Biomedical subjects

D E Krebs

Publications and source records attributed to D E Krebs.

At least 19 recordsLinked to original sources

PubMed1999

Cartilage degeneration in relation to repetitive pressure: case study of a unilateral hip hemiarthroplasty patient.

In vivo acetabular contact pressures were measured over 32 months in an elderly man with a pressure instrumented hemiarthroplasty. After death, left (hemiarthroplasty) and right (control) acetabula were explanted. Cartilage thickness and degeneration were quantified from magnetic resonance imaging and histological analysis. Highest repetitive in vivo contact pressures during gait (4.5 to 6.5 MPa) were measured in the superior dome of the acetabulum and decreased at a rate of approximately 1 MPa per year after implant (R2 = 0.48, P < .001). Contact pressure magnitudes measured during gait correlated positively with regional histology score (R2 = 0.34, P < .0001) and negatively with cartilage thickness (R2 = 0.35, P < .0001). Although histology scores were typical of early osteoarthritis (histological grade of 4-6), there were no significant differences in overall histology score for the left and right acetabula (P = .23). We conclude that acetabular cartilage degeneration was explained, in part, by repetitive stress, but the degeneration did not appear to be mediated solely by articulation with the metallic endoprosthesis.

Aged↗

PubMed1998

Moderate exercise improves gait stability in disabled elders.

BACKGROUND: Decreased muscle strength impedes elders' functional performance in daily activities such as gait. The mechanisms whereby increased strength improves gait are unknown. METHODS: A prospective, blinded, randomized trial of moderate intensity strength exercise was conducted and its impact was measured on functional mobility during gait in 132 functionally limited elders. Lower extremity strength was measured, including hip abductor, hip extensor, and knee extensor strength. Of the 132 subjects, 120 subjects (mean age, 75.1 yrs) completed 6 months of elastic band resistance training at least 3 times a week or served as no-exercise controls. RESULTS: Subjects increased their lower extremity strength in the exercise and control groups, by 17.6% and 7.3% (p < .01), respectively. Gait stability improved significantly more in the exercise group than in the control group (p < .05). Increases in forward gait velocity were not significantly different between groups. Peak mediolateral velocity and base of support improved in the exercise group, but not in the control group. Change in lower extremity strength correlated significantly but weakly with many of the gait variables. CONCLUSIONS: Gait stability, especially mediolateral steadiness, improved in the exercise group but not in the control group. These results show that even moderate strength gains benefit gait performance in elders and thus provide a sound basis for encouraging low-intensity strength training for elders with functional limitations.

Activities of Daily Living↗

PubMed1998

Cartilage and subchondral bone thickness distribution with MR imaging.

RATIONALE AND OBJECTIVES: The authors mapped articular cartilage (AC) and subchondral bone (SB) thicknesses in human acetabula in vitro by using magnetic resonance (MR) imaging and validated AC measurements by using light microscopy. MATERIALS AND METHODS: Left and right acetabula from a deceased patient who had undergone left hemiarthroplasty were imaged with fat-suppressed spoiled gradient-recalled acquisition in the steady state (repetition time = 55 msec, echo time = 15 msec, flip angle = 50 degrees, matrix = 256 x 256, field of view = 8 cm). AC and SB thickness maps were generated from image data by using analytic geometry, which enabled correction for thickness overestimation due to oblique sectioning. Cartilage bone plugs were extracted from the acetabula, and light microscopy was used to validate the thickness measurements obtained with MR imaging. RESULTS: Standard errors between thickness measurements obtained with MR imaging and light microscopy were 0.37 and 0.33 mm for the left and right AC, respectively, which is consistent with the voxel resolution of the MR imaging sequence (0.31 x 0.31 x 0.8 mm). SB thickness of the cartilage plugs could not be reliably measured with light microscopy and, therefore, could not be validated. Contour maps showed that SB thickness gradients were rapid and focal compared with the rather smooth gradients in AC thickness; however, thicker AC was accompanied by thicker SB for left (r2 = .261, P = .0001) and right (r2 = .308, P = .0001) acetabula. Average thickness differences between left and right acetabular AC and SB were 0.13 mm (P = .015) and 0.11 mm (P = .026), respectively. Although it was the operated hip that had thicker articular tissues, the differences were within the pixel resolution (< 0.31 mm). CONCLUSION: AC and SB thickness distribution can be accurately determined by combining noninvasive MR imaging and analytic geometry, which may also provide a means for quantitative, longitudinal assessment of focal AC defects.

Acetabulum↗

PubMed1998

A general computing method for spatial cartilage thickness from co-planar MRI.

Techniques for assessing cartilage thickness from planar magnetic resonance (MR) images have traditionally accounted for surface curvature only in the image plane. Many joints, such as the knee and hip, have significant curvature normal (transverse) to the image plane which results in overestimation of in-plane cartilage thickness measurements. We developed a generalized computing method for calculating spatial thickness distribution of joint cartilage from co-planar MR images which accounts for transverse surface curvature. We applied the technique using fat-suppressed SPGR (spoiled gradient recalled in the steady-state) MR images of two human acetabulae and compared the results with a previously validated spherical model of the acetabulum which also accounts for transverse curvature of the cartilage surface. The agreement between the generalized model and validated spherical model was very good for both acetabular specimens (correlation: r = 0.998, p < 0.001; differences: p > 0.63). We conclude that the generalized method is acceptable for computing spatial cartilage thickness distribution of joints with complex geometries, such as the knee.

Acetabulum↗

PubMed1998

Dynamic stability in elders: momentum control in locomotor ADL.

BACKGROUND: Momentum must be controlled in stable locomotor activities, including sit-to-stand and gait. The relationship of momentum control and balance maintenance in elders or in a balance-impaired population has not been studied. Although decreased locomotor speed has long been reported among elders, the literature is lacunar concerning the mechanical mechanisms underlying this slowing. The purpose of this study was to describe the whole body and upper body linear and angular momentum for healthy elders during sit-to-stand and gait and compare them to a group of balance-impaired elders who have bilateral vestibular hypofunction (BVH). METHODS: Ten elders with BVH were matched to 10 healthy elders aged 67-90. Linear and angular momentum were calculated for sit-to-stand and for free speed and paced gait. Means and 95% confidence intervals were used to compare groups. RESULTS: Elders with BVH used significantly less linear and angular momentum to rise from a chair than healthy elders and showed excessive lateral momentum during gait, despite walking at a slower velocity. CONCLUSIONS: Healthy elders limit momentum generation by decreasing gait velocity, apparently because they lack sufficient strength or balance control to safely dissipate the momentum that a faster, less controlled gait engenders. Elders with BVH further limit momentum in locomotor activities to decrease their risk of falling, but are apparently unable to control lateral momentum during gait. Excessive lateral momentum in gait among balance-impaired elders leads to loss of balance, a frequent occurrence in this patient population.

Activities of Daily Living↗

PubMed1998

Relationship between standing posture and stability.

BACKGROUND AND PURPOSE: This study determined whether persons with stability impairments have postural aberrations. We investigated whole-body posture and its relationship to center-of-gravity (COG) stability. SUBJECTS: Data from 27 subjects with vestibular hypofunction and 26 subjects without vestibular impairment were analyzed. METHOD: An optoelectronic full-body system measured kinematics. Force plates measured ground reaction forces while subjects stood with their feet 30 cm apart and eyes open and with their feet together and eyes closed. RESULTS: The subjects with vestibular hypofunction demonstrated less stability than the subjects without impairment, but there were no postural differences. Subjects with vestibular hypofunction had more weight on the left lower extremity during standing with feet apart. In all subjects in both groups, during standing with feet apart, the COG was anterior to the ankle, knee, back, and shoulder and posterior to the hip and neck. Subjects had an anterior pelvic tilt, extended trunk and head, right laterally flexed trunk and pelvis, and flexed knees. With their feet together, subjects increased their anterior pelvic tilt; trunk, head, and knee flexion; and anterior COG position. CONCLUSION AND DISCUSSION: Posture and stability had a low correlation. Subjects with bilateral vestibular hypofunction did not demonstrate a forward head or backward trunk lean, as has been reported anecdotally. Changing from standing with feet apart to feet together increased whole-body movement patterns to control standing stability.

Adult↗

PubMed1998

Hip biomechanics during gait.

The literature is devoid of complete descriptions of hip biomechanics during gait. We present for the first time simultaneously acquired in vivo acetabular contact pressures, ground reaction forces, kinematics, hip torques, and electromyographic (EMG) activity during gait with and without a cane from an 85-year-old male with a left instrumented femoral head prosthesis. Highest acetabular contact pressures occurred in all gait trials at the posterosuperior acetabulum, just prior to peak EMG, adductor torque, and ground reaction force during late stance phase. Contralateral cane use reduced both peak acetabular contact pressure and gluteus medius EMG but not adductor torque or ground reaction force. These data identify a small area of high acetabular and femoral head stress that could occur during each of a human's millions of gait cycles annually and indicate that muscle activity, rather than solely body weight, drives hip loading, Clinicians who desire to limit hip loads should reduce both hip muscle contraction and weight bearing in late stance.

Aged↗

PubMed1998

Posturography changes do not predict functional performance changes.

OBJECTIVE: Essentially no data exist to assess the utility of posturography, a frequently used test of standing balance in measuring change. The authors examined 1) how changes in posturography relate to functional balance changes as measured in the clinic and gait laboratory and 2) posturography's role and value in assessing patients with vestibular dysfunction. STUDY DESIGN: A correlational research design was used. SETTING: This study was conducted at a large, urban U.S. tertiary referral hospital. PATIENTS: Thirty-seven subjects (22 females and 15 males) with peripheral vestibular hypofunction and stable symptoms participated. Patients with central nervous system pathology were excluded from this study. INTERVENTIONS AND MAIN OUTCOME MEASURES: Subjects were tested before and after 6-8 weeks of vestibular rehabilitation with Equitest posturography sensory organization test (SOT), with timed quasistatic bilateral standing in tandem, on foam, and one leg; and with functional balance measures including gait velocity, a modified Timed Up & Go, gait with head rotation, gait with eyes closed, and tandem gait. RESULTS: Changes in SOT were not predictive of, nor often even directly correlated with, changes in quasistatic standing or functional performance. CONCLUSIONS: These data suggest that posturography SOT alone is not a useful tool to assess balance and functional changes in patients with vestibular hypofunction.

Female↗

PubMed1997

In vivo hip pressures during cane and load-carrying gait.

OBJECTIVE: To test the hypotheses that carrying a load reduces hip contact pressure ipsilateral to the load and that using a cane when carrying a load further reduces hip contact pressure. METHODS: A Moore-type endoprosthesis with 13 femoral-head pressure transducers was implanted in a human subject following a Garden III fracture. Hip contact pressures were measured during unaided, cane-aided, and load-carrying gait over two years. RESULTS: Relative to unloaded gait, contact pressures increased significantly when ipsilateral to the carried load. Using a contralateral cane when carrying the load reduced ipsilateral posterior-superior contact pressure; however, the hip contralateral to the load experienced significantly higher than normal pressures. CONCLUSIONS: Ipsilaterally carried loads may not always provide stress protection of the arthritic hip. Using a cane opposite to the load may aid in restoring normal pressures to the ipsilateral hip, but may expose the contralateral hip to a significant stress burden.

Aged↗

PubMed1997

Acetabular pressures during hip arthritis exercises.

OBJECTIVE: To examine in vivo maximum acetabular contact pressures during gait and hip arthritis exercises recommended by clinicians and the Arthritis Foundation. METHODS: Acetabular contact pressure data were collected for 2.5 years, at 3-4-month intervals, from an instrumented endoprosthesis implanted in an 84-year-old male who had sustained a left hip fracture. Maximum pressure data were compared for each activity. RESULTS: Mean pressures ranged from 9.0 +/- 2.3 megapascals (MPa) during maximum isometric hip abduction, 9.0 +/- 0.8 MPa during standing right hip abduction, and 8.9 +/- 2.8 MPa during standing left hip abduction to 1.2 +/- 0.3 MPa during quiet standing. Free-speed gait pressure averaged 5.6 +/- 0.9 MPa. The maximum mean pressure during side-lying hip abduction and straight leg raise at 30 degrees/second were less than the same activities at 60 degrees/second. CONCLUSIONS: These in vivo hip pressure measurements challenge traditional protocols for patients with hip osteoarthritis and provide quantitative data as a framework for designing exercise programs. Maximum isometric hip exercise and standing exercise generated much higher hip pressures, and are therefore probably more stressful to acetabular cartilage, than gait or stationary cycling. Clinicians must consider exercise velocity because of its direct correlation with hip contact pressure. Walking generated lower pressure than most activities studied and, given its other benefits, is therefore probably beneficial for patients with hip osteoarthritis.

Acetabulum↗

PubMed1997

Rehabilitation of balance in two patients with cerebellar dysfunction.

The treatment of two patients with cerebellar dysfunction is described. One patient was a 36-year-old woman with a 7-month history of dizziness and unsteadiness following surgical resection of a recurrent pilocystic astrocytoma located in the cerebellar vermis. The other patient was a 48-year-old man with cerebrotendinous xanthomatosis (CTX) and diffuse cerebellar atrophy, and a 10-year history of progressive gait and balance difficulties. Each patient was treated with a 6-week course of physical therapy that emphasized the practice of activities that challenged stability. The patient with the cerebellar tumor resection also performed eye-head coordination exercises. Each patient had weekly therapy and performed selected balance retraining exercises on a daily basis at home. Measurements taken before and after treatment for each patient included self-perception of symptoms, clinical balance tests, and stability during selected standing and gait activities; for the patient with the cerebellar tumor resection, vestibular function tests and posturography were also performed. Both patients reported improvements in symptoms and demonstrated similar improvements on several kinematic indicators of stability during gait. The patient with the cerebellar tumor resection improved on posturography following treatment, whereas the patient with CTX improved on clinical balance tests. This case report describes two individualized treatment programs and documents functional improvements in two patients with different etiologies, durations, and clinical presentations of cerebellar dysfunction. The outcomes suggest that patients with cerebellar lesions, acute or chronic, may be able to learn to improve their postural stability.

Adult↗

PubMed1997

Biomechanical analysis of failed sit-to-stand.

Background sit-to-stand (STS) failure is a transient loss of balance that can engender falls among elders. The purpose of this paper is to describe the mechanisms whereby failed STS differs from successful STS. The authors compared successful STS from 11 normal elders to 20 "sitback" and 20 "step" type failed STS's in 13 subjects. Kinematic and kinetic data were incorporated into our 11-segment whole body model to estimate the net joint forces and torques and body segment momenta. Significant between group differences in the magnitude and timing of momentum generation and dissipation, knee extensor torques and the magnitude of the vertical ground reaction force were identified. Both types of failed sit-to-stand maneuvers are less energetic than successful rises. STS failures might result from either weakness or balance control and coordination impairment, or both, resulting in an insufficiently energetic effort. Further research is required to differentiate between these two possible sources of impairment. Determining the root cause of functional limitations is necessary to develop effective interventions.

Aged↗

PubMed1997

Hip stress during lifting with bent and straight knees.

"Correct" body mechanics during lifting are believed to protect the back by employing knee and hip flexion while keeping the back straight. Lower limb joint stress, however, has been largely ignored. We compared hip cartilage contact stress during "leg lifting" with "back lifting" (lifting with bent or straight knees, respectively) in a subject fitted with a pressure instrumented hip endoprosthesis. Synchronized pressure data and whole-body kinematics and kinetics were collected simultaneously while the subject lifted an 11.8 kg mass from the floor to waist level. The highest pressure, 13.7 MPa, occurred during leg lifting at the antero-lateral femoral head transducers opposed at maximum hip flexion by the postero-superior quadrant of acetabular cartilage. In back lifting, the highest pressure, 11.5 MPa occurred in the supero-lateral aspect of the head, which during hip extension was opposed by the posterior quadrant of the acetabulum. Maximum pressures and hip torques occurred simultaneously with peak hip flexion, during the initial lifting of the burden from the floor. Acetabular contact pressures during leg lifting were on average twice as great as during back lifting, and both techniques generate much greater hip stress than gait (typically 4-6 MPa). Degenerative changes in the articular surface of the acetabulum occur primarily on the postero-superior aspect, corresponding to the locations of peak contact pressures in the present in vivo data. Thus leg lifting puts more stress on the postero-superior region, and probably contributes to more hip cartilage degeneration, than does back lifting. We conclude that although leg lifting may mechanically protect the back, it substantially increases hip cartilage stress.

Aged↗

PubMed1996

Delayed complications thirty-six years after hemispherectomy: a case report.

PURPOSE: To describe a late complication of hemispherectomy in a patient in whom symptoms of hydrocephalus developed 36 years after her left-sided hemispherectomy, the longest delay on record. METHODS: Hemispherectomy has been successfully used in the treatment of intractable epilepsy associated with infantile-type hemiplegia for a half century. Of the patients, however, up to 33% have late increased cerebrospinal fluid pressure complications attributed to superficial cerebral hemosiderosis. Through a retrospective case analysis, we describe such complications in a 52-year-old woman with cognitive impairment, gait instability, urinary incontinence, and right hemineglect 36 years after her initial procedure. RESULTS: Quantitative, objective measures of cognition and gait-laboratory testing confirmed the patient's favorable clinical response to ventriculoperitoneal shunting, as well as the complete resolution of her symptoms, including the atypical occurrence of right-sided hemineglect. CONCLUSIONS: This case uniquely demonstrates the clinical features of a late complication of hemispherectomy while documenting the longest reported delay for developing such adverse sequelae. We also emphasize the need for more extensive follow-up studies to assess the extent of posthemispherectomy complications.

Brain↗

PubMed1995

Phase plane analysis of stability in quiet standing.

We analyzed the standing balance control of 11 healthy subjects and 15 subjects with bilateral vestibular hypofunction (BVH) using phase plane (velocity versus displacement) plots. We hypothesized that maintaining postural stability requires control of both the position and momentum of the center of gravity (CG) and infer that it is advantageous to use both velocity and displacement data to characterize balance control. Phase plane plots provide insight into this dynamic aspect of balance control. We evaluated phase plane plots based on whole body CG and center of pressure (CoP). We varied stability by altering the base of support and visual information. Three different foot placements were used: feet wide apart, feet together, and semitandem stance. Feet together standing was performed with eyes open and with eyes closed. The phase plane plots show changes in stability as base of support is altered or visual input is removed and reveal stability differences between the control and BVH groups. The root mean square variance of velocity and displacement was used to quantify the phase plane information. This parameter showed significant differences between activities and between groups. We conclude that phase plane plots that combine displacement and velocity information are more useful in characterizing balance control than displacement or velocity alone.

Gravitation↗

PubMed1994

Physical therapy management of peripheral vestibular dysfunction: two clinical case reports.

We describe the treatment of two patients with peripheral vestibular dysfunction using a novel, staged exercise program. Response to treatment was documented. The first patient, a 62-year-old woman with unilateral vestibular dysfunction (UVD) and a 6-month history of disequilibrium following herpes zoster oticus resulting in damage to the right inner ear, was treated with an 8-week course of vestibular physical therapy. During the 8 weeks, the patient attended weekly physical therapy sessions and was trained to perform vestibular adaptation exercises on a daily basis at home. The second patient, a 53-year-old woman with progressive disequilibrium secondary to profound bilateral vestibular hypofunction (BVH), was treated with a 16-week course of vestibular physical therapy. During the first 8 weeks, the patient attended weekly physical therapy sessions and was trained to perform vestibular adaptation and substitution exercises on a daily basis at home. During the second 8 weeks, the patient continued performing vestibular physical therapy exercises at home independently. Vestibular function (sinusoidal vertical axis rotation testing), postural control (clinical tests and posturography), stability during the performance of selected activities of daily living (ADLs), and self-perception of symptoms and handicap were measured prior to and at the conclusion of treatment for both patients and at the midpoint of treatment for the patient with BVH. After 8 weeks of treatment, both patients reported improvements in self-perception of symptoms and handicap and demonstrated objective improvements in clinical balance tests, posturography, and several kinematic indicators of stability during the performance of selected ADLs. Further improvements were noted in the patient with BVH after 16 weeks of treatment. Improvements in postural control were noted after 8 weeks of treatment for the patient with UVD and after 16 weeks for the patient with BVH. Vestibular function improved during the course of treatment for the patient with UVD only. These case reports describe two different individualized treatment programs and document self-reported and laboratory-measured functional improvements in two patients with vestibular deficients--one with unilateral damage and one with bilateral damage.

Activities of Daily Living↗

PubMed1993

Quantitative assessment of four men using above-elbow prosthetic control.

We studied the relationship between kinematically unconstrained activities of daily living (ADL) tasks and a kinematically constrained task in above-elbow (AE) amputee subjects using myoelectrically controlled prostheses. Four men, 24 to 49 years old, with unilateral AE amputation wore a prosthesis interfaced to a programmable controller to emulate two different elbow control schemes, conventional velocity and a new "natural" controller. Subjects were timed during three ADL tasks--cutting meat, donning socks, and rolling dough--with both controllers. The prosthesis emulator was then connected to a crank device with a handle, and the subjects turned the crank from bottom to top positions in a vertical plane using each controller. Synergistic shoulder-elbow joint coordination required for crank turning was quantified as the maximum slope of the change in elbow torque versus the change in crank-angle. Performance between the two controllers differed significantly for the crank test but not for ADL tasks. One subject did not complete all crank turning tests. Positive canonical correlation of 0.77 was found between time and crank domain measures. We conclude that biomechanical assessments should be integrated with time-based clinical tests to comprehensively evaluate performance of AE amputee subjects with a myoelectric device.

Activities of Daily Living↗

PubMed1993

Reliability of eccentric isokinetic knee flexion and extension measurements.

This study assessed the test-retest reliability of knee isokinetic eccentric muscle performance in subjects with and without a history of tibio-femoral pathology. Nineteen adults were tested at 60 degrees/sec and 180 degrees/sec on three occasions using a standardized protocol that incorporates a same-session learning phase. Results revealed moderate to excellent reliability for average peak torque test-retest ICC (2,1) = .58 to .96, total work ICC = .63 to .93, and power ICC = .67 to .93. Joint angle at peak torque was unreliable (ICC = .01 to .69) for both muscle groups at both angular velocities. Knee flexion reliability was higher than extension reliability at both 60 degrees/sec and 180 degrees/sec. Subjects with tibio-femoral pathologies had ICC values lower than the healthy subjects. Reliable eccentric isokinetic measurements can be obtained for average peak torque, total work, and power. Clinicians should not assume the same degree of reliability in testing patients as in testing healthy subjects.

Adult↗