The Validity of the SRS-22 Instrument in an Adult Spinal Deformity Population Compared to the Oswestry and SF-12

• (a - Medtronic Sofamor Danek)

Hypothesis: To date, only one study has examined the SRS-22 instrument for adult spinal deformity. The hypothesis of this study was that the SRS-22, given that it is a disease-specific instrument, would out-perform the SF- 12 and the Oswestry in assessing adult spinal deformity patients.

Materials: The study group consisted of 228 adults. Data was collected prospectively from multiple centers during 2002. Eighty-three percent were women, 17% men. The average age was 50 (range 18 -81). Seventy-seven patients (34%) were currently booked for surgery. Sixty-eight patients (30%) had past surgery. The rest were being followed for their spinal deformity. This was a group with substantial deformity. Thirty-seven patients (16% of total sample) had sagittal imbalance >5cm. Fourteen patients (6% of total sample) had thoracic kyphosis >70º. Of the thoracic curves, the average curve was 52º (maximum 106º). For the thoracolumbar curves, the average curve was 49º (maximum 110º). For the lumbar curves, the average curve was 45º (maximum 102º).

Methods: The SRS-22, SF-12 and Oswestry questionnaires were prospectively applied to all patients. The SRS- 22 was broken down into domains of pain, self-image, function, and mental health. The pain, function and mental health sections were compared to the other instruments. Three assessments were performed: 1) The floor/ceiling range for the SRS-22 versus the SF-12 and Oswestry; 2) the extent to which the domains within the SRS-22 questionnaire correlated with the SF-12 and Oswestry based on Pearson's coefficients; and 3) a Cronbach's alpha analysis for internal consistency of the responses within the same domain for the SRS-22. A floor/ceiling effect between 0 and 5% is ideal to suggest that an instrument has the capacity to demonstrate change in health status. A Pearson's coefficient of r>0.7 suggests high correlation. A Cronbach's alpha demonstrating high internal consistency is alpha >0.7.

Results: For all domains, the floor and ceiling for the SRS-22 ranged from 0.0-4.8%. In terms of the ideal floor to ceiling percentages, this out-performed the SF-12 and did as well as the Oswestry (ODI). SEE ATTACHED TABLE. In terms of concurrent validity, the Pearson's coefficient was r=0.74 for the comparison between the SRS-22 Pain scale and the SF-12 Pain scale; r=0.79 for Function; r=0.87 for Mental Health. The Function domain of the SRS-22 has a high correlation with the ODI (r=0.87). The SRS-22 Cronbach's alpha for Pain was 0.73, Self-Image 0.78, Function 0.78, and Mental Health 0.83.

Conclusion: The SRS-22 has a significantly lower floor/ceiling effect than the SF-12 instrument, suggesting that the SRS-22 is a disease-specific instrument with the capacity to demonstrate change in health status more effectively than the SF-12 and in more domains than the Oswestry. The SRS-22 showed high concurrent/criterion validity with the SF-12 and Oswestry based on Pearson's correlations. High Cronbach's alpha scores suggested a high internal consistency within each domain of the SRS-22.

Table: Floor to Ceiling

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