Principles of Lower Extremity Deformity Correction in Children
Techniques change, but principles are forever. The techniques used to correct lower extremity deformities in children should be based on the principles of assessment and management of those deformities. This writing provides an introductory perspective lecture on the principles of deformity correction. The principles discussed here are based on a much larger set of principles of assessment and management of foot deformities in children.1
To begin with, definitions are in order. The terms deformity and malformation are often used interchangeably, yet they are not synonyms.1 A deformity is a congenital or acquired angular and/or rotational misshapenness of a bone, or a malalignment of bones at a joint. Examples of deformities include developmental hip dislocation, coxa vara, genu valgum, knee flexion contracture, congenital postero-medial bowing of the tibia, ankle valgus, ankle equinus, clubfoot, cavovarus foot, and congenital hallux varus. A malformation (Fig. 1) was “made wrong,” not just crooked, rotated, or malaligned. Categories of malformations are: (1) too large, (2) too small, (3) too many, (4) too few, and (5) failed to separate (syndactyly, synostosis). Examples of malformations include proximal femoral focal deficiency, cruciate ligament deficiency, fibula and tibial hemimelia, congenital subtalar synostosis (with ball-and-socket ankle malformation), cleft foot, first metatarsal longitudinal epiphyseal bracket, and polydactyly. Malformations may also be deformed. Examples of maldeformations include congenital short femur with coxa vara, subtalar synostosis with translational valgus of the hindfoot, fibula hemimelia with antero-medial tibial bowing, first metatarsal longitudinal epiphyseal bracket with hallux varus, preaxial polydactyly and first metatarsal longitudinal bracket epiphysis with hallux varus. Deformities can be reconstructed, whereas malformations need to be constructed.
It is important to differentiate deformities from age-related anatomic variations in shape. The natural history for physiological, spontaneous correction of anatomic variations in shape trumps intervention every time, particularly surgical intervention.
Examples of age-related anatomic variations are well known. Most babies are flatfooted; approximately 25% of adults are flatfooted.2 Many babies have metatarsus adductus; very few adults have metatarsus adductus.3 Most babies are bow-legged and most toddlers are knock-kneed; most adults have parallel lower extremities.4 Most children in the first decade of life have femoral anteversion; most adults have mild femoral retroversion.5
One must resist the temptation to change the normal physiological shapes of the lower extremities in children to those of adults rather than waiting for them to change spontaneously through normal growth and development.
Before treating a deformity, one must know the natural history of the deformity in regard to pain and/or functional disability. Does the deformity just look different or does/will it cause pain and/or functional disability?
It is critical that physicians who are poised to “treat” flatfoot “deformity” are aware of the conclusive evidence that flatfeet are normal and not a cause of pain or disability in most affected individuals of all ages.2,6 Those physicians must also be aware that it is not known whether any specific degree of angular deformity of the lower extremities, that is, genu varus or valgus, necessarily causes long term pain or disability. And they must know that rotational deformities, that is, femoral or tibial torsion, have not been shown to necessarily cause degenerative arthritis7 though, beyond a certain degree, they may cause functional disability.
A core principle of deformity correction is that one should correct a deformity at the site of the deformity, whenever possible.8 To correct a deformity at the site of deformity, one must accurately identify the site. The CORA method8 (Fig. 2) is the best tool for identifying the site(s) of deformity in long bones. The foot-CORA method1 (Fig. 3) is the best tool for identifying the site(s) of deformity in the foot.
When correcting an angular deformity in a long bone at the site of deformity, that is the CORA, use an opening or closing wedge osteotomy. When correcting angular deformity away from the site of deformity (because there are occasionally related or unrelated anatomic reasons that mandate it), use opening or closing wedge osteotomies and translation of the bone fragments. Correct both joint orientation and mechanical axis. Many limb deformities in children are located at the physes and can be corrected with guided growth techniques.9 These techniques are generally easy, safe, and reliable. Expect some recurrence of deformity following removal of guided growth implants, so slightly over-correct the deformities before removing the implants.
The principles of deformity correction in the foot require a full understanding of the uniqueness of foot deformities, as elucidated by the foot-CORA method.1 The long bone CORA method and the foot-CORA method both accurately identify the site(s) of deformity. However, the implications of that information in regard to deformity correction differ between the 2 methods. As stated above, the long bone CORA method identifies the site(s) of deformity, which is(are) also the site(s) of deformity correction. The foot-CORA, particularly in hindfoot deformities, identifies the site of deformity, but may not be the site of deformity correction. In fact, the site of deformity correction may not be in the bone that contains the foot-CORA.1
There is a specific set of principles for juxta-articular angular deformity correction with internal fixation.1
- Obtain control of the small and oddly-shaped juxta-articular fragment with an internal fixation device (wires or plate and screws) before the osteotomy is performed. It is nearly impossible to determine the orientation of the juxta-articular fragment after the osteotomy is performed without the orientation provided by a previously inserted internal fixation device.
- In the lower leg, cut the fibula in the proper oblique plane for tibial deformity correction. A fibula osteotomy in the wrong plane will impede tibial deformity correction or lead to a delay in fibula healing.
- Except in the proximal femur, make the first osteotomy parallel with the adjacent joint.
- Make the second osteotomy perpendicular with the mechanical axis of the limb, which is the anatomic axis of the tibia (and always easy to visualize), and 6 degrees abducted from the anatomic axis of the femur. This combination of osteotomies will prevent undesired deformity creation if rotation is added to the angular deformity correction. The alternative approach is to make the first and only osteotomy as described in bullet point #3 and align the corner of the convex cortex of the shaft fragment with the medullary canal of the juxta-articular fragment.
These are only a few of the principles of lower extremity deformity correction in children but, I believe, are the most important.
Finally, recall the aphorism that “techniques change, but principles are forever. Therefore, study principles.”1
1. Mosca VS. Principles and Management of Pediatric Foot and Ankle Deformities and Malformations. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins; 2014.
2. Mosca VS. Current concepts review: flexible flatfoot in children and adolescents. J Child Orthop. 2010;4:107–121.
3. Cappello T, Mosca VS. Metatarsus adductus and skewfoot. Foot Ankle Clin. 1998;3:683–700.
4. Salenius P, Vanka E. The development of tibiofemoral angle in children. J Bone Joint Surg Am. 1975;57:259–261.
5. Staheli LT, Corbett M, Wyss C, et al. Lower-extremity rotational problems in children. Normal values to guide management. J Bone Joint Surg Am. 1985;67:39–47.
6. Harris RI, Beath T. Army Foot Survey: An Investigation of Foot Ailments in Canadian Soldiers. Ottawa, ON: National Research Council of Canada; 1947.
7. Hubbard DD, Staheli LT, Chew DE, et al. Medial femoral torsion and osteoarthritis. J Pediatr Orthop. 1988;8:540–542.
8. Paley D. Principles of Deformity Correction. Berlin: Springer-Verlag; 2002.
9. Stevens PM. Guided growth for angular correction: a preliminary series using a tension band plate. J Pediatr Orthop. 2007;27:253–259.
Keywords:Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.
deformity correction; deformity principles; children's deformities