Abstract:BackgroundThe purpose of this study was to examine biomechanical properties and the degree of radiolucency of two cemented basic glenoid designs for total shoulder arthroplasty. Our hypothesis was that a component with increased micro-motion in the laboratory at time zero would also exhibit a greater amount of radiolucency in patients at a minimum of 2 years post total shoulder arthroplasty.MethodsThirty cadaveric shoulders were divided into 2 groups (keel vs. peg). The glenoid components were first loaded wit… Show more
“…While increased translation may resemble native glenohumeral kinematics more accurately, [12,13] this may also lead to more eccentric loading on and greater micromotion of the glenoid component in the setting of TSA. As excessive micromotion of the glenoid component has been suggested as a signi cant risk factor for glenoid loosening in the long-term, [5,[32][33][34] these biomechanical time-zero ndings may be of clinical importance, alleviating concerns of implant loosening due to increased rocking motion.…”
Background
Elliptical shape humeral head prostheses have been recently proposed to reflect a more anatomic shoulder replacement. However, its effect on obligate glenohumeral translation during axial rotation compared to a standard spherical head is still not well understood. The purpose of the study was to compare obligate humeral translation during axial rotation using spherical and elliptical shaped humeral head prostheses. It was hypothesized that the spherical head design would show significantly more obligate translation when compared to the elliptical design.
Methods
Six fresh-frozen cadaveric shoulders were utilized for biomechanical testing of internal (IR) and external (ER) rotation at various levels of abduction (0°, 30°, 45°, 60°) with lines of pull along each of the rotator cuff muscles. Each specimen underwent the following three conditions: (1) native; total shoulder arthroplasty (TSA) using (2) an elliptical and (3) spherical humeral head implant. Obligate translation during IR and ER was quantified using a 3-dimensional digitizer. The radius of curvature of the superoinferior and anteroposterior dimensions of the implants was calculated across each condition.
Results
Posterior and inferior translation of spherical and elliptical heads during ER was similar at all abduction angles (P > 0.05, respectively). Compared to the native humeral head, both implants demonstrated significantly decreased posterior translation at 45° (elliptical: P = 0.003; spherical: P = 0.004) and 60° of abduction (elliptical: P < 0.001; spherical: P < 0.001). During internal rotation at 0° abduction, the spherical head showed significantly more compound motion (P = 0.042) compared to the elliptical head. The spherical implant also demonstrated increased anterior translation and compound motion during internal rotation at 60° abduction (P < 0.001) compared to the resting state. This difference was not significant for the native or elliptical head design at this angle (P > 0.05).
Conclusions
In the setting of TSA, elliptical and spherical head implants showed similar obligate translation during axial rotation. A gained understanding of the consequences of implant head shape in TSA may guide future surgical implant choice for better recreation of native shoulder kinematics and potentially improved patient outcomes.
Level of Evidence
Controlled Laboratory Study
“…While increased translation may resemble native glenohumeral kinematics more accurately, [12,13] this may also lead to more eccentric loading on and greater micromotion of the glenoid component in the setting of TSA. As excessive micromotion of the glenoid component has been suggested as a signi cant risk factor for glenoid loosening in the long-term, [5,[32][33][34] these biomechanical time-zero ndings may be of clinical importance, alleviating concerns of implant loosening due to increased rocking motion.…”
Background
Elliptical shape humeral head prostheses have been recently proposed to reflect a more anatomic shoulder replacement. However, its effect on obligate glenohumeral translation during axial rotation compared to a standard spherical head is still not well understood. The purpose of the study was to compare obligate humeral translation during axial rotation using spherical and elliptical shaped humeral head prostheses. It was hypothesized that the spherical head design would show significantly more obligate translation when compared to the elliptical design.
Methods
Six fresh-frozen cadaveric shoulders were utilized for biomechanical testing of internal (IR) and external (ER) rotation at various levels of abduction (0°, 30°, 45°, 60°) with lines of pull along each of the rotator cuff muscles. Each specimen underwent the following three conditions: (1) native; total shoulder arthroplasty (TSA) using (2) an elliptical and (3) spherical humeral head implant. Obligate translation during IR and ER was quantified using a 3-dimensional digitizer. The radius of curvature of the superoinferior and anteroposterior dimensions of the implants was calculated across each condition.
Results
Posterior and inferior translation of spherical and elliptical heads during ER was similar at all abduction angles (P > 0.05, respectively). Compared to the native humeral head, both implants demonstrated significantly decreased posterior translation at 45° (elliptical: P = 0.003; spherical: P = 0.004) and 60° of abduction (elliptical: P < 0.001; spherical: P < 0.001). During internal rotation at 0° abduction, the spherical head showed significantly more compound motion (P = 0.042) compared to the elliptical head. The spherical implant also demonstrated increased anterior translation and compound motion during internal rotation at 60° abduction (P < 0.001) compared to the resting state. This difference was not significant for the native or elliptical head design at this angle (P > 0.05).
Conclusions
In the setting of TSA, elliptical and spherical head implants showed similar obligate translation during axial rotation. A gained understanding of the consequences of implant head shape in TSA may guide future surgical implant choice for better recreation of native shoulder kinematics and potentially improved patient outcomes.
Level of Evidence
Controlled Laboratory Study
“…Eccentric loading along with the resulting rocking (micro) motion of the glenoid component has been identified as an important biomechanical factor for subsequent implant loosening, thus the glenoid design has usually been suggested to be essential for ensuring long-term stability and clinical survival [2][3][4]. Although biomechanical studies have shown that the glenoid design is critical for initial fixation strength [29], clinical and radiographic studies demonstrating the superiority of one design over another are yet to be reported [28,29]. More importantly, the inconsistency of clinical findings along with recent anatomic studies describing the humeral head to be rather elliptical in shape than a perfect sphere may imply that the design of the humeral head prosthesis may also have a considerable influence on the long-term stability of the glenoid component [8,11,[13][14][15].…”
Section: Discussionmentioning
confidence: 99%
“…To determine micro-motion of the glenoid component, four high-resolution differential variable reluctance transducer (DVRT) strain gauges (Microstrain, Burlington, VT, USA) were placed at the anterior, posterior, superior, and inferior aspect of the glenoid component (Fig. 2 ) [ 29 ]. Fig.…”
Section: Methodsmentioning
confidence: 99%
“…A power analysis was carried out to determine detectable differences in micro-motion, using standard deviations estimated from the literature as well as pilot data prior to this study [ 29 ]. Assuming a common standard deviation of 0.1 mm, a sample size of 6 specimens would provide 80% power to detect a 0.15 mm difference in micro-motion at an α level of 0.05.…”
Section: Methodsmentioning
confidence: 99%
“…As previous studies have identified eccentric loading along with the resulting rocking of the glenoid component as an important biomechanical factor for implant loosening, the glenoid design has been suggested to be critical for long-term stability and clinical survival [2][3][4]. Biomechanically, Voss et al recently found that a pegged glenoid design showed significantly increased micro-motion during eccentric axial loading when compared to a keeled glenoid design [29]. Although with this suggesting that the glenoid design is important for initial fixation strength, Throckmorton et al did not find significant differences in clinical and radiographic outcomes between the two designs [28].…”
Introduction
Elliptical-shaped humeral head prostheses have recently been proposed to reflect a more anatomic shoulder replacement. However, its subsequent effect on micro-motion of the glenoid component is still not understood.
Materials and methods
Six fresh-frozen, cadaveric shoulders (mean age: 62.7 ± 9.2 years) were used for the study. Each specimen underwent total shoulder arthroplasty using an anatomic stemless implant. At 15°, 30°, 45° and 60° of glenohumeral abduction, 50° of internal and external rotations in the axial plane were alternatingly applied to the humerus with both an elliptical and spherical humeral head design. Glenohumeral translation was assessed by means of a 3-dimensional digitizer. Micro-motion of the glenoid component was evaluated using four high-resolution differential variable reluctance transducer strain gauges, placed at the anterior, posterior, superior, and inferior aspect of the glenoid component.
Results
The elliptical head design showed significantly more micro-motion in total and at the superior aspect of glenoid component during external rotation at 15° (total: P = 0.004; superior: P = 0.004) and 30° (total: P = 0.045; superior: P = 0.033) of abduction when compared to the spherical design. However, during internal rotation, elliptical and spherical heads showed similar amounts of micro-motion at the glenoid component at all tested abduction angles. When looking at glenohumeral translation, elliptical and spherical heads showed similar anteroposterior and superoinferior translation as well as compound motion during external rotation at all tested abduction angles. During internal rotation, the elliptical design resulted in significantly more anteroposterior translation and compound motion at all abduction angles when compared to the spherical design (P < 0.05).
Conclusion
In the setting of total shoulder arthroplasty, the elliptical head design demonstrated greater glenohumeral translation and micro-motion at the glenoid component during axial rotation when compared to the spherical design, potentially increasing the risk for glenoid loosening in the long term.
Level of evidence
Controlled Laboratory Study
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