Paprosky type 3B acetabular defects: uniform pattern or spectrum of variants?

The aims of the study — to identify variants and combinations of acetabular structural damage in patients with Paprosky type 3B defects based on the three-dimensional reconstructions of the pelvis, as well as to determine the degree of heterogeneity among these variants within type 3B defects and the dependence of the formation of different damage variants on various factors.

Methods. The study included 132 patients with Paprosky type 3B acetabular defects who underwent revision total hip arthroplasty. Based on the computer tomography data, three-dimensional reconstructions of the pelvis were created. Acetabular supporting structures were assessed. Each structure was evaluated according to three levels of integrity: anatomically preserved, partially preserved/lytic destruction, and complete loss of support/full defect. The heterogeneity of defect variants was assessed using the Shannon index. The association between identified defect variants and patient-related factors was evaluated using multivariate ordinal logistic regression with calculation of odds ratios for each factor.

Results. Five main variants of acetabular damage within Paprosky type 3B defects were identified. The most common variant was the combination of a complete medial wall defect and an anterior column defect. The normalized Shannon index was 0.91 (H/Hmax), suggesting that, for the five identified variants, the heterogeneity of type 3B defects approaches the maximum possible level. A prior periprosthetic joint infection increased the odds ratios of developing a defect pattern with more extensive involvement of load-bearing structures by nearly 2.5 times, while each additional revision procedure increased the risk by 65%.

Conclusions. At least five distinct variants of acetabular load-bearing element damage within Paprosky type 3B defects can be identified. Among the five identified variants, the diversity approaches its maximal possible level. Significant factors influencing the variant of defect were a history of periprosthetic joint infection and the number of previous revision operations. Mandatory three-dimensional visualization for extensive acetabular defects gives the surgeon a more informative picture of the lost and preserved supporting elements. Mandatory three-dimensional modeling in cases of extensive acetabular defects provides the surgeon with a more informative understanding of the lost and preserved load-bearing structures.