Cédric Barrey

Sagittal balance disorders in severe degenerative spine. Can we identify the compensatory mechanisms

IntroductionAging of the spine is characterized by facet joints arthritis, degenerative disc disease and atrophy of extensor muscles resulting in a progressive kyphosis. Recent studies confirmed that patients with lumbar degenerative disease were characterized by an anterior sagittal imbalance, a loss of lumbar lordosis and an increase of pelvis tilt. The aim of this paper was thus to describe the different compensatory mechanisms which are observed in the spine, pelvis and/or lower limbs areas for patients with severe degenerative spine.MethodsWe reviewed all the compensatory mechanisms of sagittal unbalance described in the literature.ResultsAccording to the severity of the imbalance, we could identify three different stages: balanced, balanced with compensatory mechanisms and imbalanced. For the two last stages, the compensatory mechanisms permitted to limit consequences of lumbar kyphosis on the global sagittal alignment. Reduction of thoracic kyphosis, intervertebral hyperextension, retrolisthesis, pelvis backtilt, knee flessum and ankle extension were the main mechanisms described in the literature. The basic concept of these compensatory mechanisms was to extend adjacent segments of the kyphotic spine allowing for compensation of anterior translation of the axis of gravity.ConclusionsTo avoid underestimate the severity of the degenerative spine disorder, it thus seems important to recognize the different compensatory mechanisms from the upper part of the trunk to the lower limbs. We propose a three steps algorithm to analyse the balance status and determine the presence or not of these compensatory mechanisms: measurement of pelvis incidence, assessment of global sagittal alignment and analysis of compensatory mechanisms successively in the spine, pelvis and lower limbs areas.

Spinopelvic alignment of patients with degenerative spondylolisthesis.

OBJECTIVEThe main objectives of this study were to analyze and compare spinopelvic parameters, including the pelvis shape, in a population of 40 patients with degenerative spondylolisthesis (DSPL) and to compare these patients with a control group of asymptomatic volunteers. METHODSForty patients with DSPL were included in this study. Spinopelvic parameters were analyzed on preoperative full spine x-rays in a standardized standing position. The following spinopelvic parameters were measured: pelvic incidence (PI), sacral slope, pelvic tilt, lumbar lordosis, thoracic kyphosis, and positioning of the C7 plumb line. The population of patients was compared with a control population of 154 normal and asymptomatic adults who were studied in a recently published study. In order to understand variations of spinopelvic parameters, a control group was matched according to the PI, which is a morphological parameter. RESULTSThe PI was significantly greater for patients with DSPL (60.1 ± 10.6 degrees) compared with the control group (52 ± 10.7 degrees) (P < 0.0005). After matching according to the pelvic incidence, the DSPL population was characterized by an anterior translation of the C7 plumb line (P < 0.05), a loss of lumbar lordosis (P < 0.0005), and a decrease of the sacral slope (P < 0.0005). Retrolisthesis and/or segmental intervertebral hyperextension were observed in the upper lumbar spine in 30% of the cases. CONCLUSIONMatching according to the PI between the patients in the study and the control group enabled us to understand variations of the spinopelvic parameters in a population of patients with DSPL. DSPL patients were characterized by a greater PI than the asymptomatic population; therefore, we suggest that a high PI may be a predisposing factor in developing DSPL. Finally, we observed significant variations in spinopelvic alignment, such as loss of lordosis and sagittal unbalance, which were partially compensated by pelvis back tilt and hyperextension in the upper lumbar spine.

Quantitative anatomic evaluation of cervical lateral mass fixation with a comparison of the Roy-Camille and the Magerl screw techniques.

Study Design. An anatomic and computed tomography (CT) study of the Roy-Camille and the Magerl techniques with quantitative comparison of the safety zones of the two surgical techniques. Object. The purpose of this study was to compare quantitatively the safety zones of the Roy-Camille and the Magerl techniques as a function of the vertebral level from C3–C6. Summary of Background Data. The two most popular techniques for lateral mass screws are the Roy-Camille and the Magerl technique. Nerve roots, vertebral artery, facet joints, and the spinal cord are at risk during the placement of lateral mass screws. Several anatomic studies are reported, but there is no comparative and quantitative evaluation. The influence of the vertebral level was never reported. Methods. Lateral mass screws were first implanted on four cervical spines according to the two surgical techniques. Screws were then extracted and their cavities filled with a blue casting medium. To determine the precise limits of each safety zone in the sagittal plane, the specimens were sectioned according to the sagittal angulation of the two screwing techniques. The correlations between the anatomic landmarks on the specimen and the anatomic landmarks on the CT scan were established. One hundred and sixty lateral mass screws were then implanted in 20 cervical spines from C3–C6. A CT was done before and after placing lateral mass screws. On the morphologic CT scan, we measured the sagittal safety angle (SSA) for each surgical technique and also performed a morphometry of lateral masses. On the control CT scan, we analyzed screws placement in relation to the sagittal safety zone. Results. The mean SSA was 15.8 ± 6.3° for the Roy-Camille technique and 18.7 ± 3.8° for the Magerl technique, P < 0.005. With respect to the vertebral level, the Roy-Camille safety zone decreased from C3–C6 with a greater angulation at C3–C4 (20.4 ± 4.7°) than at C5–C6 (11.6 ± 4.3°), P < 0.001. Such variations were not observed for the Magerl technique, the SSA of which was 19.4 ± 3.6° at C5–C6 and 17.9 ± 4° at C3–C4, P < 0.01. Lateral masses became more elongated and thinner at the lower segment of the cervical spine with a C3–C4 height/thickness ratio = 1.1 ± 0.3 and a C5–C6 height/thickness ratio = 1.3 ± 0.2, P < 0.005. Roy-Camille screws (19%) were found out of the safety zone at C3–C4 whereas 37.5% were found outside at C5–C6, P < 0.05. We observed opposite results for Magerl screws with 38% screws out of the safety zone at C3–C4 and only 17.5% outside at C5–C6, P < 0.05. Conclusion. The Roy-Camille technique demonstrated a progressive decrease of its safety zone from C3–C6. At C5 and C6 there is a great probability to have a transarticular screw with a Roy-Camille screw. A similar variation was not observed for the Magerl technique. These anatomic results seem to be in relation with the morphologic variability of lateral masses from C3–C6 as demonstrated by an increase of the height/thickness ratio at the lower part of the cervical spine. According to these anatomic considerations and previously published biomechanical data, Roy-Camille technique appears to be the best option at C3 and C4. On the opposite at C5 and C6, the choice is more difficult considering that there is no biomechanical difference between the two techniques and that the Magerl technique is safer but a more demanding procedure.

Complex osteotomies vertebral column resection and decancellation

Pedicle subtraction osteotomy (PSO) is nowadays widely used to treat sagittal imbalance. Some complex malalignment cases cannot be treated by a PSO, whereas the imbalance is coronal or mixed or the sagittal imbalance is major and cannot be treated by a single PSO. The aim of this article was to review these complex situations—coronal imbalance, mixed imbalance, two-level PSO, vertebral column resection, and vertebral column decancellation, and to focus on their specificities. It wills also to evoke the utility of navigation in these complex cases.

In vitro evaluation of a ball-and-socket cervical disc prosthesis with cranial geometric center

OBJECT Few biomechanical in vitro studies have reported the effects of disc replacement on motion and kinematics of the cervical spine. The purpose of this study was to analyze motion through 3D load-displacement curves before and after implantation of a ball-and-socket cervical disc prosthesis with cranial geometric center; special focus was placed on coupled motion, which is a well-known aspect of normal cervical spine kinematics. METHODS Six human cervical spines were studied. There were 3 male and 3 female cadaveric specimens (mean age at death 68.5 +/- 5 years [range 54-74 years]). The specimens were evaluated sequentially in 2 different conditions: first they were tested intact; then the spinal specimens were tested after implantation of a ball-and-socket cervical disc prosthesis, the Discocerv, at the C5-6 level. Pure moment loading was applied in flexion/extension, left and right axial rotation, and left and right lateral bending. All tests were performed under load control with a 3D measurement system. RESULTS No differences were found to be statistically significant after comparison of range of motion between intact and instrumented spines for all loading conditions. The mean range of motion for intact spines was 10.3 degrees in flexion/extension, 5.6 degrees in lateral bending, and 5.4 degrees in axial rotation; that for instrumented spines was 10.4, 5.2, and 4.8 degrees , respectively. No statistical difference was observed for the neutral zone nor stiffness between intact and instrumented spines. Finally, the coupled motions were also preserved during axial rotation and lateral bending, with no significant difference before and after implantation. CONCLUSIONS This study demonstrated that, under specific testing conditions, a ball-and-socket joint with cranial geometrical center can restore motion in the 3 planes after discectomy in the cervical spine while maintaining physiological coupled motions during axial rotation and lateral bending.

Lumbar-sacral fusion by a combined approach using interbody PEEK cage and posterior pedicle-screw fixation: Clinical and radiological results from a prospective study

INTRODUCTION This prospective series evaluated the clinical and radiological results of a circumferential lumbar fusion achieved by a combined approach in one stage (anterior then posterior) using interbody PEEK cages and posterior pedicle-screw fixation. HYPOTHESIS The combined approach in one stage is a safe and efficient technique with few complications to achieve a fusion with a satisfying clinical and radiological outcome. MATERIALS AND METHODS Thirty-nine consecutive patients were prospectively included, with a one-year clinical and radiological minimum follow-up, from December 2008 to July 2011. All patients suffering from degenerative disc disease or low-grade isthmic spondylolisthesis requiring L5S1, L4L5 or L4S1 spinal fusions were included. Clinical outcome was assessed using VAS, ODI and Rolland-Morris scores. Radiological outcome was assessed by analyzing PI, PT, lumbar lordosis, segmental lordosis, disc height, C7/CSFD ratio on full spine radiographies and the quality of bone fusion on a CT scan at 1-year follow-up. Blood loss, surgery time and adverse events were also recorded. RESULTS Twenty-nine patients (74%) were operated for a lumbar degenerative disc disease and 10 patients (26%) for an isthmic spondylolisthesis. Mean age was 46 (± 10.1) years old. Clinical outcome were satisfactory. VAS, ODI and Rolland-Morris scores substantially improved. Mean follow-up was 22.5 months (± 8.7). Mean surgery time was 227 min (± 41.4) for complete surgical procedure time. Mean blood loss was 308 mL (± 179.2) for total surgery. Fusion was assessed in all cases. Disc height and segmental lordosis significantly improved in postoperative. The segmental lordosis at operated level(s) increased by 8.5° (± 5) regardless of the level, and by 11.6° (± 6) for L5-S1. CONCLUSION The combined procedure meets the requested criteria for a lumbar fusion in terms of clinical and functional results, fusion rates, and restoration of segmental lordosis. It cumulates the advantages of the anterior and posterior approach performed alone and should be considered by surgeons before realizing a lumbar fusion.

Pedicle-Screw-Based Dynamic Systems and Degenerative Lumbar Diseases: Biomechanical and Clinical Experiences of Dynamic Fusion with Isobar TTL

Dynamic systems in the lumbar spine are believed to reduce main fusion drawbacks such as pseudarthrosis, bone rarefaction, and mechanical failure. Compared to fusion achieved with rigid constructs, biomechanical studies underlined some advantages of dynamic instrumentation including increased load sharing between the instrumentation and interbody bone graft and stresses reduction at bone-to-screw interface. These advantages may result in increased fusion rates, limitation of bone rarefaction, and reduction of mechanical complications with the ultimate objective to reduce reoperations rates. However published clinical evidence for dynamic systems remains limited. In addition to providing biomechanical evaluation of a pedicle-screw-based dynamic system, the present study offers a long-term (average 10.2 years) insight view of the clinical outcomes of 18 patients treated by fusion with dynamic systems for degenerative lumbar spine diseases. The findings outline significant and stable symptoms relief, absence of implant-related complications, no revision surgery, and few adjacent segment degenerative changes. In spite of sample limitations, this is the first long-term report of outcomes of dynamic fusion that opens an interesting perspective for clinical outcomes of dynamic systems that need to be explored at larger scale.

Pedicle Screw-Based Dynamic Stabilization Devices in the Lumbar Spine: Biomechanical Concepts, Technologies, Classification, and Clinical Results

The authors recently performed an extensive review of biomechanical and clinical investigations involving pedicle screw-based posterior dynamic stabilization devices currently available for use clinically. This current chapter presents the most significant results from this review in both the biomechanical and clinical fields.

Compensatory Mechanisms Contributing to the Maintenance of Sagittal Balance in Degenerative Diseases of the Lumbar Spine

Meticulous and exhaustive analysis of spinopelvic parameters allows for identification of the main compensatory mechanisms observed in patients with sagittal balance disorders. These mechanisms have to be considered prior to therapeutic options. This may probably optimize the management of patients with severe degenerative spine especially when surgical treatment with instrumentation of the spine is planned.

Titanium versus polyetheretherketone implants for vertebral body replacement in the treatment of 77 thoracolumbar spinal fractures

Background: Titanium and polyetheretherketone (PEEK) implants have been used in spinal surgery with low rejection rates. Compared to titanium, PEEK has many advantages, including a density more similar to that of bone, radiolucency, and a lack of artifacts in computed tomography (CT) and magnetic resonance imaging (MRI). In this study, we evaluated the effectiveness of PEEK cages as an alternative to titanium for bone fusion after fractures of the thoracolumbar spine. We also propose a classification to the impaction index. Methods: We evaluated 77 patients with fractures of the thoracic or lumbar spine who were treated by anterior fixation with titanium cages (TeCorp®) in 46 (59.7%) patients or PEEK (Verte-stak®) in 31 (40.3%) patients from 2006 to 2012 (Neurological Hospital of Lyon). Results: The titanium group achieved 100% fusion, and the PEEK group achieved 96.3% fusion. The titanium systems correlated with higher impact stress directed toward the lower and upper plateaus of the fused vertebrae; there were no nonunions for those treated with titanium group. Nevertheless, there was only one in the PEEK group. There was no significant difference in the pain scale outcomes for patients with ±10 degrees of the sagittal angle. Statistically, it is not possible to associate the variation of sagittal alignment or the impaction with symptoms of pain. The complication rate related to the implantation of cages was low. Conclusions: Titanium and PEEK are thus equally effective options for the reconstruction of the anterior column. PEEK is advantageous because its radiolucency facilitates the visualization of bone bridges.