Infections that can affect the joints and the bones are primarily either an infection of the bone ('osteomyelitis'), an infection of the joint ('septic arthritis') or an infection of a prosthesis (a component of an artificial joint replacement) referred to as 'Prosthetic Joint Infection' or simply 'PJI'.
Infections of bones, joints and prostheses are largely caused by micro-organisms such as bacteria (for example Staphylococcus Aureus – 'Golden Staph'), viruses and fungi, which get into the blood and travel to the bone tissue.
With PJI the most common causes are Staphylococcus Aureus, Staphylococcus Epidermis, Streptococcus, Enterococcus and so-called polymicrobial infections (with many bacteria present) – these account for 82% of all prosthetic knee and hip infections.
Infection can happen in the following circumstances:
- Bone trauma.
- Bone surgery (including joint replacement surgery).
- Bone fracture infection.
- Infection from elsewhere in the body carried in the bloodstream or in the blood itself (e.g.: skin infection, urinary tract infection, septicaemia).
Some people are more at risk of developing a joint infection including:
- People with existing joint conditions such as osteoarthritis, rheumatoid arthritis.
- People with other chronic conditions, for example sickle cell anaemia or cancer.
- People with poor blood circulation (e.g.: smokers, people with high blood pressure or diabetes).
- People with suppressed immune systems (medication for rheumatoid arthritis can have this effect).
- People with some skin conditions, for example psoriasis and eczema.
- People with skin injuries near a joint, for example puncture wounds (including due to injecting drugs), animal bites and / or cuts and abrasions.
- Very young children and older adults are also at higher risk of contracting septic arthritis – roughly 45% of all people affected by septic arthritis are over 65.
The main symptom of joint infection is pain in the joint itself often accompanied by:
- Swelling / redness.
- Tenderness / warmth.
- Difficulty moving the joint.
- Fever (38°C+).
- Sweating / chills.
- General feeling of being unwell.
- Otherwise unexplained loss of weight.
- Muscle spasms.
Tests / Diagnosis
After a physical examination and review of medical history, a number of tests may be required to diagnose suspected joint and bone infections. These may include:
- Blood tests (to detect any blood borne infection).
- CT scan.
- MRI scan.
- Bone scan.
- Tissue biopsy from the bone.
- Joint fluid analysis (to detect infection in the synovial fluid surrounding the joint).
Most treatment involves a course of antibiotics to treat the infection which generally runs for 4-6 weeks. In some cases, the infected joint fluid may need to be drained, and surgery may be necessary to properly drain this fluid and flush the affected bone tissue (a process referred to as 'debridement' and / or 'lavage').
In very severe cases, where the infection is affecting a foot, hand, knee or elbow, amputation may be necessary.