CUP-CAGE RECONSTRUCTION FOR PELVIC DISCONTINUITY: GOOD MID- TO LONG-TERM SURVIVAL

Pelvic discontinuity is often a difficult complication to manage in revision total hip arthroplasty. There is a paucity of data assessing mid to long term outcomes of cup cages for pelvic discontinuity, and the studies done thus far typically include small numbers of patients. The purpose of our study was to review the survivorship and radiographic outcomes of cup-cage constructs used to treat pelvic discontinuity. We retrospectively reviewed our institutional database to include all cases of cup-cage reconstruction performed for pelvic discontinuity between 1999 and 2019. The primary outcome was implant survival with end points of re-revision for aseptic loosening and all cause revision. The secondary outcome was radiological analysis utilizing Gill's classification for loosening as well as any ischial blade cut out/fracture, uncoupling of cage from cup or separation of a cemented acetabular component from cage. Forty-nine cup-cage revisions for pelvic discontinuity were included in the study with a mean follow-up of 6.5 years (range two months-19 years). Twenty-seven patients were deceased during the study time at an average of 7.5 years from the date of their discontinuity surgery (range two months to 18 years). At the time of surgery, the mean age included was 77 years (range 38-91), BMI was 27.9 (range 18-38) and 73% were female. All cup cage constructs were from the same manufacturer (Zimmer). Kaplan Meier Analysis was used to determine survival with all-cause and aseptic loosening re-revisions as the endpoints. A total of nine (18%) patients underwent revision surgery following cup-cage reconstructions at a mean time point of 31 months post index procedure (range one – 81 months). Aseptic loosening was the cause for re-revision in 3/49 (6%) of cases at a mean time point of 56 months (range 29-81 months). Of these aseptic construct failures, two of three of cases required isolated cage/liner revision as the acetabular component was well-fixed. The final case was revised to a custom manufactured tri-flanged implant. Other indications for revision included infection resistant to washout and antibiotic suppression requiring resection arthroplasty (n=three) and instability (n=three). The instability re-revisions consisted of liner exchanges as the cup-cage constructs had not failed. There were six (12%) further cases of radiological failure of the cup-cage constructs where revision surgery was considered but declined by the patients. These included five cases of cage failure and one loosening of the cemented liner with separation from the cage with an intact cup-cage construct. The all-cause re-revision survival was 82% (CI 0.67 to 0.92) at 18 years. Re-revision survival for aseptic loosening was 94% (CI 0.85 to 1.00) at 18 years. Our study has shown cup-cage constructs used to treat arthroplasty related pelvic discontinuity is a successful solution with 82% survival to 18 years and 94% for aseptic loosening survival to 18 years. As far as we know, our study is the largest case series in the literature to date with long term follow-up