A technical note on improved instrumentation for Blount staple insertion

Abstract

Purpose: Temporary hemiepiphysiodesis has gained increasing popularity after the introduction of the eight-Plate Guided Growth System. Since its introduction, the eight-Plate has largely supplanted the traditional Blount staple. The eight-Plate offers better purchase in the bone and a more precise insertion technique. However, the Blount staple is less expensive than the various guided growth plates. Further, some surgeons feel that the Blount staple may work faster, making it more appropriate for children who are approaching skeletal maturity. Unfortunately, the original instrumentation and technique for inserting the Blount staple is over 50 years old and has not been updated.

Methods: The purpose of this study was to develop new instrumentation to make Blount staple insertion as accurate and minimally invasive as eight-Plate insertion. We developed wire/drill guides to accommodate all three sizes of the Blount staple. Two wires are inserted through the wire guide under image intensifier control. After confirming the accurate position of the guidewires, a 3.2-mm cannulated step drill is used to drill over the wires to a depth of 5 mm. This creates two pilot holes for the two tines of the Blount staple. The final insertion is guided under an anteroposterior image intensifier view. We also developed a small staple holder that permits insertion through a small incision.

Results: We developed a working prototype of the new instrumentation and used it in three clinical cases.

Conclusions: With the new staple inserter and instrumentation, Blount staples can now be inserted through a smaller incision with similar accuracy as eight-Plate insertion.

Keywords: Angular deformity; Blount staple; Eight-Plate; Growth plate; Surgical instrumentation; Temporary hemiepiphysiodesis.

Figures

Fig. 1

New staple inserter is only as wide as the smallest Blount staple but still securely clamps all three staple sizes. The inserter can be combined, if needed, with a back slapper extractor for later removal of the Blount staple

Fig. 2

Combined wire and drill guide was designed to accommodate all three sizes (3/8, 5/8, and 7/8 inch) of the Blount staple. The 3.2-mm drill is designed as a step drill that reams the outer cortex of the bone to a depth of 5 mm

Fig. 3

Intraoperative image intensifier view showing two guidewires inserted over the 5/8-inch wire guide on the anteroposterior (a) and lateral views (b)

Fig. 4

a Blount staple (5/8 inch) is inserted into the pre-drilled guide holes. The direction is adjusted as needed using image intensifier control. Final intraoperative image intensifier views in the anteroposterior (b) and lateral views (c)

Fig. 5

Intraoperative photograph showing the difference in size between the original Zimmer staple inserter and our new inserter