Posterolateral Instability Key Structures LCL popliteus tendon the
Posterolateral Instability
Key Structures • LCL, popliteus tendon, the arcuate ligament and the popliteofibular ligament • Dynamic structures adding to posterolateral stability: ITB, lateral gastroc and biceps femoris
Injuries to posterolateral corner • less common then those of the medial capsule, but can produce significant functional limitations and dysfunction • The posterolateral corner resists varus and rotational forces to the knee • Diagnosis is difficult unless one has a high degree of suspicion for posterolateral corner injuries. • Several recent articles have implied that a large proportion of ACL reconstruction failures may be the result of unrecognized and untreated posterolateral instability • Isolated posterolateral corner instability is uncommon, and is most likely associated with ACL or PCL injuries.
Cause • Macrotrauma: hyperextension with varus force, severe ER of tibia with knee slightly flexed, blow to medial side of knee • Repeated microtrauma: varus thrust seen during stance phase of gait, exacerbated with genu recurvatum and lateral capsular laxity.
Subjective • Pain or diffuse tenderness in the posterolateral knee. • May complain of instability when going up and down stairs, with cutting or pivoting
External rotation-Recurvatum Test • Patient supine with both legs extended. Lift the leg. A positive test displays increased recurvatum, varus and ER compared to the other knee. The tibial tuberosity will migrate laterally. Be careful, as there is a high rate of false positives. It is rarely positive with isolated PCL injuries.
Dial Test • Patient prone. Bend both knees to 30 degrees. Externally rotate the feet. Repeat at 90 degrees. A positive test is indicated by a difference> 15 degrees. If the test is positive at 30 degrees but not at 90 degrees, this indicates that the PCL is still intact. If it is positive at both 30 and 90 degrees, it indicates that both the PCL and posterolateral corner are involved.
Posterolateral drawer test • Patient supine. Flex the knee to 80 degrees, with 15 degrees of external rotation of the tibia. Direct your force in posterolateral direction on the tibia. A positive test is indicated by excessive posterior displacement of the lateral tibia plateau on the femur, without medial plateau movement. This test as limited sensitivity.
Surgical Repair • Variety of techniques, butpoor outcomes have been reported in 9%-37% in clinical series • Technique of choice: anatomic reconstruction of the posterolateral corner, simultaneously reconstructing the LCL, and popliteofibular ligament using the anterior tibialis- or split Achilles tendon graft
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