Guided Growth to Correct Limb Deformity



Guided Growth to Correct Limb Deformity


Ryan D. Muchow

Kenneth J. Noonan





DEFINITION



  • The anatomic axis is the mid-diaphyseal line of a bone. The anatomic angle of the lower extremity consists of the angle between the anatomic axis of the femur and tibia (normal = 5 to 9 degrees valgus).


  • The mechanical axis represents the weight-bearing alignment of a bone or an extremity in either the coronal or sagittal plane. It is a straight line connecting the proximal and distal extent of the bone regardless of its anatomic alignment. For example, the normal mechanical axis of the lower extremity in the coronal plane is a straight line from the center of the femoral head to center of the distal tibia and passes through the middle of the knee (FIG 1).14






    FIG 1 • A. The mechanical axis is a straight line drawn on a full-length, standing AP, or lateral radiograph of the lower extremity connecting the center of the femoral head to the center of the distal tibia. The normal angles for LDFA, MPTA, and LDTA will assist in identifying the location of deformity in the coronal plane, and PDFA, PPTA, and ADTA likewise will locate deformity in the sagittal plane. B. Dividing the knee into zones, the mechanical axis should pass through the central one-third of the joint. Deviation into zone 2 or 3 indicates deformity which may require surgical intervention.



    • The mechanical axis is used to assess coronal and sagittal plane deformity and guide surgical correction to restore a normal weight-bearing alignment. Sagittal plane deformity can also be manipulated to improve the amount of extension at the knee or dorsiflexion at the ankle.


  • Symmetric physiologic varus is expected between birth and 18 to 24 months, which transitions to a physiologic valgus deformity that is maximal at 3 to 4 years and should correct by 6 to 8 years of age.18



  • The physis is located at the junction of the epiphysis and metaphysis of long bones and is responsible for longitudinal growth. Consisting of chondrocytes in an extracellular matrix, the cells are oriented longitudinally in four distinct zones: the resting zone, the proliferative zone, the zone of hypertrophy, and the zone of provisional calcification.



    • The zone of Ranvier is located at the periphery of the physis and contributes to circumferential growth of the physis.


    • The perichondrial ring of LaCroix is an extension of the diaphyseal bone and periosteum and stabilizes the physis to the periosteum of the bone enhancing the shear strength of the growth plate.1


  • The Heuter-Volkmann principle states that compression of the growth plate results in slowing the rate of bone growth. Delpech law is related in that tension across the growth plate increases the rate of bone growth.


  • Guided growth or growth modulation techniques use the Heuter-Volkmann principle to affect the rate of growth at one part of the physis relative to another to gain correction of deformity in the coronal or sagittal plane. Common lower limb deformities that are treated with guided growth include pathologic:



    • Genu varum and genu valgum19


    • Knee flexion contracture8, 16


    • Ankle valgus20


    • Ankle plantarflexion contracture


    • Hip varus and valgus23


ANATOMY



  • Mechanical and anatomic axis of lower extremity (see FIG 1A)15



    • Hip



      • Neck-shaft angle (NSA) = 130 degrees


    • Knee



      • Lateral distal femoral angle (LDFA) = 87 degrees


      • Medial proximal tibia angle (MPTA) = 87 degrees


      • Posterior distal femoral angle (PDFA) = 83 degrees


      • Posterior proximal tibia angle (PPTA) = 81 degrees


    • Ankle



      • Lateral distal tibia angle (LDTA) = 89 degrees


      • Anterior distal tibia angle (ADTA) = 80 degrees


  • Center of rotation of angulation (CORA) is the location of deformity in a long bone. If a single point of deformity exists, the point of intersection between the proximal mechanical axis and the distal mechanical axis is the CORA and it should correspond to anatomic deformity. If a constructed CORA does not correspond with obvious anatomic deformity, another deformity must exist. Therefore, deformity correction should occur at the CORA to restore the mechanical axis.14


  • Assessment of the physis should occur to ensure adequate growth is available for guided growth. This would include checking for physeal bars and to identify whether the physis is normal or pathologic secondary to an underlying etiology.


  • Secondary problems



    • Limb length discrepancy


    • Rotational problems


    • Osteochondritis dissecans


    • Angular problems resulting in subluxation



      • Hip—coxa valga


      • Patella—genu valgum


PATHOGENESIS



  • Physiologic


  • Idiopathic genu valgum


  • Heuter-Volkmann principle



    • Infantile and adolescent tibia vara


  • Acquired (insult to the physis)—trauma, infection, radiation, iatrogenic, juvenile inflammatory arthritis, osteochondroma


  • Congenital (condition affecting the health/growth of the physis)—skeletal dysplasia, focal fibrocartilaginous dysplasia, osteogenesis imperfecta, multiple hereditary exostosis, Ollier disease, Maffucci syndrome


  • Metabolic bone disease (the physis is susceptible to the Heuter-Volkmann principle at the age of physiologic angulation, for example, onset before 2 years of age will lead to progressive varus, after 4 or 5 years of age will lead to progressive valgus)—rickets, renal osteodystrophy


  • Adaptive response to a long bone deformity


NATURAL HISTORY



  • Physiologic = spontaneous resolution


  • Progressive angular deformity can cause gait disturbance, limitations in function, and pain.


  • There is no consistent evidence demonstrating what degree of malalignment could lead to osteoarthritis and at what age. Various biomechanical and gait studies describe increased force through the medial and lateral compartments with genu varum and valgum, respectively, but this has not been shown to cause osteoarthritis.4, 9, 12, 24


PATIENT HISTORY AND PHYSICAL FINDINGS



  • History is important to identify underlying pathology and determine growth potential.


  • Current symptoms



    • Pain, functional limitations, cosmetic concerns


  • Observe gait



    • Thrust, instability, crouch, equinus


  • Assess for limb length discrepancy and rotational profile.


  • Joint examination



    • Range of motion of affected and adjacent joints


    • Joint instability and pain


  • Foot deformities


IMAGING AND OTHER DIAGNOSTIC STUDIES



  • Plain radiographs (as indicated)


  • Bone age


  • Lower extremity



    • Standing, full-length anteroposterior (AP) alignment radiograph


    • Lateral views of the lower extremities and joints involved


    • Consider comparison views


    • Consider scanogram


    • Standing lateral foot film to assess foot height


  • Computed tomography (CT)—most accurate assessment of rotational profile and best method to assess individual bone lengths in children with sagittal plane joint contractures


  • CT or magnetic resonance imaging (MRI)—identifies a physeal bar




DIFFERENTIAL DIAGNOSIS



  • Physiologic


  • Idiopathic genu valgum



  • Infantile and adolescent tibia vara


  • Acquired: trauma, infection, radiation, iatrogenic, juvenile inflammatory arthritis, osteochondroma, adaptive response to a long bone deformity


  • Congenital: skeletal dysplasia, focal fibrocartilaginous dysplasia, osteogenesis imperfecta, multiple hereditary exostosis, Ollier disease, Maffucci syndrome


  • Metabolic bone disease: rickets, renal osteodystrophy


NONOPERATIVE MANAGEMENT



  • Pathologic conditions by definition are progressive and therefore not commonly amenable to observation or bracing.


  • Metabolic disorder—treat and optimize underlying condition first, then if progressive deformity remains, guided growth is indicated.


SURGICAL MANAGEMENT

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Jul 22, 2016 | Posted by in ORTHOPEDIC | Comments Off on Guided Growth to Correct Limb Deformity

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