The child’s medical history is important in the assessment of any previous injury or medical problem in the course of the current musculoskeletal infection. The duration of symptoms in septic arthritis is of prognostic significance. Infections that are present for more than three days may cause residual joint damage, especially in the newborn. It is important to inquire about previous antibiotic treatment.
Perform a screening examination first. Does the child appear ill? The presence of systemic signs distinguishes septic arthritis from toxic synovitis. Is spontaneous movement present? The most reliable sign of septic arthritis of the hip in the newborn is a reduction of spontaneous movement of the limb. The reduction of movement from infection is described as pseudoparalysis. Swelling, erythema, and increased temperature are signs of inflammation, often due to infection. Note the position of the limb. Most infected limbs are positioned with the joints in slight flexion to reduce the intraarticular pressure. The hip is usually positioned in slight flexion, lateral rotation, and abduction.
Note the extent of soft tissue swelling and joint effusions. Try to localize the area of tenderness about the knee, ankle, wrist, or elbow to determine whether the primary problem is in the joint or the adjacent metaphysis. This is helpful in differentiating septic arthritis from osteomyelitis.
Move the joint through a gentle range of motion to assess guarding or limitation of the arc of motion. Medial rotation is limited by inflammation about the hip.
Conventional radiographs may show soft tissue swelling and obliteration of the soft tissue planes, but little else during the early course of an infection. A reduction of bone density of about 30% is necessary before radiographic changes are present. This usually requires 10–14 days.
Bone scans are useful in evaluating infection in the early stages of the illness. Technesium scans in septic arthritis are usually “warm.” Scans in osteomyelitis are usually warm or hot but may be cold early in the disease. In the early phase, uptake may be reduced and a cold segment of bone may indicate the presence of a severe infection. In early osteomyelitis, the phasic scan may be useful. The early phase includes vascular perfusion that parallels the physical findings of swelling and inflammation. In the second or osseous phase, uptake is greater over the site of involvement. Bone scans are not necessary if radiographic changes are already present. Often the bone scan is helpful in localizing the site of involvement. Order a high-resolution scan for increased resolution. The bone scan is unaffected by bone or joint aspiration.
SPECT scans Single-photon emission computed tomography scans are tomographic bone scans to identify focal inflammatory lesions of bone.
Ultrasound evaluation for hip joint effusions may be helpful if the ultrasonologist is experienced. A negative study should not delay a diagnostic aspiration if the clinical signs suggest the possibility of an infected joint. Ultrasound is also useful in localizing abscess formations around long bones, and its use is underutilized.
MRI studies of infection may be useful in localizing an abscess. MRI studies of discitis may be alarming and can lead to overtreatment. Use newer imaging techniques only as adjuncts to conventional well-understood techniques.
CT studies are sometimes useful in evaluating deep infections, such as those about the pelvis. CT and MRI studies may be helpful in localizing abscess and planning the surgical approach for drainage.
The erythrocyte sedimentation rate, C-reactive protein and cultures are the most valuable laboratory tests. Serial measures are useful in following the course of infection. Often the white blood count (WBC) is normal.
ESR is still valuable. Following the onset of infection, the ESR slowly rises to peak at 3 days and remains elevated for about 3 weeks if treatment is successful.
CRP peaks in 2 days and follows most closely the clinical course of the infection. If treatment is successful, the values return to normal in about a week.
Cultures are essential and usually include blood, joint fluid, wound, and biopsy samples. Blood cultures are positive in 30–50% of patients. Be aware that negative cultures are common in both osteomyelitis and septic arthritis.
PCR Molecular methods are being applied to the microbiology of bone infections. Amplification techniques using polymerase chain reaction have been shown to be very sensitive when DNA probes are used for such specific infections as tuberculosis and Lyme disease. In settings of polymicrobial infections and infections where the likely organism is unknown, the ability of molecular techniques to identify the organism is as yet not superior to standard cultures. Further evolution of these techniques will likely increase their use in clinical medicine in the future.
Differentiation from Neoplasm
The differentiation of infection from neoplasm is sometimes difficult. Infections are more common, especially in younger subjects, and often show signs of inflammation. Subacute osteomyelitis may be confused with osteoid osteoma, osteosarcoma, chondroblastoma, Ewing sarcoma, fibrosarcoma, or eosinophilic granuloma. If necessary, establish the diagnosis with biopsy, curettage, and cultures. If the lesion is well demarcated, making a malignant tumor less likely, consider prescribing a course of oral antibiotics. If the lesion is due to an infection, the treatment is both diagnostic and therapeutic.
Eosinophilic granuloma may show inflammatory features.
Ewing sarcoma differentiation may pose a major problem. MRI and bone scans may be helpful. Sometimes biopsy and cultures are necessary.
Treatment of musculoskeletal infections in children
Management of musculoskeletal infections in children is guided by a number of principles that often differ from those that apply to adults.
Greater Healing Potential
The potential for healing infection is remarkable in children. For example, discitis usually resolves with time with or without treatment. Bone damaged by osteomyelitis heals. Infection of bone may be contained and localized to only a residual abscess or it may resolve completely without treatment. Chronic osteomyelitis can nearly always be cured in children. Operative wound infections are uncommon in children.
The selection of an antibiotic agent is complex. Consider the disease, organism, and special features of the child. These features include the age, concurrent illness, and the family situation. The route of administration and duration of treatment are other factors to consider. Initial therapy should be intravenous or, if access is difficult, intramuscular. Certain antibiotics are most commonly used for musculoskeletal infections.
Oral antibiotic therapy is justified if the infection is minor, the agent is well absorbed, and the family is reliable. In most serious infections, treatment may begin with parenteral antibiotics and switch to oral agents when the disease is under control. Before switching to the oral route of administration, be certain that adequate blood levels are documented following oral administration and that the family is reliable.
Methicillin-resistant organisms Consider the incidence of methicillin-resistant Staphylococcus aureus in the community. If the child appears ill, the empiric choice is vancomyocin, with modifications made after the culture and sensitivities are determined.
Duration of antibiotic treatment is controversial. Several factors should be considered in determining the duration. Consider the severity and potential for disability that the infection poses, the rapidity of response to treatment, serial determinations of the ESR, the results of published studies, and the age of the child. Treat older children slightly longer. There are some generalizations that can be made. These can be modified according to the situation. Joint suppuration in septic arthritis reduces the effectiveness of the antibiotic treatment.
Drainage may be accomplished by needle aspiration, arthroscopic decompression, or open procedures.
Indications Drainage is necessary whenever antibiotic penetration into the infected site is impaired. This penetration is most often due to the presence of an abscess or an accumulation of pus within a joint. Impaired penetration may also be due to a loss of vascularity, as occurs in chronic osteomyelitis with sequestration or in soft tissue with poor vascularization due to thrombosis of vessels and acute inflammation. The presence of an abscess may be demonstrated by clinical examination, imaging such as ultrasound or MRI, needle aspiration, or suggested by a failure of clinical response to antibiotic treatment. This failure of response to antibiotics is the failure of reduction in fever, pain, local inflammatory signs, and CRP during the first 48–72 hours after instituting antibiotic treatment. Keep in mind that this failed response may also be due to an ineffective antibiotic agent or to an immunocompromised child.
Technique may be simply needle aspiration, as is feasible for most joints, arthroscopic, or open drainage. Open drainage of abscess due to acute infections requires simply draining the abscess through a small window in the cortex. If the abscess is near a growth plate, take care to avoid injuring the physis. Monitor the position of the curette with fluoroscopy.
Drainage of Septic Joint
Drain septic joints as soon as the diagnosis is made to prevent cartilage damage. The drainage technique depends upon the joint, the duration of disease, and special considerations.
Needle drainage is suitable for most accessible joints early in the disease. Aspirate with a #18 gauge needle. Irrigation or antibiotic instillation is unnecessary. If joint content is too thick to aspirate, plan open or arthroscopic drainage.
Arthroscopic drainage is most suitable for the knee. Plan an anterolateral portal. Joint lavage may be necessary. Plan to introduce a drain through the scope at the end of the procedure to prevent reaccumulation of pus.
Open drainage is appropriate for nearly all cases of hip involvement and sometimes for the shoulder. Consider the need for drainage of the metaphysis in addition to the joint, as both may be affected.
Metaphyseal drainage Consider the potential for coexisting osteomyelitis of the adjacent metaphysis. Concurrent infections are more common than often appreciated. To drain the metaphysis, wider exposure is required. Imaging is useful to identify the growth plate to avoid operative injury.
Ankle drainage Drain through a lateral approach either posterior or anterior to the fibula.
Knee drainage is through either a medial or lateral approach.
Hip drainage is best performed open, as thorough drainage is necessary due to the vulnerability of the hip to residual deformity and the deep position, which make repetitive arthrocentesis impractical. Anterior drainage is preferable, as the approach is less likely to damage the joint vascularity, and the residual scar is more acceptable. Make a 3-cm oblique incision 2 cm distal to the iliac crest. Develop the interval between the tensor and sartorius and lateral to the rectus femoris. Open the hip joint. Excise a small segment of capsule. Thoroughly drain the joint. Consider the need for metaphyseal drainage. Place a drain in the joint and secure its position with a single skin suture. Close the skin. If the hip was subluxated or dislocated due to sepsis, or if metaphyseal osteomylitis is present, immobilize in a spica cast positioned with the hip in abduction to reduce the joint and prevent pathological fracture of the upper femur.
Shoulder Drain through an anterior skin line axillary incision to minimize residual scarring. Drain both the joint and the bursa for the biceps tendon. Place a small drain and secure it with a single skin suture to prevent premature displacement. Close the skin with a few subcutaneous sutures at the margins. Consider the possibility of concurrent osteomyelitis that may need drainage. Avoid wide skin sutures, as permanent scars are unsightly. Place in a sling with the arm held to the thorax with a dressing.
Elbow Drain through a direct lateral approach between the triceps and biceps muscles. Open the joint capsule just anterior to the lateral collateral ligament.
Wrist Drain most by needle aspiration. Open drainage is performed on the dorsomedial or lateral aspect of the joint. Avoid the superficial radial nerve on the lateral side.
Antibiotics Start IV antibiotic treatment immediately after taking the joint fluid for culture. Gram stains are sometimes useful to identify the category of organism to help with selection of an antibiotic.
Drains Remove the drain only after significant drainage has ceased. Drains usually can be removed in 2–3 days.
Activities Allow active use as the child becomes comfortable. Physical therapy usually is unnecessary because joint motion recovers spontaneously.