Spontaneous motility of passive emulsion droplets in polar active gels.

We study by computer simulations the dynamics of a droplet of passive, isotropic fluid, embedded in a polar active gel. The latter represents a fluid of active force dipoles, which exert either contractile or extensile stresses on their surroundings, modelling for instance a suspension of cytoskeletal filaments and molecular motors. When the polarisation of the active gel is anchored normal to the droplet at its surface, the nematic elasticity of the active gel drives the formation of a hedgehog defect; this defect then drives an active flow which propels the droplet forward. In an extensile gel, motility can occur even with tangential anchoring, which is compatible with a defect-free polarisation pattern. In this case, upon increasing activity the droplet first rotates uniformly, and then undergoes a discontinuous nonequilibrium transition into a translationally motile state, powered by bending deformations in the surrounding active medium.

Rebuilding cytoskeleton roads: active-transport-induced polarization of cells.

Many cellular processes require a polarization axis which generally initially emerges as an inhomogeneous distribution of molecular markers in the cell. We present a simple analytical model of a general mechanism of cell polarization taking into account the positive feedback due to the coupled dynamics of molecular markers and cytoskeleton filaments. We find that the geometry of the organization of cytoskeleton filaments, nucleated on the membrane (e.g., cortical actin) or from a center in the cytoplasm (e.g., microtubule asters), dictates whether the system is capable of spontaneous polarization or polarizes only in response to external asymmetric signals. Our model also captures the main features of recent experiments of cell polarization in two considerably different biological systems, namely, mating budding yeast and neuron growth cones.

Pushing off the walls: a mechanism of cell motility in confinement.

We propose a novel mechanism of cell motility, which relies on the coupling of actin polymerization at the cell membrane to geometric confinement. We consider a polymerizing viscoelastic cytoskeletal gel confined in a narrow channel, and show analytically that spontaneous motion occurs. Interestingly, this does not require specific adhesion with the channel walls, and yields velocities potentially larger than the polymerization velocity. The contractile activity of myosin motors is not necessary to trigger motility in this mechanism, but is shown quantitatively to increase the velocity. Our model qualitatively accounts for recent experiments which show that cells without specific adhesion proteins are motile only in confined environments while they are unable to move on a flat surface, and could help in understanding the mechanisms of cell migration in more complex confined geometries such as living tissues.

Translation of the glenohumeral joint in patients with multidirectional and posterior instability: awake examination versus examination under anesthesia.

The purpose of this study was to assist in establishing guidelines to determine the degree of shoulder instability, the value of awake clinical examination, and the value of examination under anesthesia (EUA). Forty-three patients with clinical diagnosis of multidirectional shoulder instability (MDI) and 28 patients with posterior instability underwent bilateral shoulder translation testing, both awake and while under anesthesia. Two surgeons using guidelines and translation grades developed by the American Shoulder and Elbow Surgeons examined each patient and assigned a single grade for the anterior, posterior, and inferior directions. A comparison of translational grade was performed with the use of Pearson chi2 and McNemar symmetry to determine association. The patients with MDI showed increased translation in the anterior, inferior, and posterior directions when the affected limb was compared with the noninvolved side in both preoperative examination and EUA. Furthermore, the patients with MDI showed increased anterior translation on the affected side during EUA compared with the clinical examination. Patients with posterior instability demonstrated increased anterior translation for both affected and noninvolved limbs during EUA. However, the posterior translation obtained before surgery did not change during EUA for both the affected and noninvolved limbs, and there was no side-to-side difference in posterior translation.

Arthroscopic visualization of the subscapularis tendon.

PURPOSE: This study was conducted to define what portion of the subscapularis tendon is visualized during standard diagnostic glenohumeral arthroscopy and to determine the distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve. TYPE OF STUDY: Anatomic (cadaveric) analysis. METHODS: Six fresh-frozen human cadaveric shoulders were placed in a simulated lateral decubitus position with longitudinal traction and 45 degrees of shoulder abduction. Glenohumeral arthroscopy was performed on each specimen using a standard posterior portal for visualization. The 4 corners of the visible portion of the subscapularis were tagged with arthroscopic sutures. The shoulders were subsequently dissected. The surface area defined by the 4 suture tags and the surface area of the entire subscapularis tendon were calculated for each specimen. The dimensions of these areas and the distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve were measured with calipers. RESULTS: The arthroscopically tagged portion of the subscapularis tendon represented only a small percentage (26% +/- 11%) of the entire tendon. The majority of the subscapularis tendon is veiled by the middle and inferior glenohumeral ligaments. There was a significant distance between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve (32.8 +/- 6.0 mm). The mean height of the visible portion of the tendon represented 44% of the mean overall height of the subscapularis. CONCLUSIONS: These data suggest that arthroscopic visualization of the subscapularis is incomplete. Lesions involving the concealed portion of the subscapularis tendon may not be detected arthroscopically. The wide margin of safety between the inferior aspect of the visible portion of the subscapularis tendon and the axillary nerve is relevant to the placement of anteroinferior (trans-subscapularis) arthroscopy portals as well as to performing arthroscopic anterior capsular releases.

Relationships between throwing mechanics and shoulder distraction in professional baseball pitchers.

The extreme forces and torques and the high speeds and excessive ranges of motion of baseball pitching place tremendous stress on the soft tissues of the throwing shoulder. Little is known about the relationship between pitching mechanics and shoulder joint stress, especially in professional athletes. The purpose of this study was to quantify joint loads and kinematic parameters of pitching mechanics at the major league level and to study their relationships. Three-dimensional, high-speed video data were collected on 40 professional pitchers during the 1998 Cactus League spring training. A clinically significant distraction force was calculated at the shoulder joint, which reached an average peak value of 947 +/- 162 N (108% +/- 16% body weight). Descriptive statistics and a multiple linear regression analysis were used to relate shoulder distraction to kinematic and kinetic parameters of pitching mechanics. This study was undertaken not only to investigate the peak forces and torques on the shoulder, but also to identify potential areas of intervention that might prevent throwing injuries. Knowledge of joint ranges of motion, angular velocities, and joint-reaction forces can provide a scientific basis for improved preventive and rehabilitative protocols for baseball pitchers.

Arthroscopic subacromial decompression.

In this study, we analyzed the results of two series of patients treated for impingement syndrome by undergoing arthroscopic subacromial decompression (ASD). Patients had not responded to nonoperative treatment. Group 1 included 112 consecutive patients (average age, 41 years) with 96 (77%) patients available for 2-year follow-up. Group 2 (28 patients, 29 shoulders; average age, 43 years; range, 22 to 72) had ASD and the subacromial space digitally palpated to determine if adequate decompression was performed. Twenty-two (85%) of 26 shoulders were available for follow-up. At follow-up, pain, function, range of motion, strength, impingement signs, and patient satisfaction were assessed. In group 1, according to the Neer criteria, 48% of the patients were graded as satisfactory and 52% unsatisfactory. Workers' Compensation patients had a satisfactory rate of 32%, whereas non-Workers' Compensation patients had a satisfactory rate of 59%. Twenty patients had open acromioplasty after ASD. Inadequate decompression was noted in 14 of 20 failed patients. In group 2, 86% of the patients were graded as satisfactory according to the Neer criteria, with 14% unsatisfactory, which included the 2 failures. The 2 (9%) of 22 shoulders that failed the ASD went on to further surgical treatment. Average follow-up was 56 months (range, 13 to 78 months). The average American Shoulder and Elbow Society score at follow-up was 90.4. No difference between Workers' Compensation cases and the other cases was seen (P <.7). Finger palpation can help to improve outcomes by allowing the surgeon to assess the adequacy of decompression.

Results of biceps tenotomy for treatment of pathology of the long head of the biceps brachii.

Historically, the surgical treatment of bicipital pathology has been a variety of tenodesis techniques. The purpose of this study is to report the results of simple biceps tenotomy for the treatment of bicipital pathology. Thirty shoulders in 30 consecutive patients who had a simple arthroscopic biceps tendon release were reviewed. Data was collected according to the method of the American Shoulder and Elbow Surgeons (ASES) shoulder evaluation form. Outcome was assessed with the rating system of the ASES. The mean ASES shoulder score was 81.8. There was a significant reduction in pain and improvement in function after the procedure. The complication rate was 13.3%. Bicipital pathology is a significant cause of morbidity around the shoulder. The results of this study demonstrate that functional outcome as measured by the ASES scoring system can be very good with an arthroscopic biceps tendon release for the treatment of biceps tendon pathology.

Arthroscopic stabilization plus thermal capsulorrhaphy for anterior instability with and without Bankart lesions: the role of rehabilitation and immobilization.

The use of thermal energy is an exciting new technology in the treatment of anterior instability with and without Bankart reconstruction. The current approach for treating anterior instability in the absence of a Bankart lesion as discussed here is to perform thermal capsular shrinkage with a monopolar RF heat probe to address laxity in the anterior capsule and the inferior glenohumeral ligaments. If a Bankart lesion is present, repair of the lesion with arthroscopic suture anchors followed by thermal capsulorrhaphy is our treatment of choice. We currently reserve open anterior reconstruction for patients with pathology inappropriate for arthroscopic techniques and in cases where arthroscopic suturing is found to be inadequate intraoperatively. Furthermore, patients who require revision and athletes who engage in contact sports are evaluated on an individual basis to ascertain if arthroscopic techniques are appropriate (CD-2.1). Nonetheless, basic science research has revealed the importance of a formal period of immobilization followed by guarded mobilization. By using the aforementioned algorithm and postoperative protocol, low recurrence rates have been achieved while at the same time maintaining motion in the functional range. Of course, further follow-up, more patient studies, and peer review publications are required to determine if thermal capsulorrhaphy can replace open procedures as the gold standard for addressing capsular laxity associated with anterior instability.

The effect of immobilization on rotator cuff healing using modified Mason-Allen stitches: a biomechanical study in sheep.

Long-term biomechanical integrity of the surgical site is crucial to the outcome of rotator cuff repair. Usually after rotator-cuff surgery, the arm is immobilized for 6-12 weeks to minimize disruption at the healing site. Unfortunately, currently there is very little clinical data on the effects of immobilization after rotator cuff surgery. This study analyzed the effect of immobilization on rotator cuff healing by comparing the healing strength of the tendon in a bone trough using a sheep model. In sixteen (16) female adult sheep, the right infraspinatus tendons were reattached into a bone trough using a modified Mason-Allen suture pattern. After surgery, each sheep was randomly assigned into either an immobilized or non-immobilized treatment group. The immobilized group was fitted with a softball taped under the foot to restrict limb movement for 6 weeks. The non-immobilized treatment group was allowed to fully bear weight on the treated shoulder. At 26 weeks, the animals were sacrificed and the surgical shoulders were harvested and stored in a -30 degrees C freezer. Biomechanical testing was performed using a MTS 809 Axial/Torsional Servohydraulic System. Special cryo-grips were used to test the infraspinatus tendon-bone interface in anatomical alignment. All samples were preloaded with 10 +/- 5 N, and then force was measured during a crosshead displacement of 500 mm/min until failure. Force and displacement were acquired at 100 Hz and used to calculate load-to-failure and stiffness of the bone-tendon interface. The load-to-failure (N) and stiffness (N/cm) were determined for both treatment groups. For the non-immobilized group, the loads to failure and stiffness means were 2571.95 +/- 329.9 N and 2319.09 +/- 457.72 N/cm. The immobilized group means were 2954.42 +/- 473.52 N (load-to-failure) and 2579.13 +/- 383.51 N/cm (stiffness). A two-tailed two-samples unequal variance student t-test with significance set at 0.05, found no significant difference between the treatment groups for load-to-failure (p = 0.2174) and stiffness (p = 0.8286).

The effects of extended play on professional baseball pitchers.

The purpose of this study was to investigate kinematic and kinetic changes as a result of extended play in baseball pitching. Seven major league baseball pitchers were videotaped with high-speed (120 Hz) cameras during multiple innings of the same game. For each athlete, two fastballs (one thrown during the initial inning of play and one from the final inning) were chosen for analysis. Twenty-one physical landmarks were manually digitized from the video data. Kinematic and kinetic parameters were subsequently calculated relative to four phases of the pitching motion: windup, cocking, acceleration, and follow-through. Paired t-tests revealed that seven parameters changed significantly between early and late innings. These included decreases in maximum external rotation of the shoulder, knee angle at ball release, ball velocity, maximum distraction force at both the shoulder and elbow, and horizontal adduction torque at both release and its maximum value. Ultimately, a decline in performance was evident by a 2 m/s (5 mph) drop in ball speed. It is unclear whether the kinematic and kinetic changes occurred because of fatigue or if protective mechanisms were adopted.

Toothbrushing competency among high-risk grade one students: an evaluation of two methods of dental health education.

OBJECTIVE: To evaluate the effectiveness of two methods of dental health education (DHE) for improving toothbrushing competency among grade one students at high risk for dental diseases. METHODS: Fifty elementary schools in the former city of North York, Ontario, Canada, were assigned to one of two groups. In one group, students received a classroom-based DHE lesson that was reinforced by two small group sessions (n = 243). In the other group, students received only a single classroom-based DHE lesson (n = 206). Trained examiners assessed 11 toothbrushing skills at pre- and postintervention. RESULTS: At the preintervention test, few significant differences were found between the groups and many students did not display competency in fundamental oral health skills, such as placing a toothbrush at the gum line. Following DHE interventions, students in both groups demonstrated improvements in most skills. A significantly higher proportion of students who received both classroom and small group sessions displayed gains in competency in three skills, compared to students receiving only a classroom lesson. These skills were brushing anterior lingual surfaces, brushing posterior lingual surfaces, and brushing all areas in a routine fashion. Students receiving only a classroom session did not display greater improvements in any skill areas compared to "classroom plus small group" students. Some students in both groups still lacked fundamental skills at the end of the DHE program. CONCLUSIONS: While one must exercise caution in interpreting the results due to several methodologic limitations, findings suggest that for high-risk grade one students, a classroom-based lesson combined with small group sessions is a more effective method of improving toothbrushing skills compared to a single classroom-based lesson.

Oral hygiene knowledge of high-risk Grade One children: an evaluation of two methods of dental health education.

The effectiveness of two methods of dental health education (DHE) for improving oral hygiene knowledge among high-risk Grade One students was evaluated. Fifty elementary schools in the former City of North York, Canada were assigned to one of two groups. In one group, students received a classroom-based DHE lesson which was reinforced by two small-group sessions (n=243). In the other group, students received only a single classroom-based DHE lesson (n=206). After DHE interventions, students in both groups displayed improved knowledge for most oral hygiene questions (e.g., when should you throw your toothbrush away?). However, for several questions, a significantly higher proportion of "classroom plus small-group sessions" students displayed improved knowledge compared to students receiving only a classroom lesson. These items included: awareness that cavity prevention and removal of germs are two purposes of oral hygiene; and knowledge that teeth help people to eat and talk. Results suggest a classroom-based lesson combined with small-group sessions is a more effective method of improving oral hygiene knowledge among high-risk Grade One students compared to a single classroom-based lesson.

Serratus anterior muscle activity during selected rehabilitation exercises.

The purpose of this study was to document the electromyographic activity and applied resistance associated with eight scapulohumeral exercises performed below shoulder height. We used this information to design a continuum of serratus anterior muscle exercises for progressive rehabilitation or training. Five muscles in 20 healthy subjects were studied with surface electrodes for the following exercises: shoulder extension, forward punch, serratus anterior punch, dynamic hug, scaption (with external rotation), press-up, push-up plus, and knee push-up plus. Electromyographic data were collected from the middle serratus anterior, upper and middle trapezius, and anterior and posterior deltoid muscles. Each exercise was partitioned into phases of increasing and decreasing force and analyzed for average and peak electromyographic amplitude. Resistance was provided by body weight, an elastic cord, or dumbbells. The serratus anterior punch, scaption, dynamic hug, knee push-up plus, and push-up plus exercises consistently elicited serratus anterior muscle activity greater than 20% maximal voluntary contraction. The exercises that maintained an upwardly rotated scapula while accentuating scapular protraction, such as the push-up plus and the newly designed dynamic hug, elicited the greatest electromyographic activity from the serratus anterior muscle.

Open shoulder instability surgery. Complications.

Surgical stabilization of the shoulder can be a challenging procedure. Complications can and do occur, even in the hands of the most experienced surgeons. Emphasis must be placed on proper diagnosis, appropriate technique, and an understanding of potential complications to maximize the likelihood of a successful surgical outcome. The authors hope that this review helps to outline the complications that can occur with open instability surgery. Only by understanding the complications associated with the procedures performed can surgeons hope to decrease the frequency of their occurrence.

Biceps tendon disorders in athletes.

It has been proposed that the long head of the biceps functions as a humeral head depressor and stabilizer. In addition, in many overhead sports, the biceps helps to accelerate and decelerate the arm. With improper training or fatigue, inordinate stresses can be placed on the biceps as it attempts to compensate for other muscles. This can lead to attrition and failure, either within the tendon substance or at its origin. Bicipital problems in athletes usually occur in conjunction with other types of shoulder disorders, such as rotator cuff impingement and glenohumeral instability, making determination of the role and degree of biceps involvement difficult. Conditions affecting the biceps tendon in athletes can be generally classified as degeneration, instability, and disorders of the origin. Because of the close association of biceps lesions with other abnormalities, a thorough evaluation of the shoulder with a suspected biceps disorder is essential. Treatment of bicipital problems in athletes must often be accompanied by treatment of associated shoulder conditions.

Translation of the glenohumeral joint in patients with anterior instability: awake examination versus examination with the patient under anesthesia.

Fifty patients with a clinical diagnosis of traumatic anterior shoulder instability underwent bilateral shoulder translation testing while both awake and under anesthesia. Each patient was examined by 2 surgeons following guidelines developed by the American Shoulder and Elbow Surgeons. A single translation grade was established for anterior, posterior, and inferior directions. A comparison of means was performed with a paired t test. The mean anterior translation grade was significantly higher on the affected side when compared with that of the unaffected side both during awake examination and during examination with the patient under anesthesia (EUA). Ipsilateral comparison revealed significantly greater translation for both affected and unaffected shoulders in anterior, posterior, and inferior directions during EUA than during awake examination. Side-to-side comparison of posterior and inferior translation was similar for both awake examination and EUA. Clinical translation testing was helpful in the diagnosis of anterior shoulder instability. Side-to-side differences were subtle while awake and more apparent during EUA. The usefulness of awake translation testing for traumatic anterior instability was not clearly demonstrated; however, EUA provides helpful information to confirm the direction and degree of instability.

Prospective analysis of ice hockey injuries at the Junior A level over the course of one season.

OBJECTIVE: This study was conducted to identify the circumstances, timing, frequency, and types of injuries for a Junior A hockey team in an attempt to develop injury prevention strategies. DESIGN: This study was a prospective review of injuries sustained by a hockey team during one season. SETTING: Players were evaluated in a private practice clinical setting and during practices and games. PARTICIPANTS: Twenty-two hockey players (16-20 years old) were evaluated. An injury was defined as any event requiring the attention of a physician or trainer. The players sustained 83 injuries throughout the course of the season. Seventy-four were considered independent events. MAIN OUTCOME MEASURES: The effects of the following variables on injury rates were analyzed: position, game situation versus practice, and timing of injury during the game. RESULTS: Players were 20 times more likely to injure themselves during a game than practice. Although forwards sustained the highest total percentage of injuries, defensemen had the highest incidence of injury in games. More injuries occurred in the later periods and in the later minutes of each period. Injury incidence decreased for the second half of the season compared with the first half. CONCLUSION: Our data suggest goaltenders are at the lowest risk of sustaining an injury, but forwards appear to be at a higher risk in practice situations and defensemen in games. Game situations place players at a much greater risk of injury than practice sessions, particularly in the later portions of each period and toward the end of the game. Given the propensity for injury in the early season and later in the game, endurance training before and during the season may be important in injury prevention.

Surgical treatment of full-thickness rotator cuff tears in patients 40 years of age or younger.

Full-thickness tears of the rotator cuff are uncommon in the first 4 decades of life. A retrospective analysis was conducted of 19 consecutive patients who were 40 years of age or younger and had been treated surgically for a full-thickness tear of the rotator cuff. Sixteen patients (84%) recalled an acute injury that heralded the onset of symptoms. Five of the patients had sustained an initial glenohumeral dislocation. At an average follow-up of 5.7 years, all patients were evaluated with regard to pain, function, range of motion, strength, return-to-work status, return-to-sport status, and overall postoperative satisfaction. After operation, 15 patients (79%) reported diminished pain relative to their preoperative level, and 12 (63%) of 19 were able to function with the extremity above shoulder level. Fourteen patients (74%) returned to full-time employment, and half returned to sporting activities. Thirteen patients (68%) reported subjective improvement with regard to daily functional activities after surgical intervention. The most favorable results were seen in those patients who had sustained an acute glenohumeral dislocation in conjunction with a full-thickness rotator cuff tear and underwent combined stabilization and repair. The outcome for patients who received worker's compensation was less favorable.