This deformity is bilateral and most common in Asians and may be familial. Operative treatment is seldom required. It is not clear from the literature whether and to what degree there is an increased chance of degenerative arthritis of the medial compartment.

Blount disease is a rare anomaly. It is a metaphyseal developmental disorder on the medial side in the proximal part of the tibia. The disease can cause unilateral or bilateral bowlegs at the age of 1½–3 years (infantile type), as well as starting at 8 years of age (adolescent type) (Table 10.1). A juvenile type is also recognized that occurs between the ages of 4 and 8, but it is probably an infantile type that has been diagnosed too late. That type is always bilateral. The disease affects girls as much as boys, and is most common among children of African origin.

Radiological assessment is indicated when both legs are not straight at the age of 1½–2 years, or when bowlegs develop after that age. The infantile type is bilateral in 60 % of cases (Fig. 10.3). A unilateral bowleg is always abnormal. The infantile type often presents with internal torsion of the tibia. Six stages can be distinguished radiologically (Figs. 10.4 and 10.5).

The adolescent type is generally less pronounced than the infantile type. The varus position in adolescence never exceeds 20°. In 20 % of cases this type is bilateral (Fig. 10.6). In the unilateral adolescent type a difference in leg length of 1–3 cm may be seen (Fig. 10.7).

Bowlegs can also be caused by a lack of vitamin D. This is known as rickets, infantile osteomalacia or the English disease. Children don’t generally have a vitamin D deficiency in developed countries and the disease is rare. It tends to be caused by an hereditary enzymatic defect (pseudovitamin D-deficiency I), a congenital resistance (pseudovitamin D-deficiency II) or a renal phosphate loss in familial phosphate diabetes (X-chromosome dominant hereditary renal tubular disorder).

Bowlegs can be part of generalized skeletal anomalies such as achondroplasia and multiple epiphyseal dysplasia¹. A shorter body height (Fig. 10.9) is seen in skeletal dysplasia.

In focal fibrocartilaginous dysplasia there is a unilateral genu varum resulting from a local abnormality on the medial side in the proximal part of the tibia (Fig. 10.10). MRI assessment shows an elliptical cortical bone defect. Microscopical assessment shows fibrous tissue with small areas of cartilage. This abnormal tissue stunts growth on the medial side of the tibia, but on the other side it keeps growing and a bowleg develops.

This is an osteochondral overgrowth of an epiphysis or articular cartilage. It is a rare, non-painful condition with an incidence of 1 in 1,000,000. The condition manifests itself mostly between the ages of 2 and 14 years. It is three times more common in boys than in girls. There is a hereditary factor. The anomaly is intra-articular and remains limited to half of the extremity. The medial side is affected twice as often as the lateral part, and in two-thirds of the patients the condition is present in several epiphyses simultaneously. The most common localizations are the distal part of the femur, the distal part of the tibia and talus. A varus deformity will develop if the anomaly is localized on the lateral side. A valgus deformity will develop if the anomaly is localized on the medial side (Fig. 10.22). There is also movement limitation and a swelling of the knee, in case of a bowleg on the lateral side. Radiological assessment shows a lobe-shaped swelling on the lateral side of the distal femoral epiphysis, accompanied by multiple calcifications. Histologically speaking, the anomaly cannot be distinguished from an extra-articular osteochondroma. Malignant degeneration has never been described.

A bowleg can also be caused by an infection or a fracture, in which the growth plate is damaged on the medial side just above or just below the knee. Part of the cartilage of the growth plate is replaced by bony tissue, creating a bony connection between the epiphysis and metaphysis. If the bony connection is centrally located, then only leg shortening occurs. If the bony bridge is medially located, then the medial side of the corresponding growth plate stops length growth and the lateral side keeps growing so a bowleg develops (Fig. 10.11).

There are chances of spontaneous recovery in stages I and II of Blount disease The chances of recovery are greater (90 %) if stages I and II are treated with antivarus splints (Fig. 10.15). It seems to make no difference whether splint treatment is applied for the entire day or only at night. We advise prescribing antivarus splints only for night use for children younger than 3. A proximal tibial valgus osteotomy (just distal to the tibial tuberosity) with a distal fibulotomy is indicated if there has been no recovery within 1 year or if the child is older than 3. The same applies in a child with Blount disease stage III. A similar intervention should be carried out before the age of 4 in stages I, II and III. The chances of recurrence are higher if the operation is postponed until after that age, A valgus position of 5°–10° should be aimed for. For stages I, II and III a lateral hemi-epiphysiodesis of the growth plate of the proximal part of the tibia could be an alternative. This prevents progression of the anomaly, but correction will not be achieved. What’s more, it will stagnate the growth from this growth plate. In stages IV and V children are at least 6 years of age. A growth plate distraction of the medial part of the proximal tibial growth plate and also a proximal tibial valgus osteotomy just distal of the tibial tuberosity with a fibulotomy, may be considered, in which the proximal tibial growth plate on the medial side has not yet closed.

The adolescent type of this anomaly is not as pronounced as in the infantile type (Table 10.1). A definitive hemi-epiphysiodesis in which the lateral part of the proximal tibial growth plate is destroyed is usually sufficient. A proximal tibial valgus osteotomy can be performed in combination with a distal fibulotomy for a severe type. If necessary, an epiphysiodesis of the contralateral proximal tibial growth plate should also be carried out in order to prevent progression in the leg length difference depending on the growth expectations.

Rickets should first be treated by a pediatrician. Spontaneous improvement of the deformity may occur after treatment of the underlying cause (Fig. 10.8), as healthy growth plates redirect themselves perpendicular to the weightbearing lines (Hueter-Volkmann law, 1862). A temporary hemi-epiphysiodesis of the lateral side of the growth plates in the distal part of the femur and/or the proximal part of the tibia will be performed using clamps, eight-plates or screws depending on the localization in severe cases where no improvement occurs. The fixation materials are removed as soon as the legs are straight.

Operative intervention is indicated in 50 % of achondrodysplasia² cases with such a misalignment. A temporary epiphysiodesis of the lateral side of the growth plates in the distal part of the femur and the proximal part of the tibia can be performed using clamps or eight-plates if the child is still growing. A correction osteotomy is an option if the child is no longer growing,

At first the bowleg will increase, but between the ages of 4 and 8 the defect will be spontaneously filled up with bony tissue; the bowleg position will tend to correct spontaneously if there is a varus deformity of less than 30°. A proximal valgus osteotomy of the tibia in combination with a distal fibulotomy may be performed if there is no spontaneous correction between the ages of 4 and 8.

Wedge excision at the level of the deformity, thus correcting the abnormal position. The chances of recurrence are great.

This bony bridge can be removed operatively if the bony connection between the epiphysis and metaphysis resulting from growth plate damage due to infection or fracture amounts to less than one-third of the total area of the growth plate. The growth plate usually recovers full function after this, and in a large number of cases the misalignment will correct spontaneously because the growth plate tries to direct itself perpendicular to the load line (Hueter-Volkmann law, 1862). In some cases, however, it is not possible to remove the bony bridge, or because the bone bridge consists of more than one-third of the total area of the total growth plate. In such cases it is best to destroy the lateral part of the growth plate and perform a correction osteotomy. The difference in leg length should be subsequently corrected at the appropriate time.

During the second and third years of life knock knees develop slowly with an average annual rate of 12° between the upper and lower leg after the legs with a physiological genua vara have straightened by the age of 18 months, This physiological development is bilateral. A knock knee is often optically enhanced by a simultaneous development of external rotation in the lower legs and in some cases an enhanced internal rotation in the hip joints. This can also be accentuated in cases with thick thighs and flatfeet. The valgus position corrects itself gradually, so that by the age of 7 years a normal valgus angle of 8° in girls and 7° in boys has developed in more than 95 % of cases (Fig. 10.17).

If there is still a genua valga in excess of 10° the chances of spontaneous recovery are minimal after the physiological period, after 7 years of age, (Fig. 10.18)

Rickets can give rise to bowlegs as well as knock knees (see pp. 172).

Knock knees can also develop in addition to bowlegs (Fig. 10.19) in generalized bony anomalies such as achondroplasia³ and multiple epiphyseal dysplasia,3 (see pp. 172).

This is a developmental disorder in the periphery of the epiphyseal plates. The benign bony growth develops mostly with a cartilaginous cap. The anomaly increases in size until the patient stops growing. This problem may be solitary but can also appear in multiple areas. Multiple osteochondromata are involved in a hereditary disease in more than 60 % of cases. Hereditary multiple exostoses (or osteochondromata), are abbreviated as HME or HMO. There is often a knock knee position in multiple osteochondromata (Fig. 10.20). This is caused by a large osteochondroma in the proximal part of the fibula. There is reduced growth in length of the fibula, as a result of which the bone works as a brake, causing a valgus deformity in the proximal part of the lower leg (Fig. 10.21).

This is an osteochondral overgrowth of the epiphysis on the medial side of the femur (Fig. 10.22). Besides the valgus 0 there is a limitation in movement and a swelling on the medial side of the knee (for explanatory note, see pp. 173).

A unilateral knock knee is always abnormal. Part of the cartilage of the growth plate will be replaced by bone tissue if there is damage to the growth plate caused by an infection or fracture. A knock knee develops if this bony connection appears on the lateral side of the distal femoral or proximal tibial growth plate in the distal part of the femur or the proximal part of the tibia.

A genu valgum may also be the result of a fracture on the medial side in the proximal tibial metaphysis (Fig. 10.23). A valgus deformity develops in a large number of cases after cast immobilization. This is probably caused by interposition of the periosteum at the level of the fracture, which will not allow closed (noninvasive) anatomical reduction.

Rickets should be initially treated by a pediatrician. Spontaneous improvement of the deformity occurs after treatment of the underlying cause. In this situation the growth plates are directed perpendicularly to the weight-bearing lines (Hueter-Volkmann law, 1862). A temporary hemi-epiphysiodesis on the medial side of the affected epiphysis or a correction osteotomy may be necessary in severe cases where no improvement occurs.

Temporary hemi-epiphysiodesis of the medial side of the growth plate in the distal part of the femur and proximal part of the tibia. A correction osteotomy may be considered if correction is insufficient once the child is fully grown.

In order to correct or stop the valgus misalignment a temporary hemi-epiphysiodesis on the medial side of the growth plates in the proximal part of both tibiae and a partial resection of the fibula shaft including the periosteum should be performed. The clamps or eight-plate should never be allowed to remain in place for more than 2 years, or a bony bridge will develop in the growth plate. At some point it often becomes necessary to remove the osteochondromata as much as possible and carry out a proximal tibial varus osteotomy at the end of the growth period. In young children there is very high risk of recurrence.

Wedge excision at the level of the anomaly, thus correcting the misalignment. However, the chances of recurrence are great even after a wedge excision.

Operative removal may be considered if the bony bridge covers less than one-third of the total surface of the growth plate. Once the bony bridge is removed, the abnormal position of the knee will be spontaneously corrected during growth, because the growth plates try to direct themselves towards the weight-bearing lines of the leg (Hueter-Volkmann law, 1862). Sometimes it isn’t possible to remove the bony bridge, or because the bone bridge comprises more than one-third of the total growth plate. In such cases it is advisable to destroy the rest of the growth plate and perform a correction osteotomy. A difference in leg length should be subsequently corrected at an appropriate time.

A wait-and-see policy is adopted for an entire year in the case of a genu valgum caused by a fracture on the medial side in the proximal part of the tibia just distal to the growth plate. A valgus position in the proximal part of the tibia can spontaneous be corrected by the distal tibial growth plate, because it starts directing itself perpendicular to the weight-bearing line (Hueter-Volkmann law, 1862). An S-shaped tibia develops which can only be observed on X-rays (Fig. 10.23). The leg is straight on physical assessment. If this spontaneous correction does not occur, a temporary hemi-epiphysiodesis can be performed by placing an eightplate, clamps or a screw on the medial side of the proximal tibial growth plate in older children Sometimes a decision may be made to do a correction osteotomy, preferably at the end of the growth period. One should realize that in young children there is high risk of recurrence.

The knees of normal babies have a flexion deformity of 10°–20° up to the age of 2–3 months. The knees may display a hyperextension of 20° after a breech birth (Fig. 10.25). They can be fully flexed on passive assessment. The postural anomaly corrects spontaneously within 3 months. After a breech birth one should also check for developmental dysplasia of the hips.

There may also be knees that can hyperextend 10° or more if there is general hypermobility of the joints resulting from joint laxity (Figs. 10.26 and 10.27). The knees can in this case be fully flexed. One can see the hyper-extension of the knee when these children stand and walk. Pronounced hypermobile joints are a feature of Ehlers-Danlos syndrome⁴.

In structural hyperextension the knees cannot be completely flexed actively or passively. It can be classified as congenital hyperextension, subluxation or dislocation if the anomaly is present from birth (Fig. 10.28).

Hyperextension of 15°–20°. The knee can be brought passively into 45°–90° of flexion.

Hyperextension of 25–45°. The knee can be brought passively into a neutral (0°) position.

Hyperextension position of 25–45°. Passive flexion is impossible. A congenital knee dislocation is seen in 1 in 100,000 births. There is a bilateral dislocation in one-third of cases. It is three times more common in girls than in boys. There is also a developmental dysplasia of one or both hips in 70 % of children and in 50 % of these children they additionally have congenital foot deformities. In a congenital subluxation/dislocation of the knee the proximal part of the tibia is dislocated anteriorly. The term dislocation specifies that the tibial joint surface is not in contact with the femur at all. The term subluxation is used when the proximal tibial joint surface is in partial contact with the distal femur joint surface. There can also be a lateral translation of the tibia with respect to the femur, as well as a valgus position, as a result of a contracture of the iliotibial tract. Semitendinosus and semimembranosus muscles on the medial side of the collateral ligaments may be displaced anteriorly. The quadriceps muscle is shortened, and the suprapatellar recess is fixed onto the femur. The cruciate ligaments may be absent. A congenital knee subluxation/dislocation may be part of the Larsen syndrome⁵ (Fig. 10.28) and arthrogryposis multiplex congenita5. In Larsen syndrome there may be multiple dislocations of hips, knees and elbows. These children have characteristic facial features, such as a prominent forehead, widely spaced eyes (hypertelorism), and a depressed nasal bridge.

The knee can be fully flexed and the anomaly is not in the joint but just distal to it.

A premature closure of the anterior side of the proximal tibial growth plate may occur in rare cases, after infection or a fracture of the tibial tuberosity. A recurvation deformity develops due to damage to the anterior side of this growth plate because the apophysis is in continuity with the proximal tibial growth plate, (Fig. 10.29). In extremely rare cases this can also be caused by Osgood-Schlatter disease, which is an apophysitis of the tibial tuberosity (see pp. 231–234).

In this case the quadriceps tendon is lengthened in a v-shape, the capsule is divided on the anterior side, and the tensor fascia lata is divided transversely to correct the valgus position (Fig. 10.32). The knee is reduced and immobilized in 30° of flexion for 4–6 weeks in a plaster of Paris cast. After which, a long leg orthosis is worn for an entire year in order to prevent hyperextension.

A proximal tibial osteotomy is recommended at the end of growth in cases with a recurvation deformity of the proximal part of the tibia. Note that the tibia is usually angled at about 9° posteriorally.

This is a rare condition, one of 10,000 live birth’s, that tends to be bilateral and often occurs in combination with other congenital anomalies such as developmental dysplasia of the hip, clubfoot and nail-patella syndrome (onycho-osteodysplasia)⁶. The extension mechanism of the knee remains intact and the knee can be extended actively if the quadriceps femoris muscle is normal. An active extension deficit in the knee will be present if there is reduced quadriceps muscle strength in addition to an absent patella.

Part of the hamstring insertion can be attached to the quadriceps muscle to benefit extension if there is weakness of the quadriceps femoris muscle accompanied by an active extension deficit of the knee.

This type is due to hypermobility disorders such as in Down⁷ and Ehlers-Danlos syndromes7.

This a subluxation/dislocation in normal children with no associated ligamentous laxity. In general there are knee anomalies, especially a misalignment of the extensor apparatus. The first dislocation in a habitual patellar subluxation or dislocation is generally not caused by a trauma. The patella dislocates upon knee flexion. The dislocation is a consequence of a developmental disorder with the following possible manifestations: atrophy of the vastus medialis of the quadriceps femoris muscle; a more proximal insertion of the vastus medialis: external torsion, combined with a valgus position of the leg, causing a larger Q-angle (Fig. 10.35); a shallow femoral groove; a proximally localized patella; or combinations of the above listed developmental disorders. In a proximally localized patella (patella alta) the distance between the apex of the patella and the attachment to the tibial tuberosity is greater than the length of the patella. Normally, the distance between the apex of the patella and the tibial tuberosity is as great as the length of the patella. Variation of more than 20 % indicates an abnormal position.

A traumatic patellar dislocation affects 3–4 in 10,000 children between 10 and 17 years of age. In the first instance there has been an extensive valgus/flexion trauma, causing a laxity in the medial retinaculum that can lead to recurrent dislocations. Recurrences are seen in 30–50 % of cases after an initial traumatic patellar subluxation/dislocation,.

The growth plates will be damaged in a child if one carries out an operation on bone. For this reason, soft-tissue surgery should be chosen with a Galeazzi or modified Galeazzi operation for a proximal realignment (Fig. 10.34) possibly combined with a Roux-Goldthwait procedure for distal realignment (Fig. 10.35). However, despite these interventions patellar subluxations/dislocations may keep occurring. In that case, a bony operation can be considered after the child stops growing.

An arthroscopy after the first dislocation should first be considered if osteochondral fractures are suspected. Small fragments can be removed, and large fragments can possibly be reduced and fixed. The knee is immobilized for 5–10 days in a plaster of Paris cast or a patellar anti-dislocation orthosis if there is no osteochondral fracture. This is followed by prescribing quadriceps and hamstring exercises. A release of the lateral retinaculum can be carried out and the medial capsule can be reefed and sutured if recurrent subluxations/dislocations occur after this. This treatment is based on the situation after at least three dislocations.