Design-related risk factors for revision of primary cemented stems

Figures & data

Table 1. Implant-related parameters for the polished Exeter stem entered into the statistical analysis

Classification/Name	Number
Stem
Size
light weight–0	2,781
light weight–1	8,019
narrow	6,205
standard	2,860
heavy duty	1,013
ultra heavy duty	130
Offset (mm)
37.5	4,951
44	15,416
50	641
Taper
old	5,775
V40	15,233
Head
Material
standard	5,751
alumina ceramic	630
Orthinox	14,627
Length
short	3,707
medium	14,671
long	2,542
x-long	88
Diameter (mm)
22	1,567
26	443
28	18,750
30	248

Table 2. Implant-related parameters for the Lubinus SPII stem entered into the statistical analysis. All implants were supplied with 28-mm heads

Classification/Name	Number
Stem
Size
x-small	4,445
small	11,158
medium	14,187
large	9,350
x and xx-large	3,896
CCD
117	1,388
126	36,179
135	5,469
Offset
standard (s-off)	41,276
x-offset (x-off)	1,760
Head
Material
standard	36,802
alumina ceramic	6,234
Length
short (s, 46)	12,538
medium (m, 49)	19,797
long (l, 53)	9,833
x-long (xl, 60)	868
Offset + neck ^a
1: s-off + s neck	11,727
2: s-off + m neck or x-off + s neck	19,921
3: s-off + l neck or x-off + m neck	10,290
4: s-off + xl neck or x-off + l neck or xl neck	1,098

^a Neck length as extracted from the database after assembly of the stem, coded into 4 classes. A higher number means a longer neck. Class 4 included 32 implants with combined x-off and xl-neck.

Table 3. Implant-related parameters for the Spectron EF Primary stem entered into the statistical analysis. All implants were supplied with 28-mm heads made of cobalt-chromium alloy

Classification/Name	Number
Stem
Size
1	1,101
2	3,501
3	1,987
4+5	551
Offset
standard (s-off)	4,976
h-offset (h-off)	2,164
Head
Length
short or standard (s, -3, 0)	3,847
long (l, +4)	2,264
x-long (xl, +8)	822
x-long+ (xxl, +12 or xxxl, +16)	207
Offset + neck ^a
1: s-off or h-off + s neck	2,696
2: s-off + l neck or h-off + s neck	2,716
3: s-off + xl neck or h-off + l neck	1,275
4: s-off + xx l neck or h-off + xl neck	362
5: s-off + xxxl neck or h-off + xxl neck or xxxl neck	91

^a Neck length as extracted from the database after assembly of the stem, coded into 5 classes. A higher number means a longer neck.

Table 4. Relative risks of aseptic stem revision during entire observation period (Lubinus SP, Spectron EF Primary) or within 3 years (Exeter) and 95% CI for implant-related parameters for each stem type. Data from Cox regression adjusted for age, sex, diagnosis, bilaterality, side, and implant-specific parameters (see text). Implant-related parameters with statistically significant influence are shown

	Relative Risk [Exp (B)]	95% CI		p-value
		Lower	Upper
Exeter polished (n = 21,008)
Femoral head diameter
22 mm	2.37	1.32	4.23	0.004
26 mm	0.02	0.00	30.03	0.3
28 mm, reference	1.00
30 mm	0.79	0.19	3.28	0.7
Lubinus SPII (n = 43,036)
Size
x-small	1.72	1.22	2.44	0.002
small	0.99	0.74	1.32	0.9
medium, reference	1.00
large	0.94	0.70	1.26	0.7
x and xx-large	1.01	0.69	1.47	1.0
Head
ceramic	0.52	0.36	0.76	0.001
cobalt-chromium, reference	1.00
Offset + neck
1	0.73	0.55	0.97	0.03
2 reference	1.00
3	1.11	0.86	1.43	0.4
4	1.72	1.09	2.71	0.02
Spectron EF Primary (n = 7,140)
Size
1	2.23	1.25	3.97	0.006
2 reference	1.00
3	0.75	0.40	1.41	0.4
4+5	0.55	0.17	1.84	0.3
Off-set + neck
1	1.27	0.68	2.37	0.4
2 reference	1.00
3	1.54	0.80	2.98	0.2
4	2.03	0.81	5.11	0.1
5	6.89	2.54	18.63	< 0.001

Table 5. Revisions for all the femoral stems analyzed (infections excluded)

Primary	Exeter Polished (All)	Exeter (old)	Exeter V40	Lubinus SPII	Spectron EF
	% (n)	% (n)	% (n)	% (n)	% (n)
Aseptic Loosening	0.4 (96)	1.1 (71)	0.2 (25)	0.3 (114)	0.8 (57)
Dislocation	0.5 (116)	0.6 (39)	0.5 (77)	0.5 (244)	0.5 (35)
Fracture	0.2 (43)	0.3 (18)	0.2 (25)	0.0 (17)	0.0 (3)
Implant failure	0.0 (3)	0.0 (0)	0.0 (3)	0.0 (8)	0.0 (0)
Technical reason	0.1 (12)	0.1 (7)	0.0 (5)	0.0 (12)	0.1 (4)
Pain only	0.0 (3)	0.0 (0)	0.0 (3)	0.0 (5)	0.0 (2)
Total	1.2 (273)	2.1 (135)	1.1 (138)	0.8 (400)	1.4 (101)

Table 6. Number of revisions and causes of revision for Lubinus SPII stems with either cobalt-chromium or aluminium oxide femoral heads (infections excluded)

	Cobalt-chromium% (n)	Aluminium oxide% (n)
Aseptic loosening	29 (104)	24 (9)
Dislocation	61 (222)	53 (20)
Fracture	4.4 (16)	3 (1)
Implant failure	1.1 (4)	11 (4)
Technical reason	2.5 (9)	8 (3)
Pain only	1.1 (4)	3 (1)
Other mechanical reason	1.1 (4)	0 (0)
Total	100 (363)	100 (38)