Lumbar Extensor Muscle Size and Isometric Muscle Strength in Women with Symptomatic Lumbar Degenerative Diseases

STUDY DESIGN: A cross-sectional design. PURPOSE: To determine the characteristics of lumbar extensor muscle (LEM) size and isometric muscle strength and examine their correlations in women with lumbar degenerative diseases (LDDs). OVERVIEW OF LITERATURE: Many studies have evaluated the relationship between muscle size and strength, but the results have been controversial. METHODS: Seventy-four female patients (mean age, 66 years) who consecutively underwent posterior lumbar interbody fusion (L1–S1) were recruited. The cross-sectional area (CSA) of the back extensor muscles was measured between L1–2 to L5–S1, and the total sum of the CSAs at each disc level was calculated. Back extensor muscle strength was evaluated using a MedX lumbar extension machine. The Oswestry Disability Index (ODI, 0–100) and Visual Analog Scale (VAS, 0–10) of lower back pain were determined. RESULTS: The mean CSAs of the LEM at each level (L1/2–L5/S1) and the total sum were 34.3, 36.3, 35.1, 31.4, 21.9, and 156.2 cm2, respectively. The mean isometric strength at each angle (range, 0°–72°) was 32.5, 50.1, 72.0, 88.7, 100.7, 112.2, and 126.2 ft-lb, respectively. The mean ODI and VAS scores were 54.6 and 6.6, and the mean body weight and body mass index (BMI) were 59.9 kg and 24.9 kg/m(2), respectively. The CSAs of the upper lumbar level (L1–4) and the total sum of the CSAs were associated with isometric strength, which was negatively correlated with patients’ age and ODI and positively associated with body weight and BMI, mainly at higher lumbar flexion angles (48°–72°). CONCLUSIONS: In women with LDD, LEM sizes of the upper lumbar levels (L1–4) were larger than those of the lower levels (L4–S1) and were positively associated with muscle strength. The upper lumbar levels in patients with LDDs appear to play a compensatory role when degenerative lesions are present in the lower lumbar levels.