Are enlarged peroneal tubercle and accessory anterolateral talar facet associated with calcaneal spur?

BACKGROUND: As the anatomical variations of the foot, enlarged peroneal tubercle (EPT) and accessory anterolateral talar facet (AALTF) have attracted the attention of foot surgeons in recent years. However, EPT and AALTF have not been examined for a relationship with calcaneus spur (CS) as a common osteophyte. METHODS: The subjects were 369 individuals who died in northeastern Thailand and were preserved as skeletal specimens. The authors examined for the presence of left and right EPT, AALTF, and calcaneus spur (CS). We divided the EPT (+) group with EPT and the EPT (-) group without it and also divided the AALTF (+) group with AALTF and the AALTF (-) group without it. The age at death and the presence of CS were compared statistically between the EPT (+) and EPT (-) groups and between the AATLF (+) and AALTF (-) groups. RESULTS: Out of the total 369 cases, EPT was found in 117 cases (31.7%), AALTF was positive in 91 cases (24.7%), and CS was found in 194 cases (52.3%). In comparison between EPT (+) and EPT (-) groups, CS was significantly higher (p < 0.0001) in the EPT (+) group, but there was no significant difference in age at death. In comparison between AALTF (+) and AALTF (-) groups, there was no significant difference in age at death or CS. CONCLUSION: This study showed a strong relationship between EPT and CS, and the prevalence of EPT and AALTF by age in Thailand was first reported. We believe it helps to know the pathogenesis and biomechanism of EPT and AALTF. TRIAL REGISTRATION: Not applicable.

Experimental Study of Failures of the Rigid Spinal Posterior Fixation System Under Compressive Load Conditions: A Cadaver Study.

Background Many studies have been conducted on the biomechanics of the spine to elucidate the fixation properties of spinal fusion surgery and the causes of instrumentation failure. Among these studies, there are some studies on load sharing in the spine and measurement using strain gauges and pressure gauges, but there is a lack of research on axial compressive loads. Methods Axial compressive load tests were performed on human cadaveric injured lumbar vertebrae fixed with pedicle screws (PS). Both the strain generated in the PS rod and the intradiscal pressure were measured. Subsequently, the stress generated in the PS rod and the load sharing of the spine and instrumentation were calculated. Results Even when only compressive load is applied, bending stress of more than 10 times the compression stress was generated in the rod, and the stress tended to concentrate on one rod. Rod deformation becomes kyphotic, in contrast to the lordotic deformation behavior of the lumbar spine. The stress shielding rate was approximately 40%, less than half. Conclusions This study obtained basic data useful for constructing and verifying numerical simulations that are effective for predicting and elucidating the causes of dislodgement and failure of spinal implants.

Femoral Shaft Fracture Developed Late-Onset Infection in 27 Years after Intramedullary Nailing: A Case Report.

Postoperative late-onset infections more than 1 year after intramedullary nail surgery for femoral shaft fractures are very rare. We show an extremely rare case of developed late-onset infection 27 years after surgery, report on risk factors for late-onset infection, and infer why the infection occurred.

Clinical and oncologic outcomes of posterior only total en bloc spondylectomy for spinal metastasis involving third lumbar vertebra: A case series.

INTRODUCTION: A posterior-only total en bloc spondylectomy (TES) of the L3 level was deemed a highly intricate surgical procedure, necessitating the preservation of the L3 nerve root to prevent neurological deterioration. Despite bilateral preservation efforts of the L3 nerve roots, neurological deterioration proved unavoidable. This study aims to present the clinical, neurologic, and oncologic outcomes of spinal metastasis patients who underwent a posterior-only approach TES, encompassing the L3 vertebra. MATERIALS AND METHODS: All patients with L3-involved spinal metastasis undergoing posterior TES between January 2018 and January 2022 were investigated. The primary outcomes considered were the local recurrence rate and manual muscle testing of the lumbar myotome. Secondary outcomes included Frankel neurological status, operative time, blood loss, perioperative and postoperative complications, and Eastern Cooperative Oncology Group score. RESULTS: Five patients with TES involving L3 (three females) met the inclusion criteria. All patients had solitary metastases (three in the lungs, 2 in the breasts). Postoperatively, all patients experienced weakness of the hip flexors, but they were able to ambulate independently 12 months after surgery. One patient exhibited adjacent segment (L2) disease progression and underwent corpectomy 18 months after TES. No local recurrences at the surgical site were detected on magnetic resonance imaging at the 1-year follow-up. CONCLUSION: Posterior-only TES for L3-involved vertebrae yielded excellent results in the local control of metastatic disease. Despite hip flexor weakness, all patients were able to regain independent ambulation after 12 months. TES can offer favorable clinical and oncological outcomes in patients with solitary spinal metastases.

Morphometric study and anatomical variation with its incidence of foramina transversaria on the lower cervical vertebrae / Estudio morfométrico y variación anatómica con la incidencia de forámenes transversos en las vértebras cervicales inferiores

SUMMARY: Anatomical variation of the foramina transversaria (FT) is associated with vertebral neurovascular symptoms and can cause complications after lower spine surgery, especially cervical pedicle screw (CPS) insertion. FT variation has been documented and classified in various populations, as this information can help increase cervical stability in subaxial vertebral surgery. Although the morphometry of the upper cervical spine in Thai populations has been reported, there have yet been no studies examining the features of FT. The FT of dried cervical spines (C3-C7; left and right side; n = 107, male = 53 and female = 54) were examined for morphological variation, and their anteroposterior (AP) and transverse (T) diameters were measured using a digital vernier caliper. Morphometric data and variations were compared by sex and lateral side. It was that the C3-C6 FT in both sexes were round, and the C7 FT was elliptical with an oblique right side. FT diameters did not differ significantly by sex except for the AP diameters of C6-C7 and for T diameters of C4 and C7. The left AP diameters of C3-C6 were significantly longer than the right, as were the T diameters of C4 and C7 FT. Additionally, T diameter was significantly longer than that of the AP, except that of the left C6 in male spines, which did not differ from the AP. Most FT examined were round. These findings should be considered in the provisional diagnosis of vertebral neurovascular symptoms caused by FT variation as well as that of neurovascular damage after cervical pedicle screw placement.

La variación anatómica del foramen transverso (FT) se asocia con síntomas neurovasculares vertebrales y puede causar complicaciones después de la cirugía de columna cervical inferior, especialmente la inserción de tornillos pediculares cervicales (TPC). La variación del FT se ha documentado y clasificado en varias poblaciones, ya que esta información puede ayudar a aumentar la estabilidad cervical en la cirugía vertebral subaxial. Aunque se ha informado sobre la morfometría de la columna cervical superior en poblaciones tailandesas, aún no se han realizado estudios que examinen las características de FT. Se examinó la variación morfológica del FT de vértebras cervicales secas (C3-C7; lado izquierdo y derecho; n = 107, hombres = 53 y mujeres = 54), y se midieron sus diámetros anteroposterior (AP) y transverso (T) usando un pie de metro digital. Se compararon datos morfométricos y variaciones por sexo y lado. Los FT de C3-a C6 en ambos sexos eran redondos, y el FT C7 era elíptico con el lado derecho oblicuo. Los diámetros del FT no difirieron significativamente por sexo excepto para los diámetros AP de C6- C7 y para los diámetros transversos de C4 y C7. Los diámetros AP izquierdos de C3-C6 eran significativamente más largos que los del lado derecho, al igual que los diámetros transversos de C4 y C7. Además, el diámetro transverso fue significativamente mayor que el AP, excepto el C6 izquierdo en las vértebras de hombres, que no difirió del AP. La mayoría de los FT examinados eran redondos. Estos hallazgos deben ser considerados en el diagnóstico provisional de síntomas neurovasculares vertebrales causados por la variación del FT, así como en el de daño neurovascular tras la colocación de tornillos pediculares cervicales.

Morphometric analysis of dry atlas vertebrae in a northeastern Thai population and possible correlation with sex.

PURPOSE: The uppermost segment of the cervical vertebra or atlas (C1) is a critically important anatomical structure, housing the medulla oblongata and containing the grooves for the C1 spinal nerve and the vertebral vessels. Variations of the C1 vertebra can affect upper spine stability, and morphometric parameters have been reported to differ by population. However, there are few data regarding these parameters in Thais. The use of this bone to predict sex and age has never been reported. METHODS: This study aimed to examine C1 morphometry and determine its ability to predict sex. Twelve diameter parameters were taken from the C1 vertebrae of identified skeletons (n = 104, males [n, 54], females [n, 50]). Correlation analysis was also performed for sex and age, which were predicted using machine learning algorithms. RESULTS: The results showed that 8 of the 12 measured parameters were significantly longer in the male atlas (p < 0.05), while the remaining 4 (distance between both medial-most edges of the transverse foramen, transverse dimension of the superior articular surface, frontal plane passing through the canal's midpoint, and anteroposterior dimension of the inferior articular surface) did not differ significantly by sex. There was no statistically significant difference in these parameters on the lateral side. The decision stump classifier was trained on C1 parameters, and the resulting model could predict sex with 82.6% accuracy (root mean square error = 0.38). CONCLUSION: Assertation of the morphometric parameters of the atlas is important for preoperative assessment, especially for the treatment of atlas dislocation. Our findings also highlighted the potential use of atlas measurements for sex prediction.

Clinical results of total en bloc spondylectomy using a single posterior approach in spinal metastasis patients: Experiences from Thailand.

AIM: To demonstrate a single posterior approach, total en bloc spondylectomy (TES) could be performed safely without preoperative embolization in spinal metastasis patients. MATERIALS AND METHODS: Thirteen solitary spinal metastasis patients (five males) underwent single posterior approach TES at the thoracolumbar spine without preoperative embolization from January 2018 to January 2020. The primary sites were the breast (n = 4), hepatocellular carcinoma (n = 2), colon (n = 2), and others (n = 5). All patients underwent single posterior TES. The Eastern Cooperative Oncology Group, Frankel neurological status, operative time and blood loss, and any complications were all recorded. The patients were regularly followed-up with radiography, computed tomography, and magnetic resonance imaging to detect any local recurrences. RESULTS: The mean operative time was 354.6 min, and the mean operative blood loss was 2134.62 ml. None of the patients experienced any perioperative complications. Within the follow-up period (3-24 months), no local recurrences were detected. Two patients (15.38%) were found to have distant metastasis to adjacent and remote vertebrae. Three patients were lost to follow-up, and three patients died of disease. Six patients showed an improved ECOG functional status by at least one grade. Four of Frankel A patients improved their neurological status by at least one grade. CONCLUSION: Even without embolization, single posterior TES at the thoracolumbar spine is safe and effective for short-term local control in solitary spinal metastasis. However, TES cannot prevent distant metastasis. Longer-term follow-up studies will be able to further identify the benefits of TES for the long-term local control of diseases.

Incidence and Skeletal Features of Developmental Cervical and Lumbar Spinal Stenosis.

STUDY DESIGN: Cross-sectional study. PURPOSE: To report the prevalence and relationship of developmental cervical and lumbar spinal stenosis (DCSS and DLSS) with the bone parameters of the skull and extremities. OVERVIEW OF LITERATURE: DCSS and DLSS are found occasionally in daily practice. DCSS and DLSS can cause compressive myelopathy, radiculopathy, and cauda equina syndrome; however, data on their prevalence and correlation with skull and skeletal extremity profiles is scarce. METHODS: A cross-sectional measurement study of 293 whole-body dried-bone samples was conducted. We measured the anteroposterior (AP) and transverse diameter of the fourth to sixth cervical vertebrae (C4-C6) and third to fifth lumbar vertebrae (L3-L5). Stenosis of the cervical spine and lumbar spine was defined as an AP diameter of <12 mm and <13 mm, respectively. We also measured the skull circumference, the AP and transverse diameters of the foramen magnum, the inner and outer inter distances between the left and right orbital bones, the humerus length, and the femoral length. Kruskal-Wallis and post hoc analyses were used in the statistical analyses. RESULTS: The age was 22-93 years. DCSS was found in 59 (20.1%) and DLSS in 28 (9.6%). Twelve samples had both DCSS and DLSS (development spinal stenosis, DSS). When compared to the "no spinal stenosis sample," DSS (-), DCSS and DSS had a significantly smaller skull circumference, the transverse diameter of the foramen magnum, and inner and outer distance between the orbital bone (p<0.05). There was no significant difference in humeral length, femoral length, or AP diameter of the foramen magnum. CONCLUSIONS: DCSS was correlated with a small skull, a small transverse diameter of the foramen magnum, and a small orbital bone. A small skull was strongly associated with a small cervical canal. DLSS, on the other hand, was unrelated to either a small cervical canal or a small skull.

Current status and problems of orthopaedic residents in Thailand and Myanmar.

Background: There is no research about current experiences of orthopaedic residents in Thailand and Myanmar. Methods: A questionnaire survey was distributed among Thai and Myanmar orthopaedic residents to assess their current experiences. This study included a total of 168 participants, comprising 92 orthopaedic residents in Thailand, and 76 in Myanmar who answered the questionnaire. The survey comprised nine questions about issues such as the contents of residency training programs, current training satisfaction, and future careers. The survey was administered anonymously between October 2020 and January 2021. Results: Regarding training content, 24 residents (14.3%) reported being "very satisfied", 103  (61.3%) were "satisfied", 37 (22.0%) were "moderately satisfied", and four (2.4%) were "dissatisfied", and respondents spent a mean of 3.1 h/day reading textbooks and research papers. As for salary, five (3.0%) residents answered "satisfied", 46 (27.4%) responded "moderately satisfied", and 117 (69.6%) were "dissatisfied". Conclusions: Many orthopedic residents in Thailand and Myanmar were enthusiastic about and satisfied with their training. Their only problem was that the salary was low.

Biomechanics comparison between endobutton fixation and syndesmotic screw fixation for syndesmotic injury ankle fracture; a finite element analysis and cadaveric validation study.

Introduction: Various syndesmotic fixation methods in ankle injury are recommended; however, a lack of biomechanical information persists regarding the stiffness of the fixation methods. The current study thus aimed to assess biomechanical cadaveric validation and perform a finite element analysis of syndesmotic fixation comparing endobutton vs. screw after syndesmotic injury with an ankle fracture. Method: Five pairs of ankles of fresh cadavers were used for the validity test for Anterior Inferior Tibiofibular Ligament (AITFL), Posterior Inferior Tibiofibular Ligament (PITFL), and Interosseous ligament biomechanics properties. Four finite element models (FEM) were created: an intact model, a fracture model with/without syndesmotic injury, an endobutton fixation model, and a syndesmotic screw fixation model. Each FEM was tested vis-à-vis external rotation force, anteroposterior translation force, and compression force until model failure. The primary outcomes were stiffness and force until failure. Result: The respective anteroposterior translation force for the stiffness of the intact model, the screw fixation model, and the endobutton fixation was 8.14, 9.15, and 8.17 N/mm. The respective external rotation force for the stiffness of intact, screw fixation, and endobutton model was 0.927,0.949, and 0.940 Nm/degree. The respective stress under compression force in the intact, screw fixation, and endobutton model was 39.94,25.59, and 37.30 MPa. Conclusion: Both screw and endobutton fixation models provided more translation, compression, and rotation stability than normal syndesmosis, but the screw model provided greater translation and compression force stability than the endobutton model. There was no difference in rotational stability between the two models. We thus recommend the same rehabilitation protocol for both fixation methods; however, vigorous translation and compression should be avoided when using endobutton fixation.

The relationship between traction spurs, Modic change, vacuum phenomenon, and segmental instability of the lumbar spine.

A thorough understanding of lumbar segmental motion is valuable to treat patients with degenerative lumbar disease, but kinematics associated with indicators of lumbar intervertebral instability [traction spur, Modic changes (MCs) and vacuum phenomenon (VP)] in the lumbar spine have not been well understood. The purpose of this study is to evaluate the relationships between traction spur, MCs and VP to radiographic measurements in the lumbar spine. A total of 525 lumbar discs from L1-2 to L5-S1 of 105 patients were evaluated. The sagittal translation (ST) and sagittal angulation were measured from the radiographs taken flexion-extension. The anterior disc height (ADH) was measured from the lateral radiographs, and ΔADH was measured as the difference from supine to sitting position. Logistic regression analyses were used to detect the association between the existence of traction spur, MCs and VP and related factors. Multivariate analysis showed that the traction spur was significantly related to translational motion (ST > 2 mm, OR 4.74) and the VP was significantly related to vertical motion (ΔADH > 3 mm, OR 1.94). These results suggest that the segments with traction spur and VP should be evaluated carefully because these may be a sign of lumbar intervertebral instability.

The new imaging findings: "Passing spine" without kissing.

ABSTRACT: Case-control studies by examining the lumbar spine computed tomography (CT) findings focusing on the spinous processes."Passing spine" was defined as a lumbar degenerative change observed on CT images. In contrast, kissing spine, which is also an image finding, has been acknowledged as an established clinical condition. Therefore, we compared the passing spine group and the kissing spine group to investigate whether the 2 groups belong to a similar disease group; this would help explain the clinical and imaging characteristics of patients with passing spine.Previous studies have described the gradual increase in the height and thickness of the lumbar vertebral spinous processes that can occur in individuals aged >40 years, and reported that this progressive degeneration can lead to a condition termed "kissing spine."We examined the CT imaging of 373 patients with lumbar spinal disease and divided patients into 2 groups, the kissing spine (K) group and the passing spine (P) group, and compared the clinical (age, sex, presence/absence of lower extremity pain) and imaging data (localization of kissing or passing spine, intervertebral disc height at the level of kissing or passing spine, lumbar lordosis (LL) angle, presence/absence of vacuum phenomenon (VP) in the intervertebral discs and spondylolisthesis at the level of kissing or passing spine between the 2 groups.Compared with patients with kissing spine, patients with passing spine had an increased incidence of lower extremity pain, lower intervertebral disc height at the level of passing spine, relatively static LL, and VP commonly observed in the intervertebral discs at the level of passing spine.Because the clinical and imaging characteristics of patients with passing spine are different from those of patients with kissing spine, passing spine might be a pathological condition distinct from kissing spine.

Total en bloc spondylectomy is worth doing in complete paralysis spinal giant cell tumor, a minimum 1-year follow-up.

OBJECTIVE: To investigate the neurological recovery of Frankel A spinal giant cell tumor (GCT) patients after they had received a Total En Bloc Spondylectomy (TES). MATERIALS AND METHODS: We retrospectively recorded data of three patients (two females) with mobile spine GCT (T6, T10, and L2) Enneking stage III with complete paralysis before surgery, who had undergone TES in our institute from January 2018 to September 2020. The duration of neurologic recovery to Frankel E was the primary outcome. The intra-operative blood loss, operative time, operative-related complications, and the local recurrence were the secondary outcomes. RESULTS: The duration of suffering from Frankel A to TES surgery was 2 months for the T6 patient, 3 weeks for the T10 patient, and 1 month for the L2 patient. Three patients had achieved full neurological recovery to Frankel E within 6 months after TES (T6 for 5 months, T10 for 3 months, and L2 for 3 months). The average blood loss was 2833.33 ml and the mean operative time was 400 min. Up until the last follow-up (13-25 months), no evidence of local recurrences had been found in any of the three patients. CONCLUSION: Frankel A spinal GCT patients can achieve full neurological recovery after TES, if the procedure is performed within 3 months after complete paraplegia. TES can effectively control any local recurrences.

The most appropriate titanium mesh cage size for anterior spinal reconstruction after single-level lumbar total en bloc spondylectomy: a finite element analysis and cadaveric validation study.

PURPOSE: There is little information available regarding the cage diameter that can provide the most rigid construct reconstruction after total en bloc spondylectomy (TES). The aim of this study was thus to determine the most appropriate titanium mesh cage diameter for reconstruction after spondylectomy. METHODS: A finite element model of the single level lumbar TES was created. Six models of titanium mesh cage with diameters of 1/3, 1/2, 2/3, 3/4, 4/5 of the caudad adjacent vertebra, and 1/1 of the cephalad vertebra were tested for construct stiffness. The peak von Mises stress (MPa) at the failure point and the site of failure were measured as outcomes. A cadaveric validation study also conducted to validate the finite element model. RESULTS: For axial loading, the maximum stress points were at the titanium mesh cage, with maximum stress of 44,598 MPa, 23,505 MPa, 23,778 MPa, and 16,598 MPa, 10,172 MPa, 10,805 MPa in the 1/3, 1/2, 2/3, 3/4, 4/5, and 1/1 diameter model, respectively. For torsional load, the maximum stress point in each of the cages was identified at the rod area of the spondylectomy site, with maximum stress of 390.9 MPa (failed at 4459 cycles), 141.35 MPa, 70.098 MPa, and 88.972 MPa, 42.249 MPa, 15.827 MPa, respectively. A cadaveric validation study results were coincided with the finite element model results. CONCLUSION: The most appropriate mesh cage diameter for reconstruction is 1/1 the diameter of the lower endplate of the adjacent cephalad vertebra, due to its ability to withstand both axial and torsional stress. According to the difficulty of large size cage insertion, a cage diameter of more than half of the upper endplate of the caudad vertebrae is acceptable in term of withstand stress. A cage diameter of 1/3 is unacceptable for reconstruction after total en bloc spondylectomy.

Safety and Neurologic Recovery of L2 Nerve Root Sacrificed in Total En Bloc Spondylectomy Involving the L2 Vertebra.

BACKGROUND: The L2 nerve root is considered part of the lumbar plexus that innervates the iliopsoas (IP) and quadricep muscles (Qd). Total en bloc spondylectomy (TES) at the L2 vertebra requires bilateral nerve root transection to facilitate surgical dissection and vertebral body removal. Information regarding neurological function recovery of the IP and Qd in patients with muscle weakness before TES is lacking. We aimed to report the neurological recovery of IP and Qd after TES involving the L2 vertebra in preoperative lower extremity weakness in spinal tumor patients. METHODS: We prospectively recorded all L2-involved spinal tumor patients undergoing TES between January 2018 and November 2020. As a primary outcome, we recorded the Manual Muscle Testing (MMT) grade of the IP and Qd preoperatively, immediately postoperatively, and at follow-up. Secondary outcomes included the Frankel neurological status, sensation impairment, and the Eastern Cooperative Oncology Group score. RESULTS: From 8 TES-involving L2 patients, 6 (4 males) met the inclusion criteria. One patient had first-grade deterioration of the Qd MMT immediately postoperatively. All patients could ambulate independently 6 months after surgery. Five patients required follow-up for more than 1 year and could walk without any gait aids. All patients had persistent anterior groin and bilateral thigh numbness until the final follow-up. CONCLUSION: Neurological recovery of the IP and Qd muscles as measured by MMT can occur within 6 months of bilateral L2 nerve root transection. Bilateral L2 nerve root sacrifice can have acceptable neurological outcomes and recovery, even in patients with preoperative IP and Qd weakness. LEVEL OF EVIDENCE: 4.

Pedicle Screw System May Not Control Severe Spinal Rotational Instability.

STUDY DESIGN: An in vitro biomechanical study. OBJECTIVE: The purpose of this study is to discuss whether pedicle screw systems can control spinal rotational instability in a functional spinal unit of lumbar spine on human cadaver. SUMMARY OF BACKGROUND DATA: Rotational experiments using deer lumbar cadaveric models showed that rotational range of motion (ROM) of the model fixed by a pedicle screw system with crosslinking after total facetectomy for both the sides was larger than that in the intact model, and stated that spinal rotational instability could not be controlled using a pedicle screw system. METHODS: A rotation experiment using 10 functional spinal units (L3-4) of lumbar spine on human cadavers was performed by preparing the four models (intact model, damaged model, pedicle screw model, and crosslink (CL) model) in stages, then calculating and comparing rotational ROM among the four models. RESULTS: Rotational ROM in the CL model was still larger than that of the intact model in all the samples. And, rotational ROM decreased in the order of damaged model >> pedicle screw model > CL model > intact model. Statistical analysis revealed significant differences between all models (P < 0.001). CONCLUSIONS: Pedicle screw systems may not control severe spinal rotational instability in human lumbar cadaveric models with total facetectomy on both the sides. This may represent a major biomechanical drawback to the pedicle screw system. LEVEL OF EVIDENCE: N/A.

Optimal configuration of a dual locking plate for femoral allograft or recycled autograft bone fixation: A finite element and biomechanical analysis.

BACKGROUND: Allografts and recycled bone autograft are commonly used for biological reconstruction. The dual locking plates fixation method has been advocated for increasing allograft stability and preventing fixation failure; however, the biomechanical properties of the various configurations of dual locking plates have not been extensively studied. METHODS: In a finite element (FE) analysis, we developed 6 patterns of different dual locking plate configurations for fixation of the mid shaft of the femur. The maximum strains were recorded for each of the 6 models then axial, bending and torsion stiffness were calculated. The FE analysis was validated the results with mechanical testing (axial compression, bending, and torsional stiffness) on a cadaveric femur. FINDINGS: The highest axial compression (715.41 N/mm) and lateral bending (2981.24 N/mm) was found in Model 4 (with two 10-hole locking plates placed at the medial and lateral side), while the highest torsional stiffness (193.59 N·mm /mm) was found in Model 3 (with 8- and 10-hole locking plates placed at the posterior and lateral side). Excellent agreement was found between the finite element analysis and biomechanical testing (r2 = 0.98). INTERPRETATION: The dual locking plate configuration with medial and lateral, 10-hole locking plates provided the most rigid and strongest fixation of the femur; both in terms of axial compression and lateral bending stiffness.

Biomechanical Problems Related to the Pedicle Screw System.

AIM: To assess biomechanical problems related to pedicle screw (PS) systems. MATERIAL AND METHODS: Functional spinal units (L3-4) of deer were evaluated using a 6-axis material testing machine. For the specimen models, we prepared an intact model, a damaged model, a PS model, and a crosslink model. We checked the range of motion (ROM) during bending and rotation tests. Eight directions were measured in the bending test: anterior, right-anterior, right, right-posterior, posterior, left-posterior, left, and left-anterior, and 2 directions were measured in the rotation test (right and left). RESULTS: ROMs of the PS model were smaller than those of the intact model in all directions. However, ROMs of the PS model in the rotation test were smaller than those of the damaged model and larger than those of the intact model. The stability of the crosslink model was better than that of the PS model during the bending test, but ROMs of the crosslink model were larger than those of the intact model during the rotation test. CONCLUSION: Excessive bending rigidity and rotational instability are the biomechanical problems related to PS systems. Based on these results, we speculate that one of the most significant causes of adjacent segment disease is excessive bending rigidity and one of the most important causes of instrumentation failure is rotational instability.