- Email: [email protected]
Scapular thickness—implications for fracture fixation
Scapular thickness—implications for fracture fixation Charity S. Burke, MD, Craig S. Roberts, MD, John A. Nyland, EdD, Paula G. Radmacher, MS, Robert D. Acland, MBBS, FRCS, and Michael J. Voor, PhD, Louisville, KY
The purpose of this study was to measure and map scapula osseous thickness to identify the optimal areas for internal fixation. Eighteen (9 pairs) scapulae from 2 female and 7 male cadavers were used. After harvest and removal of all soft tissues, standardized measurement lines were made based on anatomic landmarks. For consistency among scapulae, measurements were taken at standard percentage intervals along each line approximating the distance between two consecutive reconstruction plate screw holes. Two-mm-diameter drill holes were made at each point, and a standard depth gauge was used to measure thickness. The glenoid fossa (25 mm) displayed the greatest mean osseous thickness, followed by the lateral scapular border (9.7 mm), the scapula spine (8.3 mm), and the central portion of the body of the scapula (3.0 mm). To optimize screw purchase and internal fixation strength, the lateral border, the lateral aspect of the base of the scapula spine, and the scapula spine itself should be used for anatomic sites of internal fixation of scapula fractures. (J Shoulder Elbow Surg 2006;15:645-648.)
T
he internal fixation of scapula fractures is technically challenging and limited by the inherent osseous anatomy and dimensions of the scapula, particularly its limited, and sometimes wafer thin, thickness.3,6,7,10 The thicker the scapular crosssection, generally the greater amount of cortical bone available for secure screw implantation.2,8,9 In their study of 5 cadavers, Niimi et al9 reported a scapular cortical bone thickness of 1.8 mm and a significant correlation between cortical bone thickness and the torque required for implant removal. Beckers et al2 reported that age and side did not have an important influence on cortical bone dimensions or density. Although previous studies From the Department of Orthopedic Surgery, University of Louisville. Reprint requests: Dr John Nyland, Department of Orthopedic Surgery, University of Louisville, 210 East Gray Street, Suite 1003, Louisville, KY 40202 (E-mail: [email protected]). Copyright © 2006 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2006/$32.00 doi:10.1016/j.jse.2005.10.005
have reported distance plots between primary scapula osseous landmarks,3,4-6,10,11 few have reported scapular thickness measurements.3,6,10 The purpose of this study was to measure and map scapula osseous thickness to provide insight regarding the optimum implant placement for the internal fixation of scapula fractures. MATERIALS AND METHODS Nine pairs of adult cadaveric scapulae (mean age, 82 years; range, 73 to 94 years) were obtained through the bequeathal program at the University of Louisville Fresh Tissue Dissection Laboratory. The cause of death for the cadaveric specimens included vascular disease, emphysema, cerebral vascular accident, adenocarcinoma, chronic obstructive pulmonary disease, cardiopulmonary arrest, congestive heart failure, chronic atrial fibrillation, and hypertension. All soft tissue was removed from the harvested scapulae, and they were stored in a freezer at 30° F to preserve tissue integrity before thickness measurements. Each scapula was marked with an indelible marker at consistent anatomic landmarks, and lines were drawn between these designated points (Figure 1) and measured using calipers. These anatomic landmarks were chosen for their relevance to regions of interest for scapular fixation and on their measurement reproducibility among specimens. Intervals were selected based on distances that were considered relevant for scapular fracture fixation using reconstruction plates. A reconstruction plate (DePuy Ace 14330-4, TDCCB69 CE0086, DePuy Orthopaedics, Warsaw, IN) typically used for internal fixation was used to standardize the space between consecutive reconstruction plate screw holes (9.85 mm) (Figure 2). We attempted to make the measurement distance between our data points as close to 9.85 mm apart as possible. This was difficult, because each scapula displayed slightly different dimensions. After the line lengths on a sample scapula were measured, lines of interest were divided into data points that approximated reconstruction screw hole locations as closely as possible. Although line length was slightly different for each specimen, each data point was located at a set percentage of the overall line length (25% line length intervals for line 1, 7% line length intervals for lines 2, 3, 4, and 8, 20% line length intervals for line 5, 33% line length intervals for lines 6 and 9, 8% line length intervals for line 7, and 50% line length intervals for line 10). The average distance between data points along a given line was 8.94
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Figure 2 Reconstruction plate used as reference for thickness measurements. The distance between hole centers is 9.85 mm, the distance between hole inner borders is 7.2 mm, and the hole diameter is 4.5 mm.
mm. Each line length and osseous thickness measurement was performed 3 times by the primary investigator. Figure 1 Reference points: A, superior glenoid tubercle; B, inferior glenoid tubercle, C, 1/2 distance between points A and B; D, inferior angle; E, lateral, inferior base of the scapula spine; F, medial, inferior base of the scapula spine; G, lateral, inferior base of the acromion process. Reference lines: 1, between points A and B; 2, between points C and D; 3, between points D and E; 4, between points D and F; 5, 6, and 7, between points located at equal thirds along lines 3 and 4; 8, between points F and G, lines 9 and 10 were drawn between points located at equal thirds along lines 7 and 8.
mm, closely approximating reconstruction plate screw hole distance. To avoid redundancy, line intersections were not used as data points. During drilling, each scapula was aligned horizontally using a standard carpenter’s level resting on the posterior body of the scapula parallel to line 5. Modeling clay was used to stabilize the edges of each scapula further during drilling. Each scapula was repositioned vertically with the scapula spine mounted in modeling clay to enable drilling holes along lines 8 to 10. A standard electric drill with a 2.0-mm-diameter bit was used to drill holes at each point perpendicular to the table. To help preserve osseous integrity throughout the measurements, the 2.0-mm-diameter drill bit was used instead of the 2.7-mm-diameter drill bit that is usually used during scapula fixation surgery. Holes were drilled and numbered from superior to inferior, medial to lateral, or anterior to posterior, depending upon line orientation in relation to the scapula. A mini-fragment depth gauge (Synthes, Paoli, PA) was then used to determine osseous thickness at each measurement point to the nearest 0.1
Statistical methods Descriptive statistics for each line and point thickness measurement, Wilcoxon signed rank tests for side-to-side comparisons of line length and select reference point thickness measurements, and intraclass correlation coefficients (ICC) to determine intra-rater measurement reliability were calculated using SPSS version 11.0 (SPSS Institute, Chicago, IL) for Windows (Microsoft, Redmond, WA). An ␣-level of P ⬍ .05 was used to indicate statistical significance.
RESULTS Intra-rater measurement reliability was high (ICC3,1, .98-.99). Mean scapular thickness varied between 2.5 mm and 29.5 mm, with the thickest areas located near the glenoid fossa, lateral border, and scapula spine and the thinnest areas located in the middle third of the scapular body. Descriptive measurements for right and left scapula reference point thickness values are reported in Table I. Mean right and left scapular thickness measurements at every third interval are depicted in Figure 3. Although most points did not display side-to-side differences, reference points where statistically significant side-toside thickness differences were observed are reported in Table II. All other reference point thickness values failed to display statistically significant side-to-side differences.
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Table I Scapula reference point thickness values (mm) Reference point #
Right mean
Right range
Left mean
Left range
Reference point #
Right mean
Right range
Left mean
Left range
20.7 27.2 25.9 28.2 17.3 10.8 9.1 9.0 8.6 9.3 9.4 9.2 8.5 8.5 8.8 9.9 8.6 14.7 8.9 4.9 3.6 3.6 4.0 5.4 4.4 5.9 6.3 7.0 8.3 9.3 11.0 8.4 7.7 5.7 5.2 5.0 4.7 4.7 4.6 4.4 4.8
17.1-26.5 22.8-33.2 22.1-29.1 18.1-36.0 10.9-25.7 7.4-13.5 5.6-12.2 2.4-14.8 3.0-16.0 3.1-15.8 2.7-14.1 2.1-13.1 2.9-12.1 4.0-13.0 4.2-12.8 7.8-12.0 6.4-10.3 8.0-22.1 5.9-14.5 2.0-7.9 2.3-6.1 1.8-7.4 2.2-9.5 2.1-11.6 2.3-8.5 2.4-11.6 2.0-10.0 2.7-11.7 5.1-11.8 6.1-14 9.1-15.2 6.2-10.7 7.2-8.1 4.8-6.2 4.3-6.8 4.0-6.1 3.5-6.0 3.8-5.9 2.9-6.0 2.0-5.9 3.7-6.0
22.0 28.3 25.7 29.5 19.0 11.7 9.5 9.5 9.7 9.6 10.1 9.9 10.0 9.3 9.7 9.6 7.7 6.0 9.5 5.7 4.6 4.5 4.9 5.3 5.8 6.1 6.0 6.5 7.6 9.1 10.5 8.1 7.3 5.6 5.3 4.8 5.0 4.9 4.5 4.3 4.2
14.3-31.3 21.0-36.4 17.1-34 23.8-37.3 12.1-30.3 8.9-15.9 6.1-14.0 6.2-13.7 2.4-13.1 2.1-14.7 2.7-14.2 2.5-14.1 3.6-14.9 3.9-13.2 5.7-13.7 6.1-11.8 6.0-9.9 10.6-24.0 4.1-15.9 3.6-10.1 2.9-7.4 3.1-7.7 2.9-8.4 2.4-10.0 2.2-10.0 2.4-11.0 2.5-11.7 2.2-14.6 3.7-14.0 5.5-12.9 8.0-13.7 4.7-12.0 5.4-10.0 4.1-6.6 3.9-6.4 3.1-6.0 3.9-6.0 3.9-6.0 3.5-5.7 3.4-6.2 3.5-4.7
4.10 4.11 4.12 4.13 4.14 4.15 5.1 5.2 5.3 5.4 6.1 6.2 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 9.1 9.2 10.1
5.1 5.6 7.1 9.3 10.1 8.0 2.9 2.7 2.5 2.7 3.3 3.6 4.3 2.8 2.7 3.0 2.8 2.7 3.0 3.5 5.2 8.0 11.4 14.1 13.4 9.4 8.2 7.8 7.5 7.0 7.6 8.6 10.4 14.7 19.4 20.9 21.4 19.7 7.0 8.6 8.4
3.0-7.4 4.0-6.7 4.8-8.9 7.6-10.6 8.7-12.2 6.3-9.9 2.0-5.0 2.1-4.1 1.9-3.2 1.8-3.6 2.1-5.9 1.9-7.7 2.8-7.1 2.0-5.3 2.0-4.2 1.9-3.8 1.6-3.9 1.9-3.7 2.2-4.0 2.2-5.9 4.0-9.9 4.3-13.1 7.5-17.9 9.8-18.3 5.9-20.9 6.0-12.3 5.7-10.0 3.9-11.9 3.6-13.5 3.3-12.0 3.0-12.2 4.0-12.0 6.0-17.8 11.2-19.8 12.7-28.2 14.7-27.8 14.9-30.4 12.0-37.5 3.3-9.9 4.3-11.3 4.0-15.0
4.2 5.7 7.4 8.6 9.4 7.5 2.8 2.7 3.0 2.7 3.3 3.4 8.5 6.0 4.2 3.5 3.0 3.0 2.8 3.1 3.8 5.8 8.6 10.8 13.6 10.2 8.4 7.0 6.3 6.1 6.1 8.0 10.1 13.8 16.6 20.6 19.3 16.4 8.6 9.5 7.3
3.3-5.6 2.0-14.1 3.4-13.0 5.7-12.9 7.0-11.6 5.8-9.4 1.9-4.3 2.0-4.0 1.9-4.0 1.8-3.3 1.9-5.3 1.6-6.0 2.9-14.4 2.0-10.0 1.9-6.0 1.7-5.7 1.6-4.1 1.9-3.8 2.1-3.5 2.1-4.1 1.9-7.0 2.1-10.4 2.4-15.0 3.2-20.1 1.2-21.5 6.1-15.7 5.2-10.4 4.1-9.1 3.8-9.1 3.9-10.2 3.9-8.8 4.3-15.2 6.0-16.3 7.9-17.0 4.0-26.7 15.5-28.7 13.0-26.7 11.0-21.9 4.2-23.7 5.7-16.1 4.1-10.9
1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9
DISCUSSION Our study suggests that regions of superior scapula thickness for internal fixation are located near the glenoid fossa, the lateral border, and the spine from inferior to superior. We did not observe significant side-to-side differences for line length or for most of the thickness measurements that would influence the internal fixation decision-making process. However, surgeons are advised of a region of variable osseous thickness located along line 7, which is the most proximal line drawn between the lateral, inferior base of the scapula spine and the medial, inferior base of the scapula spine. The line lengths and thickness measurements we report are in agreement with previous investigations3,6,10;
however, no previous report has provided as comprehensive a map of scapular thickness as has been presented in this study. Our study is limited in that only 18 scapulae from 9 cadavers were measured. Seven cadavers were male and 2 were female, making it difficult to compare for gender differences in scapular thickness measurements. Additionally, the elderly age of the cadavers and the known osteoporosis and decreased muscle mass associated with aging suggests a worst-case scenario for our thickness measurements. The curved surface of the posterior surface of the scapula may also have contributed to measurement error, more than if measurements had been made on a flat, osseous surface.
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Figure 3 Mean scapular thickness at every third interval (interval, thickness). Reference points and reference lines are defined in Figure 1. REFERENCES
Table II References points that displayed statistically significant differences between right and left scapulae*
Reference point 3.4 3.5 4.9 5.3 7.1 7.2 7.3 7.6 7.9 7.10 8.11
Mean right scapula thickness (mm)
Mean left scapula thickness (mm)
z
P
3.6 3.6 4.8 2.5 4.3 2.8 2.7 2.7 5.2 8.0 19.4
4.6 4.5 4.2 3.0 8.5 6.0 4.2 3.0 3.8 5.8 16.6
–2.67 –2.02 –2.02 –2.25 –2.31 –2.31 –2.31 –2.5 –2.7 –2.31 –2.07
.008 .04 .04 .025 .021 .021 .021 .01 .008 .021 .038
*Wilcoxon signed rank test results
In conclusion, the anatomic constraints of the scapula, particularly its thickness, limit the location that can be used for conventional internal fixation. Improving our understanding of the osseous regions that may provide optimal screw fixation and the future development of innovative implants that target these areas may improve our ability to restore functional normalcy to patients who have sustained displaced scapular fractures.1
1. Ada JR, Miller ME. Scapular fractures. Analysis of 113 cases. Clin Orthop 1991;269:174-80. 2. Beckers A, Schenck C, Klesper B, Koebke J. Comparative densitometric study of iliac crest and scapula bone in relation to osseous integrated dental implants in microvascular mandibular reconstruction. J Craniomaxillofac Surg 1998;26:7583. 3. Ebraheim NA, Xu R, Haman SP, Miedler JD, Yeastling RA. Quantitative anatomy of the scapula. Am J Orthop 2000;29: 287-92. 4. Frich LH. Odgaard A, Dalstra M. Glenoid bone architecture. J Shoulder Elbow Surg 1998;7:356-61. 5. Goss TP. Scapular fractures and dislocations: diagnosis and treatment. J Am Acad Orthop Surg 1995;3:22-33. 6. Mallon WJ, Brown HJ, Vogler JB 3rd, Martinez S. Radiographic and geometric anatomy of the scapula. Clin Orthop 1992;277: 142-54. 7. Marra G, Stover J. Glenoid and scapular body fractures. Curr Opin Orthop 1999;10:283-8. 8. Myoung H, Kim Y, Heo M, Lee S, Choi S, Kim M. Comparative radiologic study of bone density and cortical thickness of donor bone used in mandibular reconstruction. Oral Surg Oral Med Oral Pathol Oral Radiol Endo 2001;92:23-9. 9. Niimi A, Ozeki K, Ueda M, Nakayama B. A comparative study of removal torque of endosseous implants in the fibula, iliac crest and scapula of cadavers: preliminary report. Clin Oral Implants Res 1997;8:286-9. 10. Von Schroeder HP, Kuiper SD, Botte MJ. Osseous anatomy of the scapula. Clin Orthop 2001;383:131-9. 11. Wiest S, Maillot C, Koritke JG. Dimensions of the human scapula. Arch Anat Histol Embryol 1985;68:127-37.
The purpose of this study was to measure and map scapula osseous thickness to identify the optimal areas for internal fixation. Eighteen (9 pairs) scapulae from 2 female and 7 male cadavers were used. After harvest and removal of all soft tissues, standardized measurement lines were made based on anatomic landmarks. For consistency among scapulae, measurements were taken at standard percentage intervals along each line approximating the distance between two consecutive reconstruction plate screw holes. Two-mm-diameter drill holes were made at each point, and a standard depth gauge was used to measure thickness. The glenoid fossa (25 mm) displayed the greatest mean osseous thickness, followed by the lateral scapular border (9.7 mm), the scapula spine (8.3 mm), and the central portion of the body of the scapula (3.0 mm). To optimize screw purchase and internal fixation strength, the lateral border, the lateral aspect of the base of the scapula spine, and the scapula spine itself should be used for anatomic sites of internal fixation of scapula fractures. (J Shoulder Elbow Surg 2006;15:645-648.)
T
he internal fixation of scapula fractures is technically challenging and limited by the inherent osseous anatomy and dimensions of the scapula, particularly its limited, and sometimes wafer thin, thickness.3,6,7,10 The thicker the scapular crosssection, generally the greater amount of cortical bone available for secure screw implantation.2,8,9 In their study of 5 cadavers, Niimi et al9 reported a scapular cortical bone thickness of 1.8 mm and a significant correlation between cortical bone thickness and the torque required for implant removal. Beckers et al2 reported that age and side did not have an important influence on cortical bone dimensions or density. Although previous studies From the Department of Orthopedic Surgery, University of Louisville. Reprint requests: Dr John Nyland, Department of Orthopedic Surgery, University of Louisville, 210 East Gray Street, Suite 1003, Louisville, KY 40202 (E-mail: [email protected]). Copyright © 2006 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2006/$32.00 doi:10.1016/j.jse.2005.10.005
have reported distance plots between primary scapula osseous landmarks,3,4-6,10,11 few have reported scapular thickness measurements.3,6,10 The purpose of this study was to measure and map scapula osseous thickness to provide insight regarding the optimum implant placement for the internal fixation of scapula fractures. MATERIALS AND METHODS Nine pairs of adult cadaveric scapulae (mean age, 82 years; range, 73 to 94 years) were obtained through the bequeathal program at the University of Louisville Fresh Tissue Dissection Laboratory. The cause of death for the cadaveric specimens included vascular disease, emphysema, cerebral vascular accident, adenocarcinoma, chronic obstructive pulmonary disease, cardiopulmonary arrest, congestive heart failure, chronic atrial fibrillation, and hypertension. All soft tissue was removed from the harvested scapulae, and they were stored in a freezer at 30° F to preserve tissue integrity before thickness measurements. Each scapula was marked with an indelible marker at consistent anatomic landmarks, and lines were drawn between these designated points (Figure 1) and measured using calipers. These anatomic landmarks were chosen for their relevance to regions of interest for scapular fixation and on their measurement reproducibility among specimens. Intervals were selected based on distances that were considered relevant for scapular fracture fixation using reconstruction plates. A reconstruction plate (DePuy Ace 14330-4, TDCCB69 CE0086, DePuy Orthopaedics, Warsaw, IN) typically used for internal fixation was used to standardize the space between consecutive reconstruction plate screw holes (9.85 mm) (Figure 2). We attempted to make the measurement distance between our data points as close to 9.85 mm apart as possible. This was difficult, because each scapula displayed slightly different dimensions. After the line lengths on a sample scapula were measured, lines of interest were divided into data points that approximated reconstruction screw hole locations as closely as possible. Although line length was slightly different for each specimen, each data point was located at a set percentage of the overall line length (25% line length intervals for line 1, 7% line length intervals for lines 2, 3, 4, and 8, 20% line length intervals for line 5, 33% line length intervals for lines 6 and 9, 8% line length intervals for line 7, and 50% line length intervals for line 10). The average distance between data points along a given line was 8.94
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Figure 2 Reconstruction plate used as reference for thickness measurements. The distance between hole centers is 9.85 mm, the distance between hole inner borders is 7.2 mm, and the hole diameter is 4.5 mm.
mm. Each line length and osseous thickness measurement was performed 3 times by the primary investigator. Figure 1 Reference points: A, superior glenoid tubercle; B, inferior glenoid tubercle, C, 1/2 distance between points A and B; D, inferior angle; E, lateral, inferior base of the scapula spine; F, medial, inferior base of the scapula spine; G, lateral, inferior base of the acromion process. Reference lines: 1, between points A and B; 2, between points C and D; 3, between points D and E; 4, between points D and F; 5, 6, and 7, between points located at equal thirds along lines 3 and 4; 8, between points F and G, lines 9 and 10 were drawn between points located at equal thirds along lines 7 and 8.
mm, closely approximating reconstruction plate screw hole distance. To avoid redundancy, line intersections were not used as data points. During drilling, each scapula was aligned horizontally using a standard carpenter’s level resting on the posterior body of the scapula parallel to line 5. Modeling clay was used to stabilize the edges of each scapula further during drilling. Each scapula was repositioned vertically with the scapula spine mounted in modeling clay to enable drilling holes along lines 8 to 10. A standard electric drill with a 2.0-mm-diameter bit was used to drill holes at each point perpendicular to the table. To help preserve osseous integrity throughout the measurements, the 2.0-mm-diameter drill bit was used instead of the 2.7-mm-diameter drill bit that is usually used during scapula fixation surgery. Holes were drilled and numbered from superior to inferior, medial to lateral, or anterior to posterior, depending upon line orientation in relation to the scapula. A mini-fragment depth gauge (Synthes, Paoli, PA) was then used to determine osseous thickness at each measurement point to the nearest 0.1
Statistical methods Descriptive statistics for each line and point thickness measurement, Wilcoxon signed rank tests for side-to-side comparisons of line length and select reference point thickness measurements, and intraclass correlation coefficients (ICC) to determine intra-rater measurement reliability were calculated using SPSS version 11.0 (SPSS Institute, Chicago, IL) for Windows (Microsoft, Redmond, WA). An ␣-level of P ⬍ .05 was used to indicate statistical significance.
RESULTS Intra-rater measurement reliability was high (ICC3,1, .98-.99). Mean scapular thickness varied between 2.5 mm and 29.5 mm, with the thickest areas located near the glenoid fossa, lateral border, and scapula spine and the thinnest areas located in the middle third of the scapular body. Descriptive measurements for right and left scapula reference point thickness values are reported in Table I. Mean right and left scapular thickness measurements at every third interval are depicted in Figure 3. Although most points did not display side-to-side differences, reference points where statistically significant side-toside thickness differences were observed are reported in Table II. All other reference point thickness values failed to display statistically significant side-to-side differences.
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Table I Scapula reference point thickness values (mm) Reference point #
Right mean
Right range
Left mean
Left range
Reference point #
Right mean
Right range
Left mean
Left range
20.7 27.2 25.9 28.2 17.3 10.8 9.1 9.0 8.6 9.3 9.4 9.2 8.5 8.5 8.8 9.9 8.6 14.7 8.9 4.9 3.6 3.6 4.0 5.4 4.4 5.9 6.3 7.0 8.3 9.3 11.0 8.4 7.7 5.7 5.2 5.0 4.7 4.7 4.6 4.4 4.8
17.1-26.5 22.8-33.2 22.1-29.1 18.1-36.0 10.9-25.7 7.4-13.5 5.6-12.2 2.4-14.8 3.0-16.0 3.1-15.8 2.7-14.1 2.1-13.1 2.9-12.1 4.0-13.0 4.2-12.8 7.8-12.0 6.4-10.3 8.0-22.1 5.9-14.5 2.0-7.9 2.3-6.1 1.8-7.4 2.2-9.5 2.1-11.6 2.3-8.5 2.4-11.6 2.0-10.0 2.7-11.7 5.1-11.8 6.1-14 9.1-15.2 6.2-10.7 7.2-8.1 4.8-6.2 4.3-6.8 4.0-6.1 3.5-6.0 3.8-5.9 2.9-6.0 2.0-5.9 3.7-6.0
22.0 28.3 25.7 29.5 19.0 11.7 9.5 9.5 9.7 9.6 10.1 9.9 10.0 9.3 9.7 9.6 7.7 6.0 9.5 5.7 4.6 4.5 4.9 5.3 5.8 6.1 6.0 6.5 7.6 9.1 10.5 8.1 7.3 5.6 5.3 4.8 5.0 4.9 4.5 4.3 4.2
14.3-31.3 21.0-36.4 17.1-34 23.8-37.3 12.1-30.3 8.9-15.9 6.1-14.0 6.2-13.7 2.4-13.1 2.1-14.7 2.7-14.2 2.5-14.1 3.6-14.9 3.9-13.2 5.7-13.7 6.1-11.8 6.0-9.9 10.6-24.0 4.1-15.9 3.6-10.1 2.9-7.4 3.1-7.7 2.9-8.4 2.4-10.0 2.2-10.0 2.4-11.0 2.5-11.7 2.2-14.6 3.7-14.0 5.5-12.9 8.0-13.7 4.7-12.0 5.4-10.0 4.1-6.6 3.9-6.4 3.1-6.0 3.9-6.0 3.9-6.0 3.5-5.7 3.4-6.2 3.5-4.7
4.10 4.11 4.12 4.13 4.14 4.15 5.1 5.2 5.3 5.4 6.1 6.2 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 9.1 9.2 10.1
5.1 5.6 7.1 9.3 10.1 8.0 2.9 2.7 2.5 2.7 3.3 3.6 4.3 2.8 2.7 3.0 2.8 2.7 3.0 3.5 5.2 8.0 11.4 14.1 13.4 9.4 8.2 7.8 7.5 7.0 7.6 8.6 10.4 14.7 19.4 20.9 21.4 19.7 7.0 8.6 8.4
3.0-7.4 4.0-6.7 4.8-8.9 7.6-10.6 8.7-12.2 6.3-9.9 2.0-5.0 2.1-4.1 1.9-3.2 1.8-3.6 2.1-5.9 1.9-7.7 2.8-7.1 2.0-5.3 2.0-4.2 1.9-3.8 1.6-3.9 1.9-3.7 2.2-4.0 2.2-5.9 4.0-9.9 4.3-13.1 7.5-17.9 9.8-18.3 5.9-20.9 6.0-12.3 5.7-10.0 3.9-11.9 3.6-13.5 3.3-12.0 3.0-12.2 4.0-12.0 6.0-17.8 11.2-19.8 12.7-28.2 14.7-27.8 14.9-30.4 12.0-37.5 3.3-9.9 4.3-11.3 4.0-15.0
4.2 5.7 7.4 8.6 9.4 7.5 2.8 2.7 3.0 2.7 3.3 3.4 8.5 6.0 4.2 3.5 3.0 3.0 2.8 3.1 3.8 5.8 8.6 10.8 13.6 10.2 8.4 7.0 6.3 6.1 6.1 8.0 10.1 13.8 16.6 20.6 19.3 16.4 8.6 9.5 7.3
3.3-5.6 2.0-14.1 3.4-13.0 5.7-12.9 7.0-11.6 5.8-9.4 1.9-4.3 2.0-4.0 1.9-4.0 1.8-3.3 1.9-5.3 1.6-6.0 2.9-14.4 2.0-10.0 1.9-6.0 1.7-5.7 1.6-4.1 1.9-3.8 2.1-3.5 2.1-4.1 1.9-7.0 2.1-10.4 2.4-15.0 3.2-20.1 1.2-21.5 6.1-15.7 5.2-10.4 4.1-9.1 3.8-9.1 3.9-10.2 3.9-8.8 4.3-15.2 6.0-16.3 7.9-17.0 4.0-26.7 15.5-28.7 13.0-26.7 11.0-21.9 4.2-23.7 5.7-16.1 4.1-10.9
1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9
DISCUSSION Our study suggests that regions of superior scapula thickness for internal fixation are located near the glenoid fossa, the lateral border, and the spine from inferior to superior. We did not observe significant side-to-side differences for line length or for most of the thickness measurements that would influence the internal fixation decision-making process. However, surgeons are advised of a region of variable osseous thickness located along line 7, which is the most proximal line drawn between the lateral, inferior base of the scapula spine and the medial, inferior base of the scapula spine. The line lengths and thickness measurements we report are in agreement with previous investigations3,6,10;
however, no previous report has provided as comprehensive a map of scapular thickness as has been presented in this study. Our study is limited in that only 18 scapulae from 9 cadavers were measured. Seven cadavers were male and 2 were female, making it difficult to compare for gender differences in scapular thickness measurements. Additionally, the elderly age of the cadavers and the known osteoporosis and decreased muscle mass associated with aging suggests a worst-case scenario for our thickness measurements. The curved surface of the posterior surface of the scapula may also have contributed to measurement error, more than if measurements had been made on a flat, osseous surface.
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J Shoulder Elbow Surg September/October 2006
Figure 3 Mean scapular thickness at every third interval (interval, thickness). Reference points and reference lines are defined in Figure 1. REFERENCES
Table II References points that displayed statistically significant differences between right and left scapulae*
Reference point 3.4 3.5 4.9 5.3 7.1 7.2 7.3 7.6 7.9 7.10 8.11
Mean right scapula thickness (mm)
Mean left scapula thickness (mm)
z
P
3.6 3.6 4.8 2.5 4.3 2.8 2.7 2.7 5.2 8.0 19.4
4.6 4.5 4.2 3.0 8.5 6.0 4.2 3.0 3.8 5.8 16.6
–2.67 –2.02 –2.02 –2.25 –2.31 –2.31 –2.31 –2.5 –2.7 –2.31 –2.07
.008 .04 .04 .025 .021 .021 .021 .01 .008 .021 .038
*Wilcoxon signed rank test results
In conclusion, the anatomic constraints of the scapula, particularly its thickness, limit the location that can be used for conventional internal fixation. Improving our understanding of the osseous regions that may provide optimal screw fixation and the future development of innovative implants that target these areas may improve our ability to restore functional normalcy to patients who have sustained displaced scapular fractures.1
1. Ada JR, Miller ME. Scapular fractures. Analysis of 113 cases. Clin Orthop 1991;269:174-80. 2. Beckers A, Schenck C, Klesper B, Koebke J. Comparative densitometric study of iliac crest and scapula bone in relation to osseous integrated dental implants in microvascular mandibular reconstruction. J Craniomaxillofac Surg 1998;26:7583. 3. Ebraheim NA, Xu R, Haman SP, Miedler JD, Yeastling RA. Quantitative anatomy of the scapula. Am J Orthop 2000;29: 287-92. 4. Frich LH. Odgaard A, Dalstra M. Glenoid bone architecture. J Shoulder Elbow Surg 1998;7:356-61. 5. Goss TP. Scapular fractures and dislocations: diagnosis and treatment. J Am Acad Orthop Surg 1995;3:22-33. 6. Mallon WJ, Brown HJ, Vogler JB 3rd, Martinez S. Radiographic and geometric anatomy of the scapula. Clin Orthop 1992;277: 142-54. 7. Marra G, Stover J. Glenoid and scapular body fractures. Curr Opin Orthop 1999;10:283-8. 8. Myoung H, Kim Y, Heo M, Lee S, Choi S, Kim M. Comparative radiologic study of bone density and cortical thickness of donor bone used in mandibular reconstruction. Oral Surg Oral Med Oral Pathol Oral Radiol Endo 2001;92:23-9. 9. Niimi A, Ozeki K, Ueda M, Nakayama B. A comparative study of removal torque of endosseous implants in the fibula, iliac crest and scapula of cadavers: preliminary report. Clin Oral Implants Res 1997;8:286-9. 10. Von Schroeder HP, Kuiper SD, Botte MJ. Osseous anatomy of the scapula. Clin Orthop 2001;383:131-9. 11. Wiest S, Maillot C, Koritke JG. Dimensions of the human scapula. Arch Anat Histol Embryol 1985;68:127-37.