Change of Lumbar Isometric Extensor Strengths after Posterior Lumbar Interbody Fusion in Patients with Lumbar Degenerative Disease

ABSTRACT

STUDY DESIGN: Prospective cohort study. OBJECTIVES: This study was undertaken to examine changes in lumbar isometric extensor strength after posterior lumbar interbody fusion (PLIF) surgery. SUMMARY OF LITERATURE REVIEW In most reports, the patients that have undergone PLIF surgery have been shown to have muscle weakness and atrophy. However, the research conducted regarding the changes in muscle strength throughout a follow up period is insufficient. MATERIALS AND METHODS: Forty-nine patients (mean age, 65 years (range, 45 to 77)), scheduled for posterior lumbar interbody fusion due to symptomatic degenerative diseases, were enrolled. Preoperatively and 3, 6, and 12 month after surgery, lumbar isometric extensor strength was assessed using a MedX instrument in 7 angular positions (0-72degrees). The mean isometric strength and rate of increase were calculated. Isometric strengths were compared according to patients' age ( or =70 years) and fusion level (short or =3) and the respective relationships were analyzed. RESULTS: The mean isometric strength changed from 89.0 preoperatively to 85.3, 110.4, and 120.8 ft-lb at each follow-up, respectively. The rate of increase of strength was significantly greater at 0degrees(36.1 %) than at 72degrees(24.2 %) (p=0.019). Preoperative isometric strengths were similar in each age and fusion level group, but isometric strengths at the final follow-up were significantly lower in older patients and in the long level fusion group (p=0.002 and 0.043, respectively). Mean isometric strength at the last follow-up showed significant associations with age and fusion level (r=-0.431 and -0.317, p=0.002 and 0.030, respectively). CONCLUSION: After lumbar fusion surgery, back muscle strength slightly decreased until 3 months and then significantly increased. However, postoperative strength increases were lower in older patients and those in the long level (>3) fusion group. These results could be basic data for a rehabilitation program after lumbar fusion.