Which general functional outcome measure does a better job of capturing change in clinical status in pelvic and acetabular fracture patients? An analysis of responsiveness over the first year of recovery

OBJECTIVE: To compare the responsiveness of the Short Form-36 (SF-36) physical component score (PCS) to the Short Musculoskeletal Function Assessment (SMFA) dysfunction index (DI) in pelvic and acetabular fracture patients over multiple time points in the first year of recovery. DESIGN: Prospective cohort study. SETTING: Level 1 trauma center. PATIENTS/PARTICIPANTS: Four hundred seventy-three patients with surgically treated pelvic and acetabular fractures (Orthopaedic Trauma Association B or C-type pelvic ring disruption or acetabular fracture) were enrolled into the center's prospective orthopaedic trauma database between January 2005 and February 2015. Functional outcome data were collected at baseline, 6 months, and 12 months. MAIN OUTCOME MEASUREMENTS: Evaluation was performed using the SF-36 Survey and Short Musculoskeletal Function Assessment. Responsiveness was assessed by calculating the standard response mean (SRM), the minimal clinically important difference (MCID), and floor and ceiling effects. RESULTS: Three hundred five patients had complete data for both outcome scores. SF-36 PCS and SMFA DI scores showed strong correlation for all time intervals (r = −0.55 at baseline, r = −0.78 at 6 months, and r = −0.85 at 12 months). The SRM of the SF-36 PCS was greater in magnitude than the SRM of SMFA DI at all time points; this was statistically significant between baseline and 6 months (P < .001), but not between 6 and 12 months (P = .29). Similarly, the proportion of patients achieving MCID in SF-36 PCS was significantly greater than the proportion achieving MCID in SMFA DI between baseline and 6 months (84.6% vs 69.8%, P < .001), and between 6 and 12 months (48.5% vs 35.7%, P = .01). There were no ceiling or floor effects found for SF-36 PCS at any time intervals. However, 16.1% of patients achieved the highest level of functioning detectable by the SMFA DI at baseline, along with smaller ceiling effects at 6 months (1.3%) and 12 months (3.3%). CONCLUSIONS: SF-36 PCS is a more responsive measure of functional outcome than the SFMA DI over the first year of recovery in patients who sustain a pelvic ring disruption or acetabular fracture. This superiority was found in using the SRM, proportion of patients meeting MCID, and ceiling effects. Furthermore, the SF-36 PCS correlated with the more disease-specific SMFA DI. LEVEL OF EVIDENCE: Prognostic Level II.