Bone stiffness in children: part II. Objectives criteria for children to assess healing during leg lengthening.
BACKGROUND
The decision when to remove the frame after limb lengthening through standard distraction osteogenesis remains a challenge. Multiple studies have attempted to find objective criteria to assess bone healing after fracture or bone lengthening. However, there is a paucity of such data for the pediatric population. The purpose of this study was to correlate data obtained after dual-energy x-ray absorptiometry (DXA) measurement and bending stiffness in children to find an end-point value for the safe removal of an external fixation device.


METHODS
We investigated 16 consecutive children aged between 5.5 and 16.7 years who had 22 lengthenings by callotasis. Twelve femurs and 10 tibiae were lengthened with a monoplane Orthofix external fixator. Fifty simultaneous measurements of bending bone stiffness measured with an Orthometer and DXA scans (bone mineral content [BMC], bone mineral density, volumetric bone mineral density, BMC/1 cm, Area/1 cm, BMC/1 cm, Area) were obtained during healing process. Four femoral fractures were reported after the removal of the external fixation device. Linear regression analysis was used to calculate the squared correlation coefficients for the relation between the DXA scans and the mechanical tests measuring bone stiffness.


RESULTS
The bone stiffness measurement of the intact bone was compared with consecutive measurements of the bone stiffness of the regenerate, and it was expressed as a percentage (coefficient). We compared the BMC of the regenerate with the same bone area of the opposite limb. The best correlation was observed for anteroposterior (AP) bone stiffness coefficient and BMC coefficient (R = 0.82). The linear equation was BMC coefficient = 0.5 x AP stiffness coefficient + 30. The end point of 75% of BMC of the regenerate corresponds to 75% of the AP stiffness on DXA scanning; this is the time when we should consider safe removal of the fixator.


CONCLUSIONS
Our method of comparing bone stiffness and DXA measurements gives an objective healing end point for every patient irrespective of his or her size. This method could allow noninvasive measurement of the end point and identified at-risk population of children, reducing regenerate fracture after bone lengthening.
Chotel
Franck
F
Department of Orthopaedic Paediatric Surgery, Debrousse Children Hospital, 29 rue soeur Bouvier, Lyon cedex 05, France. franck.chotel@yahoo.co.uk
Braillon
Pierre
P
Sailhan
Frédéric
F
Gadeyne
Sylvain
S
Gellon
Jean-Olivier
JO
Panczer
Gérard
G
Pedrini
Christian
C
Berard
Jérôme
J
D015502:Absorptiometry, Photon; D000293:Adolescent; D001696:Biomechanical Phenomena; D015519:Bone Density; D001852:Bone Lengthening / Q000379:methods*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005269:Femur / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007870:Leg Length Inequality / Q000601:surgery; D016014:Linear Models; D008297:Male; D011446:Prospective Studies; D013977:Tibia / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D014945:Wound Healing / Q000502:physiology