Good stability of a cementless, anatomically designed femoral stem in aging women: a 9-year RSA study of 32 patients

Figures & data

Figure 1. Patient flow throughout the study. Data from the first 2 years are presented in more detailed in a previous study (Aro et al. 2012).

Table 1. Baseline demographics and clinical characteristics

No. of cases	32
Age, years	62 (41–78)
BMI (SD)	31 (6)
WHO classification of bone mineral density
Normal bone (T-score ≥ –1.0	11
Osteopenia (–2.5 ≤ T-score < –1.0)	16
Osteoporosis (T-score < –2.5)	5
Dorr classification
Type A	17
Type B	12
Type C	3
WOMAC score, (SD)	49 (16)
HHS score, (SD)	52 (15)

Figure 2. Schematic drawing of the prosthesis with 6 tantalum RSA stem markers and the coordinate system for RSA analysis of 3D micromotion of the femoral stem. In order to explicitly record the direction of micromotion, the directions are marked with + and – signs for both the translations and rotations.

Table 2. Precision of radiostereometric analysis based on double examinations

	Translation (mm)			Rotation (°)
	x-axis	y-axis	z-axis	x-axis	y-axis	z-axis
Clinical precision	0.13	0.22	0.36	0.53	1.95	0.19

Clinical precision =2.05 x standard deviation for the mean difference between the double examinations.

Figure 3. The migration pattern of individual femoral stems (n = 28) during the 9-year follow-up. 1 patient exhibited continuous x-axis rotation (yellow-filled markers).

Table 3. Femoral stem migration between 2 and 9 years

	2 years median (range)	9 years ^a median (range)	Difference (95% CI of median)	p-value ^b
Translation compared with baseline, mm
x-axis	0.02 (–0.46 to 2.58)	0.00 (–0.48 to 2.80)	–0.02 (–0.08 to 0.07)	0.7
y-axis	–0.73 (–4.67 to 0.05)	–0.73 (–4.53 to 0.11)	–0.05 (–0.08 to 0.03)	0.2
z-axis	–0.25 (–1.03 to 2.17)	–0.29 (–1.79 to 1.52)	–0.07 (–0.17 to 0.13)	0.3
Rotation compared with baseline, degrees
x-axis	0.18 (–3.23 to 11.04)	0.39 (–3.68 to 11.06)	0.02 (–0.14 to 0.18)	0.6
y-axis	0.34 (–10.38 to 4.00)	0.24 (–10.76 to 4.12)	0.09 (–0.69 to 0.73)	0.9
z-axis	–0.16 (–1.32 to 1.03)	–0.21 (–2.29 to 1.05)	0.02 (–0.17 to 0.12)	1.0

^a Range of follow-up 7.8–9.3 years.

^b Related-samples Wilcoxon signed rank test.

Aro H T, Alm J J, Moritz N, Mäkinen T J, Lankinen P. Low BMD affects initial stability and delays stem osseointegration in cementless total hip arthroplasty in women. Acta Orthop 2012; 83(2): 107–14.

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