Marjorie E. Johnson

Quantitative measurements of hip strength in different age groups

The purpose of this study was to develop a clinically useful method of assessing the strength of the hip musculature and to develop a normal data base with this technique. The strength of 72 subjects aged 20-81 years (37 women and 35 men) was measured through the use of a modified Cybex II with an upright stabilization frame for testing sagittal and frontal plane motions; transverse plane motions of internal and external rotation were tested in the seated position. The subjects were tested at multiple isokinetic speeds and isometric angles. Regardless of age or gender, hip extensors were the strongest muscle group, following by flexors, adductors, abductors, and rotators. As the velocity of exercise increased, the magnitude of the torques produced decreased. Demographically, younger men produced the greatest torques and older women the lowest. The strength values of older men and younger women were similar. The results have clinical implications for objective assessment of strength in pathologic patient populations.

Intelligent stretching of ankle joints with contracture/spasticity

An intelligent stretching device was developed to treat the spastic/contractured ankle of neurologically impaired patients. The device stretched the ankle safely throughout the range of motion (ROM) to extreme dorsiflexion and plantarflexion until a specified peak resistance torque was reached with the stretching velocity controlled based on the resistance torque. The ankle was held at the extreme position for a period of time to let stress relaxation occur before it was rotated back to the other extreme position. Stretching was slow at the joint extreme positions, making it possible to reach a larger ROM safely and it was fast in the middle ROM so the majority of the treatment was spent in stretching the problematic extreme ROM. Furthermore, the device evaluated treatment outcome quantitatively in multiple aspects, including active and passive ROM, joint stiffness and viscous damping and reflex excitability. The stretching resulted in considerable changes in joint passive ROM, stiffness, viscous damping and reflex gain. The intelligent control and yet simple design of the device suggest that with appropriate simplification, the device can be made portable and low cost, making it available to patients and therapists for frequent use in clinics/home and allowing more effective treatment and long-term improvement.

IV immunoglobulin does not reverse established weakness in MS: A double-blind, placebo-controlled trial

Background: Immunoglobulin (Ig) administration induces remyelination in the Theiler’s virus model of MS. Methods: A randomized, double-blinded, placebo-controlled trial of IV immunoglobulin (IVIg) was performed in patients with MS who had persistent muscle weakness that had been stable for between 4 and 18 months to determine whether this would improve muscle strength (primary outcome: isometric muscle strength). Patients received either IVIg (0.4 g/kg) or placebo daily for 5 days, then single infusions every 2 weeks for 3 months (total, 11 infusions). Muscle groups identified by clinical measures to have unchanging significant weakness were the major targets for therapeutic response (targeted neurologic deficit [TND]). Results: IVIg was well tolerated. An interim analysis after 67 patients were enrolled indicated no difference in the degree of change in strength between treatment groups in either the TND or non-TND muscle groups at 6 months, and the trial was terminated. There was no apparent benefit in relapse behavior or impairment measures during the 6-month observation period. Nor was there apparent benefit in either patients who remained clinically stable or in those with evidence of disease activity. Patients with active MS during the trial worsened in both TND and non-TND muscle groups. This worsening was seen regardless of whether the clinical manifestations of disease activity involved the TND muscle groups. Conclusions: IVIg does not reverse established weakness in MS. Measurements of isometric muscle strength were reliable (reproducible) indices of strength and may be sensitive, objective methods to document functional changes in impairment in future MS trials.

Age-related changes in normal isometric shoulder strength

Normative data are useful for assessing isometric shoulder strength in patients with bilateral shoulder abnormalities. The purpose of this study was to develop a normative database for shoulder strength in the clinically relevant positions and movements. Twenty combinations of exertions and postures—including flexion, extension, abduction, adduction, internal rotation, and external rotation—were tested for both the dominant and nondominant sides. Strength was measured isometrically using a modified Cybex II dynamometer. The cross-sectional study design included 120 subjects (60 women and 60 men) ranging in age from 20 to 78 years from southern Minnesota. Tables of normative strength data were constructed. Multivariate analyses were performed to assess the effect of age, sex, and weight on strength. Age was negatively associated with all strength measures, and weight was positively associated with them. Men were stronger than women when controlling for age and weight. Statistically significant differences between dominant and nondominant shoulders were found for only some of the strength measures taken. These normal data will be useful to the clinician, as they permit a standard against which to compare shoulder strength.

Shoulder strength analysis using the Cybex II isokinetic dynamometer.

The purpose of this study was to establish a data base of normal shoulder strength of young adults using the Cybex II dynamometer and specially designed fixation devices. Fifty healthy subjects aged 21 to 40 years old (26 men, 24 women) were tested. The mean peak torque values of their shoulders were measured at speeds of 0 degree, 60 degrees, 180 degrees, and 300 degrees per second. Mean peak torque values generally decreased as speed increased. Men were significantly stronger than women for all motions and speeds tested. Shoulder extension torque was greatest followed by adduction, flexion, internal rotation, abduction, and external rotation. Torque production tended to be greater on the dominant side.

Functional laboratory assessment after oncologic shoulder joint resections

A laboratory evaluation was undertaken to assess the shoulder range of motion and distal strength after oncologic resection and reconstruction involving the shoulder joint and to compare these functional parameters based on potentially important variables. Inclusion in the study was limited to 32 patients with bone tumors of the proximal humerus or scapula treated surgically by resection of the shoulder joint including the proximal humerus from 1976 through 1992. Active shoulder range of motion and isometric elbow extension and forearm supination strength are significantly less after surgery in patients with greater amounts of bony resection and with resection of the deltoid. Patients who had a modified Tikhoff-Linberg resection were able to achieve 10° to 15° greater shoulder motion in each direction than were patients who had the classic procedure including complete scapulectomy. However, elbow flexion and extension strength and forearm pronation strength were greater for the patients with the classic resection. Osteoarticular allografts as a reconstructive alternative provide as a group the best shoulder motion and overall distal upper extremity strength, but these reconstructions were performed only when the rotator cuff muscles and deltoid were able to be reconstructed. Diminishing elbow strength was seen with longer followup in the patients with osteoarticular reconstructions, corresponding temporally to subchondral collapse observed on radiographs. Range of shoulder motion except rotation was just as good for allograft vascularized fibular arthrodeses as for the osteoarticular allografts, but strength was significantly less with the arthrodeses.

Triggering of protective stepping for the control of human balance: age and contextual dependence

Human stepping is a commonly executed control strategy for maintaining standing balance in the natural environment. Aging changes in the initiation triggering of both voluntary (longer latency) and perturbation-induced (shorter latency) stepping are associated with falling, and are a complex function of altered sensorimotor, neuromuscular, and cognitive system factors. The aim of this study was to determine the effect of contextual uncertainty about balance stability on the triggering of protective stepping in young and older individuals. Subjects initiated forward stepping during simple reaction time and waist-pull perturbation conditions with and without contextual uncertainty about balance stability. The results showed that, regardless of age, the initiation timing for triggering both voluntary and induced stepping was delayed substantially (100-300 ms) by the presence of balance uncertainty, and that age-associated timing differences were exacerbated with contextual uncertainty. The initiation timing of the first step liftoff for perturbation-induced stepping did not reflect entirely an immediate necessity or last resort strategy to balance instability determined directly by specific sensory input, but rather a decision to step. Moreover, the time to liftoff onset for perturbation-induced stepping was similar for the old and young with contextual certainty, and occurred 130 ms earlier for the old than for the young when balance stability was uncertain. Overall, we concluded that older individuals can retain a residual capacity to sustain stationary standing stability as a function of the prevailing task conditions, and that the reduced timing threshold with age may involve a pre-selected strategy triggered earlier by non-specific event-related sensory input rather than specific movement-related information.

Normative values of agonist-antagonist shoulder strength ratios of adults aged 20 to 78 years☆☆☆

OBJECTIVE To determine normative values for isometric flexion/extension, abduction/adduction, and external/internal rotation strength ratios about the shoulder and to determine if these ratios are affected by age or gender. STUDY DESIGN A cross-sectional study of 120 healthy volunteers (60 men, 60 women) aged 20 to 78 years. SETTING Orthopedic research laboratory. METHODS Flexion and extension strengths were measured isometrically using a Cybex II dynamometer at arm flexion angles of 30 degrees, 60 degrees, and 90 degrees. Abduction and adduction strengths were measured at 30 degrees, 60 degrees, and 90 degrees abduction. Internal and external rotation strengths were measured (1) with the arm abducted 15 degrees and neutral external/internal rotation and (2) with the arm abducted 90 degrees and externally rotated 30 degrees above the transverse plane. OUTCOME MEASURES Isometric strength ratios for flexion/extension, abduction/adduction, and external/internal rotation. RESULTS No statistically significant differences in agonist/antagonist strength ratios were found between dominant and nondominant sides or between genders. Age was associated with changes in strength ratios for measurements taken with the arm flexed or abducted 90 degrees. Posture was found to affect strength ratios. CONCLUSIONS These data can serve as a normative reference for clinical use.

Functional Comparison of Pronation and Supination Strengths

Studies have shown that functional activities involving pronation and supination, such as turning a doorknob or a screwdriver, involve wrist positions of extension and/or ulnar deviation. Previous studies of isometric forearm pronation and supination strength have utilized a neutral wrist position, resulting in a possible underestimation of true functional strength. Twenty healthy subjects between the ages of 24 and 45 years were assessed for isometric pronation and supination strength using cylinder, screwdriver, and doorknob handle adaptations. Maximal strength in both pronation and supination was observed with the use of the doorknob handle. Although pronation strength was exceeded by supination strength within all three handle adaptations, the difference was statistically significant for the screwdriver and doorknob handles. The results suggest that in clinical and research-oriented testing of maximal forearm rotation strength, further consideration must be given to the terminal grip device and positioning of the wrist.

A Probabilistic Model of Glenohumeral External Rotation Strength for Healthy Normals and Rotator Cuff Tear Cases

The reigning paradigm of musculoskeletal modeling is to construct deterministic models from parameters of an “average” subject and make predictions for muscle forces and joint torques with this model. This approach is limited because it does not perform well for outliers, and it does not model the effects of population parameter variability. The purpose of this study was to simulate variability in musculoskeletal parameters on glenohumeral external rotation strength in healthy normals, and in rotator cuff tear case using a Monte Carlo model. The goal was to determine if variability in musculoskeletal parameters could quantifiably explain variability in glenohumeral external rotation strength. Multivariate Gamma distributions for musculoskeletal architecture and moment arm were constructed from empirical data. Gamma distributions of measured joint strength were constructed. Parameters were sampled from the distributions and input to the model to predict muscle forces and joint torques. The model predicted measured joint torques for healthy normals, subjects with supraspinatus tears, and subjects with infraspinatus–supraspinatus tears with small error. Muscle forces for the three conditions were predicted and compared. Variability in measured torques can be explained by differences in parameter variability.