All-polyethylene vs. metal-backed tibial component in total knee arthroplasty—a randomized RSA study comparing early fixation of horizontally and completely cemented tibial components: Part 1. Horizontally cemented components: AP better fixated than MB

Figures & data

Table 1.  Patient profile with APHC (all-polyethylene horizontally cemented components) vs. MBHC (metalbacked horizontally cemented components) after randomization. MBHC/RSA denotes patient profile in group included in RSA after exclusions

	APHC	MBHC	MBHC/RSA
No. of knees	20	20	16
Excluded from RSA	1	4	–
Women; men	16; 4	16; 4	13; 3
Age, median year	73	73	73
range	45–82	58–81	58–81
Weight, median kg	79	76	75
range	56–113	56–103	56–103
Deformity > 10°	1	1	1

Figure 1. All-polyethylene and metal-backed tibia components of the AGC pros-thesis. Both are non-modular, have identical articulating surface and are similar underneath. Stem geometry is identical.

Figure 2. Standard anterior postoperative radiographs of the a) all-polyethylene, horizontally cemented (APHC), and b) metal-backed, horizontally cemented (MBHC) tibial components.

Table 2.  Precision in actual set-up

Migration	Mean error, 95% confidence limits
x-rotation	0.07° ± 0.13°
y-rotation	0.06° ± 0.17°
z-rotation	0.06° ± 0.13°
y-translation, mm	0.06 ± 0.22

Table 3.  HKA (in degrees) 3 months postoperatively, for the separate groups. Figures denote number of individuals within each HKA interval

HKA °	180 ± 2	180 ± 4	180 ± 6	180 ± >6
APHC	8	5	3	2^a
MBHC	11	4	3	0
MBHC/RSA	8	3	3	0

For abbreviations, see Table 1.

^a167° and 187°

Table 4.  Rotations along the 3 cardinal axes. Figures denote degrees

	APHC		MBHC/RSA		p-value
	median	range	median	range
X-rotation
3 months	0.12	0.02–1.8	0.37	0.07–2.5	0.03
12 months	0.18	0.01–1.2	0.38	0.12–3.5	>0.1
24 months	0.25	0.04–0.80	0.47	0.02–4.0	>0.1
Y-rotation
3 months	0.08	0.00–0.60	0.25	0.03–2.3	0.008
12 months	0.14	0.00–0.65	0.47	0.04–6.5	0.001
24 months	0.15	0.01–0.63	0.47	0.08–8.5	0.002
Z-rotation
3 months	0.14	0.06–1.0	0.56	0.06–2.1	0.009
12 months	0.28	0.04–1.6	0.48	0.02–3.6	>0.1
24 months	0.24	0.03–1.1	0.92	0.06–3.2	>0.1
Maximum lift-off
3 months	0.06	−0.33–0.48	0.32	−0.17–1.1	0.001
12 months	0.13	−0.10–0.72	0.24	−0.41–0.91	>0.1
24 months	0.14	0.00–0.58	0.26	−0.62–0.95	>0.1

For abbreviations, see Table 1.

Figure 3. Box-plot illustrating subsidence of components in all-polyethylene, horizontally cemented (APHC) and metal-backed, horizontally cemented (MBHC) groups. There were no statistically significant differences. The line within the box denotes the median, the box represents the 25–75% range, and the whiskers represent non-outlier min and max. Extremes are marked “♦”.

Table 5.  Maximal total point motion (MTPM) in mm. Values are median (range)

Group	0–3 months	0–1 year	0–2 years	1–2 years	“unstable”^a
APHC	0.22 (0.05–1.3)	0.43 (0.00–0.68)	0.36 (0.03–1.0)	0.12 (0.00–0.68)	5 of 20
MBHC/RSA	0.78 (0.16–2.3)	0.69 (0.33–6.4)	1.04 (0.25–8.7)	0.33 (0.06–2.5)	8 of 13
p-value	0.002	0.002	0.003	0.02	>0.1

For abbreviations, see Table 1.

^a The number of “unstable” components, i.e. migration > 0.2 mm during the second year, is presented.