Table 4.

Frequency of complications among patients with ankylosing spondylitis, by annual hospital volume of primary total hip arthroplasties (THA) performed among all Medicare beneficiaries.

	Low volume hospitals (1 – 44 THA per year)	Medium volume hospitals (45 – 99 THA per year)	High volume hospitals (≥ 100 THA per year)	Relative Difference: High vs. Low	P trend
Number of patients	843	963	967
Any perioperative complication, %	1.30	1.56	1.45	+11.5%	0.82
Any 30 day complication, %	0.47	1.00	0.62	+31.9%	0.76
Any 90 day complication, %	3.20	2.60	2.38	−25.6%	0.29
Revision arthroplasty within 1 year, %	3.56	3.22	3.10	−12.9%	0.59
Death within 90 days, %	0.47	0.31	0.31	−34.0%	0.56
Long length of stay, %	13.9	12.7	9.3	−33.0%	0.003
Discharged to care facility, %	39.6	42.2	42.0	+6.1%	0.33
Readmission within 90 days, %	12.3	12.8	11.9	−3.2%	0.76