Diagnosis and Clinical Findings of Knee Osteoarthritis

Key Diagnostic Criteria

The American College of Rheumatology recommends that the diagnosis of knee osteoarthritis can be made clinically without imaging in patients over 40 years old who present with usage-related pain, short morning stiffness, and characteristic physical examination findings including joint line tenderness, bony enlargement, coarse crepitus, and reduced range of motion 1, 2
The European League Against Rheumatism suggests that joint line tenderness, particularly over the medial joint line, is a common finding in knee OA, reflecting the typical medial compartment predominance of the disease 3
The American Academy of Orthopaedic Surgeons notes that reduced range of motion, with a passive arc of motion typically limited compared to the contralateral knee, is a characteristic sign of knee OA 3

The American College of Rheumatology states that imaging is not required to make the diagnosis in patients with typical presentation, including usage-related pain, short duration morning stiffness, age over 40, and symptoms affecting one or few joints 1, 2, 4
The European League Against Rheumatism recommends considering imaging if there is unexpected rapid progression of symptoms or change in clinical characteristics, to differentiate from inflammatory arthritis when diagnostic uncertainty exists, or when mechanical symptoms suggest concomitant pathology such as meniscal tears 1, 2

The American Geriatrics Society notes that the majority of people over 70 years have asymptomatic meniscal tears, and the presence of a tear on imaging does not necessarily correlate with symptoms 5

The American College of Radiology identifies articular crepitus as most commonly associated with arthritis, with crepitus occurring in approximately 81% of patients with established osteoarthritis compared to 36% in pain-free individuals 6
The presence of crepitus increases the odds of radiographic osteoarthritis by more than threefold (OR 3.79, 95% CI 1.99 to 7.24), with frequent crepitus predicting incident symptomatic knee OA longitudinally 6

The American College of Radiology recommends obtaining standing radiographs first (AP, lateral, tunnel, and tangential patellar views) when crepitus is present with pain or other symptoms, as these are the initial imaging study for chronic knee pain 7
MRI without contrast is indicated only if radiographs are normal or non-diagnostic and symptoms persist, or if mechanical symptoms (locking, catching) suggest meniscal pathology 7
Soft tissue gas must be excluded, as extremity soft-tissue crepitus could represent soft-tissue gas from recent surgery, trauma, or puncture wounds rather than articular pathology, and radiographs can detect soft-tissue gas 6

The American Academy of Orthopaedic Surgeons suggests that mechanical symptoms, such as true locking, catching, or giving way, may indicate concomitant pathology like meniscal tears or loose bodies, and thus require further evaluation 8
Management of knee osteoarthritis should focus on symptoms and function, rather than the presence of crepitus, as recommended by the American College of Rheumatology and supported by research in Arthritis and Rheumatology and Arthritis care & research 9, 10

In patients with atypical features, such as mechanical symptoms, standing radiographs should be ordered first to confirm diagnosis and exclude alternatives, and MRI without contrast may be considered if radiographs are normal or non-diagnostic 8