SLR - February 2011 - Diane M. Castro
Reference: Bixby SD, Jarrett DY, Matheney T, Johnston P, Kasser J, Kleinman PK. Unilateral Subtalar Coalition: Contralateral Sustentaculum Tali Morphology. Radiology 2010; 257(3): 830-835.
Scientific Literature Review
Reviewed by: Diane M. Castro, DPM
Residency Program: Cambridge Health Alliance; Cambridge, MA
Podiatric Relevance:
Subtalar coalitions are not an uncommon finding in the pediatric patient, with about half of the patients presenting with a bilateral coalition. Patients who present to the office complaining of a unilateral tarsal coalition may in fact have a bilateral abnormality with symptoms that have yet to manifest. It is prudent to take bilateral imaging studies and keep a watchful eye on the non-symptomatic side to see if any future symptoms develop, or to at least be aware of the possibility that they might.
Methods:
CT reports were reviewed from January 1998 to June 2008 of patients aged 0-18 years, identifying 35 patients (21 male, 14 female; mean age, 14.54 years +/- 2.91) with a unilateral subtalar coalition and 33 control patients (21 male, 12 female; mean age, 13.48 years +/- 1.79) with a triplane ankle fracture. The CT images were reviewed and new images were created by reformatting them through the subtalar joint (on the side opposite the coalition). Two radiologists used electronic calipers to obtain anteroposterior measurements of the middle facet (MF) and sustentaculum tali (ST). Then, a ratio of the length of the MF over the length of ST (MF/ST), and the portion of the ST extending posterior to the MF were calculated and recorded. Measurements between the two groups were compared using Wald tests based on linear regressions while adjusting for age, sex, and CT section thickness. Intraobserver and interobserver reliability between the measurements were estimated by means of a component of variance model.
Results:
The MF lengths for the study group (coalition group) and control group were 12.86 +/- 2.03 and 16.82+/- 2.38 (P<.001), respectively. The ST lengths for the study group and control group were 23.83 +/- 3.67 and 22.06 +/- 2.52 (P= .053), respectively. The study group had a MF/ST ratio of 0.54+/- 0.07 versus 0.76+/- 0.07(P<.001) for the control group. The study group had an ST length extending posterior to the MF of 10.97+/- 2.93 versus 5.24+/- 1.79 (P<.001) for the control group.
Conclusions:
Patients with a unilateral subtalar coalition had a contralateral middle facet that was smaller, and sustentaculum tali that was larger, resulting in a smaller MF/ST ratio compared to the control group. Also, in patients with a unilateral subtalar coalition, the ST was found to extend more posterior to the MF as compared with control patients. These findings can suggest that some patients presenting with a unilateral subtalar coalition actually have a bilateral abnormality of the talus and calcaneus that is only clinically apparent, at first, in the more severely affected foot.