The study has before mentioned the concept of "knee - spine syndrome" domestically, on the basement of which, the new study intends to perform another further study on the relationship between lumbar and lower extremity degenerative diseases.

A prosepective, single-center, factorial design, randomized study will be performed. In this study, the 120 participants with degenerative lumbar and knees disease coped with the standard were included, then were assigned into 4 groups randomly. The patients in 3 operation groups were treated with posterior lumbar interbody fusion(PLIF or PLF) or total knee arthroplasty (TKA) or both of them in one stage respectively and the forth group with no surgery. The comparison between observation and operation group and the difference on self-control pre-and post-operatively in operation group within 6 months were measured and valuated. The result will be formed by the correlation and causal relationship on sagittal parameters on photograph, biomechanics, neuroelectrophysiology and molecular biology and the conclusions drawn by the use of modern medical basic research methods will formulate the treatment principles on it.

Inclusion Criteria:

1. Patients diagnosed LSS need to be underwent PLIF or PLF
2. and Patients who need surgery and are limited by knee extension greater than 10 °
3. ineffective conservative treatment for 6 months
4. patients have never relevant surgery before
5. Participants will be volunteered randomly assigned to surgery group and observation group.

Exclusion Criteria:

1. People have had similar lumbar or knee surgery
2. patients with lumbar or knee joint tumor or congenital malformation
3. there are contraindications of surgery such as infections and serious illness.