Biomedical subjects

M E Zobitz

Publications and source records attributed to M E Zobitz.

At least 19 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

Providing quantitative feedback when teaching tendon repair: a new tool.

Flexor tendon repair remains one of the more difficult technical tasks facing the hand surgeon. A good repair must be both strong and able to glide smoothly through the tendon sheath. The purpose of this study is to present a model that allows surgeons to improve their technique of flexor tendon repair by receiving feedback on these important biomechanical parameters. The set-up requires testing equipment found in most biomechanical laboratories and should be available in many academic medical centres. Preliminary data suggest that receiving feedback about the strength and smoothness of a flexor tendon repair may be a very useful tool in helping surgeons improve the overall quality of their tendon repair technique.

General Surgery↗

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↗

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↗

PubMed2002

Biomechanical comparison of effects of supraspinatus tendon detachments, tendon defects, and muscle retractions.

BACKGROUND: Rotator cuff ruptures are frequently associated with loss of strength of the shoulder. However, the characteristics of the rotator cuff tear that are responsible for the loss of force generation and transmission have not yet been identified. The purpose of this study was to compare the effects of supraspinatus tendon detachments, tendon defects, and muscle retractions on in vitro force transmission by the rotator cuff to the humerus. METHODS: The rotator cuff tendons from ten cadaver shoulders were loaded proportionally to the respective cross-sectional areas of their muscles. A fiberglass rod was cemented into the medullary canal of the humerus and connected to a three-component load cell for the measurement of the forces transmitted by the rotator cuff to the humerus. This study was performed with the humerus in a hanging arm position and with various sizes of supraspinatus tendon detachments, tendon defects, and muscle retractions. RESULTS: Detachment or creation of a defect involving one-third or two-thirds of the supraspinatus tendon resulted in a minor reduction in the force transmitted by the rotator cuff (< or =5%), while detachment or creation of a defect involving the whole tendon resulted in a moderate reduction (11% and 17%, respectively). Simulated muscle retraction involving one-third, two-thirds, and the whole tendon resulted in losses of torque measuring 19%, 36%, and 58%, respectively. Side-to-side repair of the one-third and two-thirds defects nearly restored the force transmission capability, whereas a deficit remained after side-to-side repair following complete resection. CONCLUSIONS: Our results support the rotator cable concept and correspond to the clinical observation that patients with a small rupture of the rotator cuff may present without a loss of shoulder strength. Muscle retraction is potentially an important factor responsible for loss of shoulder strength following large rotator cuff ruptures. CLINICAL RELEVANCE: Supraspinatus muscle retraction diminishes glenohumeral abduction torque significantly more than either a defect in the tendon or a simple detachment of the tendon from the tuberosity. In cases of irreparable defects, side-to-side repair may be worthwhile to restore muscle tension and the integrity of the rotator cable.

Biomechanical Phenomena↗

PubMed2002

Pulley plasty versus resection of one slip of the flexor digitorum superficialis after repair of both flexor tendons in zone II: a biomechanical study.

BACKGROUND: The outcome of repair of zone-II lacerations of the flexor digitorum superficialis and flexor digitorum profundus tendons remains suboptimal. We investigated the effects of two strategies to improve postoperative gliding in a human cadaveric hand. METHODS: The second, third, and fourth digits were harvested from ten fresh-frozen human cadaveric hands. Complete lacerations and repairs were made to the profundus and superficialis tendons at a location where both repair sites would pass beneath the A2 pulley with the proximal interphalangeal joint in 45 degrees of flexion. The gliding resistance of the flexor digitorum profundus tendon was measured following pulley plasty and following excision of one slip of the flexor digitorum superficialis. The breaking strength of the remaining slip of the flexor digitorum superficialis tendon was then measured. RESULTS: Pulley plasty and resection of one slip of the flexor digitorum superficialis tendon both significantly decreased gliding resistance compared with repair of both slips (p < 0.001). There was no difference in the mean gliding resistance between the pulley plasty and one-slip resection groups. The flexor digitorum superficialis slip was stronger after repair with a Becker suture (28.8 +/- 9.0 N) than after repair with a modified Kessler (16.4 +/- 4.5 N) or a zigzag suture (15.0 +/- 5.7 N). CONCLUSION: Both pulley plasty and resection of one slip of the flexor digitorum superficialis reduce gliding resistance after tendon repair in zone II of the hand.

Adult↗

PubMed2001

Gliding resistance after repair of partially lacerated human flexor digitorum profundus tendon in vitro.

OBJECTIVE: This study reports the gliding resistance between repaired, partially lacerated tendon and pulley in human cadaver digits, using several commonly employed repair techniques. BACKGROUND: Suture techniques with multi-strands and locking loops have been recommended to reduce the risk of rupture of the repair tendon with early active motion. Such sutures may increase the gliding resistance, and the gliding resistance after tendon repair is also an important factor influencing the rehabilitation. METHOD: 105 specimens of second, third, or fourth fingers from 36 adult human hands were tested for the gliding resistance between flexor digitorum profundus tendon and A2 pulley in the normal condition. After an 80% laceration, each tendon was repaired with one of the following suture techniques: (1) Kessler; (2) modified Kessler; (3) Savage; (4) Lee; (5) Tsuge; and (6) Becker. All suture techniques were reinforced with a circumferential epitenon simple running suture. After tendon repair, the gliding resistance was remeasured. RESULTS: The gliding resistance of the Becker repair was significantly greater than each of the other four repairs (P<0.05). The resistance of the modified Kessler repair was significantly less than that of the Kessler, Savage, or Tsuge repairs. CONCLUSIONS: We conclude that the type of tendon repair can significantly affect the gliding resistance between the tendon and pulley system after tendon repair. RELEVANCE: The design of the tendon repair, through its effect on friction, may have an adverse effect on the clinical results of tendon mobilization.

Aged↗

PubMed2001

Gliding characteristics of tendon repair in canine flexor digitorum profundus tendons.

The gliding resistance between the flexor digitorum profundus (FDP) tendon and the proximal pulley system was measured using the method of S. Uchiyama, J.H. Coert, L. Berglund, P.C. Amadio, K.N. An (J. Orthop. Res. 13 (1995) 83) in 108 adult dog digits in vitro. The FDP tendons were then lacerated to 80% of their transverse section. Each tendon was repaired with one of the following six suture techniques: Kessler, modified Kessler, Savage, Lee, Becker and simple running suture alone. Each repaired tendon was then tested again using the same method. The Student-Newman-Keuls test for multiple comparisons was performed for statistical analysis. The average gliding resistances of the Kessler, Savage, and Becker repairs were significantly greater than the resistances of the Lee, modified Kessler, and running suture alone repairs (P < 0.05). The Lee suture technique had a significantly greater resistance than the modified Kessler repair and the running suture (P < 0.05). The results of the peak gliding resistance followed the same trends, except that the modified Kessler repair was significantly higher than the running suture alone (P < 0.05). Suture techniques with a multi-strand core suture, with knots located outside the tendon surface, and with multiple-loops on the tendon surface may result in increased gliding resistance between the tendon and pulley system after tendon repair.

Animals↗

PubMed2001

Real-time strain rate imaging: validation of peak compression and expansion rates by a tissue-mimicking phantom.

Strain rate imaging is a new modality in echocardiography intended for analysis of left ventricular function. This modality extends ultrasonographic techniques for analysis of tissue velocities by providing information about rates of local myocardial compression and expansion. Cyclic cardiac deformation is a complex process. Precision and accuracy of real-time strain rate (rtSR) measurements have not been studied under controlled laboratory conditions. Using a cyclically compressed tissue-mimicking gelatin phantom, we compared rtSR values to corresponding strain rate values calculated off line from local tissue velocities measured by Doppler echocardiography. We tested a clinically relevant range of strain rates (0.5 - 3.5 sec(-1)) and different angles of insonation. Initial tests showed high precision (r > or = 0.973, P < 0.001), but the assessment of accuracy (bias < or = 0.559 sec(-1)) suggested a trend toward systematic underestimation of the reference values. We suspected a confounding influence of a clutter filter and repeated the tests with the filter inactive. The resulting accuracy improved tenfold (bias < or = 0.045 sec(-1)), and the systematic underestimation was no longer present. We conclude that the rtSR is precise and accurate for a range of the tested values.

Echocardiography, Doppler, Color↗

PubMed2001

Tensile properties of suture methods for repair of partially lacerated human flexor tendon in vitro.

The decision to treat zone II partially lacerated flexor tendons is challenging, because there can be justification for either repair or no repair, depending on the surgeon's assessment of the strength of the residual intact portion of the tendon. In this study tensile properties of various repair techniques were compared. Cadaveric human flexor tendons (n = 118) were lacerated to 75% of their cross-section and repaired with either a core suture method (Kessler, modified Kessler, Savage, Lee, augmented Becker, or Tsuge all finished with a circumferential running suture), an epitendinous suture alone (circumferential or partial), or the tendons were left unrepaired. Among the core suture methods there was no significant difference (p >.05) in maximum failure force (overall mean, 211.2 N; SD, 53.2) or force to produce a 1.5-mm gap (74.1 N; SD, 49.7). Likewise there was no significant difference (p >.05) in tendon stiffness (41.0 N/mm; SD, 14.0) or resistance to gap formation (52.3 N/mm; SD, 23.1). In comparison, repairs without the core suture, including unrepaired tendons, were significantly weaker (144.7 N, p <.001) and had a marginally lower stiffness (p =.04) but had a similar resistance to gap formation (43.5 N/mm).

Hand Injuries↗

PubMed2001

Suture techniques with high breaking strength and low gliding resistance: experiments in the dog flexor digitorum profundus tendon.

We studied the breaking strength and gliding resistance between the pulley and flexor tendon for various suture techniques. Canine flexor digitorum profundus tendons were transected and sutured using one of eight repair techniques: modified Kessler (MK); Tsuge (Tsuge); two variations of a double modified Kessler (DK1, DK2); combined modified Kessler-modified Tsuge (MKT); augmented Becker (Becker); Cruciate (Cruciate); and modified double Tsuge (DT). The force to produce a 1.5 mm gap, ultimate failure load, resistance to gap formation, and gliding resistance were measured. The force to produce a 1.5 mm gap and the ultimate breaking force were higher with the DK1, DK2, MKT, Becker, Cruciate, and DT repairs than they were with the MK and Tsuge repair, while the gliding resistance of the Becker was higher than that of the MK, DK1, DK2, MKT. Cruciate, and UT repairs. In addition to confirming that repair strength increases as the number of strands crossing the repair increases, we also found that these stronger repairs need not produce higher gliding resistance than less robust repairs.

Animals↗

PubMed2001

The effect of suture technique on adhesion formation after flexor tendon repair for partial lacerations in a canine model.

BACKGROUND: Adhesion formation is a serious problem after flexor tendon repair. Many repair techniques have been developed to increase the suture strength after tendon repair surgery. The purpose of this study was to assess adhesion formation with different suture techniques in an in vivo canine model. METHODS: Sixty flexor digitorum profundus tendons were partially lacerated (80%) and repaired with either a modified Kessler (MK) or Becker (MGH) suture technique and supplemented with a simple running suture. The dogs were sacrificed at 1 week, 3 weeks, or 6 weeks after surgery and the repaired tendons were evaluated for adhesion breaking strength. RESULTS: At 1 week there was no significant difference between the two repair groups (p > 0.05). At 3 and 6 weeks, the adhesion breaking strength in the MK suture group was significantly less than that of the MGH suture group (p < 0.05). CONCLUSION: High friction suture techniques may cause more adhesion formation than the lower friction suture techniques under passive postoperative therapy.

Analysis of Variance↗

PubMed2001

Determination of the compressive material properties of the supraspinatus tendon.

A methodology was developed for determining the compressive properties of the supraspinatus tendon, based on finite element principles. Simplified three-dimensional models ure re reated based on anatomical thickness measurements of unloaded supraspinatus tendons over 15 points. The tendon material was characterized as a composite structure of' longitudinally arranged collagen fibers within an extrafibrillar matrix. The matrix was formulated as a hyperelastic material described by the Ogden form of the strain energy potential. The hyperelastic material parameters were parametrically manipulated until the analytical load-displacement results were similar to the results obtaizned from indentation testinrg. In the geometrically averaged tendon, the average ratio of experimental to theoretical maximum indentation displacement was 1.00 (SD: 0.01). The average normalization of residuals was 2.1 g (SD: 0.9 g). Therefjore, the compressive material properties of the supraspinatus tendo'n extrafibrillar matrix were adequately derived with a first-order hyperelastic formulation. The initial comnpressive elastic modulus ranged from 0.024 to 0.090 MPa over the tendon surface and increased nonlinearly with additional compression. Using these material properties, the stresses induced during acromional impingement can be analyzed.

Cadaver↗

PubMed2001

Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavity-compression : an in vitro study.

BACKGROUND: Although the glenohumeral joint is the most mobile articulation of the human body, it is known to exhibit ball-and-socket kinematics. Compression into the glenoid labral concavity keeps the humeral head centered. The purpose of the present study was to determine the effects of joint position on glenohumeral stability through concavity-compression. METHODS: Ten cadaveric shoulders were tested. The glenoid was mounted horizontally onto a six-component load-cell while the humerus was clamped to a vertically unconstrained slide. An x-y stage translated the load-cell with the glenoid underneath the humeral head in eight different directions. Compressive loads of 20, 40, and 60 N were applied. The tests were repeated in 0 degrees, 30 degrees, 60 degrees, and 90 degrees of glenohumeral abduction with and without the labrum. Relative translations between the glenoid and the humeral head and the forces resisting translation were recorded. Then the stability ratio, defined as the peak translational force divided by the applied compressive force, was calculated. RESULTS: The average stability ratio was higher in the hanging-arm position than it was in glenohumeral abduction. The highest stability ratio was detected in the inferior direction (59.8% 7.7%) when the labrum was intact and in the superior direction (53.3% 7.9%) when the labrum had been resected. Under both conditions, the anterior direction was associated with the lowest stability ratio (32.0% 4.4% with the labrum and 30.4% 4.1% without the labrum). Resection of the glenoid labrum resulted in an average decrease in the stability ratio of 9.6% 1.7%. With increasing compressive load, the average stability ratio slightly decreased. CONCLUSIONS: Glenohumeral stability through concavity-compression was greater in the hanging-arm position than it was in glenohumeral abduction. The average contribution of the labrum to glenohumeral stability through concavity-compression was approximately 10%, about one-half of the value previously reported. With the labrum intact, the glenohumeral joint was most stable in the inferior direction. Without the labrum, it was most stable in the superior direction. Under both conditions, it was least stable in the anterior direction. Glenohumeral joint stability through concavity-compression decreases with higher compressive loads.

Aged↗

PubMed2000

The effect of knot location, suture material, and suture size on the gliding resistance of flexor tendons.

The effect of knot location, suture material, and suture size on gliding resistance between the pulley and flexor tendon was investigated in a canine model. Different suture materials [monofilament nylon (Ethilon), braided polyester suture coated with silicone (Ticron) and uncoated braided polyester suture (Mersilene)] and suture sizes (4-0, 5-0) were tested. A knot was made on either the volar surface, on one lateral side, or on both lateral sides of canine hind-paw tendons, and gliding resistance was measured. In addition, the frictional coefficient between three suture materials (4-0 nylon, 4-0 Ticron, 4-0 Mersilene) and a nylon rod were measured. The gliding resistance of the tendon with knots on both sides was highest, while tendons with one lateral knot had the lowest resistance (p < 0.01). The gliding resistance of 4-0 suture size was higher than that of 5-0 size (p < 0.0001). The coefficient of friction of nylon was lower than that of braided polyester suture (Ticron or Mersilene) (p < 0.001). The placement of knots and choice of suture material affect gliding resistance after tendon repair, and may, therefore, have an effect on the result of tendon repair.

Animals↗

PubMed2000

Structural properties of the subscapularis tendon.

The subscapularis muscle is an important mover and stabilizer of the glenohumeral joint. The purpose of this study was to measure regional variations in the structural properties of the subscapularis tendon in two joint positions. Subscapularis tendons from cadaveric shoulders were divided into four sections superiorly to inferiorly and tested to failure at 0 or 60 degrees of glenohumeral abduction. Arm position had a significant influence on stiffness in the inferior and superior portions (p < 0.05). The inferior region showed a higher stiffness in the hanging-arm position (0 degrees) than at 60 degrees of abduction (27.4+/-17.7 compared with 9.5+/-5.9 N/mm). Meanwhile, stiffness of the superior portion was higher at 60 degrees of abduction than in the hanging-arm position (208.7+/-60.9 compared with 147.2+/-32.3 N/mm). In the hanging-arm position (0 degrees) and at 60 degrees of abduction, the superior and midsuperior portions failed at significantly higher loads (superior: 623.2+/-198.6 and 478.2+/-206.6 N at 0 and 60 degrees of abduction, respectively; midsuperior: 706.2+/-164.6 and 598.4+/-268.4 N, respectively) than did the inferior portion (75.1+/-54.2 and 30.3+/-13.0 N, respectively). Likewise, stiffness of the superior and midsuperior portions was significantly higher than that of the inferior region in both positions. Higher stiffness and ultimate load in the superior tendon region may explain the infrequent extension of rotator cuff tears into the subscapularis tendon. Conversely, the significantly lower ultimate load and stiffness in the inferior tendon region could facilitate anterior dislocation of the humeral head when this portion stabilizes the joint in a dislocated position. Therefore, repair of torn inferior portions of the subscapularis tendon should be considered in surgery for glenohumeral instability.

Aged↗

PubMed2000

The bursal and articular sides of the supraspinatus tendon have a different compressive stiffness.

OBJECTIVE: To measure the compressive stiffness of the supraspinatus tendon and to determine whether regional difference exists in the bursal and articular side of the tendon. DESIGN: Indentation testing was performed on both the bursal and articular sides of the supraspinatus tendon, focused on the 'critical area', where rotator cuff tears often occur. BACKGROUND: When the supraspinatus tendon wraps around the humeral head or is under impingement condition, compressive force on the tendon surface is expected. Therefore, compressive stress has been recently considered to be one of the important factors associated with the cuff tear. The mechanical properties would be essential for analytic modeling of stress distribution. METHODS: Indentation tests were performed at 15 locations on the bursal and articular surfaces of the supraspinatus tendon. A mathematical model with exponential relationship was used to describe the measured force-deformation relationship and to calculate the compressive stiffness of the supraspinatus tendon. RESULTS: The over-all initial stiffness on the bursal and articular sides of the tendon was significantly different. On the bursal side, the anterior third had a significantly higher initial stiffness than the other thirds on average. On the articular side, initial stiffness at location 10 mm proximal to the greater tuberosity was significantly higher than the rest on average. CONCLUSIONS: The compressive stiffness of the supraspinatus tendon was found to be non-homogenous throughout the structure.RelevanceNon-homogenous compressive stiffness of the supraspinatus tendon would affect the load transmission within the tendon, which might be associated with the potential mechanism of tear. Such characteristics needs to be considered when performing finite element modeling of stress fields in the tendon.

Aged↗

PubMed2000

Mechanical properties of the posterior rotator cuff.

BACKGROUND: The infraspinatus is an important active and passive stabilizer of the glenohumeral joint. It functions as external rotator and participates in elevation of the arm. As its main posterior component, it is frequently involved in rotator cuff tears. OBJECTIVE: The purpose of this study was to determine the structural and mechanical properties of the infraspinatus tendon structure, including the midsubstance and insertion regions, in the superior, mid-superior, mid-inferior, and inferior portions, in two joint positions. METHODS: The infraspinatus tendons from 22 fresh frozen cadaver shoulders were divided into four strips. The tendons were held in a cryo-jaw and tested with a material-testing machine in 0 degrees or 60 degrees of glenohumeral abduction corresponding to 90 degrees arm abduction. Ultimate load, displacement and failure mode were recorded. Stiffness, ultimate stress and elastic modulus were calculated. RESULTS: Significant differences between glenohumeral abduction positions were detected only for the elastic modulus. The mid-superior (676.5 N, S.D. 231.0 N) and the inferior portion (549.9 N, S.D. 284.6 N) had the highest failure loads while the superior (462.8 N, S.D. 237.2 N) and the mid-inferior portions (315.3 N, S.D. 181.5 N) were weaker. Similar trends across the tendon strips were shown for stiffness, ultimate stress and elastic modulus. RELEVANCE: Position dependent changes in mechanical properties of the infraspinatus tendon probably do not play a role in the pathomechanism of posterior shoulder dislocation. Peaks in stiffness in mid-superior and inferior tendon sections explain the low incidence of posterior dislocations. The low ultimate failure loads in the superior portions might explain the frequent extension of rotator cuff ruptures into the infraspinatus tendon.

Aged↗