Results

Outcome scores were available at the 2-year time point for 548 TKAs (516 patients, 90.8%). Five patients (5 TKAs, 0.8%) had died from unrelated causes, 9 (9 TKAs, 1.5%) had withdrawn from the study, 36 (40 TKAs, 6.6%) had been lost to follow-up, and 6 (6 TKAs, 0.99%) had been revised.

The overall revision rate was 0.49% (95% CI 0.16-1.52) at 1 year and 0.99% (95% CI 0.44-2.18) at 2 years (6 of 608 TKAs revised) (Fig. 2). Reasons for revision included general instability (N = 1), stiffness (N = 1), patella resurfacing (N = 1), valgus malalignment (N = 1), and infection (N = 2). Stiffness requiring manipulation under anesthetic was reported in 14 cases (2.3%). At the 2-year follow-up time point, 17 cases (2.8%) exhibited a flexion range less than 100°, of which 3 cases (0.5%) were still under clinical review. The mean (range) ROM for the cohort improved from 110° (55-145) preoperatively to 118° (80-150) at 1 year (P < .001) and 119° (50-148) at 2 years (P < .0001) (Fig. 3). There was no significant difference in ROM at 1 and 2 years postsurgery (P = .095). Significant improvements were seen from presurgery to 2 years for all scores, and between 1 and 2 years for the OKS, KOOS symptoms, KOOS quality of life, and the FJS (Table 2).

Figure 2: Kaplan-Meier survival curve for all-cause revision within cohort across 2-year follow-up.

Figure 3: Boxplot (mean, interquartile range, range) of maximum ROM assessed preoperatively and at 1 and 2 years postoperatively.

Score | Preoperative | 1-y postoperative | 2-y postoperative | P valuea
Preoperative – 2 y | 1 y-2 y
KOOS symptoms | 45 ± 19 (0-93)608 | 81 ± 16 (14-100)549 | 84 ± 14 (14-100)544 | <.0001 | 0.041
KOOS pain | 45 ± 17 (0-100)608 | 86 ± 16 (17-100)549 | 89 ± 14 (22-100)546 | <.0001 | 0.122
KOOS ADL | 50 ± 19 (0-99)607 | 88 ± 14 (24-100)545 | 90 ± 14 (18-100)545 | <.0001 | 0.063
KOOS QoL | 25 ± 18 (0-88)608 | 73 ± 21 (0-100)549 | 77 ± 21 (0-100)543 | <.0001 | 0.033
KOOS sports | 18 ± 21 (0-100)598 | 59 ± 30 (0-100)494 | 62 ± 30 (0-100)483 | <.0001 | 0.577
FJS | - | 64 ± 29 (0-100)522 | 70 ± 28 (0-100)542 | - | <0.0001b
OKS | 21 ± 8 (2-45)608 | 40 ± 7 (9-48)548 | 42 ± 7 (8-48)544 | <.0001 | 0.03101
UCLA | 4 ± 2 (1-10)605 | 6 ± 2 (1-10)549 | 6 ± 2 (1-10)543 | <.0001 | >0.999
EQ-5D VAS | 69 ± 20 (10-100)605 | 82 ± 16 (22-100)550 | 81 ± 17 (6-100)548 | <.0001 | >0.999

When asked “Overall, how are your problems now, compared to before your operation?” 95.7% of patients answered “much better” or “a little better” at 2 years postsurgery. When asked “How would you describe the results of your operation?” 94.5% of patients answered “good,” “very good,” or “excellent” at 2 years (Fig. 4). The median satisfaction VAS was 9.2 at 2 years (IQR 8.2-10). Figure 5 illustrates patients’ responses at the 2-year time point.

Figure 4: Satisfaction outcomes at 2 years postsurgery answering the questions (a) “Overall, how are your problems now, compared to before your operation?” and (b) “How would you describe the results of your operation?”.

Figure 5: Illustrative boxplot (mean, interquartile range, range) produced using patient responses on the VAS satisfaction scale.

The potential learning curve was assessed using the OKS, ROM, satisfaction score, and revisions for the first 10 and following 40 procedures for all surgeons who performed at least 50 operations (8 surgeons; 80 cases in the “first 10” group and 320 cases in the “last 40” group). No statistically significant differences were seen between these groups for the OKS, ROM, or satisfaction scores at either 1- or 2-year follow-up (Table 3).

Parameter | First 10 cases | Last 40 cases | P valuea1 y | P valuea2 y
1 y | 2 y | 1 y | 2 y
OKS | 41 ± 7 (10–48) | 41 ± 9 (10–48)a | 41 ± 6 (16–48) | 42 ± 6 (16–48) | 0.946 | 0.874
ROM, degrees | 117 ± 11 (80–150) | 119 ± 14 (50–145)a | 118 ± 11 (87–145) | 120 ± 11 (85–148) | 0.301 | 0.712
Satisfaction score | 8.9 ± 1.5 (4.0–10.0) | 8.7 ± 2.0 (2.0–10.0)a | 8.9 ± 1.5 (2.0–10.0) | 8.9 ± 1.7 (0.0–10.0) | 0.845 | 0.133
Revisions, n | 1 patella resurfacing (12 mo) | 1 infection (22 mo) | 1 stiffness (11 mo) | None | - | -