From the international space station to the clinic: how prolonged unloading may disrupt lumbar spine stability

Background Context

Prolonged microgravity exposure is associated with localized low back pain and an elevated risk of post-flight disc herniation. Although the mechanisms by which microgravity impairs the spine are unclear, they should be foundational for developing in-flight countermeasures for maintaining astronaut spine health. Because human spine anatomy has adapted to upright posture on Earth, observations of how spaceflight affects the spine should also provide new and potentially important information on spine biomechanics that benefit the general population.

The effects of exposure to microgravity and reconditioning of the lumbar multifidus and anterolateral abdominal muscles: implications for people with LBP

BACKGROUND CONTEXTOne of the primary changes in the neuromuscular system in response to microgravity is skeletal muscle atrophy, which occurs especially in muscles that maintain posture while being upright on Earth. Reduced size of paraspinal and abdominal muscles has been documented after spaceflight. Exercises are undertaken on the International Space Station (ISS) during and following space flight to remediate these effects. Understanding the adaptations which occur in trunk muscles in response to microgravity could inform the development of specific countermeasures, which may have applications for people with conditions on Earth such as low back pain (LBP).PURPOSEThe aim of this study was to examine the changes in muscle size and function of the lumbar multifidus (MF) and anterolateral abdominal muscles (1) in response to exposure to 6 months of microgravity on the ISS and (2) in response to a 15-day reconditioning program on Earth.DESIGNProspective longitudinal series.PATIENT SAMPLEData were collected from five astronauts who undertook seven long-duration missions on the ISS.OUTCOME MEASURESFor the MF muscle, measures included cross-sectional area (CSA) and linear measures to assess voluntary isometric contractions at vertebral levels L2 to L5. For the abdominal muscles, the thickness of the transversus abdominis (TrA), obliquus internus abdominis (IO) and obliquus externus abdominis (EO) muscles at rest and on contraction were measured.METHODSUltrasound imaging of trunk muscles was conducted at four timepoints (preflight, postflight, mid-reconditioning, and post reconditioning). Data were analyzed using multilevel linear models to estimate the change in muscle parameters of interest across three time periods.RESULTSBeta-coefficients (estimates of the expected change in the measure across the specified time period, adjusted for the baseline measurement) indicated that the CSA of the MF muscles decreased significantly at all lumbar vertebral levels (except L2) in response to exposure to microgravity (L3=12.6%; L4=6.1%, L5=10.3%; p<.001), and CSAs at L3-L5 vertebral levels increased in the reconditioning period (p<.001). The thickness of the TrA decreased by 34.1% (p<.017), IO decreased by 15.4% (p=.04), and the combination of anterolateral abdominal muscles decreased by 16.2% (p<.001) between pre- and postflight assessment and increased (TrA<0.008; combined p=.035) during the postreconditioning period. Results showed decreased contraction of the MF muscles at the L2 (from 12.8% to 3.4%; p=.007) and L3 (from 12.2% to 5%; p=.032) vertebral levels following exposure to microgravity which increased (L2, p=.046) after the postreconditioning period. Comparison with preflight measures indicated that there were no residual changes in muscle size and function after the postreconditioning period, apart from CSA of MF at L2, which remained 15.3% larger than preflight values (p<.001).CONCLUSIONSIn-flight exercise countermeasures mitigated, but did not completely prevent, changes in the size and function of the lumbar MF and anterolateral abdominal muscles. Many of the observed changes in size and control of the MF and abdominal muscles that occurred in response to prolonged exposure to microgravity paralleled those seen in people with LBP or exposed to prolonged bed rest on Earth. Daily individualized postflight reconditioning, which included both motor control training and weight-bearing exercises with an emphasis on retraining strength and endurance to re-establish normal postural alignment with respect to gravity, restored the decreased size and control of the MF (at the L3-L5 vertebral levels) and anterolateral abdominal muscles. Drawing parallels between changes which occur to the neuromuscular system in microgravity and which exercises best recover muscle size and function could help health professionals tailor improved interventions for terrestrial populations. Results suggested that the principles underpinning the exercises developed for astronauts following prolonged exposure to microgravity (emphasizing strength and endurance training to re-establish normal postural alignment and distribution of load with respect to gravity) can also be applied for people with chronic LBP, as the MF and anterolateral abdominal muscles were affected in similar ways in both populations. The results may also inform the development of new astronaut countermeasures targeting the MF and abdominal muscles.     

Analysis of clinical characteristics and surgical results of upper lumbar disc herniations

BackgroundUpper lumbar disc herniation (ULDH) is described mostly in levels L1-2, L2-3 and L3-4 of the lumbar spine in the literature and accounts for less than 10% of all disc herniations. The aim of our study was to evaluate the clinical characteristics and surgical results of ULDH.MethodsIn all, 367 patients treated for upper lumbar disc herniation and 2137 treated for lower lumbar disc herniation (LLDH) between January 2008 and January 2017 were included. They were followed up postoperatively at 12 months by radiological investigations, back and leg pain Visual Analogue Scale (VAS), and Oswestry Disability Index (ODI). Preoperative data comprised age group (20–40, 40–60, 60–80 years), gender (male, female), lumbar level (L1-2, L2-3, L3-4), side of disc herniation (left, right) and symptom duration (0–3, 3–6, 6–9 months).ResultsODI and VAS scores improved significantly postoperatively for all patients. Of the 367 ULDH patients, 169 were female (54%) and 198 male (46%), with a mean age of 55.8 ± 10.1 years (range, 35–71). In 174 (47.4%) patients symptom duration was 3 months, in 99 (27.0%) 3–6 months, and in 94 (25.6%) 6–9 months. At 12 months, ODI, back and leg pain VAS scores showed a significant difference in improvement according to ULDH symptom duration < 3 months and to LLDH symptom duration < 6 months.ConclusionMicrodiscectomy in ULDH provided sufficient and safe decompression of neural structures, with significant reduction in symptoms and disability. We suggest that early surgical treatment is an important factor for good outcome in ULDH.     

棘突间动态稳定系统治疗腰椎退行性疾病的中期疗效分析

目的:探讨Wallis和Coflex棘突间系统治疗腰椎退行性疾病的中期临床疗效以及对邻近节段退变的影响。方法:对2011年1月至2013年1月应用棘突间固定系统治疗的L_(4,5)节段腰椎退行性疾病55例患者进行回顾性分析,其中男31例,女24例;年龄25～67岁,平均43.3岁;腰椎管狭窄症21例,腰椎间盘突出症34例。根据所采用的棘突间固定系统不同将患者分为Wallis组(33例)和Coflex组(22例)。采用视觉模拟评分(visual analogue scale,VAS)对腰痛和下肢痛进行评分;根据腰椎日本骨科协会(Japanese Orthopaedic Association,JOA)评分和Oswestry功能障碍指数(Oswestry Disability Index,ODI)评价腰椎功能;通过影像学资料测量手术前后手术节段和邻近节段活动度、椎间盘高度以及上位邻近节段Pfirrmann等级的变化情况。结果:55例患者均获得随访,随访时间48～72个月,平均60.4个月。术后48个月时,两组患者腰痛VAS评分、下肢痛VAS评分、腰椎JOA评分和ODI评分较术前有明显改善(P0.01),组间比较差异无统计学意义(P0.05);两组手术节段的活动度和椎间盘高度较术前均明显减小(P0.05),而上下邻近节段的活动度和椎间盘高度无明显变化(P0.05),两组间椎间隙高度和活动度比较无统计学意义(P0.05);两组患者上位邻近节段Pfirrmann分级较术前差异不明显(P0.05)。4例腰椎间盘突出症患者手术节段在术后1～3年复发,其中Wallis组3例,Coflex组1例,平均年龄35.2岁。结论:Wallis和Coflex系统治疗腰椎退变性疾病具有相同中期疗效,可延缓邻近节段退变,但不能阻止椎间盘突出的复发。     

Disproportion of end plates and the lumbar intervertebral disc herniation

Background contextIt is suggested that the shape of the vertebral end plates may play a role in the development of abnormalities in the intervertebral disc. On midsagittal magnetic resonance images of the spine in patients with lumbar intervertebral disc herniation, a notable disproportion frequently exists between the end plates of two vertebrae to which the disc is attached. There is apparently no study in the literature examining possible association of this disproportion with development of disc herniation.PurposeTo determine whether a disproportion between two neighboring vertebral end plates is associated with the presence of disc herniation at the same level.Study designCase-control study.Patient sampleTwo hundred fifty patients with primary lumbar disc herniation in the case group and 250 age- and sex-matched normal individuals in the control group.Outcome measuresOn midsagittal sections, the difference of anteroposterior diameter of upper and lower end plates neighboring a herniated (in the case group) or normal (in the control group) intervertebral disc was calculated and expressed as “difference of end plates” or “DEP.”MethodsSubjects with previous spinal surgery, spondylolisthesis, or a significant vertebral deformity were excluded. For the main outcome variable, DEP was calculated at the level with herniated intervertebral disc in the case group, and the mean value was compared with mean DEP at the same level in the controls.ResultsMean DEP was significantly higher in the case group at both L4–L5 (2.45±0.28 vs. 2.08±0.27 mm, p=.02) and L5–S1 (3.32±0.18 vs. 2.51±0.13 mm, p<.001) levels. Similar differences were only marginally insignificant at L2–L3 (1.96±0.14 mm in the cases vs. 1.33±0.15 mm in the controls, p=.07) and L3–L4 (2.17±0.11 mm in the cases vs. 1.55±0.09 mm in the controls, p=.06) levels, with no significant difference at L1–L2 level (1.81±0.10 mm in the cases vs. 1.28±0.09 mm in the controls, p=.12). Each 1 mm increase of DEP at L4–L5 and L5–S1 levels was associated with 53% and 56% elevation in disc herniation risk at the corresponding levels, respectively.ConclusionsDifference of end plate is a significant and probably independent risk factor for lumbar disc herniation.     

Successful resolution of signs and symptoms from L4 radiculopathy with spinal manipulation: a case report

The management of a patient with L4 radiculopathy with side posture spinal manipulative therapy (SMT) is described. Dramatic improvement both subjectively and objectively followed a short course of SMT of the lumbar spine. This case is used to illustrate aspects of the natural history of lumbar discogenic radiculopathy, safety and effectiveness of SMT for disc herniations, diagnostic imaging, and differentiation of referred vs. radicular pain syndromes. Also included is a short summary of the safety and effectiveness of surgery for lumbar disc herniation. We conclude that side posture SMT in this case was safe and may be effective in the treatment of presumed lumbar spine disc herniation with L4 radiculopathy.     

腰骶部多裂肌与腰椎间盘突出症关系的研究进展

腰椎间盘突出症是临床常见疾病,既往对腰椎间盘突出症的治疗多关注对椎间盘局部的治疗,如手术疗法及其他介入治疗等,但术后并发症及高复发率一直是相关专业领域内的难点问题。随着脊柱生物力学及解剖学的发展,对腰突症的研究也日益增多。研究者们发现腰椎间盘突出症的发病和转归与局部肌肉等软组织密不可分。而作为脊旁深层肌肉,多裂肌对腰椎椎体节段间的稳定性起到重要作用,其功能的异常可使腰椎的稳定性降低,而腰椎的慢性疾病也可导致多裂肌的萎缩。     

Is level- and side-specific multifidus asymmetry a marker for lumbar disc pathology?

Background context

Several reports suggest that level- and side-specific multifidus atrophy or fat infiltration may be related to localized spinal pathology and symptoms. In particular, a study using a porcine model reported rapid level- and side-specific multifidus atrophy and adipocyte enlargement resulting from anterolateral disc or nerve root lesions.

Purpose

To investigate asymmetry in cross-sectional area (CSA) and fat infiltration in multifidus and other paraspinal muscles in patients with acute or subacute unilateral symptoms of radiculopathy and concordant posterolateral disc herniation. If multifidus asymmetry is indeed related to local pathology, this may serve as a marker for helping to target the search for less clearly identifiable pathology responsible for low back–related symptoms, which currently remains elusive in approximately 85% of those seeking care.

Study design

Cross-sectional observational study.

Patient sample

Subjects were patients referred to magnetic resonance imaging (MRI) with unilateral leg symptoms of less than 6 weeks onset suggestive of radiculopathy, with a consistent posterolateral lumbar disc herniation verified on imaging.

Methods

Using T2-weighted axial MRI, measurements were obtained for total muscle CSA and signal intensity, functional (fat-free) CSA, and the ratio of functional CSA to total CSA.

Results

Forty-three subjects met the inclusion criteria. The ratio of functional CSA to total muscle CSA was smaller on the side of the herniation than on the unaffected side, both below (mean 0.69 vs. 0.72, p=.007) and at the level of herniation (mean 0.78 vs. 0.80, p=.031). Multifidus signal intensity (fat infiltration) was greater on the side of the herniation at the level below the herniation (p=.014). Contrary to expectation, greater total multifidus CSA was found ipsilateral to the pathology at the level of herniation (p=.033). No asymmetries were found at the level above the herniation or in any other paraspinal muscles, with the exception of higher signal in the erector spinae at the level and side of herniation.

Conclusions

Multifidus may be particularly responsive to, or indicative of, localized lumbar disc or nerve root pathology within the first 6 weeks of symptoms as expressed through fat infiltration, but not through CSA asymmetry on MRI. However, such measurements are not reliable markers of lumbar pathology on an individual basis for use in clinical or research settings.     

极外侧型腰椎间盘突出症的临床研究

目的探讨极外侧型腰椎间盘突出症的临床表现、诊断、鉴别及治疗。方法通过CT或MRI将突出的腰椎间盘在椎管内所处的位置（矢状位、水平位、冠状位）予以定位,明确椎间盘突出部位。一旦确诊为极外侧型腰椎间盘突出症,即早期经横突间开放入路或后外侧椎间孔入路腰椎间盘镜监测下摘除突出的髓核。结果16例患者中15例行手术治疗,术后恢复取得了满意的疗效。结论CT或MRI为极外侧型腰椎间盘突出症的精确诊断提供了依据。早期诊断、早期手术是术后功能恢复的保证。     

Similar outcome despite slight clinical differences between lumbar radiculopathy induced by lateral versus medial disc herniations in patients without previous foraminal stenosis: a prospective cohort study with 1-year follow-up

Background contextIt has been claimed that lumbar radiculopathy induced by foraminal disc herniations had poorer outcome and different clinical features, including: 1-more progressive onset, but shorter duration between the first sign and request of medical care; 2-more severe radiculopathy; 3-less frequent/severe back pain; 4-less limitation of straight leg raising (SLR); 5-more frequent neurologic deficiencies; 6-poorer outcome.PurposeTo check whether this still holds true when including only patients without other reasons for foraminal stenosis, that is, whether patients with medial disc herniations had different features and outcome than those with more lateral disc herniations.Study designAll patients hospitalized to treat a lumbar radiculopathy within a 6-month period in two French rheumatology units in 2012 were included in this prospective study each time computed tomography scan or magnetic resonance imaging had already been performed and showed clear disc bulging/herniation but no features of medial or lateral spinal stenosis.Patient sampleFifty-nine patients (31 males, 49 with sciatica only) were included: 31 (53%) had medial disc herniations and 28 (47%) had more lateral herniations (posterolateral in 3, foraminal in 20, and far lateral in 5).Outcome measuresOutcome was assessed by a phone call 1 year after the baseline assessment using a standardized questionnaire. Patients were asked whether they experienced a relapse of their radiculopathy after discharge from the hospital; whether they had been operated or not; whether they felt it had improved or not; whether they felt cured or not; to assess their level of pain radiating in the leg when standing on a 0 to 10 verbal scale; and how long they could walk.MethodsFeatures of patients with medial disc herniations were compared with patients with more lateral herniations.ResultsNo significant differences according to the location of herniations were noticed for the speed of radiculopathy onset, time elapsed since onset, back pain (both lying or standing), and leg pain (both lying or standing), but slight significant differences (t test<0.05) were observed for other items: the 28 patients with lateral herniations were 8 years older (53.4 ±15.8 vs. 45.2±12.6), their herniations involved discs from upper levels of the lumbar spine (above L4–L5: 7/28 vs. 3/31), motor weakness was more frequent (25% vs. 3%), SLR was less restricted (65.0°±24.5° vs. 51.1°±25.7°), DN4 score of neuropathic pain was higher (4.4±2.1 vs. 3.2±1.8), anxiety level was higher (10.3±4.1 vs. 7.9±3.2), length of hospital stay was longer (5.7±2.4 days vs. 4.5±1.4 days), and physician's prognosis of a good outcome was poorer (6.6±2.2 vs. 8.0±1.6). However, at the end of follow-up (12.2±3.3 months), outcome was similar: 37% (vs. 41% for medial herniations) had transiently relapsed, 66% felt finally improved (vs. 63%), and walking capacity was nearly identical despite the fact that only 18% had to be operated (vs. 32% of those with medial herniations).ConclusionsDespite differences in clinical presentation, the outcome of radiculopathy induced by the more lateral lumbar disc herniations was not worse than the outcome of patients with only medial disc herniations. Previous claims of poorer outcome in foraminal herniations might be explained by the inclusion of patients with associated foraminal stenosis.     

Spaceflight‐induced bone loss alters failure mode and reduces bending strength in murine spinal segments

Intervertebral disc herniation rates are quadrupled in astronauts following spaceflight. While bending motions are main contributors to herniation, the effects of microgravity on the bending properties of spinal discs are unknown. Consequently, the goal of this study was to quantify the bending properties of tail discs from mice with or without microgravity exposure. Caudal motion segments from six mice returned from a 30‐day Bion M1 mission and eight vivarium controls were loaded to failure in four‐point bending. After testing, specimens were processed using histology to determine the location of failure, and adjacent motion segments were scanned with micro‐computed tomography (μCT) to quantify bone properties. We observed that spaceflight significantly shortened the nonlinear toe region of the force‐displacement curve by 32% and reduced the bending strength by 17%. Flight mouse spinal segments tended to fail within the growth plate and epiphyseal bone, while controls tended to fail at the disc‐vertebra junction. Spaceflight significantly reduced vertebral bone volume fraction, bone mineral density, and trabecular thickness, which may explain the tendency of flight specimens to fail within the epiphyseal bone. Together, these results indicate that vertebral bone loss during spaceflight may degrade spine bending properties and contribute to increased disc herniation risk in astronauts. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:48–57, 2016.     

Paraspinal muscle asymmetry and fat infiltration in patients with symptomatic disc herniation

Purpose

To investigate asymmetry in size and composition of the multifidus and erector spinae in patients with posterolateral disc herniation and concordant radicular symptoms, and determine whether symptom duration is associated with degree of asymmetry.

Methods

Thirty-three patients diagnosed with posterolateral disc herniation at L4–L5 verified on imaging and concordant leg pain were included. Multifidus and erector spinae cross-sectional area (CSA), functional cross-sectional area (FCSA, fat-free area), signal intensity and ratio of FCSA to total CSA were measured bilaterally from T ₂-weighted axial magnetic resonance imaging (MRI) at L3–L4, L4–L5, L5–S1 and S1 levels.

Results

No side-to-side differences in multifidus CSA, FCSA, and ratio of FCSA/CSA reached statistical significance at any spinal level. The multifidus signal intensity at L5–S1 was significantly greater (more fatty infiltration) on the side of the disc herniation. The erector spinae FCSA (lean muscle mass) at L5–S1 was found to be significantly smaller on the side of the herniation and the ratio of FCSA/CSA was smaller (more fatty infiltration) on the side of the herniation at L4–L5 and L5–S1. The degree of muscle asymmetry was not associated with symptoms duration.

Conclusions

There was no significant asymmetry of the multifidus at spinal level above, same or level below the disc herniation. Instead, variations in muscle composition were observed, with greater fat infiltration on the side and at spinal levels adjacent to the disc herniation. Muscle asymmetry was not correlated with symptom duration.

     

Impact of insurance type on patient-reported outcome measures in patients with lumbar disc herniation

BACKGROUNDLumbar disc herniations (LDH) are among the most common spinal conditions. Despite increased appreciation for the importance of social determinants of health, the role that these factors play in patients with lumbar disc herniations is poorly defined.PURPOSETo elucidate the association between insurance status and baseline patient reported outcome measures (PROMs) in the setting of lumbar disc herniations.STUDY DESIGN/SETTINGRetrospective cohort studyPATIENT SAMPLEBaseline patient-reported outcome measures (PROMS) were reviewed from 924 adult patients presenting for treatment of lumbar disc herniation within our institutional healthcare system (2015–2020).OUTCOME MEASURESThe Patient-Reported Outcomes Measurement Information System (PROMIS) Physical Function Short Form 10a (PF10a), PROMIS Global-Mental, PROMIS Global-Physical, and visual analogue scale (VAS) for back and leg pain were assessed.METHODSPROMIS scores at presentation were defined at the primary outcome and insurance status as the primary predictor. Differences in clinical and sociodemographic characteristics between our cohorts, stratified by insurance status, were evaluated using Wilcoxon rank-sum or chi-squared testing. We used multivariable negative binomial regression modeling to adjust for potential confounders including age, gender, race, language, ethnicity, comorbidity index, and median geospatial household income.RESULTSWe included 924 patients, with mean age of 58.4 +/- 15.2 years and 52.6% male prevalence. Patients insured through Medicaid were more likely to be Black, Hispanic, and non-English speaking patients compared with the commercially insured. The Charlson Comorbidity index was significantly higher in the Medicare group. Following adjusted analysis, patients with Medicaid insurance had significantly worse PF10a (IRR, 0.90, 95% CI 0.85–0.96), as well as PROMIS Global-Physical score (IRR 0.88, 95% CI 0.82–0.94), and VAS low back pain (IRR 1.20, 95% CI 1.04–1.40) when compared to the commercially insured.CONCLUSIONSWe encountered worse physical function, mental, and pain-related patient-reported outcomes for those with Medicaid insurance in a population of patients presenting for evaluation of lumbar disc herniation. These findings, including worse depression, anxiety, and higher axial back pain scores, merit further investigation into potential health system asymmetries, and should be accounted for by treating providers.     

多裂肌间隙入路手术治疗腰椎手术失败综合征

目的探讨利用自行研制的一套腰椎微创手术器械,以多裂肌肌间隙入路直视下微创经椎间孔腰椎椎体融合术在腰椎翻修手术中的临床疗效。方法选择我院2010年11月至2011年11月收治的腰椎手术失败综合征行直视下微创腰椎翻修手术的患者12例进行回顾性分析,其中腰椎间盘突出症行单纯性椎板开窗减压髓核摘除术后6例,腰椎间盘突出伴腰椎不稳、腰椎滑脱行后路腰椎椎体融合术后4例,腰椎管狭窄后路椎板开窗减压术后2例;术前已进行一次手术的9例,二次手术的2例,三次手术的1例。本组共融合17节段,L4～54例,L5S13例,L4～5和L5S1双节段2例,L3～4和L4～5双节段3例;通过影像学资料和末次随访的临床表现进行改良Macnab标准疗效评定。结果所有病例均获得随访,随访时间6～18个月,平均(13±3.9)个月;依据改良Macnab标准进行疗效评定,12例中,优9例,良3例,可0例,差0例,优良率100%(12/12)。结论多裂肌肌间隙入路治疗腰椎手术失败综合征,降低了手术风险,减少了术后并发症。     

The increase in dural sac area is maintained at 2 years after X-stop implantation for the treatment of spinal stenosis with no significant alteration in lumbar spine range of movement

Background contextThe X-stop interspinous process decompression (IPD) device has been used effectively in the management of symptomatic spinal stenosis. This study examines the radiological outcomes at 2 years postoperatively after X-stop implantation.PurposeTo measure the effect of X-stop IPD device on the dural sac and foraminal areas at 24 months postoperatively at instrumented level in symptomatic lumbar canal stenosis. We also aimed to assess its effect on change in lumbar spine movement.Study designProspective observational study.Patient sampleForty-eight patients treated with X-stop had preoperative positional magnetic resonance imaging (MRI) scans, 40 of whom had 2 years postoperative positional MRI scans. Complete scans were available for 39 of these patients.Outcome measuresPositional MRI scans were performed pre- and postoperatively. Measurements were done on these scans and are presented as the outcome measures.MethodsAll patients had a multipositional MRI scan preoperatively and at 6 and 24 months postoperatively. Foraminal area was measured in flexion and extension. Dural cross-sectional area was measured in standing erect and in sitting neutral, flexion, and extension (sitting) positions. The total range of movement (ROM) of the lumbar spine and individual segments was also measured.ResultsComplete scan data for 39 patients' scans were available. An increase in mean dural sac area was found in all positions. At 24 months after surgery, the mean dural sac area increased significantly in all four postures mentioned above. A small increase in mean foraminal area was noted, but this was not statistically significant. Mean anterior disc height reduced from 5.9 to 4.1 mm (p=.006) at 24 months at the instrumented level in single-level cases, from 7.7 to 6.1 mm (p=.032) in double-level cases caudally, and from 8.54 to 7.91 (p=.106) mm cranially. We hypothesize that the reduction in anterior disc heights could be a result of the natural progression of spinal stenosis with aging. There was no significant change in posterior disc heights at instrumented level or adjacent levels. The mean lumbar spine motion was 21.7° preoperatively and 23° at 24 months (p=.584) in single-level cases. This was 32.1° to 31.1° (p=.637) in double-level cases. There was no significant change in the individual segmental range of motion at instrumented and adjacent levels.ConclusionX-stop interspinous device remains effective in decompressing the stenosed spinal segment by increasing the anatomic dural cross-sectional area and foraminal area of spinal canal. It does not significantly alter the ROM of lumbar spine at instrumented and adjacent levels at 24 months postoperatively.     

Reoperation for recurrent lumbar disc herniation: a study over a 20-year period in a Japanese population

BackgroundMany studies have been reported on recurrent lumbar disc herniations covering several pathological conditions. In those studies, reoperation rate of revised disc excisions was calculated by simple division between the number of reoperations and that of the total primary disc excisions. To determine the real reoperation rate, strict definition of pathologies, a large number of patients, a long observation period, and survival function method are necessary.MethodsBetween 1988 and 2007, 5,626 patients with disc excision were enrolled by the spine registration system of the Department of Orthopaedic Surgery, Tohoku University, Japan. Among them, 192 had revised disc surgery, and we obtained data of 186 patients whose clinical features were assessed and reoperation rates analyzed using the Kaplan–Meier method.ResultsIn total, 205 disc herniations were excised in the revision surgery (including contralateral herniation at the same level and new herniation at a different level), and 101 were real recurrent herniations (recurrence at the same level and side as the primary herniation). The kappa coefficient of the spinal level and side between the primary and revision surgeries was 0.41, indicting moderate correlations. Real recurrent herniations showed shorter intervals between primary and revision surgeries. Male patients with surgery at a younger age carried a higher risk of reoperation. In the revision surgery, transligamentous extrusion was significantly more common than other types of herniation. On Kaplan–Meier analysis, the reoperation rate of overall revised excisions was 0.62% at 1 year, 2.4% at 5 years, 4.4% at 10 years, and 5.9% after 17 years. That of real recurrent herniations was 0.5%, 1.4%, and 2.1%, respectively, and 2.8% after 15.7 years.ConclusionReoperation rate of real recurrent herniations calculated using survival function method gradually increased year by year, from 0.5% at 1 year after primary surgery to 2.8% at 15.7 years.     

Analysis of factors that may influence range of motion after cervical disc arthroplasty

Background contextCervical artificial disc replacement is increasingly becoming popular among spine surgeons. Cervical disc arthroplasty aims to afford spinal stability and then balance this with flexibility. One of the fundamental benefits from performing cervical arthroplasty instead of fusion is preservation of motion in both the functional spinal unit (FSU) and the overall cervical spine. Eventually, preservation of segmental motion is believed to prevent the development of adjacent segment degeneration. But to justify its use, disc replacement prosthesis must demonstrate actual motion in vivo and preserve range of motion (ROM) after surgery as long as it allows. Without preservation of motion, disc prosthesis becomes just a functional arthrodesis equivalent.PurposeThe purpose of this study was to analyze the possible factors affecting cervical spine ROM after single-level cervical disc arthroplasty.Study design/settingThis is a retrospective radiological study of patients with symptomatic single-level cervical disc disorder who received the cervical disc prosthesis (Bryan Cervical Disc Prosthesis; Medtronic Sofamor Danek, Memphis, TN, USA).Patient sampleProcedure was performed in 39 patients.Outcome measuresThe outcome measures were statistical correlation of possible factors and ROM.MethodsWe investigated possible factors that could affect cervical ROM after surgical intervention using cervical disc replacement. For this, we focused on two main components, namely, patient factors and technical factors. First, we examined patient factors, such as age, sex, preoperative FSU ROM, and preoperative overall cervical spine (whole cervical spine) ROM. Second, we then investigated technical factors, such as the amount of bone resection, disc insertion angle, and disc insertion depth. Then, our study searched if there was any statistical correlation between these factors and the postoperative cervical ROM.ResultsSignificant correlation was found between the postoperative overall cervical spine ROM and preoperative overall cervical spine ROM (p<.0001, R²=0.9062). Postoperative FSU ROM is closely correlated to both the preoperative FSU ROM (p<.0001) and the disc insertion angle (p=.0097). However, no significant correlation was noted between age, sex, disc insertion angle, and disc insertion depth.ConclusionSignificant correlation was found between the postoperative overall cervical spine ROM and preoperative overall cervical spine ROM. Postoperative FSU ROM is closely correlated to both the preoperative FSU ROM and the disc insertion angle. Careful preoperative evaluation of the patient's radiographs and meticulous surgical technique during the surgical procedure could aid in achieving the goals and benefits of cervical disc arthroplasty.     

Analysis of the influence of species,intervertebral disc height and Pfirrmann classification on failure load of an injured disc using a novel disc herniation model

Background ContextAnnular repair devices offer a solution to recurrent disc herniations by closing an annular defect and lowering the risk of reherniation. Given the significant risk of neurologic injury from device failure it is imperative that a reliable preclinical model exists to demonstrate a high load to failure for the disc repair devices.PurposeTo establish a preclinical model for disc herniation and demonstrate how changes in species, intervertebral disc height and Pfirrmann classification impacts failure load on an injured disc. We hypothesized that: (1) The force required for disc herniation would be variable across disc morphologies and species, and (2) for human discs the force to herniation would inversely correlate with the degree of disc degeneration.Study designAnimal and human cadaveric biomechanical model of disc herniation.MethodsWe tested calf lumbar spines, bovine tail segments and human lumbar spines. We first divided individual lumbar or tail segments to include the vertebral bodies and disc. We then hydrated the specimens by placing them in a saline bath overnight. A magnetic resonance images were acquired from human specimens and a Pfirrmann classification was made. A stab incision measuring 25% of the diameter of the disc was then done to each specimen along the posterior intervertebral disc space. Each specimen was placed in custom test fixtures on a servo-hydraulic test frame (MTS, Eden Prarie, MN) such that the superior body was attached to a 10,000 lb load cell and the inferior body was supported on the piston. A compressive ramping load was placed on the specimen in load control at 4 MPa/sec stopping at 75% of the disc height. Load was recorded throughout the test and failure load calculated. Once the test was completed each specimen was sliced through the center of the disc and photos were taken of the cut surface.ResultsFifteen each of calf, human, and bovine tail segments were tested. The failure load varied significantly between specimens (p<.001) with human specimens having the highest average failure load (8154±2049 N). Disc height was higher for lumbar/bovine tail segments as compared to calf specimens (p<.001) with bovine tails having the highest disc height (7.1±1.7 mm). Similarly, human lumbar discs had a cross sectional area that was greater than both bovine tail/calf lumbar spines (p<.001). There was no correlation between disc height and failure load within each individual species (p>.05). Cross sectional area and failure load did not correlate with failure load for human lumbar spine and bovine tails (p>.05) but did correlate with calf spine (r=0.53, p=.04). There was a statistically significant inverse correlation between disc height and Pfirrmann classification for human lumbar spines (r=?0.84, p<.001). There was also a statistically significant inverse relationship between Pfirrmann classification and failure load (r=?0.58, p=.02).ConclusionsWe have established a model for disc herniation and have shown how results of this model vary between species, disc morphology, and Pfirrmann classification. Both hypotheses were accepted: The force required for disc herniation was variable across species, and the force to herniation for human spines was inversely correlated with the degree of disc degeneration. We recommend that models using human intervertebral discs should include data on Pfirrmann classification, while biomechanical models using calf spines should report cross sectional area. Failure loads do not vary based on dimensions for bovine tails.Clinical SignificanceOur analysis of models for disc herniation will allow for quicker, reliable comparisons of failure forces required to induce a disc herniation. Future work with these models may facilitate rapid testing of devices to repair a torn/ruptured annulus.     

Transdural approach for calcified central disc herniations of the upper lumbar spine. Technical note

Disc herniations of the upper lumbar spine (L1-2 and L2-3) have a frequency of 1 to 2% of all disc herniations. During posterior discectomy after laminectomy, significant manipulation of the exiting nerve root is unavoidable because of the narrow lamina and the difficulty in mobilizing the nerve root. The authors adopted a transdural approach in patients with calcified central disc herniation at the L1-2 level to reduce the risk of nerve root injury. Four patients suffering from radiating pain together with back pain were treated using the transdural approach. Preoperative neuroimaging studies revealed severe central disc herniation with calcification at the L1-2 level. After laminectomy or laminotomy, the incised dura mater was tacked, and the cauda equina rootlets were gently retracted. An intentional durotomy was performed over its maximal bulging of the ventral dura. After meticulous dissection of dense adhesions between the disc herniation and the dural sac, adequate decompression with removal of calcified disc fragments and osteophytes was accomplished. Clinical symptoms improved in all patients. Postoperative permanent cerebrospinal fluid leakage and pseudomeningocele were not observed, and no patient had a progressive lumbar deformity at an average follow-up of 53 months. Transient mild motor weakness and sensory change were observed in two patients postoperatively; however, these symptoms resolved completely within 1 week. The posterior transdural approach offers an alternative in central calcified upper lumbar disc herniation when root retraction is dangerous.