Alternative bearings in total knee arthroplasty: risk of early revision compared to traditional bearings

Figures & data

Table 1. Patients, procedures, implants, and surgeon and hospital characteristics, listed according to bearing surface

	Total cohort	CoCr-HXLPE	CoCr-CPE	OZ-CPE
	(n = 62,177)	(n = 7,618)	(n = 49,055)	(n = 1,066)	p-value
	n (%)	n (%)	n (%)	n (%)
Patient characteristics
Female ^a	38,828 (62.4)	4,692 (61.6)	30,864 (62.9)	608 (57.0)	< 0.001
Mean age (SD), years ^a	67.5 (9.3)	65.7 (9.4)	67.8 (9.2)	59.7 (8.4)	< 0.001
ASA score
1 or 2	37,090 (59.7)	4,536 (59.5)	29,196 (59.5)	656 (61.5)	0.002
> 3	23,593 (37.9)	2,719 (35.7)	18,910 (38.5)	373 (35)
Unknown	1494 (2.4)	363 (4.8)	949 (1.9)	37 (3.5)
BMI, kg/m^2
< 30	2,6314 (42.3)	2,882 (37.8)	21,028 (42.9)	339 (31.8)	< 0.001
30–35	18,066 (29.1)	2,251 (29.5)	14,191 (28.9)	323 (30.3)
≥ 35	16,597 (26.7)	2,396 (31.5)	12,840 (26.2)	385 (36.1)
Unknown	1,200 (1.9)	89 (1.2)	996 (2.0)	19 (1.8)
Race
Asian	3,034 (4.9)	274 (3.6)	2,563 (5.2)	28 (2.6)	< 0.001
Black	4,868 (7.8)	783 (10.3)	3,718 (7.6)	153 (14.4)
White	41,640 (67)	5,217 (68.5)	32,483 (66.2)	646 (60.6)
Hispanic	7,633 (12.3)	843 (11.1)	6,187 (12.6)	134 (12.6)
Other ^b	1,282 (2.1)	148 (1.9)	1,057 (2.2)	12 (1.1)
Unknown	3,720 (6.0)	353 (4.6)	3,047 (6.2)	93 (8.7)
Diabetes	16,465 (26.5)	2,036 (26.7)	13,012 (26.5)	275 (25.8)	0.8
Procedure/implant characteristics
Bilateral	5,311 (8.5)	510 (6.7)	42,74 (8.7)	113 (10.6)	< 0.001
Mean operative time (SD), min ^a	95.1 (32.5)	96.8 (31.7)	95 (32.6)	105 (36.8)	< 0.001
Implant fixation
Uncemented	1,874 (3.0)	207 (2.7)	969 (2.0)	3 (0.3)	< 0.001
Hybrid	3,137 (5.0)	570 (7.5)	2,447 (5.0)	8 (0.8)
Cemented	53,379 (85.9)	6,263 (82.2)	42,785 (87.2)	989 (92.8)
Unknown	3787 (6.1)	578 (7.6)	2854 (5.8)	66 (6.2)
Mobility and stability
Fixed: Cruciate retaining	15,811 (25.4)	3,922 (51.5)	10,736 (21.9)	404 (37.9)	< 0.001
Fixed: Posterior stabilized	38,516 (61.9)	3,695 (48.5)	31,377 (64.0)	662 (62.1)
Rotate: Cruciate retaining	858 (1.4)	0 (0.0)	856 (1.7)	0 (0.0)
Rotate: Low contact stress	1,040 (1.7)	0 (0.0)	1,020 (2.1)	0 (0.0)
Rotate: Posterior stabilized	5,096 (8.2)	0 (0.0)	5,063 (10.3)	0 (0.0)
Unknown	856 (1.4)	1 (0.0)	3 (0.0)	0 (0.0)
High flexion	7,583 (12.2)	3,363 (44.1)	3,659 (7.5)	443 (41.6)	< 0.001
Surgeon/hospital characteristics
Joint arthroplasty fellowship training ^a	21,551 (34.7)	2,404 (31.6)	17,254 (35.2)	430 (40.3)	< 0.001
Surgeon volume, cases/year ^a
< 10	1,092 (1.8)	184 (2.4)	791 (1.6)	35 (3.3)	< 0.001
10–49	26,447 (42.5)	3,231 (42.4)	21,040 (42.9)	516 (48.4)
≥ 50	34,638 (55.7)	4,203 (55.2)	27,224 (55.5)	515 (48.3)
No. of cases performed by surgeon, median (IQR)	95 (33–205)	39 (13–98)	117 (48–235)	14 (5–40)	< 0.001
Hospital volume, cases/year ^a
< 99	2,022 (3.3)	438 (5.7)	1442 (2.9)	63 (5.9)	< 0.001
100–199	11,443 (18.4)	1,082 (14.2)	9,604 (19.6)	264 (24.8)
≥ 200	48,712 (78.3)	6,098 (80)	38,009 (77.5)	739 (69.3)

^a Missing data: sex < 0.1%, age < 0.1%, operative time 17.7%, fellowship training 0.1%.

^b Includes native American, multi-race, and other.

ASA: American Society of Anaesthesiologists score; BMI: body mass index; HXLPE: highly crosslinked polyethylene;

CoCr: cobalt-chromium; CPE: conventional polyethylene; OZ: oxidized zirconium.

Figure 1. Adjusted cumulative hazard function estimate by knee bearing surface; aseptic revisions only. Adjustment based on the propensity score weights with stratification on the bearing surface groups using data from one of the 20 imputed data sets. HXLPE: highly crosslinked polyethylene; CoCr: cobalt-chromium; CPE: conventional polyethylene; OZ: oxidized zirconium.

Figure 2. Adjusted cumulative hazard function estimate by knee bearing surface with stratification by highly crosslinked materials; aseptic revisions only. Adjustment based on the propensity score weights with stratification on the bearing surface groups using data from one of the 20 imputed data sets. For abbreviations, see Figure 1.

Table 2. All-cause, aseptic, and septic revision rates per 100 observation years, and reasons for revision for the overall cohort, listed according to bearing surface ^a

	Total cohort ^b	CoCr-HXLPE	CoCr-CPE	OZ-CPE
	(n = 62,177)	(n = 7,618)	(n = 49,055)	(n = 1,066)
All-cause revisions, n ^c	1,362	157	1,095	33
Total observation years	201,014	16,478	166,224	3,276
Revisions per 100 obs. years, % (95% CI)	0.68 (0.64–0.71)	0.95 (0.81–1.11)	0.66 (0.62–0.7)	1.01 (0.72–1.42)
Aseptic revisions, n ^d	789	86	626	22
Total observation years	201,014	16,478	166,224	3,276
Revisions per 100 obs. years, % (95% CI)	0.39 (0.37–0.42)	0.52 (0.4 –0.64)	0.38 (0.35–0.41)	0.67 (0.44–1.02)
Septic revisions, n ^e	573	71	469	11
Total observation years	201,014	16,478	166,224	3,276
Revisions per 100 obs. years, % (95% CI)	0.29 (0.26–0.31)	0.43 (0.34–0.54)	0.28 (0.26–0.31)	0.34 (0.19–0.61)
Reasons for revision ^f
Infection	573 (42.1)	71 (45.2)	469 (42.8)	11 (33.3)
Instability	258 (18.9)	43 (27.4)	196 (17.9)	9 (27.3)
Pain	238 (17.5)	25 (15.9)	187 (17.1)	7 (21.2)
Aseptic loosening	178 (13.1)	11 (7.0)	152 (13.9)	2 (6.1)
Arthrofibrosis	136 (10.0)	15 (9.6)	108 (9.9)	7 (21.2)
Femoral fracture	27 (2.0)	2 (1.3)	21 (1.9)	0 (0.0)
Polyethylene liner wear	16 (1.2)	0 (0.0)	14 (1.3)	1 (3.0)
Hematoma	15 (1.1)	1 (0.6)	14 (1.3)	0 (0.0)
Patello-femoral joint malfunction	15 (1.1)	2 (1.3)	12 (1.1)	0 (0.0)
Wound dehiscence	11 (0.8)	0 (0.0)	11 (1.0)	0 (0.0)
Wound drainage	12 (0.9)	3 (1.9)	8 (0.7)	0 (0.0)
Failed extensor mechanism	9 (0.7)	1 (0.6)	8 (0.7)	0 (0.0)
Synovial impingement	9 (0.7)	2 (1.3)	6 (0.5)	0 (0.0)
Ingrowth failure	10 (0.7)	2 (1.3)	6 (0.5)	0 (0.0)
Seroma	1 (0.1)	0 (0.0)	1 (0.1)	0 (0.0)
Tibial fracture	3 (0.2)	0 (0.0)	2 (0.2)	0 (0.0)
Other	70 (5.1)	9 (5.7)	54 (4.9)	2 (6.1)

^a Comparison of revision rate per 100 observation years was analyzed using Poisson regression with exact tests. No adjustments were made for confounders.

^b Inclusive of cases with missing bearing surface.

^c Overall comparison of all-cause revision per 100 observation years across groups, p < 0.001. Contrasts: CoCr-HXLPE vs. CoCr-CPE, p < 0.001; OZ-CPE vs. CoCr-CPE, p = 0.03.

^d Overall comparison of aseptic revision per 100 observation years across groups, p = 0.001. Contrasts: CoCr-HXLPE vs. CoCr-CPE, p = 0.007; OZ-CPE vs. CoCr-CPE p=0.02.

^e Overall comparison of septic revision per 100 observation years across groups, p=0.005. Contrasts: CoCr-HXLPE vs. CoCr-CPE p=0.002. OZ-CPE vs. CoCr-CPE p=0.7.

^f Number (%), reasons for revision (except for infection) are not mutually exclusive.

For other abbreviations, see Table 1.

Table 3. All-cause, aseptic, and septic revision rates per 100 observation years, and reasons for revision, listed according to type of highly crosslinked polyethylene (all on cobalt-chromium alloy) ^a

	Total CoCr-HXLPE	CoCr-Durasul	CoCr-Prolong	CoCr-Sigma XLK	CoCr-Other HXLPE
	(n = 7,618)	(n = 557)	(n = 5,132)	(n = 1,481)	(n = 448)
All-cause revisions, n ^b	157	20	115	18	4
Total observation years	16,478	1,908	11,713	2,431	427
Revisions per 100 obs. years, % (95% CI)	0.95 (0.81–1.11)	1.05 (0.68–1.62)	0.98 (0.82–1.18)	0.74 (0.47–1.18)	0.94 (0.35–2.50)
Aseptic revision, n ^c	86	13	66	4	3
Total observation years	16,478	1,908	11,713	2,431	427
Revisions per 100 obs. years, % (95% CI)	0.52 (0.42–0.64)	0.68 (0.40–1.17)	0.56 (0.44–0.72)	0.16 (0.06–0.44)	0.70 (0.23–2.18)
Septic revision, n ^d	71	7	49	14	1
Total observation years	16,478	1,908	11,713	2,431	257
Revisions per 100 obs. years, % (95% CI)	0.43 (0.34–0.54)	0.37 (0.17–0.77)	0.42 (0.32–0.55)	0.58 (0.34–0.97)	0.39 (0.05–2.76)
Reasons for revision ^e
Infection	71 (45.2)	7 (35.0)	36 (39.6)	14 (77.8)	1 (25.0)
Instability	43 (27.4)	3 (15.0)	39 (33.9)	0 (0.0)	1 (25.0)
Pain	25 (15.9)	3 (15.0)	19 (16.5)	3 (16.7)	0 (0.0)
Arthrofibrosis	15 (9.6)	4 (20.0)	9 (7.8)	1 (5.6)	1 (25.0)
Aseptic loosening	11 (7.0)	2 (10.0)	6 (5.2)	2 (11.1)	1 (25.0)
Wound drainage	3 (1.9)	0 (0.0)	3 (2.6)	0 (0.0)	0 (0.0)
Femoral fracture	2 (1.3)	0 (0.0)	2 (1.7)	0 (0.0)	0 (0.0)
Ingrowth failure	2 (1.3)	2 (10.0)	0 (0.0)	0 (0.0)	0 (0.0)
Patello-femoral joint malfunction	2 (1.3)	1 (5.0)	1 (0.9)	0 (0.0)	0 (0.0)
Synovial impingement	2 (1.3)	0 (0.0)	2 (1.7)	0 (0.0)	0 (0.0)
Hematoma	1 (0.6)	1 (5.0)	0 (0.0)	0 (0.0)	0 (0.0)
Failed extensor mechanism	1 (0.6)	0 (0.0)	1 (0.9)	0 (0.0)	0 (0.0)
Polyethylene liner wear	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)
Other	9 (5.7)	1 (5.0)	7 (6.1)	1 (5.6)	0 (0.0)

^a Comparison of revision rate per 100 observation years was analyzed using Poisson regression with exact tests. No adjustments were made for confounders.

^b Overall comparison of all-cause revision per 100 observation years across groups, p = 0.7. No contrasts were performed because the overall test was not significant.

^c Overall comparison of aseptic revision per 100 observation years across groups, p = 0.02. Contrasts: CoCr-Durasul vs. CoCr-Prolong, p = 0.6; CoCr-Other HXLPE vs. CoCr-Prolong, p = 0.9; CoCr-Sigma XLK vs. CoCr-Prolong, p = 0.009.

^d Overall comparison of septic revision per 100 observation years across groups, p = 0.7. No contrasts were performed because the overall test was not significant.

^e Number (%), reasons for revision (except for infection) are not mutually exclusive.

For other abbreviations, see Table 1.

Table 4. Propensity score weighted regression results for risks from all causes, and of aseptic and septic revision, according to type of knee bearing. Hazard ratios and 95% confidence Intervals

	All-cause		Aseptic		Septic
	HR (95% CI)	p-value	HR (95% CI)	p-value	HR (95% CI)	p-value
Model 1
CoCr-HXLPE vs. CoCr-CPE	1.2 (0.9–1.5)	0.2	1.3 (0.9–1.8)	0.2	1.1 (0.8–1.6)	0.6
OZ-CPE vs. CoCr-CPE	1.4 (0.3–5.9)	0.7	0.7 (0.3–1.4)	0.3	2.2 (0.3–16.3)	0.4
Model 2
CoCr-Durasul vs. CoCr-CPE	0.9 (0.5–1.5)	0.6	0.7 (0.2–2.0)	0.5	1.2 (0.6–2.2)	0.6
CoCr-Prolong vs. CoCr-CPE	1.1 (0.8–1.6)	0.4	1.2 (0.7–1.9)	0.5	1.1 (0.7–1.7)	0.7
CoCr-Sigma XLK vs. CoCr-CPE	1.1 (0.4–3.1)	0.9	1.2 (0.2–6.8)	0.8	0.9 (0.3–2.6)	0.9
OZ-CPE vs. CoCr-CPE	1.5 (0.4–5.1)	0.6	0.8 (0.4–1.4)	0.4	2.4 (0.4–14.4)	0.3