Identification of Pedicle Screw Pullout Load Paths for Osteoporotic Vertebrae

Abstract

Study Design: A biomechanical study.Purpose: To determine the actual load path and compare pullout strengths as a function of screw size used in revision surgeries using postmortem human subject specimens.Overview of Literature: Pedicle screw fixation has become the standard of care in the surgical management of spinal instability. However, pullout failures are widely observed in osteoporotic spines and treated by revision surgeries using a higher diameter screw, performing cement augmentation, or increasing the levels of fixation. While the peak forces to final pullout are reported, the actual load path to achieve the final force level is not available. Methods: Six osteoporotic lumbar spines (L2–L5) were instrumented with 5.5×40 mm polyaxial screws and loaded along the axis of the screw using a material testing machine according to American Society for Testing of Materials 543-07 test protocol. Tests were again conducted by replacing them with 6.5×40 mm (group A) or 7.5×40 mm (group B) screws. Force-displacement data were grouped and load paths (mean±1 standard deviation) were compared.Results: Pullout strength decreased by 36% when the size of the revision screw was increased by 1 mm, while it increased by 35% when the size of the revision screw was increased by 2 mm compared to the index screw value. While the morphologies of the load paths were similar in all cases, they differ between the two groups: the larger screw responded with generally elevated stiffer path than the smaller screw, suggesting that revision surgery using a larger screw has more purchase along the inserted body-pedicle axis.Conclusions: A larger screw enhances strength and increases biomechanical stability in revision surgeries, although the final surgical decision is made by the clinician, which includes the patient’s anatomy and associated characteristics.

Bone density optimized pedicle screw instrumentation improves screw pull-out force in lumbar vertebrae

“…The reported incidence of loosening at the screw-bone interface spans a wide range, mainly between 10 and 30%, with highest rates observed in patients with poor bone quality (Ohlin et al 1994;Abul-Kasim and Ohlin 2014;Bredow et al 2016;Kim et al 2020;Zou et al 2020). The most commonly reported cause for failed fusion is low bone mineral density (BMD) (Krishnan et al 2020), which can lead to postoperative pain and ultimately requiring revision surgery to stabilize the spinal segment.…”

Long-Segmental Posterior Fusion Combined With Vertebroplasty and Wiring: Alternative Surgical Technique for Kummell’s Disease With Neurologic Deficits – A Retrospective Case Series

“…Some studies have recommended anterior reconstructive surgeries such as corpectomy with anterior fusion or circumferential fusion. [9][10][11] Anterior reconstructive surgery has yielded favorable results including a good fusion rate and kyphosis correction, but the anterior approach may cause pulmonary, intra-abdominal and retroperitoneal complications. Moreover, long operative time and greater blood loss may be a drawback considering patient age and condition.…”

“…Moreover, long operative time and greater blood loss may be a drawback considering patient age and condition. 9 - 11 …”

“…Moreover, long operative time and greater blood loss may be a drawback considering patient age and condition. [9][10][11] Only posterior-approach surgery is considered a surgical option because of lower morbidity and fewer complications, especially for the elderly patients. VP combined with shortsegment posterior fixation showed favorable results in shortterm follow-up.…”

Comparison of pedicle screw fixation with or without cement augmentation for treating single-segment isthmic spondylolisthesis in the osteoporotic spine

“…However, some scholars 10 proposed that double-threaded screws and ordinary pedicle screws showed the same axial extraction force and anti-fatigue strength. Studies have shown that larger diameter screws increase the pullout strength and that the pullout strength increases 35% when the screw diameter is increased by 2 mm 11 , 23 . PMMA-PSs are one of the most common ways to prevent the failure of internal fixation in osteoporotic lumbar internal fixation surgery.…”