Based on the patient's symptoms of a swollen, sore, and tender knee with limited range of motion, along with the analysis of the synovial fluid sample being thin and cloudy, the most likely diagnosis is:
Acute septic arthritis
Septic arthritis refers to joint inflammation caused by a bacterial, viral, or fungal infection. It leads to swelling, pain, and tenderness in the affected joint along with restricted range of motion.
The cloudy, thin appearance of the synovial fluid sample indicates increased white blood cell count and debris, which is consistent with septic arthritis. This distinguishes it from other forms of arthritis that would have clear, viscous joint fluid.
Given the acute onset of symptoms and lack of mention of any chronic joint issues, this fits with an acute septic arthritis infection rather than a chronic inflammatory type of arthritis.
Prompt diagnosis and treatment is important for septic arthritis to prevent rapid joint destruction. Typical treatment involves antibiotic therapy along with drainage of the infected joint fluid. Identifying the infectious organism through synovial fluid culture can help guide antibiotic selection.
In summary, based on the clinical presentation and synovial fluid analysis results, acute septic arthritis is the most likely diagnosis for this patient's sore, swollen knee. Let me know if you need any clarification or have additional details to provide.