Tibial Bowing Treatment & Management


Background

There are multiple etiologies for tibial bowing (see Etiology). Tibial bowing specifically refers to bowing of the diaphysis of the tibia with the apex of the deformity directed anterolaterally, anteromedially, or posteromedially. Each type of bowing tends to have a classic etiology. [1 Anterolateral bowing is associated with pseudarthrosis of the tibia and neurofibromatosis. [2Anteromedial bowing is associated with fibular hemimelia. The focus of this article is posteromedial tibial bowing.

Posteromedial bowing is a congenital bowing of the tibia (with the apex directed posteriorly and medially) and a calcaneovalgus foot deformity. [345Both of these deformities tend to resolve with little clinical disability; however, a leg-length inequality commonly develops that often requires treatment. [6If a significant leg-length inequality results, the patient will have an abnormal gait and may be at risk for increased back pain or deformity.

Treatment options vary depending on the degree of limb-length inequality, age of the patient, expected height, and desires of the patient or family. Treatment options include slowing the growth of the longer limb and lengthening the shorter limb.

Limb-length equalization procedures have primarily been performed by following one of two general approaches: slowing the growth of the longer limb with an epiphysiodesis or lengthening the shorter limb.

Phemister described his classic technique for epiphysiodesis. [78He removed a section of the epiphysis, rotated it 90°, and replaced the bone. Today, the most common technique is the percutaneous drill epiphysiodesis, performed with the aid of an image intensifier. This technique has been reported to result in physeal closure in 85-100% of patients with few complications. [9]

The first published report of a limb-lengthening procedure in the English literature dates to 1904 in Italy (Codivilla). [10Subsequently developed techniques, such as the Ilizarov and Wagner techniques, have been performed for 50 years. The Ilizarov technique and variations thereof are the procedures most often used today. [1112It is named after Gavril Abramovich Ilizarov, a Russian physician who used his technique to treat injured World War II veterans. Lengthening is usually performed using corticotomy and gradual distraction with a ring fixator and fine wires. This technique can result in an increase of 25% or more in bone length.

Pathophysiology

Posteromedial bowing is defined by the apex of the tibial curve being directed posteriorly and medially. Bowing in other directions is usually associated with different disorders.

The pathophysiology of the resultant limb-length inequality may be related to the bowing. The degree of initial tibial deformity (which largely resolves by age 8 years) has been shown to be ultimately associated with the severity of tibial shortening and resulting limb-length inequality. Animal models have demonstrated that unbalanced longitudinal pressures affect physeal growth. It is speculated that bowing results in unbalanced longitudinal pressures and, ultimately, in a decreased rate of growth.

This theory is contradicted by the observation that tibial growth inhibition remains constant as the child grows even though the deformity improves. The rate of growth of the affected tibia would be expected to approach that of the unaffected leg as the bowing resolves; this is not the case. Additionally, in the few patients who underwent early realignment osteotomy, tibial growth was still inhibited, resulting in a subsequent limb-length inequality.

Etiology

Each type of tibial bowing tends to have its own etiology. Causes of tibial bowing include the following:

  • Posteromedial bowing (congenital) [13]
  • Anteromedial bowing (fibular hemimelia) [14]
  • Anterolateral bowing (tibial pseudarthrosis)
  • Blount disease (infantile tibia vara)
  • Physiologic bowing
  • Trauma (ie, Cozen fracture)
  • Dysplasias

The developmental etiology of posteromedial bowing is unknown, but most authors believe it occurs secondary to abnormal fetal positioning, with the dorsiflexed foot plastered against the anterior aspect of the tibia. Primary abnormal embryologic development, such as limb bud or circulatory abnormalities and intrauterine fracture, [15has also been suggested as a possible developmental etiology.

Epidemiology

The true incidence of tibial bowing is unknown. It is generally agreed that this is a relatively infrequent disorder.

Prognosis

Although the angulation and foot deformity associated with posteromedial bowing improve dramatically, some degree of deformity, including tibial torsion and muscle atrophy, often remains. This is usually not a significant disability.


History and Physical Examination

Tibial bowing is often obvious and is present at birth. The foot is usually dorsiflexed to such a degree that it makes contact with the anterior aspect of the distal tibia. The posterior bow of the tibia is less obvious but can be easily palpated. A dimple may be present in the skin posterior to the apex of the bow. [16]

The Galeazzi test (see the image below), typically used to assess hip dislocation, can also be used to assess any congenital disorder that results in a significant limb-length inequality. The examination is performed with the patient supine and the hips and knees flexed. The result is considered positive if knee height is asymmetrical. It is also helpful to assess whether the limb-length inequality is primarily from the femur or from the tibia and to assess limb length in someone with knee or hip flexion contractures.

Posteromedial tibial bowing. The Galeazzi test. NoPosteromedial tibial bowing. The Galeazzi test. Note the difference in the height of the flexed knees.

Differential diagnoses include the other types of tibial bowing, such as anterolateral and anteromedial bowing. Intrauterine fracture or osteogenesis imperfecta may also result in tibial bowing. [1718These are often easily differentiated on the basis of physical examination findings in which the direction of the tibial bowing and the associated foot deformity are noted.

Anteromedial bowing is often associated with congenital loss of the lateral rays of the foot and fibular deficiency. Anterolateral bowing is associated with a pseudarthrosis of the tibia that may be obvious radiographically at birth or may develop with growth. Approximately 50% of children with anterolateral bowing are eventually diagnosed with neurofibromatosis.



Laboratory Studies

No studies are necessary other than radiographic images unless concern exists regarding the diagnosis, in which case other studies (eg, a metabolic study to assess for rickets) may be ordered.

Imaging Studies

Radiography

The initial evaluation should include an anteroposterior (AP) radiograph of the lower extremity with a ruler to measure limb length and to assess the deformity. Hip dysplasia, though not normally seen in patients with this disorder, can be assessed at age 6-12 weeks. Obtain a lateral radiograph of both tibiae. Obtain radiographs of the foot if the foot fails to correct by age 4-6 weeks. This should include AP and lateral views of the foot and a plantarflexion lateral view of the foot to assess for a vertical talus. (See the images below.)

Anteroposterior radiograph of a 1-year-old child wAnteroposterior radiograph of a 1-year-old child with posteromedial tibial bowing.
Lateral radiograph of a 1-year-old child with postLateral radiograph of a 1-year-old child with posteromedial tibial bowing.
Anteroposterior and lateral radiograph of a 9-yearAnteroposterior and lateral radiograph of a 9-year-old child with posteromedial tibial bowing. Note that the bowing has significantly improved.

Limb-length inequality at skeletal maturity must be assessed before any type of limb equalization procedure (epiphysiodesis, lengthening, or shortening) is performed. [1920 Typically, an epiphysiodesis is required at about age 11 years in females and age 13 years in males, but this varies, depending on the patient's skeletal age and the degree of the limb-length inequality. Epiphysiodesis can be indicated as early as age 8 years. As mentioned previously, if the degree of limb inequality is large (>5 cm) and the patient is not expected to be tall, a lengthening may be considered.

Limb-length inequality at skeletal maturity is most reliably predicted from a series of at least three radiographs taken at least 6 months apart. Various radiographic measures have been used to determine limb-length inequality, including the following:

  • The teleoroentgenogram is a single-exposure AP radiograph of the lower extremity with a ruler; this study is subject to a magnification error of 5-10% at the outer border of the film but has the advantage of showing coronal (angular) deformities and is not subject to movement errors
  • Orthoradiography incorporates three separate exposures (hip, knee, and ankle) in an effort to avoid magnification errors [21]
  • Scanography (see the image below) uses a similar technique, but exposure size is reduced, and all three exposures are on a single film cassette
Scanogram of a patient with posteromedial tibial bScanogram of a patient with posteromedial tibial bowing and a limb-length inequality.

Both orthoradiography and scanography are subject to movement errors, and angular deformities cannot be assessed.

All of the techniques are inaccurate if the patient has knee or hip flexion contractures or if the patient is simply flexing the knee or hip asymmetrically at the time of exposure. If the knee appears as a tunnel view, there is undoubtedly a significant degree of knee flexion. Lateral radiographs or separate (prone) radiographs of the femur and tibia with a radiopaque ruler can be obtained to assess limb length in patients with knee flexion contractures.

Other modalities

The use of computed tomography (CT) to assess limb length has increased. CT uses less radiation and is more accurate than conventional radiographic techniques in patients with knee or hip flexion contractures. [22 EOS three-dimensional imaging has the ability to decrease the amount of radiation and provide data in both the AP and lateral planes. Ultrasonography is now being used as well, primarily as a screening tool. [23]

Procedures

Once the current limb-length inequality has been measured, a prediction of the ultimate limb-length inequality at skeletal maturity is needed to determine treatment. [2425 This has generally been accomplished by using one of the following three methods [26:

  • Arithmetic method
  • Growth-remaining curve
  • Moseley straight-line graph

The simplest of these is the arithmetic method. This method assumes that the growth rate of the distal femur is 1 cm/y, that the growth rate of the proximal tibia is 0.6 cm/y, and that boys reach skeletal maturity at age 16 years and girls at age 14 years.

The growth-remaining curve relates chronologic age to limb length to determine a child's growth percentile. By using this, the remaining growth of the tibia or femur can be determined graphically.

The advantage of the Moseley straight-line graph, which combines information from both the arithmetic method and the growth-remaining curve, is that several measurements (preferably at least three, separated by 6 months) can be plotted on a single graph. The Moseley straight-line graph relies on determination of the bone age as estimated from a left hand/wrist film.

When these three techniques were evaluated, their accuracy rates showed little significant difference.

 A fourth method, known as the multiplier method, uses an arithmetic formula to determine limb inequality at maturity, [272829 simply taking the current limb-length inequality and multiplying it by a constant listed in a table by chronologic age. Timing of the epiphysiodesis can then be estimated by use of an arithmetic formula to determine limb-inequality at maturity. This method is as precise as the other three methods for determining limb length at maturity and can accurately estimate the timing for epiphysiodesis.

Histologic Findings

The histology of posteromedial bowing is unknown, but animal studies performed to model angular deformities demonstrate increased trabecular bone formation in the area of the apex of the angular deformity, with no new cartilage cells, and subepiphyseal bone condensation with subsequent thinning of the epiphyseal plate.



Approach Considerations

Initial treatment of the tibial bowing foot deformity includes stretching, serial casting, or splinting. The bowing deformity rapidly corrects. A 50% correction is usually seen by age 2 years, though a mild deformity often persists. The rationale for corrective tibial osteotomy is less clear, as a tibial osteotomy is rarely indicated; however, a significant deformity that interferes with development, especially if little or no correction is seen by age 2 years or a symptomatic and persistent deformity is seen in children older than 10 years, may be an indication for tibial osteotomy. [30]

Performing a tibial osteotomy does not seem to decrease the need for later limb equalization. Most children with posteromedial bowing will require a limb-equalizing procedure. The type of procedure depends on the degree of projected limb-length inequality at skeletal maturity. Typically, limb-length inequality is 2-6 cm at skeletal maturity. Usually, an appropriately timed epiphysiodesis can restore limb-length equality, though a lengthening procedure may be indicated for more severe projected limb-length inequalities (>5 cm), especially in children of short stature. [312532]

Understanding the nature of the deformity and establishing the correct diagnosis are very important. Tibial osteotomies in children with anterolateral deformities can be disastrous. This type of tibial deformity can be associated with persistent pseudarthrosis even without any surgical procedures, and performing an osteotomy may promote or instigate an early nonunion. If the bowing has a metabolic etiology, the metabolic disorder should be treated before surgical options are considered. Posteromedial bowing typically self-resolves, leaving only the limb-length inequality to be addressed.

Experimental methods of producing lengthening, such as cultured chondrocyte transfer, vascular surgery, [33and periosteal sleeve resection, [34are being studied.

Medical Therapy

Currently, no medical therapies exist for limb-length inequality. Nonsurgical treatment includes stretching, serial casting, or splinting. This should be initiated at birth. If significant correction is not obtained by age 4-6 weeks, the diagnosis should be questioned; the possibility of a more serious foot deformity (eg, vertical talus), must be ruled out radiographically. After the foot has fully corrected, a splint can be made to maintain correction until age 12-24 months. Bracing of the bowing deformity has been suggested, but it is not currently believed to significantly alter the natural history. [35]

Most children with posteromedial tibial bowing have a limb-length inequality averaging 3 cm, but this can range from about 2 cm to 6 cm. Typically, a limb-length inequality of 2 cm or less is not a functional problem. Often, limb length can be equalized with a shoe lift. About two thirds of limb-length inequalities are corrected with a lift; up to 1 cm can be inserted in the shoe. Larger limb-length inequalities require the shoe to be built up. This is necessary for every shoe worn and limits the type of shoe that the patient can wear.

Limb-length inequalities greater than 5 cm are difficult to treat with a shoe lift. The shoe looks unsightly, and often the patient complains of instability with such a large lift. A foot-in-foot prosthesis can be used for larger limb-length inequalities. This is often a temporizing measure for very young children with significant limb-length inequalities. The prosthesis is bulky, and a fixed equinus contracture may result.

Surgical Therapy

The type of surgical treatment depends on the degree of projected limb-length inequality at skeletal maturity. Epiphysiodesis is a reliable procedure that inhibits growth with few complications. Typically, predicted limb-length inequalities of 2-6 cm can be corrected with an appropriately timed epiphysiodesis. [3637]

Epiphysiodesis cannot be performed on patients who are skeletally mature, and the final limb-length inequality and the degree of growth inhibition must be predicted and are subject to error. In addition, epiphysiodesis effectively shortens the longer leg and is a procedure that is usually performed on the uninvolved side, both of which may be unappealing to the patient and family.

Lengthening is usually performed with corticotomy and gradual distraction. This technique can result in an increase of 25% or more in bone length, but typically a lengthening of 15% (or about 6 cm) is recommended. The limits of lengthening depend on patient tolerance, bony consolidation, maintenance of joint range of motion (ROM), and stability of the joints above and below the lengthened limb. [383940]

Kennedy et al reported a case in which guided growth was employed to prevent the progression of anterolateral bowing of the tibia to tibial pseudoarthrosis in a child with neurofibromatosis. [41]

Procedural details

Predicted limb-length inequality at skeletal maturity must be carefully assessed, and the effect of the given procedure on future growth must be estimated. Estimated height is also important, especially with a large limb-length inequality, because this may determine whether epiphysiodesis or lengthening should be performed. Preoperative teaching is important, especially for lengthening procedures that can last several months and require a great deal of tolerance and cooperation from the patient and family.

The bone is typically lengthened about 1 mm/day, after a 7- to 10-day latency period. The total time in the fixator is about 1 month per 1 cm (10 mm) of lengthening and includes both the time to lengthen and time for the bone to consolidate and become strong enough to bear weight.

Numerous fixation devices are available for lengthening, such as the ring fixator with fine wires, the monolateral fixator with half pins, and the hybrid frame. The choice of fixation device depends on the desired goal. [4243]

A monolateral device is easier to apply and is better tolerated by the patient. The disadvantages of monolateral fixation devices include the following:

  • Limitation of the degree of angular correction that can be obtained concurrently
  • Cantilever effect on the pins, which may result in angular deformity, especially with lengthening of the femur in large patients
  • Difficulty of making adjustments without placing new pins

Monolateral fixators and circular fixators appear to have similar success rates, especially with more modest lengthenings of 20% or less.

Self-lengthening (automated) intramedullary rods can also be used to gain length, without the need of external fixation. Care must be taken not to injure the growth plates in skeletally immature patients. Complication rates are similar to lengthening with external fixation, but patients tend to tolerate these implants better.

Postoperative Care

Postoperative care is minimal for patients who have an epiphysiodesis. Knee ROM should be monitored. [4445Full extension and 90° of flexion should be obtained by 2 weeks after surgery. Weightbearing can begin immediately, and the patient can return to sports at 6-12 weeks.

Postoperative care for patients undergoing lengthening with an external fixator or automated self-lengthening nails is quite demanding. Lengthening begins 5-7 days postoperatively and continues at 1 mm/day until the desired length is obtained. Careful assessment of the joints adjacent to the fixator is mandatory in order to assess for ROM and joint subluxation.

Complications

Epiphysiodesis has been reported to result in physeal closure in 85-100% of patients with few complications. In the author's review [46of 44 patients who underwent proximal tibial epiphysiodesis, no complications occurred, though lack of growth inhibition, angular deformity, and knee stiffness can occur. [47]

Numerous complications can occur when performing limb-lengthening procedures, even in experienced hands. [48Complication rates vary significantly among reported studies and seem to depend on the degree of lengthening, definition of complication, and the surgeon's experience. Complication rates from most series, including that of the authors, [4649are about one per procedure, and many of these require operative treatment. Fortunately, the ultimate objective can usually still be obtained.

The most common complication is pin-site infection. Depending on how this complication is diagnosed, treated, and reported, it may occur in nearly every patient. Numerous pin-care protocols have been developed. Some authors are demonstrating good success with a shower regimen after the incisions have healed. The author uses this regimen in combination with standard cleaning of the pin sites and oral antibiotics if excessive discharge, redness, or swelling is present. Periosteal reaction occurs around the pin sites in most patients, and this may be an early indication of loosening.

Newer pins, coated with hydroxyapatite, have improved fixation to bone and may reduce the rate of infection and loosening during external fixation for distraction osteogenesis. Use of hydroxyapatite-coated pins should be considered in clinical situations requiring prolonged external fixation.

Knee ROM decreases uniformly in femoral lengthening by an average of 37°, but at follow-up, the mean loss in ROM is usually minimal.

Other, more ominous complications include fracture, osteomyelitis, and joint subluxation. The incidence of these more serious complications is about 25% with an experienced surgeon.

Less commonly considered effects of limb lengthening include muscle weakness, pain, and possible physeal inhibition. The last effect is extremely important if lengthening procedures are planned for younger patients with an open physis. Some reports, including this author's, [46found little difference in prelengthening and postlengthening growth velocities, indicating little effect of lengthening on the adjacent growth plates (with moderate lengthenings). Other reports have found growth inhibition, especially in the tibia and in children after extensive lengthening procedures (> 30%). [50]

Unlike pain associated with conventional surgery, pain with lengthening seems to continue beyond the postoperative period and through the lengthening and consolidation phases, until the fixator is removed.

The use of somatosensory evoked potential (SSEP) monitoring may be helpful in preventing neurologic injuries, especially of the peroneal nerve. The use of ultrasound stimulation, [51electrical stimulation, [52or both, though not routinely prescribed, may decrease the time to consolidation.

Long-Term Monitoring

Continued monitoring of limb-length inequality is needed for patients undergoing an epiphysiodesis. An orthoroentgenogram or scanogram should be taken every 6 months until skeletal maturity. The expected goal is limb-length equality within 1 cm at skeletal maturity.

For patients undergoing limb lengthening, the fixator can sometimes be removed in an outpatient setting, but usually these devices are removed with the patient under sedation.


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