eMedicine Specialties > Radiology > Pediatrics

Clubfoot: Imaging

Author: Ellen M Chung, MD, Chief, Pediatric Radiology Section, Department of Radiologic Pathology, Armed Forces Institute of Pathology
Coauthor(s): Veronica Rooks, MD, Military Chief of Pediatric Radiology, Pediatric Radiologist, Tripler Army Medical Center; Assistant Professor of Radiology and Radiological Sciences, Uniformed Services University of the Health Sciences
Contributor Information and Disclosures

Updated: Mar 11, 2008

Radiography

Findings

The 3 main components of the deformity are evident on radiographs and can be reproducibly quantified.

Hindfoot equinus is plantar flexion of the anterior calcaneus (similar to a horse's hoof) such that the angle between the long axis of the tibia and the long axis of the calcaneus (tibiocalcaneal angle) is greater than 90° (see Image 1 ).

In hindfoot varus, the talus is assumed to be fixed relative to the tibia. The calcaneus is considered to rotate around the talus into a varus (toward midline) position. On the lateral view, the angle between the long axis of the talus and the long axis of the calcaneus (talocalcaneal angle) is less than 25°, and the 2 bones are more nearly parallel than in the normal condition (see Images 2-3). On the DP view, the talocalcaneal angle is less than 15°, and the 2 bones appear to overlap more than normal. Also, the longitudinal axis through the middle of the talus (midtalar line) passes lateral to the base of the first metatarsal, because the forefoot is medially deviated (see Images 4-5).

Forefoot varus and supination increase the convergence of the bases of the metatarsals on the DP view, compared with the normal slight convergence (see Image 6). On the lateral view, instead of having the normal overlapped appearance, the metatarsals are arranged in a ladderlike configuration, with the first being most dorsal (see Image 7). The following table contains a summary of the normal and clubfoot measurements:

Open table in new window

In an incompletely corrected or recurrent clubfoot, characteristic abnormalities are observed.⁴ The talocalcaneal angle is normal on the DP view (see Image 8), but talocalcaneal parallelism persists on the lateral view. Flattening of the talar dome persists on this view as well (see Image 9). Cavus of the plantar arch may be present, particularly if no plantar release was performed. Also, a periosteal reaction, sclerosis, or fracture of the lateral metatarsals may occur as a result of abnormal weight bearing on this side of the foot in cases of inadequate correction of forefoot varus (see Images 10-11).

Tarraf and Carroll found that residual forefoot adduction and supination were, by far, the most common deformities that lead to repeat surgery for clubfoot. In addition to hindfoot alignment, these deformities should be actively evaluated on intraoperative radiographs.⁵

Degree of Confidence

With proper positioning and exposure, quantification of alignment abnormalities on plain radiographs is reliable. No confirmatory imaging is routinely used.

False Positives/Negatives

Oblique positioning of the heel on the DP view can simulate hindfoot varus. If the lateral view is one of the foot rather than the ankle, the flat talar dome has a spurious appearance.

Computed Tomography

Findings

Few articles about the use of CT in the elevation of clubfoot have been published. Disadvantages of CT include the risk of ionizing radiation, the lack of ossification of the tarsal bones, susceptibility of the images to motion artifact, and the need for expensive equipment and software applications for multiplanar reconstruction. On the other hand, this complex 3-dimensional deformity may be better assessed in the future with 3-dimensional reconstructions than with 2-dimensional radiographs. The utility of CT in the evaluation of talar articulations in trauma and tarsal coalition is already well established.

In preliminary study of CT with 3-dimensional reconstructions, Johnston et al showed that wire-frame surface renderings of the bones in clubfoot can be created and that the axes of inertia can be computed around the center of mass in 3 perpendicular planes for each bone involved.⁶ These renderings can be manually rotated to elucidate deformities and misalignments that are obscured because of overlap on plain radiographs. The relationship between the hindfoot bones and ankle mortise can be evaluated in this way, because the information from the lower leg does not overlap. Similarly, the vertical axes of the talus and calcaneus can be compared with a reference line perpendicular to the floor in a coronal reconstruction of the heel. This view can be obtained only with CT.

These analyses revealed that, in the normal foot, both the talus and the calcaneus are medially rotated relative to a line perpendicular to the mortise in the transverse plane, but the rotation in the calcaneus is much less. This difference is the normal divergence of the long axes of the 2 bones. In the clubfoot, the talus is laterally rotated, and the calcaneus is more medially rotated than normal; these rotations cause convergence of the long axes.

Additionally, the authors observed mild pronation of the talus and calcaneus in the coronal plane in the clubfoot, in contrast to mild supination of both in the normal foot. These findings imply that surgical correction should involve supination and medial rotation of the talus in the mortise and supination and lateral rotation of the calcaneus.

Magnetic Resonance Imaging

Findings

MRI is not currently used to image clubfoot, and limited experiences are published in the literature. The use of MRI is limited because of its multiple disadvantages, including the need for equipment and patient sedation, the software-related expenses, the loss of signal caused by the ferromagnetic effects of fixation devices, and the additional time required for data transfer and postprocessing. On the other hand, the advantages of MRI compared with plain radiography and CT are its multiplanar imaging capability and its excellent depiction of ossific nuclei, cartilaginous anlage, and surrounding soft-tissue structures.

Results of a pilot study of MRI and of preliminary work in magnetic resonance multiplanar reconstructions have shown that these methods can be used to elucidate the complex pathoanatomy of this disorder. Intermediate- and T2-weighted spin-echo images are most useful for depicting the cartilaginous anlage and the articular surfaces, respectively.⁷ When 3-dimensional gradient-echo acquisitions are used to create multiplanar reconstructions, the center of mass and the principle axes of inertia of each bone or cartilaginous structure can be determined. These axes can be compared with each other or a standard of reference to obtain reproducible, objective measurements of the deformities.⁸

The talar deformity, which many researchers believe is primary in clubfoot, is not precisely defined by using any other imaging modality. However, with the method described above, MRI with multiplanar reconstructions can depict the intraosseous deformity of the talus defined by the elevated talar body-neck angle.

Particularly well defined is the talonavicular relationship, which is not seen on radiographs obtained in young children because of the lack of ossification in the navicular. In most patients, the navicular is medially dislocated.⁹

Ultrasonography

Findings

Few studies of the ultrasonographic findings in normal feet or clubfeet have been performed, and the clinical utility of this modality has yet to be established. The main disadvantage of ultrasonography is the inability of the beam to penetrate all of the bones, particularly if a postoperative scar is present. Advantages of ultrasonography include the lack of ionizing radiation, no need for sedation, its ability to depict nonossified portions of bones, and its capacity for dynamic imaging.¹⁰

Preliminary studies have shown that reproducible views and objective assessments of some of the interosseus relationships in normal feet and clubfeet can be obtained with ultrasonography. In the future, these may assist in directing surgical and conservative therapies for clubfoot and in assessing the results.¹¹

A 7.5-MHz linear transducer and stand-off pad are used to obtain several reproducible and helpful views. The posterior-sagittal view is obtained with the transducer aligned with the midline sagittal plane and placed on the posterior and upper part of the heel. The anteromedial view is obtained from that position at the junction of the ankle and foot, with the foot plantar flexed. The transducer is aligned along the distal tibia, talus, and navicular. The medial transverse view is transverse to the foot on its medial side. A lateral transverse view of the foot may also be useful. Furthermore, these views can be obtained through a dynamic range of motion.

The Achilles tendon can be measured on the posterior-sagittal view. It is often shortened in clubfoot and spastic deformities. On this view, the distal tibia, talus, and calcaneus are perfectly aligned. The distance between the distal ossified tibia and the superior ossified calcaneus can be measured. With plantar flexion, this distance decreases in the normal foot but not in clubfoot. This view permits evaluation of the talonavicular relationship in the DP plane, which is often persistently abnormal after complete subtalar release.

On the anterior-medial view, the medial malleolus, talus, navicular, and medial cuneiform can be seen (see Image 12). The important and elusive talonavicular relationship can be quantified by measuring the distances or angles. The distance between the medial malleolar epiphysis and the cartilaginous navicular can be measured. With medial displacement of the navicular in clubfoot, this measurement is shorter than in the normal foot (see Images 13-16).

Hamel and Becker introduced an angle to quantify the talonavicular relationship. With medial subluxation of the navicular, the angle is positive rather than negative, as it is in normal feet. These measurements can be used to preoperatively estimate the amount of medial release necessary or to assess the success of conservative manipulation and use of braces and/or casts.¹²

The lateral transverse view may be used to assess the important calcaneocuboid (lateral column) relationship. Future investigations may show that reproducible quantification of this relationship may be useful in directing surgical release of this joint.

The dynamic imaging that is possible with ultrasonography may complement physical examination in the assessment of the rigidity of the foot. Thus, it may aid in the selection of patients for surgical rather than conservative therapy.¹³

In summary, ultrasonographic evaluation may be used in the future to determine the necessity, site, and amount of soft tissue release and to evaluate the success of therapy.

Nuclear Imaging

Findings

Nuclear imaging is not used in the evaluation of clubfoot because its depiction of the anatomic detail is insufficient.

Angiography

Findings

Angiograms can show the abnormal size and distribution of the small vessels in the clubfoot, but these findings are of limited clinical usefulness.

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