- Email: [email protected]
The bicipital tuberosity and distal radius are unreliable landmarks for radial head implant alignment
J Shoulder Elbow Surg (2013) 22, 1242-1247
www.elsevier.com/locate/ymse
The bicipital tuberosity and distal radius are unreliable landmarks for radial head implant alignment Ryan N. Katchky, MD, Graham J.W. King, MD, MSc, FRCSC, James A. Johnson, PhD, George S. Athwal, MD* Hand and Upper Limb Centre, St. Joseph’s Health Care, London, ON, Canada Background: As more anatomic asymmetric radial head implants emerge, it is necessary to determine the optimal landmarks to ensure correct rotational orientation. The bicipital tuberosity and distal radius are possible bony landmarks that can be used for rotational alignment of asymmetric prostheses; however, they have not been validated. The purpose of this study was to evaluate the reliability of the bicipital tuberosity and distal radius as rotational landmarks for orientation of asymmetric radial head prostheses. Methods: Measurements were made from computer tomography scans of 50 elbows in order to determine the rotational relationships between the radial head, bicipital tuberosity, biceps tendon footprint, and distal radius. Results: The maximum radial head diameter was oriented 65 28 from the bicipital tuberosity, 119 38 from the biceps tendon footprint, 82 29 from the radial styloid, and 76 28 from the volar surface of the distal radius. All of these landmarks had a significantly greater variance than a proposed acceptable clinical tolerance of 10 (P < .001). Conclusion: The results demonstrate that the measured landmarks show no consistent rotational relationship with the maximum diameter of the radial head. In order to maximize the utility of more anatomic asymmetric radial head implant systems, further studies are necessary to identify more reliable rotational landmarks to ensure optimal implant positioning. Level of evidence: Anatomic Study, Imaging. Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Radial head arthroplasty; radial head fracture; implant design; bicipital tuberosity; elbow
The radial head is an important elbow stabilizer, acting through its articulations at the proximal radioulnar joint and the radiocapitellar joint.5,9 Comminuted fractures of the radial head are common,9,16 and when associated with
IRB approval was not required for this study as per the University of Western Ontario IRB. *Reprint requests: George S. Athwal, MD, Hand and Upper Limb Centre, St. Joseph’s Health Care, 268 Grosvenor St., London, ON N6A 4L6, Canada. E-mail address: [email protected] (G.S. Athwal).
certain injury patterns can lead to instability, restricted range of motion, arthritis, and pain.3,9 The optimal treatment for displaced radial head fractures associated with complex elbow instability or a mechanical block to motion consists of open reduction and internal fixation; however, if unreconstructable, radial head arthroplasty has demonstrated good outcomes.1,5,8 Since the first reported radial head replacement in 1941, there have been numerous improvements to the surgical technique, prosthetic composition, and implant morphology.16 These developments have resulted in improved
1058-2746/$ - see front matter Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2013.02.013
Insertional landmarks for radial head implants patient outcomes.8,11 The radial head has been shown to be asymmetric10,18; however, most current radial head implants have axisymmetric designs. Although radial head arthroplasty has demonstrated generally positive patient outcomes, problems can occur. These issues, which are inherent to all types of hemiarthroplasties, include implant wear, joint wear, instability, and stiffness.3,12 Prostheses that better replicate native radial head anatomy may more effectively restore joint kinematics and load transfer, potentially leading to superior patient outcomes.7,17 In order for asymmetric implants to be effective, measures must be taken to ensure that they can be correctly rotationally aligned relative to the native radial head. Based on their ease of identification via fluoroscopy or palpation, structures such as the bicipital tuberosity, volar distal radius, and radial styloid could potentially represent useful rotational landmarks to assist with anatomic orientation of an asymmetric implant. For these landmarks to be effective, however, a reliable relationship must exist between the orientations of these structures and the orientation of the radial head. To date, none of these landmarks has been completely validated. The objective of this study was to examine the relationship between anatomical landmarks of the bicipital tuberosity, biceps tendon footprint, and distal radius with the native radial head, in order to assess their utility as rotational landmarks for insertion of asymmetric radial head implants.
Materials and methods Computed tomography (CT) images of 50 fresh-frozen elbow specimens (mean age 70 years [range, 42-97]) with no evidence of previous surgery, trauma or arthritis were obtained using a 64-slice scanner (Light Speed Ultra; GE, New Berlin, WI, USA). Imaging parameters included a field of view of 16 16 cm, a 512 512 reconstruction matrix, technique factors 120 kVp and 90 mAs, and a voxel size of 0.3 0.3 0.625 mm. Three-dimensional (3D) models of the radii were created using Mimics Medical Imaging Software (Materialise, Ann Arbor, MI, USA). These models were created by segmenting the CT data so it would only include bone and exclude soft tissue, and then manually segmenting each model to isolate the radius from the humerus and the ulna. On each 3D model, a coronal plane was drawn to establish a coordinate system for the radius. The 3 landmarks that were used to establish the coronal plane were the deepest point of the articular dish on the radial head, radial styloid, and midpoint of the articulation at the distal radioulnar joint. As the radial styloid is rounded, it was assessed in 2 planes by selecting the most distal point of the styloid and the highest point on the radial side of the styloid. This plane was also used to represent the orientation of the radial styloid. Two anatomical features were used to define the bicipital tuberosity: the tuberosity orientation plane and biceps tendon footprint plane. The tuberosity orientation plane was defined by a line drawn from the center of the spine of the radial tuberosity to the center of the radial canal. For specimens where the bicipital tuberosity had a bifid morphology, the
1243
Figure 1 3-dimensional model of a supinated right radius, with orientations of the maximal diameter of the radial head (blue), bicipital tuberosity (green), biceps footprint (purple), volar distal radius (yellow), and radial styloid (red).
medial ridge was selected as the spine because it corresponds anatomically to the spine in the single ridge type. While it was very small in certain specimens, the ridge was identifiable on each one, indicating that none of our specimens would be truly classified as smooth. The biceps footprint plane was drawn along the flat spot of the bicipital tuberosity, representing the insertional footprint of the distal biceps tendon. Another plane was defined by the relatively flat volar cortex of the distal radius metaphysis. In order to reference the above planes to the radial head, a line was drawn through the maximum diameter of the radial head, as calculated using an iterative approach measuring many distinct diameters around the circumference of the radial head. This line was used to define the radial head’s asymmetric rotational orientation. A 3D model of the radius, showing the orientation of each of the aforementioned landmarks, is presented in Figure 1. The angle that each landmark made with the maximal radial head diameter was calculated using Matlab (MathWorks, Natick, MA, USA), with all angles converted into the internally rotated direction from neutral forearm position. The relationship between the orientations of each of the aforementioned landmarks with respect to the maximum diameter of the radial head was assessed. For each proposed landmark, the absolute value of the difference between each measurement and the mean was calculated. Using a 1-sided t test, these differences were compared with a 10 and 15 tolerance, which we considered to be the maximum acceptable error in placing an asymmetric radial head implant. To evaluate the reliability of the measurements, inter-rater, and intra-rater reliability assessments were completed. Two trained observers each measured 5 specimens, and the primary observer also evaluated five specimens a second time at an interval of at least 4 weeks. Intra-class correlation coefficients were determined in order to assess the repeatability of the measurements.
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Table Relationships between the studied landmarks; all angles are measured in the internally rotated direction, and are expressed in degrees Landmarks
Orientation with respect to maximal radial head diameter
Standard deviation
Range
P value compared to 10 tolerance
P value compared to 15 tolerance
Bicipital tuberosity Biceps tendon footprint Radial styloid Volar distal radius
65 119 82 76
28 38 29 28
4-152 30-178 24-161 28-134
<.001 <.001 <.001 <.001
.008 <.001 .005 .009
Figure 2 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the bicipital tuberosity (green) 1 SD (shaded in dark green) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the bicipital tuberosity and radial head is also shown.
Results
Discussion
Inter-rater reliability was excellent for all measurements, yielding an intra-class correlation coefficient of 0.90. Intra-rater reliability was also excellent for all measurements and yielded an intra-class correlation coefficient of 0.92. The relationships between the orientations of the radial head, bicipital tuberosity, biceps tendon footprint, radial styloid, and volar distal radius are summarized in the Table. Models of the radial head elucidating its relationships with the bicipital tuberosity, biceps tendon footprint, radial styloid, and volar distal radius are shown in Figs. 2-5, respectively. Scatterplots showing the relative orientations of each landmark and the maximum radial head diameter are also shown accompanying the radial head models in Figs. 2-5, respectively. The absolute deviations for each landmark were found to be significantly greater than a 10 tolerance (P < .001 for all landmarks). The absolute deviations were also significantly greater than the extended tolerance of 15 (P < .01 for all landmarks). This indicates the poor reliability of any of the aforementioned landmarks to rotationally orient asymmetric radial head prostheses.
Numerous morphological studies have shown the radial head to be elliptical, with the mean difference between the maximum and minimum diameters approaching 2 mm.10,15,19 Traditional radial head implants have modeled the radial head as circular, but more anatomic implants are starting to emerge, which are eccentric. These asymmetric implants, like the native radial head itself, have maximum and minimum diameters. In order for these more anatomic designs to have the desired effect on joint kinematics, they must be inserted such that the maximum and minimum diameters of the implant align with the corresponding diameters of the native radial head. An optimal landmark will have a consistent, dependable relationship with respect to the native radial head, so that it can be used to guide the rotational alignment of nonaxisymmetric radial head prostheses. Our data demonstrate that the rotational orientation of the proposed landmarks to the radial head are highly variable. The large standard deviations and range in the data suggest that the maximum diameter of the radial head does not show a consistent relationship with anatomical landmarks on the bicipital tuberosity or the distal radius. Even with generous
Insertional landmarks for radial head implants
1245
Figure 3 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the biceps footprint (purple) 1 SD (shaded in light purple) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the biceps footprint and radial head is also shown.
Figure 4 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the radial styloid (red) 1 SD (shaded in light red) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the radial styloid and radial head is also shown.
tolerances of up to 15 , none of these landmarks are reliable for the rotational orientation of asymmetric radial head implants. While the effects of malrotation for radial head arthroplasty have not been reported, they have been studied extensively in relation to hip, knee, and shoulder arthroplasty. The literature suggests that malrotation can cause pain, wear, instability, and failure.2,4,6,19 It is possible that these same complications may result from component malrotation during radial head arthroplasty. This underscores the importance of finding a reliable landmark for insertion of the emerging asymmetric radial head implants. Further studies are required in order to identify more reliable landmarks for the orientation of more anatomic radial head implants. Until a landmark with a consistent
rotational relationship with the native radial head can be established, it may be difficult to verify whether axisymmetric radial head prostheses are consistently being inserted in an anatomic fashion. One potential solution that may help ensure anatomic orientation of asymmetric radial head implants may rely on the use of contralateral limb imaging. A CT scan of the uninjured arm can likely be added at limited additional cost to the usual imaging of the injured elbow; although it does subject the patient to increased radiation exposure. Contralateral proximal radii have been shown to be nearly identical; so it may be possible to elucidate the orientation of the injured native radial head based on the contralateral anatomy.13 While this technique may be promising, it has not yet been validated. Identification of a reliable landmark
1246
R.N. Katchky et al.
Figure 5 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the volar distal radius (yellow) 1 SD (shaded in light yellow) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the volar distal radius and radial head is also shown.
on the ipsilateral radius would represent a less costly method than use of the contralateral anatomy. However, the authors believe that no reliable landmarks exist on the ipsilateral radius for rotational alignment of asymmetric radial head prostheses. The inter- and intra-rater reliability assessment confirms that the methods employed are repeatable, and helps validate the results of the study. The most significant weakness of the study is that it is difficult to define 2-dimensional orientations of complex structures such as the bicipital tuberosity and radial styloid. While reproducible methods were developed, the complex morphology of the landmarks measured introduces error into the results. Another weakness of this study is that articular cartilage was not measured. This is relevant because cartilage thickness is nonuniform, and these variations may alter the true maximum diameter of the radial head; however, it is unlikely that this will affect the outcomes in a significant way. Furthermore, there may be error introduced to the methodology through the segmentation and thresholding techniques; although this error has been shown to be small.14
Conclusion This study has examined possible rotational landmarks for insertion of asymmetric radial head implants. Through examinations of their respective relationships with the orientation of the radial head, the bicipital tuberosity and the radial styloid have been shown to be unreliable landmarks. Neither of these landmarks possesses consistent, reliable relationships with the orientation of the radial head. In order for emerging asymmetric radial head prostheses to function at full effectiveness, they must be
inserted in an anatomic orientation. Further studies are necessary in order to develop reliable rotational landmarks for insertion of asymmetric radial head prostheses.
Acknowledgment Funding for this project was provided through research grants by the Canadian Institute of Health Research.
Disclaimer Dr. King receives royalties from and is a consultant for Wright Medical Technologies for products related to the subject of this research. The other authors, their immediate families, and any research foundation with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article. The funding sources did not have any involvement in the data collection, data analysis, or the preparation of or editing of the manuscript.
References 1. Ashwood N, Bain GI, Unni R. Management of Mason type-III radial head fractures with a titanium prosthesis, ligament repair, and early mobilization. J Bone Joint Surg Am 2004;86-A:274-80. 2. Bindra RR, Cole RJ, Yamaguchi K, Evanoff BA, Pilgram TK, Gilula LA, et al. Quantification of the radial torsion angle with
Insertional landmarks for radial head implants
3.
4.
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6.
7.
8.
9.
10.
computerized tomography in cadaver specimens. J Bone Joint Surg Am 1997;79:833-7. Brinkman JM, Rahusen FT, de Vos MJ, Eygendaal D. Treatment of sequelae of radial head fractures with a bipolar radial head prosthesis: good outcome after 1-4 years follow-up in 11 patients. Acta Orthop 2005;76:867-72. http://dx.doi.org/10.1080/17453670510045516 Callanan MC, Jarrett B, Bragdon CR, Zurakowski D, Rubach HE, Freiberg AA, et al. The John Charnley Award: risk factors for cup malpositioning: quality improvement through a joint registry at a tertiary hospital. Clin Orthop Relat Res 2011;469:319-29. http://dx. doi.org/10.1007/s11999-010-1487-1 Cebesoy O, Baltaci ET, Isik M. Importance of radial head on elbow kinematics: radial head prosthesis. Arch Orthop Trauma Surg 2006; 126:501. http://dx.doi.org/10.1007/s00402-006-0164-z Compito C, Self E, Bigliani L. Arthroplasty and acute shoulder trauma. Reasons for success and failure. Clin Orthop 1994;307: 27-36. Frank SG, Grewal R, Johnson J, Faber KJ, King GJ, Athwal GS. Determination of correct implant size in radial head arthroplasty to avoid overlengthening. J Bone Joint Surg Am 2009;91:1738-46. http:// dx.doi.org/10.2106/JBJS.H.01161 Harrington IJ, Sekyi-Otu A, Barrington TW, Evans DC, Tuli V. The functional outcome with metallic radial head implants in the treatment of unstable elbow fractures: a long-term review. J Trauma 2001;50:46-52. Johnson JA, Beingessner DM, Gordon KD, Dunning CE, Stacpoole RA, King GJW. Kinematics and stability of the fractured and implant-reconstructed radial head. J Shoulder Elbow Surg 2005; 14:195S-201S. http://dx.doi.org/10.1016/j.jse.2004.09.034 King GJW, Zarzour ZDS, Patterson SD, Johnson JA. An anthropometric study of the radial head: implications in the design of a prosthesis. J Arthroplasty 2001;16:112-6.
1247 11. King GJW, Zarzour ZDS, Rath DA, Dunning CE, Patterson SD, Johnson JA. Metallic radial head arthroplasty improves valgus stability of the elbow. Clin Orthop Relat Res 1999;368:114-25. 12. Liew VS, Cooper IC, Ferreira LM, Johnson JA, King GJW. The effect of metallic radial head arthroplasty on radiocapitellar joint contact area. Clin Biomech (Bristol, Avon) 2003;18:115-8. http://dx.doi.org/ 10.1016/S0268-0033(02)00172-9 13. McDonald CP, Peters TM, King GJW, Johnson JA. Computer assisted surgery of the distal humerus can employ contralateral images for preoperative planning, registration, and surgical intervention. J Shoulder Elbow Surg 2009;18:469-77. http://dx.doi.org/10.1016/j.jse.2009.01.028 14. Rathnayaka K, Sahama T, Schuetz MA, Schmutz B. Effects of CT image segmentation methods on the accuracy of long bone 3D reconstructions. Med Eng Phys 2011;33:226-33. http://dx.doi.org/ 10.1016/j.medengphy.2010.10.002 15. Swieszkowski W, Skalski K, Pomianowski S, Kedzior K. The anatomic features of the radial head and their implication for prosthesis design. Clin Biomech (Bristol, Avon) 2001;16:880-7. 16. Van Riet RP, Van Glabbeek F. History of radial head prosthesis in traumatology. Acta Orthop Belg 2007;73:12-20. 17. Van Riet RP, Van Glabbeek F, Baumfeld JA, Neale PG, Morrey BF, O’Driscoll SW, et al. The effect of the orientation of the noncircular radial head on elbow kinematics. Clin Biomech (Bristol, Avon) 2004; 19:595-9. http://dx.doi.org/10.1016/j.clinbiomech.2004.03.002 18. Van Riet RP, Van Glabbeek F, Neale PG, Bortier H, An KN, O’Driscoll SW. The noncircular shape of the radial head. J Hand Surg Am 2003;28:972-8. http://dx.doi.org/10.1016/S0363-5023(03)00426-x 19. Verlinden C, Uvin P, Labey L, Luyckx JP, Bellemans J, Vandenneucker H. The influence of malrotation of the femoral component in total knee replacement on the mechanics of patellofemoral contact during gait: an in vitro biomechanical study. J Bone Joint Surg Br 2010;92-B:737-42. http://dx.doi.org/10.1302/0301-620X.92B5.22603
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The bicipital tuberosity and distal radius are unreliable landmarks for radial head implant alignment Ryan N. Katchky, MD, Graham J.W. King, MD, MSc, FRCSC, James A. Johnson, PhD, George S. Athwal, MD* Hand and Upper Limb Centre, St. Joseph’s Health Care, London, ON, Canada Background: As more anatomic asymmetric radial head implants emerge, it is necessary to determine the optimal landmarks to ensure correct rotational orientation. The bicipital tuberosity and distal radius are possible bony landmarks that can be used for rotational alignment of asymmetric prostheses; however, they have not been validated. The purpose of this study was to evaluate the reliability of the bicipital tuberosity and distal radius as rotational landmarks for orientation of asymmetric radial head prostheses. Methods: Measurements were made from computer tomography scans of 50 elbows in order to determine the rotational relationships between the radial head, bicipital tuberosity, biceps tendon footprint, and distal radius. Results: The maximum radial head diameter was oriented 65 28 from the bicipital tuberosity, 119 38 from the biceps tendon footprint, 82 29 from the radial styloid, and 76 28 from the volar surface of the distal radius. All of these landmarks had a significantly greater variance than a proposed acceptable clinical tolerance of 10 (P < .001). Conclusion: The results demonstrate that the measured landmarks show no consistent rotational relationship with the maximum diameter of the radial head. In order to maximize the utility of more anatomic asymmetric radial head implant systems, further studies are necessary to identify more reliable rotational landmarks to ensure optimal implant positioning. Level of evidence: Anatomic Study, Imaging. Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Radial head arthroplasty; radial head fracture; implant design; bicipital tuberosity; elbow
The radial head is an important elbow stabilizer, acting through its articulations at the proximal radioulnar joint and the radiocapitellar joint.5,9 Comminuted fractures of the radial head are common,9,16 and when associated with
IRB approval was not required for this study as per the University of Western Ontario IRB. *Reprint requests: George S. Athwal, MD, Hand and Upper Limb Centre, St. Joseph’s Health Care, 268 Grosvenor St., London, ON N6A 4L6, Canada. E-mail address: [email protected] (G.S. Athwal).
certain injury patterns can lead to instability, restricted range of motion, arthritis, and pain.3,9 The optimal treatment for displaced radial head fractures associated with complex elbow instability or a mechanical block to motion consists of open reduction and internal fixation; however, if unreconstructable, radial head arthroplasty has demonstrated good outcomes.1,5,8 Since the first reported radial head replacement in 1941, there have been numerous improvements to the surgical technique, prosthetic composition, and implant morphology.16 These developments have resulted in improved
1058-2746/$ - see front matter Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2013.02.013
Insertional landmarks for radial head implants patient outcomes.8,11 The radial head has been shown to be asymmetric10,18; however, most current radial head implants have axisymmetric designs. Although radial head arthroplasty has demonstrated generally positive patient outcomes, problems can occur. These issues, which are inherent to all types of hemiarthroplasties, include implant wear, joint wear, instability, and stiffness.3,12 Prostheses that better replicate native radial head anatomy may more effectively restore joint kinematics and load transfer, potentially leading to superior patient outcomes.7,17 In order for asymmetric implants to be effective, measures must be taken to ensure that they can be correctly rotationally aligned relative to the native radial head. Based on their ease of identification via fluoroscopy or palpation, structures such as the bicipital tuberosity, volar distal radius, and radial styloid could potentially represent useful rotational landmarks to assist with anatomic orientation of an asymmetric implant. For these landmarks to be effective, however, a reliable relationship must exist between the orientations of these structures and the orientation of the radial head. To date, none of these landmarks has been completely validated. The objective of this study was to examine the relationship between anatomical landmarks of the bicipital tuberosity, biceps tendon footprint, and distal radius with the native radial head, in order to assess their utility as rotational landmarks for insertion of asymmetric radial head implants.
Materials and methods Computed tomography (CT) images of 50 fresh-frozen elbow specimens (mean age 70 years [range, 42-97]) with no evidence of previous surgery, trauma or arthritis were obtained using a 64-slice scanner (Light Speed Ultra; GE, New Berlin, WI, USA). Imaging parameters included a field of view of 16 16 cm, a 512 512 reconstruction matrix, technique factors 120 kVp and 90 mAs, and a voxel size of 0.3 0.3 0.625 mm. Three-dimensional (3D) models of the radii were created using Mimics Medical Imaging Software (Materialise, Ann Arbor, MI, USA). These models were created by segmenting the CT data so it would only include bone and exclude soft tissue, and then manually segmenting each model to isolate the radius from the humerus and the ulna. On each 3D model, a coronal plane was drawn to establish a coordinate system for the radius. The 3 landmarks that were used to establish the coronal plane were the deepest point of the articular dish on the radial head, radial styloid, and midpoint of the articulation at the distal radioulnar joint. As the radial styloid is rounded, it was assessed in 2 planes by selecting the most distal point of the styloid and the highest point on the radial side of the styloid. This plane was also used to represent the orientation of the radial styloid. Two anatomical features were used to define the bicipital tuberosity: the tuberosity orientation plane and biceps tendon footprint plane. The tuberosity orientation plane was defined by a line drawn from the center of the spine of the radial tuberosity to the center of the radial canal. For specimens where the bicipital tuberosity had a bifid morphology, the
1243
Figure 1 3-dimensional model of a supinated right radius, with orientations of the maximal diameter of the radial head (blue), bicipital tuberosity (green), biceps footprint (purple), volar distal radius (yellow), and radial styloid (red).
medial ridge was selected as the spine because it corresponds anatomically to the spine in the single ridge type. While it was very small in certain specimens, the ridge was identifiable on each one, indicating that none of our specimens would be truly classified as smooth. The biceps footprint plane was drawn along the flat spot of the bicipital tuberosity, representing the insertional footprint of the distal biceps tendon. Another plane was defined by the relatively flat volar cortex of the distal radius metaphysis. In order to reference the above planes to the radial head, a line was drawn through the maximum diameter of the radial head, as calculated using an iterative approach measuring many distinct diameters around the circumference of the radial head. This line was used to define the radial head’s asymmetric rotational orientation. A 3D model of the radius, showing the orientation of each of the aforementioned landmarks, is presented in Figure 1. The angle that each landmark made with the maximal radial head diameter was calculated using Matlab (MathWorks, Natick, MA, USA), with all angles converted into the internally rotated direction from neutral forearm position. The relationship between the orientations of each of the aforementioned landmarks with respect to the maximum diameter of the radial head was assessed. For each proposed landmark, the absolute value of the difference between each measurement and the mean was calculated. Using a 1-sided t test, these differences were compared with a 10 and 15 tolerance, which we considered to be the maximum acceptable error in placing an asymmetric radial head implant. To evaluate the reliability of the measurements, inter-rater, and intra-rater reliability assessments were completed. Two trained observers each measured 5 specimens, and the primary observer also evaluated five specimens a second time at an interval of at least 4 weeks. Intra-class correlation coefficients were determined in order to assess the repeatability of the measurements.
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Table Relationships between the studied landmarks; all angles are measured in the internally rotated direction, and are expressed in degrees Landmarks
Orientation with respect to maximal radial head diameter
Standard deviation
Range
P value compared to 10 tolerance
P value compared to 15 tolerance
Bicipital tuberosity Biceps tendon footprint Radial styloid Volar distal radius
65 119 82 76
28 38 29 28
4-152 30-178 24-161 28-134
<.001 <.001 <.001 <.001
.008 <.001 .005 .009
Figure 2 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the bicipital tuberosity (green) 1 SD (shaded in dark green) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the bicipital tuberosity and radial head is also shown.
Results
Discussion
Inter-rater reliability was excellent for all measurements, yielding an intra-class correlation coefficient of 0.90. Intra-rater reliability was also excellent for all measurements and yielded an intra-class correlation coefficient of 0.92. The relationships between the orientations of the radial head, bicipital tuberosity, biceps tendon footprint, radial styloid, and volar distal radius are summarized in the Table. Models of the radial head elucidating its relationships with the bicipital tuberosity, biceps tendon footprint, radial styloid, and volar distal radius are shown in Figs. 2-5, respectively. Scatterplots showing the relative orientations of each landmark and the maximum radial head diameter are also shown accompanying the radial head models in Figs. 2-5, respectively. The absolute deviations for each landmark were found to be significantly greater than a 10 tolerance (P < .001 for all landmarks). The absolute deviations were also significantly greater than the extended tolerance of 15 (P < .01 for all landmarks). This indicates the poor reliability of any of the aforementioned landmarks to rotationally orient asymmetric radial head prostheses.
Numerous morphological studies have shown the radial head to be elliptical, with the mean difference between the maximum and minimum diameters approaching 2 mm.10,15,19 Traditional radial head implants have modeled the radial head as circular, but more anatomic implants are starting to emerge, which are eccentric. These asymmetric implants, like the native radial head itself, have maximum and minimum diameters. In order for these more anatomic designs to have the desired effect on joint kinematics, they must be inserted such that the maximum and minimum diameters of the implant align with the corresponding diameters of the native radial head. An optimal landmark will have a consistent, dependable relationship with respect to the native radial head, so that it can be used to guide the rotational alignment of nonaxisymmetric radial head prostheses. Our data demonstrate that the rotational orientation of the proposed landmarks to the radial head are highly variable. The large standard deviations and range in the data suggest that the maximum diameter of the radial head does not show a consistent relationship with anatomical landmarks on the bicipital tuberosity or the distal radius. Even with generous
Insertional landmarks for radial head implants
1245
Figure 3 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the biceps footprint (purple) 1 SD (shaded in light purple) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the biceps footprint and radial head is also shown.
Figure 4 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the radial styloid (red) 1 SD (shaded in light red) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the radial styloid and radial head is also shown.
tolerances of up to 15 , none of these landmarks are reliable for the rotational orientation of asymmetric radial head implants. While the effects of malrotation for radial head arthroplasty have not been reported, they have been studied extensively in relation to hip, knee, and shoulder arthroplasty. The literature suggests that malrotation can cause pain, wear, instability, and failure.2,4,6,19 It is possible that these same complications may result from component malrotation during radial head arthroplasty. This underscores the importance of finding a reliable landmark for insertion of the emerging asymmetric radial head implants. Further studies are required in order to identify more reliable landmarks for the orientation of more anatomic radial head implants. Until a landmark with a consistent
rotational relationship with the native radial head can be established, it may be difficult to verify whether axisymmetric radial head prostheses are consistently being inserted in an anatomic fashion. One potential solution that may help ensure anatomic orientation of asymmetric radial head implants may rely on the use of contralateral limb imaging. A CT scan of the uninjured arm can likely be added at limited additional cost to the usual imaging of the injured elbow; although it does subject the patient to increased radiation exposure. Contralateral proximal radii have been shown to be nearly identical; so it may be possible to elucidate the orientation of the injured native radial head based on the contralateral anatomy.13 While this technique may be promising, it has not yet been validated. Identification of a reliable landmark
1246
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Figure 5 Model of a right radial head in slight supination, showing the distribution of the relative orientation of the volar distal radius (yellow) 1 SD (shaded in light yellow) with respect to the maximum diameter of the radial head (blue). Graphical representation of the distribution of the relative orientations of the volar distal radius and radial head is also shown.
on the ipsilateral radius would represent a less costly method than use of the contralateral anatomy. However, the authors believe that no reliable landmarks exist on the ipsilateral radius for rotational alignment of asymmetric radial head prostheses. The inter- and intra-rater reliability assessment confirms that the methods employed are repeatable, and helps validate the results of the study. The most significant weakness of the study is that it is difficult to define 2-dimensional orientations of complex structures such as the bicipital tuberosity and radial styloid. While reproducible methods were developed, the complex morphology of the landmarks measured introduces error into the results. Another weakness of this study is that articular cartilage was not measured. This is relevant because cartilage thickness is nonuniform, and these variations may alter the true maximum diameter of the radial head; however, it is unlikely that this will affect the outcomes in a significant way. Furthermore, there may be error introduced to the methodology through the segmentation and thresholding techniques; although this error has been shown to be small.14
Conclusion This study has examined possible rotational landmarks for insertion of asymmetric radial head implants. Through examinations of their respective relationships with the orientation of the radial head, the bicipital tuberosity and the radial styloid have been shown to be unreliable landmarks. Neither of these landmarks possesses consistent, reliable relationships with the orientation of the radial head. In order for emerging asymmetric radial head prostheses to function at full effectiveness, they must be
inserted in an anatomic orientation. Further studies are necessary in order to develop reliable rotational landmarks for insertion of asymmetric radial head prostheses.
Acknowledgment Funding for this project was provided through research grants by the Canadian Institute of Health Research.
Disclaimer Dr. King receives royalties from and is a consultant for Wright Medical Technologies for products related to the subject of this research. The other authors, their immediate families, and any research foundation with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article. The funding sources did not have any involvement in the data collection, data analysis, or the preparation of or editing of the manuscript.
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