Introduction: The original Harris hip score (HHS) does not contain ability to perform squatting and sitting cross legged as items in the questionnaire and hence a need was felt to modify the Harris hip score so that it could stay relevant in functional assessment of Indian patients in the rural setting. Validity, responsiveness and ceiling floor effect of the Harris hip score after internal fixation of pertrochanteric fracture has not been previously described. The objective of the study was to investigate construct validity, responsiveness and ceiling floor effects of the modified Harris hip score (mHHS).
Methods: For evaluation of construct validity two hypotheses were formulated: first, there would be no difference in mHHS in cohort of patients treated with short or long proximal femoral nail and second, patients younger than 65 years will have higher mHHS compared to patients older than 65 years postoperatively. Proportion of patients obtaining lowest score of 0 point (floor effect) and those obtaining highest score of 100 points (ceiling effect) was evaluated at one, three and six months postoperatively. It is recommended that the proportion of ceiling and floor effect should be lower than 15% in order to deduce satisfactory internal and content validity of an outcome instrument. Responsiveness was evaluated using distribution based methods (effect size and standardised response mean) and anchor based method (area under the curve using receiver operating curve). Ability to perform cross leg sitting and squatting at six months postoperatively were chosen as two different external anchors. Effect size and standardised response mean values higher than 0.80 and area under the curve value higher than 0.70 are indicators of adequate responsiveness of an outcome instrument.
Results: Eighty one consecutive patients with pertrochanteric hip fractures and treated with long and short proximal femoral nail were included in this prospective observational study. Six patients were lost to follow-up due to mortality and complete functional outcome data was available in 75 patients (92.6%). The mean age was 68 years (range: 38-89 years). The mHHS at one, three and six months postoperatively was 39.9 ± 9.5, 61.6 ± 14.7 and 81.0 ± 15.9 respectively. The improvement in mHHS was significant at all time intervals. In accordance with the hypothesis, there was no significant difference in mHHS at one, three and six months postoperatively in patients treated with short or long proximal femoral nail. In accordance with the hypothesis, patients younger than 65 years had significantly better mHHS at one, three and six months postoperatively as compared to patients older than 65 years. There were no floor or ceiling effects at one, three and six months postoperatively. mHHS showed adequate internal responsiveness (Effect size = 4.34; standardised response mean = 4.26) and adequate external responsiveness (Area under curve = 0.77 and 0.89) using different external anchors.
Conclusion: The mHHS has adequate construct validity, internal validity and responsiveness to evaluate functional outcome of intramedullary nail fixation in pertrochanteric hip fractures in the Indian population.
Keywords: AUC, Area under the curve; Ceiling floor effect; ES, Effect size; HHS, original Harris hip score; Harris hip score; Internal fixation; Intertrochanteric fracture; Long PFN, long proximal femoral nail; Modified harris hip score; Pertrochanteric fracture; Proximal femoral nail; Psychometric properties; ROC, receiver operating curve; Responsiveness; SRM, standardised response mean; Short PFN, short proximal femoral nail; Validity; mHHS, modified Harris hip score.