Long term results of the Exeter Femoral Stem – A 30 year review

The material of this review includes the first 433 Exeter hips that were performed at the PrincessElizabethOrthopaedicHospital in Exeter. This represents the first use of what was for 1970 a radical design, using the original polished monoblock stems that were manufactured from the ductile stainless steel EN58J with a 29.75mm head size. There were two stem sizes available and they were almost all used in conjunction with a distal metal centraliser.

The operations were performed in roughly equal numbers by three consultants and 13 registrars. The cementing technique was crude, with no use of lavage or intramedullary plugs , and no form of pressurisation of cement was employed other than thumbing-down Simplex cement into the medullary canal.

Not all of these cases were primary joint replacements. The series includes 56 hips that had undergone previous hip surgery, of which 21 were revision hip arthroplasties (17 from failed total hip arthroplasties and 4 from failed hemi-arthroplasties). The mean age at operation was 66.8, and 69 patients were under the age of 60. There was a predominance of the female gender. From this group of 433 cases, 28 hips (6.46%) have been lost to follow-up.

From the series altogether the revision rate was of 3.46% for stem neck fracture, all occurring in a group of 90 stems that had been excessively machined in the neck. Revision for stem fracture was undertaken in 3.92% of cases in the series and 3.46% had revision for aseptic stem loosening. Revision for sepsis, recurrent dislocation and periprosthetic fracture was uncommon. The revisions for neck and stem fracture are now only of historic interest due to changes in the metallurgy and manufacturing process that have strengthened the stem and thus addressed these issues.

At the end of 2003, there were 25 surviving patients with 30 surviving hips: the average age at operation of this group was 56.1 years. None of the survivors has needed a revision for aseptic stem loosening.

Survivorship with the end point revision for aseptic stem loosening in to the 30^th year is 91.5% and it is noteworthy that there have been no failures since the 24^th year. If all cases that were lost to follow-up (28 hips) were regarded as failures (i.e. the ‘worst case’ scenario) the survivorship is approximately 83% and again with no changes since the 24^th year.

Subsidence of the stem within the cement is the characteristic feature of the behaviour of the Exeter polished stems in vivo and this first became apparent to us in the early 1970s. The mean  subsidence of the stem in the cement mantle in the survivors is 3.9mms, ranging from 0-45. In this group of survivors there were two outliers whose cement mantles were both very poor and whose subsidence was 45mm and 18.8mm respectively. If we exclude these outliers , the mean subsidence in the survibg patients is 1.8mms. We know now that such subsidence is functionally important  because  it is an essential component of the taper action of the stem  which produces residual hoop strain in the cement mantle that sets the stage for hoop tensile stress relaxation, leading, in turn, to a loading regime that is dominated by compression, both at the interfaces and in the cement itself. This is one of the main reasons for the outstanding long-term success of the stem, even with first generation cementing.

In conclusion, these findings show that even with what was, by modern standards, indifferent cementing, the stem has survived well up to the 30^th year. We believe that the failures from loosening were in major part a consequence of  surgical and cementing  techniques, , which have of course been significantly improved over the last 35 years.