Posteromedial Bowing of the Tibia

Key Points:

  • Posteromedial bow of the tibia is a congenital deformity of the tibia with associated findings in the foot and ankle
  • There is typically spontaneous but incomplete correction of the bowing within the first 4 years of life
  • The growth inhibition of the tibia remains constant
  • Treatment focuses on addressing any leg length discrepancy if it is anticipated to be greater than 2 cm at skeletal maturity
  • The average leg length discrepancy without treatment is 3.5 cm
  • Unless severe angular deformity does not correct with growth, operative treatment is best delayed until closer to skeletal maturity

Description:

  A congenital anomaly in which there is both posterior and medial bowing of the tibia and fibula.  The deformity is obvious at birth. The foot assumes a calcaneovalgus position and is typically in extreme dorsiflexion.  The foot at birth will occasionally be abutting the concave tibia and a skin dimple is often present over the apex of the bow.  The growth inhibition of the tibia remains constant.

Epidemiology:

Unknown

Clinical Findings:

  Patients will typically present at birth with a notable deformity of the leg.  The abnormality is unilateral.  Some studies show a preponderance of the left foot more commonly affected than the right (Shah, 2009). The foot is typically resting dorsiflexed against the tibial shaft.  The patient will lack normal passive plantarflexion of the ankle due to contracture of the dorsal structures of the leg and foot.  Other associated findings are underdevelopment of the calf muscles, decreased length and width of the foot and decreased ankle range of motion (Hofmann, 1981).  Some studies have also noted ankle valgus.  This has been attributed to either a proximally located distal fibular physis or wedging of the distal tibia physis (Shah, 2009).

  The posteromedial bow of the tibia will improve with growth with the most rapid correction occurring in the first year of life.  Of the two methods of remodeling that occur, reorientation of the physis contributes to greater correction than remodeling at the diaphysis via Wolf’s law (Shah, 2009). Since the growth inhibition of the tibia remains constant, the leg length discrepancy at maturity can be predicted based on x-rays obtained at a young age.  Studies have shown the greater the medial bow, the greater the ultimate leg length discrepancy.  The percentage of growth inhibition ranges from 15-40% with an average discrepancy of 3.5 cm.

Imaging Studies:

  AP and lateral tibia radiographs are the initial imaging studies to evaluate the deformity. The bowing of the tibia improves with growth but a residual leg length discrepancy persists due to growth inhibition and may be monitored with periodic leg length radiographs.

Etiology:

The cause of posteromedial bow is unknown.  Theories include mechanical forces (the dorsiflexed foot against the tibia) and placental abnormalities (amnion rupture).

Treatment:

  Initial treatment in infant begins with a stretching program of the dorsal structures of the ankle. Parents perform this at home after they have been given appropriate instruction.  Severe contractures may require serial casting for a few weeks in infancy.  The remainder of treatment focuses on managing the resulting leg length discrepancy and residual bowing deformity.  Several methods of treatment have been proposed with various success rates.  Treatment for leg length discrepancy can involve either appropriately timed contralateral epiphysiodesis or a lengthening procedure with a frame.  The advantage of osteotomy with external fixationis that any residual angular deformity can also be addressed with the device. (Kaufman, 2012)  Prior studies have also shown successful deformity correction with Sofield osteotomies and k-wire fixation in young children.(Napiontek, 2014)  Initial studies suggested surgery at the age of 3 for angular deformities greater than 30 degrees.(Pappas, 1984)  However, more recent studies suggest that since the final angular deformities with and without surgery are not different at maturity, delaying surgery until closer to skeletal maturity allows the patient to have more accurate correction of their leg length discrepancy and has a higher success rate as the patient is able to be more compliant with their care.(Johari, 2010) 

Complications:

  The arc of ankle range of motion remains unchanged despite surgery.  Complications typically occur as a result of operative treatment of the leg length discrepancy such as pin tract infections, non-union or residual angular deformity.  Complications of non-operative treatment are the long-term need for an orthosis and the associated cost of an orthosis.  If the leg length discrepancy is greater than 2 cm, there is concern for the future development of back, hip or knee arthritis.

References:

  1. Johari AN, Dhawale AA, Salaskar A, Aroojis AJ. Congenital postero-medial bowing of the tibia and fibula: is early surgery worthwhile?  J Pediatr Orthop B. 2010;19(6):479-486
  2. Kaufman SD, Fagg JA, Jones S, Bell MJ, Saleh M, Fernandes JA. Limb lengthening in congenital posteromedial bow of the tibia.  Strat Traum Limb Recon. 2012;7:147-153
  3. Napiontek M, Shadi M. Congenital posteromedial bowing of the tibia and fibula: treatment option by multilevel osteotomy. J Pediatri Orthop B. 2014;23:130-134
  4. Pappas AM. Congenital postero-medial bowing of the tibia and fibula. J Pediatr Orthop. 1984;4:525-531
  5. Shah HH, Doddabasappa SN, Joseph BJ. Congenital posteromedial bowing of the tibia: a retrospective analysis of growth abnormalities in the leg. J Pediatr Orthop B. 2009;18(3):120-128

Figures and Tables:



Fig 1 A,B-AP and Lateral x-ray of tibia reveal posteromedial bow in a newborn infant.


Fig 2 – Standing bilateral lower extremity x-ray of same child at 4 years of age reveals 2.5 cm leg length discrepancy and evidence of residual deformity of the tibia and fibula

Top Contributors:

Author and Case images Vinitha Shenava MD