Frank Kandziora

AOSpine thoracolumbar spine injury classification system: fracture description, neurological status, and key modifiers.

Study Design. Reliability and agreement study, retrospective case series. Objective. To develop a widely accepted, comprehensive yet simple classification system with clinically acceptable intra- and interobserver reliability for use in both clinical practice and research. Summary of Background Data. Although the Magerl classification and thoracolumbar injury classification system (TLICS) are both well-known schemes to describe thoracolumbar (TL) fractures, no TL injury classification system has achieved universal international adoption. This lack of consensus limits communication between clinicians and researchers complicating the study of these injuries and the development of treatment algorithms. Methods. A simple and reproducible classification system of TL injuries was developed using a structured international consensus process. This classification system consists of a morphologic classification of the fracture, a grading system for the neurological status, and description of relevant patient-specific modifiers. Forty cases with a broad range of injuries were classified independently twice by group members 1 month apart and analyzed for classification reliability using the Kappa coefficient (&kgr;). Results. The morphologic classification is based on 3 main injury patterns: type A (compression), type B (tension band disruption), and type C (displacement/translation) injuries. Reliability in the identification of a morphologic injury type was substantial (&kgr;= 0.72). Conclusion. The AOSpine TL injury classification system is clinically relevant according to the consensus agreement of our international team of spine trauma experts. Final evaluation data showed reasonable reliability and accuracy, but further clinical validation of the proposed system requires prospective observational data collection documenting use of the classification system, therapeutic decision making, and clinical follow-up evaluation by a large number of surgeons from different countries. Level of Evidence: 4

The initial phase of fracture healing is specifically sensitive to mechanical conditions

Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing.

Comparison between sheep and human cervical spines: An anatomic, radiographic, bone mineral density, and biomechanical study

Study Design. The quantitative anatomic, radiographic, computerized tomographic, and biomechanical data of sheep and human cervical spines were evaluated. Objectives. To compare the anatomic, radiographic, computerized tomographic, and biomechanical data of human and sheep cervical spines to determine whether the sheep spine is a suitable model for human spine research. Summary of Background Data. Sheep spines have been used in several in vivo and in vitro experiments. Quantitative data of the normal sheep cervical spine are lacking, yet these data are crucial to discussion about the results of such animal studies. Methods. In this study, 20 fresh adult female Merino sheep cervical spines and 20 fresh human cadaver cervical spines were evaluated anatomically, radiographically, computerized tomographically, and biomechanically. Three linear and two angular parameters were evaluated on four digital radiographic views: anteroposterior, right lateral in neutral position, flexion, and extension. Quantitative computed tomography scans at the center of each vertebral body and 3 mm below both endplates were analyzed for bone mineral density measurements. Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending by a nondestructive stiffness method using a nonconstrained testing apparatus. Range of motion and stiffness of each motion segment were calculated. Additionally, 10 linear anatomic parameters of each vertebra were measured using a digital ruler. Results. Anterior and mean disc space height in the sheep cervical spine increased constantly from C2–C3 to C6–C7, whereas middle disc space height decreased and posterior disc space height remained unchanged. Anterior and mean disc space height were significantly higher in sheep. In both sheep and human cervical spines, intervertebral angles were not significantly different. Standard deviations of bone mineral density in the human cervical spine were fourfold higher than in the sheep cervical spine, yet no significant differences were found in bone mineral density values between the two species. Range of motion differed significantly between the two species except in flexion–extension of C3–C4, C5–C6, axial rotation of C2–C3, and lateral bending of C2–C3, C3–C4, and C4–C5. Stiffness also was significantly different except in flexion–extension of C2–C3, C4–C5, C5–C6, and lateral bending of C2–C3, C3–C4, and C4–C5. Anatomic evaluation showed no difference in upper endplate parameters for C4 and C5. Conclusions. Although several differences were found between human and sheep cervical spines, the small intergroup standard deviations and the good comparability with the human spine encourage the use of the sheep cervical spine as a model for cervical spine research. On the basis of the quantitative data obtained in this study, the sheep motion segment C3–C4 seemed to be the most reliable model for the corresponding human motion segment.

Bone morphogenetic protein-2 coating of titanium implants increases biomechanical strength and accelerates bone remodeling in fracture treatment: A biomechanical and histological study in rats

Bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor (TGF)-beta superfamily, is known to be a very potent osteoinductive growth factor. The purpose of this study was to investigate the effect of BMP-2 (5% [w/w], 50 microg on each nail), locally released from poly(D,L-lactide) (PDLLA)-coated intramedullary implants, on fracture healing. A closed fracture of the right tibia of 5-month-old Sprague-Dawley rats (n = 64) was intramedullary stabilized with uncoated vs. BMP-2-coated titanium Kirschner wires. X-ray examinations (posteroanterior and lateral) were performed throughout the experiment. At 28 and 42 days after fracture, the animals were killed and both tibiae were dissected for biomechanical torsional testing. For histological and histomorphometric evaluation, 5 microm sections were obtained, stained with Safranin-O/light green and von Kossa, and examined using an image analysis system. The radiological results demonstrated progressed callus consolidation in the BMP-2-treated groups compared with the uncoated groups at both timepoints. Histomorphometric evaluation showed progressed callus remodeling with significantly increased mineralization and less cartilage of the periosteal callus. Due to the BMP-2 treatment, increased mineralization of the cortices was detected at 28 and 42 days after fracture. Biomechanical testing revealed significantly elevated maximum load and torsional stiffness in the BMP-2-treated groups compared with controls at both timepoints. The results clearly demonstrate that local application of BMP-2 from PDLLA-coated implants is feasible and significantly accelerates fracture healing. Local administration of growth factors from coated implants could reduce clinical problems in fracture treatment without opening of the fracture, implantation of further devices, or injection with the risk of infection or side effects caused by other carriers.

Biomechanical Comparison of Cervical Spine Interbody Fusion Cages

Study Design. An in vitro biomechanical study of cervical spine interbody fusion cages using a sheep model was conducted. Objectives. To evaluate the biomechanical effects of cervical spine interbody fusion cages, and to compare three different cage design groups. Summary and Background Data. Recently, there has been a rapid increase in the use of cervical spine interbody fusion cages as an adjunct to spondylodesis. These cages can be classified into three design groups: screw, box, or cylinder designs. Although several comparative biomechanical studies of lumbar interbody fusion cages are available, biomechanical data for cervical spine constructs are lacking. Additionally, only limited data are available concerning comparative evaluation of different cage designs. Methods. In this study, 80 sheep cervical spines (C2–C5) were tested in flexion, extension, axial rotation, and lateral bending with a nondestructive stiffness method using a nonconstrained testing apparatus. Three-dimensional displacement was measured using an optical measurement system (Qualysis). Complete discectomy (C3–C4) was performed. Cervical spine interbody fusion cages were implanted according to manufacturers’ information. Eight spines in each of the the following groups were tested: intact, autologous iliac bone graft, two titanium screws (Novus CTTi; Sofamor Danek, Koln, Germany), two titanium screws (BAK-C 8 mm; Sulzer Orthopedics, Baar, Switzerland), one titanium screw (BAK-C 12 mm; Sulzer Orthopedics), carbon box (Novus CSRC; Sofamor Danek), titanium box (Syncage; Synthes, Bochum, Germany), titanium mesh cylinder (Harms; DePuy Acromed, Sulzbach, Germany), titanium cylinder (MSD; Ulrich, Ulm, Germany), and titanium cylinder (Kaden; BiometMerck, Berlin, Germany). The mean apparent stiffness values were calculated from the corresponding load-displacement curves. Additionally, cage volume and volume-related stiffness was determined. Results. After cervical spine interbody fusion cage implantation, flexion stiffness increased, as compared with that of the intact motion segment. On the contrary, rotation stiffness decreased after implantation of a cervical spine interbody fusion cage, except for the Novus CSRC, Syncage, and Kaden-Cage. If two screws were inserted (Novus CTTi and BAK-C 8 mm), there was no significant difference in flexion stiffness between screw and cylinder design groups. If one screw was inserted (BAK-C 12 mm), flexion stiffness was higher for cylinder designs (P < 0.05). Extension and bending stiffness were always higher with cylinder designs (P < 0.05). Volume-related stiffnessfor flexion extension and bending was highest for theHarms cage (P < 0.05). There was no difference for rotation volume-related stiffness between Harms and Syncage. Conclusions. The biomechanical results indicate that design variations in screw and cylinder design groups are of little importance. In this study, however, cages with a cylinder design were able to control extension and bending more effectively than cages with a screw design.

Synergistic effect of IGF-I and TGF-beta1 on fracture healing in rats: single versus combined application of IGF-I and TGF-beta1.

During the last few decades, knowledge about growth factors and their function has increased. However, little is known about the interaction of these factors during bone growth and fracture healing. In vitro studies have shown a higher rate of cell proliferation and cell metabolism after the use of IGF-I and TGF-ß1 in combination, as compared to the single use of these factors. The purpose of this study was to investigate a possible synergistic effect of these growth factors in vivo, using a fracture model. A midshaft fracture of rat tibia (n= 84) was intramedullary stabilized with poly(D,L-lactide)-coated or uncoated titanium K-wires. The growth factors IGF-I and TGF-ß1, singly or in combination, were incorporated in the coating and continuously released during fracture healing. 28 days after fracture, we performed mechanical tests and histomorphological analyses. We found a greater stimulating effect of IGF-I on fracture healing than of TGF-ß1. The combined application of both growth factors resulted in a significantly higher maximum load and torsional stiffness than the use of only one of them. The histomorphometric analyses showed an increase in remodeling of the fracture callus in this group with less cartilaginous and more mineralized tissue than in the other groups. Both growth factors seem to have a synergistic effect on fracture healing in this model.

Biomechanical assessment of transoral plate fixation for atlantoaxial instability.

Study Design. In an experimental study using human cadaver specimens the biomechanical data of anterior atlantoaxial plating according to Harms were evaluated. Objectives. The purpose of this study was to evaluate this method biomechanically. Summary and Background Data. The optimum fixation method to achieve fusion at the atlantoaxial joint after odontoid resection is still a matter of discussion. Isolated posterior surgical procedures for treatment of irreducible atlantoaxial kyphosis with spinal cord compression are associated with high rates of morbidity and mortality. Transoral atlantoaxial plate fixation has been designed by Harms as a fixation technique after odontoid resection. In a modification, this procedure has been combined with the posterior wire fusion according to Brooks. Method. Eight human cadaver craniocervical specimens were tested in flexion, extension, rotation, and bending with a nondestructive flexibility method using a nonconstrained testing apparatus. Five different groups were examined: 1) control group (intact); 2) unstable group (after dissection of the atlantoaxial ligaments and odontoidectomy), 3) Harms group (transoral atlantoaxial plate fixation) 4) Harms–Brooks group (transoral atlantoaxial plate fixation and dorsal atlantoaxial wire fixation); and 5) Magerl group (transarticular atlantoaxial screw fixation). In a second experimental series, failure loads of the Harms–Brooks and the Magerl fixation methods were determined. Results. The angular displacement of the Harms–Brooks group and the Magerl group was less than in any other group. Stiffness values at 0–3.0 Nm loads in any direction were larger for the Harms–Brooks-and Magerl-fixated specimens than for the Harms, control, or unstable specimens. No statistically significant difference was observed between Harms–Brooks and Magerl reconstruction stiffness. Ultimate failure load in the Harms–Brooks group was higher than in the Magerl group. Conclusions. Experimentally, isolated anterior atlantoaxial plating was less stable than the combined reconstruction procedures. Transoral plate fixation according to Harms in combination with posterior wire fixation ac-cording to Brooks provided a failure load and stiffness equal to transarticular screw fixation according to Magerl.

Biomechanical Comparison of Expandable Cages for Vertebral Body Replacement in the Thoracolumbar Spine

Study Design. An in vitro biomechanical study of expandable cages for vertebral body replacement in the human thoracolumbar spine. Objectives: The purpose of this study was to compare the in vitro biomechanical properties of 3 different expandable cages with a nonexpandable cage. Summary and Background Data. Recently, there has been a rapid increase in the use and the commercial availability of expandable cages for vertebral body replacement in the thoracolumbar spine. Although all 3 expandable cages, evaluated in this study, are approved for clinical use in Europe, little information is available concerning the biomechanical properties of these implants. Material and Methods. Thirty-two human thoracolumbar spines (T11 to L3) were tested in flexion, extension, axial rotation, and lateral bending with a nondestructive loading technique using an unconstrained testing apparatus. Three-dimensional displacement was measured using an optical measurement system. First, all motion segments were tested intact. After complete corporectomy of L1, cages were implanted according to producer’s information. The following implants (n = 8/group) were tested: 1) meshed titanium cage (nonexpandable cage, DePuy AcroMed); 2) X-tenz (expandable cage, DePuy AcroMed); 3) Synex (expandable Cage; Synthes); and 4) VBR (expandable cage, Ulrich). Finally, posterior stabilization using the Universal Spine System (Synthes), posterior-anterior stabilization using the Universal Spine System (Synthes), and anterior plating (Locking Compression Plate, Synthes) was applied to each test specimen. The mean apparent stiffness values, range of motion, and neutral and elastic zone were calculated from the corresponding load-displacement curves. Results. No significant differences could be determined between the in vitro biomechanical properties of expandable and nonexpandable cages. In comparison to the intact motion segment, isolated anterior stabilizationusing cages and anterior plating significantly decreased stiffness and increased range of motion in all directions. In contrast, additional posterior stabilization significantly increased stiffness and decreased range of motion in all directions compared to the intact motion segment. The combined anterior-posterior stabilization demonstrated greatest stiffness results. Conclusion. Biomechanical results indicate that design variations of expandable cages for vertebral body replacement are of little importance. Additionally, no significant difference could be determined between the biomechanical properties of expandable and nonexpandable cages. After corporectomy, isolated implantation of expandable cages plus anterior plating was not able to restore normal stability of the motion segment. Therefore, isolated anterior stabilization using cages plus Locking Compression Plate should not be used for vertebral body replacement in the thoracolumbar spine.

A New Stand-alone Anterior Lumbar Interbody Fusion Device: Biomechanical Comparison with Established Fixation Techniques

Study Design. Established lumbar fixation methods were assessed biomechanically, and a comparison was made with a new stand-alone anterior lumbar interbody cage device incorporating integrated anterior fixation. Objectives. To compare the stability of a new stand-alone anterior implant (Test-device) with established fixation methods to assess its suitability for clinical use. Our hypothesis being that the Test-device would provide stability comparable to that provided by an anterior cage when supplemented with posterior pedicle screw fixation. Summary of Background Data. It is accepted that the use of rigid pedicle screw instrumentation increases the chance of achieving a solid fusion, but its use may be associated with a significant increase in postoperative morbidity caused by disruption of the posterior musculature. It is also evident that this increased fusion rate is generally not associated with increased clinical success. This dilemma has led to a search for a solution and to the development of the Test-device anterior lumbar interbody device. Methods. The kinematic properties of either the L3–L4 or L4–L5 lumbar motion segment of 8 cadaveric lumbar spines have been tested using the following sequence of fixation: intact, Test-device, Test-device and translaminar facet screws (TS), Cage and TS, Cage and Universal Spine System (USS), and Cage and small stature USS. Results. All fixation techniques except the cage and TS decreased (P < 0.05) range of motion (ROM), neutral zone (NZ), and elastic zone (EZ), and increased (P < 0.05) stiffness in comparison to the intact motion segment in all test modes. There was a significant increase (P < 0.01) in the ROM, NZ, and EZ, and decrease in the stiffness of the cage and TS group in comparison to all other stabilizationtechniques in flexion and rotation. There was no significant difference in the ROM, NZ, EZ, and stiffness between the Test-device and cage and USS groups in flexion, extension, and bending. The Test-device resulted in a significantly lower EZ (P < 0.05) and a significantly higher stiffness (P < 0.05) in rotation than all other fixation methods. Conclusions. The Test-device alone provided similar and the Test-device and TS higher stability than the pedicle screw constructs evaluated. These results support progression to clinical trials using the Test-device as a stand-alone implant.

A new stand-alone cervical anterior interbody fusion device: biomechanical comparison with established anterior cervical fixation devices.

Study Design. A new anchored spacer—a low-profile cervical interbody fusion cage with integrated anterior fixation—was compared biomechanically to established anterior cervical devices. Objective. To evaluate the fixation properties of the new stand-alone device and compare these properties with established fixation methods. The hypothesis is that the new device will provide stability comparable to that provided by an anterior cervical cage when supplemented with an anterior plate. Summary of Background Data. It is accepted that the use of anterior cervical plating increases the chance of achieving a solid fusion. However, its use may be associated with an increase in operation time and a higher postoperative morbidity caused by a larger anterior approach and disruption of the anterior musculature. This dilemma has led to the development of a new, low profile stand-alone cervical anterior cage device with integrated screw fixation. Methods. Twenty-four human cadaveric C4–C7 cervical spines were loaded nondestructively with pure moments in a nonconstraining testing apparatus to induce flexion, extension, lateral bending, and axial rotation while angular motion was measured optoelectronically. The specimens were tested:1. Intact (N = 24).2. After discectomy and anterior stabilization.a. Interbody cage + locking plate (N = 8).b. Interbody cage + dynamic plate (N = 8).c. Anchored spacer (N = 8).3. After ventral plate removal of group 2a and 2b (N = 16). Results. All fixation techniques decreased range of motion (ROM) and lax zone (LZ) (P < 0.05) in all test modes compared with the intact motion segment and cage-only group. There were no significant differences between the anchored spacer and cage + locking plate or cage + dynamic plate. Conclusion. The anchored spacer provided a similar biomechanical stability to that of the established anterior fusion technique using an anterior plate plus cage and has a potentially lower perioperative and postoperative morbidity. These results support progression to clinical trials using the cervical anchored spacer as a stand-alone implant.