Biomechanical analysis of a newly developed shape memory alloy hook in a transforaminal lumbar interbody fusion (TLIF) in vitro model.

The objective of this biomechanical study was to evaluate the stability provided by a newly developed shape memory alloy hook (SMAH) in a cadaveric transforaminal lumbar interbody fusion (TLIF) model.Six human cadaveric spines (L1-S2) were tested in an in vitro flexibility experiment by applying pure moments of ±8 Nm in flexion/extension, left/right lateral bending, and left/right axial rotation. After intact testing, a TLIF was performed at L4-5. Each specimen was tested for the following constructs: unilateral SMAH (USMAH); bilateral SMAH (BSMAH); unilateral pedicle screws and rods (UPS); and bilateral pedicle screws and rods (BPS). The L3-L4, L4-L5, and L5-S1 range of motion (ROM) were recorded by a Motion Analysis System.Compared to the other constructs, the BPS provided the most stability. The UPS significantly reduced the ROM in extension/flexion and lateral bending; the BSMAH significantly reduced the ROM in extension/flexion, lateral bending, and axial rotation; and the USMAH significantly reduced the ROM in flexion and left lateral bending compared with the intact spine (p<0.05). The USMAH slightly reduced the ROM in extension, right lateral bending and axial rotation (p>0.05). Stability provided by the USMAH compared with the UPS was not significantly different. ROMs of adjacent segments increased in all fixed constructs (p>0.05).Bilateral SMAH fixation can achieve immediate stability after L4-5 TLIF in vitro. Further studies are required to determine whether the SMAH can achieve fusion in vivo and alleviate adjacent segment degeneration

Range of motion at L5-S1.

<p>Abbreviations: F, flexion; E, extension; LLB, left lateral bending; RLB, right lateral bending; LR, left rotation; RR, right rotation. USMAH, unilateral shape memory alloy hook; BSMAH, bilateral shape memory alloy hook; UPS, unilateral pedicle screws and rods; BPS, bilateral pedicle screws and rods.</p

Surgical constructs.

<p>1. Transforaminal lumbar interbody fusion (TLIF) with unilateral shape memory alloy hook (USMAH) at L4-5; 2. TLIF with bilateral shape memory alloy hook (BSMAH) at L4-5; 3. TLIF with unilateral pedicle screws and rods (UPS) at L4-5; 4. TLIF with bilateral pedicle screws and rods (BPS) at L4-5.</p

Range of motion at L4-5.

<p>Abbreviations: F, flexion; E, extension; LLB, left lateral bending; RLB, right lateral bending; LR, left rotation; RR, right rotation. USMAH, unilateral shape memory alloy hook; BSMAH, bilateral shape memory alloy hook; UPS, unilateral pedicle screws and rods; BPS, bilateral pedicle screws and rods. * significant difference vs. the intact spine (p<0.05). # significant difference vs. the BPS construct (p<0.05). + significant difference vs. the BSMAH construct (p<0.05).</p

Range of motion at L3-4.

<p>Abbreviations: F, flexion; E, extension; LLB, left lateral bending; RLB, right lateral bending; LR, left rotation; RR, right rotation. USMAH, unilateral shape memory alloy hook; BSMAH, bilateral shape memory alloy hook; UPS, unilateral pedicle screws and rods; BPS, bilateral pedicle screws and rods.</p

45 mm Shape memory Alloy Hook (SMAH).

<p>Left, prototype; right, unfolded in ice and water mixture.</p