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MRI of Knee Dislocation

Knee dislocation is a severe and relatively rare orthopedic injury that occurs when the bones comprising the knee joint become completely displaced from their normal alignment. This typically involves the femur (thigh bone) and tibia (shin bone) losing their connection, resulting in a complete disruption of the knee joint. Knee dislocations are often caused by high-impact trauma, such as car accidents, sports injuries, or falls from significant heights.

Causes

  • High-impact Trauma: Often caused by significant forces, such as in car accidents or contact sports.
  • Low-impact Injuries: Can occur in individuals with ligamentous laxity, where less force is required to dislocate the knee.
  • Twisting Movements: Sudden, awkward movements can lead to dislocation, especially in athletes.

Symptoms

  • Severe Pain: Usually immediate and intense.
  • Visible Deformity: The knee may look out of place or misshapen.
  • Swelling and Bruising: Develops rapidly after the injury.
  • Inability to Move the Knee: The knee may feel unstable or incapable of bearing weight.
  • Numbness or Weakness: In the lower leg or foot, if nerves are affected.

Treatment

  1. Immediate Medical Attention: Due to the severity of the injury and potential for blood vessel and nerve damage, immediate medical care is crucial.
  2. Reduction: The doctor may try to gently move the bones back into place.
  3. Immobilization: The knee is often immobilized with a brace or splint.
  4. Surgery: Often required, especially if there is damage to the ligaments, blood vessels, or nerves.

MRI Appearance of Knee Dislocation

  • T1-Weighted Images: This sequence provides excellent anatomical detail. In the case of knee dislocation, T1 can help identify any disruption in the continuity of ligaments or tendons. It also helps in assessing the condition of bones and any associated fractures.

  • T2-Weighted Images: T2 images are highly sensitive to fluid, making them useful in detecting edema or hemorrhage which is common in dislocation injuries. They can show high signal intensity areas around the knee, indicating inflammation or injury to soft tissues.

  • Proton Density (PD) Fat Saturation: This sequence is effective in visualizing both the bone and soft tissue anatomy. It helps in identifying subtle changes in the soft tissues, such as ligament tears, which are common in dislocations. The fat saturation technique increases the contrast between injured and normal tissues.

  • Short Tau Inversion Recovery (STIR): STIR is particularly sensitive to water, hence it’s excellent for detecting edema. In knee dislocations, STIR images can highlight areas of bone bruising and soft tissue swelling, which are not always apparent on other sequences.

T1 TSE sagittal image shows Knee Dislocation

MRI T1 sagittal image shows knee dislocation

STIR sagittal image shows Knee Dislocation

MRI PD fat saturated sagittal image shows knee dislocation

PD fat saturated coronal shows Knee Dislocation

MRI PD fat saturated coronal shows knee dislocation

PD fat saturated axial image shows Knee Dislocation

MRI PD fat saturated axial image shows knee dislocation

References

  • Walker, R. E. A., McDougall, D., Patel, S., Grant, J. A., Longino, P. D., & Mohtadi, N. G. (2013). Radiologic Review of Knee Dislocation: From Diagnosis to Repair. American Journal of Roentgenology, 201(3). https://doi.org/10.2214/AJR.12.10221
  • Mohan, K., Ellanti, P., Lincoln, M., & McCarthy, T. (2018). Magnetic Resonance Imaging Features of Traumatic Patellofemoral Dislocation. Cureus, 10(12), e3730. doi: 10.7759/cureus.3730. PMID: 30800540. PMCID: PMC6384034.
  • Henrichs, A. (2004). A Review of Knee Dislocations. Journal of Athletic Training, 39(4), 365–369. PMCID: PMC535529. PMID: 16410830.
  • Howells, N. R., Brunton, L. R., Robinson, J., Porteus, A. J., Eldridge, J. D., & Murray, J. R. (2011). Acute knee dislocation: An evidence-based approach to the management of the multiligament injured knee. Injury, 42(11), 1198-1204.