01Approach to the Critical Patient/attcp44

Immediate threats and red flags

›Time-critical threats

›If knee dislocation suspected

›Immediate reduction if gross deformity and neurovascular compromise

›Distal pulses

›ABI threshold 0.9 for vascular imaging pathway

›If hard vascular signs

›Absent distal pulses

›Expanding hematoma

›Active hemorrhage

›Immediate vascular surgery and CT angiography

›If compartment syndrome concern

›Pain out of proportion

›Pain with passive stretch

›Paresthesia

›Emergent orthopedic evaluation

›If open fracture or open joint

›Tetanus status

›IV antibiotics

›Emergent orthopedic evaluation

›If septic arthritis concern

›Fever

›Immunocompromise

›Marked pain with minimal ROM

›Arthrocentesis pathway

Initial stabilization and analgesia

›Early stabilization priorities

›Pain control strategy

02History/hx56

Mechanism and symptom pattern

›Injury narrative

›Mechanism

›Noncontact pivot or deceleration

›Direct blow

›Hyperextension

›Twisting with foot planted

›Pop sensation

›Audible or felt pop

›Immediate instability episode

›Onset of swelling

›Within 2 hours suggests hemarthrosis and ACL rupture

›Delayed swelling suggests meniscal injury or synovitis

›Weight bearing ability

›Inability to bear weight at injury

›Progressive difficulty over hours

Functional impact and mechanical symptoms

›Function and symptoms

›Instability

›Giving way episodes

›Difficulty with stairs or pivoting

›Mechanical symptoms

›Locking with inability to fully extend

›Catching or clicking

›Joint line pain with twisting

›Range limitation

›Extension block

›Flexion limitation from effusion

03Physical Exam/exam61

Neurovascular and general inspection

›Safety exam first

›Distal perfusion

›Dorsalis pedis pulse

›Posterior tibial pulse

›Capillary refill

›ABI measurement if dislocation concern

›ABI less than 0.9 threshold for vascular imaging pathway

›Serial exams for evolving findings

›Neurologic function

›Common peroneal nerve dorsiflexion and sensation

›Tibial nerve plantarflexion and plantar sensation

›Skin and soft tissue

›Lacerations suggesting open joint

›Ecchymosis pattern

Effusion, ROM, and palpation

›Core knee exam

›Effusion assessment

›Ballottement and bulge sign

›Tense hemarthrosis appearance

›Range of motion

›Extension deficit

›Flexion deficit

›Pain with passive ROM

›Joint line tenderness

›Medial joint line tenderness

›Lateral joint line tenderness

›Patellofemoral assessment

04Differential Diagnosis/ddx40

Traumatic knee internal derangement

›Internal derangement differential

›ACL rupture acute

›ICD-10 S83.51 series

›SNOMED CT anterior cruciate ligament rupture

›Meniscal tear acute

›ICD-10 S83.24 series medial meniscus

›ICD-10 S83.28 series lateral meniscus

›SNOMED CT meniscal tear

›MCL sprain or tear

›ICD-10 S83.41 series

›LCL sprain or tear

›ICD-10 S83.42 series

›PCL tear

›ICD-10 S83.52 series

›Osteochondral injury

›Loose body with locking

Fracture and dislocation mimics

›Bony injury differential

›Tibial plateau fracture

›Pain with weight bearing

›Large effusion

›Tibial spine avulsion pediatric

›ACL equivalent injury

›Patellar fracture

›Direct anterior blow

›Extensor mechanism failure

›Knee dislocation

05Laboratory Tests/lt24

Labs when alternative diagnosis or procedure planned

›Selective labs

›Infection evaluation set

›CBC for systemic infection concern

›CRP for inflammatory process concern

›ESR for inflammatory process concern

›Hemarthrosis and bleeding risk set

›INR for warfarin use

›Platelet count for thrombocytopenia concern

›Pre-procedure considerations

›Pregnancy test for imaging and medication planning in reproductive age

›Type and screen only if operative pathway and significant trauma

Synovial fluid studies if arthrocentesis performed

›Arthrocentesis panel

›Cell count and differential

›WBC threshold interpretation based on clinical context

›Gram stain

›Limited sensitivity

›Culture

›Prior antibiotics reduce yield

›Crystals

›Gout and CPPD evaluation

PITFALLS

›Lab limitations

›Normal CBC and CRP do not exclude septic arthritis early

›Elevated inflammatory markers are nonspecific after acute trauma

›Hemarthrosis presence does not distinguish ACL from osteochondral injury

06Diagnostic Tests/dt45

Scoring Systems

›Decision tools and functional scores

›Ottawa Knee Rule for radiographs

›Age 55 years or older

›Isolated patellar tenderness

›Tenderness at fibular head

›Inability to flex to 90 degrees

›Inability to bear weight four steps immediately and in ED

›Pittsburgh Knee Rule for radiographs

›Blunt trauma or fall

›Age younger than 12 years

›Age older than 50 years

›Inability to walk four weight-bearing steps

›KOOS or IKDC for follow-up monitoring

›Baseline function documentation

›Tracking response to rehab and surgery

MRI

›MRI knee without contrast

›Indications

›Suspected ACL rupture with functional instability

›Suspected meniscal tear with mechanical symptoms

›Locked knee suspicion

›Persistent pain or effusion beyond expected course

›What MRI clarifies

›ACL continuity and associated bone bruising

›Meniscal tear type and displacement

›Chondral and osteochondral injury

›Multiligament injury pattern

07Disposition/dispo25

Criteria for urgent consultation and admission

›Escalation and consult triggers

›Emergent orthopedic consult

›Locked knee with inability to extend

›Suspected bucket handle meniscal tear

›Gross instability suggesting multiligament injury

›Open injury or fracture

›Vascular surgery consult

›ABI less than 0.9 after suspected dislocation

›Absent pulses or ischemic limb signs

›Admission criteria

›Neurovascular compromise

›Uncontrolled pain despite ED management

›Inability to ambulate safely with supports

Discharge criteria and follow-up

›Outpatient pathway

›Discharge suitable

›Stable neurovascular exam

›No fracture requiring admission

›Pain controlled with oral meds

›Safe ambulation with crutches or brace plan

›Follow-up timing

›Orthopedics or sports medicine within 1 to 2 weeks for suspected ACL tear

›Earlier within 3 to 7 days for locked knee or severe instability concern

›Rehab initiation

›Early physiotherapy referral when appropriate

›Home ROM exercises if safe

08Treatment/t57

Immobilization, activity, and rehab

›Nonoperative immediate care

›Protection and support

›Hinged knee brace for instability

›Knee immobilizer for locked knee or severe pain

›Weight bearing guidance

›Weight bearing as tolerated when stable and no fracture concern

›Crutches until gait normalizes

›Swelling management

›Ice 15 to 20 minutes every 2 to 3 hours first 48 hours

›Compression wrap if tolerated

›Elevation above heart when resting

›Early motion

›Avoid prolonged full immobilization when no locking or fracture

›Quadriceps activation exercises if tolerated

Analgesia and anti-inflammatory therapy

›Pain control options

›Acetaminophen

›1000 mg PO every 6 to 8 hours as needed

›Maximum 3000 mg per 24 hours typical outpatient limit

›Ibuprofen

›400 mg PO every 6 to 8 hours as needed

›Maximum 2400 mg per 24 hours for short course

›Naproxen

›500 mg PO then 250 to 500 mg PO every 12 hours as needed

›Maximum 1000 mg per 24 hours

›Topical diclofenac

›1 percent gel 2 to 4 g to knee up to 4 times daily

09Special Populations/sp28

Pregnancy

›Pregnancy considerations

›Imaging and radiation

›Knee radiographs with shielding acceptable when indicated

›MRI without gadolinium preferred if advanced imaging needed

›Medication choices

›Acetaminophen preferred first line

›NSAID avoidance in later pregnancy based on obstetric guidance

›DVT risk context

›Lower threshold to evaluate for DVT if calf symptoms present

Geriatric

›Older adult considerations

›Higher fracture likelihood with low energy mechanisms

›Lower threshold for radiographs

›Consider tibial plateau fracture even with mild trauma

›Medication risk

›NSAID renal and GI risk

›Fall risk with sedating analgesics

›Degenerative meniscus tears

›Mechanical symptoms may be less specific

›Rehab and OA management overlap

Pediatrics

›Pediatric considerations

›Physeal injuries

›Tibial spine avulsion as ACL equivalent

›Lower threshold for imaging with hemarthrosis

›Exam limitations

›Guarding affects Lachman reliability

10Background/b30

Epidemiology

›Epidemiology facts

›ACL rupture frequency

›Common in pivoting sports

›Higher incidence in female athletes in certain sports

›Meniscal tear patterns

›Medial meniscus commonly involved with ACL injuries

›Degenerative tears increase with age

Pathophysiology

›Mechanisms and injury patterns

›ACL rupture biomechanics

›Anterior tibial translation and rotational instability

›Bone bruise patterns with pivot shift mechanism

›Meniscal tear biomechanics

›Shear forces with twisting

›Bucket handle tear causes mechanical block

›Combined injury patterns

›Unhappy triad style patterns with valgus and rotation

›Multiligament injuries increase dislocation and vascular risk

Therapeutic Considerations

›Treatment rationale

›Early swelling control and ROM restoration

›Reduces stiffness risk

›Improves later surgical outcomes when applicable

›Immobilization tradeoffs

›Prolonged immobilization increases stiffness and quadriceps atrophy

›Short-term immobilization appropriate for locking or severe pain

›Meniscal preservation rationale

11Patient Discharge Instructions/pdi26

Copy discharge instructions

›Discharge instructions

›Diagnosis explanation

›Suspected ligament or meniscus injury based on mechanism and exam

›X-ray may be normal despite significant soft tissue injury

›Home care

›Ice 15 to 20 minutes every 2 to 3 hours for 48 hours

›Compression wrap if comfortable

›Elevation when resting

›Crutches use until walking without limp

›Brace use as instructed

›Medications

›Acetaminophen as directed on label or clinician plan

›NSAID only if safe for you and no contraindications

›Activity

›Avoid pivoting, running, jumping until cleared

›Gentle ROM exercises if not locked and tolerated

›Follow-up

›Orthopedics or sports medicine within 1 to 2 weeks

›Earlier follow-up within 3 to 7 days if locking or severe instability

›Return to ED now

›Foot becomes cold, pale, numb, or weak

›New severe calf pain or swelling

›Fever or redness with rapidly worsening pain

›Inability to move the knee or suddenly locked knee

›Uncontrolled pain despite medication

›New deformity or inability to bear weight after a new twist or fall

12References/r12

Guidelines and key sources

›Core references

›AAOS clinical practice guideline resources for ACL injury management

›Emphasis on rehabilitation and individualized surgical decision making

›ACR Appropriateness Criteria for acute knee trauma imaging

›Radiographs first line when fracture risk criteria met

›MRI for internal derangement evaluation when radiographs negative and symptoms persist

›Ottawa Knee Rule validation studies

›High sensitivity for knee fracture exclusion

›Reduced unnecessary radiography

›Sports medicine consensus statements on meniscal preservation

›Repair favored when tear pattern and tissue quality suitable

›Avoid unnecessary meniscectomy in young active patients

Evidence & Review

Evidence & Review