HAND Surgery

THE-JOURNALOF.......... kL 0 1988 HAND 13A, NUMBER1 SURGERY N AMERICAN VOLUME journal SOCIETY FOR SURGERY OF THE HAND ORIGINAL COMMUNICATIONS Relative motion of selected carpal bones: [cGrouther A kinematic analysis of the normal wrist al The relative motion of selected carpal bones and the radius was studied using five cadaver specimens labeled with metal markersto precisely quantitate their motions. Data was obtained by meansof a combinationof orthoradiography, sonic digitization, and computeranalysis. We conclude that the wrist functions as two carpal rows wiith the distal row bones relatively tightly airman: boundto one another and the proximal row bones less so but still movingtogether. Therefore, we theorize that the proximal row functions as a variable geometryintercalated segmentbetween the distal row and the radius-triangular fibrocartilage. (J HANoSURG 1988;13A:1-10.) L. K. Ruby, MD, W. P. Cooney III, MD, K. N. An, PhD, R. L. Linscheid, MD, and E. Y. S. Chao, PhD, Boston, Mass., and Rochester, Minn. The study of wrist motion, both normal pathologic, has interested investigators since the of the 19th century. 1-3 Before 1895, investiga- consisted of direct visualization of the carpus, indirect methods were not available. In 1896, reported the first radiologic study of a col- i:.:~li! lea’gue’s hand, and Johnson,5 Fisk6 and others, 7’3 stud- ~i[’!i~iiied wrist motion with x-ray examination. Recently, ¯ ~icomputer analysis has been used to increase the ac- :ii~!ii.~!iicuracy and-precision of measurements of wrist ! i~/ik motion. ~" 2o :":~/i Although some of the recent authors’" have studied Fig. 1. Three dimensional carpal bone motion is measured the Section of HandSurgery, Departmentof OrthopedicSur- from a fixed reference of orthogonal radiographs and defined gery, Tufts UniversitySchool of Medicine,Boston, Mass. and the as x,y,z axis system based on the distal radius. Orthopedic BiomeehanicsLaboratory, MayoClinic/Mayo Foun-. ~ clarion, Rochester,Minn. Receivedfor publicationFeb. 9, 1987;accepted in revised formJune individual° carpal motions, none except Delange et al) 10, 1987.,. -. have reported individual carpal bone motion with re- in~nyform have been receivedor will be receivedfrom spect to another carpal using computer analysis. We a commercialparty related directly or indirectly to the subjectof undertook this study to test some of the currently pop- this article. ular theories of wrist function and directly measure Reprint requests: LeonardK. Ruby,MD, Tufts’New England Medical Center, 750 WashingtonSt., Boston, MA02111-1854. intracarpal motion. THEJOURNAL OF HANDSURGERY 1 2 Ruby et al. TheJournal of HAND Fig. 2. Customdesigned tendon loading device and plexiglass biplanar x-raygrid. Theradius andulnar are rigidly mounted to the frame. Tendonforces to movethe wrist is actuated throughcalibrated springs. Fig. 3. Biplanar radiographsdemonstrate "U"-shaped metal Materials and methods staples embeddedinto each carpal bone(scaphoid, lunate, Froma group of 12 fresh-frozen humanforearm spec- triquetrum, capitate, and hamate)to serve as markersfor imens, five were chosen for study that were free of tracing carpal bonemotion. A, xy or anteroposteriorview. disease and traumatic changes. The age range of the B, xz or lateral view. five specimens was from 23 to 55 years. There were four males and one female. By meansof the techniques surface of the radius. The dorsal wrist capsule was described below, in four wrists the radius, scaphoid, lunate, triquetmm, and capitate were labeled; in the opened, preserving major dorsal carpal ligaments. markers were placed into the appropriate carpal bones fifth wrist, the radius, trapezoid, capitate, hamate,and triquetrum were labeled. The trapezium was not labeled and the dorsal capsule was closed. Each specimen was in any wrist. then rigidly mountedin a holding device with the radius and ulna fixed by two Steinmanpins (Fig: 2). To apply The motions of the selected carpal bones were de- active force across the wrist and to movethe wrist under termined using biplanar orthoradiographs (two radio- gramspositioned at 90° to one another and fixed relative active tendon loading, each musculotendinousunit that to the x-ray source) (Fig. 1). The selected bones were crossed the wrist was loaded by attaching heavy (25 pound test) to each tendon group. The degree labeled with heavy duty "U"-shaped staples (Crafts- load was based on forearm muscle cross-sectional area man, Sears RobuckCo., Chicago, Ill.) embeddedinto each carpal bone. Four identifiable positions on each studies. The tension was delivered by calibrated springs staple served as reference points to record carpal bone attached to the .holding device. Thus, active tendon motion. A separate T marker was placed on the dorsal loading was simulated to determine wrist motion and carpal bone alignment under phys!ologic conditions. oumalof ;,.- /ol. 13A,No. 1 Relative motion of selected carpal bones3 JRGERY: January1988 Fig. 4. Screwdisplacement axis defines individual carpal bonemotion along rotation andtranslation axis systems,in- dividualcarpal bones rotate andtranslate similarto the threads of a screw. The loaded specimen was brought to the x-ray room where a fixed distance orthogonal x-ray system was available. Biplanar radiographs were taken in five po- s .!ons for each specimen:neutral, flexion, extension, r~.dial deviation, and ulnar deviation. Thesewrist positions were obtained by using the spring loaded tendons 1~ ¯ to simulate physiologic motion and force. The load Fig. 5. Wrist motiondefined by x,y,z, axis system. Xaxis on each tendon group was measured in each position. alignedparallelwith the shaft of radius, positiveend proximal: This averaged 10.6 kg total load for each of the five y axis alignedtransversely across the carpusat 90° to the x specimens, axis, ppsitiveend radial. Z axis aligned90 ° to boththe x and Multidirectional wrist positions were measuredfrom y axis. ~edmetal ~:,~. biplanar films (Fig. 3, Aand B) taken througha custom lunate, designedplexiglass x-ray grid that providedlocalization xkers for and:three_dimensionalorientation of the carpal bones. ior view. Relative motions betweentwo selected carpal bones._ 2"he data points from the U markers and T marker were or between an individual carpal bone and the radius then digiti2ed with the sonic digitizer (Graf/PenScience during wrist motion were described using the concept Accessories Corp., Southport, Conn.) and the Apple of screw displacementaxis.Z~’ zz The screwaxis concept ;ule was IIe computer(USI International, Brisane, Calif.). The implies that each carpal boneboth rotates and translates digitized two-dimensionalcoordinates for each of the nts. The along its ownaxis system, whichis not fixed but moves al bones four identifiable "points" of each U marker and four up and down, similar to the threads of a screw aaen was I "points" of the T markersin both anteriorposterior (x,y) (Fig. 4). In this study, carpal bones were shownto both ae radius and lateral (x,z) planes were then used to reconstruct rotate and translate along an individual "screwaxis" as the corresponding three-dimensional coordinates in ro apply the ,wrist movedfrom flexion to extensionor from radial ist under space. Since the markerswere rigidly fixed to the bones, to ulnar deviation although the predominantmotion was unit that ,~ilithei definedlocationby andmarkers orientation alongthe of specific each labeledaxissystem bone ~see was rotatory. :avy line To ensure that these observations were accurate and egree of below). These data were analyzed by PDP11/34 (Dig- reproducible, repeat testing was performed. The exact ~nal area ital Equipment Corp., Maynard, MA.) computer pro- alignment of carpal bones was described by an. x,y,z t springs gramsfor calculation of the relative three-dimensional axis system (Fig. 5). This system was based on the motionof individual carpal bones in space and applied : tendon bone structure of the distal radius. The x axis was de- tion and to carpal bone kinematics during maximumwrist fined as that axis that lies along the shah of the radius aditions. motion. 4 Ruby et al. The Journal HAND SURG Y axis Global 1 Y axis Y axis $caphotd-Lunate 24* Fig. 6. A, Pronation-supinationof carpal bone(s) occursabout thex axis longitudinal.B, Flexion-extensionof carpal bone(s) occursabout the y axis (transverse).C, Radial-ulnardeviation Fig. 7. A, Wrist-flexion-extensionis 112° and occursabout.:’ of carpal bone(s)occurs about the z axis (or vertical axis). the y axis. B, Scapholunatemotion is (24°) and occurs madlyabout the y axis. C, Lunotriquetral motionis andoccurs primadly about the y axis (flexion-extensionaxis). with the positive end pointing in the proximaldirection. The y axis was defined as that axis that lies perpendicular to the x axis with the positive end pointing in the ulnar rotation (Fig. 6, C). Wrist motionof the capitate radial direction in the right hand. Thez axis is that axis with respect to the distal radius is called global motion.’ formedby the "right hand rule" of free body analysis; Motionbetween the proximal and distal carpal rows that is, perpendicular to both x and y axes, with the referred to as intercarpal motion. Individual. positive end pointing in the palmardirection in the right tion (e.g., motion betweenthe scaphoid and the hand. In clinical terms of wrist motion, the x axis rep- within the proximal carpal row) is called resents the axis of longitudinal rotation (or pronation- bone motion. The results of relative motion of carpal

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