Jean-Yves Lazennec

Hip–spine relations and sagittal balance clinical consequences

IntroductionThe role of the pelvic area in sagittal balance is evident for spinal surgeons, but the influence of the coxofemoral joint is underestimated and inadequately explained by conventional imagery. Comprehensive analysis of the pelvic and subpelvic sectors as part of the sagittal, frontal and cross-sectional balance of the trunk sheds new light on some spinal diseases and their relation to the pelvis.MethodsThis analysis, based on innovative radiologic methods as the EOS® technology but also on a new look at conventional imaging makes it possible to better analyze standing lateral images and seated images.ResultsDisturbances can come from atypical morphotypes or from unusual postures as in aging spine. The measurement of available extension and the concept of available flexion provide new information regarding individual’s adaptation to the imbalance induced by disorders of the spine or lower limbs.ConclusionA comprehensive assessment of each patient and in particular of the complex comprising the spine and the pelvis, is essential for understanding each individual’s adaptation to the imbalance induced by disorders of the spine or lower limbs.

The LP-ESP® lumbar disc prosthesis with 6 degrees of freedom: development and 7 years of clinical experience

The viscoelastic lumbar disk prosthesis-elastic spine pad (LP-ESP®) is an innovative one-piece deformable but cohesive interbody spacer providing 6 full degrees of freedom about the 3 axes, including shock absorption. A 20-year research program has demonstrated that this concept provides mechanical properties very close to those of a natural disk. Improvements in technology have made it possible to solve the problem of the bond between the elastic component and the titanium endplates and to obtain an excellent biostability. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. It thus differs substantially from current prostheses, which are 2- or 3-piece devices involving 1 or 2 bearing surfaces and providing 3 or 5 degrees of freedom. This design and the adhesion-molding technology differentiate the LP-ESP prosthesis from other mono-elastomeric prostheses, for which the constraints of shearing during rotations or movement are absorbed at the endplate interface. Seven years after the first implantation, we can document in a solid and detailed fashion the course of clinical outcomes and the radiological postural and kinematic behavior of this prosthesis.

Healthy vs. osteoarthritic hips: A comparison of hip, pelvis and femoral parameters and relationships using the EOS® system

BACKGROUNDnOsteoarthritis is a debilitating disease, for which the development path is unknown. Hip, pelvis and femoral morphological and positional parameters relate either to individual differences or to changes in the disease state, both of which should be taken into account when diagnosing and treating patients. These have not yet been comprehensively quantified. Previous imaging studies have been limited by a number of factors: supine rather than standing measurements; high radiation dose; a limited field of view; and 2D rather than 3D measurements. EOS®, a new radiographic imaging modality that acquires simultaneous frontal and lateral (sagittal) X-ray images of the full body, allows 3D reconstruction of the hip, pelvis and lower limb. The aim of the study was to explore similarities and differences between healthy and osteoarthritis groups.nnnMETHODSnTwo groups of subjects, 30 healthy and 30 with hip osteoarthritis, were assessed and compared for pelvic, acetabular and femoral parameters in the standing position.nnnFINDINGSnThere were not only significant differences between groups but also considerable overlap amongst the individuals. Sacral slope, acetabular angle of Idelberger and Frank, femoral mechanical angle and femoral head eccentricity as well as right-left asymmetries in centre-edge acetabular angle and femoral head diameter were higher on average in osteoarthritic patients compared to healthy subjects, whereas acetabular abduction was lower in the osteoarthritic group (P<0.05). Correlations were identified between key parameters in both groups.nnnINTERPRETATIONnDifferences between the groups suggest either degenerative changes over time or inherent differences between individuals that may contribute to the disease progression. These data provide a basis for longitudinal and post-surgery studies. Due to the considerable variability amongst individuals and the considerable overlap between groups, patients should be evaluated individually and at multiple joints when planning hip, knee and spine surgery.

What is the impact of a spinal fusion on acetabular implant orientation in functional standing and sitting positions

BACKGROUNDnThis study used EOS imaging of primary total hip arthroplasty (THA) patients, with and without predating spinal fusion, to investigate (1) the impact of spinal fusion on acetabular implant anteversion and inclination, and (2) whether more extensive spinal fusion (fusion starting above the thoracolumbar junction or extension of fusion to the sacrum) affects acetabular implant orientation differently than lumbar only spinal fusion.nnnMETHODSnNinety-three patients had spinal fusion (case group), and 150 patients were without spinal fusion (controls). None of the patients experienced dislocation. The change in sacral slope (SS) and cup orientation from standing to sitting was measured.nnnRESULTSnMean SS change from the standing to sitting positions was -7.9°in the fusion group vs -18.4°in controls (P = .0001). Mean change in cup inclination from the standing to sitting positions was 4.9°in the fusion group vs 10.2°in controls (P = .0001). Mean change in cup anteversion from standing to sitting positions was 7.1°in the fusion group vs 12.1°in controls (P = .0001). For each additional level of spinal fusion, the change in SS from standing to sitting positions decreased by 1.6(95% confidence interval [CI], 2.2073-1.0741), the change in cup inclination decreased by 0.8(95% CI, 0.380-1.203), and the change in cup anteversion decreased by 0.9(95% CI, 0.518-1.352; P < .001 in all cases).nnnCONCLUSIONnPatients with spinal fusion demonstrated less adaptability of the lumbosacral junction. Longer spinal fusion or inclusion of the pelvis in the fusion critically impacts hip-spine biomechanics and significantly affects the ability to compensate in the standing-to-sitting transition.

Hip-Spine Relations: An Innovative Paradigm in THR Surgery

The sagittal balance of the trunk is considered to be a key point for spinal fusion and disc replacement. This balance is the manifestation of a postural strategy conditioned by anatomic and functional characteristics that can differ greatly from one person to another (Duval-Beaupere et al., 1992). The role of the pelvic area is evident for spinal surgeons in their planning and analyses; they pay special attention to the sacral slope, which is closely related to the pelvic tilt (Chanplakorn et al., 2011; Dorr et al., 1983; Jackson & McManus, 1994; Kobayashi et al., 2004; Murray, 1993; Vialle et al., 2005). Dubousset underlined this concept as early as 1984, in treating the pelvis as a pelvic vertebra” (Dubousset, 1984). Although the concept of spinopelvic balance is well accepted today (Lazennec et al., 2004), conventional imagery underestimates the influence of the coxofemoral joint and explains it inadequately. The EOS imaging system (Dubousset et al., 2008), by optimizing radiologic data in functional situations, is revolutionizing our understanding of hip-spine relations (Lazennec et al., 2011b). These anatomic and functional considerations often remain foreign to hip surgeons, who focus on the bone landmarks of the pelvis for their navigation, individualized adjustments, and failure analyses (Woo & Morrey, 1982; Woolson & Rahimtoola, 1999). Although the hip is a highly mobile joint, surgical concepts are still based on the static AP view of the pelvis in standing or supine position to assess cup orientation, which is an essential risk factor for prosthesis instability and wear (Kennedy et al., 1998). Influenced by the classic anatomic culture of cross-sectional slices, they consider the CT scan a reference tool for the horizontal assessment of the coxofemoral joints (Ackland et al., 1986; Dorr et al., 1983; Kennedy et al., 1998; Murray, 1993; Seki et al., 1998; Wan et al., 2009). Nonetheless, as this chapter will show, lateral views of the hips and the evaluation of sitting position provide new information about “normal” hip function and THR failures. The concept of cumulative anteversion between the acetabular cup and the femur is considered a key factor in the stability of the hip prosthesis. This concept, however, is based on the measurements taken by computed tomography in a supine position, which do not take into account the functional dimension of the problem.

Good vs Poor Results After Total Hip Arthroplasty: An Analysis Method Using Implant and Anatomic Parameters With the EOS Imaging System

BACKGROUNDnExisting imaging techniques and single-parameter analyses, in nonfunctional positions, fail to detect the differences between patients with good vs poor results after total hip arthroplasty.nnnMETHODSnThe present study developed an analysis method using the EOS full-body, low-dose, biplanar, weightbearing imaging system to compare good vs poor patients after total hip arthroplasty and to report on our preliminary experiences (17 good, 18 poor).nnnRESULTSnAll revision cases were found to have at least 4 high or low implant or anatomic parameters relative to the good group. These included acetabular cup orientation, sagittal pelvic tilt, sacral slope, femoral offset, and neck-shaft angle. Acetabular cup orientation differed significantly between groups.nnnCONCLUSIONnWith the EOS system, a large cohort can be studied relatively quickly and at low dose, which could lead to patient-specific guidelines.

The innovative viscoelastic CP ESP cervical disk prosthesis with six degrees of freedom: biomechanical concepts, development program and preliminary clinical experience

AbstractnThe viscoelastic cervical disk prosthesis ESP is an innovative one-piece deformable but cohesive interbody spacer. It is an evolution of the LP ESP lumbar disk implanted since 2006. CP ESP provides six full degrees of freedom about the three axes including shock absorbtion. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. The concept of the ESP prosthesis is fundamentally different from that of the devices currently used in the cervical spine. The originality of the concept of the ESP® prosthesis led to innovative and intense testing to validate the adhesion of the viscoelastic component of the disk on the titanium endplates and to assess the mechanical properties of the PCU cushion. The preliminary clinical and radiological results with 2-year follow-up are encouraging for pain, function and kinematic behavior (range of motion and evolution of the mean centers of rotation). In this series, we did not observe device-related specific complications, misalignment, instability or ossifications. Additional studies and longer patient follow-up are needed to assess long-term reliability of this innovative implant.

The LP-ESP Lumbar Disc Prosthesis: Concept, Development and Clinical Experience

Because of its impairment of patients personal, social, and professional lives, degenera‐ tive disk disease has become an important public health problem with multiple dimen‐ sions. The current therapeutic strategy remains controversial and is also a medical and surgical challenge. Conservative treatment, based mostly based on physical therapy, constitutes the first-line approach, but persistent symptomatic disease may be treated surgically in selected patients [1-4]. Lack of pain relief, stiffening of the lumbar spine, nonunion, sagittal balance misalignment, bone graft donor site morbidity, and, last but not least, adjacent segment disease are the pitfalls of intervertebral fusion that led to the idea of total disk replacement (TDR) [5-12]. Since 1966 and Fernstrom’s first TDR implantation [13], many designs and concepts have been proposed [14-23]. The devices are usually articulated implants, and their mobility depends on the designs of the bearing surfaces. Ball-and-socket two-piece prostheses have 3 degrees of freedom in every rotation around a single fixed center of rotation. Three-piece devices allow additional translation compo‐ nents, providing 5 degrees of freedom. Articulated TDRs have demonstrated their clinical utility in several patient series. Specifically, the non-inferiority of TDR versus fusion is now generally accepted [18-20, 24]. However, in vitro testing of the two types of implants reveals that both designs have biomechanical advantages and limitations.

All Ceramic Tripolar THA to Prevent Dislocations in Risky Patients

Dislocation remains one of the most common complications after total hip arthroplasty (THA), especially for ceramic-on-ceramic prostheses. Suboptimal implant positioning, mus‐ cular insufficiency, significant lower limb discrepancies, and neurological problems are standard causes for THA dislocations or subluxations [1-3]. Instability may also be linked to 2 specific mechanisms, lever-out (with impingement) and shear-out (without impingement).

Indications, stratégies et techniques de la chirurgie pour le traitement du rachis cervical dégénératif

Les phenomenes degeneratifs sont d’une extreme banalite au niveau du rachis cervical. Il s’agit avant tout des deteriorations anatomiques traduisant une evolution normale liee a l’âge, mais aussi de phenomenes plus specifiques engendres par des pathologies modifiant la statique ou la mecanique de la region ou par des microtraumatismes repetes, notamment dans le cadre de certaines activites sportives, Les indications operatoires sont rares et s’adressent essentiellement a deux situations anatomo-cliniques particulieres: la nevralgie cervico-brachiale (NCB) chronique et la myelopathie cervicarthrosique.