Predictors of return to desired activity 12 months following unicompartmental and total knee arthroplasty

Figures & data

Participant recruitment flow chart. UKA: unicompartmental knee arthro­plasty; TKA: total knee arthroplasty.

Table 1. Patient characteristics at baseline and 12 months post-arthroplasty

	All patients	Missing	UKA	TKA
	(n = 995)	data	(n = 420)	(n = 575)	p-value a
Baseline characteristics
Age at operation^b	69 (9)	0 (0%)	67 (10)	70 (9)	< 0.001
Female sex^c	549 (55%)	0 (0%)	220 (52%)	329 (57%)	0.1
BMI^b	30 (5)	5 (0.5%)	30 (5)	31 (6)	0.006
Education level^c		159 (16%)
Did not complete GCSE or above	385 (39%)		144 (42%)	241 (49%)	0.04
Completed GCSE or above	451 (45%)		201 (58%)	250 (51%)
Baseline EQ-5D^d	0.62 (0.16–0.69)	106 (11%)	0.62 (0.16–0.69)	0.59 (0.16–0.69)	0.05
Postoperative pain expectation^c^,e		273 (27%)
No pain expected	389 (39%)		172 (56%)	217 (52%)	0.3
Mild to extreme pain expected	333 (34%)		133 (44%)	200 (48%)
Baseline UCLA Activity Score^d	4 (3–5)	283 (28%)	4 (3–5)	4 (3–5)	0.1
No reported comorbidities^c^, f	140 (14%)	245 (25%)	75 (25%)	65 (15%)	< 0.001
Baseline OKS^b	20.4 (7.7)	79 (8%)	21.6 (7.6)	19.5 (7.7)	< 0.001
12 months post-surgery
Non-return to desired activity^c^,g	341 (34%)	0 (0%)	105 (25%)	236 (41%)	<0.001

a p-values for differences between UKA and TKA groups, assessed using unequal t-tests, chi-squared tests or Mann–Whitney U-tests as appropriate.

b Mean (SD)

c Number (%)

d Median (IQR)

^e Postoperative pain expectation: assessed preoperatively using a 5-point Likert scale (Not at all, Mildly, Moderately, Severely, Extremely) in response to the question: “Overall, how much do you expect that pain in your knee will interfere with your life 12 months after surgery?”

f No reported comorbidities: the number of patients who had not been diagnosed with any of the following comorbidities (compared with a diagnosis of 1 or more of these comorbidities): osteoporosis, gout, hypertension, stroke, heart attack, heart failure, high cholesterol, diabetes, renal, bowel, lung, and liver problems.

g Non-return to desired activity: Proportion of patients that responded “No” to the following question at 12-month follow-up: “Have you been able to return to the activity (or activities) that your knee stopped you from doing 12 months ago?”

UKA: unicompartmental knee arthroplasty; TKA: Total knee arthroplasty; BMI: body mass index; GCSE: General Certificate of Secondary Education; EQ-5D: EuroQol 5 dimensions questionnaire; UCLA: University of California, Los Angeles; OKS: Oxford Knee Score.

Table 2. Multivariable analysis reporting risk ratios for non-return to desired activity following a generalized linear model for all, UKA, and TKA patients

	All patients (n = 995)		UKA (n = 420)		TKA (n = 575)
Predictors	RR (95% CI)	p-value	RR (95% CI)	p-value	RR (95% CI)	p-value
Age	1.00 (0.99–1.01)	1.0	0.99 (0.97–1.01)	0.2	1.01 (1.00–1.02)	0.09
Sex^a	1.15 (0.96–1.38)	0.1	1.43 (0.99–2.05)	0.06	1.04 (0.85–1.27)	0.7
BMI	1.00 (0.98–1.01)	0.7	1.04 (1.01–1.08)	0.006	0.99 (0.97–1.00)	0.1
Baseline OKS	0.97 (0.95–0.99)	0.001	0.96 (0.93–0.99)	0.02	0.98 (0.96–1.00)	0.04
Baseline UCLA-AS	1.02 (0.95–1.10)	0.6	1.07 (0.94–1.23)	0.3	1.00 (0.92–1.09)	1.0
Baseline EQ-5D Score	0.71 (0.47–1.07)	0.1	0.91 (0.43–1.92)	0.8	0.53 (0.33–0.85)	0.008
Pain expectation^b	1.34 (1.09–1.65)	0.005	1.86 (1.24–2.78)	0.003	1.15 (0.92–1.45)	0.2
Education^c	0.94 (0.78–1.13)	0.5	1.08 (0.76–1.52)	0.7	0.95 (0.76–1.18)	0.6
Comorbidities^d	1.04 (0.98–1.11)	0.2	1.08 (0.95–1.22)	0.3	1.03 (0.95–1.11)	0.5
Procedure^e	1.47 (1.21–1.78)	< 0.001

All variables were included in these multivariable analyses, except for “Procedure” in the UKA and TKA analyses.

Outcome coded as Returned-to-desired-activity =0, and Did-not-return-to-desired-activity =1

a Female =1 (compared with Male =0).

b Pain expectation: “Some =1” (mildly, moderately, severe or extremely) compared with “none =0” (not at all) (preoperative response to the following question: “Overall, how much do you expect that pain in your knee will interfere with your life 12 months after surgery?”).

c “Completed GCSE or above” = 1 (compared with “did not complete GCSE or above” = 0).

d ≥ 1 comorbidity =1 (compared with no comorbidities =0).

e TKA =1 (compared with UKA =0).

For abbreviations, see Table1