Orthopedics

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CONSULTATION CORNER 

Coxa Vara

Robyn Peckham, MD; Victoria M Dvonch, MD

Abstract

D.W. was born weighing 6 Ib 6 oz at 36 weeks gestation by repeat cesarean section to a 29-year-old woman with no history of prenatal infections. At birth, he had findings of hypospadias and gastroesophageal reflux. He was developmentally delayed, rolling over at 7 months of age, sitting at 18 months, and standing with assistance at 21 months. At 18 months of age, he had abduction of the hip of 60° on the right and of 70° on the left and had a negative Allis' sign. At 2 Vi years of age, he was enrolled in an infant developmental therapy program, and at 3Í4 years, he was referred by his therapist to an orthopedic surgeon for evaluation of a "limping" gait and leg length discrepancy. A roentgenogram taken at 4/2 years (Figure) demonstrated a right proximal femur with a neck-shaft angle of 94° and a Hilgenreiner's epiphyseal angle (HE) of 89°.

Discussion

Coxa vara may refer descriptively to any varus deformity of the femoral neck or it may refer to more specific entities which have commonly been designated as congenital coxa vara and developmental coxa vara. The history, and physical and radiographic examination of the case presented classically illustrate the diagnosis of developmental coxa vara.

Developmental coxa vara usually occurs as an isolated deformity of the proximal femur and often goes unnoticed until the child reaches walking age and is brought for evaluation of a leg length discrepancy or abnormal gait. The leg length discrepancy due to coxa vara does not progress to more than 2 cm.1 Gait abnormalities associated with the deformity include a limb that is generally painless and a waddling gait seen when the deformity is bilateral. The involved hip will often display limitations of abduction and internal rotation. By contrast, congenital coxa vara is associated with other abnormalities of the proximal femur such as a congenitally short femur. In this instance, the diagnosis may be made earlier as an incidental finding in the investigation of the more readily visible defect, such as a resultant gross leg length discrepancy.

The roentgenographic appearance of coxa vara is distinctive in the AP view of the pelvis. The neckshaft angle is less than 120°, the growth plate is tilted to a near verticle orientation, and the greater trochanter may be evaluated above the femoral head. The femoral neck may appear short and poorly ossified and, in a classic case, a triangular fragment of bone may be seen on the inferomedial side of the femoral neck.

The histopathology of coxa vara has been described by several investigators and the occurrence of cartilage islands in metaphyseal bone and disordered cellular arrangement of the growth plate is commonly recognized. Chung and Riser report a case of a 5-year-old boy with unilateral congenital coxa vara whose vessels were perfused with barium sulfate at autopsy and when examined radiographically.2 They found a decreased number and caliber of vessels on the metaphyseal side of the proximal femoral growth plate and, on histologic preparation, found abnormal endochondral cartilage, absence of metaphyseal and epiphyseal trabeculation, widened growth plate, decreased numbers of osteoblasts, and a cartilagenous fissure extending from the growth plate through the cortex on the inferior aspect of the femoral neck. The origin of this fissure is not certain but it may be responsible for the appearance of the triangular bone fragment seen roentgenographically. Abnormal endochondral ossification was also noted in the clinically and roentgenographically normal femur of the same patient.

The etiology of developmental coxa vara is not understood well. Given the evidence that there is a vascular derangement associated with the deformity, it seems tempting…

D.W. was born weighing 6 Ib 6 oz at 36 weeks gestation by repeat cesarean section to a 29-year-old woman with no history of prenatal infections. At birth, he had findings of hypospadias and gastroesophageal reflux. He was developmentally delayed, rolling over at 7 months of age, sitting at 18 months, and standing with assistance at 21 months. At 18 months of age, he had abduction of the hip of 60° on the right and of 70° on the left and had a negative Allis' sign. At 2 Vi years of age, he was enrolled in an infant developmental therapy program, and at 3Í4 years, he was referred by his therapist to an orthopedic surgeon for evaluation of a "limping" gait and leg length discrepancy. A roentgenogram taken at 4/2 years (Figure) demonstrated a right proximal femur with a neck-shaft angle of 94° and a Hilgenreiner's epiphyseal angle (HE) of 89°.

Discussion

Coxa vara may refer descriptively to any varus deformity of the femoral neck or it may refer to more specific entities which have commonly been designated as congenital coxa vara and developmental coxa vara. The history, and physical and radiographic examination of the case presented classically illustrate the diagnosis of developmental coxa vara.

Developmental coxa vara usually occurs as an isolated deformity of the proximal femur and often goes unnoticed until the child reaches walking age and is brought for evaluation of a leg length discrepancy or abnormal gait. The leg length discrepancy due to coxa vara does not progress to more than 2 cm.1 Gait abnormalities associated with the deformity include a limb that is generally painless and a waddling gait seen when the deformity is bilateral. The involved hip will often display limitations of abduction and internal rotation. By contrast, congenital coxa vara is associated with other abnormalities of the proximal femur such as a congenitally short femur. In this instance, the diagnosis may be made earlier as an incidental finding in the investigation of the more readily visible defect, such as a resultant gross leg length discrepancy.

The roentgenographic appearance of coxa vara is distinctive in the AP view of the pelvis. The neckshaft angle is less than 120°, the growth plate is tilted to a near verticle orientation, and the greater trochanter may be evaluated above the femoral head. The femoral neck may appear short and poorly ossified and, in a classic case, a triangular fragment of bone may be seen on the inferomedial side of the femoral neck.

The histopathology of coxa vara has been described by several investigators and the occurrence of cartilage islands in metaphyseal bone and disordered cellular arrangement of the growth plate is commonly recognized. Chung and Riser report a case of a 5-year-old boy with unilateral congenital coxa vara whose vessels were perfused with barium sulfate at autopsy and when examined radiographically.2 They found a decreased number and caliber of vessels on the metaphyseal side of the proximal femoral growth plate and, on histologic preparation, found abnormal endochondral cartilage, absence of metaphyseal and epiphyseal trabeculation, widened growth plate, decreased numbers of osteoblasts, and a cartilagenous fissure extending from the growth plate through the cortex on the inferior aspect of the femoral neck. The origin of this fissure is not certain but it may be responsible for the appearance of the triangular bone fragment seen roentgenographically. Abnormal endochondral ossification was also noted in the clinically and roentgenographically normal femur of the same patient.

Figure: AP of pelvis demonstrating coxa vara. Note the vertical orientation of the growth plate and the triangle of bone on the infero med i al side of the neck.

Figure: AP of pelvis demonstrating coxa vara. Note the vertical orientation of the growth plate and the triangle of bone on the infero med i al side of the neck.

The etiology of developmental coxa vara is not understood well. Given the evidence that there is a vascular derangement associated with the deformity, it seems tempting to postulate that developmental coxa vara could be a manifestation of vascular insufficiency. It is also possible that the vascular changes in Chung and Riser's case were secondary to an unknown primary process or to the patient's prior surgery.2 The disordered histology raises the issue of a dyschondroplastic process, and the occurrence of coxa vara with concomitant cerebral palsy3 makes one wonder about the role of various biomechanical forces. What is generally agreed on is that coxa vara is a developmental defect in the growth of the proximal femur, whether or not this is due to some postnatal event or a congenital disorder that precludes normal development.

The etiology of congenital coxa vara is perhaps no better understood, but the fact that it is not infrequently seen in conjunction with other disorders of the proximal femur leads to the suspicion that these disorders are related to a spectrum that involves various degrees of proximal femoral dysgenesis and failure of endochondral ossification. A type A proximal focal femoral deficiency involves distortion of the morphology and a disordered ossification of a large segment of the proximal femur. A similar derangement limited to a portion of the femoral neck could easily describe the findings in coxa vara.

The goal of treatment for coxa vara is restoration of the neck-shaft angle and reorientation of the growth plate to decrease shear forces and promote ossification of the femoral neck defect. This is surgically accomplished with a valgus osteotomy. The accepted indications ??t surgical treatment of coxa vara include a neck-shaft angle of less than 90°, progressive deformity, vertical physis, and a significant limp. Weinstein studied the use of HE, which is the angle between Hilgenreiner's line and a line drawn parallel to the growth plate to determine the need for surgical intervention.4 In his retrospective study, HE angles greater than 60° were associated with progressive deformity requiring surgery. HE angles less than 45° went on to spontaneous correction of the deformity, and angles from 45° to 60° fell in a gray zone that requires observation.

The case presented clearly meets the criteria for surgical intervention which should be carried out immediately. Conservative management will only lead to increasing deformity and eventual pseudoarthrosis.5

References

1. MacEwen GD. Bunnell WP. Ramsey PL: The hip. in Lovell WW. Winter RB (eds): Pediatric Orthopaedics, ed 2. Philadelphia. JB Lippincott. 1986.

2. Chung SMK. Riser WH: The histological characteristics of congenital coxa vara. A case report of a five year old boy. Clin Orthop 1978: 132:71-81.

3. Gordon SL. Coder JM: Coxa vara in three patients with concomitant cerebral palsy. Clin Orthop 1978: 137:175-180.

4. Weinstein JN. Kuo KN, Millar EA: Congenital coxa vara. A retrospective review. J Pediatr Orthop 1984: 4:70-77.

5. Babb FS. Ghormley RK. Chattertop CC: Congenital coxa vara. J Bone Joint Surg 1949: 31 A: 115-131.

10.3928/0147-7447-19890601-16

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