The Visual Assessment of Cup Position on Anteroposterior Pelvis Radiographs Before Revision Total Hip Arthroplasty for Instability Is Highly Deceiving.

Background: Is "eyeballing" enough to determine cup malposition on anteroposterior (AP) pelvis radiographs before revision total hip arthroplasty (rTHA) for instability? We aimed to determine the following: (1) the reliability of eyeballing cup inclination/anteversion on AP pelvis radiographs vs geometrical measurements and (2) whether visual assessments are affected by surgeon experience.

Materials and methods: Fifteen de-identified standing AP pelvis radiographs obtained before rTHA for instability were evaluated by one orthopedic surgeon who measured inclination/anteversion of the cups (n=15) using a new simplified method based on basic geometry. Subsequently, 4 orthopedic surgeons and 4 fellows (postgraduate year 6) assessed inclination/anteversion by eyeballing. A modified Lewinnek safe zone range was employed to categorize each value (in degrees) by geometrical measurements or by raters' eyeballing as within or outside the safe zones. Cohen's kappa (κ) statistics were performed. Mean κ values of attending surgeons and fellows were compared.

Results: According to geometrical measurements, 8 and 12 cups were in malposition (for inclination and anteversion, respectively). By just eyeballing, no attending surgeon or fellow attained an excellent (κ>0.8) level of agreement when compared with geometrical measurements. Only 1 attending surgeon attained a substantial (κ=0.6-0.8) level of agreement (κ=0.737, for inclination, P=.003). Mean κ values of attending surgeons and fellows were 0.476 and 0.187, respectively, for inclination (P=.2) and 0.416 and 0.428, respectively, for anteversion (P=.9).

Conclusion: Eyeballing cup position on AP pelvis radiographs before rTHA for instability is extremely misleading, regardless of surgeon experience. It is imperative to always measure the inclination and anteversion of the cup. [Orthopedics. 2025;48(1):e22-e26.].