Summary
Objective: Evaluate variability associated with assessing changes in the position of uncemented
femoral stems.
Methods: Stem level, canal fill, stem angle, and version angle were measured on craniocaudal
horizontal beam (CCHB) and open leg lateral (OLL) radiographic projections of the
femur of 20 dogs that had uncemented total hip replacement. Intraobserver and inter
-observer repeatability were determined on immediate postoperative (PO) images. Differences
in position were calculated between the first (3 months – R1) and second (6 months – R2) re-evaluation (R1-R2) time points, and between PO and R1.
Results: The measurement process was very repeatable. For R1-R2, the stem appeared to subside 0.8 ± 1.4 mm for measurements based on the greater
trochanter on the CCHB images, but there was a wide range (-3.9 to 2 mm; positive
values indicate proximad movement). Measurements based on the inter-trochanteric crest
on the OLL images had the same mean, and also a wide range (-4.4 to 2.1 mm; negative
values indicate proximad movement). For PO-R1, the stem appeared to subside 1.8 ± 2.0 mm (CCHB, based on the greater trochanter,
range -7.7 to 2.2 mm), 1.6 ± 1.5 mm (CCHB, based on the intertrochanteric crest, range
-0.7 to 4.3 mm); and 2.1 ± 2.1 mm (OLL, based on the intertrochanteric crest, range
-1.6 to 6.8 mm).
Conclusion: The position of a stable stem can appear different on subsequent re-evaluations,
but this may be due to variability associated with inconsistency of positioning of
the patient and limb.
Clinical significance: Documenting subsidence in individual patients should not rely on calculations based
on a single measurement.
Keywords
Uncemented total hip replacement - stem level - variability - measurements
