Comparison of dual-mobility cup and unipolar cup for prevention of dislocation after revision total hip arthroplasty

Figures & data

Table 1. Baseline characteristics of the dual-mobility and unipolar cup THAs^a

	Dual-mobility (n = 150)	Unipolar (n = 166)	Mean/Risk difference^b(95% CI)	p-value
Mean age (SD)	73 (11.1)	65 (15.2)	−7.9 (−11 to −4.9)	< 0.001
Mean BMI (SD)	26 (5.8)	26 (5.2)	−0.2 (−1.4 to 1.0)	0.8
Mean operating time (SD), min	152 (60)	185 (69)	33 (19 to 48)	< 0.001
Women (%)	84 (56)	76 (46)	10 (−0.7 to 21)	0.07
BMI ≥30 (%)	38 (25)	39 (24)	1.8 (−7.7 to 11)	0.7
Smoking status^c(%)
Ever-smoker	58 (46)	59 (52)	−6.5 (−19 to 6.1)	0.3
Never-smoker	69 (54)	54 (48)
ASA score (%)
1–2	96 (64)	116 (70)	−5.9 (−16 to 4.5)	0.3
3–4	54 (36)	50 (30)
Diabetes (%)	26 (17)	19 (11)	5.9 (−1.9 to 14)	0.1
Previous THA revision (%)	38 (25)	36 (22)	6.7 (−5.7 to 13)	0.4
Surgical approach (%)
With osteotomy	33 (22)	48 (29)	−6.9 (−17 to 2.7)	0.2
Without osteotomy	117 (78)	118 (71)
Posterior	68 (46)	43 (26)
Anterior Hueter	15 (10)	14 (8.4)
Antero-lateral	34 (23)	61 (37)
Indication for revision (%)
Aseptic loosening	51 (34)	76 (46)	−12 (−23 to −1.1)	0.03
Dislocation	41 (27)	17 (10)	17 (8.6 to 26)	< 0.001
Infection	22 (15)	26 (16)	−1.0 (−8.9 to 6.9)	0.8
Pain/impingement	4 (2.7)	19 (11)	−8.8 (−14 to −3.3)	0.003
Polyethylene wear	5 (3.3)	5 (3.0)	0.3 (−3.6 to 4.2)	0.9
Adverse local tissue reaction	7 (4.7)	7 (4.2)	0.5 (−4.1 to 5)	0.9
Periprosthetic fracture	17 (11)	11 (6.6)	4.7 (−1.6 to 11)	0.1
Other	3 (2.0)	5 (3.0)	−1.0 (−4.4 to 2.4)	0.6
Head size (%)
≤ 32 mm	150 (100)	114 (69)	31 (24 to 38)	< 0.001
> 32 mm	–	52 (31.3)
Acetabular reinforce-ment ring (%)	53 (35)	77 (46)	−11 (−22 to −0.3)	0.05

a Percentages calculated on total no. of patients with information available.

b Age, BMI, and operating time is Mean difference, the rest is Risk difference

c Information on smoking status missing for 23 patients in group 1 and for 53 patients in group 2.

Table 2. Risk, risk ratio, and risk difference for dislocation within 6 months according to type of cup

Dislocation	Dual-mobility (n = 150)	Unipolar (n = 166)	Unadjusted risk ratio (95% CI)	p-value	Adjusted risk ratio (95% CI)	p-value	Unadjusted risk difference (95% CI)	p-value	Number needed to treat
Within 6 months (%)	4 (2.7)	13 (7.8)	0.34 (0.11–1.02)	0.06	0.28 (0.09–0.87)	0.03	−5.1 (−9.9 to −0.3)	0.04	19

Table 3. Indication for re-revision

	Dual-mobility (n = 150)	Unipolar (n = 166)
Aseptic loosening	1	8
Infection	4	4
Dislocation	1	7
Periprosthetic fracture	1
Persistent pain		1
Impingment		1