The effect of lumbar total disc replacement on the spinopelvic alignment and range of motion of the lumbar spine

A lumbar total disc replacement (TDR) is a type of motion-preserving surgery, which aims to restore and maintain the normal range of motion (ROM) and the sagittal balance of the spine. However, little is known regarding how the spinopelvic alignment and ROM of the lumbar spine are influenced by the lumbar TDR with ProDisc. This study retrospectively analyzed the sagittal alignment and ROM of the lumbar spine in 26 consecutive patients who had undergone the TDR with ProDisc with a minimum follow-up of 24 months. A standing lateral radiograph, which included the femoral heads and dynamic flexion-extension lateral radiographs of the spine were taken before surgery and at the follow-up visit. The radiological parameters included the sacral tilt, the pelvic tilt, and the lumbar lordosis. The segmental lordosis and ROM were also measured at each operative level. Nineteen patients underwent a single-level TDR and 7 patients underwent a double-level TDR. The mean lumbar lordosis increased significantly from 30.5 degrees to 40.8 degrees in all patients who underwent TDR without any significant changes in the sacral tilt and pelvic tilt at the latest follow-up (P<0.05). In the patients who underwent single-level TDR, the mean segmental lordosis at the L5-S1 and L4-5 operative levels increased significantly from 15.8 degrees to 23.2 degrees and from 14.1 degrees to 24.9 degrees, respectively. The mean ROM at L5-S1 and L4-5 increased significantly from 7.1 degrees to 11.2 degrees and from 11.4 degrees to 14.6 degrees, respectively. The sagittal balance and ROM of the lumbar spine improved significantly after the lumbar TDR.     

Measurement of total disc replacement radiographic range of motion: a comparison of two techniques

OBJECTIVE: Current methods used to measure total disc replacement (TDR) radiographic range of motion (ROM) have not been previously evaluated. Sagittal ROM is measured by determining the change in the Cobb angle of the prosthesis from the flexion to the extension radiographs. Either the metallic endplates or the keels of the TDR prosthesis can be used as radiographic landmarks in measuring ROM. We hypothesized that use of the prosthesis keels as radiographic landmarks, when compared with the use of prosthesis endplates, might lead to more precise measurements of TDR sagittal ROM. METHODS: Two observers (a fifth-year orthopedics resident and an attending orthopedic spine surgeon) measured the ROM of 51 Prodisc II TDRs on standard flexion and extension lumbar spine radiograph sets. Repeated measurements were made on two occasions using either the keels or the endplates as landmarks. Precision was defined as the mean of the absolute differences between measurements. RESULTS: For observer A, the mean absolute difference between two measurements was 1.4 degrees with the keel method compared with 3.0 degrees with the endplate method (P < 0.001). For observer B, the mean absolute difference between two measurements was 1.8 degrees with the keel method and 3.3 degrees with the endplate method (P < 0.001). When the interobserver differences were examined, the mean absolute difference was 1.8 degrees with the keel method and 3.3 degrees with the endplate method (P < 0.001). CONCLUSIONS: Our results show that the use of TDR prosthesis keels as radiographic landmarks, when compared with the use of prosthesis endplates, yields greater precision in ROM measurement. For TDR prostheses with a keel, we recommend using the keel to measure ROM.     

Factors influencing segmental range of motion after lumbar total disc replacement using the ProDisc II prosthesis

OBJECT: The purpose of this prospective controlled study was to evaluate possible factors that could affect postoperative segmental range of motion (ROM) after lumbar total disc replacement (TDR) using the ProDisc II prosthesis. METHODS: Thirty-two consecutive patients with intractable discogenic pain underwent lumbar TDR using the ProDisc II prosthesis, 30 of whom were followed up for at least 24 months. Segmental ROM was assessed preoperatively and every 6 months postoperatively using dynamic x-ray films. Segmental ROM at the reference level was assessed in relation to patient age, sex, body mass index (BMI), levels with implants, preoperative ROM, prosthesis size, and prosthesis position. RESULTS: At the last follow-up visit, mean ROM of the disc prostheses was significantly increased from 4.23 +/- 3.12 degrees to 6.81 +/- 3.76 degrees at L3-4, and from 3.66 +/- 2.47 degrees to 6.09 +/- 2.11 degrees at L4-5. Mean ROM at L5-S1, however, was decreased from 3.12 +/- 1.56 degrees to 2.86 +/- 1.26 degrees (p > 0.05). This difference in the changes in postoperative ROM between L5-S1 and the other operated levels was the only statistically significant factor (p = 0.025) among the variables related to the postoperative ROM that the authors assessed, but other factors such as patient age, sex, BMI, disc height, and the size and position of the prosthesis were not related to segmental ROM. CONCLUSIONS: The data demonstrate that after TDR using the ProDisc II prosthesis, ROM of the prosthesis at L5-S1 is significantly lower compared with ROM at the other levels. In preserving ROM, the advantage of lumbar TDR using the ProDisc II might be minimal at L5-S1. Among the variables related to postoperative ROM, the level at which the ProDisc II prosthesis was implanted was the only one found to be statistically significant.     

Clinical outcomes,radiologic kinematics,and effects on sagittal balance of the 6 df LP-ESP lumbar disc prosthesis

Background contextSurgical treatment of degenerative disc disease remains a controversial subject. Lumbar fusion has been associated with a potential risk of segmental junctional disease and sagittal balance misalignment. Motion preservation devices have been developed as an alternative to fusion. The LP-ESP disc is a one-piece deformable device achieving 6 df, including shock absorption and elastic return. This is the first clinical report on its use.PurposeTo assess clinical outcomes and radiologic kinematics in the first 2 years after implantation.Study designProspective cohort of patients with LP-ESP total disc replacement (TDR) at the lumbar spine.Patient sampleForty-six consecutive patients.Outcome measuresClinical outcomes were the visual analog scale (VAS) for pain, the Oswestry disability index (ODI), and the GHQ28 (General Health Questionnaire) psychological score. Radiologic data were the range of motion (ROM), sagittal balance parameters, and mean center of rotation (MCR).MethodsPatients had single-level TDR at L4–L5 or L5–S1. Outcomes were prospectively recorded for 2 years (before and at 3, 6, 12, and 24 months after surgery). The SpineView software was used for computed analysis of the radiographic data. Paired t tests were used for statistical comparisons.ResultsNo intraoperative complication occurred. All clinical scores improved significantly at 24 months: the back pain VAS scores by a mean of 4.1 points and the ODI by 33 points. The average ROM of the instrumented level was 5.4°±4.8° at 2 years and more than 2° for 76% of prostheses. The MCR was in a physiological area in 73% of cases. The sagittal balance (pelvic tilt, sacral slope, and segmental lordosis) did not change significantly at any point of the follow-up.ConclusionsResults from the 2-year follow-up indicate that LP-ESP prosthesis recreates lumbar spine function similar to that of the healthy disc in terms of ROM, quality of movement, effect on sagittal balance, and absence of modification in the kinematics of the upper adjacent level.     

Range of motion and adjacent level degeneration after lumbar total disc replacement.

BACKGROUND CONTEXT: There are no published studies on the relationship between total disc replacement (TDR) motion and the development of adjacent level degeneration (ALD). Because prevention of ALD is the underlying justification for TDR, studies investigating the validity of this concept are essential. PURPOSE: To examine the relationship between range of motion (ROM) and ALD 8.7 years after lumbar TDR. STUDY DESIGN/SETTING: Retrospective radiographic and chart review. PATIENT SAMPLE: Forty-two patients 8.7 years after lumbar TDR. OUTCOME MEASURES: Radiographic flexion-extension and ALD. Modified Stauffer-Coventry score. Oswestry Disability Questionnaire. Subjective patient ratings of back pain, leg pain, and disability. METHODS: We reviewed the flexion-extension radiographs of 42 patients 8.7 years after TDR. Cephalad adjacent levels were evaluated for degeneration: loss of disc space height, anterior osteophyte formation, or dynamic flexion-extension instability. Graphical analysis of motion and the prevalence of ALD was performed. A statistical relationship between ALD and clinical outcome was sought. RESULTS: Ten of 42 patients evaluated (24%) had radiographic ALD. The mean motion was 3.8 degrees +/-2.0 degrees. The patients with ALD had mean motion of 1.6 degrees +/-1.3 degrees whereas the patients without ALD had motion of 4.7 degrees +/-4.5 degrees (p=.035). A clear relationship between motion and the presence of ALD at 8.7-year follow-up was observed. Patients with motion 5 degrees or greater (n=13) had a 0% prevalence of ALD. Patients with motion less than 5 degrees (n=29) had a 34% prevalence of ALD (p=.021, odds ratio 13.5). ALD had no statistically significant effect on clinical outcome although the sample size was small. CONCLUSIONS: At 8.7-year follow-up, the prevalence of ALD after TDR is higher in patients with motion less than 5 degrees. The presence of ALD had no significant effect on clinical outcome, but the sample size was small. These data suggest that patients with significant ROM after lumbar TDR may have reduced risk for radiographic ALD.     

Clinical and radiological outcomes with the Charité artificial disc: a 10-year minimum follow-up

This is the first report of clinical and radiologic outcomes for the CHARITE artificial disc with a minimum follow-up of 10 years. A total of 107 patients indicated for total lumbar disc replacement were implanted with the CHARITE prosthesis. Of these 107, 100 were followed for a minimum of 10 years (range 10-13.4 years). A total of 147 prostheses were implanted with 54 one-level and 45 two-level procedures and 1 three-level procedure. The prostheses were placed through a standard anterior retroperitoneal approach. Clinically, 62% had an excellent outcome, 28% had a good outcome, and 10% had a poor outcome. Of the 95 eligible to return to work, 88 (91.5%) either returned to the same job as prior to surgery or a different job. These included 63.2% (12) of those working in heavy labor employment returning to the same job. Mean flexion/extension motion was 10.3 degrees for all levels (12.0 degrees at L3-L4, 9.6 degrees at L4-L5, 9.2 degrees at L5-S1). Mean lateral motion was 5.4 degrees . In the sagittal plane, 9 (6.1%) were anterior of geometric center, 50 (34.0%) were centered, and 88 (59.9%) were posterior of center. In the frontal plane, 110 (75%) were centered, and 37 (25%) were noted to be lateral to center. Slight subsidence was observed in two patients, but they did not require further surgery. No subluxation of the prostheses and no cases of spontaneous arthrodesis were identified. There was one case of disc height loss of 1 mm. Five patients required a secondary posterior arthrodesis. A good or excellent clinical outcome rate of 90% and a return to work rate of 91.5% compare favorably with results described in the literature for fusion for the treatment of lumbar degenerative disc disease. With a minimum follow-up of 10 years, the CHARITE artificial disc demonstrated excellent flexion/extension and lateral range of motion with no significant complications.     

Lumbar total disc replacement. Seven to eleven-year follow-up

BACKGROUND: Symptomatic lumbar degenerative disc disease is a challenging entity to treat. The results of arthrodesis may be compromised in the short term by pseudarthrosis and in the long term by pain at the iliac-crest donor site and by junctional degeneration. Total disc replacement has the potential to provide long-lasting relief to these patients. The purpose of this study was to present the clinical and radiographic results assessed seven to eleven years following a Prodisc total lumbar disc replacement. METHODS: Sixty-four patients had single or multiple-level implantation of a total lumbar disc replacement between 1990 and 1993. The mean duration of follow-up was 8.7 years. Clinical results were evaluated by assessing preoperative and postoperative lumbar pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Preoperative and postoperative radiographs were evaluated as well. Subgroup analysis was performed to determine if gender, an age of less than forty-five years, previous surgery, or multilevel surgery had an effect on outcome. RESULTS: At an average of 8.7 years postoperatively, there were significant improvements in the back-pain, radiculopathy, disability, and modified Stauffer-Coventry scores. Thirty-three of the fifty-five patients with sufficient follow-up had an excellent result, eight had a good result, and fourteen had a poor result. Neither gender nor multilevel surgery affected outcome. An age of less than forty-five years and prior lumbar surgery had small but significant negative effects on outcome. Radiographs did not demonstrate loosening, migration, or mechanical failure in any patient. Five patients had approach-related complications. CONCLUSIONS: The Prodisc lumbar total disc replacement appears to be effective and safe for the treatment of symptomatic degenerative disc disease. Gender and multilevel surgery did not affect the outcomes, whereas prior lumbar surgery or an age of less than forty-five years was associated with slightly worse outcomes. Longer follow-up of this cohort of patients and randomized trials comparing disc replacement with arthrodesis are needed.     

椎间盘源性腰痛人工椎间盘置换术的中期随访研究

 目的 探讨椎间盘源性腰痛人工椎间盘置换术(artificial disc replacement,ADR)的中期疗效。方法 2004年7月至2007年7月采用ADR治疗椎间盘源性腰痛21例(24个椎间盘),男9例,女12例;年龄26~67岁,平均46岁。均经椎间盘造影明确诊断。手术节段：L4-5 5例,L5S1 13例,L4-5+L5S1 3例。SB Charité Ⅲ型椎间盘假体22个,Activ L型椎间盘假体2个。集中随访时行X线、CT和MR检查,评估疼痛视觉模拟评分(visual analogue scale,VAS)及Oswestry功能障碍指数(Oswestry disability index,ODI)。结果 随访时间4~7年,平均5.1年。(1)腰腿痛较术前明显缓解,腰痛、腿痛VAS及ODI与术前比较差异均有统计学意义。(2)未出现椎间盘假体脱出、断裂、塌陷及手术节段自发性融合。1例双间隙手术者术后出现腰椎轻度侧凸,1例单间隙手术者出现相邻节段骨质增生加重。(3)手术节段椎间隙前缘高度较术前平均增加6.3 mm,后缘高度平均增加1.9 mm,节段性前凸角平均增加2.9°,椎间活动度平均为4.6°。近侧相邻节段椎间活动度平均减少2.5°。腰椎前凸角平均增加7.8°,腰椎屈伸活动范围平均增加2.4°。(4)近侧相邻节段椎间盘退变MR分级及关节突关节退变CT分级无明显变化,手术节段关节突关节退变CT分级增加。结论 椎间盘源性腰痛ADR术后5年手术节段仍保留一定的活动度,近侧相邻节段椎间盘和关节突关节退变缓慢,但手术节段关节突关节存在退变加速现象。     

Long-term kinematic analysis of cervical spine after single-level implantation of Bryan cervical disc prosthesis

Background contextCervical arthroplasty theoretically reduces the risk of adjacent level disc degeneration and segmental instability that may be seen after a cervical fusion. An essential argument in confirming the utility of cervical arthroplasty is long-term confirmation that cervical disc replacements can maintain physiological kinematics at the index and adjacent levels.PurposeThe purpose of this in vivo prospective study was to characterize the long-term segmental kinematic outcomes after cervical arthroplasty.Study design/settingProspective cohort study.Patient sampleTwenty patients with a 5-year clinical follow-up who underwent anterior cervical discectomy with insertion of the Bryan cervical disc.Outcome measuresPhysiological measures (kinematic analysis of lateral neutral, flexion, and extension radiographic imaging).MethodsTwenty consecutive patients with degenerative disc disease were followed with regular radiographic imaging after implantation of the Bryan cervical disc prosthesis. Lateral neutral, flexion, and extension radiographs (n=240) were analyzed using Quantitative Motion Analysis software (Medical Metrics, Inc., Houston, TX, USA) to measure the biomechanical profile at the index level and adjacent levels up to 5 years after surgery. Parameters collected included range of motion (ROM), functional spinal unit (FSU) angle, anterior and posterior disc heights, sagittal translation, and center of rotation (COR).ResultsBiomechanics of the implanted artificial cervical disc was maintained up to 5 years with no significant changes in ROM, FSU angle, disc height, sagittal translation, and COR values when compared with early postoperative performance. Artificial discs were able to adequately restore and maintain preoperative kinematics. Early differences seen in disc height and FSU angle did not change during the duration of follow-up. No significant kyphotic changes or decrease in ROM were seen at the adjacent spinal levels.ConclusionsThe Bryan cervical disc prosthesis provides for a durable solution for functional spinal motion at the operated level and maintained the preoperative kinematics at adjacent levels at the 5-year follow-up.     

全椎间盘置换术治疗腰椎间盘源性退行性疾病

目的 评价腰椎全椎间盘置换治疗腰椎间盘源性退行性疾病的效果.方法 应用两种人工腰椎间盘移植物治疗90例108节段具有明确腰椎间盘源性退行性疾病且6个月保守治疗无效的患者,男28例,女62例;年龄25~54岁,平均39.2岁;单节段植入85例,双节段10例,三节段1例;L3-4节段6例,L4-5节段39例,L5S1A节段63例.使用Prodisc L人工腰椎间盘48节段,Maverick人工腰椎间盘60节段.手术均取腹膜后人路.术后采用改良Odom评估、Oswestry评分、VAS评分及影像学检查四种方法对症状及疼痛改善程度进行评价.结果 手术时间75~160min,平均115.5min.术中血管损伤1例.术后并发深静脉血栓1例.术后90例患者均随访12个月.随访时间分别为:术后4、6、26、52周.术后Odom评估显示:优76例,良10例,可4例,优良率95.55%.住院时间2.5~6d.平均3.4d.术后翻修2例.影像学检查:假体下沉2例,两种假体移植物均无明显向前或后迁移.结论 应用腰椎全椎间盘置换可恢复退变节段的间盘高度和神经根管的高度及前、后径,保留腰椎后柱结构的完整性和稳定性.     

Effects of a cervical disc prosthesis on maintaining sagittal alignment of the functional spinal unit and overall sagittal balance of the cervical spine

The object of this study is to review the early clinical results and radiographic outcomes following insertion of the Bryan Cervical Disc Prosthesis (Medtronic Sofamor Danek, Memphis, TN), together with its effect on maintaining sagittal alignment of the functional spinal unit (FSU) and overall sagittal balance of the cervical spine for the treatment of single-level or two-level symptomatic disc disease. Forty-seven patients with symptomatic single or two-level cervical disc disease who received the Bryan Cervical Artificial Disc were reviewed prospectively. A total of 55 Bryan disc were placed in 47 patients. A single-level procedure was performed in 39 patients and a two-level procedure in the other eight. Radiographic and clinical assessments were made preoperatively and at 1.5, 3, 6, 9, 12, and 18 and up to 33 months postoperatively. Mean follow-up duration was 24 months, ranging from 13 to 33 months. Periods were categorized as early follow up (1.5–3 months) and late follow up (6–33 months). The visual analogue scale (VAS), neck disability index(NDI), Odom’s criteria were used to assess pain and clinical outcomes. Static and dynamic radiographs were measured by hand and computer to determine the range of motion (ROM), the angle of the functional segmental unit (FSU), and the overall cervical alignment (C2–7 Cobb angle). With all of these data, we evaluated the change of the preoperative lordosis (or kyphosis) of the FSU and Overall sagittal balance of the cervical spine during the follow-up period. There was a statistically significant improvement in the VAS score from 7.0 ± 2.6 to 2.0 ± 1.5 (paired-t test, P = 0.000), and in the NDI from 21.5 ± 5.5 to 4.5 ± 3.9 (paired-t test P = 0.000). All of the patients were satisfied with the surgical results by Odom’s criteria. The postoperative ROM of the implanted level was preserved without significant difference from preoperative ROM of the operated level. Only 36% of patients with a preoperative lordotic sagittal orientation of the FSU were able to maintain lordosis following surgery. However, the overall sagittal alignment of the cervical spine was preserved in 86% of cases at the final follow up. Interestingly, preoperatively kyphotic FSU resulted in lordotic FSU in 13% of patients during the late follow-up, and preoperatively kyphotic overall cervical alignment resulted in lordosis in 33% of the patients postoperatively. Clinical results are encouraging, with significant improvement seen in the Bryan Cervical Artificial disc. The Bryan disc preserves motion of the FSU. Although the preoperative lordosis (or kyphosis) of the FSU could not always be maintained during the follow-up period, the overall sagittal balance of the cervical spine was usually preserved.     

Bryan人工颈椎间盘置换术的中期随访结果分析

目的 观察Bryan人工颈椎间盘置换术后临床和影像学结果以及相邻节段退变的情况.方法 回顾性分析术后随访时间超过2年的26例单节段置换患者的临床资料,临床效果采用JOA和Odom评分进行评定.采用x线片观察手术节段活动度和椎旁骨化.采用X线片和MRI观察对比相邻节段退变情况.术前X线片示置换节段的活动度为2°～12°,平均为6.9°.结果 (1)临床结果:18例脊髓型颈椎病患者随访时JOA评分平均16分,平均改善率84%,8例神经根型颈椎病患者随访时临床症状全部消失.Odom分级:优秀15例,良好7例,一般4例.(2)X线片:术后置换节段的活动度为1°～14°,平均7.8°;7例出现假体周围异位骨化,仅1例假体运动消失,其余6例平均活动度为5.3°.相邻节段椎间隙高度术后无明显变化.(3)MRI T2加权像:根据Pfirrmann椎间盘退变分级方法,相邻节段椎间盘的分级术后无明显加重表现;相邻节段黄韧带肥厚对椎管的侵占率术后无明显加重;但是上下相邻椎间盘侵占率均略有增加.结论 Bryan人工颈椎间盘置换术保留了置换节段的运动性,避免了相邻节段的加速退变,2年以上随访效果优良.     

Total disc arthroplasty: consequences for sagittal balance and lumbar spine movement

This in vivo biomechanical study was undertaken to analyze the consequences for sagittal balance and lumbar spine movement in three different lumbar disc prostheses. A total of 105 patients underwent total disc replacement in three different centers. The Maverick^® prosthesis was used in 46 patients, the SB Charité^® device was used in 49 patients and the Prodisc^® device was utilized in 10 patients. The analysis was computer assisted, using Spineview^® and Matlab^® softwares. The intra and inter-observer reliability and measurement uncertainty was performed. The analysis of lateral X-ray films in flexion–extension allowed to measure the prosthesis positioning, the range of motion (ROM), the localization of the mean center of rotation (MCR), the vertebral translation and the disc height, for each prosthesis device. The sagittal balance was analyzed on a full spine film. The parameters studied were described by Duval-Beaupère. The results were compared to the data found in literature, and compared to 18 asymptomatic volunteers, and 61 asymptomatic subjects, concerning the sagittal balance. The prostheses allowed an improvement of the ROM of less than 2°. The ROM of L5–S1 prostheses ranged from 11.6 to 15.6% of the total lumbar motion during flexion–extension. At L4–L5 level, the ROM decreased when there was an arthrodesis associated at the L5–S1 level. There was no difference of ROM between the three prostheses devices. The MCR was linked to the ROM, but did not depend on the prosthesis offcentering. The disc height improved for any prosthesis, and decreased in flexion or in extension, when the prosthesis was offcentered. An increase of translation indicated a minor increase of the ROM at L4–L5 level after Maverick^® or SB Charité^® implantation. The L5–S1 arthrodesis was linked with an increase of the pelvic tilt. The lumbar lordosis curvature increased between L4 and S1, even more when a prosthesis was placed at the L3–L4 level. Total disc arthroplasty is useful in the surgical management of discogenic spinal pathology. The three prostheses studied allowed to retorate the disc height, the ROM, without disrupting the sagittal balance, but induced modification of the lumbar curvature.     

The acute effects of posterior fusion instrumentation on kinematics and intradiscal pressure of the human lumbar spine

Nine cadaver lumbar spines were analyzed by applying nonconstraining nondestructive bending moments while measuring global range of motion, mechanical reaction at the sacrum, applied moment at the top of the specimen, segmental range of motion at L1-L5, and IDP at L1-L4. Each specimen was examined in an intact and instrumented state (with L3-L4 posterior instrumentation) using range of motion-based biomechanical testing, while achieving a similar global ROM in the sagittal, frontal, and transverse planes. An increase in applied moment was required during instrumented testing when compared with intact, and a significant increase in segmental range of motion during instrumented testing was found at all uninstrumented levels. Significant decreases in segmental range of motion were measured at the instrumented level when compared with intact testing. The most significant decreases and increases in IDP occurred at the instrumented level during sagittal and transverse plane testing.     

Kinematic evaluation of the adjacent segments after lumbar instrumented surgery: a comparison between rigid fusion and dynamic non-fusion stabilization

The aim of the current study was to evaluate changes in lumbar kinematics after lumbar monosegmental instrumented surgery with rigid fusion and dynamic non-fusion stabilization. A total of 77 lumbar spinal stenosis patients with L4 degenerative spondylolisthesis underwent L4–5 monosegmental posterior instrumented surgery. Of these, 36 patients were treated with rigid fusion (transforaminal lumbar interbody fusion) and 41 with dynamic stabilization [segmental spinal correction system (SSCS)]. Lumbar kinematics was evaluated with functional radiographs preoperatively and at final follow-up postoperatively. We defined the contribution of each segmental mobility to the total lumbar mobility as the percent segmental mobility [(sagittal angular motion of each segment in degrees)/(total sagittal angular motion in degrees) × 100]. Magnetic resonance imaging was performed on all patients preoperatively and at final follow-up postoperatively. The discs were classified into five grades based on the previously reported system. We defined the progress of disc degeneration as (grade at final follow-up) − (grade at preoperatively). No significant kinematical differences were shown at any of the lumbar segments preoperatively; however, significant differences were observed at the L2–3, L4–5, and L5–S1 segments postoperatively between the groups. At final follow-up, all of the lumbar segments with rigid fusion demonstrated significantly greater disc degeneration than those with dynamic stabilization. Our results suggest that the SSCS preserved 14% of the kinematical operations at the instrumented segment. The SSCS may prevent excessive effects on adjacent segmental kinematics and may prevent the incidence of adjacent segment disorder.     

Cervical kinematics after fusion and bryan disc arthroplasty

INTRODUCTION: Disc arthroplasty has been shown to provide short-term clinical results that are comparable with those attained with traditional anterior cervical discectomy and fusion. One proposed benefit of arthroplasty is the ability to prevent or delay adjacent level operations by retaining motion at the target level and eliminating abnormal adjacent activity. This paper compares motion parameters for single-level anterior cervical discectomy and fusion and disc replacement patients at the index level and adjacent segments. METHODS: Radiographic data from patients enrolled in a prospective, randomized clinical trial were selected for kinematic assessment of cervical motion. All patients received either a single-level fusion with allograft and anterior cervical plate (Atlantis anterior cervical plate, n=13) or a single-level artificial cervical disc (Bryan Cervical Disc prosthesis, n=9) at either C5/C6 or C6/C7. Flexion, extension, and neutral lateral radiographs were obtained preoperatively, immediately postoperatively, and at regular intervals up to 24-month time points. Cervical vertebral bodies were tracked on the digital radiographs using quantitative motion analysis software (QMA, Medical Metrics) to calculate the functional spinal unit motion parameters including range of motion (ROM), translation, and center of rotation. If visible, the functional spinal unit parameters were obtained at the operative level, and also the level above and the level below. RESULTS: As expected, significantly (P<0.006 at 3, 6, 12, and 24 mo) more flexion/extension motion was retained in the disc replacement group than the plated group at the index level. The disc replacement group retained an average of 6.7 degrees at 24 months. In contrast, the average ROM in the fusion group was 2.0 degrees at the 3-month follow-up and gradually decreased to 0.6 degrees at 24 months. The flexion/extension ROM both above and below the operative level was not statistically different for the disc-replaced and fusion patients, however, mobility increased for both groups over time. The anterior/posterior translation that occurs with flexion/extension motion remained unchanged for the disc replacement group at the level above the target disc preoperatively and postoperatively. In contrast, the translation increased for the level above the fusion. At the 6-month follow-up, the increase in translation was significantly greater for patients that were fused (P<0.02) than for patients that received a disc replacement. This change was not significant at 12 months. DISCUSSION: Previous studies have shown the Bryan disc to maintain mobility at the level of the prosthesis. The long-term clinical benefit of maintenance of motion is postulated to be the ability to delay or avoid adjacent level operations. This study reveals that there is no difference in flexion/extension ROM at the level above and below either a fusion or Bryan arthroplasty. There is, however, an increase in anterior/posterior translation at the cephalad adjacent level in patients with arthrodesis while the Bryan arthroplasty retains normal translation for the same amount of flexion/extension at the adjacent level. CONCLUSION: The Bryan disc may delay adjacent level degeneration by preserving preoperative kinematics at adjacent levels.     

颈椎曲度和活动度参数的影响因素

 目的 探讨颈椎曲度和活动度的测量参数及影响因素。方法 回顾性分析2012年1月至2013年6月,212位正常志愿者的颈椎标准侧位、前屈位、后伸位X线片,男84位,女128位;年龄20~79岁,以10年为一组,分成6组;颈椎间盘退变程度依据颈椎9分法,分为4组。影像资料由3名脊柱外科医生分3次运用Mimics软件测量。测量参数包括C2~C7曲度及椎间各节段和整体活动度。对颈椎曲度和整体活动度的关系进行Pearson 相关性分析,对年龄、性别和间盘退变三个因素进行多重线性回归分析。组内相关系数（ICC）评估测量者组内和组间一致性。结果 C₂~C₇曲度为21.40°±12.15°,C₂~C₇整体活动度为 63.59°±15.37°。性别对颈椎曲度的影响有统计学意义（回归系数=-2.472,P＜ 0.05）。性别和年龄两因素对颈椎整体活动度的影响有统计学意义（回归系数=3.863和-6.463,P＜0.05）。性别对C_2,3、C_5,6两个节段活动度的影响有统计学意义;年龄对C₂~C₇所有五个节段活动度的影响有统计学意义;间盘退变对C_4,5、C_5,6和C_6,7三个节段活动度的影响有统计学意义。颈椎曲度与颈椎整体及后伸活动度无明显相关性（r=-0.106和0.215,P＞0.05）,但与前屈活动度呈负相关（r=-0.401,P＜0.05）。颈椎曲度、整体活动度和节段活动度的测量结果均具有很高的组内一致性（ICC=0.97,0.96~0.97;ICC=0.91,0.90~0.92;ICC=0.89,0.87~0.91）和组间一致性（ICC=0.94,0.92~0.95;ICC=0.89,0.86~0.91;ICC=0.83,0.79~0.86）。结论 性别是颈椎曲度的影响因素,性别和年龄两因素是颈椎整体活动度的影响因素,性别、年龄和间盘退变程度是颈椎节段活动度的影响因素。     

Effect of cervical dynamics on adjacent segment degeneration after anterior cervical fusion with cages

The objective of this study is to evaluate the effect of anterior cervical discectomy and fusion (ACDF) on the motion of the cervical spine and dynamic stress (tendency to kyphosis) on adjacent segments and on the overall spinal alignment which may predispose to symptomatic disc diseases at other levels. Twenty consecutive patients underwent ACDF with a mean follow-up of 28 months (range 13-38). Preoperative and postoperative clinical assessments were done by using the neck disability index (NDI) and the Japanese Orthopedic Association (JOA) score. In all cases, at the last follow-up control, a neuro-radiographic assessment [cervical spine static and dynamic X-ray and magnetic resonance imaging (MRI)] was done. The angle of the operated disc space, the disc space angle of contiguous segments, and their range of motion (ROM) and the kyphotic Cobb angle (C2-7) were measured by computer software. The study was done at Sant'Andrea Hospital, Rome, Italy in the period from November 2003 to November 2005. We observed that: the mean Cobb angle improved significantly (p < 0.001) from 3.4 degrees (kyphosis) to postoperative 14.5 degrees . This normalization of angle showed a direct effect on improvement of myelopathic patients, but it had a statistically nonsignificant effect on adjacent segments degeneration (ASD). The mean segmental ROM of adjacent segments did not show significant instability. The mean was 11.1 degrees at upper and 10.2 degrees at lower levels (close to normal). In six cases, the ROM was higher than normal: five of these patients demonstrated symptomatic adjacent segment pathology. Postoperative improvement of mean JOA and NDI scores was statistically significant (p < 0.001). Anyway, symptomatic ASD was observed in five patients (20%): in four of them, the higher disc spaces and in one, the lower disc spaces were involved. In four cases, the preoperative MRI showed slight and asymptomatic disc degeneration at the same levels involved subsequently. This ASD was significantly related to the increased ROM at the segments involved. Follow-up X-rays showed solid fusion with absence of movement in all but one case (at 13-month follow-up), who showed slight movement in the operated level in spite of clinical improvement. The follow-up MRI showed, in all cases, good decompression in the treated levels. Compensatory increase in ROM of the contiguous motion segments in patients subjected to ACDF may lead to ASD especially in those cases with asymptomatic adjacent subclinical degenerative disease. If these preliminary results will be confirmed by larger series, it could be reasonable in young selected patients with soft disc herniation to adopt total disc arthroplasty instead of fusion after cervical micro-discectomy.     

Lumbar total disc replacement using ProDisc II: a prospective study with a 2-year minimum follow-up

A lumbar total disc replacement (TDR) is believed to be a promising substitute in the surgical treatment for lumbar degenerative disc disease. The purpose of this study is to report the clinical and radiographic outcomes of 36 consecutive patients who underwent lumbar TDR using ProDisc II, and the factors associated with a better clinical outcome after a 2-year minimum follow-up. At the time of the latest follow-up, the success rate was 94% of 36 patients according to the criteria of the US Food and Drug Administration. Of the 10 patients unable to work preoperatively, 7 patients returned to work. Moreover, mean score on the visual analog scale for low back and leg pain improved significantly from 7.5 and 4.7 to 3.0 and 1.2, respectively (P<0.001). In addition, mean Oswestry disability index scores improved significantly from 69.2 to 21.0 (P<0.001). Mean disc height at the operative level increased significantly from 9.0 to 17.6 mm, and mean range of motion increased significantly from 9.7 to 12.7 degrees (P<0.01). Statistical analysis showed that the factors associated with a better clinical outcome were single level, and a higher postoperative segmental ROM at the operative level. At a minimum follow-up of 2 years, the lumbar TDR using ProDisc II showed excellent clinical and radiographic outcomes without any significant complication. However, future efforts need to be directed toward the evaluation of a larger number of patients with longer follow-up.