A comparison of parallel and diverging screw angles in the stability of locked plate constructs

Abstract

We investigated the static and cyclical strength of parallel and angulated locking plate screws using rigid polyurethane foam (0.32 g/cm(3)) and bovine cancellous bone blocks. Custom-made stainless steel plates with two conically threaded screw holes with different angulations (parallel, 10° and 20° divergent) and 5 mm self-tapping locking screws underwent pull-out and cyclical pull and bending tests. The bovine cancellous blocks were only subjected to static pull-out testing. We also performed finite element analysis for the static pull-out test of the parallel and 20° configurations. In both the foam model and the bovine cancellous bone we found the significantly highest pull-out force for the parallel constructs. In the finite element analysis there was a 47% more damage in the 20° divergent constructs than in the parallel configuration. Under cyclical loading, the mean number of cycles to failure was significantly higher for the parallel group, followed by the 10° and 20° divergent configurations. In our laboratory setting we clearly showed the biomechanical disadvantage of a diverging locking screw angle under static and cyclical loading.

Biomechanical characteristics of pedicle screws in osteoporotic vertebrae—comparing a new cadaver corpectomy model and pure pull‐out testing

“…Along with an increasing angle, the screws converge more, and stability reduces. This effect for converging and diverging screws in an osteoporotic bone model has already been described …”

“…This effect for converging and diverging screws in an osteoporotic bone model has already been described. 25,26 With a constant screw length of 45 mm the screw tip was likely to end in the middle of the vertebra for several specimens of larger dimensions. In clinical practice, for osteoporotic vertebra screws in a converging alignment, the longest ones possible are chosen.…”

A Retrospective Study Using the String of Pearls Tibial Plateau Levelling Osteotomy Locking Plate for the Treatment of Cranial Cruciate Ligament Disease

“…8 Angulating locking screws may improve anchorage in bone, although in a biomechanical study, diverging screws may decrease construct stiffness in cyclical loading and static pull out testing. 20,22 The proximal screw of the distal plate segment is angulated to prevent intraosteotomy placement, but intraosteotomy screw placement was noted in two cases at 6 to 8 weeks' radiographic follow-up, potentially delaying bone union predisposing to implant failure. 20 No complica-tions were noted but osteotomy union scores of grades 1 and 2 were achieved.…”

An Optimization Study of the Screw Orientation on the Interfacial Strength of the Anterior Lumbar Plate System Using Neurogenetic Algorithms and Experimental Validation

“…Anterior lumbar interbody fusion surgery has been widely used to treat lumbar de generative disc disease [3][4][5][6]. However, patients with spinal decompression treatment using the ALP system still face compli cations such as implant loosening and breakage [7][8][9]. Many types of ALP systems with varied insertion angles of locking screws have been proposed to improve the biomechanical performances of the ALP systems.…”

“…However, patients with spinal decompression treatment using the ALP system still face compli cations such as implant loosening and breakage [7][8][9]. Past studies suggested that locking screws should be inserted with a particular inclined angle to strengthen the biomechanical performances of ALP systems [10], but oppo site conclusion has also been reached [9], Unfortunately, the screw orientations determined in past studies are mainly based on the surgeon's experience without biomechanical evidence. Past studies suggested that locking screws should be inserted with a particular inclined angle to strengthen the biomechanical performances of ALP systems [10], but oppo site conclusion has also been reached [9], Unfortunately, the screw orientations determined in past studies are mainly based on the surgeon's experience without biomechanical evidence.…”