The Kaplan fibers are the distal deep capsular attachments of the iliotibial band to the distal lateral femur, distinct from the main IT band tibial insertion at Gerdy's tubercle. They consist of proximal and distal bundles running from the lateral distal femoral metaphysis to the posterior aspect of the IT band. The distal Kaplan fibers are key components of the anterolateral complex of the knee providing rotational stability.
Provide rotational stability to the lateral knee by connecting the femur to the IT band, creating a dynamic restraint to internal tibial rotation especially at low flexion angles.
The Kaplan fibers are the anatomical basis of the anterolateral ligament (ALL) concept and the anterolateral complex. Combined ACL and anterolateral structure injuries produce the pivot shift phenomenon (subluxation of the tibia internally), and isolated ACL reconstruction may leave residual rotational instability if the Kaplan fibers and lateral capsular structures are not addressed. Lateral extra-articular tenodesis (LET) and anterolateral ligament reconstruction target this region to augment ACL reconstruction in high-grade pivot shift injuries.
Disruption of the Kaplan fibers with ACL injury produces a high-grade pivot shift from combined anteroposterior and rotational instability; combined ACL reconstruction with lateral extra-articular tenodesis or anterolateral ligament reconstruction addresses the Kaplan fiber deficit to restore both anterior and rotational knee stability.
