Chris A. McGibbon

Can Tai Chi improve vestibulopathic postural control

OBJECTIVESnTo evaluate the rationale and scientific support for Tai Chi as an intervention for vestibulopathy and to offer recommendations for future studies.nnnDATA SOURCESnA computer-aided search, including MEDLINE and Science Citation Index, to identify original Tai Chi studies published in English; relevant references cited in the retrieved articles were also included.nnnSTUDY SELECTIONnA preliminary screening selected all randomized controlled trials (RCTs), non-RCTs, case-control studies, and case series that included Tai Chi as an intervention and had at least 1 outcome variable relevant to postural stability.nnnDATA EXTRACTIONnAuthors critically reviewed studies and summarized study designs and outcomes in a summary table.nnnDATA SYNTHESISnTwenty-four Tai Chi studies met screening criteria. No studies specifically studying Tai Chi for vestibulopathy were found. Collectively, the 24 studies provide sometimes contradictory but generally supportive evidence that Tai Chi may have beneficial effects for balance and postural impairments, especially those associated with aging. Ten RCTs were found, of which 8 provide support that Tai Chi practiced alone, or in combination with other therapies, can reduce risk of falls, and/or impact factors associated with postural control, including improved balance and dynamic stability, increased musculoskeletal strength and flexibility, improved performance of activities of daily living (ADLs), reduced fear of falling, and general improvement in psychologic well-being. Studies using other designs support the results observed in RCTs.nnnCONCLUSIONSnAt present, few data exist to support the contention that Tai Chi specifically targets the impairments, functional limitations, disability, and quality of life associated with peripheral vestibulopathy. There are, however, compelling reasons to further investigate Tai Chi for vestibulopathy, in part because Tai Chi appears useful for a variety of nonvestibulopathy etiologic balance disorders, and is safe. Especially needed are studies that integrate measures of balance relevant to ADLs with other psychologic and cognitive measures; these might help identify specific mechanisms whereby Tai Chi can remedy balance disorders.

Mechanical energy analysis identifies compensatory strategies in disabled elders' gait

Current concepts in disablement emphasize the importance of identifying mobility impairments in aging humans to enable timely intervention and, ultimately, prevent disability. Because mobility impairments are likely to result in compensatory movement strategies, recognizing and understanding those strategies may be critical in designing effective interventions for preventing disability. We sought to determine if mechanical energy methods are useful for identifying and understanding lower extremity compensatory movement strategies due to disabilities. Aleshinskis method was used to compute mechanical energy expenditure (MEE) and mechanical energy compensation (MEC) for the sagittal plane stance leg and low-back joints of healthy elders (HE) and disabled elders (DE) during preferred speed and paced (120 steps min(-1)) gait. DE subjects expended less ankle energy in late-stance and more low-back energy in mid-stance than did the HE subjects. When controlling for walking speed, the difference in ankle MEE disappeared, but mid-stance hip MEE was significantly higher for the DE subjects. Despite increased hip and low-back MEE, the DE subjects compensated hip and low-back muscles greater then HE subjects by increasing energy transferred into the pelvis, particularly when walking faster than their self-selected speed. Increased energy transfers into the pelvis during mid-stance may be a strategy used to assist in advancing and controlling the contralateral limbs swing phase. Increased trunk energy, however, may compromise dynamic stability and increase the risk of falling. We conclude that mechanical energy methods are useful for identifying and understanding compensatory movement strategies in elders with disabilities.

Accuracy of cartilage and subchondral bone spatial thickness distribution from MRI

To assess three‐dimensional measurement accuracy of articular cartilage (AC) and subchondral bone (SB) thickness from MRI.

Cartilage and Subchondral Bone Thickness Distribution with MR Imaging

RATIONALE AND OBJECTIVESnThe 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.nnnMATERIALS AND METHODSnLeft 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.nnnRESULTSnStandard 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).nnnCONCLUSIONnAC 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.

High curvature and jerk analyses of arm ataxia.

Abstract. We investigated high curvature analysis (HCA) and integrated absolute jerk (IAJ) for differentiating healthy and cerebellopathy (CB) patients performing pointing tasks. Seventeen CB patients and seventeen healthy controls were required to move a pointer at their preferred pace between two 50.8u2009cm laterally spaced targets while standing with their arm extended in front of their body. HCA was used to quantify the frequency of sharp turns in the horizontal-plane (anterior-posterior and medio-lateral) velocity trajectory of the hand-held pointer. IAJ was assessed by integration of absolute jerk (second time derivative of velocity) time histories in the anterior-posterior and medio-lateral directions. HCA scores and IAJ scores were then compared between CB patients and healthy controls; for both analyses, higher scores indicate less smooth movements. We hypothesized that CB patients would have less smooth movement trajectories than healthy controls due to upper extremity ataxia associated with cerebellar disease and degeneration. We found that CB patients had higher HCA scores than healthy controls (Pu2009=u20090.014). Although CB patients had higher IAJ scores in both anterior-posterior (Pu2009=u20090.060) and medio-lateral (Pu2009=u20090.231) directions compared to the healthy controls, the differences were not significant. The difference in sensitivity between the HCA and the IAJ analysis might be explained by primitive neural activation commands, ubiquitous though only evident with some cerebellar dysfunctions, which produce sub-movements which are themselves minimal jerk curves. We conclude that HCA may be a useful tool for quantifying upper extremity ataxia in CB patients performing a repeated pointing task.

Kinetic analysis of planned gait termination in healthy subjects and patients with balance disorders

We examined the stability and strategies used by balance impaired (vestibular hypofunction, VH: n=25; cerebellar damage, CB: n=20) patients and healthy (HE: n=52) controls during planned gait termination. Upper body strategies (during final stride and final step) were investigated using peak positive kinetic power (KP((+)): kinetic energy increasing), and peak negative kinetic power (KP((-)): kinetic energy decreasing) of the head-arms-trunk segment. Compared to HE controls (P<0.05): CB patients medio-lateral KP((+)) and KP((-)) and were 53 and 71% higher during final stride, respectively; VH patients medio-lateral KP((+)) and KP((-)) was 78 and 57% higher during final step, respectively, and; during the final, standing stage VH patients were 32% less stable (from phase plane analysis) in the frontal plane. The excessive energy transfers in final stride for CB patients was likely due to poor eccentric muscle control when preparing for the stop. VH patients had difficulty controlling lateral stability during final step and once they had stopped walking, probably due to the lack of vestibular feedback regarding forward velocity changes. A better understanding of these abnormal movement patterns or compensatory strategies may assist in rehabilitation of patients with balance dysfunction.

Subchondral bone and cartilage thickness from MRI: effects of chemical-shift artifact

Magnetic resonance imaging (MRI) is the modality of choice for visualizing and quantifying articular cartilage thickness. However, difficulties persist in MRI of subchondral bone using spoiled gradient-echo (SPGR) and other gradient-echo sequences, primarily due to the effects of chemical-shift artifact. Fat-suppression techniques are often used to reduce these artifacts, but they prevent measurement of bone thickness. In this report, we assess the magnitude of chemical-shift effects (phase-cancellation and misregistration artifacts) on subchondral bone and cartilage thickness measurements in human femoral heads using a variety of pulse sequence parameters. Phase-cancellation effects were quantified by comparing measurements from in-phase images (TE=13.5xa0ms) to out-of-phase images (TE=15.8xa0ms). We also tested the assumption of the optimal in-phase TE by comparing thickness measures at small variations on TE (13.0, 13.5 and 14.0xa0ms). Misregistration effects were quantified by comparing measurements from water+fat images (water-only+fat-only images) to the measurements from in-phase (TE=13.5) images. A correction algorithm was developed and applied to the in-phase measurements and then compared to measurements from water+fat images. We also compared thickness measurements at different image resolutions. Results showed that both phase-cancellation artifact and misregistration artifact were significant for bone thickness measurement, but not for cartilage thickness measurement. Using an in-phase TE and correction algorithm for misregistration artifact, the errors in bone thickness relative to water+fat images were non-significant. This information may be useful for developing pulse sequences for optimal imaging of both cartilage and subchondral bone.

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.

Kalman filter detection of blinks in video-oculography: applications for VVOR measurement during locomotion.

A Kalman filter algorithm was implemented for automatic detection of blink artifacts in video-oculography (VOG) data, and a cubic spline used to patch the eliminated data. The algorithm was tested by randomly introducing artificial blinks into eye movement data and computing the errors introduced by the patches. We also computed visual vestibulo-ocular reflex (VVOR) gain and phase in healthy and vestibulopathic subjects during a locomotor task, before and after blink removal, to demonstrate the interpretive importance of eliminating blink artifacts. The error introduced by the patched data was small (0.50+/-0.32 degrees ) and within the resolution of head angle measurements. Comparison of gain and phase shift before and after removing blinks revealed that even when calculated values are within expected limits, coherence of the VVOR signal was significantly (p=0.003) lower prior to blink removal (0.51+/-0.37) compared to that after blink removal (0.92+/-0.08). Comparison of VVOR calculations between healthy and vestibulopathic subjects (after removal of blinks) revealed that vestibulopathic subjects had significantly decreased gains (p=0.018) and increased phase shifts (p=0.009): these results agree with data reported in literature. We conclude that the Kalman filter detection and cubic spline patching algorithms are useful tools for VOG and should enable reliable VVOR measurements during unconstrained, ecologically meaningful locomotor activities.

Vestibular rehabilitation outcomes : velocity trajectory analysis of repeated bench stepping

OBJECTIVESnTo quantify vestibular rehabilitation (VR) outcomes in patients with vestibulospinal reflex pathology (VSP) using a new technique, high curvature analysis (HCA), that measures space trajectory stability.nnnMETHODSnTwelve patients with VSP and 10 healthy controls performed a repeated stepping task in a motion analysis laboratory. Patients with VSP were tested before and after a 12 week VR program. Three dimensional whole body center of gravity (CG) was captured during repeated bench stepping trials (step up forward/step down backward), and the resulting horizontal plane CG velocity trajectories were analyzed using HCA.nnnRESULTSnVSP patients were significantly less stable than healthy subjects prior to VR (P=0.022), but these differences disappeared following VR (P=0.148). The stability of the VSP patients during the stepping task at 3 months increased significantly from baseline values (P=0.013).nnnCONCLUSIONSnEvaluating the efficacy of VR requires analysis techniques that are sensitive to changes in stability. We conclude that HCA can be used for assessing improvements in CG stability of VSP patients while performing a repeated bench stepping activity.