The primary stability of angle-stable versus conventional locked intramedullary nails

Abstract

Purpose The aim of this study was to compare the initial biomechanical characteristics of the angle-stable locking system for intramedullary nails using the new biodegradable sleeve with conventional locking in the treatment of unstable distal tibial fractures. Methods Eight pairs of fresh, frozen porcine tibiae were used for this study. The expert tibial nail (Synthes) was equipped with either conventional locking screws (CL) or the angle-stable locking system (AS). This system consists of a special ASLS screw with a biodegradable sleeve. For this investigation distal tibias (5.5 cm) were used and the nails were locked with three screws in both groups. Biomechanical testing included non-destructive torsional and axial loading. Results The AS group showed a significantly higher torsional stiffness (70%) compared to the CL group. The range of motion was 0.5 times smaller for the AS constructs. The neutral zone was eight times higher in the CL group (p<0.001). In axial loading the AS group also showed a 10% higher axial stiffness and a 12% lower range of motion (p<0.001). Conclusion The angle-stable locking system (ASLS) using a special screw and sleeve locking for intramedullary nails provides a significantly higher primary stability. The differences determined in this study may have clinical relevance particularly for torsional loads. For the new biodegradable angle-stable sleeve we found a comparable stability to the PEEK-based sleeve system. This system has the potential to decrease complications such as secondary loss of reduction and mal-/non-union.

Long-term stability of angle-stable versus conventional locked intramedullary nails in distal tibia fractures

“…In a former study our group already investigated the primary biomechanical fixation stability of the new biodegradable sleeve. In this study we found the angle-stable locked constructs providing a significantly higher torsional and axial primary stability compared to conventional locking [17]. In the present study we could affirm the advantage of the angle-stable locking especially for torsional fixation stability over a time of 12 weeks.…”

“…First using a PEEK (polyetheretherketone) sleeve, the manufacturer completely changed the sleeve material to biodegradable 70:30 poly(L-lactide-co-D,L-lactide). In a previous study our group could already show the significant increase of initial torsional stability due to angle-stable locking [17]. …”

Fatigue performance of angle-stable tibial nail interlocking screws

“…When using ASLS, the sleeve might create a superior condition of continuous load transfer and may act as an additional shock absorber truncating force peaks. Angle stable locking diminishes screw toggling as indicated by increased construct stiffness, which contributes to interfragmentary stability at the fracture site [21].…”

A new angle stable nailing concept for the treatment of distal tibia fractures

“…Biomechanical studies have demonstrated the advantages for the angular-stable locked nails with regard to a significantly higher axial and torsional stiffness, significantly less fracture gap movement and a significant reduction of the neutral zone in bending [6][7][8][9]. Biomechanically, two ASLS locking screws provide equal stability to three standard locking screws [10].…”