Bilateral humeral lengthening and deformity correction with hexapod external fixator in an achondroplastic patient: A case report

Abstract

Introduction and importance

Achondroplasia, a prevalent skeletal dysplasia, often results in limb asymmetry and functional limitations, typically managed surgically with bone lengthening techniques.

Case presentation

We present the case of a 10-year-old girl with achondroplasia who underwent bilateral humeral lengthening using hexapod external fixators. The patient, previously treated for lower limb lengthening, exhibited significant upper limb shortening affecting daily activities. Surgical intervention involved two stages, employing two hexapod external fixators for precise correction and lengthening. Symmetrical lengthening of 6 cm in both humeri was achieved without major complications. Follow-up assessments revealed improved functionality and satisfactory outcomes, emphasizing the importance of addressing upper limb deformities in achondroplasia patients.

Clinical discussion

While humeral lengthening is less common than lower extremity lengthening due to historical concerns about neurovascular complications and functional implications, recent advancements highlight its potential benefits, particularly in achieving functional and aesthetic balance.

Conclusion

This case highlights the efficacy and safety of hexapod fixators in achieving multiplanar correction and functional improvement in upper limb lengthening. Further investigation should be carried out to study broader application in similar cases.

Highlights

• •Humeral lengthening in achondroplasia provides functional and aesthetic balance.
• •Hexapod fixators achieve simultaneous bilateral lengthening and deformity correction.
• •Hexapod fixators seem to guarantee favorable outcomes while reducing discomfort.

1. Introduction

Achondroplasia is a skeletal dysplasia representing the most common form of rhizomelic dwarfism, with a prevalence of 1 in 20,000 live births. It primarily affects long bones (i.e., femur and humerus), causing proximal shortening and limb asymmetry while maintaining a normal chest and soft tissues growth that lead to redundancy of soft parts. This affects patients' functionality and quality of life and is usually surgically managed by bone lengthening techniques using external fixators [[1], [2], [3]].

Lengthening of the humerus is not as common a procedure as for other bones, due to the higher risk of neurovascular complications given the upper extremity's anatomy and the historic underestimation of the functional implications humeral shortening causes on achondroplasia patients. In recent years, an increasing number of professionals have highlighted the functional improvement achievable by bilateral humeral lengthening, along with a significant aesthetic and psychological improvement when attaining a proper balance between upper and lower limbs with the lengthening of all four extremities [4,5].

Over the years, new models of external fixation for bone lengthening based on Ilizarov's principles have emerged. The computer-assisted hexapod fixators allow the precise correction of deformities in up to six axes of space simultaneously without the need for changes in the fixator's arrangement but have been mostly used in lower limbs [3,6].

Herein, we present a pediatric achondroplasia case describing bilateral humeral lengthening achieved with two hexapod external fixators treated in a tertiary Spanish hospital.

2. Case presentation

This report describes the case of a 10-year-old girl diagnosed with neonatal achondroplasia who underwent a lower limb lengthening procedure two years prior, using hexapod circular external fixators on both legs for seven months. During a follow-up visit where we observed satisfactory clinical outcomes, she highlighted significant limitations in maintaining personal hygiene in the perineal area due to upper limb shortening and asymmetry compared to her lower limbs.

Control radiographs revealed symmetrical shortening of the proximal and middle segments of both upper limbs. The left humerus measured 14.7 cm, the left ulna 13.2 cm, and the left radius 11.6 cm. On the contralateral side, the right humerus measured 14.2 cm, the right ulna 13.2 cm, and the right radios 11.6 cm. Moreover, bilateral dislocation of the radial heads and a posterior apex deformity of 37° on the left and 30° on the right distal humerus' sagittal plane were observed (Fig. 1). These humeral deformities caused a lack of elbow extension for the patient. Magnetic resonance imaging revealed no other abnormalities, leading to the recommendation of bilateral lengthening.

Fig. 1.

Pre-treatment anteroposterior radiographs of both of the patient's upper extremities, where shortening can be observed.

A two-stage intervention was performed to conduct an osteotomy and place a TrueLok Hexapod System (TL-HEX™) (Orthofix S.R.L., Bussolengo, Verona, Italy) on both upper limbs, choosing this device as to lengthen the humerus and to correct deformities simultaneously. Surgical planification was carried out using the TL-HEX™ software, through which we inputted the osteotomy references concerning the rings in the three spatial planes.

In the first surgical stage, the left upper limb was intervened. Under general anesthesia and antibiotic prophylaxis with cefazolin 1 g, a hydroxyapatite pin was placed 30 mm lateral and distal to the proximal physis in the anterolateral part of the humerus, considering safety corridors in the upper limb as described by Ilizarov [7]. A proximal ring with a 120 mm diameter, opened medially, and a distal ring with a 120 mm diameter, opened anteriorly, were applied. A second hydroxyapatite pin was then placed at a 70° angle to the proximal one in the anterior part of the humerus, with special care taken to avoid the radial nerve. These steps were performed under radiographic control to prevent damage to vulnerable structures by using long pins. After positioning the struts, a third pin was inserted from lateral to medial at the lateral epicondyle in a slightly anterior direction to avoid the ulnar nerve, and a final pin was placed from posterolateral to anteromedial. An anterolateral incision was made distal to the proximal ring, and the osteotomy was again performed under radiographic control (Fig. 2a). Following the treatment planification, a latency period of 10 days was established from the intervention until the initiation of strut modification. Subsequently, correction proceeded at a rate of 1 mm/day with a maximum angulation of 0.8°/day, completing the correction at 51 days.

Fig. 2.

Anteroposterior radiograph of the TL-HEX™ assembly in two stages. A) Left upper extremity, positioned during the first surgical stage. B) Right upper extremity, positioned during the second surgical stage.

A month later, the same procedure was performed on the right upper limb, with a slightly less angular deformity compared to the contralateral side (Fig. 2b, Fig. 3). Correction was initiated after a latency period of 7 days, also at a rate of 1 mm/day, and it required 31 days to complete.

Fig. 3.

Patient during simultaneous bilateral humeral lengthening. A) Simultaneous bilateral humeral lengthening with two TL-HEX™ devices. B) The patient could perform arm flexion with the TL-HEX™.

After achieving symmetric bilateral lengthening of 6 cm in both humeri, the lengthening process was halted, and removal was scheduled after 4 months without incidents during the intervention. Consolidation outcomes are reported in Table 1. Active and passive shoulder and elbow mobility exercises were instructed, initially avoiding bearing weights.

Table 1.

Humeral consolidation outcomes.

	Consolidation index (day/cm)	Consolidation period (days)
Left	26.8	18.3
Right	21.8	13.3

At the two-month follow-up, radial head dislocation and a slight elbow flexion were evident (Fig. 4). Despite this, the patient reported satisfactory functional outcomes with joint mobility allowing autonomous personal hygiene, which remained consistent in the subsequent reviews. Regarding the occurrence of complications during or after surgery, none have been reported seven months after the removal of the hexapod fixators.

Fig. 4.

Post-treatment anteroposterior radiograph of both of the patient's upper extremities.

The work has been reported in line with the SCARE criteria [8].

3. Discussion

Upper limb shortening in achondroplasia patients is often combined with notable asymmetry relative to their lower limbs, resulting in significant limitations in performing daily activities such as maintaining personal hygiene, dressing, or rising from a chair. These challenges ultimately contribute to the psychological burden associated with this condition. Bilateral humeral lengthening is accepted for cases of achondroplasia or other genetic malformations not only for the aesthetic benefits it provides but also for the functional ones, with no contraindication for simultaneous lengthening [4,5].

Historically, humeral lengthening was performed with circular external fixators. In their series of bilateral humeral lengthening in ten achondroplasia patients, Kashiwagi et al. (2001) [4] reported that despite the occurrence of complications, circular fixators allowed for improvement in function and proportion of the upper limbs, while Hosny et al. (2016) [5] verified their effectiveness in correcting shortening, rotation, and angulation. However, circular fixators may prove too uncomfortable for achondroplasia patients due to their bulky size compared to their shortened limbs, although they can be more tolerable for patients by using 5/8 rings. In recent years, monolateral fixators are often chosen, whose smaller size allows for simpler implantation for the surgeon and greater comfort for the patient. Nevertheless, not all of them can be used for multiaxial deformity corrections, which are unfortunately common in achondroplasia [3,6].

Hexapod fixators address this issue by allowing multiplanar correction and reducing the discomfort by using open rings medially, which do not force the patient to maintain perpetual arm abduction. Additionally, they are unique in allowing the management of any deformity that may arise during treatment without the need to reposition any fixation elements, simply by readjusting through the software. In recent years, some cases have been described using hexapod fixators to correct upper limb deformities in children. Although none specifically for achondroplasia patients, Al-Sayyad et al. (2012) [6] demonstrated its effectiveness in correcting upper limb deformities. However, most literature on hexapod fixators focuses on their use in lower limbs, which aligns with the general tendency to prioritize lower extremities due to their weight-bearing nature and influence on gait.

Regarding the lengthening and consolidation results in our patient, they appear to be similar to those reported in the patient series by Ko et al. (2019) [9] and Pawar et al. (2013) [10], who used monolateral fixators and achieved a consolidation index of 27.2 and 32 day/cm, respectively, compared to our 21.8 and 26.8 day/cm for the left and right humeri. As for complications related to humeral lengthening, they typically include pin site infection, nerve injuries—especially radial nerve injuries—and, with lower prevalence, non-unions and post-treatment fractures [3,11,12]. In our case, the patient did not experience any complications throughout the treatment period.

To our knowledge, this is the first reported case of bilateral humeral lengthening using hexapod external fixators in achondroplasia patients. Based on this positive experience, we believe that the use of the hexapod frame is a safe and reproducible technique. However, further studies should be conducted to obtain robust results.

Parental consent

Written informed consent was obtained from the patient's parents/legal guardian for publication and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Ethical approval

Not required, since the article depicts clinical practice not constituted as research by the IRB of Hospital Universitario 12 de Octubre.

Funding

None.

Author contribution

Methodology: José María García López, Juan Carlos García de la Blanca, Rafael Martí Ciruelos, Guillermo Núñez Ligero; Formal analysis: José María García López, Juan Carlos García de la Blanca; Validation: Rafael Martí Ciruelos, Guillermo Núñez Ligero; Investigation: José María García López; Writing – original draft: José María García López; Writing – Review & Editing: Juan Carlos García de la Blanca, Rafael Martí Ciruelos, Guillermo Núñez Ligero.

Guarantor

All authors.

Research registration number

N/A.

Conflict of interest statement

Juan Carlos García de la Blanca has worked as a medical consultant for Orthofix S.R.L.