Table 3. Request Rates for Individual Imaging Tests for the Main Comparisona.
| Observed rates per 1000 patient consultations, median (IQR)b | Model-based estimatesb,c | |||||
|---|---|---|---|---|---|---|
| Mean per 1000 patient consultations (95% CI) | Adjusted mean difference (95% CI) | P value | ||||
| Intervention (n = 2933) | Control (n = 727) | Intervention (n = 2933) | Control (n = 727) | |||
| Lumbosacral spine | ||||||
| X-ray | ||||||
| Baseline | 1.6 (0.7-2.8) | 1.6 (0.7-1.7) | .13 | |||
| 12 mo | 1.2 (0.5-2.3) | 1.2 (0.5-2.3) | 1.41 (1.37-1.44) | 1.47 (1.40-1.54) | −0.06 (−0.14 to 0.02) | |
| Computed tomography | ||||||
| Baseline | 1.6 (0.7-2.8) | 3.6 (2.3-5.2) | <.001 | |||
| 12 mo | 2.9 (1.7-4.5) | 3.6 (2.1-5.0) | 3.01 (2.96-3.06) | 3.46 (3.35-3.56) | −0.45 (−0.56 to −0.33) | |
| Shoulder | ||||||
| X-ray | ||||||
| Baseline | 4.2 (2.8-5.7) | 4.2 (2.8-5.6) | <.001 | |||
| 12 mo | 3.5 (2.5-4.9) | 3.8 (2.5-5.1) | 3.38 (3.33-3.43) | 3.71 (3.60-3.82) | −0.33 (−0.44 to −0.22) | |
| Ultrasound | ||||||
| Baseline | 5.1 (3.9-6.5) | 5.2 (4.1-6.5) | <.001 | |||
| 12 mo | 4.4 (3.2-5.8) | 4.8 (3.5-6.2) | 4.27 (4.23-4.31) | 4.61 (4.53-4.69) | −0.35 (−0.43 to −0.26) | |
| Cervical spine | ||||||
| X-ray | ||||||
| Baseline | 0.8 (0.3-1.6) | 0.8 (0.3-1.5) | .16 | |||
| 12 mo | 0.6 (0.2-1.2) | 0.5 (0.2-1.4) | 0.74 (0.72-0.76) | 0.77 (0.74-0.81) | −0.03 (−0.07 to 0.01) | |
| Computed tomography | ||||||
| Baseline | 0.9 (0.4-1.7) | 0.9 (0.4-1.8) | <.001 | |||
| 12 mo | 0.7 (0.3-1.4) | 0.9 (0.3-1.7) | 0.89 (0.87-0.91) | 1.02 (0.96-1.07) | −0.12 (−0.17 to −0.07) | |
| Magnetic resonance imaging | ||||||
| Baseline | 0.4 (0.0-1.2) | 0.5 (0.0-1.3) | .05 | |||
| 12 mo | 0.4 (0.0-1.0) | 0.5 (0.0-1.2) | 0.62 (0.60-0.64) | 0.67 (0.63-0.71) | −0.05 (−0.09 to −0.0003) | |
| Knee | ||||||
| X-ray | ||||||
| Baseline | 5.2 (3.8-6.7) | 5.0 (3.7-6.6) | <.001 | |||
| 12 mo | 4.4 (3.0-5.7) | 4.6 (3.3-5.9) | 4.21 (4.15-4.26) | 4.44 (4.33-4.57) | −0.24 (−0.36 to −0.12) | |
| Hip | ||||||
| X-ray | ||||||
| Baseline | 3.9 (2.7-5.3) | 3.9 (2.7-5.4) | <.001 | |||
| 12 mo | 3.2 (2.2-4.5) | 3.7 (2.6-4.8) | 3.25 (3.20-3.29) | 3.60 (3.51-3.69) | −0.35 (−0.45 to −0.25) | |
| Ultrasound | ||||||
| Baseline | 3.2 (2.0-4.5) | 3.2 (2.0-4.5) | <.001 | |||
| 12 mo | 2.7 (1.6-3.9) | 2.9 (1.8-4.3) | 2.62 (2.58-2.65) | 2.90 (2.82-2.98) | −0.29 (−0.37 to −0.20) | |
| Ankle | ||||||
| X-rayd | ||||||
| Baseline | 4.0 (2.9-5.4) | 3.9 (3.0-5.4) | <.001 | |||
| 12 mo | 5.2 (3.8-7.1) | 5.5 (4.1-7.5) | 5.37 (5.31-5.43) | 5.98 (5.84-6.12) | −0.44 (−0.58 to −0.29) | |
| Ultrasound | ||||||
| Baseline | 1.6 (0.9-2.6) | 1.6 (0.8-2.6) | <.001 | |||
| 12 mo | 1.3 (0.6-2.1) | 1.4 (0.7-2.4) | 1.42 (1.40-1.44) | 1.54 (1.50-1.59) | −0.12 (−0.17 to −0.07) | |
See eTable 4 in Supplement 2 for request rates for individual imaging tests for the main comparison at all time points.
Imaging request rates for each general practitioner (GP) were calculated as the total number of diagnostic imaging requests from baseline to the end of the follow-up period (ie, 6, 12, and 18 months) divided by the total number of consultations over the corresponding period.
Data aggregated at the GP level were analyzed using multilevel mixed-effects linear regression adjusted for the baseline imaging rate of each GP and locality. See text for details.
Ankle x-ray was not targeted by the feedback intervention but was considered to be a potential substitute for ankle/hind foot ultrasound, so it was included as a secondary outcome to check for switching.