A Roentgen Stereophotogrammetric Analysis of Growth Arrest by Stapling

Abstract

To evaluate the growth-arresting effect of Blount staples and to detect early signs of complications and failure to control growth, a roentgen stereophotogrammetric analysis was performed. In a 9 1/2-yr-old boy with a leg-length discrepancy of 6.8 cm, 6 Blount staples were introduced medially and laterally in the distal femur and 10 tantalum balls in the metaphysis and bony epiphysis. Growth is presented as changes in distance between the reference implants in the metaphysis and bony epiphysis, a representation mainly of longitudinal growth, but also as rotations and translations between the 2 bone segments. Staple movements are presented graphically as 3-dimensional movements of the tips in a coordinate system fixed to the metaphysis, but also numerically as total translations of the metaphyseal staple tips in relation to the metaphysis and the epiphyseal tips in relation to the epiphysis. The longitudinal component of these movements (movements toward or away from the growth plate) are separately presented. The widening of the staple gaps and mean rotations and translations of medial and lateral group of staples are presented. The rate of longitudinal growth was initially low, but increased markedly in 3 mo. In the next 6 mo., a continuous decrease was found to a basal level, which lasted for about 2 yr. A simultaneous widening and movement in peripheral direction was found for the staples. Kinematic analysis showed a small varus deformity indicating a more pronounced growth-arresting effect medially than laterally. About 3 yr after stapling, the longitudinal growth rate increased both medially and laterally with simultaneous widening and extrusion resulting in loosening of staples. This was confirmed by standard radiographs and was evident at reoperation. The widening of staples amounted to about 4 mm in 4 yr. The staples moved in peripheral direction from the center of the femur. The epiphyseal tips moved more peripherally than the metaphyseal tips, resulting in a rotation of the staples. The tips of the staples moved in the preformed channels by the leg of the staples, but also outside these channels, indicating a cutting through bone or bone resorption around the tips. The imbalance between the transverse growth of the bony epiphysis and metaphysis and the movements of the staples in peripheral direction result in a loosening of staples. The increase from basal level of longitudinal bone growth was found to be an early sign of loosening of staples.