Transforaminal lumbar interbody fusion using unilateral pedicle screws and a translaminar screw

Lumbar spinal fusion is advancing with minimally invasive techniques, bone graft alternatives, and new implants. This has resulted in significant reductions of operative time, duration of hospitalization, and higher success in fusion rates. However, costs have increased as many new technologies are expensive. This study was carried out to investigate the clinical outcomes and fusion rates of a low implant load construct of unilateral pedicle screws and a translaminar screw in transforaminal lumbar interbody fusion (TLIF) which reduced the cost of the posterior implants by almost 50%. Nineteen consecutive patients who underwent single level TLIF with this construct were included in the study. Sixteen patients had a TLIF allograft interbody spacer placed, while in three a polyetheretherketone (PEEK) cage was used. Follow-up ranged from 15 to 54 months with a mean of 32 months. A clinical and radiographic evaluation was carried out preoperatively and at multiple time points following surgery. An overall improvement in Oswestry scores and visual analogue scales for leg and back pain (VAS) was observed. Three patients underwent revision surgery due to recurrence of back pain. All patients showed radiographic evidence of fusion from 9 to 26 months (mean 19) following surgery. This study suggests that unilateral pedicle screws and a contralateral translaminar screw are a cheaper and viable option for single level lumbar fusion

A new lumbar posterior fixation system, the memory metal spinal system:an in-vitro mechanical evaluation

<p>Background: Spinal systems that are currently available for correction of spinal deformities or degeneration such as lumbar spondylolisthesis or degenerative disc disease use components manufactured from stainless steel or titanium and typically comprise two spinal rods with associated connection devices (for example: DePuy Spines Titanium Moss Miami Spinal System). The Memory Metal Spinal System of this study consists of a single square spinal rod made of a nickel titanium alloy (Nitinol) used in conjunction with connecting transverse bridges and pedicle screws made of Ti-alloy. Nitinol is best known for its shape memory effect, but is also characterized by its higher flexibility when compared to either stainless steel or titanium. A higher fusion rate with less degeneration of adjacent segments may result because of the elastic properties of the memory metal. In addition, the use of a single, unilateral rod may be of great value for a TLIF procedure. Our objective is to evaluate the mechanical properties of the new Memory Metal Spinal System compared to the Titanium Moss Miami Spinal System.</p><p>Methods: An in-vitro mechanical evaluation of the lumbar Memory Metal Spinal System was conducted. The test protocol followed ASTM Standard F1717-96, "Standard Test Methods for Static and Fatigue for Spinal Implant Constructs in a Corpectomy Model."</p><p>1. Static axial testing in a load to failure mode in compression bending,</p><p>2. Static testing in a load to failure mode in torsion,</p><p>3. Cyclical testing to estimate the maximum run out load value at 5.0 x 10(boolean AND)6 cycles.</p><p>Results: In the biomechanical testing for static axial compression bending there was no statistical difference between the 2% yield strength and the stiffness of the two types of spinal constructs. In axial compression bending fatigue testing, the Memory Metal Spinal System construct showed a 50% increase in fatigue life compared to the Titanium Moss Miami Spinal System. In static torsional testing the Memory Metal Spinal System constructs showed an average 220% increase in torsional yield strength, and an average 30% increase in torsional stiffness.</p><p>Conclusions: The in-vitro mechanical evaluation of the lumbar Memory Metal Spinal System showed good results when compared to a currently available spinal implant system. Throughout testing, the Memory Metal Spinal System showed no failures in static and dynamic fatigue.</p>