Radiomorphological Manifestations of Femoral and Tibial Cortical Bones at Different Stages of Limb Lengthening

Abstract

Background: There has been a lot of research done on Ilizarov's limb lengthening; however, very few publications focus on the quantitative assessment of the distractional bone regeneration in tibial and femur lengthening. Data regarding quality of the bone after lengthening are needed to consider the time of frame removal and develop a rehabilitation program.

Materials and methods: Computed tomography (CT) assessment of a parent bone was performed on 136 patients with limb length discrepancy and bone deformity of various etiologies before and after lengthening. Transosseous osteosynthesis technique with the Ilizarov's external fixation was used for limb lengthening and deformity correction in all the cases. A 64-slice scanner was used for CT assessments. Specific Roentgen-negative units of the Ilizarov apparatus and techniques for interpreting CT findings were employed for artifact-free densitometric assessment.

Results: Cortical density of the femur and tibia in patients with limb length discrepancy and bone deformity of various etiologies was shown to have differences as compared to the contralateral limb. The lengthening process was accompanied by decreased cortical density of the segment being lengthened, and the decrease in the density was greater in the areas adjacent to the distractional bone regeneration. The cortical structure underwent characteristic changes. Osteonal density of the cortical bone was higher in the norm and at long term followup as compared to the density of external and internal plates.

Conclusion: Cortical bone of the femur and tibia in patients with limb length discrepancy and bone deformity of various etiologies showed various preoperative local densities of external, internal, and osteon layers. The cortical bone demonstrated heterogenic structures with resorption areas of various magnitude and density, with minimal values at the boundary with regenerate bone during distraction and fixation with frame on and at short-term followup. Complete organotypical restructuring of the bone was shown to occur at a 1-to-3-year followup depending on the etiology of the disease and amount of lengthening performed.

Keywords: Corticotomy; Ilizarov; femur; limb lengthening; radiologic assessment; regenerate; tibia.

Figure 1

Anteroposterior radiograph shows tibial bones of a patient with subjectively low height after Ilizarov limb lengthening of 9 cm. Proximal regenerate bone appears increased

Figure 2

Preoperative computed tomography scan of the left femur in a 16-year-old achondroplasia patient. Multiplanar reconstructions, cortical density measurement

Figure 3

Computed tomography scan axial cut of tibiae in a 51-year-old patient with subjectively low height after tibial lengthening of 7 cm. Cortical bone density measurement

Figure 4

Tibial cortical bone density 2–3 days of external frame removal and at a 1-year followup of limb lengthening in patients with different pathologies

Figure 5

Computed tomography and multiplanar reconstruction of the distractional bone regeneration and adjacent portions of the parent bone at the upper- and middle-third of the femur 12 months after frame removal in a 13-year-old patient with achondroplasia. Complete organotypical restructuring occurred, with cortical bone density being similar to preoperative values

Figure 6

Computed tomography scan of tibia in a 15-year-old patient with achondroplasia at 18-month followup. Axial cut made at the boundary of the upper- and middle-third of the left tibia, three-dimensional reconstruction, employing workstation hardware-enhanced filter, scheme for measuring local cortical bone density

Figure 7

Computed tomography scan of tibiae in a 16-year-old patient at 18-month followup; axial cut of the right tibia and cortical bone fragment in bone window. Cortical bone density in the point located at the central zone (osteonal layer) (measurement № 66) measured 1548 HU

Figure 8

Computed tomography scan of tibiae in a 16-year-old patient at 18-month followup; axial cut of the right tibia and cortical bone fragment after the usage of hardware-enhanced filter. Points are marked to measure osteonal density (Point 3), inner cortical bone – system of inner bone plates (Point 2), external layer – system of external cortical bone (Point 1). HU = Hounsfield units

Figure 9

Density of external, osteonal, and inner layers of the tibial cortical bone in achondroplasia patients at a long term followup. HU=Hounsfield units

Figure 10

Density of external, osteonal, and inner layers of the tibial cortical bone of intact limb in patients with unilateral pathology bone fracture, HU = Hounsfield units