Mindful of the limb-threatening consequences that can arise if one does not properly diagnose and treat calcaneal osteomyelitis, this author examines the most effective modalities for diagnosing the bone infection, as well as non-invasive and surgical treatments.
Calcaneal osteomyelitis is a complicated clinical scenario that is often very difficult to treat. It can occur in individuals of any age who are injured or immunocompromised, and requires aggressive management.
Treatment ranges from antibiotics alone to radical debridement or amputation. If there is a delay in both diagnosis and treatment, calcaneal osteomyelitis can be limb-threatening or even life-threatening. The calcaneus is a completely cancellous bone that never forms an involucrum and seldom forms an isolated sequestrum. With calcaneal osteomyelitis, pus perforates the periosteum without destroying much of its cortex.1
Osteomyelitis is an infection involving the bone caused by various microorganisms such as bacteria and fungi. These organisms can infect the bones in several ways:2
• injury (bacteria enter the bone through a traumatic wound)
• direct extension (spread to the bone from an adjacent wound or infection)
• hematogenous (enters the bone via the bloodstream)
Although the most common bacterial pathogens are species of Staphylococcus and Pseudomonas, it is important to identify the organism(s) responsible for each individual osteomyelitis infection. After irrigation with 20 cc normal saline to eradicate contaminant bacteria from the site, obtain culture and tissue specimens for quantitative analysis from the deepest point of the wound.
In regard to appropriate antibiotics, patients may take oral or intravenous antibiotics. Other options may involve direct application into the wound via antibiotic beads, gels, ointments, patches or suppositories.
In some instances, osteomyelitis can persist and become chronic due to the presence of injured tissue and foreign material within the wound. Osteomyelitis is classified according to what parts of the bone are involved in the disease and the health of the patient. Based on their medical history, patients are classified as either compromised (B-hosts) or uncompromised (A-hosts). Compromised patients have decreased healing potential in comparison to uncompromised patients. Conditions that may classify a patient as an immunocompromised healer include:
• use of steroids
• poor nutrition
• extensive scarring
• use of tobacco products
• previous radiation therapy
• organ failure
• chronic lymphedema
• old age
• peripheral arterial disease
Tobacco use (smoking in particular) is the most common compromising factor in patients treated for osteomyelitis. With failures ranging from 30 to 100 percent in many protocols, the use of tobacco products during treatment may make the difference between limb salvage and amputation.3
For review, the Cierny-Mader classification of osteomyelitis is based on a combination of anatomic and physiologic staging to determine appropriate therapy (see the table “A Review Of Osteomyelitis Classification” at left).4
Differentiating osteomyelitis from other bone diseases is fairly simple. Infectious osteitis occurs with suppuration of cortex without marrow involvement. Infectious periostitis does not show bone marrow edema but has periosteal contamination and inflammation.
Osteolysis of bone only occurs after the infectious hyperemic process has “washed out” 30 to 50 percent of osseous mineralization.5 This process takes anywhere from 10 to 14 days after the onset of symptoms. Sclerosis and new perisoteal bone formation called involucrum surrounds infected and necrotic bone and sequestrum. A channel, cloaca, forms in new bone as bacteria and exudates drain. Chronic osteomyelitis involves the presence of bacteria living and surviving in sequestrum surrounded by involucrum. Chronic osteomyelitis can survive dormant for many years before a flare-up can occur.5
Radionuclide bone scans are useful in suspected osteomyelitis and are usually positive within 72 hours of infection.6 Tc-99 and In-111 are the most common initial scan techniques but the most useful radionucleotide scan for osteomyelitis is the Ceretec scan. While Ceretec scans are sensitive, the level of specificity lags behind the specificity of magnetic resonance imaging (MRI).7
Computed tomography (CT) provides excellent multiplanar reconstructions of the axial images, allowing delineation of even the subtlest osseous changes. In chronic osteomyelitis, CT scans demonstrate abnormal thickening of the affected cortical bone with sclerotic changes, encroachment of the medullary cavity and a chronically draining sinus. Although CT scans may show these changes earlier than plain radiographs, CT scans are less desirable than MRI because of the decreased soft tissue contrast as well as exposure to ionizing radiation.5,8
The major role of this technique in osteomyelitis is the detection of sequestra in cases of chronic osteomyelitis as surrounding osseous abnormalities on conventional radiography can mask these pieces of necrotic bone. The presence of pieces of sequestered bone suggests that the activity of the infectious process and its detection is helpful to guide the therapeutic options. Computed tomography is superior to MRI for the detection of sequestra, cloacas, involucra or intraosseous gas.5
Ultrasound has multiple advantages. It is readily accessible and one can perform it quickly and with minimal discomfort to the patient. Ultrasound is useful in regions that are not easily visible due to the presence of operative orthopedic instrumentation and therefore might not be easy to visualize with MRI or CT. Similarly, ultrasound is useful in patients in whom MRI is contraindicated. Finally, ultrasound has a lower cost, does not use ionizing radiation and offers real-time imaging. For these reasons, ultrasound is a useful tool in the evaluation of musculoskeletal infections and is particularly helpful in differentiating acute or chronic infections from tumors or non-infective conditions.
Ultrasound is also able to localize the site and extent of infection, identify precipitating factors such as foreign bodies or fistulae, and provide guidance for diagnostic or therapeutic aspiration or biopsy.9 Ultrasonography can detect features of osteomyelitis several days earlier than conventional radiographs (predominately in children). Using ultrasound, one would recognize acute osteomyelitis via elevation of the periosteum by a hypoechoic layer of purulent material.10 In cases of chronic osteomyelitis, ultrasonography can also assess the involvement of the adjacent soft tissues. Soft tissue abscesses related to chronic osteomyelitis appear as hypoechoic or anechoic fluid collections, which may extend around the bony contours. Finally, cortical erosions can become apparent on ultrasonography.10
Magnetic resonance imaging is the imaging modality of choice for patients with osteomyelitis of the calcaneus. There is altered intensity of the affected bone. The MRI captures soft tissue infections, which makes it helpful to distinguish sensitivity. Researchers report MRI to be 90 to 100 percent sensitive for osteomyelitis while the specificity ranges between 80 to 100 percent.11 The normal high signal intensity of T1 images is replaced with decreased signal intensity and T2 images, which are dark normally, show increased signal intensities.12
The underlying treatment principle with non-surgical treatment is to provide an environment where antibiosis can work effectively. Unfortunately, no antibiotic has proven to be superior in the complete eradication of osteomyelitis infections.13 In treating osteomyelitis of the heel non-surgically, it is imperative to cover for Staphylococcus due to its high incidence and prevalence.14 There is no preferred route as research has shown neither parenteral nor oral to be more effective than the other.13,14
Classically, clinicians provide four to six weeks of parenteral therapy with concomitant serial debridements to remove the infected bone. It is of course reasonable to have a shorter duration of treatment with parenteral therapy and a longer duration with oral therapy.14 Additionally, there is no current substantial scientific evidence that gives a consistently predictable result with medical, parenteral or oral therapy for the treatment of osteomyelitis.15
Hyperbaric oxygen therapy (HBOT) can be a useful adjunct in the non-operative management of osteomyelitis as well as improving post-surgical outcomes. Hyperbaric oxygen therapy helps fight this disease in the following three ways.
• HBOT helps strengthen the osteoclasts that reabsorb dead bone, allowing the osteoclasts to remove bony debris more effectively.
• HBOT enhances the function of the immune system’s white blood cells, which depend on oxygen. For this reason, HBOT is especially effective when one uses it with antibiotics as it supports the action of the antibiotics.
• HBOT helps the body create new capillaries.16
As a result of these three factors, the body is able to get rid of the diseased bone and replace it with healthy bone.
Oxygen is important in wound healing. When the environment of the fibroblast cell has an oxygen tension of less than 10 mmHg, the cell can divide but it can no longer make collagen. It also cannot migrate to where it is needed for healing. When the oxygen tension increases, the fibroblast can again carry out these wound healing functions. The collagen produced by these cells forms a fibrous matrix and new capillaries grow into this. Wound healing is a dynamic process and an adequate oxygen tension is mandatory for this process to proceed to healing. Hyperbaric oxygen provides oxygen to promote collagen production, angiogenesis and wound healing in the ischemic or infected wound. An adequate supply of oxygen is integral in the treatment of osteomyelitis.17
In its online guidelines on refractory osteomyelitis treatment, the Undersea and Hyperbaric Medical Society (UHMS) notes that HBOT delivery ordinarily occurs with daily treatments of 90 to 120 minutes at 2.0 to 3.0 ATA, starting soon after surgical debridement and continuing for four to six weeks.16 The UHMS notes that this recommendation is based on best clinical practice and there are no randomized clinical trials to support it.16 However, the substantial majority of available animal data, human case series and non-randomized prospective trials suggest that adding HBOT therapy to routine surgical and antibiotic management of osteomyelitis is safe and improves the ultimate rate of infection resolution. As antibiotics and other traditional weapons against these worrisome microscopic invaders begin to weaken, HBOT provides a vital backstop.
When conservative management fails or the infection within the calcaneus is grossly beyond the point of conservative care, surgical management is necessary to resolve the infection and preserve the extremity. The partial calcanectomy with resection of all non-viable tissue and bone is necessary to ensure limb preservation.
When doing perioperative planning for a partial calcanectomy, patient and family education are paramount. One should state that the procedure is a “salvage” procedure and that below-knee amputation may still occur in the future. Further debridements may also be necessary and one should explain this to the patient and/or the patient’s family.17
Direct the surgical approach as a linear-posterior or posterior-medial orientation. Alternatives can include a hockey-stick, posterior-lateral approach, which gives extensive exposure. Ensure prone positioning of the patient for the procedure. If there are anesthesia concerns, the patient should be in a lateral recumbent position with vacuum beanbag positioning.18
When planning the incision, make sure the flaps of skin are in full thickness. Do not undermine the subcutaneous tissues. Handle the skin gently with minimal use of retraction. Avoid using a tourniquet in these cases as the healthy bleeding tissue serves as a guide during the surgical resections. Detach the Achilles tendon and resect any non-viable portions. It is important to retain the length of the Achilles for the reattachment procedure.
Remove the posterior calcaneus at an angle consistent with a posterior-proximal to plantar-distal axis, removing all non-bleeding bone. When performing a partial calcanectomy, it is useful to combine power and hand instrumentation.19 The total amount of bone removed is usually one-half to two-thirds of the calcaneal body but one will determine this by the extent of the clinical presentation and infectious process. Surgeons may apply antibiotic beads directly to the open medullary bone as local antibiosis after resecting the posterior calcaneus.
In the past, polymethylmethacrylate (PMMA) beads were in use and had to be removed from patients. Additionally, while commercial formulations of PMMA beads are available outside the United States, they currently are not available within the United States, leaving the hospital pharmacies or podiatric surgeons to produce their own formulation.20 Clinicians may combine commercially available PMMA cements and antibiotic powder to form a liquid-like substance. Then they place this substance into molds or hand roll it in the operating room to form beads.
More recently, there has been expanding use of calcium sulfate-antibiotic impregnated beads for local use in bone. There have been reports in the literature of packing calcium sulfate beads as an antibiotic delivery system within bony defects with good success.21 The use of calcium sulfate beads is off-label and without FDA approval. As with PMMA, the surgeon must mix the antibiotic with the calcium sulfate mixture to create the antibiotic beads. Complete resorption of the beads occurs at six months or sooner, and one can use serial radiographs to follow the progress clinically.
Sulfate-antibiotic impregnated beads also have the advantage of a more reliable elution profile of antibiotics than traditional PMMA as there is more delivery of the antibiotic in the postoperative period. The antibiotic releases completely over a two- to three-month period with high concentrations detectable for at least four weeks.21
Reattachment of the Achilles tendon needs to occur under physiological tension. Modalities for reattachment include suture anchors, plain sutures, locking bridge sutures or plating. Closure of the wound can be difficult if tension is present. Primary closure is preferable but in cases in which tension on the tissues is an issue, one may use bolster sutures. Otherwise, the use of negative pressure wound therapy may assist with closure.22
For initial post-op management, one should apply a Jones compression cast with a posterior splint applied in plantarflexion. Non-weightbearing lasts for a period of six to eight weeks. Inspect the incision and wound weekly and reduce the amount of plantarflexion to more dorsiflexion on a week-to-week basis. Physical therapy is beneficial when the wounds have fully healed. Then the patient can transfer to a pneumatic walking boot.
Coordinate IV antibiotics with the infectious disease specialist as well as other medical providers for a continual multidisciplinary approach. One should leave grossly infected wounds open or treat them with negative pressure wound therapy, routinely re-debriding them as necessary. Vascular surgery consultations are critically important for these patients given the need to heal rapidly. These patients are in high-risk populations and have multiple comorbidities that can derail your surgery, and prospectively place the patients in less tenable positions that may require higher level amputation, further debridement or longer-term antibiotic coverage.
Understanding the complex nature of calcaneal osteomyelitis and its effect on the outcome of care in patients are of profound importance. A team approach is absolutely necessary in order to have positive outcomes for patients. These patients are high risk and require substantial perioperative evaluations regarding their history. There is no current medical literature that determines when it is appropriate to treat osteomyelitis alone medically and when to initiate surgical treatment. A comprehensive patient-oriented approach will help to determine the course of treatment. Acting decisively, whether through medical or surgical means, can facilitate beneficial outcomes in these difficult to treat patients.
Dr. Lullove is in private practice in Boca Raton, Fla. He is a Fellow of the American College of Clinical Wound Specialists.
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Editor’s note: For further reading, see “Osteomyelitis: Keys To Diagnosis And Treatment” in the December 2012 issue of Podiatry Today, “Current Concepts In Treating Osteomyelitis” in the July 2007 issue or “Current Concepts In Treating Diabetic Foot Osteomyelitis” in the October 2009 issue.