Acetabular cage survival and analysis of factors related to failure

Abstract

The reported results of acetabular cage reconstruction for pelvic deficiency are widely variable. Our primary question was: what is the survivorship of cage reconstruction with a primary end point of cage revision and secondary end points of radiographic loosening and any reoperation? Secondary questions were: which factors predict cage failure, and what is the functional outcome (SF-36, WOMAC, Harris hip score) of this reconstructive method? We reviewed 72 cage reconstructions in 68 patients. Minimum followup was 1.2 years (mean, 5.1 years; range, 1.2-10.7 years). Five-year cage revision-free survivorship was 87.8%. Five-year loosening-free and acetabular reoperation-free survivorships were 80.7% and 81.3%, respectively. No single preoperative factor (age, gender, severity of pelvic defect, degree of heterotopic ossification, difference in limb lengths and centers of rotation) or intraoperative factor (type of bone graft, type of cage, changes in limb length and center of rotation) predicted cage failure. Functional outcomes were 28.9 (SF-36 Physical Component), 52.4 (SF-36 Mental Component), 33.7 (WOMAC), and 44.2 (Harris). We judged these outcomes acceptable for this sometimes challenging problem. Future techniques for treating pelvic deficiency will need to be compared with these and other outcomes in the literature.

Level of evidence: Level IV, therapeutic study.

Fig. 1A–B

Representative final hip radiographs are shown. (A) A loose acetabular cage is evidenced by loss of inferior fixation and resultant migration and radiolucency. (B) A well-fixed acetabular cage has an intact cage and screws and no radiolucency or migration.

Fig. 2

The Kaplan-Meier survivorship curve of cage reconstruction with an end point of cage removal shows acceptable 5-year survivorship of 87.8%. CI = confidence interval.

Fig. 3

The Kaplan-Meier survivorship curve of cage reconstruction with an end point of radiographic loosening or revision shows stepwise progression of loosening up to 6 years and a 5-year survivorship of 80.7%. CI = confidence interval.

Fig. 4

The Kaplan-Meier survivorship curve of cage reconstruction with an end point of any acetabular reoperation shows a 5-year survivorship of 81.3%. In addition to cage revisions, other reoperations were polyethylene liner revisions for dislodgement or cup malpositioning. CI = confidence interval.

Fig. 5

Kaplan-Meier survivorship curves by type of pelvic deficiency according to the Paprosky classification [22] failed to show a correlation between worsening pelvic deficiency and likelihood of cage failure defined as either cage removal or radiographic loosening.

Fig. 6

Kaplan-Meier survivorship curves by type of pelvic deficiency according to the Toronto classification [29] failed to show a correlation between worsening pelvic deficiency and likelihood of cage failure defined as either cage removal or radiographic loosening.

Fig. 7

Mean SF-36 physical component score (PCS), SF-36 mental component score (MCS), the WOMAC osteoarthritis index, and Harris hip score for all patients with unrevised acetabular cages still show considerable impairment. This may be partly attributable to effects of medical comorbidities and other systemic illnesses. In the WOMAC, a lower score suggests better function.