Biomechanical evaluation of reinsertion and revision screws in the subaxial cervical vertebrae.

BACKGROUND: This study aimed to evaluate the biomechanical effects of reinserted or revised subaxial cervical vertebral screws. METHODS: The first part aimed to gauge the maximum insertional torque (MIT) of 30 subaxial cervical vertebrae outfitted with 4.0-mm titanium screws. A reinsertion group was created wherein a screw was wholly removed and replaced along the same trajectory to test its maximum pullout strength (MPOS). A control group was also implemented. The second part involved implanting 4.0-mm titanium screws into 20 subaxial cervical vertebrae, testing them to failure, and then reinserting 4.5-mm revision screws along the same path to determine and compare the MIT and MPOS between the test and revision groups. RESULTS: Part I findings: No significant difference was observed in the initial insertion's maximum insertion torque (MIT) and maximum pull-out strength (MPOS) between the control and reinsertion groups. However, the MIT of the reinsertion group was substantially decreased compared to the first insertion. Moderate to high correlations were observed between the MIT and MPOS in both groups, as well as between the MIT of the first and second screw in the reinsertion group. Part II, the MIT and MPOS of the screw in the test group showed a strong correlation, while a modest correlation was observed for the revision screw used in failed cervical vertebrae screw. Additionally, the MPOS of the screw in the test group was significantly higher than that of the revision screw group. CONCLUSION: This study suggests that reinsertion of subaxial cervical vertebrae screws along the same trajectory is a viable option that does not significantly affect fixation stability. However, the use of 4.5-mm revision screws is inadequate for failed fixation cases with 4.0-mm cervical vertebral screws.

The biomechanical study of a modified lumbar interbody fusion-crenel lateral interbody fusion (CLIF): a three-dimensional finite-element analysis.

To analyze the biomechanical stability of a redesigned cage, a new lateral plate and the effect of length of cage in CLIF, an L4-L5 finite element model was performed. Six different internal fixation methods were designed and operated under six conditions (Stand-alone CLIF; CLIF with unilateral pedicle screws (CLIF + UPS); CLIF with bilateral pedicle screws (CLIF + BPS); CLIF with lateral plate (CLIF + LP); CLIF with lateral plate and unilateral pedicle screws (CLIF + LP + UPS); CLIF with lateral plate and bilateral pedicle screws (CLIF + LP + BPS)). Ranges of motion (ROM) and stress distribution were evaluated. The effect of the length of cage was analyzed. The ROMs of stand-alone CLIF group and other internal fixation groups were decreased by >90% compared with the intact group. The CLIF + LP + BPS group has the minimum ROM. The CLIF + LP group has smaller ROM than stand-alone group. The stand-alone group has the minimum stress except for extension condition. The CLIF + LP model has less ROM, but a greater stress load was observed in the lateral plate. As for the length of cage, the largest stress is located at the junction between cage and distal end plate, especially in the epiphyseal ring and cortical compact. We conduct a new 'cylinder wall theory' that the cage should be placed to cover the epiphyseal ring. We recommend the length of cage should cover the epiphyseal ring to reduce the subsidence of cage.

[Clinical and radiological results of thoracic and lumbar fracture and dislocation treated with posterior transforaminal decompression and interbody fusion].

OBJECTIVE: To evaluate the clinical and radiological results of patients with thoracic and lumbar fracture and dislocation treated by posterior transforaminal decompression and interbody fusion. METHODS: From June 2010 to June 2017, posterior transforaminal decompression, interbody fusion combined with pedicle screw fixation were performed in 21 patients with thoracic and lumbar fracture and dislocation. Their clinical and radiological data were collected and retrospectively analyzed, including 15 males and 6 females, aged from 25 to 58 years with an average of 45 years old. According to the criterion of American Spinal Injury(ASIA), preoperative neurological function was graded A in 3 cases, B in 7 cases, C in 6 cases, D in 4 cases and E in 1 case. Operative time and intraoperative blood loss and correlative complications were recorded. And VAS score, ODI and Cobb angle were evaluated before and after surgery. The improvement of neurological function was also analyzed at the final follow-up. Intervertebral bony fusion was observed during the follow-up by CT three-dimensional reconstruction. RESULTS: The operative time was 150 to 240 min with an average of (192±47) min. The intraoperative blood loss was 380 to 750 ml with an average of(603±120) ml. Dura sac tearing and cerebral fluid leakage occurred in 3 cases and were repaired during operation; superficial wound infection occurred in 1 case, and got healing after dressing change. The postoperative follow-up duration was 24 to 45 months with an average of(37.0±9.5) months. VAS score was improved from preoperative 8.9±0.4 to immediately postoperative 4.2±1.3(P<0.05). At the final follow-up, VAS score decreased further to 3.6±0.8. ODI was decreased from preoperative (95.30±3.52)% to (32.51±6.30)% at the final follow-up (P<0.05). Cobb angle was corrected from preoperative (21.2±8.8)° to immediately postoperative(2.3±3.1)° (P<0.05). At the final follow-up, Cobb angle was (3.2±2.5)°, showing no significant difference with immediately postoperative value. The neurological function was grade A in 3 cases, B in 3 cases, C in 5 cases, D in 6 cases and E in 4 cases at the final follow-up. All the patients got solid intervertebral bone fusion in 8 to 13 months after operation, with an average fusion time of (10.3±2.5) months. CONCLUSIONS: For the patients with thoracic and lumbar fracture and dislocation mainly involving intervertebral disc and endplate plane, posterior transforaminal decompression and interbody fusion not only is less invasive, but also can effectively reconstruct spinal three column and obtain good biomechanical stability. And, it is beneficial for the good recovery of neurological function.

[Acetabular morphological analysis in patients with high dislocated DDH using three-dimensional surface reconstruction technique].

OBJECTIVE: To simulate acetabular morphology and perform acetabular quantitative analysis in high dislocated developmental dysplasia of the hip (DDH) patients using three-dimensional (3D) surface reconstruction technique, in order to understand the acetabular anatomic features and develop operative strategies for acetabular reconstruction. METHODS: 3D pelvic images were reconstructed by Mimics software from CT data of 13 patients (13 hips) with high developmental DDH and 13 normal persons (26 hips). True acetabular superior-inferior diameter, anterior-posterior diameter, acetabular depth, medial wall thickness, abduction angle and anteversion angle were measured and compared between the two groups of participants. RESULTS: Irregular acetabular shape was found in high dislocated group, showing a triangle with wide upper and narrow lower. The acetabular quantitative analysis revealed (38.29 +/- 2.71) mm superior-inferior diameter, (21.74 +/- 5.33) mm anterior-posterior diameter, (15.50 +/- 2.93) mm acetabular depth, (6.80 +/- 2.97) mm medial wall thickness, (49.29 +/- 7.40) degrees abduction angle and (23.82 +/- 11.21) degrees anteversion angle in high dislocated patients. The superior-inferior diameter, anterior-posterior diameter and acetabular depth of high dislocated patients were significantly smaller than those of the normal contirols (P<0.05). However, the medial wall thickness, abduction angle and anteversion angle of high dislocated patients were significantly bigger than those of the normal controls (P<0.05). CONCLUSION: 3D reconstruction technique can restore true acetabular morphology and perform quantitative analysis. Compared with normal controls, high dislocated DDH patients have acetabular features: irregular shape, lower opening, higher medial wall and bigger abduction and anteversion angles. Joint arthroplasty surgery in high dislocated DDH patients needs to look at these acetabular features.

Three-dimensional computerized preoperative planning of total hip arthroplasty with high-riding dislocation developmental dysplasia of the hip.

OBJECTIVE: To assess whether computed tomography (CT)-based 3-dimensional (3D) computerized pre-operative planning is accurate and reliable in patients with high-riding dislocation developmental dysplasia of the hip (DDH) undergoing total hip arthroplasty (THA). METHODS: Between September 2009 and February 2011, a prospective study with an inbuilt means of comparing predictive techniques in 20 patients (20 hips) with high-riding dislocation DDH was undertaken. All patients had pre- and post-operative CT scans, data from which were transferred digitally to Mimics software. 3D pre-operative planning to predict the acetabular component size, hip rotation center position and acetabular component coverage was performed using Mimics software. The results and post-operative course were compared with those of the traditional acetate templating technique. RESULTS: Using 3D computerized planning, 14/20 components (70%) were predicted exactly and 6/20 (30%) within one size, whereas with the conventional acetate templating technique, 5/20 components (25%) were predicted exactly, 9/20 (45%) within one size and 6/20 (30%) within two or more sizes. There was a strong correlation between the 3D computerized planned acetabular component size, hip rotation center distance, acetabular component host coverage and that found postoperatively. Five patients were considered to need structural bone graft on the basis of 3D computerized planning; this was highly coincident with the intraoperative findings in all five cases. CONCLUSION: CT-based 3D computerized pre-operative planning using Mimics software is an accurate and reliable technique for patients with high-riding dislocation DDH undergoing THA.