Biomedical subjects

John A Hipp

Publications and source records attributed to John A Hipp.

11 recordsLinked to original sources

PubMed2007

Reduction in head and intervertebral motion provided by 7 contemporary cervical orthoses in 45 individuals.

STUDY DESIGN: Biomechanical evaluation of cervical orthoses. OBJECTIVE: To provide data to help clinicians select an orthosis for immobilization of the adult cervical spine. SUMMARY OF BACKGROUND DATA: There are limited data on the effectiveness of cervical orthoses at restricting intervertebral motion, and many of the commonly used, contemporary braces have not been evaluated. Additionally, no data exist comparing the effectiveness of braces in the supine versus the upright position. New technology is available to measure intervertebral motion with greater accuracy. METHODS: Overall range of motion of the head in 3 planes as well as intervertebral motion in the sagittal plane were measured in 45 healthy adult volunteers while wearing 7 cervical orthoses. Subject-reported comfort of each brace was also recorded. RESULTS: All braces significantly reduced intervertebral motion. Effectiveness and comfort varied between braces. In general, orthoses could be grouped as cervical braces or cervicothoracic braces. The latter was consistently better at limiting motion, with some differences within these groups as well. CONCLUSION: These data will help to guide the clinician in selecting the appropriate cervical orthosis for their adult patient based on comfort, morphologic considerations, and degree of immobilization required.

Adult↗

PubMed2006

Assessment of magnetic resonance imaging in the diagnosis of lumbar spine foraminal stenosis--a surgeon's perspective.

STUDY DESIGN: A 2-part cadaveric study. OBJECTIVES: Part 1: To assess the reliability of a semiquantitative classification system for grading lumbar spine foraminal stenosis and the variability in magnetic resonance imaging (MRI) examinations carried out in different institutions. Part 2: to assess the difference between the foraminal measurements carried out on MRI images and on cadaveric specimens. SUMMARY OF BACKGROUND DATA: There are limited data to suggest that MRI examinations are sensitive or specific for the diagnosis of lumbar spine foraminal stenosis. The effect of the variability in techniques, used by different imaging centers, is not well understood. METHODS: Three fresh, frozen human lumbar spines were examined with 3 different clinical MRI systems. Eight spine surgeons used the MRI images to grade the foramina, on the basis of a previously suggested semiquantitative classification. In addition, the dimensions of all foramina were measured using software available on each of the MRI systems. The dimensions of the specimens' foramina were then measured in situ, graded, and compared with the MRI measurements. RESULTS AND CONCLUSIONS: There was poor intraobserver agreement using the semiquantitative grading system. The parameters associated with the grade of stenosis assigned to the foramen were as follows: (1) the observer doing the grading, (2) the place it was imaged, and (3) the location of the foramen. There was poor correlation between measurements of the foramina carried out on MRI and the specimens.

Aged↗

PubMed2006

Low back pain: prediction of short-term outcome of facet joint injection with bone scintigraphy.

PURPOSE: To prospectively evaluate use of bone scintigraphy with single photon emission computed tomography (SPECT) for identification of patients with low back pain who would benefit from facet joint injections. MATERIALS AND METHODS: The protocol was reviewed and approved by the institutional review board. All patients provided informed consent. Forty-seven patients (23 men and 24 women) with low back pain, who were scheduled for facet joint injections, were prospectively enrolled and randomized into groups A and B (mean ages, 43.3 and 44.2 years, respectively) with a group A-group B ratio of 2:1. Group A patients underwent bone scintigraphy with SPECT prior to injection. Group A patients with bone scans positive for facet joint abnormalities received injections at the levels where abnormalities were identified on the scan (group A1). Group A patients with negative scans (group A2) received injections at the levels that were decided as in group B. Group B patients received injections at the levels indicated by the referring physician and did not undergo bone scintigraphy. All patients completed a pain and function questionnaire before injection and at 1, 3, and 6 months afterward. The change in the American Academy of Orthopaedic Surgeons pain scores after 1, 3, and 6 months compared with baseline scores was analyzed with analysis of variance and post hoc Bonferroni multiple-comparison tests between groups. Cost analysis was performed. RESULTS: The change in the pain score at 1 month was significantly higher (P < .004) in group A1 than it was in the other two groups. In group A1, 13 of 15 patients had improvement in pain score of greater than 1 standard deviation at 1 month, whereas improvement occurred in only two of 16 patients in group A2 and five of 16 patients in group B. In patients with positive scans, the number of facets treated with injection was decreased from 60, which was the number originally indicated by the referring physician, to 27. The Medicare cost was reduced from $2191 per patient to $1865 with the use of SPECT. CONCLUSION: Bone scintigraphy with SPECT can help identify patients with low back pain who would benefit from facet joint injections.

Adult↗

PubMed2006

Predicting fracture through benign skeletal lesions with quantitative computed tomography.

BACKGROUND: There are no proven radiographic guidelines for predicting fracture risk in children and young adults with a benign skeletal lesion. An in vivo diagnostic study was conducted to determine whether a reduction in the load-carrying capacity of a bone measured with quantitative computed tomography was more accurate than current radiographic guidelines for predicting pathologic fracture in patients with a benign skeletal lesion. METHODS: Eighteen patients who presented with a fracture through a benign skeletal lesion were compared with eighteen patients who had a benign skeletal lesion that had been thought to be at increased risk for fracture on the basis of currently used radiographic criteria but had not fractured over a two-year period. Structural analysis was performed to calculate the resistance of the affected bones to compressive, bending, and torsional loads with use of serial transaxial quantitative computed tomography data obtained along the length of the bone containing the lesion and from homologous cross sections through the contralateral, normal bone. At each cross section, the ratio of the structural rigidity of the affected bone divided by that of the normal, contralateral bone was determined. The cross section with the greatest reduction in compressive, bending, and torsional rigidity was identified as that most likely to fracture. RESULTS: The mean age (and standard deviation) of the thirty-six patients was 12.5 +/- 3.6 years. Twenty lesions were located in the femur; eleven, in the tibia; three, in the humerus; one, in the ulna; and one, in the pelvis. A combination of the minimum bending and torsional rigidities calculated from the tomographic data provided optimal performance in differentiating between the fracture and non-fracture groups (100% sensitivity and 94% specificity). In contrast, plain radiographic criteria demonstrated 28% to 83% sensitivity and 6% to 78% specificity. CONCLUSIONS: The combination of bending and torsional rigidity measured noninvasively with quantitative computed tomography was more accurate (97%) for predicting pathologic fracture through benign bone lesions in children than were standard radiographic criteria (42% to 61% accuracy). We believe that this method can provide accurate objective criteria for planning treatment of benign bone lesions and monitoring treatment response.

Adolescent↗

PubMed2005

Intervertebral motion after incremental damage to the posterior structures of the cervical spine.

STUDY DESIGN: Compare intervertebral motion after incremental damage to posterior cervical structures in whole cadavers to motion in asymptomatic subjects. OBJECTIVE: Determine if damage to the posterior structures of the cervical spine can be detected by quantitative analysis of flexion-extension radiographs. SUMMARY OF BACKGROUND DATA: Simulated damage to the posterior structures of the cervical spine can change intervertebral motion, if intervertebral motion before damage is known. It is not known if intervertebral motion measured from flexion-extension radiographs can be used to detect damage to the posterior structures if motion before damage is not known. METHODS: Incremental injury to posterior ligaments and facet joints was simulated in 12 whole cadavers. Intervertebral motion was measured from flexion-extension images using validated and clinically applicable software. Measurements were compared to previously published measurements for asymptomatic subjects. RESULTS: Extensive damage could be simulated in all the cervical spines without intervertebral motion exceeding the 95% confidence limits for asymptomatic subjects. After sectioning all posterior ligaments, destroying both facet joints, and then sectioning the posterior longitudinal ligaments, intervertebral motion exceeded the 95% confidence intervals in 69% of the cadavers. Intervertebral shear decreased with incremental damage to posterior structures. CONCLUSIONS: Radiographic assessment of the cervical spine may not be sufficient to exclude even extensive damage to the posterior structures of the cervical spine.

Arthrography↗

PubMed2005

Defining pseudoarthrosis in the cervical spine with differing motion thresholds.

STUDY DESIGN: Calculate the apparent pseudarthrosis rate for anteriorly plated cervical spine fusions using different threshold levels of intervertebral rotation. OBJECTIVES: Determine whether the apparent pseudarthrosis rate depends on the amount of intervertebral rotation used to characterize a fusion as a pseudarthrosis. SUMMARY OF BACKGROUND DATA: Intervertebral motion at a spine fusion site is an important outcome measure in most spine fusion research studies. Intervertebral motion measures are used to determine if a device can be sold for use in spine fusion surgery. There is no consensus on how much motion is too much motion at a spine fusion site, and the intervertebral motion threshold that is used to define a pseudarthrosis is arbitrary. There are only limited data on the dependence of the pseudarthrosis rate on the threshold used to define a pseudarthrosis. METHODS: Intervertebral motion at the fusion site was measured from flexion extension radiographs taken 1 year after cervical spine fusion using anterior plates and allograft in 200 patients. The number of cases where intervertebral motion at the fusion site exceeded thresholds between 1 degrees and 4 degrees were calculated. RESULTS.: The apparent pseudarthrosis rate varied from 6% when the intervertebral motion threshold was 4 degrees to 44% when the intervertebral motion threshold was 1 degrees . CONCLUSIONS: The apparent pseudarthrosis rate was highly dependent on the threshold of motion used to define a pseudarthrosis.

Bone Plates↗

PubMed2004

Intervertebral motion between flexion and extension in asymptomatic individuals.

STUDY DESIGN: Measure and analyze variation in intervertebral motion in asymptomatic subjects. OBJECTIVES: 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. SUMMARY OF BACKGROUND DATA: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Adolescent↗

PubMed2004

Changes in segmental intervertebral motion adjacent to cervical arthrodesis: a prospective study.

STUDY DESIGN: Prospective, observational. OBJECTIVES: Quantify the changes in intervertebral motion adjacent to cervical arthrodesis over time. SUMMARY OF BACKGROUND DATA: One of the frequently acknowledged sequelae following anterior cervical fusion is the development of adjacent segment disease. It has been argued that a spine fusion transfers stress to adjacent levels and results in increased compensatory motion. However, there are conflicting reports as to whether this actually occurs, and most of these are in vitro or retrospective clinical studies. METHODS: Patients undergoing anterior cervical discectomy and fusion underwent a preoperative dynamic fluoroscopic study, followed by imaging at regular intervals after surgery. Imaging data were analyzed by a validated software system. Relative motion between adjacent vertebrae was then calculated, and changes in motion cephalad to the fusion followed over time. RESULTS: Twenty-one patients were analyzed. Mean follow-up was 13 months (10-22 months). Intervertebral motion adjacent to the fusion changed by more than 4 degrees in 4 of the 21 patients. However, on average, there was no difference between preoperative and postoperative motion for shear, flexion-extension, or vertical displacement at the anterior or posterior disc space. CONCLUSIONS: Although there was some individual variation, at a mean of 13 months following surgery, there was no significant change in the average junctional intervertebral motion. If fusion is going to affect adjacent motion, it appears that this does not consistently occur in the first 1 to 2 years following surgery. Additionally, there was no observable relationship between motion and development of degenerative changes during this time.

Cervical Vertebrae↗

PubMed2004

Failure of trabecular bone with simulated lytic defects can be predicted non-invasively by structural analysis.

Pathologic fracture is a significant risk for patients afflicted with metastatic or benign skeletal tumors. The quandary for physicians who treat these patients is that after making the diagnosis they must try to predict the load bearing capacity of the involved bone and the fracture risk from images seen in radiological examinations. Since bone fails at a relatively constant strain independent of density we demonstrate that using a mechanics of materials approach that the cross-sectional structural properties of the bone most affected by the lytic defect governs the load bearing capacity of the entire bone. Homogeneous cylindrical cores of trabecular bone were harvested from the vertebral bodies of whale spines, and prepared with circular or slotted through-hole defects of varying sizes to simulate lytic skeletal tumors. Each specimen was imaged using quantitative computed tomography (CT), dual energy X-ray absorptiometry (DXA), and magnetic resonance imaging (MRI) to obtain data for calculating cross-sectional structural properties: axial, flexural, and torsional rigidity. The specimens were then divided into groups uniformly distributed with respect to defect sizes and shapes, and subjected to uniaxial tension, four-point bending or torsion until failure. A strong positive relationship was found between measured tensile yield loads, bending, and torsional yield moments vs. axial, flexural and torsional structural rigidities respectively, calculated from QCT, DXA, and MRI data [QCT: tension r2=0.951 , bending r2=0.909, torsion r2=0.914; DXA: tension r2=0.926, bending r2=0.841, torsion r2=0.916 (p<0.001); MRI: tension r2=0.916; bending r2=0.856, torsion r2=0.852]. For cylindrical cores of trabecular bone with simulated lytic defects, the load bearing capacity of the entire core was directly proportional to the axial, bending, or torsional rigidity at the weakest cross-section through the core containing the defect. Therefore structural rigidity analysis of cross-sectional geometric data measured non-invasively by QCT, DXA, and MRI of bones containing lytic defects may be used to predict the load bearing capacity of the involved bone and the relative fracture risk in vivo.

Biomechanical Phenomena↗

PubMed2003

Load sharing and kinematics of threaded cages for lumbar interbody fusion.

The load-sharing characteristics of threaded interbody cages before and after cyclic loading are poorly understood. In the current study, lumbar interbody cages were filled with epoxy, sectioned longitudinally, and pressure sensors were placed between halves of the cages to measure the distribution of loads between and within the cages. Human lumbar spine segments were instrumented anteriorly with bilateral cages and subjected to cyclic compression loads combined with flexion and extension moments. Sagittal plane motion between vertebrae on either side of the cages also was measured during application of cyclic compression and flexion loads. A small but statistically significant asymmetry was found in the distribution of load between the left and right cages, and the extent of asymmetry varied during compression and flexion loading. With ligament tension only, 66% of the load was supported by the posterior regions of the cages, whereas during peaks in the combined compression and flexion loading, only 33% of the load was supported by the posterior regions. The cages reduced intervertebral motion 78% during forward flexion, whereas extension resulted in a 100% increase in motion. Surgeons should recognize that bilateral cages may not share loads equally, and the results of this study suggest that early extension should be restricted after the placement of anterior lumbar interbody cages.

Adult↗

PubMedDate not supplied

Coracoclavicular ligament reconstruction using the lateral half of the conjoined tendon.

To preserve the coracoacromial (CA) ligament, we have used the lateral half of the conjoined tendon as an autograft source to replace the coracoclavicular (CC) ligament. The purpose of this study is to compare the ultimate tensile strength of the lateral 12 mm of the conjoined tendon with that of the CA ligament and the CC ligament. Eight paired cadaveric male shoulders were tested to tensile failure with a custom pneumatic testing apparatus. Although the lateral 12 mm of the conjoined tendon was stronger than the CA ligament, this difference was not statistically significant (P =.37). However, the intact CC ligament (621 +/- 209 N) was approximately 250% stronger than either the lateral 12 mm of the conjoined tendon (265 +/- 79 N, P <.001) or the CA ligament (246 +/- 69 N, P <.001). We believe that the lateral half of the conjoined tendon is a viable alternative autograft source for reconstruction of the CC ligament in cases of symptomatic acromioclavicular joint dislocation. Though not as strong as the native CC ligaments, the conjoined tendon is slightly stronger than the commonly used CA ligament.

Acromioclavicular Joint↗