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16th Mar 2021

Kiernan, D et al. 2021 has recently published a paper on "Lower limb biomechanics during gait in children with Achondroplasia". Based on the current literature it is difficult to fully understand how gait in children with achondroplasia is altered compared to the general peer population. There are few studies in the field of biomechanics and kinematic on abnormalities in the mobility of children with achondroplasia, especially in regard to the availability of 3-dimensional data.
But before we proceed, is important to know:

What is Biomechanics?
The term biomechanics combines the prefix bio, meaning "life," with the field of mechanics, which is the study of the actions of forces. The international community of scientists adopted the term biomechanics during the early 1970s to describe the science involving the study of the mechanical aspects of living organisms.

What is Kinematics?
Kinematics is a branch of physics and a subdivision of classical mechanics concerned with the geometrically possible motion of a body or system of bodies without consideration of the forces involved (i.e., causes and effects of the motions).


What is still to be understood?

Cases studies in the late 1990s and early 2000s have presented varied results and shown to have limited data2,3,4. And more recent studies indicated differences, showing that subjects with achondroplasia were reported to have greater overall involvement compared to the general population and a more flexed position throughout gait for the lower limbs 5,6.

 

Another point that needs to be addressed is that it would not be prudent to assume that kinematics is similar in adult and in the pediatric groups, thus, using published adult data as a reference for treatment planning in children is not indicated 1, as kinematics may differ between younger and older individuals with achondroplasia, particularly with respect to frontal plane kinematics.

It is of crucial importance to develop studies that allow a thorough understanding of gait in children with achondroplasia.

Recently, Dr. Damien Kiernan (Movement analysis Laboratory - Central Remedial Clinic, Dublin) published the results of a 3-dimensional kinematic evaluation study1 of the differences between children with achondroplasia and the general peer population regarding lower limb movement during gait. A retrospective data analysis was conducted over a 20-year period. 



Study Method and Results

 

A full 3-dimensional kinematic analysis (click here for the study’s protocol) was performed in 8 children with achondroplasia and 32 average height children. Children walked unassisted at a self-selected pace with one representative trial analyzed for each child. Data were collected and analyzed using the software. Anthropometric and clinical examination data were also recorded for each subject.

 

Results found in children with achondroplasia, compared to the average height children were as follows:

 

  • Increased anterior pelvic tilt and increased hip flexion (Fig. 1)
pelvic tilt hip abduction

  • Increased flexed knee position during mid-to-late stance and an increased dorsiflexion at the late stance and throughout swing (Fig. 1)
  • Increased hip abduction (Fig. 2)
  • Increased foot supination in the coronal plane (Fig. 2)
supination


  • In contrast to previous studies, increased knee varus was not an issue for the children in this study (Fig. 2)
knee varus

  • Increased pelvic rotation during very early stance and late stance (Fig. 3)
Pelvic Rotation No Spine

  • Increased external hip rotation (Fig. 3).





fig1 3Dgait
Fig. 1. Red solid line and red band: Children with Achondroplasia Mean ± 1SD; Black solid line
and grey band: Children with Typical Development Mean ± 1SD. Red vertical line:
Toe-Off for children with Achondroplasia. Black vertical line: Toe-Off for children with Typical Development.


fig2 3Dgait
Fig. 2. Results of SPM{t} two-sample t-test for coronal plane kinematics. Red solid line and red band:
Children with Achondroplasia Mean ± 1SD; Black solid line and grey band: Children withTypical Development Mean ± 1SD.
Red vertical line: Toe-Off for children with Achondroplasia. Black vertical line: Toe-Off for children with Typical Development.


fig3 3Dgait
Fig. 3. Results of SPM{t} two-sample t-test for transverse plane kinematics. Red solid line and red band:
Children with Achondroplasia Mean ± 1SD; Black solid line and grey band: Children with Typical Development
Mean ± 1SD. Red vertical line: Toe-Off for children with Achondroplasia. Black vertical line: Toe-Off for children with Typical Development.



Based on the analysis of the differences during gait between children with achondroplasia and age matched controls, this study provides a comprehensive baseline for planning rehabilitation strategies and help to target deficits in functional capacity in children with achondroplasia. The author stresses the importance to consider these findings when discussing treatment in children with achondroplasia, whether for AFOs (ankle-foot orthosis) or strengthening or otherwise.



References:

 

  1. Kiernan, D. 2021. Lower limb biomechanics during gait in children with Achondroplasia, J. Biomech V 119.
  2. Inan, M. et al, 2006. Dynamic lower extremity alignment in children with Achondroplasia. J. Pediatr. Orthop. B 26, 526–529.
  3. Rethlefsen, S., Tolo, V., 1998. Gait analysis before and after tibial osteotomy in Achrondroplasia. Gait & Posture 7, 174–175.
  4. Egginton, R., et al, T. 2006. Kinematic characteristics of Achondroplasia. Gait & Posture, 24, S249-S250
  5. Sims, D.T., et al, 2019. A quantitative description of self-selected walking in adults with Achondroplasia using the gait profile score. Gait Posture 68, 150–154.
  6. Sims, D.T., et al, 2020. A spatiotemporal and kinematic description of self-selected walking in adults with Achondroplasia. Gait Posture 80, 391–396.
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