Length Changes of the Lateral Knee: Fibular Collateral Ligament, Anterolateral Ligament, and Iliotibial Band Fibers

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.

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.

Descriptive laboratory study.

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.

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).

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.

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.