The use of modular femoral head trials to centre the Explant blade facilitates retrieval of well-fixed acetabular components with minimal bone loss

A Novel Method of Determining Acetabular Component Size to Guide Explant in Revision Hip Arthroplasty

Revision hip arthroplasty is a frequently performed procedure and is projected to increase annually. Removal of a well-fixed acetabular component can involve loss of much needed bone stock. Contemporary instruments allow acetabular removal with minimal morbidity; however, their use requires accurate knowledge of the component size. We describe a technique that allows sizing to be determined accurately, without specialized equipment, in situations where component details are unavailable. Our technique multiplies ratio of head:cup on pre-operative X-ray by the diameter of the index femoral head which is removed intra-operatively to predict index cup size. This novel surgical technique appears accurate in prediction of cup size to guide explant in revision hip arthroplasty.

Removal of Well-Fixed Cementless Acetabular Components in Revision Total Hip Arthroplasty

The Zimmer Explant Acetabular Cup Removal System (Warsaw, Indiana) has been touted as a superior method for removing well-fixed cementless acetabular components while minimizing bone loss; however, no comparative data support this. This study compares bone loss following the removal of well-fixed acetabular components with Aufranc gouges and with the Explant System. A review of 623 revision total hip arthroplasties (THAs) at the authors' institution between 2002 and 2013 identified cases involving the revision of well-fixed cementless hemispherical acetabular components for any reason except infection. Twenty-four cases using Aufranc gouges and 27 cases using the Explant System were included. The following surrogates for bone loss were used: (1) the difference between the initial acetabular component outer diameter (OD) and the final reamer OD; (2) the difference between the initial acetabular component OD and the new acetabular component OD; and (3) the use of impaction bone grafting. A 2-tailed Wilcoxon-Mann-Whitney test was used to assess the difference in bone loss between the 2 groups. The use of bone grafting was compared between the groups with the chi-square test. The median differences between the initial acetabular component and the final reamer (P=.004), as well as between the initial and new acetabular components (P=.002), were 2 mm less with the Explant System. Hips in the Aufranc group were more likely to have bone grafting (54% vs 26%; P=.04). These results suggest less bone loss when removing well-fixed acetabular components with the Zimmer Explant System compared with Aufranc gouges.

A pilot trial comparing the tear-out behavior in screw-sockets and cemented polyethylene acetabular components - a cadaveric study

BACKGROUND

The removal of well-fixed acetabular components following THA (total hip arthroplasty) is a difficult operation and could be accompanied by the loss of acetabular bone stock. The optimal method for fixation is still under debate. The aim of this pilot study was to compare the tear-out resistance and failure behavior between osseo-integrated and non-integrated screw cups. Furthermore, we examined whether there are differences in the properties mentioned between screw sockets and cemented polyethylene cups.

HYPOTHESIS

Tear-out resistance and related mechanical work required for the tear-out of osseo-integrated screw sockets are higher than in non-integrated screw sockets.

PATIENTS AND METHODS

Ten human coxal bones from six cadavers with osseo-integrated screw sockets (n=4), non-integrated (implanted post-mortem, n=3) screw sockets and cemented polyethylene cups (n=3) were used for tear-out testing. The parameters axial failure load and mechanical work for tear-out were introduced as measures for determining the stability of acetabular components following THA.

RESULTS

The osseo-integrated screw sockets yielded slightly higher tear-out resistance (1.61±0.26kN) and related mechanical work compared to the non-integrated screw sockets (1.23±0.39kN, P=0.4). The cemented polyethylene cups yielded the lowest tear-out resistance with a failure load of 1.18±0.24kN. Compared to the screw cups implanted while alive, they also differ on a non-significant level (P=0.1). Osseous failure patterns differed especially for the screw sockets compared to the cemented polyethylene cups.

DISCUSSION

Osseo-integration did not greatly influence the tear-out stability in cementless screw sockets following axial loading. Furthermore, the strength of the bone-implant-interface of cementless screw sockets appears to be similar to cemented polyethylene cups. However, given the high failure load, high mechanical load and because of the related bone failure patterns, removal should not be performed by means of tear-out but rather by osteotomes or other curved cutting devices to preserve the acetabular bone stock.

LEVEL OF EVIDENCE

Level III, case-control-study.

Should well-fixed uncemented femoral components be revised in infected hip arthroplasty? Report of five trial cases

BACKGROUND

Well-fixed femoral component removal remains difficult and complicated.

METHODS

We report herein the outcomes of two-stage surgery involving retention of bone-ingrown uncemented stems, aggressive soft-tissue debridement, and delayed reimplantation of an acetabular component in 5 patients for infected hip arthroplasty.

RESULTS

By a mean follow-up point of 4.2 years after the second-stage operation, none of the 5 patients experienced recurrence of infection, and the mean Harris hip score had improved from 63 to 86 points by the latest follow-up evaluation.

CONCLUSION

Two-stage revision with retention of well-fixed uncemented stems could be an alternative treatment option in hip periprosthetic infection.