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This is an uncommon, localized bone infection arising from one of the following situations: 1 After trauma to bone, e.g. open fracture or penetrating injury. Bullet wounds with much and then into the joint itself. Osteomyelitis of the

acetabulum may be diffi cult to distinguish from septic arthritis

2 From haematogenous spread , particularly in infants, where multiple joint infections may occur and be relatively silent

3 In rheumatoid joints , especially in patients on steroids. The infection may arise by haematoge- nous spread or by direct implantation from an intra - articular injection, particularly if a steroid has been injected

4 Following penetrating injuries .

The infection is usually staphylococcal but may be by other organisms. The synovium becomes infl amed and thickened; fl uid is increased and quickly becomes purulent. Muscle spasm and sof- tening of ligaments and capsule may allow disloca- tion (especially of the hip in an infant — Smith ’ s arthritis). Pus eventually ruptures through the capsule and points, but by then the articular carti- lage is usually severely damaged. In the hip the increased pressure may cause ischaemic necrosis of the femoral head.

The patient is usually ill with high fever and rigors due to septicaemia. The joint is acutely painful and swollen, and is hot and very tender. There is almost always extreme muscle spasm, often allowing no movement of the joint or the limb. The differential diagnosis is from osteomyeli- tis with a sympathetic effusion, rheumatic fever, rheumatoid arthritis or Still ’ s disease (usually mul- tiple joints), Reiter ’ s syndrome and gout.

Radiology

There may be no X - ray changes in the early stages. Later, sub - periosteal new bone may become visible with generalized periarticular porosis. Pathological subluxation or dislocation may occur and this may

● Infl ammatory arthritides

Clinical c ourse

The disease is characterized by ‘ fl ares ’ of infection with pain and swelling, and often pus formation, alternating with periods of quiescence, sometimes lasting several years. Occasionally, particularly fol- lowing penetrating injuries, open fractures and replacement arthroplasty, a sinus may form and discharge continuously. Often when the discharge stops the condition becomes acute until the result- ing abscess is drained.

Investigations

X - rays demonstrate the abnormal bone texture with thickening and diffuse cavity formation (Fig. 13.2 ). A sequestrum usually shows up as a localized mass of bone, denser than its surroundings. Culture of the pus from a persistent sinus usually yields mixed organisms from secondary infection. The ESR is raised and the white cell count shows a moderate leucocytosis.

contamination are particularly liable to result in pyogenic osteomyelitis

2 By haematogenous spread, the source of which may remain unknown. The infection may take the form of a cavity in the bone with surrounding scle- rosis, giving rise to intermittent attacks of pain — Brodie ’ s abscess. It may contain pus but organisms are not always cultivated (especially if there has been prior antibiotic exposure)

3 As a result of inadequately treated acute osteo- myelitis. In the typical case the infection is perpet- uated by necrosis of bone, often resulting in sequestra ranging in size from a few millimetres to almost the whole shaft. The living bone becomes thickened and honeycombed and may surround the sequestrum completely, preventing its dis- charge (involucrum)

4 As a complication of surgery, particularly when foreign material is implanted. The infection usually results in failure of the implant.

Figure 13.2 Chronic osteomyelitis

Pathology

The prominent features are:

1 Destruction of bone and articular cartilage by tuberculous granulation tissue with areas of healing by fi brosis

2 Thickening of synovial membrane which becomes studded with tubercles and extends as a pannus under the edges of the articular cartilage, destroying it

3 Abscess formation , especially in spinal tubercu- losis. The pus tracks along tissue planes, particu- larly within the psoas sheath in association with spinal infections and may point some distance from the original site, e.g. in the groin. Spread can occur through cartilaginous epiphyses and end - plates and across the intervertebral discs

4 Fibrosis occurs in the healing phase. The joint may remain mobile or may develop a fi brous or bony ankylosis (Fig. 13.3 ).

2 Attempts at eradication . This is often impossi- ble, but long - term antibiotics combined with exci- sion of sequestra and opening up of poorly draining cavities may be successful. For the extensively involved bone, the procedure of ‘ guttering ’ , which involves opening the medullary cavity widely and allowing the wound to granulate and heal from the bottom, used to be popular. Newer methods involve opening the bone widely, scraping out cavities and closing the defect with muscle on a vascular pedicle or a split - skin or pedicle - skin graft. There is interest in removing the infected segment completely and closing the gap by per- forming an osteotomy some distance away and transporting the healthy bone to fi ll the gap using an Ilizarov frame and bone lengthening tech- niques. A technique whereby the medullary canal is continuously lavaged with a system of tubing with antibiotics in the wash for several weeks (Lautenbach procedure) has been described but is the remit of specialist bone infection units.

Chronic osteomyelitis occurring as a com- plication of replacement arthroplasty presents for- midable problems and is becoming increasingly common.

3 Amputation may occasionally be required.