Biomechanical analysis of five fixation techniques used in glenohumeral arthrodesis

Background: The purpose of the present study is to compare five fixation techniques in shoulder fusion. The most common complications resulting from shoulder fusion, non‐union and unacceptable arm position, might reflect a failure to achieve rigid fixation during the surgical procedure. Methods: Twenty‐five shoulder fusions were carried out on human cadaveric specimens using the following techniques: screw fixation, external fixation, external fixation supplemented with screw fixation, single plate fixation and double plate fixation. Each specimen was tested on a servohydraulic machine to determine stiffness. Results: There was a statistically significant difference in bending and torsional stiffness between all five fixation techniques. Normalized bending (B) and torsional stiffness (T), in descending order, were: double plate (B = 1.00, T = 1.00), single plate (B = 0.77, T = 0.89), external fixation with screws (B = 0.68, T = 0.74), external fixation alone (B = 0.40, T = 0.53), and screws alone (B = 0.13, T = 0.26). Conclusion: The risk of the most common complications resulting from shoulder fusion might be minimized if these biomechanical findings are applied to surgical decision making.     

胸腰椎爆裂骨折三种后路内固定方法的稳定性生物力学研究

[目的]比较长节段固定术、短节段固定术和短节段结合椎体成形固定术治疗胸腰椎爆裂骨折的稳定性。[方法]收集6具新鲜尸体的脊柱(T9～L5)标本,对每一具标本依次按完整状态、骨折状态、长节段固定、短节段固定和短节段结合椎体成形的顺序进行测试,计算其在屈曲、背伸、左右侧弯和左右旋转6个方向的运动范围,比较各组间差异。[结果]骨折后脊柱在6个方向上的运动范围均增加(P<0.05);各内固定组的运动范围均小于完整组(P<0.05);长节段固定和短节段结合椎体成形固定的运动范围小于单纯短节段固定组(P<0.05);短节段结合椎体成形固定在屈曲和左右侧屈方向上的运动范围与长节段固定无差别(P>0.05),而在背伸和左右旋转方向上的运动范围短节段结合椎体成形固定则大于长节段固定(P<0.05)。[结论]通过延长固定节段与联合椎体成形均能够增加短节段固定的稳定性,在屈曲和左右侧屈方向上短节段联合椎体成形已经能够达到长节段固定所能够达到的稳定性。     

Complications and outcome of four-corner arthrodesis: circular plate fixation versus traditional techniques

PURPOSE: To review the clinical and radiographic results of scaphoid excision and four-corner arthrodesis using a circular plate and screws compared with traditional fusion techniques (wires, staples, screws). METHODS: Fifty-eight patients with four-corner arthrodesis (plate fixation, n = 27; traditional fixation, n = 31) were evaluated for radiographic and clinical success using wrist radiographs and functional assays. Patients were subjectively surveyed using the standardized Disabilities of the Arm, Shoulder, and Hand questionnaire and classification scales for pain and satisfaction. Objective measurements included grip-strength and range-of-motion measurements. RESULTS: Radiographic analysis showed 26% nonunion with loose hardware in the plate group compared with 3% in the traditional group and 22% hardware impingement in the plate group compared with 3% in the traditional group. Clinical evaluation yielded a mean grip strength of 31 kg (70% of opposite side) for plate fixation and 33 kg (79% of opposite side) for traditional fixation. The mean flexion-extension arc was 48% and 50% of the opposite wrist for plate and traditional patients, respectively. The mean adjusted Disabilities of the Arm, Shoulder, and Hand questionnaire scores were 27 out of 100 for plate patients and 8 out of 100 for traditional patients. Pain classification scores showed that only 2 patients in the plate group were pain free whereas there were 8 patients in the traditional group who were pain free. Overall patient satisfaction was 60% for the plate group whereas the traditional patient group reported 100% satisfaction. CONCLUSIONS: The rate of major complications (nonunion or impingement) was much greater with circular plate fixation (48%) versus traditional fixation techniques (6%). With the plate procedure the grip strength and arc of motion decreased approximately 30% and 52%, respectively, compared with decreases of 21% and 50%, respectively, for traditional fusion methods. Additionally, subjective patient dissatisfaction was 40% in the plate group compared with 0% in the traditional group. We postulate that the increased complication and dissatisfaction rates associated with plate fixation may be attributable to possible biomechanical imperfections or increased technical demands with this fusion system.     

Biomechanical analysis of internal fixation techniques for proximal interphalangeal joint arthrodesis

Although numerous fixation techniques have been developed for performing small joint arthrodesis, no previous study of the biomechanical properties of these constructs has been published. The strength of specimens of arthrodesis of the proximal interphalangeal joint performed with cadaver material was determined for three-point anteroposterior bending, axial torsion, and lateral cantilever bending stress. Crossed Kirschner wires, intraosseous wiring, and figure of eight tension-band wiring were studied. Figure of eight tension-band wiring demonstrates superior strength in anteroposterior bending and torsion. For lateral bending stress, no significant difference exists among the techniques studied.     

Biomechanical comparison of spondylolysis fixation techniques

STUDY DESIGN: A load-controlled biomechanical analysis of flexion, extension, and torsional stiffness in instrumented calf spines. OBJECTIVES: To compare biomechanically the performance of various fixation techniques for the repair of spondylolytic defects in the pars interarticularis. SUMMARY OF BACKGROUND DATA: Several techniques have been developed to stabilize a spondylolytic defect in the lumbar spine. There are, however, no comprehensive biomechanical studies in which these techniques are compared. METHODS: Nine fresh-frozen and thawed calf cadaveric lumbar L2-L6 spines were used for mechanical testing. Scott's technique, Buck's technique (screw fixation in the lamina across the defects), modified Scott's technique (wire loops around cortical screws placed into both pedicles and tightened under the spinous process), and screw-rod-hook fixation were applied on the calf lumbar spines in which bilateral spondylolytic defects were created in the L4 vertebra. Motion across the defects for each direction of loading in flexion, extension, and rotation was measured using extensometers. The intervertebral rotations and the strain at the site of the spondylolytic defect were computed from the acquired load-displacement data. RESULTS: Each fixation technique significantly increased stiffness and returned the intervertebral rotational stiffness to nearly intact levels. Displacement across the defect under flexion loading was significantly suppressed by each instrumentation technique, but the least motion (P < 0.05) was allowed with the screw-rod-hook fixation or Buck's technique. CONCLUSIONS: All four fixation techniques restored the intervertebral rotational displacements under flexion and torsional loading to the intact condition. The screw-rod-hook fixation allowed the least amount of motion across the defect during flexion.     

Biomechanical comparison of two fixation methods for first metatarsophalangeal joint arthrodesis

PURPOSE: The aim of this study was to compare the mechanical stability of two methods of fixation for arthrodesis of the hallux metatarsophalangeal joint: 1. a technique using an intramedullary screw and 2. a standard technique using crossed interfragmentary compression screws. METHODOLOGY: The metatarsophalangeal joint was mechanically evaluated in cantilever bending using a servohydraulic testing machine. Differences in stiffness and strength parameters between the two techniques were checked for significance (P<0.05) using a paired t-test. RESULTS: Fixation provided by the intramedullary screw was stiffer and stronger than that from crossed compression screws. CONCLUSIONS: The stronger and stiffer intramedullary screw technique offers mechanical advantages over the crossed interfragmentary screw technique.     

Results of four-corner arthrodesis using dorsal circular plate fixation

PURPOSE: Four-corner arthrodesis with scaphoid excision has been used to reduce pain and preserve functional range of motion for patients with radioscaphoid arthritis. Early results of 4-corner arthrodesis with scaphoid excision using dorsal circular plate fixation are compared with reported results in the literature. METHODS: We reviewed retrospectively the first 18 four-corner arthrodeses performed with this system by 4 hand surgeons. Two patients had revision surgery for nonunions before the study that were considered failures. Eight patients returned for final radiographs, objective examination, and functional questionnaire. The average follow-up period was 20 months (range, 13-33 mo). These results were compared with reported results in the literature using alternate fixation methods. RESULTS: Radiographic union was achieved in only 3 wrists. Range of motion was 46% that of the opposite normal wrist and grip strength compared with the opposite wrist was 56%. Five patients would have the procedure again and 6 of 8 have returned to their original employment. CONCLUSIONS: Four-corner arthrodesis with scaphoid excision using a circular internal fixation plate produced a high number of nonunions. Grip strength and range of motion results also were inferior to those reported in the literature.     

Biomechanical comparison of three fixation techniques for unstable thoracolumbar burst fractures. Laboratory investigation

OBJECT: Increased structural stability is considered sufficient justification for higher-risk surgical procedures, such as circumferential fixation after severe spinal destabilization. However, there is little biomechanical evidence to support such claims, particularly after traumatic lumbar burst fracture. The authors sought out to compare the biomechanical performance of the following 3 fixation strategies for spinal reconstruction after decompression for an unstable thoracolumbar burst fracture: 1) short-segment anterolateral fixation; 2) circumferential fixation; and 3) extended anterolateral fixation. METHODS: Thoracolumbar spines (T10-L4) from 7 donors (mean age at death 64+/-6 years; 1 female and 6 males) were tested in pure moment loading in flexion-extension, lateral bending, and axial rotation. Thoracolumbar burst fractures were surgically induced at L-1, and testing was repeated sequentially for each of the following fixation techniques: short-segment anterolateral, circumferential, and extended anterolateral. Primary and coupled 3D motions were measured across the instrumented site (T12-L2) and compared across treatment groups. RESULTS: Circumferential and extended anterolateral fixations were statistically equivalent for primary and off-axis range-of-motions in all loading directions, and short-segment anterolateral fixation offered significantly less rigidity than the other 2 methods. CONCLUSIONS: The results of this study strongly suggest that extended anterolateral fixation is biomechanically comparable to circumferential fusion in the treatment of unstable thoracolumbar burst fractures with posterior column and posterior ligamentous injury. In cases in which an anterior procedure may be favored for load sharing or canal decompression, extension of the anterior instrumentation and fusion one level above and below the unstable segment can result in near equivalent stability to a 2-stage circumferential procedure.     

Biomechanical comparison of occipitoatlantal screw fixation techniques

OBJECT: The stability provided by 3 occipitoatlantal fixation techniques (occiput [Oc]-C1 transarticular screws, occipital keel screws rigidly interconnected with C-1 lateral mass screws, and suboccipital/sublaminar wired contoured rod) were compared. METHODS: Seven human cadaveric specimens received transarticular screws and 7 received occipital keel-C1 lateral mass screws. All specimens later underwent contoured rod fixation. All conditions were studied with and without placement of a structural graft wired between the skull base and C-1 lamina. Specimens were loaded quasistatically using pure moments to induce flexion, extension, lateral bending, and axial rotation while recording segmental motion optoelectronically. Flexibility was measured immediately postoperatively and after 10,000 cycles of fatigue. RESULTS: Application of Oc-C1 transarticular screws, with a wired graft, reduced the mean range of motion (ROM) to 3% of normal. Occipital keel-C1 lateral mass screws (also with graft) offered less stability than transarticular screws during extension and lateral bending (p < 0.02), reducing ROM to 17% of normal. The wired contoured rod reduced motion to 31% of normal, providing significantly less stability than either screw fixation technique. Fatigue increased motion in constructs fitted with transarticular screws, keel screws/lateral mass screw constructs, and contoured wired rods, by means of 19, 5, and 26%, respectively. In all constructs, adding a structural graft significantly improved stability, but the extent depended on the loading direction. CONCLUSIONS: Assuming the presence of mild C1-2 instability, Oc-C1 transarticular screws and occipital keel-C1 lateral mass screws are approximately equivalent in performance for occipitoatlantal stabilization in promoting fusion. A posteriorly wired contoured rod is less likely to provide a good fusion environment because of less stabilizing potential and a greater likelihood of loosening with fatigue.     

Biomechanical comparison of intramedullary nail and blade plate fixation for tibiotalocalcaneal arthrodesis

OBJECTIVE: Tibiotalocalcaneal arthrodesis is used to manage severe bone loss, arthritis, and/or instability. The goal is to relieve pain through a stable, well-aligned hindfoot and ankle. The purpose of this study was 2-fold: to biomechanically compare 1) initial stability, and 2) the effect of bone density on the stability of intramedullary nail and blade plate fixation in tibiotalocalcaneal arthrodesis. DESIGN: Biomechanical study using anatomic specimens. METHODS: Ankle and subtalar joint capsules were exposed for 7 pairs of fresh-frozen anatomic specimens. One ankle from each pair was instrumented with an interlocked intramedullary nail inserted retrograde across the subtalar and ankle joint while the contralateral hind foot was stabilized with a lateral cannulated blade plate. Specimen stability was tested in plantar/dorsiflexion and inversion/eversion to a maximum bending moment of 12 Nm and in internal/external rotation to a maximum torque of 7 Nm. Physical measurements of bone density were made to determine its effect on stability. MAIN OUTCOME MEASURES: Maximum angular displacement of the constructs in plantarflexion, dorsiflexion, inversion, eversion, internal rotation, and external rotation. RESULTS: No significant differences were observed between the plated and nailed constructs in the 3 loading configurations (Power = 0.77). Only 6 pairs were included in the results because of fixation failures. A small but significant reduction in internal rotation alone of 1.8 degrees was found with the plated compared with the nailed construct (P = 0.045). Reduced stability was associated with lower bone density in torsion and inversion/eversion in the plated constructs (r = 0.67- 0.87) with a similar trend seen in torsion in the nailed constructs (r = 0.5). CONCLUSION: Initial construct stabilities and the effect of reduced bone density were found to be similar between the blade plate and the intramedullary nail in tibiotalocalcaneal arthrodesis, thus implant choice may be based on other clinical factors, such as surgeon preference or soft-tissue status.     

四种骶骨钉固定技术的生物力学比较

目的通过骨质疏松骶骨标本对4种骶骨椎弓根钉（双皮质、三皮质、标准骨水泥强化和终板下骨水泥强化）载荷后的下沉位移进行比较。方法取自11具新鲜骨质疏松尸体的骶骨标本用于实验。采用DEXA测定骨密度后在同一骶骨的左右侧随机置入直径7mm的双皮质和三皮质骶骨椎弓根钉。使用MTS试验机对螺钉进行30～250N压力加载2000次后取出螺钉。钉道内注入骨水泥（polymethylmethacrylate,PMMA）,将比双皮质或三皮质固定短5mm的螺钉再次置人（分别定义为标准和终板下PMMA强化）,并重复上述加载。记录加载后螺钉的下沉位移,进行比较。结果11具标本的骨密度为0．55～0．78g／cm^2,平均0．7lg／cm^2。三皮质和标准PMMA强化椎弓根钉间的下沉位移差异无统计学意义,此2种固定技术的下沉位移显著低于双皮质固定。终板下PMMA强化椎弓根钉的下沉位移显著低于其他固定技术。结论在骨质疏松状态下PMMA强化可显著提高骶骨钉一骨界面的结合强度。在上述4种骶骨固定技术中终板下PMMA强化椎弓根钉可获得最坚强的锚定。     

Biomechanical comparison of five different atlantoaxial posterior fixation techniques

STUDY DESIGN: Five different reconstructions of the atlantoaxial complex were biomechanically compared in vitro in a nondestructive test. OBJECTIVES: To determine whether non-bone graft-dependent one-point fixation affords stability levels equivalent to three-point reconstructions. SUMMARY OF BACKGROUND DATA: Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize motion around C1-C2. However, placement of transarticular screws is technically demanding. Posterior wiring techniques affording one-point fixation have failure rates of approximately 15%, with failure considered to be secondary to structural bone graft failures. One-point, non-bone graft-dependent fixations have not been tested. METHODS: Eight human cervical specimens, C0-C3 were loaded nondestructively. Unconstrained three-dimensional segmental motion was measured. The reconstructions tested were two one-point fixations, one two-point fixation, and two three-point fixations. RESULTS: Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P < 0.05). During flexion-extension, higher stiffness levels were observed in one- and three-point fixations when compared with the intact spine (P < 0.05). In lateral bending no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provided greater stability than one-point fixations. CONCLUSION: The current findings substantiate the use of three-point fixation as the treatment of choice for C1-C2 instability. [l: atlantoaxial fixation, biomechanics, cervical spine, instability, spinal instrumentation, transarticular screws]     

Biomechanical analysis of screw-augmented intramedullary fixation for tibiotalocalcaneal arthrodesis

BACKGROUND: This study compared intramedullary (IM) fixation for tibiotalocalcaneal arthrodesis with and without a tibiotalocalcaneal augmentation screw. METHODS: Each specimen in six matched pairs of fresh frozen cadavers underwent tibiotalocalcaneal arthrodesis with an IM nail. One specimen from each pair also received a tibiotalocalcaneal augmentation screw. Initial and final stiffness, load to failure, and construct deformation at failure were calculated with dorsiflexion loading. Bone mineral density of each pair was determined. Statistical analysis was done using a paired Student t-test and a Pearson correlation. RESULTS: Initial and final stiffness and load to failure were significantly higher for the tibiotalocalcaneal screw augmented fixation group as compared with the specimens with no additional screw (initial stiffness, 128.0 versus 78.4 N/mm, p = 0.04; final stiffness, 230.9 versus 164.7 N/mm, p = 0.04; load to failure, 875.5 versus 660.2 N, p = 0.03). There was a significant negative correlation between bone mineral density and average construct deformation in the samples without the added tibiotalocalcaneal screw (r = -0.90, p = 0.02). CONCLUSIONS: In tibiotalocalcaneal arthrodesis with intramedullary nail fixation, a tibiotalocalcaneal augmentation screw provides more stable fixation. CLINICAL RELEVANCE: Use of an augmentation screw as described in this study may lead to lower complication rates, particularly in patients with osteopenic bone.     

Biomechanical comparison of three different fixation techniques for anterior column posterior hemitransverse acetabular fractures using anterior intrapelvic approach

ObjectivesThe aim of this study was to biomechanically compare three different fixation methods for the fixation of anterior column posterior hemitransverse type acetabular fracture (ACPHT).MethodsACPHT fracture models were created on twenty-four foam cortical shell artificial hemipelvis models. Three fixation methods were assessed - Group 1: posterior column lag screws over a suprapectineal plate; Group 2: Posterior column lag screws over a suprapectineal plate and an infrapectineal plate; Group 3: A suprapectineal plate and a vertical infrapectineal plate. Stiffness and displacement amounts of fixation methods under dynamic and static axial loading conditions were measured.ResultsIn the dynamic and static tests, Group 3 showed the less stable fixation compared to Group 2. There was no statistically significant difference between the stiffness values of the fixation groups. In the static tests, there was no statistically significant difference between Group 1 and 2, although less displacements were obtained in Group 2.ConclusionsA combination of posterior lag screws over a suprapectineal plate and an infrapectineal plate supporting the pelvic brim along both sides of the linea terminalis resulted in a better fixation construct than a suprapectineal plate accompanying with a vertical infrapectineal plate provide better stability with less fracture displacement.