Background/Purpose

Rheumatoid arthritis (RA) patients have excellent total hip arthroplasty (THA) survival, and methotrexate (MTX), an anti-inflammatory disease modifying drug which may affect bone reabsorption, may play a role. The purpose of this study is to determine the diagnosis leading to revision THA (rTHA) in RA patients and to assess the association of radiographic lucency with MTX use.

Methods

All patients with validated diagnosis of RA in the institution’s THA registry undergoing rTHA from May 2007 – February 2011 were eligible. Diagnosis leading to rTHA and medication use was determined by chart review. Osteolysis was evaluated on available radiographs by measuring maximum lucency in each Gruen zone. Differences within RA patients with/without MTX in osteolysis, demographics, and medications were assessed with chi-squared, Fisher’s exact tests or Mann-Whitney U tests as appropriate. The error rate for multiple comparisons of lucency in the different Gruen zones was corrected via false discovery rate methods. A secondary analysis was performed to determine differences in diagnoses leading to revision between RA and matched OA controls (2:1 match by sex age +/- 5 years). OA exclusion criteria included presence of rheumatic diseases, use of MTX, and lack of records.

Results

51 RA rTHA were identified and compared with 103 OA (Table 1). Mean age for RA was 57.7 v 59.4 years for OA (p = 0.240). 82.4% RA were female v 83.5% OA (p = 0.859). RA had lower BMI than OA (25.5 v 28.2; p = 0.166). There was no difference in diagnosis leading to rTHA, including infection (RA 3.9 v OA 6.8%; p = 0.719) or dislocation (RA 23.5 v OA 23.3%; p = 0.975). There was no significant difference in the length of time the implant was in before revision: RA 11.0 v OA 8.8 years (p = 0.060). Among RA with/without MTX, (Table 2) there was no difference in use of biologics (30.0 v 43.3%, p = 0.283), steroids (47.6 v 50.0%, p = 0.867) or bisphosphonates (23.8 v 33.3%, p = 0.543). There was no difference in rTHA diagnosis with/without MTX, including loosening (52.4 v 56.7%, p = 0.762). There was no significant difference in lucencies with MTX use in any Gruen zone. Patients with MTX had femoral stem subsidence of 3.7mm v no subsidence without MTX (p = 0.006).

Conclusion

There was no difference in the diagnosis leading to rTHR in RA and OA, although RA trended longer prior to rTHA. In this small retrospective study, there were no significant differences associated with MTX exposure or radiographic lucency among RA patients. The significance of subsidence is not clear. Further study of arthroplasty survival in RA patients is warranted.

 

Table 1: Demographic characteristics and reason for revision for OA vs. RA patients*
	RA, N=51	OA, N=103	p-value
Age, Mean (Std Dev)	57.7 (14.1)	59.4 (15.0)	0.240
BMI, Mean (Std Dev)	25.5 (5.2)	28.2 (11.4)	0.166
Female, N (%)	42 (82.4)	86 (83.5)	0.859
Years Implanted, Mean (StDev)	11.0 (8.3)	8.8 (8.8)	0.060
Diagnosis, N (%)
Infection	2 (3.9)	7 (6.8)	0.719
Loosening	28 (54.9)	59 (57.3)	0.779
Fracture	7 (13.7)	7 (6.8)	0.232
Wear	12 (23.5)	19 (18.4)	0.459
Dislocation	12 (23.5)	24 (23.3)	0.975
Mech Failure	2 (3.9)	7 (6.8)	0.862
Other	1 (2.0)	0 (0.0)	0.331
*28 patients were ascribed more than 1 diagnosis.

 

Table 2: Demographic characteristics and radiographic analysis of RA patients with/without MTX*
	MTX, N=20	No MTX, N=30	p-value
Age, Mean (Std Dev)	59.3 (14.9)	56.6 (13.7)	0.461
BMI, Mean (Std Dev)	27.2 (5.9)	24.2 (4.3)	0.059
Years Implanted, Mean (Std Dev)	10.7 (9.1)	11.3 (7.9)	0.737
Diagnosis, N (%)
Infection	1 (4.8)	1 (3.3)	>0.999
Loosening	11 (52.4)	17 (56.7)	0.762
Fracture	3 (14.3)	4 (13.3)	>0.999
Wear	6 (28.6)	6 (20.0)	0.351
Dislocation	6 (28.6)	6 (20.0)	0.581
Mech Failure	0 (0.0)	2 (6.7)	0.506
Other	0 (0.0)	1 (3.3)	>0.999
Medication, N (%)
Bisphosphonates	5 (23.8)	10 (33.3)	0.543
Biologics	6 (30.0)	13 (43.3)	0.283
Prednisone	10 (47.6)	15 (50.0)	0.867
Cemented Cup, N (%)	3 (18.8)	5 (22.7)	>0.999
Cemented Femur, N (%)	5 (31.3)	13 (59.1)	0.112
Lucency, Mean (Std Dev) [mm]
Femur Zone 1	11.4 (16.8)	7.4 (10.2)	0.954
Femur Zone 2	0.0 (0.0)	0.9 (1.7)	0.225
Femur Zone 3	0.2 (0.8)	0.5 (1.8)	0.954
Femur Zone 4	2.7 (8.7)	0.0 (0.0)	0.189
Femur Zone 5	0.3 (0.9)	0.7 (2.6)	0.954
Femur Zone 6	1.3 (3.3)	0.8 (2.8)	0.954
Femur Zone 7	3.7 (5.6)	3.0 (5.5)	0.954
Femur Zone 8	5.7 (7.9)	5.0 (6.3)	0.954
Femur Zone 9	0.0 (0.0)	1.8 (3.5)	0.189
Femur Zone 10	0.2 (0.9)	0.0 (0.0)	0.954
Femur Zone 11	0.8 (2.3)	0.7 (2.4)	0.954
Femur Zone 12	0.1 (0.4)	0.8 (3.6)	0.954
Femur Zone 13	2.2 (5.0)	1.3 (3.6)	0.954
Femur Zone 14	3.5 (6.1)	3.3 (6.3)	0.954
Subsidence (mm)	3.7 (7.1)	0.0 (0.0)	0.006
*11 patients were ascribed more than 1 diagnosis.

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