[Odontoid bending stiffness after anterior fixation with a single lag screw: biomechanical study]. / Ohybová tuhost zubu cepovce po prední fixaci jedním tahovým sroubem - biomechanická studie.

PURPOSE OF THE STUDY The aim of the experiment was to compare the bending stiffness of an intact odontoid process with bending stiffness after its simulated type II fracture was fixed with a single lag screw. The experiment was done with a desire to answer the question of whether a single osteosynthetic screw is sufficient for good fixation of a type II odontoid fracture. MATERIAL AND METHODS The C2 vertebrae of six cadavers were used. With simultaneous measurement of odontoid bending stiffness, the occurrence of a fracture (type IIA, Grauer's modification of the Anderson- D'Alonzo classification) was simulated using action exerted by a tearing machine in the direction perpendicular to the odontoid axis. Each odontoid fracture was subsequently treated by direct osteosynthesis with a single lag screw inserted in the axial direction by a standard surgical procedure in order to provide conditions similar to those achieved by routine surgical management. The treated odontoid process was subsequently subjected to the same tearing machine loading as applied to it at the start of the experiment. The bending stiffness measured was then compared with that found before the fracture occurred. The results were statistically evaluated by the t-test for paired samples at the level of significance α = 0.05. RESULTS The average value of bending stiffness for odontoid processes of intact vertebrae at the moment of fracture occurrence was 318.3 N/mm. After single axial lag screw fixation of the fracture, the average bending stiffness for the odontoid processes treated was 331.3 N/mm. DISCUSSION Higher values of bending stiffness after screw fixation were found in all specimens and, in comparison with the values recorded before simulated fractures, the increase was statistically significant. CONCLUSIONS The results of our measurements suggest that the single lag screw fixation of a type IIA odontoid fracture will provide better stability for the fracture fragment-C2 body complex on antero-posterior perpendicular loading than can be found in intact C2 vertebrae. Key words: odontoid fracture, odontoid fixation, bending stiffness, lag screw.

[Odontoid fracture combined with lateral atlanto-axial dislocation. Report of two cases]. / Zlomenina zubu cepovce II. typu spojená s laterální dislokací atlasu. Popis dvou prípadu.

The authors describe their experience with treatment of two neurologically intact male patients, aged 70 and 74 years, presenting with combined lateral atlanto-axial dislocation and odontoid type II fracture. The mechanism of these two craniovertebral junction injuries had been lateroflexion of the neck. The initial attempt at closed reduction using axial traction failed. The authors succeeded with a closed reduction maneuver under general anaesthesia in the first patient in whom long-term stability was achieved by transarticular C2-C1 fixation, together with interlaminar fusion. In the second patient, closed reduction was unsuccessful due to intra-articular soft tissue interposition. Release and reduction were achieved by instrumentation of C1 lateral masses and transpedicular anchorage of screws into the C2. The subsequent Harms C1-C2 stabilisation proved to be effective both in achieving long-term stability and segmental fusion of lateral masses. Aspects of biomechanics as well as a review of pertinent literature are presented.

[Surgical treatment of fracture of the ring of axis - "hangman's fracture"]. / Chirurgické resení fraktury oblouku epistrofeu - "katovské zlomeniny".

PURPOSE OF THE STUDY: To evaluate surgical management of the fracture of the ring of axis (FRA), known as "hangman's fracture", and to discuss adequacy of this treatment. MATERIAL AND METHODS: Between 1994 and 2004, 41 patients with FRA were surgically treated in our hospital. We present a retrospective study of 30 cases treated by anterior cervical fixation and fusion and 11 cases treated by a posterior, CT-guided approach (published recently). Our diagnostic algorithm for evaluation of FRA included plain radiographs for basic diagnosis, detailed CT scan, MRI and finally passive lateral flexion-extension fluoroscopy (performed by physician) to assess stability. We also consider discography in selected cases, allowing further evaluation of discoligamentous injury. Fractures were classified according to Levine. Posterior compressive osteosynthesis according to Judet was performed in 11 patients with Levine type I fractures with fracture fragment distraction > 3 mm. Anterior graft and plate fixation was chosen in 30 patients with type II (25 patients) and type I (5 patients) fractures where C2/3 disc injury was confirmed by MRI or discography. There was no case of facet dislocation in our series (type III). Pain, motion restriction and overall satisfaction with neck status were assessed on a scale 1-5 (1 = best) in patients treated with anterior approach. Self-evaluation questionnaires were administered during follow-up (average, 7.3 years; 24 months to 11 years). RESULTS: Anatomically reduced fracture fusion was achieved in all cases (100%) at one year follow-up. Both autologous tricortical (22) and fibular allografts (8) were used for anterior approach. No perioperative complications occurred and no case was aborted. Average hospital stay in patients with standalone FRA was 6.8 days (3-15). Patients wore Philadelphia collar for 4-6 weeks. One patient died during follow up due to unrelated causes. None of the 29 patients treated with the anterior approach reported severe or very severe pain (grades 4 or 5). The average pain score was 1.28. Three patients with isolated FRAs reported slight subjective restriction of movement (grade 2). The "satisfaction with overall neck status" scale showed an average score of 1.62, never worse than grade 2. DISCUSSION: Despite increasing popularity of anterior surgical approach in the treatment of type II FRA, most authors still recommend conservative treatment. Surgical treatment is consensually recommended in type III fractures only. Type I is treated exclusively conservatively. There is currently no evidence-based data supporting any method of treatment of so called "hangman's fracture". The majority of treating surgeons do not consider the status of the intervertebral disc. Dynamic films, simulating the peak point of injury, are usually not performed. Hence, potentially unstable fractures are overlooked. This also explains the lack of long term follow-up data regarding the radiological status of C2/3 intervertebral disc as well as patients' subjective complaints. CONCLUSIONS: Surgery provides plausible results. Compared to conservative treatment, it can offer significant benefits: 1) immediate, better and stable reposition; 2) high fusion rate; 3) shortening of the treatment period with better quality of life. Contrary to conservative treatment modalities, surgery possesses a potential for further development.

[Multiple-level instrumented anterior cervical fusion: a risk factor for pseudoarthrosis? A prospective study with a minimum of 3-year follow-up]. / Je víceetázová instrumentovaná prední krcní fúze rizikovým faktorem vzniku pseudoartrozy? Prospektivní studie s minimálne 3letou délkou sledování.

PURPOSE OF THE STUDY: This prospective study with minimal 3-year follow-up was performed to compare fusion rates, course of fusion, collapse incidence and occurrence of subsidence in one- and two-level instrumented anterior cervical fusions (ACDF) and thus to proof the hypothesis that use of internal fixation decreases the risk of non-union in bi-segmental ACDFs to the same level that can be expected in mono-segmental procedure. MATERIAL: In 79 consecutive patients operated upon by the Smith-Robinson technique for degenerative process of cervical spine in one or two levels was applied single instrumentation system in order to ensure ideal condition for solid bone fusion of 113 grafts (45 in one and 68 in two levels). All the patients were invariably followed for a minimum of 3 years. METHODS: Radiological criteria were used for evaluation of intervertebral fusion, graft collapse and its subsidence and results were statistically analyzed using M-L Chi-square test for the comparison of fusion and collapse incidence and further Chi-square test for the analysis of fusion course. All these figures were calculated at the level of significance 0.05 (alpha=0.05). RESULTS: Overall, no significant difference was observed in achieving solid bone fusion 3 years after the surgery in one- and two-level procedures (95.6% vers. 92.6%, p=0.522), neither the bone graft collapse rate was of significant difference (2.2% vers. 7.6%, p=0.208). In single-level group the time to bone fusion was significantly shorter (p<0.001). When pooling the data into autologous and allogenic graft subgroup, there was observed no statistically significant difference in achieving union in autologous subgroup (100% vers. 90.9%, p=0.142); in allogenic subgroup this situation was similar: no significant difference in fusion rate (93.3% vers. 93.5%, p=0.980) was observed. In both auto- and allogenic subgroups monosegmentally implanted grafts fused more readily (p<0.001). There was no case of graft subsidence in any investigated group. DISCUSSION: Our prospective study did not find any statistically significant difference in graft collapse and fusion rate when comparing one- and two-level instrumented ACDFs 3 years after the surgery. Plating system used in our patients brings more stability to operated segments and thus presumably prevents micromotions in postoperative period. Micromovements seems to be the major risk factor for non-union in non-instrumented multilevel cervical fusion. Other risk factor that should be considered in non-instrumented procedure is increase in compressive forces that are also partially eliminated by the semirigid internal fixation. Significantly delayed time to union observed in two level fusions shows most probably on increased number of surfaces that must be consolidated during the bone-healing process. CONCLUSION: This study demonstrates that internal fixation used in multilevel ACDF decreases risk of pseudoarthrosis to the same level that can be expected in monosegmental procedures.

[Traumatic spondylolisthesis of L5-S1]. / Traumatická spondylolistéza L5-S1.

Pure traumatic bilateral lumbosacral dislocation is a rare injury with just eight cases reported in the literature. This condition occurred also in 36-year-old man, who was struck into the lower back by a falling tree, during a woodcutting, at the moment when he was kneeling and his spine was flexed. Neurological examination showed no signs of spinal nerves injury. X-ray examination of the lumbosacral spine revealed the presence of a 40% anterior dislocation of L5 over S1 with locked facets and multiple fractures of transverse processes. Computer tomography confirmed these findings and also revealed massive medial L5-S1 disc herniation. Surgery performed 9 days after the injury consisted of L5 laminectomy, L5-S1 discectomy and segmental reduction and stabilization with transpedicular screws. Posterior lumbar interbody fusion was carried out using titanium PLIF-blocks. The patient healed without complications. At a 24-month follow-up he was without any subjective complaints, neurologically asymptomatic and without restriction of mobility in the lumbosacral spine. He was able to resume his previous work. This rare case is discussed in a view of the relevant literature, biomechanics of trauma and the appropriate therapy with an emphasis on open reduction and internal fixation techniques.

[Are screws in anterior cervical fusion with bicortical fixation truly inserted bicortically? Retrospective study]. / Jsou srouby pri prední krcní fúzi s bikortikální fixací skutecne bikortikálne zavedeny? (Retrospektivní studie).

PURPOSE OF THE STUDY: To examine the exact position of screws in anterior cervical fusion that were intended to be bicortically anchored at the time of surgery. MATERIAL: A randomly selected, representative sample (26) of our patient series undergoing anterior cervical fusion with bicortical screw fixation (250) during period of 1993-1999 is reviewed in this study with respect to an exact position of the tips of the screws to the posterior vertebral cortex. A total of 109 screws were assessed. METHODS: The position of 109 screws was assessed using an axial CT scan. On the basis of the distance of the screw tip from the posterior cortex of the vertebra, the screws were divided into several categories: mono- and bicortically anchored. Bicortically inserted screws were statistically evaluated using the confidence interval. RESULTS: Statistical analysis shows that the confidence interval of the screws being bicortically anchored lies between 66.7 and 87.5% (alpha value = 0.01). No screw was introduced more than 3 mm behind the posterior vertebral cortex. Monocortical introduction more than 1.5 mm in front of the cortex was observed in 7 screws (6.4%) in lower cervical spine and cervico-thoracic junction. DISCUSSION: All the screws that were classified as being too short were introduced in the cervico-thoracical junction or lower cervical spine known for its reduced X-ray transparency. The majority of screws, primarily described as bicortical, indeed penetrated both vertebral cortices. Considering the results of confidence interval for bicortical screw anchoring we conclude that 1 of 4 screws in monosegmental and 2 of 6 screws in bisegmental stabilization could fail to be bicortically inserted. CONCLUSION: [corrected] Intraoperative methods used for an accurate and safe bicortical screw insertion during anterior cervical fusion, i.e. intraoperative fluoroscopy, peak insertion torgue of the screw and the length measurement of the taped screw canal, are reliable enough to fulfill these goals.