Study Design: A single-blind, 2-factor (4 treatments by 8 time points) repeated-measures study design.

Objective:To analytically determine dexamethasone and dexamethasone phosphate concentrations in plasma derived from proximal effluent venous blood, following cathodic iontophoresis.

Methods and Measures: Six volunteers received the following dexamethasone phosphate (2.5 ml, 4 mg/ml) treatments to their wrists on separate occasions: cathodic iontophoresis (4 mA, 10 minutes or 4 mA, 20 minutes), passive application (10 or 20 minutes). Plasma samples from the ipsilateral antecubital vein were obtained 10 minutes prior to and half way through the treatment (5 or 10 minutes), at the end of the treatment (10 or 20 minutes), and posttreatment (15, 30, 60, 90, and 120 minutes). The present investigation examined: (1) the sensitivity and linearity of extraction and analysis of dexamethasone and dexamethasone phosphate; (2) the necessity for determining both; and (3) the plasma levels from proximal effluent venous blood following cathodic iontophoresis. Results: The aggregate (n = 18) of the 6-point standard curves were linear for dexamethasone (r > 0.974) and dexamethasone

phosphate (r > 0.829). In vitro dephosphorylation of dexamethasone phosphate to dexamethasone occurred in plasma at 37°C and during freeze-thaw. Measurable dexamethasone or dexamethasone phosphate concentrations were absent at all time points and under all conditions in the human subjects.

Conclusions: These results demonstrate the sensitivity of the current assay and the need for evaluating both forms of the drug, as in vitro dephosphorylation results in the presence of dexamethasone and dexamethasone phosphate in samples. Absence of measurable dexamethasone or dexamethasone phosphate in the proximal effluent venous blood may require re-evaluation of the extent of drug delivery during the clinical iontophoresis of dexamethasone phosphate.

J Orthop Sports Phys Ther. 2002; 32(9):461–468.

Keywords: anti-inflammatory agents, cutaneous administration, pharmacokinetics, tissue distribution

Study Design: A multifactorial cross-sectional nonexperimental design.

Objectives: To collectively investigate the association among 17 mechanical factors and occurrence of low back pain (LBP).

Background: Several physical characteristics, based on assumptions, clinical findings, and scientific experiments, have been associated with the development of LBP. Controversy exists regarding the degree of association between some of these physical characteristics and LBP. Information regarding the degree of association of each factor to LBP is needed for effective prevention and appropriate treatment strategies.

Methods and Measures: A total of 600 subjects participated in this study. Subjects were categorized into 4 groups: asymptomatic men (n = 150, age [mean ± SD] = 43 ± 15 years), asymptomatic women (n = 150, age [mean ± SD] = 43 ± 13 years), men with LBP (n = 150, age [mean ± SD] = 43 ± 14 years), and women with LBP (n = 150, age [mean ± SD] = 43 ± 13 years). Seventeen physical characteristics were measured in each group and the relative association of each characteristic with LBP was assessed.

Results: Among all the factors tested, endurance of the back extensor muscles had the highest association with LBP. Other factors such as the length of the back extensor muscles, and the strength of the hip flexor, hip adductor, and abdominal muscles also had a significant association with LBP.

Conclusion: It appears that muscle endurance and weakness are associated with LBP and that structural factors such as the size of the lumbar lordosis, pelvic tilt, leg length discrepancy, and the length of abdominal, hamstring, and iliopsoas muscles are not associated with the occurrence of LBP. J Orthop Sports Phys Ther. 2002; 32(9):447–460.

Keywords: back extensor endurance, low back pain, lumbar lordosis, muscle length, muscle strength