Phantom design

This experimental phantom study did not require prior approval by an ethics committee. A total of three similar phantoms were built, differing only in the composition of the femoral stem.

The femoral implant of a hip prosthesis was placed within the centre of a rectangular plastic box with a dimension of 40 × 33.5 × 17 cm. Distances to the box walls were defined and reproducible. The implants were circumnavigated by five cylindrical, calibrated calcium hydroxyapatite pellets (200 mg of hydroxyapatite/calcium carbonate; HA/CC, from QRM, Möhrendorf, Germany) placed in a predefined positions around the prosthesis according to Gruen et al. 1979¹⁴: Zone 2, Zone 3, Zone 4, Zone 5, Zone 6, with a distance of 5 mm to the surface of the stem. A sixth pellet was positioned away from the implant at a box corner to avoid interference and serve as a reference value (Fig. 1) Each pellet was 30 mm in height and 20 mm in diameter.

Image illustrates a phantom with implanted metal alloys. The construction was made for stainless steel, chrome-cobalt and titanium. Six calcium hydroxyapatite pellets (P1–P6) were implanted. Five pellets are surrounding the femoral stem and one pellet was placed far away from the implant and was used as the reference value.

To achieve stable suspension and position of the devices the box was filled with gelatinous water (5%).

The femoral stems consisted mainly of titanium, cobalt chrome and stainless. All implants (Zimmer Biomet, Winterthur, Switzerland)¹⁵ were of identical shape, size, surface character and geometry:

Protasul S30 is very hard iron-based forging alloy with high content of chrome and nickel. (Stainless steel implant)

Protasul 100 is a heavy-duty forging alloy composed of titanium, aluminium and niobium. (Titanium implant)

Protasul 10 is heavy-duty forging alloy composed of cobalt, chromium, nickel, molybdenum and minor constituents of other substances. (Chrome-Cobalt implant)