AJSM - 2026-08-03 - Journal Article
Length Changes of the Lateral Knee: Fibular Collateral Ligament, Anterolateral Ligament, and Iliotibial Band Fibers.
Augustin EJ, Oppenheim ZR, Vega J, Gomez Verdejo F, Casanova FJ, Escribano G, Koluman AC, Bi AS, Chahla J, Yanke AB
Topics
Key Takeaway
FCL and ALL attachment distances decrease by 7.59 mm and 6.44 mm respectively from 0° to 90° flexion, while ITB Kaplan fiber distances demonstrate relative isometry with midflexion lengthening of 2–6 mm that returns to baseline at 90°.
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Summary
This cadaveric study quantified native length changes of the FCL, ALL, and ITB Kaplan fibers across 0°–90° of flexion using 3D digitizer coordinate mapping to inform graft fixation strategies. FCL and ALL attachment distances decreased progressively and significantly with flexion (−7.59 mm and −6.44 mm at 90°, both P≤.05), while distal and proximal Kaplan ITB fiber distances showed midflexion lengthening of 2–6 mm before returning to near-baseline at 90° (P=.853 and P=.506, respectively). These findings suggest FCL and ALL reconstruction should be fixed closer to extension to avoid overconstraint, while LET graft fixation angle is less critical given ITB relative isometry.
Key Limitation
Unloaded cadaveric testing without simulated muscle forces or weight-bearing conditions limits direct applicability to intraoperative tensioning decisions.
Original Abstract
BACKGROUND
The lateral knee is stabilized by the fibular collateral ligament (FCL), anterolateral ligament (ALL), and iliotibial band (ITB) fibers. Understanding their flexion-dependent behavior is critical for guiding graft fixation during reconstruction.
HYPOTHESIS/PURPOSE
The hypothesis was that the FCL and ALL would shorten with flexion, while ITB fibers would show more minor, transient changes. The purpose was to characterize native length changes of these structures in cadaveric knees.
STUDY DESIGN
Descriptive laboratory study.
METHODS
Ten fresh-frozen knees were dissected with preservation of lateral soft tissue attachments. Bony landmarks were marked for the attachment sites: FCL (n = 10), ALL (n = 7), and ITB (n = 10 distal Kaplan fibers, n = 9 proximal). A 3-dimensional digitizer recorded coordinates at 0°, 15°, 30°, 45°, 60°, and 90° of flexion. Attachment distances were calculated, and paired t tests or Wilcoxon tests (based on Shapiro-Wilk normality) compared 0° with each flexion angle.
RESULTS
Distances between the FCL and ALL attachment sites progressively decreased with flexion, with mean reductions of -7.59 and -6.44 mm, respectively, from 0° to 90° (both P ≤ .05). Distances from the Gerdy tubercle to the distal and proximal Kaplan attachments of the ITB increased significantly by 2 to 6 mm between 15° and 60° before returning toward baseline at 90°: distal Kaplan, -0.78 mm ( P = .853); proximal Kaplan, -3.99 mm ( P = .506).
CONCLUSION
FCL and ALL attachment distances decreased throughout flexion. In contrast, the distances from the Gerdy tubercle to the proximal and distal Kaplan attachments demonstrated midflexion lengthening with a return toward baseline at deeper flexion angles, reflecting relative isometry of these ITB segments. This study is the first to describe the simultaneous length change behavior of all 3 structures, providing integrated anatomic data that may inform graft tensioning and fixation strategies for ALL, FCL, and lateral extra-articular tenodesis reconstruction of the lateral knee.
CLINICAL RELEVANCE
The relative isometry observed in ITB attachment distances suggests that lateral extra-articular tenodesis graft fixation may be less sensitive to knee flexion angle. In contrast, the flexion-dependent decreases in FCL and ALL attachment distances suggest that fixation at knee flexion angles closer to extension may be favorable for avoiding overconstraint in reconstruction of these ligaments. These findings are anatomic and descriptive rather than prescriptive. Further loaded biomechanical studies are needed to determine optimal graft tensioning protocols.