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absence of anything better accepted, it was chosen as the
PTOA outcome metric to which we compared the WBCTbased technique.
In our study, the observers performed better than previously reported for KL reliability scores, demonstrating moderate inter- and intrarater reliability. In comparison, the
reliability of the WBCT-based JSW measures between
repeated measurement sessions, as well as between raters,
was almost perfect. The greatest difference in mean or minimum JSW measurement for both inter- and intrarater reliability was 0.3 mm, with the average difference for both reliability
studies between the mean and minimum ranging from 0.1 to
0.2 mm. Since the isotropic voxel edge length was 0.37 mm,
these results show the difference in measurements to be less
than a voxel. Therefore, changes in our measures of JSW
greater than the edge length of a voxel can confidently be
attributed to true anatomical changes in the JSW.

Validity
As a secondary goal of this study, we assessed whether
WBCT images used to quantify the preservation/loss of
JSW in patients with IACF were correlated with clinical
outcomes. We found that lower global 3D JSW values were
strongly correlated with higher VAS pain scores, even in
this relatively small cohort of patients. WBCT allows
regional measures of 3D JSW, and several of these outperformed KL grade by better correlating with VAS pain, particularly in the central and posterior subtalar regions. A
smaller 3D JSW may lead to higher patient pain scores secondary to locally accelerated cartilage degradation. The
correlation of 3D JSW to clinical outcomes was stronger
than for KL grade, suggesting that JSW represents PTOA
clinical status more accurately than KL grade.

Limitations
There were several limitations to this study. At clinical follow-up, 42% of subtalar joints had evidence of PTOA. Given
only a portion of participants demonstrated evidence of
arthritic progression and there were no controls (or contralateral WBCT scans obtained), the study was susceptible to
selection bias. Nevertheless, as this is a novel measurement
technique, even a select cohort of patients and follow-up
scans provided the ability to develop a technique, confirming its reliability and validity. Future development and
expansion upon this image analysis technique and prospective studies with larger numbers of patients are necessary.
The quality of the plain weightbearing radiographs
obtained in the study was variable. Although the nature of
our radiographs represents the standard quality of radiographs obtained in the context of routine clinical care, rotated
images may have impacted the reliability of reviewers to
assess PTOA. The inconsistency in radiographs is consistent

Foot & Ankle International 41(9)
with other studies demonstrating that assessing subtalar joint
space loss and severity of PTOA using radiographs is imprecise and insensitive, with variable reliability.6,14,15 We did not
utilize radiographs or WBCT to evaluate alignment, although
this is potentially very important and the weightbearing
position allows this to be the subject of further studies. While
WBCT has potential to provide reliable 3D assessment of
subtalar joint space, WBCT is not yet widely available, making its future clinical applicability unknown. It is currently
unclear whether WBCT will be predominantly a research
tool or whether wider availability will allow it to be incorporated in more routine clinical care.
Another limitation is the need for human effort to obtain
accurate manual segmentations of the calcaneal and talar
bone edges, due to the differences in bone density within
regions of the subtalar joint. This was time-consuming,
which limits the near-future clinical utility of 3D JSW measurements on WBCT and is part of the reason our study
included a relatively small number of subjects. We anticipate
that the time required for the JSW measurement technique
will be significantly reduced in the future with the advent of
tools like CubeVue Autometics (Curvebeam LLC), and this
may lead to wider clinical use of JSW measures.
Lastly, the current study was designed to assess correlations between radiographic and 3D JSW measurements by
WBCT in a cross-sectional manner. In future studies, the
new method should be applied on a longitudinal dataset of
WBCT scans, to determine whether the proposed method
demonstrates a loss or maintenance of subtalar joint space
over time and whether loss of JSW can be detected earlier
in the disease process. The current study was only a snapshot at relatively longer-term follow-up.

Future Research and Clinical Impact
Currently, little is known about the interaction of acute
mechanical damage and chronic elevated contact stress and
the biological processes that lead to PTOA. However,
emerging research of therapeutic targets for PTOA prevention that can be applied before or concomitant with open
reduction and internal fixation procedures holds promise
for mitigating PTOA and preserving a patient's quality of
life.4 The prolonged clinical course of a joint evolving to
PTOA makes early indication of joint space loss with
WBCT not only of potential clinical value, but also important to evaluate the influence of candidate treatment intervention in research studies. Objectively measuring subtalar
joint cartilage preservation or loss will enable research to
assess the joint outcome relatively early after fracture. The
high incidence of PTOA after calcaneal fracture makes it a
good target to study novel biologic treatments for the prevention and treatment of PTOA.
WBCT also has the potential for clinical application as an
improved assessment tool. Quick scan time, low radiation

Foot & Ankle International - September 2020

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