Design of a Novel Variable-Diameter Cortical Threaded Screw and its Application in Improving Cortical Bone Trajectory in Lumbar Spine / 医用生物力学

Objective A novel variable-diameter cortical threaded screw used in a modified cortical bone trajectory(MCBT)was designed to verify its mechanical properties using the MCBT technique.Methods According to MCBT technology,the screw pitch was fixed at 2 mm,the total length was 45 mm,the diameter of the thick rod was 5.5 mm,the diameter of the thin rod was 4.0-4.5 mm,and the length of variable-diameter position connecting the thick rod and the thin rod was 2 mm.The parameters were set based on three aspects:variable-diameter position,thread depth,and thread type.Three-factor and three-level L9 tests were conducted and screw models were established.The torsion and the bending and pull-out force of the designed screws were calculated based on the finite element method,the results were analyzed using range analysis,and then the screw models were determined.The three-dimensional(3D)model of L4 vertebral body in osteoporosis specimens was established and screws were placed according to the MCBT technique.The pull-out force of the novel variable-diameter cortical threaded screw was compared with that of a conventional non-variable-diameter cortical threaded screw.Results Range analysis showed that screw No.6(variable-diameter position:24 mm from the screw head,thread depth:0.7 mm,45° symmetrical thread)was the optimal screw.The anti-pull-out force of the No.6 variable-diameter cortical threaded screw was 13.1%higher than that of the 4.5 mm conventional non-variable-diameter cortical threaded screw,and no statistical difference in anti-pull-out force was found between the No.6 variable-diameter cortical threaded screw and the 5.5 mm conventional non-variable-diameter cortical threaded screw.Conclusions The variable-diameter position has the smallest influence on pull-out force of the screw,the thread type has the largest influence on pull-out force,and the thread depth has the largest influence on torsion and bending.Compared with that of the conventional non-variable-diameter cortical threaded screw,the variable-diameter cortical threaded screw had a smaller front end,which prevented splitting at the entrance point of the screw.The screw has a large diameter at rear end,thereby showing improved pull-out performance.The results provide a new theoretical basis for the clinical application of MCBT technology.

Mechanical analysis of cortical bone trajectory screw placement in lumbar revision / 中国组织工程研究

BACKGROUND:At present,there are shortcomings and risks in the surgical revision of vertebral bodies that failed to be fixed in clinical practice.To avoid the risks of conventional revision surgery,the cortical bone trajectory technique is used to perform revision surgery on vertebral bodies that failed to be fixed.However,the mechanical properties of cortical bone trajectory technique screws in revision surgery are not clear. OBJECTIVE:The mechanical properties of cortical bone trajectory in lumbar revision surgery were analyzed by the finite element method to provide a theoretical basis for the clinical application of cortical bone trajectory in revision surgery. METHODS:CT scan data of the osteoporotic vertebral body were obtained and the L4 vertebral body model was established.The initial cortical bone trajectory placement and traditional pedicle screw in the L4 vertebral body model were completed,respectively,and their mechanical data were taken as the baseline standard for later evaluation of revision surgical performance.The traditional pedicle screw was removed and the screw path was retained.The cortical bone trajectory screw was used for secondary screw placement on the vertebral body to achieve lumbar refixation.The axial pull-out force,stability,and lumbar motion range of the revised screw were analyzed by the finite element method. RESULTS AND CONCLUSION:(1)The screw axial pull-out force of the cortical bone trajectory revision group was 25.6%higher than that of the traditional pedicle initial group.(2)In the lower,left,and right working conditions,the load-displacement ratio of screws in the cortical bone trajectory revision group increased by 18.5%,41.3%,and 35.0%,respectively,compared with the traditional pedicle initial group.The load-displacement ratio of screws in the cortical bone trajectory revision group was slightly higher than that in the traditional pedicle initial group under the above condition,but there was no statistically significant difference(P>0.05).(3)In anterior and posterior flexion conditions,lumbar motion range in the cortical bone trajectory revision group was increased by 45.5%and 36.1%compared with the traditional pedicle initial group,but there was no statistically significant difference in left bend,right bend,and axial rotation conditions(P>0.05).(4)There were no statistically significant differences in screw axial pull-out force,screw load-displacement ratio,and lumbar motion range between the cortical bone trajectory revision group and cortical bone trajectory initial group(P>0.05).(5)The mechanical data exhibited that although the revised nail track bone was damaged or lost to a certain extent,the mechanical properties of the cortical bone trajectory revision group were still better than those of the traditional pedicle initial group to a certain extent.Moreover,there was no significant difference in the mechanical properties between the cortical bone trajectory revision group and the cortical bone trajectory initial group.It provides a reference for revision surgery of lumbar internal fixation with cortical bone trajectory technique in patients with failed traditional pedicle fixation.

Progress in minimally invasive surgery for adjacent segment disease after lumbar fusion / 中华外科杂志

Adjacent segment disease (ASDis) is a common complication of posterior lumbar spine fusion and often requires surgical treatment. In the treatment of ASDis, percutaneous spinal endoscopy can be used for simple decompression without removal of the original internal fixation, or for posterior fixation and fusion under the scope or in combination with other access fixation and fusion techniques, with the advantages of less surgical trauma, less bleeding, and faster postoperative recovery. Traditional trajectory screw technique is one of the risk factors for adjacent segment degeneration because of its tendency to cause damage to the adjacent synovial joint during surgery. In contrast, the cortical tone trajectory (CBT) screw placement technique not only reduces the damage to the articular joint during the screw placement process, but also preserves the original internal fixation in the treatment of ASDis, which significantly reduces the surgical trauma. Secondly, the implantation of CBT screws with the aid of digital technologies such as three-dimentinal printed guides, CT navigation, and robotics allows for more precise "double nailing" of ASDis patients to complete the fusion of adjacent segments, and is a minimally invasive procedure to be considered for patients who meet the clinical indications for fusion. This article reviews the literature on the use of percutaneous spinal endoscopy and CBT in the surgical management of ASDis.

Cadaveric study of anatomical measurement of isthmus parameters of lumbar spine to guide cortical bone screw placement

SUMMARY OBJECTIVE: To reduce surgical exposure and improve accuracy, this study evaluated the anatomical distance parameter D (including D1, D2, and D3) of the lumbar isthmus for cortical bone screw insertion. METHODS: A total of 25 structurally complete lumbar dry specimens were used for lumbar anatomy measurements. The six cadaver specimens were divided into upper and lower parts on the plane of the T11-T12 vertebrae, and we use the lower parts. Therefore, six lumbar wet specimens and another four complete lumbar dry specimens were selected. The lumbar isthmus tangent point was considered a coordinate origin, and the insertion point was determined through translating the distance of D1 value to the midline of the vertebral body horizontally and then vertically moved toward inferior board of the transverse process with the distance of D3 value. RESULTS: In four dry and six wet intact lumbar specimens, cortical bone screws were placed according to the average value of the isthmus parameter D. A total of 100 trajectories were verified in specimens by X-ray and computed topography scan to evaluate the safety, accuracy, and feasibility of the surgical use of isthmus parameter D. Using this parameter, the rates of excellent screw placement were 95% (38/40) in four dry specimens and 88.7% (53/60) in six wet specimens. CONCLUSION: The isthmus parameter D is easier to use by the operator, which can improve surgical accuracy and reduce operation time. LEVEL OF EVIDENCE: Level IV, prospective study.

Pulmonary hypertension could be a risk for deep vein thrombosis in lower extremities after joint replacement surgery

SUMMARY A background of Pulmonary Hypertension (PH) indicates a progressive elevation of pulmonary vascular resistance, leading to overfilling, elevation of venous pressure, congestion in various organs, and edema in the venous system. This study aimed to investigate whether PH is a risk factor for deep vein thrombosis (DVT) of the lower extremities after hip and knee replacement surgery. METHODS A total of 238 patients who received joint replacement of lower extremities in our department of orthopedics from January 2009 to January 2012 were examined by echocardiography and Color Doppler flow imaging (CDFI) of the lower extremities. Based on pulmonary artery pressure (PAP), the patients were divided into a normal PAP group (n=214) and PH group (n=24). All the patients were re-examined by CDFI during post-operative care. RESULTS Among the 238 patients, 18 had DVT in the lower extremities after the operation. DVT total incidence rate was 7.56% (18/238). In the PH group, 11 patients had DVT (45.83%, 11/24), but in the normal PAP group, only 7 had DVT (3.27%, 7/214). The incidence of DVT was significantly lower in the normal PAP group than in the PH group (P<0.01). In addition, there was a positive correlation between PAP and the incidence of DVT. CONCLUSION PH could be a high-risk factor for the occurrence of DVT in patient's lower extremities after joint replacement surgeries.

RESUMO OBJETIVO A hipertensão pulmonar (HP) indica elevação progressiva da resistência vascular pulmonar, levando ao excesso de enchimento, elevação da pressão venosa, congestão em vários órgãos e edema no sistema venoso. Este estudo teve como objetivo investigar se a HP é um fator de risco para trombose venosa profunda (TVP) das extremidades inferiores após cirurgia de prótese de quadril e joelho. MÉTODOS Um total de 238 pacientes que receberam a substituição da articulação das extremidades inferiores em nosso departamento de ortopedia de janeiro de 2009 a junho de 2012 foi examinado por ecocardiograma e fluxo de imagem Doppler colorido (CDFI) dos membros inferiores. De acordo com a pressão arterial pulmonar (PAP), os pacientes foram divididos em grupo PAP normal (n=214) e grupo PH (n=24). Todos os pacientes foram reexaminados por CDFI durante os cuidados pós-operatórios. RESULTADOS Entre os 238 pacientes, 18 pacientes tiveram TVP nas extremidades inferiores após a operação. A taxa de incidência total de TVP foi de 7,56% (18/238). No grupo PH, 11 pacientes tiveram TVP (45,83%, 11/24), mas no grupo PAP normal, apenas sete pacientes tiveram TVP (3,27%, 7/214). A incidência de TVP foi significativamente menor no grupo PAP normal do que no grupo PH (P<0,01). Além disso, houve uma correlação positiva entre a PAP e a incidência de TVP. CONCLUSÃO A HP poderia ser um fator de alto risco para a ocorrência de TVP nas extremidades inferiores do paciente após cirurgias de substituição articular.