[Magnetic resonance imaging for detection of rotational deformities in children with femoral shaft fractures treated by the ESIN method].

PURPOSE OF THE STUDY

The aim of the study was to evaluate the results of elastic stable intramedullary nailing (ESIN).used in the treatment of children with femoral shaft fractures, with a focus on post-traumatic rotational deformity assessed by magnetic resonance imaging (MRI). An alternative hypothesis was established assuming a significantly high incidence of this post-traumatic complication. Also, the advantages of MRI for the diagnosis of rotational deformity were assessed in comparison with ultra- sonography and physical examination.

MATERIAL AND METHODS

A total of 26 patients, 18 boys and 8 girls, between 6 and 14 years of age (average, 12.5), were included. The range of knee and hip motion was evaluated and the length of both lower extremities was measured. The radiograph of each patient contained a contrast, marked scale to facilitate an exact determination of femur length. In these 26 patients, MRI examination was included as a novel approach in this system of evaluation. On the basis of transversal sections through the proximal and the distal femoral epiphysis, the angle formed by the femoral neck axis and a dorsally led line tangential to both femoral condyles was measured The difference in this anteversion angle between the injured and the healthy extremity was taken as a value of post-traumatic rotational deformity. The difference equal to or larger than 10 degrees was regarded as a pathological finding. The results were evaluated using the Wilcoxon signed-rank test.

RESULTS

The average value of the difference was 5.8 degrees. A pathological persistent post-traumatic rotational deformity of 10 and more degrees was found in three patients (15 %). The results of statistical analysis did not confirm our alternative hypothesis that use of the ESIN method for femoral shaft fractures might be associated with a significantly increased probability of rotational deformity development (p=0.450).

DISCUSSION

As described in the literature, post-traumatic rotational deformity following a femoral shaft fracture can be up to 20 degrees in 10 % to 20 % of the patients.The results of this study are notably better. Routinely, measurement of the angle of anteversion is based on physical examination of hip range of motion. This finding was completed by X-ray examination in semi-axial projection, as described by Schulz whose error of measurement was 10 or more degrees. The angle of femoral anteversion and the difference between the extremity after femoral shaft fracture and the contralateral one can also be determined by ultrasonography, but the error of measurement can be about 5 degrees. An exact measurement of the angle of anteversion can be achieved with computed tomography, but this examination means radiation exposure for the patient. The method which combines exact measurement and no risk of exposure for the child is magnetic resonance imaging.

CONCLUSIONS

The method of measuring rotational deformity after femoral shaft fracture using MRI gave exact results and posed no risk for the child, and is therefore presented as a novel and important part of post-traumatic follow-up of children with this injury. In the ESIN- treated patients, this diagnostic method did not reveal any statistically significant occurrence of serious post-traumatic rotational deformity during the healing of a femoral shaft fracture.