SEPTIC ARTHIRITIS

Infection in a joint is caused by an open wound or puncture directly into the joint, from spread through the bloodstream from an infection elsewhere or from adjacent osteomyelitis. Pyogenic infections result most frequently from staphylococcus species. Other organisms responsible for joint infections include mycobacterium tuberculosis, brucellosis, salmonella and various types of fungus.

Enzymes released by organisms within the joint destroy the articular cartilage, leading to loss of motion, degenerative arthritis and spread of the infection to surrounding tissues. Prompt drainage of the purulent fluid and administration of antibiotics is necessary to preserve joint function.

Evaluation and diagnosis

Patients have pain and tense swelling of the joint. The area around the joint is warm, red and tender and any joint motion is painful. A fever is usually present and, if laboratory studies are available, they will show an elevated white blood cell count and sedimentation rate. A history of a wound near the joint, or of an infection elsewhere in the body, should increase suspicion. Confirm the diagnosis by needle aspiration of the joint. Infected fluid is cloudy or overtly purulent. Send it for culture and sensitivity testing, but do not wait for the results before beginning treatment.

Aspiration technique
Perform a surgical scrub, and drape a sterile field about the joint. Use 1% lidocaine anaesthesia for the skin and tissue down to the joint capsule. Sedation may be necessary for aspiration of the hip joint. Insert a large bore needle directly into the joint and withdraw as much fluid as possible. Send the initial aspirate for culture.

Hip

With the patient supine, insert a spinal needle just anterior to the greater trochanter at an angle of 45 degrees (Figure 19.6). Advance the needle while aspirating. You will feel a “pop” when the needle goes through the joint capsule and fluid will fill the syringe.

Figure 19.6

Knee

Aspirate the knee through a medial or lateral approach at the superior margin of the patella (Figure 19.7).

Figure 19.7

Ankle

Aspirate the ankle through an anterior lateral or anterior medial approach at the level of the distal tibia, and just lateral or medial to the extensor tendons.

Treatment

Treat septic joints with prompt drainage and systemic antibiotics. Drain the joint by open lavage, if it is possible at your hospital. If it is not, perform repeated daily aspirations until the fluid becomes clear and free of infection. Apply a splint to rest the joint during the initial treatment phase. Do not allow the patient to bear weight on the affected joint. Continue antibiotics for a total of at least 6 weeks. Switch to oral doses when joint swelling subsides and motion is no longer painful. This is usually after about 10–14 days.


PYOGENIC OSTEOMYELITIS

Infection of bone, osteomyelitis, occurs by direct inoculation from an overlying wound or from haematogenous spread from another infected site. It occurs as an acute form or, if untreated, as a chronic form.

In many areas of the world, osteomyelitis is endemic, existing as a chronic quiescent disease. The most common organism is staphylococcus and the most common sites of infection are the femur and tibia.

Haematogenous infections begin with the lodging of bacteria in the postcapillary sinusoids on the metaphyseal side of the epiphyseal plate. The organisms proliferate in this area of sluggish circulation, forming an intramedullary infection. This is the acute phase. If the infection is not treated, it forms an abscess cavity within the bone. Pressure within the abscess causes purulent material to penetrate the cortical bone. The periosteum is elevated and a subperiosteal abscess forms (Figure 19.8).

Figure 19.8

This marks the physiological beginning of the chronic form of the disease. There is usually clinical evidence of soft tissue involvement at this point, with swelling, redness and tenderness. If left untreated, the infection will either drain through the skin to decompress the abscess and/or dissect under the periosteum, encompassing much of the diaphysis. When the latter occurs, the original diaphysis becomes engulfed in the abscess, is devoid of a blood supply and becomes a sequestrum.

The most important aspect of this process now occurs: the elevated periosteal sleeve begins to form new bone which becomes the involucrum (Figure 19.9).

Figure 19.9

The integrity of the involucrum determines the final form and function of the limb. Injury to the periosteum, either from overwhelming infection or from premature surgical debridement, results in incomplete involucrum formation and impaired limb morphology. The epiphyseal plate might also be injured if the infection is severe.

Evaluation and diagnosis

Patients with acute osteomyelitis have pain, fever, malaise, local swelling and limited use of the limb. There may be a history of trauma, sore throat or other intercurrent infection.

Tenderness is greatest in the metaphyseal region of the involved bone. Movement of neighbouring joints is limited, but some painless motion is usually possible. X-rays of the bone are usually normal during this phase but may show soft tissue swelling.

In the quiescent phase, chronic osteomyelitis may be without signs or symptoms other than minimal persistent swelling of the limb. When the infection reactivates, the limb becomes swollen and painful, as it would with an acute infection. As the infection pushes to the surface, a draining sinus forms. This often relieves some of the swelling and pain. X-rays taken during this phase show a deformed bone, usually with a cavity containing a dense piece of dead bone – the sequestrum.

Treatment

When the patient is seen less than 48 hours from the beginning of symptoms, treat acute osteomyelitis with intravenous antibiotics. Switch to oral antibiotics at 4–6 weeks if the infection is controlled. This will be evident by absence of fever, decreased pain, swelling and tenderness, and an increased use of the limb.

X-rays taken after 2–3 weeks of treatment may show decreased bone density and minimal periosteal new bone formation. These are typical findings and do not mean that the infection is out of control. X-rays should be repeated in 2–4 weeks. If the infection is controlled, the X-rays will return towards normal. If an abscess forms, the infection is beyond the acute phase and surgical drainage is necessary.

Technique for draining the abscess