An Uncommon Deformity of the Collarless, Polished, Double-Taper (CPT) Stem After a Periprosthetic Fracture in Total Hip Arthroplasty.

We present an uncommon case of a Collarless, Polished, Double-Taper (CPT) stem deformity (irreversible stem bending) occurring due to a Periprosthetic Fracture (PPF) in Total Hip Arthroplasty (THA). The entire course of the case, including treatment, risk factors, and failure analysis of the deformed CPT by its manufacturer, Zimmer Biomet (Warsaw, USA),is described. The discussion considers in detail the (risk) factors that led to this particular stem deformity, incorporating current literature. We conclude with learning points on how to prevent stem abnormalities in PPFs in the future.  In our case, there were some case-specific risk factors associated with bending of the CPT stem. These factors are a relative varus angle, relative under-sizing of the stem, and a potentially inadequate cement mantle around the primary stem. No material or manufacture failure of the stem could be found. Still, it is very unusual that the femoral stem deforms without fracturing. Taken together, we present a unique case of a Periprosthetic Fracture with CPT stem deformity following Total Hip Arthroplasty.