[Development and clinical application of an adjustable digital cannulated nail guide based on Mimics software]

To evaluate effectiveness of self-designed adjustable cannulated screw guide, and to provide an effective auxiliary tool for inverted triangular arrangement of compression cannulated screws in clinical treatment for transcervical femoral neck fractures.

The sketch of instrument was drawn with Solidworks software, and physical product was obtained after production. The data were obtained by Mimics software. Combined with the guide, it was first used on 22 cadaveric bones, 22 dry cadaveric bones, including 12 males and 10 females. Then the distribution of guide pins was evaluated by X-ray film. The anatomical size and screw distance of femoral head and neck were measured in different ways, and statistically compared. From January 2018 to June 2020, 45 hospitalized patients with femoral neck fracture were selected and divided into new guide group (22 patients) and free hand nail group (23 patients) according to whether the instrument was used or not. The clinical data and operation conditions between two groups were recorded and compared.

The anatomical data of X-ray, three-dimensional and physical measurement were basically the same, whlie had no difference (P>0.05). There was no significant difference between physical measurement and three-dimensional measurement (P>0.05). The distance between screws and needle entry point was designed as an isosceles triangle(r=0.992 8, P<0.000 1), but due to the existence of femoral anteversion and torsion angle, it was an approximate isosceles triangle in the femoral neck (r=0.824 1, P<0.000 1). The patients between two groups were followed up for an average of 2 years. There was no significant difference in the number of fluoroscopy and puncture between new guide group and free hand nail group(P>0.05). The screw parallelism was better and operation time was shorter which had statistically difference(P<0.05). However, there was no significant difference in final Harris score and incidence of complications between two groups(P>0.05).

Self-made femoral neck cannulated screw guide combined with preoperative planning of Mimics software is conducive to placement of inverted triangular arrangement of cannulated screws, but it still needs to be improved and followed up in the later large-scale use.