Objective To design customized titanium alloy lunate prosthesis, construct three-dimensional finite element model of wrist joint before and after replacement by finite element analysis, and observe the biomechanical changes of wrist joint after replacement, providing biomechanical basis for clinical application of prosthesis. Methods One fresh frozen human forearm was collected, and the maximum range of motions in flexion, extension, ulnar deviation, and radialis deviation tested by cortex motion capture system were 48.42°, 38.04°, 35.68°, and 26.41°, respectively. The wrist joint data was obtained by CT scan and imported into Mimics21.0 software and Magics21.0 software to construct a wrist joint three-dimensional model and design customized titanium alloy lunate prosthesis. Then Geomagic Studio 2017 software and Solidworks 2017 software were used to construct the three-dimensional finite element models of a normal wrist joint (normal model) and a wrist joint with lunate prosthesis after replacement (replacement model). The stress distribution and deformation of the wrist joint before and after replacement were analyzed for flexion at and 15°, 30°, 48.42°, extension at 15°, 30°, and 38.04°, ulnar deviation at 10°, 20°, and 35.68°, and radial deviation at 5°, 15°, and 26.41° by the ANSYS 17.0 finite element analysis software. And the stress distribution of lunate bone and lunate prosthesis were also observed. Results The three-dimensional finite element models of wrist joint before and after replacement were successfully constructed. At different range of motion of flexion, extension, ulnar deviation, and radial deviation, there were some differences in the number of nodes and units in the grid models. In the four directions of flexion, extension, ulnar deviation, and radial deviation, the maximum deformation of wrist joint in normal model and replacement model occurred in the radial side, and the values increased gradually with the increase of the range of motion. The maximum stress of the wrist joint increased gradually with the increase of the range of motion, and at maximum range of motion, the stress was concentrated on the proximal radius, showing an overall trend of moving from the radial wrist to the proximal radius. The maximum stress of normal lunate bone increased gradually with the increase of range of motion in different directions, and the stress position also changed. The maximum stress of lunate prosthesis was concentrated on the ulnar side of the prosthesis, which increased gradually with the increase of the range of motion in flexion, and decreased gradually with the increase of the range of motion in extension, ulnar deviation, and radialis deviation. The stress on prosthesis increased significantly when compared with that on normal lunate bone. Conclusion The customized titanium alloy lunate prosthesis does not change the wrist joint load transfer mode, which provided data support for the clinical application of the prosthesis.
Objective To simulate anterosuperior instabil ity of the shoulder by a combination of massive irreparable rotator cuff tears and coracoacromial arch disruption in cadaveric specimens, use proximally based conjoined tendon transfer forcoracoacromial l igament (CAL) reconstruction to restrain against superior humeral subluxation, and investigate its feasibility and biomechanics property. Methods Nine donated male-adult and fresh-frozen cadaveric glenohumeral joints were applied to mimic a massive irreparable rotator cuff tear in each shoulder. The integrity of the rotator cuff tendons and morphology of the CAL were visually inspected in the course of specimen preparation. Cal ipers were used to measure the length of the CAL’s length of the medial and the lateral bands, the width of coracoid process and the acromion attachment, and the thickness in the middle, as well as the length, width and thickness of the conjoined tendon and the lateral half of the removed conjoined tendon. The glenohumeral joints were positioned in a combination of 30° extension, 0° abduction and 30° external rotation. The value of anterosuperior humeral head translation was measured after the appl ication of a 50 N axial compressive load to the humeral shaft under 4 sequential scenarios: intact CAL, subperiosteal CAL release, CAL anatomic reattachment, entire CAL excision after lateral half of the proximally based conjoined tendon transfer for CAL reconstruction. Results All specimens had an intact rotator cuff on gross inspection. CAL morphology revealed 1 Y-shaped, 4 quadrangular, and 4 broad l igaments. The length of the medial and lateral bands of the CAL was (28.91 ± 5.56) mm and (31.90 ± 4.21) mm, respectively; the width of coracoid process and acromion attachment of the CAL was (26.80 ± 10.24) mm and (15.86 ± 2.28) mm, respectively; and the thickness of middle part of the CAL was (1.61 ± 0.36) mm. The length, width, and thickness of the proximal part of the proximally based conjoined tendon was (84.91 ± 9.42), (19.74 ± 1.77), and (2.09 ± 0.45) mm, respectively. The length and width of the removed lateral half of the proximally conjoined tendon was (42.67 ± 3.10) mm and (9.89 ± 0.93) mm, respectively. The anterosuperior humeral head translation was intact CAL (8.13 ± 1.99) mm, subperiosteal CAL release (9.68 ± 1.97) mm, CAL anatomic reattachment (8.57 ± 1.97) mm, and the lateral half of the proximally conjoined tendon transfer for CAL reconstruction (8.59 ± 2.06) mm. A significant increase in anterosuperior migration was found after subperiosteal CAL release was compared with intact CAL (P lt; 0.05). The translation after CAL anatomic reattachment and lateral half of the proximally conjoined tendon transfer for CAL reconstruction increased over intact CAL, though no significance was found (P gt; 0.05); when they were compared with subperiosteal CAL release, the migration decreased significantly (P lt; 0.05). The translation of lateral half of the proximally conjoined tendon transfer for CAL reconstruction increased over CAL anatomic reattachment, but no significance was evident (P gt; 0.05). Conclusion The CAL should be preserved or reconstructed as far as possible during subacromial decompression, rotator cuff tears repair, and hemiarthroplasty for patients with massive rotator cuff deficiency. If preservation or the insertion reattachment after subperiosteal release from acromion of the CAL of the CAL is impossible, or CAL is entirely resected becauseof previous operation, the use of the lateral half of the proximally based conjoined tendon transfer for CAL reconstruction isfeasible.
To provide the scientific theoretical basis for cl inical practice by comparing biomechanicalcharacteristics of single compressed plate with intramedullary pin, locking intramedullary nail and simple arm externalfixator with simple internal fixation devices. Methods Eighteen wet humeral bone specimens of adult cadaver were madecompl icated fracture models of humeral shaft and divided into 3 groups according to fixation methods. Fracture was fixed by single compressed plate with intramedullary pin in plate group, by locking intramedullary nail in intramedullary nail group and by external fixator with simple internal fixation devices in external fixator group. The intensity and rigidity of compl icated fracture models of humeral shaft was measured in compress test and torsion test. Results In compress test, the maximum load in plate group (6 162.09 ± 521.06) N and in intramedullary nail group (6 738.32 ± 525.89) N was significantly larger than that in external fixator group (2 753.57 ± 185.59) N (P lt; 0.05); but there was no significant difference between plate group and intramedullary nail group (P gt; 0.05). Under 600 N physiological compress load, the rigidity was (171.69 ± 6.49) N/mm in plate group, (333.04 ± 36.85) N/mm in intramedullary nail group and (132.59 ± 2.93) N/mm in external fixator group; showing no significant difference between plate group and external fixator group (P gt; 0.05), and showing significant difference between intramedullary nail group and plate, external fixator groups (P lt; 0.05). In torsion test, the maximum torque in plate group (38.24 ± 7.08) Nm was significantly larger than those in intramedullary nail group (17.12 ± 5.73) Nm and external fixator group (20.26 ± 6.42) Nm (P lt; 0.05), but there was no significant difference between intramedullary nail group and external fixator group (P gt; 0.05). Under 0.80 Nm physiological torque, the rigidity was (16.36 ± 2.07) Ncm/° in plate group and (18.79 ± 2.62) Ncm/° in external fixator group, which was significantly larger than that in intramedullary nail group (11.45 ± 0.22) Ncm/° (P lt; 0.05); but there was no significant difference between plate group and external fixator group (P gt; 0.05). Conclusion Those fracture models fixed by single compressed plate with intramedullary pin have better compress and torsion intensity, they also have better torsion rigidity but less compress rigidity. Those fracture models fixed by locking intramedullary nail have better compress intensity but less torsion intensity, they also have better compress rigidity but less torsion rigidity. Those fracture models fixed by external fixator with simple internal fixation device have less compress and torsion intensity, they also have less compress rigidity but better torsion rigidity.
Objective To summarize the function of fibula in stability of ankle joints.Methods Recent original articles were extensively reviewed, which were related to the physiological function and biomechanical properties of fibula, the influence of fibular fracture on stability of ankle joints and mechanism of osteoarthritis of ankle joints. Results The fibula had the function of weightbearing; and it was generally agreed that discontinued fibula could lead to intra articular disorder of ankle joint in children; but there were various viewpoints regarding the influence of fibular fracture on the ankle joint in adults. Conclusion Fibula may play an important role in stability of ankle joint.
Objective To investigate the cl inical appl icabil ity and value of internal fixator for the reconstruction of lumbar isthmus in the treatment of lumbar vertebral spondylolysis and to lay a fundation for its cl inical appl ication. Methods Sixteen healthy goats weighing 22.65-31.22 kg were selected to establ ish the models of vertebral spondylolysis at L5, which thereafter were randomized into two groups (n=8): bone graft group in which 0.8-1.1 g fresh autogenous bone was transplanted into the isthmus spondylolysis area, and internal fixation with bone graft group in which internal fixator was installed before transplanting 0.8-1.1 g fresh autogenous bone into the isthmus spondylolysis area. All animals were killed 8 weeks after operation to receive imaging, topographic anatomy and histology detection. Meanwhile, biomechanics test was performed by using 5 donated vertebral body specimens (4 males and 1 female aged 35-51 years old). The left isthmus of L5 vertebra was transected to serve as lumbar vertebral spondylolysis model. A mini-displacement sensor was put at the transected ends of the isthmus. Then loading was conducted with a constant velocity of 2 mm/min by electronic omnipotent tester simulating the direction of fixation force of the internal fixator, and the deformation value of the transected ends was collected by a dynamic data collector and analyzer. The loading wascontinued until the vertebra specimens were damaged. The deformation of displacement sensor and the closure of transected ends of the lumbar isthmus were observed. Results All the goats behaved normally shortly after operation, and no nerve injury induced by operation and no wound infection occurred. Bilaterally obl ique X-ray films of lumbar vertebra and topographic anatomy 8 weeks after operation showed the fusion rate of the internal fixation and bone graft group and the bone graft group was 100% and 62.5%, respectively, indicating there was a significant difference (P lt; 0.05). Histology observation showed 3 goats in the bone graft group presented empty bone trabecula, empty bone lacuna and the disappearance of osteocytes at the transected ends of lumbar isthmus; while in the internal fixation and bone graft group, the bone trabecula grew into cancellous structures with hematopoietic and fatty bone marrow tissue inside, and parts of the bone trabecula had various degrees of mosaic-l ike pattern. During the upload, the biomechanics test and data processing results showed when the external load was 40 N, the deformation of displacement sensor was identified and the gap between the transected ends of lumbar isthmus started to close; then with the increase of external load, the displacement sensor tended to ascend in a l inearity manner; while when the external load was 212 N, the displacement sensor had no further deformation, the gap between the transected ends of lumbar isthmus wascompletely closed, and the pressor effect appeared. Conclusion The internal fixator for the reconstruction of lumbar isthmus has mechanical effects of stabil izing and elevating pressure with a high fusion rate.
Objective To ascertain whether augmentation pedicle screw fixation with polymethylmethacrylate (PMMA) can enhance the stability of unstable thoracolumbar burst fractures of osteoporotic spine. Methods Six fresh frozen female osteoporotic spines (T10-L5) were harvested and an anterior and posterior columnunstable model of L1 was made. Each specimen was fixated with plate and the stability test were performed by flexion, extension, axial rotation and lateral bending. The test of fatigue was done with MTS 858.The tests were repeated after screws were augmented with PMMA. To compare the biomechanical stability of 6 different conditions:○anormal specimens(control), ○bdefectmodel fixed with plate, not augmented and not fatigued, ○cafter fatigued, not augmented, ○dscrews augmented with PMMA, not fatigued, ○e after augmented and fatigued. ResultsIn ○b,○d and ○e conditions, the ranges of motion(ROM) were 6.23±1.56，4.49±1.00，4.46±1.83 inflexion and 6.60±1.80，4.41±0.82，4.46±1.83 in extension. There was no significant difference (Pgt;0.05), they were significantly smaller than those in ○a and ○c conditions (8.75±1.88，1.47±2.25 and 8.92±2.97，12.24±3.08) (Plt;0.01).Conclusion The results demonstrated that augmentation pedicle screws fixation with PMMA can increase the stability of osteoporotic spine.
ObjectiveTo evaluate the effect of reconstruction of forearm interosseous membrane (IOM) using extensor carpi radialis longus combined with radial head replacement for restoring the forearm longitudinal stability. MethodsTen fresh-frozen adult cadaveric forearms were selected, including 8 males and 2 females with a mean age of 38.2 years (range, 29-74 years). Each forearm was treated as following steps: radial head excision (group A), radial head excision+the distal ulnar radial joints separation (group B), radial head excision+the distal ulnar radial joints separation+IOM central band excision (group C), reconstructed IOM with extensor carpi radialis longus tendon (group D), radial head prothesis replacement (group E), and reconstructed IOM with extensor carpi radialis longus tendon+radial head prothesis replacement (group F). The distance between ulna and radius and radioulnar joint displacement were observed under load and non load. The force loading on both ends of specimen was recorded when the radius shifted 5 mm proximally. ResultsRestoring the radial length could maintain normal distance between radius and ulna. The interosseous membrance reconstruction could restore the load transmission between radius and ulna. The force loading specimen was (74.507±4.967), (49.227±1.940), (17.827±1.496), (24.561±1.390), (140.247±8.029), and (158.423±9.142)N in groups A, B, C, D, E, and F respectively when the radius shifted 5 mm proximally, showing significant difference among groups (P < 0.01). ConclusionReconstruction of the IOM with the extensor carpi radialis longus tendon is insufficient to restore the forearm longitudinal stability. Reconstruction using extensor carpi radialis longus tendon combined with radial head replacement may be a new choice for treatment of forearm longitudinal instability.
Objective To review the recent anatomy and biomechanical research progress of knee posteromedial corner, to analyze deficient aspect, and to predict future research directions. Methods Domestic and international l iterature about the anatomy and function of knee posteromedial corner in recent years was reviewed extensively, at the same time, the biomechanics of corresponding structure was summarized and analyzed. Results The anatomical structures ofknee posteromedial corner included the static stabil ity structures and the dynamic stabil ity structures. The dynamic stabil ity structures were more important, including posterior root of medial meniscus, posterior obl ique l igament, semimembranosus extensions, meniscotibial l igament and obl ique popl iteal l igament. The posterior obl ique l igament was most important structure to contribute to stabil ization of valgus, anterior internal rotation of knee and posterior movement of tibia. Conclusion Anatomical reconstruction of knee posteromedial corner especially the posterior obl ique l igament is the key to the reconstruction of knee posteromedial function stabil ity.
Objective To evaluate the biomechanical stability of a newly-designed Y type pedicle screw (YPS) in osteoporotic synthetic bone. Methods The osteoporotic synthetic bone were randomly divided into 3 groups (n=20). A pilot hole, 3.0 mm in diameter and 30.0 mm in deep, was prepared in these bones with the same method. The YPS, expansive pedicle screw (EPS), and bone cement-injectable cannulated pedicle screw (CICPS) were inserted into these synthetic bone through the pilot hole prepared. X-ray film examination was performed after 12 hours; the biomechanical stability of YPS, EPS, and CICPS groups was tested by the universal testing machine (E10000). The test items included the maximum axial pullout force, the maximum running torque, and the maximum periodical anti-bending. Results X-ray examination showed that in YPS group, the main screw and the core pin were wrapped around the polyurethane material, the core pin was formed from the lower 1/3 of the main screw and formed an angle of 15° with the main screw, and the lowest point of the inserted middle core pin was positioned at the same level with the main screw; in EPS group, the tip of EPS expanded markedly and formed a claw-like structure; in CICPS group, the bone cement was mainly distributed in the front of the screw and was dispersed in the trabecular bone to form a stable screw-bone cement-trabecular complex. The maximum axial pullout force of YPS, EPS, and CICPS groups was (98.43±8.26), (77.41±11.41), and (186.43±23.23) N, respectively; the maximum running torque was (1.42±0.33), (0.96±0.37), and (2.27±0.39) N/m, respectively; and the maximum periodical anti-bending was (67.49±3.02), (66.03±2.88), and (143.48±4.73) N, respectively. The above indexes in CICPS group were significantly higher than those in YPS group and EPS group (P<0.05); the maximum axial pullout force and the maximum running torque in YPS group were significantly higher than those in EPS group (P<0.05), but there was no significant difference in the maximum periodical anti-bending between YPS group and EPS group (P>0.05). Conclusion Compared with EPS, YPS can effectively enhance the maximum axial pullout force and maximum rotation force in the module, which provides a new idea for the design of screws and the choice of different fixation methods under the condition of osteoporosis.
In the present study, a finite element model of L4-5 lumbar motion segment was established based on the CT images and a combination with image processing software, and the analysis of lumbar biomechanical characteristics was conducted on the proposed model according to different cases of flexion, extension, lateral bending and axial rotation. Firstly, the CT images of lumbar segment L4 to L5 from a healthy volunteer were selected for a three dimensional model establishment which was consisted of cortical bone, cancellous bone, posterior structure, annulus, nucleus pulposus, cartilage endplate, ligament and facet joint. The biomechanical analysis was then conducted according to different cases of flexion, extension, lateral bending and axial rotation. The results showed that the established finite element model of L4-5 lumbar segment was realistic and effective. The axial displacement of the proposed model was 0.23, 0.47, 0.76 and 1.02 mm, respectively under the pressure of 500, 1 000, 1 500 and 2 000 N, which was similar to the previous studies in vitro experiments and finite element analysis of other people under the same condition. The stress distribution of the lumbar spine and intervertebral disc accorded with the biomechanical properties of the lumbar spine under various conditions. The established finite element model has been proved to be effective in simulating the biomechanical properties of lumbar spine, and therefore laid a good foundation for the research of the implants of biomechanical properties of lumbar spine.