31st May 2024

Bone, Skin and Soft Tissue Infections

Bone and cartilage infection

Background

This encompasses osteomyelitis, spondylodiscitis and septic arthritis (native and prosthetic joint infection). Risk factors and common organisms causing infection tend to be similar across presentations of such infections, with only subtle differences. Risk factors include underlying joint disease, as well as liver or kidney failure, as well as immune suppression and IV drug use.

Staphylococcus aureus tends to be the most common causative organism, although coagulase negative staphylococcus spp, as well as streptococcus spp also contribute to a significant minority of infections.

Presentation

Systemic features tend to include fevers, rigors and malaise. Localised erythema, joint pain and reduced range of movement are found in infected peripheral joints, whilst vertebral infections will cause secondary spinal cord or nerve compression as they progress. Whilst infection can be difficult to diagnose, this difficulty is more pronounced in prosthetic joints. This is because often used markers such as CRP are not sensitive markers for low virulence organisms, whilst swabs from draining sinuses can be difficult to interpret.

Diagnosis

Inflammatory markers are often elevated; however, this is not always the case; therefore, there must be a high index of suspicion. Inflammatory markers are more likely to be raised in septic arthritis or prosthetic joint infections, less so in osteomyelitis or spondylodiscitis. Blood cultures may be positive, again more likely in joint infections. Joint aspirate, preferably prior to administration of antibiotics is a key investigation in joint infections, whilst imaging has a more key role in osteomyelitis and spondylodiscitis.

Management

Antibiotics, with or without surgical intervention, are the mainstay of management. Antibiotic choice is often based on the fact that the most common organisms are gram positive cocci such as staphylococcus spp. The below table demonstrates the common management regime for septic arthritis of a native joint or osteomyelitis/spondylodiscitis.

The management of prosthetic joint infection requires more timely joint washout and with consideration of removal of prosthesis.

Hyperglycaemia and hypertension should be addressed as per NICE targets and those with stage III or higher disease should be offered atorvastatin 20mg.  Patients should be advised to stop smoking and encouraged to lose excess body weight.

References

• Bennett, J, Dolin, R, Blaser, M. Mandell, Douglas and Bennett’s Principles and Practice of Infectious Disease 9ᵗʰ Edition. Philadelphia Elsevier. 2019.
• Torok E, Moran E, Cooke F. Oxford Handbook of Infectious Diseases and Microbiology, 2ⁿᵈ Edition. Oxford. Oxford University Press. 2017.

Skin infection

Background

This encompasses primary cellulitis, an infection that involves the subcutaneous tissue often caused by group A streptococcus, as well as beta-haemolytic streptococcus and staphylococcus aureus.

Diagnosis and Management

Most infections are caused by the above gram-positive organisms, though diabetics and those with peripheral vascular disease may also develop gram-negative infections such as pseudomonas. Diagnosis is clinical, based on the appearance and spread of erythema. Pain tends to be localised and patients can be systemically unwell in more severe cases.

Infection can occur due to breaks in the skin acting as a portal of entry, or occasionally, haematogenous spread can seed to the skin.

Management involves IV or oral Flucloxacillin as a first line, with Clindamycin often used as the second line. Vancomycin, Teicoplanin and metronidazole can also be used, the latter for anaerobic infections.

References

• Bennett, J, Dolin, R, Blaser, M. Mandell, Douglas and Bennett’s Principles and Practice of Infectious Disease 9ᵗʰ Edition. Philadelphia Elsevier. 2019.
• Torok E, Moran E, Cooke F. Oxford Handbook of Infectious Diseases and Microbiology, 2ⁿᵈ Edition. Oxford. Oxford University Press. 2017.