01Approach to the Critical Patient/attcp36

Immediate threats

›Neurovascular emergency screen

›Peroneal nerve palsy

›Foot drop on presentation

›Inability to dorsiflex or evert ankle

›Numbness over lateral leg and dorsal foot

›Present in 25 to 31% of posterolateral corner injuries

›Popliteal artery injury

›Absent or diminished dorsalis pedis or posterior tibial pulse

›ABI < 0.9 warrants emergent CT angiography

›Vascular surgery consultation without delay

›Knee dislocation equivalent

›Gross varus instability in full extension implies multiligament injury

›Even spontaneously reduced dislocations require vascular evaluation

Stabilization priorities

›Initial triage actions

›Limb neurovascular status before imaging

›Pulses bilateral comparison

›Peroneal motor and sensory testing

›Immobilization

›Long leg posterior splint or hinged knee brace

›Non-weight-bearing if grade III or neurovascular concern

›Analgesia

›Ibuprofen 400 to 600 mg PO every 6 to 8 hours

›Acetaminophen 650 to 1000 mg PO every 6 hours as adjunct

›Ice and elevation acutely for 48 to 72 hours

Consult triggers

›Mandatory orthopedic consultation

02History/hx65

Mechanism and onset

›Injury mechanism

›Anteromedial varus force to knee

›Direct blow to medial tibia or knee

›Non-contact hyperextension with varus stress

›External rotational torque with planted foot

›Combined ACL and LCL injuries most common pattern

›Football and rugby primary sports contexts

›High-energy mechanism

›Motor vehicle collision

›Fall from height

›Event details

›Contact vs. non-contact

›Witness account critical for force vector reconstruction

›Video review in athletic settings if available

›Audible or sensed pop at time of injury

›Suggests complete ligamentous disruption

›Ability to bear weight immediately after injury

›Loss of weight-bearing implies grade III or fracture

Symptoms

›Primary complaints

›Lateral knee pain

›Over fibular head or lateral femoral epicondyle

›Worse with varus loading

›Knee instability or giving way

›Especially in extension and pivoting

›Chronic recurrent episodes if missed acutely

›Swelling

03Physical Exam/exam62

Varus stability testing

›Varus stress test

›At 30 degrees knee flexion

›Isolates the LCL from cruciate and posterior capsule

›Primary clinical test for LCL integrity

›Compare to contralateral side routinely

›At full extension

›Instability implies combined LCL plus cruciate plus posterolateral corner injury

›Multiligament injury or knee dislocation equivalent

›Grading by lateral joint opening

›Grade I: pain without increased laxity, 0 to 5 mm opening

›Grade II: laxity with firm endpoint, 5 to 10 mm opening

›Grade III: laxity with no endpoint, greater than 10 mm opening

Posterolateral corner tests

›Dial test (external rotation recurvatum)

›Prone position with knee at 30 and 90 degrees flexion

›Greater than 10 degrees asymmetric external rotation suggests PLC injury

›Positive at both 30 and 90 degrees implies combined PLC and PCL injury

›Sensitivity for PLC injury when combined with other tests

›Most sensitive combined test battery

›Reverse pivot shift

›Valgus and external rotation load while extending knee

›Positive clunk implies posterolateral rotatory instability

›PLC and LCL insufficiency pattern

›External rotation recurvatum test

›Heel height inequality in supine extension

›Facilitates detection of combined ACL and LCL injury

04Differential Diagnosis/ddx47

Lateral knee pain with instability

›Posterolateral corner injury

›ICD-10 S83.419A lateral collateral ligament sprain unspecified

›Nearly always co-exists with LCL tears

›Popliteus tendon and popliteofibular ligament involvement

›Differentiating features

›Positive dial test and reverse pivot shift

›MRI confirms popliteus and popliteofibular ligament disruption

›ACL tear

›ICD-10 S83.511A

›Varus-internal rotation mechanism for combined ACL-LCL

›Pivot shift and positive Lachman differentiate

›Second most common multiligament pattern in NFL

›Requires concurrent evaluation always

›PCL tear

›ICD-10 S83.521A

›Posterior tibial sag sign and posterior drawer positive

›Combined PCL and PLC creates rotatory instability

›Dial test positive at both 30 and 90 degrees

Fractures mimicking LCL injury

›Proximal fibula fracture

›Arcuate sign on radiograph

›Avulsion fracture fibular styloid process

›Pathognomonic for PLC avulsion mechanism

›Maisonneuve equivalent at knee

›High-energy mechanism

›Lateral tibial plateau fracture

›ICD-10 S82.121A

05Laboratory Tests/lt27

Acute injury workup

›Standard labs for isolated LCL injury

›Labs generally not indicated for isolated low-grade injury

›Clinical diagnosis based on mechanism and exam

›No biomarker specific to ligamentous injury

›Point-of-care glucose

›Diabetes screening if injury context suggests

›Wound healing risk stratification

›Preoperative workup if surgical repair anticipated

›Complete blood count

›Hemoglobin baseline

›Platelet count for coagulation planning

›Basic metabolic panel

›Renal function for anesthetic and NSAID dosing

›Electrolyte status

High-energy or multiligament workup

›Vascular injury concern

›Type and screen

›Active hemorrhage or vascular repair anticipated

›ABI less than 0.9 triggers further vascular imaging

›Coagulation profile

›PT INR and aPTT baseline

›Anticoagulant effect assessment

›Polytrauma context

›Standard trauma laboratory panel

›CBC metabolic panel coagulation

›Lactate if hemodynamic instability

›Urinalysis

06Diagnostic Tests/dt84

Scoring Systems

›LCL injury grading

›Grade I sprain

›Microscopic tears with ligament stretch

›No increased laxity on varus stress at 30 degrees

›Pain only, conservative management

›Grade II partial tear

›Macroscopic partial disruption

›5 to 10 mm lateral opening with firm endpoint

›Usually conservative management with monitoring for instability

›Grade III complete tear

›Complete ligamentous disruption

›Greater than 10 mm lateral opening with no endpoint

›Often surgical especially if combined injuries present

›Ottawa Knee Rules

›Indications for knee radiography

›Age 55 years or older

›Isolated patella tenderness

›Fibular head tenderness

›Inability to flex to 90 degrees

›Inability to bear weight four steps

›Sensitivity approaching 100% for fracture exclusion

›Reduces unnecessary radiography in low-risk injuries

›ACEP Level B recommendation for use in adults

MRI

›MRI knee without contrast

›Gold standard for soft tissue evaluation

›Confirms LCL tear grade and location

›Edema only vs. partial vs. complete fiber disruption

›Optimal sequences for LCL

›Fat-saturated proton density or T2-weighted coronal images

›Coronal plane best for LCL long axis visualization

›Axial images for peroneal nerve edema

›Associated injury detection

›Posterolateral corner structures

›Popliteus tendon and popliteofibular ligament

›Cruciate ligaments and menisci

›Bone bruise patterns

›Anteromedial femoral condyle bruise highly associated with PLC and peroneal nerve injury

›Pattern guides prognosis and surgical planning

›MRI limitations

›Sensitivity for LCL in multiligament injuries 56 to 80%

›PLC structures frequently underdiagnosed

›Clinical exam must complement MRI findings

›Timing considerations

›Acute hemarthrosis does not preclude MRI

›Immediate MRI preferred for surgical planning

CT

›CT knee without contrast

›Fracture characterization

›Arcuate sign avulsion fragment size and displacement

›Lateral tibial plateau fracture morphology

›Fibular head fracture extent

›Preoperative bony anatomy mapping

›Tunnel placement planning for reconstruction

›Complex multiligament injury assessment

›ACR Appropriateness Criteria for acute knee trauma

›CT appropriate when radiograph shows fracture requiring surgical planning

›CT not first-line for soft tissue evaluation

›CT angiography

›Indications

›ABI less than 0.9 after knee dislocation or multiligament injury

›Absent or diminished distal pulses

›High clinical suspicion despite normal ABI

›Performance

›Sensitivity and specificity exceeding 95% for popliteal artery injury

›Replaces conventional angiography in most centers

Ultrasound

›Diagnostic ultrasound for LCL

›Structural assessment

›LCL fiber continuity assessment in experienced hands

›Fibular attachment visualization

›Dynamic varus stress imaging under ultrasound

›Limitations

›Operator-dependent accuracy

›Inferior soft tissue contrast compared to MRI

›Not first-line for complete LCL evaluation

›Point-of-care ultrasound applications

›Vascular assessment

›Dorsalis pedis and posterior tibial artery Doppler

›Preliminary vascular injury screen

›Adjunct to ABI measurement

›Effusion detection

›Suprapatellar bursa fluid quantification

›Hemarthrosis vs. simple effusion characterization

›Peroneal nerve visualization

›Hyperechoic nerve at fibular neck level

›Edema or discontinuity in injury

07Disposition/dispo38

Discharge criteria

›Safe for discharge

›Isolated grade I or II LCL injury

›Intact neurovascular exam

›Stable varus stress testing without gross instability

›Ability to ambulate safely with assistive device

›Crutch training completed

›Non-weight-bearing to touch-down weight-bearing depending on grade

›Reliable orthopedic follow-up arranged

›Grade I: within 1 to 2 weeks

›Grade II: within 5 to 7 days

Admission and observation indications

›Mandatory admission or observation

›Suspected or confirmed knee dislocation

›Vascular evaluation and monitoring minimum 6 to 8 hours

›Vascular surgery on standby

›Vascular injury confirmed or suspected

›Absent pulses or ABI less than 0.9

›OR preparation if vascular repair needed

›Compartment syndrome concern

›Massive swelling post high-energy injury

›Pain out of proportion to exam

›Polytrauma patient

›Trauma surgery or orthopedic admission

Orthopedic referral parameters

›Urgent orthopedic consultation

›Grade III LCL tear

›Same-day or next-day evaluation preferred

08Treatment/t100

Acute phase management

›RICE protocol

›Rest

›Non-weight-bearing to partial weight-bearing with crutches

›Duration based on injury grade

›Ice

›15 to 20 minutes every 2 to 3 hours for 48 to 72 hours

›Barrier between ice and skin

›Compression

›Elastic bandage or neoprene sleeve

›Monitor for neurovascular compromise

›Elevation

›Above heart level when resting

›Reduces edema and pain

Analgesia

›NSAIDs

›Ibuprofen

›400 to 600 mg PO every 6 to 8 hours with food

›Maximum 2400 mg per day

›Duration 5 to 7 days acutely

›Naproxen

›500 mg PO twice daily

›Renal function monitoring if prolonged use

›Diclofenac gel topical

›Apply to lateral knee 3 to 4 times daily

›Lower systemic side effect profile

›Adjunct analgesia

›Acetaminophen

›650 to 1000 mg PO every 6 hours

›Maximum 4 g per day; 2 g per day in hepatic impairment

›Short-course opioids for severe acute pain only

›Lowest effective dose shortest duration

›Reserve for grade III or combined injury perioperative use

Immobilization and bracing

›Grade I injury

›Elastic compression sleeve

›Permits range of motion

›Worn during activity

›Weight-bearing as tolerated

›No brace requirement in most cases

›Grade II injury

›Hinged knee brace

›Locked at 40 to 45 degrees for 2 to 3 weeks

›Progressive unlocking as pain and stability improve

›Crutches until pain-free gait achieved

›Grade III injury

›Long leg posterior splint or hinged knee brace

›Immobilization in extension initially if surgical planning

›Coordinated with orthopedic surgeon preference

›Non-weight-bearing pending surgical decision

›Early repair within 2 to 3 weeks for combined injuries

Rehabilitation

›Phase 1 (weeks 0 to 3) — acute

›Isometric quadriceps and hamstring sets

›No varus stress through knee

›Ankle pumps for venous stasis prevention

›Cryotherapy and elevation continue

›Pain-guided activity

›Phase 2 (weeks 3 to 8) — subacute

›Progressive isotonic strengthening

›Closed kinetic chain exercises

›Stationary bike with low resistance

›Range of motion restoration

›Goal full extension and 90 degrees flexion by week 6

›Proprioception training initiation

›Single-leg balance progression

›Phase 3 (weeks 8 to return to sport) — functional

›Sport-specific agility drills

›Lateral cutting and deceleration

›Return to sport typically 3 to 6 months for grade II

›Functional brace use during return to activity

›Provides proprioceptive and mechanical support

›ACEP Level C recommendation for functional bracing in knee ligament injuries

Surgical management

›Indications for operative repair

›Grade III LCL with combined PLC injury

›Early repair within 2 to 3 weeks strongly recommended

›Delayed treatment leads to worse outcomes

›Grade III in young active patients

›Nonoperative grade III shows high long-term laxity and osteoarthritis rates

›Surgical repair preferred for restoration of stability

›Combined multiligament injury

›Concurrent cruciate ligament reconstruction

›Anatomic reconstruction preferred for PLC

›Surgical options

›Primary repair

›Effective within 2 to 3 weeks of acute injury

›Ligament-to-bone healing possible in acute phase

›Anatomic reconstruction

›Modified Larson technique or fibular-based reconstruction

›Preferred for chronic or irreparable injuries

›In NFL athletes with isolated grade III LCL

›Nonoperative returned to play average 2 weeks vs. 14.5 weeks surgical

›Equivalent long-term outcomes reported

›Decision individualized to injury pattern and demands

›Peroneal nerve palsy management

›Initial observation

›Ankle-foot orthosis for foot drop

›Serial neurologic exams

›EMG/NCS at 3 to 6 weeks

›Axonotmesis pattern may recover over months

›Complete palsy prognosis poor with only 12% regaining function

›If no recovery by 3 to 6 months

›Neurolysis consideration

›Tendon transfer for functional restoration

09Special Populations/sp52

Pregnancy

›Pregnancy considerations for LCL injury

›Imaging approach

›Radiograph with abdominal shielding acceptable when clinically indicated

›MRI without gadolinium preferred for soft tissue if needed

›CT angiography for vascular emergency despite radiation given maternal priority

›Analgesia

›Acetaminophen preferred first-line analgesic

›NSAIDs generally avoided especially after 30 weeks gestation

›Opioids short-term only with neonatal monitoring awareness

›Surgical timing

›Defer elective reconstruction to post-partum when feasible

›Emergent vascular repair takes priority over gestational age

›Immobilization

›Hinged brace biomechanically safe in pregnancy

›Thromboprophylaxis consideration with immobilization

›LMWH for venous thromboembolism prophylaxis if non-weight-bearing

Geriatric

›Older adult considerations

›Mechanism differences

›Low-energy falls more common than sports injuries

›Higher likelihood of concomitant fractures

›Reduced bone density increases avulsion fracture risk

›Comorbidity impact on management

›Anticoagulant use review

›Peripheral vascular disease lowers threshold for vascular imaging

›Diabetes impairs ligamentous healing and surgical outcomes

›Analgesia adjustments

10Background/b72

Epidemiology

›Incidence and prevalence

›Isolated LCL injuries are uncommon

›Isolated mechanism of pure varus force is unusual in practice

›Most LCL tears co-exist with PLC and cruciate injuries

›Sports context

›NFL athletes combined ACL-LCL is second most common multiligament pattern

›Isolated LCL more recognized than historically; Warren noted underestimation

›Complications prevalence

›Peroneal nerve palsy in 25 to 31% of PLC injuries

›Vascular injury in approximately 14% of multiligament knee injuries

›Post-traumatic osteoarthritis with untreated chronic instability

›ICD-10 coding

›S83.419A sprain of fibular collateral ligament of knee initial encounter

›S83.419D subsequent encounter

›SNOMED CT lateral collateral ligament sprain of knee

Pathophysiology

›Anatomy of the LCL

›Course and attachments

›From lateral femoral epicondyle to fibular head

›Also called fibular collateral ligament

›Cord-like structure separate from joint capsule

›Primary varus stabilizer

›Resists varus stress throughout range of motion

›Maximum contribution at 30 degrees flexion

›Posterolateral corner relationship

›LCL is component of three-layer lateral complex

›Popliteus tendon and popliteofibular ligament provide additional rotatory stability

›Injury mechanisms

›Failure under varus loading

›Direct anteromedial blow causing varus moment

›Non-contact varus-hyperextension

›Isolated vs. combined failure

›Isolated LCL tears rare due to PLC redundancy

›Sequential failure: LCL then popliteofibular ligament then popliteus

›Peroneal nerve vulnerability

›Common peroneal nerve winds around fibular neck

›Tethering makes it susceptible to traction injury with varus force

›Healing biology

›LCL healing potential

›Grade I and II heal with conservative management

›Grade III complete tears have limited intrinsic healing in chronic setting

›PLC healing constraints

›PLC complex has poor healing capacity due to anatomy

›Early surgical repair superior to reconstruction when feasible

Therapeutic Considerations

›Conservative management evidence

›Grade I and II

›Well-supported by literature; excellent outcomes with RICE and rehabilitation

›Return to sport 4 to 8 weeks for grade II

›Kannus 1989 demonstrated good outcomes with nonoperative care in grade II and III sprains

›Grade III isolated in athletes

›Bushnell 2010 NFL study: nonoperative returned to play average 2 weeks

›Long-term nonoperative grade III shows persistent laxity and osteoarthritis risk

›Decision depends on activity level and combined injury status

›Surgical evidence

›Early repair superiority

›Repair within 2 to 3 weeks allows ligament-to-bone healing

›Delayed treatment requires reconstruction rather than repair

›Grade III combined injuries consistently demonstrate better outcomes with early surgery

›Reconstruction techniques

›Anatomic fibular-based and modified Larson techniques proven

›Graft selection and tunnel placement influence outcomes

›Rehabilitation principles

›Progressive loading based on biological healing timeline

›Protect repair for 6 weeks while allowing controlled motion

›Proprioception training essential for dynamic stability restoration

›Return-to-sport criteria

›Quadriceps strength greater than 90% limb symmetry index

›Hop tests and agility testing

›Full pain-free range of motion

›Peroneal nerve recovery

›Neuropraxia recovers weeks to months

›Axonotmesis slower recovery months to 1 year

›Complete palsy 12% recovery rate; early AFO prevents contracture

11Patient Discharge Instructions/pdi39

copy discharge instructions

›LCL sprain home care

›Rest the knee and avoid activities that cause pain

›Use crutches if walking is painful

›Weight-bearing as instructed by your doctor

›Ice

›15 to 20 minutes three to four times daily for 48 to 72 hours

›Always put a cloth between ice and skin

›Compression and elevation

›Wear the elastic bandage or brace as instructed

›Keep the leg elevated above heart level when resting

›Medications

›Take ibuprofen or naproxen with food as prescribed

›Acetaminophen is safe to alternate with ibuprofen for better pain control

›Brace and activity instructions

›Hinged knee brace wear

›Keep locked at the angle specified until follow-up

›Do not adjust the brace without guidance

›Crutch use

›Keep weight off as instructed

›Walk short distances only and rest often

›No return to sport, running, or pivoting movements until cleared by your orthopedic surgeon

›Warning signs to return to ER

›Foot drop or inability to lift the foot

›New or worsening since your injury

›Numbness or tingling in the foot spreading or worsening

›Cold, pale, or blue foot or toes

›Signs of vascular compromise

12References/r25

Guidelines and key sources

›Primary clinical guidelines

›ACR Appropriateness Criteria Acute Trauma to the Knee (Taljanovic et al., JACR 2020)

›Imaging recommendations for acute knee injury

›CT angiography indications for vascular injury

›American Society of Pain and Neuroscience STEP Guidelines (Hunter et al., Journal of Pain Research 2022)

›Interventional therapies for knee pain

›Ottawa Knee Rules for radiograph decision (validated across multiple centers)

›ACEP Level B recommendation

›Key studies

›Grawe et al. JAAOS 2018 — anatomy evaluation and management of LCL injuries

›Bushnell et al. Am J Sports Med 2010 — isolated grade III LCL in NFL athletes

›Kannus 1989 Am J Sports Med — nonoperative treatment grade II and III lateral compartment sprains

›Kahan et al. Am J Sports Med 2020 — pathoanatomy of PLC disruption predicting peroneal nerve injury

›Ridley et al. Knee Surg Sports Traumatol Arthrosc 2018 — peroneal nerve injuries with PLC injuries

›Sanchez-Munoz et al. Am J Sports Med 2023 — MRI accuracy in multiligament knee injuries

›Solomon et al. JAMA 2001 — physical examination accuracy for knee ligament injuries

›Maniar et al. JAAOS 2024 — posterolateral corner evaluation and management update

›Imaging and diagnostic references

›Recondo et al. Radiographics 2000 — lateral stabilizing structures MRI assessment

›Mirowitz and Shu JMRI 1994 — MRI sequences for collateral ligament evaluation

›Moran et al. Am J Sports Med 2022 — bone bruise patterns in multiligament injuries with peroneal palsy

›ICD-10 coding references

›S83.419A fibular collateral ligament sprain unspecified initial encounter

›S83.511A sprain of anterior cruciate ligament right knee initial encounter

›S82.121A displaced fracture lateral tibial condyle initial encounter

Evidence & Review

Evidence & Review