Three-Dimensional Analysis of the Contact Patternbetween the Cortical Bone and Femoral Prosthesis afterCementless Total Hip Arthroplasty

The cementless stem Excia (B. Braun, Melsungen, Germany) implant has a rectangular cross-sectional shape with back-and-forthflanges and a plasma-sprayed, dicalcium phosphate dihydrate coating from the middle to proximal portion to increase initialfixation and early bone formation. Here, the conformity of the Excia stem to the femoral canal morphology was three-dimensionallyassessed using computed tomography. Forty-three patients (45 hips) were examined after primary total hip arthroplasty with a meanfollow-up of 27±3months(range:24–36months).Spotweldsoccurredatzone2in16hipsandatzone6in24hips,with83%(20/24 hips) of those occurring within 3 months after surgery. First- (𝑛=12hips), second- (𝑛=32), and third- (𝑛=1)degreestress shielding were observed. The stem was typically in contact with the cortical bone in the anterolateral mid-portion (100%)and posteromedial distal portions (85%). Stress shielding didnot progress, even in cases where the stems were in contact withthe distal portions. The anterior flange was in contact with the bone in all cases. The stability of the mid-lateral portion with thedicalcium phosphate dihydrate coating and the anterior flange may have inhibited the progression of stress shielding beyond thesecond degree.