Comparison of the primary stability and seating force of two uncemented cup designs used for total hip replacement

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13145
Qualification Level
Qualification Name
Department, School or Faculty
  • The primary stability of uncemented press-fit acetabular cups is critical for osseointegration and implant longevity. Cup design is fundamental in achieving an initial (primary) stability between the acetabular component and the reamed cavity, thereby minimising micromotion and promoting long term bone ingrowth. Different cup designs are commercially available but the choice of geometry is controversial. A study was undertaken to compare the primary stability of two commercially available cup designs in-vitro; these cups are produced by the same manufacturer and differ only in geometry -one being purely Hemispheric and the other being peripherally enhanced (peripheral self-locking - PSL). The cups were seated in reamed polyethylene bone substrate of low (0.22g/cm3) and high (0.45g/cm3) density, mimicking two qualities of bone (softer and harder). The primary stability of each design was investigated by recording the peak failure load during uniaxial pull-out and tangential lever-out tests. Potential between-cup differences in peak seating force, pull-out force and lever-out moment were evaluated for each test using independent samples t-tests (p<0.05). There was no statistically significant difference in seating force or pull-out and lever-out stability between the PSL and Hemispheric designs in the low density substrate. In the high density substrate, the Hemispheric design required a significantly lower seating force than the PSL (p=0.016). Once seated, there was no statistically significant difference in pull-out and lever-out stability between the cup designs in the high density substrate. The high density substrate represents the harder bone of younger patients where uncemented cups are mainly used anyway. If translated clinically, the findings of the study are crucial because high seating forces during cup insertion may result in bony fracture or implant malposition. On this basis, the Hemispheric cup geometry would seem preferable.
Resource Type
  • Strathclyde theses - ask staff. Thesis no. : T13145
Date Created
  • 2012
Former identifier
  • 947067