Etiology
Torsional variations of the lower extremity are extremely common and are defined as rotational differences that fall within 2 standard deviations (SDs) of the mean.[2] Most rotational issues in normal infants and children are physiologic or postural variations.
Torsional deformities are defined as rotational abnormalities outside the normal range of 2 SDs. Deformities are caused by:
Genetics: similar to other congenital deformities. Although a genetic predisposition exists for torsional abnormalities, no single cause has been identified.
Intrauterine positioning: abnormal shaping of structures caused by mechanical forces. These are deformations distinguished from dysplasias (which are genetic or cellular abnormalities that result in structural abnormalities).
Muscle action: abnormalities in muscle function and tone (e.g., cerebral palsy, myelomeningocele, polio). These strongly affect torsional development during growth.[13][16][17][18][19][20]
These factors can cause torsional deformities at any of three levels of the lower extremity: foot, tibia, and femur.[2] Excessive pelvic rotation can also contribute to gait abnormalities, especially in children with cerebral palsy.
Medial (internal) femoral torsion (MFT) describes the amount of angulation between the axes of the femoral neck and the femoral condyles. When the angle is increased there is increased medial (internal) rotation of the hip.[21] MFT is very common in normally developing children but can also be associated with ligamentous laxity, developmental dysplasia of the hip, cerebral palsy, and hypotonia.[22] Sitting in the W position may be seen in children with MFT because they have more hip internal rotation than external rotation. However, W-sitting does not cause MFT.[Figure caption and citation for the preceding image starts]: Photo of a child sitting in the W positionFrom the collection of Tamir Bloom, MD [Citation ends].
MFT: the most common cause of intoeing in children older than 6 years. MFT decreases through adolescence, with correction of intoeing by late childhood in most.
Medial (internal) tibial torsion (MTT): most often a variation during normal development. MTT is the most common cause of intoeing in children younger than 5 years. However, many children, regardless of age, will demonstrate a combination of MTT and MFT as the cause of their intoeing.
Metatarsus adductus (MA): hypothesized to be due to abnormal intrauterine mechanical forces acting on the foot.
Equinovarus foot deformity (clubfoot): a congenital deformity with a foot that is turned inward and points downward. It may be idiopathic or associated with myelomeningocele, arthrogryposis, and other syndromes.
Skewfoot: may be caused by improper casting of MA. Most cases occur due to an unknown cause.
Causes of Out-toeing
Out-toeing is less common than intoeing and the following causes are all quite uncommon.
Persistent hip abduction contractures: in infants out-toeing is usually a result of persistent hip abduction contractures that develop in utero. Abduction contractures usually improve during the first year of walking.
Lateral (external) tibial torsion (LTT): one in five fetuses is positioned with the lower limbs in external rotation leading to LTT and calcaneovalgus feet.
Slipped capital femoral epiphysis (SCFE): a cause of out-toeing in adolescents due to displacement of the proximal femoral epiphysis around the axis of the femoral metaphysis. This results in an external rotation deformity of the affected lower extremity.
Brain-injured children (e.g., cerebral palsy) have loss of selective muscle control, difficulties with balance, and abnormal muscle tone (primary abnormalities). Torsional deformities develop because the effects of brain injury impose abnormal forces on both muscle and bone. Skeletal deformities may emerge gradually, directly proportional to the rate of skeletal growth.
Pathophysiology
Intoeing
MTT: if severe, gait may be compromised by disrupting shock absorption of the foot during loading response and may compromise limb clearance in the swing phase.[25][26] Quantitative gait analysis studies of patients with extreme intoeing gait because of MTT have demonstrated increased varus loading of the knee during stance phase, in addition to other primary and compensatory gait deviations.[26][27][28] Longstanding severe MTT, related dynamic gait deviations, and associated abnormal loading may be associated with degenerative arthritis of the knee in adults, although the nature of this association is not clear.[26][27][29][30][31][32]
MFT: in utero femoral anteversion is about 55°. As a child begins to walk, the hip extends and the anterior iliofemoral ligament stretches over the proximal femur, pushing it backward.[33] This mechanism remodels the proximal femur. Femoral anteversion measures on average 10° to 15° by adulthood. Ligamentous laxity or neuromuscular conditions may have insufficient tension to bring about normal remodeling, resulting in persistent fetal alignment.[34] Limited remodeling of the proximal femur is common in cerebral palsy due to delayed onset of walking and abnormal muscle forces. When walking does begin, the hips are flexed. These factors weaken the iliofemoral ligament tension promoting anteversion. To seat the femoral head in the acetabulum and to optimize hip abductor strength, children with MFT walk with the femur in internal rotation, which results in internal rotation of the entire lower limb.[33] While it has been suggested that sitting in the W position (hips internally rotated) can promote maintenance of femoral anteversion by placing an increased torsional load on the femur, there is no evidence that this is true. It is more likely that patients with increased anteversion choose to sit this way because it is more comfortable than sitting cross-legged (with hips externally rotated).
MA: abnormalities in bony anatomy, such as a deformity of the medial cuneiform, and muscle imbalance or contracture have been suggested.
Skewfoot: this is a complex deformity of the foot composed of forefoot adduction, midfoot abduction, and hindfoot valgus.
Equinovarus foot deformity (clubfoot): this is a rigid deformity consisting of ankle equinus, midfoot cavus, heel varus, and midfoot and forefoot adductus.
Blount disease: infantile type (0-4 years old) is a nonphysiologic form of genu varum and MTT caused by a growth disorder of the medial proximal tibia. Deformity is restricted to the proximal tibia and is associated with early walking and obesity. Adolescent type (after age 9 years) shares similar pathophysiology with the infantile type with excessive loads on a varus knee resulting in abnormal growth of the proximal tibial physis. Unlike the infantile type, deformity may also involve the distal femur.
Out-toeing
LTT: if severe, may compromise the stability and lever function of the foot during mid and terminal stance phase of the gait cycle.[35]
Lateral (external) femoral torsion (LFT): intrauterine positioning of the legs causes lateral rotation hip (abductor) contractures, which result in increased hip external rotation relative to internal rotation and apparent out-toeing in infancy.[3][36] This usually resolves with early walking.[37]
SCFE: the femoral neck slips anteriorly and laterally through the physis (growth plate) resulting in an apparent posterior shift of the epiphysis. Increased hip external rotation, decreased hip internal rotation, and increased external foot progression angle, as well as other anatomic, clinical, and gait abnormalities, are associated with deformity of the proximal femur. SCFE most commonly presents unilaterally and results in asymmetric foot progression with the symptomatic leg externally rotated. Functional abnormalities may improve after treatment and recovery, and are influenced by severity of residual anatomic deformity.[38][39]
Flexible flat feet: this is a normal variation of foot alignment in early childhood, with spontaneous resolution in the first decade of life in nearly all children. Arch height is determined by the bone-ligament complex of the foot and is not influenced by shoe wear.
Effect of torsion on the patellofemoral joint
Bone alignment is one factor that may contribute to patellofemoral joint mechanics.[40] Abnormal limb alignment in the axial plane may alter the balance of body-weight transfer to the ground, overloading biologic tissues (ligaments, articular cartilage, bone, muscle, and tendon).
Greater-than-normal internal knee rotation during gait, due to either excess femoral anteversion or lateral tibial torsion, or both, increases the lateral patellofemoral joint compression forces and the strain on the medial patellofemoral ligaments. If severe enough, the physiologic threshold of biologic tissues may be exceeded, producing anterior knee pain, patellar instability, or knee osteoarthrosis in later life.[29][30][31][41][42][43] This is called miserable malalignment syndrome.[44]
Deformities in children with neuromuscular disease
Torsional deformities arise because of abnormal forces acting on the growing skeleton by the effects of the primary brain injury.[33] Bones fail to mold, remodel, or model normally with growth.
Torsional malalignment is a type of lever-arm dysfunction. Improper transverse plane orientation of the bone causes pathologic gait. Bones are levers, rigid bodies on which a load and force act. Their purpose is to produce a mechanical advantage over the load or rapid motion of the load. In normal gait, having the lever-arms of the lower extremity (femur, tibia, and foot) and their associated joints (hip, knee, ankle, and foot joints) aligned near the foot progression angle is the most mechanically advantageous, and increases the efficiency of walking. Malrotated levers produce pathologic dysfunction by rotating out of this plane, which decreases the efficiency of gait by:
Reduction of the magnitude of moments, reducing the ability of muscles to rotate joints of the limb. A moment is the rotatory impetus occurring at a pivot point (fulcrum) generated by forces acting at a distance of a lever arm.
Introduction of secondary moments that alter leverage necessary for normal gait, and promoting further deformities of the long bones by applying abnormal stresses on plastic, growing bones.
Classification
Direction of deformity[1]
Clinical assessment of the direction of lower-extremity rotational alignment is classified as follows.
Intoeing: the long axis of the foot is internally (medially or toward midline) rotated to the line of progression when walking or running.
Out-toeing: the long axis of the foot is externally (laterally or away from midline) rotated to the line of progression when walking or running.
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