Prosthesis design influences segmental contribution to total cervical motion after cervical disc arthroplasty.

INTRODUCTION: We investigated a new metric for assessing the quality of motion of the cervical segments over the arc of extension-to-flexion motion after cervical disc arthroplasty (CDA). We quantified: (1) the amount of motion contributed by individual spinal segments to the total cervical spine motion, termed segmental motion fraction, and its variation throughout the arc of extension-to-flexion motion and (2) how cervical disc arthroplasty using two distinct prosthesis designs may influence the segmental motion contributions. MATERIALS AND METHODS: We tested 16 human C3-T1 spine specimens under physiologic loads; first intact, after CDA at C5-C6, and then at C5-C6 and C6-C7. The M6-C (Orthofix, USA) and Mobi-C (Zimmer, USA) disc prostheses were used in eight specimens each. RESULTS AND CONCLUSIONS: The designs of the cervical disc prostheses tested significantly influenced the variation in segmental motion fraction as the spine underwent motion between the endpoints of extension and flexion. While the mean segmental motion contribution to the total cervical motion was not influenced by prosthesis design, the way the motion took place between the extension and flexion endpoints was significantly influenced. The M6-C artificial disc restored physiologic motion quality such that implanted segments continued to function in harmony with other segments of the cervical spine as measured before arthroplasty. Conversely, the Mobi-C prosthesis, while maintaining average motion contributions similar to the pre-implantation values, demonstrated large deviations in motion contribution over the extension-to-flexion arc motion in ten of 16 implanted segments. Such non-physiologic implant kinematics could cause excessive prosthesis wear and motion and stress shielding at adjacent segments. These slides can be retrieved under Electronic Supplementary Material.

Pain & Motion Recovery Patterns After Rotator Cuff Repair According to Tear Size / 대한정형외과학회잡지

PURPOSE: The purpose of this study was to evaluate the recovery patterns of pain and motion as well as final outcomes after rotator cuff repair according to tear size. MATERIALS AND METHODS: Sixty-one patients of rotator cuff repair (29 small to medium tear; group I, 32 large to massive tear; group II) through July 2000 to July 2003 were evaluated. Visual analogue scale (VAS) for pain, range of motion (ROM) and motion fraction (MF) between glenohumeral and scapulothoracic joint were checked serially 2, 6 and 12 months after operation. Final outcomes were accessed by ASES, SST, and UCLA score. RESULTS: Regardless of tear size, final outcomes were similar. But, recovery patterns of night pain were different from ROM and MF. In group I, night pain shown rapid initial recovery compared to more slow and gradual recovery pattern of group II. ROM and MF shown similar recovery patterns. MF recovery were gained after 12 months in group I, and 6 months in group II. CONCLUSION: After careful evaluation of recovery patterns of pain, ROM and MF according to tear size, appropriate rehabilitation protocol could be applied to assist normal functional recovery.

Recovery of Motion Fraction and Shoulder Function ofter Operative Treatment of Shoulder Instability / 대한정형외과학회잡지

PURPOSE: We expected the motion fraction could be checked, with simple radiographic examination, according to the guide-line of fluoroscopic technique, and recovery of the function also could be correlated with the improvement of the motion fraction. MATERIALS AND METHODS: We measured the motion fraction of the glenohumeral and scapulothoracic movement using fluoroscope in 30-degree intervals of arm elevation in the scapular plane. The ratio of glenohumeral to scapulothoracic movement (thetaGH/thetaST) was 1.6 for the full range of motion in scapular plane. During arm elevation, scapular tilting from the coronal plane was decreased from 42 degrees to 20 degrees tilting as well as internal rotation (scapular extension). We also measured the motion fraction (thetaGH/thetaST) and functional recovery of the shoulder in 11 patients after operative treatment of the shoulder instability in 15 patients from December 1996 to August 1997. RESULTS: We could find out a significant correlation between the recovery of motion fraction and shoulder function. These results would be applied in planing rehabilitation program after treatment of the shoulder instability. CONCLUSIONS: The measuring technique of glenohumeral to scapulothoracic movement (thetaGH/thetaST) with fluoroscopy could be applied to the simple radiographic measurement at the out-patient clinic in order to identify the pathology and recovery of shoulder motion after treatment