Effects of Dorsal Flanges on Fixation of a Cemented Total Hip Replacement Femoral Stem

• Published in: Journal of bone and joint surgery. American volume Vol. 86; no. 4; pp. 813 - 820
• Main Authors: Sangiorgio, Sophia N, Ebramzadeh, Edward, Longjohn, Donald B, Dorr, Lawrence D
• Format: Journal Article
• Language: English
• Published: Boston, MA Copyright by The Journal of Bone and Joint Surgery, Incorporated 01.04.2004; Journal of Bone and Joint Surgery Incorporated; Journal of Bone and Joint Surgery AMERICAN VOLUME
• Edition: American volume
• Subjects: Adult; Arthroplasty, Replacement, Hip - instrumentation; Biological and medical sciences; Biomechanical Phenomena; Bone Cements; Diseases of the osteoarticular system; Hip Prosthesis; Humans; Materials Testing - methods; Medical sciences; Models, Anatomic; Human; Femur; Fixation; Prosthesis; Orthopedics; Diseases of the osteoarticular system; Cement; Rheumatology; Total; Hip; Stem
• ISSN: 0021-9355; 1535-1386
• DOI: 10.2106/00004623-200404000-00022

BackgroundAlthough current designs of cemented femoral stems for total hip replacement include both those with and those without a flanged shape at the proximal end, the influence of anteroposterior dorsal flanges on the fixation of the stem is not completely understood. The purpose of this study was to assess the effects of flanges on femoral stem stability and load transfer to the femur with use of an in vitro model.MethodsWe measured femoral surface strains and three-dimensional micromotion in synthetic femora under cyclic loading with four types of stemsthose with flanges and those without flanges in two sizes each. The four types of stems were otherwise identical; that is, all of them were straight, polished, and collarless. Stem-cement micromotion measurements and strain measurements were repeated with three stems of each type, whereas bone-cement micromotion measurements were made with one stem of each type.ResultsFlanges had a greater influence on femoral strains and micromotion than did the difference in the cement thickness resulting from the different stem sizes. Specifically, the flanged stems produced greater strains on the medial femoral surface but smaller strains on the anterior surface than did the non-flanged stems. Flanged stems achieved tighter mechanical interlock within the cement, but these stems increased bone-cement micromotion. Specifically, the motion per cycle of flanged stems within the cement mantle was smaller than that of non-flanged stems, whereas the motion per cycle of the cement mantle within the femoral canal was greater with the flanged stems than with the non-flanged stems.ConclusionsFlanges on a total hip femoral stem increase the interlock between the stem and the cement and decrease the proximal-medial stress-shielding. However, these advantages occur with increased bone-cement interface motion, which may be detrimental to the survival of the implant.Clinical RelevanceThe findings help to predict the consequences of the use of dorsal flanges for femoral stems and should be considered in the design of new femoral stems.