W.J. FARRINGTON, D.G. DUNLOP and A.J.TIMPERLEY
Princess Elizabeth Orthopaedic Hospital and The Royal Devon and Exeter Hospital, Barrack Road, Exeter, EX2 5DW, UKJ.R.Coll.Surg.Edinb., 47, April 2002, 500-501

When revision hip surgery is undertaken to remove a cemented cup from the pelvis the preservation of bone stock and structural integrity of the acetabulum is a major concern. We describe a safe technique for cup removal, which helps avoid a rim fracture occurring during this procedure. This should ensure the defect remains a cavitatory defect and does not become a segmental one with a more uncertain prognosis.

Keywords: revision arthroplasty, hip, loosening

INTRODUCTION

We describe a commonly used technique for removal of a cemented acetabular cup in revision hip arthroplasty. Although a cemented cup may be loose at the time of surgery it can still be difficult to remove the cup and attached cement without damaging the surrounding host bone. The cup usually remains firmly fixed to the cement with the movement occurring at the bone-cement interface. The cup needs to be removed before access to the remaining acetabular cement and fibrous lining membrane is possible. As loose cups tend to migrate superiorly, this can create a large cavitatory defect with a thin superior bony rim. This thin bony rim can be easily fractured or damaged if any form of leverage is applied to this region. We advocate the following method as a safe way to remove the cup in this situation.

METHOD

Once the soft tissue around the margin of the acetabulum has been cleared and the cup is clearly visible, the inferior region (tear drop and transverse ligament) of the true acetabulum is identified and cleared of soft tissue. This gives an indication of how far superiorly the cup has migrated. Using radial and curved cement splitters the cement inferior to the cup is removed first. This involves splitting the cement into small fragments that can be removed piecemeal. Once a space has been created inferior to the cup (Figure 1), the cup can then be tapped down into this space with a blunt instrument (Figure 2) and removed.

Figure 1 Cement and soft tissue cleared to create a space inferior to the cup (arrow).

Figure 2 Cup tapped down into space created inferiorly.

Removal can be aided with large forceps or by a tap on a T-handle threaded into the polyethylene via a suitably large drill hole (Figure 3). If removal remains difficult, after the cup has been tapped down, attention can be turned to the space created superiorly for cement removal.

Figure 3 Cup removed from acetabulum using a T-handled tap

Further cement can be chipped away once the cup has been knocked down. This allows removal of the cup from the socket without the need to remove the cement superiorly or anteriorly until after the cup has come out. The bone is thinnest and most likely to fracture at this site. The cement in these regions can be taken out once the cup is removed.

DISCUSSION

The type of acetabular defect is a major factor in determining the success of revision arthroplasty. It is generally considered that a cavitatary defect is easier to deal with and has a better prognosis than a segmental defect.(1) Disruption of the lateral rim converts a cavitatory defect into a segmental one, which will then require augmentation with a rim mesh or block allo-graft. The results using these forms of reconstruction are less predictable than when the defect is solely cavitatory. (2,3) We have used this method successfully over the last 10 years of revision surgery without causing rim damage. We find it is a reliable technique and safe to perform. It is particularly useful when there is a significant amount of superior migration of the cup or where the bony acetabular rim is thin.

REFERENCES

1. H.C.Amstutz. Hip Arthroplasty. Churchill Livingstone Inc.1991.Chapter IX. P.813
2. Schreurs BW, Slooff TJ, Buma P, Gardeniers JW, Huiskes R.Acetabular reconstruction with impacted morcellised cancellous bone graft and cement.A 10 to 15 year follow-up of 60 revision arthroplasties. JBJS (B) 1998; 80(3); 391-5
3. Wilson MG, Nikpoor N,Aliabdi P et al The fate of acetabular allografts after bipolar revision arthr plasty of the hip JBJS (A) 1989; 71:1469