From the Guidelines
Yes, it is possible to have a septic knee that is only tender with movement and not tender to touch, as the presentation of septic arthritis can vary significantly from patient to patient 1. Septic arthritis (joint infection) can present with symptoms that are not always typical, and while most cases involve significant pain both at rest and with touch, some patients may primarily experience pain only when moving the joint. This is particularly true in early stages of infection or in patients with compromised immune systems who may have blunted inflammatory responses.
Some key points to consider in the diagnosis of septic knee include:
- Pain is the most common presenting symptom of infection, but it can be nonspecific and may not always be present at rest 1
- Night pain or pain at rest is characteristic of infection, whereas pain on weightbearing is more characteristic of mechanical loosening 1
- Other important signs of septic knee to watch for include swelling, warmth, redness, limited range of motion, and systemic symptoms like fever
- Diagnosis typically involves joint fluid aspiration (arthrocentesis) with fluid analysis, and treatment usually consists of intravenous antibiotics and often surgical drainage
The variation in pain presentation occurs because inflammation can affect different structures within the joint, and movement may stress infected tissues in ways that static pressure does not. It is crucial to seek medical attention immediately if septic arthritis is suspected, as it represents a medical emergency. Never delay seeking medical care for a suspected joint infection based solely on the absence of touch tenderness. Laboratory findings, such as C-reactive protein (CRP) and erythrocyte sedimentation rates (ESRs), can be useful in addition to imaging studies and clinical findings, but a normal CRP level does not exclude infection 1.
In terms of diagnosis, the American Academy of Orthopaedic Surgeons (AAOS) guidelines strongly recommend the use of ESR, CRP, and serum interleukin-6 testing for patients being assessed for peri-prosthetic joint infection 1. Additionally, the use of an alpha-defensin laboratory test has been described for the diagnosis of peri-prosthetic joint infection, and has been demonstrated to be highly accurate in the diagnosis of prosthetic joint infection 1.
From the Research
Septic Knee Characteristics
- A septic knee can exhibit varying levels of tenderness, with some cases being tender only with movement, while others may be tender to touch as well 2, 3.
- The diagnosis of septic arthritis is primarily based on history and clinical presentation of a red, warm, swollen, and painful joint with limited range of motion 2.
- Laboratory values and inflammatory markers from serum and joint fluid may serve as adjuncts when there is clinical suspicion of septic arthritis 2, 3.
Factors Influencing Septic Knee Tenderness
- The level of tenderness in a septic knee can be influenced by various factors, including the causative organism, the severity of the infection, and the patient's overall health status 4, 3.
- Some patients may experience more pain and tenderness with movement due to the inflammation and infection in the joint, while others may have more constant pain and tenderness 5.
Importance of Prompt Diagnosis and Treatment
- Delayed or inadequate treatment of septic arthritis can result in joint destruction, osteomyelitis, and sepsis, highlighting the importance of prompt diagnosis and treatment 4, 2, 3.
- Early targeted intervention, including antibiotic therapy and surgical management, can improve outcomes in septic arthritis 4, 2, 6.