Biomechanical evaluation of seven fixation methods to treat pubic symphysis diastasis using finite element analysis.

BACKGROUND: Pubic symphysis diastasis (PSD) hinders the connection between bilateral ischia and pubic bones, resulting in instability of the anterior pelvic ring. PSD exceeding 25 mm is considered disruptions of the symphyseal and unilateral/bilateral anterior sacroiliac ligaments and require surgical intervention. The correct choice of fixation devices is of great significance to treat PSD. This study aimed to evaluate the construct stability and implant performance of seven fixation methods to treat PSD using finite element analysis. METHODS: The intact skeleton-ligament pelvic models were set as the control group. PSD models were simulated by removing relevant ligaments. To enhance the stability of the posterior pelvic ring, a cannulated screw was applied in the PSD models. Next, seven anterior fixation devices were installed on the PSD models according to standard surgical procedures, including single plates (single-Plate group), single plates with trans-symphyseal cross-screws (single-crsPlate group), dual plates (dual-Plate group), single cannulated screws, dual crossed cannulated screws (dual-canScrew group), subcutaneous plates (sub-Plate group), and subcutaneous pedicle screw-rod devices (sub-PedRod group). Compression and torsion were applied to all models. The construct stiffness, symphyseal relative micromotions, and von Mises stress performance were recorded and analyzed. RESULTS: The construct stiffness decreased dramatically under PSD conditions. The dual-canScrew (154.3 ± 9.3 N/mm), sub-Plate (147.1 ± 10.2 N/mm), and sub-PedRod (133.8 ± 8.0 N/mm) groups showed better ability to restore intact stability than the other groups (p < 0.05). Regarding regional stability, only single-plate fixation provided unexpected regional stability with a diastasis of 2.1 ± 0.2 mm (p < 0.001) under a compressive load. Under a rotational load, the single-crsPlate group provided better regional angular stability (0.31° ± 0.03°, p < 0.001). Stress concentrations occurred in the single-Plate, sub-Plate, and sub-PedRod groups. The maximum von Mises stress was observed in the single-plate group (1112.1 ± 112.7 MPa, p < 0.001). CONCLUSION: The dual-canScrew fixation device offers ideal outcomes to maintain stability and prevent failure biomechanically. The single-crsPlate and dual-Plate methods effectively improved single-Plate device to enhance regional stability and disperse stresses. The subcutaneous fixation devices provided both anterior pelvic ring stability and pubic symphysis strength.

Hollow-bone-graft dynamic hip screw can fix and promote bone union after femoral neck fracture: an experimental research.

BACKGROUND: Delayed bone union, nonunion or osteonecrosis often occur after femoral neck fractures in young adults. Secondary bone healing requires strong internal fixation, intramedullary pressure reduction and early functional exercise. OBJECTIVE: To compare bone healing of femoral neck fractures treated with hollow-bone-graft dynamic hip screws (Hb-DHS) and standard dynamic hip screws (DHS) in an animal model. DESIGN: Testing of specifically designed fixation devices in a pig animal model. INTERVENTIONS/METHODS: We designed Hb-DHS and DHS devices appropriate to the femoral neck and head of experimental animals and used them in eight pigs (4-month-old, male or female, 30-40 kg/each). Under anesthesia, we induced medium neck type, Garden III type femoral neck fractures in each pig with fracture gaps of 0.5 mm and then fixed each left femur with Hb-DHS and each right femur with DHS. We assessed the animals radiographically and by postmortem visual appraisal of evidence of bone healing 8 and 16 weeks postoperatively. RESULTS: There were significant differences in radiographic and general findings between the Hb-DHS and DHS groups at weeks 8 and 16 postoperatively. We found statistically significant differences between the Hb-DHS and DHS groups in bone healing scores, trabecular bone volume percentage and bone mineral density as assessed on plain radiographs and computed tomography images (P < 0.05). There were also significant differences between the Hb-DHS and DHS groups in postmortem visually assessed indicators of bone healing at both 8 and 16 weeks postoperatively. CONCLUSIONS: The Hb-DHS device promotes femoral neck bone union, stimulates trabecular bone formation, increases BMD and has advantages over DHS for internal fixation of femoral neck fractures. This animal experiment will contribute to developing optimal treatment for femoral neck fractures in young adults.

Rap system of stress stimulation can promote bone union after lower tibial bone fracture: a clinical research.

BACKGROUND: Lower tibial bone fracture may easily cause bone delayed union or nonunion because of lacking of dynamic mechanical load. OBJECTIVE: Research Group would design a new instrument as Rap System of Stress Stimulation (RSSS) to provide dynamic mechanical load which would promote lower tibial bone union postoperatively. METHODS: This clinical research was conducted from January 2008 to December 2010, 92 patients(male 61/female 31, age 16-70 years, mean 36.3 years) who suffered lower tibial bone closed fracture were given intramedullary nail fixation and randomly averagely separated into experimental group and control group(according to the successively order when patients went for the admission procedure). Then researchers analysed the clinical healing time, full weight bearing time, VAS (Visual Analogue Scales) score and callus growth score of Lane-Sandhu in 3,6,12 months postoperatively. The delayed union and nonunion rates were compared at 6 and 12 months separately. RESULTS: All the 92 patients had been followed up (mean 14 months). Clinical bone healing time in experimental group was 88.78±8.80 days but control group was 107.91±9.03 days. Full weight bearing time in experimental group was 94.07±9.81 days but control group was 113.24±13.37 days respectively (P<0.05). The delayed union rate in 6 months was 4.3% in experimental group but 10.9% in control group(P<0.05). The nonunion rate in 12 months was 6.5% in experimental group but 19.6% in control group(P<0.05). In 3, 6, 12 months postoperatively, VAS score and Lane-Sandhu score in experimental group had more significantly difference than them in control group. CONCLUSIONS: RSSS can intermittently provide dynamic mechanical load and stimulate callus formation, promote lower tibial bone union, reduce bone delayed union or nonunion rate. It is an adjuvant therapy for promoting bone union after lower tibial bone fracture.