Basics
Description
- Defined by the position of the tibia in relation to the distal femur:
- Anterior dislocation:
- Most common dislocation, accounts for 60%
- Hyperextension of the knee
- Rupture of the posterior capsule at 30 ‚ °
- Rupture of the posterior cruciate ligament (PCL) and popliteal artery (PA) occurs at 50 ‚ °
- Posterior dislocation:
- Direct blow to the anterior tibia with the knee flexed at 90 ‚ °, "dashboard injury " ť
- Anterior cruciate ligament (ACL) is usually spared.
- Medial dislocation:
- Varus stress causing tear to the ACL, PCL, and lateral collateral ligament (LCL)
- Lateral dislocation:
- Valgus stress causing tear to the ACL, PCL, and medial collateral ligament (MCL)
- Associated injuries:
- PA injury:
- Occurs in 35% of dislocations.
- Anterior dislocations place traction on PA and cause contusion or intimal injury, which may result in delayed thrombosis.
- Posterior dislocations cause direct intimal fracture and transection of the artery with immediate thrombosis.
- Peroneal nerve injury:
- Less common than PA injury
- If present, must rule out concomitant arterial insult
- Medial dislocation causes injury by traction of the nerve.
- Rotary injuries have a high incidence of traction and transection.
Etiology
High-energy injuries such as motor vehicle crashes, auto " “pedestrian accidents, and athletic injuries (football most common) ‚
Diagnosis
Signs and Symptoms
- Grossly deformed knee
- Grossly unstable knee in AP plane or on varus/valgus stress
- Lack of distal pulse:
- PA injury is primary concern.
- Signs of distal ischemia:
- Pallor, paresthesia, pain, paralysis
History
Mechanism of injury with high level of suspicion ‚
Physical Exam
- Distal pulses
- Distal nerve function:
- Hypesthesia of 1st web space, inability to dorsiflex foot
- Ligamentous laxity
Essential Workup
- History of mechanism of injury
- Complete and careful physical exam:
- Pulses " ”palpation, Doppler, ankle " “brachial index (ABI), and cap refill
- Neurologic " ”sensation to 1st web space and great toe, movement of toes, dorsiflexion of foot
- AP and lateral knee radiographs
- Documented repeat exam if any closed reduction is attempted
Diagnosis Tests & Interpretation
Imaging
- AP/lateral radiograph of knee:
- Essential to rule out concomitant fractures
- MRI within 1 wk of injury to define ligamentous injury
Diagnostic Procedures/Surgery
- ABI " ”likelihood of significant arterial injury requiring surgery low if ≥0.9
- Peripheral vascular ultrasonography
- Arteriogram should be considered:
- High suspicion of PA injury
- Poor pulses or distal perfusion after reduction
- Peroneal nerve injury
- Ischemic symptoms despite normal pulses
Differential Diagnosis
- Tibial plateau fracture
- Supracondylar femoral fracture
- Ligamentous/tendonous avulsion fracture
Treatment
Pre-Hospital
- Management of ABCs
- Documentation of pulses and motor response essential
- Splint knee in slight flexion to prevent PA traction or compression.
Initial Stabilization/Therapy
- ABCs especially when motor vehicle crash or auto " “pedestrian accident
- Fluid resuscitation; hypotension may alter distal pulses and perfusion.
- Closed reduction immediately for any limb ischemia
- Early surgical consult in an open injury or high suspicion of arterial injury
Ed Treatment/Procedures
- Closed reduction by longitudinal traction and lifting femur into normal alignment without placing pressure on popliteal fossa
- Posterior leg splint/knee immobilizer with knee in 15 " “20 ‚ ° of flexion
- Repeat neurovascular exam after manipulation and at frequent intervals.
- IV analgesia for patient comfort
- Surgical consult (orthopedic and vascular): Open injury, PA injury, or unable to reduce
Medication
First Line
- Narcotic analgesia IV
- Avoid PO meds, as surgery may be necessary.
Follow-Up
Disposition
Admission Criteria
All patients require admission for observation of limb perfusion and PA repair if necessary. ‚
Discharge Criteria
All patients should be admitted. ‚
Issues for Referral
Eventual repair of ligamentous injuries: ‚
- Usually at 3 wk
- Arthroscopic surgery is contraindicated for 2 wk after injury to prevent compartment syndrome.
Follow-Up Recommendations
- Orthopedics for ligamentous repair
- Vascular for PA injury
Pearls and Pitfalls
- Failure to revascularize PA within 6 " “8 hr: Amputation rate approaches 90%.
- Peroneal nerve injury:
- Poor prognosis for recovery
- Delayed compartment syndrome may occur.
Additional Reading
- Kelleher ‚ HB, Mandavia ‚ D. Dislocation, knee. eMedicine [serial online]. 2011. Available at www.emedicine.medscape.com/article/823589-overview
- Mills ‚ WJ, Barei ‚ DP, McNair ‚ P. The value of ankle-brachial index for diagnosing arterial injury after knee dislocation: A prospective study. J Trauma. 2004;56(6):1261 " “1265.
- Nicandri ‚ GT, Chamberlain ‚ AM, Wahl ‚ CJ. Practical management of knee dislocations: A selective angiography protocol to detect limb-threatening vascular injuries. Clin J Sport Med. 2009;19(2):125 " “129.
- Seroyer ‚ ST, Musahl ‚ V, Harner ‚ CD. Management of the acute knee dislocation: The Pittsburgh experience. Injury. 2008;97(7):710 " “718.
Codes
ICD9
- 836.50 Dislocation of knee, unspecified, closed
- 836.51 Anterior dislocation of tibia, proximal end, closed
- 836.52 Posterior dislocation of tibia, proximal end, closed
- 836.53 Medial dislocation of tibia, proximal end, closed
- 836.54 Lateral dislocation of tibia, proximal end, closed
- 836.59 Other dislocation of knee, closed
ICD10
- S83.106A Unspecified dislocation of unspecified knee, init encntr
- S83.116A Anterior disloc of proximal end of tibia, unsp knee, init
- S83.126A Posterior disloc of proximal end of tibia, unsp knee, init
- S83.136A Medial dislocation of proximal end of tibia, unsp knee, init
- S83.104A Unspecified dislocation of right knee, initial encounter
- S83.105A Unspecified dislocation of left knee, initial encounter
- S83.146A Lateral disloc of proximal end of tibia, unsp knee, init
SNOMED
- 58320001 Traumatic dislocation of knee joint (disorder)
- 41359009 Closed anterior dislocation of proximal end of tibia (disorder)
- 208938001 Closed traumatic dislocation knee joint, posterior (disorder)
- 208939009 Closed traumatic dislocation knee joint, medial (disorder)
- 208940006 Closed traumatic dislocation knee joint, lateral (disorder)
- 64213003 Closed anterior dislocation of distal end of femur (disorder)