Table 2

Comparison of primary TKA recipients, after matching

<70 cases/year≥70 cases/yearStandardized difference*
Number of patientsN=51 658 N=51 658
Demographics
 Age (years) (median (IQR))68 (61–75) 69 (62–75)0.01
 Female (N (%))32 310 (62.54%) 32 355 (62.63%)0
Income quintile (N (%))
  Lowest9438 (18.27%) 9527 (18.44%)0
  210 727 (20.76%) 10 505 (20.33%)0.01
  310 556 (20.43%) 10 732 (20.77%)0.01
  410 552 (20.42%) 10 555 (20.43%)0
  Highest10 385 (20.10%) 10 339 (20.01%)0
Comorbidities (N (%))
 Coronary artery disease1634 (3.16%) 1749 (3.38%)0.01
 Congestive heart failure3047 (5.89%) 3120 (6.03%)0.01
 Chronic obstructive pulmonary disease9999 (19.35%) 10 246 (19.83%)0.01
 Diabetes13 789 (26.69%) 13 860 (26.83%)0
 Hypertension38 040 (73.63%) 38 216 (73.97%)0.01
 Frail3667 (7.09%) 3718 (7.19%)0
 Charlson score (N (%))
  036 624 (70.89%) 36 404 (70.47%)0.01
  19602 (18.58%) 9762 (18.89%)0.01
  23433 (6.64%) 3470 (6.71%)0
  3 or more1999 (3.86%) 2022 (3.91%)0
Admission characteristics
 Hospital volume (median (IQR))299 (207–410) 315 (230–420)0.07
 Surgeon years in practice (median (IQR))13 (5–23) 14 (7–21)0.03
  • *The standardized difference allows for a comparison of baseline variables (both continuous and dichotomous) between groups and is not affected by the size of the samples, as opposed to p values, which are 39. Because the standardized difference looks at the entire distribution of each sample, it is perfectly normal to see a difference for example, in median age of 1 year to be reflected in a 1% standardized difference as illustrated here.

  • TKA, total knee arthroplasty.