Comparison of short-segment monoaxial and polyaxial pedicle screw fixation combined with intermediate screws in traumatic thoracolumbar fractures: a finite element study and clinical radiographic review

OBJECTIVES: No studies have compared monoaxial and polyaxial pedicle screws with regard to the von Mises stress of the instrumentation, intradiscal pressures of the adjacent segment and adjacent segment degeneration. METHODS: Short-segment monoaxial/polyaxial pedicle screw fixation techniques were compared using finite element methods, and the redistributed T11-L1 segment range of motion, largest maximal von Mises stress of the instrumentation, and intradiscal pressures of the adjacent segment under displacement loading were evaluated. Radiographic results of 230 patients with traumatic thoracolumbar fractures treated with these fixations were reviewed, and the sagittal Cobb's angle, vertebral body angle, anterior vertebral body height of the fractured vertebrae and adjacent segment degeneration were calculated and evaluated. RESULTS: The largest maximal values of the von Mises stress were 376.8 MPa for the pedicle screws in the short-segment monoaxial pedicle screw fixation model and 439.9 MPa for the rods in the intermediate monoaxial pedicle screw fixation model. The maximal intradiscal pressures of the upper adjacent segments were all greater than those of the lower adjacent segments. The maximal intradiscal pressures of the monoaxial pedicle screw fixation model were larger than those in the corresponding segments of the normal model. The radiographic results at the final follow-up evaluation showed that the mean loss of correction of the sagittal Cobb's angle, vertebral body angle and anterior vertebral body height were smallest in the intermediate monoaxial pedicle screw fixation group. Adjacent segment degeneration was less likely to be observed in the intermediate polyaxial pedicle screw fixation group but more likely to be observed in the intermediate monoaxial pedicle screw fixation group. CONCLUSION: Smaller von Mises stress in the pedicle screws and lower intradiscal pressure in the adjacent segment were observed in the polyaxial screw model than in the monoaxial pedicle screw fixation spine models. Fracture-level fixation could significantly correct kyphosis and reduce correction loss, and adjacent segment degeneration was less likely to be observed in the intermediate polyaxial pedicle screw fixation group.

Bilateral C1 laminar hooks combined with C2 pedicle screw fixation in the treatment of atlantoaxial subluxation after Grisel syndrome.

BACKGROUND CONTEXT: Many etiologies can lead to atlantoaxial subluxaion. In Grisel syndrome (GS), this subluxation occurs spontaneously after inflammatory processes of the head and neck. Diagnosis is typically based on clinical history and a strong suspicion of this syndrome. Nonsurgical treatment most often resolves the symptoms; however, in some cases surgical treatment is necessary to repair the subluxation. Various surgical techniques and instrumentation systems have been used to treat atlantoaxial subluxation, although there is no consensus regarding the best treatment method for the pediatric population. PURPOSE: To describe a case of atlantoaxial subluxation in a child with GS treated surgically with an alternative construct. STUDY DESIGN/SETTING: This is a case report and literature review. MATERIALS AND METHODS: Our case study involves a 5-year-old girl with a 6-month history of unresolved Fielding type II atlantoaxial subluxation caused by GS. Despite conservative treatment, the patient's symptoms continued to progress. After two failed closed reduction attempts, open reduction and C1-C2 fusion were performed with atlas laminar hook and axis pedicle polyaxial screws. A literature review of the surgical treatment of GS was also performed. RESULTS: After surgery, the patient exhibited full clinical and functional recovery with complete resolution of symptoms. At the 36-month follow-up examination, there was continual evidence of satisfactory reduction and fusion. No complications were observed. Upon completion of the literature review, eight GS cases were found to have been treated surgically with the minimum patient age being 9 years. CONCLUSIONS: Conservative management of GS is the most common and effective treatment; however, a few surgical cases have been reported in the literature with good results. Satisfactory clinical results and fusion at 36 months post surgery were seen in a pediatric patient with atlantoaxial subluxation and instability using atlas laminar hook and axis pedicle polyaxial screws.