13.16 Developmental deformities of the lower limbs

There are a group of rare angular deformities of the lower limbs such as coxa vara, congenital dislocation of the knee, tibia vara, and two types of tibial bowing, posteromedial and anterolateral, that may present at birth or at walking age. All can lead to problems with function in the long term; and all but one (posteromedial bow) deteriorate without intervention.

Infantile coxa vara is a rare condition that causes the femoral neck-shaft angle to be reduced (<125 degrees), associated with a characteristic defect in the femoral neck (Figure 13.16.1).

The quoted incidence is 1:25 000 births. However, the condition is not evident at birth and although often noticed when the child begins walking, in half of the cases it is not recognized until age 5 years. There is an equal sex distribution, little geographical variation and, in up to a third of cases, both hips are affected.

Radiographically, the normal neck shaft angle increases from 130 degrees in the newborn to 145 degrees by 1 year of age. It then decreases to 125 degrees by adulthood. Microscopically, the femoral neck physis is typical of other long bone growth plates.

Radiographs show a decreased neck-shaft angle (typically 85–115 degrees initially) and a short femoral neck but with a normal head and a straight shaft. In 25% hips the neck–shaft angle worsens with time. There is a characteristic triangular osseous fragment (Fairbanks’ triangle) at the inferomedial corner of the metaphysis (Figure 13.16.1) and abnormal irregular ossification of the femoral neck metaphysis. The physis is wide and vertical with disturbance of the normal cellular organization. The affected growth plate closes early, usually at the age of 10 years.

Infantile coxa vara should be differentiated from other causes of coxa vara, including congenital dysplasias and acquired abnormalities (Box 13.16.1).

A limp is noticed as the child begins to walk or in early childhood. Children may complain of stiffness after resting and pain after walking.

Examination identifies a short leg with a high trochanter. Hip abduction is significantly reduced but the adduction range is maintained. There is often a fixed flexion deformity of the hip associated with a lumbar lordosis. The poor lever-arm of the hip abductors leads to a Trendelenburg gait.

Pelvic x-rays show the characteristic features outlined earlier. Imaging of other bones may be needed to rule out a generalized skeletal dysplasia. Two radiographic lines are commonly used to assess the deformity the neck–shaft angle and the Hilgenreiner–epiphyseal (HE) angle (Figure 13.16.2). Both angles may be affected by lower limb rotation.

In some cases of isolated coxa vara, computed tomography (CT) studies have shown a decrease in the physeal–femoral neck angle (as seen in adolescent slipped capital femoral epiphysis). The epiphysis and attached triangular fragment slip from the normal superoanterior portion of the neck in an inferioposterior direction. Often, in severe congenital coxa vara, there is a marked femoral retroversion.

Magnetic resonance imaging (MRI) studies in patients with congenital coxa vara reveal a widened growth plate with expansion of cartilage mediodistally between the capital femoral epiphysis and metaphysis but do not identify a true slip.

Histological studies have found the growth plate is made of few irregularly distributed germinal cells. Similar changes found in the growth zone of the iliac bone seem to indicate that the ossification disturbances are multifocal.

If the neck-shaft angle is less than 110 degrees, coxa vara tends to worsen with time. Hips with HE angles less than 45 degrees will usually correct spontaneously without surgery. Those with HE angles of 45–60 degrees represent a ‘grey zone’ and should be observed. However, progression of deformity is the rule if the HE angle is greater than 60 degrees. Progression is often accompanied by other problems such as a pseudarthrosis at the site of the defect, leg length differences, mechanical axis deviation, and rotational deformity. There are associated dysplastic changes in the acetabulum.

The indications for surgery are a Trendelenburg gait and a HE angle greater than 60 degrees, or evidence of progressive deformity. The conventional operative procedure is a valgus extension proximal femoral osteotomy, as described by Pauwels. The aim of surgery is to correct varus to a HE angle less than 45 degrees, equalize leg lengths, and normalize abductor muscle length. However, these operations are often technically difficult and may lead to joint stiffness without sufficient correction of the coxa vara or associated deformities.

The valgus osteotomy may be combined with a greater trochanter epiphysiodesis or trochanteric advancement if the trochanter is high. Circular fixators can also be used to correct the deformity.

In some series recurrence rates of up to 50% are seen following a valgus extension osteotomy. However, when the HE angle is well-corrected (<38 degrees), the recurrence rate is only 5%. If deformity correction is achieved and maintained before age 10 years, 87% of children have excellent acetabular depth, spherical congruency, no pain, and a correction of Trendelenburg gait in the short to medium term. The triangular defect closes within 6 months of surgery.

Premature capital femoral physeal closure is frequent, leading to relative overgrowth of the greater trochanter and, in unilateral cases, unequal leg lengths. The leg length discrepancy is sufficient to require treatment in 40% of cases, usually with contralateral epiphysiodesis.

This spectrum of hyperextension disorders of the knee includes congenital genu recurvatum (CGR) and congenital dislocation of the knee (CDK) (Figure 13.16.3).

The incidence is estimated to be 2:100 000 with equal sex distribution.

Cadaver studies of neonatal knees demonstrate that 5–15 degrees of hyperextension is normal which could be increased by 10 degrees with prolonged pressure. By 3 months, fixed flexion of 5 degrees develops. Extension can be achieved with prolonged pressure but at this age, hyperextension does not occur.

Knee hyperextension greater than 30 degrees is demonstrated with associated limited flexion. There are two groups: those involving anomalies of the elastic tissues and those with a postural deformity secondary to intrauterine problems. In 60% of children with CGR/CDK there are other anomalies, including hip dysplasia, foot deformities, cleft lip and palate, chest wall deformities, and elbow dislocation. CDK is commonly seen in conditions such as arthrogryposis, spina bifida, and syndromes associated with joint laxity, such as Down syndrome. The combination of CDK or joint laxity with other malformations should raise the possibility of a chromosomal abnormality.

At operation, an absent cruciate ligament is a common finding. Other aetiological theories include fetal molding or quadriceps contracture.

The classification system by Leveuf and Pais (1946) has been used to determine management. Essentially these types are: hyperextension of the knee, anterior subluxation of the tibia, or anterior dislocation of the tibia (Table 13.16.1) (Figure 13.16.3).

The diagnosis is usually obvious at birth: 30% are associated with a breech delivery.

The knee appears ‘back to front’ (Figure 13.16.4). There is a deep anterior skin fold and the femoral condyles are easily palpable in the popliteal fossa. The patella is deep and often difficult to feel. As the child lies flat, the hyperextension tends to externally rotate the leg giving an impression of valgus.

The diagnosis may be made on antenatal ultrasound. After birth, ultrasound can be used to follow the progress of the condition; radiographs are less helpful due to the cartilaginous nature of the neonatal knee joint.

As the deformity is often very striking in the newborn, the parents need prompt reassurance that most children can be treated successfully by conservative means. The aim of treatment is to gain a range of movement adequate for activities of daily living. Other associated conditions such as developmental dysplasia of the hip and talipes equinovarus should be treated as appropriate: most authors suggest that the knee be treated first. The presence of associated deformities, delay in treatment, and generalized joint laxity adversely affect the prognosis.

Immediate reduction or serial casting should be tried when the patient is seen within the first week or so of life. In the infant, it is important to ensure that the manipulation and casting is performed in the correct direction: the limb lies in external rotation and there is a tendency to ‘flex’ the knee into valgus. The deep anterior skin crease helps in orientation of the limb. Flattening of the tibial plateau and anterior bowing of the tibia is common after prolonged conservative treatment but remodels eventually. If the patient is seen late and serial casting proves to be unsuccessful, traction in the Bryant position or in a prone position should be used for 1–2 weeks, and then gentle closed reduction of the CDK can be tried with or without anaesthesia.

Not all children respond to serial casting. Those with fibrous changes in the quadriceps muscles often require operative treatment, (10–50%). This is performed with an arthrogram to assess the knee, a V–Y plasty of the quadriceps and anterior release of the adherent capsule. This allows the collaterals, the iliotibial band, and the hamstrings to return from the extensor to the flexor side of the knee axis. Intraoperatively the aim is to achieve 90 degrees of flexion and this is maintained with a cast in 90 degrees of flexion for 6 weeks. An operation at age 9 months appears to be optimal, enabling the children to walk and function normally.

Non-operative correction appears to be most effective if it starts immediately after birth. This may restore complete function and joint range, although some children may lack full flexion.

In patients with valgus alignment and hyperlaxity, ongoing bracing or even a corrective osteotomy may be required. Selected patients may benefit from transposition of the pes anserinus and the tibial insertion of the medial collateral ligament to reinforce the medial aspect of the knee joint.

Good results are more difficult to achieve in children with Larsen’s syndrome and arthrogryposis: conservative treatment usually fails and operative treatment may need to be more aggressive. Indications for surgery need to be considered carefully.

Infantile tibia vara is characterized by an acute varus angulation of the tibia just below the knee joint, secondary to disturbance of the posteromedial proximal tibial physis (Figure 13.16.5). This is a multiplanar deformity with proximal tibial varus, procurvatum, and internal torsion (Figure 13.16.6).

The condition is most commonly known as Blount’s disease as Blount described the first series of cases, although he acknowledged that Erlacher described it first in 1922. He also described a similar deformity in adolescence that is considered a different disorder (as are two other types: late onset tibia vara and fibrocartilagenous dysplasia).

This condition is rare and never seen until walking age. It is more common in girls, early walkers, and children with obesity. There is a significant relationship between the magnitude of obesity and biplanar radiographic deformities especially those children with a body mass index higher than 40. The two population groups who appear to be particularly susceptible are African Americans and Scandinavians.

The normal lower limb alignment of a child under the age of 2 years is of knee varus (‘bow-legs’) that normally progresses to maximum knee valgus (‘knock-knees’) by the age of 5 years see (Chapter 13.10).

If a child walks early, whilst they are in varus alignment, their mechanical axis will fall medial to the knee and put pressure on the medial growth plate. If there is excessive varus or excessive force (related to body mass) going through the medial growth plate then this may damage the growth plate. There is also tension on the convex side. According to the principles of Heuter, Volkmann, and Delpech, this encourages increased growth laterally. In turn this leads to a positive feedback phenomenon of worsening varus deformity, leading to even further force medially.

Histological examination of tibia vara in 6–7-year-olds shows widening and depression of the medial growth plate, small and deep intrusions of cartilage into the metaphysis, oedema of the medial tibial epiphysis, medial and lateral metaphysis; widening of the lateral growth plate, hypertrophy of the medial meniscus and focal bone bridging. Patients with infantile tibia vara have normal alignment of the distal femur unlike adolescent tibia vara.

Langenskiöld described a classification system that is based on stages of progression with age, not prognosis. The stages, from I to VI, show progressively increasing deformity with bone bridge formation between the tibial epiphysis and metaphysis (see Figure 13.16.6).

Many young children are referred to orthopaedic clinics with bowlegs. Predicting whether these deformities will progress can be challenging. There is no consensus as to whether children with radiographic medial tibial beaking should all be classified as having Blount’s disease.

As noted earlier these children have varus alignment of one or both knees, and are often obese. A differential diagnosis must be considered (Box 13.16.2).

Radiographs of the knees show the deformity with medial tibial depression and beaking progressing onto physeal bridging, as described by Langenskiöld.

Levine and Drennan described the tibial metaphyseal-diaphyseal angle (TMDA) (Figure 13.16.7). An angle greater than 11 degrees can distinguish between physiological and pathological varus. Subsequent work shows that there is a grey area between 9–16 degrees, where there is some overlap between physiological and pathological. The epiphyseal–metaphyseal angle (EMA) is also helpful under the age of 3 years. Children with TMDA above 9 degrees and EMA over 20 degrees are at greater risk for Blount’s disease and should be followed closely. A combination of a body mass index higher than 22 and a TMDA greater than 10 degrees has a high predictive value for tibia vara in children between 2–4 years.

MRI has been used to confirm the pathological changes and to plan surgical management (Figure 13.16.8B).

Bracing (knee–ankle–foot–orthoses, KAFOs) has been used for children with a significant degree of varus before the age of 3 years. There is an overlap between toddlers with a marked physiological varus and those with a mild tibia vara and thus debate as to whether bracing works. It is agreed that bracing is only effective in Langenskiöld stages I and II, and in half of those treated.

The conventional operation that has been used for tibia vara is a proximal tibial valgus osteotomy often combined with external rotation. It is important to avoid damaging the apophysis, and to aim for some overcorrection into overall valgus alignment. Such surgery, performed early (under 4 years of age) may prevent recurrence of varus deformity in Blount’s disease at long-term follow-up. On its own, a lateral staple physeodesis does not seem to be effective although recently, encouraging results have been seen following the use of a physeal plate that acts as a tension band tether to physeal growth.

Elevation of the medial hemi-plateau of the tibia for correction of severe varus deformity secondary to Blount’s disease produces satisfactory results but a tibial osteotomy may also be required for full correction (Figure 13.16.8C). On the basis of knee arthrograms and MRIs, there is some disagreement as to whether the medial tibial plateau is truly depressed or simply filled with unossified cartilage (Figure 13.16.8B).

Circular frames have been used effectively to treat the combined problem of a complex tibial deformity and leg length difference in older children.

The most significant early complication of a proximal tibial osteotomy is compartment syndrome or neurological damage and close postoperative monitoring is essential.

Recurrence of deformity requiring repeated osteotomy occurred more frequently in children who underwent a late (>4 years of age) initial osteotomy and/or were Langenskiöld stage III or more. Patients who underwent a single osteotomy for correction of their deformity had significantly decreased pain in the affected knee at maturity. All patients who were symptomatic or who had significant knee instability or both had abnormal ligamentous, meniscal, or bony changes on MRI, confirmed by arthroscopy.

Congenital pseudarthrosis of the tibia is characterized by an apex anterolateral angulation of the lower leg through an area of abnormal tissue. It continues to pose one of the most difficult problems in paediatric orthopaedic surgery.

Congenital pseudarthrosis of the tibia is rare with an incidence of 1: 250 000 live births.

The pseudarthrosis is usually not present at birth (and therefore not truly congenital) but develops during the first decade of life. The male: female ratio is 3:2, left and right sides are equally affected, but only 1% of cases are bilateral.

Most of the lesions are initially found in the middle or distal third of the tibia. In 29% the localization changes during the course of the disease. The fibula is also affected.

Signs and symptoms of neurofibromatosis (NF) are present in 55%. It has also been noted that many have curly or overlapping toes on the affected leg. Screening for the NF gene is advised.

Various morphologic classification systems have been proposed but because the appearance changes during the course of the disease, all classification systems have some limitation. The most common classification is that by Boyd (Table 13.16.2).

Presentation depends on degree of tibial deformity and the presence of a fracture.

Typically there is bowing of the tibia, apex anterolateral. This must be differentiated from posteromedial bowing (see later). The affected segment is short and there may be the scars of previous operations (Figure 13.16.9). Stigmata of NF should be sought.

X-ray changes as described previously are seen depending on type (see Table 13.16.2).

MRI of congenital pseudarthrosis allows assessment of the type and extent of the disease. It is especially recommended for the evaluation of periosteal and soft tissue changes near the pseudarthrosis.

Histological examination shows a non-specific fibrous appearance in 45%; in 16% the ultrastructure resembles fibrous dysplasia; and in 39% there is evidence of NF1.

Histological comparison of the pathologic samples of patients with and without NF reveals no significant differences. The pseudarthrosis gap is continuous with periosteal soft tissues and filled by fibrous tissue, fibrocartilage, and hyaline cartilage with features of enchondral ossification.

A single pathologic process appears to occur in all cases: growth of an abnormal, fibromatosis-like tissue either within the periosteum or within the endosteal or marrow tissues. This may represent a skeletal expression of NF, either within the fully expressed syndrome (patients with known NF) or as isolated lesion (patients with unknown/cryptic NF). Fibrous hamartoma cells maintain some of the mesenchymal lineage cell phenotypes but do not undergo osteoblastic differentiation in response to bone morphogenic protein.

Once the condition has been diagnosed, protective bracing should be started usually with a KAFO or clamshell orthosis. If the tibia remains intact surgery may be avoided.

There is debate about surgical intervention; in particular regarding the age at first operation, whether the resection should be conservative or radical and whether reconstruction or amputation would be the better option.

The aim of reconstructive surgery is to manage the biological and mechanical abnormality by:

The surgical techniques most frequently used for treating congenital pseudarthrosis of the tibia are intramedullary nailing associated with bone grafting, vascularized fibular grafting, and the Ilizarov circular external fixator device for stabilization and correction of deformity.

Recent studies using an intramedullary rod suggest that the best results are seen in children under 3 years of age at surgery: this contradicts the previous belief that surgery should be deferred until after 3 years.

Ipsilateral or contralateral vascularized fibular grafts are effective treatments and can be considered as a primary option. Both techniques involve resection of the abnormal tissue with transfer of normal living tissue into the defect and stabilization of the bone and the ankle joint.

Circular frames have become increasingly popular in the management of this condition. The technique may be used in various ways: for acute compression and stabilization after resection, for simple longitudinal compression of the ‘non-union’, side to side compression of over-riding atrophic bone ends or segmental bone transport to fill a bone defect.

For all of these techniques, a brace is advocated until the end of growth and often beyond.

An alternative approach to reconstruction is amputation. Following Syme’s amputation, a solid union may be seen across the pseudarthrosis site, even without internal fixation or bone grafting. Healing is achieved by vertical alignment of the limb in a total contact prosthesis, along with the compressive forces of weight bearing (Box 13.16.3).

A multicentre study by the European Paediatric Orthopaedic Society found that the Ilizarov technique had the highest rate of fusion (75.5%) of the pseudarthrosis and the best success in correcting the associated deformities. The Japanese multicentre study showed that the Ilizarov method with a vascularized fibular graft provided the best results. The worst outcomes seem to occur in patients with an associated fibular pseudarthrosis.

Despite good anatomical results, gait and muscle strength of patients with ‘healed’ congenital pseudarthrosis of the tibia are markedly disturbed. Early onset of disease, early surgery, and transankle fixation lead to an inefficient gait, comparable to that of amputees.

Even when union is achieved, the residual deformities in the affected limb often result in significant disability. These deformities include leg-length discrepancy, angular tibial deformities, ankle valgus and fibular non-union. Refracture is common. Factors predisposing to non-union/refracture are distal location of the tibial pseudarthrosis and the presence of concomitant pseudarthrosis of the fibula (Figures 13.16.9 and 13.16.10).

Various adjuvant treatments such as bone morphogenic protein and bisphosphonates have been tried and although early results suggest that bone healing may be enhanced, none have yet documented a reduction in the refracture rate.

This variety of bowed tibia is usually associated with a dimple at the apex and with a calcaneovalgus foot (Figure 13.16.11A).

The deformity is very rare and much less common than an anterolateral bow. There is equal sex distribution.

This is alarming to parents as the acute angular deformity of the lower leg is obvious at birth. There is usually a skin dimple at the site of the bow and an associated calcaneovalgus foot deformity.

It may be detected on the antenatal ultrasound scan and spontaneous correction starting before birth has been noted. X-rays show sclerosis at the site of the bow with the deformity as seen clinically (Figure 13.16.11B).

Histology has been performed in one case of an aborted fetus and this demonstrated evidence of amniotic perforation, abnormal periosteal ossification, and remodeling.

The natural history is of resolution but this may be incomplete (Box 13.16.4).

Serial casting is often advocated but there are no studies of the effectiveness of this compared to the natural history. The process of spontaneous resolution may continue for several years and a conservative approach to treatment is recommended.

Tibial osteotomy to correct deformity is not usually required but there is always an associated leg length discrepancy which averages 3cm (2–6cm) at maturity. The degree of leg length difference and difference in calf size appears to be related to the degree of deformity. Operative techniques described elsewhere may be needed to correct this leg length discrepancy.

The degree of limitation of ankle movement is related directly to the severity of the initial deformity and the subsequent leg length discrepancy. It is probably due to a contracture of the heel cord and posterior capsule resulting from chronic use of an abnormally short limb.