Posted: 30/09/2021
Emily Reville, senior associate in our clinical negligence team, continues the sepsis series by discussing the surprisingly common, potentially life-threatening, and often joint-destructive condition of septic arthritis, and its diagnosis, management, and complications, with consultant orthopaedic surgeon, Mr Andrew Unwin.
Sepsis is a serious condition, and left untreated it can lead to life-changing injuries including shock, multi-organ failure, limb amputation, and even death. It happens when the body’s immune system overreacts to infection, and is also known as septicaemia or blood poisoning. Lyndsey Banthorpe has provided an overview of the condition, and discusses the difficulties in its diagnosis, with microbiology expert Professor Robert Masterton in the first article in this series.
This instalment looks more specifically at what happens when that infection gets into the joints and bones, how this differs from sepsis, and how it is diagnosed and treated.
“Septic arthritis” is a commonly used term, but a misnomer as the condition has nothing to do with “arthritis” at its onset. Instead, it refers to the presence of a “deep joint cavity infection”. Without treatment this can lead to systemic sepsis (which can be fatal), but it can also cause local problems of articular cartilage damage, premature osteoarthritis, spread to adjacent bones (osteomyelitis), and spread to adjacent soft tissues.
Septic arthritis can occur in any joint, but it often develops in the knee joint and hip joint. Like septicaemia, it is most commonly seen in native (non-surgical) cases in the young and the elderly. Risk factors, including inflammatory joint disease, an immunosuppressed patient, or cases where patients are on steroids or other immunosuppressive drugs or treatments, increase the likelihood of the condition. Usually, the cause is haematogenous (blood-borne), but septic arthritis can be caused by penetrating trauma.
Infection can be introduced into a knee joint at the time of surgery (inoculation), or it can spread from a superficial wound infection to the deep joint cavity.
Where prosthetic joints are implanted, these can become infected and this type of septic arthritis is termed “prosthetic joint infection”.
The risk of surgically-associated deep joint cavity infection is minimised with the use of prophylactic intravenous antibiotics, especially where foreign material is introduced into the joint.
Deep joint cavity infection can also complicate intra-articular injections, most notably steroid injections.
The classical presentation for septic arthritis is recent onset of fever and malaise, often accompanied by local findings of pain, warmth, swelling, and decreased range of motion in the involved joint. The pain can be severe enough to affect standing or walking. The difficulties in diagnosing septic arthritis arise when a patient has a mild fever and pain in a joint without the warmth or swelling.
The history of the injury is therefore essential to the diagnosis of septic arthritis i.e. whether there has been any recent trauma or surgical intervention at that joint.
Up to a third of all cases of septic arthritis are missed in diagnosis. The differential diagnosis can be broad, with other conditions mimicking the disease, particularly where the fever is minimal and the patient is treated as having a musculoskeletal injury. Delays in diagnosis are commonly up to 10 days from first symptoms appearing. Most patients come into hospital by way of a GP referral, but can be directed to several different specialties depending on the GP’s diagnosis, such as surgical, medical, rheumatology or orthopaedic areas of specialism. Therefore, it is essential that each area is familiar with the signs and symptoms of septic arthritis.
The physical symptoms of septic arthritis may be wide-ranging and non-specific, leading clinicians away from the correct diagnosis. Diagnostic testing is the only definitive way to ensure that the right diagnosis is made. Blood tests may show a rise in the inflammatory markers known as C-Reactive Protein (CRP) and Erythrocyte Sedimentation Rate (ESR). The number of white cells in the blood may also be raised. Taking a sample of fluid from the joint provides a more definitive assessment. This sample must then be considered by a microbiologist to understand the organism causing the infection. The most common of these amongst adults is staphylococcus aureus.
If a diagnosis is delayed by more than a week, an x-ray may be of benefit as abnormalities can be revealed where the joint is deteriorating due to septic arthritis.
Antibiotic therapy will be required, which is usually delivered intravenously into the body. The antibiotic regime will depend on the organism isolated. However, this treatment is rarely sufficient on its own. The patient may also require surgery performed by an orthopaedic surgeon to wash out the joint, removing the infected material. This is done by way of a procedure called an arthroscopy where a fine, metal tube is passed into the affected joint to allow the infection to be drained. It may also be necessary to undertake more extensive, open surgery (an arthrotomy) by way of debridement to remove the infected and dead tissue from the joint.
Delay in the diagnosis of septic arthritis will increase the chance of a poor outcome. Once the delay becomes longer than 1-2 days, the risk of prolonged consequences is significant. Up to 30% of patients diagnosed with septic arthritis will have long-term complications, and around 75% of those complications will occur where therapy is delayed more than 1-2 days.
The most common complications are osteoarthritis, a condition that causes joints to become painful and stiff, and osteomyelitis, infection of the bone itself. When the cartilage in a joint gets destroyed or worn down, there is a risk of joint replacement surgery.
Such complications can lead to loss of long-term function in the joint, which may impact on employment, and social and domestic activities.
In severe cases, septic arthritis can lead to admission to intensive care, and even death.
Continue to follow the Penningtons Manches Cooper sepsis series with part 4, written by Amy Milner, which will discuss the impact of ITU on patients with sepsis.
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