Abstract
Traditionally, open approaches have been used for deformity correction surgeries; chief among these includes the pedicle subtraction osteotomy (PSO), which provides significant sagittal correction. While minimally invasive approaches offer a potentially lower complication profile, little is known about their stability and performance compared to open techniques. Anterior column realignment (ACR) is a new minimally invasive approach for deformity correction with similar degree of lordosis to pedicle subtraction osteotomy (PSO). No prior studies have compared the stability of ACR and PSO constructs.
Understanding the biomechanical difference between ACR and PSO may equip the surgeons to maximize the outcomes, increase implant longevity, lower their complication rates and avoid implant failure. The goal of this study was to compare the biomechanical profiles ACR compared to PSO in terms of range of motion stability (ROM) and posterior rod strain (RS) to gain greater insight into the ACR technique and necessary surgical strategies to optimize longevity and stability. We hypothesized ACR will provide greater stability than PSO and yield lower degree of posterior rod strain.
In vitro biomechanical study using human cadaveric specimens.
A total of 14 fresh-frozen lumbar spine cadaveric specimens (T11–sacrum) were selected for this study.
Primary outcome measures of interest were range of motion (ROM) stability and posterior rod strain (RS) at L3/4.
Standard flexibility testing (7.5 Nm) was performed on 14 human cadaveric specimens, separated into two groups by L1-S1 intact ROM. For Group 1, a 30° hyperlordotic ACR was performed at L3/4; for Group 2, a 30° L3 PSO was performed. Flexion(FL), extension(EX), axial rotation (AR), lateral bending (LB), and compression(C). Conditions tested: (1) intact, (2) Pedicle Screw/ 2 rod (PSR) (3) ACR or PSO+2 rods (2R), 4) ACR or PSO+4R. Data were normalized, and analyzed using RM-ANOVA or ANOVA (p<0.05).
No difference was observed between PSO and ACR in lumbar lordosis (p=.83) or focal bend (p=.75). While there were no differences in stability between ACR+2R and PSO+2R (p>.065), ACR appeared to be significantly destabilized compared to PSR in FL and EX (p<.032). ACR+4R was more stable than ACR+2R in FL, EX, and left AR (p<.022). PSO + 4R appeared more stable than ACR in EX, and right LB (p<.021). Both ACR and PSO resulted in significant increases in RS in FL and EX compared to PSR (p<.032), with significant decreases in RS in the 4R condition (p<.047). ACR+4R demonstrated lower RS than PSO+2R in FL and EX (p<.015).
While ACR appears to be more destabilizing than PSO in a biomechanical model, both techniques result in significant increases in posterior rod strain. The 4R technique increases stability for ACR and decreases RS in both in ACR and PSO, but may be more effective in ACR.
This abstract does not discuss or include any applicable devices or drugs.