Scapular inclination and glenohumeral joint stability: a cadaveric study.
ABSTRACT In shoulders with multidirectional instability, translation of the humeral head on the glenoid is increased in the midrange because of the following three reasons: the increased retroversion, a hypoplastic posteroinferior rim, and decreased scapular abduction during arm elevation. This study aimed to clarify the relationship between glenoid inclination and glenohumeral joint stability.
Nine fresh-frozen cadaveric shoulders were tested. With a 50-N compressive load, the translation force was measured in the 3-o'clock, 6-o'clock, 9-o'clock, and 12-o'clock directions by using a tilt of 0 degrees , 5 degrees , 10 degrees , 15 degrees , and 20 degrees . When the glenoid was tilted in one direction, the translation force was measured in the direction of inclination and in the opposite direction. The stability ratio was then calculated.
The stability ratio in the 3-o'clock direction significantly decreased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 9-o'clock direction significantly decreased with a tilt of more than 15 degrees in the 9-o'clock direction and significantly increased with a tilt of more than 5 degrees in the 3-o'clock direction. The stability ratio in the 6-o'clock direction significantly increased with a tilt of more than 10 degrees in the 6-o'clock direction.
The posterior and inferior stability increased with an anterior tilt of more than 5 degrees and with a superior tilt of 10 degrees , respectively. The anterior and posterior stability decreased with an anterior tilt of 5 degrees and with a posterior tilt of 15 degrees , respectively.
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ABSTRACT: The treatment of recurrent posterior glenohumeral instability remains an unsolved clinical problem. Although various types of capsulorraphy have been advocated, outcome studies indicate that it is difficult to achieve a balance between stability and mobility. Alterations of the bony glenoid for posterior instability have been proposed, but are not well understood from a mechanical perspective. This investigation had 2 purposes: (1) to determine in a cadaver model if posteroinferior glenoplasty can change the shape of the glenoid, and (2) to determine if altering the shape of the glenoid can increase the mechanical stability of the glenohumeral joint. We determined the effective glenoid shape in 7 normal cadaver glenoids by tracking the path of the center of the humeral head as it was translated across the glenoid face in 8 different directions. These determinations enabled us to calculate the maximum effective slope of the glenoid in each direction. We then determined the mechanical stability of the glenoids in each of the 8 directions by measuring the tangential force required to dislocate the shoulder under a 50-N compressive load. The ratio of the dislocating force to the compressive load was defined as the stability ratio. All measurements were repeated after a standardized posteroinferior glenoplasty was performed. Posteroinferior glenoplasty increased the posteroinferior glenoid depth from 3.8 +/- 0.6 mm to 7.0 +/- 1.8 mm and shifted the center of the humeral head an average of 2.2 mm anteriorly and 1.8 mm superiorly. These changes in dimension could be directly visualized as an immediate mechanical consequence of the glenoplasty procedure, particularly because of the insertion of the bone wedge. Glenoplasty increased the posteroinferior glenoid slope from 0.55 +/- 0.07 to 0.83 +/- 0.12 and increased the posteroinferior stability ratio from 0.47 +/- 0.10 to 0.81 +/- 0.17. This is a more than 70% increase in the tangential force that can be resisted before dislocation. The increase can be quantitatively understood as a direct mechanical consequence of the altered shape of the glenoid concavity. These numbers indicate that, in this cadaveric model, posteroinferior glenoplasty results in defined changes in the effective glenoid shape and in the mechanical stability of the glenohumeral joint. However, this study does not establish the role of this procedure in the clinical management of posterior glenohumeral instability.Journal of Shoulder and Elbow Surgery 01/1999; 8(3):205-13. · 2.32 Impact Factor
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ABSTRACT: The Neer I (polyethylene glenoid), Neer II (plastic glenoid surface with metal backing), Cofield, and Gristina monospherical total shoulder prostheses were tested for joint subluxation resistance and glenoid component fixation strength. Synthetic glenoid models with consistent structural properties and standard under-cutting geometry were used for glenoid component fixation with bone cement. It was found that joint subluxation resistance varied linearly with axial compressive force applied. Higher subluxation strength was associated with the amount of curvature of the glenoid articulating surface. Consequently, joint stability was consistently higher for the Gristina design, and all had lower resistance in the anteroposterior direction. After complete joint dislocation under high axial compressive force, the polyethylene material at the site of subluxation experienced gross plastic deformation. The fixation strength of the glenoid component was lowest for the Neer I design and highest for the Cofield design. Fatigue loading at the joint did not seem to affect the glenoid component fixation strength. In general, all glenoid components appeared to have sufficient fixation strength against normal shoulder joint forces except the Neer I design. Loosening and fracture of the plastic glenoid component may occur under excessive loads.Orthopedics 02/1988; 11(1):141-9. · 1.05 Impact Factor
- The Journal of Bone and Joint Surgery 05/1967; 49(3):471-6. · 3.23 Impact Factor