- Email: [email protected]
Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis
Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis Richard W. Nyffeler, MD,a Clément M. L. Werner, MD,b and Christian Gerber, MD,b Lausanne and Zurich, Switzerland
The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. It is thought that this notch is a result of mechanical contact between the polyethylene cup of the humeral implant and the inferior glenoid pole during adduction of the arm. This in vitro study assessed the effect of glenoid component positioning on glenohumeral range of motion in 8 shoulder specimens. Four different positions of the glenosphere were tested: glenosphere centered on the glenoid, leaving the inferior glenoid rim uncovered (configuration A); glenosphere flush with the inferior glenoid rim (configuration B); glenosphere extending beyond the inferior glenoid rim (configuration C); and glenosphere tilted downward 15° (configuration D). The respective mean adduction and abduction angles in the scapular plane were ⫺25° and 67° for configuration A, ⫺14° and 68° for configuration B, ⫺1° and 81° for configuration C, and ⫺9° and 75° for configuration D. Placing the glenosphere distally (test configuration C) significantly improved adduction and abduction angles compared with all other test configurations (P ⬍ .001). (J Shoulder Elbow Surg 2005;14:524-528.)
T he treatment of patients with arthritis of the shoulder
and irreparable tears of the rotator cuff is difficult. Superior migration of the humeral head results in eccentric superior loading of the glenoid and is a relative contraindication for conventional (unconstrained) total shoulder replacement. Hemiarthroplasty may reduce pain; the gain in active motion, however, is limited as a result of the lack of rotator cuff function, and there is a risk of erosion of the From the Orthopaedic Hospital, University of Lausanne, Lausannea, and Department of Orthopaedic Surgery, University of Zurich, Balgristb, Zurich. Reprint requests: Richard W. Nyffeler, MD, Orthopaedic Hospital, University of Lausanne, Av Pierre-Decker 4, CH-1005 Lausanne, Switzerland (E-mail: [email protected]). Copyright © 2005 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2005/$30.00 doi:10.1016/j.jse.2004.09.010
524
acromion and glenoid by the humeral component. In 1987 Grammont et al4 described a semiconstrained total shoulder prosthesis that reverses the scapular and humeral components (Delta III total shoulder prosthesis; DePuy International Ltd, Leeds, England). Early results of treatment of arthritic shoulders with rotator cuff deficiency with this prosthesis have been encouraging with regard to pain relief and improvement of function.1,2 A major concern remains regarding the formation of a notch at the inferior pole of the scapular neck6 (Figure 1), a possible source of mechanical failure. It is thought that this notch is related to the design of the prosthesis (Figure 2) and a result of mechanical contact between the polyethylene of the epiphyseal implant and the glenoid during adduction of the arm, resulting in polyethylene wear, chronic inflammation of the joint capsule, and local osteolysis.5 We hypothesized that the mechanical contact at the inferior scapular neck must be related to the placement of the glenoid prosthesis and that the recommendation of the manufacturer may be incorrect. The purpose of this study was, therefore, to assess the influence of glenoid component positioning on glenohumeral range of motion and mechanical impingement between the prosthesis and the glenoid. MATERIALS AND METHODS A total of 8 fresh-frozen human shoulder specimens were obtained from the Department of Pathology of our university. There were 3 right and 5 left shoulders consisting of the whole scapula and the proximal half of the humerus. After thawing, all muscles, tendons, and ligaments were stripped off. Special attention was paid to clean the inferior glenoid pole and the tuberosities of any soft tissue. The coracoacromial ligament was carefully preserved. Gross inspection did not show any posttraumatic deformity or degenerative changes such as glenoid wear. The articular cartilage of the glenoid was removed with a curette, and the craniocaudal and anteroposterior diameters of the bony glenoid were measured with a caliper.
Preparation of humerus The humeral head was cut by use of the resection guide. Normal retroversion of the specimen was not changed. The metaphysis and medullary canal were prepared by use of the appropriate-sized reamers. Reaming was completed
J Shoulder Elbow Surg Volume 14, Number 5
Figure 1 Anteroposterior radiograph of a left shoulder 5 years after implantation of a reverse Delta III prosthesis shows a big notch at the inferior part of the scapular neck.
when the flange of the reamer was level with the osteotomy. A cementless humeral prosthesis (stem size, 1; epiphysis, 36.2 mm) with a lateralized humeral cup (036 mm ⫹ 6) was inserted in normal retroversion. The lateralized humeral cup corresponds to the most frequently used cup of the Delta III prosthesis. Normal retroversion was chosen because the distal part of the humeri and the forearms were not available in the specimens used in these experiments. The neck-shaft angle of the prosthesis measured 155°.
Preparation of glenoid The superoinferior and anteroposterior axes of the glenoid were marked with a pencil. A 1.5-mm guide pin was inserted perpendicular to the articular surface just inferior and posterior to the intersection of the 2 axes, as recommended by the manufacturer.3 A 6.5-mm centering hole was then drilled over the guide pin, and the glenoid was prepared with a flat reamer. A hydroxyapatite-coated glenoid base plate (metaglene) with a central plug was inserted and fixed to the bone with at least two 3.5-mm spherical-head screws. A glenosphere with a diameter of 36 mm was then attached to the metaglene. This position of the glenoid prosthesis corresponded to test configuration A and was characterized by a small area of uncovered glenoid bone below the glenosphere (Figure 3).
Nyffeler, Werner, and Gerber 525
Figure 2 Photograph of a reverse Delta III total shoulder prosthesis. In the neutral position, the stem of the humeral component is vertical and the polyethylene cup extends beyond the inferior border of the scapular component (glenosphere).
Figure 3 Illustration of the 4 positions of the glenoid component examined: glenosphere centered on the glenoid, leaving the inferior part of the glenoid bone uncovered (A); glenosphere flush with the inferior glenoid rim (B); glenoid base plate (metaglene) flush with the glenoid rim and glenosphere extending beyond the inferior border of the glenoid (C); and glenosphere tilted downward by 15° and flush with the scapular neck (D).
Measurement protocol The scapula was fixed in a vice with the scapular blade and the glenoid base plate oriented vertically. The humerus was centered on the glenoid component and passively abducted and adducted in the scapular plane, in the frontal plane (30° behind the scapular plane), and in the sagittal plane (perpendicular to the frontal plane). Movements were stopped as soon as either the humeral head or the humeral prosthesis abutted against the bone of the scapula. The corresponding glenohumeral abduction and adduction an-
526
Nyffeler, Werner, and Gerber
J Shoulder Elbow Surg September/October 2005
Figure 4 Photographs showing how the guiding pin can be positioned by use of the metaglene. Placing the border of the base plate precisely at the inferior rim (A) allows fixation of the prosthesis in such a way that the glenosphere extends beyond the inferior scapular neck (B).
gles were measured with a mounted plastic goniometer, with the neutral axis being vertical. The position of the glenosphere was then changed, and the above-described abduction and adduction angle measurements were repeated. The following additional positions of the glenosphere were examined (Figure 3): glenosphere flush with the inferior glenoid rim (configuration B), glenoid base plate flush with the inferior glenoid rim and glenosphere extending beyond the inferior border of the bone (configuration C), and glenosphere tilted downward 15° and flush with the inferior border of the scapular neck (configuration D). Optimal positioning of the glenoid implant in test configuration C was achieved by holding the base plate flat against the glenoid bone, with the border of the plate being flush with the inferior glenoid rim and the central peg oriented toward the joint (Figure 4). The hole in the central fixation peg served as a drill guide for the insertion of a 3.5-mm guide pin. The pin was then overdrilled, and the base plate was inserted and solidly fixed in the scapular neck with 3.5-mm spherical-head screws. In the original implant the superior and inferior fixation screws are monoaxial threaded head screws that form an angle of 40° to the axis of the central peg of the metaglene. If the metaglene is placed flush with the inferior glenoid rim, then the inferior screw may be too distal with respect to the lateral scapular pillar and may potentially run out of bone. We, therefore, used spherical head screws inserted at an angle of 10° to 20° to the central peg. The use of a spherical rather than a threaded head screw may, however, reduce the stability of the glenoid prosthesis in vivo. Inclination of the glenoid prosthesis in test configuration D was obtained by performing an oblique osteotomy with resection of the inferior glenoid pole. The inclination of the osteotomy was determined by use of a goniometer and marked on the scapular neck with a pencil. The resection of bone was done with an oscillating saw.
Statistical analysis A repeated-measures analysis of variance with post hoc test (Bonferroni-Dunn) was used to determine whether changing the position of the glenoid component resulted in significant differences in the abduction and adduction angles. The level of significance was set at P ⫽ .05.
RESULTS The craniocaudal diameter of the cartilage-free glenoids averaged 37.3 mm (range, 33-43 mm). As a result of the rounding of the glenoid rim, this diameter increased slightly after reaming. The mean anteroposterior diameter was 26.5 mm (range, 23-32 mm). In 3 shoulders the craniocaudal diameter of the glenoid was smaller than or equal to the diameter of the glenosphere, and there was no uncovered bone at the inferior glenoid rim after insertion of the glenosphere. Therefore, position A of the glenosphere could only be assessed in 5 specimens. Positions B, C, and D, however, could be tested in all specimens. The results of the glenohumeral abduction and adduction angle measurements are listed in Table I. In all cases, abduction and adduction angles were better in the scapular plane than in the frontal or sagittal plane. Abduction was limited by direct contact between the greater tuberosity and coracoacromial arch. Adduction was limited by abutment of the polyethylene cup against the uncovered inferior glenoid rim or the inferior part of the scapular neck (Figure 5). This mechanical contact between the implant and bone hindered the arm reaching the vertical (neutral) position. The highest abduction and the best adduction angles were measured when the glenosphere extended beyond the inferior glenoid pole (test con-
Nyffeler, Werner, and Gerber 527
J Shoulder Elbow Surg Volume 14, Number 5
Table I Mean glenohumeral abduction and adduction angles (range) for different glenosphere positions tested Position
Abduction (°) Scapular plane 30° posterior 60° anterior Adduction (°) Scapular plane 30° posterior 60° anterior
A (n ⴝ 5)
B (n ⴝ 8)
C (n ⴝ 8)
D (n ⴝ 8)
67 (56 to 78) 58 (48 to 74) 39 (35 to 46)
68 (55 to 82) 56 (35 to 74) 48 (26 to 46)
81 (70 to 90) 66 (48 to 85) 48 (24 to 55)
75 (68 to 82) 61 (50 to 80) 46 (26 to 52)
–25 (–20 to –30) –30 (–20 to –46) –30 (–12 to –46)
–14 (–7 to –22) –18 (–5 to –30) –19 (–12 to –32)
–1 (0 to –5) –6 (0 to –18) –4 (0 to –8)
–9 (0 to –12) –15 (–5 to –22) –11 (0 to –15)
Negative values correspond to an adduction deficit. n, Number of specimens tested in each position of the glenosphere.
Figure 5 Drawings illustrating the effect of the position of the glenosphere on range of motion of the humerus. With the glenosphere centered on the glenoid, adduction was limited by direct contact of the polyethylene cup on the inferior glenoid rim and abduction was limited by subacromial or subcoracoid impingement (A). Positioning the glenosphere more distally resulted in a significant improvement of adduction and abduction (B).
figuration C). This was true for the measurements in the scapular plane, in the frontal plane, and in the sagittal plane. The abduction and adduction angles measured in this position were significantly better than in all other test configurations in the scapular plane (P ⬍ .001). The second best position with respect to range of motion was position D, with the glenosphere inclined downward by 15°. The oblique osteotomy of the scapular neck also resulted in a reduction of the surface area of the inferior part of the glenoid (Figure 6). Positioning the glenoid prosthesis in the center of the glenoid or only slightly inferior, as recommended by the manufacturer of the prosthesis (test condition A), resulted in poor abduction and adduction angles in the specimens tested. DISCUSSION The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. In a retrospective study Sirveaux et al6 found a scapular notch in 50 of 77 patients (65%) at a mean
Figure 6 Lateral views of a shoulder specimen before (A) and after (B) an oblique resection of the glenoid was performed to increase the inclination angle. The oblique osteotomy resulted in a substantial reduction of the surface area necessary to fix the glenoid base plate (metaglene).
follow-up of 44.5 months. The notch was limited to the pillar in 26 patients, it was in contact with the lower screw in 10 cases, it extended above the lower screw in 7 cases, and it denuded the inferior part of the base plate in 6 cases. Three glenoid components were considered to be loose. In their study a notch extending over the inferior screw significantly affected the Constant score. To date, the reported rate of glenoid component loosening in the reverse Delta III shoulder prosthesis has been relatively low (2%-5%).6,7 There are, however, only a few studies published, most of which included a small number of patients and a short follow-up. There are no long-term results available, and it is, therefore, not known whether inferior notching will result in late component failure. A big notch extending above the inferior screw and denuding the inferior part of the glenoid base plate theoretically diminishes the stability of the glenoid implant. Efforts
528
Nyffeler, Werner, and Gerber
should, therefore, be made to reduce the risk for the formation of such a notch. In vitro, the mechanical contact at the inferior scapular neck correlated with the position of the glenosphere. Placing the metaglene more distally significantly improved adduction and abduction angles. If the glenoid base plate (metaglene) is placed flush with the inferior glenoid rim (test configuration C), then the glenosphere extends beyond the scapular neck. This results in better clearance and complete adduction of the arm without abutment of the polyethylene cup against the bone of the scapula. It is suggested that polyethylene wear, chronic inflammation, and osteolysis diminish when the inferior mechanical contact can be avoided. Some surgeons recommend an oblique resection of the glenoid to insert the metaglene with a slightly inferior tilt in order to reduce the risk of inferior notching. Our study has shown that this technique improves adduction angles compared with the standard technique (test conditions A and B) but does not yield results as good as those obtained when placing the metaglene distally on the uncut glenoid. It should also be noted that an oblique osteotomy of the funnelshaped scapular neck reduces the surface area of the glenoid and may compromise stable fixation of the glenoid base plate. Many surgeons use a deltoid split for the insertion of the Delta III prosthesis. The length of the muscular incision is limited by the axillary nerve, and exposure of the inferior aspect of the glenoid may be difficult. Adequate soft-tissue release at the inferior glenoid pole and distal placement of the glenoid component may be more easily performed through a deltopectoral approach. Placing the glenoid implant more distally than recommended by the manufacturer may result in asymmetric inferior loading of the glenoid. However, if we assume that full adduction of the arm is only possible when the glenosphere extends beyond the inferior
J Shoulder Elbow Surg September/October 2005
glenoid rim, then placing the glenosphere distally with a small overhang seems to be a better option than placing it centrally and creating the necessary overhang by removing the strong cortical bone of the inferior glenoid rim with a chisel. Further studies assessing the influence of prosthetic placement on fixation strength and stability of the implant should be done. In conclusion, this in vitro study has shown that the range of glenohumeral motion after implantation of a reverse Delta III total shoulder prosthesis depends on the position of the glenoid implant. Placing the glenoid component 2 to 4 mm more distally than recommended significantly improves abduction and adduction angles and may, therefore, reduce the risk of inferior glenoid notching. REFERENCES
1. Baulot E, Chabernaud D, Grammont PM. Results of Grammont’s inverted prosthesis in omarthritis associated with major cuff destruction. Apropos of 16 cases [in French]. Acta Orthop Belg 1995; 61(Suppl 1):112-9. 2. Baulot E, Garron E, Grammont PM. Grammont prosthesis in humeral head osteonecrosis. Indications—results [in French]. Acta Orthop Belg 1999;65(Suppl 1):109-15. 3. Delta reverse shoulder prosthesis. Surgical technique. DePuy International Ltd, Leeds, England; 2002. 4. Grammont PM, Trouilloud P, Laffay JP, Deries X. Etude et réalisation d’ une nouvelle prothèse d’ épaule. Rhumatologie 1987;39:407-18. 5. Nyffeler RW, Werner CML, Simmen BR, Gerber C. Analysis of a retrieved Delta III total shoulder prosthesis. J Bone Joint Surg Br 2004;86:1187-91. 6. Sirveaux F, Favard L, Oudet D, Huguet D, Lautman S. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive and non repairable cuff rupture. In: Walch G, Mole D, editors. 2000 shoulder prostheses . . . two to ten year follow-up. Montpellier: Sauramps Medical; 2001. p. 247-52. 7. Valenti P, Boutens D, Nerot C. Delta 3 reversed prosthesis for osteoarthritis with massive rotator cuff tear: long term results (⬎5 years). In: Walch G, Mole D, editors. 2000 shoulder prostheses . . . two to ten year follow-up. Montpellier: Sauramps Medical; 2001. p. 253-9.
The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. It is thought that this notch is a result of mechanical contact between the polyethylene cup of the humeral implant and the inferior glenoid pole during adduction of the arm. This in vitro study assessed the effect of glenoid component positioning on glenohumeral range of motion in 8 shoulder specimens. Four different positions of the glenosphere were tested: glenosphere centered on the glenoid, leaving the inferior glenoid rim uncovered (configuration A); glenosphere flush with the inferior glenoid rim (configuration B); glenosphere extending beyond the inferior glenoid rim (configuration C); and glenosphere tilted downward 15° (configuration D). The respective mean adduction and abduction angles in the scapular plane were ⫺25° and 67° for configuration A, ⫺14° and 68° for configuration B, ⫺1° and 81° for configuration C, and ⫺9° and 75° for configuration D. Placing the glenosphere distally (test configuration C) significantly improved adduction and abduction angles compared with all other test configurations (P ⬍ .001). (J Shoulder Elbow Surg 2005;14:524-528.)
T he treatment of patients with arthritis of the shoulder
and irreparable tears of the rotator cuff is difficult. Superior migration of the humeral head results in eccentric superior loading of the glenoid and is a relative contraindication for conventional (unconstrained) total shoulder replacement. Hemiarthroplasty may reduce pain; the gain in active motion, however, is limited as a result of the lack of rotator cuff function, and there is a risk of erosion of the From the Orthopaedic Hospital, University of Lausanne, Lausannea, and Department of Orthopaedic Surgery, University of Zurich, Balgristb, Zurich. Reprint requests: Richard W. Nyffeler, MD, Orthopaedic Hospital, University of Lausanne, Av Pierre-Decker 4, CH-1005 Lausanne, Switzerland (E-mail: [email protected]). Copyright © 2005 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2005/$30.00 doi:10.1016/j.jse.2004.09.010
524
acromion and glenoid by the humeral component. In 1987 Grammont et al4 described a semiconstrained total shoulder prosthesis that reverses the scapular and humeral components (Delta III total shoulder prosthesis; DePuy International Ltd, Leeds, England). Early results of treatment of arthritic shoulders with rotator cuff deficiency with this prosthesis have been encouraging with regard to pain relief and improvement of function.1,2 A major concern remains regarding the formation of a notch at the inferior pole of the scapular neck6 (Figure 1), a possible source of mechanical failure. It is thought that this notch is related to the design of the prosthesis (Figure 2) and a result of mechanical contact between the polyethylene of the epiphyseal implant and the glenoid during adduction of the arm, resulting in polyethylene wear, chronic inflammation of the joint capsule, and local osteolysis.5 We hypothesized that the mechanical contact at the inferior scapular neck must be related to the placement of the glenoid prosthesis and that the recommendation of the manufacturer may be incorrect. The purpose of this study was, therefore, to assess the influence of glenoid component positioning on glenohumeral range of motion and mechanical impingement between the prosthesis and the glenoid. MATERIALS AND METHODS A total of 8 fresh-frozen human shoulder specimens were obtained from the Department of Pathology of our university. There were 3 right and 5 left shoulders consisting of the whole scapula and the proximal half of the humerus. After thawing, all muscles, tendons, and ligaments were stripped off. Special attention was paid to clean the inferior glenoid pole and the tuberosities of any soft tissue. The coracoacromial ligament was carefully preserved. Gross inspection did not show any posttraumatic deformity or degenerative changes such as glenoid wear. The articular cartilage of the glenoid was removed with a curette, and the craniocaudal and anteroposterior diameters of the bony glenoid were measured with a caliper.
Preparation of humerus The humeral head was cut by use of the resection guide. Normal retroversion of the specimen was not changed. The metaphysis and medullary canal were prepared by use of the appropriate-sized reamers. Reaming was completed
J Shoulder Elbow Surg Volume 14, Number 5
Figure 1 Anteroposterior radiograph of a left shoulder 5 years after implantation of a reverse Delta III prosthesis shows a big notch at the inferior part of the scapular neck.
when the flange of the reamer was level with the osteotomy. A cementless humeral prosthesis (stem size, 1; epiphysis, 36.2 mm) with a lateralized humeral cup (036 mm ⫹ 6) was inserted in normal retroversion. The lateralized humeral cup corresponds to the most frequently used cup of the Delta III prosthesis. Normal retroversion was chosen because the distal part of the humeri and the forearms were not available in the specimens used in these experiments. The neck-shaft angle of the prosthesis measured 155°.
Preparation of glenoid The superoinferior and anteroposterior axes of the glenoid were marked with a pencil. A 1.5-mm guide pin was inserted perpendicular to the articular surface just inferior and posterior to the intersection of the 2 axes, as recommended by the manufacturer.3 A 6.5-mm centering hole was then drilled over the guide pin, and the glenoid was prepared with a flat reamer. A hydroxyapatite-coated glenoid base plate (metaglene) with a central plug was inserted and fixed to the bone with at least two 3.5-mm spherical-head screws. A glenosphere with a diameter of 36 mm was then attached to the metaglene. This position of the glenoid prosthesis corresponded to test configuration A and was characterized by a small area of uncovered glenoid bone below the glenosphere (Figure 3).
Nyffeler, Werner, and Gerber 525
Figure 2 Photograph of a reverse Delta III total shoulder prosthesis. In the neutral position, the stem of the humeral component is vertical and the polyethylene cup extends beyond the inferior border of the scapular component (glenosphere).
Figure 3 Illustration of the 4 positions of the glenoid component examined: glenosphere centered on the glenoid, leaving the inferior part of the glenoid bone uncovered (A); glenosphere flush with the inferior glenoid rim (B); glenoid base plate (metaglene) flush with the glenoid rim and glenosphere extending beyond the inferior border of the glenoid (C); and glenosphere tilted downward by 15° and flush with the scapular neck (D).
Measurement protocol The scapula was fixed in a vice with the scapular blade and the glenoid base plate oriented vertically. The humerus was centered on the glenoid component and passively abducted and adducted in the scapular plane, in the frontal plane (30° behind the scapular plane), and in the sagittal plane (perpendicular to the frontal plane). Movements were stopped as soon as either the humeral head or the humeral prosthesis abutted against the bone of the scapula. The corresponding glenohumeral abduction and adduction an-
526
Nyffeler, Werner, and Gerber
J Shoulder Elbow Surg September/October 2005
Figure 4 Photographs showing how the guiding pin can be positioned by use of the metaglene. Placing the border of the base plate precisely at the inferior rim (A) allows fixation of the prosthesis in such a way that the glenosphere extends beyond the inferior scapular neck (B).
gles were measured with a mounted plastic goniometer, with the neutral axis being vertical. The position of the glenosphere was then changed, and the above-described abduction and adduction angle measurements were repeated. The following additional positions of the glenosphere were examined (Figure 3): glenosphere flush with the inferior glenoid rim (configuration B), glenoid base plate flush with the inferior glenoid rim and glenosphere extending beyond the inferior border of the bone (configuration C), and glenosphere tilted downward 15° and flush with the inferior border of the scapular neck (configuration D). Optimal positioning of the glenoid implant in test configuration C was achieved by holding the base plate flat against the glenoid bone, with the border of the plate being flush with the inferior glenoid rim and the central peg oriented toward the joint (Figure 4). The hole in the central fixation peg served as a drill guide for the insertion of a 3.5-mm guide pin. The pin was then overdrilled, and the base plate was inserted and solidly fixed in the scapular neck with 3.5-mm spherical-head screws. In the original implant the superior and inferior fixation screws are monoaxial threaded head screws that form an angle of 40° to the axis of the central peg of the metaglene. If the metaglene is placed flush with the inferior glenoid rim, then the inferior screw may be too distal with respect to the lateral scapular pillar and may potentially run out of bone. We, therefore, used spherical head screws inserted at an angle of 10° to 20° to the central peg. The use of a spherical rather than a threaded head screw may, however, reduce the stability of the glenoid prosthesis in vivo. Inclination of the glenoid prosthesis in test configuration D was obtained by performing an oblique osteotomy with resection of the inferior glenoid pole. The inclination of the osteotomy was determined by use of a goniometer and marked on the scapular neck with a pencil. The resection of bone was done with an oscillating saw.
Statistical analysis A repeated-measures analysis of variance with post hoc test (Bonferroni-Dunn) was used to determine whether changing the position of the glenoid component resulted in significant differences in the abduction and adduction angles. The level of significance was set at P ⫽ .05.
RESULTS The craniocaudal diameter of the cartilage-free glenoids averaged 37.3 mm (range, 33-43 mm). As a result of the rounding of the glenoid rim, this diameter increased slightly after reaming. The mean anteroposterior diameter was 26.5 mm (range, 23-32 mm). In 3 shoulders the craniocaudal diameter of the glenoid was smaller than or equal to the diameter of the glenosphere, and there was no uncovered bone at the inferior glenoid rim after insertion of the glenosphere. Therefore, position A of the glenosphere could only be assessed in 5 specimens. Positions B, C, and D, however, could be tested in all specimens. The results of the glenohumeral abduction and adduction angle measurements are listed in Table I. In all cases, abduction and adduction angles were better in the scapular plane than in the frontal or sagittal plane. Abduction was limited by direct contact between the greater tuberosity and coracoacromial arch. Adduction was limited by abutment of the polyethylene cup against the uncovered inferior glenoid rim or the inferior part of the scapular neck (Figure 5). This mechanical contact between the implant and bone hindered the arm reaching the vertical (neutral) position. The highest abduction and the best adduction angles were measured when the glenosphere extended beyond the inferior glenoid pole (test con-
Nyffeler, Werner, and Gerber 527
J Shoulder Elbow Surg Volume 14, Number 5
Table I Mean glenohumeral abduction and adduction angles (range) for different glenosphere positions tested Position
Abduction (°) Scapular plane 30° posterior 60° anterior Adduction (°) Scapular plane 30° posterior 60° anterior
A (n ⴝ 5)
B (n ⴝ 8)
C (n ⴝ 8)
D (n ⴝ 8)
67 (56 to 78) 58 (48 to 74) 39 (35 to 46)
68 (55 to 82) 56 (35 to 74) 48 (26 to 46)
81 (70 to 90) 66 (48 to 85) 48 (24 to 55)
75 (68 to 82) 61 (50 to 80) 46 (26 to 52)
–25 (–20 to –30) –30 (–20 to –46) –30 (–12 to –46)
–14 (–7 to –22) –18 (–5 to –30) –19 (–12 to –32)
–1 (0 to –5) –6 (0 to –18) –4 (0 to –8)
–9 (0 to –12) –15 (–5 to –22) –11 (0 to –15)
Negative values correspond to an adduction deficit. n, Number of specimens tested in each position of the glenosphere.
Figure 5 Drawings illustrating the effect of the position of the glenosphere on range of motion of the humerus. With the glenosphere centered on the glenoid, adduction was limited by direct contact of the polyethylene cup on the inferior glenoid rim and abduction was limited by subacromial or subcoracoid impingement (A). Positioning the glenosphere more distally resulted in a significant improvement of adduction and abduction (B).
figuration C). This was true for the measurements in the scapular plane, in the frontal plane, and in the sagittal plane. The abduction and adduction angles measured in this position were significantly better than in all other test configurations in the scapular plane (P ⬍ .001). The second best position with respect to range of motion was position D, with the glenosphere inclined downward by 15°. The oblique osteotomy of the scapular neck also resulted in a reduction of the surface area of the inferior part of the glenoid (Figure 6). Positioning the glenoid prosthesis in the center of the glenoid or only slightly inferior, as recommended by the manufacturer of the prosthesis (test condition A), resulted in poor abduction and adduction angles in the specimens tested. DISCUSSION The presence of a notch at the inferior part of the scapular neck is a common radiographic finding in patients treated with a reverse Delta III shoulder prosthesis. In a retrospective study Sirveaux et al6 found a scapular notch in 50 of 77 patients (65%) at a mean
Figure 6 Lateral views of a shoulder specimen before (A) and after (B) an oblique resection of the glenoid was performed to increase the inclination angle. The oblique osteotomy resulted in a substantial reduction of the surface area necessary to fix the glenoid base plate (metaglene).
follow-up of 44.5 months. The notch was limited to the pillar in 26 patients, it was in contact with the lower screw in 10 cases, it extended above the lower screw in 7 cases, and it denuded the inferior part of the base plate in 6 cases. Three glenoid components were considered to be loose. In their study a notch extending over the inferior screw significantly affected the Constant score. To date, the reported rate of glenoid component loosening in the reverse Delta III shoulder prosthesis has been relatively low (2%-5%).6,7 There are, however, only a few studies published, most of which included a small number of patients and a short follow-up. There are no long-term results available, and it is, therefore, not known whether inferior notching will result in late component failure. A big notch extending above the inferior screw and denuding the inferior part of the glenoid base plate theoretically diminishes the stability of the glenoid implant. Efforts
528
Nyffeler, Werner, and Gerber
should, therefore, be made to reduce the risk for the formation of such a notch. In vitro, the mechanical contact at the inferior scapular neck correlated with the position of the glenosphere. Placing the metaglene more distally significantly improved adduction and abduction angles. If the glenoid base plate (metaglene) is placed flush with the inferior glenoid rim (test configuration C), then the glenosphere extends beyond the scapular neck. This results in better clearance and complete adduction of the arm without abutment of the polyethylene cup against the bone of the scapula. It is suggested that polyethylene wear, chronic inflammation, and osteolysis diminish when the inferior mechanical contact can be avoided. Some surgeons recommend an oblique resection of the glenoid to insert the metaglene with a slightly inferior tilt in order to reduce the risk of inferior notching. Our study has shown that this technique improves adduction angles compared with the standard technique (test conditions A and B) but does not yield results as good as those obtained when placing the metaglene distally on the uncut glenoid. It should also be noted that an oblique osteotomy of the funnelshaped scapular neck reduces the surface area of the glenoid and may compromise stable fixation of the glenoid base plate. Many surgeons use a deltoid split for the insertion of the Delta III prosthesis. The length of the muscular incision is limited by the axillary nerve, and exposure of the inferior aspect of the glenoid may be difficult. Adequate soft-tissue release at the inferior glenoid pole and distal placement of the glenoid component may be more easily performed through a deltopectoral approach. Placing the glenoid implant more distally than recommended by the manufacturer may result in asymmetric inferior loading of the glenoid. However, if we assume that full adduction of the arm is only possible when the glenosphere extends beyond the inferior
J Shoulder Elbow Surg September/October 2005
glenoid rim, then placing the glenosphere distally with a small overhang seems to be a better option than placing it centrally and creating the necessary overhang by removing the strong cortical bone of the inferior glenoid rim with a chisel. Further studies assessing the influence of prosthetic placement on fixation strength and stability of the implant should be done. In conclusion, this in vitro study has shown that the range of glenohumeral motion after implantation of a reverse Delta III total shoulder prosthesis depends on the position of the glenoid implant. Placing the glenoid component 2 to 4 mm more distally than recommended significantly improves abduction and adduction angles and may, therefore, reduce the risk of inferior glenoid notching. REFERENCES
1. Baulot E, Chabernaud D, Grammont PM. Results of Grammont’s inverted prosthesis in omarthritis associated with major cuff destruction. Apropos of 16 cases [in French]. Acta Orthop Belg 1995; 61(Suppl 1):112-9. 2. Baulot E, Garron E, Grammont PM. Grammont prosthesis in humeral head osteonecrosis. Indications—results [in French]. Acta Orthop Belg 1999;65(Suppl 1):109-15. 3. Delta reverse shoulder prosthesis. Surgical technique. DePuy International Ltd, Leeds, England; 2002. 4. Grammont PM, Trouilloud P, Laffay JP, Deries X. Etude et réalisation d’ une nouvelle prothèse d’ épaule. Rhumatologie 1987;39:407-18. 5. Nyffeler RW, Werner CML, Simmen BR, Gerber C. Analysis of a retrieved Delta III total shoulder prosthesis. J Bone Joint Surg Br 2004;86:1187-91. 6. Sirveaux F, Favard L, Oudet D, Huguet D, Lautman S. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive and non repairable cuff rupture. In: Walch G, Mole D, editors. 2000 shoulder prostheses . . . two to ten year follow-up. Montpellier: Sauramps Medical; 2001. p. 247-52. 7. Valenti P, Boutens D, Nerot C. Delta 3 reversed prosthesis for osteoarthritis with massive rotator cuff tear: long term results (⬎5 years). In: Walch G, Mole D, editors. 2000 shoulder prostheses . . . two to ten year follow-up. Montpellier: Sauramps Medical; 2001. p. 253-9.