Klaus J. Schnake

Dynamic stabilization in addition to decompression for lumbar spinal stenosis with degenerative spondylolisthesis

Study Design. Prospective clinical study. Objective. To test whether elastic stabilization with the Dynesys system (Zimmer Spine, Minneapolis, MN) provides enough stability to prevent further progression of spondylolisthesis as well as instability after decompression for spinal stenosis with degenerative spondylolisthesis. Summary of Background Data. In spinal stenosis with degenerative spondylolisthesis, decompression and fusion is widely recommended. However, patients have donor site pain. In 1994, a dynamic transpedicular system (Dynesys) was introduced to the market, stating that stabilization is possible without bone grafting. Methods. A total of 26 patients (mean age 71 years) with lumbar spinal stenosis and degenerative spondylolisthesis underwent interlaminar decompression and dynamic stabilization with the Dynesys system. Minimum follow-up was 2 years. Operative data, clinical outcome, and plain and flexion/extension radiographs were obtained and compared to preoperative and postoperative data. Results. Mean leg pain decreased significantly (P < 0.01), and mean walking distance improved significantly to more than 1000 m (P < 0.01). There were 5 patients (21%) who still had some claudication. A total of 21 patients (87.5%) would undergo the same procedure again. Radiographically, no significant progression of spondylolisthesis could be detected. The implant failure rate was 17%, and none of them were clinically symptomatic. Conclusions. In elderly patients with spinal stenosis with degenerative spondylolisthesis, dynamic stabilization with the Dynesys system in addition to decompression leads to similar clinical results as seen in established protocols using decompression and fusion with pedicle screws. It maintains enough stability to prevent further progression of spondylolisthesis or instability. With the Dynesys system, no bone grafting is necessary, therefore, donor site morbidity can be avoided.

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

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.

Mechanical concepts for disc regeneration

Different strategies exist to treat intervertebral disc degeneration. Biological attempts to regenerate the disc are promising. However, degeneration of the disc is always accompanied by alterations of disc height, intradiscal pressure, load distribution, and motion patterns, respectively. Since those preconditions are independent factors for disc degeneration, it is unlikely that regeneration may occur without firstly restoring the physiological status of the affected spinal segment. In vitro and in vivo animal studies demonstrate that disc distraction normalizes intradiscal height and pressure. Furthermore, histological and radiological examinations provided some evidence for regenerative processes in the disc. Only dynamic stabilization systems currently offer the potential of a mechanical approach to intervertebral disc regeneration. Dynamic stabilization systems either using pedicle screws or with an interspinous device, demonstrate restabilization of spinal segments and reduction of intradiscal pressure. Clinical reports of patients with degenerative disc disease who underwent dynamic stabilization are promising. However, there is no evidence that those implants will lead to disc regeneration. Future treatment concepts should combine intradiscal cell based therapy together with dynamic restoration of the affected spinal segment.

Bioabsorbable interbody cages in a sheep cervical spine fusion model

Study Design. An experimental study using a sheep cervical spine interbody fusion model. Objectives. To compare interbody fusion of an autologous tricortical iliac crest bone graft with two bioabsorbable cages and to determine whether there are differences between the three interbody fusion techniques in 1) the ability to preserve postoperative distraction, 2) the biomechanical stability, and 3) the histologic characteristics of intervertebral bone matrix formation. Summary and Background Data. Bioabsorbable cages would be beneficial compared with metallic cages; however, currently no suitable bioabsorbable interbody fusion cage is available. Method. Twenty-four sheep underwent C3/C4 discectomy and fusion. The following stabilization techniques were used: Group 1) autologous tricortical iliac crest bone graft (n = 8); Group 2) bioabsorbable cage made of 70/30 poly(l-lactide-co-d,l-lactide) (experimental) filled with autologous cancellous bone graft (n = 8); Group 3) bioabsorbable cage made of a polymer-calciumphosphate composite (Biomet Europe, Dordrecht, The Netherlands) filled with autologous cancellous bone graft (n = 8). Radiographic scans to determine disc space height were performed before and after surgery and after 1, 2, 4, 8, and 12 weeks, respectively. After 12 weeks, animals were killed, and fusion sites were evaluated using functional radiographic views in flexion and extension. Quantitative computed tomographic scans were used to assess bone mineral density, bone mineral content, and bony callus volume. Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending to determine stiffness, ROM, and neutral and elastic zone. Histomorphological and histomorphometrical analysis were performed to evaluate fusion and foreign body reactions associated with the bioabsorbable cages. Results. Over a 12-week period, the polymer-calciumphosphate composite cage showed significantly higher values for disc space height compared with the bone graft and the poly(l-lactide-co-d,l-lactide) cage. Additionally, the polymer-calciumphosphate composite cage demonstrateda significantly higher stiffness and lower ROM, neutral zone, and elastic zone in axial rotation and lateral bending than any other group. However, quantitative computed tomographic scans demonstrated cracks in six of the eight polymer-calciumphosphate composite cages after 12 weeks. Histologically, the highest bone volume/total volume ratio and the highest fusion rate were found in the polymer-calciumphosphate composite cage group. Although the poly(l-lactide-co-d,l-lactide) cage showed grade I through III foreign body reactions in all fusion areas, only two animals developed grade I foreign body reactions with the polymer-calciumphosphate composite cage. Conclusion. After 12 weeks, there was no significant difference between the bioabsorbable poly(l-lactide-co-d,l-lactide) cage and the tricortical bone graft. In comparison to the tricortical bone graft, the bioabsorbable polymer-calciumphosphate composite cage showed significantly better distractive properties, a significantly higher biomechanical stiffness, and an advanced interbody fusion; however, six of eight polymer-calciumphosphate composite cages cracked. Although the fate of the foreign body reactions and the cracks is currently unclear for both bioabsorbable cages, the early appearance of large osteolysis associated with use of the poly(l-lactide-co-d,l-lactide) cage allows skepticism regarding the value of this bioabsorbable implant.

Biomechanical evaluation of different asymmetrical posterior stabilization methods for minimally invasive transforaminal lumbar interbody fusion.

OBJECT Beside several other advantages, the transforaminal approach for lumbar interbody fusion offers the possibility of reducing surgical trauma by limiting the approach to only 1 side. This requires posterior stabilization methods, which are applied without the need to damage contralateral muscles and soft tissues. The goal in this study was to compare different posterior stabilization methods for minimally invasive transforaminal lumbar interbody fusion (TLIF) biomechanically. METHODS Stiffness testing was performed in 8 fresh-frozen human cadaveric lumbar spine motion segments, including the following sequentially tested configurations: 1) native motion segment; 2) TLIF and bilateral pedicle screw (PS) construct; 3) TLIF and ipsilateral PS construct; 4) TLIF and ipsilateral PSs plus contralateral translaminar facet screws according to the Magerl technique; and 5) TLIF and ipsilateral PSs plus contralateral lumbar facet interference screw (LFIS). RESULTS In extension, the unilateral range of motion (uROM) and elastic zone (EZ) were significantly lower than native motion segments for bilateral PS and LFIS. There were no significant differences among the different stabilization methods. In flexion, uROM and EZ were significantly lower than the native segment in the spines treated with bilateral PSs and translaminar facet screws. The LFIS differed from the native segment in EZ only. Again, there were no significant differences between the different posterior stabilization methods. In lateral bending, the EZ of spines treated with uni- and bilateral PS differed significantly. There were no additional significant differences. In rotation, the stiffness values of bilateral PS were significantly higher than native, unilateral PS, and LFIS. The comparison between ipsi- and bilateral PS showed a tendency, but not a significant difference for uROM and EZ. There was no statistically significant evidence that the TLIF method led to an asymmetrical motion behavior in our study. CONCLUSIONS Bilateral PS augmentation offers significantly more stability than unilateral PSs in the majority of the test modes. There was no significant difference between the other tested methods. All tested stabilization methods could achieve at least the stability of the native segment.

Therapieempfehlungen zur Versorgung von Verletzungen der Brust- und Lendenwirbelsäule

ZusammenfassungIn dieser Arbeit werden Empfehlungen zur Versorgung von Frakturen der Brust- (BWS) und der Lendenwirbelsäule (LWS) gegeben. Die Empfehlungen beruhen auf der Erfahrung der beteiligten Wirbelsäulenchirurgen der Arbeitsgemeinschaft „Wirbelsäule“ der Deutschen Gesellschaft für Unfallchirurgie unter Berücksichtigung der aktuellen Literatur. Grundlagen der Diagnostik, der konservativen und operativen Therapie werden dargestellt. Die Frakturen werden Anhand von morphologischen Kriterien, wie der Zerstörung des Wirbelkörpers, der Fragmentdislokation, der Einengung des Spinalkanals, der Achsabweichungen und der Abweichung vom individuellen sagittalen Profil beurteilt. Die Abweichung von dem individuellen sagittalen Profil wird anhand der Änderung des monosegmentalen oder bisegmentalen Grund-Deckplatten-Winkels bestimmt. Es werden die Therapieoptionen für den knochengesunden Patienten aufgezeigt.AbstractThis paper gives recommendations for treatment of thoracolumbar and lumbar spine injuries. The recommendations are based on the experience of the involved spine surgeons, who are part of a study group of the “Deutsche Gesellschaft für Unfallchirurgie” and a review of the current literature. Basics of diagnostic, conservative, and operative therapy are demonstrated. Fractures are evaluated by using morphologic criteria like destruction of the vertebral body, fragment dislocation, narrowing of the spinal canal, and deviation from the individual physiologic profile. Deviations from the individual sagittal profile are described by using the monosegmental or bisegmental end plate angle. The recommendations are developed for acute traumatic fractures in patients without severe osteoporotic disease.

Implant removal after posterior stabilization of the thoraco-lumbar spine

IntroductionImplant removal because of pain after posterior fusion in the thoracic and lumbar spine is a widely performed operation. We conducted a retrospective study to examine whether patients benefit from implant removal.Patients and methods57 patients (29 males, 28 females, mean age 46.5 years) who have undergone removal of pedicle screws because of pain and discomfort were interviewed 6–24 months postoperatively. Fracture was the initial diagnosis in 40% of the patients and degenerative spine disease in 58%. The following factors were evaluated: patient satisfaction and postoperative outcome, patients’ native language and psychological background, operative data, hospital stay and complications.ResultsPain decreased significantly from 62 to 48 on visual analogue scale postoperatively. Complications occurred in five patients (8.8%). 36 patients (61%) stated they had some benefit from the operation, but only seven patients (12%) were free of pain completely. 36 patients (63%) would undergo the same procedure again. Outcome in the subgroup of foreigners was significantly worse, though the psychological background did not affect the outcome. Preoperative diagnostic infiltration was helpful in 9 of 13 patients.ConclusionRemoval of pedicle screws because of back pain may be effective, but complete remission of symptoms could be achieved in only 12% of patients. However, 63% of patients would undergo hardware removal again. Preoperative diagnostic infiltration can help to predict the outcome but results are inconsistent. Communication difficulties may worsen the outcome. Surgeons should consider these results when planning implant removal and patients should be informed thoroughly to avoid too high expectations.

The effect of repetitive pilot-hole use on the insertion torque and pullout strength of vertebral system screws.

Study Design. In vitro biomechanical investigation of the screw-holding capacity. Objective. To evaluate the effect of repetitive screw-hole use on the insertional torque and retentive strength of vertebral system screws. Summary and Background Data. Placement and removal of vertebral system screws is sometimes necessary during the surgical procedures in order to assess the walls of the pilot hole. This procedure may compromise the holding capacity of the implant. Methods. Screws with outer diameter measuring 5, 6, and 7 mm were inserted into wood, polyurethane, polyethylene, and cancellous bone cylindrical blocks. The pilot holes were made with drills of a smaller, equal, or wider diameter than the inner screw diameter. Three experimental groups were established based on the number of insertions and reinsertions of the screws and subgroups were created according to the outer diameter of the screw and the diameter of the pilot hole used. Results. A reduction of screw-holding capacity was observed between the first and the following insertions regardless the anchorage material. The pattern of reduction of retentive strength was not similar to the pattern of torque reduction. The pullout strength was more pronounced between the first and the last insertions, while the torque decreased more proportionally from the first to the last insertions. Conclusion. Insertion and reinsertion of the screws of the vertebral fixation system used in the present study reduced the insertion torque and screw purchase.

Establishing the Injury Severity of Thoracolumbar Trauma : Confirmation of the Hierarchical Structure of the AOSpine Thoracolumbar Spine Injury Classification System

Study Design. Survey of spine surgeons. Objective. To develop a validated regional and global injury severity scoring system for thoracolumbar trauma. Summary of Background Data. The AOSpine Thoracolumbar Spine Injury Classification System was recently published and combines elements of both the Magerl system and the Thoracolumbar Injury Classification System; however, the injury severity of each fracture has yet to be established. Methods. A survey was sent to 100 AOSpine members from all 6 AO regions of the world (North America, South America, Europe, Africa, Asia, and the Middle East). Each respondent was asked to numerically grade the severity of each variable of the AOSpine Thoracolumbar Spine Injury Classification System including the morphology, neurological grade, and patient specific modifiers. A grade of zero was considered to be not severe at all, and a grade of 100 was the most severe injury possible. Results. Seventy-four AOSpine surgeons from all 6 AO regions of the world numerically graded the severity of each variable of the AOSpine Thoracolumbar Spine Injury Classification System to establish the injury severity score. The reported fracture severity increased significantly (P < 0.0001) as the subtypes of fracture type A and type B increased, and a significant difference (P < 0.0001) in severity was established for burst fractures with involvement of 2 versus 1 endplates. Finally, no regional or experiential difference in severity or classification was identified. Conclusion. Development of a globally applicable injury severity scoring system for thoracolumbar trauma is possible. This study demonstrates no regional or experiential difference in perceived severity or thoracolumbar spine trauma. The AOSpine Thoracolumbar Spine Injury Classification System provides a logical approach to assessing these injuries and enables rational strategies for treatment. Level of Evidence: 4