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Kinematics of the distal radioulnar joint in rheumatoid arthritis: An In vivo study using centrode analysis
Kinematics of the Distal Radioulnar Joint in Rheumatoid Arthritis: An In Vivo Study Using Centrode Analysis Peter I. Weiler, MD, Earl R. Bogoch, MD, Toronto, Ontario, Canada The kinematics of the distal radioulnar joint were examined using the method of centrode analysis in vivo. A group of normal subjects was studied along with a group of rheumatoid arthritis patients who had distal radioulnar joint involvement. Serial computed tomographic scans were obtained through the distal radioulnar joint of nine subjects (10 wrists) in varying degrees of pronation and supination. For normal subjects, the movement that occurs in a stable distal radioulnar joint is not erratic and the center of rotation lies within a well-defined area. When subjects with rheumatoid arthritis were analyzed, it was determined that early in the disease process bone erosions may occur in the sigmoid notch of the distal radius. When the joint contour in this region is maintained, the kinematics are not markedly altered. Erosion involving the dorsal border of the sigmoid notch of the radius is associated with subluxation of the distal radioulnar joint. The ulna becomes dorsally positioned relative to the radius, and significant alteration in the kinematics of the distal radioulnar joint occurs. (J Hand Surg 1995;20A:937-943.)
The wrist and hand are c o m m o n l y affected by rheumatoid arthritis and its effects can be Crippling. Part of the functional hand unit includes the distal radioulnar joint (DRUJ). It has been estimated that DRUJ involvement occurs in up to 30% of patients suffering f r o m rheumatoid arthritis. 1 Involvement of the D R U J follows a predictable pattern of destruction, ultimately resulting in an unstable dysfunctional wrist. Proliferative synovitis causes destruction of cartilage, bone, and ligaments,
From the Division of Orthopaedic Surgery, Department of Surgery, Toronto East General and Orthopaedic Hospital and the Division of Orthopaedic Surgery, Department of Surgery, The Wellesley Hospital, Toronto, Ontario, Canada. Receivedfor publicationJan. 2, 1992; acceptedin revisedformApril 13, 1995. No benefits in any form have been received or will be receivedfrom a commercialparty related directly or indirectly to the subject of this article. Reprint requests: Dr. E.R. Bogoch, Division of Orthopaedic Surgery, Rm. 429, E.K. Jones Building, The Wellesley Hospital, 160 Wellesley Street East, Toronto,Ontario, Canada M4Y 1J3.
leading to a loss of static wrist stabilizers. 2 Supination of the hand and carpus relative to the radius and ulna 3 leads to an apparent dorsal prominence of the distal ulna, which, along with tenosynovitis of the extensor tendon sheath, can produce rupture of one or more extensor tendons. This loss of dynamic wrist stabilizers can sometimes progress to anterior and ulnar subluxation of the carpus relative to the radius. The result can be a painful, weakened wrist with limited supination, and sometimes limited pronation, as a result of D R U J synovitis and subluxation. The constellation of these s y m p t o m s and signs has been well described b y Backdahl, 4 who coined the term "caput ulnae syndrome." A great deal of information exists concerning the p a t h o l o g i c changes of the wrist afflicted with rheumatoid arthritis. However, limited information exists concerning how these changes alter the kinematics of the DRUJ. Joint motion can be accurately characterized by identifying the center of rotation of one body relative to the other. 5 During pronation and supination of the foreThe Journal of Hand Surgery
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Weiler and Bogoch / Kinematics of the Distal Radioulnar Joint
arm, the radius rotates relative to the ulna. In addition, translation occurs between the two bones and, consequently, the instant center of rotation is not a fixed point but rather describes a locus called a centrode. The kinematics of the normal wrist have been studied by several investigators in vitro6.7; however, a review of the literature failed to reveal any study that has attempted to correlate these findings in vivo. This study determines how the mechanics of the DRUJ are altered in rheumatoid arthritis. First, a technique was developed that was suitable for determining the kinematics of the DRUJ in vivo based on the method of centrode analysis. Then, a group of normal subjects was studied and the results were compared to a previous in vitro investigation. Finally, the technique was applied to a group of patients with rheumatoid arthritis in which the DRUJ was involved.
Materials and Methods A total of 10 wrists in 9 patients were scanned and analyzed. There were four normal subjects and five patients with rheumatoid arthritis. One patient in the rheumatoid arthritis group with bilateral disease had both wrists studied; all other subjects had only a single wrist studied. The normal subjects had no history of prior injury to the wrist and had no complaint of wrist pain. Each of the rheumatoid patients had involvement of the wrist and DRUJ; however, the severity varied from moderate inflammation only to more severe involvement corresponding to the caput ulnae syndrome. There were three women and one man in the normal group and five women in the rheumatoid arthritis group. The average age of the normal subjects was 34 years. The rheumatoid arthritis group was significantly older, with an average age of 53 years (p = .05). Serial computed tomography (CT) scans were obtained through the DRUJ of subjects, with the wrists adjusted in varying degrees of pronation and supination. These images were used to determine the centrode pattern. Subjects were positioned prone on the movable scan table with their arms maximally elevated. The wrist was placed in a neutral position and a scout film of the distal forearm was obtained to locate the DRUJ. Using the external laser cursor of the scanner, the level of the DRUJ was identified on the subject's distal forearm using an elastic band. In this way, it was possible to reposition the limb to relocate the DRUJ, ensuring that the same level was scanned repeatedly. A total of five CT scan images were obtained for each subject: full pronation, midpronation, neutral, midsupination, and full supination. Standard bone window routines were used (Fig. 1).
Processing of the images was similar to the method outlined by King et al. 6 for the analysis of cadaver extremities. For each subject, the CT image of the wrist in neutral position was chosen first and traced a total of eight times. Then a grid consisting of eight standard marker points was applied to the images of the radius and ulna, respectively. Tracings of the radius and ulna were then made for each of the four remaining scans. The traced images were then superimposed upon the template scan and the corresponding grid of marker points was transferred. The grid points for each of the traced images were then digitized using a standard graphics tablet (resolution, 0.025 mm) 8interfaced into a personal computer to yield a set of Cartesian coordinates that described the relative position of the radius and ulna for each position. To minimize errors, each image was independently traced, contour matched, and digitized eight times. The digitized data were processed using a computer program specifically written in BASIC for the project. There were a total of five images for each subject, yielding a total of four motion arcs and,
Figure 1. Composite of five computed tomography scans obtained from a typical normal subject.
The Journal of Hand Surgery / Vol. 20A No. 6 November 1995 hence, four centers of rotation. In addition, the magnitudes of the angles subtending each motion arc were computed. Calculations were performed using standard formulas. A graphics routine was included to draw a composite of the five individual CT images along with the resulting centrode pattern (Fig. 2). The accuracy and precision of the method have been studied extensively.912 It has been shown that reliable results can be obtained provided the magnitude of individual motion arcs exceeds 10~ ',13 For several subjects, it was determined on initial review that one or more of the incremental motion arcs was less than 10 ~ For these cases, the data for the intermediate CT scans were not included in the kinematic calculations. Although this resulted in a fewer number of individual motion arcs for some subjects, this ensured that all motion arcs included in the analysis were in excess of 10 ~ In this way, the precision of the resulting instant center calculations was preserved. As a final check on the global reliability of the technique, all subjects' CT images were traced, contour matched, and digitized at a remote time interval by a second, independent observer blinded to each subject's diagnosis. The resulting pairs of data for incremental motion arc angles and instant centers of rotation were then compared following Shrout and Fleiss' recommendations, using the F-statistic 14 to compute the interclass correlation coefficient. Based on their technique, the aggregate interclass correlation coefficients for the computed instant centers of rotation and the motion arc angles were 67% and 95%, respectively. Thus, it was felt that the method was reliable in terms of predicting the biomechanical behavior of the DRUJ during forearm rotation for the subjects studied. In addition to the kinematic analysis outlined above, the CT scans were analyzed to determine the magnitude of dorsal subluxation of the ulna relative to the
939
radius for three positions--maximum supination, neutral, and maximum pronation. There are several methods outlined in the literature for this purpose15-i9; however, we used a modified method in order to minimize the confounding effect of resorption of bony landmarks (Fig. 3). A single line was drawn along the lateral border of the radius. A second line was then drawn perpendicular to the first line to intersect Lister's tubercle. A circle was then constructed of an appropriate radius of curvature to overlie the sigmoid notch of the distal radius. The distance between the circle and the line drawn through Lister's tubercle was measured for the two positions. This measurement was then divided by the diameter of the inscribed circle. The ratio was converted to a percentage that expressed the magnitude of dorsal subluxation for each subject. A negative value of this measurement would correspond to no subluxation, whereas an increasingly positive value corresponded to increasing severity of subluxation. Quantitative comparison of results between the two groups was performed using standard statistical formulas based on a double-sided t-test. Results were deemed to be significant if p < .05.
Results The average total range of motion was compared among the groups along with the individual averages for pronation and supination (Fig. 4). For the normal group, the average total range of motion was 133 ~. The average amounts of supination and pronation were roughly equal at 70 ~ and 63 ~, respectively. The average total range of motion in the rheumatoid group was lower compared to the normal group. The average amount of supination was significantly lower in the rheumatoid group (p < .01). The individual centers of rotation were analyzed based on their location relative to the geometric area
line - 1 - - - /
~
Lister's tubercle line - 2
radius of curvature of distal ulna- R c
dorsalsubluxation = E Figure 2. Example of the graphic output from the computer program, illustrating the centrode pattern for a typical normal subject.
~'
2-Ro
],100O/o
Figure 3. Graphic technique for determining the magnitude of dorsal subluxation of the ulna relative to the radius.
940 1@1
Weiler and Bogoch / Kinematics of the Distal Radioulnar Joint D~
75 50 26 0
i l l i I ' l l -60 9 9 -75
I I
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N2
N3
" N4
I I i
R1 P~ SUBJECT
I
R3-r
R3-1
R4
R5
IIPRONATION =SUPINATION I
Figure 4. Range of motion for pronation and supination for all subjects studied. N, normal subjects; R, rheumatoid patients.
circumscribing the head of the ulna. In the normal group all but one were found to lie within this area (15 of 16). This was consistent with the in vitro data of King et al. 6 Conversely, in the rheumatoid patient group, fewer centers of rotation were found to lie within this area (13 of 17). In addition, as illustrated in the following examples, there was substantial subjectto-subject variability, which appeared to correlate with the severity of the erosive changes within the DRUJ. Erosions were observed in the anterior and dorsal borders of the sigmoid notch of the radius. In three wrists with minor anterior erosions, the centrode pattern was similar to that of the normal subjects (Fig. 5).
With more extensive deformation of the DRUJ, associated with loss of the articular cartilage space and osteophyte and cyst formation, the joint kinematics were still relatively preserved (Fig. 6). However, with erosion of the dorsal border of the sigmoid notch of the radius, the position of the ulna relative to the radius was altered (Fig. 7A). The resulting kinematics were profoundly erratic (Fig. 7B). Thus, it appeared that a normal or near-normal contour of the sigmoid notch may be required to maintain joint stability and normal motion. Finally, the magnitude of dorsal subluxation was measured using the method outlined above, with a positive value indicating subluxation. The more positive the value, the larger the degree of subluxation. The values for the three positions of full supination, neutral, and full pronation were analyzed first for the normal group. The amount of dorsal subluxation was maximum in pronation and minimum in supination. The values for all three positions of each group were averaged to yield a single value representing the mean dorsal subluxation over the entire arc of movement (Fig. 8). None of the subjects in the normal group had any degree of subluxation. In the rheumatoid group, there was a tendency toward dorsal subluxation, however, the results were not statistically significant. The two patients with the largest amount of subluxation (R1 and R2) were those with erosions in the region of the dorsal border of the sigmoid notch of the radius.
Discussion To fully describe the centrode for a particular joint, the relative position of the two bones must be known continuously during a particular movement. From the mathematical function relating the relative position of the bodies, the centrode can be determined2 As an
B Figure 5. Results from a rheumatoid patient with minor inflammatory changes. (A) Note the location of the erosive changes on the anterior aspect of the radius within the distal radioulnar joint. (B) When erosion is minor, the centrode pattern is similar to that of normal subjects.
The Journal of Hand Surgery / Vol. 20A No. 6 November 1995
941
B
Figure 6. Results from a rheumatoid patient with moderate erosive changes. (A) More extensive deformation of the DRUJ is associated with loss of articular cartilage space and osteophyte and cyst formation. (B) However, the joint kinematics are still relatively preserved.
Figure 7. Results from a rheumatoid patient with severe inflammatory changes. (A) With erosion of the dorsal border of the sigmoid notch of the radius (cross-hatched area), the position of the ulna relative to the radius is altered. (B) The resulting kinematics are profoundly erratic.
942
Weiler and Bogoch / Kinematics of the Distal Radioulnar Joint
% - Sul~mcaUon
-40
N1
N2
N3
N4
R1
R2
R~r
R3-1
114
1:15
SUBJECT
Figure 8. Magnitude of dorsal subluxation for both groups averaged over the total arc of motion. None of the subjects in the normal group shows any degree of subluxation. In the rheumatoid group, there is a tendency toward dorsal subluxation.
approximation, a continuous movement can be divided into a finite set of discrete motion arcs. For each motion arc, a single center of rotation can be computed. When the centers of rotation for each motion arc are connected, an approximation of the true centrode is obtained. In a previous study using centrode analysis, King et al. analyzed the normal DRUJ in five cadaver limbs mounted in an adjustable apparatus. 6 Serial CT scans were obtained and analyzed to determine the range of motion and the normal centrode patterns. The average passive range of motion for the arc of motion from hyperpronation to hypersupination was about 190 ~ The pattern of the centrodes was generally consistent with all instant centers lying within the geometric area circumscribing the head of the ulna. Thus, for a normal, stable wrist, the centers of rotation should be located close to each other within this predefined area. Conversely, if their location varied considerably, it would imply that the joint motion was erratic, corresponding to an unstable DRUJ. In the present study, for the normal group in vivo, all but one instant center were found to lie within this area. This was consistent with the in vitro data of King et al. ~ In the present study, the average amount of supination and pronation were roughly equal, at 70 ~ and 63 ~, respectively. These values are somewhat smaller than the in vitro data reported by King et al.6; however, their data were based on passive movements of cadaver wrists fitted into an externally applied positioning jig, compared with our study in which the movements were active.
In the present study, the average total range of motion was 133 ~ in the normal group. This value is somewhat smaller than the generally accepted normal range of 180 ~ quoted in standard texts on clinical examination, using a pencil held in the clenched fist with the elbow flexed at 90o. 20However, it should be noted that this clinical measurement does not represent movement occurring solely at the DRUJ. Rather, it represents a sum total of the individual contributions from each of the joints interposed between the elbow and the hand (ie, the proximal and distal radioulnar joints, the radiocarpal, midcarpal, and carpometacarpal joints). Centrode analysis has been applied, in the past, to various joints in the body, including the elbow, the lumbar spine, and the knee. The technique provides a complete and accurate description of the kinematics occurring between two bodies. However, it does have certain limitations. First, the precision of the method can be adversely affected if the magnitude of the rotation occurring during discrete motion arcs is small. 9-13In this study, this effect was minimal as the magnitude of all individual motion arcs was ensured to be no less than 10 ~ It has been suggested previously that during pronation and supination translation occurs along the longitudinal axis o f the forearm. 21 Thus, within the DRUJ, the movement is not purely planar, but rather three-dimensional in nature. With centrode analysis, it is assumed that motion occurs only in a single plane. This may affect the accuracy of our results. In a previous study by Epner et al., the effect of pronation and supination on ulnar variance was measured in vitro using cadaver extremities. = With the wrist in a relaxed position, the change in ulnar variance from pronation to supination was determined to be, on average, about 1 ram. Thus, the effect of translation along the long axis of the forearm is small and likely would not affect the accuracy of our results significantly. Third, the study was imperfectly controlled for the ages of the control subjects compared to the patient group, but there is no reason to expect that this variable would have altered the observed results. Finally, only a small number of subjects were analyzed. The application of statistical analysis in this setting may have limitations. Nonetheless, certain useful observations were made concerning the kinematics of the normal wrist and the altered kinematics in some rheumatoid arthritis patients with anatomic lesions of the DRUJ.
The Journal of Hand Surgery / Vol. 20A No. 6 November 1995 The authors gratefullyacknowledgeMs. Marge Henke for her assistance in the processing of the computed tomography scan image.
References 1. Nalebuff EA, Feldon PG, Millender LH. Rheumatoid arthritis in the hand and wrist. In: Green DR ed. Operative hand surgery. 2nd ed. New York: Churchill Livingstone, 1988:1655-784. 2. O'Donovan TM, Ruby LK. The distal radioulnar joint in rheumatoid arthritis. Hand Clin North Am 1989;5:249-56. 3. Hastings DE, Evans J. Rheumatoid wrist deformity and its relationship to ulnar drift. J Bone Joint Surg 1975; 57A:930-4. 4. Backdahl M. The caput ulnae syndrome in rheumatoid arthritis: a study of the morphology, abnormal anatomy, and clinical picture. Acta Rheumatol Scand 1963;5:1-75. 5. Reuleaux F. The kinematics of machinery: outline of a theory of machines. New York: Dover Publications, 1963. 6. King GJ, McMurtry RY, Rubenstein JD, Gertzbein SD. Kinematics of the distal radioulnar joint. J Hand Surg 1986;11A:798-804. 7. Caret JR Fischer LR Gonon GP, Dimnet J. Etude cinematique de la prosupination au niveau des articulations radiocubitalea. Bull Assoc Anat (Nancy) 1976;60:279-95. 8. Scriptel SPD series graphics tablets: user's manual. Columbus, OH: Scriptel Corporation, 1985. 9. Woltring HJ, Huiskes R, DeLange A, Veldpaus FE. Finite centroid and analytical axis estimation from noisy landmark measurements in the study of human joint kinematics. J Biomech 1985;18:379-89. 10. Panjabi M. Centers and angles of rotation of body joints: a study of errors and optimization. J Biomech 1979; 12:911-20. 11. Panjabi M, Goel VK, Walter SD. Errors in kinematic parameters of a planar joint: guidelines for optimal experimental design. J Biomech 1982;15:537-44.
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12. Bryant JT, Wevers HW, Lowe PJ. One parameter model for error in instantaneous center of rotation estimates. J Biomech 1984;17:317-23. 13. Gertzbein SD, Chan KH, Tile M, Seligman J, Kapasouri A. Moire patterns: an accurate technique for determination of the locus of the centers of rotation. J Biomech 1985; 18:501-9. 14. Shrout PE, Fleiss JL. Interclass correlations: uses in assessing rater reliability. Psychol Bull 1979;86:420-8. 15. Cone RO, Szabo R, Resnick D, Gelberman R, Taleisnik J, Gilula LA. Computed tomography of the normal radioulnar joints. Invest Radiol 1983;18:541-5. 16. Mino DE, Palmer AK, Levinsohn EM. The role of radiography in the diagnosis of subluxation and dislocation of the distal radioulnar joint. J Hand Surg 1983;8:23-31. 17. Mino DE, Palmer AK, Levinsohn EM. Radiography and computerized tomography in the diagnosis of incongruity of the distal radioulnar joint. J Bone Joint Surg 1985; 67A:247-52. 18. Space TC, Louis DS, Francis I, Braunstein EM. CT findings in distal radioulnar dislocation. J Comput Assist Tomogr 1986;10:689-90. 19. Wechsler RJ, Wehbe MA, Rifkin MD, Edeiken J, Branch HM. Computed tomography diagnosis of distal radioulnar subluxation. Skeletal Radiol 1987;16:1-5. 20. Hoppenfeld S. Physical examination of the spine and extremities. Norwalk, CT: Appleton-Century-Crofts, 1976: 50-1. 21. Kapandji IA. The physiology of the joints. Vol. 1. Upper limbs. 6th ed. Edinburgh: Churchill Livingstone, 1982:98-129. 22. Epner RA, Bowers WH, Guilford WB. Ulnar variance: the effect of wrist positioning and roentgen filming technique. J Hand Surg 1982;7:298-305.
The wrist and hand are c o m m o n l y affected by rheumatoid arthritis and its effects can be Crippling. Part of the functional hand unit includes the distal radioulnar joint (DRUJ). It has been estimated that DRUJ involvement occurs in up to 30% of patients suffering f r o m rheumatoid arthritis. 1 Involvement of the D R U J follows a predictable pattern of destruction, ultimately resulting in an unstable dysfunctional wrist. Proliferative synovitis causes destruction of cartilage, bone, and ligaments,
From the Division of Orthopaedic Surgery, Department of Surgery, Toronto East General and Orthopaedic Hospital and the Division of Orthopaedic Surgery, Department of Surgery, The Wellesley Hospital, Toronto, Ontario, Canada. Receivedfor publicationJan. 2, 1992; acceptedin revisedformApril 13, 1995. No benefits in any form have been received or will be receivedfrom a commercialparty related directly or indirectly to the subject of this article. Reprint requests: Dr. E.R. Bogoch, Division of Orthopaedic Surgery, Rm. 429, E.K. Jones Building, The Wellesley Hospital, 160 Wellesley Street East, Toronto,Ontario, Canada M4Y 1J3.
leading to a loss of static wrist stabilizers. 2 Supination of the hand and carpus relative to the radius and ulna 3 leads to an apparent dorsal prominence of the distal ulna, which, along with tenosynovitis of the extensor tendon sheath, can produce rupture of one or more extensor tendons. This loss of dynamic wrist stabilizers can sometimes progress to anterior and ulnar subluxation of the carpus relative to the radius. The result can be a painful, weakened wrist with limited supination, and sometimes limited pronation, as a result of D R U J synovitis and subluxation. The constellation of these s y m p t o m s and signs has been well described b y Backdahl, 4 who coined the term "caput ulnae syndrome." A great deal of information exists concerning the p a t h o l o g i c changes of the wrist afflicted with rheumatoid arthritis. However, limited information exists concerning how these changes alter the kinematics of the DRUJ. Joint motion can be accurately characterized by identifying the center of rotation of one body relative to the other. 5 During pronation and supination of the foreThe Journal of Hand Surgery
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938
Weiler and Bogoch / Kinematics of the Distal Radioulnar Joint
arm, the radius rotates relative to the ulna. In addition, translation occurs between the two bones and, consequently, the instant center of rotation is not a fixed point but rather describes a locus called a centrode. The kinematics of the normal wrist have been studied by several investigators in vitro6.7; however, a review of the literature failed to reveal any study that has attempted to correlate these findings in vivo. This study determines how the mechanics of the DRUJ are altered in rheumatoid arthritis. First, a technique was developed that was suitable for determining the kinematics of the DRUJ in vivo based on the method of centrode analysis. Then, a group of normal subjects was studied and the results were compared to a previous in vitro investigation. Finally, the technique was applied to a group of patients with rheumatoid arthritis in which the DRUJ was involved.
Materials and Methods A total of 10 wrists in 9 patients were scanned and analyzed. There were four normal subjects and five patients with rheumatoid arthritis. One patient in the rheumatoid arthritis group with bilateral disease had both wrists studied; all other subjects had only a single wrist studied. The normal subjects had no history of prior injury to the wrist and had no complaint of wrist pain. Each of the rheumatoid patients had involvement of the wrist and DRUJ; however, the severity varied from moderate inflammation only to more severe involvement corresponding to the caput ulnae syndrome. There were three women and one man in the normal group and five women in the rheumatoid arthritis group. The average age of the normal subjects was 34 years. The rheumatoid arthritis group was significantly older, with an average age of 53 years (p = .05). Serial computed tomography (CT) scans were obtained through the DRUJ of subjects, with the wrists adjusted in varying degrees of pronation and supination. These images were used to determine the centrode pattern. Subjects were positioned prone on the movable scan table with their arms maximally elevated. The wrist was placed in a neutral position and a scout film of the distal forearm was obtained to locate the DRUJ. Using the external laser cursor of the scanner, the level of the DRUJ was identified on the subject's distal forearm using an elastic band. In this way, it was possible to reposition the limb to relocate the DRUJ, ensuring that the same level was scanned repeatedly. A total of five CT scan images were obtained for each subject: full pronation, midpronation, neutral, midsupination, and full supination. Standard bone window routines were used (Fig. 1).
Processing of the images was similar to the method outlined by King et al. 6 for the analysis of cadaver extremities. For each subject, the CT image of the wrist in neutral position was chosen first and traced a total of eight times. Then a grid consisting of eight standard marker points was applied to the images of the radius and ulna, respectively. Tracings of the radius and ulna were then made for each of the four remaining scans. The traced images were then superimposed upon the template scan and the corresponding grid of marker points was transferred. The grid points for each of the traced images were then digitized using a standard graphics tablet (resolution, 0.025 mm) 8interfaced into a personal computer to yield a set of Cartesian coordinates that described the relative position of the radius and ulna for each position. To minimize errors, each image was independently traced, contour matched, and digitized eight times. The digitized data were processed using a computer program specifically written in BASIC for the project. There were a total of five images for each subject, yielding a total of four motion arcs and,
Figure 1. Composite of five computed tomography scans obtained from a typical normal subject.
The Journal of Hand Surgery / Vol. 20A No. 6 November 1995 hence, four centers of rotation. In addition, the magnitudes of the angles subtending each motion arc were computed. Calculations were performed using standard formulas. A graphics routine was included to draw a composite of the five individual CT images along with the resulting centrode pattern (Fig. 2). The accuracy and precision of the method have been studied extensively.912 It has been shown that reliable results can be obtained provided the magnitude of individual motion arcs exceeds 10~ ',13 For several subjects, it was determined on initial review that one or more of the incremental motion arcs was less than 10 ~ For these cases, the data for the intermediate CT scans were not included in the kinematic calculations. Although this resulted in a fewer number of individual motion arcs for some subjects, this ensured that all motion arcs included in the analysis were in excess of 10 ~ In this way, the precision of the resulting instant center calculations was preserved. As a final check on the global reliability of the technique, all subjects' CT images were traced, contour matched, and digitized at a remote time interval by a second, independent observer blinded to each subject's diagnosis. The resulting pairs of data for incremental motion arc angles and instant centers of rotation were then compared following Shrout and Fleiss' recommendations, using the F-statistic 14 to compute the interclass correlation coefficient. Based on their technique, the aggregate interclass correlation coefficients for the computed instant centers of rotation and the motion arc angles were 67% and 95%, respectively. Thus, it was felt that the method was reliable in terms of predicting the biomechanical behavior of the DRUJ during forearm rotation for the subjects studied. In addition to the kinematic analysis outlined above, the CT scans were analyzed to determine the magnitude of dorsal subluxation of the ulna relative to the
939
radius for three positions--maximum supination, neutral, and maximum pronation. There are several methods outlined in the literature for this purpose15-i9; however, we used a modified method in order to minimize the confounding effect of resorption of bony landmarks (Fig. 3). A single line was drawn along the lateral border of the radius. A second line was then drawn perpendicular to the first line to intersect Lister's tubercle. A circle was then constructed of an appropriate radius of curvature to overlie the sigmoid notch of the distal radius. The distance between the circle and the line drawn through Lister's tubercle was measured for the two positions. This measurement was then divided by the diameter of the inscribed circle. The ratio was converted to a percentage that expressed the magnitude of dorsal subluxation for each subject. A negative value of this measurement would correspond to no subluxation, whereas an increasingly positive value corresponded to increasing severity of subluxation. Quantitative comparison of results between the two groups was performed using standard statistical formulas based on a double-sided t-test. Results were deemed to be significant if p < .05.
Results The average total range of motion was compared among the groups along with the individual averages for pronation and supination (Fig. 4). For the normal group, the average total range of motion was 133 ~. The average amounts of supination and pronation were roughly equal at 70 ~ and 63 ~, respectively. The average total range of motion in the rheumatoid group was lower compared to the normal group. The average amount of supination was significantly lower in the rheumatoid group (p < .01). The individual centers of rotation were analyzed based on their location relative to the geometric area
line - 1 - - - /
~
Lister's tubercle line - 2
radius of curvature of distal ulna- R c
dorsalsubluxation = E Figure 2. Example of the graphic output from the computer program, illustrating the centrode pattern for a typical normal subject.
~'
2-Ro
],100O/o
Figure 3. Graphic technique for determining the magnitude of dorsal subluxation of the ulna relative to the radius.
940 1@1
Weiler and Bogoch / Kinematics of the Distal Radioulnar Joint D~
75 50 26 0
i l l i I ' l l -60 9 9 -75
I I
-25
4011
N1
N2
N3
" N4
I I i
R1 P~ SUBJECT
I
R3-r
R3-1
R4
R5
IIPRONATION =SUPINATION I
Figure 4. Range of motion for pronation and supination for all subjects studied. N, normal subjects; R, rheumatoid patients.
circumscribing the head of the ulna. In the normal group all but one were found to lie within this area (15 of 16). This was consistent with the in vitro data of King et al. 6 Conversely, in the rheumatoid patient group, fewer centers of rotation were found to lie within this area (13 of 17). In addition, as illustrated in the following examples, there was substantial subjectto-subject variability, which appeared to correlate with the severity of the erosive changes within the DRUJ. Erosions were observed in the anterior and dorsal borders of the sigmoid notch of the radius. In three wrists with minor anterior erosions, the centrode pattern was similar to that of the normal subjects (Fig. 5).
With more extensive deformation of the DRUJ, associated with loss of the articular cartilage space and osteophyte and cyst formation, the joint kinematics were still relatively preserved (Fig. 6). However, with erosion of the dorsal border of the sigmoid notch of the radius, the position of the ulna relative to the radius was altered (Fig. 7A). The resulting kinematics were profoundly erratic (Fig. 7B). Thus, it appeared that a normal or near-normal contour of the sigmoid notch may be required to maintain joint stability and normal motion. Finally, the magnitude of dorsal subluxation was measured using the method outlined above, with a positive value indicating subluxation. The more positive the value, the larger the degree of subluxation. The values for the three positions of full supination, neutral, and full pronation were analyzed first for the normal group. The amount of dorsal subluxation was maximum in pronation and minimum in supination. The values for all three positions of each group were averaged to yield a single value representing the mean dorsal subluxation over the entire arc of movement (Fig. 8). None of the subjects in the normal group had any degree of subluxation. In the rheumatoid group, there was a tendency toward dorsal subluxation, however, the results were not statistically significant. The two patients with the largest amount of subluxation (R1 and R2) were those with erosions in the region of the dorsal border of the sigmoid notch of the radius.
Discussion To fully describe the centrode for a particular joint, the relative position of the two bones must be known continuously during a particular movement. From the mathematical function relating the relative position of the bodies, the centrode can be determined2 As an
B Figure 5. Results from a rheumatoid patient with minor inflammatory changes. (A) Note the location of the erosive changes on the anterior aspect of the radius within the distal radioulnar joint. (B) When erosion is minor, the centrode pattern is similar to that of normal subjects.
The Journal of Hand Surgery / Vol. 20A No. 6 November 1995
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B
Figure 6. Results from a rheumatoid patient with moderate erosive changes. (A) More extensive deformation of the DRUJ is associated with loss of articular cartilage space and osteophyte and cyst formation. (B) However, the joint kinematics are still relatively preserved.
Figure 7. Results from a rheumatoid patient with severe inflammatory changes. (A) With erosion of the dorsal border of the sigmoid notch of the radius (cross-hatched area), the position of the ulna relative to the radius is altered. (B) The resulting kinematics are profoundly erratic.
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Weiler and Bogoch / Kinematics of the Distal Radioulnar Joint
% - Sul~mcaUon
-40
N1
N2
N3
N4
R1
R2
R~r
R3-1
114
1:15
SUBJECT
Figure 8. Magnitude of dorsal subluxation for both groups averaged over the total arc of motion. None of the subjects in the normal group shows any degree of subluxation. In the rheumatoid group, there is a tendency toward dorsal subluxation.
approximation, a continuous movement can be divided into a finite set of discrete motion arcs. For each motion arc, a single center of rotation can be computed. When the centers of rotation for each motion arc are connected, an approximation of the true centrode is obtained. In a previous study using centrode analysis, King et al. analyzed the normal DRUJ in five cadaver limbs mounted in an adjustable apparatus. 6 Serial CT scans were obtained and analyzed to determine the range of motion and the normal centrode patterns. The average passive range of motion for the arc of motion from hyperpronation to hypersupination was about 190 ~ The pattern of the centrodes was generally consistent with all instant centers lying within the geometric area circumscribing the head of the ulna. Thus, for a normal, stable wrist, the centers of rotation should be located close to each other within this predefined area. Conversely, if their location varied considerably, it would imply that the joint motion was erratic, corresponding to an unstable DRUJ. In the present study, for the normal group in vivo, all but one instant center were found to lie within this area. This was consistent with the in vitro data of King et al. ~ In the present study, the average amount of supination and pronation were roughly equal, at 70 ~ and 63 ~, respectively. These values are somewhat smaller than the in vitro data reported by King et al.6; however, their data were based on passive movements of cadaver wrists fitted into an externally applied positioning jig, compared with our study in which the movements were active.
In the present study, the average total range of motion was 133 ~ in the normal group. This value is somewhat smaller than the generally accepted normal range of 180 ~ quoted in standard texts on clinical examination, using a pencil held in the clenched fist with the elbow flexed at 90o. 20However, it should be noted that this clinical measurement does not represent movement occurring solely at the DRUJ. Rather, it represents a sum total of the individual contributions from each of the joints interposed between the elbow and the hand (ie, the proximal and distal radioulnar joints, the radiocarpal, midcarpal, and carpometacarpal joints). Centrode analysis has been applied, in the past, to various joints in the body, including the elbow, the lumbar spine, and the knee. The technique provides a complete and accurate description of the kinematics occurring between two bodies. However, it does have certain limitations. First, the precision of the method can be adversely affected if the magnitude of the rotation occurring during discrete motion arcs is small. 9-13In this study, this effect was minimal as the magnitude of all individual motion arcs was ensured to be no less than 10 ~ It has been suggested previously that during pronation and supination translation occurs along the longitudinal axis o f the forearm. 21 Thus, within the DRUJ, the movement is not purely planar, but rather three-dimensional in nature. With centrode analysis, it is assumed that motion occurs only in a single plane. This may affect the accuracy of our results. In a previous study by Epner et al., the effect of pronation and supination on ulnar variance was measured in vitro using cadaver extremities. = With the wrist in a relaxed position, the change in ulnar variance from pronation to supination was determined to be, on average, about 1 ram. Thus, the effect of translation along the long axis of the forearm is small and likely would not affect the accuracy of our results significantly. Third, the study was imperfectly controlled for the ages of the control subjects compared to the patient group, but there is no reason to expect that this variable would have altered the observed results. Finally, only a small number of subjects were analyzed. The application of statistical analysis in this setting may have limitations. Nonetheless, certain useful observations were made concerning the kinematics of the normal wrist and the altered kinematics in some rheumatoid arthritis patients with anatomic lesions of the DRUJ.
The Journal of Hand Surgery / Vol. 20A No. 6 November 1995 The authors gratefullyacknowledgeMs. Marge Henke for her assistance in the processing of the computed tomography scan image.
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