Table 2.
Univariate and multivariable-adjusted risk of periprosthetic fracture following primary total knee arthroplasty
| Total | Periprosthetic fractures | Univariate hazard | Multivariable a model 1 hazard | Multivariable b model 2 hazard | Multivariable c model 3 hazard | |
|---|---|---|---|---|---|---|
| Variable | (n = 17,633) | (n = 188) | ratio (95% CI) | ratio (95% CI) | ratio (95% CI) | ratio (95% CI) |
| Sex | p = 0.2 | p = 0.2 | ||||
| Male | 7,852 | 74 (1%) | 1.00 (ref) | 1.00 (ref) | ||
| Female | 9,781 | 114 (1%) | 1.23 (0.91–1.64) | 1.24 (0.92–1.68) | ||
| Age category | p < 0.001 | p < 0.001 | p = 0.001 | p = 0.002 | ||
| ≤ 60 | 3,352 | 52 (2%) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) |
| 61–70 | 6,206 | 59 (1%) | 0.52 (0.36–0.76) | 0.51 (0.35–0.74) | 0.52 (0.36–0.76) | 0.52 (0.36–0.77) |
| 71–80 | 6,493 | 58 (1%) | 0.56 (0.38–0.81) | 0.55 (0.38–0.80) | 0.55 (0.37–0.80) | 0.54 (0.36–0.80) |
| > 80 | 1,582 | 19 (1%) | 0.97 (0.57–1.65) | 0.97 (0.57–1.64) | 0.94 (0.55–1.61) | 0.90 (0.52–1.58) |
| Body mass index, kg/m2 | p = 0.4 | p = 0.5 | ||||
| Normal, < 25.0 | 2,362 | 29 (1%) | 1.00 (ref) | 1.00 (ref) | ||
| Overweight, 25–29.9 | 5,961 | 75 (1%) | 0.77 (0.50–1.18) | 1.09 (0.70–1.68) | ||
| Obese, 30–39.9 | 7,710 | 71 (1%) | 0.94 (0.49–1.81) | 0.83 (0.54–1.30) | ||
| Morbidly obese, ≥ 40.0 | 1,533 | 13 (1%) | 0.99 (0.64–1.51) | 0.87 (0.44–1.71) | ||
| Deyo-Charlson index | p = 0.06 | p = 0.05 | p = 0.04 | |||
| 0 | 7,985 | 75 (1%) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) | |
| 1 | 3,598 | 42 (1%) | 1.27 (0.87–1.86) | 1.21 (0.82–1.79) | 1.22 (0.82–1.81) | |
| 2 | 2,291 | 25 (1%) | 1.35 (0.86–2.13) | 1.39 (0.88–2.19) | 1.42 (0.90–2.26) | |
| 3+ | 3,759 | 46 (1%) | 1.66 (1.15–2.40) | 1.68 (1.16–2.44) | 1.75 (1.18–2.59) | |
| Previous cardiac event | p = 0.2 | p = 0.07 | ||||
| No | 14,404 | 166 (1%) | 1.00 (ref) | 1.00 (ref) | ||
| Yes | 3,229 | 22 (1%) | 0.76 (0.49–1.19) | 0.65 (0.40–1.04) | ||
| Previous thromboembolism | p = 0.6 | p = 0.6 | ||||
| No | 16,869 | 181 (1%) | 1.00 (ref) | 1.00 (ref) | ||
| Yes | 764 | 7 (1%) | 1.21 (0.57–2.58) | 1.20 (0.56–2.57) | ||
| Operative diagnosis | p = 0.2 | p = 0.2 | p = 0.3 | |||
| Osteoarthritis | 16,372 | 159 (1%) | 1.00 (ref) | 1.00 (ref) | 1.00 (ref) | |
| Rheumatoid arthritis | 657 | 13 (2%) | 1.13 (0.28–4.57) | 1.16 (0.64–2.11) | 1.01 (0.55–1.87) | |
| Avascular necrosis | 152 | 2 (1%) | 1.73 (0.99–3.01) | – | – | |
| Other | 452 | 14 (3%) | 1.51 (0.85–2.65) | 1.57 (0.94–2.65) | 1.55 (0.92–2.61) | |
| Implant fixation | p = 0.3 | p = 0.6 | ||||
| Uncemented | 1555 | 14 (1%) | 1.00 (ref) | 1.00 (ref) | ||
| Cemented or hybrid | 16,078 | 174 (1%) | 0.76 (0.44–1.31) | 0.87 (0.50–1.51) | ||
| ASA class | p = 0.5 | p = 0.6 | ||||
| 1 | 291 | 5 (2%) | 1.00 (ref) | 1.00 (ref) | ||
| 2 | 9,614 | 97 (1%) | 0.64 (0.26–1.58) | 0.75 (0.30–1.86) | ||
| 3 | 7,544 | 83 (1%) | 0.79 (0.32–1.94) | 0.93 (0.36–2.37) | ||
| 4 | 117 | 1 (1%) | 0.66 (0.08–5.68) | 0.80 (0.09–6.99) |
a Multivariable model 1 was a Cox regression model that considered all significant variables from the univariate analyses with a p-value of < 0.05–and retained only those significantly associated in the multivariable model by using a backward-selection process; the c-statistic of the multivariable model was 0.58.
b Multivariable model 2 was a Cox regression model obtained by retaining all variables from the univariate analyses with a p-value of < 0.20 and forcing all of them in the model; the c-statistic of the multivariable model was 0.61.
c Multivariable model 3 was a Cox regression model obtained by retaining all variables from the univariate analyses regardless of p-value and forcing all of them in the model; the c-statistic of the multivariable model was 0.62.
ASA: American Society of Anesthesiologists; CI: confidence interval; ref: reference category.