Lumbar Degenerative Kyphosis (LDK) is a clinical entity showing kyphosis in the lumbar spine in elderly with multilevel disc narrowing and a varied degree of osteoporosis. LDK patient complains of stooped gait with persistent low back pain and weakness. Purpose of this paper is to study the lumbar muscle in LDK patients with histopathologic and biophysical evaluations to investigate the pathogenesis.

Materials and Methods: 1. Intramuscular pressure (IMP) (a) of the lumbar extensor compartment and hemoglobin content (Hb)□@(b) of 25 young volunteers were also investigated comparing in standing upright and flexion positions using (a)□@pressure monitoring kits and an non-invasive oxygenation monitor. 2.Muscle biopsy specimens obtained from the lumbar extensors of 9 LDK patients were histopathologically examined with HE, cytochrome c oxidase and other methods. These data were compared with muscles taken from age-match controls. Mitochondria function was also examined on biochemistry.

1. IMP of the extensors markedly increased in the flexion position (130.0□}45.4 in males and 86.3 mmHg in fem.) comparing to straight upright□@(22.8□}14.4, 17.0□}6.0). Oxy-Hb concentration decreased from 100% to 92.9, 95.5 % respectively in flexion, which was a sign of ischemia. 2. Both multifidus and sacrospinalis m. showed moderate to marked interstitial fibrosis, decreased number of muscle fibers and decreased stain intensity of cytochrome c oxidase. These finding were similar to those seen in repeatedly compressed muscles of an animal model of the chronic compartment syndrome. In comparison the rectus abd. and psoas muscles in the patients showed almost normal except for some aging changes. Conclusion: There appeared to be definite atrophy of the lumbar extensor muscles with histochemical and biochemical methods in LDK patients, whereas the flexors showed no change. This extensor atrophy is limited in the lumbar region in LDK. These localized atrophy of the lumbar extensors would suggest a result of high IMP during working in deep bending position of the spine for many years and may play important role in etiology of this disease condition.