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Published online before print August 18, 2005, 10.1148/radiol.2371041065
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(Radiology 2005;237:242-249.)
© RSNA, 2005

Musculoskeletal Imaging

Spring Ligament Complex: MR Imaging–Anatomic Correlation and Findings in Asymptomatic Subjects1

Bernard Mengiardi, MD, Marco Zanetti, MD, Philip B. Schöttle, MD, Patrick Vienne, MD, Beata Bode, MD, Juerg Hodler, MD, MBA and Christian W. A. Pfirrmann, MD

1 From the Departments of Radiology (B.M., M.Z., J.H., C.W.A.P.) and Orthopedic Surgery (P.B.S., P.V.), Orthopedic University Hospital Balgrist, Forchstrasse 340, CH-8008 Zurich, Switzerland; and Department of Pathology, Zurich University Hospital, Zurich, Switzerland (B.B.). Received June 16, 2004; revision requested August 25; revision received October 16; accepted November 15. Address correspondence to B.M. (e-mail: mengiardi{at}yahoo.de).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
PURPOSE: 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.

MATERIALS AND METHODS: 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.

RESULTS: 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.

CONCLUSION: 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.

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
The spring ligament complex includes the ligaments between the calcaneus and the navicular bones at the superomedial to inferoplantar aspect of the foot. The spring ligament complex—together with the posterior tibialis tendon (PTT), the plantar fascia, and the plantar ligaments—is an important stabilizer for the longitudinal arch of the foot (1,2). Lesions in these stabilizers result in flatfoot deformity. The acquired flatfoot deformity in adults is most often caused by PTT dysfunction (3–5). Isolated reconstruction of the PTT has been reported to yield a promising short-term outcome (4–7). However, long-term results have been disappointing, with a reported failure rate as high as 50% (8). With extended procedures involving reconstruction of associated lesions of the spring ligament complex (9–11), reconstruction of the medial collateral ligament, or lengthening of the lateral column of the foot by means of calcaneal osteotomy, more of the normal biomechanics of the hind foot are restored to result in more favorable clinical results (12).

Magnetic resonance (MR) imaging is the imaging modality of choice for evaluating the PTT in cases of acquired flatfoot deformity (13). In addition to evaluation of the PTT, attention should be directed toward the assessment of other stabilizers of the longitudinal arch, such as the spring ligament. Little is known about the MR imaging appearance of the spring ligament in asymptomatic subjects (14). There are conflicting reports regarding the detailed anatomy of the spring ligament in the literature (14–18). Most authors describe two major parts of the spring ligament complex: the superomedial calcaneonavicular ligament (CNL) and the inferoplantar longitudinal CNL (17). However, the medioplantar oblique CNL recently has been described as a distinct third ligament (18). Thus, the purposes of our study were to use MR imaging to assess the detailed MR imaging anatomy of the spring ligament complex in cadaveric feet and to prospectively evaluate the MR imaging depiction of the spring ligament complex in asymptomatic subjects.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Anatomic Specimen Study
Cadaveric feet were obtained and used according to institutional guidelines and with institutional approval from Zurich University Hospital and informed consent from the donor (prior to death) or the appropriate family member.

Five feet excised from five frozen nonembalmed human cadavers (four women [two left and two right feet], one man [right foot]; age range at death, 68–85 years; mean age, 76 years) were examined in our study. The cadaveric foot specimens were allowed to thaw for 24 hours at room temperature prior to MR imaging.

MR images were obtained with a 1.5-T system (Symphony; Siemens Medical Solutions, Erlangen, Germany) by using a standard extremity coil. All cadaveric feet were placed in a neutral position and immobilized. T1-weighted spin-echo MR images were obtained in the transverse (626/20 [repetition time msec/echo time msec]), coronal (470/20), and sagittal (626/20) planes. In each plane, MR imaging was performed by using a 3-mm section thickness, a 10-cm field of view, a matrix size of 256 x 512, and two acquisitions. The MR images were not analyzed before the feet were dissected.

After imaging, an orthopedic surgeon (P.B.S., with 6 years experience in orthopedic surgery) dissected the foot specimens to assess the detailed anatomy of the spring ligament complex. The relationships between the tibiospring ligament (a part of the superficial layer of the medial collateral ligament of the ankle) and both the PTT and the superomedial CNL were analyzed. Thereafter, the PTT was removed and the spring ligament complex was dissected from the medioplantar side. The courses and attachments of the individual parts of the spring ligament complex were analyzed, and the ability to differentiate the superomedial CNL, the medioplantar oblique CNL, and the inferoplantar longitudinal CNL was recorded.

The MR imaging and anatomic dissection findings were compared by consensus between a radiologist (B.M., with 2 years experience in musculoskeletal radiology) and the orthopedic surgeon (P.B.S.). In one specimen, in which the anatomy was highly visible both at dissection and on MR images, the PTT and the superomedial CNL were removed for histologic evaluation. Coronal histologic sections that corresponded to the coronal MR imaging plane were obtained. The histologic specimens were evaluated by a board-certified pathologist (B.B., with 6 years experience in musculoskeletal pathology). Criteria for the MR imaging analysis of the spring ligament complex in the asymptomatic subjects were defined on the basis of the MR imaging–anatomic comparisons.

Asymptomatic Volunteer Study
A total of 78 asymptomatic volunteers (41 women, 37 men; age range, 23–83 years; mean age, 48 years) were prospectively examined in the study. Seven women and seven men with ages corresponding to each decade between 20 and 70 years were included. The older-than-70-years group comprised six women and two men. Criteria for inclusion were (a) no prior foot surgery, (b) no foot pain, (c) never having seen a physician because of foot complaints, (d) no history of trauma to the ankle or foot in the past 2 years, and (e) no systemic inflammatory disease. This part of the study was approved by the institutional review board of Orthopedic University Hospital Balgrist, and informed consent was obtained from each volunteer.

MR imaging was performed with the Symphony 1.5-T system. The volunteer subjects were examined while in the supine position, with one ankle that was set in a neutral position placed in the extremity coil. The examination was performed according to our standard protocol for imaging ankles: Sagittal T1-weighted spin-echo MR images were obtained in the coronal (450/14, 4-mm section thickness, 16-cm field of view, matrix size of 256 x 512, two acquisitions), transverse oblique (45° between the coronal and transverse planes, 435/14, 4-mm section thickness, 15-cm field of view, matrix size of 256 x 512, two acquisitions), and sagittal (450/14, 3-mm section thickness, 22-cm field of view, matrix size of 256 x 512, one acquisition) planes. T2-weighted fast spin-echo MR images were obtained in the coronal (4000/91, 3-mm section thickness, 16-cm field of view, matrix size of 256 x 512, two acquisitions) and transverse (4000/86, 4-mm section thickness, 15-cm field of view, matrix size of 256 x 512, two acquisitions) planes. In addition, a fast spin-echo short-tau inversion-recovery sequence—short inversion time inversion recovery (4000/30/150 [repetition time msec/echo time msec/inversion time msec], 3-mm section thickness, 17-cm field of view, matrix size of 256 x 256, two acquisitions)—was performed in the sagittal plane. Imaging in the transverse oblique plane is part of the standard ankle imaging protocol that we use to perform a true cross-sectional evaluation of the ankle tendons.

MR Image Analysis
Qualitative evaluation.—MR images were analyzed by consensus between two experienced staff musculoskeletal radiologists with 12 (M.Z.) and 7 (C.W.A.P.) years of experience in musculoskeletal radiology. The following qualitative features of each of the three parts (ie, superomedial, medioplantar oblique, and inferoplantar longitudinal CNLs) of the spring ligament complex were evaluated (Table): (a) visibility, (b) best imaging plane (transverse, sagittal, coronal, or transverse oblique) for visibility (ie, the plane in which the anatomic course of the ligament was best depicted), (c) signal intensity on T1- and T2-weighted MR images (low [dark appearance of normal tendon], intermediate [high compared with the low signal intensity of normal tendon], or striated [alternating layers of fiber bundles with fat tissue and low or intermediate signal intensity]), and (d) ability to discriminate the superomedial CNL from the PTT (good [clearly distinguishable borders along the entire contact area], partially possible [distinguishable borders along only a portion of the contact area], or not possible).


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  		Qualitative and Quantitative Evaluations of the Spring Ligament Complex in Asymptomatic Subjects

 
Quantitative evaluation.—A fellowship-trained musculoskeletal radiologist (B.M.) who was not involved in the qualitative analysis performed quantitative measurements (obtained to the nearest 1/10 of a millimeter and then rounded to the nearest millimeter) on the MR images by using a picture archiving and communication system, or PACS, workstation (Image Devices, Idstein, Germany). The thickness of the superomedial CNL was measured on transverse oblique or coronal MR images, at the medial portion just inferior to the PTT. The thickness of the inferoplantar longitudinal CNL was measured on coronal MR images, and the thickness of the medioplantar oblique CNL was measured on transverse oblique MR images. In addition, the maximal mediolateral diameter of the distal PTT was measured at the region before the tendon inserted into the navicular bone.

Statistical Analyses
The measurements obtained in men and women were compared by using the two-tailed Mann-Whitney U test. To analyze associations between ligament thickness and the variables patient age, patient sex, and distal PTT diameter, we calculated Pearson correlation coefficients. P < .05 was considered to indicate statistical significance. For statistical analyses, SPSS for Windows, version 10.0.1, 1999 (SPSS, Chicago, Ill), was used.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Anatomic Specimen Study
The anatomic location of the spring ligament complex and the course of the three components of this complex are illustrated in Figure 1.



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  		Figure 1. Schematic drawing of medioplantar aspect of the hindfoot shows the three components of the spring ligament complex. iplCNL = inferoplantar longitudinal CNL, mCun = medial cuneiform, mpoCNL = medioplantar oblique CNL, nb = beak of navicular bone, nt = tuberosity of navicular bone, smCNL = superomedial CNL, sust = sustentaculum tali, tspL = tibiospring ligament.

 
Superomedial CNL.—In all anatomic specimens, the superomedial CNL originated from the medial aspect of the sustentaculum tali, bypassed the tuberosity of the navicular bone, and had a broad attachment at the superomedial aspect of the navicular bone close to the talonavicular joint (Figs 1, 2). In all five specimens, the inner portion of the superomedial CNL articulated directly with the talar head and had a very smooth surface, similar to an articular surface.



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  		Figure 2. Medioplantar view of spring ligament complex. Dissected cadaveric foot (left) and corresponding line drawing (right) show superomedial CNL (smCNL, solid arrows), medioplantar oblique CNL (mpoCNL, white arrowheads), and inferoplantar longitudinal CNL (iplCNL, black arrowheads). * = gliding floor of the PTT, which was removed. mCun = medial cuneiform, nb = beak of navicular bone, nt = tuberosity of navicular bone and insertion of medioplantar oblique CNL (open arrows), sust = sustentaculum tali.

 
In all specimens, loose connective tissue was found between the superomedial CNL and the PTT (Fig 3). This area served as a gliding layer between the PTT and the superomedial CNL. The thickness of this layer of connective tissue between the superomedial CNL and the PTT was variable (1–3 mm). In all specimens, this tissue was tightly connected to the superomedial CNL. Some connecting fibers between the dorsal and plantar portions of the PTT and the superomedial CNL were seen in four specimens (Fig 3).



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  		Figure 3a. Relationships between superomedial CNL and PTT in (a, b) a dissected cadaveric foot, on (c) a coronal T1-weighted MR image, and in (d) a corresponding histologic specimen of the dissected cadaveric foot. (a, b) Medial views of the dissected cadaveric foot. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (straight arrows) and courses superiorly, with a broad attachment at the superomedial aspect of the navicular bone. On top of the superomedial CNL lies a gliding layer (*) of the distal PTT. (b) When the PTT is pulled inferiorly, some connecting fibers between the dorsal and plantar portions (curved arrows) of the PTT and the superomedial CNL become visible. Note the broad attachment of the tibiospring ligament (part of the superficial layer of the medial collateral ligament of the ankle, white arrowheads) at the superomedial CNL. (c, d) On the coronal T1-weighted MR image (470/20) (c) and the corresponding histologic specimen (hematoxylin-eosin stain; original size, 1:1; no magnification) (d), the superomedial CNL (smCNL, arrowheads) toward the talus has a thin layer of dense collagen fibers with a few chondroid cells covered by flat synovial cells (curved arrows). The superomedial CNL is separated from the distal PTT by gliding zones that are lined by a single layer of synovial cells and contain some fibrocartilage (straight solid thick arrows) superficially. The corresponding surface of the PTT has similar histologic features, with a layer of fibrocartilage and flat synovial cells (open arrows). The PTT is attached to the superomedial CNL by peritendinous connective tissue (straight solid thin arrows) in the dorsal and plantar regions. At the inferior border of the gliding zone, fat tissue (*) is visible.

 


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  		Figure 3b. Relationships between superomedial CNL and PTT in (a, b) a dissected cadaveric foot, on (c) a coronal T1-weighted MR image, and in (d) a corresponding histologic specimen of the dissected cadaveric foot. (a, b) Medial views of the dissected cadaveric foot. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (straight arrows) and courses superiorly, with a broad attachment at the superomedial aspect of the navicular bone. On top of the superomedial CNL lies a gliding layer (*) of the distal PTT. (b) When the PTT is pulled inferiorly, some connecting fibers between the dorsal and plantar portions (curved arrows) of the PTT and the superomedial CNL become visible. Note the broad attachment of the tibiospring ligament (part of the superficial layer of the medial collateral ligament of the ankle, white arrowheads) at the superomedial CNL. (c, d) On the coronal T1-weighted MR image (470/20) (c) and the corresponding histologic specimen (hematoxylin-eosin stain; original size, 1:1; no magnification) (d), the superomedial CNL (smCNL, arrowheads) toward the talus has a thin layer of dense collagen fibers with a few chondroid cells covered by flat synovial cells (curved arrows). The superomedial CNL is separated from the distal PTT by gliding zones that are lined by a single layer of synovial cells and contain some fibrocartilage (straight solid thick arrows) superficially. The corresponding surface of the PTT has similar histologic features, with a layer of fibrocartilage and flat synovial cells (open arrows). The PTT is attached to the superomedial CNL by peritendinous connective tissue (straight solid thin arrows) in the dorsal and plantar regions. At the inferior border of the gliding zone, fat tissue (*) is visible.

 


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  		Figure 3c. Relationships between superomedial CNL and PTT in (a, b) a dissected cadaveric foot, on (c) a coronal T1-weighted MR image, and in (d) a corresponding histologic specimen of the dissected cadaveric foot. (a, b) Medial views of the dissected cadaveric foot. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (straight arrows) and courses superiorly, with a broad attachment at the superomedial aspect of the navicular bone. On top of the superomedial CNL lies a gliding layer (*) of the distal PTT. (b) When the PTT is pulled inferiorly, some connecting fibers between the dorsal and plantar portions (curved arrows) of the PTT and the superomedial CNL become visible. Note the broad attachment of the tibiospring ligament (part of the superficial layer of the medial collateral ligament of the ankle, white arrowheads) at the superomedial CNL. (c, d) On the coronal T1-weighted MR image (470/20) (c) and the corresponding histologic specimen (hematoxylin-eosin stain; original size, 1:1; no magnification) (d), the superomedial CNL (smCNL, arrowheads) toward the talus has a thin layer of dense collagen fibers with a few chondroid cells covered by flat synovial cells (curved arrows). The superomedial CNL is separated from the distal PTT by gliding zones that are lined by a single layer of synovial cells and contain some fibrocartilage (straight solid thick arrows) superficially. The corresponding surface of the PTT has similar histologic features, with a layer of fibrocartilage and flat synovial cells (open arrows). The PTT is attached to the superomedial CNL by peritendinous connective tissue (straight solid thin arrows) in the dorsal and plantar regions. At the inferior border of the gliding zone, fat tissue (*) is visible.

 


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  		Figure 3d. Relationships between superomedial CNL and PTT in (a, b) a dissected cadaveric foot, on (c) a coronal T1-weighted MR image, and in (d) a corresponding histologic specimen of the dissected cadaveric foot. (a, b) Medial views of the dissected cadaveric foot. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (straight arrows) and courses superiorly, with a broad attachment at the superomedial aspect of the navicular bone. On top of the superomedial CNL lies a gliding layer (*) of the distal PTT. (b) When the PTT is pulled inferiorly, some connecting fibers between the dorsal and plantar portions (curved arrows) of the PTT and the superomedial CNL become visible. Note the broad attachment of the tibiospring ligament (part of the superficial layer of the medial collateral ligament of the ankle, white arrowheads) at the superomedial CNL. (c, d) On the coronal T1-weighted MR image (470/20) (c) and the corresponding histologic specimen (hematoxylin-eosin stain; original size, 1:1; no magnification) (d), the superomedial CNL (smCNL, arrowheads) toward the talus has a thin layer of dense collagen fibers with a few chondroid cells covered by flat synovial cells (curved arrows). The superomedial CNL is separated from the distal PTT by gliding zones that are lined by a single layer of synovial cells and contain some fibrocartilage (straight solid thick arrows) superficially. The corresponding surface of the PTT has similar histologic features, with a layer of fibrocartilage and flat synovial cells (open arrows). The PTT is attached to the superomedial CNL by peritendinous connective tissue (straight solid thin arrows) in the dorsal and plantar regions. At the inferior border of the gliding zone, fat tissue (*) is visible.

 
The tibiospring ligament was visible in all specimens. It always had a broad attachment at the superomedial CNL (Fig 3). The tibiospring ligament is part of the superficial layer of the medial collateral ligament of the ankle.

In all specimens, the medial portion of the superomedial CNL was highly visible on the coronal MR images. From the sustentaculum tali, this ligament tapered along its course around the talar head while turning superiorly. Close to the attachment at the superior border of the navicular bone, the ligament was thin and difficult to depict.

A histologic specimen that comprised the PTT and the superomedial CNL and that corresponded to the coronal MR imaging plane was obtained from one cadaveric foot (Fig 3). The superomedial CNL was composed of parallel collagen bundles. The deep portion of this ligament, which articulated with the talar head, consisted of a fibrocartilage layer covered with a single layer of synovial cells. The superomedial CNL was separated from the distal PTT by a gliding zone that was lined with a single layer of synovial cells and contained some fibrocartilage superficially. The corresponding surface of the PTT had similar histologic features, including a layer of fibrocartilage and flat synovial cells. The PTT was attached to the superomedial CNL by peritendinous connective tissue in the dorsal and plantar regions.

Medioplantar oblique CNL.—The anatomic location and the course of the medioplantar oblique CNL are illustrated in Figure 2. In all specimens, the medioplantar oblique CNL originated at a region just anterior to the middle articular facet of the calcaneus in a small fossa at the anterior aspect of the calcaneus called the coronoid fossa (16). The medioplantar oblique CNL always had a medial oblique course and always was attached at the medioplantar portion of the navicular bone, just below the tuberosity of this bone (Fig 3). In all specimens, this ligament was consistently seen at dissection. However, the medioplantar oblique CNL could be clearly distinguished from the adjacent fibers of the superomedial CNL in only three cadavers. In all specimens, the medioplantar oblique CNL could be identified as a distinct ligament at MR imaging owing to its course, insertion sites, and typical laminated appearance.

Inferoplantar longitudinal CNL.—The anatomic location and the course of the inferoplantar longitudinal CNL are illustrated in Figures 2 and 4. The short thick inferoplantar longitudinal CNL was well defined in all specimens. It was easy to dissect and was consistently well distinguished from the medioplantar oblique CNL. In all specimens, this ligament originated from the coronoid fossa of the calcaneus anterior to the medioplantar oblique CNL, from which it was separated by a fat plane (Fig 2). The course of the inferoplantar longitudinal CNL was slightly oblique to the long axis of the foot. In all specimens, the distal attachment of this ligament was located at the inferior beak of the navicular bone (Fig 4). The inferoplantar longitudinal CNL in all specimens could be easily seen at MR imaging and was best seen on the sagittal and coronal images.



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  		Figure 4a. Gross-specimen and MR imaging anatomy of inferoplantar longitudinal CNL. (a) Dissected cadaveric foot (left) and corresponding line drawing (right). (b, c) Sagittal (626/20) (b) and coronal (470/20) (c) T1-weighted spin-echo MR images of the same cadaveric foot. The short inferoplantar CNL (iplCNL in a, black arrowheads) originates in the coronoid fossa (cf in a, solid arrows). This ligament runs longitudinally and attaches distally at the beak of the navicular bone (white arrowheads). The small coronoid fossa lies between the anterior (white open arrows) and the middle (black open arrows) articular facets of the calcaneus. In a, sust = sustentaculum tali.

 


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  		Figure 4b. Gross-specimen and MR imaging anatomy of inferoplantar longitudinal CNL. (a) Dissected cadaveric foot (left) and corresponding line drawing (right). (b, c) Sagittal (626/20) (b) and coronal (470/20) (c) T1-weighted spin-echo MR images of the same cadaveric foot. The short inferoplantar CNL (iplCNL in a, black arrowheads) originates in the coronoid fossa (cf in a, solid arrows). This ligament runs longitudinally and attaches distally at the beak of the navicular bone (white arrowheads). The small coronoid fossa lies between the anterior (white open arrows) and the middle (black open arrows) articular facets of the calcaneus. In a, sust = sustentaculum tali.

 


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  		Figure 4c. Gross-specimen and MR imaging anatomy of inferoplantar longitudinal CNL. (a) Dissected cadaveric foot (left) and corresponding line drawing (right). (b, c) Sagittal (626/20) (b) and coronal (470/20) (c) T1-weighted spin-echo MR images of the same cadaveric foot. The short inferoplantar CNL (iplCNL in a, black arrowheads) originates in the coronoid fossa (cf in a, solid arrows). This ligament runs longitudinally and attaches distally at the beak of the navicular bone (white arrowheads). The small coronoid fossa lies between the anterior (white open arrows) and the middle (black open arrows) articular facets of the calcaneus. In a, sust = sustentaculum tali.

 
Volunteer Study
Results of the volunteer portion of the study are summarized in the Table.

Qualitative evaluation.—The superomedial CNL was visible in all asymptomatic subjects and was best seen on transverse oblique (in 60% of the subjects) or coronal (in 40% of the subjects) MR images (Fig 5). The signal intensity of this ligament was usually intermediate on T1-weighted images (in 99% of the subjects) and low on T2-weighted images (in 96% of the subjects). Discrimination of the superomedial CNL from the PTT was very difficult: The discrimination was graded as good in only one subject and as partially possible in 10 (13%) subjects. In 86% of the subjects, the discrimination between these structures was not possible.



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  		Figure 5a. (a) Coronal T1-weighted spin-echo (450/14), (b) coronal T2-weighted fast spin-echo (4000/91), and (c) transverse oblique T1-weighted (435/14) MR images of superomedial CNL in 59-year-old asymptomatic man. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (arrows in c) and courses superomedially. Laterally, the ligament articulates with the talar head (white arrows in a and b). In a and c, the ligament has intermediate signal intensity, whereas in b, it has low signal intensity. Medially, the superomedial CNL is difficult to discriminate from the PTT (white arrowheads); there is an area of intermediate signal intensity (long arrow in a) between these two structures on T1-weighted images. In this region, the gliding floor of the PTT, as well as a fibrocartilaginous portion of the PTT, can be found. The tibiospring ligament (short black arrows in a and b) is highly visible and has a broad attachment at the superomedial CNL.

 


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  		Figure 5b. (a) Coronal T1-weighted spin-echo (450/14), (b) coronal T2-weighted fast spin-echo (4000/91), and (c) transverse oblique T1-weighted (435/14) MR images of superomedial CNL in 59-year-old asymptomatic man. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (arrows in c) and courses superomedially. Laterally, the ligament articulates with the talar head (white arrows in a and b). In a and c, the ligament has intermediate signal intensity, whereas in b, it has low signal intensity. Medially, the superomedial CNL is difficult to discriminate from the PTT (white arrowheads); there is an area of intermediate signal intensity (long arrow in a) between these two structures on T1-weighted images. In this region, the gliding floor of the PTT, as well as a fibrocartilaginous portion of the PTT, can be found. The tibiospring ligament (short black arrows in a and b) is highly visible and has a broad attachment at the superomedial CNL.

 


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  		Figure 5c. (a) Coronal T1-weighted spin-echo (450/14), (b) coronal T2-weighted fast spin-echo (4000/91), and (c) transverse oblique T1-weighted (435/14) MR images of superomedial CNL in 59-year-old asymptomatic man. The superomedial CNL (black arrowheads) originates from the sustentaculum tali (arrows in c) and courses superomedially. Laterally, the ligament articulates with the talar head (white arrows in a and b). In a and c, the ligament has intermediate signal intensity, whereas in b, it has low signal intensity. Medially, the superomedial CNL is difficult to discriminate from the PTT (white arrowheads); there is an area of intermediate signal intensity (long arrow in a) between these two structures on T1-weighted images. In this region, the gliding floor of the PTT, as well as a fibrocartilaginous portion of the PTT, can be found. The tibiospring ligament (short black arrows in a and b) is highly visible and has a broad attachment at the superomedial CNL.

 
The medioplantar oblique CNL was visible in 77% of the subjects, was best seen (in 95% of the subjects) in the transverse oblique plane, and had mainly a characteristic striated appearance (in 82% of the subjects), with alternating layers of fiber bundles and fat, on both T1- and T2-weighted MR images (Fig 6).



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  		Figure 6. Transverse oblique T1-weighted spin-echo MR image (435/14) of medioplantar oblique CNL in 31-year-old asymptomatic man. The medioplantar oblique CNL (black arrowheads) originates anteriorly to the middle articular facet of the calcaneus (calc) in a small fossa called the coronoid fossa (arrows). The ligament has a medial oblique course and attaches to the medioplantar portion of the navicular bone (nav), just below the tuberosity of the navicular bone (white arrowheads). It has a typical laminated appearance. ta = talar head.

 
The inferoplantar longitudinal CNL was visible in 91% of the asymptomatic subjects. It was best seen (in 69% of the subjects) on the coronal MR images and had mainly intermediate signal intensity (in 93% of the subjects) on T1-weighted images and variable signal intensity on T2-weighted images (Fig 7).



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  		Figure 7a. (a) Coronal T1-weighted spin-echo (450/14), (b) coronal T2-weighted fast spin-echo (4000/91), and (c) sagittal T1-weighted (450/14) MR images of inferoplantar longitudinal CNL in 61-year-old asymptomatic woman. The inferoplantar longitudinal CNL (black arrowheads) originates from the coronoid fossa anterior to the medioplantar oblique CNL. It courses longitudinally and attaches at the inferior beak of the navicular bone (white arrowhead in c). In a and b, the inferoplantar longitudinal CNL has intermediate signal intensity.

 


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  		Figure 7b. (a) Coronal T1-weighted spin-echo (450/14), (b) coronal T2-weighted fast spin-echo (4000/91), and (c) sagittal T1-weighted (450/14) MR images of inferoplantar longitudinal CNL in 61-year-old asymptomatic woman. The inferoplantar longitudinal CNL (black arrowheads) originates from the coronoid fossa anterior to the medioplantar oblique CNL. It courses longitudinally and attaches at the inferior beak of the navicular bone (white arrowhead in c). In a and b, the inferoplantar longitudinal CNL has intermediate signal intensity.

 


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  		Figure 7c. (a) Coronal T1-weighted spin-echo (450/14), (b) coronal T2-weighted fast spin-echo (4000/91), and (c) sagittal T1-weighted (450/14) MR images of inferoplantar longitudinal CNL in 61-year-old asymptomatic woman. The inferoplantar longitudinal CNL (black arrowheads) originates from the coronoid fossa anterior to the medioplantar oblique CNL. It courses longitudinally and attaches at the inferior beak of the navicular bone (white arrowhead in c). In a and b, the inferoplantar longitudinal CNL has intermediate signal intensity.

 
Quantitative evaluation.—The inferoplantar longitudinal CNL was the thickest ligament (mean thickness, 4.0 mm; range, 2–6 mm). The superomedial CNL was slightly thinner (mean thickness, 3.2 mm; range, 2–5 mm), with a diameter of 4 mm or less in 73 (94%) of the 78 subjects. The medioplantar oblique CNL was the thinnest portion of the spring ligament complex (mean thickness, 2.8 mm; range, 1–5 mm).

The thickness of none of the three ligaments was significantly correlated with subject age (for superomedial CNL, r = –0.06; for medioplantar oblique CNL, r = –0.12; for inferoplantar longitudinal CNL, r = 0.02; P > .35). Women had significantly thinner superomedial (mean thickness, 3.3 vs 3.5 mm; P = .015) and inferoplantar longitudinal (mean thickness, 3.8 vs 4.2 mm; P = .02) CNLs compared with men. There was no significant correlation between distal PTT thickness (mean maximal mediolateral diameter, 5.2 mm; range, 3–8 mm) and superomedial CNL thickness (r = 0.1, P = .37).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
The term spring in spring ligament complex is a misnomer and is based on a report describing elastic fibers within the plantar CNL. The ligament was initially believed to act as a "spring" for the longitudinal arch of the foot (19). However, histologic and biomechanical analyses of the plantar CNL have revealed that this structure is purely collagenous and has no elastic properties (17,20). Nevertheless, the term spring is still used.

The spring ligament complex has two important functions. First, it supports the head of the talus, forming the medial and plantar parts of the articular cavity of the talar head. The articular cavity of the talar head is also called the acetabulum pedis (21). This complex cavity consists of the anterior and middle articular facets of the calcaneus, the proximal articular surface of the navicular bone, and the spring ligament complex. Second, the spring ligament—together with the PTT, the plantar fascia, and the plantar ligaments—is an important stabilizer of the longitudinal arch of the foot. Lesions in these structures can result in flatfoot deformity. In contrast to the plantar parts of the CNL, which are purely collagenous, the superomedial CNL also contains fibrocartilage and is the widest and strongest of the three ligaments (17).

In the orthopedic literature, lesions of the spring ligament complex are described as being most commonly located within the superomedial CNL, whereas tears of the inferoplantar longitudinal ligament are rare (22). Gazdag and Cracchiolo (9) reported that 18 of 22 patients with PTT tears also had injuries of the superomedial CNL. Repair of these associated lesions has been recommended (9–12).

The imaging literature on the spring ligament complex is sparse (14,15,23,24). Yao et al reported MR imaging findings in 13 cases of surgically proved spring ligament insufficiency (14). The exact anatomic location of the lesions was not described. In 7%–50% of the subjects in the control group (18 subjects) in that study, heterogeneity of the medial spring ligament was seen on long echo time MR images, and in 17%–33% of the subjects heterogeneity of the ligament was seen on short echo time MR images. These findings are in contrast to the findings of our investigation involving asymptomatic subjects: The superomedial CNL in the volunteers typically had low signal intensity on T2-weighted MR images (in 96% of the subjects) and intermediate signal intensity on T1-weighted MR images (in 99% of the subjects).

In an anatomic study performed by Taniguchi et al (18), the mean thickness of the superomedial CNL medially was 2.5 mm (range, 1.4–4.6 mm), whereas Yao et al (14) measured a mean thickness of 4.7 mm at this location on MR images. In their study, interobserver agreement regarding MR imaging findings—particularly those in the medial portion of the spring ligament—was moderate (14). These findings reflect the difficulty in differentiating the PTT, the gliding layer, and the superomedial CNL on MR images. We encountered such difficulty in our study: In 86% of the volunteers, no clear discrimination of these structures was possible. Our measurement of the superomedial CNL was performed closer to the origin at the sustentaculum and revealed a mean thickness of 3.2 mm, which better correlates with the values calculated in the anatomic study of Taniguchi et al (18).

In an MR imaging investigation of PTT injuries and associated lesions, Balen and Helms (23) considered the superomedial CNL to be abnormal in cases in which it was more than 5 mm thick and had heterogeneous signal intensity characteristics. On the basis of our data, a thickness threshold of 4 mm may be more appropriate: In 94% of the volunteers, the thickness of the superomedial CNL was less than or equal to 4 mm. In our study, the signal intensity of the superomedial CNL in the asymptomatic subjects was typically low on T2-weighted MR images and intermediate on T1-weighted MR images.

In contrast, the less frequently injured inferoplantar longitudinal CNL had mainly intermediate signal intensity on T1-weighted MR images (in 93% of the subjects) and variable signal intensity on T2-weighted MR images (low signal intensity in 52% of the subjects, intermediate signal intensity in 48% of the subjects). Thus, intermediate signal intensity on T2-weighted MR images is not a reliable finding for diagnosing lesions in this ligament. The thicknesses of the inferoplantar longitudinal CNLs in our study (mean thickness, 4 mm) were comparable to those in other investigations (18). Like Taniguchi et al (18), we also were able to consistently identify a third portion of the spring ligament complex—the medioplantar oblique CNL, which had a typical striated appearance on both T1- and T2-weighted MR images.

All three parts of the spring ligament complex were highly discernible at MR imaging in our study. The two most important imaging planes for visualizing the spring ligament complex were the coronal (for visualizing the superomedial and inferoplantar longitudinal CNLs) and the transverse oblique (for visualizing the superomedial and medioplantar oblique CNLs) planes. Yao et al evaluated the superomedial CNL on transverse MR images (14). In our experience, the anatomic course of the superomedial CNL is better depicted in the coronal or the transverse oblique plane. Schneck et al (25) suggested using the sagittal plane to evaluate the inferoplantar longitudinal CNL, which seems reasonable owing to the longitudinal course of this ligament. In 69% of our volunteer subjects, the coronal plane was considered to be the best plane for evaluating this ligament. The slight sagittal oblique orientation of the inferoplantar longitudinal CNL, which had a mean thickness of 4 mm in our study, frequently results in partial volume visualization on standard sagittal images. Therefore, other investigators have suggested a sagittal oblique plane for the evaluation of the inferoplantar longitudinal CNL (24). However, imaging in this plane is rarely a part of a standard imaging protocol.

The fact that the measurements were performed by only one person may have been a study limitation. However, owing to the good contrast with the surrounding fat tissue, measurements of the inferoplantar longitudinal and medioplantar oblique CNLs were easy to perform and the superomedial CNL was measured in a location inferior to the area in contact with the PTT.

In conclusion, MR imaging allowed us to distinguish three parts of the spring ligament complex in asymptomatic volunteers. The superomedial CNL and the inferoplantar longitudinal CNL were consistently visible portions of the spring ligament complex, whereas the medioplantar oblique CNL was thinner, was seen less consistently, and had mainly a characteristic striated appearance.


   FOOTNOTES
 

Abbreviations: CNL = calcaneonavicular ligament • PTT = posterior tibialis tendon

Authors stated no financial relationship to disclose.

Author contributions: Guarantor of integrity of entire study, B.M.; study concepts, B.M., C.W.A.P., M.Z., J.H.; study design, B.M., C.W.A.P.; literature research, B.M., M.Z.; experimental studies, B.M., P.B.S., P.V., B.B.; data acquisition, B.M., P.B.S., C.W.A.P., M.Z., P.V., B.B.; data analysis/interpretation, B.M., P.B.S., C.W.A.P., B.B.; statistical analysis, B.M., C.W.A.P.; manuscript preparation, B.M., C.W.A.P.; manuscript definition of intellectual content, B.M., C.W.A.P., J.H., M.Z.; manuscript editing, B.M.; manuscript revision/review, C.W.A.P., J.H., M.Z., P.B.S.; manuscript final version approval, B.M., J.H., C.W.A.P.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

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