CASE 115

By: Dr. Nizar Al-Nakshabandi MD, FRCPC

HISTORY: 16-year-old involved in motor vehicle accident in which his knees hit the dashboard.

What are your findings?

What is the diagnosis?

What are the causes?

FINDINGS:

The AP radiograph of the right knee [A] demonstrates an abnormal alignment of the tibia and femur with the tibia laterally mal-aligned in relation to the femur. There is evidence of intramedullary rod and screws in the distal femur. Previous screw tracts in the tibia are also seen.

Lateral view of the right knee joint [B] demonstrates a posteriorly subluxed tibia in relation to the femur.

Sagittal T1 weighted image of the right knee demonstrate bicruciate ligamentous tear [ACL, and PCL].

DIAGNOSIS:

Posterior knee dislocation with evidence of bicruciate ligamentous tear and possible lateral ligament tears as well.

PEARLS AND DISCUSSION:

Posterior knee dislocation accounts for approximately 33% of knee dislocations. They are always associated with ligamentous injuries. The common pattern is bicruciate [anterior and posterior cruciate] ligaments. Medial collateral and lateral collateral ligamentous tear can occur.

Mechanism of injury is hyper extension which occurs in motor vehicle collisions but can also occur in sport injury traumas.

The most severe complication is compression on the popliteal artery which occurs in 30% of the cases. Therefore, it is crucial to ask for a Doppler in an exam setting to show the examiner that this is the #1 feared complication which may lead to loss of a limb.

Nerve damage to the peroneal nerve leads to a drop foot in 30% of cases.

These cases are treated by immediate closed reduction after full evaluation of associated injuries. Ligamentous injuries assessment is carried out several weeks later.

FURTHER READING:

1.      Henrichs A. A review of knee dislocations. J Athl Train. 2006;39 (4): 365-9.

2.      Robertson A, Nutton RW, Keating JF. Dislocation of the knee. J Bone Joint Surg Br. 2006;88 (6): 706-11

3.      Walker RE, McDougall D, Patel S et-al. Radiologic review of knee dislocation: from diagnosis to repair. AJR Am J Roentgenol. 2013;201 (3): 483-95.