How should I evaluate and initially manage a patient presenting with knee pain?

Evaluation of Knee Pain

Begin with a focused history targeting mechanism of injury, ability to bear weight, age, and presence of constitutional symptoms, followed by systematic physical examination of joint line tenderness, effusion, range of motion, and ligament stability—then apply clinical decision rules to determine if radiographs are needed. 1, 2

Critical History Elements

Obtain specific information about:

• Mechanism of injury: Direct blow, fall, twisting injury, or atraumatic onset 1, 2
• Ability to bear weight: Immediately after injury and currently (4 steps in examination room) 1
• Age: Patients >55 years have increased fracture risk; children <5 years with effusion require septic arthritis evaluation 1, 2, 3
• Constitutional symptoms: Fever, refusal to bear weight, and inability to move joint suggest septic arthritis—an orthopedic emergency 3
• Timing and pattern: Acute versus chronic, unilateral versus bilateral 2
• Location specificity: Anterior, medial, lateral, or posterior knee pain 2, 4

Physical Examination Protocol

Always examine the uninjured knee first for comparison. 5

Inspection and Palpation

• Joint effusion: Measure on lateral aspect; >10mm in patients <40 years warrants MRI consideration 3
• Focal tenderness: Palpate fibular head, joint lines (medial/lateral), patella, tibial tubercle 1, 4
• Gross deformity or palpable mass: Mandates immediate radiographs regardless of other criteria 1, 3
• Gait assessment: Observe for antalgic gait or inability to bear weight 1, 2

Range of Motion

• Flexion to 90 degrees: Inability to flex is an Ottawa Knee Rule criterion 1
• Active and passive range of motion: Compare to contralateral side 5

Ligament Stability Testing

• Valgus/varus stress testing: Evaluates collateral ligaments 5, 6
• Lachman and pivot shift tests: Assess anterior cruciate ligament 5, 6
• Posterior drawer and tibial sag tests: Evaluate posterior cruciate ligament 5, 6

Meniscal Testing

• McMurray's test, Apley's grind test, bounce test: Aid in meniscal tear diagnosis 5, 7

Critical Additional Examinations

• Hip examination with range of motion and impingement testing: Never overlook referred pain from hip pathology 2
• Spine examination: Rule out lumbar spine pathology 2
• Neurologic examination: Assess for deficits 2

Imaging Decision Algorithm

When to Order Radiographs (Ottawa Knee Rule)

Obtain plain radiographs if ANY of the following criteria are met: 1

• Age ≥55 years
• Isolated patellar tenderness (no other bony tenderness)
• Tenderness at head of fibula
• Inability to flex knee to 90 degrees
• Inability to bear weight immediately after injury
• Inability to take 4 weight-bearing steps in examination room

Radiographic Views Required

• Anteroposterior (AP) view 1, 4
• Lateral view at 25-30 degrees flexion: Critical for detecting lipohemarthrosis (fat-fluid level indicating intra-articular fracture) 1, 3, 4
• Patellofemoral (sunrise/Merchant) view: For suspected patellar pathology 1, 4

Clinical Judgment Supersedes Rules

Order radiographs even without Ottawa criteria if: 1, 4

• Gross deformity present
• Palpable mass
• Penetrating injury
• Prosthetic hardware
• Altered mental status (head injury, intoxication, dementia)
• Neuropathy (paraplegia, diabetes)
• Multiple injuries affecting reliability of examination
• History suggesting increased fracture risk

When to Proceed to MRI

MRI without contrast is indicated when: 3, 4

• Radiographs negative but significant joint effusion present
• Mechanical symptoms persist (locking, catching)
• Clinical suspicion for meniscal tear, ligamentous injury, or osteochondritis dissecans remains high
• Symptoms persist after 4-6 weeks of conservative treatment 2
• Surgical intervention being considered 2

Critical pitfall: Never order MRI without recent radiographs—approximately 20% of patients inappropriately receive MRI first, which is suboptimal care. 4

Red Flags Requiring Urgent Action

Septic Arthritis (Orthopedic Emergency)

• Age <5 years PLUS C-reactive protein >2.0 mg/dL predicts >90% probability of septic arthritis 3
• Fever, refusal to bear weight, inability to move joint, bacteremia require urgent aspiration 3
• Atraumatic effusion in young children mandates urgent aspiration—do not delay 3

Vascular Emergency

• Knee dislocation has 30% vascular injury rate with posterior dislocations 3

Fracture Indicators

• Lipohemarthrosis on cross-table lateral radiograph indicates intra-articular fracture 3, 4

Initial Management Pending Imaging

For patients without red flags: 2, 4

• Activity modification and relative rest
• Ice application
• NSAIDs if not contraindicated
• Conservative treatment trial for 4-6 weeks before advanced imaging (if radiographs negative)

Age-Specific Considerations

Pediatric Patients (5-18 years)

• Consider Osgood-Schlatter disease, Sinding-Larsen-Johansson syndrome, patellofemoral pain syndrome 2
• Children 5-12 years fall outside Ottawa/Pittsburgh rule validation—radiographs may be beneficial despite lack of clinical symptoms 1
• Always examine hip in children—referred pain is common 2

Adults

• Bone marrow contusions on MRI are highly predictive of focal osteoarthritis development within 1 year 3
• Asymptomatic meniscal tears are common, especially in older adolescents—correlate imaging with clinical findings 2

Common Pitfalls to Avoid

• Assuming negative radiographs exclude significant injury: Occult fractures, bone contusions, and soft tissue injuries require MRI if clinical suspicion persists 3
• Overlooking posterolateral corner injuries: Associated with ACL ruptures in 19.7% of cases and cause significant morbidity if missed 3
• Missing septic arthritis in young children: Urgent aspiration is mandatory for atraumatic effusion 3
• Failing to examine hip and spine: Referred pain is common 2
• Ordering MRI before radiographs: Violates standard imaging algorithm 4