Sanchez-Santos et al reported a model for predicting outcomes 12 months after a total knee arthroplasty (TKA). The authors are from the University of Oxford and University of Southampton in the UK.
Patient selection: total knee arthroplasty (TKA)
Outcome: Oxford Knee Score (OKS) at 12 months
Parameters:
(1) age at the time of the operation, in years
(2) sex
(3) age and sex
(4) index of multiple deprivation (IMD) 2004 score (per 10 points), from 2.1 to 79.3
(5) body mass index in kg per square meters (per 10 units)
(6) anxiety or depression (fifth question of the EQ-5D0
(7) Oxford knee score at baseline, from 0 (severe) to 48 (no problem)
(8) ASA grade, from1 to 3
(9) previous knee arthroscopy
(10) other condition affecting mobility
(11) fixed flexion deformity
(12) pre-operative status of anterior cruciate ligament
|
Parameter |
Finding |
Points (beta-coefficient) |
|
age |
< 60 |
0 |
|
|
60 to 69 |
0.8 |
|
|
70 to 79 |
1.4 |
|
|
>= 80 |
-2.5 |
|
sex |
female |
0 |
|
|
male |
-4.8 |
|
age and sex |
female |
0 |
|
|
male and < 60 |
0 |
|
|
male and 60-69 |
4.8 |
|
|
male and 70 to 79 |
4.3 |
|
|
male and >= 80 |
8.1 |
|
IMD 2004 |
|
-0.6 * (IMD) / 10 |
|
BMI |
|
-1.5 * (BMI) / 10 |
|
anxiety or depression |
no |
0 |
|
|
yes (moderate or severe) |
-1.6 |
|
Oxford knee score |
|
0.4 * (score) |
|
ASA |
ASA 1 |
0 |
|
|
ASA 2 |
0 |
|
|
ASA 3 or 4 |
-2 |
|
previous knee arthroscopy |
no |
0 |
|
|
yes |
-1.6 |
|
other condition |
no |
0 |
|
|
yes |
-3.3 |
|
fixed flexion deformity |
no |
0 |
|
|
yes |
1.7 |
|
ACL status |
intact (< 5 mm) |
0 |
|
|
damaged or absent |
1 |
value of X =
= SUM(points for all of the beta-coefficients)
The coefficient given in Table 2 is 32.9. Adding this to the sum of beta-coefficients results in a value incompatible with a standard logistic regression model.
Options:
(1) The natural logarithm of 32.9 (3.49) is used. This is what is implemented.
(2) The summation with 32.9 indicates a predicted Oxford knee score (OKS).
