A biomechanical definition of spinal segmental instability taking personal and disc level differences into account

Full endoscopic laminotomy decompression versus anterior cervical discectomy and fusion for the treatment of single-segment cervical spinal stenosis: a retrospective, propensity score-matched study

OBJECTIVE

Anterior cervical discectomy and fusion (ACDF) is the standard procedure for the treatment of cervical spinal stenosis (CSS), but complications such as adjacent segment degeneration can seriously affect the long-term efficacy. Currently, posterior endoscopic surgery has been increasingly used in the clinical treatment of CSS. The aim of this study was to compare the clinical outcomes of single-segment CSS patients who underwent full endoscopic laminotomy decompression or ACDF.

METHODS

138 CSS patients who met the inclusion criteria from June 2018 to August 2020 were retrospectively analyzed and divided into endoscopic and ACDF groups. The propensity score matching (PSM) method was used to adjust the imbalanced confounding variables between the groups. Then, perioperative data were recorded and clinical outcomes were compared, including functional scores and imaging data. Functional scores included Visual Analog Scale of Arms (A-VAS) and Neck pain (N-VAS), Japanese Orthopedic Association score (JOA), Neck Disability Index (NDI), and imaging data included Disc Height Index (DHI), Cervical range of motion (ROM), and Ratio of grey scale (RVG).

RESULTS

After PSM, 84 patients were included in the study and followed for 24-30 months. The endoscopic group was significantly superior to the ACDF group in terms of operative time, intraoperative blood loss, incision length, and hospital stay (P < 0.001). Postoperative N-VAS, A-VAS, JOA, and NDI were significantly improved in both groups compared with the preoperative period (P < 0.001), and the endoscopic group showed better improvement at 7 days postoperatively (P < 0.05). The ROM changes of adjacent segments were significantly larger in the ACDF group at 12 months postoperatively and at the last follow-up (P < 0.05). The RVG of adjacent segments showed a decreasing trend, and the decrease was more marked in the ACDF group at last follow-up (P < 0.05). According to the modified MacNab criteria, the excellent and good rates in the endoscopic group and ACDF group were 90.48% and 88.10%, respectively, with no statistically significant difference (P > 0.05).

CONCLUSION

Full endoscopic laminotomy decompression is demonstrated to be an efficacious alternative technique to traditional ACDF for the treatment of single-segment CSS, with the advantages of less trauma, faster recovery, and less impact on cervical spine kinematics and adjacent segmental degeneration.

Comparative analysis of three types of minimally invasive posterior cervical foraminotomy for foraminal stenosis, uniportal endoscopy, biportal endoscopy, and microsurgery: Radiologic and mid-term clinical outcomes

Objective

Methods

Results

Conclusion

The Novel Technique of Uniportal Endoscopic Interlaminar Contralateral Approach for Coexisting L5-S1 Lateral Recess, Foraminal, and Extraforaminal Stenosis and Its Clinical Outcomes

BACKGROUND

Multifocal intra-and-extraspinal lumbar stenotic lesions could be decompressed with one endoscopic surgical approach, which has the advantages of functional structure preservation, technical efficacy, and safety.

METHODS

A retrospective study was performed on 48 patients who underwent uniportal endoscopic contralateral approach due to coexisting lateral recess, foraminal, and extraforaminal stenosis at the L5-S1 level. Foraminal stenosis grade and postoperative dysesthesia (POD) were analyzed. Visual analog scale (VAS) pain scores, modified Oswestry Disability Index (ODI) scores, and MacNab criteria for evaluating pain disability and response were analyzed.

RESULTS

The foraminal stenosis grade of the treated spinal levels was grade 1 (n = 16, 33%), grade 2 (n = 20, 42%), and grade 3 (n = 12, 25%). The rate of occurrence of POD grade 2 and above, which may be related to intraoperative dorsal root ganglion (DRG) retraction injury, was revealed to be 4.2% (two with grade 2, none with grade 3). The patients showed favorable clinical outcomes.

CONCLUSIONS

Uniportal endoscopic interlaminar contralateral approach is an effective procedure to resolve combined stenosis (lateral recess, foraminal, and extraforaminal region) with one surgical approach at the L5-S1 level. It may be a minimal DRG retracting and facet joint preserving procedure in foraminal and extraforaminal decompression.

Requirements for an artificial intervertebral disc

Intervertebral disc degeneration is an important social and economic problem. Presently available artificial intervertebral discs (AIDs) are insufficient and the main surgical intervention is still spinal fusion. The objective of the present study is to present a list of requirements for the development of an AID which could replace the human lumbar intervertebral disc and restore its function. The list addresses geometry, stiffness, range of motion, strength, facet joint function, center of rotation, fixation, failsafety and implantation technique. Date are obtained from the literature, quantified where possible and checked for consistency. Existing AIDs are evaluated according to the presented list of requirements. Endplate size is a weak point in existing AIDs. These should be large and fit vertebral bodies to prevent migration. Disc height and wedge angle should be restored, unless this would overstretch ligaments. Finally, stiffness and range of motion in all directions should equal those of the healthy disc, except for the axial rotation to relieve the facet joints.

Upright, Weight-Bearing, Dynamic-Kinetic MRI of the Spine pMRI/kMRI

The purpose of this study was to demonstrate the general utility of the first dedicated magnetic resonance imaging (MRI) unit enabling upright, weight-bearing positional evaluation of the spinal column ( pMRI) during various dynamic- kinetic maneuvers ( kMRI) in patients with degenerative conditions of the spine.

This study consisted of a prospective analysis of cervical and lumbar imaging examinations. All studies were performed on a recently introduced whole body MRI system (Stand-Up™ MRI, Fonar Corp, Melville, NY). The system operates at 0.6T using an electromagnet with a horizontal field, transverse to the longitudinal axis of the patient's body. Depending upon spinal level, all examinations were acquired with either a cervical or lumbar solenoidal radiofrequency receiver coil. This unit is configured with a top/front-open design, incorporating a patient-scanning table with tilt, translation and elevation functions. The unique motorized patient handling system developed for the scanner allows for vertical (upright, weight bearing) and horizontal (recumbent) positioning of all patients. The top/front-open construction also allows dynamic-kinetic flexion and extension maneuvers of the spine. Patterns of bony and soft tissue change occurring among recumbent ( rMRI) and upright neutral positions ( pMRI), and dynamic- kinetic acquisitions ( kMRI) were sought.

Depending on the specific underlying pathologic degenerative condition, significant alterations observed on pMRI and kMRI that were either more or less pronounced than on rMRI included: fluctuating anterior and posterior disc herniations, hypermobile spinal instability, central spinal canal and spinal neural foramen stenosis and general sagittal spinal contour changes. No patient suffered from feelings of claustrophobia that resulted in termination of the examination.

In conclusion, the potential relative beneficial aspects of upright, weight-bearing ( pMRI), dynamic-kinetic ( kMRI) spinal imaging on this system over that of recumbent MRI ( rMRI) include: the revelation of occult disease dependent on true axial loading, the unmasking of kinetic-dependent disease, and the ability to scan the patient in the position of clinically relevant signs and symptoms. This imaging unit also demonstrated low claustrophobic potential and yielded relatively high-resolution images with little motion/chemical-shift artifact.

Functional Evaluation of the Lumbar Spine with Axial Loaded Computed Tomography (AL-CT) and Cine AL-CT

This study reports a personal experience in the functional study of the lumbar spine with original diagnostic techniques called Axial Loaded Computed Tomography (AL-CT) and Cine AL-CT, based on the use of the Axial Loader, a device that develops a variable and reproducible axial load in a supine patient during computed tomography or magnetic resonance investigation3,4.

We built a non ferromagnetic, X-ray transparent bed (the Axial Loader), with double blocking rests for shoulders and feet, that can be used during CT and MR spine studies. The inferior block is a platform that moves continuously in a longitudinal direction, with a micrometric mechanism. A dynamometer placed between the inferior platform and the patient's feet can measure the load applied.

We studied 75 patients, with a clinical and diagnostic suspicion of lumbar spine instability. The examinations were performed on a conventional CT unit (GE Sytec 3000, General Electric, Milwaukee) with a “volumetric” approach to the lumbar spine.

In conclusion, AL-CT and Cine AL-CT is currently the only diagnostic modality that can give dynamic information on the differents UFSs in all their components in one mildy invasive, easily reproducible diagnostic examination.

The Fernstrom ball revisited

INTRODUCTION

In 1959, Harmon was the first to implant a vitallium sphere into the intervertebral disc space in order to preserve mobility and maintain disc height in patients with back pain secondary to degenerative disc disease. Fernstrom reported good results after implantation of stainless steel spheres. However, a reduction in disc height frequently occurred secondary to sphere subsidence into the endplates. This often led to revision surgery, and the concept was abandoned.

MATERIALS AND METHODS

We report on four patients who underwent cobalt-chrome sphere implantation, and later presented to us with symptoms that were a direct result of sphere subsidence. All four patients presented with low back pain and/or lower extremity pain, and some with weakness. Imaging demonstrated that all patients had a loss of disc space height with sphere subsidence. Three patients underwent sphere removal, anterior interbody fusion using femoral ring allograft and posterior pedicle or facet screw fixation. In the fourth patient, the sphere was subsided into both the L5 and S1 endplates prohibiting removal. The patient underwent a posterior L5-S1 posterolateral fusion and facet screw fixation. The length of time from sphere implantation to the revision surgery ranges from 8 to 41 months.

RESULTS

Ten months to 3 years after the revision surgery, all four patients reported an improvement in outcome.

CONCLUSION

To the best of our knowledge, this is the first report describing the complications resulting from cobalt chrome sphere implantation and revision strategies for managing the recently resurrected cobalt chrome sphere.

Do early stages of lumbar intervertebral disc degeneration really cause instability? Evaluation of an in vitro database

Early stages of intervertebral disc degeneration are postulated to cause instability. In the literature, however, some authors report the opposite. These contradictory positions are probably supported by the mostly small number of segments which are investigated. The aim of this project therefore was to investigate the influence of intervertebral disc degeneration on lumbar spine rotational stability using a large data set. The flexibility data from all spine specimens tested in our institute so far were collected in a large in vitro database. From this database, all lumbar spine specimens were selected, which had been tested for flexibility under pure moment loads of ±7.5 N m and for which radiographs were accessible. 203 segments met these criteria. Their radiographic degree of disc degeneration was determined on a scale from 0 (no degeneration) to 3 (severe degeneration) and their influence on the respective range of motion and neutral zone was examined. The different lumbar levels differ in flexibility, which increases the variability of the data if pooled together. To minimise this effect a statistical model was fitted. The model-based mean estimates showed a decrease of the range of motion from grade 0 to 3 in flexion/extension (by 3.1°, p < 0.05) and lateral bending (by 3.4°, p < 0.05). In contrast, in axial rotation the range of motion tended to increase; however, not only from grade 0 to 1 but also towards grade 3 (by 0.2°) (p > 0.05). The neutral zone was affected in a similar way but to a smaller degree (p > 0.05). In conclusion, the results indicated that early stages of intervertebral disc degeneration do not necessarily cause rotational instability. In contrast, stability increased in flexion/extension and lateral bending. Only in axial rotation stability tended to decrease.

The influence of sagittal instability factors on clinical lumbar spinal symptoms

STUDY DESIGN

Cross-sectional and prospective study.

OBJECTIVE

To find the critical order of 3 radiographic factors observed in standing flexion-extension films and to discover their combined effect on lumbar symptoms.

SUMMARY OF BACKGROUND DATA

Many previous reports have described relationships between degenerative change in the lumbar disc and segmental instability; however, few reports have attempted to show any relationship between instability and symptoms. Little is known about which type of instability is the most critical in the sagittal plane of the lumbar spine.

METHODS

Excessive segmental motion (factors): >3 mm slip, >3 mm translation, and >10 degrees angulation, at the L4/5 segment in 880 patients (389 men and 491 women; mean age, 49.4 y) with low back and/or leg pain were investigated at initial visit. Symptoms of low back and leg pain, and walking ability were evaluated at initial visit and 4.6-year follow-up using Japanese Orthopaedic Association's scoring system. Severity and continuity of symptoms were evaluated and compared among the groups according to various combinations of excessive motion.

RESULTS

Of the 3 factors, patients with >3 mm slip had the lowest scores, and patients with >10 degrees angulation had the highest, both at initial visit and follow-up (P<0.001). In the comparative study of various factors, the groups with >3 mm slip had significantly lower scores than the group with no factors, and these groups had significantly lower scores in leg pain and walking ability than the nonfactor group (P<0.05).

CONCLUSIONS

Of the 3 factors, >3 mm slip had the strongest effect on symptoms followed by >3 mm translation and then >10 degrees angulation. Therefore, patients with low back and/or leg pain at initial visit and >3 mm slip, may expect symptoms of a duration exceeding 4 years. More than 10 degrees angulation had the least effect on symptoms as shown by the similarity in scores with the nonfactor group.

Results of instrumented posterolateral fusion in failed back surgery

The success rate following revision surgery for failed back surgery is inherently low. However, a general consensus for a satisfactory surgical intervention after failed disc surgery has not yet been reached. We present a cohort study of 25 adult cases treated by instrumented posterolateral fusion with or without nerve root exploration/decompression for recurrence or persistence of symptoms after previous disc surgery. The average age at surgery was 47 years (range 39-56 years). Complications were seen in four patients in the form of intraoperative dural tears. A satisfactory clinical outcome was seen in 80% of the patients, and the overall fusion rate was 93%.

Continuous dynamic spinal motion analysis

STUDY DESIGN

Continuous dynamic lumbar intervertebral flexion-extension is assessed by a videofluoroscopy with a new auto-tracking system.

OBJECTIVES

To develop and validate a new method for the continuous assessment of lumbar kinematics.

SUMMARY OF BACKGROUND DATA

Instability of the lumbar spine is thought to be associated with low back pain, but the diagnosis remains difficult. Functional radiographs have been used for diagnosis of spinal instability but error and limitation exist, whereas videofluoroscopy provides a cost-effective way for such analysis. However, common approaches of image analysis of videofluoroscopic video are tedious and time-consuming because of the low quality of the images. Physicians have to extract the vertebrae manually in most cases; thus, continuous motion analysis is hardly achieved.

METHODS

A new system that can perform automatic vertebrae segmentation and tracking is developed. In vitro and in vivo validity were evaluated. Intervertebral flexion and extension was assessed in 30 healthy volunteers.

RESULTS

In vitro and in vivo validity tests have been conducted with good results. A linear-liked pattern of the intervertebral flexion-extension (IVFE) curves in different levels was found, and the IVFE decreased in descending order from L1-L5 at different points of range of motion in flexion. Conversely, extension is evenly contributed at different levels, and the concavity of lumbar lordosis increases steadily in backward movement.

CONCLUSIONS

The newly developed technique in assessing the dynamic lumbar motion is reliable and able to analyze the lumbar intervertebral movement from videofluoroscopic images automatically and accurately. The proposed system requires less human intervention than common approaches. It may have a potential value in the evaluation of spinal "instability" in clinical practice.

Upright, weight-bearing, dynamic-kinetic MRI of the spine: initial results

The potential relative beneficial aspects of upright, weight-bearing (pMRI), dynamic-kinetic (kMRI) spinal imaging over that of recumbent MRI (rMRI) include the revelation of occult spinal disease dependent on true axial loading, the unmasking of kinetic-dependent spinal disease and the ability to scan the patient in the position of clinically relevant signs and symptoms. This imaging unit under study also demonstrated low claustrophobic potential and yielded comparatively high resolution images with little motion/magnetic susceptibility/chemical shift artifact. Overall, it was found that rMRI underestimated the presence and maximum degree of gravity-dependent spinal pathology and missed altogether pathology of a dynamic nature, factors that are optimally revealed with p/kMRI. Furthermore, p/kMRI enabled optimal linkage of the patient's clinical syndrome with the medical imaging abnormality responsible for the clinical presentation, thereby allowing for the first time an improvement at once in both imaging sensitivity and specificity.

Failed back surgery syndrome: the role of symptomatic segmental single-level instability after lumbar microdiscectomy

Segmental instability represents one of several different factors that may cause or contribute to the failed back surgery syndrome after lumbar microdiscectomy. As segmental lumbar instability poses diagnostic problems by lack of clear radiological and clinical criteria, only little is known about the occurrence of this phenomenon following primary microdiscectomy. Retrospectively, the records of 2,353 patients were reviewed according to postoperative symptomatic segmental single-level instability after lumbar microdiscectomy between 1989 and 1997. Progressive neurological deficits increased (mean of 24 months; SD: 12, range 1-70) after the initial surgical procedure in 12 patients. The mean age of the four men and eight women was 43 years (SD: 6, range 40-77). The main symptoms and signs of secondary neurological deterioration were radicular pain in 9 of 12 patients, increased motor weakness in 6 of 12 patients and sensory deficits in 4 of 12 patients. All 12 symptomatic patients had radiological evidence of segmental changes correlating with the clinical symptoms and signs. All but one patient showed a decrease in the disc height greater than 30% at the time of posterior spondylodesis compared with the preoperative images before lumbar microdiscectomy. All patients underwent secondary laminectomy and posterior lumbar sponylodesis. Postoperatively, pain improved in 8 of 9 patients, motor weakness in 3 of 6 patients, and sensory deficits in 2 of 4 patients. During the follow-up period of 72+/-7 months, one patient required a third operation to alleviate spinal stenosis at the upper end of the laminectomy. Patients with secondary segmental instability following microdiscectomy were mainly in their 40s. Postoperative narrowing of the intervertebral space following lumbar microdiscectomy is correlated to the degree of intervertebral disc resection. It can therefore be concluded that (1) patients in their 40s are prone to postoperative narrowing of the intervertebral disc space and hence subsequent intervertebral instability and (2) that a small extent of intervertebral disc resection and preservation of the "segmental frame" may be beneficial in those patients. The present study demonstrated for the first time that the degree of extensive operative techniques in microdiscectomy increased the risk of subsequent segmental instability. In addition, narrowing of the intervertebral space of more than 30% represents a clear radiological sign of segmental instability.

Neuroradiology of spine degenerative diseases

Degenerative disease of the spine is one of the most common clinical entities and affects the intervertebral discs, including opposing vertebral endplates, the intervertebral posterior joints and the ligaments. The most severe primary spinal degenerative changes are found in the lower cervical and lumbar spine regions. The spine contains three different types of joints, each of which presents its own pattern of degenerative disease: (i) cartilaginous joints, represented by the intervertebral disc or, more specifically, the functional unit defined as the 'vertebro-disc connection'; (ii) synovial joints, represented by the posterior intervertebral joints, sacro-iliac and costovertebral joints; (iii) fibrous joints, mainly found in the principal ligaments such as the posterior longitudinal ligament and the yellow ligaments. With regard to radicular pain, root compression alone does not fully account for root pain following disc-root conflict, but it is, nevertheless, considered to be the main cause of pain. We will try to explain that the origin of pain is multi-factorial and that inflammation probably predominates over merely mechanical mechanisms. To conclude, we will consider whether vertebral arthrosis can be construed as the body's decision to favour the spine's static function over its dynamic role when joint 'hypermobility' linked to chronic load in old age could cause severe structural damage to the bony vertebral structures. This hypothesis should also embrace a further concept: ageing of the spine is not merelychronological. Themostaccurate interpretation tha tcan account for similar degenerative phenomena encountered in the young is that of abnormal static and dynamic loading stress.

Cineradiographic motion analysis of normal lumbar spine during forward and backward flexion

STUDY DESIGN

Motion characteristics of the lumbar spine in the sagittal plane were investigated in vivo using cineradiography.

OBJECTIVES

To evaluate the differences in motion characteristics of the normal lumbar spine between forward and backward flexion.

SUMMARY OF BACKGROUND DATA

Despite previous lumbar kinematic studies, differences in motion characteristics of the lumbar spine between forward and backward flexion remain unclear.

METHODS

Cineradiographic motion analysis was performed in 10 asymptomatic healthy male volunteers for two different lumbar motions. The motions consisted of active forward flexion (from maximum extension to maximum flexion) and active backward flexion (from maximum flexion to maximum extension). Displacements of the anterior and posterior vertebral corners from L3/L4 to L5/S1 were measured continuously in reference to the local coordinate system. Parameters investigated were onset of segmental motion, velocity of segmental motion, and continuous motion profiles of the vertebral corners during the two different motions.

RESULTS

During forward flexion, initial lumbar motion started stepwise from the upper level (L3/L4) to the lower levels with phase lags. Angular velocity at the onset of motion increased as the level descended. On the contrary, during backward flexion, initial motion started from the lower level (L5/S1) to the upper levels. There was no relation between velocity and spinal levels during backward flexion. Motion profiles of both anterior and posterior vertebral corners at L3/L4 and L4/L5 segments during forward flexion were similar to those during backward flexion. However, the motion profiles at L5/S1 segment during forward flexion were different from those during backward flexion.

CONCLUSIONS

During forward flexion of the lumbar spine, initial motion started from upper segments to the lower segments with phase lags. During backward flexion, initial motion started from the lower segments to the upper segments. Motion profiles of the vertebral corners during forward flexion were similar to those during backward flexion at L3/L4 and L4/L5. The motion profiles at L5/S1 were different between both flexions.

Effects of degeneration on the elastic modulus distribution in the lumbar intervertebral disc

STUDY DESIGN

Local elastic moduli of sliced intervertebral disc specimens were studied after establishing the relation between the elastic modulus and indentation behaviors by model tests using polyurethane specimens.

OBJECTIVES

This study presents a method to quantify the distribution of compressive elastic moduli in the lumbar intervertebral disc and to clarify the effects of degeneration on the distribution.

SUMMARY OF BACKGROUND DATA

No study has been performed to evaluate the distribution of axial compressive elastic moduli, which is supposed to relate previous biomechanical, biological, and biochemical findings regarding the intervertebral disc.

METHODS

Local compressive elastic moduli of the intervertebral disc were estimated by indentation tests. To evaluate the distribution of elastic moduli, indentation tests were performed at nodal points of a 10 mm x 10 mm network on a specimen. Nine cadaveric lumbar discs (L3-L4 and L4-L5) with various degrees of degeneration were tested. The age of subjects ranged 39 to 90 years (mean, 58.4 years).

RESULTS

The distribution of elastic moduli in normal discs was symmetric about the midsagittal plane. The mean elastic modulus in the nucleus pulposus was 5.8 kPa and those of the anterior and posterior anulus fibrosus were 110.7 and 75.8 kPa, respectively. The elastic moduli in the lateral portions were the lowest in the normal anulus, and were close to the values of the nucleus. Compared to normal discs, degenerated discs showed irregular distributions of elastic moduli. The elastic moduli of the degenerated nucleus were higher than those in normal discs.

CONCLUSIONS

The distribution of elastic moduli is much different between discs with and without degeneration.

Epidemiological and aetiological aspects of low back pain in vibration environments - an update

The article reviews the substantial body of epidemiological evidence linking vibration exposure and low back pain. Drivers appear to be at particular risk if exposures exceed those recommended by the ISO exposure limit. Various aetiological factors associated with vehicular vibration, flattening of the lumbar lordosis, increased motion segment flexibility, disc pressure and mechanical softening are discussed. Vibration studies of functional spinal units are also discussed, as are in vivo whole-body vibration experiments. Animal models have shown that vibration leads to compromised nutrition, higher disc pressures, release of neuropeptides, increased creep and histological changes.

Mechanical stress reduction during seated jolt/vibration exposure

The risk of experiencing low back pain is associated with mechanical factors. Anatomic factors, such as advancing pregnancy, can also place extra mechanical stress on the lower back. Mechanical factors, such as those related to the workplace, can be minimized by ergonomic interventions. A constrained, seated posture, in combination with exposure to whole-body, jolt/vibration can impose significant stresses on the posterior intervertebral disc and can lead to back muscle fatigue. Interventions that reduce the jolt/vibration magnitude and duration of exposure will decrease the mechanical work performed on the intervertebral disc. Such interventions range from jolt/vibration isolating seats and vehicle cabs, to decreasing exposure time and maintaining simple supported postures during ingress and egress. Improvements in seat configuration can reduce the intervertebral disc pressure and the strain on the posterior disc.