| Abstract / Summary | The calcaneal lengthening osteomy (CLO) is among the most widely used surgical
techniques for correction of pes planovalgus deformities in paediatric patients. The choice of
structural bone graft material has been debated ever since the introduction of the operation.
Most studies have focused on the feasibility of allograft as an alternative to tricortical iliac
crest autograft. Over the past decades, there has been a growing interest in bone graft
substitutes, especially calcium ceramics owing to their resemblance to native bone. If calcium
ceramic could be proven viable as a structural bone graft, it would be a promising alternative
to iliac crest autograft for CLO. When assessing the efficacy of a structural bone graft, two
major aspects need to be determined: The mechanical properties of the bone graft and the
clinical outcome.
Radiostereometric analysis (RSA) is a valuable tool in the measurement of
migration of implants.1 It has not yet been used to assess bone incorporation and osteotomy
stability in paediatric foot surgery.
Recent trends in using Patient Reported Outcome Measures (PROMs) to measure
patient health have resulted in development of tailored PROMs, seeking to ascertain
patients’ views on how their symptoms affect their daily lives. The specific English Oxford
Foot Ankle Questionnaire (OxAFQ) has been proven valid in paediatric patients and their
parents. For Danish paediatric patients with foot-ankle deformities including pes
planovalgus, such a PROM would be of great clinical value to aid the assessment of how
children are affected by their foot deformity.
This dissertation seeks to investigate the feasibility and efficacy of a novel structural calcium
ceramic for paediatric CLO. The osteotomy stability is assessed with RSA and is thus a
surrogate measure of the structural bone graft durability. Secondary, the outcome will be
assessed by the OxAFQ to assess the patient's perspective on the outcome.
The first aim (Study I) of this thesis was to translate the English version of OxAFQ
into Danish with subsequent validation. The second aim (Study II) was to assess the precision
and feasibility of RSA measurements for CLO. The third and central aim (Study III) was to
investigate the noninferiority of structural hydroxyapatite-tricalciumphosphate (HATCP) to
tricortical iliac crest autograft in CLO for peadiatric pes planovalgus by using RSA as the
primary measurement instrument.
Study I. The English version of OxAFQ (child and teenager, and proxy version) was
translated into Danish. The subsequent validation included reliability measurements (testretest,
child-parent, internal consistency), construct validity and feasibility (number of
VIII
missing items, time to completion and floor and ceiling effects). The generic child health
questionnaire was used for comparison. Overall the OxAFQ was valid and feasible in
assessment of health-related quality of life in children with a variety of foot/ankle disorders.
Study II. Precision and feasibility of RSA measurements for CLO were tested in three fixed
adult cadavers (six feet) with the primary focus on the stability of the osteotomy and
secondary the calcaneal-cuboid joint (CCJ). Precision was good for translations at the
osteotomy site and at the CCJ. As expected, rotations were less precise, but without clinical
significance. RSA proved to be feasible for CLO in fixed cadaver feet, and is expected to be
more feasible in paediatric feet.
Study III. The study was designed as a randomised controlled noninferiority trial. The
primary outcome measure was x-translation of the distal (anterior) calcaneal fragment with
reference to the proximal (posterior) calcaneal fragment measured by RSA. If there was truly
no difference between the new and the standard treatment, 20 patients would be required to
be 90% sure that the upper limit of a one-sided 95% CI would be above a noninferiority limit
of 2 mm. For safety reasons an interim-analysis was embedded into to the trial. Data from
ten patients with six months RSA follow-up were analysed with respect to the primary
outcome measure considering both sides of a 99.8% CI. The interim results of Study III are
reported in this dissertation. The report includes eleven patients (11 feet). One patient was
excluded from further follow-up after eight weeks due to infection of the graft material
(HATCP), which necessitated reoperation. With six patient in the HATCP group and five
patients in the AUTO group, a difference of 1.97 mm (99.8%CI: -1.65; 5.60) was found in the
x-translation of the distal calcaneal fragment with reference to the proximal calcaneal
fragment (HATCP graft minus AUTO graft). In general, the AUTO group obtained stability
of the osteotomy at six weeks follow-up, while the HATCP group stabilised at six months.
This is the first clinical study to compare the structural durability of iliac crest autograft with
HATCP for CLO in paediatric patients by using RSA. The results suggest that HATCP is of
limited value as a structural bone graft in unfixed CLOs compared to tricortical iliac crest
autograft.
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