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    Direct vertebral rotation significantly decreases the pullout strength of the pedicle screw: a biomechanical study in adult cadavers
    (2021) Sarıyılmaz, Kerim; Özkunt, Okan; Gemalmaz, Halil Can; Cingöz, Tunca; Pehlivanoğlu, Tuna; Aksoy, Tamer; Kaya, Özcan; Baydoğan, Murat; Dikici, Fatih
    The pullout strength of the pedicle screws after direct vertebral rotation (DVR) maneuver is not known. This biomechanical study was performed to quantitatively analyze the pullout strength of a pedicle screw after DVR maneuver using human cadaveric vertebrae. Thoracic vertebral bodies from three cadavers were harvested and stripped of soft tissues. Thirty pedicles of 15 vertebrae were separated into two groups after bone mineral density measurements. Polyaxial 5.5 mm pedicle screws with appropriate length were inserted with a freehand technique for each pedicle. One Kirschner wire was inserted to the anterior part of each vertebral corpus the half depth of each corpus was embedded into PVC pipes using polyester paste. In the DVR group, each screw was pulled horizontally with 2 kg (~20 N) load over a screwdriver rigidly attached to the screw, and a DVR maneuver was simulated. The control group did not load with a DVR maneuver. Samples were placed on a universal testing machine and pullout loads were measured. The Mann-Whitney U test was utilized, and the P value <0.05 was considered as statistically significant. In the DVR group, the mean pullout strength was 183.35 N (SD ± 100.12), and in the control group, the mean pullout strength was 279.95 N (SD ± 76.26). Intergroup comparisons revealed that DVR maneuver significantly decreases the pullout strength (P = 0.012). The results of this study confirm that the pullout strength of pedicle screw significantly decreases by approximately 35% when DVR maneuver is applied.
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    Effectiveness of posterior structures in the development of proximal junctional kyphosis following posterior instrumentation: A biomechanical study in a sheep spine model
    (Turkish Assoc Orthopaedics Traumatology, 2019) Korkmaz, Murat; Akgül, Turgut; Sarıyılmaz, Kerim; Özkunt, Okan; Dikici, Fatih; Yazıcıoğlu, Önder
    Introduction: Proximal junctional kyphosis - PJK has been defined by a 10 or greater increase in kyphosis at the proximal junction as measured by the Cobb angle from the caudal endplate of the uppermost instrumented vertebrae (UIV) to the cephalad endplate of the vertebrae 1 segments cranial to the UIV. In this biomechanical study, it is aimed to evaluate effects of interspinosus ligament complex distruption and facet joint degeneration on PJK development. Materials and methods: Posterior instrumentation applied between T2 - T7 vertebrae using pedicle screws to randomly selected 21 sheeps, divided into 3 groups. First group selected as control group (CG), of which posterior soft tissue and facet joints are protected. In second group (spinosus group, SG) interspinosus ligament complex which 1 segment cranial to UIV has been transected, and third group (faset group-FG) was applied facet joint excision. 25 N, 50 N, 100 N, 150 N and 200 N forces applied at frequency of 5 Hertz as 100 cycles axial to the samples. Then, 250 N, 275 N and 300 N forces applied static axially. Interspinosus distance, kyphosis angle and discus heights was measured in radiological evaluation. Abnormal PJK was defined by a proximal junctional angle greater than 100 and at least 100 greater than the corresponding preoperative measurement. Results: In CG group, average interspinosus distancewas 6,6 +/- 1.54 mm and kyphosis angle was 2,2 +/- 0.46 degrees before biomechanical testing, and they were measured as 9,4 +/- 1.21 mm and 3,3 +/- 0.44 degrees respectively after forces applied to samples. In SG group, average interspinosus distance was 6,2 +/- 1.72 mm and kyphosis angle was 2,7 +/- 1.01 degrees before experiment, and they were measured as 20,8 +/- 5.66 mm and 15,1 +/- 2.34 degrees respectively after forces applied to samples. In FG group, average interspinosus distancewas 4,8 +/- 1.15 mm and kyphosis angle was -1 +/- 4.14 degrees before experiment, and they were measured as 11,1 +/- 1:96 mm and 11 +/- 2.87 degrees respectively after forces applied to samples. In comparison to group CG, statistically significant junctional kyphosis was seen on both FG and SG group after statistical analysis. (p < 0.05). PJK was seen statistically significant more on SG group than FG group. (p < 0.05). Not any statistically significant difference was seen on measurement of disk distances among three groups. (p > 0.05) Conclusions: Protecting interspinosus ligament complex and facet joint unity during posterior surgical treatment for spine deformation is vital to prevent PJK development. Based on our literature review, this is the first biomechanical study that reveals interspinosus ligament complex are more effective on preventing PJK development than facet joints. (C) 2019 Turkish Association of Orthopaedics and Traumatology. Publishing services by Elsevier B.V.
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    Treatment of adolescent idiopathic scoliosis with global (rod) derotation maneuver using pedicle screws
    (2018) Kaya, Özcan; Akgül, Turgut; Özkunt, Okan; Dikici, Fatih; Yazıcıoğlu, Önder; Domanic, Ünsal
    Introduction: Adolescent idiopathic scoliosis is a three dimensional deformity. For the treatment of deformity, nature of deformity should be well understood and treatment strategy has to be directed to the coronal, sagittal and axial components of deformity. Global Derotation (GD) maneuver is based on simple rod derotation from concave side aiming to correct the deformity on coronal, sagittal and axial profile. In this report we reviewed AIS surgery results treated by global derotation maneuver with all pedicle screw instrumentation. Material& Methods: Between 2003 and 2011, 253 patients had been operated using GD technique.80 of 253 patients was included to our study. The patients routinely evaluated with preoperative-postoperative and last follow up standing ortho-x-rays. Coronal and sagittal profile parameters measured on x-rays with digital software using Cobb method. Rotational component of the deformity was measured according to Nash-Moe method at the apical vertebra. Results: 80 patients (71 female ; 9 male)had been followed up average 19,8 (7-37) months. Patients age average were 15,1(12-21) at operation date. Coronal cobb angle measure in thoracic curves preoperative were 48,9° decreased to mean 3,2° postoperatively. The mean coronal thoracolumbar curve were 45,8° preoperatively and decreased to mean 2°. Apical vertebra rotation measure regressed to mean 0,68 (0-1). Thoracic kyphosis showed downward tendency from mean 37,8° to mean 27,8°. Conclusion: Rod derotation technique enable to correct coronal and axial profile. Coronal Cobb angle improvement seen obviously with correction of axial profile rotation. Sagittal hypokyphotic effect of GD should be kept in mind.