13.10 Common disorders of the lower limb

Abnormalities of lower-limb alignment, particularly during walking, often cause parental concern and require assessment in the paediatric orthopaedic clinic. Rotational deviations that lead to in-toeing or out-toeing gait, coronal plane knee deformities (genu varum or valgum), and pes planovalgus are the most common causes of parental concern. In the majority of these children, deviations are physiological and of no functional consequence. However, in a small number of children, these abnormalities may be representative of an underlying condition that requires treatment. Therefore, careful clinical assessment of these children is necessary before adequate reassurance can be offered to the parents.

An assessment of gait must include watching the child stand, walk, and run. Many children are on ‘best behaviour’ in the consulting room and parents are frequently concerned that the doctor has not seen their child’s ‘normal’ walk. Every effort must be made to ensure that the child is as relaxed as possible before the assessment is made: often more can be learnt from watching the child leave the room than watching them come in.

Observational (clinical) gait analysis skills must be used to exclude a generalized problem such as a neuromuscular abnormality or skeletal dysplasia before a more specific assessment of their walking pattern is made. Assessment of the child’s torsional profile may help determine where the main deformity lies and reveal the extent of any compensatory deformity (Box 13.10.1 and Figure 13.10.1).

The foot progression angle is defined as the angle between the longitudinal axis of the foot and the line of progression of walking. The average foot progression angle in the adult healthy population is approximately 10 degrees external, with a range between 5 degrees internal and 20 degrees external being considered as normal. Mild deviations from the norm are well tolerated and do not cause functional problems or symptoms. Significant deformities may cause frequent tripping and falling, particularly when children are tired and their compensatory mechanisms are failing. It is not known how significant these deviations need be before they cause abnormal joint loading and moments that may lead to long-term joint degeneration. Measurement of joint moments through instrumented gait analysis may have a role in assessing children with significant deviations who are candidates for treatment. This can establish if these deviations are purely cosmetic or likely to cause long-term clinical problems (Figure 13.10.2).

Femoral anteversion is the angle between the longitudinal axis of the femoral neck and the frontal plane of the femur defined by the transcondylar axis and the femoral diaphysis. Femoral anteversion is approximately 40 degrees at birth and gradually remodels to the average adult 15 degrees, usually within the first 3–4 years of life. Little remodelling is expected after the age of 8 years. Early remodelling occurs as a result of pressure on the anterior femoral neck by the soft tissues, particularly the ligaments and the joint capsule, which results from the upright human posture. Conditions preventing upright posture or associated with ligament laxity or joint instability are usually associated with failure of remodelling and persistent femoral anteversion. However, persistent femoral anteversion is also present in a significant number of normal children. In addition to their in-toeing gait, children often have a typical running pattern with their lower legs swinging out to the side and they are able to ‘W’ sit comfortably (Figure 13.10.3).

Clinical assessment of femoral anteversion is performed with the child in the prone position and the knee in 90 degrees of flexion. The hip is rotated until the most prominent part of the greater trochanter is palpated in the mid-lateral position. In this position, the angle between the tibia and the vertical is equal to the femoral anteversion (see Figure 13.10.1B,C). The range of hip rotation is often affected and excessive internal rotation is present, at the expense of external rotation. During walking or running, the knees are facing inwards and, as the tibia flexes, the visual impression of genu valgum is often present. Computed tomography (CT) scan or, preferably, the radiation-free magnetic resonance imaging (MRI) scan can be used for a more accurate measurement of anteversion, particularly when surgical correction is contemplated.

In the absence of any underlying or associated conditions, persistent femoral anteversion rarely requires treatment. Whilst increased femoral anteversion is often present in developmental hip dysplasia, patients with the condition would rarely present with in-toeing as their main complaint. It is important to ensure that examination of the hips is normal in children who present with increased femoral anteversion and, if necessary, a pelvic radiograph should be taken to exclude hip dysplasia. Reassurance can be offered to parents of children under the age of 8 years as in the majority of cases the deformity is likely to remodel spontaneously. Non-surgical treatment does not influence the rate of remodelling. Significant anteversion causing functional problems and persisting beyond the age of 8 years may require surgical correction. Given the potential risks and complications involved in bilateral femoral derotation osteotomies, patients should be carefully selected and treatment indications discussed thoroughly with their families.

Tibial torsion is defined as the angle between the transcondylar axis of the proximal tibia and the transmalleolar axis of the ankle (Figure 13.10.1E). The normal adult average is approximately 20 ±10 degrees of external torsion. Clinically tibial torsion is measured by palpating the above landmarks, defining the axes and using a goniometer to measure the angle. The thigh–foot angle is also used as an estimate of tibial torsion. This is the angle between the longitudinal axis of the foot and the femur assessed in the prone position with the knee flexed at 90 degrees (Figure 13.10.1D). Both clinical measurements can be inaccurate, the former because of the difficulty in defining the transcondylar axis and the latter because of knee rotation and foot deformity compromising the measurement. During walking, the knees are facing forward but the foot progression is internal. In the absence of foot deformity this clinical picture would suggest that internal tibial torsion is present. CT or MRI scan can be used for the accurate measurement of tibial torsion, particularly in surgical candidates.

Internal tibial torsion is probably caused by moulding in utero and resolves spontaneously in the vast majority of infants within the first few years of life. When the deformity is purely torsional, reassurance can be offered to parents of young children. Tibial bowing associated with torsion may require further investigation with radiographs, particularly if it persists after the age 3 years, in order to rule out underlying pathology. If the deformity persists after the age of 6–8 years it is unlikely to remodel spontaneously. Surgical treatment may be appropriate in a small minority of selected cases with significant deformity and functional problems. A supramalleolar tibial derotation osteotomy is undertaken and stabilized, often with internal fixation. A concomitant fibular osteotomy is usually unnecessary.

Adduction of the forefoot with a normal hindfoot is present in approximately 1:1000 newborn infants and is probably caused by moulding in utero. It can be associated with hip dysplasia and careful assessment of the hips should be undertaken. The deformity is usually observed immediately after birth but a significant number of children present later with parental concerns over in-toeing. Older children may complain of pain from excessive pressure over the lateral plantar area and/or difficulty with shoe fitting.

Clinical examination reveals a curved lateral border of the foot with a normally aligned hindfoot and sometimes a mild degree of forefoot supination. When the deformity is flexible, the forefoot can be manipulated easily to the neutral position or beyond. When the deformity is rigid, further assessment is required to rule out a congenital skeletal abnormality or a varus deformity of the hindfoot that would suggest a mild form of congenital talipes equinovarus.

Dynamic adduction and supination of the forefoot in toddlers with a normal but immature gait pattern can sometimes be confused with metatarsus adductus. This is caused by the predominant use of tibialis anterior tendon for foot dorsiflexion during the swing phase of gait while the peronei are silent. The foot assumes normal alignment at rest and clinical examination is entirely normal. This should be considered as a normal stage of gait maturation that will resolve spontaneously over time.

Flexible metatarsus adductus deformity usually resolves spontaneously within the first 1–2 years of life. Rigid deformity should be treated with early serial above-knee casting. The role of orthotic management and/or splinting in older children is unclear as evidence on the effectiveness of such treatment is lacking. Persistent symptomatic deformity may require surgical treatment in a minority of patients. Relatively mild deformity in younger children responds to soft tissue surgery, including medial capsular release of the appropriate joint(s) at the apex of the deformity (usually navicular–cuneiform or cuneiform–first metatarsal). Lengthening of the abductor hallucis may also be necessary. When forefoot supination is present, lengthening or transfer of tibialis anterior tendon may be appropriate. Rigid deformity in older children requires bony procedures in the form of basal metatarsal or midtarsal osteotomies: this is very rarely necessary and should not be undertaken without considerable thought.

Common causes of external foot progression include external tibial torsion, planovalgus foot deformity (see Chapter 13.22) or more rarely, external hip rotation due to femoral neck retroversion.

This may be present at birth or may develop overtime as compensation for increased femoral anteversion. Planovalgus foot deformity may further compromise the rotational alignment of the foot in relation to the knee. As a result of this malalignment, the physiological knee extension moment generated by the foot plantarflexors, using the foot as the lever-arm, is compromised. This, in turn, causes excessive strain on the knee and particularly, the patellofemoral joint.

Mild deviations of external tibial torsion are usually asymptomatic, at least during childhood, and cause no functional problems. Significant rotational anomalies may cause symptoms at the knee and/or the foot. Spontaneous correction can only be expected in young infants and toddlers with congenital deviations. Acquired or persistent deformity causing symptoms or functional problems after the age of 5 years is unlikely to remodel and may require surgical treatment. As with deformity due to internal torsion a supramalleolar derotational tibial osteotomy is performed and stabilized with internal fixation. Again a fibular osteotomy is seldom necessary (Box 13.10.3).

Predominant external rotation at the hips due to reduced femoral anteversion or retroversion is a rare cause of out-toeing gait. Children with the condition walk with knees facing outwards and an external foot progression. Clinical examination reveals excessive external rotation of the hips at the expense of internal rotation. Usually the condition is idiopathic and of no functional consequence in childhood, therefore no treatment is indicated. Coxa vara can be an underlying cause in younger children while chronic bilateral slipped upper femoral epiphysis should be considered in children of prepubertal age. Radiographic evaluation should be undertaken when these diagnoses are considered.

Walking on tip-toes is a normal stage in the development of a mature gait pattern but by the age of 3 a child should have outgrown this phase. Most children with idiopathic toe walking (ITW) can get their heel to the ground and will do so when standing but when walking or running there is a toe–toe or toe–heel pattern. In both situations there is disturbance of the ankle rockers (Box 13.10.4). The aetiology of ITW is not known but it may be due to an undefined and minor ‘error’ in the central nervous system (CNS).

A full history and examination is required as it is imperative to distinguish ITW from mild cerebral palsy, muscular dystrophy, or other neurological disorders. It is particularly important to clarify if toe walking developed late in children who had previously walked normally as this would suggest a progressive neurological disorder. The foot may be triangular in shape with a splayed forefoot and a relatively under-developed heel. Neurological examination is essentially normal but there may be some symmetrical loss of ankle dorsiflexion. Formal gait analysis distinguishes ITW from mild cerebral palsy but this is rarely necessary.

Many children stop toe walking spontaneously over time and perhaps with an increase in body mass and compensatory external tibial torsion. Persistent ITW with maintenance of 5 degrees of dorsiflexion is unlikely to cause any functional problems. Treatment with Achilles tendon stretches and dorsiflexion strengthening exercises may help improve gait pattern. Serial casting and/or botulinum toxin injections may be successful but if there is significant tightness of the Achilles tendon a surgical lengthening will be necessary. Although the operation itself is simple and reliable, the procedure changes the gait pattern dramatically and the parents must be forewarned. The gait improves in the rehabilitation phase as the plantar flexors regain their strength. Recurrent toe walking is not uncommon perhaps because the cause lies in the CNS. Toe walking in children with behavioural problems or autistic syndrome disorders should be distinguished from ITW as it is rarely associated with tightness of the Achilles tendon and responds less well to surgical treatment (Box 13.10.5).

The coronal alignment of the knee changes in the first 6–7 years of life. These changes can cause parental concerns, particularly at times of development when they reach peak values. Knowledge of the physiological evolution of the coronal knee alignment is therefore important when advising parents about the natural history of the deformity.

At birth and during the first year of life the knee alignment is 15 degrees (±5 degrees) varus. It remodels to neutral alignment during the second year of life, presumably as the result of weight bearing. After the age of 2 years the knee progresses to valgus alignment to reach a maximum of 10 degrees (±5 degrees) valgus at the age of 3–4 years. From there it gradually remodels to the average adult value of 7 degrees valgus by the age of 6–7 years (Figure 13.10.4).

A wide variety of conditions, including metabolic bone diseases, bone dysplasias, and Blount’s disease, can lead to coronal plane knee deformity. Consideration should be given to those conditions if knee alignment deviates from the pattern described earlier. While varus knee alignment at the age of 18 months is likely to be physiological, if it deteriorates overtime or persists after the age of 3 years it may require further investigation. Similarly, the combination of significant tibial torsion with a varus deformity raises concern regarding underlying pathology.

Persistent varus or valgus alignment of the knee after the age of 8 years is unlikely to remodel spontaneously. Although there are no long-term studies to substantiate this, it is logical to assume that significant coronal knee deviations will lead to degenerative arthropathy, particularly if the mechanical axis lies outside the joint. Therefore, severe deformity may be an indication for surgical correction, particularly if symptomatic. It is essential to establish the level of the deformity with appropriate radiographs: is it in the distal femur or the proximal tibia? Furthermore, it is important to confirm that the deformity is truly and entirely in the coronal plane as increased femoral anteversion combined with external tibial torsion may give the false impression of genu valgum. During growth, coronal knee alignment can be corrected with temporary hemiepiphyseodesis at the appropriate level (Figure 13.10.5). After the end of growth, osteotomy of the distal femur or proximal tibia would be necessary.