Sagittal Plane Translation Research Articles

Can Cervical Arthroplasty Impact Alignment? A Comparison of the Synergy Disc with Cervical Fusion

Background context: Synergy disc is a new cervical disc prosthesis that incorporates alignment restoration while providing full intervertebral disc kinematics.Purpose: This follow-up study with 40 Synergy Disc patients with 24-month follow-up compared cervical alignment changes with a retrospective cohort of 30 single level anterior cervical discectomy and fusion (ACDF) patients.Study design/setting: The pilot trial was a multi-center, prospective, consecutive patient enrollment study using the Synergy Disc for the treatment of single and two-level degenerative disc disease of the cervical spine.Patient sample: The procedure was performed on 43 patients (45 implants) with follow-up on 40 patients (42 implants). For the historical cohort ACDF arm, 30 patients with similar follow-up with single level anterior discectomy, fusion and plating were used for segmental lordosis measurements.Outcome measures: For the Synergy Disc group, the kinematic parameters included: range of motion (ROM), shell angle (SA), disc height (DH), sagittal plane translation and center of rotation (COR) in the X and Y direction. Standard assessments of clinical outcomes were also measured (Neck Disability Index, Visual Analog Scale). For the fusion arm, only functional spinal unit (FSU) angle was recorded using a single pre-operative and post-operative standing lateral cervical radiograph.Methods: In the Synergy Disc group, static and dynamic radiological assessments were performed in 43 consecutive patients prior to the placement of the Synergy Disc. Forty patients were studied for the course of the study protocol (3 patients lost to follow-up). For the Synergy Disc group, all kinematic parameters were examined at a minimum of 24 months follow-up. Neck Disability Index and Visual Analog Scale for arm and neck pain were collected and analyzed. For the fusion group, standing lateral radiographs were reviewed.Results: At a mean of 28 months with all patients having a minimum of 24-month follow-up (40 patients, 42 implants), the average SA of the Synergy Disc was maintained at 6 ± 2.7˚ of lordosis. There was significant improvement in all clinical outcome measures. In the fusion group, with a similar follow-up period, there was a 4˚ increase in lordosis of the FSU.Conclusion: The Synergy Disc had an endplate angle of 6 ± 2.7˚ at 2 years following surgery. This was comparable to the lordotic correction provided by an anterior cervical discectomy with interbody fusion and plating.

Validation of three-dimensional total knee replacement kinematics measurement using single-plane fluoroscopy

Instability of the knee after total knee arthroplasty (TKA) is today the number one reason for aseptic revision surgery. In vivo evaluation of knee kinematics using single-plane fluoroscopy has become an important method to investigate knee stability and compare dierent implant designs. A validation experiment was performed to assess the accuracy of this method. A total knee implant was installed on sawbones and a flexion extension movement was performed with the sagittal plane parallel to the detector panel of the fluoroscope. Simultaneously, the sawbones were tracked using a conventional motion tracking system and rigidly attached markers. That measurement can be seen as a golden standard and is therefore believed to represent the real positions. The results indicate that knee rotations can be measured with an accuracy of approximately 0.6 and sagittal plane translations can be measured with an accuracy of approximately 0.4 mm. These results prove that the method is sufficiently accurate for clinical use.

Accuracy and repeatability of quantitative fluoroscopy for the measurement of sagittal plane translation and finite centre of rotation in the lumbar spine

Quantitative fluoroscopy (QF) was developed to measure intervertebral mechanics in vivo and has been found to have high repeatability and accuracy for the measurement of intervertebral rotations. However, sagittal plane translation and finite centre of rotation (FCR) are potential measures of stability but have not yet been fully validated for current QF. This study investigated the repeatability and accuracy of QF for measuring these variables. Repeatability was assessed from L2-S1 in 20 human volunteers. Accuracy was investigated using 10 consecutive measurements from each of two pairs of linked and instrumented dry human vertebrae as reference; one which tilted without translation and one which translated without tilt. The results found intra- and inter-observer repeatability for translation to be 1.1mm or less (SEM) with fair to substantial reliability (ICC 0.533–0.998). Intra-observer repeatability of FCR location for inter-vertebral rotations of 5° and above ranged from 1.5mm to 1.8mm (SEM) with moderate to substantial reliability (ICC 0.626–0.988). Inter-observer repeatability for FCR ranged from 1.2mm to 5.7mm, also with moderate to substantial reliability (ICC 0.621–0.878). Reliability was substantial (ICC>0.81) for 10/16 measures for translation and 5/8 for FCR location. Accuracy for translation was 0.1mm (fixed centre) and 2.2mm (moveable centre), with an FCR error of 0.3mm(x) and 0.4mm(y) (fixed centre). This technology was found to have a high level of accuracy and with a few exceptions, moderate to substantial repeatability for the measurement of translation and FCR from fluoroscopic motion sequences.

Development of a novel radiographic measure of lumbar instability and validation using the facet fluid sign.

Lumbar spinal instability is frequently referenced in clinical practice and the scientific literature despite the lack of a standard definition or validated radiographic test. The Quantitative Stability Index (QSI) is being developed as a novel objective test for sagittal plane lumbar instability. The QSI is calculated using lumbar flexion-extension radiographs. The goal of the current study was to use the facet fluid sign on MRI as the "gold standard" and determine if the QSI is significantly different in the presence of the fluid sign. Sixty-two paired preoperative MRI and flexion-extension exams were obtained from a large FDA IDE study. The MRI exams were assessed for the presence of a facet fluid sign, and the QSI was calculated from sagittal plane intervertebral rotation and translation measurements. The QSI is based on the translation per degree of rotation (TPDR) and is calculated as a Z-score. A QSI > 2 indicates that the TPDR is > 2 std dev above the mean for an asymptomatic and radiographically normal population. The reproducibility of the QSI was also tested. The mean difference between trained observers in the measured QSI was between -0.28 and 0.36. The average QSI was significantly (P = 0.047, one-way analysis of variance) higher at levels with a definite fluid sign (2.3±3.2 versus 0.60±2.4). Although imperfect, the facet fluid sign observed may be the best currently available test for lumbar spine instability. Using the facet fluid sign as the "gold standard" the current study documents that the QSI can be expected to be significantly higher in the presence of the facet fluid sign. This supports that QSI might be used to test for sagittal plane lumbar instability. A validated, objective and practical test for spinal instability would facilitate research to understand the importance of instability in diagnosis and treatment of low-back related disorders.

Kinetic magnetic resonance imaging analysis of abnormal segmental motion of the functional spine unit

The authors conducted a retrospective observational study using kinetic MR imaging to investigate the relationship between instability, abnormal sagittal segmental motion, and radiographic variables consisting of intervertebral disc degeneration, facet joint osteoarthritis (FJO), degeneration of the interspinous ligaments, ligamentum flavum hypertrophy (LFH), and the status of the paraspinal muscles. Abnormal segmental motion, defined as > 10 degrees angulation and > 3 mm of translation in the sagittal plane, was investigated in 1575 functional spine units (315 patients) in flexion, neutral, and extension postures using kinetic MR imaging. Each segment was assessed based on the extent of disc degeneration (Grades I-V), FJO (Grades 1-4), interspinous ligament degeneration (Grades 1-4), presence of LFH, and paraspinal muscle fatty infiltration observed on kinetic MR imaging. These factors are often noted in patients with degenerative disease, and there are grading systems to describe these changes. For the first time, the authors attempted to address the relationship between these radiographic observations and the effects on the motion and instability of the functional spine unit. The prevalence of abnormal translational motion was significantly higher in patients with Grade IV degenerative discs and Grade 3 arthritic facet joints (p < 0.05). In patients with advanced disc degeneration and FJO, there was a lesser amount of motion in both segmental translation and angulation when compared with lower grades of degeneration, and this difference was statistically significant for angular motion (p < 0.05). Patients with advanced degenerative Grade 4 facet joint arthritis had a significantly lower percentage of abnormal angular motion compared to patients with normal facet joints (p < 0.001). The presence of LFH was strongly associated with abnormal translational and angular motion. Grade 4 interspinous ligament degeneration and the presence of paraspinal muscle fatty infiltration were both significantly associated with excessive abnormal angular motion (p < 0.05). This kinetic MR imaging analysis showed that the lumbar functional unit with more disc degeneration, FJO, and LFH had abnormal sagittal plane translation and angulation. These findings suggest that abnormal segmental motion noted on kinetic MR images is closely associated with disc degeneration, FJO, and the pathological characteristics of interspinous ligaments, ligamentum flavum, and paraspinal muscles. Kinetic MR imaging in patients with mechanical back pain may prove a valuable source of information about the stability of the functional spine unit by measuring abnormal segmental motion and grading of radiographic parameters simultaneously.

The Significance of Increased Fluid Signal on Magnetic Resonance Imaging in Lumbar Facets in Relationship to Degenerative Spondylolisthesis

Retrospective radiographic review of consecutive patients with universally applied standard. To define MRI findings at the facet joints that may suggest abnormal sagittal plane translation seen on standing lateral flexion-extension (SLFE) radiographs. MRI findings, including facet joint orientation, facet joint osteoarthritis, and the presence of synovial cysts, have all been linked with degenerative spondylolisthesis (DS). MRI can also detect facet joint effusion; however, there has not been a study specifically addressing the association of facet fluid signal to degenerative spondylolisthesis (DS). MRI and SLFE films of all patients seen at a single institution for an orthopedic spine consultation over a 2-year period were analyzed. The presence of facet effusions, synovial cysts, increased intensity within the interspinous ligament, degenerative changes at the facets, and anterior sagittal plane translation were all recorded. The data were analyzed to determine if there was a significant association between the presence of DS and the following: facet effusion, degenerative changes of the facets, synovial cysts, increased signal in the interspinous ligament, age, and gender. There were 139 patients without DS at (NegDS) and 54 with DS (PosDS) on SLFE films at L4-L5 (n = 193). PosDS patients were more likely to be older (P < 0.0001), female (P = 0.0042), have synovial cysts (P < 0.0001), have higher osteoarthritis grade (P < 0.0001), and have larger facet effusion size (P < 0.0001). For both groups, facet joint effusions were also found to be significantly larger in patients with Grade 2 or less osteoarthritis, than in patients with Grade 3 osteoarthritis. Twenty-two percent of the listheses were not detectable on supine MRI. Large (> 1.5 mm) facet effusions are highly predictive of degenerative spondylolisthesis at L4-L5 in the absence of measurable anterolisthesis on supine MRI. A clinically measurable facet effusion (> or = 1 mm) suggests the need for SLFE films to diagnose degenerative spondylolisthesis that can be missed with supine positioning on MRI.

Evaluation of Spinal Kinematics Following Lumbar Total Disc Replacement and Circumferential Fusion Using In Vivo Fluoroscopy

In vivo fluoroscopic analysis of lumbar spinal motion with total disc replacement (TDR), fusions, and controls. Compare and contrast lumbar spinal motion profiles in TDR, circumferential fusion, and controls. TDR has been shown to preserve motion and possibly prevent abnormal loading at the adjacent level. Although in vitro cadaveric studies have provided invaluable information, they are not capable of assessing the physiologic motion profile of the lumbar spine that is initiated and stabilized by in vivo trunk muscular contractions. Cross-sectional evaluation using high-frequency low-dose pulsated video fluoroscopy to evaluate lumbar spinal motion in subjects who underwent TDR (n = 8), circumferential fusion (n = 5), and controls (n = 4). Angulation and translation were recorded at 20 time points during the extension-flexion arc. Motion gradients, or slopes of the motion curves, were generated to allow for comparison of lumbar spinal motion profiles. Circumferential fusions exhibited significantly steeper motion gradients at the proximal adjacent level compared with TDR during flexion. TDR had more physiologic motion profiles at the proximal adjacent level than fusions during flexion and extension. At operative levels L4/5 and L5/S1, TDR and controls exhibited similar motion profiles in flexion, while fusions exhibited significantly less motion. In extension, however, TDR had a steeper slope than controls at the L4/5 operative level. Between L3 and S1, the total range of motion accounted for by the L4/5 proximal adjacent level was 59% in 1-level fusions, 38% in 1-level TDR, and 29% in controls. While no control or TDR subjects underwent sagittal plane translation >3 mm during flexion-extension, 80% of fusions did (average 3.7 mm), most notably during the latter phase of extension. TDR produces physiologic lumbar spinal motion profiles in flexion and extension at the operative and proximal adjacent levels. Fusions, however, produced steeper motion gradients at the proximal adjacent level, while undergoing significantly greater sagittal plane translation during flexion-extension.

Neurological and functional outcome after unstable cervicothoracic junction injury treated by posterior reduction and synthesis

Background context Unstable lesions of the cervicothoracic junction present a severe clinical problem for diagnosis, treatment, and prognosis. Purpose The objective of the present study was to evaluate the neurological and functional outcomes following surgical treatments which combine in all cases posterior reduction and stabilization. Study design Retrospective clinical and radiological study. Patient samples Between September 1996 and September 2003, 30 patients underwent surgery for unstable fracture at the cervicothoracic junction. This group included 23 patients who sustained a motor vehicle accident, 5 who had fallen from a height, 1 case of ballistic trauma, and 1 person injured by diving in shallow water. There were 22 male and 8 female patients aged between 18 and 80, with an average age of 49. In 18 cases the lesion level was vertebra C7, in 5 cases vertebra T1, in 2 cases vertebra T2, and in 5 cases vertebra T3. Neurologically, on initial clinical examination 16 patients were classified Frankel A, 6 Frankel B, 2 Frankel C, and 6 Frankel D. Surgically, all the patients underwent posterior reduction and synthesis. Posterior stabilization was performed using rods and screws 3 times, plate-screw fixation 25 times, and rods and screws at the thoracic level linked to plate-screw at the cervical level 2 times. Spinal cord compression of more than two levels was associated with 25 cases. In these 25 cases, spinal cord decompression was associated with reduction and stabilization. Outcome measures Clinical outcome using neurological scale of Frankel, radiological outcomes using computed tomographic (CT) scans and plain X-ray evaluations. Methods Follow-up periods ranged from 11 to 48 months, with an average of 18 months. Seven patients died as a result of cardiopulmonary insufficiency within 4 months postoperative. Twenty-eight CT scans with sagittal and frontal slides were examined to evaluate postoperative reduction and to control screw placement. Results The observed reductions were satisfactory in 27 cases. In one case, reduction was satisfactory in the sagittal plane but lateral translation persisted in the frontal plane. Two mechanical failures with delayed mobilization of implants occurred. Bony fusion was recorded in all cases on CT scan evaluation. Complete or partial neurological recovery was observed in only 10 of 14 patients. The initial neurological status of these 14 patients was Frankel B, C, or D. Conclusion The surgical procedure was chosen according to the particularity of the anatomical region and the possibility of associated medullar decompression. Insertion of pedicle screws in the upper thoracic portion in T1, T2, and T3 requires a careful technique and knowledge of the posterior projection points of the pedicles and their orientation in space. The high rate of fusion observed in these patients justified posterior reduction and stabilization. The high death rate and the low rate of neurological recovery in this group of patients emphasizes the severe prognosis of unstable injuries of the cervicothoracic junction. Considering the few mechanical failures observed at the last examination, the choice of the posterior approach was appropriate as the one stage procedure. Plate synthesis is preferable in fractures that do not require extension of synthesis beyond T2, whereas screws and rods systems are more appropriate for superior thoracic injuries. Despite early diagnosis and surgical treatment, the presence of neurological or pulmonary lesions resulted in increased mortality of the operated patients.

Measurement of glenohumeral joint laxity using the KT-2000 knee ligament arthrometer: Reliability analysis

Objective To establish reliability of the KT-2000 knee ligament arthrometer (MEDmetric Corporation, San Diego, CA, USA) in measuring glenohumeral (GH) joint laxity. Design and Setting Subjects reported on two occasions to the Athletic Training/Sports Medicine Research Laboratory for measurement of GH translation. A two-way mixed effect model was employed to establish reliability of the KT-2000. Participants Forty-six subjects (19 male, 27 female, age=22.4±3.5 yr) with no previous history of dominant shoulder pathology. Main outcome measures Participants were instructed to relax while an anteriorly directed pulling force of increasing magnitude (67, 89, and 134 N) was applied to the GH joint using the KT-2000 knee ligament arthrometer. Translation measurements were recorded for three trials at each of three load levels. This procedure was followed for each subject on 2 separate days. Results Sagittal plane translation measurements varied from 7 to 18 mm at 67 N, 11 to 25 mm at 89 N, and 14 to 36 mm at 134 N. The intraclass correlation coefficients involving the translation measurements were 0.89, 0.88, and 0.91, respectively. Conclusions These results indicate the KT-2000 used as described is a reliable method for measuring GH joint laxity. Although our findings are promising, we stress the importance of additional validation of this technique for measuring GH joint laxity.

Comparing precision of distortion-compensated and stereophotogrammetric Roentgen analysis when monitoring fusion in the cervical spine

Two methods to measure sagittal plane segmental motion in the cervical spine are compared. Translational and rotational motion was measured in nine cervical motion segments of nine patients by distortion-compensated (DCRA) as well as by stereophotogrammetric Roentgen analysis (RSA). To compare measurement precision of the new DCRA protocol with the established RSA technique under realistic clinical conditions and to discuss advantages and disadvantages of both methods in clinical studies. RSA constitutes the most precise method available to assess segmental motion or to monitor fusion in the cervical spine. Due to the invasive nature of the procedure there is an interest in alternative, non-invasive protocols, based on conventional, lateral radiographic views. In nine patients, segmental motion of nine cervical segments with spinal surgery and fusion had previously been assessed from stereo views by RSA. From the archive radiographs, sagittal plane segmental motion was re-assessed by DCRA. Results for sagittal plane translational and rotational motion obtained by both methods are compared. With respect to RSA, sagittal plane rotation was determined by DCRA with an error of 2.4 degrees and a mean difference not significantly different from zero. Sagittal plane translation was determined by DCRA with an error of less than 0.78 mm and a mean difference not significantly different from zero. As two methods are compared, these errors represent the combined (propagated) errors of RSA and DCRA. Averaged over the cohort investigated, measurement of sagittal plane segmental motion exhibited no significant difference between DCRA and RSA.

Theoretical Accuracy of Model-Based Shape Matching for Measuring Natural Knee Kinematics with Single-Plane Fluoroscopy

Quantification of knee motion under dynamic, in vivo loaded conditions is necessary to understand how knee kinematics influence joint injury, disease, and rehabilitation. Though recent studies have measured three-dimensional knee kinematics by matching geometric bone models to single-plane fluoroscopic images, factors limiting the accuracy of this approach have not been thoroughly investigated. This study used a three-step computational approach to evaluate theoretical accuracy limitations due to the shape matching process alone. First, cortical bone models of the femur tibia/fibula, and patella were created from CT data. Next, synthetic (i.e., computer generated) fluoroscopic images were created by ray tracing the bone models in known poses. Finally, an automated matching algorithm utilizing edge detection methods was developed to align flat-shaded bone models to the synthetic images. Accuracy of the recovered pose parameters was assessed in terms of measurement bias and precision. Under these ideal conditions where other sources of error were eliminated, tibiofemoral poses were within 2 mm for sagittal plane translations and 1.5 deg for all rotations while patellofemoral poses were within 2 mm and 3 deg. However, statistically significant bias was found in most relative pose parameters. Bias disappeared and precision improved by a factor of two when the synthetic images were regenerated using flat shading (i.e., sharp bone edges) instead of ray tracing (i.e., attenuated bone edges). Analysis of absolute pose parameter errors revealed that the automated matching algorithm systematically pushed the flat-shaded bone models too far into the image plane to match the attenuated edges of the synthetic ray-traced images. These results suggest that biased edge detection is the primary factor limiting the theoretical accuracy of this single-plane shape matching procedure.

Intervertebral Motion Between Flexion and Extension in Asymptomatic Individuals

Measure and analyze variation in intervertebral motion in asymptomatic subjects. Gain further insight into intervertebral motion during flexion and extension in asymptomatic individuals, identify factors that contribute to variation in motion, and establish a quantitative database using a clinically practical imaging tool. Several authors have reported on normal values for intervertebral motion during flexion and extension of the cervical spine. However, the sources of the wide variations in intervertebral motion are poorly understood. Fluoroscopic images of the cervical spine in maximum flexion and extension were analyzed for 140 asymptomatic volunteers using a validated and clinically applicable image analysis system. Several independent variables were analyzed for their contribution to variation in motion. The dependent variables studied included sagittal plane rotation and translation, and displacements between vertebrae measured at the anterior and posterior aspects of each motion segment. There was considerable variation in measured intervertebral motion. Intervertebral level and total gross rotation between C2 and C6 significantly affected all measures of intervertebral motion. The intervertebral motion measures were all interrelated. After adjusting for differences in gross motion between C2 and C6, intervertebral levels and the three displacement measures could be used to explain almost 90% of the variation in sagittal plane intervertebral rotations. In addition, the data suggest that currently accepted clinical guidelines for shear should be raised at all levels except C6-C7. A database describing intervertebral motion in asymptomatic subjects representing both sexes and a wide age range was established that should aid in interpreting intervertebral motion in patients. Evaluating various aspects of intervertebral motion may improve the clinical efficacy of radiographic flexion-extension studies of the cervical spine.

Sagittal Plane Translation during Level Walking in Poor-Functioning and Well-Functioning Patients with Anterior Cruciate Ligament Deficiency

Background Some patients with anterior cruciate ligament deficiency can function well and participate in high-level sports, whereas others have functional limitations even during activities of daily living. Hypothesis Patients who function well after an anterior cruciate ligament injury can stabilize the knee joint during gait by an anterior positioning of the tibia. Study Design Controlled laboratory study. Methods Sagittal tibial translation was registered with the CA-4000 electrogoniometer, during the Lachman test and walking, in 20 patients with a unilateral anterior cruciate ligament injury. Eleven patients functioned well (Lysholm score [.greaterequal]84), and 9 patients had poor knee function (Lysholm score <84). Results During gait, the well-functioning group had 24% greater anterior translation in the injured leg compared to the noninjured leg. In the poor-functioning group, the anterior translation in the injured leg was 16% smaller compared to the noninjured leg (P = .0003). Tibial translation during the Lachman test was similar in the injured leg in the 2 groups. Conclusion Patients who function well position their tibiae near the anterior border of the joint play. This position may encourage functional stability. Clinical Relevance Rehabilitation that emphasizes training to stabilize the tibia in an anterior position may improve functional stability of the anterior cruciate ligament-deficient knee.

A Comparison of Injury Criteria Used in Evaluating Seats for Whiplash Protection

A protocol has been proposed for testing seats for whiplash protection, however injury criteria have not yet been chosen. Assuming that whiplash symptoms arise from non-physiological motions of vertebral segments, we determined the ability of proposed criteria to predict peak individual vertebral displacements. Twenty-eight volunteers were subjected to rear impacts while seated in a car seat with head restraint, mounted onto a sled. Accelerometers were used to record head and torso accelerations. The volunteer data was used as a basis for testing post-mortem human specimens (PMHS). The seat was replaced by a platform onto which was mounted each of 11 cervico-thoracic spines. An instrumented headform was mounted to the upper end of the spine. The head restraint, head-to-restraint geometry, sled, and impact pulse remained the same. Head and T1 accelerations were measured and individual vertebral sagittal (XZ) plane rotations and translations were obtained from high speed video. Proposed injury criteria (NIC, Nkm, Nte, Nd) were tested for their ability to predict average, total, and peak intervertebral displacements. PMHS specimens had chest and head X (horizontal) and Z (vertical) linear accelerations similar to volunteers whose heads hit the head restraint. The best predictors were: Nd shear and peak intervertebral posterior translation (r2 = 0.80), Nd extension and peak extension angle (r2 = 0.70), and Nd distraction and peak distraction (r2 = 0.51). Therefore consideration should be given to a displacement based injury criteria such as Nd in assessment of whiplash protection devices.

Sagittal plane rotational and translational motion of lumbar segments with decreascd intervertebral disc height

Employing a precise measurement protocol, it was investigated whether decreased height of lumbar discs is related to an increase of sagittal plane segmental motion or to a displacement of the cranial vertebra into a retrolisthesis position. The height of the intervertebral discs, the dorsoventral displacement of the cranial vertebra and the range of sagittal plane rotational and transitional motion were measured for all segments of the lumbar spine from flexion-extension views of 30 patients. In each patient, at least one lumbar disc exhibited a significant height decrease. The measurement was performed using a new protocol compensating for distortion in central projection, off-centre position, axial rotation and lateral tilt of the spine. Measured data on retrolisthesis position, rotational and translational motion were compared with previously compiled age- and gender-appropriate normal data. In the cohort investigated there was no statistically significant relation between a decrease of disc height and segmental hypermobility with respect to sagittal plane rotation or translation. There was no relation between a decrease of disc height and a displacement of the adjacent cranial vertebra into a retrolisthesis position. The results challenge the often postulated relation between low disc height and segmental hypermobility ("instability") and retrolisthesis position of the cranially adjacent vertebra.

Clinicoradiologic study of cervical laminoplasty with posterolateral fusion or bone graft.

A retrospective study of cervical expansive laminoplasty for cervical myelopathy from a clinicoradiologic perspective. To clarify the correlation among sagittal curvature of the cervical spine, cervical range of motion, sagittal plane translation, spinal cord atrophy, and myelopathic symptoms in patients who have undergone laminoplasty. Laminoplasties were developed to diminish the undesirable effects of laminectomy, which include postoperative kyphotic changes and instability. However, the superiority of laminoplasty over laminectomy remains controversial. Fifty-one patients with cervical spondylotic myelopathy or ossification of the cervical posterior longitudinal ligament who underwent laminoplasty were radiologically assessed before and after surgery. The index of the sagittal curvature, intervertebral range of motion, listhesis, and the transverse area of the spinal cord at the site of maximal compression were measured to evaluate interrelations among those parameters and myelopathic symptoms. There were no patients with kyphotic curvature before surgery. The postoperative curvature tended to be less lordotic. This tendency did not adversely affect postoperative symptoms. The intervertebral range of motion was significantly decreased except at C1-C2. The final C4-C5 range of motion and the postoperative myelopathic symptoms were negatively correlated. A significant correlation was observed between the postoperative spinal cord atrophy and the final myelopathic symptoms. The decrease in the lordotic curvature index and the decrease in the intervertebral range of motion after laminoplasty did not cause neurologic deterioration. In the C4-C5 intervertebral segment with a high incidence of listhesis, the restriction of the C4-C5 range of motion improved the clinical myelopathic symptoms. The radiologic prognostic factors were the postoperative restriction of intervertebral range of motion in preoperatively unstable segments and the anatomic reversibility of spinal cord insult.

Evaluation And Treatment Of Clinical Instability Associated With Pseudarthrosis After Anterior Cervical Surgery For Ossification Of The Posterior Longitudinal Ligament

Background Between 1989 to 1993, clinical instability associated with pseudarthrosis was evaluated in 76 patients with cervical ossification of the posterior longitudinal ligament (OPLL). Average 2.5 level extended anterior diskectomy and fusion and average 3.0 level anterior corpectomy and fusion were performed without anterior plate instrumentation using iliac crest or fibular strut autografts. Methods Fusion versus pseudarthrosis resulting in clinical instability, as defined by White and Panjabi, was assessed using flexion and extension X-rays 3 and 6 months postoperatively. Radiographic instability was defined by > 3.5 mm. of sagittal plane translation (or 20%) and > 20° of sagittal plane rotation on dynamic X-rays. Two and 3 dimensional (D) computed tomography (CT) scans, also obtained 3 months postoperatively, either confirmed fusion or indicated failed bony union. The average clinical follow up period was 3 years (range, 25–52 months). Results Three months postoperatively, dynamic X-rays in 20 patients demonstrated radiographic instability consistent with pseudarthrosis, whereas 2 and 3D CT studies indicated a lack of fusion. At 6 months, flexion and extension X-rays revealed that 10 patients were fused and that another 7 were clinically stable despite persistent, irregular, linear lucencies at graft/body interfaces. Three (4%) patients with clinical instability associated with pseudarthrosis required secondary posterior wiring and fusion. Conclusion Only 4% of patients undergoing average 2.75 level anterior OPLL surgery without anterior plate instrumentation required secondary posterior wiring and fusion for clinical instability associated with pseudarthrosis.

Sagittal plane translations of the knee in anterior cruciate deficient subjects and controls.

Static anterior-posterior (AP) laxity is one of the commonly used criteria in selecting patients for cruciate ligament reconstructions, but in reality dynamic AP laxity plays a more important role. The aim of this in vivo study was to compare the sagittal translation of the knee during active and passive motion, signifying dynamic AP laxity, with static AP laxity in healthy subjects (controls) and patients with anterior cruciate ligament deficiency. The sagittal plane knee translations were recorded and compared in both knees of nine healthy subjects (Controls) and seven patients with confirmed unilateral ACL deficiency during dynamic and static situations with an electrogoniometer system. In all groups during the ascents the tibia moved anteriorly in relation to the femur, whereas during the descents it moved posteriorly. The static anterior-posterior translation was significantly smaller in the control knee than in both healthy and injured knees of the ACL deficient group (P < 0.05). The injured knee showed the same laxity (92%) as the uninjured knee during dynamic activities, but it was 46% of static laxity. Also in the injured knees, the dynamic active laxity was larger during descents than ascents (P < 0.05). The results indicate that there is also a change in mechanics of the noninjured knee following injury to the contralateral knee and that this population of patients with ACL deficiency had good control over their abnormal anterior-posterior laxity.

Precision measurement of segmental motion from flexion—extension radiographs of the lumbar spine

Objective. To measure sagittal plane motion of lumbar vertebrae from lateral radiographic views. Previously identified factors of imprecision such as distortion in central projection, off-centre position, axial rotation, and lateral tilt of the spine were compensated. Study design. This study presents a new protocol to measure sagittal plane rotational and translational motion from lateral flexion-extension radiographs of the lumbar spine. Background. Conventional methods to determine sagittal plane rotation and translation are prone to error from the distortional effects of the divergence of the radiographic beam and the measurement error inherent in constructing tangents to the contours of the vertebral body. High precision is attained by roentgen-stereophotogrammetric methods, but because of their invasive nature they can be applied only in exceptional cases. Agreement has been reached only in that measurement of sagittal plane motion from lumbar spine flexion-extension radiographs is inaccurate. Normal patterns of sagittal plane motion and the definition of what is an abnormal flexion-extension radiograph have not been settled. Method. Starting from an analysis of vertebral contours in the lateral view, geometric measures are identified which are virtually independent of distortion, axial rotation or lateral tilt. Applying a new protocol based on those geometric measures, the pattern of translational and rotational motion was determined from flexion—extension radiographs of 61 symptom-free, adult subjects. Measurement errors were quantified in a specimen experiment; a reproducibility study quantified inter- and intraobserver errors. Results. Magnitude and sign of ‘translation per degree of rotation’ determined from a cohort of 61 adult subjects were very uniform for all levels of the lumbar spine. An auxiliary study evaluating a cohort of 10 healthy subjects where flexion—extension radiographs had been taken standing and side-lying showed no dependence of the rotation/translation pattern on posture. The error study demonstrated errors in angle ranging between 0.7 and 1.6 degrees and errors in displacement ranging between 1.2% and 2.4% of vertebral depth (the largest errors occurring at the L 5 S 1 segment). Intra- and interobserver tests showed no or only negligibly small bias and an sd virtually equal to the measurement error multiplied by √2. The relation of displacement to angle observed in the normal cohort can be used in individual cases to predict translational motion depending on the rotation actually performed. A comparison of the predicted translation (determined from normal controls) and the value actually measured allows translational hypo-, normal, or hypermobility to be quantified. Examples illustrate application of the new method in cases of normal, hypo-, and hypermobility and in the case of an instrumented spine. Conclusions. The results of this study show that precision of the measurement of rotational and translational motion can be considerably enhanced by making allowance for radiographic distortional effects and by minimizing subjective influence in the measurement procedure.

Accurate measurement of three-dimensional knee replacement kinematics using single-plane fluoroscopy.

A simple extension of a previously reported object recognition technique has been used to implement a six-degree-of-freedom position/orientation estimator for the measurement of knee replacement motion from two-dimensional (2-D) fluoroscopic images. Computer modeling studies and controlled mechanical tests were performed to assess the accuracy of the technique. The results indicate that knee rotations can be measured with an accuracy of approximately one degree and that sagittal plane translations can be measured with an accuracy of approximately 0.5 mm. The measurement technique is uniquely well suited for performing dynamic kinematic measurements on individuals with knee replacements, and for performing comparative studies among subjects with different designs of knee replacements.