The Effect of Dilation of Immature Pedicles on Pullout Strength of the Screws: Part 2: In Vivo Study

Experimental study. To evaluate the biomechanical stability of screws placed in expanded pedicles, and to compare those with the screws placed in the nonexpanded pedicles in an in vivo model. Pullout strength of a pedicle screw increases as the diameter of the screw gets larger. Small pedicles of pe...

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Bibliographic Details
Published in:Spine (Philadelphia, Pa. 1976) Pa. 1976), 2009-10, Vol.34 (22), p.2378-2383
Main Authors: YILMAZ, Guney, DEMIRKIRAN, Gokhan, OZKAN, Cenk, DAGLIOGLU, Kenan, PEKMEZCI, Murat, ALANAY, Ahmet, YAZICI, Muharrem
Format: Article
Language:English
Subjects:
Age Factors
Aging - physiology
Animals
Biological and medical sciences
Biomechanical Phenomena - physiology
Bone Development - physiology
Bone Screws - adverse effects
Bone Screws - standards
Cerebrospinal fluid. Meninges. Spinal cord
Child
Equipment Failure
Equipment Failure Analysis - methods
Humans
Medical sciences
Models, Animal
Nervous system (semeiology, syndromes)
Neurology
Neuropharmacology
Neuroprotective agent
Pharmacology. Drug treatments
Postoperative Complications - etiology
Postoperative Complications - physiopathology
Postoperative Complications - prevention & control
Spinal Fusion - instrumentation
Spinal Fusion - methods
Spine - anatomy & histology
Spine - growth & development
Spine - surgery
Stress, Mechanical
Sus scrofa
Tensile Strength - physiology
Weight-Bearing - physiology
Wound Healing - physiology
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Summary:Experimental study. To evaluate the biomechanical stability of screws placed in expanded pedicles, and to compare those with the screws placed in the nonexpanded pedicles in an in vivo model. Pullout strength of a pedicle screw increases as the diameter of the screw gets larger. Small pedicles of pediatric patients prevent the use of large size pedicle screws in this age group. As shown in an in vitro study one option to overcome this problem is to dilate and use larger screw in immature spine. But dilation reduces the pullout strength of pedicle screws in in vitro model. Six-week-old 3 pigs were used. One of them was lost in the postoperative period. After posterior subperiosteal exposure of lumbar segments (L1-L5), 4.0 mm diameter and 20 mm long pedicle screws were placed on the left. The right pedicles were dilated with stainless steel dilators and instrumented with screws of same dimension. At the end of 3 months the pigs were killed and the pull out strength of each screw were measured. The average pull out strength of the expanded and nonexpanded screws was 378.7 +/- 73 (542-308) Newton and 397 +/- 80 (535-289) Newton, respectively. There was no statistically significant difference between the 2 groups. The biomechanical stability of the same size screws inserted at the expanded and nonexpanded pedicles are the same after 3 months. Even dilation of the pedicle decreases the pullout strength of the screw at the beginning, and the pull out strength of both sides became equal after 3 months. The remodeling capacity of pedicles and overgrowth of bone on screws may have an effect on this result.
ISSN:0362-2436
1528-1159
DOI:10.1097/BRS.0b013e3181b0bb9b