Kinematics of the midcarpal and radiocarpal joints in radioulnar deviation: an in vitro study

PURPOSE: Carpal kinematics have been studied widely yet remain difficult to understand fully. The noninvasive measurement of carpal kinematics through medical imaging has become popular. Studies have shown that with radial deviation the scaphoid and lunate flex whereas the capitate moves radiodorsally relative to the lunate. This study investigated the midcarpal and radiocarpal contributions to radial and ulnar deviation of the wrist. This was accomplished through noninvasive characterization of the scaphoid, lunate, and capitate using 3-dimensional medical imaging of the wrist in radial and ulnar deviation. METHODS: Eight fresh-frozen and thawed cadaveric wrists were used in an experimental set-up that positioned the wrist through spring-scale actuation of the 4 wrist flexor and extensor tendon groups. The wrists were scanned by computed tomography in neutral and full radial and ulnar deviation. Body mass-based local coordinate systems were used to track the motion of the capitate, lunate, and scaphoid with the radius as a fixed reference. Helical axis motion and Euler angles were calculated from neutral to radial and ulnar deviation for the capitate relative to the radius, lunate, and scaphoid and for the lunate and scaphoid relative to the radius. RESULTS: The capitate, scaphoid, and lunate moved in a characteristic manner relative to the radius and to one another. Radial and ulnar deviation occurred primarily in the midcarpal joint. Midcarpal motion accounted for 60% of radial deviation and 86% of ulnar deviation. In radial deviation the proximal row flexed and the capitate extended; the converse was true in ulnar deviation. CONCLUSIONS: Radioulnar deviation (in-plane motion) occurred mostly through the midcarpal joint, with a lesser contribution from the radiocarpal joint. The results of our study agree with previous investigations that found the scaphoid and lunate flex in radial deviation (out-of-plane motion) relative to the radius whereas the capitate extends (out-of-plane motion) relative to the scaphoid/lunate (with the converse occurring in ulnar deviation). Our study shows how these out-of-plane motions combine to produce in-plane wrist radioulnar deviation. The use of 3-dimensional visualization greatly aids in the understanding of these motions. The results of our study may be useful clinically in understanding the consequences of isolated midcarpal fusions in the treatment of wrist instability.     

In vivo radiocarpal kinematics and the dart thrower's motion

BACKGROUND: Wrist motion is dependent on the complex articulations of the scaphoid and lunate at the radiocarpal joint. However, much of what is known about the radiocarpal joint is limited to the anatomically defined motions of flexion, extension, radial deviation, and ulnar deviation. The purpose of the present study was to determine the three-dimensional in vivo kinematics of the scaphoid and lunate throughout the entire range of wrist motion, with special focus on the dart thrower's wrist motion, from radial extension to ulnar flexion. METHODS: The three-dimensional kinematics of the capitate, scaphoid, and lunate were calculated from serial computed tomography scans of both wrists of fourteen healthy male subjects (average age, 25.6 years; range, twenty-two to thirty-four years) and fourteen healthy female subjects (average age, 23.6 years; range, twenty-one to twenty-eight years), which yielded data on a total of 504 distinct wrist positions. RESULTS: The scaphoid and lunate primarily flexed or extended in all directions of wrist motion, and their rotation varied linearly with the direction of wrist motion (R2= 0.90 and 0.82, respectively). Scaphoid and lunate motion was significantly less along the path of the dart thrower's motion than in any other direction of wrist motion (p < 0.01 for both carpal bones). The scaphoid and lunate translated radially (2 to 4 mm) when extended, but they did not translate appreciably when flexed. CONCLUSIONS: The dart thrower's path defined the transition between flexion and extension rotation of the scaphoid and lunate, and it identified wrist positions at which scaphoid and lunate motion approached zero. These findings indicate that this path of wrist motion confers a unique degree of radiocarpal stability and suggests that this direction, rather than the anatomical directions of wrist flexion-extension and radioulnar deviation, is the primary functional direction of the radiocarpal joint.     

Capitate-based kinematics of the midcarpal joint during wrist radioulnar deviation: an in vivo three-dimensional motion analysis

PURPOSE: The purpose of this study was to obtain qualitative and quantitative information regarding in vivo 3-dimensional (3D) kinematics of the midcarpal joint during wrist radioulnar deviation (RUD). METHODS: We studied the in vivo kinematics of the midcarpal joint during wrist RUD in the right wrists of 10 volunteers by using a technology without radioactive exposure. The magnetic resonance images were acquired during RUD. The capitate was registered with the scaphoid, the lunate, and the triquetrum by using a volume registration technique. Animations of the relative motions of the midcarpal joint were created and accurate estimates of the relative orientations of the bones and axes of rotation (AORs) of each motion were obtained. RESULTS: The scaphoid, lunate, and triquetrum motions relative to the capitate during RUD were found to be similar, describing a rotational motion around the axis obliquely penetrating the head of the capitate in almost a radial extension/ulnoflexion plane of motion of the wrist. The AORs of the scaphoid, the lunate, and the triquetrum were located closely in space. In the axial plane the AORs of the scaphoid, lunate, and triquetrum formed a radially and palmarly opening angle of 43 degrees +/- 7 degrees, 41 degrees +/- 11 degrees, and 42 degrees +/- 14 degrees with the wrist flexion/extension axis, respectively. CONCLUSIONS: This study reports the in vivo 3D measurements of midcarpal motion relative to the capitate. Isolated midcarpal motion during RUD could be approximated to be a rotation in a plane of a radiodorsal/ulnopalmar rotation of the wrist, which may coincide with a motion plane of one of the most essential human wrist motions, known as the dart-throwing motion.     

The effects of wrist distraction on carpal kinematics

Changes in carpal kinematics under wrist distraction were studied in fresh cadaveric specimens. A magnetic tracking device measured kinematic motions of the scaphoid, lunate, and third metacarpal relative to the fixed radius in 3 planes of passive motion (coronal, sagittal, and "dart throwers") under progressive distraction loads. The change in percent contribution of the radiocarpal and midcarpal joints was calculated. Radiocarpal motion during extension was decreased as increasing traction was applied, but it increased with flexion. Motion of the scaphoid relative to the lunate was smaller in the oblique plane, resulting in less radiocarpal motion than in the sagittal plane. In the coronal plane, traction had little effect on radial deviation, but ulnar angulation of the scaphoid was greater with ulnar deviation of the wrist. These results suggest that different degrees of tension exist in the palmar and dorsal ligaments with the wrist under traction and during different planes of wrist motion. If wrist motion is desired during fixed traction, such as used clinically with external fixation, the dart-throwers motion (wrist extension with radial deviation and wrist flexion with ulnar deviation) appears to have the least impact on radiocarpal motion. If greater radiocarpal motion is desired, however, such as during postoperative mobilization, flexion-extension and radioulnar deviation will create more radiocarpal motion than the dart-thrower's motion.     

部分腕骨融合术或切除术对腕关节运动影响的实验研究

目的 研究临床常用的部分腕骨融合术或切除术对腕关节运动的影响程度。方法 将１２侧新鲜上肢处理后,固定于特制的测试架上,在腕背部打入２根或多根克氏针,作舟头骨、舟大小多角骨、舟月骨、月三解骨、桡月骨、ｆｏｕｒ ｃｏｒｎｅｒ、头月骨融合术、舟骨切除＋ｆｏｕｒ ｃｏｒｎｅｒ、舟骨切除＋头月融合术。观测腕关节正常运动活动范围,及作上述不同部分腕骨融合术后腕关节屈曲、伸腕、尺偏、桡偏度数。结果 桡舟月骨融合     

Reliability of carpal angle determinations

The radioscaphoid, radiolunate, and radiocapitate angles of nine lateral projections of the wrist (three in flexion, three in extension, and three in neutral position) of three fresh cadaver specimens were measured. Seven orthopedic surgeons (six hand surgeons and one orthopedic surgeon) made the measurements with a standard goniometer using both the axial and tangential methods of angle determination. The overall standard deviation for all measurements was 5.2 degrees, and no significant difference in variability between axial and tangential methods was found. By comparing the same angles from different wrist positions, the amount of flexion-extension motion of the capitate, scaphoid, and lunate with respect to the radius was estimated. To assess the accuracy of such a method of carpal motion determination, a more accurate stereoradiographic method of analysis of carpal kinematics was utilized. The overall estimated error of this standard goniometric method of carpal motion determination averaged 7.4 degrees.     

Radiocarpal fusion

Limited wrist fusion is a common and often effective method of treatment for many painful wrist conditions. When post-traumatic, inflammatory and noninflammatory arthritis affects only the articular surfaces of the proximal carpal joint, a limited radiocarpal fusion can be considered. Specific indications are painful arthritis following distal radial fractures, rheumatoid arthritis with ulnar shift of the carpus, scapholunate instability with radioscaphoid arthritis, and stage IV Kienbock's disease. It is necessary for the midcarpal joint surfaces to be essentially normal. Either a radioscapholunate or radiolunate fusion can be performed, depending on the underlying condition. Up to 70 degrees of wrist flexion-extension can be obtained after a radioscapholunate fusion. Keys to a successful postoperative result are proper alignment of the scaphoid and lunate, use of bone graft or bone graft substitute and careful positioning of internal fixation devices. Evidence of radiographic union is usually seen by eight weeks. Nonunion rates are quoted to be from 10 to 20%.     

Sagittal wrist motion of carpal bones following intraarticular fractures of the distal radius

Forty patients (mean age, 37 years) with intraarticular C2 and C3 Colles fractures were treated by open reduction, internal fixation and bone grafting. At a mean follow-up of 8 years radiocarpal and midcarpal motion was evaluated, the depth of the articular surface of the distal radius in the sagittal plane was measured and the presence of arthritis was noted. The fractures healed with a mean palmar tilt of 6 degrees , a mean ulnar tilt of 18 degrees and ulna variance within 1 mm of the contralateral side. The depth of the articular surface of the distal radius was 1.3 mm greater than the uninvolved side. Measurement of carpal bone angles relative to the radius in maximum flexion and extension revealed lunate extension of 23 degrees , lunate flexion of 15 degrees , capitate extension of 62 degrees , capitate flexion of 40 degrees . There was a significant correlation between articular surface depth and radiocarpal motion.     

晚期月骨无菌性坏死舟骨环形征的解剖学及生物力学研究

目的明确稳定舟骨近极的韧带及断裂后桡腕关节面应力的改变,阐明舟骨环形征的临床意义. 方法实验分为两部分,分别通过5侧上肢标本的解剖学观察,确定稳定舟骨近极的韧带;通过桡侧、尺侧屈腕肌腱及桡侧、尺侧伸腕肌腱,垂直加载12 kg负荷5分钟,应用压敏薄膜及FPD-305E、FPD-306E系统,分别测量腕关节中立、掌屈、背伸、尺偏及桡偏时,正常及韧带断裂后舟骨窝、月骨窝应力的变化. 结果解剖学观察发现,稳定舟骨近极的韧带为:桡舟头韧带、长桡月韧带及舟月骨间韧带,其中长桡月韧带和舟月骨间韧带起到限制舟骨近极向背侧移位的作用.生物力学研究结果表明,在稳定舟骨近极的韧带断裂后,背伸位时,舟骨窝桡侧亚区应力(0.90±0.43)与正常(0.85±0.15)无差异,但掌侧(0.59±0.20)、尺侧(0.52±0.05)及背侧亚区(0.58±0.23)应力较正常(相对应力为0.77±0.13、0.75±0.08、0.68±0.09)减小;中立、掌屈、桡偏及尺偏位时,舟骨窝内各亚区应力与正常相比增大或无差异;而月骨窝在中立位时,各亚区的应力增大;掌屈、背伸、桡偏及尺偏位时,各亚区的应力减小或无差异. 结论在月骨无菌性坏死ⅢB期,舟骨窝承受的负荷增加,在治疗方法的选择上,应注意矫正舟骨的旋转半脱位,防止后期出现桡舟关节创伤性关节炎.     

In vivo scaphoid, lunate, and capitate kinematics in flexion and in extension

Carpal kinematics have been previously limited to in vitro models with cadaveric specimens. Using a newly developed markerless bone registration algorithm, we noninvasively studied the in vivo kinematics of the capitate, scaphoid, and lunate during wrist extension and flexion in both wrists of 5 men and 5 women. Computed tomography volume images were acquired in neutral and in 2 positions in both extension and flexion. The 3-dimensional kinematics of the capitate, scaphoid, and lunate relative to the radius were the determined. Scaphoid and lunate rotations differed for flexion and extension but were found to vary linearly with capitate rotation. In flexion the scaphoid contributed 73% of capitate motion and the lunate contributed 46%. In extension the scaphoid contributed 99% of capitate motion and the lunate contributed 68%. Contributions of the scaphoid and lunate to wrist extension were 15% greater than values reported in previous in vitro studies, while scaphoid and lunate contributions to wrist flexion were more similar to previous studies. The findings support a relative "engagement" of the scaphoid, capitate, and lunate during wrist extension. The only difference between male and female kinematics was a more distal location of the rotation axes; we believe this was due to a difference in carpal bone size, not gender. This study reports the 3-dimensional in vivo measurement of carpal motion using a noninvasive technology. This technique may prove useful in the study of more complex motions of the hand and wrist and of the abnormal kinematics that occur following ligamentous injury.     

2007 IFSSH committee report of wrist biomechanics committee: biomechanics of the so-called dart-throwing motion of the wrist

The dart-throwing motion (DTM) plane can be defined as a plane in which wrist functional oblique motion occurs, specifically from radial extension to ulnar flexion. Most activities of daily living are performed using a DTM. The DTM utilizes the midcarpal joint to a great extent. Scaphotrapezio-trapezoidal anatomy and kinematics may be important factors that cause a DTM to be a more stable and controlled motion. During a DTM, there is less scaphoid and lunate motion than during pure flexion-extension or radioulnar deviation. Clinically, a DTM at the plane approximately 30 degrees to 45 degrees from the sagittal plane allows continued functional wrist motion while minimizing radiocarpal motion when needed for rehabilitation.     

Distal scaphoid excision after radioscaphoid arthrodesis

Radioscaphoid and radioscapholunate arthrodeses are effective surgical procedures for the treatment of nonsalvageable and isolated radiocarpal arthritis. These procedures, however, limit wrist motion significantly as the immobile scaphoid bridges the remaining midcarpal joint. A cadaver study of radioscaphoid arthrodesis followed by distal scaphoid excision was undertaken. Range of motion after radioscaphoid K-wire fixation alone demonstrated a 58% decrease in the preoperative flexion-extension arc to 60 degrees. After distal scaphoid excision (with the radioscaphoid pins still in place) the flexion-extension arc increased to 122 degrees or 86% of the preoperative range of motion; most of the increase in motion occurred at the midcarpal joint. Distal scaphoid excision releases the midcarpal joint following radioscaphoid fixation and results in a significantly greater wrist motion. If the results of this cadaver study are extrapolated to clinical practice the addition of this step to the previously described procedures of radioscaphoid or radioscapholunate arthrodesis addresses their major limitation, restricted motion.     

Kienbock's disease: diagnosis and treatment

Kienbock's disease, or osteonecrosis of the lunate, can lead to chronic, debilitating wrist pain. Etiologic factors include vascular and skeletal variations combined with trauma or repetitive loading. In stage I Kienbock's disease, plain radiographs appear normal, and bone scintigraphy or magnetic resonance imaging is required for diagnosis. Initial treatment is nonoperative. In stage II, sclerosis of the lunate, compression fracture, and/or early collapse of the radial border of the lunate may appear. In stage IIIA, there is more severe lunate collapse. Because the remainder of the carpus is still uninvolved, treatment in stages II and IIIA involves attempts at revascularization of the lunate-either directly (with vascularized bone grafting) or indirectly (by unloading the lunate). Radial shortening in wrists with negative ulnar variance and capitate shortening or radial-wedge osteotomy in wrists with neutral or positive ulnar variance can be performed alone or with vascularized bone grafting. In stage IIIB, palmar rotation of the scaphoid and proximal migration of the capitate occur, and treatment addresses the carpal collapse. Surgical options include scaphotrapeziotrapezoid or scaphocapitate arthrodesis to correct scaphoid hyperflexion. In stage IV, degenerative changes are present at the midcarpal joint, the radiocarpal joint, or both. Treatment options include proximal-row carpectomy and wrist arthrodesis.     

In vivo three-dimensional wrist motion analysis using magnetic resonance imaging and volume-based registration.

This study represents a new attempt to non-invasively analyze three-dimensional motions of the wrist in vivo. A volume-based registration method using magnetic resonance imaging (MRI) was developed to avoid radiation exposure. The primary aim was to evaluate the accuracy of volume-based registration and compare it with surface-based registration. The secondary aim was to evaluate contributions of the scaphoid and lunate to global wrist motion during flexion-extension motion (FEM), radio-ulnar deviation (RUD) and radial-extension/ulnoflexion, "dart-throwing" motion (DTM) in the right wrists of 12 healthy volunteers. Volume-based registration displayed a mean rotation error of 1.29 degrees +/-1.03 degrees and a mean translation error of 0.21+/-0.25 mm and was significantly more accurate than surface-based registration in rotation. Different patterns of contribution of the scaphoid and lunate were identified for FEM, RUD, and DTM. The scaphoid contributes predominantly in the radiocarpal joint during FEM, in the midcarpal joint during RUD and almost equally between these joints during DTM. The lunate contributes almost equally in both joints during FEM and predominantly in the midcarpal joint during RUD and DTM.     

Changes in patterns of scaphoid and lunate motion during functional arcs of wrist motion induced by ligament division

PURPOSE: To determine the in vitro motion of the scaphoid and lunate during wrist circumduction and wrist dart-throw motions and to see how these motions change after the ligamentous stabilizers of the scaphoid and lunate are sectioned in a manner simulating scapholunate instability. METHODS: Twenty-one fresh-frozen cadaver forearms were moved through a dart-throw motion and a circumduction motion using a wrist joint simulator. Scaphoid and lunate motion were measured with the wrist ligaments intact and after sectioning of the scapholunate interosseous ligament, the scaphotrapezium ligament, and the radioscaphocapitate ligament. RESULTS: In the intact wrist the scaphoid and lunate moved more during circumduction than during the dart-throw motion. With ligamentous sectioning the scaphoid flexed more and the lunate extended more during both the circumduction and dart-throw motions. During the circumduction motion both before and after sectioning the global motion of the scaphoid was greater than that of the lunate. After sectioning the scaphoid motion increased and the lunate motion decreased. CONCLUSIONS: The scaphoid and lunate motions were observed to change remarkably after ligamentous sectioning. The observed changes in carpal motion correlate with the clinical observation that after ligamentous injury arthritic changes occur in the radioscaphoid joint and not in the radiolunate joint. Analysis of the injured wrist in positions that combine flexion-extension and radial-ulnar deviation may allow noninvasive diagnosis of specific wrist ligament injuries.     

Partial arthrodesis of the wrist: An investigation in cadavers

Partial arthrodesis of the wrist was performed on six cadavers in order to study the residual excursion of the wrist. Arthrodesis between the radius and scaphoid left 40 per cent extension/flexion and 61 per cent radial/ulnar deviation. Arthrodesis between the radius, scaphoid and lunate left 36 per cent extension/flexion and 59 per cent radial/ulnar deviation. Arthrodesis between the capitate, scaphoid and lunate left 59 per cent extension/flexion and 91 per cent radial/ulnar deviation.     

The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor into the radiocarpal joint on scaphoid and lunate kinematics.

The role of the dorsal radiocarpal wrist ligament has been the subject of several investigations. Several biomechanical studies have used sensors inserted dorsally into the wrist joint to evaluate its pressure distribution. The purpose of this study was to evaluate whether a dorsal capsulotomy that sections the dorsal radiocarpal ligament or insertion of a flexible pressure sensor alters scaphoid or lunate kinematics. Eight cadaver upper extremities were instrumented with motion sensors and placed in a wrist joint simulator. Each arm was moved through continual cycles of wrist flexion/extension and radial/ulnar deviation. Motion data were obtained in the intact state, after a capsulotomy, and after insertion of the sensor. We found that either a dorsal capsulotomy sectioning the dorsal radiocarpal ligament or insertion of the pressure sensor alters scaphoid and lunate kinematics during dynamic wrist motion. This study supports the clinical belief that this dorsal wrist ligament should be spared during surgical approaches to the carpus.     

Treatment of radiocarpal degenerative osteoarthritis by radioscapholunate arthrodesis and distal scaphoidectomy

PURPOSE: The purpose of this study was to assess wrist pain, range of motion, and the presence of radiographic midcarpal degenerative joint disease (DJD) in patients who had a distal scaphoidectomy in association to a radioscapholunate (RSL) arthrodesis and to compare these findings with prior studies of patients with only an RSL fusion. METHODS: Sixteen patients with radiocarpal DJD treated by RSL arthrodesis and distal scaphoidectomy were evaluated retrospectively for pain relief and range of motion at an average follow-up period of 37 months (range, 12-84 mo). Radiographs were assessed for the presence of secondary radiographic midcarpal DJD. RESULTS: Complete pain relief was obtained in 10 patients, 3 patients complained of slight pain during strenuous loading, and 3 patients had occasional pain with regular activities. The average postoperative ranges of motion were 32 degrees of flexion, 35 degrees of extension, 14 degrees of radial deviation, and 19 degrees of ulnar deviation. Two patients exhibited secondary midcarpal DJD. These results are significantly better compared with those previously published about RSL arthrodesis alone in terms of residual pain and decrease of wrist radial deviation and flexion. CONCLUSIONS: Patients who require an RSL arthrodesis for the treatment of severe localized radiocarpal DJD appear to have less pain and to retain more flexion and radial deviation if the distal scaphoid is excised concomitantly. This associated procedure also may help prevent secondary midcarpal DJD.     

Mediokarpale Teilarthrodese des Handgelenks mittels Spiderplatte

Objective

Pain relief while preserving wrist motion in advanced carpal collapse.

Indications

Advanced carpal collapse stage II/III due to scaphoid non-union, scapholunate ligament tear, idiopathic radiocarpal osteoarthritis, aseptic osteonecrosis of the scaphoid (Preisser??s disease). A relative indication is chronic midcarpal instability.

Contraindications

Osteoarthrisis of the lunate. Radiocarpal instability with ulnar translation of the wrist.

Surgical technique

Dorsal curved incision between the 3rd and 4th dorsal extensor compartment. Partial wrist denervation (posterior interosseous nerve). Raising of a radial pedicled capsule flap. Complete extirpation of the scaphoid without fragmentation. Cartilage removal of all the joint facets for arthrodesis. Reduction of the lunate and temporary fixation with K?wires between the triquetrum and capitate and the triquetrum and lunate. Milling the plate hole exactly in central position of the four carpal bones. The plate should not protrude from the bone to avoid impingement with the dorsal limb of the radius. Transferring of spongiosa harvested from the removed scaphoid into the arthrodesis gap. Fixation of the 8-hole plate with 2?screws in each of the four carpal bones. Fluoroscopy of the screw fitting. Control of the correct wrist articulation (motion test). Lavage of the wrist. Suture of the capsule flap. Redon drain, wound closure, dorsal splinting.

Postoperative management

Dorsal splint for 3?weeks; finger mobilization up to complete fist closure starting on postoperative day?1. From week 4?C6, active wrist motion, from week 7?C10 with increasing load. Return to work after 11?C12 weeks. CT scan in cases of delayed union, abnormal function, or persistence of pain.

Results

Between 2002 and 2008, 36?four-corner fusions (32?male, 4?female) with the spider plate were performed in 24 right and 12 left wrists. The mean age of the patients at surgery was 48?years (range 32?C71?years). Follow-up examinations were performed in 11 patients. The Krimmer and Rudolf scores were determined: 1?excellent, 7?good, 2?satisfactory, and 1?poor result were found. The mean grip strength was 51% relative to the opposite wrist. The mean range of motion (ROM) for wrist extension/flexion was 56% of the opposite side. Wrist extension/flexion averaged 24/0/32° and ulnar/radial deviation was on average 20/0/19°. Pain during activity was on average 2.2 based on the visual analogue scale (0?C10). One delayed bony union due to a screw breakage, which required total wrist fusion, was observed.     

Analysis of radiocarpal and midcarpal motion in stable and unstable rheumatoid wrists using 3-dimensional computed tomography

PURPOSE: The kinematic evaluation of carpal motion, especially midcarpal motion, in rheumatoid arthritis (RA) has been extremely difficult because of limited imaging techniques previously available. The purpose of this study was to evaluate the amount of radiocarpal and midcarpal motion in the flexion-extension plane in both stable and unstable rheumatoid wrists using three-dimensional computed tomography. METHODS: We acquired in vivo kinematic data on 30 wrists with RA by three-dimensional computed tomography with the wrist in 3 positions: neutral, maximum flexion, and maximum extension. All cases were radiographically classified into 1 of 2 subtypes, the stable form or unstable form, according to the classification by Flury et al. We evaluated the precise range of radiocarpal and midcarpal motion using a markerless bone registration technique and calculated the individual contributions to the total amount of wrist motion in the flexion-extension plane in the different radiographic subtypes of RA. RESULTS: The average range of motion of radiocarpal and midcarpal joint was 27 degrees +/-15 and 32 degrees +/-17, respectively. The average contribution of midcarpal motion to the total amount of wrist motion was 54%. The average contribution of midcarpal motion in the unstable form was 67%, which was significantly higher than 47% (p< .05) in the stable form. CONCLUSIONS: Midcarpal motion of rheumatoid wrists in the flexion-extension plane was better preserved than previously thought. The contribution of midcarpal motion to the total amount of wrist motion was significantly greater (p< .05) in the unstable form than in the stable form of RA.