Load-sharing biomechanics of lumbar fixation and fusion with pedicle subtraction osteotomy

Abstract

Pedicle subtraction osteotomy (PSO) is an invasive surgical technique allowing the restoration of a well-balanced sagittal profile, however, the risks of pseudarthrosis and instrumentation breakage are still high. Literature studied primary stability and posterior instrumentation loads, neglecting the load shared by the anterior column, which is fundamental to promote fusion early after surgery. The study aimed at quantifying the load-sharing occurring after PSO procedure across the ventral spinal structures and the posterior instrumentation, as affected by simple bilateral fixation alone, with interbody cages adjacent to PSO level and supplementary accessory rods. Lumbar spine segments were loaded in vitro under flexion–extension, lateral bending, and torsion using an established spine tester. Digital image correlation (DIC) and strain-gauge (SG) analyses measured, respectively, the full-field strain distribution on the ventral surface of the spine and the local strain on posterior primary rods. Ventral strains considerably decreased following PSO and instrumentation, confirming the effectiveness of posterior load-sharing. Supplemental accessory rods considerably reduced the posterior rod strains only with interbody cages, but the ventral strains were unaffected: this indicates that the load transfer across the osteotomy could be promoted, thus explaining the higher fusion rate with decreased rod fracture risk reported in clinical literature.

Comparative Analysis of Optoelectronic Accuracy in the Laboratory Setting Versus Clinical Operative Environment: A Systematic Review

“…Ilharreborde et al 87 reported dynamic kinematic evaluation of the multi-segmental lumbar spine under dynamic loading conditions indicated peak accuracy to within 1.10 ± 0.18 degrees (L2-L3) and corresponding translations of 0.48 ± 0.06 mm rotation (L3-L4) with application of 7.5 Nm pure moment load. In a complex kinematic study utilizing a Vicon optoelectronic system, La Barbera et al 18 , 19 investigated lumbar interbody cages with Ponte osteotomy versus pedicle subtraction osteotomy for severe sagittal imbalance, the peak accuracy of neutral zone measurements (degrees) across the intact L3-L5 segments demonstrated values of 0.7 (Range 0.3-1.9) in flexion-extension, 1.0 (Range 0.1-3.8) in lateral bending and 0.2 (Range 0.1-0.9) in axial rotation in flexion-extension.…”

“…From a kinematic standpoint, the sacroiliac junction (SIJ) presents formidable challenge to definitive and accurate measurement using optoelectronics—reaching the 0.1 degree accuracy error measurement limitations of most optoelectronic systems. 18 , 19 Jeong et al 88 was able to differentiate the range of motion (degrees) of the SIJ in lateral bending when comparing the intact condition (1.5 ± 1.5), unilateral fusion (1.4 ± 1.6) and bilateral fusion (1.1 ± 1.0). Despite quantification of SIJ motion within a range of 0.5 degrees of accuracy, the comparisons were not significant.…”

“…Multidirectional flexibility testing is typically performed along 3 predominant loading axes-flexionextension, lateral bending, and axial rotation under controlled displacement rates of 1 to 3 degrees per second for multiple cycles. To this end, a series of laboratory investigations using the NDI Certus and Vicon MX13 camera systems (Vicon Motion Systems Ltd., Oxford, UK) reported the peak limits of optoelectronic accuracy when evaluating kinematics of the osteoligamentous spine [13][14][15][16][17][18][19][86][87][88][89][90][91][92] (Figure 5A and B).…”

“…The principles of optoelectronic measurement systems are founded on the basis of devices which have the capability to source, detect and control light and are typically considered a subdivision of photonics. The spectrum of optoelectronic technology platforms are quite diverse, with utilization in sports performance activities such as speed skating and soccer, 1 - 4 human ergonomics, 5 , 6 clinical gait and motion analysis, 7 - 12 musculoskeletal kinematics, 13 - 20 and clinical operative procedures. 21 - 33 To this end, the degree of accuracy and errors acceptable across optoelectronic motion measurement platforms differ considerably based on application.…”

Pedicle Subtraction Osteotomy Construct Optimization

“…The 4-rod (4R) configuration described by Gupta et al 9 will be referred to as a satellite rod (SR) configuration in this study because of the lack of connectors linking with the main structure. Experimental studies using in vitro and computational models have found a significant reduction in posterior strain associated with those above-mentioned techniques 10–15 . In addition, clinical studies have similarly reported reduced fracture rates associated with multirod constructs 8,16 …”