Proximally Versus Fully Porous-coated Femoral Stems: A Multicenter Randomized Trial

Abstract

There are two broad-based categories of cementless femoral component designs: proximally porouscoated and fully porous-coated. While both have been widely used, there remains debate regarding differences in clinical outcome scores, relative incidence of thigh pain, and development of stress shielding. We investigated these variables in a multicenter prospective randomized blinded clinical trial of 388 patients from three centers: 198 patients had a proximally porous-coated tapered cementless femoral component and 190 patients had a fully porous-coated cementless femoral component. A minimum followup of 2 years (mean, 6.7 years; range, 2.0-8.65 years) was available in 367 of the 388 patients (95%).

Influence of cementless hip stems on femoral cortical strain pattern depending on their extent of porous coating

“…The fi rst generation of anatomically shaped cementless stems had a complete or extended porous coating of their surface [16] . However, the clinical impact of periprosthetic bone resorption particularly seen with fully coated stems has not been defi nitely clarifi ed [40] . Aiming to reduce stress-shielding effects and resorptive bone remodeling, the second generation with only proximal coating was introduced [14,39,41] and was followed by a third generation with an additional hydroxyapatite layer [38] .…”

“…Furthermore, a more proximal load transfer should prevent persistent thigh pain for which a prevalence of up to 39 % is reported after cementless total hip replacement [1,4,11,23,42,47] . However, it is controversially discussed whether that discomfort is actually associated with the extent of porous coating [17,23,39,40] . Well-fi xed fully coated stems lead to a more distal load transfer and cortical hypertrophy [14,16,22,40,63] , whereas proximally coated stems show greater interface micromotion of the distal tip of the endoprosthesis [1,15,33,56] .…”

“…However, it is controversially discussed whether that discomfort is actually associated with the extent of porous coating [17,23,39,40] . Well-fi xed fully coated stems lead to a more distal load transfer and cortical hypertrophy [14,16,22,40,63] , whereas proximally coated stems show greater interface micromotion of the distal tip of the endoprosthesis [1,15,33,56] . The importance of these observations must be evaluated in view of many other infl uences on the prevalence of thigh pain after total hip arthroplasty (THA).…”

“…The importance of these observations must be evaluated in view of many other infl uences on the prevalence of thigh pain after total hip arthroplasty (THA). Several authors emphasize the contribution of factors related to patients (e.g., obesity, depression), implants (e.g., material, design), or operative techniques (e.g., overreaming) [4,18,35,37,39,40,55] .…”

“…Nevertheless, a circular proximal porous coating should reduce the effective joint space and migration of wear particles [12,29,53] . The controversial results of clinical and radiological follow-up studies have still left over the question which concept is superior from the biomechanical and clinical view [40] . Experimental studies with autopsy retrievals demonstrated the infl uence of the extent of porous coating on periprosthetic bone density and structure as well as interface micromotion [15,16] .…”