https://onlinelibrary.wiley.com/doi/pdf/10.1002/jor.20026

Radiographic Classification of Osteogenesis During Bone Distraction

Any lower limb discrepancy may be equalised by conservative means (insoles, prosthesis and orthosis). However, their long-term acceptance is low in regard to function, costs, expenditure and appearance. Timely epiphysiodesis is the best option in uniplanar deformities with adequate remaining growth and for patients whose predicted final body height is above the 50th percentile. However, many patients present late or with multi-planar deformities, which warrant more sophisticated operative approaches. The history of surgical bone lengthening comprises 100 exciting years of struggling, development and ongoing learning. The initial strategy of acute or rapid incremental distraction had lasted almost half a century until Ilizarov recognised the benefits of biological periosteum-preserving osteotomies and incremental lengthening at slow rates (1 mm/day) at a 4 × 0.25-mm daily rhythm, well appreciated as callotasis. In parallel, ring and wire constructs made complex three-dimensional axial, translational and rotational bone moulding possible. Taylor Spatial Frames—built on hexapod strut-linked platform technology as known from flight simulators—took limb correction to a more reliable, more precise and aesthetical level, all the more that the whole process became web-based. It represents state-of-the-art methodology and technology for complex, multi-plane deformities. Due to the significant risk of secondary malalignment, indications for lengthening by unilateral fixation have shrunken to moderate amounts of length disparity and uni- to bi-planar deformities in patients with still open physes. Mechanical or motorised, minimally invasively placed nails prevent muscle fixation and, therefore, ease rehabilitation, increase patient comfort and potentially shorten the overall time of sick leave and refrain from sports activities. Hence, they offer a valuable alternative for low-grade complexity situations. It remains to be proved if the significantly higher implant costs are compensated by lower treatment costs. Overall, limb lengthening, particularly in combination with multi-planar deformity correction, can still be an arduous endeavour. In any case, wise judgement of the patient’s deformity, medical and biological situation, psychosocial environment, selection of the appropriate method and hardware, as well as meticulous operating technique by an experienced surgeon are the cornerstones of successful outcomes.

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Current concepts of leg lengthening.

Ultrasound of fracture and bone healing.

High-resolution real-time ultrasound (US) scanning was used to monitor serially 24 patients with an acute long-bone fracture and three patients with humeral non-union, looking at the fracture site over a period of 12 months following the fracture. In both these groups, we found that US gave important information about the soft tissues surrounding the fracture site, and indicated callus formation at an early stage. US was more sensitive than conventional radiography at showing the early phases of organization of the callus, and its progression to bridging new bone formation. US also clearly showed a disorganized echopattern at the fracture site of the patients with non-union.

Ultrasonographic appearance of external callus in long-bone fractures.

Assessment of biomechanical stability of diaphyseal bone lengthened by callus distraction is an unsolved problem. A middiaphyseal corticotomy was performed in the left tibia of 24 sheep. After 7 days, callus distraction was begun at a rate of 0.5 mm every 12 hours for 30 days using a standard unilateral fixator system. Animals were euthanized 4, 8, or 12 weeks after the end of distraction. The lengthened tibia and the contralateral control tibia from each animal were evaluated by radiographic, densitometric (dual energy xray absorptiometry, quantitative computed tomography), and biomechanical (axial compression testing, torsion testing to failure) methods. The bone mineral density and maximum torque for the lengthened tibia were significantly greater in the 8-week group than in the 4-week group. However, the values in the 12-week group were significantly smaller than in the 8-week group. In the lengthened tibias, there was a correlation between the maximum torque and the bone mineral density, and between the maximum torque and the bone density. Bone density measurements are useful prognosticators for the safe removal of external fixators after leg lengthening procedures. By using these methods, clinical fractures after leg lengthening could be avoided in the future.

Biomechanical and densitometric bone properties after callus distraction in sheep.

Limb lengthening in nine patients was monitored by radiographs and by ultrasound scans. The distraction gap appeared as a sonolucent area within which echogenic foci developed soon after distraction commenced. By seven weeks a new cortex was detected, and medullary canal began to develop between seven and eight weeks. Ultrasound scanning can be used to measure distraction, but it was not as useful as radiographs in detecting angulation. Its use in patients undergoing limb lengthening could reduce their exposure to radiation.

Ultrasonographic monitoring of limb lengthening.

We report our experience in radiographic imaging in limb lengthening procedures using callotasis for limb lengthening discrepancy with the Orthofix dynamic monoaxial external fixator. Seventeen patients (average age at operation 10.8 years) completed 22 bone segments (7 femora, 11 tibiae, 4 ulnae) lengthening procedures. The average time for formation of good medullary bridging was over 6 months. The commonest radiographic abnormality was a periosteal reaction around the pin sites seen in 14 patients, while evidence of pin loosening was present in 10. All patients with pin loosening also showed periosteal reaction which pre-dated the loosening in 5 of 12 patients by an average of 47 days. Angulation was detected in 9 patients in the a.p. plane, and in 6 in the lateral plane. Six patients developed a ragged radiolucent region through the newly forming bone at an average of 95 days from the corticotomy but with uneventful healing.

Radiographic Features of Limb Lengthening in Children

Ultrasonographic monitoring of limb lengthening

The appearance of regenerate bone during the process of limb lengthening using a mono-axial device was studied using radiographs and ultrasound scanning in nine patients. The corticotomy site initially appeared as a sonolucent area. Poorly organized echogenic foci were detectable 2 weeks after the distraction was begun. After 4 weeks, these areas became aligned. At 7-8 weeks, a clear impression of a new cortical margin was seen. The formation of a medullary canal started at this point, progressing to a radiographically evident canal. Ultrasound scanning can reduce considerably exposure to ionising radiation in patients undergoing limb lengthening. Accurate measurements are possible in the early stages, and ossification can be monitored. Axial deviation can be seen but not evaluated. The maturity of the regenerate bone still has to be assessed clinically.

T. H. Hughes

Papers

Ultrasonographic monitoring of limb lengthening.

Radiographic Features of Limb Lengthening in Children

Ultrasonographic monitoring of limb lengthening

Ultrasonographic appearance of regenerate bone in limb lengthening.