise and then in 460 to 370 BC when Hippocrates reported on infection after bone fracture.¹^,² Prior to the development of antibiotics, treatment of osteomyelitis was predominantly surgical and was associated with high morbidity and mortality rates. In the last century, despite an improved understanding behind the pathophysiology of osteomyelitis, few advances have been made in development of novel treatment options that prevent or decrease rates of recurrent infection in the foot and ankle, leaving the core principles of treatment still focused on a combination of antibiotic therapy and surgical resection. With the advent of adjunctive therapies such as negative pressure wound therapy, antibiotic delivery systems and orthobiologics, along with various innovative podoplastic surgical techniques and external fixation, options have grown for revisional surgery to combat infection, address soft-tissue and bone defects, and correct residual deformity. The populations most vulnerable to the development of osteomyelitis are those in which blood flow to the bone is adversely affected, including but not limited to trauma, surgery, diabetes mellitus, peripheral vascular disease, and immune deficiencies.³

Diabetic Foot Osteomyelitis

An increasing trend in the prevalence of foot and ankle osteomyelitis has been seen over the last few decades as related to improved diagnostic methods and according to the rise in the prevalence of diabetes mellitus worldwide. A closer look at the literature reveals that the pathophysiology of osteomyelitis in the diabetic foot is different from that found in nondiabetic patients who have developed osteomyelitis following elective or nonelective surgery.⁴ Diabetic foot osteomyelitis (DFO) is the most frequent complication of diabetic foot ulcerations, often leads to hospitalization, and is associated with high rates of amputation.⁵ These infections are most commonly polymicrobial, and the most common anatomic location for development of DFO is the forefoot based on the anatomy composed of thinner barriers between the external environment and the bone, allowing bacteria to have easier access to cause infection upon entry. Toe, partial ray (toe and metatarsal), and transmetatarsal amputations make up the majority of minor amputations in DFO. High complication rates have been associated with these surgeries including recurrence of ulcerations and DFO, hospital readmissions, reoperations, and sometimes more proximal minor foot or major amputations (below-the-knee or above-the-knee).⁶^,⁷ Following minor amputation, imbalance of the foot during gait with increased plantar pressures may lead to new open wounds and foot/ankle instability causing compensatory deformities. In 2012 with a systematic review of partial first ray amputations, Borkosky and Roukis found a 19.8% incidence of reamputation.⁸ While in 2016, in a systematic review of transmetatarsal amputations, Thorud et al found an estimated reoperation rate of 24.43% and the reamputation rate was estimated at 28.37%.⁷ Development of Charcot neuroarthropathy (CN) after minor diabetic foot amputations has also been reported as a complication, either as a result of mechanical trauma following altered foot function postamputation or due to the trauma of surgery itself.⁹

Diabetic Charcot Foot and Ankle Osteomyelitis

Complications after diabetic CN foot and ankle surgical reconstruction are common; however, rates of reoperation and amputation for CN with concomitant osteomyelitis are known to be even higher.¹⁰ ^–¹⁴ In a study of 116 patients surgically reconstructed CN patients using external fixation, Ramanujam et al analyzed amputation and mortality rates and found that osteomyelitis was a statistically significant predictor for the mortality rate.¹¹ Berli et al determined that osteomyelitis within the CN region was associated with a higher level of amputation and longer durations of antibiotic therapy and immobilization.¹² In a systematic review on published studies of 1089 patients who had surgical reconstruction for CN, Ha et al found an overall complication rate of 36%, while fixation-specific complications were determined to be 25% in the external fixation, 41.4% in the internal fixation, and 70% in combined fixation groups.¹³ For a systematic review of surgical treatment of diabetic midfoot CN with osteomyelitis, Ramanujam et al placed the surgical procedures from the selected studies into 3 main categories to analyze outcomes: (1) debridement and simple exostectomy, (2) debridement and arthrodesis with or without internal and/or external fixation, and (3) those requiring additional soft-tissue reconstruction using plastic surgical techniques such as flaps.¹⁴ Categories 1 and 2 had overall high success rates with only minor complications, while higher minor and major complication rates were found in Category 3 which the authors reasoned that such cases requiring consideration for advanced plastic surgical techniques are often composed of more complex, extensive soft-tissue and/or bone defects that are prone to healing problems.¹⁴ As seen in DFO, the most common bacterial isolate reported in diabetic CN foot osteomyelitis is Staphylococcus aureus; however, anaerobes and Pseudomonas aeruginosa have more recently been implicated in severe diabetic CN foot infections.¹⁵

Nondiabetic Foot and Ankle Osteomyelitis

Most of the literature pertaining to outcomes of nondiabetic patients with foot and/or ankle osteomyelitis includes management of open fractures and procedures including placement of hardware and/or prostheses. Placement of foreign material into a biological environment provides a great source for bacteria to potentially cause infection. Furthermore, movement induced wear on implants causes release of debris resulting in local inflammation and may create an optimal site for infection.¹⁶ Risks factors in these cases include older age, history of smoking, and peripheral neuropathy of nondiabetic etiology.¹⁷ The predominant pathogenic organism in these infections is Staphylococcus aureus, with methicillin-resistant Staphylococcus aureus (MRSA) involved in over half of reported cases. Success in these cases of revisional surgery is dependent on complete removal of infected and devitalized tissue and hardware. In addition, maintenance of stability and anatomical alignment at the site of fractures or arthrodesis is crucial for positive outcomes.

Indications and Contraindications

Decision for any revisional surgery for foot and ankle osteomyelitis is highly dependent on the specific clinical presentation of the patient. General indications for revisional surgery may include but are not limited to signs of local and/or systemic infection, osteomyelitis at the same or contiguous site as the previous episode, development of large soft-tissue defects, wound dehiscence, abscess, evidence of ischemia and/or necrotic tissue, exposed bone, reulceration despite local wound care and failure of conservative off-loading, reinfection that has failed antibiotic therapy, exposed hardware, hardware infection and/or failure, infected nonunion or malunion, and development of worsening foot or ankle deformity with instability that cannot be accommodated by shoe gear or bracing. Contraindications for revisional surgery may include the presence of medical comorbidities that preclude optimization for surgical intervention, peripheral vascular disease that is not amenable to intervention with vascular procedures, severe patient noncompliance, and patient’s refusal of reoperation.

Preoperative Considerations

A multidisciplinary team approach should be employed in cases of revisional surgery for foot and ankle osteomyelitis since these patients often present with multiple medical comorbidities that require management prior to surgical intervention. Overall medical status including cardiac issues, kidney and vascular disease, elevated glycosylated hemoglobin (HbA1C), and anemia should be optimized to proceed safely to surgery. A thorough past medical history including all prior surgical interventions pertinent to the site of osteomyelitis as well as retained hardware and previous or current antibiotic therapy is imperative for surgical planning. Recently, an increase in the occurrence of chronic wound infections with multiple drug–resistant organisms (MDROs) in the diabetic population has been noted and primarily attributed to MRSA, but antibiotic-resistant gram-negative organisms, particularly Pseudomonas aeruginosa, have also been implicated.¹⁸^,¹⁹ Physical examination should include vital signs, thorough wound evaluation, and assessment of biomechanical function to determine whether any issues should be addressed surgically to prevent reulceration. Preoperative imaging studies includes plain film radiographs of the foot and ankle with weight-bearing views, tibia-fibula and calcaneal axial views based on the given pathology, computed tomography (CT) for joint involvement and full deformity assessment in cases of fractures, arthrodesis, and CN, and magnetic resonance imaging (MRI) to evaluate the extent of osteomyelitis. Nuclear imaging through a combination of technetium-99m-MDP scan, indium-111–labeled leukocyte scan, and bone marrow scintigraphy has become useful in determining CN with and without osteomyelitis.²⁰

Laboratory analysis to assess hemodynamic stability should include a comprehensive metabolic profile, coagulation studies, and complete blood cell count; however, impaired immune response often encountered in diabetic patients might not show abnormalities. Inflammatory markers erythrocyte sedimentation rate and C-reactive protein are nonspecific but can be useful to trend response before and after antibiotic therapy and surgical debridement. Staged procedures are frequently employed to allow for complete eradication of infection prior to definitive reconstruction. Careful attention to the patient’s bone stock is crucial in determining appropriate osseous stabilization procedures. Extensive patient education perioperatively is necessary to keep both the patient’s and surgeon’s expectations clear throughout the reconstructive process. Surgical reconstruction may include the use of adjunctive modalities such as negative pressure wound therapy, nonbiodegradable antibiotic cemented beads and/or spacers, bone grafting, and allogenic skin grafts.

In cases of large bone and soft-tissue defects, nonbiodegradable antibiotic cemented beads and/or spacers can be considered. The vehicle of delivery is most commonly polymethylmethacrylate (PMMA), which is combined with a heat stabile antibiotic, and this mixture is formed into either beads or spacers for local application within the surgical wound after adequate surgical debridement ²⁰ (Figure 30.1). The antibiotic-loaded PMMA cemented beads or spacers are maintained intact and within the surgical wound while the patient is also receiving culture-specific systemic or oral antibiotic therapy and are removed surgically depending on the clinical, medical imaging, and systemic presentation. While delivering antibiotic locally, the antibiotic-loaded PMMA cemented beads or spacers also provide a void filler to stabilize the soft tissues and bone structures surrounding them. The ability of these local antibiotic delivery systems to facilitate sterilization at the site with decreased bacterial count can also be optimal in preparation for further soft-tissue reconstructive procedures such as local random, muscle, and pedicle flaps and osseous reconstruction with an arthrodesis procedure²⁰ (Figure 30.2).