Kaplan Fiber Injuries in The Anterior Cruciate Ligament-Injured Knee: Current Concepts

Kaplan fibers are the deep femoral attachments of the iliotibial band and are increasingly recognized as important secondary restraints to anterolateral rotatory instability in the anterior cruciate ligament-injured knee. However, their clinical significance, magnetic resonance imaging diagnosis, natural history after anterior cruciate ligament reconstruction, and indications for surgical treatment remain incompletely defined. This Current Concepts Review summarizes contemporary evidence on Kaplan fiber anatomy, biomechanics, imaging, healing potential, clinical outcomes, and surgical management. Current evidence suggests that Kaplan fibers contribute substantially to restraint of internal tibial rotation, particularly at higher flexion angles, but available biomechanical data are derived largely from cadaveric studies and show considerable inter-specimen variability. Magnetic resonance imaging studies report Kaplan fiber injury rates ranging from 18.6% to 43% in acute anterior cruciate ligament tears, although comparisons across studies are limited by heterogeneity in imaging protocols, diagnostic criteria, and poor inter-rater reliability in some grading systems. Recent clinical data suggest that many Kaplan fiber abnormalities resolve after anterior cruciate ligament reconstruction, and short-term comparative studies have not shown consistent differences in laxity, functional outcomes, or return to sport between knees with and without preoperative Kaplan fiber injury. At present, the literature does not support routine Kaplan fiber reconstruction on the basis of magnetic resonance imaging findings alone. Lateral augmentation procedures that incorporate Kaplan fiber anatomy may be considered in selected high-risk situations, including persistent high-grade pivot shift, revision anterior cruciate ligament reconstruction, and generalized ligamentous laxity, but direct evidence supporting isolated Kaplan fiber reconstruction remains limited. Current best practice is therefore a selective, individualized approach that integrates imaging findings, intraoperative assessment, and patient-specific risk factors. Future work should prioritize standardized magnetic resonance imaging criteria, prospective natural history studies, and comparative clinical trials evaluating Kaplan fiber-based augmentation against established lateral extra-articular procedures. LEVEL OF EVIDENCE: Level V (Expert Opinion - Narrative Review).