Univariate analyses

Prosthetic survivorship was estimated using the Kaplan-Meier technique, and hazard ratios were estimated by univariate Cox analyses (Table 4). The overall survival of the revision prostheses, with repeat revision as the end point, was 95% (95% confidence interval, 94% to 96%) at two years (1,874 knees), 89% (95% confidence interval, 88%

to 90%) at five years (944 knees), and 79% (95% confidence interval, 78% to 81%) at ten years (141 knees) (Figure 5).

Figure 5. Overall cumulative survival as a function of time in years for revision total knee arthroplasty implants. In this analysis revision of the revision TKA implants, not loosening per se, was used as the end point.

Table 4. Estimated hazard ratios in uni- and multivariate Cox analyses.

Univariate analysis Multivariate analysis

Factor Hazard

Not included in multivariate analysis (not significant in univariate analysis)

Year of first revision operation (compared with 1990-1995

1996-2002) 0.56* 0.43 – 0.72 < 0.0005 0.67* 0.50 – 0.90 < 0.01 Time between previous operation

and revision

(compared with < 5 years

≥ 5 years) 0.52* 0.41 – 0.67 < 0.0005 0.62* 0.47 – 0.82 < 0.005 Reason for revision

(compared to the overall effect) infection

Type of implanted prosthesis (compared with hinged)

condylar 1.18 0.86 – 1.62 0.32

Not included in multivariate analysis (not significant in univariate analysis)

Not included in multivariate analysis because of missing values

Fixation

(compared with cementless)

Not included in multivariate analysis because of missing values

Not included in multivariate analysis (not significant in univariate analysis)

Type of operating hospital (compared with other)

Not included in multivariate analysis (not significant in univariate analysis)

*) non-proportional hazards, hazard ratio is not constant

Prosthetic survival at five years, with repeat revision as the end-point, was 82% (95%

confidence interval, 78% to 87%) for patients younger than fifty-six years of age, 87%

(95% confidence interval, 84% to 89%) for those between the ages of fifty-six and seventy years, and 92% (95% confidence interval, 90% to 94%) for those older than seventy years of age. Prosthetic survival was significantly better for the patients older than seventy years than it was for the patients younger than seventy years (p < 0.005).

However, it was not better for the patients between the ages of fifty-six and seventy years than it was for those younger than fifty-six years (Figure 6).

Figure 6. Cumulative survival as a function of time in years for revision total knee arthroplasty implants in three different age groups (groups compared against each other are “< 56 years”,

“56-70 years” and “> 70 years”). Revision of the rTKA was used as the end point.

Prosthetic survival at five years, with repeat revision as the end-point, was 84% (95%

confidence interval, 81% to 87%) for men and 90% (95% confidence interval, 88% to 91%) for women (p = 0.07). The five-year survival rate was significantly worse (p <

0.0005) for patients who had had their first revision operation between 1990 and 1995 (85%; 95% confidence interval, 84% to 87%) than it was for patients who had had their first revision between 1996 and 2002 (92%; 95% confidence interval, 91% to 94%) (Figure 7).

Figure 7. Cumulative survival of revision total knee arthroplasty implants according to the period of the first revision. The first revisions were divided into those performed between 1990 and 1995 (group “1990-1995”) and compared to those in whom the first revision was performed later, between 1996 and 2002 (group “1996-2002”). The revision of the rTKA was used as the end-point.

Similarly, the survival rate following the revision arthroplasties performed less than five years after the primary operation (85%; 95% confidence interval, 83% to 87%) was significantly lower (p < 0.0005) than the rate following the revisions performed five years or more after the primary operation (92%; 95% confidence interval, 91% to 94%) (Figure 8).

Figure 8. Cumulative survival of revision total knee arthroplasty implants in those patients in whom the primary TKA lasted for less than five years(group “< 5 years”) compared to those, in whom it lasted for longer than five years(group “> 5 years”), i.e. according to the time between the primary and revision TKA. Revision of the rTKA was used as the end-point.

The survival of revisions done in patients with patellar subluxation was worse (p <

0.005) than the overall survival of revisions performed for other reasons (Figure 9).

Pairwise comparisons with use of the log-rank test indicated that the survival of revisions done because of subluxation differed significantly from that of revisions performed because of a fracture of the prosthesis (p < 0.005), but did not differ significantly from the survival of revisions due to loosening, malposition, infection, or other patellar complications.

The five-year survival rate, with repeat revision as the end-point, was 93% (95%

confidence interval, 88% to 95%) for the AGC Dual Articular prosthesis (Biomet Merck Inc., Bridgend, UK), 90% (95% confidence interval, 84% to 93%) for the AGC V2 prosthesis (Biomet), 87% (95% confidence interval, 83% to 90%) for the Duracon prosthesis (Stryker Howmedica Osteonics, Allendale, New Jersey), 98% (95%

confidence interval, 96% to 99%) for the Duracon Modular prosthesis (Stryker Howmedica Osteonics), 89% (95% confidence interval, 85% to 93%) for the Link Endo-Modell prosthesis (Waldemar Link, Hamburg, Germany), and 98% (95%

confidence interval, 94% to 100%) for the NexGen prosthesis (Zimmer, Warsaw, Indiana) (survival curves not shown). No patient in the registry had had a P.F.C.

Sigma prosthesis (DePuy Orthopaedics, Warsaw, Indiana) for five years, but the survival rate of that prosthesis at 4.5 years was 98% (95% confidence interval, 93% to 99%). The NexGen and Duracon Modular prostheses had better survival rates (p <

0.05) than the Duracon implant, which had the shortest time-to-event survival.

Figure 9. Cumulative survival of revision total knee arthroplasty compared in different sub-populations based on the reason (indication) for re-revision. The groups compared against each other are “Fracture of prosthesis”, “Infection”, “loosening, any component or both components”, “subluxation”, “malposition of prosthesis”, “other reason” or “patellar complication”. Revision of the rTKA was used as the end-point.

Cement fixation (p < 0.005, Figure 10) and bone-grafting (p = 0.05, Figure 11) improved prosthetic survival, whereas hybrid fixation did not differ significantly from cementless fixation with regard to prosthetic survival

The diagnosis, type of prosthesis, primary complications, and type of hospital did not significantly affect prosthetic survival.

Figure 10. Cumulative survival of revision total knee arthroplasty implants based on the use of cement for fixation. Cement was used for the fixation of both components (group “cemented”), one component only (group “hybrid”) or was not used at all (group “cementless”). Revision of the rTKA was used as the end-point.

Figure 11. Cumulative survival of revision total knee arthroplasty based on the use of structural bone allografts, which were used if considered necessary and available (group “used”) or, alternative, not used (group “not used”). Revision of the rTKA was used as the end-point.

.