Achondroplasia
The most significant advancement in recent years for patients with achondroplasia is the pharmacological treatment option through Vosoritide, which inhibits the pathological function of the mutated FGFR3 receptor to allow physiological endochondral ossification.
An additional annual height gain of 1.57 cm has been observed in the initial randomized controlled trial, with safe and persistent growth after 2 years.
Savarirayan R, Tofts L, Irving M, et al. Once-daily, subcutaneous vosoritide therapy in children with achondroplasia: a randomised, double-blind, phase 3, placebo-controlled, multicentre trial. Lancet 2020; 396(10252): 684–692.
Savarirayan R, Tofts L, Irving M, et al. Safe and persistent growth-promoting effects of vosoritide in children with achondroplasia: 2-year results from an open-label, phase 3 extension study. Genet Med 2021; 23(12): 2443–2447.
Regarding angular deformity correction, studies have shown that eight plates reliably correct genu varum in achondroplasia. Starting with guided growth at an early age (average: 6.5 years), it reduces the need for later corrective osteotomies.
Ulusaloglu AC, Asma A, Silva LC, et al. Growth modulation by tension band plate in achondroplasia with varus knee deformity: comparison of gait analysis measurements. J Pediatr Orthop 2023; 43(3): 168–173.
Makarewich CA, Zhang E and Stevens PM. Hemiepiphysiodesis for lower extremity coronal plane angular correction in the distal femur and proximal tibia in children with achondroplasia. J Pediatr Orthop 2023; 43(8): e639–e42.
Height Gain Expectations with Surgery
Expectations are very good; achondroplasia with rhizomelic limb shortening is the most common form of dwarfism in humans, with an estimated prevalence of 3 to 5 per 100,000 births. Interestingly, bone lengthening in these patients shows high success rates due to excellent bone formation. Soft tissues are redundant, and joints are stable enough. In contrast, congenital hypoplasias such as hemimelias and congenital femur deficiencies represent the most challenging pathologies to lengthen.
Bone Growth Protocol for Height Surgery in Achondroplasia
When planning height increase treatment (total length gain of 20-30 cm in adulthood) for a patient with achondroplasia, different stages are scheduled. This is generally achieved first with a simultaneous bilateral femur lengthening of 5 to 8 cm using a monorail external fixator (LRS recommended) at the age of 3 to 4 years and a second simultaneous bilateral tibial lengthening of 5 to 7 cm using an external fixator (hexapod circular recommended) before patients begin their first year of school.
Subsequent simultaneous bilateral lengthenings of the femurs and tibias with a target of 5 to 7 cm per segment are scheduled between 12 and 15 years of age.
Intramedullary lengthening nails are planned once the bone size is suitable for the available implants. The timing of the last lengthening is left to the patients’ and families’ preferences based on their individual situation, but not before the age of 8 for girls and 10 for boys.
If patients decide to lengthen the humerus due to functional impairments related to daily activities and perineal hygiene, this is generally performed bilaterally between the ages of 6 and 10, with the goal of achieving an 8-10 cm lengthening.
Limb lengthening to increase average adult height and minimize functional impairment during daily life is a topic of debate.
Currently, global bone segment lengthening is the only effective treatment that allows normalization of limb size in individuals with achondroplasia, improving limb alignment and reducing functional limitations associated with skeletal deformities. It provides individuals with a body height that allows them to overcome physical and architectural barriers, reduce their level of disability, and improve their social development and integration.
If patients and their families wish to undergo limb lengthening, a thorough evaluation must be conducted with all parties involved to discuss the potential short- and long-term benefits and complications of such treatment. If a significant height increase is strongly desired, repeated limb lengthening, including simultaneous lengthening of the lower leg and femur, can be performed.
At Bone Growth, we advocate for meticulous clinical and radiographic monitoring to detect and promptly address common complications such as joint stiffness and premature consolidation. Limb lengthening in patients with achondroplasia is a treatment that addresses only one feature of this complex condition. The potential long-term side effects of lengthening and its physical and psychosocial impact remain unclear. Comprehensive counseling should prioritize limb deformities and monitor possible spinal complications, with lengthening as an option only if explicitly requested by patients and their families.
