Influence of reduced tip‐apex distance on helical blade fixation—a biomechanical study

Abstract

Migration profile of helical blades differs from conventional screw design. Tip‐apex distance (TAD) greater than 25 mm is associated with early failure in hip screws. This study investigates the effect of a reduced TAD on helical blade fixation. Six pairs of human femoral heads were used. Bone mineral density (BMD) was determined by pQCT. Local bone quality was evaluated by breakaway torque. Helical blades were implanted with TAD of 20 mm (normal) and 6 mm (reduced). Specimens were cyclically tested under progressively increasing physiologic loading at 2 Hz with starting peak force of 1′000N, increasing by 0.1N/cycle. Implant migration was monitored by radiographs every 250 cycles. Paired Student's t‐test and Spearman rank correlation coefficient were used for statistical evaluation (p < 0.05). Mean BMD was 246.7 mgHA/cm3 SD48.7 (normal), 244.3 mgHA/cm3 SD47.6 (reduced); p = 0.93. Mean breakaway torque was 3.59 Nm SD2.11 (normal), 3.72 Nm SD1.83 (reduced); p = 0.91. Number of cycles to failure (1 mm vertical migration) was 16′416 SD7972 (normal), 20′000 SD5232 (reduced); p = 0.38. They correlated significantly with BMD (p = 0.01;R2 = 0.91) and breakaway torque (p < 0.049; R2 = 0.814) (normal). Breakaway torque correlated significantly with BMD (p = 0.02; R2 = 0.898) (normal). In reduced TAD these parameters did not correlate significantly. Normal TAD resulted in failure in varus collapse (n = 6), whereas reduced TAD showed blade perforation (n = 3), rotation (n = 2), varus collapse (n = 1). Fixation stability of helical blades correlates with bone quality when implants are fixed in cancellous bone. Near cortical blade fixation might increase the risk of intraarticular blade perforation. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1–6, 2019.

Biomechanical comparison of lag screw and non-spiral blade fixation of a novel femoral trochanteric nail in an osteoporotic bone model

“…Figure 6 shows the protrusion of the Conventional-Blade on the surface of the polyurethane foam block following the push-in test. According to Nikoloski et al and Lenz et al, the blade type behaves differently to the lag screw type, and placement too close to the subchondral bone may lead to penetration through the head 23 , 24 ; the result of our push-in test supports their finding. In addition, this protrusion may worsen owing to excessive intraoperative insertion force and postoperative weight-bearing and may lead to ‘cut through’, i.e.…”

Comparison of Clinical and Radiological Outcomes in Intertrochanteric Fractures Treated with InterTAN Nail Against Conventional Cephalomedullary Nails: A Systematic Review

“…A lower TAD limit is equally debated within the literature. A biomechanical study from Lenz et al demonstrated no significant differences in number of cycles to failure between cadavers with normal (20 mm) and reduced (6 mm) TAD; however, the clinical relevance is yet to be determined [ 29 ]. Each intramedullary nailing system may have unique TAD requirements, as opposed to the one-size-fits-all approach used today.…”