Posterolateral Corner (PLC) Reconstruction: Reverse Pivot Shift and Instability
In short
Missed posterolateral corner injuries cause 40% of all ACL and PCL graft failures; early anatomical reconstruction and rotational bracing restore multi-planar stability.
In this guide (4 sections)
The Anatomy of the Posterolateral Corner (The Dark Corner)
The Posterolateral Corner (PLC) is often referred to as the 'dark corner of the knee' due to its anatomical complexity and historically high rate of missed clinical diagnoses. The PLC consists of three primary stabilizing structures: the Fibular Collateral Ligament (FCL / LCL), the Popliteus Tendon, and the Popliteofibular Ligament (PFL).
Collectively, these structures resist primary varus opening, primary external tibial rotation, and secondary posterior tibial translation. When an undiagnosed PLC tear accompanies an ACL or PCL reconstruction, the unchecked rotational torque and varus thrust place immense stress on the central graft, causing premature graft rupture in up to 40% of cases.
Provocative Examination: Reverse Pivot Shift and Varus Stress
| Diagnostic Test | Maneuver Description | Positive Test Indication | Clinical Implication | |
|---|---|---|---|---|
| Reverse Pivot Shift (Jakob Test) | Knee flexed to 90°, valgus stress and external rotation applied while slowly extending knee | At 30° flexion, subluxated lateral tibial plateau suddenly reduces forward with a palpable clunk | Pathognomonic indicator of gross posterolateral rotatory instability (PLRI) | |
| Varus Stress Test at 30° Flexion | Knee flexed 30° over examination table edge; examiner applies direct varus stress | Excessive lateral joint line opening compared to sound side | Isolates tear of the Fibular Collateral Ligament (FCL) | |
| Varus Stress Test at 0° Extension | Knee held in full terminal extension; examiner applies direct varus stress | Gross lateral joint line opening in full extension | Confirms catastrophic combined tear of FCL and both cruciate ligaments | |
| External Rotation Recurvatum | Patient supine; examiner lifts both legs by the great toes off the plinth | Injured knee falls into excessive hyperextension, varus, and external tibial rotation | Indicates severe multi-ligamentous disruption |
Post-Surgical Rehabilitation Protocols for Anatomical PLC Reconstructions
- Strict Avoidance of External Tibial Rotation (Weeks 1 to 6): Lock hinged knee brace at 0 degrees for ambulation; prevent any passive or active external foot rotation which torques the popliteofibular graft.
- Early Passive Motion in Prone (Weeks 2 to 6): Perform gentle passive range of motion from 0 to 90 degrees with the tibia manually maintained in neutral or slight internal rotation to protect the lateral suture anchors.
- Elimination of Varus Hyperextension Thrust: Assess dynamic walking mechanics in the mirror; athletes with chronic PLC laxity develop a bone-jarring lateral thrust gait that must be retrained using gait cues and medial unloader braces.
Frequently Asked Questions
Why is a torn posterolateral corner called the 'dark corner' of the knee?
It earned that nickname because its multiple small ligaments are difficult to see on standard MRI scans and are frequently missed during routine emergency room exams, leading to chronic knee instability.
Can a missed PLC injury cause a new ACL graft to fail?
Yes. If the posterolateral corner is loose, your knee twists outward every time you step. This constant twisting force snaps new ACL or PCL grafts within months of surgery.
What is the Reverse Pivot Shift test?
The Reverse Pivot Shift test checks for rotational slipping. As your bent knee is slowly straightened by a physiotherapist, your displaced shin bone suddenly pops back into place with a noticeable clunk, confirming the corner ligaments are torn.
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