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Ulnar Variance: Its Relationship to Ulnar Foveal Morphology and Forearm Kinematics
SCIENTIFIC ARTICLE
Ulnar Variance: Its Relationship to Ulnar Foveal Morphology and Forearm Kinematics Toshiyuki Kataoka, MD, Hisao Moritomo, MD, PhD, Shohei Omokawa, MD, PhD, Akio Iida, MD, Tsuyoshi Murase, MD, PhD, Kazuomi Sugamoto, MD, PhD
Purpose It is unclear how individual differences in the anatomy of the distal ulna affect kinematics and pathology of the distal radioulnar joint. This study evaluated how ulnar variance relates to ulnar foveal morphology and the pronosupination axis of the forearm. Methods We performed 3-dimensional computed tomography studies in vivo on 28 forearms in maximum supination and pronation to determine the anatomical center of the ulnar distal pole and the forearm pronosupination axis. We calculated the forearm pronosupination axis using a markerless bone registration technique, which determined the pronosupination center as the point where the axis emerges on the distal ulnar surface. We measured the depth of the anatomical center and classified it into 2 types: concave, with a depth of 0.8 mm or more, and flat, with a depth less than 0.8 mm. We examined whether ulnar variance correlated with foveal type and the distance between anatomical and pronosupination centers. Results A total of 18 cases had a concave-type fovea surrounded by the C-shaped articular facet of the distal pole, and 10 had a flat-type fovea with a flat surface without evident central depression. Ulnar variance of the flat type was 3.5 ⫾ 1.2 mm, which was significantly greater than the 1.2 ⫾ 1.1 mm of the concave type. Ulnar variance positively correlated with distance between the anatomical and pronosupination centers. Conclusions Flat-type ulnar heads have a significantly greater ulnar variance than concave types. The pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance. Clinical relevance This study suggests that ulnar variance is related in part to foveal morphology and pronosupination axis. This information provides a starting point for future studies investigating how foveal morphology relates to distal ulnar problems. (J Hand Surg 2012;37A:729–735. Copyright © 2012 by the American Society for Surgery of the Hand. All rights reserved.) Key words Forearm kinematics, foveal morphology, ulnar variance. HE ANATOMIC ULNAR FOVEA is a central, roughened bony depression on the distal pole of the ulna.1 It is the primary attachment site for the deep fibers of the radioulnar ligaments2,3 and is critical in providing rotation and translation guidance4 because
T
From the Departments of Orthopaedic Surgery and Orthopedic Biomaterial Science, Osaka University Graduate School of Medicine, Osaka; the Department of Orthopedic Surgery, Nara Medical University, and the Department of Orthopedic Surgery, Hanna Central Hospital, Nara, Japan. TheauthorsthankJunichiMiyake,MD,ShinsukeOmori,MD,RyojiNakao,computerprogrammer,and SumikaIkemoto,clinicalassistant,attheDepartmentofOrthopaedicSurgery,OsakaUniversityGraduate School of Medicine, for contributions to this study. Received for publication May 16, 2011; accepted in revised form January 23, 2012.
the pronosupination axis of the forearm runs through it.5–7 Conversely, the distal ulna shows individual differences in length relative to the radius8,9 and in shape, from partially spherical to nearly flat.10 In addition, foveal morphology also varies. It remains unclear as to No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Hisao Moritomo, MD, PhD, Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan; e-mail: [email protected]. 0363-5023/12/37A04-0015$36.00/0 doi:10.1016/j.jhsa.2012.01.033
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how these individual anatomical differences affect the kinematics and pathology of the distal radioulnar joint (DRUJ). We measured 3-dimensional morphologic changes to accurately locate the pronosupination axis of the forearm in vivo by using a markerless bone registration technique with 3-dimensional bone models constructed from computed tomography (CT) data.11–14 The purpose of this study was to evaluate how ulnar variance relates to ulnar foveal morphology and the pronosupination axis of the forearm. MATERIALS AND METHODS We studied 28 forearms (12 right and 16 left) in 28 subjects (18 women and 10 men; mean age 40 y, range 16 –78 y). All subjects were Japanese and initially presented to our hospital with contralateral forearm disorders such as triangular fibrocartilage complex (TFCC) injury, ulnocarpal impaction syndrome, malunion of the radius or ulna, or osteoarthritis of the DRUJ. We used only the CT data from the normal side in this study, although we performed CT scans bilaterally for comparison. Our institutional review board approved the study. We took plain radiographs to confirm the absence of skeletal degeneration or abnormalities in the wrist and distal forearm. Image acquisition We performed the CT with subjects positioned prone with the arm elevated over the head and the elbow flexed to prevent rotation of the humerus (helical CT, LightSpeed Ultra16; General Electric, Maukesha, WI). We obtained images with a slice thickness of 1.25 mm in maximum supination and maximum pronation. Maximum position was defined as an extreme position that the subject could easily maintain without active muscle contraction. We saved data in digital imaging and communication in medicine format. Creation of 3-dimensional models of radius and ulna We transferred the digital data to an original computer program based on the Visualization Toolkit (Kitware, Clifton Park, NY), we extracted regions of the radius and ulna in all slice images semiautomatically by segmentation. Three-dimensional models of the radius and ulna were created from the segmentation data. We visualized these images using software developed in our laboratory (Orthopaedics Viewer, Osaka, Japan). Measurement of ulnar variance We measured ulnar variance using 3-dimensional models of the radius and ulna as the distance between the
farthest point on the distal margin of the ulnar head and the center of the concavity on the farthest border of the sigmoid notch along the ulnar longitudinal axis (Fig. 1). Determination of anatomical center of the fovea and its depth The depth of the fovea’s anatomical center was measured to investigate foveal morphology because the anatomic ulnar fovea is located near the center of curvature of the ulnar head.15 We measured the depth of the anatomical center by first determining the axial plane perpendicular to the longitudinal axis of the ulnar shaft at the center of the DRUJ. We determined the centroid of the contour of the ulnar head on the axial plane using the circle approximation technique. Then we determined the anatomical center as the point where a line parallel to the ulnar longitudinal axis passing through the centroid emerged on the distal surface of the ulna (Fig. 2). Finally, we calculated foveal depth by measuring the distance from the farthest point on the distal margin of the ulnar head in coronal section view (Fig. 3). We classified foveal morphology into 2 types according to the depth of the anatomical center: (1) concave (depth ⱖ 0.8 mm), and (2) flat (depth ⬍ 0.8 mm). The mean depth of the anatomical center was 1.4 ⫾ 0.4 mm and 0.5 ⫾ 0.2 mm in the concave- and flat-type fovea, respectively. Determination of the pronosupination axis and pronosupination center We used a markerless surface-based registration technique to determine the pronosupination axis of the forearm. This technique allows mathematical descriptions of the motion of individual bones and relative motions by superimposing a bone in 1 position on another position based on similarity measures.16 We calculated the rotation of the radius relative to the ulna from maximum supination to maximum pronation using a screw displacement axis system17 identical to the pronosupination axis of the forearm.18 We determined the pronosupination center on each ulnar head as the point where the pronosupination axis emerged on the distal surface of the ulna (Fig. 2). Data analysis We evaluated whether ulnar variance correlated with the distance between the anatomical and pronosupination centers: namely, the interaxial distance (Fig. 2), which expresses a gap between the center of the distal pole and the pronosupination axis. We also investigated the relationship between ulnar variance and foveal morphology.
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FIGURE 1: Three dimensional models of A the right radius viewed from the medial aspect and B the right radius and ulna viewed from the volar medial aspect. We measured ulnar variance as the distance between the farthest point on the distal margin of the ulnar head and the center of the concavity.
FIGURE 2: Three dimensional model of the right ulnar head viewed from the distal aspect. The anatomical center is the point where a line parallel to the ulnar longitudinal axis passing through the centroid of the contour of the ulnar head emerges on the distal surface of the ulna. The pronosupination center is the point where the pronosupination axis emerges on the distal surface of the ulna. The interaxial distance is the distance between the anatomical center and pronosupination center.
FIGURE 3: Coronal section view of the ulnar head showing the anatomical center. We measured the depth of the anatomical center as the distance between the farthest point on the distal margin of the ulnar head and the anatomical center along the ulnar longitudinal axis.
For statistical analysis, we used Student’s t-test to determine whether there were significant differences in ulnar variance between the concave and flat types. We
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FIGURE 4: Representative 3-dimensional models of the left distal ulna with A concave-type and B flat-type fovea and their pronosupination axes and anatomical centers. The concave type has a deep anatomic ulnar fovea surrounded by the C-shaped articular facet of the distal ulna, whereas the flat type has either a flat or domelike surface with no evident foveal depression.
calculated the correlation of ulnar variance with the interaxial distance using the Pearson correlation coefficient (r). We set the level of significance at P ⬍ .05. RESULTS Classification of foveal morphology Of the 28 cases, 18 (64%) showed a concave-type fovea that was deep and surrounded by the C-shaped articular facet of the distal ulna (Fig. 4A). Ten cases (36%) showed a flat-type fovea that had either a flat or domelike surface with no evident depression (Fig. 4B). Relationship between ulnar variance and location of the forearm pronosupination axis Ulnar variance correlated positively with the interaxial distance (r ⫽ 0.38, P ⬍ .05), which infers that the pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance (Fig. 5). Mean ulnar variance and interaxial distance were 2.0 ⫾ 1.6 and 2.6 ⫾ 1.2 mm, respectively. The interaxial distance for concave and flat types was 2.6 ⫾ 1.2 and 2.5 ⫾ 1.2 mm, respectively. There was no significant difference in interaxial distance between the types of ulnar head morphology measured (P ⫽ .44).
Relationship between ulnar variance and foveal morphology Ulnar variance of the flat type was 3.5 ⫾ 1.2 mm, which was significantly greater than the 1.2 ⫾ 1.1 mm variance of the concave type (P ⬍ .05). DISCUSSION Some investigators have described variation of shape in ulnar head anatomy. Hyams et al19 noted that moderate correlation existed between ulnar variance and ulnar head peak distance, which is the distance from the most radial point of the ulnar head to the most distally prominent point of the ulnar head along the direction perpendicular to the ulnar longitudinal axis. Schuind et al20 noted there was a trend toward a positive linear relationship between ulnar variance and the angle formed by the ulnar longitudinal axis and a line drawn between the most radial and ulnar points of the ulnar dome. We found that foveal morphology varies individually and that ulnar variance in the flat type was significantly greater than that in the concave type. The anatomic ulnar fovea of the flat type was shallow or often nonexistent, and the surface line of the spherical articular facet of the ulnar head directly continued to the base of the ulnar styloid. We found no significant difference in interaxial distance between the concave and flat types
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FIGURE 5: Relationship between ulnar variance and interaxial distance. Interaxial distance positively correlates with ulnar variance. The correlation coefficient (r) was 0.38.
because both had distinct variation in interaxial distance (Fig. 5). We speculate that this is because other factors such as the TFCC, interosseous membrane, forearm muscle contraction, and forearm bone morphology excluding foveal morphology may influence interaxial distance. Using posteroanterior radiography with the forearm in neutral rotation, we were often able to distinguish the concave from the flat type. The typical concave type showed (1) a double-floor configuration at the anatomic ulnar fovea, in which the cortices of the surrounding C-shaped articular facet were superimposed on the foveal floor; and (2) the clear line of the radial edge of the extensor carpi ulnaris groove. The flat type did not generally show these characteristics (Fig. 6). It has been suggested that the pronosupination axis of the forearm runs distally through the anatomic ulnar fovea5,6 and that the anatomic ulnar fovea is located near the center of curvature of the ulnar head.16 However, our data indicate that the pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance. This finding implies that the axis in the wrist with positive ulnar variance tends to pass more medially near
the base of the ulnar styloid than that in the wrist with neutral or negative variance. This may be related to the finding that the axis runs obliquely from the proximal, radial aspect to the distal, ulnar aspect where the axis gradually orients medially as it runs distally. The fact that the cases with greater interaxial distance showed discrepancy between the anatomical and pronosupination centers raises questions about the point of insertion of the deep fibers. Do the deep fibers insert on a more medial aspect around the axis rather than near the anatomical center, or do they insert around the anatomical center away from the axis and behave in an extrinsic manner? The radioulnar ligaments, consisting of the superficial and deep fibers, are 1 of the important stabilizers of the DRUJ.1 The anatomic ulnar fovea is believed to be the primary attachment site for these deep fibers.2 The degree of development of the anatomic ulnar fovea may influence the thickness of the deep fibers or the frequency of the TFCC injury. Furthermore, a greater cam effect would occur in the ulnar head where the interaxial distance is increased. If the deep fibers attach to the pronosupination center, these may be more prone to injury because of this potential cam effect. Further
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FIGURE 6: Posteroanterior x-rays of the ulnar head of representative cases of A concave type and B flat type. The typical concave type shows a double-floor configuration of the anatomic ulnar fovea (green arrowheads) and a clear line of the radial edge of the extensor carpi ulnaris groove (blue arrowheads). A typical flat type is devoid of any evident depression of the anatomic ulnar fovea and groove.
studies regarding the relationship between foveal TFCC avulsion and foveal morphology will be necessary to verify these hypotheses. This study has several limitations. First, the series of wrists investigated in this study may not represent a normal population because this series contains almost exclusively ulna-positive wrists. Mean ulnar variance in this study was ⫹2.0 mm, whereas mean ulnar variance reported in a Japanese and a white population by means of x-ray was a positive 0.2 mm21 and negative 0.9 mm,20 respectively. We speculate that this discrepancy may be because the subjects were not normal volunteers, but patients with a painful condition in the contralateral side. Second, we could not evaluate the precise shape of the surface of the articular cartilage because the 3-dimensional model created from CT data reflected the shape of only the subchondral bone and bone cortex and not the overlying cartilage. Third, the size of the CT cuts was 1.25 mm (ie, the margin of measurement error), but the difference in average ulnar variance (2.0 mm) and interaxial distance (2.6 mm) was 0.6 mm. This margin of measurement error could in-
fluence the results. This study suggests that ulnar variance is related to foveal morphology and the pronosupination axis. The results of this study could provide a starting point for future studies investigating how foveal morphology relates to the pathology of the DRUJ, such as foveal avulsion of the TFCC. REFERENCES 1. Garcia-Elias M. Soft-tissue anatomy and relationships about the distal ulna. Hand Clin 1998;14:165–176. 2. Stuart PR, Berger RA, Linscheid RL, An KN. The dorsopalmar stability of the distal radioulnar joint. J Hand Surg 2000;25A:689 – 699. 3. Ishii S, Palmer AK, Werner FW, Short WH, Fortino MD. An anatomic study of the ligamentous structure of the triangular fibrocartilage complex. J Hand Surg 1998;23A:977–985. 4. Kleinman WB. Distal radius instability and stiffness: common complications of distal radius fractures. Hand Clin 2010;26:245–264. 5. Kapandji A. Biomechanics of pronation and supination of the forearm. Hand Clin 2001;17:111–122, vii. 6. Youm Y, Dryer RF, Thambyrajah K, Flatt AK, Spraque BL. Biomechanical analyses of forearm pronation-supination and elbow flexion-extension. J Biomech 1979;12:245–255. 7. Hollister AM, Gellman H, Waters RL. The relationship of the interosseous membrane to the axis of rotation of the forearm. Clin Orthop Relat Res 1994;298:272–276.
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8. Palmer AK, Glisson RR, Werner FW. Ulnar variance determination. J Hand Surg 1982;7A:376 –379. 9. Steyers CM, Blair WF. Measuring ulnar variance: a comparison of techniques. J Hand Surg 1989;14A:607– 612. 10. Adams BD. Distal radioulnar joint instability. In: Green D, Hotchkiss R, Pederson WC, eds. Green’s operative hand surgery. 5th ed. New York: Churchill Livingston, 2005:605– 644. 11. Oka K, Doi K, Suzuki K, Murase T, Goto A, Yoshikawa H, et al. In vivo three-dimensional motion analysis of the forearm with radioulnar synostosis treated by the Kanaya procedure. J Orthop Res 2006;24:1028 –1035. 12. Moritomo H, Noda K, Goto A, Murase T, Yoshikawa H, Sugamoto K. Interosseous membrane of the forearm: length change of ligaments during forearm rotation. J Hand Surg 2009;34A:685– 691. 13. Tay SC, van Riet R, Kazunari T, Koff MF, Amrami KK, An KN, et al. A method for in-vivo kinematic analysis of the forearm. J Biomech 2008;41:56 – 62. 14. Tay SC, van Riet R, Kazunari T, Koff MF, Amrami KK, An KN, et al. In-vivo kinematic analysis of forearm rotation using helical axis analysis. Clin Biomech 2010;25:655– 659.
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15. af Ekenstam F, Hagert CG. Anatomical studies on the geometry and stability of the distal radio ulnar joint. Scand J Plast Reconstr Surg 1985;19:17–25. 16. Audette MA, Ferrie FP, Peters TM. An algorithmic overview of surface registration techniques for medical imaging. Med Image Anal 2000;4:201–217. 17. Kinzel GL, Hall AS Jr, Hillberry BM. Measurement of the total motion between two body segments. I. Analytical development. J Biomech 1972;5:93–105. 18. Van Sint Jan S, Salvia P, Hilal I, Sholukha V, Rooze M, Clapworthy G. Registration of 6-DOFs electrogoniometry and CT medical imaging for 3D joint modeling. J Biomech 2002;35: 1475–1484. 19. Hyams E, Yazaki N, Nakamura R, Nakao E, Watanabe K. Radiographic morphology of the ulnar head. Hand Surg 2004;9:175–180. 20. Schuind FA, Linscheid RL, An KN, Chao EY. A normal data base of posteroanterior roentgenographic measurements of the wrist. J Bone Joint Surg 1992;74A:1418 –1429. 21. Nakamura R, Tanaka Y, Imaeda T, Miura T. The influence of age and sex on ulnar variance. J Hand Surg 1991;16B:84 – 88.
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Ulnar Variance: Its Relationship to Ulnar Foveal Morphology and Forearm Kinematics Toshiyuki Kataoka, MD, Hisao Moritomo, MD, PhD, Shohei Omokawa, MD, PhD, Akio Iida, MD, Tsuyoshi Murase, MD, PhD, Kazuomi Sugamoto, MD, PhD
Purpose It is unclear how individual differences in the anatomy of the distal ulna affect kinematics and pathology of the distal radioulnar joint. This study evaluated how ulnar variance relates to ulnar foveal morphology and the pronosupination axis of the forearm. Methods We performed 3-dimensional computed tomography studies in vivo on 28 forearms in maximum supination and pronation to determine the anatomical center of the ulnar distal pole and the forearm pronosupination axis. We calculated the forearm pronosupination axis using a markerless bone registration technique, which determined the pronosupination center as the point where the axis emerges on the distal ulnar surface. We measured the depth of the anatomical center and classified it into 2 types: concave, with a depth of 0.8 mm or more, and flat, with a depth less than 0.8 mm. We examined whether ulnar variance correlated with foveal type and the distance between anatomical and pronosupination centers. Results A total of 18 cases had a concave-type fovea surrounded by the C-shaped articular facet of the distal pole, and 10 had a flat-type fovea with a flat surface without evident central depression. Ulnar variance of the flat type was 3.5 ⫾ 1.2 mm, which was significantly greater than the 1.2 ⫾ 1.1 mm of the concave type. Ulnar variance positively correlated with distance between the anatomical and pronosupination centers. Conclusions Flat-type ulnar heads have a significantly greater ulnar variance than concave types. The pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance. Clinical relevance This study suggests that ulnar variance is related in part to foveal morphology and pronosupination axis. This information provides a starting point for future studies investigating how foveal morphology relates to distal ulnar problems. (J Hand Surg 2012;37A:729–735. Copyright © 2012 by the American Society for Surgery of the Hand. All rights reserved.) Key words Forearm kinematics, foveal morphology, ulnar variance. HE ANATOMIC ULNAR FOVEA is a central, roughened bony depression on the distal pole of the ulna.1 It is the primary attachment site for the deep fibers of the radioulnar ligaments2,3 and is critical in providing rotation and translation guidance4 because
T
From the Departments of Orthopaedic Surgery and Orthopedic Biomaterial Science, Osaka University Graduate School of Medicine, Osaka; the Department of Orthopedic Surgery, Nara Medical University, and the Department of Orthopedic Surgery, Hanna Central Hospital, Nara, Japan. TheauthorsthankJunichiMiyake,MD,ShinsukeOmori,MD,RyojiNakao,computerprogrammer,and SumikaIkemoto,clinicalassistant,attheDepartmentofOrthopaedicSurgery,OsakaUniversityGraduate School of Medicine, for contributions to this study. Received for publication May 16, 2011; accepted in revised form January 23, 2012.
the pronosupination axis of the forearm runs through it.5–7 Conversely, the distal ulna shows individual differences in length relative to the radius8,9 and in shape, from partially spherical to nearly flat.10 In addition, foveal morphology also varies. It remains unclear as to No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Hisao Moritomo, MD, PhD, Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan; e-mail: [email protected]. 0363-5023/12/37A04-0015$36.00/0 doi:10.1016/j.jhsa.2012.01.033
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how these individual anatomical differences affect the kinematics and pathology of the distal radioulnar joint (DRUJ). We measured 3-dimensional morphologic changes to accurately locate the pronosupination axis of the forearm in vivo by using a markerless bone registration technique with 3-dimensional bone models constructed from computed tomography (CT) data.11–14 The purpose of this study was to evaluate how ulnar variance relates to ulnar foveal morphology and the pronosupination axis of the forearm. MATERIALS AND METHODS We studied 28 forearms (12 right and 16 left) in 28 subjects (18 women and 10 men; mean age 40 y, range 16 –78 y). All subjects were Japanese and initially presented to our hospital with contralateral forearm disorders such as triangular fibrocartilage complex (TFCC) injury, ulnocarpal impaction syndrome, malunion of the radius or ulna, or osteoarthritis of the DRUJ. We used only the CT data from the normal side in this study, although we performed CT scans bilaterally for comparison. Our institutional review board approved the study. We took plain radiographs to confirm the absence of skeletal degeneration or abnormalities in the wrist and distal forearm. Image acquisition We performed the CT with subjects positioned prone with the arm elevated over the head and the elbow flexed to prevent rotation of the humerus (helical CT, LightSpeed Ultra16; General Electric, Maukesha, WI). We obtained images with a slice thickness of 1.25 mm in maximum supination and maximum pronation. Maximum position was defined as an extreme position that the subject could easily maintain without active muscle contraction. We saved data in digital imaging and communication in medicine format. Creation of 3-dimensional models of radius and ulna We transferred the digital data to an original computer program based on the Visualization Toolkit (Kitware, Clifton Park, NY), we extracted regions of the radius and ulna in all slice images semiautomatically by segmentation. Three-dimensional models of the radius and ulna were created from the segmentation data. We visualized these images using software developed in our laboratory (Orthopaedics Viewer, Osaka, Japan). Measurement of ulnar variance We measured ulnar variance using 3-dimensional models of the radius and ulna as the distance between the
farthest point on the distal margin of the ulnar head and the center of the concavity on the farthest border of the sigmoid notch along the ulnar longitudinal axis (Fig. 1). Determination of anatomical center of the fovea and its depth The depth of the fovea’s anatomical center was measured to investigate foveal morphology because the anatomic ulnar fovea is located near the center of curvature of the ulnar head.15 We measured the depth of the anatomical center by first determining the axial plane perpendicular to the longitudinal axis of the ulnar shaft at the center of the DRUJ. We determined the centroid of the contour of the ulnar head on the axial plane using the circle approximation technique. Then we determined the anatomical center as the point where a line parallel to the ulnar longitudinal axis passing through the centroid emerged on the distal surface of the ulna (Fig. 2). Finally, we calculated foveal depth by measuring the distance from the farthest point on the distal margin of the ulnar head in coronal section view (Fig. 3). We classified foveal morphology into 2 types according to the depth of the anatomical center: (1) concave (depth ⱖ 0.8 mm), and (2) flat (depth ⬍ 0.8 mm). The mean depth of the anatomical center was 1.4 ⫾ 0.4 mm and 0.5 ⫾ 0.2 mm in the concave- and flat-type fovea, respectively. Determination of the pronosupination axis and pronosupination center We used a markerless surface-based registration technique to determine the pronosupination axis of the forearm. This technique allows mathematical descriptions of the motion of individual bones and relative motions by superimposing a bone in 1 position on another position based on similarity measures.16 We calculated the rotation of the radius relative to the ulna from maximum supination to maximum pronation using a screw displacement axis system17 identical to the pronosupination axis of the forearm.18 We determined the pronosupination center on each ulnar head as the point where the pronosupination axis emerged on the distal surface of the ulna (Fig. 2). Data analysis We evaluated whether ulnar variance correlated with the distance between the anatomical and pronosupination centers: namely, the interaxial distance (Fig. 2), which expresses a gap between the center of the distal pole and the pronosupination axis. We also investigated the relationship between ulnar variance and foveal morphology.
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FIGURE 1: Three dimensional models of A the right radius viewed from the medial aspect and B the right radius and ulna viewed from the volar medial aspect. We measured ulnar variance as the distance between the farthest point on the distal margin of the ulnar head and the center of the concavity.
FIGURE 2: Three dimensional model of the right ulnar head viewed from the distal aspect. The anatomical center is the point where a line parallel to the ulnar longitudinal axis passing through the centroid of the contour of the ulnar head emerges on the distal surface of the ulna. The pronosupination center is the point where the pronosupination axis emerges on the distal surface of the ulna. The interaxial distance is the distance between the anatomical center and pronosupination center.
FIGURE 3: Coronal section view of the ulnar head showing the anatomical center. We measured the depth of the anatomical center as the distance between the farthest point on the distal margin of the ulnar head and the anatomical center along the ulnar longitudinal axis.
For statistical analysis, we used Student’s t-test to determine whether there were significant differences in ulnar variance between the concave and flat types. We
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FIGURE 4: Representative 3-dimensional models of the left distal ulna with A concave-type and B flat-type fovea and their pronosupination axes and anatomical centers. The concave type has a deep anatomic ulnar fovea surrounded by the C-shaped articular facet of the distal ulna, whereas the flat type has either a flat or domelike surface with no evident foveal depression.
calculated the correlation of ulnar variance with the interaxial distance using the Pearson correlation coefficient (r). We set the level of significance at P ⬍ .05. RESULTS Classification of foveal morphology Of the 28 cases, 18 (64%) showed a concave-type fovea that was deep and surrounded by the C-shaped articular facet of the distal ulna (Fig. 4A). Ten cases (36%) showed a flat-type fovea that had either a flat or domelike surface with no evident depression (Fig. 4B). Relationship between ulnar variance and location of the forearm pronosupination axis Ulnar variance correlated positively with the interaxial distance (r ⫽ 0.38, P ⬍ .05), which infers that the pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance (Fig. 5). Mean ulnar variance and interaxial distance were 2.0 ⫾ 1.6 and 2.6 ⫾ 1.2 mm, respectively. The interaxial distance for concave and flat types was 2.6 ⫾ 1.2 and 2.5 ⫾ 1.2 mm, respectively. There was no significant difference in interaxial distance between the types of ulnar head morphology measured (P ⫽ .44).
Relationship between ulnar variance and foveal morphology Ulnar variance of the flat type was 3.5 ⫾ 1.2 mm, which was significantly greater than the 1.2 ⫾ 1.1 mm variance of the concave type (P ⬍ .05). DISCUSSION Some investigators have described variation of shape in ulnar head anatomy. Hyams et al19 noted that moderate correlation existed between ulnar variance and ulnar head peak distance, which is the distance from the most radial point of the ulnar head to the most distally prominent point of the ulnar head along the direction perpendicular to the ulnar longitudinal axis. Schuind et al20 noted there was a trend toward a positive linear relationship between ulnar variance and the angle formed by the ulnar longitudinal axis and a line drawn between the most radial and ulnar points of the ulnar dome. We found that foveal morphology varies individually and that ulnar variance in the flat type was significantly greater than that in the concave type. The anatomic ulnar fovea of the flat type was shallow or often nonexistent, and the surface line of the spherical articular facet of the ulnar head directly continued to the base of the ulnar styloid. We found no significant difference in interaxial distance between the concave and flat types
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FIGURE 5: Relationship between ulnar variance and interaxial distance. Interaxial distance positively correlates with ulnar variance. The correlation coefficient (r) was 0.38.
because both had distinct variation in interaxial distance (Fig. 5). We speculate that this is because other factors such as the TFCC, interosseous membrane, forearm muscle contraction, and forearm bone morphology excluding foveal morphology may influence interaxial distance. Using posteroanterior radiography with the forearm in neutral rotation, we were often able to distinguish the concave from the flat type. The typical concave type showed (1) a double-floor configuration at the anatomic ulnar fovea, in which the cortices of the surrounding C-shaped articular facet were superimposed on the foveal floor; and (2) the clear line of the radial edge of the extensor carpi ulnaris groove. The flat type did not generally show these characteristics (Fig. 6). It has been suggested that the pronosupination axis of the forearm runs distally through the anatomic ulnar fovea5,6 and that the anatomic ulnar fovea is located near the center of curvature of the ulnar head.16 However, our data indicate that the pronosupination axis passes through the ulnar head more medially and farther from the anatomical center with increasing ulnar variance. This finding implies that the axis in the wrist with positive ulnar variance tends to pass more medially near
the base of the ulnar styloid than that in the wrist with neutral or negative variance. This may be related to the finding that the axis runs obliquely from the proximal, radial aspect to the distal, ulnar aspect where the axis gradually orients medially as it runs distally. The fact that the cases with greater interaxial distance showed discrepancy between the anatomical and pronosupination centers raises questions about the point of insertion of the deep fibers. Do the deep fibers insert on a more medial aspect around the axis rather than near the anatomical center, or do they insert around the anatomical center away from the axis and behave in an extrinsic manner? The radioulnar ligaments, consisting of the superficial and deep fibers, are 1 of the important stabilizers of the DRUJ.1 The anatomic ulnar fovea is believed to be the primary attachment site for these deep fibers.2 The degree of development of the anatomic ulnar fovea may influence the thickness of the deep fibers or the frequency of the TFCC injury. Furthermore, a greater cam effect would occur in the ulnar head where the interaxial distance is increased. If the deep fibers attach to the pronosupination center, these may be more prone to injury because of this potential cam effect. Further
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FIGURE 6: Posteroanterior x-rays of the ulnar head of representative cases of A concave type and B flat type. The typical concave type shows a double-floor configuration of the anatomic ulnar fovea (green arrowheads) and a clear line of the radial edge of the extensor carpi ulnaris groove (blue arrowheads). A typical flat type is devoid of any evident depression of the anatomic ulnar fovea and groove.
studies regarding the relationship between foveal TFCC avulsion and foveal morphology will be necessary to verify these hypotheses. This study has several limitations. First, the series of wrists investigated in this study may not represent a normal population because this series contains almost exclusively ulna-positive wrists. Mean ulnar variance in this study was ⫹2.0 mm, whereas mean ulnar variance reported in a Japanese and a white population by means of x-ray was a positive 0.2 mm21 and negative 0.9 mm,20 respectively. We speculate that this discrepancy may be because the subjects were not normal volunteers, but patients with a painful condition in the contralateral side. Second, we could not evaluate the precise shape of the surface of the articular cartilage because the 3-dimensional model created from CT data reflected the shape of only the subchondral bone and bone cortex and not the overlying cartilage. Third, the size of the CT cuts was 1.25 mm (ie, the margin of measurement error), but the difference in average ulnar variance (2.0 mm) and interaxial distance (2.6 mm) was 0.6 mm. This margin of measurement error could in-
fluence the results. This study suggests that ulnar variance is related to foveal morphology and the pronosupination axis. The results of this study could provide a starting point for future studies investigating how foveal morphology relates to the pathology of the DRUJ, such as foveal avulsion of the TFCC. REFERENCES 1. Garcia-Elias M. Soft-tissue anatomy and relationships about the distal ulna. Hand Clin 1998;14:165–176. 2. Stuart PR, Berger RA, Linscheid RL, An KN. The dorsopalmar stability of the distal radioulnar joint. J Hand Surg 2000;25A:689 – 699. 3. Ishii S, Palmer AK, Werner FW, Short WH, Fortino MD. An anatomic study of the ligamentous structure of the triangular fibrocartilage complex. J Hand Surg 1998;23A:977–985. 4. Kleinman WB. Distal radius instability and stiffness: common complications of distal radius fractures. Hand Clin 2010;26:245–264. 5. Kapandji A. Biomechanics of pronation and supination of the forearm. Hand Clin 2001;17:111–122, vii. 6. Youm Y, Dryer RF, Thambyrajah K, Flatt AK, Spraque BL. Biomechanical analyses of forearm pronation-supination and elbow flexion-extension. J Biomech 1979;12:245–255. 7. Hollister AM, Gellman H, Waters RL. The relationship of the interosseous membrane to the axis of rotation of the forearm. Clin Orthop Relat Res 1994;298:272–276.
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8. Palmer AK, Glisson RR, Werner FW. Ulnar variance determination. J Hand Surg 1982;7A:376 –379. 9. Steyers CM, Blair WF. Measuring ulnar variance: a comparison of techniques. J Hand Surg 1989;14A:607– 612. 10. Adams BD. Distal radioulnar joint instability. In: Green D, Hotchkiss R, Pederson WC, eds. Green’s operative hand surgery. 5th ed. New York: Churchill Livingston, 2005:605– 644. 11. Oka K, Doi K, Suzuki K, Murase T, Goto A, Yoshikawa H, et al. In vivo three-dimensional motion analysis of the forearm with radioulnar synostosis treated by the Kanaya procedure. J Orthop Res 2006;24:1028 –1035. 12. Moritomo H, Noda K, Goto A, Murase T, Yoshikawa H, Sugamoto K. Interosseous membrane of the forearm: length change of ligaments during forearm rotation. J Hand Surg 2009;34A:685– 691. 13. Tay SC, van Riet R, Kazunari T, Koff MF, Amrami KK, An KN, et al. A method for in-vivo kinematic analysis of the forearm. J Biomech 2008;41:56 – 62. 14. Tay SC, van Riet R, Kazunari T, Koff MF, Amrami KK, An KN, et al. In-vivo kinematic analysis of forearm rotation using helical axis analysis. Clin Biomech 2010;25:655– 659.
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15. af Ekenstam F, Hagert CG. Anatomical studies on the geometry and stability of the distal radio ulnar joint. Scand J Plast Reconstr Surg 1985;19:17–25. 16. Audette MA, Ferrie FP, Peters TM. An algorithmic overview of surface registration techniques for medical imaging. Med Image Anal 2000;4:201–217. 17. Kinzel GL, Hall AS Jr, Hillberry BM. Measurement of the total motion between two body segments. I. Analytical development. J Biomech 1972;5:93–105. 18. Van Sint Jan S, Salvia P, Hilal I, Sholukha V, Rooze M, Clapworthy G. Registration of 6-DOFs electrogoniometry and CT medical imaging for 3D joint modeling. J Biomech 2002;35: 1475–1484. 19. Hyams E, Yazaki N, Nakamura R, Nakao E, Watanabe K. Radiographic morphology of the ulnar head. Hand Surg 2004;9:175–180. 20. Schuind FA, Linscheid RL, An KN, Chao EY. A normal data base of posteroanterior roentgenographic measurements of the wrist. J Bone Joint Surg 1992;74A:1418 –1429. 21. Nakamura R, Tanaka Y, Imaeda T, Miura T. The influence of age and sex on ulnar variance. J Hand Surg 1991;16B:84 – 88.
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