Identifying skeletal growth patterns in children with unilateral fibular hemimelia

Fibular hemimelia is a rare congenital anomaly with an estimated incidence of 1:50,000 to 1:175,000 births. This disease entity causes deformity of the lower extremity affecting both the foot and long-bones, resulting in limb-length discrepancy. The disease spectrum is variable, ranging from mild to severe forms of the condition, with the most severe form requiring amputation. It is unilateral in 80% of the cases.¹

Limb lengthening with reconstruction is the preferred treatment for patients with mild-to-moderate leg length discrepancy and mild foot deformities. However, treatment strategy and timing are critical in success and future livelihood of these patients. An in-depth and comprehensive knowledge of skeletal growth and maturation patterns of this disease entity is paramount. Yet, these patterns have not been well characterized due to the disease rarity.

Radiologists at Boston Children’s Hospital conducted a retrospective study to establish the patterns of skeletal growth and maturation in children with unilateral fibular hemimelia. They verified the constant inhibition of growth that typifies this disease entity. Constant inhibition of growth is a process by which the length ratios between the shorter and longer limbs remain constant through growth.

This concept is widely utilized, but scientific data supporting this concept is sparce. Lead author Andy Tsai, MD, PhD, a pediatric musculoskeletal specialist, and colleagues detailed the skeletal growth and maturation patterns in children with unilateral hemimelia in a data-driven article published online September 28th in Pediatric Radiology.

The authors identified 23 children who had been treated over a 17 year period at Boston Children’s Hospital. The children ranged in age from 2.5 to 18.3 years for the 15 boys, and from 1.3 to 11.7 years for the eight girls. The children had between 2 to 11 scanograms performed during the study interval to measure their LLD, for a total of 115 scanograms for the 23 children. (Scanograms are often created by digitally stitching together three anteroposterior radiographs of the hips, knees, and ankles with a single ruler fixed along the long axis of each lower extremity separately.)

To assess the growth curves of these children, their femoral and tibial bone lengths were plotted against chronological ages and compared to the published reference growth standards Anderson, Messner, and Green.² The authors calculated the longitudinal length ratios between the shorter and longer limbs for both femurs and tibias to assess for constant inhibition of growth. To assess the skeletal maturation pattern, the authors plotted the estimated bone ages against chronological age, and compared them to published reference skeletal maturation standards of Greulich and Pyle.³

The authors found that the femoral and tibial growth curves for both the shorter and longer limbs had similar slopes and overall trajectories to the normal femoral and tibial growth curves. They reported that the percentage shortening of the shorter limb to the longer limb remained relatively constant throughout skeletal growth, in support of constant inhibition of growth. The estimated bone ages of these children followed their respective chronological ages, indicating normal skeletal maturation pattern.

The findings of the study support the Moseley straight-line graph method of predicting LLD for surgical management, a popular method published in 1978 that had been questioned by orthopedic specialists at Semmelweis University in Budapest, Hungary.^2,4  The authors stated that their research refuted the suggestion by the physicians at Semmelweis University that bone ages of children with unilateral fibular hemimelia are delayed between the ages of 4 to 6 years and advance from age 6 to maturity.

“Our study confirms the relatively normal growth curves of the lower-extremity long bones with constant inhibition of growth of the affected extremity, as well as normal skeletal maturation of children with unilateral fibular hemimelia,” wrote the authors. “These data lend further support to the customary approach of predicting ultimate limb-length and LDD - informing decisions for therapy timing in children.”

“It is imperative to understand the skeletal maturation pattern because growth and maturation are intimately related to each other. The skeletal growth pattern in these children needs to be fully characterized because it can affect treatment planning,” they added.

REFERENCES

1. Paley D. Surgical reconstruction for fibular hemimelia. J Child Orthop. 2016;10(6):557-583.
2. Anderson M, Messner MB, Green WT. Distribution of lengths of the normal femur and tibia in children from one to eighteen years of age. J Bone Joint Surg Am. 1964;46(6);1197-1202.
3. Gruelich WW, Pyle SI. Radiogaphic atlas of the hand and wrist. Palo Alto, CA: Stanford University Press, 1959.
4. Szoke G, Mackenzie WG, Domos G, et al. Possible mistakes in prediction of bone maturation in fibular hemimelia by Mosely chart. Int Orthop. 2011;35(5):755-9.
5. Tsai A, Kleinman PD, Laor T, et al. Lower-extremity growth patterns and skeletal maturation in children with unilateral fibular hemimelia. Pediatr Rad. Published online September 29, 2018. doi.org/10.1007/s00247-018-4263-0.