Highly cross-linked versus conventional polyethylene inserts in total hip arthroplasty, a five-year Roentgen stereophotogrammetric analysis randomised controlled trial

Table 1 Inclusion and exclusion criteria

Inclusion	Exclusion
Primary arthroplasty due to:	Patients who recently suffered:
Primary osteoarthritis	Post-operative osteoarthritis
Avascular necrosis	Charnley C osteoarthritis
Femoral neck fracture	Infection of the hip
Hip dysplasia
Age between 60 - 75 yr at surgery	Prior osteotomy or arthroplasty of the affected hip
Willing to comply with the post-operative review program	Under treatment for osteoporosis
	Body mass index > 35 kg/m2
	Requiring cortisone medication

Table 2 Patient and baseline characteristics

	Conventional PE	REXPOL
Number of patients, n (%)	25 (49)	26 (51)
Gender, n (%)
Male	10 (40)	10 (39)
Female	15 (60)	16 (59)
BMI, mean ± SD kg/m2	26.7 ± 2.9	27.2 ± 3.4
Age at operation in years, mean ± SD	68.5 ± 4.6	68.6 ± 5.1
HOOS pain, mean ± SD	46.5 ± 21.6	51.1 ± 17.7
HOOS ADL, mean ± SD	41.1 ± 16.6	46.0 ± 17.2
HHS, mean ± SD	50.6 ± 12.7	54.6 ± 10.9

PE: Polyethylene; BMI: Body mass index; HOOS: Hip injury and osteoarthritis outcome score; ADL: Activity of daily living; HHS: Harris hip score.

Table 3 Total wear in all directions at the five-year follow-up, presented as mean with ranges

	Conventional PE (Polyethylene)	REXPOL	P value
Medial (mm)	-0.128 (-0.202 to -0.054)	0.013 (-0.054 to 0.081)	0.006
Proximal (mm)	0.196 (0.054 to 0.338)	0.017 (-0.120 to 0.154)	0.07
Volume (mm3)	113.39 (-2.48 to 229.26)	-30.59 (-167.16 to 105.98)	0.10
Corrected volume (mm3)	121.6 (17.76 to 225.46)	-12.45 (-122.94; 98.03)	0.07

Table 4 Mean wear rates per year, presented as mean with ranges

	Conventional PE (Polyethylene)	P value	REXPOL	P value
Medial (mm/yr)	-0.021 (-0.028 to -0.015)	< 0.001	0.004 (-0.002 to 0.009)	0.21
Proximal (mm/yr)	0.033 (0.018 to 0.047)	< 0.001	0.003 (-0.011 to 0.017)	0.66
Volume (mm3/yr)	15.94 (2.729 to 29.15)	0.02	-5.545 (-20.36 to 9.269)	0.46
Corrected volume (mm3/yr)	18.53 (7.188 to 29.86)	0.002	-2.142 (-14.13 to 9.841)	0.72

Table 5 Functional outcomes at the five-year follow-up, presented as mean with 95%CI

	Univariate			Multivariate
	Conventional PE (n = 17)	REXPOL (n = 17)	P value	Adjusted β-coefficient	P value
HOOS pain	93.8 (86.8; 100)	85.9 (77.1; 94.7)	0.15	-3.3 (-14.9; 8.3)	0.57
HOOS ADL	89.0 (81.2: 96.8)	77.6 (66.6; 88.5)	0.08	-8.6 (-23.3; 6.1)	0.24
HHS	89.7 (83.0; 96.4)	86.5 (78.8; 94.2)	0.51	0.15 (-10.1; 10.4)	0.98

PE: Polyethylene; HOOS: Hip injury and osteoarthritis outcome score; ADL: Activity of daily living; HHS: Harris hip score.