J. C. Le Huec

Pelvic parameters: origin and significance

IntroductionThe adoption by humans of an upright position resulted in broadening and verticalisation of the pelvis together with the appearance of characteristic spinal curves, has profoundly modified the structure of the muscles supporting the spine.MaterialIn order to characterise the sagittal balance of the pelvis, it is necessary to define parameters based on notable biomechanical forces involved in the transmission of constraints. The angle of incidence was constructed to enable reproducible analysis of the anatomical characteristics of the pelvis in the sagittal plane. The angle of incidence is the algebraic sum of two complementary angles: pelvic tilt (PT) and sacral slope (SS). Since the value of incidence is fixed for any given patient, the sum of pelvic tilt and sacral slope is a constant value: when one increases, the other necessarily decreases.ResultThe position of the lumbar spine, attached to the sacral plateau, is thus affected by the pelvic tilt and by the sacral slope. Consequently, the pelvic parameters affect the entire underlying sagittal spinal profile.ConclusionGlobal spinal balance involves harmonisation of lumbar lordosis and thoracic kyphosis taking into account the pelvic parameters.

Equilibrium of the human body and the gravity line: the basics.

IntroductionBipedalism is a distinguishing feature of the human race and is characterised by a narrow base of support and an ergonomically optimal position thanks to the appearance of lumbar and cervical curves.MaterialsThe pelvis, adapted to bipedalism, may be considered as the pelvic vertebra connecting the spine to the lower limbs. Laterally, the body’s line of gravity is situated very slightly behind the femoral heads laterally, and frontally it runs through the middle of the sacrum at a point equidistant from the two femoral heads.ResultsAny abnormal change through kyphosis regarding the spinal curves results in compensation, first in the pelvis through rotation and then in the lower limbs via knee flexion. This mechanism maintains the line of gravity within the base of support but is not ergonomic. To analyse sagittal balance, we must thus define the parameters concerned and the relationships between them.ConclusionThese parameters are as follows: for the pelvis: incidence angle, pelvis tilt, sacral slope; for the spine: point of inflexion, apex of lumbar lordosis, lumbar lordosis, spinal tilt at C7; for overall analysis: spino-sacral angle, which is an intrinsic parameter.

Vertebroplasty for osteoporotic spine fracture: prevention and treatment.

There is a relatively high prevalence of osteoporotic vertebral compression fractures (VCFs) in the elderly population, especially in women aged 50 or older. The result of these VCFs is increased morbidity and mortality in the short and long term. Medical treatment of these fractures includes bed rest, orthotics, analgesic medication and time. Percutaneous vertebroplasty (PVP) consists of percutaneous injection of biomaterial, such as methylmethacrylate, into the VCF to produce stability and pain relief. Biomechanical testing has shown that PVP can restore strength and stiffness of the vertebral body to the pre-fracture levels. Clinical results show immediate and maintained pain relief in 70–95% of the patients. Possible major complications include cement leakage into the spinal canal or into the venous system. Additionally, percutaneous vertebroplasty may alter the normal loading behavior of the adjacent vertebral body, and there is an increased risk of adjacent segment VCF. Kyphoplasty is a new technique, which introduces a balloon into the vertebral body transpedicularly to reduce the VCF while creating a cavity for the cement injection. This technique has the benefit of kyphosis reduction as well as less cement leakage. Research continues into the development of injectable biomaterials that are resorbable and allow for new bone formation. Vertebroplasty and kyphoplasty are safe and effective in the treatment of osteoporotic VCFs. They may allow for a faster return to function, and thus avoid the morbidity associated with medical treatment.

Sagittal spino-pelvic balance is a crucial analysis for normal and degenerative spine

Human beings are the only vertebrates to maintain an upright, totally vertical, bipedal position submitted to the law of gravity. Unlike other vertebrates, the human spine comprises successive, opposing curves which allows the trunk to maintain an erect position. Lumbar lordosis is found in no other species. Bipedal locomotion in non-human primates is extremely limited. Those species often use their long forelimbs in pronation position to keep balance when trying to perform a bipedal displacement. Erect position is linked with pelvic rotation and enlargement, associated with modifications of the spine sagittal curvatures and muscle adaptation [1]. Human bipedalism is exclusive, stable and ergonomic. In order to maintain this posture for prolonged periods, the erect position should be economical in terms of energy expenditure. To correctly analyze the erect posture, it is necessary to define spinal and pelvic parameters, and to correlate those parameters with global parameters in full standing position. Since Hippocrates provided a precise description of the segments and normal curves of the spine over 2000 years ago, clinicians have attempted to understand the mechanics underlying spinal balance [2]. For an individual to stand, it is necessary that the projection of the centre of the body mass on the ground plane lies behind the toes and is in front of the heels (the base of support). In order to maintain this position, for any individual, there will be an optimal combination of spinal, spino-pelvic and lower limb joint alignments, requiring the least muscle energy expenditure combined with the least discomfort, potentially caused by stretching of ligaments and joint capsules. Understanding the diversity of human spinal shape and orientation is pivotal to the understanding of the achievement of this optimal position, and to its restoration, in cases of sagittal imbalance. Despite ongoing interest in assessing the nature of the ‘normal’ curvature of the spine, there are no universally accepted parameters for its form [5, 6]. The hip joint, instead of being considered as a joint solely capable of allowing femoral movement against a fixed pelvis, should be considered as a joint that allows rotation of the pelvis against fixed femurs [5]. Rotation of the hip joint can, therefore, be considered as a fundamental factor that can interfere with the spinal shape through the pelvic anatomy. The aims of this supplement are to review published data using the current techniques, to compare these different methods and to demonstrate that it is possible today to obtain clear parameters allowing a correct analysis of the sagittal plane of our substantial patient population. Case studies will be used to illustrate the importance of proper consideration of the thoracic kyphosis in relation to the lumbo-pelvic lordosis and the pelvic shape. Those cases will also demonstrate the importance of the degenerative process acting as a new parameter and its influence on modification of the spine balance. The initial spino-pelvic organization will also interfere with the degenerative process of the spine [3]. The biomechanics of the spine differ according to the spino-pelvic shape [4]. Some spinal curvatures and spino-pelvic situations are more frequently subject to specific degenerative evolution [7]. As spine-aging process is also genetically driven, it is easy to understand that the degenerative process can vary dramatically from one patient to another leading to different imbalance situation with a similar spino-pelvic organization at the beginning. Sagittal balance analysis, and the spino-pelvic organization linked to it, is a major tool when attempting to propose a diagnosis and a treatment for lumbalgia and degenerative spine disease. Spinal imbalance should be taken into consideration before initiation of any kind of treatment including conservative or surgical procedures.

Electrical conductivity measurement: a new technique to detect iatrogenic initial pedicle perforation

Pedicle screw fixation has achieved significant popularity amongst spinal surgeons for both single and multi-level spinal fusion. Misplacement and pedicle cortical violation occurs in over 20% of screw placement and can result in potential complications such as dysthesia, paraparesis or paraplegia. There have been many advances in techniques available for navigating through the pedicle; however, these techniques are not without drawbacks. A new electrical conductivity-measuring device, previously evaluated on the porcine model to detect the pedicle violation, was evaluated amongst nine European Hospitals to be used in conjunction with the methods currently used in that centre. This new device is based on two original principles; the device is integrated in the drilling or screwing tool. The technology allows real-time detection of perforation through two independent parameters, impedance variation and evoked muscle contractions. Data was collected twofold. Initially, the surgeon was given the device and a comparison was made between the devices ability to detect a breech and the surgeon’s ability to detect one using his traditional methods of pedicle preparation. In the second module of the study, the surgeon was limited to using the electrical conductivity detection device as their sole guide to detect pedicle breaches. A comparison was made between the detection ability of the device and the other detection possibilities. Post-operative fine cut CT scanning was used to detect the pedicle breaches. Overall, the 11 trial surgeons performed a total of 521 pedicle drillings on 97 patients. Initially there were 147 drillings with 23 breaches detected. The detection rate of these breaches were 22/23 for the device compared to 10/23 by the surgeon. Over both parts of the study 64 breaches (12.3%) were confirmed on post-operative CT imaging. The electrical conductivity detection device detected 63 of the 64 breaches (98.4%). There was one false negative and four false positives. This gives the device an overall sensitivity of 98% and specificity of 99% for detecting a pedicle breach. The negative predictive value was 99.8%, with a positive predictive value of 94%. No adverse event was noted with the use of the electrical conductivity device. Electrical conductivity monitoring may provide a simple, safe and sensitive method of detecting pedicle breech during routine perforation of the pedicle, in the course of pedicle screw placement.

Minimally invasive endoscopic approach to the cervicothoracic junction for vertebral metastases: report of two cases

The anterior cervicothoracic junction is difficult to expose and many techniques have previously been described. Most of them require an extensile exposure, which can lead to significant morbidity. The aim of this study is to present a less invasive approach, allowing the same exposure on the spine as a larger one. The approach begins with the same incision as the Smith-Robinson technique: a blunt dissection of the posterior face of the manubrium is performed with the finger. An endoscope is inserted through 10-mm trocars, one above the manubrium and the second through the second rib space. The upper mediastinal space is exposed; the dissection is performed on the left side, between the esophagus and trachea medially, between the innominate vein and brachio-cephalic artery distally, and between the left common carotid and internal jugular vein laterally. The recurrent nerve must be protected. Two patients with spine metastases underwent this new approach. A strut graft was fixed anteriorly after decompression of the spinal cord. Levels T1–T3 can be well exposed through this approach, allowing complete vertebral body removal at level T1 or T2. After body removal, the posterior longitudinal ligament is well exposed, allowing complete release of the spinal cord. The use of the endoscope is the key to providing a good view of the spine without an extensile exposure. This new approach is technically feasible. The exposure is sufficient for vertebral body resection and reconstruction by strut graft. The procedure is less aggressive and painful than sternotomy.

Dislocations with intervertebral disc prosthesis: two case reports

To date, only three cases of artificial disc prosthesis dislocation have been reported in the literature. We present in detail two additional cases of prosthesis dislocation and discuss the surgical interventions undertaken that resulted in a good clinical outcome in both patients.

Pedicle subtraction osteotomy for sagittal imbalance

The patient is pain-free at night but endures increasing pain during daily activities and work. He cannot stand straight and is permanently bent forward. He has transient radicular claudication; neurologic exam is normal at rest. MRI shows multiple degenerative discs in the lumbar spine without canal stenosis or hernia. Facet arthrosis is present but posterior muscles are still good. Full standing films show a straight spine on AP view and a significant lumbar kyphosis with global imbalance on lateral view. The C7 plumb line falls in front of the femoral heads and the pelvic parameters show a pelvic incidence of 75 and a pelvic tilt (PT) of 33 , which is too high for an incidence of 75 . This is the characteristic of a compensation phenomenon. It is possible to see that femoral shafts are not vertical and the clinical exam shows that the knees are flexed. The conclusion is that this patient has a global imbalance, compensated by pelvic retroversion and knee flexion. Back muscles are constantly struggling to restore a better sagittal alignment but this is ineffective and increases back pain by muscle fatigue. A correction is requested.

Sagittal balance measures are more reproducible when measured in 3D vs in 2D using full-body EOS® images

PurposeAn innovative low-dose X-ray biplanar imager (EOS®) allows measurement of the whole-body in standing-position which is necessary for the evaluation of spinal deformities.MethodsA total of 60 asymptomatic subjects (ages 20–81 years) were evaluated using the 3D workflow called postural assessment and 2D measures. Subjects were measured twice each by two new observers following training, including: lordosis/kyphosis, pelvic parameters, sagittal-vertical axis, and spinal-sacral angle. Intra- and inter-observer reproducibility and similarity were compared between 2D and 3D measures.ResultsThe intraclass correlation coefficient (ICC) was very high for the 3D measures (>0.9) and excellent for the 2D measures (>0.75). In all cases, the overall mean absolute difference between repeated 3D measures was less than 2°, or 2 mm. For all parameters, the inter- and intra-observer reproducibility in 3D measures were significantly superior to 2D measures (p < 0.03).ConclusionThis study demonstrated that 3D measures have better reproducibility than 2D for sagittal balance.Key Points• Reproducibility of sagittal balance 2D/3D measurements was evaluated using EOS® full-body radiographs.• Inter- and intra-observer reproducibility were significantly superior for 3D measures vs. 2D.• 3D measures have better reproducibility than 2D for sagittal balance.

Surgical techniques in pediatric spine surgery

Pediatric orthopedics is the basis of orthopedic surgery. ‘‘ortho’’ from the Greek word ‘‘orthos’’ meaning ‘‘to make straight’’ and ‘‘pedis’’ meaning ‘‘child’’ are the roots of the term ‘‘orthopedic’’, which has gradually evolved to include treatment of the entire osteo-articular system. Pediatric surgery presents particular growth-related problems [1]. Vertebral surgery of spine deformities is a major branch of pediatric surgery and it is vital to comply with strict procedures to avoid damaging effects on patients once they have become adults [2]. Non-surgical treatments are often poorly understood or not well taught, resulting in unsuitable forms of therapy. Bracing [3] has been seen to be effective. Three-dimensional analysis using a low-dose imaging system [4] such as EOS (EOS Imaging Paris, France) provides an accurate analysis of vertebral rotations as well as predictive information as to the possible evolution of scoliosis deformities [5]. Surgical treatment of deformities in children can correct or halt any unfavorable evolution of kyphoscoliotic curvature [6] and dysplastic spondylolisthesis [6]. The high potential risk of spontaneous fusion of vertebra after surgical decompression has led to performing surgical procedures at a distance from the vertebral axis by spineto-rib-cage distraction in strict compliance with operating procedures [7]. It is very important to know how to use screws, hooks, and other means of laminar fixation correctly to avoid any hypercorrection and post-surgical flatback syndrome, which causes long-term sagittal balance disorders. Early surgery during growth should take into account the risk of the crankshaft phenomenon described by Dubousset [8]. This supplement summarizes the current techniques used in pediatric spinal surgery based on the experience of teams recognized as experts in the field.