Septic arthritis

Arthritis caused by sepsis is a rare but important surgical emergency. Some organisms such as S. aureus may have a collagenase, which actually dissolves the articular surface. If the joint is not sterilised within 24—48 hours, irreversible damage will occur to the articular surface, which will inevitably lead to aggressive arthritis and even ankylosis (fusion) of the joint. Pus in the joint may interfere with the nutrition of the articular cartilage, which has no blood supply itself but derives nutrients from the synovial fluid. In acute arthritis the rapid accumulation of pus leads to a sharp rise in intra-articular pressure. This is extremely painful for the patient, but also tamponades the blood vessels in the capsule. This is the main blood supply to both the femoral head and the humeral head, and so avascular necrosis will occur if the pressure is not quickly relieved.

  Epidemiology

Septic arthritis occurs most commonly in children but can also occur in adults whose resistance to infection has been reduced, such as diabetics, and can also occur after surgical intervention, such as arthroscopy. The onset is sudden with extreme pain in the joint. The patient may have rigors and will certainly feel shivery and generally unwell.

Examination

The joint may be red, hot and swollen, and held in the posi­tion of comfort (see Table 24.1). However, the most characteristic feature is the quite extraordinary amount of pain experienced by the patient when any attempt whatsoever is made to move the joint. If the joint moves even 10 the patient cries out with pain. If this sign is present, then both diagnosis and treatment run hand in hand. The pressure in the joint needs to be relieved without delay and the organism needs to be identified. Needle aspiration of the joint will provide fluid for microscopy and culture and start the decompression of the hip. In the child this will need to be done under a general anaesthetic, and is most easily performed using an image intensifier. If pus is found in the joint then the best treatment is to proceed immediately to a complete decompression of the joint and wash out either through the arthroscope or by open arthrotomy. It is important that organisms are washed out of the joint as quickly as possible to prevent collagenase from damaging the articular surface. It is equally important that the pressure within the joint is reduced to normal to prevent avascular necrosis and to allow normal nutrition of the articular cartilage. Intravenous antibiotics should also be given as the patient is likely to be septicaemic (Fig. 24.5). The initial antibiotic should be chosen according to whether the organism identified at microscopy is Gram-negative or Gram-positive. The antibiotic can be changed later when the sensitivity is known.

Late diagnosis of septic arthritis

In immunocompromised patients the symptoms of septic arthritis may not be so florid, and initially the diagnosis may not be suspected. If it is likely that septic arthritis has been present for several days, then it is unlikely that the infection can be brought under control without a synovectomy, and the prognosis for the joint is poor. It should be splinted in a position of best function, as a painless arthrodesis will be the best outcome that can be hoped for. The position of function is not the same as the position of comfort, and therefore the joint will need careful splintage. After acute septic arthritis there is usually bony ankylosis. This provides a stable painless limb, but if the ankylosis is not solid, or if the joint has fused in a poor position, a formal arthrodesis may need to be performed once the infection has been brought under control. This operation will need to be covered with antibiotics, as it may produce a further recurrence of septicaemla.