Hip Replacement in Ankylosing Spondylitis Patients with Advanced Hip Involvement: Factors Associated with Bilateral Total Hip Arthroplasty

Figures & data

Table 1 Baseline Characteristics of AS Patients with Advanced Hip Involvement

	Values	Range
Demographics
Age at surgery (years)	32	19 to 67
Male (n, %)	218(89.7%)
BMI (kg/m^2)	22.50	11.87 to 41.62
Clinical characteristics
Age at onset (years)	18	5 to 56
Bilateral onset in hips (n, %)	238(63.8%)
Disease duration (years)	10.5	0.5 to 40.3
Administration of TNF inhibitors (n, %)	36(9.7%)
Family history of rheumatism (n, %)	39(10.5%)
Smoking history (n, %)	53(14.2%)
BASRI-hip (No. of cases in hips)
0 (n, %)	20(2.7%)
1 (n, %)	39(5.2%)
2 (n, %)	37(4.9%)
3 (n, %)	313(42.0%)
4 (n, %)	337(45.2%)
Bilateral THA (n, %)	251(67.3%)
Preoperative laboratory values
ESR (mm/h)	17	1 to 108
CRP (mg/dL)	1.61	0.10 to 17.87

Note: The continuous values are presented as medians, with ranges from minimum to maximum.

Abbreviations: AS, ankylosing spondylitis; BMI, body mass index; TNF, tumour necrosis factor; BASRI-hip, the Bath Ankylosing Spondylitis Radiology Hip Index; THA, total hip arthroplasty; ESR, erythrocyte sedimentation rate; CRP, C-reactive protein.

Table 2 Comparison Between the Patients Who Underwent Unilateral and Bilateral THA

	Unilateral THA (n=122)	Bilateral THA (n=251)	P
Demographics
Age at surgery (years)	31(19 to 67)	32(19 to 67)	0.911
Male (n, %)	106(86.9%)	234(93.2%)	0.043
BMI (kg/m^2)	22.66(14.42 to 38.58)	22.49(11.87 to 41.62)	0.533
Clinical characteristics
Age at onset (years)	19(8 to 56)	18(5 to 49)	0.065
Bilateral onset in hips (n, %)	35(28.7%)	203(80.9%)	<0.001
Disease duration (years)	9(0.5 to 40.3)	12(0.5 to 34.0)	0.002
Administration of TNF inhibitors (n, %)	21(17.2%)	15(6.0%)	0.001
Family history of rheumatism (n, %)	10(8.2%)	29(11.6%)	0.320
Smoking history (n, %)	17(13.9%)	36(14.3)	0.916
Flexion contracture in the hip (n, %)	38(31.1%)	126(97.7%)	0.001
BASRI-hip score of 4 (n, %)	36(29.5%)	172(68.5%)	<0.001
Preoperative laboratory values
ESR (mm/h)	13(2 to 97)	19(1 to 108)	0.051
CRP (mg/dL)	1.49(0.10 to 10.30)	1.69(0.10 to 17.87)	0.073

Note: The continuous variables are presented as medians (minimum to maximum).

Abbreviations: THA, total hip arthroplasty; BMI, body mass index; TNF, tumour necrosis factor; BASRI-hip, the Bath Ankylosing Spondylitis Radiology Hip Index; ESR, erythrocyte sedimentation rate; CRP, C-reactive protein.

Table 3 Logistic Regression on Factors Associated with Bilateral THA in AS Patients with Advanced Hip Involvement

Parameter	OR (95% CI)	P value
Male	1.013 (0.402 to 2.549)	0.979
Age at onset	1.021(0.984 to 1.059)	0.272
Disease duration	1.009(0.974 to 1.045)	0.631
Bilateral onset in hips	10.177(5.713 to 18.130)	<0.001
Administration of TNF inhibitors	0.346(0.142 to 0.838)	0.019
Flexion contracture	1.447(0.802 to 2.612)	0.220
BASRI-hip score of 4	4.133(2.308 to 7.400)	<0.001
ESR	1.018(1.001 to 1.035)	0.043
CRP	0.920(0.788 to 1.073)	0.287

Abbreviations: THA, total hip arthroplasty; AS, ankylosing spondylitis; OR, odds ratio; CI, confidence interval; TNF, tumour necrosis factor; BASRI, the Bath Ankylosing Spondylitis Radiology Hip Index; ESR, erythrocyte sedimentation rate; CRP, C-reactive protein.