Distance mapping of the foot and ankle joints using weightbearing CT: The cavovarus configuration

The primary aim of this study was to evaluate the true incidence of osteochondral lesions on the talar dome by location and by morphologic characteristics on MRI. Because no universally accepted localization system for talar dome osteochondral lesions currently exists, we established a novel, nine-zone anatomical grid system on the talar dome for an accurate depiction of lesion location. We assigned nine zones to the talar dome articular surface in an equal 3 x 3 grid configuration. Zone 1 was the most anterior and medial, zone 3 was anterior and lateral, zone 7 was most posterior and medial, and zone 9 was the most posterior and lateral. The grid was designed with all nine zones being equal in surface area. Two observers reviewed MRI examinations of 428 ankles in 424 patients (211 males and 213 females; mean age 43 years; age range 6 to 85 years) with reported osteochondral talar lesions. We recorded the frequency of involvement and size of lesion for each zone. Statistical analyses were performed using ANOVA and Scheffe tests. Four hundred and twenty-eight lesions were identified on MRI. The medial talar dome was more frequently involved (n = 269, 62%) than the lateral talar dome (n = 143, 34%). In the AP direction, the mid talar dome (equator) was much more frequently involved (n = 345, 80%) than the anterior (n = 25, 6%) or posterior (n = 58, 14%) thirds of the talar dome. Zone 4 (medial and mid) was most frequently involved (n = 227, 53%), and zone 6 (lateral and mid) was second most frequently involved (n=110, 26%). Lesions in the medial third of the talar dome were significantly larger in surface area involvement and deeper than those at the lateral talar dome. Our established nine-grid scheme is a useful tool for localizing and characterizing osteochondral talar lesions, which are most frequently located in zone 4 at the medial talar dome, and second most in zone 6 at the lateral talar dome near its equator. Medial talar dome lesions are not only more common but are larger in surface area and in depth than lateral lesions. Posteromedial and anterolateral lesions rarely were found.

A modification of Cobey's method for radiographically imaging the coronal plane alignment of the hindfoot is described. Using this view, we estimated the moment arm between the weightbearing axis of the leg and the contact point of the heel. Normative data on 57 asymptomatic adult subjects are presented. The weightbearing line of the tibia falls within 8 mm of the lowest calcaneal point in 80% of subjects and within 15 mm of the lowest calcaneal point in 95% of subjects. The technique for measuring coronal plane hindfoot alignment is reliable, with an interobserver correlation coefficient of 0.97. This radiographic technique should help in the evaluation of complex hindfoot malalignments.

In the last decade, cone-beam computed tomography technology with improved designs allowing flexible gantry movements has allowed both supine and standing weight-bearing imaging of the lower extremity. There is an increasing amount of literature describing the use of weightbearing computed tomography in patients with foot and ankle disorders. To date, there is no review article summarizing this imaging modality in the foot and ankle. Therefore, we performed a systematic literature review of relevant clinical studies targeting the use of weightbearing computed tomography in diagnosis of patients with foot and ankle disorders. Furthermore, this review aims to offer insight to those with interest in considering possible future research opportunities with use of this technology.