Guided growth: the importance of a single tether. An experimental study

During the last few years, the use of the 8-plate as a technique for hemiepiphysiodesis has gained wide acceptance, as it has been shown that it works in a more physiological way than other methods such as staples or transphyseal screws. It has mechanically been compared with a tension band plate, and for this reason, only a single plate is needed. The following study was undertaken to test the 8-plate against the staples and assess factors that can influence the difference in results.

A prospective experimental study was designed to compare the ability of 2 hemiepiphysiodesis methods, the 8-plate and the double staple, to produce angular deformity in the rabbit's tibia (group I). The variable studied was the variations in the articular line-diaphysis angle at 6 weeks. As the results showed that the 8-plate produced a bigger deformity, a second group was designed (group II) comparing single against double staple, under the hypothesis that the differences observed in the first group could be related to the number of anchors put across the physis and consequently depend on the volume of physis involved by the staples.

In group I, the 8-plate produced a bigger angulation at 6 weeks' time than the 2 staples (a difference of 6.5 degrees, P = 0.03). Similarly, in group II, the single staple produced a greater angulation than the 2 staples (difference 6 degrees, P = 0.08). When both groups were compared, no differences in the angulation produced by the 8-plate and the single staple with respect to the 2 staples were found.

These results suggest that one of the reasons why the 8-plate may act in a more "physiological way" (vs. the traditional 2-staple or 3-staple hemiepiphysiodesis) could be the fact that the growth plate is tethered only at a single point. Therefore, the physis retains a major potential for growth and deformity.

The 8-plate is superior in producing/correcting angular deformity when compared with the traditionally used staples (2 or more) but not when compared with a single staple.