Working Diagnosis:
Based on the physical examination and findings on MRI of multiligament disruption, the patient seems to have sustained a knee dislocation with spontaneous reduction. There is not a clear mechanism of injury nor do we have a witnessed event to confirm the diagnosis.

Treatment:
Had we seen the patient in the acute phase, the treatment would have been:
1 Reduction of the dislocation as soon as possible.
2 Non weight bearing knee immobilization.
3 Screening for vascular injury.
4 Posterior lateral corner reconstruction followed by ACL and PCL repair 2 to 3 months later

Outcome:
Since the patient had a multi-ligament knee injury that necessitated surgical consultation, patient was referred to orthopedics for further care. The standard of care is open reconstruction of the posterolateral corner structures as they are extra capsular and arthroscopic reconstruction of the cruciate ligaments.

The return to activity will be determined by the orthopedic/rehab team caring for her.

Author's Comments:
Even when the patient was seen 9 days after sustaining the injury, without obvious evidence of vascular compromise, a knee arteriogram should have been done to rule out any intima lesion of the popliteal vessels.

Editor's Comments:
Thankfully knee dislocations are rare with an estimated incidence of less than 1 in 100,000 hospital admissions. They are, however, orthopedic emergencies with a risk of limb loss secondary to vascular injury. Many times the diagnosis is difficult because of spontaneous reduction occurring immediately following the injury. Evidence of multi-ligament damage in the knee should raise the index of suspicion for a dislocation. If there is an obvious knee deformity seen, the dislocation is classified by the position of the proximal tibia compared to the distal femur. For example, if the proximal tibia is translated (dislocated) anterior to the distal femur, it is an anterior dislocation.

Vascular injuries following knee dislocation are not rare, and based on literature can occur in 16-64% of cases with most studies showing around 32%. These injuries range from frank transection to intimal damage with delayed thrombosis. In some institutions angiography is performed on all suspected knee dislocations. However, recent studies have shown that serial evaluation of the distal pulse may be sufficient. Other studies have shown that duplex ultrasonography is an effective imaging study which exposes the patients to less radiation, and has a 98% accuracy rating in one study. In any regard, it is crucial to carefully monitor the vascular status, as the popliteal artery is a terminal artery of the leg with small collateral vessels. Any suspected disruption should prompt an emergent vascular surgery consult.

Nerve damage is also not uncommon in knee dislocations with an incidence reported in literature from 20-30%. As in the case presented, the most common nerve affected is the common peroneal nerve. It is more commonly affected when the posterior-lateral corner and LCL are involved in the injury. Most injuries involve a stretch neurapraxia as opposed to a laceration or complete transection. Nerve recovery is unpredictable. Electromyography (EMG) and nerve conduction studies (NCS) are helpful in the evaluation of nerve injury; however, findings may not be present for several weeks following the injury. Management is based on the type of injury and ranges from observation to microsurgical repair.

This case shows the importance of having a high index of suspicion for a knee dislocation in the presence of multi-ligament disruption (3 or more ligaments). It also demonstrates one of the potentially serious complications of nerve injury related to the dislocation. While these cases may present to the physician several days following the injury, it is important to treat them as the orthopedic emergencies they are in an effort to prevent limb loss or other permanent damage.

References:
1 Cho, Dosang, et al. "Peroneal nerve injury associated with sports-related knee injury."Neurosurgical Focus"�31.5 (2011): 11.

2 Howells, Nick R., et al. "Acute knee dislocation: An evidence based approach to the management of the multiligament injured knee."Injury"�42.11 (2011): 1198-1204.

3 Boss, Stuart E., et al. "Critical orthopedic skills and procedures."Emergency medicine clinics of North America"�31.1 (2013): 261-290.

4 Sekiya, Jon K., et al. "A clinically relevant assessment of posterior cruciate ligament and posterolateral corner injuriesEvaluation of isolated and combined deficiency."The Journal of Bone & Joint Surgery"�90.8 (2008): 1621-1627.

5 Frassica, FRANK J., et al. "Dislocation of the knee."Clinical orthopaedics and related research"�263 (1991): 200.

6 Fanelli, Gregory C., et al. "Management of complex knee ligament injuries."The Journal of Bone & Joint Surgery"�92.12 (2010): 2235-2246.

7 Fanelli, Gregory C., and Daniel D. Feldmann. "Management of combined anteriorcruciate ligament/posterior cruciate ligament/posterolateral complex injuries of the knee."Operative Techniques in Sports Medicine"�7.3 (1999): 143-149.

Fanelli, Gregory C., Justin D. Harris, Daniel J. Tomaszewski, John T. Riehl, Craig J. Edson, and Kristin N. Reinheimer. "Multiple Ligament Knee Injuries." Delee & Drez's Orthopaedic Sports Medicine: Principles and Practice. By Jesse DeLee, David Drez, and Mark D. Miller. 3rd ed. Philadelphia: Saunders/Elsevier, 2010. 1747-766. Print.

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