Basics
Description
- Cruciate ligament injuries:
- Anterior cruciate ligament (ACL):
- From the posteromedial aspect of the lateral femoral condyle to the intraspinus area on the tibia
- Prevents excessive anterior translation of the tibia, internal rotation of the tibia on the femur, or hyperextension of the knee.
- Posterior cruciate ligament (PCL):
- Twice as strong and twice as thick as the normal ACL, less commonly injured
- From anterolateral aspect of medial femoral condyle to the posterior tibia
- Meniscal tears:
- Medial meniscus injury most common
- More firmly attached to the joint capsule and less mobile than lateral meniscus
- Tears are the result of tensile or compressive forces between the femoral and tibial condyles
- Extension of meniscal tear may result in a free segment that may become displaced into the joint, resulting in a true locked joint.
- Medial collateral ligament:
- From the posterior aspect of medial femoral condyle to the tibia, distal to joint
- Often accompanied by other injury:
- Hyperextension with external rotation (ACL/PCL injured 1st)
- Anterior stress (ACL injured 1st)
Epidemiology
Incidence and Prevalence Estimates
- ACL:
- Most commonly injured knee ligament
- 200,000 ACL injuries annually in US
- 2/3 of all ACL injuries are noncontact
- Female gender: 3 greater risk
- Associated injuries:
- ’ Ό50% ACL injuries are associated with meniscal tears
- ACL injuries commonly have chondral and subchondral injuries
- Meniscus:
- Medial meniscus injury 10 more common than lateral
- True locked joint in only 30%
Etiology
- Cruciate ligament injuries:
- ACL: Often deceleration with flexion and rotation, or hyperextension
- Usually sports-related, especially skiing and football
- Plant-and-pivot or stop-and-jump mechanism
- PCL:
- "Dashboard injury " : Flexed knee with posteriorly directed force to the anterior proximal tibia (motor vehicle crash or direct trauma)
- Fall on flexed knee
- Meniscus Injury:
- Sudden rotary motion of knee associated with squatting, pivoting, turning, and bending
- Common in sports with low stance positions (wrestling/football) or kneeling position (carpet installers, plumbers)
- Medial collateral ligament injuries:
- Direct trauma to lateral knee
- Most common: Valgus stress with external rotation on flexed knee:
- From catching a ski tip
- Side tackle (football)
- The ACL is the most frequently injured knee ligament in children.
- Isolated MCL injury infrequent before growth plate closure (<14-yr old)
Diagnosis
Signs and Symptoms
History
- Cruciate ligament injuries:
- Feeling knee "give way, " pop, tearing sensation
- Most patients report immediate knee dysfunction, but some may ambulate despite complete ACL rupture because of stability from supporting structures.
- Large, almost immediate effusion " patients report significant swelling
- Medial collateral ligament:
- Tearing sensation and immediate pain in medial aspect of knee
- Medial pain and tenderness may be more pronounced with partial tears than with complete tears.
- Medial meniscus injury:
- Patient may recall the knee "giving way "
- Inability to fully extend knee is common
- Effusion is found in 50% and usually occurs over 6 " 12 hr.
- Pain is often intermittent and localized to the joint line
- Unlike ligamentous injury, patients often report completion of activities at time of injury
- Degenerative meniscal tears tend to have a more insidious, atraumatic presentation, with mild swelling, vague joint line pain, and sometimes with mechanical symptoms. Often associated with osteoarthritis.
Physical Exam
- Ability to bear weight reduced with all injuries
- Palpate for pain on:
- bony prominences for fracture
- growth plates in children
- medial and lateral joint line (meniscus and collateral ligament injury)
- Range of motion:
- Locking: May occur with ACL (interposition of torn cruciate), meniscus injury, loose body (arthritis)
- Pseudolocking may be present from pain, effusion, or spasm
- Effusion:
- Immediate (within 2 " 3 hr) usually indicates a significant intra-articular injury including ACL
- About 70% of acute knee hemarthroses are caused by ACL injury, but lack of effusion does not rule out ACL injury
- MCL, meniscus, PCL injuries have more delayed effusion (12 " 24 hr)
- Warmth, erythema: Consider infection
- Neurovascular exam:
- Distal pulses
- 1st dorsal web-space sensation (deep peroneal nerve)
- Ankle/toe dorsiflexion
- Stress testing: Always compare the injured to the uninjured side (asymmetry is more reliable than absolute degree of laxity):
- Pain and spasm can limit the utility of all stress testing in the acute phase
- Lachman test is most reliable for ACL:
- Knee flexed 20 °, patient supine with thigh supported and hip slightly externally rotated. Quickly bring the tibia forward on the femur, 1 hand holding proximal tibia, the other stabilizing the femur just above the patella, evaluating for quality of the endpoint and degree of anterior translation of the tibia
- Pain with motion = partial tear or disruption
- Quantification of degree of movement less important then simply positive or negative interpretation of test
- Pivot shift test: More specific for ACL injury but unreliable without anesthesia and painful acutely. Not recommended routinely in the ED.
- Anterior/posterior drawer sign:
- Knee flexed 90 °, patient supine, hip flexed 45 °, foot neutral and stabilized (sit on foot)
- Observe for posterior sag of tibia, positive with PCL injury
- Posterior drawer (PCL): Movement of tibia back with application of posterior pressure
- Anterior drawer (ACL): Movement of tibia forward with anterior distraction force
- Quadriceps active test (PCL):
- Patient supine, knee flexed at 90 °, hip flexed at 45 °
- Patient attempts to extend knee against examiners counterforce
- Positive if the tibia translates anteriorly during quad activation
- Varus/valgus stress testing: Evaluate in extension and 20 ° flexion for MCL and LCL laxity
- Meniscus: Wait until acute pain is controlled:
- McMurray: While palpating joint lines, extend the knee while internally and then externally rotating. Pain and click is positive.
- Apley: With patient prone, flex knee to 90 °, provide axial load and internally/externally rotate lower leg. Pain is positive.
- Children and adolescents show more laxity on exam than adults
- Examine hip and obtain radiograph if any concern for hip pathology (especially slipped capital femoral epiphysis)
- Have a high suspicion for epiphyseal growth plate injuries
Diagnosis Tests & Interpretation
Lab
- If cause of knee effusion not clearly traumatic, synovial aspirate can be sent for cell count, Gram stain, culture, crystals
- Arthrocentesis is usually not indicated after trauma except to relieve symptoms from tense effusion
Imaging
- Ottawa knee rules (adults): Plain films required for patients with any of 5 findings:
- Age ≥55
- Isolated tenderness of patella
- Tenderness at head of fibula
- Inability to flex 90 °
- Inability to bear weight both immediately and in ED (4 steps)
- Standard radiography:
- Obtain on all suspected ACL injuries due to high risk of fractures
- Important in children to evaluate for tibial spine and growth plate fractures
- Views: AP, lateral, oblique, notch
- Special attention to avulsion fractures of the medial/lateral tibial spine and lateral tibial plateau, which can be seen with ACL/PCL injuries and may be more likely to be treated operatively
- Fat " fluid level for fracture.
- MRI is around 95% sensitive for ACL tears and other intra-articular disorders (menisci, PCL, osteonecrosis, osteochondral lesions, occult fractures) and even more specific, but it is rarely indicated emergently.
- Arteriograms to evaluate vascular integrity for suspected dislocations
- US useful to diagnose cysts and popliteal artery aneurysms
Ottawa knee rules do not apply to children.
Essential Workup
- Neurovascular evaluation
- Exclusion of fractures and infection
- Evaluate for multidirectional instability
- Valgus/varus stress at 20 ° of flexion
- Extensor mechanism function
- Lachman test for ACL injury
Differential Diagnosis
- Growth plate injury
- Tibial plateau bony injury, other fracture
- Transient knee dislocation
- Transient patellar dislocation
- Hip injury causing referred pain
- Nontraumatic causes of knee effusion and pain including septic joint, gout, osteoarthritis, rheumatoid arthritis
Treatment
Initial Stabilization/Therapy
- ABC 's, ATLS
- Immobilize knee
- Document neurovascular function
- Apply ice, elevate, analgesia
Ed Treatment/Procedures
- Reduce locked knee from meniscus injury within 1st 24 hr after injury:
- With patient seated, hang extremity off edge of exam table at 90 °: This with analgesia alone may reduce locked joint.
- Assist with applying gentle traction and rotation of tibia
- Arthrocentesis may afford relief with large effusions and assist in reducing locked joint:
- Follow with compressive dressing
- Treatment (if no fracture):
- Rest, Ice, Compression, Elevation
- Weight Bearing as Tolerated, crutches for comfort if needed
- May provide knee immobilization for protection, but encourage motion out of brace as much as possible, especially if follow-up may be delayed
Medication
- Pain control: NSAIDs preferred over opioids
- Ibuprofen: 400 " 600 mg (peds: 5 " 10 mg/kg) PO QID.
Follow-Up
Disposition
Admission Criteria
- Isolated ACL, PCL, meniscus, or collateral ligament injury rarely requires emergent hospitalization
- Low threshold to admit possible knee dislocations for monitoring
- Fractures often need ORIF to limit post-traumatic arthritis
Discharge Criteria
Most patients can be managed as outpatients with appropriate referral.
Issues for Referral
- Re-exam is recommended at 48 hr if ED exam is inconclusive or if history suggests more significant injury than initial exam demonstrates (i.e., severe symptoms, hearing "pop " ).
- Orthopedic referral within 1 " 2 wk if significant ligamentous injury is present.
- Surgical repair of all lesions may be considered for patients wishing to return to sports or active lifestyles.
Pearls and Pitfalls
- Do a careful neurovascular exam, and always examine 1 joint above and below the pain for associated injury or referred pain
- Have a high index of suspicion for a reduced total knee dislocation if patient has multidirectional knee instability or injuries to multiple ligaments
- Do not miss: Knee dislocation, fractures, septic joint, referred pain from hip, neurovascular injury
Additional Reading
- Chen L, Kim PD, Ahmad CS, et al. Medial collateral ligament injuries of the knee: Current treatment concepts. Curr Rev Musculoskelet Med. 2008;1(2):108 " 113.
- Meuffels DE, Poldervaart MD, Diercks RL, et al. Guideline on anterior cruciate ligament injury: A multidisciplinary review by the Dutch Orthopaedic Association. Acta Orthop. 2012;83(4):379 " 869.
- Noyes FR. Noyes ' Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes. Philadelphia, PA: Saunders-Elsevier; 2010.
- Ryzewicz M, Peterson B, Siparsky PN, et al. The diagnosis of meniscus tears: The role of MRI and clinical examination. Clin Orthop Relat Res. 2007;455:123 " 133.
Codes
ICD9
- 836.0 Tear of medial cartilage or meniscus of knee, current
- 844.1 Sprain of medial collateral ligament of knee
- 844.2 Sprain of cruciate ligament of knee
- 844.0 Sprain of lateral collateral ligament of knee
ICD10
- S83.419A Sprain of medial collateral ligament of unsp knee, init
- S83.519A Sprain of anterior cruciate ligament of unsp knee, init
- S83.529A Sprain of posterior cruciate ligament of unsp knee, init
- S83.249A Oth tear of medial meniscus, current injury, unsp knee, init
- S83.409A Sprain of unsp collateral ligament of unsp knee, init encntr
- S83.509A Sprain of unsp cruciate ligament of unsp knee, init encntr
SNOMED
- 444470001 Injury of anterior cruciate ligament
- 433162006 injury of posterior cruciate ligament (disorder)
- 444448004 Injury of medial collateral ligament of knee (disorder)
- 302932006 Tear of medial meniscus of knee
- 239725005 Rupture of anterior cruciate ligament (disorder)
- 239727002 Rupture of posterior cruciate ligament (disorder)