Biomedical subjects

John T Jolly

Publications and source records attributed to John T Jolly.

3 recordsLinked to original sources

PubMed2006

Decreasing glenoid inclination improves function in shoulders with simulated massive rotator cuff tears.

BACKGROUND: A massive rotator cuff tear leads to poor shoulder function as evidenced by diminished glenohumeral abduction and superior translation of the humeral head compared to its normal position. The inclination angle of the glenoid has been associated with rotator cuff tears. The objective of this study was to quantify the effect of a decreased glenoid inclination angle on glenohumeral kinematics during active abduction in shoulders with a simulated, massive rotator cuff tear. METHODS: Eight fresh-frozen full upper extremities were tested using a dynamic shoulder testing apparatus. After recording the kinematics of the intact shoulder, a massive rotator cuff tear was surgically simulated. An osteotomy of the glenoid was then performed and the inclination angle was decreased by 30 degrees . The translation of the humeral head during abduction and the maximum abduction angle were recorded. FINDINGS: With an intact rotator cuff minimal humeral head translation on the glenoid occurred and the maximum abduction angle was mean 85.5 degrees (SD 7.4 degrees ). A massive rotator cuff tear resulted in superior translation of the humeral head with impingement on the acromion. The maximum abduction angle was mean 15.5 degrees (SD 9.4 degrees ). Decreasing the inclination angle of the glenoid resulted in a significant reduction of superior humeral head translation during abduction and there was no impingement on the acromion. The maximum abduction achieved was mean 28.5 degrees (SD 17.0 degrees ). INTERPRETATION: From a clinical perspective the reduced superior translation may decrease shoulder pain since the humeral head no longer impinges on the acromion. Further investigations are necessary to assess if the improvement in abduction is clinically significant.

Cadaver↗

PubMed2006

Thoracohumeral muscle activity alters glenohumeral joint biomechanics during active abduction.

Normal function of the glenohumeral joint depends on coordinated muscle forces that stabilize the joint while moving the shoulder. These forces can either provide compressive forces to press the humeral head into the glenoid or translational forces that may destabilize the glenohumeral joint. The objective of this study was to quantify the effect of pectoralis major and latissimus dorsi muscle activity on glenohumeral kinematics and joint reaction forces during simulated active abduction. Nine fresh-frozen whole upper extremities were tested using a dynamic shoulder testing apparatus. Seven muscle force combinations were examined: a standard combination and 10%, 20%, or 30% of the deltoid force applied to the latissimus dorsi or pectoralis major tendon, respectively. Pectoralis major and latissimus dorsi muscle activity decreased the maximum angle of glenohumeral abduction and external rotation, and increased the maximum horizontal adduction angle compared to the standard muscle combination. Thoracohumeral muscle activity also created a more anteriorly directed joint reaction force that resulted in anterior translation compared to the standard muscle combination. Therefore, the ratio between anteriorly directed translational forces and compressive forces increased during abduction due to this muscle activity, suggesting that thoracohumeral muscle activity may decrease glenohumeral stability based on the joint position and applied loads. A better understanding of the contribution of muscle forces to stability may improve rehabilitation protocols for the shoulder aimed at maximizing compression and minimizing translation at the glenohumeral joint.

Aged↗

PubMed2004

Active stability of the glenohumeral joint decreases in the apprehension position.

BACKGROUND: Muscle forces that compress the glenohumeral joint during mid-ranges of motion may lead to increased translational forces in end-range positions, such as the apprehension position, where symptoms of anterior instability occur. OBJECTIVE: The objective of this study was to quantify active stability provided by eight shoulder muscles in mid-range and end-range positions through muscle force vector analysis. METHODS: Lines of action were derived from a geometric model and muscle force magnitudes were estimated with electromyography-based techniques. Resultant muscle force vectors were calculated by summing individual muscle force vectors. RESULTS: Compared to mid-range positions, lines of action of resultant force vectors were more anteriorly directed in end-range positions compared to 15 degrees of abduction, up to 26 degrees. Consequently, anterior stability was lowest in the apprehension position. The magnitudes of the resultant force vectors were comparable to other studies. Based on a sensitivity analysis, lines of action of resultant force vectors vary up to 6 degrees within the population. CONCLUSIONS: Data obtained from this model will improve conservative management, post-surgical rehabilitation, and strength training protocols.

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