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Biomedical subjects

K-N An

Publications and source records attributed to K-N An.

15 recordsLinked to original sources
PubMed2006

Scleral penetration force requirements for commonly used intravitreal needles.

INTRODUCTION: Repeated intraocular injections have become routine practice. It is important to determine how to make them as painless as possible. We wished to examine the force required to penetrate the sclera with different gauge needles. METHODS: Recently enucleated eyes had 4 mm scleral punch biopsies performed. The scleral disks were mounted on a fixed load cell and either a new needle or a needle that had previously penetrated a rubber vial was attached to a linear stage and the maximum penetration force measured. RESULTS: The 27-gauge needles required almost twice as much force to penetrate the sclera than either the 30- or the 31-gauge. In addition, the 30- and 31-gauge appeared to require similar force. In all cases, following vial perforation, there was an increase in the amount of force required to penetrate the sclera. The amount of force was variable. DISCUSSION: Smaller gauge needles require less force to penetrate the sclera and needles that have been used to penetrate rubber vials require more force.

Biopsy↗
PubMed2005

Hyaluronic acid diminishes the resistance to excursion after flexor tendon repair: an in vitro biomechanical study.

Adhesion between the tendon and tendon sheath after primary flexor tendon repair is seen frequently, and postoperative finger function is occasionally unsatisfactory. A reduction of the friction may facilitate tendon mobilization, which in turn may reduce the risk of the adhesion and restriction of range of motion. We considered the possibility of utilizing the hyaluronic acid (HA) as a lubricant. To evaluate the effect of HA, the gliding resistance between the canine flexor digitorum profundus tendon repaired by a modified Kessler suture technique with running epitendinous suture and the annular pulley located on the proximal phalanx (corresponding to the A2 pulley in humans) was evaluated and compared before and after administration of HA. The HA solution measurement groups were identified as follows; intact tendon as a control; repaired tendon; tendon soaked in 0.1, 1, and 10 mg/ml HA. The resistance increased after repairing, then it decreased after soaking in 10 mg/ml HA solution. The results of this study revealed that HA diminishes the excursion resistance after flexor tendon repair. We believe that some style of administration of the HA might reduce the excursion resistance and prevent adhesion until the synovial surface is fully developed.

Animals↗
PubMed2004

Effects of glenohumeral rotations and translations on supraspinatus tendon morphology.

OBJECTIVE: The purpose of this study was to evaluate the effects of glenohumeral rotations and humeral head translations on supraspinatus tendon morphology. DESIGN: A convenience sample of cadaver shoulders was used to measure supraspinatus tendon shape and dimensions from MRI images. BACKGROUND: Epidemiological evidence has indicated that shoulder elevation and external rotation may be risk factors for rotator cuff tendon pathology, but little is known about how these postures affect tendon morphology. METHODS: Measurements of supraspinatus tendon morphology were made from three-dimensional reconstructions based on T2-weighted fast spin-echo magnetic resonance images. Seven cadaver arms were imaged at neutral, 45 degrees external and 45 degrees internal rotations at 0 degrees, 30 degrees, and 60 degrees of glenohumeral abduction. Measurements of the anterior, middle, and posterior portions of the tendon were made using ANALYZE software. RESULTS: The supraspinatus tendon was twisted at the muscle-tendon junction of the middle and posterior portions in 45 degrees external and 45 degrees internal axial rotations of the humerus, especially over 30 degrees of abduction. Abduction over 30 degrees shortened the entire supraspinatus tendon. External and internal rotation motions elongated the anterior and posterior portions, respectively. CONCLUSIONS: Arm posture affects morphology of the supraspinatus tendon. RELEVANCE: The results support the epidemiologic evidence linking external rotation and abduction to supraspinatus tendon disorders.

Aged↗
PubMed2004

The effect of the orientation of the noncircular radial head on elbow kinematics.

OBJECTIVE: The objective of this study was to identify the effect of radial head shape and orientation on elbow kinematics in the otherwise intact elbow. DESIGN: Biomechanical study, analyzing simulated active motion of cadaveric arms. BACKGROUND: A discrepancy exists between the noncircular anatomy of the radial head and radial head prostheses. The effect of radial head shape is unknown. METHODS: Kinematic effects of radial head shape were tested in six fresh-frozen upper extremities. A custom-made native radial head prosthesis was used to simulate altered shape conditions, by rotating the radial head 90 degrees. Three-dimensional spatial orientation of the ulna was recorded, during simulated active motion. A three factor ANOVA was used to compare (a) nominal and 90 degrees oriented conditions, (b) throughout the flexion arc (c) in three forearm positions (P < 0.05). Post-hoc Tukey tests were done to assess significance. RESULTS: No significant effect of altering radial head shape was found on total ulnohumeral laxity and angulation during gravity valgus stress. We did find a significant effect on total ulnar axial rotation and rotation during gravity valgus stress. CONCLUSION: The outer shape of the radial head seems to change rotation of the ulna during flexion-extension in an otherwise intact elbow. RELEVANCE: The shape of the radial head effects intact elbow kinematics. Clinical importance of this finding is clear. If a sub-optimally placed radial head prosthesis were to be used in an otherwise intact elbow, the elbow could be at risk for early ulnohumeral arthritis.

Biomechanical Phenomena↗
PubMed2004

Detrimental effects of overstuffing or understuffing with a radial head replacement in the medial collateral-ligament deficient elbow.

BACKGROUND: Comminuted radial head fractures associated with an injury of the medial collateral ligament can be treated with a radial head implant. We hypothesized that lengthening and shortening of the radial neck would alter the kinematics and the pressure through the radiocapitellar joint in the medial collateral ligament-deficient elbow. METHODS: The effects of lengthening (2.5 and 5 mm) and shortening (2.5 and 5 mm) of the radial neck were assessed in six human cadaveric upper extremities in which the medial collateral ligament had been surgically released. The three-dimensional spatial orientation of the ulna was recorded during simulated active motion from extension to flexion. Total varus-valgus laxity and ulnar rotation were measured. Radiocapitellar joint pressure was assessed with use of pressure-sensitive film. RESULTS: Radial neck lengthening or shortening of >/=2.5 mm significantly changed the kinematics in the medial collateral ligament-deficient elbow. Lengthening caused a significant decrease (p < 0.05) in varus-valgus laxity and ulnar rotation (p < 0.05), with the ulna tracking in varus and external rotation. Shortening caused a significant increase in varus-valgus laxity (p < 0.05) and ulnar rotation (p < 0.05), with the ulna tracking in valgus and internal rotation. The pressure on the radiocapitellar joint was significantly increased after 2.5 mm of lengthening. CONCLUSIONS: This study suggests that accurate restoration of radial length is important and that axial understuffing or overstuffing of the radiohumeral joint by >/=2.5 mm alters both elbow kinematics and radiocapitellar pressure. CLINICAL RELEVANCE: This in vitro cadaver study indicates that a radial head replacement should be performed with the same level of concern for accuracy and reproducibility of component position and orientation as is appropriate with any other prosthesis.

Aged↗
PubMed2003

Elasticity of alveolar bone near dental implant-bone interfaces after one month's healing.

Information is scarce about Young's modulus of healing bone surrounding an implant. The purpose of this preliminary study is to quantify elastic properties of pig alveolar bone that has healed for 1 month around titanium threaded dental implants, using the nanoindentation method. Two 2-year-old Sinclair miniswine were used for the study. Nanoindentation tests perpendicular to the bucco-lingual cross section were performed on harvested implant-bone blocks using the Hysitron TriboScope III. Nomarski differential interference contrast microscopy was used to identify pyramidal indentation measurements that were from bone. Reduced moduli, averaged for all anatomical regions, were found to start low (6.17 GPa) at the interface and gradually increase (slope=0.014) to a distance of 150 microm (7.89 GPa) from the implant surface, and then flatten to a slope of 0.001 from 150 to 1500 microm (10.13 GPa). Mean reduced modulus and its relationship to distance did not differ significantly by anatomic location (e.g., coronal, middle, and apical third; P>/=0.28 for all relevant tests) at 1 month after implantation.

Alveolar Bone Loss↗
PubMed2003

Gliding properties of the long head of the biceps brachii.

To elucidate the role of mechanical forces that resist motion of the long head of the biceps brachii, the gliding resistance of the tendon during abduction and adduction was measured. Nine human cadaveric glenohumeral joints were obtained (mean age 68 years, range 47-84). A testing device was developed to simulate glenohumeral abduction and adduction motion. Gliding resistance was calculated as the force differential on the proximal and distal ends of the biceps brachii at five glenohumeral angles (15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees ). The average gliding resistance in abduction at 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees for a 4.9 N load was 0.41, 0.40, 0.36, 0.32 and 0.28 N, respectively. At these same angles, but during adduction motion, the force on the proximal tendon end was either identical or less than the distal tendon end (p>0.46) indicating a lack of resistance and even a phenomena of "negative" resistance in which some other force overcame the friction. The difference in gliding resistance between abduction and adduction was significant (p<0.05). The results indicate that forces opposing biceps tendon gliding are more complicated than simply due to friction. Tendon deformation inside the bicipital groove produces a direction-dependent effect due to a mechanism of elastic recoil. Understanding forces that are absorbed by the tendon during active motion may provide insight into pathological changes that develop inside and around the tendon.

Friction↗
PubMed2003

[Radioulnar impingement after distal ulnar resection and ulnar head hemiresection interposition arthroplasty (Bowers procedure). An experimental biomechanical study].

Resection of the distal ulna (Darrach operation) and the ulnar head hemiresection interposition arthroplasty (Bowers procedure) are common methods of treating the arthrotic distal radioulnar joint (DRUJ). The purpose of this study was to evaluate the dynamic effects of both the Bowers operation and the resection of the distal ulna on radioulnar impingement and dorsal-palmar displacement and to compare their biomechanical performances. With a dynamic forearm simulator forearm rotation was performed with simultaneous loading of relevant muscles. Torque along the forearm axis was generated by simulated muscle action with loading of the relevant tendons while the wrist was constrained to prescribed ranges of motion. The instability of the radius relative to the ulna was evaluated using displacement data of digitized landmarks in an ulnar coordinate system. Seven fresh-frozen cadaver upper extremities were used. Resection of the distal ulna created a significant instability of the forearm with movement of the radius ulnarly. Anteroposterior translations in each loading condition could be detected as well but the magnitude of displacement was little and less predictable. The results of the Bowers operation demonstrated significantly less instability compared with the Darrach results. Our data demonstrates that the dynamic behavior of the Bowers procedure is superior to the mechanical performance of complete resection of the distal ulna.

Arthroplasty↗
PubMed2003

Effects of implant healing time on crestal bone loss of a controlled-load dental implant.

The universally accepted concept of delay-loaded dental implants has recently been challenged. This study hypothesizes that early loading (decreased implant healing time) leads to increased bone formation and decreased crestal bone loss. We used 17 minipigs to study implants under a controlled load, with non-loaded implants for comparison. Radiographic and histological assessments were made of the osseointegrated bone changes for 3 healing times (between implant insertion and loading), following 5 months of loading. The effect of loading on crestal bone loss depended on the healing time. Early loading preserved the most crestal bone. Delayed loading had significantly more crestal bone loss compared with the non-loaded controls (2.4 mm vs. 0.64 mm; P < 0.05). The histological assessment and biomechanical analyses of the healing bone suggested that loading and bioactivities of osteoblasts exert a synergistic effect on osseointegration that is likely to support the hypothesis that early loading produces more favorable osseointegration.

Alveolar Bone Loss↗
PubMed2003

Partial posteromedial olecranon resection: a kinematic study.

BACKGROUND: The posteromedial aspect of the olecranon process is a site of impingement and subsequent osteophyte development in throwing athletes. Treatment with débridement, with resection of osteophytes and varying amounts of normal olecranon bone, is common. We found no reports in the literature concerning the effects of resecting different amounts of normal bone from the posteromedial aspect of the olecranon. We hypothesized that excessive resection would increasingly alter elbow kinematics and that an optimum amount of olecranon resection could be identified. METHODS: We investigated the kinematic effects of increasing valgus and varus torques and posteromedial olecranon resections, in twelve cadaveric elbows, with use of an electromagnetic tracking device. Two valgus and two varus torques were applied, and three sequential resections were performed in 3-mm steps from 0 mm to 9 mm. Statistical analyses included paired t tests, 95% confidence intervals, a one-factor analysis of variance with repeated measures, and a post hoc test when significance was established. RESULTS: Sequential partial resection of the posteromedial aspect of the olecranon resulted in stepwise increases in valgus angulation with valgus torque. Clear differences were seen at each level of resection. A pattern of increased valgus angulation also was seen in association with increased valgus torque. Increased valgus torque resulted in a trend toward increased axial internal rotation of the ulna, whereas increased osseous resection resulted in a decrease in the absolute degree of internal rotation or, in some specimens, increased external rotation. CONCLUSIONS: Although no single critical amount of olecranon resection was identified, valgus angulation of the elbow increased in association with all resections, with a marked increase occurring in association with a 9-mm resection. Our findings challenge the rationale of removing any amount of normal olecranon bone in throwing athletes as doing so may increase strain on the medial collateral ligament. The implications for the professional throwing athlete are important, and we recommend that bone removal from the olecranon be limited to osteophytes, without the removal of normal bone.

Aged↗
PubMed2002

Effect of pregnancy on joint contracture in the rat knee.

As there is evidence that ligamentous laxity is affected by the female hormones, we hypothesized that hormonal changes occurring during pregnancy could have a therapeutic role in preventing the development of a joint contracture. Knee joint contractures were created in pregnant and nonpregnant rats. After 2 wk of immobilization, the degree of contracture was measured with structural properties of the medial collateral and anterior cruciate ligaments and the pubic symphysis. Although not statistically significant, there was a general trend toward reduced contracture in pregnant compared with nonpregnant rats. Cutting the posterior capsule significantly decreased contracture for both the pregnant and nonpregnant groups, confirming the contribution of capsular structures to contracture. Ultimate loads of the medial collateral and anterior cruciate ligaments significantly decreased after immobilization compared with control, but there was no significant effect due to pregnancy. Stiffness and ultimate load of the pubic symphysis were not significantly different between pregnant and nonpregnant groups. The trend toward reduced contracture with pregnancy points toward a possible therapeutic role for female hormones in the prevention of postoperative and/or posttraumatic joint contracture.

Animals↗
PubMed1997

Valgus-varus motion of the knee in normal level walking and stair climbing.

OBJECTIVE: The knee valgus-varus moment and the knee angles were compared between normal level walking and stair climbing. DESIGN: Ten healthy subjects were tested for ascent, descent, and level walking. BACKGROUND: An understanding of the normal valgus-varus motion of the knee during stair climbing is needed to apply biomechanical analysis of stair climbing as a evaluation tool for knee osteoarthritis patients. METHODS: A motion analysis system, three force plates, and a flight of stairs were used to collect kinematic and kinetic data. The knee angles and moments were calculated from the collected kinematic and kinetic data. RESULTS: The knee varus angle for the maximum knee valgus moments in stair climbing was significantly greater than that in level walking. The knee valgus moment was significantly correlated to ground reaction forces and knee valgus-varus angle during stair climbing and level walking. CONCLUSIONS: There is a coupling between the knee valgus-varus motion and flexion-extension motion. Ground reaction forces are the major contributors to the within-subject variation in the knee valgus-varus moment during stair climbing and level walking. The knee valgus-varus angle is a major contributor to the between-subject variation in the knee valgus moment during stair climbing and level walking.

Journal Article↗
PubMed1996

Rotational laxity and stiffness of the radiocarpal joint.

OBJECTIVE: To investigate the constraint and potential mechanism of torque transmission across the wrist joint. DESIGN: In vitro experiment using human cadaveric specimens. BACKGROUND: Transmission of torque from the forearm to the hand requires rotational stability at the wrist. Better appriciation of the constraints would have applicability to several clinical problems where the stability is compromised. METHODS: Thirteen fresh-frozen cadaveric specimens were used in this experiment to investigate the rotational laxity and stiffness of the radiocarpal joint in unloaded and axially loaded (100 N) conditions, and three forearm orientations in a neutral, pronation (60 degrees ), or supination (60 degrees ) position. RESULTS: In pronation or supination, there was no difference between loaded and unloaded conditions in primary or total laxity at a maximum torque of 2.3 Nm. Unloaded specimens showed a mean total rotational laxity of 42.1 degrees. Supination or pronation of the forearm caused a decrease in laxity with respect to neutral forearm rotation (35 degrees and 41.6 degrees versus 49.6 degrees respectively). The primary rotational laxity accounted for half of the total laxity. With axial compression, total rotational laxity did not change, but primary laxity dropped to 50% of its unloaded value. The primary stiffness was very low -- approximately 11% of the secondary stiffness. CONCLUSION: The ligamentous structures and the joint articulation restricted excessive axial rotation of the wrist. However, a laxity of approximately 20 degrees was identified for normal wrists. RELEVANCE: This study demonstrated that the primary axial rotational laxity of the radiocarpal joint was approximately 20 degrees. In the mathematical model and implant design, muscular balance of the joint within such laxity should be considered.

Journal Article↗
PubMedDate not supplied

Contraction of collagen gels seeded with tendon cells.

Knowledge of the adaptation of the soft tissue to mechanical factors and biomolecules would be essential to better understand the mechanism of tendon injury and to improve the outcome of tendon repair. The responses to these factors could be different for the distinct types of cells in the tendon: cells from the tendon sheath, fibroblasts from the epitenon surface, or fibroblasts from the internal endotenon. In this study, we examined the mechanical and histological characteristics of the rate of contraction of the collagen gel seeded with epitenon and endotenon fibroblasts. The rate of contraction and the mechanical property of the contracted construct depend on the gel concentration and also the treatment of TGF-beta1.

Animals↗