Roles of the screw types, proximity and anterior band wiring in the surgical fixation of transverse patellar fractures: a finite element investigation

Abstract

Background Cannulated screws with an anterior wire are currently used for managing transverse patellar fracture. However, the addition of anterior wiring with various types of screws via open surgery to increase the mechanical stability is yet to be determined. Hence, this study aimed to compare the mechanical behaviors of a fractured patella fixed with various screws types and at various screw locations with and without the anterior wire. The present study hypothesized that using the anterior wire reduces the fracture gap formation. Methods A finite element (FE) model containing a fractured patella fixed with various types of cannulated screws and anterior wiring was created in this study. Three types of screws, namely partial thread, full thread, and headless compression screws, and two screw depths, namely 5 and 10 mm away from the anterior surface of the patella, were included. The effect of the anterior wire was clarified by comparing the results of surgical fixation with and without the wire. Two magnitudes and two loading directions were used to simulate and examine the mechanical responses of the fractured patella with various fixation conditions during knee flexion/extension. Results Compared with partial thread and headless compression screws, the full thread screw increased the stability of the fractured patella by reducing fragment displacement, fracture gap formation, and contact pressure while increasing the contact area at the fracture site. Under 400-N in the direction 45°, the full thread screw with 5-mm placement reduced the gap formation by 86.7% (from 2.71 to 0.36 mm) and 55.6% (from 0. 81 to 0. 36 mm) compared with the partial thread screw with 10-mm placement, respectively without and with the anterior wire. Conclusion The anterior wire along with the full thread screw is preferentially recommended for maintaining the surgical fixation of the fractured patella. Without the use of anterior wiring, the full thread screw with 5-mm placement may be considered as a less invasive alternative; however, simple screw fixation at a deeper placement (10 mm) is least recommended for the fixation of transverse patellar fracture.

Role of an additional third screw in the fixation of transverse patellar fracture with two parallel cannulated screw and anterior wire

“…The superficial (leading) surface is on the tension side, whereas the articular surface is on the compression side. Therefore, no screw was in place to resist torsion when screws were deeply placed without the anterior wire [ 17 , 18 ]. Therefore, adding a screw on the tension side was helpful for the two deeply placed screws to resist the torsional loading and thereby reduce the gap opening distance.…”

“…Alternatively, when the original two parallel screws and the anterior wire were superficially placed on the tension side in knee flexion 45°, the additional third screw on the compression side was helpless to increase the resistance to torsional loading. Otherwise, in two parallel superficial screws, the applied load developed a tensile load on the fractured patella in full extension and the patellar fragment sliding along the screws and separated from each other [ 17 , 18 ]. In such cases, the additional third screw was also not useful in preventing the separation while maintaining the contact between the fragments.…”

“…Less surgical damage should be considered as the first priority to fasten the recovery of the patients. In our previous study [ 18 ], the deep cannulated screw alone was not suggested in the fixation of patellar fracture because of its weakness to the torsional load. Hence, the anterior wire was suggested for deep screw placement, and thus an anterior incision of the soft tissue above the patella was almost inevitable.…”

“…However, the proximity of cannulated screws in the fixation of the fractured patella remains controversial. According to our previous studies [ 17 , 18 ], the superficial placement of screw (5 mm depth from the anterior surface of the patella) was better than its deep placement (10 mm depth from the anterior surface of the patella) in reducing the fracture gap opening particular in knee flexion, whereas the deeply placed screw was better than the superficially located screw in maintaining the contact of the fracture site in knee full extension. Furthermore, in clinical practice, some surgeons prefer deep placement of screws to prevent bone rupture during drilling and insertion of screws, whereas others prefer superficial screw placement to obtain higher stability in the fixation of the patellar fracture with cannulated screws.…”

Fixation of Closed Transverse Patella Fracture with Cannulated Cancellous Screws and Anterior Tension Band Wiring- A Prospective Study

“…Recent studies with two cannulated screws instead of two wires for anterior tension band principle have shown to increase the structural stiffness and stability of fracture ixation. Screws with tension band wiring are bio mechanically superior to K-wires and SS wires (Ramu et al, 2019;Chen et al, 2019).…”