Design modifications of the uncemented Furlong hip stem result in minor early subsidence but do not affect further stability

Figures & data

Figure 1. A. Furlong HAC. B. Furlong Active, both with tantalum markers. C. Superimposition of outlines (right image).

Table 1. Patient characteristics

Variables	HAC	Active	Total
No. of patients	25	25	50
Age, years (range)	63 (49–75)	62 (50–77)	63 (49–77)
Gender (M; F)	18; 7	9; 16	27; 23
BMI (SD)	26 (3.4)	29 (5.0)	27 (4.4)

Table 2. Precision of the RSA measurements a

Axis	Translation, mm	Rotation, °
Transverse (X)	0.12	0.23
Longitudinal (Y)	0.08	0.30
Sagittal (Z)	0.12	0.09

^a The precision is based on 50 double examinations of the patients in the study. The value given represents the smallest migration that is considered statistically significant and is based on 2 standard deviations of the error obtained. This therefore corresponds to the 95% confidence limit.

Table 3. Stem translation and rotation at 3 months, 1 year, 2 years, and 5 years

	3 Months		12 months		24 months		60 months
Type of motion	Mean	95% CI	Mean	95% CI	Mean	95% CI	Mean	95% CI
Stem translation, segment motion, mm
Y-translation ^a
HAC	–0.31	–0.50 to –0.13	–0.33	–0.52 to –0.14	–0.26	–0.46 to –0.07	–0.29	–0.51 to –0.07
Active	–0,99	–1.64 to –0.35	–0.98	–1.66 to –0.30	–0.98	–1.66 to –0.29	–1.04	–1.75 to –0.34
X-translation
HAC	0.04	–0.04 to 0.12	0.04	–0.05 to 0.13	0.07	–0.02 to 0.15	0.07	–0.02 to 0.17
Active	–0.10	–0.38 to 0.17	–0.09	–0.37 to 0.20	–0.08	–0.35 to 0.18	–0.08	–0.38 to 0.21
Z-translation
HAC	–0.22	–0.33 to –0.11	–0.21	–0.32 to –0.09	–0.13	–0.27 to 0.00	–0.19	–0.32 to –0.05
Active	–0.22	–0.49 to 0.05	–0.15	–0.42 to 0.11	–0.18	–0.46 to 0.10	–0.22	–0.51 to 0.07
Stem rotation, segment motion, degrees
Y-rotation ^b
HAC	0.80	0.38 to 1.22	0.80	0.37 to 1.23	0.92	0.53 to 1.32	0.86	0.41 to 1.30
Active	1.18	0.44 to 1.93	1.28	0.47 to 2.09	1.26	0.46 to 2.05	1.32	0.48 to 2.16
X-rotation
HAC	–0.07	–0.20 to 0.07	–0.08	–0.25 to 0.09	–0.25	–0.41 to –0.10	–0.15	–0.37 to 0.07
Active	0.02	–0.17 to 0.21	–0.22	–0.39 to –0.04	–0.23	–0.42 to–0.04	–0.22	–0.37 to –0.07
Z-rotation
HAC	–0.19	–0.32 to –0.06	–0.22	–0.34 to –0.09	–0.22	–0.34 to –0.10	–0.25	–0.40 to –0.09
Active	–0.28	–0.59 to 0.03	–0.29	–0.63 to 0.05	–0.30	–0.64 to 0.03	–0.32	–0.68 to 0.04

^a proximal (+), distal (–)

^b retroversion (+)

Figure 2. Graph showing the mean stem subsidence for the HAC and Active stems, with SEM bars. The p-values for the difference in mean subsidence were 0.05 at 3 months, 0.07 at 1 year, 0.05 at 2 years, and 0.04 at 5 years.

Figure 3. Graph showing stem retroversion (°) for both stems, with SEM bars. The difference in retroversion between the 2 stems was not significantly different at any time point (p = 0.4 at 3 months, p = 0.3 at 1 year, p = 0.5 at 2 years, and p = 0.3 at 5 years).