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ABSTRACT: Rotator cuff tears disrupt the force balance in the shoulder and the glenohumeral joint in particular, resulting in compromised arm elevation torques. The trade-off between glenohumeral torque and glenohumeral stability is not yet understood. We hypothesize that compensation of lost abduction torque will lead to a superior redirection of the reaction force vector onto the glenoid surface, which will require additional muscle forces to maintain glenohumeral stability. Muscle forces in a single arm position for five combinations of simulated cuff tears were estimated by inverse dynamic simulation (Delft Shoulder and Elbow Model) and compared with muscle forces in the non-injured condition. Each cuff tear condition was simulated both without and with an active modeling constraint for glenohumeral stability, which was defined as the condition in which the glenohumeral reaction force intersects the glenoid surface. For the simulated position an isolated tear of the supraspinatus only increased the effort of the other muscles with 8%, and did not introduce instability. For massive cuff tears beyond the supraspinatus, instability became a prominent factor: the deltoids were not able to fully compensate lost net abduction torque without introducing destabilizing forces; unfavorable abductor muscles (i.e. in the simulated position the subscapularis and the biceps longum) remain to compensate the necessary abduction torque; the teres minor appeared to be of vital importance to maintain glenohumeral stability. Adverse adductor muscle co-contraction is essential to preserve glenohumeral stability.
Journal of biomechanics 06/2009; 42(11):1740-5. · 2.66 Impact Factor
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ABSTRACT: To study the effect of botulinum toxin A in the subscapular muscle on shoulder pain and humerus external rotation.
22 stroke patients with spastic hemiplegia, substantial shoulder pain and reduced external rotation of the humerus participated in a randomised, double blind, placebo controlled effect study. Injections of either botulinum toxin A (Botox, 2x50 units) or placebo were applied to the subscapular muscle at two locations. Pain was scored on a 100 mm vertical Visual Analogue Scale; external rotation was recorded by means of electronic goniometry. Assessments were carried out at 0 (baseline), 6 and 12 weeks.
21 patients completed the study. We observed no significant changes in pain or external rotation as a result of administration of botulinum toxin A. External rotation improved significantly (p = 0.001) for both the treatment group (20.4 degrees (16.6) to 32.1 degrees (14.0)) and the control group (10.3 degrees (19.5) to 23.7 degrees (20.7)) as a function of time.
Application of botulinum toxin A into the subscapular muscle for reduction of shoulder pain and improvement of humeral external rotation in spastic hemiplegia does not appear to be clinically efficacious.
Journal of neurology, neurosurgery, and psychiatry 06/2008; 79(5):581-3. · 4.87 Impact Factor
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ABSTRACT: Clonus is a self sustained oscillatory movement of the extremities often seen after lesions of the central nervous system. There is still controversy about the origin of clonus whether it is i) an autonomous pacemaker-like oscillator, ii) a reflexive mediated feedback property or iii) a combination of both. With the use of a haptic robot we were able to initiate clonus in patients (n=7). We would conclude the underlying mechanism to be autonomous when the frequency of movement would not change with additional external damping and inertia. Results however showed distinct changes in frequency of movement, varying the peripheral conditions. Furthermore, when the clonus was suddenly stopped by a controlled increase of a huge external damper, clear bursting was observed in the triceps EMG while there was no rotation of the ankle. In conclusion, i) clonus is initiated by spinal reflexes (probably la or lb afferents), ii) also during clonus the same spinal reflexes are likely to contribute to the maintenance of ankle rotation and iii) the after bursting directs to self sustained firing of neural circuitry. These conclusions implicate the existence of a reflexive controlled oscillator. Future research will be performed using detailed model simulations to test different gains between reflexive feedback and neural oscillations, e.g. from the alpha - motorneurons.
Rehabilitation Robotics, 2007. ICORR 2007. IEEE 10th International Conference on; 07/2007
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ABSTRACT: A mechanical deficit due to a massive rotator cuff tear is generally concurrent to a pain-induced decrease of maximum arm elevation and peak elevation torque. The purpose of this study was to measure shoulder muscle coordination in patients with massive cuff tears, including the effect of subacromial pain suppression. Ten patients, with MRI-proven cuff tears, performed an isometric force task in which they were asked to exert a force in 24 equidistant intervals in a plane perpendicular to the humerus. By means of bi-polar surface electromyography (EMG) the direction of the maximal muscle activation or principal action of six muscles, as well as the external force, were identified prior to, and after subacromial pain suppression. Subacromial lidocaine injection led to a significant reduction of pain and a significant increase in exerted arm force. Prior to the pain suppression, we observed an activation pattern of the arm adductors (pectoralis major pars clavicularis and/or latissimus dorsi and/or teres major) during abduction force delivery in eight patients. In these eight patients, adductor activation was different from the normal adductor activation pattern. Five out of these eight restored this aberrant activity (partly) in one or more adductor muscles after subacromial lidocaine injection. Absence of glenoid directed forces of the supraspinate muscle and compensation for the lost supraspinate abduction torque by the deltoideus leads to destabilizating forces in the glenohumeral joint, with subsequent upward translation of the humeral head and pain. In order to reduce the superior translation force, arm adductors will be co-activated at the cost of arm force and abduction torque. Pain seems to be the key factor in this (avoidance) mechanism, explaining the observed limitations in arm force and limitations in maximum arm elevation in patients suffering subacromial pathologies. Masking this pain may further deteriorate the subacromial tissues as a result of proximal migration of the humeral head and subsequent impingement of subacromial tissues.
Manual Therapy 09/2006; 11(3):231-7. · 1.88 Impact Factor
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ABSTRACT: Massive rotator cuff tears impose restraints on overhand arm functionality and are often accompanied by pain. After musculotendinous Teres Major transfer, overhand arm function is generally restored and pain is reduced. The assumed mechanical abduction insufficiency and Teres Major muscle function adaptation will be experimentally verified.
Principal Teres Major muscle activation (surface IEMG averaged over 3s) is recorded for 12-24 isometric and isotonic force directions perpendicular to the 60 degrees forward flexed humerus in three conditions: prior to surgery (n = 6 patients), prior to surgery and after subacromial anaesthetic (n = 6) and post-surgery (n = 3). Principal direction and on-, offset directions were estimated.
Teres Major activation adapts both to pathological and post surgery conditions: the normal activation during adduction changes into activation during forward flexion or abduction. Glenohumeral stabilisation, not abduction torque, seems to be the explanation for post surgery Teres Major transfer success.
The pathological absence of Supraspinatus and Infraspinatus forces during forward flexion result in increased upward glenohumeral instability. The superior translations are compensated for by Teres Major activity during forward flexion. This translation-'force' function conflicts with the adduction-generating rotation-'torque' function. This may explain the pain-induced reduction of arm elevation in these patients. Musculotendinous transfer solves the force-torque conflict by changing the moment arm of the Teres Major from adduction to abduction. Teres Major can now both compensate for the loss of Supraspinatus and Infraspinatus forces needed for glenohumeral stabilisation and contribute to forward flexion of the arm.
Clinical Biomechanics 02/2006; 21 Suppl 1:S27-32. · 2.07 Impact Factor
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ABSTRACT: Recent evidence showed that exposure of tape-tutored zebra finch (Taeniopygia guttata castanotis) males to the tutor song involves neuronal activation in brain regions outside the conventional 'song control pathways', particularly the caudal part of the neostriatum (NCM) and of the hyperstriatum ventrale (CMHV). Zebra finch males were reared with a live tutor during the sensitive period for song learning. When, as adults, they were re-exposed to the tutor song, the males showed increased expression of Fos, the protein product of the immediate early gene c-fos, in the NCM and CMHV, compared with expression in two conventional 'song control nuclei', high vocal centre (HVC) and Area X. The strength of the Fos response (which is a reflection of neuronal activation) in the NCM (but not in the other three regions) correlated significantly and positively with the number of song elements that the birds had copied from the tutor song. Thus, socially tutored zebra finch males show localized neural activation in response to tutor song exposure, which correlates with the strength of song learning.
European Journal of Neuroscience 07/2001; 13(11):2165-70. · 3.63 Impact Factor
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J H de Groot
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ABSTRACT: The objective of this study is to illustrate the low accuracy of two-dimensional (2-D) X-ray projection methods for the quantification of the three-dimensional (3-D) shoulder motions.
The traditional method for the quantification of the gleno-humeral motion is by means of 2-D X-ray recording. The motion was characterized by the scapulo-humeral rhythm: the ratio of the nett humeral elevation over nett scapular rotation. The method was based on the quantification of the planar projection of the spatial positions of X-ray dense structures of the scapula. The deformations introduced by the central projection method, a feature of X-ray projection, cannot be compensated for by calibration: the position of the scapula with respect to the camera setting is unknown, and skeletal landmarks of the scapula cannot uniquely be identified. The transformation from 3-D orientations to 2-D angles will, therefore, be inaccurate.
A 2-D X-ray projection of the scapula during a typical arm abduction was simulated. The 3-D motion was obtained by means of palpation and subsequent digitization of skeletal landmarks of the scapula. The 3-D positions of the recorded landmarks were projected on a plane by a simulation based on the parameters of the X-ray equipment. The scapulo-humeral rhythm was calculated for the different scapular landmarks, and for the orientation of the subject with respect to the projection axis. The results were compared with previous published scapulo-humeral rhythms.
The scapulo-humeral rhythm depends both on the choice of the skeletal landmarks, used to quantify the scapular rotations, and on the orientation of the subject in the X-ray setting. The full range of results obtained from earlier published experiments could be obtained from a simulation based on a single 3-D arm abduction.
The 2-D scapulo-humeral rhythm, obtained from planar X-ray projection, is an inaccurate parameter to define the scapular motions.
The 2-D scapulo-humeral rhythm is an insensitive parameter to identify clinical disorders in the gleno-humeral motions, 3-D motion recording should be applied. Only when stringent precautions are taken with respect to repeatability of positioning of the subjects, can the method be used to study intra-individual effects, e.g., the follow-up of patients during treatment.
Clinical Biomechanics 01/1999; 14(1):63-8. · 2.07 Impact Factor
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ABSTRACT: OBJECTIVE: To describe a recording and processing methodology for obtaining kinematic data of the shoulder which meets three more criteria besides usual requirements regarding precision and accuracy: sufficient speed, obtaining complete 3D kinematics including joint rotations, and usage of coordinate systems based on reference points. DESIGN: Static recordings of shoulder bone orientations during standardized humerus elevations based on the palpation technique using a six-degree-of-freedom electromagnetic tracking device. BACKGROUND: An easy, fast, well standardized measurement methodology for obtaining complete 3D shoulder kinematic data is urgently needed for fundamental musculoskeletal and clinical research. METHODS: A measurement methodology was designed and developed. Shoulder kinematics were obtained from repeated measurements on 15 healthy subjects performed by two observers. Inter-trial, inter-day, inter-observer and inter-subject variability were established. Results were compared to literature. RESULTS: Complete kinematic descriptions were obtained. A measurement speed of about one position per second could be reached. The measured kinematics and accuracy of the measurements were found to be in concordance with the literature. CONCLUSION: All previously formulated criteria for a clinical useful method for obtaining shoulder kinematics have been met.
Clinical biomechanics (Bristol, Avon) 07/1998; 13(4-5):280-292. · 1.76 Impact Factor
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ABSTRACT: Non-invasive dynamical measurements of 3D scapular motion can be performed easily by attachment of a 6 DOF electromagnetic receiver onto the skin above the acromion. To quantify the introduction of possible errors due to skin displacement, we assessed 3D scapular positions on n=8 subjects by both tripod and skin-fixed method. Error analysis included the variables method (tripod, skin-fixed simultaneously with tripod, separate skin-fixed at 0 and 0.25Hz of elevation speed), plane of elevation (0 degrees and 90 degrees ) and observation (receiver replacement: n=3). Inter-individual 'group' differences depended on elevation plane and showed an average underestimation of scapular rotation of 6.5 degrees (worst case 13 degrees ) using the skin-fixed method. Only the group RMSE, not the individual RMSE, could be successfully lowered using linear regression (to about 2 degrees ). Inter-trial reliability (RMSE <3.24 degrees , ICC>0.94) and RMSE between 0 and 0.25Hz recordings (about 2.5 degrees ) were satisfactory. Intra-observer RMSE after replacement of the skin-fixed receiver was 5 degrees . The skin-fixed method is suitable for dynamic recordings of scapular rotations; however, measurements are precise only when the acromion receiver is not replaced. Combined with a relatively low accuracy, we conclude that the skin-fixed method should be used only in combination with tripod 'calibration'
J.Biomech. 40(4).
