Spring ligament complex: MR imaging-anatomic correlation and findings in asymptomatic subjects

To use magnetic resonance (MR) imaging to assess the anatomy of the spring ligament complex (SLC) in cadaveric feet and to prospectively evaluate the MR imaging depiction of this complex in asymptomatic subjects.

Cadaveric feet were obtained and used according to institutional guidelines and with institutional approval and consent from the donors (before death) or the appropriate family members. Healthy volunteers were examined, with institutional review board approval and informed consent from each volunteer. MR imaging findings of the SLC in five cadaveric feet were analyzed and correlated with the findings in dissected foot specimens. Then, the MR imaging findings in the feet of 78 asymptomatic subjects were analyzed. For all three parts of the SLC, visibility, optimal imaging plane, and signal intensity characteristics were analyzed. The thicknesses of all SLC parts were measured. The measurements obtained in men and women were compared by using the Mann-Whitney U test, and Pearson correlation coefficients for associations between ligament thickness and subject age and sex were calculated.

In the cadaveric feet, MR imaging enabled differentiation of all three parts of the SLC. The superomedial calcaneonavicular ligament (CNL) was visible in all; the medioplantar oblique CNL, in 60; and the inferoplantar longitudinal CNL, in 71 volunteers. The superomedial CNL had a mean thickness of 3.2 mm, was best seen on transverse oblique or coronal MR images, and had mainly intermediate signal intensity on T1-weighted images and low signal intensity on T2-weighted images. The medioplantar oblique CNL had a mean thickness of 2.8 mm, was best seen on transverse oblique MR images, and had mainly a typical striated appearance on T1- and T2-weighted images. The inferoplantar longitudinal CNL was the thickest (mean thickness, 4.0 mm), was best seen on coronal MR images, and had mainly intermediate signal intensity on T1-weighted images and variable signal intensity on T2-weighted images. Women had significantly thinner superomedial (mean thickness, 3.3 vs 3.5 mm; P = .015, Mann-Whitney U test) and inferoplantar longitudinal (mean thickness, 3.8 vs 4.2 mm; P = .02) CNLs than men. There was no significant correlation between ligament thickness and subject age.

The superomedial and inferoplantar longitudinal CNLs are consistently visible portions of the SLC. The medioplantar oblique ligament is thinner, is seen less consistently, and has mainly a characteristic striated MR imaging appearance.