What is the initial assessment and management approach for a knee injury?

How to Assess a Knee Injury

Begin with the Ottawa Knee Rule to determine if radiographs are needed: obtain X-rays if the patient is ≥55 years old, has isolated patellar tenderness, has tenderness at the fibular head, cannot flex the knee to 90°, or cannot bear weight for 4 steps immediately after injury or in the emergency department. 1, 2

Initial Clinical Assessment

History - Key Elements to Elicit

• Mechanism of injury: direct blow, fall, or twisting injury 1
• Immediate symptoms: audible pop, immediate swelling (suggests hemarthrosis and possible ACL tear or fracture), or delayed swelling 3
• Ability to bear weight: immediately after injury and currently 1
• Mechanical symptoms: locking, catching, or giving way 2
• Age and risk factors: age >55 years increases fracture risk due to decreased bone mineral density 1

Physical Examination - Systematic Approach

• Always examine the uninjured knee first for comparison 3
• Inspection: look for gross deformity, effusion, ecchymosis, or palpable mass 1
• Palpation: assess for focal tenderness at the patella, fibular head, joint line, and tibial plateau 1
• Range of motion: test ability to flex knee to 90° (both actively and passively) 1
• Weight-bearing status: observe patient taking 4 steps 1
• Ligamentous stability testing: perform valgus/varus stress tests for collateral ligaments, Lachman and pivot shift tests for anterior cruciate ligament, and posterior drawer test for posterior cruciate ligament 3
• Meniscal testing: perform McMurray's test, Apley's grind test, and bounce test 3
• Patellar stability: assess for apprehension with lateral patellar translation 4

Imaging Decision Algorithm

When to Order Radiographs

Obtain radiographs if ANY Ottawa Knee Rule criteria are met 1, 2:

• Age ≥55 years
• Isolated patellar tenderness (no other bony tenderness)
• Tenderness at the fibular head
• Inability to flex knee to 90°
• Inability to bear weight immediately after injury
• Inability to take 4 steps in the emergency department

Override the Ottawa Rule and obtain radiographs regardless if the patient has 1:

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

Standard Radiographic Views

Obtain minimum of two views 1, 2:

• Anteroposterior (AP) view
• Lateral view: with knee at 25-30° flexion in lateral decubitus position, demonstrating patella in profile 1

Additional views based on clinical suspicion 1, 2:

• Cross-table lateral with horizontal beam: to visualize lipohemarthrosis (indicates intra-articular fracture) 1
• Patellofemoral view: for suspected patellar fracture or subluxation/dislocation 1
• Internal and external oblique views: for better fracture characterization 1

Management Based on Initial Findings

If Radiographs Show Fracture

• Orthopedic consultation for definitive management 1
• Immobilization and non-weight-bearing status pending specialist evaluation 1

If Radiographs Are Negative But Clinical Suspicion Remains High

Consider diagnostic arthrocentesis if significant effusion is present 5:

• To rule out septic arthritis (orthopedic emergency requiring urgent intervention) 5
• To identify lipohemarthrosis (indicates occult intra-articular fracture despite negative radiographs) 5
• To exclude crystal arthropathy precipitated by minor trauma 5

Send synovial fluid for 5:

• Cell count with differential
• Gram stain and culture if infection suspected
• Crystal analysis
• Assess gross appearance for fat globules (lipohemarthrosis)

Order MRI without contrast as next imaging study if 2:

• Significant joint effusion persists
• Inability to fully bear weight after 5-7 days
• Mechanical symptoms suggesting meniscal injury (locking, catching)
• Joint instability suggesting ligamentous injury
• High clinical suspicion for internal derangement despite negative radiographs

Consider CT for better characterization of suspected occult fractures 1, 2, particularly tibial plateau fractures where CT shows 100% sensitivity compared to 83% for radiographs 1

Initial Conservative Management for Soft Tissue Injuries

For the first 24-72 hours, implement RICE protocol 6:

• Rest
• Ice application
• Compression
• Elevation
• Anti-inflammatory medication 6

Critical Pitfalls to Avoid

• Do not skip radiographs in patients with altered mental status, neuropathy, or multiple injuries even if they can bear weight, as examination is unreliable 1
• Do not assume negative radiographs rule out significant injury: occult fractures and soft tissue injuries (meniscal tears, ligament ruptures) may still be present 2, 5
• Do not delay arthrocentesis when septic arthritis is a consideration: this is an orthopedic emergency 5
• Do not routinely order MRI, CT, or ultrasound as initial imaging: radiographs are the appropriate first-line study 1
• Physician judgment should supersede clinical guidelines when appropriate, particularly in complex presentations 1

Follow-Up Strategy

Arrange expedited follow-up within 5-7 days if 2, 7:

• Negative radiographs but persistent symptoms
• Inability to fully bear weight
• Mechanical symptoms develop
• Joint instability noted

Refer to orthopedics if 2:

• Instability with walking or activities (suggests significant ligamentous injury)
• Mechanical symptoms persist
• Athletic patients desiring surgical reconstruction 6