Musculoskeletal Infections: Symptoms, Causes & Treatment

What Are Musculoskeletal Infections?

Musculoskeletal infections are infections that affect the bones, joints, and muscles of the body. The three main types are osteomyelitis (bone infection), septic arthritis (joint infection), and myositis/pyomyositis (muscle infection). These infections are typically caused by bacteria, most commonly Staphylococcus aureus, and require prompt antibiotic treatment to prevent serious complications.

Musculoskeletal infections represent a spectrum of serious conditions that can affect people of all ages, though certain populations face higher risk. The musculoskeletal system, consisting of bones, joints, muscles, tendons, and ligaments, provides structural support and enables movement. When bacteria, fungi, or other microorganisms invade these tissues, they can cause significant damage and potentially life-threatening complications if not treated promptly and appropriately.

The pathophysiology of musculoskeletal infections involves the complex interplay between invading pathogens and the host immune response. When bacteria reach bone or joint tissue, they trigger an inflammatory response that, while intended to fight the infection, can also cause tissue destruction. In bones, this process leads to formation of pus, death of bone tissue (sequestrum formation), and disruption of blood supply. In joints, the accumulation of pus and inflammatory mediators rapidly destroys the protective cartilage that lines joint surfaces.

Understanding the different types of musculoskeletal infections is essential for recognizing symptoms and seeking appropriate care. Each type has distinct characteristics, risk factors, and treatment considerations, though they share common features including the need for rapid diagnosis and aggressive treatment.

Osteomyelitis (Bone Infection)

Osteomyelitis is an infection of the bone that can occur at any age and in any bone of the body. The infection can be acute, developing rapidly over days to weeks, or chronic, persisting for months or years with periods of relative quiet punctuated by flares of active infection. In children, osteomyelitis most commonly affects the metaphysis (the growing ends) of long bones such as the femur (thigh bone), tibia (shin bone), and humerus (upper arm bone). This predilection occurs because the rich blood supply and unique vascular anatomy of growing bone make these areas particularly susceptible to bacterial seeding from the bloodstream.

In adults, the pattern of osteomyelitis differs significantly. Vertebral osteomyelitis, affecting the bones of the spine, becomes increasingly common with age and is the most frequent form in adults over 50. The lumbar spine is most commonly affected, followed by the thoracic and cervical regions. Adults also frequently develop osteomyelitis in the feet, particularly those with diabetes mellitus, where infection typically arises from ulcers or wounds that penetrate to bone.

Septic Arthritis (Joint Infection)

Septic arthritis, also known as infectious arthritis or pyogenic arthritis, is a medical emergency. Bacteria within a joint space trigger an intense inflammatory response that rapidly destroys articular cartilage, the smooth protective tissue covering bone ends within joints. Studies have shown that irreversible cartilage damage can begin within 24-48 hours of infection onset, making rapid diagnosis and treatment absolutely critical.

The knee is the most commonly affected joint in both children and adults, accounting for approximately 40-50% of cases. The hip is the second most common site, followed by the shoulder, ankle, elbow, and wrist. In intravenous drug users, unusual sites such as the sternoclavicular joint (where the collarbone meets the breastbone) and sacroiliac joints (in the pelvis) are more frequently infected.

Myositis and Pyomyositis (Muscle Infection)

Pyomyositis is a bacterial infection of skeletal muscle that results in abscess formation within the muscle tissue. While historically considered a tropical disease, pyomyositis is increasingly recognized in temperate climates, particularly among immunocompromised patients. The quadriceps and gluteal muscles are most commonly affected, likely due to their large size and susceptibility to minor trauma that may allow bacterial entry.

Infectious myositis can also be caused by viruses, leading to inflammation and muscle pain without abscess formation. Viral myositis, often associated with influenza or other respiratory infections, typically causes diffuse muscle aching (myalgia) that resolves as the viral illness clears. In rare cases, parasitic infections can also affect muscle tissue.

What Causes Musculoskeletal Infections?

Musculoskeletal infections are primarily caused by bacteria, with Staphylococcus aureus responsible for 40-50% of cases. Bacteria reach bones, joints, or muscles through three main routes: spread through the bloodstream (hematogenous), direct inoculation from trauma or surgery, or extension from adjacent infected tissue. Risk factors include diabetes, immunosuppression, prosthetic implants, and recent surgery.

Understanding the causes and mechanisms of musculoskeletal infections is fundamental to both prevention and treatment. The causative organisms, routes of infection, and underlying risk factors all influence how these infections are managed and what outcomes can be expected.

Causative Organisms

Staphylococcus aureus dominates as the leading cause of musculoskeletal infections across all age groups and anatomical locations. This bacterium possesses an array of virulence factors that make it particularly adept at invading and surviving within bone and joint tissue. Surface proteins called adhesins allow S. aureus to attach to bone matrix and prosthetic material. The organism can also form biofilms, protective communities of bacteria encased in a self-produced matrix that shields them from both the immune system and antibiotics.

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as an increasingly important pathogen in musculoskeletal infections. Community-acquired MRSA strains now cause a substantial proportion of bone and joint infections, even in patients without traditional healthcare exposure. These strains are often more virulent than their hospital-acquired counterparts and can cause severe, rapidly progressive infections.

Other important bacterial causes include:

• Streptococcus species: Group A streptococcus (Streptococcus pyogenes) and Group B streptococcus (Streptococcus agalactiae) are significant causes, particularly in neonates and the elderly
• Gram-negative bacteria: Escherichia coli, Pseudomonas aeruginosa, and other gram-negative organisms are more common in certain populations, including the elderly, intravenous drug users, and immunocompromised patients
• Kingella kingae: This fastidious organism has emerged as a leading cause of bone and joint infections in children under 4 years of age
• Mycobacterium tuberculosis: Tuberculous osteomyelitis and arthritis remain important causes globally, particularly in endemic regions
• Fungi: Candida species and other fungi can cause musculoskeletal infections in severely immunocompromised patients

Routes of Infection

Bacteria and other pathogens reach the musculoskeletal system through three primary routes, each with distinct clinical implications:

Hematogenous spread occurs when organisms traveling in the bloodstream seed into bone, joint, or muscle tissue. This is the most common route in children with osteomyelitis and is frequently the cause of vertebral osteomyelitis in adults. Any source of bacteremia, from skin infections to dental procedures to endocarditis, can potentially lead to musculoskeletal seeding. The unique vascular anatomy of growing bones, with their slow, sinusoidal blood flow in the metaphysis, creates an environment conducive to bacterial settling and multiplication.

Direct inoculation occurs when organisms are introduced directly into tissue through penetrating trauma, open fractures, or surgical procedures. This route is particularly important in post-traumatic osteomyelitis following compound fractures and in prosthetic joint infections following arthroplasty. Even with meticulous surgical technique and prophylactic antibiotics, a small percentage of orthopedic implants become infected.

Contiguous spread happens when infection extends from adjacent infected soft tissue into bone or joint. This mechanism underlies diabetic foot osteomyelitis, where infected ulcers gradually erode through soft tissue to reach underlying bone. Pressure ulcers (bedsores) can similarly lead to underlying osteomyelitis, particularly in the sacrum, ischium, and greater trochanter.

Risk Factors

Certain conditions and circumstances significantly increase the risk of developing musculoskeletal infections. Understanding these risk factors is essential for prevention and early recognition:

Diabetes mellitus is one of the most important risk factors, increasing susceptibility to all types of musculoskeletal infections. Diabetic patients have impaired immune function, poor circulation, and neuropathy that prevents them from feeling injuries. Diabetic foot osteomyelitis affects up to 20% of patients with diabetic foot infections and is a leading cause of non-traumatic lower extremity amputation.

Immunosuppression from any cause increases infection risk. This includes HIV/AIDS, chemotherapy, organ transplantation requiring immunosuppressive medications, chronic corticosteroid use, and primary immunodeficiency disorders. These patients may also present atypically with muted symptoms and delayed diagnosis.

Prosthetic joints and orthopedic hardware provide surfaces for bacterial attachment and biofilm formation. Despite prophylactic antibiotics and sterile technique, approximately 1-2% of primary joint replacements and higher percentages of revision surgeries become infected.

Intravenous drug use dramatically increases risk through repeated bacterial inoculation from non-sterile injection practices. This population also frequently develops infections in unusual locations and with unusual organisms.

What Are the Symptoms of Musculoskeletal Infections?

Common symptoms include localized pain that worsens over time, swelling, redness, and warmth over the affected area, fever (often high in acute infections), and inability to use the affected limb or joint. In children, refusal to walk or use an arm may be the primary sign. Symptoms typically develop over days for acute infections but may be subtle in chronic or low-grade infections.

The clinical presentation of musculoskeletal infections varies depending on the specific type of infection, the causative organism, the patient's age and immune status, and whether the infection is acute or chronic. However, certain symptoms and signs are common across different infection types and should prompt immediate medical evaluation.

Symptoms of Osteomyelitis (Bone Infection)

Acute hematogenous osteomyelitis, most common in children, typically presents with the rapid onset of pain, swelling, and warmth over the affected bone. The child often develops high fever (frequently above 39°C/102°F) and appears systemically unwell with fatigue, decreased appetite, and irritability. In young children and infants who cannot verbalize pain, the hallmark sign may be refusal to use the affected limb, described as "pseudoparalysis." Parents may notice the child refusing to walk, crawl, or move an arm without any preceding injury.

Vertebral osteomyelitis in adults presents quite differently. Back pain is the predominant symptom, typically localized to the affected spinal segment and often described as severe and unrelenting. The pain may worsen at night and is not relieved by rest, distinguishing it from mechanical back pain. Fever is present in only about half of cases, and its absence should not falsely reassure patients or clinicians. Some patients develop neurological symptoms if the infection extends to involve the spinal canal, including weakness, numbness, or bowel and bladder dysfunction, which constitute a medical emergency.

Chronic osteomyelitis may present more indolently, with persistent mild to moderate bone pain, intermittent low-grade fevers, and sometimes the development of draining sinuses (channels from the infected bone to the skin surface through which pus drains). Some patients experience periods of relative quiescence alternating with acute flares.

Symptoms of Septic Arthritis (Joint Infection)

Septic arthritis typically causes acute onset of joint pain, swelling, warmth, and redness. The affected joint is often exquisitely tender, and patients strongly resist any movement due to severe pain. The joint may visibly swell and appear red and hot compared to the opposite, unaffected joint. Fever is common but not universal, particularly in elderly or immunocompromised patients.

The knee, being the most commonly affected joint, typically presents with obvious swelling, inability to fully straighten or bend the knee, and reluctance to bear weight. Hip septic arthritis is more challenging to diagnose because the joint is deep and swelling may not be visible. Patients typically hold the hip in a position of slight flexion and external rotation, which maximizes joint volume and minimizes pain. Children with hip infection may present with referred pain to the knee or thigh, potentially misdirecting initial evaluation.

Symptoms of Pyomyositis (Muscle Infection)

Pyomyositis typically progresses through three clinical stages. In the first (invasive) stage, which may last 1-3 weeks, patients experience mild muscle pain, low-grade fever, and general malaise. The affected muscle may be slightly swollen but not dramatically so. At this early stage, pus has not yet formed, and diagnosis can be challenging.

The second (suppurative) stage occurs as frank abscess develops within the muscle. Fever becomes more prominent, often with rigors (severe shaking chills). The affected muscle becomes tender, swollen, and may develop overlying redness and warmth. If untreated, the infection can progress to the third stage with septic shock, requiring intensive care support.

How Are Musculoskeletal Infections Diagnosed?

Diagnosis combines clinical evaluation, laboratory tests, and imaging studies. Blood tests showing elevated inflammatory markers (CRP, ESR) and white blood cells suggest infection. MRI is the most sensitive imaging test for bone and soft tissue infections. Joint aspiration (arthrocentesis) is essential for diagnosing septic arthritis. Cultures from blood, joint fluid, or bone biopsy identify the causative organism and guide antibiotic selection.

Prompt and accurate diagnosis of musculoskeletal infections is essential for optimal outcomes. The diagnostic approach combines careful clinical assessment with laboratory testing, imaging studies, and often invasive sampling to confirm infection and identify the causative organism. Each of these components provides complementary information that together builds the diagnostic picture.

Clinical Evaluation

The diagnostic process begins with a thorough history and physical examination. Clinicians ask about symptom onset and progression, any recent infections elsewhere in the body, history of trauma or surgery, and the presence of risk factors such as diabetes, immunosuppression, or prosthetic joints. Physical examination focuses on the affected area, assessing for swelling, erythema (redness), warmth, tenderness, and range of motion. For suspected septic arthritis, the examiner notes the joint's resting position and assesses for effusion (fluid accumulation).

Laboratory Tests

Several blood tests help support the diagnosis of musculoskeletal infection and monitor response to treatment:

C-reactive protein (CRP) is an acute phase reactant that rises within hours of infection onset and typically becomes markedly elevated in musculoskeletal infections. CRP levels help distinguish infection from other inflammatory conditions and are useful for monitoring treatment response, as levels should decline with effective therapy.

Erythrocyte sedimentation rate (ESR) is another inflammatory marker that rises in infection but more slowly than CRP. ESR may remain elevated for weeks even with successful treatment, making it less useful for monitoring acute response but valuable for detecting chronic infection or relapse.

White blood cell count (WBC) may be elevated, particularly in acute bacterial infections, though a normal count does not exclude infection. The differential count showing a leftward shift (increased proportion of immature neutrophils) suggests bacterial infection.

Blood cultures should be obtained before starting antibiotics whenever possible. Positive blood cultures occur in approximately 30-50% of acute hematogenous osteomyelitis cases and provide valuable information about the causative organism without requiring invasive sampling.

Imaging Studies

Plain radiographs (X-rays) are often the first imaging study obtained but have significant limitations in early infection. Bone changes from osteomyelitis, such as periosteal elevation or bone destruction, may not be visible until 10-14 days after infection onset. However, X-rays are useful for excluding other conditions and may show soft tissue swelling or joint effusion.

Magnetic resonance imaging (MRI) is the gold standard for diagnosing musculoskeletal infections, with sensitivity and specificity exceeding 90% for osteomyelitis. MRI can detect bone marrow edema and soft tissue abnormalities within days of infection onset, far earlier than plain radiographs. It also precisely delineates the extent of infection, identifies abscesses, and reveals complications such as epidural extension in vertebral osteomyelitis.

Computed tomography (CT) provides excellent bone detail and is useful for identifying sequestra (fragments of dead bone) and guiding biopsy procedures. CT with contrast enhancement can identify soft tissue abscesses and is valuable when MRI is contraindicated.

Nuclear medicine imaging, including bone scintigraphy and white blood cell scans, may be helpful in specific situations, such as evaluating for multifocal infection or distinguishing infection from other bone abnormalities.

Invasive Sampling

Joint aspiration (arthrocentesis) is mandatory when septic arthritis is suspected. Analysis of synovial (joint) fluid provides critical diagnostic information. In septic arthritis, the white blood cell count typically exceeds 50,000 cells/mm³ (often much higher), with a predominance of neutrophils. Gram stain may reveal bacteria, and cultures identify the organism in 60-80% of cases if obtained before antibiotic initiation.

Bone biopsy provides definitive diagnosis for osteomyelitis when other tests are inconclusive and is particularly valuable for identifying unusual organisms or antibiotic-resistant bacteria. The procedure can be performed percutaneously under CT or fluoroscopic guidance or as part of surgical debridement.

How Are Musculoskeletal Infections Treated?

Treatment combines prolonged antibiotic therapy with surgical intervention when needed. Antibiotics are typically given intravenously for 2-4 weeks initially, followed by oral antibiotics to complete a 4-6 week course for osteomyelitis. Septic arthritis requires urgent joint drainage, either by repeated needle aspiration or surgical washout, alongside antibiotics. Surgery may also be needed to remove infected tissue, drain abscesses, or remove infected hardware.

The treatment of musculoskeletal infections has evolved considerably with improved understanding of microbiology, antibiotic pharmacology, and surgical techniques. Successful treatment typically requires a combination of appropriate antibiotic therapy and, in many cases, surgical intervention. The specific approach depends on the type and location of infection, the causative organism, the patient's overall health, and whether prosthetic material is involved.

Antibiotic Therapy

Antibiotics form the cornerstone of treatment for all musculoskeletal infections. Initial antibiotic selection is empiric, based on the most likely pathogens and local resistance patterns, while awaiting culture results. For suspected staphylococcal infection, empiric coverage typically includes an anti-staphylococcal penicillin (such as nafcillin or flucloxacillin) or a first-generation cephalosporin (such as cefazolin). In areas with high MRSA prevalence or in high-risk patients, vancomycin or another MRSA-active agent is added or substituted.

Once culture and susceptibility results are available, antibiotic therapy is tailored to the specific organism. This targeted approach ensures optimal efficacy while minimizing the risk of promoting antibiotic resistance or causing unnecessary side effects.

The route and duration of antibiotic therapy depend on the type and severity of infection:

Recent studies have demonstrated that oral antibiotics with high bioavailability (meaning they are well absorbed from the gut and achieve good tissue levels) can be equally effective as prolonged intravenous therapy for many bone and joint infections. Antibiotics such as fluoroquinolones, rifampin (in combination with other agents), clindamycin, and certain modern antibiotics like linezolid achieve excellent bone penetration when given orally. This has allowed earlier transition to oral therapy, reducing hospitalization time and avoiding complications associated with prolonged intravenous access.

Surgical Treatment

Surgery plays a crucial role in many musculoskeletal infections and may be required for several purposes:

Joint drainage in septic arthritis is essential to remove purulent material containing bacteria, inflammatory mediators, and enzymes that destroy cartilage. Drainage can be accomplished through repeated needle aspiration, arthroscopic lavage (washing out the joint through small incisions with a camera and instruments), or open surgical drainage. The choice depends on the joint involved, the thickness of the pus, and local expertise. Hip septic arthritis in children typically requires open surgical drainage due to the joint's deep location and the risk of femoral head damage from increased pressure.

Debridement involves surgical removal of infected and necrotic (dead) tissue. In osteomyelitis, this may include removal of sequestra (pieces of dead bone), excision of infected soft tissue, and thorough irrigation. Adequate debridement is critical for infection control, as antibiotics cannot sterilize devitalized tissue or biofilm-coated bone fragments.

Abscess drainage is necessary for pyomyositis once an abscess has formed, as antibiotics alone cannot penetrate the abscess cavity effectively. Drainage may be performed percutaneously (through a needle or catheter placed under imaging guidance) or through open surgery, depending on abscess location and size.

Hardware removal or exchange may be necessary for prosthetic joint infections or osteomyelitis associated with orthopedic implants. Bacteria form biofilms on prosthetic surfaces that are extremely resistant to antibiotic penetration. In many cases, cure requires either removal of the infected implant (with delayed or immediate reimplantation) or long-term suppressive antibiotics if removal is not feasible.

Treatment of Specific Conditions

Vertebral osteomyelitis is usually treated with antibiotics alone unless there are specific indications for surgery, such as spinal instability, neurological compromise from epidural abscess or bone fragments, failure to improve with antibiotics, or the need for tissue diagnosis. When surgery is required, it typically involves debridement of infected tissue and stabilization of the spine with instrumentation.

Diabetic foot osteomyelitis presents unique challenges because the infection typically arises from chronic wounds and involves poor blood supply. Management includes antibiotics, wound care, offloading (reducing pressure on the affected foot), and often surgical debridement. In severe cases with extensive bone destruction, amputation may be necessary.

What Complications Can Occur?

Untreated or inadequately treated musculoskeletal infections can lead to serious complications including chronic infection requiring prolonged treatment, permanent joint destruction and arthritis, bone death requiring surgical removal, sepsis (life-threatening bloodstream infection), growth plate damage in children affecting bone development, and in severe cases, amputation.

The potential complications of musculoskeletal infections underscore the importance of prompt diagnosis and aggressive treatment. These complications can significantly impact quality of life and may result in permanent disability.

Chronic Infection

Acute musculoskeletal infections can transition to chronic infection if initial treatment is inadequate or delayed. Chronic osteomyelitis is particularly challenging to eradicate because bacteria form biofilms within dead bone (sequestrum) and can remain dormant within bone cells, reactivating months or years later. Treatment of chronic osteomyelitis typically requires prolonged antibiotic courses (often 3-6 months) combined with surgical debridement, and even then, recurrence rates remain significant.

Joint Destruction

Septic arthritis can cause rapid and irreversible destruction of articular cartilage. The combination of bacterial enzymes, host inflammatory mediators, and mechanical damage from distension leads to cartilage breakdown within hours to days. Even with successful infection clearance, many patients develop post-infectious arthritis with chronic pain, stiffness, and accelerated osteoarthritis requiring eventual joint replacement.

Growth Disturbance in Children

Musculoskeletal infections in children pose special risks because growing bones contain growth plates (physes) that are susceptible to damage. Osteomyelitis involving or adjacent to the growth plate can result in premature closure, leading to limb length discrepancy or angular deformity. Septic arthritis of the hip in infancy can damage the femoral head's blood supply, leading to avascular necrosis and severe hip deformity.

Sepsis

Musculoskeletal infections can serve as sources for bloodstream infection and sepsis. Sepsis occurs when the body's response to infection becomes dysregulated, causing widespread inflammation and organ dysfunction. Severe sepsis and septic shock carry significant mortality and require intensive care support. Early recognition and treatment of musculoskeletal infections help prevent this life-threatening complication.

How Can Musculoskeletal Infections Be Prevented?

Prevention strategies include proper wound care to prevent bacterial entry, prophylactic antibiotics before orthopedic surgery, maintaining good blood sugar control in diabetics, prompt treatment of skin infections, and careful management of prosthetic joints. Early medical attention for signs of infection can prevent progression to more serious disease.

While not all musculoskeletal infections can be prevented, several strategies can significantly reduce risk:

Wound Care

Proper care of cuts, scrapes, and open wounds prevents bacterial entry that can lead to soft tissue infection and potentially spread to bone or joint. Wounds should be thoroughly cleaned, and signs of infection (increasing redness, swelling, warmth, pus, or fever) should prompt medical evaluation. For deeper wounds or those occurring in high-risk individuals, medical attention ensures adequate cleaning and potentially prophylactic antibiotics.

Surgical Prophylaxis

Prophylactic antibiotics administered before orthopedic surgery significantly reduce the risk of postoperative infection. These are typically given within one hour before incision and discontinued within 24 hours after surgery. Surgical site infections after orthopedic procedures can lead to devastating consequences, so adhering to prophylaxis protocols is essential.

Diabetes Management

People with diabetes can reduce their risk of foot osteomyelitis through meticulous foot care, daily foot inspections, appropriate footwear, prompt treatment of foot wounds, and maintaining optimal blood glucose control. Regular visits to a podiatrist and participation in diabetes foot care programs can help prevent the wounds that lead to infection.

Prosthetic Joint Care

Patients with prosthetic joints should discuss antibiotic prophylaxis with their orthopedic surgeon before dental procedures or other surgeries that may cause transient bacteremia. Prompt treatment of infections elsewhere in the body (such as urinary tract or skin infections) prevents bacteria from seeding to the prosthetic joint.