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Titel på arbejdet Assessment of Radiostereometric Analysis Stability across Osteotomies in Feet and Hips
Navn Peter Buxbom
Årstal 2016
Afdeling / Sted Hvidovre Hospital
Universitet Københavns Universitet
  • Orthopaedic Pediatrics
Abstract / Summary

There are only published few pediatric orthopedic radiostereometric analysis (RSA) studies within the last decades and none concerning stability and migration across osteotomies. This thesis have evaluated three types of osteotomies with RSA; two regarding the surgical treatment of hip displacement in children with neuromuscular disorders (1) the periacetabular Dega osteotomy (DO) and (2) the femoral varisation derotation osteotomy (VDRO), and one regarding surgical treatment of children with pes planovalgus (flatfoot) treated with (3) calcaneal lengthening osteotomy (CLO). These surgeries have a reported relapse of 16-32 % and 18-36 %, respectively.

The purpose of this thesis was to establish whether RSA was a feasible method to evaluate small scale osteotomies (e.g. CLO), and subsequent to investigate the RSA stability and migration across the three mentioned osteotomy types DOs, VDROs and CLOs.

Study I assessed the RSA feasibility across a small-scale osteotomy by test-retest observations on a cadaver foot phantom model. The test-retest 95 % repeatability limits (RPLs) were compared with international results. RSA output with mean error of rigid body fitting (ME) above 0.35 mm or condition number above 150 mm-1 were excluded. In study II-IV insertion of 4-6 tantalum markers peroperatively on each side of the DOs, VDROs and CLOs, respectively. RSA follow-ups were for DOs and VDROs planned at 0, 5 weeks, 3, 6, and 12 months and for CLOs the follow-ups were planned at 0, 5, 10 weeks, 6 and 12 months. To evaluate stability across the osteotomies we defined RSA stability as migration below internal RPL in five out of six orientations. Migration was evaluated according to RSA community guidelines.

In study I the feasibility was confirmed achieving acceptable values of RPL, ME and CN, which showed comparability with the RSA results across the CLOs in study IV. In study II-IV we found RSA stability across the majority osteotomies within the first 5 weeks and
across all osteotomies within 3 months.
In study II the mean translations (±SD) at the one-year follow-up of distal periacetabular fragment across RSA stable DOs were 0.55 mm (±0.63) medial, 0.33 mm (±0.33) superior and 0.13 mm (±0.24) posterior. The mean rotations were 1.47° (±2.91) posterior tilt, 0.27° (±1.28) retroversion and 1.76° (±3.10) medial inclination.
In study III the mean translations (±SD) at the one-year follow-up of distal femoral shaft fragment across RSA stable VDROs were 0.51 mm (±1.12) medial, 0.69 mm (±1.61) superior and 0.21 mm (±1.28) posterior. The mean rotations were 0.39° (±2.90) anterior tilt, 0.02° (±3.07) internal rotation and 2.17° (±2.29) varus angulation.
In study IV the mean translations (±SD) at the one-year follow-up of the anterior calcaneal fragment across RSA stable CLOs were 0.23 mm (±0.51) superior and 0.14 mm (±0.40) lateral. The mean rotations were 0.49° (±2.09) supination, 0.78° (±2.03) external rotation and 0.91° (±1.98) dorsiflexion.

Radiostereometric analysis is a feasible method to evaluate RSA stability and migration osteotomies performed on pediatric orthopedic patients - even across small-scale osteotomies. Using the RSA stability definition the majority osteotomies stabilized within the first 5 weeks. All osteotomies were by definition RSA stable within 3 months in accordance to the definition of RSA stability used
in this study. The mean migrations at the one-year follow-up significantly differ from zero (the postoperative RSA) across DO for medial, superior and posterior direction and with posterior tilt and medial inclination. For VDROs only significant migration was observed for varus angulation at the one-year follow-up. For CLOs none of the orientations differ significantly from the zero at the one-year follow-up.

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