CPR Distance

Each company has its own design implant design specific measurement. The correct implant design has to be chosen for an accurate calculation. Values for head coverage are used in this calculator are taken from published tables [Ranges of coverage angles, p 103. “The hip resurfacing handbook”©Woodhead Publishing Limited, 2013].

This calculator relies on the correct head diameter.

The Radiographic Inclination (RI) (Figure 1) can be measured from a coronal series CT-scan or a plain Antero-posterior X-ray of the pelvis.

CT scan

Plain X-ray AP pelvis

Figure 1. J Bone Joint Surg Br. 1993 Mar;75(2):228-32. The definition and measurement of acetabular orientation. Murray DW.

Measuring the anteversion of the acetabular component from an axial series of a CT scan gives the Anatomical Anteversion (AA) [use option 1].

Measuring the anteversion from a plain X-ray by using EBRA or Martell imaging software provides the Radiographic Anteversion (RA)(figure1). Errors related to X-ray beam divergence are corrected by the software [use option 2].

Measuring anteversion by elliptical measurement methods such as Ackland, Lewinneck, Liaw depends on the incident angle of the X-ray beam. For an accurate anteversion measurement the X-ray must be centered over the hip joint [use option 2].

If the X-ray is centered over the pelvis, there will be an error of approximately 5° related to the X-ray beam divergence¹ [use option 3].

Figure 1. J Bone Joint Surg Br. 1993 Mar;75(2):228-32. The definition and measurement of acetabular orientation. Murray DW.

¹ British Editorial Society of Bone and Joint Surgery 1986. Anteversion of the acetabular cup. Measurment of angle after total hip replacement. Ackland MK.