Acetabular Revision With Custom Implants

Key Points

A thorough preoperative radiographic examination, including thin-slice computed tomography, is necessary to evaluate osseous defects and help identify a pelvic discontinuity.
Extensive planning is necessary in the design of custom triflanged acetabular components (CTACs), which is a dynamic process often requiring multiple iterations.
Obtaining an adequate buttress between the implant and remaining ilium is vital to reducing shear stresses on the flange screws.
Failure of ischial fixation has been observed and the surgeon should attempt to place 4 to 6 screws into the ischium. Locking screws should be used to enhance fixation.
The liberal use of a standard or extended trochanteric osteotomy allows for improved visualization and protection of the superior gluteal nerve during placement of the iliac flange.
When the ischium is exposed, careful identification of the sciatic nerve with the hip in extension and the knee in flexion will minimize the risk of sciatic nerve injury.
In selective cases of pelvic discontinuity, an additional posterior column plating may improve construct stability and decrease the likelihood of mechanical failure.
To minimize the risk of dislocation, a large femoral head with use of high-wall, face-changing, or constrained modular polyethylene liners versus a dual mobility construct may be necessary.

Introduction

The goal of acetabular revision surgery is to achieve a stable, pain-free, and functional construct. This can frequently be achieved with the use of hemispheric acetabular components with supplemental screw fixation. However, in the setting of massive periacetabular bone loss or pelvic discontinuity, stable fixation with standard hemispheric acetabular components may not be possible, and other reconstruction options must be considered.

Numerous treatment methods are available for management of massive acetabular defects in revision total hip arthroplasty (THA). Unfortunately, the clinical results of managing these complex cases are highly variable and are often associated with a high incidence of complications. Currently used treatment methods include jumbo acetabular components with or without the use of metal augments or massive structural allografts, acetabular impaction bone grafting, oblong acetabular components, noncustom acetabular reconstruction rings or cages, cup-cage constructs, and custom triflanged acetabular components (CTACs). This chapter will focus on the treatment of massive periacetabular bone loss in revision THA with CTACs.

Bone Loss Classification

The severity of acetabular bone loss in revision THA has been classified by Paprosky ( Table 95.1 ) and the American Academy of Orthopaedic Surgeons (AAOS; Table 95.2 ). The bone loss is classified according to the magnitude of bone loss, the amount of acetabular component migration, and the degree of destruction of the anterior and posterior columns.

TABLE 95.1

Paprosky Classification of Acetabular Defects

Type	Description
1	Columns intact Hemisphere intact > 70% of prosthesis can be in contact with host bone
2A	Columns intact Defect below superior dome Migration of head center < 2 cm No ischial or teardrop lysis Köhler line intact
2B	Columns intact Superior lateral migration, creating dome defect Migration of head center < 2 cm Minimal ischial lysis Köhler line intact
2C	Columns intact Medial wall defect Medial migration with minimal superior migration of head center
3A	Columns intact Severe superior lateral migration, creating > 50% dome defect Migration of head center > 2 cm Köhler line intact
3B	Posterior column deficient Severe superior medial migration Severe ischial lysis Köhler line broken Possible pelvic discontinuity

TABLE 95.2

AAOS Classification of Acetabular Defects

Type	Description
I	No significant bone loss
II	Columns and rim intact Contained cavitary loss
III	Columns may be deficient Uncontained defect involving < 50% of acetabulum
IV	Columns deficient Uncontained defect involving > 50% of acetabulum Pelvic discontinuity may be present

AAOS, American Academy of Orthopaedic Surgeons.

Indications

The presence of massive periacetabular bone loss (Paprosky type IIIB and AAOS type III and type IV) that precludes the ability to obtain a stable acetabular reconstruction with a traditional hemispheric component is the primary indication for the use of a CTAC. The use of bulk allograft and impaction grafting with traditional acetabular components in these cases has failure rates as high as 36% in some series. The ability of these allografts to incorporate and withstand physiologic loads is questionable and is a likely cause of the unacceptably high failure rates. With the use of a CTAC, however, the ability to bridge the defects and obtain fixation to remaining available host bone is obtained, providing stable fixation and preventing early component migration. An additional advantage of a CTAC is the ability to place the acetabular component at a correct anatomic level, thereby restoring hip biomechanics and stability.

Contraindications

The cost and complexity of CTACs limit their indication to cases in which adequate host bone for standard hemispheric cups is not available. In cases in which adequate pelvic bone quality to obtain screw fixation does not exist or in the setting of persistent infection, CTACs are contraindicated. Finally, in cases with massive bone loss associated with the presence of a pelvic discontinuity, consideration should be given to combining the CTAC with column plating.

Preoperative Planning

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