Validation of a self-report instrument for assessment of hallux valgus

To validate an instrument for self-reported hallux valgus (HV).

The self-report instrument consists of five line drawings for each foot depicting a sequential increase in HV angle of 15 degrees developed from a photograph of a normal foot. Participants were asked to select the picture which best represented their left and right feet in turn. Four hundred and fifty-nine subjects completed the self-report instrument: 100 attending a hospital rheumatology clinic and 359 who participated in a community questionnaire study. Three hundred and eighty-four completed it on two occasions (1-2 months apart in 71 subjects and 3-6 months apart in 313) and were assessed once by a blinded observer. Twenty-five subjects were assessed by the blinded observer on two occasions. Validity of the instrument was assessed by the weighted kappa statistic for subject-observer agreement and reliability by the weighted kappa statistics for subject repeatability and observer repeatability. These analyses were repeated for HV dichotomised as present or absent.

For the five-grade HV scale, weighted kappa scores (left and right feet combined) were 0.45 for subject-observer agreement, 0.53 at 1-2 months and 0.51 at 3-6 months for subject repeatability, and 0.82 for observer repeatability. For the dichotomised scale (left and right feet combined), sensitivity was 75% and specificity was 82%: kappa scores were 0.55 for subject-observer agreement, 0.63 at 1-2 months and 0.61 at 3-6 months for subject repeatability and 0.83 for observer repeatability.

The HV self-report instrument provides a valid and reliable assessment of the presence and severity of HV and appears suitable for use in epidemiological studies.