Biomedical subjects

Patrick J McMahon

Publications and source records attributed to Patrick J McMahon.

12 recordsLinked to original sources

PubMed2003

Shoulder muscle reflex latencies under various levels of muscle contraction.

Previous research in relaxed muscles shows that muscle reflex latencies are too slow to protect the shoulder. However, during athletic activity when injury occurs, some level of shoulder muscle contraction typically exists. The purpose of the current study was to assess shoulder muscle reflex latencies under various levels of muscle contraction. Seventeen healthy subjects participated. A perturbation consisting of an external rotation collision force to the anterior forearm in a position of apprehension under various levels of muscle contraction (0%, 20%, and 50% of a maximum voluntary muscle contraction) was applied. Muscle reflex latencies were measured as the time from perturbation application to onset of muscle activity. Electromyography measured activity onset of the rotator cuff muscles and the primary humeral movers. During 0%, the latissimus dorsi muscle reflex latency was significantly slower than most other muscles. No difference existed between muscles in the 20% and 50% conditions. For the rotator cuff muscles, the reflex latencies significantly quickened for 20% and 50% compared with the relaxed state (0%). Overall, introducing muscle contraction significantly quickened muscle reflex latencies. These results provide clinicians with a better understanding of the role that these reflexes play in joint stability in a position of injury vulnerability like a position of apprehension.

Adult↗

PubMed2002

Elbow injuries.

The elbow is a commonly injured joint, yet physicians may be less comfortable treating injuries to the elbow compared with knee and shoulder injuries. Common injuries involving the elbow are tendinosis, instability, tendon ruptures, osteochondritis dissecans, and fractures. Tendinosis is a common overuse injury and may occur on the lateral, medial, or infrequently, the posterior side of the elbow. Injury to the medial or lateral ulnar collateral ligaments may result in instability. Repetitive trauma from overuse is the most common etiologic factor in athletes. Distal biceps and triceps tendon injuries may result in elbow disability in active individuals. Partial tears are more difficult to diagnose than complete ruptures. Osteochondritis dissecans of capitellum affects adolescents involved in overhead throwing athletics. Fractures about the elbow most commonly involve the radial head in adults, and the distal humerus in children. Athletes are prone to elbow injuries resulting from both overuse and acute trauma. Our purpose is to describe the diagnosis and treatment of these common elbow injuries in athletes of all ages.

Adolescent↗

PubMed2002

Variation in the glenoid origin of the anteroinferior glenohumeral capsulolabrum.

Restoration of the anteroinferior capsulolabrum, including the labrum and origin of the anterior band of the inferior glenohumeral ligament is crucial during Bankart repair. The purpose of the current study was to describe variations in this anatomy near the glenoid. The histologic and gross anatomy were studied in 10 fresh-frozen glenohumeral joints from adult cadavers. Each joint was placed in the apprehension position of abduction, external rotation, and horizontal abduction because anterior dislocation occurs in this shoulder position. The joints then were sectioned serially in the transverse plane from cephalad to caudad. Three glenohumeral joints were embedded in Techovit 7200 resin, polymerized, and then mounted onto an acrylic slide. Ground sections were prepared by attaching a microscope slide to the face of each and cutting 200 microm-thick sections. The thin sections were ground to a thickness of 30 microm. Finally, sections were stained with 1% toluidine blue zero in 1% sodium tetraborate for light microscopic examination. The other seven glenohumeral joints were frozen in the apprehension position and held with a custom jig while sectioned serially at 3-mm intervals. The surfaces then were recorded with a tabletop computer and a scanning device. Two distinct patterns of the anteroinferior capsulolabrum attachment to the glenoid were identified. In eight joints (80%) it had its major origin from the labrum with some fibers extending onto the glenoid neck, a Type I origin. In two joints (20%), it emanated solely from the glenoid neck, a Type II origin. Failure to repair the glenoid origin of the anteroinferior capsulolabrum, the location of the anterior band of the inferior glenohumeral ligament, because of variations in its anatomy may be a reason for failure after Bankart repair.

Humans↗

PubMed2002

Open surgical repair restores joint forces that resist glenohumeral dislocation.

Traumatic anterior shoulder instability is a clinical problem often observed in athletes participating in overhead activities. The standard treatment for this condition is surgical repair, which may be accomplished by an open or arthroscopic procedure. The current authors assessed the strength of open repair, by comparing glenohumeral joint forces in intact specimens with specimens with anterior dislocation and open repair. Eighteen shoulders from cadavers were tested on a custom shoulder dislocation device with simulated muscle forces. Bankart lesions were repaired using a three-suture anchor technique combined with capsular advancement. Capsular failures were addressed by sharp dissection of the labrum from bone, then repaired as above, and the experiment was repeated. One-way analysis of variance was used for analyses. All specimens dislocated anteroinferiorly, eight dislocated by bony Bankart failure, and 10 dislocated by capsular failure. Maximum joint compression force for the initial dislocation was 760 +/- 79 N for the specimens with Bankart failures and 690 +/- 59 N for the specimens with capsular failures. The maximum joint compression force for dislocation after repair measured 541 +/- 50 N for the specimens with Bankart failures and 536 +/- 46 N for the specimens with capsular failures. The forces after repair were normalized with respect to the intact shoulders. For specimens with Bankart failures, joint compression and pectoralis major forces were 72% and 62%, respectively, and 79% and 61% for specimens with capsular failures. A three-dimensional digitizing system confirmed restoration of glenohumeral position. These results support clinical data, showing that open Bankart repair adequately restores the static restraints of the glenohumeral joint that resist anteroinferior dislocation.

Aged↗

PubMed2002

Cadaveric study of glenohumeral translation using electromagnetic sensors.

Clinical methods for measuring shoulder translation rely heavily on the experience of the examiner and remain largely subjective, prone to errors of interobserver and intraobserver reproducibility. Accurate in vitro methods of measuring glenohumeral translation exist. The purpose of the current study was to evaluate the accuracy of computerized electromagnetic spatial sensors applied to the skin, in measuring glenohumeral translation under simulated conditions of a standard shoulder examination. Seven thawed, fresh-frozen shoulder specimens from cadavers were used in the study. Soft tissue and skin were not removed. The specimens were mounted to simulate clinical positions of patients having an anteroposterior drawer or load-and-shift test. A series of anterior and posterior displacements were done manually under two conditions. Condition I: Electromagnetic position sensors were taped to skin and held beneath the examiner's fingers; and Condition II: Sensors were fixed rigidly to pins inserted into the glenoid and humeral head, respectively. Displacement values between conditions, within trials, and among specimens were compared for accuracy and reproducibility. Strong agreement was shown between Condition I and Condition II for the anterior and posterior directions (interclass correlation coefficients 0.81 and 0.86, respectively). Simple linear regression revealed a significant association between conditions in the anterior and posterior directions. Reproducibility between trials under each condition was extremely high, with interclass correlation coefficients greater than or equal to 0.98 regardless of direction of displacement or testing condition. The data from the current study show that cutaneous application of electromagnetic position sensors to the shoulder can accurately and reproducibly measure true glenohumeral translation under testing conditions that mimic a standard, clinical shoulder examination.

Cadaver↗

PubMed2002

Quantitative assessment of glenohumeral translation.

Cutaneous electromagnetic position sensors were used to quantify anteroposterior laxity of the shoulder. Forty-three female athletes were tested (27 were soccer players and 16 were swimmers). The athletes had a mean age of 18.8 years (range, 17-24 years), and all were free of shoulder disorders. Dominant and nondominant shoulders were tested. Each shoulder was suspended in 90 degrees abduction and neutral rotation. Serial anteroposterior translations were done manually similar to an anteroposterior drawer examination of the shoulder. The glenohumeral translation for the soccer players was 9.6 mm (range, 5.8-15.1 mm) in the dominant shoulder and 10.7 mm (range, 5.2-16.7 mm) in the nondominant shoulder. The translations in the swimmers were significantly greater at 12.4 mm (range, 8.9-15.9 mm) in the dominant and 13.8 mm (range, 8.8-17.4 mm) in the nondominant shoulders. The mean of the differences between the dominant and nondominant shoulders was 2.1 mm for the swimmers and soccer players. For the soccer players, the range for the side to side differences was 0.1 to 5.3 mm. For the swimmers, the range was 0.1 to 4.3 mm. Finding a clinical device for objective measurement of joint laxity in the shoulder that is accurate, reproducible, noninvasive, and easy to use has been evasive.

Adolescent↗

PubMed2002

Gender differences in patellofemoral joint biomechanics.

Patellofemoral pain is associated with patellar malalignment and quadriceps weakness which are seen more commonly in women. The objective of the current study was to determine the effects of gender, vastus medialis strength, and tibial rotation on patellofemoral joint biomechanics. Twelve fresh-frozen knees from cadavers were tested using a custom knee jig. Anatomic multiplane loading of the extensor mechanism was used with varying vastus medialis loads. Patellofemoral contact area and pressure were measured using pressure sensitive film at knee flexion angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees with the tibia in neutral and 15 degrees internal and external tibial rotation. Patellofemoral joint contact areas in specimens from men were larger at knee flexion angles greater than 30 degrees. A significant increase in mean patellofemoral contact pressures was seen for specimens from women when compared with specimens from men at 0 degrees and 30 degrees knee flexion. The knees from women also showed a greater change in contact pressures to varying vastus medialis load at knee flexion angles of 0 degrees, 30 degrees, and 60 degrees. The results of the current study indicate that there are gender differences in patellofemoral contact areas and pressures. These differences may help explain the increased incidence of patellofemoral disorders in women.

Aged↗

PubMed2002

Muscles may contribute to shoulder dislocation and stability.

Joint instability is one of the most common human afflictions, affecting not only the hip, knee, and shoulder but all joints of the body. Surgical repair for joint instability is done commonly, yet has not been able to restore function consistently. Pain, recurrence of instability, joint stiffness, muscle injury, and degenerative joint disease are all too common sequelae. Because the glenohumeral joint is most commonly dislocated, efforts have been directed to understanding shoulder instability. Study has included not only the static restraints (capsulolabrum, articular surfaces, intracapsular pressure), but also their important interplay with the dynamic restraints (shoulder muscles). Furthermore, not only were muscles known to stabilize the joint studied but also may have contributed to dislocation. An in vitro, cadaveric model that included relevant shoulder muscles and a mechanism of dislocation similar to an in vivo mechanism was developed. The capsulolabral pathoanatomy that occurred after dislocation was studied. Increased understanding of joint dislocation may improve functional results after rehabilitation and surgical repair, not only at the shoulder, but also at all other joints.

Biomechanical Phenomena↗

PubMed2002

Shoulder biomechanics and muscle plasticity: implications in spinal cord injury.

After spinal cord injury, excessive burden falls on the upper extremity, especially the shoulder. Overall, 51% of persons with spinal cord injury have shoulder problems. Common shoulder problems in persons with spinal cord injury begin with muscle imbalance that can lead to glenohumeral instability, impingement disease, rotator cuff tears, and subsequent degenerative joint disease. These problems can be attributed to the functional demands placed on the shoulder that are specific to patients with spinal cord injury, including overhead activities, wheelchair use, and transfers. Despite preventive exercises, shoulder problems in persons with spinal cord injury remain a significant problem, causing pain and functional limitations. The biomechanics of the shoulder for persons with spinal cord injury resulting from changes in muscle plasticity will be elucidated. Specifically, the effects of scapular protraction that can result from muscle imbalance, the age-dependent properties of the anterior band of the inferior glenohumeral ligament, and the influence of the dynamic restraints around the shoulder will be addressed.

Biomechanical Phenomena↗

PubMed2002

The efficacy of using a personal stereo to treat auditory hallucinations. Preliminary findings.

This article presents preliminary findings from the first participant to complete an experiment assessing the efficacy of the personal stereo in treating auditory hallucinations. O.C., a 50-year-old woman, took part in a controlled treatment trial in which 1-week baseline, personal stereo, and control treatment (nonfunctioning hearing aid) stages were alternated for 7 weeks. The Positive and Negative Syndrome Scale, Clinical Global Impression Scales, Beliefs About Voices Questionnaire, Rosenberg Self-Esteem Scale, and Topography of Voices Rating Scale were used. The personal stereo led to a decrease in the severity of O.C.'s auditory hallucinations. For example, she rated her voices as being fairly distressing during baseline and control treatment stages but neutral during personal stereo stages. A slight decrease in other psychopathology also occurred during personal stereo stages. Use of the personal stereo did not lead to a decrease in self-esteem, contradicting suggestions that counterstimulation treatments for auditory hallucinations may be disempowering.

Antipsychotic Agents↗

PubMedDate not supplied

Glenohumeral translations are only partially restored after repair of a simulated type II superior labral lesion.

BACKGROUND: The effect on joint stability of repair of type II superior labrum and biceps anchor lesions is unknown. HYPOTHESIS: Increased translations of the glenohumeral joint after a simulated type II lesion will be reduced after the lesion is repaired. STUDY DESIGN: Controlled laboratory study. METHODS: A robotic/universal force-moment testing system was used to simulate load-and-shift and apprehension tests on eight cadaveric shoulders to determine joint kinematics of the shoulder after venting, creation of a type II lesion, and repair of the lesion. RESULTS: At 30 degrees of abduction, anterior translation of the vented joint in response to an anterior load was 18.7 +/- 8.5 mm and was significantly increased to 26.2 +/- 6.5 mm after simulation of a type II lesion. Repair did not restore anterior translation (23.9 +/- 8.6 mm) to that of the vented joint. The inferior translation that also occurred during application of an anterior load was 3.8 +/- 4.0 mm in the vented joint and increased significantly to 8.5 +/- 5.4 mm with a simulated type II lesion. After repair, the inferior translation decreased significantly to 6.7 +/- 5.3 mm. CONCLUSIONS: Repair of a type II lesion only partially restored glenohumeral translations to that of the vented joint. CLINICAL RELEVANCE: Surgical techniques including improved repair of passive stabilizers injured in the type II lesion should be considered.

Biomechanical Phenomena↗

PubMedDate not supplied

Effects of simulated vastus medialis strength variation on patellofemoral joint biomechanics in human cadaver knees.

Selective strengthening of the vastus medialis (VM) muscle is a conservative treatment used to address some patellofemoral joint (PFJ) problems. The objective of this study was to examine the effects of varying VM strength on PFJ kinematics and contact pressures and areas. We tested five fresh-frozen cadaveric knees using a custom knee jig, which permits the simulation of physiologic quadriceps loading while also allowing the VM force to be varied. PFJ kinematics were measured with a magnetic tracking device. PFJ contact pressures and areas were measured with Fuji pressure-sensitive film. For PFJ kinematics, the change in the medial-lateral and superior-inferior translation was significant at 0% of VM strength and 150% of VM strength with respect to the 100% of VM strength condition (p < 0.05). Extreme changes in the VM force had a statistically significant effect on patellofemoral contact pressures (0% of VM strength (19 +/- 10%) and 150% of VM strength (17 +/- 3%) with respect to 100% of VM strength condition (p < 0.05)). No statistically significant differences were shown in the patellofemoral contact areas (p > 0.05). The functional range of VM strength is between 75% and 125% of total VM strength. The PFJ kinematics and contact pressures were not significantly influenced by VM strength except at extreme conditions (0% of VM strength or 150% of VM strength) in human cadaveric knees.

Analysis of Variance↗