[Comparative roentgenographical study on the incidence of ossification of the posterior longitudinal ligament and other degenerative changes of the cervical spine among Japanese, Koreans, Americans and Germans (author's transl)].

Ossification of the posterior longitudinal liagment (OPLL) of the cervical spine which causes narrowing of the spinal canal has been reported to occur in about three percent of adult Japanese, whereas only sporadical cases have been reported outside Japan. Whether this indicates a real ethnic difference of the disease incidence or simply reflects a difference of attention toward this disease has been one of the questions raised by many workers. In order to clarify this, the author reviewed a large number of roentgenograms of the cervical spine in Japan (Juntendo University Hospital), Korea (Sebrance Hospital and Hanko Sacred Heart Hospital), the United States (Mayo Clinic and Dr. Cloward's Office in Hawaii), and West Germany (Mainz University Hospital). The rate of appearance of OPLL was compared between these ethnic groups. In addition to this, the rate of appearance of calcification of the nuchal ligament and other degenerative changes of the cervical spine such as osteophyte formation and narrowing of the intervertebral disc space was also studied and statistically analysed. Results 1. OPLL: The author found OPLL in 143 out of 6,994 (2.06%) Japanese individuals above 20 years of age. The incidence was lower in Koreans being 0.95%. This was much more pronounced and significant in the United States (Mayo Clinic) and in Germany, where only a few cases were found (Table 6). However, it is interesting to note that six cases found at Dr. Cloward's office in Hawaii included two Japanese. The author concludes that the incidence of OPLL is significantly higher in Japanese than in Caucasians, although the reason for this still remains to be studied. 2. Calcification of the nuchal ligament: This calcification (Barsony) was found in 10.2% among Japanese and in 11.3% among Koreans, whereas in 6.1% among Americans and in 4.5% among GErmans (Table 13). The author proposes that this significantly higher incidence of this calcification among Japanese and Koreans may have something to do with the higher incidence of OPLL in these two countries. 3. Osteophyte: In Japanese and Koreans, the most frequent site of the osteophyte formation was at C-5 between the third and the sixth decades, and then moved to C-6 above 60 years of age, whereas in Americans and Germans, C-6 was the most common site throughout the ages. Although severe osteophytes were found even in younger age group in Japanese and Koreans, the severity of the osteophytes tend to increase comparatively more with age in Americans and Germans. 4. Narrowing of the intervertebral disc space: The narrowing was the most frequent in C-5-6 interspace regardless the age and the ethnic background.