Original article
Effect of Reduced Diameter Neck Stem on Incidence of Radiographic Cup Loosening and Revisions in Charnley Low-Frictional Torque Arthroplasty

https://doi.org/10.1016/j.arth.2008.01.312Get rights and content

Abstract

Previous studies of the Charnley low-frictional torque arthroplasty have established an exponential correlation between the depth of cup penetration and the incidence of ultrahigh molecular weight polyethylene cemented cup migration. Impingement of the neck of the stem on the rim of the cup was considered to be the cause. We compared the incidence of radiographic loosening and revision of the cup in 2 groups of patients: those with 12.5-mm-diameter neck stem (972 hips) and those with 10-mm-diameter neck stem (261 hips) over a 20-year period, at comparable depths of cup penetration. The benefit of the 10-mm-diameter neck could be expressed as delaying radiographic loosening and revision of the cup by approximately 2 mm of cup penetration because loosening occurred at 2 mm penetration with a 12.5-mm-diameter neck but not until 4-mm penetration with a 10-mm-diameter neck. When a particular depth of cup penetration is reached will clearly depend on factors affecting wear.

Section snippets

Materials and Methods

The Charnley stem has been consistently manufactured in stainless steel—originally in EN58J then in 316L. The introduction of high nitrogen content stainless steel, together with the cold-forming process (1982), resulted in a very strong material ORTRON (DePuy International, Leeds, UK). Fatigue tests of the 10-mm-diameter neck in ORTRON carried out by the manufacturer “in-house” conformed to the then relevant British Standards Institution test DD91. The first stem was implanted on November 17,

Results

The details of the 2 groups of patients including cup wear data are shown in Table 1. The correlation between the depth of cup penetration and the incidence of cup loosening is shown in Table 2 and Fig. 1 and between the depth of penetration and revision for aseptic cup loosening in Table 3 and Fig. 2. At zero penetration, none of the cups were radiologically loose, and none had been revised, irrespective of the neck diameter. With increasing depth of cup penetration, there was an increasing

Discussion

We set out to establish the effect of reducing the diameter of the neck of the Charnley stem from 12.5 to 10 mm on the incidence of radiographic cup loosening and revisions for aseptic cup loosening. It has been suggested that impingement of the neck of the stem on the rim of the cup is the likely cause 4, 5. The exponential correlation between the depth of cup penetration and the incidence of cup migration has been documented 2, 3. Reducing the diameter of the neck could not be expected to

References (17)

  • R.M. Hall et al.

    Prevalence of impingement in explanted Charnley acetabular components

    J Orthop Sci

    (1998)
  • J.A. Feller et al.

    Activity and socket wear in the Charnley low-friction arthroplasty

    J Arthroplasty

    (1994)
  • J. Charnley et al.

    Rate of wear in total hip replacement

    Clin Orthop

    (1975)
  • B.M. Wroblewski

    Charnley low-friction arthroplasty in patients under the age of 40 years

  • B.M. Wroblewski et al.

    Charnley low-friction arthroplasty in the young patient

    Clin Orthop

    (1992)
  • B.M. Wroblewski

    Direction and rate of wear in Charnley low-friction arthroplasty

    J Bone Joint Surg Br

    (1985)
  • G.H. Isaac et al.

    The role of cement in the long term performance and premature failure of Charnley low friction arthroplasties

    Eng Med

    (1986)
  • B.M. Wroblewski et al.

    Quality of the surface finish of the head of the femoral component and the wear rate of the socket in long-term results of the Charnley low-friction arthroplasty

    Proc Inst Mech Eng [H]

    (1992)
There are more references available in the full text version of this article.

Cited by (0)

Research supported by The Peter Kershaw and The John Charnley Trusts.

No benefits or funds were received in support of the study.

View full text