Many researchers have evaluated the motions of the shoulder girdle, especially scapular and humeral motion. However, few reports exist that describe motions of the acromioclavicular joint. The purpose of the present study was to analyze the 3D kinematics of the acromioclavicular joint during arm abduction using 3D MR images obtained by a vertically open MRI. Fourteen shoulders of seven volunteers were examined in seven static positions from 08 to the maximum abduction in a seated position. 3D surface models of the clavicle and scapula were created, and the movements of the acromioclavicular joint from 08 to each position were calculated using the volume-based registration technique. From these calculations, the translations were evaluated and the rotational motions were analyzed using the concept of the screw axis. In the anteroposterior direction, the clavicle translated most posteriorly (À1.9 AE 1.3 mm) at 908 of abduction and most anteriorly (1.6 AE 2.7 mm) at maximum abduction. In the superoinferior direction, the clavicle translated slightly superiorly (0.9 AE 1.9 mm). When analyzing relative motion of the scapula with respect to the clavicle, the scapula generally rotated about a specific screw axis passing through the insertions of both the acromioclavicular and the coracoclavicular ligaments on the coracoid process. The average rotation was 34.9 AE 8.48. ß

There have been several reports about the clavicular and acromioclavicular motion, but a precise motion has been unknown. The purpose of this study was to analyze the 3D kinematics of the clavicle and acromioclavicular joint during arm abduction, using 3D MR images obtained by a vertically open MRI. Seven subjects participated in this investigation, which included 14 shoulders. From a seated position, we obtained MR images of their shoulder in seven abducted positions of the arm in the coronal plane. We evaluated the 3D movements of each bone in the shoulder using the volume-based registration technique, and analyzed the clavicular positions relative to the lung and the scapular positions relative to the clavicle. During arm abduction, the clavicular motion relative to the lung showed 30.68 retraction, 7.38 elevation, and 33.28 posterior axial rotation. During arm abduction, the scapular motion relative to the clavicle showed 15.68 protraction, 21.58 upward rotation, and 22.28 posterior tilting. This study succeeded in describing the 3D clavicular and acromioclavicular motion including the axial rotation of the clavicle, and it revealed that both motions had large degrees of rotations. ß

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Background: Medical image processing has facilitated simulation of 3-dimensional (3-D) corrective osteotomy, and 3-D rapid prototyping technology has further enabled the manufacturing of patient-matched surgical guides and implants (patient-matched instruments, or PMIs). However, 3-D corrective osteotomy using these technologies has not been the standard procedure. We aimed to prospectively verify the efficacy and safety of PMIs in corrective osteotomy for deformities of the upper extremity. Methods: We enrolled 16 patients with a total of 17 bone deformities in the upper extremity. Eight patients had distal radial malunion; 5, distal humeral malunion; and 3, forearm diaphyseal malunion. All cases underwent 3-D corrective osteotomy with PMIs. The primary end point was the residual maximum deformity angle (MDA), which was calculated from 2 deformity angles—1 on the anteroposterior and 1 on the lateral postoperative radiograph. Secondary end points included the deformity angle on radiographs, 3-D error between the preoperative planning model and the postoperative result, range of motion, grip strength, pain measured with a visual analog scale (VAS), patient satisfaction, and Disabilities of the Arm, Shoulder and Hand (DASH) score. Results: The average MDA significantly improved from 25.5° preoperatively to 3.3° at the final follow-up (p < 0.001). The angular deformity was within 5° in all cases, except for 1 with distal radial malunion who had a higher angle on the anteroposterior radiograph. The error between the correction seen on the postoperative 3-D bone model and the planned correction was <1° and <1 mm. Flexion and extension of the wrist and pronation of the forearm of the patients treated for distal radial malunion improved significantly, and pronation improved for those treated for forearm diaphyseal malunion. The average VAS score, grip strength, and DASH score significantly improved as well. Of the 16 patients, 15 were very satisfied or satisfied with the outcomes. Conclusions: Corrective osteotomy using PMIs achieved accurate correction and good functional recovery in the upper extremity. Although our study was limited to cases without any deformity on the contralateral side, 3-D corrective osteotomy using PMIs resolved treatment challenges for complex deformities in upper extremities. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.