Stem subsidence of polished and rough double-taper stems

Abstract

Background and purpose Many clinical reports have indicated that polished hip stems show better clinical results than rough stems of the same geometry. It is still unknown, however, what the mechanical effects are of different surface finishes on the cement at the cement-bone interface. We compared mechanical effects in an in vitro cemented hip arthroplasty model.Methods Two sizes of double-taper polished stems and matt-processed polished stems (rough stems) were fixed into composite femurs. A 1-Hz dynamic load was applied to the stems for 1 million cycles. An 8-h no-load period was set after every 16 h of load. Stem subsidence within the cement, and compressive force and horizontal cement creep at the cement-bone interface, were measured.Results Compared to rough stems, stem subsidence, compressive force and cement creep for polished stems were a maximum of 4, 12, and 7-fold greater, respectively. There was a strong positive correlation between stem subsidence and compressive force for polished stems. In contrast, a strong negative correlation was found between stem subsidence and compressive force for rough stems. There was also a statistically significant relationship between compressive force on the cement and cement creep for the polished stems, but no significant relationship was found for rough stems.Interpretation This is the first evidence that different surface finishes of stems can have different mechanical effects on the cement at the cement-bone interface. Stem subsidence in polished stems resulted in compressive force on the cement and cement creep. The mechanical effects that polished taper stems impart on cement at the cement-bone interface probably contribute to their good long-term fixation and excellent clinical outcome.

Biomechanical behaviour of a French femoral component with thin cement mantle

“…Stem subsidence strongly correlated with compressive force at the proximal medial region in both groups, and may have generated compressive force similar to that for the CPT stem. 14 In addition, the proximal medial region showed perpendicular ball movement less than perpendicular stem movement, and horizontal ball movement greater than perpendicular ball movement. We speculate that stem subsidence in the thin cement mantle led to strong hoop stress and radial cement creep, producing compressive force at the cement-bone interface, especially in the proximal medial region.…”

“…With polished tapered stems, cement creep may result from stem subsidence, and increased compressive force at the bone-cement interface may contribute to stem stabilization 2 , 3 , 13 , 14 , 20 , 21 (‘force-closed fixation’ 22 , 23 ).…”

“…We followed the methodology of Kaneuji et al 14 to create a biomechanical model using cemented femoral components that were inserted into composite femurs (#3403, Pacific Research Laboratories, Vashon, Washington), 15 and performed loading tests. The cancellous bone of this composite femur is much harder than cadaveric bone, and the cement did not penetrate into the cancellous bone.…”

“…A digital displacement gauge (DTH-A5 5 mm; Kyowa Electronic Instruments Co., Tokyo, Japan), placed at the stem shoulder, was used to measure stem subsidence over time. Data was collected using the metshod described by Kaneuji et al 14 The 16-hour loading period for each day was divided into early, middle and late phases and the first two files from each phase (a total of 20 000 values) were collected and used. Data was transmitted automatically to a computer through data collection and analysis software (Sensor Interface PCD-300A; Kyowa Electronic Instruments Co.).…”

Biomechanical Performance of the Cemented Hip Stem with Different Surface Finish

“…The subsidence of the femoral stem is recognized as being related to stem shape design and surface finish [55]. However, different surface finishes of stems can have different mechanical effects on the cement at the cement-bone interface, thus resulting in the progress of subsidence in different post implantation period [56]. Ebramzadeh et al [55] and Choi et al [57], respectively, employed physical cemented composite constructions to assess the effects of stem design in terms of geometry and surface finish on migration of the femoral component under cyclic joint loads.…”