Objective To explore the biomechanical difference between the different fixations of cortical bone plate allograft. Methods Twenty-seven cadaveric femurs were harvested and were made into the simulated fracture models, which were equally divided into Groups A, B and C. In Group A, the models were fixed with 2 bone plate allografts (110 mm×10 mm×3 mm); in Group B, the models were fixed with 2 struts (110 mm×10 mm×3 mm) and 5 bone screws; in Group C, the models were fixed with 1 strut (110 mm×10 mm×3 mm) and 5 bone screws. The biomechanical tests for the three-piont bending, torsion, and compression were performed. The parameters studied included the values of the displacements in the three-piont bending tests and the compression tests, and the maximum loads during the bending, the compression, and the torsion. Results As for all the stiffness parameters tested, Group A showed the greatest displacements among the threegroups（P＜0.05）, except the compressive stiffness parameter, which was similar to that in Group B. The maximum loads of the three-point bending, the torsion, and the compression in Group A were 1.65±0.34 kN, 554.3±49.34 N, and 7.78±0.82 Nm, respectively; in Group B, they were 1.12±0.37 kN, 428.00±37.40 N,and 3.39±0.22 Nm, respectively; in Group C, they were 0.71±0.46 kN, 218.67±36.53N, and 1.74±0.12 Nm, respectively. Group A had a significantly greater strengththan the other 2 groups(P＜0.05). Conclusion The strength of the cortical bone plate allograft is related to its different fixations. The two cortical bone plate allografts have a greater strength and stiffness than the struts fixed with the bone screws, which can meet the clinical requirement.
To study project of simpl icity and util ity for screw-plate system by pedicle of atlanto-axis mani pulatively hand by X-ray film and CT to prove the one success rate of putting screws. Methods Formulate personal program was used in operation by image save transmission of X-ray film and CT during January 2002 and September 2006 in 31 patients. There were 18 males and 13 femals, aged from 23 to 61 years old with an average age of 43.5 years. Putting screw points bypedicle of atlas were measured: left (19.93 ± 1.32) mm, right (19.16 ± 1.30) mm; putting screw obl iquity angle to inside by pedicle of atlas: left (23.72 ± 2.09)°, right (23.35 ± 1.91)°; putting screw obl iquity angle to side of head by pedicle of atlas: (9.00 ± 1.20)°. Screw points by pedicle of axis: left (13.14 ± 0.82) mm right (13.85 ± 0.79) mm; putting screw obl iquity angle to inside by pedicle of axis: left (24.52 ± 1.26)°, right (20.42 ± 1.42)°; putting screw obl iquity angle to side of head by pedicle of axis: (25.00 ± 3.00)°. The domestic location toward speculum was employed in operation and putting screw points and angles were formulated by X-CT program. The pedicle screws of suitable diameter and length were of exception and screws into pedicle of atlanto-axis were put by hand. Results Pain of the greater occipital nerve occurred in 2 patients after operation and was fully recovered by treatment 1 month after operation. The lateral cortical bone of pedicle was cut by 2 screws, but the spinal cord and vertebral artery were fine. The atlas and the fracture of odontoid process of axis were completely replaced in X-ray films of all patients 1 day after operation.The position relation of lag screw and vertebral artery or spinal cord was very good in CT sheets. All cases were followed up with an average of 10.5 months during 9 months to 5 years and 4 months, and obtained atlantoaxial arthrodesis. The breakage of screw and plate was not found in all cases. According to JOA score standard, 16 cases were excellent, 12 were good, 2 were fair, 1 was poor, and the excellent and good rate was 90.32% . Conclusion The personal design and cl inical appl ication of X-ray films and CT sheets are of great significance to screw-plate system by pedicle of atlanto-axis because of simpl ification of designs and methods and better personal ity.
Although metal blocks have been widely used for reconstructing uncontained tibial bone defects, the influence of their elastic modulus on the stability of tibial prosthesis fixation remains unclear. Based on this, a finite element model incorporating constrained condylar knee (CCK) prosthesis, tibia, and metal block was established. Considering the influence of the post-restraint structure of the prosthesis, the effects of variations in the elastic modulus of the block on the von Mises stress distribution in the tibia and the block, as well as on the micromotion at the bone-prosthesis fixation interface, were investigated. Results demonstrated that collision between the insert post and femoral prosthesis during tibial internal rotation increased tibial von Mises stress, significantly influencing the prediction of block elastic modulus variation. A decrease in the elastic modulus of the metal block resulted in increased von Mises stress in the proximal tibia, significantly reduced von Mises stress in the distal tibia, decreased von Mises stress of the block, and increased micromotion at the bone-prosthesis fixation interface. When the elastic modulus of the metal block fell below that of bone cement, inadequate block support substantially increased the risk of stress shielding in the distal tibia and fixation interface loosening. Therefore, this study recommends that biomechanical investigations of CCK prostheses must consider the post-constraint effect, and the elastic modulus of metal blocks for bone reconstruction should not be lower than 3 600 MPa.
Prosthesis loosening is the leading cause of postoperative revision in unicompartmental knee arthroplasty (UKA). The deviation of medial and lateral translational installation of the prosthesis during surgery is a common clinical phenomenon and an important factor in increasing the risk of prosthesis loosening. This study established a UKA finite element model and a bone-prosthesis fixation interface micromotion prediction model. The predicted medial contact force and joint motion of the knee joint from a patient-specific lower extremity musculoskeletal multibody dynamics model of UKA were used as boundary conditions. The effects of 9 femoral component medial and lateral translational installation deviations on the Von Mises stress of the proximal tibia, the contact stress, and the micro-motion of the bone prosthesis fixation interface were quantitatively studied. It was found that compared with the neutral position (a/A of 0.492), the lateral translational deviation of the femoral component significantly increased the tibial Von Mises stress and the bone-prosthesis fixation interface contact stress. The maximum Von Mises stress and the maximum contact stress of the fixation interface increased by 14.08% and 143.15%, respectively, when a/A was 0.361. The medial translational deviation of the femoral component significantly increased the bone-prosthesis fixation interface micro-motion. The maximum value of micromotion under the conditions of femoral neutral and medial translation deviation was in the range of 20–50 μm, which is suitable for osseointegration. Therefore, based on considerations such as the micromotion range suitable for osseointegration reported in the literature, the risk of reducing prosthesis loosening, and factors that may induce pain, it is recommended that clinicians control the mounting position of the femoral component during surgery within the safe range of 0–4 mm medial translation deviation.
Objective To observe the relationship between position of normal central fixation and the position of the optic disc, and to find out the features of stability of fixation. Methods The position of central fixation of 120 eyes of 60 healthy adults was determined by MP-1 microperimeter. The position of central fixation relative to the position of the optic disk was measured. The relationship between the central fixation and the age or refraction was analyzed statistically. The difference between the right and left eye in each individual was analyzed with t test. Results The central fixation located at the retina with the horizontal distance of 14.48deg;plusmn;1.85deg; and vertical distance of －2.14deg;plusmn;1.26deg; from the temporal edge of the optic disk. In the 120 eyes, 90% of the central fixation located in a bivariate normal ellipse. The normal eyes usually kept in a slightly moving condition when a normal person fixing on a subject. The median of horizontal and vertical deviation was 0.4deg; and 0.3deg; respectively. Conclusion The distribution of central fixation in healthy adults is a bivariate normal ellipse. When fixing on a subject, the moving extent of the eyes in the horizontal direction is larger than that in the vertical direction.
Objective To evaluate the clinical results of bioabsorbable interference screw in knee ligament reconstruction. Methods From April 2002 to August 2004, 39 patients with knee ligament injury were treated, including 33 males and6 females with a median age of 25 years (15 to 65 years). The involved ligament included 29 anterior cruciate ligament of knee(ACL), 6 posterior cruciate ligament of knee(PCL)，4 combined ACL and PCL, 3 medial collateral or lateral collateral ligaments of knee point and 1 posterolateral complex injury of knee. All of patients underwent anatomic ligament reconstructions under arthroscopy or open surgery by autografts and fixation with bioabsorbable interference screw. Results All 34 patients were followed up 6 to 28 months (mean 13.7months). The patients were evaluated by Lysholm knee functional scales, the knee scores were 43.6±13.4 before operation and 85.4±16.3 after operation, showing significant difference (Plt;0.05). There was no limitation of rangeof motion and loosening of the screw. However, one case suffered from infection, and 3 cases suffered from effusion and synovitis after surgery and recovered after management. Conclusion Bioabsorbable interference screw fixation is a reliable method in knee ligament reconstruction and is effective to restore knee joint stability.
ObjectiveTo explore a better segment of fixation and fusion for high-grade spondylolisthesis.
MethodsA total of 21 patients with high-grade spondylolisthesis who had undergone reduction and posterior instrumented fusion between July 2007 and March 2012, were retrospectively reviewed. All cases underwent posterior spinal canal decompression, Schanz screws fixation and reduction, and intervertebral and posterolateral fusion. The concept of "unstable zone" and the feature of spinal deformity helped us to identify the most appropriate segment to fuse. The pre/post-operative differences on slip percentage, pelvic incidence (PI) and lumbosacral angle were compared and analyzed. The nerve function was evaluated by physical examination and neurological Frankel grade. The Visual Analogue Scale (VAS) and Oswestry Disability Index were used to assess clinical and functional outcomes of lower limbs. Bone fusion was assessed using CT reconstruction.
ResultsAll patients were followed up between 12 and 48 months. The clinical and radiological outcomes such as VAS scores and PI angle were all improved compared with that of preoperative, and the differences were all statistically significant (P<0.05).
ConclusionFor children with severe spondylolisthesis, if not combined with structural scoliosis, the fixation and fusion level should be up to the upper vertebra which PI angle>60°, and try to protect the posterior longitudinal ligament complex in case adjacent segments become instability or even slip. For adults with severe spondylolisthesis, if not combined with other spinal disorders such as severe osteoporosis, only mono-segmental fusion is recommended after reduction. If the slipped vertebrae could not be reduced to Meyerding gradeⅠ, two or more segments would need to be fixed and fused.
ObjectiveTo observe the changes of visual acuity and fixation properties of eyes with idiopathic macular hole (IMH) before and after surgery. MethodsA prospective clinical study. From September 2019 to December 2020, 25 patients with 25 eyes of IMH diagnosed in Department of Ophthalmology of The Fourth People's Hospital of Shenyang were included in the study. All patients underwent pars plana vitrectomy (PPV) combined with internal limiting membrane stripping. All eyes underwent best corrected visual acuity (BCVA), optical coherence tomography (OCT), and microperimetry before and after surgery. The BCVA examination was carried out using the Snellen visual acuity chart, which was converted into logarithmic minimum resolution angle (logMAR) visual acuity during statistics. The 12° macular sensitivity (MS) and bivariate contour ellipse area (BCEA) were measured by MP-3 microperimetry. The minimum diameter (MIN) and base diameter (BASE) of the macular hole were measured by OCT; the distance between the preferred retinal location (PRL) and the center of the fovea was measured by Image-proplus 6.0 image processing software. At 1 and 3 months follow-up after surgery, the same equipment and methods as before surgery were used to conduct related examinations. The changes of BCVA, PRL distance from the fovea, MS, BCEA, and macular hole shape before and after surgery were compared and observed. One-way analysis of variance was used to compare the indicators before and after surgery. Pearson correlation analysis was used for the correlation between BCVA and preoperative BCVA, PRL and foveal center distance at 3 months after surgery. The correlation between MIN, BCVA, PRL and foveal center before surgery distance, MS, BCEA and BCVA at 3 months after surgery were analyzed by multiple linear regression. ResultsAmong 25 eyes of 25 cases, 1 male had 1 eye, and 24 females had 24 eyes. The macular hole in stage Ⅲ and Ⅳ were 11 eyes and 14 eyes, respectively. MIN and BASE were 537.68±200.09 and 905.48±278.79 μm, respectively. One month after surgery, the hiatus was closed. Before surgery and 1 and 3 months after surgery, the logMAR BCVA of the affected eyes were 0.80±0.17, 0.70±0.21, 0.60±0.25, and the MS were 22.20±3.86, 23.60±3.14, 24.38±2.68 dB, the distances between PRL and the center of the fovea were 537.72±426.05, 402.00±395.06, 236.80±219.54 μm, and BCEA were 7.90±3.43, 6.40±2.67, 4.80±2.32 deg2. Compared with before operation, BCVA (F=7.047, 20.104) and MS (F=1.980, 5.390) were significantly improved at different time after operation, the distance between PRL and fovea center (F=1.265, 9.530), BCEA (F=2.762, 13.617) were decreased, the difference were statistically significant (P＜0.05). The results of correlation analysis showed that BCVA at 3 months after surgery was significantly associated with preoperative MIN (r=0.810), BASE (r=0.664), BCVA before surgery and 1 month after surgery (r=0.854, 0.940), preoperative and surgical MS at 1 month after surgery (r=－0.548, －0.578), distance between PRL and foveal center before surgery and at 1 month after surgery (r=0.833, 0.915), BCEA before surgery and at 1 month after surgery (r=0.636, 0.732) were significantly correlated (P＜0.05). The results of multiple linear regression analysis showed that the distance between PRL and foveal center before surgery and BCVA were risk factors for poor prognosis of BCVA at 3 months after surgery. ConclusionsThe BCVA and MS of eyes with IMH are significantly improved after surgery, and the distance between PRL and foveal center and BCEA decreased. BCVA, PRL and foveal center distance before surgery are risk factors for poor visual acuity after surgery.
Objective To study the effect of anterior plate fixation on the treatment of middle and lower thirds fractures of humerus and the possibility of operating without injuring the radial nerve. Methods Forty-nine patients with the middle and lower thirds fractures of the humerus were treated with anterior plate fixation from March 1998 to December 2002. Of the 49 patients, 27 were with new fractures, 12 with old fractures, and 10 with nonunion fractures. According to AO classification, of the 49 patients, there were 19 type A, 14 type B1, 9 type B2, 5 type B3, 2 type C1. Thirty-seven patients had closed fractures and 12 had open fractures. Of the 12 patients, 8 were type Gustilo Ⅰ, 4 were type Gustilo Ⅱ. Four out of the 49 patients were associated with radial nerve palsy. All patients were treatedwith anterior plate fixation through the anterior approach to the humerus. The radial nerves injured were explored. Results Of the 49 patients, 48 were followed up 6 to 48 months(28.7 months on average). All fractures were healed within 3 to 9 months(4.7 months on average). Fixed plates of 37 patients out of the 49 were removed. No iatrogenic radial nerve injury occurred in the82 times of the operations among the 49 patients. Conclusion The treatment of middle and lower thirds fractures of humerus by anterior platefixation through the anterior approach to the humerus does not interfere with the fracture healing and can prevent the iatrogenic radial nerve injury.
Objective To investigate the distribution of the preferred retinal locus (PRL) of eccentric fixation in eyes with high myopia.Methods A total of 40 highly myopic patients (54 eyes ) with eccentric fixation were examined by MP1 microperimeter to identify the PRL. The position of PRL relative to the fovea was estimated using the 90% confidence ellipse of normal adult foveal fixation. The differences of visual acuity between ldquo;desirablerdquo; and ldquo;undesirablerdquo; PRL were tested by analysis of variance.Results In 54 eyes with high myopia, 24 eyes (44.44%) had PRL of eccentric fixation below the scotoma after loss of central vision; 19 eyes ( 35.19% ) had a leftfield PRL; 6 eyes ( 11.11% ) had an upperfield PRL; and 5 eyes ( 9.26% ) had rightfield PRL. In 14 patients who had binocular eccentric fixation, 13 had the same fixation pattern in both eyes, including lowerfield PRL in 7 （50.00%）, leftfield PRL in 5 （35.71%）, and upperfield PRL in 1 patient （7.14%）. The difference of visual acuity between lower and leftfield PRL group and right and upperfield undesirable PRL group was not statistically significant（F=0.144, Pgt;0.05）. Conclusions The eccentric fixation in eyes with high myopia is usually situated as near as possible to the fovea. The optimal PRL is inferior visual field.
