Time-dependent improvement in functional outcome following LCS rotating platform knee replacement

Abstract

Background and purpose: Long-term follow-up studies after total knee replacement (TKR) using an LCS rotating platform have shown survival rates of up to 97%. Few studies have evaluated short-term functional outcome and its improvement over time. We determined the time course of functional outcome as evaluated by the knee injury and osteoarthritis outcome score (KOOS) over the first 4 years after TKR using the LCS mobile bearing.

Patients and methods: 50 unselected patients (mean age 70 (40-85) years, 33 women) with osteoarthritis in one knee underwent TKR with an LCS mobile bearing. Data were collected by an independent investigator preoperatively and at 6 weeks, 3 months, 6 months, 1 year, 2 years and 4 years postoperatively. KOOS, a self-assessment function score validated for this purpose, and range of motion (ROM) were determined at all follow-ups.

Results: The mean KOOS pain score increased from 43 before surgery to 66 at 6 weeks and 88 at 2 years. It was 84 at 4 years. The mean KOOS activities of daily living score (ADL) increased from 49 before surgery to 73 at 6 weeks, then gradually to 90 at 2 years. It decreased to 79 at 4 years. Mean passive ROM was 112° before surgery, 78° at departure from hospital, and then gradually increased to 116° at 2 years and 113° at 4 years.

Interpretation: Recovery after TKR is time-dependent. Most of the expected improvement in pain and function is achieved at 6 months postoperatively, but some further improvement can be expected up to 2 years postoperatively. ROM will also gradually improve up to 2 years after TKR, and reach the same level as before surgery.

Figure 1.

Graph showing improvement in the KOOS pain subscale with time. Values are mean ± CI. Pairwise comparisons revealed statistically significant improvement between P and all other time points (p<0.001), and between 3 months and 2 years (p = 0.02). P: preoperatively.

Figure 2.

Graph showing improvement in the KOOS ADL subscale with time. Values are mean ± CI. Pairwise comparisons revealed statistically significant improvement between values preoperatively and at all other time points (p < 0.001) and between those at 6 months and 2 years (p = 0.005). Values at 4 years were significantly worse than at 2 years (p < 0.001). See legend to Figure 1 for explanation of abbreviations.

Figure 3.

Graph showing improvement in the KOOS symptoms subscale with time. Values are mean ± CI. Pairwise comparisons revealed statistically significant improvement between values preoperatively and at 6m (p < 0.001), between values preoperatively and at 1 year (p < 0.001), between values preoperatively and at 2 years (p < 0.001), between values preoperatively and at 4 years (p < 0.001), and between values at 6 months and 4 years.

Figure 4.

Graph showing improvement in the KOOS QoL subscale with time. Values are mean ± CI. Pairwise comparisons revealed statistically significant improvement between values preoperatively and all other time points (p < 0.001), between values at 3 months and 1 year (p = 0.02), between values at 3 months and 2 years (p < 0.001), and between values at 3 months and 4 years (p < 0.001).

Figure 5.

Graph showing improvement in the KOOS sport/rec subscale with time. Values are mean ± CI. Pairwise comparisons revealed statistically significant improvement between values preoperatively and at 6 months (p < 0.001), between values preoperatively and at 1 year (p < 0.001), between values preoperatively and at 2 years (p < 0.001), between values preoperatively and at 4 years (p < 0.001), and between values at 3 months and 6 months (p < 0.001).

Figure 6.

Graph showing improvement in active ROM (red line) and passive ROM (blue line) with time. Values are mean ± CI. Pairwise comparisons for active ROM revealed statistically significant differences between values at discharge from hospital and at all other time points (p < 0.001), between values at 6 months and 1 year (p = 0.004), between values at 6 months and 2 years (p < 0.001), and between values at 6 months and 2 years (p = 0.001). Pairwise comparisons for passive ROM revealed statistically significant differences between values at discharge from hospital and at all other time points (p < 0.001), between values at 6 months and 2 years (p < 0.001), and between values at 1 year and 2 years (p = 0.005). P: preoperatively; D: discharge from hospital.