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Biomedical subjects

R J Pawluk

Publications and source records attributed to R J Pawluk.

26 records · Page 2Linked to original sources
PubMedDate not supplied

Inferior glenohumeral ligament: geometric and strain-rate dependent properties.

The inferior glenohumeral ligament (IGHL) is an important structure for maintaining shoulder stability. This study was aimed at determining the geometric and anatomic characteristics of the IGHL and its tensile properties at a higher strain rate than previously tested. Eight fresh-frozen human cadaver shoulders (average age 69 years, age range 62 to 73 years) from four female and four male cadavers were used to harvest bone-ligament-bone specimens from the three regions of the IGHL (superior band, anterior axillary pouch, and posterior axillary pouch). Uniaxial tensile tests were performed at the moderately high strain rate of approximately 10% per second with a servo-hydraulic testing machine. This represented a strain rate that was approximately 100 to 1000 times faster than that previously reported. During tensile testing, bone-ligament-bone strains were calculated from grip-to-grip motion on the testing machine, and mid-substance strains were determined by a video dimensional analyzer. Although all regions of the IGHL had similar lengths (averaging 43.4 mm), their thickness varied by region and by proximal-to-distal location. The superior band was the thickest (2.23 +/- 0.38 mm) of the three regions. Of the remaining two regions the anterior axillary pouch (1.94 +/- 0.38 mm) was thicker than the posterior axillary pouch (1.59 +/- 0.64 mm). By proximal-to-distal location the IGHL was thicker for all three regions near the glenoid (2.30 +/- 0.57 mm) than near the humerus (1.61 +/- 0.52 mm). The superior band had a greater stiffness (62.63 +/- 9.78 MPa) than either the anterior axillary pouch (47.75 +/- 17.89 MPa) or the posterior axillary pouch (39.97 +/- 13.29 MPa). Tensile stress at failure was greater in the superior band (8.4 +/- 2.2 MPa) and the anterior axillary pouch (7.8 +/- 3.1 MPa) than the posterior axillary pouch (5.9 +/- 1.7 MPa). The anterior axillary pouch demonstrated greater bone-to-bone and mid-substance strains (30.4% +/- 4.3% and 10.8% +/- 2.4%, respectively) before failure than the other two regions (superior band: 20.8% +/- 3.8% and 9.1% +/- 2.8%, respectively; posterior axillary pouch: 25.2% +/- 5.8% and 7.8% +/- 2.6%, respectively). Bone-to-bone strain was always greater than mid-substance strain, indicating that when the IGHL is stretched, the tissue near the insertion sites will experience much greater strain than the tissue in the mid-substance. insertion failures were more likely at slower strain rates, and ligamentous failures were predominant at the fast strain rate. When compared with other tensile studies of the IGHL at slower strain rates (0.01% per second and 0.1% per second), the superior band and the anterior axillary pouch demonstrated the viscoelastic effects of increased stiffness and failure stress. This superior band and anterior axillary pouch pouch viscoelastic stiffening effect suggests that these two regions may function to restrain the humeral head from rapid abnormal anterior displacement in the clinically vulnerable position of abduction and external rotation.

Aged↗
PubMedDate not supplied

Effects of repetitive subfailure strains on the mechanical behavior of the inferior glenohumeral ligament.

The mechanical response of the inferior glenohumeral ligament to varying subfailure cyclic strains was studied in 33 fresh frozen human cadaver shoulders. The specimens were tested as bone-ligament-bone preparations representing the 3 regions of the inferior glenohumeral ligament (superior band and anterior and posterior axillary pouches) through use of uniaxial tensile cycles. After mechanical preconditioning, each specimen was subjected to 7 test segments, consisting of a baseline strain level L1 (400 cycles) alternating with either 1 (group A, 10 shoulders), 10 (group B, 13 shoulders), or 100 (group C, 10 shoulders) cycles at increasing levels (L2, L3, L4) of subfailure strain. Cycling to higher levels of subfailure strain (L2, L3, L4) produced dramatic declines in the peak load response of the inferior glenohumeral ligament for all specimens. The group of ligaments subjected to 100 cycles of higher subfailure strains demonstrated a significantly greater decrease in load response than the other 2 groups. Ligament elongation occurred with cyclic testing at subfailure strains for all 3 groups, averaging 4.6% +/- 2.0% for group A, 6.5% +/- 2.6% for group B, and 7.1% +/- 3.2% for group C. Recovery of length after an additional time of nearly 1 hour was minimal. The results from this study demonstrate that repetitive loading of the inferior glenohumeral ligament induces laxity in the ligament, as manifested in the peak load response and measured elongations. The mechanical response of the ligament is affected by both the magnitude of the cyclic strain and the frequency of loading at the higher strain levels. The residual length increase was observed in all of the specimens and appeared to be largely unrecoverable. This length increase may result from accumulated microdamage within the ligament substance, caused by the repetitively applied subfailure strains. The clinical relevance of the study is that this mechanism may contribute to the development of acquired glenohumeral instability, which is commonly seen in the shoulders of young athletes who participate in repetitive overhead sports activities.

Adult↗
PubMedDate not supplied

Glenohumeral mechanics: a study of articular geometry, contact, and kinematics.

Stereophotogrammetry was used to investigate the functional relations between the articular surface geometry, contact patterns, and kinematics of the glenohumeral joint. Nine normal shoulder specimens were elevated in the scapular plane by using simulated muscle forces in neutral rotation (NR) and starting rotation (SR). Motion was quantified by analyzing the translations of the geometric centers of the humeral head cartilage and bone surfaces relative to the glenoid surface. In both NR and SR, the ranges of translations of the center of the humeral head cartilage surface were greatest in the inferior-superior direction (NR 2.0 +/- 0.7 mm, SR 2.9 +/- 1.2 mm). Results of this study also show that joints with less congruence of the articular surfaces exhibit larger translations, and elevation in SR yields greater translations than in NR. Kinematic analyses with the humeral head bone surface data yielded larger values of translation than analyses that used the cartilage surface data, suggesting that similar overestimations may occur in radiographic motion studies. Results of this study demonstrate that small translations of the humeral head center occurred in both SR and NR. The proximity of the origin of the helical axes to the geometric center of the humeral head articular surface confirmed that glenohumeral elevation is mainly rotation about this geometric center with small translations.

Adult↗
PubMedDate not supplied

In vivo effects of direct current in the mandible.

The application of low level direct current (3 to 5 mua in situ, that is, 50 mua/cm2), within the mandible of mature Beagle dogs results in an increased osteogenesis at the cathode (negative electrode) when compared to responses about nonactive (control) packs within the same dog. The increased osteogenesis suggests a stimulation of cellular activity rather than the electrophoretic migration of cells. Significant differences observed between platinum-iridium and stainless-steel electrodes seem to suggest that faradaic results play little or no role in the osteogenic response at the platinum-iridium cathode. Conversely, at all other electrodes, faradaic reactions compete to some extent with an osteogenic response. Careful consideration of current density and electrode composition must be taken into account when direct current stimulation is to be used.

Animals↗
PubMedDate not supplied

Excursion of the rotator cuff under the acromion. Patterns of subacromial contact.

Nine fresh-frozen, human cadaveric shoulders were elevated in the scapular plane in two different humeral rotations by applying forces along action lines of rotator cuff and deltoid muscles. Stereophotogrammetry determined possible regions of subacromial contact using a proximity criterion; radiographs measured acromiohumeral interval and position of greater tuberosity. Contact starts at the anterolateral edge of the acromion at 0 degrees of elevation; it shifts medially with arm elevation. On the humeral surface, contact shifts from proximal to distal on the supraspinatus tendon with arm elevation. When external rotation is decreased, distal and posterior shift in contact is noted. Acromial undersurface and rotator cuff tendons are in closest proximity between 60 degrees and 120 degrees of elevation; contact was consistently more pronounced for Type III acromions. Mean acromiohumeral interval was 11.1 mm at 0 degrees of elevation and decreased to 5.7 mm at 90 degrees, when greater tuberosity was closest to the acromion. Radiographs show bone-to-bone relationship; stereophotogrammetry assesses contact on soft tissues of the subacromial space. Contact centers on the supraspinatus insertion, suggesting altered excursion of the greater tuberosity may initially damage this rotator cuff region. Conditions limiting external rotation or elevation may also increase rotator cuff compression. Marked increase in contact with Type III acromions supports the role of anterior acromioplasty when clinically indicated, usually in older patients with primary impingement.

Acromion↗