Pedicle screw fixation is a challenging procedure in thoracic spine, as inadvertently misplaced screws have high risk of complications. The accuracy of pedicle screws is typically defined as the screws axis being fully contained within the cortices of the pedicle. One hundred and eighty-five thoracic pedicle screws in 19 patients that were drawn from a total of 1.797 screws in 148 scoliosis patients being suspicious of medial and lateral malpositioning were investigated, retrospectively. Screw containment and the rate of misplacement were determined by postoperative axial CT sections. Medial screw malposition was measured between medial pedicle wall and medial margin of the pedicle screw. The distance between lateral margin of the pedicle screw and lateral vertebral corpus was measured in lateral malpositions. A screw that violated medially greater than 2 mm, while lateral violation greater than 6 mm was rated as an "unacceptable screw". The malpositions were medial in 20 (10.8%) and lateral in 34 (18.3%) screws. Medially, nine screws were rated as acceptable. Of the 29 acceptable lateral misplacement, 13 showed significant risk; five to aorta, six to pleura, one to azygos vein and one to trachea. The acceptability of medial pedicle breach may change in each level with different canal width and a different amount of cord shift. In lateral acceptable malpositions, the aorta is always at a risk by concave-sided screws. This CT-based study demonstrated that T4-T9 concave segments have a smaller safe zone with respect to both cord-aorta injury in medial and lateral malpositions. In these segments, screws should be accurate and screw malposition is to be unacceptable.
Although several studies have been reported on the adult vertebral pedicle morphology, little is known about immature thoracic pedicles in patients with idiopathic scoliosis. A total of 310 pedicles (155 vertebrae) from T1 to T12 in 10-14 years age group were analyzed with the use of magnetic resonance imaging and digital measurement program in 13 patients with right-sided thoracic idiopathic scoliosis. Each pedicle was measured in the axial and sagittal planes including transverse and sagittal pedicle width and angles, chord length, interpedicular distance and epidural space width on convex and concave sides of the curve. The smallest transverse pedicle widths were in the periapical region and the largest were in the caudal region. No statistically significant difference in transverse pedicle widths was detected between the convex and concave sides. The transverse pedicle angle measured 15.56°at T1 and decreased to 6.32°at T12. Chord length increased gradually from the cephalad part of the thoracic spine to the caudad part as the shortest length was seen at T1 convex level with a mean of 30.45 mm and the largest length was seen at T12 concave level with a mean of 41.73 mm. The width of epidural space on the concave side was significantly smaller than that on the convex side in most levels of the curve. Based on the anatomic measurements, it may be reasonable to consider thoracic pedicle screws in preadolescent idiopathic scoliosis.
In posterior pedicle screw instrumentation of thoracic idiopathic scoliosis, screw malposition might cause significant morbidity in tems of possible pleural, spinal cord, and aorta injury. Preoperative axial magnetic resonace images (MRI) in 12 consecutive patients with right thoracic adolescent scoliosis, all with King type 3 curves, were analyzed in order to evaluate the relationship between the inserted pedicle screw position to pleura, spinal cord, aorta. Axial vertebral images for each thoracic level were scanned and the simulation of pedicle screw insertion was performed using a digital measurement programme. The angular contact value for each parameter regarding the pleura and spinal cord was measured on both sides of the curve. The aorta-vertebral distance was also measured. Aorta-vertebral distance was found to be decreasing gradually from the cephalad to the caudad with the shortest distance being measured at T12 with a mean of 1.2 mm. Concave-sided screws on T5-T9 and convexsided screws on T2-T3 had the greatest risk to spinal cord injury. Pleural injury is most likely on T4-T9 segments by the convex side screws. T4-T8 screws on the concave side and T11-T12 screws on the convex side may pose risk to the aorta. This MRI-based study demonstrated that in pedicle instrumentation of thoracic levels, every segment deserves special consideration, where computer scanning might be mandatory in immature spine and in patients with severe deformity.
The reverse sural artery flap is a reliable alternative for small to moderate size defects and can be used with modifications of the original technique.
The application of MSCs to decrease re-ruptures has a positive effect on tendon strength, probably due to their anti-apoptotic effects. Mesenchymal stem cell application can be used percutaneously and is effective in clinical practice in the late stages of tendon healing.
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