Weight affects survival of primary total knee arthroplasty: study based on the Danish Knee Arthroplasty Register with 67,810 patients and a median follow-up time of 5 years

Figures & data

Figure 1. Inclusion and exclusion of patients in the study population. Patients with inverse hybrid fixation techniques were excluded from analyses as this method is rare and the registration is most likely due to error.

Table 1. Demography across weight groups

Parameter Value	No. of patients	Weight (kg)						p-value ^a
		45–-60	60–69	70–79	80–89	90–99	99–200
Subjects ^b	67,810	3,074 (4.5)	9,336 (13.8)	16,336 (24.1)	16,538 (24.4)	10,585 (15.6)	11,941 (17.6)
Sex ^b
Women	41,506	2,947 (4.3)	8,182 (12.1)	11,492 (16.9)	9,072 (13.4)	4,767 (7.0)	5,046 (7.4)	< 0.001
Men	26,304	127 (0.2)	1,154 (1.7)	4,844 (7.1)	7,466 (11.0)	5,818 (8.6)	6,895 (10.2)
Age at primary TKA (overall median age: 68) median, years	67,810	74	72	70	68	66	64	< 0.001
Charlson’s Comorbidity Index (CCI) ^c
Low (CCI 0)	38,355	1,535 (49.9)	5,255 (56.3)	9,349 (57.2)	9,502 (57.5)	6,090 (57.5)	6,624 (55.5)
Medium (CCI 1–2)	11,356	471 (15.3)	1,519 (16.3)	2,758 (16.9)	2,786 (16.8)	1,785 (16.9)	2,037 (17.1)
High (CCI >2)	18,099	1,068 (34.7)	2,562 (27.4)	4,229 (25.9)	4,250 (25.7)	2,710 (25.6)	3,280 (27.5)
Indication for primary TKA ^c^, d
Primary arthrosis	55,683	2,266 (74.2)	7,536 (81.3)	13,599 (84.1)	13,662 (83.4)	8,707 (83.0)	9,913 (83.7)
Secondary arthrosis	7,220	257 (8.4)	850 (9.2)	1,519 (9.4)	1,867 (11.4)	1,303 (12.4)	1,424 (12.0)
Sequelae after fracture	1,538	157 (5.1)	267 (2.9)	384 (2.4)	316 (1.9)	199 (1.9)	216 (1.8)
Arthritis	2,182	337 (11.0)	506 (5.5)	552 (3.4)	413 (2.5)	184 (1.8)	190 (1.6)
Other ^e	595	39 (1.3)	108 (1.2)	121 (0.8)	134 (0.8)	97 (0.9)	96 (0.8)
Fixation technique of primary TKA ^c
Cemented		2,465 (80.2)	7,237 (77.5)	12,307 (75.3)	12,766 (77.2)	8,058 (76.1)	9,125 (76.4)
Uncemented		215 (7.0)	697 (7.5)	1,346 (8.2)	1,275 (7.7)	812 (7.7)	906 (7.6)
Hybrid		394 (12.8)	1,402 (15.0)	2,683 (16.4)	2,497 (15.1)	1,715 (16.2)	1,910 (16.0)
Revision TKA (rTKA) ^c	3,270	136 (4.4)	337 (4.0)	751 (4.6)	807 (4.9)	530 (5.0)	709 (5.9)
Perioperative complications ^c	589	35 (1.1)	105 (1.1)	136 (0.8)	130 (0.8)	77 (0.7)	106 (0.9)
Time to revision (overall median time to revision: 1.88 years) median, years	3,270	1.86	1.94	1.85	1.95	1.89	1.78	0.9
Indication for rTKA ^c
Aseptic loosening	1,109	43 (31.6)	98 (29.1)	276 (36.8)	272 (33.7)	177 (33.4)	243 (34.3)
Infection	173	4 (2.9)	19 (5.6)	37 (4.9)	42 (5.2)	34 (6.4)	37 (5.2)
Other ^e	1,988	89 (65.4)	220 (65.3)	438 (58.3)	493 (61.1)	319 (60.2)	429 (60.5)
Deaths and emigration (overall 18.6%) during follow-up ^c	12,632	906 (29.5)	2,153 (23.1)	3,407 (20.9)	2,879 (17.4)	1,532 (14.5)	1,755 (14.7)
Follow-up time (years), median
Non-revised	64,540	5.4	5.7	5.8	5.6	5.2	5.0
Revision—all cause	3,270	1.9	1.9	1.9	2.0	1.9	1.8
Revision—aseptic loosening	1,109	3.6	2.8	3.0	3.0	2.6	2.9
Revision—infection	173	3.4	1.9	1.6	0.6	1.3	0.8

^a For categorical variables the chi-squared test was used and for continuous variables the Kruskal–Wallis test was used. P-value <0.05 indicates a significant difference between values in same row.

^b Frequency and % of total

^c Frequency and % of patients in each weight group

^d The total number of included patients is 67,810; due to missing data on indication for primary TKA only 67,218 patients are listed.

^e Other indications for revision TKA include: pain without loosening, instability, secondary insertion of patellar component, replacement of polyethylene, 2nd part of 2-stage revision, progression of arthrosis and other causes.

Figure 2. Cumulative all-cause incidence curves for revision of primary TKA according to weight groups.

Table 2. Crude and adjusted hazard ratio (HR) with 95% confidence interval (CI) for revision (all causes) according to different weight and age groups. Values are number of subjects (95% CI)

HR	No. of patients	Weight (kg)						p-value ^a
		45–-60	60–69	70–79 (ref.)	80–89	90–99	99–200
Crude HR	67,810	0.98 (0.82–1.20)	0.79 (0.69–0.89) ^b	1	1.09 (0.99–1.21)	1.17 (1.05–1.31) ^b	1.40 (1.27–1.55) ^b	< 0.001
Adjusted HR ^c
18–55 years	7,151	0.91 (0.61–1.36)	0.73 (0.54–0.98) ^b	1	0.92 (0.74–1.15)	0.89 (0.70–1.13)	0.96 (0.78–1.18)	< 0.001
55–70 years	32,218	0.86 (0.63–1.18)	0.84 (0.70–1.00)	1	0.90 (0.78–1.04)	0.89 (0.76–1.04)	1.07 (0.93–1.23)
> 70 years	27,849	1.40 (1.05–1.87) ^b	0.90 (0.71–1.13)	1	1.48 (1.22–1.79) ^b	1.68 (1.34–2.11) ^b	1.60 (1.25–2.05) ^b

^a P-value for linear trend

^b Significant, p < 0.05

^c Adjusted for sex, comorbidities, perioperative complications, years after primary TKA, type of fixation, and indication for primary TKA.

Due to missing values in data, the total number of patients in the adjusted calculations is 67,218.

Figure 3. Cumulative incidence curves for revision of primary TKA due to aseptic loosening for weight groups. For color codes, see Figure 2

Table 3. Crude and adjusted hazard ratio (HR) with 95% confidence interval (CI) for revision due to aseptic loosening according to different weight and age groups. Values are number of subjects (95% CI)

Parameter	No. of patients	Weight (kg)						p-value ^a
		45–-60	60–69	70–79 (ref.)	80–89	90–99	99–200
Crude HR	67,810	0.85 (0.62–1.18)	0.62 (0.50–0.79) ^b	1	1.02 (0.86–1.20)	1.09 (0.91–1.32)	1.35 (1.13–1.60) ^b	< 0.001
Adjusted HR ^c	67,218	0.91 (0.65–1.26)	0.66 (0.52–0.83) ^b	1	0.97 (0.82–1.15)	0.96 (0.79–1.17)	1.09 (0.91–1.30)	0.004

^a P-value for linear trend

^b Significant, p < 0.05

^c Adjusted for sex, age, comorbidities, perioperative complications, years after primary TKA, type of fixation, and indication for primary TKA.

Due to missing values in data, the total number of patients in the adjusted calculations is 67,218.

Table 4. Crude and adjusted hazard ratio (HR) with 95% confidence interval (CI) for revision due to infection according to different weight and age groups. Values are number of subjects (95% CI)

Parameter	No. of patients	Weight (kg)						p-value ^a
		45–-60	60–69	70–79 (ref.)	80–89	90–99	99–200
Crude HR	67,810	0.58 (0.21–1.64)	0.90 (0.52–1.56)	1	1.14 (0.74–1.78)	1.49 (0.93–2.37)	1.45 (0.92–2.29)	0.2
Adjusted HR ^b	67,218	0.71 (0.25–2.02)	0.98 (0.55–1.73)	1	0.98 (0.62–1.53)	1.08 (0.67–1.75)	1.00 (0.62–1.62)	1.0

^a P-value for linear trend

^b Adjusted for sex, age, comorbidities, perioperative complications, years after primary TKA, type of fixation, and indication for primary TKA.

Due to missing values in data, the total number of patients in the adjusted calculations is 67,218.