Calcaneal apophysitis (CA) is a common cause of activity-related heel pain in children,
which is widely regarded as an overuse injury of the cartilaginous-layer of the calcaneal
apophysis. Foot mobility and heightened ground reaction force have been purported to be
clinically associated with the development of the injury. Additional variables clinically
thought to be associated with CA include altered functional properties of the Achilles
tendon and ankle range of movement. There is a paucity of research, however, evaluating
the presence of these potential risk factors and, of the few investigated, scientific support is
often contradictory. The present research aimed to better understand factors clinically
associated with CA through a series of quasi-experimental case-control studies that
investigated foot mobility and stiffness, vertical ground reaction force, functional Achilles
tendon properties and dynamic ankle movement during walking and running in children
with and without the condition.
Since the measurement techniques adopted for the individual experiments in this program
of research have not been widely used in children with CA, the thesis has also
methodologically identified, quantified and described inherent limitations and potential
errors of using these clinical measures in children. The findings indicate that while the
reliability of measures of foot mobility and stiffness were similar to those reported in
adults, foot mobility values in children (8 ± 2 mm) were smaller than those previously
reported in adults (≈18 mm). A follow-up exploratory investigation, in which clinical foot
mobility measures were compared to those obtained from radiographic skin markers in a
small sub-sample of children (n=3), suggested that clinical measures of foot mobility likely
reflect a varied combination of soft tissue distortion and osseous movement in children. In
a further methodological study evaluating the reliability of gait parameters derived from an
instrumented treadmill that incorporated a pressure platform, it was observed that
conventional measures of ground reaction force and temporospatial parameters were highly
repeatable (SEM typically <5%) in children during both walking and running at selfselected speeds. Finally, consistent with previously consolidated repeatability analyses
reported for adults, the within-subject repeatability of measuring ultrasound velocity of the
Achilles tendon and also ankle electrogoniometric measures in children during running was
highly reproducible from one gait cycle to the next.
In the experimental component of this thesis, a series of quasi-experimental case-control
studies were performed to analyze foot mobility and stiffness, vertical ground reaction
force, functional Achilles tendon properties and dynamic ankle movement during gait in
children with and without CA. Collectively, these studies have shown that foot mobility
and stiffness, peak vertical ground reaction force during walking and running, and peak
ultrasound velocity in the Achilles tendon during running, a measure of the instantaneous
material stiffness of the tendon, may not clinically differ in children with and without CA.
However, children with CA were characterized by a consistently higher cadence than those
without heel pain specifically during running (≈ 5%). Children with CA also had greater
ankle dorsiflexion (≈ 4°) than those without CA during running despite adopting a similar
foot strike pattern. While these findings may question the rationale behind current
treatments aimed at modifying foot mobility and improving functional Achilles tendon
properties through enhanced ankle dorsiflexion in CA, self-reported pain was inversely
related to peak ankle dorsiflexion and positively related to peak vertical ground reaction
force during running. Hence symptom improvement during running may be linked to
heightened ankle dorsiflexion and lower peak vertical ground reaction force. Although
further research is required, this thesis has provided greater insight into factors associated
with CA in children, and raises a number of questions for further clinical consideration.
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