A non-response analysis of 2-year data in the Swedish Knee Ligament Register

PURPOSE: To analyse the non-response group in the Swedish Knee Ligament Register (SKLR). METHODS: All 3588 patients in the SKLR who had undergone anterior cruciate ligament surgery in 2010 were included. Respondents (n = 1865) and non-respondents (n = 1723) at the 2-year follow-up survey were assessed for potential differences in demographics and baseline data. KOOS/EQ5D questionnaires were sent to non-respondents together with a non-response survey asking questions about reasons for dropout. RESULTS: Respondents had a significantly higher mean age (27.8 years, range 9-64) than non-respondents (25.9 years, range 12-65) (p < 0.001). Women had a higher rate of response 927 (62.8 %) than men 938 (44.4 %) even after correction for age (p < 0.001). Alpine/telemark skiing was the only activity at time of injury that showed higher rate of respondents 280 (62.5 %) compared to non-respondents 168 (37.5 %) (p < 0.001). No differences in EQ5D at 2-year follow-up were found between the groups. The change in KOOS from 0 to 2 years showed difference in the subscale pain with 9.4 in the response group compared to 6.3 in the late-response group (p < 0.05) and the subscale quality of life with a difference of 26.1 and 22.6, respectively (p < 0.05). The non-response questionnaire showed shortcomings in patient information regarding the importance of the SKLR. CONCLUSION: The register is valid concerning baseline surgical data, but higher age, female gender and perhaps higher socioeconomic status improve the response rates. KOOS showed small differences of questionable clinical significance. The SKLR patient information could be improved. LEVEL OF EVIDENCE: Retrospective comparative study, Level III.