Posterior C1–C2 screw and rod instrument for reduction and fixation of basilar invagination with atlantoaxial dislocation

Purpose

To report the surgical technique and preliminary clinical results for the treatment of basilar invagination (BI) with atlantoaxial dislocation (AAD) by posterior C1–C2 pedicle screw and rod instrument.

Methods

Between July 2012 and August 2013, 33 patients who had BI with AAD underwent surgery at our institution. Pre and postoperative three-dimensional computed tomographic (CT) scans were performed to assess the degree of dislocation. Magnetic resonance (MR) imaging was used to evaluate the compression of the medulla oblongata. For all patients, reduction of the AAD was conducted by two steps: fastening nuts and rods was performed to achieve the horizontal reduction. Distraction between C1 and C2 screws was performed to obtain the vertical reduction.

Results

No neurovascular injury occurred during surgery. Follow-up ranged from 6 to 15 months (mean 10.38 months) in 32 patients. Post-operative three-dimensional CT showed that complete horizontal reduction was obtained in 30/33 (90.9 %), and complete vertical reduction was obtained in 31/33 (93.9 %). The repeated three-dimensional CT and MR image demonstrated that bony fusion and the decompression of the medulla oblongata were obtained in all patients. Clinical symptoms improved significantly 3 months after surgery.

Conclusions

This C1–C2 pedicle screw and rod instrument is a promising technique for the treatment of BI with AAD.     

Posterior realignment of irreducible atlantoaxial dislocation with C1–C2 screw and rod system: a technique of direct reduction and fixation

Background contextTreatment of chronic and irreducible atlantoaxial dislocation (AAD) with ventral compression is challenging for surgeons. The main procedures are occipitocervical/C1–C2 fusion after transoral odontoidectomy or release of the periodontoid tissues. These surgical procedures, which are performed simultaneously or intermittently, have many disadvantages that may discount their effectiveness. Therefore, a more effective way to achieve surgical reduction and to keep solid stability with only a single procedure is needed.PurposeWe describe a technique to reduce chronic and irreducible AAD with C1 lateral mass and C2 pedicle screw and rod system.Study designThis was a retrospective case series.Patient sampleOur sample comprised 26 patients (9 men and 17 women) with irreducible AAD who ranged in age from 15 to 54 years (mean, 35 years).Outcome measuresPatients' neurologic status was evaluated with the Japanese Orthopedic Association (JOA) scale.MethodsTwenty-six symptomatic patients underwent posterior realignment and reduction through the C1 lateral mass and C2 pedicle screw and rod system. The proposed mechanism of reduction is that the implanted screws and rods between C1 and C2 acting as a lever system drew C1 backward and pushed C2 downward and forward after removing circumambient obstruction and scars and thoroughly releasing the facet joints. The preoperative and postoperative JOA score, the extent of reduction, and the conditions of C1–C2 bony fusion were examined.ResultsNo neurovascular injury occurred during surgery. Follow-up ranged from 6 to 40 months (mean 20.7 months). Radiographic evaluation showed that solid bony fusion was achieved in all patients, and that complete reduction was attained in 18 patients and partial reduction (>60% reduction) in 8 patients. The mean postoperative JOA score at last follow-up was 15.7, compared with the preoperative score of 12.1 (p<.01).ConclusionsThis C1–C2 screw and rod system provides reliable stability and sufficient reduction of the anatomic malalignment at the craniovertebral junction and meanwhile retains the mobility of atlanto-occipital joints in the treatment of chronic and irreducible AAD. Sophisticated skills, thorough release of the facet joints, and intraoperative protection of the vertebral artery are key points to accomplish this technique.     

Morphological and clinical feasibility of C3 pedicle screw instrumentation in patients with congenital C2–3 fusion

Purpose

Congenital C2–3 fusion (C2–3CF) is often involved in patients with atlantoaxial dislocation, and posterior occipitocervical fixation surgery is usually required. Hypoplasia of C2 pedicle is common in such patients, making C2 pedicle screws (PS) instrumentation inapplicable. Because of congenital fusion, C3PS instrumentation would be an ideal alternative for it will not sacrifice an additional motion segment; however, the morphological and clinical feasibility has not been previously reported.

Methods

We included 42 C2–3CF patients to this study and evaluated pedicle trajectories of C2 and C3 using a three-dimensional CT. Clinical applications of C3PS instrumentation were evaluated and followed.

Results

Among the 42 patients, 23 (54.8 %) and 8 (19.0 %) had C2 and C3 pedicle trajectory diameters <4.0 mm, respectively. The bisection line of the fused C2–3 lamina was used to represent the superior border of C3 articular mass; the entry point of C3 pedicle was located at 3 mm inferior to the assumed superior border and 3.2 mm medial to the lateral border. Bilateral C3PS instrumentations were successfully adopted in 22 patients. No spinal cord or vertebral artery injury occurred; postoperative CT showed a trajectory breach rate of 17.4 % for C3PS. After mean of 3.6-year follow-up, no implant failure was documented.

Conclusions

C3PS instrumentation is morphologically and clinically feasible for a large proportion of patients with C2–3CF and can serve as another reliable alternative for C2PS instrumentation. Preoperative evaluation of pedicle trajectory of C2–3CF with three-dimensional CT is highly valuable in the choice of proper fixation methods.     

Freehand technique for C2 pedicle and pars screw placement: is it safe?

Background Context

During placement of C2 pedicle and pars screws, intraoperative fluoroscopy is used so that neurovascular complications can be avoided, and screws can be placed in the proper position. However, this method is time consuming and increases radiation exposure. Furthermore, it does not guarantee a completely safe and accurate screw placement.

Computed tomography morphometric analysis of C2 translaminar screw fixation of Wright’s technique and a modified technique in the pediatric cervical spine

Purpose

To establish reference data on the dimensions of C2 lamina to guide the use of translaminar screws with Wright’s technique and a modified technique for pediatric patients in different age groups.

Methods

113 pediatric patients were divided into six age groups, and their cervical vertebrae were studied on CT scans. Laminar height, width, length and screw angle were measured. Statistical analysis was performed using Student t tests, Pearson’s correlation and linear regression analysis.

Results

Mean laminar height was 10.95 ± 2.81 mm, and mean width was 6.01 ± 0.90 mm. For Wright’s technique, mean laminar length was 30.65 ± 3 mm, and the screw angle was 56.02° ± 3.62°. For the modified technique, mean laminar length was 22.07 ± 2.38 mm, and the screw angle was 67.40° ± 3.39°. 95.6 % (108/113) of the children could insert a screw into the lamina (laminar width ≥4.5 mm), 72.6 % (82/113) could accept bilateral translaminar screws (laminar width ≥4.5 mm and laminar height ≥9 mm).

Conclusion

Our investigation provides insight into the anatomy of C2 lamina in six pediatric age groups. Compared to adults, the benefits of C2 translaminar screws fixation are more obvious in the pediatric spine which has a large C2 lamina. Compared to Wright’s technique, the modified technique should insert a screw with bigger insert angle and shorter screw length.     

C2 translaminar screw as the optimal choice for atlantoaxial dislocation with C2–C3 congenital fusion

Objective and importance  

The entry point and trajectory are very important for transarticular screw (TAS) and C2 pedicle screw (PDS) plantation. When the physical size is not large enough for the screw passing through, an accurate entry point is the most important point for successful screw insertion without vertebral artery (VA) injury and spinal cord injury. Once the laminas of C2 and C3 are fused, the normal anatomic mark might disappear and the insertion point would be hard to find. As a result, the complication of TAS or PDS implantation increases rapidly. We used C2 translaminar screws (TLSs) with C1 lateral mass screws as the optimal fixation for atlantoaxial dislocation in order to reduce the risk of VA injury and spinal cord injury.     

Mini-open approach combined with percutaneous transarticular screw fixation for C1–C2 fusion

This paper describes a limited exposure for posterior C1–C2 arthrodesis aided by percutaneous transarticular fixation. The purpose of this study was to report the fusion rate using the aforementioned method. Fifty-seven patients (54 females and three males) with C1–C2 instability due to rheumatoid disease constituted the material of this study. The exposure was restricted to C0–C3 levels. The drilling and insertion of the screws was done through two mini stab wounds. A special sleeve and screwdriver were developed to facilitate this step. An autogenous iliac bone graft was fixed between the decorticated posterior arch of the atlas and the lamina of the axis vertebra. The mean of the atlantodental interval decreased from 8.5 mm (SD 2.3 mm) to 2.6 mm (SD 0.6 mm) at the immediate postoperative periods and reached 2.7 mm (SD 0.7 mm) after a mean follow-up of 30.4 months (SD 5.6 months). Malposition of the screws was observed in two patients and warranted a second operation in one. Fusion was evident in 98% of the cases. Percutaneous insertion of the screws in posterior C1–C2 transarticular fixation reduces the size of the exposure and the surgical trauma to the cervical segments below the fixation.     

C1 lateral mass screw insertion caudally from C2 nerve root – An alternate method for insertion of C1 screws: A technical note and preliminary clinical results

Background

C1 lateral mass screw was widely used for fixation of the upper cervical spine. However, massive bleeding from the C1–2 venous plexus is sometimes encountered. In this study, we proposed an alternate method for C1 lateral mass screw insertion, which involves insertion of the screws caudally from the C2 nerve root to reduce bleeding from C1–2 venous plexus.

Modified translaminar screw fixation in the cervicothoracic junction (C7–T2): a technical note

Purpose

To describe and illustrate a modified technique for using translaminar screw in the cervicothoracic junction (C7–T2).

Methods

12 patients (8 males and 4 females, average age was 52 years) underwent insertion of unilateral or bilateral translaminar screws by using our modified technique. With this modified technique, a tiny unicortical “hole” was made at the middle of the contralateral lamina, and the screw can be directly visualized through the unicortical “hole” to prevent violating the spinal canal.

Results

With this modified technique, the mean operation time was 205 min (range 145–360) and mean estimated blood loss was 445 ml (range 260–1250). The mean length of the laminar screws was 27 (range 24–30) mm. The results of the 12 patients with an average follow-up of 17 (6–33) months demonstrated this modified technique to be safe and effective in the fixation of cervicothoracic junction.

Conclusion

In this modified technique, a tiny unicortical “hole” which was made at the middle of the dorsal lamina of cervicothoracic junction (C7–T2). By directly visualizing the screw inserting against the dorsal cortices of the lamina, this modified technique can reduce the risk of violation of the spinal canal and shorten the operation time.

     

Assessment of pedicle screw pullout strength based on various screw designs and bone densities—an ex vivo biomechanical study

Background contextThe pedicle screw fixation system has been used for various spinal disorders. Many studies have been conducted on the fixation ability of the pedicle screw, but variable results have been reported based on bone qualities, pedicle screw properties, insertion techniques, and experimental methods.Study designAn experimental and biomechanical study.PurposeTo evaluate the geometric factors of screws affecting fixation ability after assessing pullout strength based on various pedicle screw designs and different bone densities.MethodsNine types of pedicle screws were prepared according to the outer diameter shape (cylindrical or conical), the inner diameter shape (cylindrical or conical), and thread shape (V shape, buttress shape, and square shape). The pedicle screws were inserted into standardized polyurethane foams of Grades 5, 15, and 20. The pullout strength of each pedicle screw was determined using an MTS 858 machine (Material Testing System Corp., Minneapolis, MN, USA), and the results were analyzed statistically.ResultsPullout strength based on the shape of thread was the highest in the V shape and lowest in the square shape for all foam grades (p<.05). The outer cylindrical and inner conical shape of pedicle screw showed the highest pullout strength in Grades 5 and 15 foam (p<.05). An outer cylindrical and inner conical shape with a V-shaped thread showed the highest pullout strength in all foam grades (p<.05).ConclusionsPedicle screw with an outer cylindrical and inner conical configuration with a V-shaped thread may have maximum pullout strength, regardless of bone density.     

Risk of vertebral artery injury: comparison between C1–C2 transarticular and C2 pedicle screws

Background contextTo our knowledge, no large series comparing the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw have been published. In addition, no comparative studies have been performed on those with a high-riding vertebral artery and/or a narrow pedicle who are thought to be at higher risk than those with normal anatomy.PurposeTo compare the risk of vertebral artery injury by C1–C2 transarticular screw versus C2 pedicle screw in an overall patient population and subsets of patients with a high-riding vertebral artery and a narrow pedicle using computed tomography (CT) scan images and three-dimensional (3D) screw trajectory software.Study designRadiographic analysis using CT scans.Patient sampleComputed tomography scans of 269 consecutive patients, for a total of 538 potential screw insertion sites for each type of screw.Outcome measuresCortical perforation into the vertebral artery groove of C2 by a screw.MethodsWe simulated the placement of 4.0 mm transarticular and pedicle screws using 1-mm-sliced CT scans and 3D screw trajectory software. We then compared the frequency of C2 vertebral artery groove violation by the two different fixation methods. This was done in the overall patient population, in the subset of those with a high-riding vertebral artery (defined as an isthmus height ≤5 mm or internal height ≤2 mm on sagittal images) and with a narrow pedicle (defined as a pedicle width ≤4 mm on axial images).ResultsThere were 78 high-riding vertebral arteries (14.5%) and 51 narrow pedicles (9.5%). Most (82%) of the narrow pedicles had a concurrent high-riding vertebral artery, whereas only 54% of the high-riding vertebral arteries had a concurrent narrow pedicle. Overall, 9.5% of transarticular and 8.0% of pedicle screws violated the C2 vertebral artery groove without a significant difference between the two types of screws (p=.17). Among those with a high-riding vertebral artery, vertebral artery groove violation was significantly lower (p=.02) with pedicle (49%) than with transarticular (63%) screws. Among those with a narrow pedicle, vertebral artery groove violation was high in both groups (71% with transarticular and 76% with pedicle screws) but without a significant difference between the two groups (p=.55).ConclusionsOverall, neither technique has more inherent anatomic risk of vertebral artery injury. However, in the presence of a high-riding vertebral artery, placement of a pedicle screw is significantly safer than the placement of a transarticular screw. Narrow pedicles, which might be anticipated to lead to higher risk for a pedicle screw than a transarticular screw, did not result in a significant difference because most patients (82%) with narrow pedicles had a concurrent high-riding vertebral artery that also increased the risk with a transarticular screw. Except in case of a high-riding vertebral artery, our results suggest that the surgeon can opt for either technique and expect similar anatomic risks of vertebral artery injury.     

Syndesmotic screw fixation in Weber C ankle injuries--should the screw be removed before weight bearing?

OBJECTIVE: To compare the outcomes of Weber C ankle fractures treated with syndesmotic screw fixation where the screw was removed prior to weight bearing against those where the screw was left in situ indefinitely. DESIGN: Retrospective observational analysis of a consecutive series. SETTING: Acute tertiary hospital. PATIENTS: Thirty-three patients with ankle fractures and syndesmotic disruption were treated with open reduction, internal fixation, and syndesmotic stabilisation with a syndesmotic screw. Three patients defaulted follow-up after 1-3 months. In the remaining 30, the syndesmotic screw was removed prior to weight bearing in 23 patients and was left in situ in 7 patients. Mean follow-up was 15 months. METHODS: Assessment with subjective, objective, and radiographic criteria was used. Statistical analysis was performed with independent groups t-test and chi-square test. RESULTS: There was no statistically significant difference between ankle scores, functional outcome or range of motion between the two groups. However, there was a significantly higher incidence of syndesmotic screw breakage and osteolysis in the group where screws were retained. CONCLUSIONS: Judicious fixation of Weber C type injuries with syndesmotic screw fixation allows for good functional outcome. Retaining of the syndesmotic screw on commencement of weight bearing seems to increase the risk of subsequent screw breakage. Removal of the screw prior to weight bearing should be performed to avoid such an eventuality.     

Does position of syndesmotic screw affect functional and radiological outcome in ankle fractures?

The optimum level of syndesmotic screw used in ankle fractures with a tibiofibular diastasis is not clear in the literature. In a retrospective cohort study, we evaluated the clinical and radiological outcomes in two groups of patients-those who had a syndesmotic screw placed through the syndesmosis itself (transsyndesmotic, 17 patients) and those who had a syndesmotic screw placed just above the syndesmosis (suprasyndesmotic, 19 patients). The study suggests that the two groups do not differ significantly in terms of clinical and radiological outcomes.     

Effect of pilot hole on biomechanical and in vivo pedicle screw–bone interface

Purpose

To experimentally study the influence of pilot hole diameter (smaller than or equal to the internal (core) diameter of the screw) on biomechanical (insertion torque and pullout strength) and histomorphometric parameters of screw–bone interface in the acute phase and 8 weeks after pedicle screw insertion.

Methods

Fifteen sheep were operated upon and pedicle screws inserted in the L1–L3 pedicles bilaterally. The pilot hole was smaller (2.0 mm) than the internal diameter (core) of the screw on the left side pedicle and equal (2.8 mm) to the internal diameter (core) of the screw on the right side pedicle. Ten animals were sacrificed immediately (five animals were assigned to pullout strength tests and five animals were used for histomorphometric bone–screw interface evaluation). Five animals were sacrificed 8 weeks after pedicle screw insertion for histomorphometric bone–screw interface evaluation.

Results

The insertion torque and pullout strength were significantly greater in pedicle screws inserted into pilot holes smaller than internal (core) diameter of the screw. Histomorphometric evaluation of bone–screw interface showed that the percentage of bone-implant contact, the area of bone inside the screw thread and the area of bone outside the screw thread were significantly higher for pilot holes smaller than the internal (core) diameter of the screw immediately after insertion and after 8 weeks.

Conclusion

A pilot diameter smaller than the internal (core) diameter of the screw improved the insertion torque and pullout strength immediately after screw insertion as well the pedicle screw–bone interface contact immediately and 8 weeks after screw placement in sheep with good bone mineral density.     

Can insertional torque predict screw loosening and related failures? An in vivo study of pedicle screw fixation augmenting posterior lumbar interbody fusion

STUDY DESIGN: An investigation of the relation between intraoperative insertional torque of pedicle screws, bone mineral density of the vertebra, and development of screw loosening in vivo. OBJECTIVES: To determine the usefulness of intraoperative measurement of the insertional torque of pedicle screws. SUMMARY OF BACKGROUND DATA: Some biomechanical studies have demonstrated that the insertional torque is highly correlated with bone mineral density and the stability of pedicle screws in vitro. METHODS: Pedicle screw fixation was performed with posterior lumbar interbody fusion in 62 consecutive patients. The mean age of the patients at the time of surgery was 58 years. The insertional torque of pedicle screws was measured intraoperatively in all patients. The mean follow-up period was 2.7 years. RESULTS: The mean insertional torque was 1.28 +/- 0.37 Nm in patients with screw loosening and 1.50 +/- 0. 40 Nm in patients without the problem. The mean insertional torque in patients with compression fractures in the upper vertebra adjacent to the fixed segment was 0.83 +/- 0.23 Nm. There was no significant difference between the mean insertional torque in patients with screw loosening and those without the condition. The mean insertional torque in patients without screw loosening was significantly greater than in patients with compression fractures (P < 0.01). A high correlation was found between insertional torque and bone mineral density (P < 0.01). CONCLUSIONS: Although a high correlation was found between the insertional torque of pedicle screws and bone mineral density in vivo, the insertional torque could not objectively predict screw loosening.     

Surgical simulation of circumferential osteotomy and correction of cervico-thoracic kyphoscoliosis for an irreducible old C6–C7 fracture dislocation

Background  Many different surgical procedures have been employed in the treatment of fracture dislocation at the middle to lower cervical spine. However, consistent protocols and procedures have not been fully established for the surgical correction of an irreducible old cervical fracture dislocation associated with spinal deformity. Methods  We report a case of irreducible cervical fracture dislocation and kyphoscoliosis, in which surgical simulation using a three-dimensional full-scale model was useful for circumferential corrective osteotomy at the C6–C7 level. A 56-year-old man was diagnosed with an irreducible fracture dislocation at the C6–C7 level 2 months after a motor vehicle accident. He showed torticollis, and complained of severe pain in his neck and left upper arm. Radiographic examinations revealed that the C6 vertebra was translated anteriorly and laterally to the C7 vertebra. A bony union had progressed at the fracture site, showing rigid cervico-thoracic kyphoscoliosis. To assist in the preoperative planning, we created a three-dimensional, full-scale model from the patient's computed tomography data. Using the model, we performed a simulation of the planned circumferential corrective osteotomy at the C6–C7 level. Results  Through the simulation, we could evaluate the deformed bony structures around the vertebral arteries at the C6–C7 level accurately. At the time of the actual surgery, corrective osteotomy combined with spinal fusion (C5–T2) with a pedicle screw-rod system was accomplished successfully without any neurovascular complications. After surgery, the patient experienced relief from pain, and his neck posture became normal. Conclusions  Surgical simulation using a three-dimensional, full-scale model was useful for improving the accuracy and safety of circumferential corrective osteotomy of the cervical spine.     

Analysis of the s2 alar-iliac screw as compared with the traditional iliac screw: does it increase stability with sacroiliac fixation of the spine?

Background Context

Arthrodesis of the lumbosacral junction continues to be a challenge in pediatric and adult spinal deformity surgery.