Early migration of tibial components is associated with late revision

Figures & data

Figure 1. PRISMA flow chart of both reviews. Details of the 28 PFI combinations are given in Table 1. RSA: radiostereometric analysis; TKP: total knee prosthesis; FU: follow-up; PFI: prosthesis-fixation-insert combination.

Table 1. Prosthesis, Fixation and Insert (PFI) characteristics.

PFI	89Prosthesis	Fixation	Insert	Number of RSA studies	Number of survival studies	Number of combinations
1	Anatomic Modular Knee, CR, MB	Cement	Fixed, Modular	2	2	4
2	Tricon M, PE pegs, MB	Porous coated, no stem, no screws	Fixed	3	1	3
3	Duracon, CR, MB	Cement	Fixed, Modular	1	1	1
4	Total Condylar, no CR	Cement	All PE	1	5	5
5	Freeman-Samuelson	Uncoated	All PE (HDP)	2	2	4
6	Freeman-Samuelson, PE pegs, MB	Uncoated	Fixed	1	2	2
7	Anatomic Graduated Component 2000, CR, MB	Porous coated	Fixed, Non-modular	1	1	1
8	Miller-Galante I, 4 pegs, CR, MB	Cement	Fixed, Modular	2	1	2
9	Miller-Galante II, 4pegs, CR, MB	Cement	Fixed, Modular	2	1	2
10	Optetrak, PS, MB, finned stem	Cement	Fixed	1	1	1
11	Kinemax Plus, no PS	Cement	All PE	1	1	1
12	Profix, stemmed, CR, MB	Cement	Fixed, Modular	1	3	3
13	Porous Coated Anatomic, cruciform stem, CR, MB	Cement	Fixed, Modular	1	1	1
14	Kinematic Condylar, CR, MB	Cement	Fixed, Non-modular	6	1	6
15	Miller-Galante I, 4 pegs, CR, MB	Porous coated, 4 screws	Fixed, Modular	2	2	4
16	Anatomic Graduated Component, CR, MB	Cement	Fixed, Non-Modular	3	3	9
17	Press Fit Condylar, CR, MB	Porous coated	Fixed, Modular	1	1	1
18	Duracon, CR, MB	HA/PA coated	Fixed, Modular	1	5	5
19	Press Fit Condylar, CR, MB	Cement	Fixed, Modular	9	1	9
20	Press Fit Condylar Sigma, CR, MB	Cement	Fixed, Modular	3	2	6
21	NexGen Legacy, PS, MB	Cement	Fixed, Modular	2	2	4
22	Freeman-Samuelson, PE pegs, MB	Cement	Fixed	2	1	2
23	Freeman-Samuelson, metal pegs, MB	Cement	Fixed, Modular	2	2	4
24	NexGen, CR, MB, stem	Cement	Fixed, Modular	1	2	2
25	NexGen, 4 pegs, CR, MB	Cement	Fixed, Modular	1	2	2
26	Miller-Galante II, 4 pegs, CR, MB	Porous coated, 4 screws	Fixed, Modular	1	2	2
27	Porous Coated Anatomic, no PS, MB, no stem	Porous coated, 1 screw	Fixed	1	2	2
28	Interax, CR, MB	Uncoated	Fixed, two halfbearings	2	1	2
Total				50	56	89

CR = cruciate retaining

HA/PA = Hydroxyapatite/periapatite

HDP = high density poly-ethylene

MB = metal backed

PE = poly-ethylene

PS = posterior stabilized

Figure 2. Scatter plot showing association between migration in the first postoperative year expressed as maximal total point motion (MTPM) in mm and revision rate for aseptic loosening of the tibial component at 5 years, as a percentage. The colored lines are derived from weighted regression according to match quality, survival study quality, and RSA study quality (the coefficients and 95% CI are given in Table 2).

Table 2. Association between MTPM at 1 year and revision rate for aseptic loosening at 5 years

	Increase in revision (%) / mm MTPM	95% CI
Crude	7.6	5.7–9.5
Adjusted for ^a :
N survival ^b	7.4	5.6–9.2
N RSA ^b	7.1	5.4–8.8
Survival study quality	8.4	6.5–10.3
RSA study quality	7.4	5.4–9.4
Total Match Score	7.6	5.6–9.4
Range of values:	7.1–8.4	5.4–10.3

Table 2 shows the increase in the 5-year revision (%) for each mm increase in MTPM at 1 year. In the crude analysis (unadjusted) 7.6% [95%CI 5.7–9.5], p<0.001, is added to the 5-year revision rate for every mm increase in MTPM at 1 year.

^a When adjusted for e.g. the number of TKP in survival studies (N survival) 7.4% [95%CI 5.6–9.2], p<0.001, is added to the 5-year revision rate for every mm increase in MTPM at 1 year.

The association between MTPM1 and revision rate for aseptic loosening remains significant, when adjusting for confounders (all p-values <0.001).

^b The square rote of N was used for the weighted regression, so larger studies weigh heavier.

N survival = number of TKP in survival studies

N RSA = number of TKP in RSA studies

Figure 3. Scatter plot showing the relation between MTPM at 1 year and revision of the tibial component for aseptic loosening at 5 years. The thresholds of 0.54 mm and 1.6 mm for the three categories (acceptable, at risk, and unacceptable) are shown.

Figure 4. Scatter plot showing the relation between MTPM at 1 year and revision of the tibial component for aseptic loosening at 10 years. The thresholds of 0.45 mm and 1.6 mm for the three categories (acceptable, at risk, and unacceptable) are shown.

Figure 5. Dot chart showing the pooled MTPM ranked by the pooled revision rate for each PFI combination. The acceptable PFI combinations (based on migration) had excellent track records and low revision rates in several national registries, whereas the unacceptable PFI combinations (based on migration) have been abandoned. Thus, the potential influence of publication bias on the results is small. A detailed description of each PFI combination is given in Table 1. R5(%): pooled revision rate at 5-year follow-up, as a percentage.

Figure 6. Flow chart showing the role of RSA studies in the phased evidence-based introduction of new TKPs, modified according the Malchau proposal. Stabilization is defined as migration of less than 0.2 mm in the second postoperative year (MTPM from year 1 to year 2) as described by Ryd et al. (1995). See discussion for details of each phase.

Ryd L, Carlsson L, Herberts P. Micromotion of a noncemented tibial component with screw fixation. An in vivo roentgen stereophotogrammetric study of the Miller-Galante prosthesis. Clin Orthop 1993; (295): 218-25.

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