Use of Simple Algorithms to Predict Screw Length Facilitates Navigation-controlled Medial Opening-wedge Osteotomy Using the TomoFix HTO System

Abstract

This study was performed to establish simple algorithms to predict proper screw lengths for the 4 proximal holes of TomoFix plates (Synthes GmbH; Solothurn, Switzerland) based on radiographic mediolateral (ML) and anteroposterior (AP) dimensions of the proximal tibia and to determine how well these algorithms function for navigation-controlled medial opening-wedge high tibial osteotomy (HTO) using TomoFix. Experimental HTO surgery was performed in proximal tibial models manufactured for 30 patients undergoing HTO to determine the longest screw lengths for the 4 proximal holes of TomoFix plates. Eight algorithms were created for the 4 proximal screws by investigating the relationships between measured screw lengths and radiographic dimensions and were used for 30 navigation-controlled medial opening-wedge HTOs. The algorithms used to predict screw length were: screw A=ML width-20 mm and AP length+5 mm; screw B=ML width-25 mm and AP length; screw C=ML width-35 mm and AP length-10 mm; and screw D=ML width-40 mm and AP length-15 mm. All 30 surgeries were performed with no perioperative adverse events. Mean operative time was 47.1 minutes, and no far cortex perforation of more than 3 mm was observed for any of the 4 proximal screws. Mean mechanical tibiofemoral angle and weight load line coordinate at the knee joint were valgus 3.7° and 62.9%, respectively. Targeted alignment was achieved in 28 (93%) knees for a mechanical tibiofemoral angle between valgus 2° and 6°, and in 25 (83%) knees for a weight load line coordinate between 55% and 70%. The authors propose the use of the developed algorithms to select proper screw lengths for medial opening wedge HTO using the TomoFix HTO system.

The use of navigation in medial opening wedge high tibial osteotomy can improve tibial slope maintenance and reduce radiation exposure

“…Screws selected for holes A, B, C, and D by using the simple algorithms were inserted without the use of fluoroscopy (Fig. 1j) [21]. The algorithms consisted of eight sub-algorithms, which were based on the anteroposterior (AP) length or mediolateral (ML) width measured on the pre-operative radiographs, and two algorithms for each of the four screws ( Fig.…”

“…The authors recently reported a novel method to estimate the length of the proximal screws of the plate, using a pre-operative plain radiograph, which has so far functioned well in our navigated medial opening wedge HTO series [21]. These simple algorithms helped us to predetermine the screw length, without the need for fluoroscopy, so we anecdotally experienced reduced fluoroscopy use and operative time.…”