Knee Dislocation

Written by: Andrew Rogers, MD, MBA (NUEM ‘22) Edited by: Amanda Randolph, MD (NUEM ‘21) Expert Commentary by: Matt Levine, MD

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Introduction

Tibiofemoral dislocations are a relatively uncommon injury with high risk of morbidity to patients, and therefore represent an injury that the Emergency Physician should familiar with diagnosing and treating.  The incidence of knee dislocation is quite low, representing approximately 0.02% of all orthopedic injuries. [1] Morbidity is high, with rates of vascular injury of 7-40%, neurologic injury of 5-40%, and amputation rates of around 12%. [2,3]  Delays in identifying vascular injury >8 hours can result in higher rate of amputation approaching 86%. [3,4] Timely identification, treatment, and disposition directly impacts patient’s lives and limbs. 

Anatomic Review

The knee is stabilized by ligaments, tendons, muscles, menisci, and cartilage.  Figure 1 highlights key anatomic structures that stabilize the knee joint, including the major ligaments of the ACL, PCL, MCL, and LCL.  These ligaments, in various combinations, are disrupted in knee dislocations.

The neurovascular anatomy is also important to review and understand (Figure 2).  The popliteal artery courses posterior to the joint and is tethered both proximally (at the tendinous hiatus of the adductor magnus) and distally (at the tendinous arch of the soleus muscle), making it susceptible to injury. [2]  The sciatic nerve divides into the tibial and common peroneal nerves proximal to the popliteal fossa, with the common peroneal nerve tethered about the fibular neck. This attachment similarly increases the risk of common peroneal nerve injury. [2]

Figure 1: Structural Anatomy of the Knee [5]

Figure 2: Neurovascular Anatomy of the Knee [6]

Mechanism of injury

The mechanism of a knee dislocation can be high-energy, low-energy, or ultra-low energy. [2] 

• High energy: MVCs, falls from heights, crush injuries –  ~50% of knee dislocations

• Low energy: Sports injuries – ~33% of knee dislocations

• Low energy: Falls from standing - ~10% of knee dislocations

• Ultra-low energy: ADLs in morbidly obese (BMI >40) population [7, 8] 

Classifications of Knee Dislocations

Two main classifications are used to categorize knee dislocations. [2] The Kennedy Classification defines the injury based on the direction of displacement of the tibia relative to the femur (Figure 3)  The Schenck Classification is based on the pattern of ligamentous injury, with the Wascher modifications specifying lateral ligaments ruptured (Figure 4).  

Figure 3: Kennedy Classification of knee dislocations with example illustrations [9]

Figure 4: Schenck Classification System with Wascher Modification [2]

ED Evaluation

Approximately 50% of knee dislocations spontaneously reduce so the Emergency Physician should maintain spontaneously reduced knee dislocation on their differential in all patients presenting with knee pain, especially for the obese patient with an ultra-low energy mechanism. [2, 3] Figure 5 is a summary diagram from Gottlieb, et al summarizing the algorithm for evaluation and management of knee dislocations.

Figure 5: Algorithm for the evaluation and management of knee dislocations in the Emergency Department [10]

History

Some historical details to inquire about include:

• Mechanism of injury

• Sensation of instability

• Deformity at any point in time

• History of injury or surgery to the joint

• Timing of injury

Initial Physical Exam

As 50% of dislocations spontaneously reduce or due to an obese patient population, there may not be an obvious physical deformity.  Key points to include (and document) on the physical exam include: [3, 10]

• Gross deformity

• Vascular exam

  • Assess for presence of dorsalis pedis and posterior tibialis pulses

  • Look for hard signs of vascular injury: pallor, coolness, pulsatile hematoma, pulsatile hemorrhage, palpable thrill, audible bruit, absent or diminished pulses

• Neurologic exam

  • Sensory and motor deficits

  • Signs of common peroneal nerve injury:

    • Sensory deficit to lateral leg and dorsal foot

    • Inability or weakness in eversion and dorsiflexion of foot

• Skin exam

  • Look for pinched, discolored, tented, or threatened skin

  • Assess for open dislocation or fracture

  • Bruising without effusion suggests capsule disruption – may hint toward dislocation [11]

• Ligamentous laxity

  • May be limited by pain, effusion, or deformity

• Compartments exam

 In high-energy mechanisms, consider other injuries as a knee dislocation may be distracting, or consider careful examination of the knee if other injuries limit history (for example a head injury sustained in an MVC).

Initial imaging

• AP and lateral radiographs of the knee

• Recommended to also obtain radiographs of femur, tibia and fibula, as well as ankle and hip joints, although additional radiographs should not delay closed reduction if indicated, and may be obtained after reduction of the knee [11]

• If patient cannot tolerate plain films, can consider urgent CT

• Assess for dislocation and fractures (Figure 6)

• Some subtle signs of spontaneously reduced knee dislocation include: [11]

  • Widening of medial joint space on AP film

  • Segond fracture – avulsion fracture of lateral tibial plateau which is frequently associated with ACL disruption (Figure 7)

  • Fibular head avulsion fracture (AKA arcuate fracture) – avulsion of LCL or arcuate ligament complex (Figure 7)

Figure 6: Lateral knee dislocation [12]

Figure 6: Posterior knee dislocation [13]

Figure 7: Segond fracture with red circle showing lateral tibial plateau avulsion fracture [14]

FIgure 7: Fibular head avulsion fracture with white arrow showing avulsed fragment [15]

Reduction

Once the diagnosis of knee dislocation is made, reduction should be attempted in the Emergency Department under adequate analgesia and conscious sedation. Early orthopedics consultation is recommended. Reduction technique requires at least two team members to perform, and involves reversing the mechanism of injury (Figure 8). [3, 10] One team member stabilizes the distal femur while the other team member provides in-line traction on the lower leg. If this is unsuccessful, then apply anterior or posterior pressure to the proximal tibia and/or distal femur with in-line traction still applied to facilitate relocation. Avoid applying pressure to the popliteal fossa, which may cause or worsen neurovascular injury. Some knee dislocations may not be reducible in the Emergency Department and may require open reduction by orthopedics in the operating room. 

Figure 8: Technique for reduction of knee dislocation [20]

Post reduction

After successful reduction, splint in 20 degrees of flexion and/or use a knee immobilizer to stabilize the joint. [3, 10] Cut out windows in the splint to perform regular neurovascular checks. Prior to splint placement, consider full ligamentous examination while the patient is under conscious sedation prior to splinting to assess ligamentous injury. 

Repeat evaluation of neurovascular status is imperative. Evaluation of peripheral pulses is key, but normal pulses may not rule out vascular injury due to collateral flow about the knee. [16, 17] An Ankle-Brachial Index (ABI) should be obtained in all patients (Figure 9). An ABI is <0.9 has been shown to be 100% sensitive for vascular injury requiring operative repair. [3] Patients with an ABI >0.9 still require close monitoring and repeat exams.

Figure 9: Ankle brachial Index [18]

Some authors advocate for angiography in all knee dislocations while others advocate for angiography only in those with an abnormal ABI. [3, 17, 19] Given the time-sensitivity of a vascular injury threatening the limb, early consultation with vascular surgery in patients with concern for vascular injury is recommended.  Vessel imaging should never delay operative intervention if indicated. [3]

Options for vessel imaging include:

• CTA – quick and readily available in the ED with high sensitivity (95-100%) and specificity (99.7-100%) [10]

• Direct or selective angiography – considered standard of care but is invasive and introduces risks of vessel cannulation.

• Duplex ultrasonography – has good sensitivity (95-100%) and specificity (97-100%) but is operator dependent, may miss small intimal injuries, and availability may be limited. [10]

Disposition

Emergency surgery is indicated for:

• Open dislocation

• Irreducible dislocation

• Ischemic limb

• Vascular injury

• Compartment syndrome

All patients not taken to the operating room for emergent exploration should be admitted for at least 24 hours of neurovascular and compartment checks. [3,10] The knee should be immobilized as described above, with the leg made non-weight bearing. If evidence of common peroneal nerve injury, will need ankle-foot orthotics and physical therapy. Nearly all knee dislocations will require eventual reconstruction 2-3 weeks post-injury with nerve exploration and repair as indicated at that time. [19]

Summary and Key Points

• Knee dislocations are rare but significant injuries that require time-sensitive diagnosis and management.

• There is high morbidity, with up to 40% vascular and/or nerve injury, and up to 10% leading to amputation.

• Consider early consultation with orthopedic surgery and vascular surgery, as appropriate

• Early closed reduction in the Emergency Department is key, with appropriate post-reduction immobilization

• The neurovascular exam is critical, both pre- and post-reduction

• All patients should have an ABI check post-reduction, regardless of the presence of a pulse, with vessel imaging pursued in those with abnormal ABI

• All patients require admission for neurovascular and compartment checks

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Expert Commentary

Thank you, Dr. Rogers, for providing an excellent comprehensive review of knee dislocations. Over the course of my career in the last 20+ years, imaging workup for knee dislocations has evolved substantially.  It used to be dogma that all knee dislocations get traditional IR angiography.  This was based on reports of undiagnosed popliteal artery thrombosis, where patients presented with a clinically and radiographically reduced knee and a palpable dorsalis pedis pulse that progressed to ischemic compartment syndrome and amputation. This paradigm has shifted because:

• More recent studies indicate that the true incidence of popliteal artery injury is 7.5-14%. This is lower than initial older data suggested. [1, 2, 3]

• The vast majority of intimal tears do not progress

• CT angiography has emerged as a less invasive and highly sensitive option.

• Emerging data have shown that observation periods for serial pulse checks and ABIs are highly sensitive for detecting clinically significant vascular lesions.

Remember that the first priorities in knee dislocations are rapid diagnosis and reduction. Reduction can restore absent pulses.  Remember the algorithm provided by Dr. Rogers depends on what the vascular exam is AFTER reduction, not before.

Time sensitivity for those cases with vascular deficits cannot be emphasized enough. Delay dramatically affects outcome. Residual amputation rates post-surgery are 10%. [1] In cases of delay exceeding 8 hours, amputation rates have been reported to reach as high as 86%. [4] If required, on-table angiography in the operating theatre, rather than in radiology, has been reported to save 3 hours. [5, 6] So patients with ischemia/pulselessness after reduction need to be taken emergently to the OR, not to the CT suite.

Magnetic resonance (MR) angiography has been proposed as an alternative to define the vascular anatomy and diagnose asymptomatic vascular lesions, particularly as all these patients are likely to have MRI at some point to define the extent of ligamentous injury. In a small series of knee dislocations, findings were comparable to traditional angiography. Consider advocating for this when your consultant suggests CTA for patients with normal vascular exams and ABIs.

References:

1. Boisrenoult P, Lustig S, Bonneviale P, et al. Vascular lesions associated with bicruciate and knee dislocation ligamentous injury  Rev Chir Orthop Traumatol, 9 (2009), 621-626.

2. Harner CD, Waltrip RL, Bennett CH, et al. Surgical management of knee dislocations  J Bone Joint Surg Am, 86 (2004), 262-273.

3. Rios A, Villa A, Fahandezh H, et al. Results after treatment of traumatic knee dislocations: a report of 26 cases  J Trauma, 5 (2003), 489-494.

4. Green NE, Allen BL. Vascular injuries associated with dislocation of the knee  J Bone Joint Surg Am, 5 (1977), 236-239.

5. Lim LT, Michuda MS, Flanigan DP, Pankovich A.  Popliteal artery trauma 31 consecutive cases without amputation  Arch Surg, 11 (1980), 1307-1313.

6. Ottolenghi CE.  Vascular complications in injuries about the knee joint  Clin Orthop Relat Res (1982), 148-156.

Matthew R Levine, MD

Associate Professor of Emergency Medicine

Northwestern Memorial Hospital

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How To Cite This Post:

[Peer-Reviewed, Web Publication] Rogers, A. Randolph, A. (2021, Feb 22). Knee Dislocation. [NUEM Blog. Expert Commentary by Levine, M]. Retrieved from http://www.nuemblog.com/blog/knee-dislocation.

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References

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11. Lachman, et al. “Traumatic Knee Dislocations: Evaluation, Management, and Surgical Treatment.” Orthopedic Clinics of North America. October 2015. 46{(4):479-93

12. Murphy, Andrew. “Lateral Knee Dislocation”. Wikimedia Commons. 20 May 2017. https://commons.wikimedia.org/wiki/File:Lateral-knee-dislocation-1.jpg

13. Duprey K and Lin M. “Posterior Knee Dislocation”. Wikimedia Commons. 2 February 2010. https://commons.wikimedia.org/wiki/File:PosteriorKneeDIsclocation.jpg

14. Ellisbjohns “Segond Fracture”. Wikimedia Commons. 2 November 2009. https://commons.wikimedia.org/wiki/File:SegondFracture.JPG

15. Thrush, et al. “Fractures Associated with Knee Ligamentous Injury.” Complex Knee Ligament Injuries, pp149-159. January 2019.

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17. Barnes et al. “Does the pulse examination in patients with traumatic knee dislocation predict a surgical arterial injury? A meta-analysis.” Journal of Trauma; Injury, Infection, and Critical Care. December 2002. 53(6):1109-14.

18. Jmarchn. “Ankle-Brachial Index” Wikimedia Commons. 14 February 2014.https://commons.wikimedia.org/wiki/File:Pad_abi_ENG.svg

19. Fanelli, Gregory C. “”Knee Dislocation and Multiple Ligament Injuries of the Knee.” Sports Medicine and Arthroscopy Review. December 2018. Issue: Volume 26(4), p150-152.

20. Henretig, et al. “Textbook of Pediatric Emergency Procedures. Philadelphia, PA: Williams & Wilkins. 1997. P1098. https://aneskey.com/knee-dislocation-and-reduction/