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. 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. [33]
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. [34, 35, 28, 36]
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, [37] and periosteal sleeve resection, [38] are being studied.
Nonoperative Therapy
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 have a significant effect on the natural history. [39]
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. [40, 41]
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. [42, 43, 44] Younger patients may have lower complication rates and require a shorter duration of external fixation than older patients. [45]
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. [46]
Operative 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. [47, 48]
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. [49, 50] Full 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 [51] of 44 patients who underwent proximal tibial epiphysiodesis, no complications occurred, though lack of growth inhibition, angular deformity, and knee stiffness can occur. [52]
Numerous complications can occur when performing limb-lengthening procedures, even in experienced hands. [53] Complication 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, [51, 54] are 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 have demonstrated 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.
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, [51] found 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%). [55]
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, [56] electrical stimulation, [57] or 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.
-
Anteroposterior radiograph of a 1-year-old child with posteromedial tibial bowing.
-
Lateral radiograph of a 1-year-old child with posteromedial tibial bowing.
-
Anteroposterior and lateral radiograph of a 9-year-old child with posteromedial tibial bowing. Note that the bowing has significantly improved.
-
Posteromedial tibial bowing. The Galeazzi test. Note the difference in the height of the flexed knees.
-
Scanogram of a patient with posteromedial tibial bowing and a limb-length inequality.
-
A hydroxyapatite-coated Schanz pin used to secure external fixator devices to the bone.
