The Effect of Nonspecific Knee Injury on Radiographic OA
Weighted characteristics of the full sample (N = 163.0) are described in Table 1. 54.0 % were female. At baseline, average BMI was 26.1 (range = 18.1–43.2, SD = 4.2). 39.4% had baseline ROA. By follow-up, 35.0% had progressed on the KL grade (0/1 collapsed) of their study knee. The vast majority of subjects' study knees progressed or remained the same, with only n = 3.0 (1.8%) moving backwards on the collapsed KL scale. Those were treated as non-progressors. At baseline, 24.4% had experienced moderate knee NSI, and 10.8% severe knee NSI. 7.8% had experienced moderate knee SI, and 11.0% severe knee SI. Duration from the oldest SI to baseline radiographic assessment ranged from 1–58 years, while duration from the oldest NSI to baseline radiographic assessment ranged from 0–70 years.
Table 2 lists the odds ratios and 95% confidence intervals from the regression models, adjusted for age, sex, baseline BMI, baseline KL grade and years of follow-up. Interactions were dropped due to non-significance at alpha = 0.05, so the odds ratios apply to both sexes. In the dichotomous model, SI had a significant association with ROA incidence and progression (OR = 2.90; 95% CI = 1.04, 8.09), but NSI did not show an association in the multivariable model (OR = 1.36; 95% CI = 0.61, 3.02). In the trichotomous model, the effects of SI were monotonic. Severe SI was significantly associated with ROA incidence and progression, while moderate SI was not: moderate SI OR = 1.51 (95% CI = 0.33, 6.84); severe SI OR = 4.35 (95% CI = 1.26, 15.02). NSI showed no effect: moderate NSI OR = 1.51 (95% CI = 0.61, 3.74); severe NSI OR = 0.90 (95% CI = 0.24, 3.40). Both models passed the goodness of fit test at alpha = .05. Fixing the weighted number of progressors and subjects with knee NSI to what we observed post-hoc, we had a post-hoc power of 80% to detect an odds ratio of 2.9 when defining NSI as a binary variable.
The results of the sensitivity analyses were as follows. In the models fit on the subgroup without history of SI, odds ratios for NSI were similar to the above results, with slightly wider confidence intervals. In the dichotomous model, OR = 1.55; 95% CI = 0.63, 3.83. In the trichotomous model, moderate NSI OR = 1.79 (95% CI = 0.66, 4.85); severe NSI OR = 1.03 (95% CI = 0.23, 4.70). In the analysis accounting for time between NSI or SI and baseline radiographic assessment, results were similar in that SI was significant while NSI was not. Only old (>20 years) severe SI was significant vs. no injury, with OR = 5.47 (95% CI = 1.41, 21.27), not recent SI or any NSI. For the analysis treating SI/NSI occurring between baseline and follow-up as additional history of injury, there were no new SIs to the study knee in that time, but there were 11 new knee NSIs, two of them severe. Addition of these events did not change the conclusions and hardly changed the estimates in dichotomous or trichotomous models. Odds ratios were within 0.01 in the significant categories, and within 0.1 in the non-significant categories. In the final sensitivity analysis, in separate incidence and progression models, we observed a significant effect of SI on progression, but none on incidence. NSI had no effect in either model. In the complementary cross-tabulation comparing the baseline prevalence of ROA versus history of knee SI and knee NSI, we found that ROA prevalence increased monotonically for levels of SI; that is, ROA prevalence was 35.0%, 49.7% and 64.3% for none, moderate and severe SI respectively. However, again, no such trend was seen for levels of NSI, where ROA prevalence was 41.0%, 34.6% and 40.7% respectively. The combination of these results (prevalence rates and separate models for incidence and progression) together support combining the outcome into incidence/progression: the length of time between injury and baseline radiographic assessment has precluded separation of the outcome into incidence and progression alone because any effect of injury on incidence has already acted by the time of radiographic assessment at study baseline. In this two-pronged sensitivity analysis, an effect of SI on incidence is detected (as differences in ROA prevalence at study baseline), yet no evidence of an effect of NSI is seen.
Finally, there were no statistically significant differences between the followed up subsample of 163/255 vs. the subsample that was not followed up (92/255), on baseline values of specific injury, non-specific injury, KL grade, gender, age and BMI.
Results
Weighted characteristics of the full sample (N = 163.0) are described in Table 1. 54.0 % were female. At baseline, average BMI was 26.1 (range = 18.1–43.2, SD = 4.2). 39.4% had baseline ROA. By follow-up, 35.0% had progressed on the KL grade (0/1 collapsed) of their study knee. The vast majority of subjects' study knees progressed or remained the same, with only n = 3.0 (1.8%) moving backwards on the collapsed KL scale. Those were treated as non-progressors. At baseline, 24.4% had experienced moderate knee NSI, and 10.8% severe knee NSI. 7.8% had experienced moderate knee SI, and 11.0% severe knee SI. Duration from the oldest SI to baseline radiographic assessment ranged from 1–58 years, while duration from the oldest NSI to baseline radiographic assessment ranged from 0–70 years.
Table 2 lists the odds ratios and 95% confidence intervals from the regression models, adjusted for age, sex, baseline BMI, baseline KL grade and years of follow-up. Interactions were dropped due to non-significance at alpha = 0.05, so the odds ratios apply to both sexes. In the dichotomous model, SI had a significant association with ROA incidence and progression (OR = 2.90; 95% CI = 1.04, 8.09), but NSI did not show an association in the multivariable model (OR = 1.36; 95% CI = 0.61, 3.02). In the trichotomous model, the effects of SI were monotonic. Severe SI was significantly associated with ROA incidence and progression, while moderate SI was not: moderate SI OR = 1.51 (95% CI = 0.33, 6.84); severe SI OR = 4.35 (95% CI = 1.26, 15.02). NSI showed no effect: moderate NSI OR = 1.51 (95% CI = 0.61, 3.74); severe NSI OR = 0.90 (95% CI = 0.24, 3.40). Both models passed the goodness of fit test at alpha = .05. Fixing the weighted number of progressors and subjects with knee NSI to what we observed post-hoc, we had a post-hoc power of 80% to detect an odds ratio of 2.9 when defining NSI as a binary variable.
The results of the sensitivity analyses were as follows. In the models fit on the subgroup without history of SI, odds ratios for NSI were similar to the above results, with slightly wider confidence intervals. In the dichotomous model, OR = 1.55; 95% CI = 0.63, 3.83. In the trichotomous model, moderate NSI OR = 1.79 (95% CI = 0.66, 4.85); severe NSI OR = 1.03 (95% CI = 0.23, 4.70). In the analysis accounting for time between NSI or SI and baseline radiographic assessment, results were similar in that SI was significant while NSI was not. Only old (>20 years) severe SI was significant vs. no injury, with OR = 5.47 (95% CI = 1.41, 21.27), not recent SI or any NSI. For the analysis treating SI/NSI occurring between baseline and follow-up as additional history of injury, there were no new SIs to the study knee in that time, but there were 11 new knee NSIs, two of them severe. Addition of these events did not change the conclusions and hardly changed the estimates in dichotomous or trichotomous models. Odds ratios were within 0.01 in the significant categories, and within 0.1 in the non-significant categories. In the final sensitivity analysis, in separate incidence and progression models, we observed a significant effect of SI on progression, but none on incidence. NSI had no effect in either model. In the complementary cross-tabulation comparing the baseline prevalence of ROA versus history of knee SI and knee NSI, we found that ROA prevalence increased monotonically for levels of SI; that is, ROA prevalence was 35.0%, 49.7% and 64.3% for none, moderate and severe SI respectively. However, again, no such trend was seen for levels of NSI, where ROA prevalence was 41.0%, 34.6% and 40.7% respectively. The combination of these results (prevalence rates and separate models for incidence and progression) together support combining the outcome into incidence/progression: the length of time between injury and baseline radiographic assessment has precluded separation of the outcome into incidence and progression alone because any effect of injury on incidence has already acted by the time of radiographic assessment at study baseline. In this two-pronged sensitivity analysis, an effect of SI on incidence is detected (as differences in ROA prevalence at study baseline), yet no evidence of an effect of NSI is seen.
Finally, there were no statistically significant differences between the followed up subsample of 163/255 vs. the subsample that was not followed up (92/255), on baseline values of specific injury, non-specific injury, KL grade, gender, age and BMI.
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