- Email: [email protected]
Patterns of subchondral bone mineralization in the distal radioulnar joint
Patterns of Subchondral Bone Mineralization in the Distal Radioulnar Joint Riccardo E. Giunta, MD, PhD, Christof Krolak, MD, Edgar Biemer, MD, PhD, Magdalena Müller-Gerbl, MD, PhD, Munich, Germany
Purpose: Studies have shown that it is possible to derive direct knowledge about the actual mechanical conditions of the wrist by analyzing the subchondral mineralization. The aim of the present study was to evaluate the distribution of the subchondral bone mineralization of the distal radioulnar joint (DRUJ) noninvasively in living subjects by using computed tomography (CT) osteoabsorptiometry to gain new information about the long-term loading conditions. Methods: Twenty-two wrist joints were investigated in 11 healthy young subjects by means of CT osteoabsorptiometry. The CT scans of the DRUJ were taken in the axial plane in neutral position of the forearm and in both maximum pronation and supination. The CT datasets of 1.5-mm sections were obtained and then transferred to an image-analyzing system. The subchondral bone plate in each section was isolated, reconstructed in 3 dimensions, and converted into a false color series. Results: The maximum subchondral bone density in the sigmoid notch of the radius was found along the distal border in all wrists. It was located dorsally in 10 wrists, palmarly in 8 wrists, and centrally in 4 wrists. The maximum bone density on the corresponding articular surface of the ulna was found dorsally in 10 cases, centrally in 8 cases, and palmarly in 4 cases. In 13 cases the maximum bone density was found in direct opposition on radius and ulna in neutral position. A statistically significant difference could not be detected in subjects with an ulna minus variance nor in those with a DRUJ angulation greater than 10°. Conclusions: Our results show that in the sigmoid notch the load is transmitted through either the dorsal or palmar parts of the joint. In contrast the maximum bone density on the side of the ulna was found dorsally and centrally. We conclude that the ulna receives the maximum load in neutral position and supination, whereas because of the dorsopalmar translation of the ulnar head the radius may lead the ulna with either its palmar or dorsal borders during pronosupination. The ligamentous apparatus, the shape of the joint, and the ulna variance, however, may influence load transmission. (J Hand Surg 2005;30A:343–350. Copyright © 2005 by the American Society for Surgery of the Hand.) Key words: Wrist, DRUJ, distal radioulnar joint, load, mineralization, biomechanics.
From the Department of Plastic and Reconstructive Surgery, University of Technology, Munich, Germany; and the Institute of Anatomy and the Department of Radiology, Ludwig-Maximilians University, Munich, Germany. Received for publication April 1, 2004; accepted in revised form September 29, 2004. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Priv-Doz. Dr. med. Riccardo E. Giunta, Department of Plastic and Reconstructive Surgery, Rechts der Isar Hospital, University of Technology, Ismaningerstrae 22, 81675 München, Germany. Copyright © 2005 by the American Society for Surgery of the Hand 0363-5023/05/30A02-0017$30.00/0 doi:10.1016/j.jhsa.2004.09.013
The Journal of Hand Surgery
343
344
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
The distal radioulnar joint (DRUJ) is one of the key elements required for forearm pronation and supination. Its close anatomic relationship to the proximal wrist joint influences axial load transmission through the forearm because the percentage of radiocarpal to ulnocarpal load transmission is somewhat dependent on the relative lengths of the ulna and radius (ulnar variance). In cadaveric specimens an iatrogenic lengthening of the ulna of 2.5 mm increases the percentage of load transmission through the ulna from 18% to 42%. On the other hand, a relative shortening of 2.5 mm decreases the load transmitted through the ulna down to 4%.1–3 Ulna shortening also causes a certain amount of joint incongruence within the DRUJ that alters contact areas and load transmission through the joint in laboratory specimens.4 In clinical series it has been shown that ulna shortening is followed by joint incongruence and leads to a certain amount of asymptomatic joint remodeling and radiologic evidence of osteoarthritis in up to 25% of the patients.5 During forearm rotation load transmission occurs not only in an axial direction but also between the sigmoid notch and the medial articular surface of the ulnar head. Because the sigmoid notch has a greater radius of curvature than the ulnar head joint there is incongruency in the DRUJ joint. This allows a large translational component of movement within the joint in a dorsopalmar plane.6,7 In full pronation the palmar ligamentous apparatus seems to become taut only when acting as a restraint to translational movement of the distal radius on the ulnar head.8 The dorsal parts of the ligamentous apparatus are supposed to elongate and therefore are under greater tension in pronation.9,10 Contact surfaces are located mainly on the dorsal aspects of the articular surfaces.8 –10 The reverse is expected in supination. Because of this relatively large incongruence and the subsequent relative wide range of translational movements the contact areas are relatively small and highly dependent on the pronation and supination positioning of the forearm.7,11 Nevertheless a direct evaluation of the actual loading conditions within the DRUJ in the living patient currently is impossible. In our previous studies we could show that an indirect assessment of the loading history in the distal articular surface of the radius is possible in living subjects by means of computed tomography (CT) osteoabsorptiometry.12–18 Major parts of these observations have been confirmed by other workgroups in the meantime.19,20
The aim of the present study was to evaluate subchondral bone mineralization patterns within articular surfaces of the sigmoid notch and the corresponding articular surface of the ulna head in healthy subjects by means of CT osteoabsorptiometry. A further loading history was obtained by repeating the examination with the forearm in neutral position, pronation, and supination. Lastly we examined the degree of ulnar variance and the DRUJ tilt relative to the forearm axis as influencing parameters to mineralization patterns.
Patients and Methods Twenty-two wrist joints of 11 healthy young subjects with no history of trauma or wrist pain were examined by conventional radiographs of the wrist and by CT. Nine men and 2 women with a mean age of 29 years (range, 21–33 y) were examined. The patients all were right handed. Ulna variance was determined on conventional radiographs with the mean measurement being ⫺1.0 mm (⫺3.0 to 1.0 mm). The mean tilt of the DRUJ toward the forearm axis (radial head to mid lunate) measured in conventional radiographs21,22 was ⫹ 8° (⫺5.0° to 25.0°). Subjects with ulna-minus wrists (n ⫽ 11; average, ⫺1.8 mm) and subjects with a DRUJ tilt toward the forearm axis of greater than 10° (n ⫽ 8; average, 15.6° tilt) were analyzed as separate subgroups against the remaining subjects. Because of radiation exposure concerns for healthy young subjects the study was approved by the ethics committee of the Ludwig-Maximilians University in Munich. The subjects were exposed to radiation of a total of 25 to 35 sections depending on the length of the DRUJ. The CT of both wrist joints was performed with the patient lying in a prone position with both arms maximally abducted at the shoulder joint and positioned parallel to the body axis. The CT scans were taken perpendicular to the axis of the DRUJ to provide maximum resolution (Siemens Somatom Plus 4, Erlangen, Germany). Five to 12 axial scans through both DRUJs were performed with a slice thickness of 2.0 mm at 1.5-mm intervals so as to provide improved datasets with overlapping sections for 3-dimensional reconstruction23 (Fig. 1). The field of view chosen was as small as possible to include both DRUJs together with the radius and ulna.23 The joint was examined in neutral position and in maximum pronation and supination.22,23 No intra-articular or intravenous dye was applied. After transfer of CT datasets to an image analyzing system (Analyze;
Giunta et al / Subchondral Bone Mineralization in the DRUJ
345
Figure 1. (A) Axial CT sections are obtained through the DRUJ with the patient lying in the prone position. (B) In each section subchondral bone is isolated with an image analyzing software (yellow line). Then 3-dimensional reconstruction is performed.
Mayo Clinic, Rochester, MN), CT osteoabsorptiometry was performed.12–14 As a first step the distal radius and ulna, which make up the 2 condyles of the DRUJ, are separated, and the articulating bones are reconstructed in 3 dimensions. Both then are rotated to provide a perpendicular view of the joint surface. The subchondral bone plate in each section then is isolated and also reconstructed in 3 dimensions. For densitometric evaluation the maximum bone density within the subchondral bone plate is projected onto the articular surface (maximum intensity projection),14 and the degree of bone mineralization is assessed in steps of 100 HU and converted into false color series. Finally an image of the subchondral bone density is projected onto that of the corresponding bones.14 Direct opposition of subchondral bone mineralization was assessed in the original datasets by using false color series in the various CT sections without separating the articulating bones and without changing their rotation against each other. Our evaluation is based on topographic and semiquantitative parameters intraindividually. The CT osteoabsorptiometry does not provide absolute values for direct interindividual evaluations. The location of peak mineralization is assessed as palmar, dorsal, or central, as well as distal to proximal in the coronal plane. Furthermore the direct opposition of the areas with peak mineralization is assessed in neutral position, full pronation, and full supination. Statistical analysis for nonparametric data was performed by means of Fisher exact test in a statistical software package (SPSS for Windows; SPSS, Chicago, IL).
Results Location of Peak Mineralization The highest mineralization in the sigmoid notch of all subjects was found in the distal marginal rim (Table 1). The peak mineralization was localized dorsally in 10 cases, palmarly in 8 cases, and centrally in 4 cases (Fig. 2). On the ulna head the mineralization maximum was localized dorsally in 10 cases, centrally in 8 cases, and palmarly in the remaining 4 cases (Fig. 3).
Direct Opposition of Peak Mineralization in Various DRUJ Positions In 16 cases peak mineralization of the sigmoid notch and ulna head was found in direct opposition in neutral position of the DRUJ (Fig. 4). Direct opposition of maximum mineralization in full pronation was found in 3 cases and in full supination in the remaining 3 cases.
Intraindividual Results In 8 cases peak mineralization within the sigmoid notch was located identically on both wrists of the subjects, the ulna head showed similar patterns of mineralization bilaterally in 3 cases (Table 1).
Ulna-Minus Wrist Of the 22 subjects, 11 had an ulna-minus wrist (Fig. 5). In these subjects the peak mineralization was localized dorsally in 7 cases, palmarly in 3 cases, and centrally in 1 case. On the ulna head the mineralization
346
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
Table 1. Subjects and Results in the DRUJ Subject Number and Side (n ⴝ 22) 1R 1L 2R 2L 3R 3L 4R 4L 5R 5L 6R 6L 7R 7L 8R 8L 9R 9L 10 R 10 L 11 R 11 L
Gender
Age
Ulnar Variance
Tilt of DRUJ in Relation to Forearm Axis
M M M M M M F F M M M M M M F F M M M M M M
33 33 32 32 30 30 26 26 28 28 21 21 29 29 29 29 33 33 28 28 29 29
⫺2.0 ⫺2.5 0.0 0.0 ⫺1.5 ⫺2.5 0.0 0.0 0.0 0.0 ⫺3.0 ⫺1.5 0.0 0.0 0.0 ⫺1.5 0.0 1.0 ⫺0.5 ⫺1.0 ⫺2.0 ⫺2.0
5° 5° 5° 10° 0° 5° 5° 0° 5° 5° 25° 20° 10° 20° 0° 0° 15° ⫺5° 5° 0° 20° 15°
Position of Peak Mineralization in Sigmoid Notch
Position of Peak Mineralization in Articular Surface of Ulna Head (DRUJ)
Position of Forearm With Peak Mineralization Being in Direct Opposition
Dorsally Dorsally Centrally Centrally Palmarly Palmarly Palmarly Palmarly Dorsally Centrally Dorsally Dorsally Palmarly Palmarly Dorsally Dorsally Dorsally Palmarly Dorsally Dorsally Palmarly Centrally
Dorsally Palmarly Centrally Dorsally Dorsally Centrally Dorsally Centrally Dorsally Palmarly Centrally Palmarly Dorsally Centrally Centrally Centrally Dorsally Dorsally Centrally Centrally Dorsally Palmarly
Neutral Neutral Neutral Neutral Neutral Neutral Full pronation Full pronation Full supination Neutral Full supination Full supination Neutral Neutral Neutral Full pronation Neutral Neutral Neutral Neutral Neutral Neutral
Average age was 29 years; average ulnar variance was ⫺1.0 mm; average tilt of DRUJ was 8°.
maximum was localized dorsally in 3 cases, centrally in 5 cases, and palmarly in the remaining 3 cases. In 8 cases the peak mineralization of the sigmoid notch and ulna head was found in direct opposition when the forearm was in neutral position (Fig. 6). Direct opposition of maximum mineralization in full
pronation was found in 1 case and in full supination in the remaining 2 cases. Neither location of peak mineralization in both sigmoid notch and ulna head nor direct opposition showed major differences against the remaining subjects by means of Fisher exact test.
Figure 2. Patterns of mineralization and frequency in the sigmoid notch. The color saturation represents the absorption in HU (see left bar).
Giunta et al / Subchondral Bone Mineralization in the DRUJ
347
Figure 3. Patterns of mineralization and frequency in the ulna head.
Distal Radioulnar Joint Tilt Seven of 22 subjects had a DRUJ tilt of greater than 10° against the forearm axis (Fig. 5). In these subjects the peak mineralization was localized dorsally
in 3 cases, palmarly in 3 cases, and centrally in 2 cases. On the ulna head the mineralization maximum was localized dorsally in 4 cases, centrally in 2 cases, and palmarly in the remaining 2 cases. In 6 cases
Figure 4. CT sections in false colors through the DRUJ of 3 different wrists. (A) Areas of peak mineralization are in direct opposition in full pronation in 3 cases (14%). (B) Direct opposition of peak mineralization is encountered in full supination in another 3 cases (14%). (C) The most common situation (n ⫽ 16, 73%), with direct opposition of peak bone density areas in neutral position of the DRUJ.
348
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
Figure 5. Location of peak mineralization in the sigmoid notch in all patients and the subgroups with ulna-minus variance or high degree of DRUJ angulation. (B) Location of peak mineralization in the articular surface of the ulna in all patients and the subgroups with ulna-minus variance or high degree of DRUJ angulation.
peak mineralization of the sigmoid notch and ulna head was found in direct opposition in neutral position of the DRUJ (Fig. 6). Direct opposition of maximum mineralization in full supination was found in the remaining 2 cases. No case showed direct opposition in full pronation. Neither location of peak mineralization in both sigmoid notch and ulna head nor direct opposition showed major differences against the remaining subjects by means of Fisher exact test.
Discussion The marked clinical relevance of the DRUJ is based on its anatomic exposure to injuries, especially in those of the distal radius.11,24 –26 Every change in configuration of the articulating bones leads to pathologic joint incongruence, which may lead to degenerative osteoarthritis. This is true not only in posttraumatic malunions of the distal radius with multiplane pathologic tilts but also with a relative lengthening of the ulna caused by partial collapse of the distal radial fragment or as a result of jointleveling procedures such as radius and ulna lengthening or shortening procedures.
Figure 6. Forearm position with direct opposition of peak mineralization in all patients and in the subgroups with ulna-minus variance or high degree of DRUJ angulation.
In laboratory specimens an ulnar shortening of 2 mm causes a decrease in contact areas and an increase in radioulnar separation.4 This was observed especially in cases with a large DRUJ angulation or a sigmoid notch with a depth greater than 1 mm.4,27 Joint remodeling and asymptomatic radiologic evidence of osteoarthritis was observed in 7 of 25 patients with a mean follow-up period of 35 months.5 Our own findings in the distal articular surface of the radius previously had shown statistically different loading patterns for the ulna-plus wrist.21 In the present study neither the nonposttraumatic ulna-minus variance nor the DRUJs with a large angulation showed significant differences. This does not, however, automatically exclude both factors from influencing parameters in clinical posttraumatic cases. From a kinematics viewpoint forearm pronosupination of some 180° occurs as the radius with the closely applied hand rotates around the ulnar head.26,28 –30 This movement is performed around the PRUJ and DRUJ with ligamentous guidance from the interosseous membrane and the triangular fibrocartilage. All skeletal components have to be assessed in pathologic situations of the DRUJ.6,9,32 The ulnar head appears to move distally in pronation and proximally in supination, altering the ulna variance in these extreme rotatory positions of the forearm.33 Additionally there is an increased dorsopalmar translational movement of the ulnar head in the DRUJ as a result of the incongruence dictated by the greater radius of curvature in the sigmoid notch as opposed to the ulnar head.6,7 There is some controversy regarding the tensions produced in the dorsal and palmar radioulnar ligaments during the course of pronsupination.8,9 It is widely accepted, however, that pronation seems to lead to maximal contact areas on the dorsal side of the sigmoid notch and the palmar
Giunta et al / Subchondral Bone Mineralization in the DRUJ
borders of the ulna head and in supination contact areas mainly are localized between palmar aspects of the sigmoid notch and dorsal aspects of the ulna head articular surface.6,8 –10 This physiologic incongruence of the articulating bones together with an extensive translational course lead to very limited contact areas.7,11 Our results confirm these considerations because the patterns of mineralization show either a predominant dorsal mineralization (45%) or a predominant palmar peak mineralization (36%) within the sigmoid notch. The ulna head shows a mainly central or dorsal peak mineralization (each 41%). Our previous studies that showed a strong correlation between peak mineralization and long-term stresses acting on the joint provided useful information on the long-term loading history of the joint.17 On the basis of this data we believe the articular surface of the ulna receives the main load in neutral to supination positions, whereas the sigmoid notch mainly has contact with its dorsal and palmar lips when rotating around the ulna. The ulnar head in the DRUJ seems to receive the main load from the radius on the distal aspects of the joint surface, where it also accumulates the most clinical pathologies.7,33 Our own results show peak mineralization always in the distal parts of the joint’s surface, which supports this hypothesis. The evaluation of CT osteoabsorptiometry in various positions of the wrist showed direct opposition of the regions with peak mineralization mainly in neutral positions of the forearm (73%). We therefore consider the neutral position of the forearm not only as the most frequent position in a long-term history of a patient’s kinematics, but also as the position where the main load is acting. The 3 types of loading: palmar, central, and dorsal, both in the sigmoid notch and the articular surface of the ulnar head, have to be regarded as physiologic. The most frequent is the dorsal loading type in both articulating bones of the DRUJ. In the majority of the cases, however, loading history seems to occur mainly in neutral position of the DRUJ.
4.
5.
6. 7. 8. 9.
10.
11.
12.
13.
14. 15.
16.
17.
18. 19.
References 1. Werner FW, Glisson RR, Murphy DJ, Palmer AK. Force transmission through the distal radioulnar carpal joint: effect of ulnar lengthening and shortening. Handchir Mikrochir Plast Chir 1986;18:304 –308. 2. Palmer AK, Glisson RR, Werner FW. Relationship between ulnar variance and triangular fibrocartilage complex thickness. J Hand Surg 1984;9A:681– 682. 3. Palmer AK, Werner FW, Glisson RR, Murphy DJ. Partial
20.
21.
349
excision of the triangular fibrocartilage complex. J Hand Surg 1988;13A:391–394. Deshmukh SC, Shanahan D, Coulthard D. Distal radioulnar joint incongruity after shortening of the ulna. J Hand Surg 2000;25B:434 – 438. Minami A, Kato H. Ulnar shortening for triangular fibrocartilage complex tears associated with ulnar positive variance. J Hand Surg 1998;23A:904 –908. af Ekenstam F. Anatomy of the distal radioulnar joint. Clin Orthop 1992;275:14 –18. Linscheid RL. Biomechanics of the distal radioulnar joint. Clin Orthop 1992;275:46 –55. Putz R, Giunta R, Müller-Gerbl M. Der ligamentäre Bauplan der Hand. Phys Rehab Kur Med 1995;5:1– 6. Schuind F, An KN, Berglund L, Rey R, Cooney WP 3rd, Linscheid RL, et al. The distal radioulnar ligaments: a biomechanical study. J Hand Surg 1991;16A:1106 –1114. Stuart PR, Berger RA, Linscheid RL, An KN. The dorsopalmar stability of the distal radioulnar joint. J Hand Surg 2000;25A:689 – 699. 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. Muller-Gerbl M, Putz R, Hodapp N, Schulte E, Wimmer B. Computed tomography-osteoabsorptiometry for assessing the density distribution of subchondral bone as a measure of long-term mechanical adaptation in individual joints. Skeletal Radiol 1989;18:507–512. Muller-Gerbl M, Putz R, Kenn R. Demonstration of subchondral bone density patterns by three-dimensional CT osteoabsorptiometry as a noninvasive method for in vivo assessment of individual long-term stresses in joints. J Bone Miner Res 1992;7(suppl 2):411– 418. Muller-Gerbl M. The subchondral bone plate. Adv Anat Embryol Cell Biol 1998;141:III–XI, 1–134. Giunta R, Lower N, Kierse R, Wilhelm K, Muller-Gerbl M. Die Beanspruchung des Radiokarpalgelenks - CT-Untersuchungen der subchondralen Knochendichte in vivo. [Stress on the radiocarpal joint. CT studies of subchondral bone density in vivo] Handchir Mikrochir Plast Chir 1997;29:32–37. Giunta R, Löwer N, Wilhelm K, Kierse R, Rock C, MüllerGerbl M. Altered patterns of subchondral bone mineralization in Kienböck’s disease. J Hand Surg 1997;22B:16 –20. Giunta RE, Krimmer H, Krapohl B, Treutlein G, Lanz U, Muller-Gerbl M. Patterns of subchondral bone mineralization in the wrist after midcarpal fusion. J Hand Surg 1999; 24A:138 –147. Giunta R. Subchondral bone mineralization patterns in Kienbock’s disease. J Hand Surg 2001;26A:561–562. Iwasaki N, Minami A, Miyazawa T, Kaneda K. Force distribution through the wrist joint in patients with different stages of Kienbock’s disease: using computed tomography osteoabsorptiometry. J Hand Surg 2000;25A:870 – 876. Hoogbergen MM, Niessen WJ, Schuurman AH, Spauwen PH, Kauer JM. Subchondral bone mineral density patterns representing the loading history of the wrist joint. J Hand Surg 2002;27B:150 –154. Giunta R, Biemer E, Müller-Gerbl M. Ulna-variance and subchondral bone mineralization patterns in the distal articular surface of the radius. J Hand Surg 2004;29A:835– 840.
350
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
22. Schmitt R, Lanz U. Bildgebende Diagnostik der Hand. Stuttgart: Hippokrates Verlag, 1996:136 –139. 23. Yin Y, McEnery KW, Gilula LA. Computed tomography. Applications and tailored approach. In: Gilula LA, Yin Y, ed. Imaging of the Wrist and Hand. Philadelphia: W.B. Saunders Company, 1996:411– 419. 24. Hagert CG. The distal radioulnar joint. Hand Clin 1987;3:41–50. 25. Hagert CG. The distal radioulnar joint in relation to the whole forearm. Clin Orthop 1992;275:56 – 64. 26. Hagert CG. Distal radius fracture and the distal radioulnar joint—anatomical considerations. Handchir Mikrochir Plast Chir 1994;26:22–26. 27. Sagerman SD, Zogby RG, Palmer AK, Werner FW, Fortino MD. Relative articular inclination of the distal radioulnar joint: a radiographic study. J Hand Surg 1995; 20A:597– 601.
28. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin Orthop 1984;187:26 –35. 29. Kapandji AI, Martin-Bouyer Y, Verdeille S. Etude du carpe au scanner á trois dimensions sous contraintes de pronosupination. [Three-dimensional CT study of the carpus under pronation-supination constraints.] Ann Chir Main Memb Super 1991;10:36 – 47. 30. Lutz J. Perigraphie der Umwendbewegung des Vorderarmes. [Perigraphy of the rotation movements of the forearm.] Anat Anz 1958;105:231–240. 31. Kauer JM. The distal radioulnar joint. Anatomic and functional considerations. Clin Orthop 1992;275:37– 45. 32. Palmer AK, Glisson RR, Werner FW. Ulnar variance determination. J Hand Surg 1982;7:376 –379. 33. Koebke J. A biomechanical and morphological analysis of human hand joints. Adv Anat Embryol Cell Biol 1983;80:1–85.
Purpose: Studies have shown that it is possible to derive direct knowledge about the actual mechanical conditions of the wrist by analyzing the subchondral mineralization. The aim of the present study was to evaluate the distribution of the subchondral bone mineralization of the distal radioulnar joint (DRUJ) noninvasively in living subjects by using computed tomography (CT) osteoabsorptiometry to gain new information about the long-term loading conditions. Methods: Twenty-two wrist joints were investigated in 11 healthy young subjects by means of CT osteoabsorptiometry. The CT scans of the DRUJ were taken in the axial plane in neutral position of the forearm and in both maximum pronation and supination. The CT datasets of 1.5-mm sections were obtained and then transferred to an image-analyzing system. The subchondral bone plate in each section was isolated, reconstructed in 3 dimensions, and converted into a false color series. Results: The maximum subchondral bone density in the sigmoid notch of the radius was found along the distal border in all wrists. It was located dorsally in 10 wrists, palmarly in 8 wrists, and centrally in 4 wrists. The maximum bone density on the corresponding articular surface of the ulna was found dorsally in 10 cases, centrally in 8 cases, and palmarly in 4 cases. In 13 cases the maximum bone density was found in direct opposition on radius and ulna in neutral position. A statistically significant difference could not be detected in subjects with an ulna minus variance nor in those with a DRUJ angulation greater than 10°. Conclusions: Our results show that in the sigmoid notch the load is transmitted through either the dorsal or palmar parts of the joint. In contrast the maximum bone density on the side of the ulna was found dorsally and centrally. We conclude that the ulna receives the maximum load in neutral position and supination, whereas because of the dorsopalmar translation of the ulnar head the radius may lead the ulna with either its palmar or dorsal borders during pronosupination. The ligamentous apparatus, the shape of the joint, and the ulna variance, however, may influence load transmission. (J Hand Surg 2005;30A:343–350. Copyright © 2005 by the American Society for Surgery of the Hand.) Key words: Wrist, DRUJ, distal radioulnar joint, load, mineralization, biomechanics.
From the Department of Plastic and Reconstructive Surgery, University of Technology, Munich, Germany; and the Institute of Anatomy and the Department of Radiology, Ludwig-Maximilians University, Munich, Germany. Received for publication April 1, 2004; accepted in revised form September 29, 2004. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Priv-Doz. Dr. med. Riccardo E. Giunta, Department of Plastic and Reconstructive Surgery, Rechts der Isar Hospital, University of Technology, Ismaningerstrae 22, 81675 München, Germany. Copyright © 2005 by the American Society for Surgery of the Hand 0363-5023/05/30A02-0017$30.00/0 doi:10.1016/j.jhsa.2004.09.013
The Journal of Hand Surgery
343
344
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
The distal radioulnar joint (DRUJ) is one of the key elements required for forearm pronation and supination. Its close anatomic relationship to the proximal wrist joint influences axial load transmission through the forearm because the percentage of radiocarpal to ulnocarpal load transmission is somewhat dependent on the relative lengths of the ulna and radius (ulnar variance). In cadaveric specimens an iatrogenic lengthening of the ulna of 2.5 mm increases the percentage of load transmission through the ulna from 18% to 42%. On the other hand, a relative shortening of 2.5 mm decreases the load transmitted through the ulna down to 4%.1–3 Ulna shortening also causes a certain amount of joint incongruence within the DRUJ that alters contact areas and load transmission through the joint in laboratory specimens.4 In clinical series it has been shown that ulna shortening is followed by joint incongruence and leads to a certain amount of asymptomatic joint remodeling and radiologic evidence of osteoarthritis in up to 25% of the patients.5 During forearm rotation load transmission occurs not only in an axial direction but also between the sigmoid notch and the medial articular surface of the ulnar head. Because the sigmoid notch has a greater radius of curvature than the ulnar head joint there is incongruency in the DRUJ joint. This allows a large translational component of movement within the joint in a dorsopalmar plane.6,7 In full pronation the palmar ligamentous apparatus seems to become taut only when acting as a restraint to translational movement of the distal radius on the ulnar head.8 The dorsal parts of the ligamentous apparatus are supposed to elongate and therefore are under greater tension in pronation.9,10 Contact surfaces are located mainly on the dorsal aspects of the articular surfaces.8 –10 The reverse is expected in supination. Because of this relatively large incongruence and the subsequent relative wide range of translational movements the contact areas are relatively small and highly dependent on the pronation and supination positioning of the forearm.7,11 Nevertheless a direct evaluation of the actual loading conditions within the DRUJ in the living patient currently is impossible. In our previous studies we could show that an indirect assessment of the loading history in the distal articular surface of the radius is possible in living subjects by means of computed tomography (CT) osteoabsorptiometry.12–18 Major parts of these observations have been confirmed by other workgroups in the meantime.19,20
The aim of the present study was to evaluate subchondral bone mineralization patterns within articular surfaces of the sigmoid notch and the corresponding articular surface of the ulna head in healthy subjects by means of CT osteoabsorptiometry. A further loading history was obtained by repeating the examination with the forearm in neutral position, pronation, and supination. Lastly we examined the degree of ulnar variance and the DRUJ tilt relative to the forearm axis as influencing parameters to mineralization patterns.
Patients and Methods Twenty-two wrist joints of 11 healthy young subjects with no history of trauma or wrist pain were examined by conventional radiographs of the wrist and by CT. Nine men and 2 women with a mean age of 29 years (range, 21–33 y) were examined. The patients all were right handed. Ulna variance was determined on conventional radiographs with the mean measurement being ⫺1.0 mm (⫺3.0 to 1.0 mm). The mean tilt of the DRUJ toward the forearm axis (radial head to mid lunate) measured in conventional radiographs21,22 was ⫹ 8° (⫺5.0° to 25.0°). Subjects with ulna-minus wrists (n ⫽ 11; average, ⫺1.8 mm) and subjects with a DRUJ tilt toward the forearm axis of greater than 10° (n ⫽ 8; average, 15.6° tilt) were analyzed as separate subgroups against the remaining subjects. Because of radiation exposure concerns for healthy young subjects the study was approved by the ethics committee of the Ludwig-Maximilians University in Munich. The subjects were exposed to radiation of a total of 25 to 35 sections depending on the length of the DRUJ. The CT of both wrist joints was performed with the patient lying in a prone position with both arms maximally abducted at the shoulder joint and positioned parallel to the body axis. The CT scans were taken perpendicular to the axis of the DRUJ to provide maximum resolution (Siemens Somatom Plus 4, Erlangen, Germany). Five to 12 axial scans through both DRUJs were performed with a slice thickness of 2.0 mm at 1.5-mm intervals so as to provide improved datasets with overlapping sections for 3-dimensional reconstruction23 (Fig. 1). The field of view chosen was as small as possible to include both DRUJs together with the radius and ulna.23 The joint was examined in neutral position and in maximum pronation and supination.22,23 No intra-articular or intravenous dye was applied. After transfer of CT datasets to an image analyzing system (Analyze;
Giunta et al / Subchondral Bone Mineralization in the DRUJ
345
Figure 1. (A) Axial CT sections are obtained through the DRUJ with the patient lying in the prone position. (B) In each section subchondral bone is isolated with an image analyzing software (yellow line). Then 3-dimensional reconstruction is performed.
Mayo Clinic, Rochester, MN), CT osteoabsorptiometry was performed.12–14 As a first step the distal radius and ulna, which make up the 2 condyles of the DRUJ, are separated, and the articulating bones are reconstructed in 3 dimensions. Both then are rotated to provide a perpendicular view of the joint surface. The subchondral bone plate in each section then is isolated and also reconstructed in 3 dimensions. For densitometric evaluation the maximum bone density within the subchondral bone plate is projected onto the articular surface (maximum intensity projection),14 and the degree of bone mineralization is assessed in steps of 100 HU and converted into false color series. Finally an image of the subchondral bone density is projected onto that of the corresponding bones.14 Direct opposition of subchondral bone mineralization was assessed in the original datasets by using false color series in the various CT sections without separating the articulating bones and without changing their rotation against each other. Our evaluation is based on topographic and semiquantitative parameters intraindividually. The CT osteoabsorptiometry does not provide absolute values for direct interindividual evaluations. The location of peak mineralization is assessed as palmar, dorsal, or central, as well as distal to proximal in the coronal plane. Furthermore the direct opposition of the areas with peak mineralization is assessed in neutral position, full pronation, and full supination. Statistical analysis for nonparametric data was performed by means of Fisher exact test in a statistical software package (SPSS for Windows; SPSS, Chicago, IL).
Results Location of Peak Mineralization The highest mineralization in the sigmoid notch of all subjects was found in the distal marginal rim (Table 1). The peak mineralization was localized dorsally in 10 cases, palmarly in 8 cases, and centrally in 4 cases (Fig. 2). On the ulna head the mineralization maximum was localized dorsally in 10 cases, centrally in 8 cases, and palmarly in the remaining 4 cases (Fig. 3).
Direct Opposition of Peak Mineralization in Various DRUJ Positions In 16 cases peak mineralization of the sigmoid notch and ulna head was found in direct opposition in neutral position of the DRUJ (Fig. 4). Direct opposition of maximum mineralization in full pronation was found in 3 cases and in full supination in the remaining 3 cases.
Intraindividual Results In 8 cases peak mineralization within the sigmoid notch was located identically on both wrists of the subjects, the ulna head showed similar patterns of mineralization bilaterally in 3 cases (Table 1).
Ulna-Minus Wrist Of the 22 subjects, 11 had an ulna-minus wrist (Fig. 5). In these subjects the peak mineralization was localized dorsally in 7 cases, palmarly in 3 cases, and centrally in 1 case. On the ulna head the mineralization
346
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
Table 1. Subjects and Results in the DRUJ Subject Number and Side (n ⴝ 22) 1R 1L 2R 2L 3R 3L 4R 4L 5R 5L 6R 6L 7R 7L 8R 8L 9R 9L 10 R 10 L 11 R 11 L
Gender
Age
Ulnar Variance
Tilt of DRUJ in Relation to Forearm Axis
M M M M M M F F M M M M M M F F M M M M M M
33 33 32 32 30 30 26 26 28 28 21 21 29 29 29 29 33 33 28 28 29 29
⫺2.0 ⫺2.5 0.0 0.0 ⫺1.5 ⫺2.5 0.0 0.0 0.0 0.0 ⫺3.0 ⫺1.5 0.0 0.0 0.0 ⫺1.5 0.0 1.0 ⫺0.5 ⫺1.0 ⫺2.0 ⫺2.0
5° 5° 5° 10° 0° 5° 5° 0° 5° 5° 25° 20° 10° 20° 0° 0° 15° ⫺5° 5° 0° 20° 15°
Position of Peak Mineralization in Sigmoid Notch
Position of Peak Mineralization in Articular Surface of Ulna Head (DRUJ)
Position of Forearm With Peak Mineralization Being in Direct Opposition
Dorsally Dorsally Centrally Centrally Palmarly Palmarly Palmarly Palmarly Dorsally Centrally Dorsally Dorsally Palmarly Palmarly Dorsally Dorsally Dorsally Palmarly Dorsally Dorsally Palmarly Centrally
Dorsally Palmarly Centrally Dorsally Dorsally Centrally Dorsally Centrally Dorsally Palmarly Centrally Palmarly Dorsally Centrally Centrally Centrally Dorsally Dorsally Centrally Centrally Dorsally Palmarly
Neutral Neutral Neutral Neutral Neutral Neutral Full pronation Full pronation Full supination Neutral Full supination Full supination Neutral Neutral Neutral Full pronation Neutral Neutral Neutral Neutral Neutral Neutral
Average age was 29 years; average ulnar variance was ⫺1.0 mm; average tilt of DRUJ was 8°.
maximum was localized dorsally in 3 cases, centrally in 5 cases, and palmarly in the remaining 3 cases. In 8 cases the peak mineralization of the sigmoid notch and ulna head was found in direct opposition when the forearm was in neutral position (Fig. 6). Direct opposition of maximum mineralization in full
pronation was found in 1 case and in full supination in the remaining 2 cases. Neither location of peak mineralization in both sigmoid notch and ulna head nor direct opposition showed major differences against the remaining subjects by means of Fisher exact test.
Figure 2. Patterns of mineralization and frequency in the sigmoid notch. The color saturation represents the absorption in HU (see left bar).
Giunta et al / Subchondral Bone Mineralization in the DRUJ
347
Figure 3. Patterns of mineralization and frequency in the ulna head.
Distal Radioulnar Joint Tilt Seven of 22 subjects had a DRUJ tilt of greater than 10° against the forearm axis (Fig. 5). In these subjects the peak mineralization was localized dorsally
in 3 cases, palmarly in 3 cases, and centrally in 2 cases. On the ulna head the mineralization maximum was localized dorsally in 4 cases, centrally in 2 cases, and palmarly in the remaining 2 cases. In 6 cases
Figure 4. CT sections in false colors through the DRUJ of 3 different wrists. (A) Areas of peak mineralization are in direct opposition in full pronation in 3 cases (14%). (B) Direct opposition of peak mineralization is encountered in full supination in another 3 cases (14%). (C) The most common situation (n ⫽ 16, 73%), with direct opposition of peak bone density areas in neutral position of the DRUJ.
348
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
Figure 5. Location of peak mineralization in the sigmoid notch in all patients and the subgroups with ulna-minus variance or high degree of DRUJ angulation. (B) Location of peak mineralization in the articular surface of the ulna in all patients and the subgroups with ulna-minus variance or high degree of DRUJ angulation.
peak mineralization of the sigmoid notch and ulna head was found in direct opposition in neutral position of the DRUJ (Fig. 6). Direct opposition of maximum mineralization in full supination was found in the remaining 2 cases. No case showed direct opposition in full pronation. Neither location of peak mineralization in both sigmoid notch and ulna head nor direct opposition showed major differences against the remaining subjects by means of Fisher exact test.
Discussion The marked clinical relevance of the DRUJ is based on its anatomic exposure to injuries, especially in those of the distal radius.11,24 –26 Every change in configuration of the articulating bones leads to pathologic joint incongruence, which may lead to degenerative osteoarthritis. This is true not only in posttraumatic malunions of the distal radius with multiplane pathologic tilts but also with a relative lengthening of the ulna caused by partial collapse of the distal radial fragment or as a result of jointleveling procedures such as radius and ulna lengthening or shortening procedures.
Figure 6. Forearm position with direct opposition of peak mineralization in all patients and in the subgroups with ulna-minus variance or high degree of DRUJ angulation.
In laboratory specimens an ulnar shortening of 2 mm causes a decrease in contact areas and an increase in radioulnar separation.4 This was observed especially in cases with a large DRUJ angulation or a sigmoid notch with a depth greater than 1 mm.4,27 Joint remodeling and asymptomatic radiologic evidence of osteoarthritis was observed in 7 of 25 patients with a mean follow-up period of 35 months.5 Our own findings in the distal articular surface of the radius previously had shown statistically different loading patterns for the ulna-plus wrist.21 In the present study neither the nonposttraumatic ulna-minus variance nor the DRUJs with a large angulation showed significant differences. This does not, however, automatically exclude both factors from influencing parameters in clinical posttraumatic cases. From a kinematics viewpoint forearm pronosupination of some 180° occurs as the radius with the closely applied hand rotates around the ulnar head.26,28 –30 This movement is performed around the PRUJ and DRUJ with ligamentous guidance from the interosseous membrane and the triangular fibrocartilage. All skeletal components have to be assessed in pathologic situations of the DRUJ.6,9,32 The ulnar head appears to move distally in pronation and proximally in supination, altering the ulna variance in these extreme rotatory positions of the forearm.33 Additionally there is an increased dorsopalmar translational movement of the ulnar head in the DRUJ as a result of the incongruence dictated by the greater radius of curvature in the sigmoid notch as opposed to the ulnar head.6,7 There is some controversy regarding the tensions produced in the dorsal and palmar radioulnar ligaments during the course of pronsupination.8,9 It is widely accepted, however, that pronation seems to lead to maximal contact areas on the dorsal side of the sigmoid notch and the palmar
Giunta et al / Subchondral Bone Mineralization in the DRUJ
borders of the ulna head and in supination contact areas mainly are localized between palmar aspects of the sigmoid notch and dorsal aspects of the ulna head articular surface.6,8 –10 This physiologic incongruence of the articulating bones together with an extensive translational course lead to very limited contact areas.7,11 Our results confirm these considerations because the patterns of mineralization show either a predominant dorsal mineralization (45%) or a predominant palmar peak mineralization (36%) within the sigmoid notch. The ulna head shows a mainly central or dorsal peak mineralization (each 41%). Our previous studies that showed a strong correlation between peak mineralization and long-term stresses acting on the joint provided useful information on the long-term loading history of the joint.17 On the basis of this data we believe the articular surface of the ulna receives the main load in neutral to supination positions, whereas the sigmoid notch mainly has contact with its dorsal and palmar lips when rotating around the ulna. The ulnar head in the DRUJ seems to receive the main load from the radius on the distal aspects of the joint surface, where it also accumulates the most clinical pathologies.7,33 Our own results show peak mineralization always in the distal parts of the joint’s surface, which supports this hypothesis. The evaluation of CT osteoabsorptiometry in various positions of the wrist showed direct opposition of the regions with peak mineralization mainly in neutral positions of the forearm (73%). We therefore consider the neutral position of the forearm not only as the most frequent position in a long-term history of a patient’s kinematics, but also as the position where the main load is acting. The 3 types of loading: palmar, central, and dorsal, both in the sigmoid notch and the articular surface of the ulnar head, have to be regarded as physiologic. The most frequent is the dorsal loading type in both articulating bones of the DRUJ. In the majority of the cases, however, loading history seems to occur mainly in neutral position of the DRUJ.
4.
5.
6. 7. 8. 9.
10.
11.
12.
13.
14. 15.
16.
17.
18. 19.
References 1. Werner FW, Glisson RR, Murphy DJ, Palmer AK. Force transmission through the distal radioulnar carpal joint: effect of ulnar lengthening and shortening. Handchir Mikrochir Plast Chir 1986;18:304 –308. 2. Palmer AK, Glisson RR, Werner FW. Relationship between ulnar variance and triangular fibrocartilage complex thickness. J Hand Surg 1984;9A:681– 682. 3. Palmer AK, Werner FW, Glisson RR, Murphy DJ. Partial
20.
21.
349
excision of the triangular fibrocartilage complex. J Hand Surg 1988;13A:391–394. Deshmukh SC, Shanahan D, Coulthard D. Distal radioulnar joint incongruity after shortening of the ulna. J Hand Surg 2000;25B:434 – 438. Minami A, Kato H. Ulnar shortening for triangular fibrocartilage complex tears associated with ulnar positive variance. J Hand Surg 1998;23A:904 –908. af Ekenstam F. Anatomy of the distal radioulnar joint. Clin Orthop 1992;275:14 –18. Linscheid RL. Biomechanics of the distal radioulnar joint. Clin Orthop 1992;275:46 –55. Putz R, Giunta R, Müller-Gerbl M. Der ligamentäre Bauplan der Hand. Phys Rehab Kur Med 1995;5:1– 6. Schuind F, An KN, Berglund L, Rey R, Cooney WP 3rd, Linscheid RL, et al. The distal radioulnar ligaments: a biomechanical study. J Hand Surg 1991;16A:1106 –1114. Stuart PR, Berger RA, Linscheid RL, An KN. The dorsopalmar stability of the distal radioulnar joint. J Hand Surg 2000;25A:689 – 699. 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. Muller-Gerbl M, Putz R, Hodapp N, Schulte E, Wimmer B. Computed tomography-osteoabsorptiometry for assessing the density distribution of subchondral bone as a measure of long-term mechanical adaptation in individual joints. Skeletal Radiol 1989;18:507–512. Muller-Gerbl M, Putz R, Kenn R. Demonstration of subchondral bone density patterns by three-dimensional CT osteoabsorptiometry as a noninvasive method for in vivo assessment of individual long-term stresses in joints. J Bone Miner Res 1992;7(suppl 2):411– 418. Muller-Gerbl M. The subchondral bone plate. Adv Anat Embryol Cell Biol 1998;141:III–XI, 1–134. Giunta R, Lower N, Kierse R, Wilhelm K, Muller-Gerbl M. Die Beanspruchung des Radiokarpalgelenks - CT-Untersuchungen der subchondralen Knochendichte in vivo. [Stress on the radiocarpal joint. CT studies of subchondral bone density in vivo] Handchir Mikrochir Plast Chir 1997;29:32–37. Giunta R, Löwer N, Wilhelm K, Kierse R, Rock C, MüllerGerbl M. Altered patterns of subchondral bone mineralization in Kienböck’s disease. J Hand Surg 1997;22B:16 –20. Giunta RE, Krimmer H, Krapohl B, Treutlein G, Lanz U, Muller-Gerbl M. Patterns of subchondral bone mineralization in the wrist after midcarpal fusion. J Hand Surg 1999; 24A:138 –147. Giunta R. Subchondral bone mineralization patterns in Kienbock’s disease. J Hand Surg 2001;26A:561–562. Iwasaki N, Minami A, Miyazawa T, Kaneda K. Force distribution through the wrist joint in patients with different stages of Kienbock’s disease: using computed tomography osteoabsorptiometry. J Hand Surg 2000;25A:870 – 876. Hoogbergen MM, Niessen WJ, Schuurman AH, Spauwen PH, Kauer JM. Subchondral bone mineral density patterns representing the loading history of the wrist joint. J Hand Surg 2002;27B:150 –154. Giunta R, Biemer E, Müller-Gerbl M. Ulna-variance and subchondral bone mineralization patterns in the distal articular surface of the radius. J Hand Surg 2004;29A:835– 840.
350
The Journal of Hand Surgery / Vol. 30A No. 2 March 2005
22. Schmitt R, Lanz U. Bildgebende Diagnostik der Hand. Stuttgart: Hippokrates Verlag, 1996:136 –139. 23. Yin Y, McEnery KW, Gilula LA. Computed tomography. Applications and tailored approach. In: Gilula LA, Yin Y, ed. Imaging of the Wrist and Hand. Philadelphia: W.B. Saunders Company, 1996:411– 419. 24. Hagert CG. The distal radioulnar joint. Hand Clin 1987;3:41–50. 25. Hagert CG. The distal radioulnar joint in relation to the whole forearm. Clin Orthop 1992;275:56 – 64. 26. Hagert CG. Distal radius fracture and the distal radioulnar joint—anatomical considerations. Handchir Mikrochir Plast Chir 1994;26:22–26. 27. Sagerman SD, Zogby RG, Palmer AK, Werner FW, Fortino MD. Relative articular inclination of the distal radioulnar joint: a radiographic study. J Hand Surg 1995; 20A:597– 601.
28. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin Orthop 1984;187:26 –35. 29. Kapandji AI, Martin-Bouyer Y, Verdeille S. Etude du carpe au scanner á trois dimensions sous contraintes de pronosupination. [Three-dimensional CT study of the carpus under pronation-supination constraints.] Ann Chir Main Memb Super 1991;10:36 – 47. 30. Lutz J. Perigraphie der Umwendbewegung des Vorderarmes. [Perigraphy of the rotation movements of the forearm.] Anat Anz 1958;105:231–240. 31. Kauer JM. The distal radioulnar joint. Anatomic and functional considerations. Clin Orthop 1992;275:37– 45. 32. Palmer AK, Glisson RR, Werner FW. Ulnar variance determination. J Hand Surg 1982;7:376 –379. 33. Koebke J. A biomechanical and morphological analysis of human hand joints. Adv Anat Embryol Cell Biol 1983;80:1–85.