Lumbar Stiffness Disability Index: Pilot testing of consistency, reliability, and validity

Background context: The primary goal of surgical arthrodesis is to eliminate the motion of spinal segments in an effort to alleviate pain, improve deformity, and reduce disability. However, decreased spinal mobility may impair performance of activities of daily living (ADLs) due to the resulting stiffness or the lack of mobility of the fused segment. Current clinical outcome instruments do not seek information regarding the impact of spinal stiffness on functional ability. Therefore, a patient-reported outcome questionnaire measuring the impact of lumbar stiffness on functional abilities was devised and assessed for internal consistency, retest repeatability, and external validity. Purpose: To develop and validate an outcome instrument to measure the collateral effect of stiffness after lumbar fusion on functional ability. Study design: Cross-sectional pilot study. Patient sample: Consecutive cohort of lumbar spine fusion patients from a single surgeon's practice. Outcome measures: Lumbar Stiffness Disability Index (LSDI) and Cobb angle measurements from digital radiographs. Methods: We developed and evaluated a 10-item questionnaire, referred to as the LSDI, which seeks information on the impact of spinal stiffness on ADLs after lumbar spinal arthrodesis. The questionnaire yields a score from 0 to 100, with higher scores indicating greater difficulty resulting from lumbar spinal stiffness in performing 10 different ADLs. The study sample comprised 32 lumbar arthrodesis patients at a minimum of 1 year postoperatively. All patients completed the questionnaire twice via telephone interviews conducted 4 weeks apart. Internal consistency was assessed using the Cronbach alpha, and retest reliability was measured using an intraclass correlation coefficient (ICC). External validity of the questionnaire was evaluated by correlating the scores with lumbar range of motion (LROM) as measured from the angular change between the inferior end plate of T12 and the superior end plate of S1 on standardized digital flexion and extension lateral radiographs. Results: The study sample included 22 women (69%) and 10 men (31%) with an average age of 63 years. The questionnaire demonstrated high internal consistency (Cronbach alpha=0.89). Retest reliability was also high (ICC=0.87). External validity was demonstrated by a statistically significant inverse relationship between LROM and LSDI scores (r=-0.71; p<.001). Conclusions: This pilot study demonstrates that the LSDI questionnaire is a reliable and valid instrument for assessing functional limitations due to lumbar stiffness among spinal arthrodesis patients. The questionnaire is proposed for use in prospective evaluation of lumbar stiffness impacts after arthrodesis.