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Although in theory, the differences in design between fixed-core and mobile-core prostheses should influence motion restoration, in vivo kinematic differences linked with prosthesis design remained unclear. The aim of this study was to investigate the rationale that the mobile-core design seems more likely to restore physiological motion since the translation of the core could help to mimic the kinematic effects of the natural nucleus. In vivo intervertebral motion characteristics of levels implanted with the mobile-core prosthesis were compared with untreated levels of the same population, levels treated by a fixed-core prosthesis, and normal levels (data from literature). Patients had a single-level implantation at L4L5 or L5S1 including 72 levels with a mobile-core prosthesis and 33 levels with a fixed-core prosthesis. Intervertebral mobility characteristics included the range of motion (ROM), the motion distribution between flexion and extension, the prosthesis core translation (CT), and the intervertebral translation (VT). A method adapted to the implanted segments was developed to measure the VT: metal landmarks were used instead of the bony landmarks. The reliability assessment of the VT measurement method showed no difference between three observers (p < 0.001), a high level of agreement (ICC = 0.908) and an interobserver precision of 0.2 mm. Based on this accurate method, this in vivo study demonstrated that the mobile-core prosthesis replicated physiological VT at L4L5 levels but not at L5S1 levels, and that the fixed-core prosthesis did not replicate physiological VT at any level by increasing VT. As the VT decreased when the CT increased (p < 0.001) it was proven that the core mobility minimized the VT. Furthermore, some physiologic mechanical behaviors seemed to be maintained: the VT was higher at implanted the L4L5 level than at the implanted L5S1 level, and the CT appeared lower at the L4L5 level than at the L5S1 level. ROM and motion distribution were not different between the mobile-core prosthesis and the fixed-core prosthesis implanted levels. This study validated in vivo the concept that a mobile-core helps to restore some physiological mechanical characteristics of the VT at the implanted L4L5 level, but also showed that the minimizing effect of core mobility on the VT was not sufficient at the L5S1 level.

Background: An artificial disc prosthesis is thought to restore segmental motion in the lumbar spine. However, it is reported that disc prosthesis can increase the intervertebral translation (VT). The concept of the mobile-core prosthesis is to mimic the kinematic effects of the migration of the natural nucleus and therefore core mobility should minimize the VT. This study explored the hypothesis that core translation should influence VT and that a mobile core prosthesis may facilitate physiological motion., Methods: Vertebral translation (measured with a new method presented here), core translation, range of motion (ROM), and distribution of flexion-extension were measured on flexion-extension, neutral standing, and lateral bending films in 89 patients (63 mobile-core [M]; 33 fixed-core [F])., Results: At L4-5 levels the VT with M was lower than with F and similar to the VT of untreated levels. At L5-S1 levels the VT with M was lower than with F but was significantly different compared to untreated levels. At M levels a strong correlation was found between VT and core translation; the VT decreases as the core translation increases. At F levels the VT increases as the ROM increases. No significant difference was found between the ROM of untreated levels and levels implanted with either M or F. Regarding the mobility distribution with M and F we observed a deficit in extension at L5-S1 levels and a similar distribution at L4-5 levels compared to untreated levels., Conclusion: The intervertebral mobility was different between M and F. The M at L4-5 levels succeeded to replicate mobility similar to L4-5 untreated levels. The M at L5-S1 succeeded in ROM, but failed regarding VT and mobility distribution. Nevertheless M minimized VT at L5-S1 levels. The F increased VT at both L4-5 and L5-S1., Clinical Relevance: This study validates the concept that the core translation of an artificial lumbar disc prosthesis minimizes the VT.

Study Objective: To study the electrophysiologic and clinical effects of epidural morphine combined with either bupivacaine 0.125% or ropivacaine 0.2%., Design: Comparative, randomized, double-blind study., Settings: Intensive care unit and hospital ward of a university hospital., Patients: 18 adult ASA physical status I and II patients with degenerative or idiopathic scoliosis, undergoing posterior spinal fusion with instrumentation., Interventions: Patients received epidural administration of 10-mL bolus of either bupivacaine or ropivacaine followed by a 6-mL/h infusion for 48 hours of unlabeled local anesthetic. In all patients, epidural morphine 5 mg was added daily., Measurements: Assessment was focused mainly on somatosensory cortical evoked potentials, soleus H-reflex, and F waves. These electrophysiologic data were recorded before and after epidural medications. Second, respiratory rate, Paco(2), visual analog score (VAS), and side effects such as postoperative nausea and vomiting (PONV), gastrointestinal (GI) transit delay, and urinary retention were noted., Main Results: Bupivacaine 0.125% + morphine was given to 9 patients, and ropivacaine 0.2% + morphine was given to 9 other patients. H-reflex, F waves, and somatosensory cortical evoked potential recording remained unchanged across the time of assessment. Respiratory rate and Paco(2) values were normal. VASs were indifferently low at rest, but they were lower with bupivacaine than with ropivacaine on mobilization. The frequency of PONV was indifferently high. No altered GI transit or urinary retention was noted., Conclusion: After epidural administration during the study conditions, bupivacaine 0.125% and ropivacaine 0.2% combined with morphine allow for neurologic examination.

Purpose of the Study: The aim of this study was to determine the predictive value of the traction radiograph in adults with stiff curve (preoperative Cobb angle>60 degrees and reduction of less than 35% with traction) thoracic scoliosis. We wanted to compare this predictive value with that observed in reducible scoliosis., Material and Methods: A traction radiograph was obtained using a standard protocol with dynamometric control of the force applied. Patients with stiff scoliosis had 47 thoracic curves and 11 thoracolumbar curves (with primary anterior release for ten thoracic curves and eight thoracolumbar curves) and patients with reducible scoliosis had 56 thoracic curves. Cortre-Dubousset instrumentation was used for treatment in all patients., Results: The postoperative Cobb angle for the stiff curves (without anterior release) was strongly correlated with the preoperative angle with traction (r=0.91; p<0.0001). The correlation between the postoperative Cobb angle and the preoperative Cobb angle without traction was less pronounced (r=0.86; p<0.0001). The traction radiographs were less predictive of the Cobb angle correction than the postoperative Cobb angle. The difference was 17.5+/-7 degrees , which corresponds to a supplementary gain in reduction after surgery. For the thoracic curves alone, the differences between the traction Cobb angle and the postoperative Cobb angle was 14.5 degrees for stiff curves and 6.5 degrees for reducible curves. Furthermore, the correlation between the Cobb angle with traction and the postoperative Cobb angle was stronger for stiff curve thoracic scoliosis (r=0.90) than reducible thoracic scoliosis (r=0.78)., Discussion and Conclusion: The standard traction radiographs were highly predictive of postoperative reduction of stiff thoracic and thoracolumbar curves treated by segmental instrumentation. The postoperative result can thus be estimated with a margin of error of +/-7 degrees . For the stiff curves, the postoperative Cobb angle was 17.5 degrees on average less than predicted on the traction radiograph (on average 20% supplementary gain in reduction). This angle gain, which was greater for stiff than reducible curves, corresponds to the determining effect of release occurring with stiff curves. Finally, because of the stronger correlation between the traction Cobb angle and the postoperative Cobb angle for stiff curves, the predictive value of the traction radiograph is greater for stiff curves than for reducible curves. In conclusion, one of the contributions of the traction radiograph, which results from the predictability of the postoperative angle with a small margin of error, is to enable adequate prediction of the postoperative outcome for a given patient or a specific sub-group of patients, e.g. with or without anterior release.

The ability of bone substitutes to promote bone fusion is contingent upon the presence of osteoinductive factors in the bone environment at the fusion site. Osteoblast progenitor cells are among these environmental osteoinductive factors, and one of the most abundant and available sources of osteoblastic cells is the bone marrow. As far as biological conditions are concerned, the vertebral interbody space appears as a favorable site for fusion, as it is surrounded by spongy bone, theoretically rich in osteogenic cells. This site may, however, not be as rich in osteogenic precursor cells especially at the time of grafting, because decortication of the vertebral end plates during the grafting process may modify cell content of the surrounding spongy bone. We tested this hypothesis by comparing the abundance of human osteogenic precursor cells in bone marrow derived from the iliac crest, the vertebral body, and the decorticated intervertebral body space. The number of potential osteoblast progenitors in each site was estimated by counting the alkaline phosphatase-expressing colony-forming units (CFU-AP). The results, however, demonstrate that the vertebral interbody space is actually poorer in osteoprogenitor cells than the iliac crest (P<0.001) and vertebral body (P<0.01), especially at the time of graft implantation. In light of our results, we advocate addition of iliac crest bone marrow aspirate to increase the success rate of vertebral interbody fusion.

Study Design: A retrospective outcome study was conducted., Objective: To analyze the clinical and radiographic outcome of surgical treatment for idiopathic scoliosis in patients treated at the age of 20 years or older., Summary of Background Data: Idiopathic scoliosis continues to pose problems in many patients after adolescence. Surgical treatment of idiopathic scoliosis in adults still is a challenging subject, but no outcome analysis in terms of different age groups had been performed., Methods: In this study, 58 adult patients with idiopathic scoliosis who underwent surgery using Cotrel-Dubousset instrumentation were followed up for 2 to 7 years, and the results were studied clinically and radiographically., Results: The prevalence of pain that requires specific treatment decreased from 16% to 5%, and the pain improvement was reliably obtained in the older patients. Radiographically, the mean rate of Cobb angle correction was 53% for both the thoracic and lumbar curves, whereas it decreased age dependently, especially in relation to the thoracic curve. The sagittal plane correction generally was satisfactory in patients younger than 50 years, but appropriate lumbar lordosis was difficult to maintain after the age of 50 years. Frontal and sagittal balance often was difficult to achieve in patients older than 50 years., Conclusions: This study clarified specific characteristics and problems in the surgical treatment of adult idiopathic scoliosis according to different age groups. Although pain was the most important indication for surgery in patients older than 40 years, it was improved reliably by surgery in most of these patients. On the other hand, the radiographic results tended to be less satisfactory in the older patients in an age-dependent manner. These results provide useful information concerning the indications and strategies of adult scoliosis surgery.

Study Design: Neurogenic mixed evoked potentials are used routinely to monitor the spinal cord during spine surgery. This study investigates the differential sensory-motor contribution by using collision techniques., Objective: To demonstrate that neurogenic mixed evoked potentials do contain a motor component., Summary of Background Data: Spinal cord monitoring is now routinely used during spine deformity surgery. Neurogenic mixed evoked potentials (i.e., potentials recorded from lower limb nerves after spinal cord stimulation) represent a reliable and sensitive technique. However, their specificity (sensory and motor spinal pathways) remains debated., Methods: Neurogenic mixed evoked potentials and collisions were performed in 24 consecutive patients during scoliosis surgery. Neurogenic mixed evoked potentials were elicited by a high thoracic spinal test stimulation and recorded from the tibial nerve at the ankle. A peripheral conditioning stimulation was delivered at the popliteal fossa 15 ms before spinal stimulation, inducing an ascending volley. The antidromic ascending motor component stops at the anterior horn cell level, whereas the orthodromic sensory component reaches the dorsal columns. The 15-ms interstimulus interval between peripheral conditioning and spinal test stimulation makes the collision with descending volleys occur in the spinal cord. The descending sensory volley is blocked, whereas the descending motor volley is unaffected., Results: Reproducible evoked potentials were recorded from the tibial nerve in all the patients studied when the conditioning stimulation was performed. These conditioned neurogenic mixed evoked potentials consist of a small and polyphasic wave whose amplitude represents approximately 26% that of the wave of unconditioned neurogenic mixed evoked potentials. It is likely that they correspond to motor spinal pathway activation., Conclusion: Both standard and conditioned neurogenic mixed evoked potentials are proposed to provide combined sensory and motor spinal pathway monitoring.

Study Design: A case was reported in which paradoxical air embolism arose from the patent foramen ovale in scoliosis surgery., Objectives: To present a case of suspected paradoxical air embolism after scoliosis surgery., Summary of Background Data: Embolic accident during scoliosis surgery may be caused by air, thrombus, or fat. There is growing attention on patent foramen ovale involved in paradoxical embolism. The devastating consequences are caused by multiple artery occlusions., Methods: Details of a recent documented neurologic complication (paraplegia, weakness of right arm, and blurry vision) after scoliosis surgery have been analyzed in medical publications., Results: The surgical procedure was not imputed. The causative role of epidural catheter for analgesia was considered, but it is likely that a paradoxical embolism occurred in this case, based on the multifocal (cerebral and spinal) neurologic dysfunction, the evidence of cerebral ischemia (on computed tomography), and the presence of a patent foramen ovale (on postoperative transesophageal echocardiography). Although no intraoperative embolism detection was available, air embolism was highly suspected because there was no absolute argument to exclude cruor or fatty embolism., Conclusions: It is critical to detect a patent foramen ovale before surgery and cerebral embolization intraoperatively. This might permit ascertainment of the etiologic diagnosis in case of a complication in surgery for scoliosis.

Quantitative experimental data showed differences in bone quality and ceramic incorporation between bone-rich and bone-poor implantation sites. Bone in-growth was significantly lower for ceramic implanted at a lumbar intertransverse than a laminar site. Bone-marrow enrichment of the lumbar intertransverse site (regarded as bone-poor) greatly facilitated ceramic osteointegration. The vertebral interbody site, despite theoretical richness in osteogenic precursor cells, might be bone-poor at the time of grafting as compared to the reference iliac crest site. These data have important clinical implications concerning the potential benefit of enriching both bone-poor and bone-rich sites.

Study Design: Two cases of intraspinal metallosis causing delayed neurologic symptoms secondary to spinal instrumentation surgery are reported., Objective: To present an unusual delayed neurologic complication after spinal instrumentation surgery., Summary of Background Data: Metal-related complications caused by orthopedic implants have long been a concern in the field of arthroplasty or internal fixation of fractures, but no such complications have been reported for spinal instrumentation., Methods: Retrospective case report of two patients with degenerative scoliosis who presented with delayed neurologic symptoms months to years after uneventful, but without secondary degenerative changes or dislodgement of the implants., Results: In both reported cases, a granulation-tissue mass characterized by marked metallosis had been formed in the spinal canal adjacent to a loosened laminar hook., Conclusions: Intraspinal metallosis should be kept in mind as a rare cause of delayed neurologic symptoms after spinal instrumentation surgery. With the metal implants in place, myelography was the sole informative examination for diagnosis.

Purpose of the Study: Bone grafts or bone substitutes are required to fill bone defects resulting from trauma or surgical resection of tumors. Calcium-phosphate ceramics are synthetic bone substitutes which promote new bone formation by osteoconduction. These ceramics possess osteoconductive properties but have no intrinsic osteoinductive capacity. They are unable to induce new bone formation in extraossesous sites. One solution to develop bone substitutes with osteogenic properties would be to associate biomaterials with osteoprogenitors., Materials and Methods: We studied the in vitro osteogenic potential of human bone-marrow cells cultured on macroporous calcium phosphate (CaP) ceramic, examining stromal cell proliferation and differentiation. Osteogenic differentiation was evaluated in terms of alkaline phosphatase activity and immunological characterization of the extracellular fibrillar matrix formed by these cells. The specimens were examined by scanning and transmission electron microscopy., Results: Human bone-marrow cells proliferated on CaP ceramic. The proliferating bone-marrow cells expressed an osteoblastic phenotype as shown by alkaline phosphatase activity and synthesis in ceramic pores of an extracellular matrix composed of fibronectin, osteocalcin and collagen I. In addition, numerous microcrystals of apatite precipitated on the fibrillar matrix, producing a mineralized fibrillar network within the ceramic., Conclusion: This study demonstrates that human bone-marrow cells cultured on macroporous CaP ceramic do not lose their osteoblastic phenotype even after 21 days of culture, and that they can induce osteogenesis in a CaP ceramic in vitro. This type of new "hybrid material" appears promising for the future.

Study Design: A prospective randomized study., Objectives: To assess the clinical and radiologic performances of a synthetic ceramic as a bone graft substitute in scoliosis surgery., Summary of Background Data: Surgery on the skeleton frequently requires harvesting of autogenous bone grafts from the pelvis, but this procedure often is complicated by problems., Methods: Fifty-eight patients with idiopathic scoliosis, ages 13 to 25 years, were treated by posterior correction and arthrodesis using Cotrel-Dubousset instrumentation. Posterior spinal fusion was performed using local bone grafts combined with autogenous iliac bone grafts in 30 patients, and combined with porous biphasic calcium phosphate ceramic blocks comprising hydroxyapatite and tricalcium phosphate in another 28 patients. The patients were observed for a minimum of 24 months after surgery, with a mean postoperative observation time of 48 months. The results were assessed clinically and radiographically., Results: Patients in the ceramic group had a lower average blood loss than those in the iliac graft group. They also were free from postoperative local complications in the iliac region, which were experienced by a significantly high proportion of patients belonging to the iliac graft group. Radiography demonstrated successful incorporation of the ceramic blocks within 12 months. The correction of the deformity was maintained similarly and satisfactorily in both groups., Conclusions: These results justify and favor the use of calcium phosphate ceramics as bone graft substitutes for instrumented posterior spinal fusion in teenagers and young adults. Potentially hazardous harvesting of pelvic bone is no longer necessary for such operations.

Introduction: We report a retrospective analysis of spinal cord monitoring with neurogenic mixed evoked potentials (NMEPs) combined with somatosensory evoked potentials (SSEPs) in 149 patients undergoing surgery for spinal deformity., Material and Methods: 149 patients (104 females and 45 males), mean age 28 yrs (13-72 yrs) were studied. NMEPs were elicited by electrical spinal cord stimulation in the rostral part of the surgical field, via two needle electrodes set in the epidural space and in the interspinous ligament above. They were recorded from the sciatic nerve at the knee and the sural nerve at the ankle. SSEPs were recorded from the scalp after stimulation of the posterior tibial nerve at the ankle. A decrease in amplitude of more than 50 p. 100 and/or an increase in latency of more than 10 p. 100 were defined as significant warning criteria., Results: No false-negative result was observed. NMEP modifications did not reach critical value in 143 cases. In 6 cases, significant changes were observed. Moving the stimulation electrodes along the spinal cord allowed spinal lesion localization and helped the surgeon to perform the adapted maneuver, clearly avoiding the occurrence of postoperative neurological defect in 5 of the 6 cases., Conclusion: NMEP monitoring is a sensitive and specific method useful for detecting an impending lesion of the spinal cord. NMEPs are also helpful in localizing the spinal level of the lesion. They represent a primary choice tool for neuromonitoring during scoliosis surgery.

Study Design: Neurogenic mixed evoked potentials were recorded after thoracoscopic spinal cord stimulation in patients undergoing video-assisted spine surgery., Objective: To demonstrate the feasibility and value of thoracoscopic spinal cord monitoring., Summary of Background Data: Video-assisted thoracic surgery recently has been proposed as a new technique for thoracic spine surgery. It can be used for anterior spinal release of patients with severe spinal deformities and for thoracic hernia removal., Methods: Five patients undergoing video-assisted thoracic surgery for spinal fusion were studied. Neurogenic mixed evoked potentials were elicited by electrodes seated into intervertebral discs through thoracoscopy and recorded from peripheral nerves of the lower limbs. Moreover, the study included the case of a patient with a thoracic hernia who underwent video-assisted thoracic surgery with combined thoracoscopic neurogenic mixed evoked potential and standard somatosensory evoked potential monitoring., Results: Neurogenic mixed evoked potentials were recorded consistently after spinal cord stimulation in all patients. For the patient with a thoracic hernia, neurogenic mixed evoked potentials suddenly disappeared, whereas somatosensory evoked potentials were not significantly modified, leading to surgery interruption. Neurogenic mixed evoked potentials progressively reappeared after a 30-minute delay. Postoperation examination revealed a Brown-Sequard's syndrome with incomplete right motor deficit., Conclusions: Neurogenic mixed evoked potentials evoked by anterior stimulation through thoracoscopy are of interest for spinal cord monitoring when posterior electrical stimulation is impossible, and they provide reliable information regarding spinal motor pathways.

Neurogenic motor evoked potential (NMEP) monitoring, which basically represents a monitoring of both motor and somatosensory tracts, has been proposed as a warning system in preventing neural damage during spinal surgery. The aim of this study was to report our clinical experience in 112 consecutive patients undergoing surgery for spinal deformity, and to emphasize the interest of NMEP monitoring. NMEPs were elicited in each patient by electrical stimulation of the spinal cord via needle electrodes placed by the surgeon in the rostral part of the surgical field, and recorded from the right and left sciatic nerves. Concomitantly, somatosensory evoked potentials (SSEPs) were obtained using a standard method. No false-negative cases of intra-operative spinal cord damage were reported. In 3 patients, both NMEPs and SSEPs suddenly disappeared during specific surgical manipulations of the vertebral implants. In these patients, the level of the lesion was easily recognized by moving the stimulating electrodes of NMEPs along the spinal cord, allowing the surgeon to perform laminectomy at the appropriate vertebral level. Spinal cord decompression was a success in two patients, the last unfortunately being paraplegic. Two additional patients exhibited transient reduction in NMEP amplitude at the insertion of a rod while SSEPs did not change significantly. In these two cases, the surgeon modified his procedure according to the NMEP changes, possibly avoiding a neurological complication. Each time evoked potentials were significantly altered, significant information was more rapidly acquired with NMEPs than with SSEPs. These results suggest that NMEPs can be used as primary choice for detecting impeding lesion of the spinal cord during critical steps of spinal surgery.

Study Design: An analysis of a standardized method of traction radiography for the evaluation of reducibility of scoliosis., Objectives: To determine whether and how preoperative fraction radiography can provide objective information and to compare traction radiography with supine side-bending radiography., Summary of Background Data: Flexibility of scoliosis deformity remains an arbitrary concept. No objective method of preoperative evaluation of reducibility has been established., Methods: The utility of a standardized method of traction radiography was evaluated in 74 patients with idiopathic scoliosis who were aged 14-22 years and treated with Cotrel-Dubousset instrumentation., Results: In thoracic curves, the postoperative Cobb angle was highly correlated with the preoperative Cobb angle in traction (r = 0.82). However, such correlation was much lower with lumbar curves (r = 0.54). The reducibility of the thoracic curve by traction as expressed by the ratio to the original curve was dependent on the magnitude of the original curve (P = 0.005), and this parameter proved less informative than the absolute angle values. Time-related analysis of 30 patients who were observed for more than 5 years revealed that the high correlation between the preoperative angle of thoracic curves in traction and their postoperative angle decreased with the follow-up time (r = 0.80-0.65). A comparison of traction radiography and supine side-bending radiography showed that these two tests were practically equivalent in terms of evaluating the reducibility of curves., Conclusion: The results provide an objective interpretation of traction radiographs for scoliosis.

Objectives: To evaluate bone growth into macroporous ceramic in a canine model in terms of the effect at the lumbar spine site (lamina versus transverse process site) and the depth of the area within the ceramic block (peripheral or central areas)., Summary of Background Data: Previous comparative studies have assessed that the efficacy of bone graft substitutes for spine fusion depends on their physicochemical properties and on the mechanical environment, but rarely on the grafting site at the lumbar spine level., Methods: Posterior and lateral arthrodesis using pedicular instrumentation was performed at L2, L3, and L4 with a parallelepipedic ceramic block in an experimental group of dogs. A second group of dogs was fused with only autogenous bone graft to compare the fusion stiffness obtained with this material with the stiffness obtained with ceramic. Dogs were studied for 9 months. A biomechanical test and histomorphometric analysis were conducted., Results: With the biomechanical test, no significant differences were found between ceramic and autogenous bone. The percentage of newly formed bone was higher (P < 0.0001) at the lamina (26.52 +/- 6.45%) than at the transverse process site (17.33 +/- 2.54%). For both locations, the highest amount of newly formed bone was observed in the area of close contact between ceramic and bone, and the lowest was observed in central areas (24.6 +/- 5.9% for the laminar site, 14.79 +/- 1.75% for the transverse process site)., Conclusion: This animal study, which replicated the human procedure in posterolateral lumbar fusion, showed a significant difference of ceramic incorporation between laminar and intertransverse sites. This histomorphometric analysis also confirmed the relationship between bone in-growth and ceramic thickness and ceramic contact area with bone.

Study Design: Postoperative changes in the lumbar spine were studied retrospectively in patients with adolescent idiopathic scoliosis who had been treated with Cotrel-Dubousset instrumentation., Objective: To examine middle-term changes in the unfused lumbar segments below an instrumented scoliosis fusion., Summary of Background Data: Scoliosis fusion by the Harrington method is known to be associated with a flat back in the fused area and subsequent degenerative changes in the segments below the fusion. No data have yet been published concerning a segmental instrumentation system., Patients and Methods: Thirty patients with idiopathic scoliosis, between the ages of 14 and 22 years at the time of surgery, were observed for 5-9 years after surgery. Activity, pain, complications, and 21 radiographic parameters were assessed., Results: The prevalence of low back pain increased from 3% before surgery to 20% at the final follow-up visit, although in none of the patients was the pain so severe that specific treatment was required. Radiographically, uninstrumented lumbar segments generally were realigned successfully in the frontal plane. Analyses in the sagittal plane revealed tendencies to a gradual increase in lumbar lordosis, anterior-upward tilting of the lowest instrumented vertebra, and posterior shift of the sagittal spinal balance. During the follow-up period, seven patients (23%) developed degenerative changes, including mild junctional kyphosis, retrolisthesis, narrowing of disc spaces, or osteophytes., Conclusion: Whereas the overall clinical and radiographic results of surgery were satisfactory, the unfused lumbar segments required careful surveillance, especially in the sagittal plane.

Compressive strength measurements were conducted on 32 macroporous biphasic calcium phosphate (MBCP) samples to evaluate the influences and interactions of five synthesis factors: chemical composition, percentage of macropores, mean size of macropores, isostatic compaction pressure, and sintering temperature. These parameters were varied simultaneously between two limit levels. Experiments used a factorial design method (FDM) allowing optimization of the number of samples as well as statistical analysis of results. FDM showed that compressive strength, in a defined experimental area, can be described by a first-order polynomial equation in which the percentage of macroporosity and sintering temperature are the major influences. This study leads up to an isoresponse line diagram that will allow the manufacture of some classes of MBCP with fitted compressive strength.

Purpose of the Study: The authors report their experience with the use of a biphasic macroporous calcium phosphate bone substitute., Materials and Methods: In 23 cases (22 patients) a biphasic macroporous calcium phosphate ceramic was used to fill a pathological bone defect. The ceramic used in this study was a macroporous (400 to 600 mu) component consisting of 60 per cent hydroxyapatite and 40 per cent beta-tricalcium phosphate. It was in the form of granules (2 to 3 mm), sticks (20 x 5 x 5 or 10 x 5 x 5 mm) or custom made blocks. In 6 cases, the ceramic was used alone; in 12 cases with autologous bone marrow and in 5 cases with autologous cancellous bone grafts. In 14 cases, the bone defect was due to conservative treatment of a benign tumor, in 3 cases due to aseptic post-traumatic non union, in 3 cases due to wide resection for malignant tumors of the pelvis and in 3 cases following osteotomy. Post operative assessment was made from clinical, radiographic and histological findings., Results: 2 patients died 6 and 8 months post operatively and 2 were lost to follow up at 2 and 5 months with both having good clinical and radiographic results when last seen. For the remaining 19 cases, the average follow-up was 20 months (from 6 to 62 months). No local, regional or general deleterious effects were noted. Radiologically the bone ceramic junction healed in all cases except 2 within 3 months. In these last two cases, healing required 6 and 7 months. No radiolucent line appeared around the ceramic. No stress fractures occurred in the substitute. Histologically, 3 biopsies showed new bone formation throughout the ceramic with apposition of a well differentiated lamellar bone directly apposed to the ceramic., Discussion: Animal experimentations have proven the interest of similar ceramics: macroporosity enhances bone rehabilitation and the biphasic characteristics associate the advantages of slow resorption of hydroxyapatite and more easily resorbed beta-calcium phosphate. No deleterious clinical, radiographical or histological effects were observed, confirming the biocompatibility of this substitute. Despite the poor mechanical properties of this macroporous ceramic before implantation, good clinical and radiographic results suggest improvement of these properties in the composite new formed bone-ceramic after implantation., Conclusion: We believe that macroporous biphasic ceramic is a good substitute for use in bone defects when good primary mechanical stability and contact with the host bone are present. Further clinical and experimental studies are necessary to determine the limits of such a substitute in terms of volume and to control its mechanical properties following implantation.

We emphasize the opportunity of an in vivo bone mass measurement with an easy and accurate technique for orthopedic practice. At the present time, Dual Energy X Ray Absorptiometry (DEXA) is the most used technique, and is a safe and short examination. It can assess the quantity of mineral of any region of the body with a remarkable reproducibility (1 to 3 per cent). New machines are improved, and they permit many practical applications beyond the osteoporosis field. Thus, in orthopedics, we can distinguish several interesting topics. Peripheral risk of fracture can be evaluated because of good correlation between bone mineral content and biomechanical properties of bone. Even if a peripheral fracture occurs after a fall, low bone mineral density plays an important role, as in the case of femoral neck fractures in elderly patients. In traumatological practice, a DEXA with a specialized advice has to be requested if the traumatism cannot fully explain the occurrence of the peripheral fracture. Low bone mineral density defines an osteoporotic state, with the possibility of selecting adequate therapy. The good reproducibility of the measurement allows early estimation of bone loss following a period of immobilization. Varying models of osteosynthesis can be compared in vivo, to evaluate a decrease of "stress shielding" bone resorption. The role of stiffness of an implant on regional bone mineral content can be assessed. Likewise, periprosthetic bone mineral content can be measured in various regions, and followed over time. Specific software allows the exclusion of the region where the metallic prosthesis is projected. The reproducibility of this peripheral bone mineral content is 2 to 3 per cent, which individually allows an estimation of variations of more than 5 per cent. It will be possible to evaluate in vivo the influence of various parameters of the prosthesis on bone mineral content in controlled studies, such as the role of the shape, the position, the structure, the coating. Mineral content of biomaterials and bone grafts are taken into account. Focusing the X Ray beam allows ultrahigh resolution. Precise measurements of very small parts of bone such as rodent tibia or vertebra are possible. The good reproducibility (2 per cent) authorizes the evaluation of various parameters which modify bone remodeling, such as immobilization or activity, ovariectomy. Preventive or curative therapeutics which change bone mass can be evaluated in animal pre clinical studies. There are other methods of measurement of bone mineral content. Digitalization of radiographs is not sufficiently accurate and CT Scan generate high levels of radiation. The DEXA is actually the best compromise for an accurate and reproducible measurement of the bone mineral content in vivo. This method will certainly be an important tool in orthopedics for several clinical or animal investigations in the future.