Abstract
We present the case of a fifteen-year-old achondroplastic (ACH) woman who requested to have her femurs lengthened by intramedullary nails. She had undergone bilateral tibial lengthening at the age of eleven and presented with a varus deformity of the right lower limb, lateral thrust of the right knee and valgus deformity of the left lower limb. We performed deformity analyses based on mechanical axis measurements, and we came with a staged surgical plan. In ACH adolescences, correction of bony deformity needs to encounter continuous fibula growth dynamics. Lateral knee thrust was corrected by gradual distal translation of the fibula head via an Ilizarov frame and the amount of translation we decided clinically. Tibial lengthening and valgus osteotomy of the distal femur accentuate lateral collateral ligament (LCL) complex laxity. In patients with ACH, tibial lengthening and valgus osteotomy of the distal femur—if needed—should precede LCL complex tightening, and femoral lengthening should follow.
Keywords: paediatric surgery, orthopaedic and trauma surgery, congenital disorders, healthcare improvement and patient safety, genetics
Background
Achondroplasia (ACH) is a rare disease of the skeleton exhibiting a prevalence of 1:26 000 live births.1 The incidence of axial malalignment of the lower limb in achondroplastics is relatively high (40%–60%)1 2 and mainly related to fibular overgrowth early during childhood and then again later during adolescence.
When lateral knee thrust coexists, it has to be managed carefully, considering the above facts, especially when the patient expresses the will to undergo limb-lengthening surgery.
Newer means for limb lengthening, like intramedullary (IM) nails, lengthen along the long bone’s anatomical axis, thus exaggerating any pre-existing bone deformity.
Prioritisation of correction surgeries is essential to avoid deformity relapse; therefore, patients need to be treated in centres of expertise to avoid undue complications.
Case presentation
A fifteen-year-old achondroplastic (ACH) woman presented to our clinic with the request to have her femurs lengthened by IM nails (PRECICE Intramedullary Limb Lengthening System, NuVasive, San Diego, USA). She was a de novo mutation of the Fibroblast Growth Factor Receptor (FGFR) gene, as there was no ACH history in the family.
At the age of eleven, she had undergone bilateral tibial lengthening of approximately 10 cm by the use of hexapods (Taylor Spatial Frame (TSF), Smith & Nephew, Tennessee, USA).
At presentation, she walked with an apparent lateral thrust of the right (Rt) knee, which was bowed (in varus), while the left (Lt) knee demonstrated valgus deformity. We studied her mechanical axis on the long leg (pelvis to feet) standing X-rays, and we recorded the sources of deformities (figure 1).
Figure 1.
Long leg (pelvis to feet) standing X-ray. Mechanical axis analyses for both limbs were performed, and the senior author recorded sources of malalignment. mLDFA, mechanichal Lateral Distal Femoral Angle; mLDTA, mechanichal Lateral Distal Tibial Angle.
According to Kopits,2 she demonstrated type C malalignment of both legs, with one major joint, on each side, out of alignment (the hips). Mechanical axis deviation (MAD) on the Rt side was 22 mm medial to the knee centre, and on the Lt side, it was 20 mm lateral to the knee centre.
There was a slight leg discrepancy, the Rt leg being longer by 12 mm than the Lt, and concomitant lumbar scolioses, with the convex on the Lt, partially fixed and partially postural.
She had no pain at walking but suffered from Rt knee instability and lateral gapping of the knee at the stance and also had difficultly climbing stairs.
The varus malalignment and lateral knee thrust of the Rt leg were multifactorial:
An overgrown fibula that was fixed distally to the tibia—during previous tibial lengthening—was now growing proximally. The fibula was pushing primarily the tibia and secondarily the ankle into varus.
Because the fibula’s head was moving proximally, it caused further laxity to the lateral collateral ligament (LCL), accentuating the lateral knee thrust.
The lateral knee thrust pre-existed to tibia lengthening, but it had worsened since the frames were removed (2 years before).
The Rt distal femur was in varus as well.
MAD on the Lt was due to valgus deformity of the distal femur. The Lt knee was stable.
A strategic surgical plan consisting of several stages was developed and discussed with the patient and the family.
The main aim was that the patient would suffer the least possible discomfort.
Correction strategy on the Rt side
We decided that correction of the Rt leg’s mechanical axis should precede any femur lengthening because the total amount of the deformity was already severe (32 degrees of varus and multifactorial aetiology) and would become uncontrollable during lengthening:
The Rt distal femur’s valgus osteotomy should precede LCL tightening because femoral correction would create additional LCL laxity.
The distal femoral correction would be acute3 and stabilised by a locking plate.
The tibial varus would be corrected together with the lateral thrust.
The LCL tightening on the Rt side would be gradual by translating the head of the fibula distally with the use of a circular Ilizarov type of frame. Tibia varus would be corrected simultaneously.
The distal ankle needed no correction once the fibula was osteotomised and shortened.
Correction strategy on the Lt side
The deformity on the Lt side—a distal femur valgus—was decided to be corrected following the lengthening because lengthening along the anatomical axis would accentuate the existing distal femur valgus. The distal femoral correction would be acute3 and stabilised by a locking plate at the end of lengthening.
Femoral bilateral lengthenings were to be performed using IM lengthening nails (PRECICE Intramedullary Limb Lengthening System, NuVasive). The starting lengths of the femurs were too short, so we decided to perform two lengthenings on each side, based on the available nails’ working lengths. At first, we performed 50 mm bilateral lengthening with 190 mm PRECICE nails, followed by an additional 80 mm with the 245 mm exchanged nails).
Investigations
Mechanical axis planning was performed on the long leg (pelvis to feet) standing X-rays, and we recorded the sources of deformities (figure 1).
On the Rt side, a total of 32 degrees of varus malalignment of the leg consisted of the following:
Fifteen degrees of varus deformity of the Rt distal femur (Rt lateral distal femoral angle (LDFA)=100 degrees).
Eight degrees of varus midshaft deformity of the Rt tibia.
Nine degrees of varus Rt ankle (Rt lateral distal tibial angle=99).
Lt side malalignment consisted of 13 degrees of valgus deformity of the Lt distal femur (Lt LDFA=75 degrees).
Additionally, there was a 12 mm discrepancy between legs with the Rt femur > Lt femur’s anatomical length:
Rt femur length=220 mm.
Lt femur length=208 mm.
LDFA=lateral distal femoral angle
LDTA=lateral distal tibial angle
Differential diagnosis
The phenotype and radiographic findings of ACH are distinctive. Hypochondroplasia can be differentially diagnosed from ACH due to its lack of craniofacial involvement and milder phenotypic changes in the spine and hands.
Treatment
Stage A
Corrective osteotomy of Rt distal femur and hexapod assisted plating was performed. A TSF hexapod (Smith & Nephew) was used during surgery to correct with precision the deformity (15 degrees of varus) as planned, and a locking distal femoral plate replaced it in theatre (figure 2A, B).
Figure 2.
(A) Anteroposterior X-ray of right (Rt) distal femur following the healing of distal femoral osteotomy and application of Ilizarov frame (stages A–B). (B) Lateral X-ray of Rt distal femur following the healing of distal femoral osteotomy and application of Ilizarov frame (stages A–B).
Stage B
Once the Rt distal femur’s osteotomy healed (4 months later), we proceeded with the tibial and fibular osteotomy and distal translation of the head of the fibula. We osteotomised the fibula and removed 10 mm from its distal diaphyses. We selected an Ilizarov circular frame that was separately fixing the tibia and fibula. Initially, the tibial deformity was corrected from hinges set at the deformity level on the frontal plane (figure 3A, B). The correction of the tibia was gradual, at 1 degree/day, and at the end of the tibial correction, we started to translate the head of the fibula distally. The amount of translation was determined by the clinical findings. The patient was walking full weight-bearing with no lateral thrust observed or any discomfort. The proximal fibula was then stabilised to the proximal tibia with two cannulated syndesmotic screws (figure 4A–C).
Figure 3.
(A) Anteroposterior X-ray of right (Rt) tibia with the application of Ilizarov frame in stage B. (B) Lateral X-ray of RT tibia with the application of Ilizarov frame in stage B.
Figure 4.
(A) Anteroposterior X-ray of right (Rt) tibia and fibula. The fibula has been translated distally and fixed with two cannulated screws proximally. Distal fibular fixation pre-existed. (B) Lateral X-ray of Rt tibia and fibula. The fibula has been translated distally and fixed with two cannulated screws proximally. Distal fibular fixation pre-existed. (C) Collage of anteroposterior X-rays (pelvis to midtibia), standing, showing all corrections at the end of stage B. mLDFA, mechanichal Lateral Distal Femoral Angle.
In retrospect, we measured the total amount of translation to be 20 mm.
Stage C
The first set of femoral lengthening was performed with the 190 mm PRECICE (NuVasive) nails, up to 50 mm, using the proposed standard technique (figure 5A, B).
Figure 5.
(A) Anteroposterior X-rays, standing, of the hips and femurs bilaterally with the first set of intramedullary nails in situ, at the end of stage C. (B) Photo of the patient’s lower limbs at the end of stage C.
Stage D
The second set of femoral lengthening was performed with the 245 mm PRECICE nails, up to 80 mm, using the proposed standard technique.
Stage E
Following the healing of both regenerates, we performed corrective osteotomy of the Lt distal femur by the use of 3-D planned and 3-D prefabricated cutting jigs (MyOsteotomy, Medacta, Switzerland), and the 13 degrees of varus osteotomy of Lt distal femur was fixed with a distal femur locking plate. The IM nail was removed on the same side at the same surgery (figure 6).
Figure 6.
Intraoperative X-ray of 13 degrees of varus osteotomy of the left distal femur and stabilisation plate (stage E).
Stage F
Removal of the nail on the Rt side and the Lt distal femur plate was planned on consolidation of the femoral osteotomy.
The patient received physiotherapy during every stage, twice a week but not in-between stages.
During the whole treatment, she received professional psychological support and developed unique coping mechanisms and determination.
Outcome and follow-up
It is now 3 years and 10 months since the osteotomy of the Rt distal femur (stage A) and 8 months following complete healing of the osteotomy of the Lt distal femur (stage E) (figure 7A, B).
Figure 7.
(A) Photo of the patient’s lower limbs at the end of stage E (bilateral double lengthening of the femurs and bilateral correction osteotomies). (B) Long leg (pelvis to feet) standing X-ray. Mechanical axis analyses for both limbs were performed. ×1–×2 and ×3–×4: knee and ankle joints, respectively, mechanical axis deviation (MAD) at the right ankle=12 mm lateral. mLDFA, mechanichal Lateral Distal Femoral Angle.
The patient walks without instability or pain. Limb lengths have been equalised, and there is an 8 mm discrepancy (Rt leg > Lt leg), which is anticipated by the fixed component of the lumbar scolioses. The patient felt very comfortable, and the longest admission time at any stage was 2 days. She tolerated the lengthening nails very well, and she was walking on crutches during the lengthening period.
Figure 7B depicts the outcome on the mechanical axis. The axis on the Rt side falls by 12 mm laterally (MAD=12 mm) at the Rt ankle joint and/or 8 mm medially (MAD=8 mm) at the knee joint level. MAD is mainly due to the 9 degrees of residual varus of the Rt ankle joint.
There were no significant complications apart from temporary knee stiffness following both distal femur osteotomies and the fibular head’s distal translation. All resolved within a reasonable time following physiotherapy.
Discussion
To prevent, treat and prioritise the management of knee deformities in ACH, we need to understand better the aetiology and the biomechanics of genu varum and accompanying disorders that develop under the same entity.
The incidence of axial malalignment of the lower limb in achondroplastics is relatively high (40%–60%), and a 17.3%–40% is reported to exhibit symptomatic malalignment that requires deformity correction.1 2 4 Kopits et al4 described four types of malalignment with increasing severity:
Normal parallelogram.
Bowleg deformity with good alignment.
One major joint out of alignment.
Two major joints out of alignment.
Several authors have studied genu varum with or without lateral thrust in the patient with with ACH, and it is concluded that it has a complex and multifactorial aetiology.5–7
Possible causes have been identified:
Irregular-slow endochondral ossification (intramembranous and periosteal are normal)6
Inappropriate differentiation of the growth-plate cartilage and uneven vascular invasion of the growth plate, which is cut off by a barrier of fibrotic cartilage and the bone.6
Laxity of the LCL.5
A differential growth rate between the tibia and fibula.5
Based on histological evidence, fibular overgrowth is the cause.6
A combination of overgrowth of the fibula and laxity of the LCL in juveniles and fibular overgrowth alone in adolescents.7
Tibial or femoral deformities or both.1
The fibula in humans may keep growing until the age of 20 years.8 The physes of the lower extremity in ACH close at about 14–15 years of age.7 The centre of ossification of the upper end of the human fibula fuses 2 years after fusion of the lower epiphysis, and this is a general mammalian characteristic.8 Inevitably, distal fibula in patients with ACH still grows until the age of 13 years, and proximal fibula may still grow until the age of fifteen.
In ACH, fibular growth may exceed tibial growth both proximally and distally and progresses rapidly at various ages,2 resulting in varus deformity within the tibia at variable sites.7 Therefore, any correction of bony deformity of patients with ACH needs to encounter continuous fibula growth dynamics. During previous bilateral tibial lengthening, both distal and proximal fibulae were fixed to the tibia in our patient. Distal fixation was performed with one syndesmotic screw bilaterally, and proximal fixation was performed via K-wires, stabilised on the TSF frames. When the frames were removed, at the age of eleven, proximal fixation was removed. On the Rt side, the fibula continued to grow mainly proximally—once it was distally fixed—and resulted in the LCL complex laxity’s accentuation. On the Lt side, things progressed naturally.
ACH deformity correction and limb lengthening
During tibial lengthening of patients without ACH, the posterolateral soft tissues and the fibular regenerate resist distraction and cause tibial valgus angulation following the proximal tibiofibular joint distraction as well as distal migration of the fibular head9 that is usually asymptomatic.10 11
In patients with ACH during childhood and adolescence, the opposite occurs. Fibula overgrows and pushes the tibia and distal tibial metaphyses into varus. If the distal fibula is fixed to the tibia—during tibial lengthening—and the patient is younger to 16 years of age, the proximal fibula may still keep growing following the end of lengthening and push the tibia into varus at several points.
Shyam et al9 showed that following tibial lengthening—of any patient—the distraction-resisting forces decrease during the consolidation period; the LCL–lateral complex–biceps–IT band (Ilio-Tibial band) (initially elongated) undergoes stress relaxation. It may result in lateral knee joint laxity and fibular head subluxation (delayed creep deformation).
For this reason, when performing limb lengthening in patients with ACH who are predisposed to or exhibit lateral knee laxity/thrust, we need to keep in mind that LCL laxity will possibly get accentuated following tibial lengthening. Therefore, we believe that lateral thrust correction should be performed either after or at the end of tibial lengthening.
When limb deformity and lateral thrust coexist, they produce the most significant amount of MAD per degree of angulation.1 Thus, when correcting lower extremity malalignment, the ligamentous component must be considered. Paley et al12 have shown that collateral ligament tightening is a safe adjunctive procedure to bony realignment surgery, resulting in a greater degree of correction for the same amount of surgery without significantly increasing the risks. We have shown that this technique can be applied to patients with ACH. The stabilisation of the LCL complex can be done gradually through the translation of the fibular head distally. The translation amount is decided on clinical grounds (stable walking without pain and the full range of knee motion).
The fibula should be transfixed to the tibia both distally and proximally with stable fixation (one or two syndesmotic screws) and followed up carefully for possible overgrowth. If this occurs, straightforward shortening of the fibula is enough to prevent deformity.
Alternative methods to control fibular overgrowth in ACH have been proposed, like early epiphysiodesis of the proximal fibular growth plate or late partial excisional osteotomy of the proximal fibula/fibular head to minimise the progression of the genu varum deformity in severe cases.5 6 However, Stanley et al7 have shown no adequate data to support epiphysiodesis of either proximal or distal fibular physis by now.
Patient’s perspective.
I am delighted with the final results. However, the operations were too many, and the recovery was consuming. There were adverse effects like joint stiffness, and I had to receive physiotherapy. Limb lengthening and deformity correction were the only effective treatment to increase my height and the quality of my life. The stitches do bother me because I think they will never fade away. As for the legs, the structure suffices to say that the proportions are even, giving the figure of normal limbs and specifically the ideal shaping that cannot be distinguished as modified. In conclusion, the advantages are more compared to the disadvantages. I will recommend it to everyone who wants a little bit of lengthening because he has the guts and the best specialised medical experts by his side, as I did.
Learning points.
In achondroplasia (ACH), fibular overgrowth results in varus deformity within the tibia at variable sites.
Correction of bony deformity of patients with ACH needs to encounter continuous fibula growth dynamics (15–20 years of age).
During reconstruction surgery in patients with ACH (deformity correction or lengthening), the fibula is reasonable to be transfixed to the tibia both distally and proximally with stable fixation.
Lateral knee thrust in patients with ACH is better corrected by gradual distal translation of the fibula head via an Ilizarov frame, and the amount of translation is decided on clinical grounds.
When limb lengthening is performed in patients with ACH, tibial lengthening and valgus osteotomy of the distal femur—if needed—are reasonable to precede lateral collateral ligament complex tightening, and femoral lengthening would follow.
Footnotes
Contributors: AD, GB and LK contributed substantially to the conception of the work as they are members of the Center of Rare Bone Diseases at Laikon Hospital, Athens, Greece. The center awaits nomination as Centre of Excellence for Rare Bone Diseases by the Greek Ministry of Health. AD performed the surgeries and the mechanical axis analyses and prepared the initial manuscript. They have all contributed to the acquisition of data and have critically revisited the work for important intellectual content. MP has worked on literature research and helped with the technical preparation of the manuscript and images. All authors have given final approval of the version to be published and agree to be accountable for all aspects of the work. AD is the corresponding author as well as the guarantor who accepts full responsibility for the finished work, had access to the data and controlled the decision to publish.
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests: None declared.
Provenance and peer review: Not commissioned; externally peer reviewed.
Ethics statements
Patient consent for publication
Parent/guardian consent obtained.
References
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