Insufficient lateral stem contact is an influencing factor for significant subsidence in cementless short stem total hip arthroplasty

Table 1 Intraclass correlation coefficients

	Neck-filling ratio	Seating height	Lateral stem contact	Subsidence
Intra-observer
Observer 1	0.85 (95%CI: 0.72-0.93)	0.99 (95%CI: 0.99-0.99)	0.98 (95%CI: 0.97-0.99)	0.99 (95%CI: 0.99-0.99)
Observer 2	0.83 (95%CI: 0.68-0.91)	0.98 (95%CI: 0.98-0.99)	0.97 (95%CI: 0.95-0.99)	0.99 (95%CI: 0.99-1.0)
Inter-observer	0.77 (95%CI: 0.71-0.81)	0.99 (95%CI: 0.99-0.99)	0.97 (95%CI: 0.96-0.98)	0.99 (95%CI: 0.98-0.99)

Table 2 Demographic data

Parameters	Values
No. of hips	274
Gender (male/female)	186/88
mean age (yr) (range, SD)	48.1 (18-73, 11.2)
mean BMI (range, SD) (kg/m2)	23.8 (14.7-40.9, 4.3)
Dorr’s classification, n (%)
Dorr’s type A	223 (81.4)
Dorr’s type B	51 (18.6)
Diagnosis, n (%)
ONFH	213 (77.7)
DDH	33 (12.1)
Primary osteoarthritis of the hip	19 (6.9)
Femoral neck fracture	9 (3.3)

BMI: Body mass index; ONFH: Osteonecrosis of the femoral head; DDH: Developmental dysplasia of the hip.

Table 3 Results of subsidence of any radiographic parameters in the entire cohort

Parameters (n)	Value, mean (mm) (range, SD)	P value
Subsidence of the entire cohort (75/274)	0.5 (0-12.7, 1.68)
Subsidence of any radiographic parameters
Neck-filling ratio < 0.8 (232)	0.51 (0-11.89, 1.44)	0.99
Neck-filling ratio ≥ 0.8 (42)	0.5 (0-12.7, 2.02)
Seating height < 5 mm (110)	0.51 (0-12.7, 0.16)	0.99
Seating height ≥ 5 mm (164)	0.5 (0-11.89, 0.11)
Lateral stem contact < 1 mm (178)	0.39 (0-11.89, 1.26)	0.09
Lateral stem contact ≥ 1 mm (96)	0.71 (0-12.7, 1.94)

Table 4 Results of univariate regression analysis of 12 cases with significant subsidence

Variables	Univariate analysis
	OR	95%CI	P value
Age (≥ 60 yr)	0.96	0.2-4.6	0.96
DDH	0.65	0.1-5.2	0.69
ONFH	3.3	0.4-25.8	0.26
BMI (≥ 30 kg/m2)	0.95	0.1-7.6	0.96
Dorr’s type B	2.29	0.6-7.9	0.19
Seating height (< 5 mm)	0.91	0.3-2.9	0.87
NFR (< 0.8)	1.98	0.2-15.7	0.52
Insufficient lateral stem contact (≥ 1 mm)	5.02	1.3-18.9	0.0171

¹Significant value.

DDH: Developmental dysplasia of the hip; ONFH: Osteonecrosis of the femoral head; BMI: Body mass index; OA: Osteoarthritis; NFR: Neck filling ratio; OR: Odds ratio.

Table 5 Summary of stem subsidence at two years follow-up for different types of short stems

Ref.	Femoral stem	Khanuja et al[18] classification	Follow-up (mo)	Subsidence(mm)	n
Christiansen et al[26]	Primoris, Biomed, UK	1	24	0.38	50
Schwarze et al[25]	Metha, Aesculap, Germany	2A	24	0.86	39
Jahnke et al[24]	Metha, Aesculap, Germany	2A	24	1.28 ± 2.24	71
This study	Metha, Aesculap, Germany	2A	24	0.5	274
Budde et al[27]	Nanos, Smith + nephew, Germany	2A	24	0.46 ± 0.31	18
Ferguson et al[28]	MiniHip, Corin, UK	2A	24	0.26	20
Kutzner et al[23]	Optimys, Mathys AG, Switzerland	2B	24	1.23 (contact); 2.07 (non-contact)	191
Klein et al[31]	CFP, Link, Germany	2B	24	0.3 (0.2-0.4)	39
Mahmoud et al[29]	Proxima, DePuy, UK	3	24	0.22	28
Acklin et al[30]	Fitmore, Zimmer, Switzerland	4	24	0.39	24