Biomedical subjects

Colin S Gregersen

Publications and source records attributed to Colin S Gregersen.

4 recordsLinked to original sources

PubMed2006

Biomechanical comparison of traditional and locked suture configurations for arthroscopic repairs of the rotator cuff.

BACKGROUND: The optimal suture configuration for arthroscopic rotator cuff repairs is controversial. "Locked" suture configurations, which use a combination of simple and transverse suture loops, have demonstrated better fixation strength than have traditional simple and horizontal mattress techniques. PURPOSE: To compare traditional arthroscopic suture configurations to locked arthroscopic configurations in ability to resist gap formation under cyclic loading. STUDY DESIGN: Controlled laboratory study. METHODS: Crescent-shaped defects were created at the infraspinatus tendon insertion in 32 bovine shoulders. Four arthroscopic suture configurations were tested (8 specimens in each group): simple (group 1), horizontal mattress (group 2), locked mattress (group 3), and locked inverted mattress (group 4). A metal corkscrew suture anchor doubly loaded with No. 2 Fiberwire suture was used for the repairs. A cyclic loading protocol with application of forces from 10 to 180 N for a maximum of 2,500 cycles was used. The number of cycles required to form gaps of 5 mm and 10 mm was recorded. RESULTS: The locked mattress configuration (group 3) outperformed all other groups in resisting 5-mm gap formation (P < .0001), requiring a mean of 628 cycles in comparison to 65, 193, and 197 cycles for groups 1, 2, and 4, respectively. Both locked configurations (groups 3 and 4) were superior to traditional simple and horizontal mattress configurations in resisting 10-mm gap formation. CONCLUSION: The locked mattress suturing technique (group 3) provided the most secure tendon fixation of all arthroscopic configurations tested. CLINICAL RELEVANCE: The use of locked suture configurations for arthroscopic rotator cuff repairs may enhance tendon fixation and limit gap formation in the early postoperative period.

Animals↗

PubMed2006

How changing the inversion/eversion foot angle affects the nondriving intersegmental knee moments and the relative activation of the vastii muscles in cycling.

Nondriving intersegmental knee moment components (i.e., varus/valgus and internal/external axial moments) are thought to be primarily responsible for the etiology of overuse knee injuries such as patellofermoral pain syndrome in cycling because of their relationship to muscular imbalances. However the relationship between these moments and muscle activity has not been studied. Thus the four primary objectives of this study were to test whether manipulating the inversion/eversion foot angle alters the varus/valgus knee moment (Objective 1) and axial knee moment (Objective 2) and to determine whether activation patterns of the vastus medialis oblique (VMO), vastus lateralis (VL), and tensor fascia latae (TFL) were affected by changes in the varus/valgus (Objective 3) and axial knee moments (Objective 4). To fulfill these objectives, pedal loads and lower limb kinematic data were collected from 15 subjects who pedaled with five randomly assigned inversion/eversion angles: 10 deg and 5 deg everted and inverted and 0 deg (neutral). A previously described mathematical model was used to compute the nondriving intersegmental knee moments throughout the crank cycle. The excitations of the VMO, VL, and TFL muscles were measured with surface electromyography and the muscle activations were computed. On average, the 10-deg everted position decreased the peak varus moment by 55% and decreased the peak internal axial moment by 53% during the power stroke (crank cycle region where the knee moment is extensor). A correlation analysis revealed that the VMO/VL activation ratio increased significantly and the TFL activation decreased significantly as the varus moment decreased. For both the VMO/VL activation ratio and the TFL activation, a path analysis indicated that the varus/valgus moment was highly correlated to the axial moment but that the correlation between muscle activation and the varus moment was due primarily to the varus/valgus knee moment rather than the axial knee moment. The conclusion from these results is that everting the foot may be beneficial towards either preventing or ameliorating patellofemoral pain syndrome in cycling.

Adaptation, Physiological↗

PubMed2004

Gear ratios at the limb joints of jumping dogs.

An increase in gear ratio of the limb extensor muscles during joint extension has been suggested to be a mechanism that facilitates optimal power production by skeletal muscles. The objectives of this study were to: (1) measure gear ratios at the wrist, elbow, shoulder, ankle, knee, and hip joints of jumping dogs, (2) compute the work performed by each of these joints, and (3) measure muscle shortening velocity for a joint exhibiting an increasing gear ratio during joint extension. The gear ratio out-lever was computed by dividing the ground reaction force (GRF) moment by the GRF, whereas the in-lever was directly measured as the perpendicular distance from the joint center to the line of action of the extensor muscle. In addition, changes in fascicle length were measured from the vastus lateralis muscle using sonomicrometry. Of the joints examined, only the gear ratios at the shoulder and knee joints increased during jumping in a manner that could facilitate peak power production of actively shortening muscles. The vastus lateralis was found to shorten at an average velocity of 3.20 muscle lengths per second. This is similar to estimates of shortening velocity that produce peak muscular power in mammals the size of dogs. Additionally, the knee extensors were found to produce a large proportion (26.6%) of the positive external work of the limbs. These observations suggest that dynamic gearing in jumping dogs may allow the extensor muscles of the knee joint to shorten in a way that maximizes their power production.

Animals↗

PubMed2003

Non-driving intersegmental knee moments in cycling computed using a model that includes three-dimensional kinematics of the shank/foot and the effect of simplifying assumptions.

Assessing the importance of non-driving intersegmental knee moments (i.e. varus/valgus and internal/external axial moments) on over-use knee injuries in cycling requires the use of a three-dimensional (3-D) model to compute these loads. The objectives of this study were: (1) to develop a complete, 3-D model of the lower limb to calculate the 3-D knee loads during pedaling for a sample of the competitive cycling population, and (2) to examine the effects of simplifying assumptions on the calculations of the non-driving knee moments. The non-driving knee moments were computed using a complete 3-D model that allowed three rotational degrees of freedom at the knee joint, included the 3-D inertial loads of the shank/foot, and computed knee loads in a shank-fixed coordinate system. All input data, which included the 3-D segment kinematics and the six pedal load components, were collected from the right limb of 15 competitive cyclists while pedaling at 225 W and 90 rpm. On average, the peak varus and internal axial moments of 7.8 and 1.5 N m respectively occurred during the power stroke whereas the peak valgus and external axial moments of 8.1 and 2.5 N m respectively occurred during the recovery stroke. However, the non-driving knee moments were highly variable between subjects; the coefficients of variability in the peak values ranged from 38.7% to 72.6%. When it was assumed that the inertial loads of the shank/foot for motion out of the sagittal plane were zero, the root-mean-squared difference (RMSD) in the non-driving knee moments relative to those for the complete model was 12% of the peak varus/valgus moment and 25% of the peak axial moment. When it was also assumed that the knee joint was revolute with the flexion/extension axis perpendicular to the sagittal plane, the RMSD increased to 24% of the peak varus/valgus moment and 204% of the peak axial moment. Thus, the 3-D orientation of the shank segment has a major affect on the computation of the non-driving knee moments, while the inertial contributions to these loads for motions out of the sagittal plane are less important.

Adolescent↗