Biomedical subjects

J A Sidles

Publications and source records attributed to J A Sidles.

At least 19 recordsLinked to original sources

PubMed2000

The Bloch equations in high-gradient magnetic resonance force microscopy: theory and experiment.

We report theory and observations of paramagnetic resonance in a measured field gradient of 44,000 T per meter by the technique of magnetic resonance force microscopy (MRFM). Resonance was induced in a dilute solid solution of diphenylpicrylhydrazyl in polystyrene at 77 and 10 K by an amplitude-modulated microwave field. This modulated the force between resonant sample spins and a micrometer-scale SmCo magnetic tip on a force microscope cantilever. The force signals were typically of order 10 fN, and were detected above a thermal noise floor of 80 aN per root hertz at 10 K, equivalent to a magnetic moment noise of 200 micro(B) per root hertz of bandwidth. Resonance saturation was readily observed. Starting with the Bloch equations, we derived simple analytic expressions for the predicted cantilever signal amplitudes and T(1)-dependent phase lags, valid at low microwave power levels. For power levels below saturation, the data were in good agreement with the Bloch equation predictions, while above saturation the measured force increased more slowly with power than predicted. Several ESR mechanisms which might lead to non-Bloch dynamics in the MRFM environment are reviewed. Spin-relaxation mechanisms are also reviewed. A detailed description of the experimental apparatus is offered.

Electron Spin Resonance Spectroscopy↗

PubMed1999

Glenohumeral motion after complete capsular release.

The range of glenohumeral motion is primarily limited by the joint capsule. If the capsule is contracted, greater restriction in glenohumeral motion is exhibited. Release of a tight capsule has been an effective means of managing refractory stiffness of the glenohumeral joint. The effect of a complete capsular release on glenohumeral kinematics has not been previously studied in a cadaver model. Elevation, rotation, and translation of eight cadaveric glenohumeral preparations were studied before and after complete capsular release. As the intact joint was positioned near the limits of motion, glenohumeral torque rose rapidly with relatively small concomitant increases in elevation and rotational angles. Notable torque, due to tension in the capsule or cuff, ensued only after glenohumeral elevation reached approximately 80% of maximal range. After complete capsular release, maximal elevation increased on average 15%, yet retained definitive endpoints due to residual tension in the rotator cuff. Axial humeral rotation with an intact capsule decreased as maximum elevation approached, especially at elevation angles greater than 60 degrees. Maximum internal rotation was less than external, for all planes except +90 degrees. After complete capsular release, the greatest net gains for external rotation tended to be in the posterior scapular planes, whereas gains for internal rotation tended to be in the anterior scapular planes. Maximal translation in an intact vented capsule was 21 mm, 14 mm, and 15 mm in the anterior, posterior, and inferior directions, respectively. After complete capsular release, translation increased in all positions with maximal anterior, posterior, and inferior translations of 28 mm, 25 mm, and 28 mm, respectively. In general, relative gains in translation were greater in planes posterior to the scapula and at extremes of the range of motion. Although large glenohumeral translations were measured, no preparation could be dislocated before or after complete capsular release. Complete capsular release significantly increased glenohumeral range of motion and translation. The intact rotator cuff myotendinous units serves to limit the range of motion and translation after all capsuloligamentous attachments are rendered incompetent by complete capsular release.

Cadaver↗

PubMed1998

The correlation of comorbidity with function of the shoulder and health status of patients who have glenohumeral degenerative joint disease.

We studied the effect of comorbidities on function of the shoulder and health status in a group of eighty-five consecutive patients who had glenohumeral degenerative joint disease of sufficient severity to meet one surgeon's criteria for the performance of shoulder arthroplasty. A questionnaire was used to identify the comorbidities, such as other diseases, social factors, or a work-related injury, for each patient. The number of functions on the Simple Shoulder Test that the patient could perform had a significant negative correlation with the number of comorbidities (r = -0.32, intercept = 4.6 per cent, slope = -0.6, and p = 0.0031). Each parameter on the Short Form-36 (except for physical role function) had a significant negative correlation with the number of comorbidities (p < 0.05). This negative relationship was strongest for general health perception (r = -0.42) and vitality (r = -0.35). We concluded that the number of comorbidities has a quantitative effect on function of the shoulder. In the evaluation of the functional status of patients and the effectiveness of treatment, the effects of comorbidity must be controlled. The results of the present study demonstrate that the scores on the Short Form-36 are quantitatively related to the number of comorbidities. The six parameters that are unrelated to function of the shoulder (physical function, social function, emotional role function, mental health, vitality, and general health perception) may provide a practical way to integrate the effects of all potential comorbidities on individual patients. Future clinical research will be strengthened by efforts to measure the impact of comorbidities and by strategies to control for their effects.

Adult↗

PubMed1998

The humeroscapular motion interface.

Motion between the humerus and scapula commonly is described as glenohumeral motion. However, humeroscapular motion occurs at two distinct sites. In addition to the motion at the diarthrodial glenohumeral joint, movement occurs between the proximal humerus and related structures and the surrounding sleeve of structures, including the acromion, deltoid, coracoid, coracoacromial ligament, and the muscles attached to the coracoid. This site of nonarticular shoulder motion is defined as the humeroscapular motion interface. Nonarticular humeroscapular motion can be documented and measured using standard magnetic resonance imaging techniques. The maximum average interfacial motion using axial images was 29.1 mm, which occurred at the level of the maximum diameter of the humeral head. Interfacial motion varied depending on the site measured. If pathologic conditions such as adhesions secondary to trauma or surgery interfere with or obliterate this space at sites of significant sliding motion, overall shoulder motion will be limited. Successful treatment of shoulder stiffness related to humeroscapular restraints is likely to require restoration of the normal sliding motion at the humeroscapular motion interface, in addition to resolving restraints affecting the glenohumeral joint motion.

Adult↗

PubMed1997

Arthroscopic management of refractory shoulder stiffness.

Glenohumeral stiffness is a major cause of shoulder disability and pain. Conventional management strategies often fail to yield consistent or prompt return of comfort and function. Over the past 5 years, we have employed a prospective approach to the evaluation and management of glenohumeral stiffness using arthroscopic release of capsular contractures for the most refractory. This report concerns the first 30 patients who failed at least 6 months (28 month mean) of nonoperative management for unilateral refractory shoulder stiffness and who were managed by arthroscopic capsular release. Fourteen patients were diabetic. Follow-up averaged 33 months (range 12 to 56 months). Each patients' motion and strength was documented according to the American Shoulder and Elbow Surgeons standard examination. Functional outcome measures were patient-assessed using the Simple Shoulder test before and after surgery. Before surgery, active range-of-motion of the affected shoulder average 41% of the opposite asymptomatic side. The day after surgery, motion had improved dramatically to a mean of 78%. An additional 15% of motion was gained after discharge from the hospital. The final motion averaged 93% of the opposite side. All Simple Shoulder Test (SST) parameters and six of nine SF-36 health status scores were improved significantly. Only 6% of patients were able to sleep comfortably on their side and 35% could place 1 lb. on a shelf at shoulder height before surgery. After surgery, 73% were able to sleep comfortably on the affected side and 83% were able to place 1 lb. on a shelf at shoulder height. There were no differences among all outcome measures between diabetic or nondiabetic patients. Three patients developed recurrent refractory stiffness. The only complication was a single axillary neuropraxia which resolved spontaneously. No patient developed instability. Arthroscopic capsular release can be a safe and effective tool in the management of refractory shoulder stiffness.

Adult↗

PubMed1996

Effect of a chondral-labral defect on glenoid concavity and glenohumeral stability. A cadaveric model.

One of the primary stabilizing mechanisms of the glenohumeral joint is concavity-compression, the maintenance of the humeral head in the concave glenoid fossa by the compressive force generated by the surrounding muscles. This mechanism is active in all glenohumeral positions but it is particularly important in the functional mid-range, in which the capsule and ligaments are slack. The effectiveness of concavity-compression in the stabilization of a joint can be characterized in terms of the ratio between the maximum dislocating force that can be stabilized in a given direction and the load compressing the head into the glenoid (the stability ratio). Glenoid concavity can be described by the lateral humeral displacement during translation across the glenoid. The purpose of the present investigation was to characterize the concavity and stability ratios of normal cadaveric glenoids, to measure the effect of an anteroinferior chondral-labral defect on these parameters, and to measure the effectiveness of a simulated operative reconstruction on the restoration of glenoid concavity and the stability ratio. The chondral-labral defect created in this study reduced the height of the glenoid by approximately 80 per cent and the stability ratio by approximately 65 per cent for translation in the direction of the defect. Reconstruction of the anteroinferior aspect of the glenoid concavity with use of an autogenous biceps-tendon graft restored normal values for these variables.

Aged↗

PubMed1995

Optimizing arthroscopic knots.

Arthroscopic repairs, such as those for shoulder instability, are commonly performed. However, the failure rate after arthroscopic repair appears to be higher than with open surgery. These failures may relate to the challenge of tying secure knots arthroscopically. Many knots tied arthroscopically commonly consist of an initial slip knot to remove slack, and a series of half-hitches. Half-hitches, instead of square throws, are difficult to avoid and result when asymmetrical tension is applied to the strands. For this reason, the security of knots tied arthroscopically may not be equivalent to square knots and a greater rate of failure may occur. The purpose of this study was to determine (1) the security of various arthroscopic knots under cyclic and peak loading conditions, (2) how the surgeon can modify the method or sequence of half-hitch throws to minimize knot slippage or breakage, and (3) whether using an arthroscopic knot pusher affects the security of the same knot tied by hand. The most secure knot configurations were achieved by reversing the half-hitch throws and alternating the posts. These knots performed significantly better than all other knots tested (P < .002). Thus the surgeon can control the holding capacity and minimize suture loop displacement by proper alternation of the tying strands and reversal of the loop when placing the hitches.(ABSTRACT TRUNCATED AT 250 WORDS)

Arthroscopy↗

PubMed1995

The effect of articular conformity and the size of the humeral head component on laxity and motion after glenohumeral arthroplasty. A study in cadavera.

We used a cadaveric model to examine the mechanical effects of changes in the conformity of the articular surfaces and the size of the humeral head component in glenohumeral arthroplasty. The experimental system permitted a manual clinical examination of the glenohumeral joint while sensors monitored the humeroscapular position and orientation as well as the forces and torques applied by the examiner. Four preparations were compared: an anatomical humeroscapular preparation and three glenohumeral arthroplasty preparations (one with anatomically sized components and a radius of curvature of the glenoid that was four millimeters larger than that of the humeral head, one with anatomically sized components and a radius of curvature of the glenoid that was equal to that of the humeral head, and one with a non-anatomical, large humeral head component and a radius of curvature of the glenoid that was equal to that of the humeral head). All motions, including flexion, external and internal rotation, and maximum elevation, were diminished with use of the non-anatomical, large humeral head component. Laxity of the joint on drawer and sulcus tests was not affected by the conformity of the articular surfaces but was decreased significantly by implantation of the large humeral head component. The kinematics of the glenohumeral joint were not markedly altered by reduction of the uniformity between the articular surfaces of the prosthetic components. In all preparations, obligate displacement of the humeral head associated with a passive range of motion occurred at smaller angles with the large humeral head component.

Aged↗

PubMed1994

Arthroscopic labral repair to the glenoid rim.

The purpose of this study was to develop a new arthroscopic approach for traumatic instability that effectively reattaches avulsed capsulolabral tissue to the glenoid articular rim with sutures. This technique does not depend on fixation devices, trans-scapular drilling, or implantation of suture anchors. We attached a three-dimensional position sensor and force and torque transducer to the humerus and scapula of eight normal cadaveric shoulders to measure the normal, surgically unstable (arthroscopic Bankart lesion), and repaired preparations. We assessed eight motion ranges and six laxity tests. Capsulolabral release increased all passive ranges and allowed significant translational increases on posterior drawer and crank testing. After repair, motion was never decreased and there were no differences in laxity relative to normal. Neurovascular structures were never at risk. Our arthroscopic repair provides anatomic reattachment and effective deepening of the glenoid con-cavity similar to that achieved by open repair. This new method restores joint stability, preserves motion, and can withstand forceful loads. Ongoing clinical trials will substantiate whether the technique is as safe and reliable as shown cadaverically.

Adult↗

PubMed1993

Robotic assistance in orthopaedic surgery. A proof of principle using distal femoral arthroplasty.

The term "robot" refers to a precision mechanical device that is accurately controlled by a computer using intelligent software. The term "robotic assistance" refers to the use of such a device to aid a surgeon in the optimal conduct of a procedure, particularly one requiring specified geometrical relationships. The authors have been exploring the application of robotic assistance in situations in which accuracy and precision are required in orthopaedic surgery. The initial application concerned the planning, positioning, and orientation cuts and holes of the bone required for the femoral component of a total knee arthroplasty. A three-dimensional digitizing template allowed the surgeon to specify the desired position and orientation of the component's articular surfaces in relation to the distal femur. The robotic system used this spatial relationship, along with its knowledge of the geometry of the component selected by the surgeon, to plan the precise location of the required bone cuts and holes. Finally, the robotic assistant sequentially positioned saw and drill guides with respect to the distal femur so that the surgeon made these cuts and holes in the locations necessary for optimal component fit, position, and orientation. The robotic assistant functioned easily in the operating room environment; increased the accuracy; and decreased the time, equipment, and personnel required for the conduct of the geometrical part of this surgical procedure.

Hip Prosthesis↗

PubMed1992

The role of the rotator interval capsule in passive motion and stability of the shoulder.

The purpose of this study was to characterize the role of the capsule in the interval between the supraspinatus and subscapularis tendons with respect to glenohumeral motion, translation, and stability. We used a six-degrees-of-freedom position-sensor and a six-degrees-of-freedom force and torque-transducer to determine the glenohumoral rotations and translations that resulted from applied loads in eight cadaver shoulders. The range of motion of each specimen was measured with the capsule in the rotator interval in a normal state, after the capsule had been sectioned, and after it had been imbricated. Operative alteration of this capsular interval was found to affect flexion, extension, external rotation, and adduction of the humerus with respect to the scapula. Modification of this portion of the capsule also affected obligate anterior translation of the humeral head on the glenoid during flexion. Limitation of motion and obligate translation were increased by operative imbrication and diminished by sectioning of the rotator interval capsule. Passive stability of the glenohumeral joint was evaluated with the use of anterior, posterior, and inferior stress tests. Instability and occasional frank dislocation of the glenohumeral joint occurred inferiorly and posteriorly after section of the rotator interval capsule. Imbrication of this part of the capsule increased the resistance to inferior and posterior translation.

Aged↗

PubMed1991

A geometric theory of the equilibrium mechanics of fibers in ligaments and tendons.

This paper presents a theoretical analysis of the equilibrium mechanics of bending and twisting fiber geometries in ligaments and tendons. The theory predicts that the bending of loaded fibers is necessarily accompanied by large transverse pressures and pressure gradients. The predicted pressures are especially large at the bone tunnel entries of ligament grafts, where they can equal or exceed the applied tensile loads. Experimental measurements of internal pressures confirm these predictions.

Achilles Tendon↗

PubMed1991

Mechanics of glenohumeral instability.

The glenohumeral joint is designed for mobility and is normally lax. It is stabilized in its midrange by its limited joint volume and concavity-compression. It is stabilized at the extremes of motion by its ligaments. An enhanced understanding of these stabilizing mechanisms helps us in the diagnosis and management of glenohumeral instability.

Humans↗

PubMed1991

The effect of capsular venting on glenohumeral laxity.

Anesthetized shoulders are frequently stable against forces applied during drawer and sulcus tests, even though the shoulder muscles are inactive and do not contribute to stability. This passive stability is also evident in the glenohumeral joints of anatomic specimens. The translational laxity of anatomic specimen shoulders was measured, and it was demonstrated that this laxity was substantially increased when air was admitted into the capsule. Eight shoulders, aged 57-87 years, including six contralateral pairs, were analyzed using a six degrees-of-freedom force transducer and a six degrees-of-freedom spatial tracker. Capsules were vented by admitting air ad libitum through an 18-gauge needle. Venting reduced the force necessary to translate the humeral head with respect to the glenoid fossa by an average of 15.3 N (55%) for anterior forces, 10.8 N (43%) for posterior forces, and 19.0 N (57%) for inferior forces. It is likely that passive stability will also be diminished by a similar mechanism in patients with intact but excessively lax capsules. The principle of limited joint volume should be considered and tested when investigating glenohumeral stability.

Aged↗

PubMed1990

The interrelation of fiber bundles in the anterior cruciate ligament.

The anterior cruciate ligaments (ACL) of dogs, humans, and rabbits were studied by light and scanning electron microscopy after fixation in situ. In all species, the ACL was composed of multiple 20 microns-wide collagen fiber bundles separated by columns of cells in fibrous capsules. These bundles were in turn grouped into fascicles of varied size. The fascicles were surrounded by thin membranous sheets that ran through the ligament forming single or multiple layers between fascicles. Splaying of the ACL at insertion was created by increased volume in the cellular intervals. Bending of the fiber bundles occurred in this region--which corresponds to the fibrocartilaginous zone. We propose that the cell layers accommodate compressive forces and the membranes allow slipping among fascicles without compromising blood supply.

Aged↗

PubMed1990

Translation of the humeral head on the glenoid with passive glenohumeral motion.

We have demonstrated that certain passive motions of the glenohumeral joint are reproducibly accompanied by translation of the head of the humerus on the glenoid. We investigated the relationship of these translations to the position of the glenohumeral joint and to applied torques and forces in seven isolated glenohumeral joints from fresh cadavera, using a six-degrees-of-freedom position sensor and a six-axis force and torque transducer. Reproducible and significant translation occurred in an anterior direction with glenohumeral flexion and in a posterior direction with extension. We also observed translation with cross-body movement. The translation occurring with flexion was obligate in that it could not be prevented by the application of an oppositely directed force of thirty to forty newtons. Operative tightening of the posterior portion of the capsule increased the anterior translation on flexion and cross-body movement and caused it to occur earlier in the arc of motion compared with the intact glenohumeral joint. Operative tightening of the posterior part of the capsule also resulted in significant superior translation with flexion of the glenohumeral joint.

Aged↗

PubMed1990

The relationship of the glenohumeral joint capsule to the rotator cuff.

The glenohumeral joint capsules of 23 shoulders in which the rotator cuff was not torn were studied by gross dissection and histologic methods. The cuff tendons were resected, leaving the intact capsule attached to the bones. This dissection method provided a unique overview of the capsule in situ and allowed the areas of cuff tendon and muscle attachment to be mapped. The capsule was found to be a continuous cylinder between humerus and glenoid. On approximately one-third of the capsule (the portion adjacent to the humeral tuberosities), tight insertions of cuff tendons were noted. The superior segment between subscapularis and supraspinatus contained the coracohumeral ligament. This segment appeared to reinforce the cuff through a transversely oriented band similar to the glenohumeral ligaments.

Aged↗

PubMed1989

Reliability of the Genucom Knee Analysis System. A pilot study.

Instrumented knee laxity testing is now common practice in many orthopedic and rehabilitative practices around the country. The Genucom Knee Analysis System is marketed as a comprehensive quantitative knee joint laxity testing device. To examine the intrarater reliability of the Genucom, the authors evaluated five normal subjects, each on three independent occasions. All testing was done by a single examiner. Anteroposterior (AP) drawer, valgus/varus, and tibial rotation tests were performed. The average variability for repeated testing was determined and this variability was then used to estimate the smallest statistically significant difference for a single repeat examination that would represent true change, i.e., change over and above the inherent variability of the measurement. The results indicate that: (1) anterior drawer variability and tibial rotational variability are dependent on the knee flexion angle; (2) reporting anterior drawer may be more reproducible than reporting total AP motion; and (3) on average, changes exceeding 3 mm for anterior drawer tests, 5 mm for total valgus-varus motion, and 7 degrees-17 degrees of tibial rotation are needed to be 95% confident that the change in a measure from one time to the next is real and not due to measurement variability.

Adult↗