Jumbo Cups

CHAPTER 47 Jumbo Cups



Brian A. Klatt, Matthew S. Austin, William J. Hozack



CHAPTER OUTLINE



Key Points 353

Indications and Contraindications 353

Preoperative Planning 354

Technique 354

Perioperative Management 356

Complications 356

Results 356



KEY POINTS



image Adequate exposure of the remaining acetabular bone stock must be obtained.

image Fit the reamer to the remaining bone, minimizing removal of host bone.

image Significant structural bone loss may be augmented with autograft, allograft, or metal.

image A fine balance exists between adequate fixation and loss of structural integrity of the bone.

image Impact the acetabular component gently, and augment fixation with at least two screws.

Acetabular revision with cementless components has been remarkably successful, with some series reporting no revisions for aseptic loosening at an average follow-up of 13.9 years.1 Cementless acetabular revision is now feasible for a wide range of revision situations, including some cases of pelvic discontinuity. The Paprosky classification is useful in predicting the reconstructive technique that will be required (see Table 33-3). Type I and many type II defects may be reconstructed with standard cementless components. A standard cup may be ineffective with increasing bone loss.


Many type II and type III defects, which involve the loss of additional structural bone, can be reconstructed with a jumbo cup. A jumbo cup is defined by Whaley and colleagues as a component that is >61 mm in women and >65 mm in men, a definition that is based on a shell that is >10 mm greater than the diameter of the average cup implanted in women and men.2


The jumbo cup has the advantage of an increased contact area between host bone and cup, which maximizes the surface area for ingrowth or ongrowth. The increased area of contact also prevents cup migration by allowing for force dissipation over a large area. Use of a jumbo cup may also decrease the need to use bone graft. In contrast to positioning the cup in the so-called high hip center, a jumbo cup can help to restore the hip’s center of rotation.


The disadvantages of this technique are that host bone may have to be removed to implant the cup, that bone stock is not restored by the reconstruction, and that hemispherical cups have limited applicability in situations of oblong bone stock deficiency.


Jumbo acetabular components can be used in combination with both structural and cancellous bone graft. In these cases the cementless cup must achieve adequate contact with host bone in order to allow bone ingrowth to occur. The percentage of host bone contact that is considered adequate is not known exactly, but a recent study suggests that 50% contact with host bone is desirable.3


Another option for cementless reconstruction includes placement of the socket in a high hip center. The advantage of this technique is the ability to achieve increased host bone contact for fixation while avoiding the use of bone or metal supplementation. A disadvantage is an increase in the joint reaction force that may lead to increased wear. Furthermore, there is increased potential for bony impingement against either the anterior or posterior column, with a resultant increased risk of dislocation. It appears that these disadvantages can be minimized by limiting the proximal placement of the cup to under 2 cm from the anatomic position and by avoiding lateral placement of the center of rotation of the hip.



INDICATIONS AND CONTRAINDICATIONS


Jumbo cups are indicated for revision of type II and III defects in which stable two-point fixation can be achieved. The two points of fixation can be obtained between the anterior and posterior walls, between the anterosuperior and posteroinferior acetabulum, or between the posterosuperior and anteroinferior acetabulum (Fig. 47-1). The initial stability of the cup should be adequate before the use of screws for supplemental fixation. The cup can be used for segmental, cavitary, and combined defects of the acetabulum. There must be adequate bone to provide initial support for the cup, and the cup must have minimal micromotion in the healing phase for bony ingrowth to occur. Also, there must be adequate bony contact and bone quality to allow biologic ingrowth to occur.


image

FIGURE 47-1 Fully exposed acetabulum demonstrating acetabular landmarks. The defect is central with an intact acetabular rim.

Related posts:

The Cementless Tapered Stem Femoroacetabular Osteoplasty Reconstruction of Acetabular Bone Deficiencies Using the Antiprotrusio Cage The Cemented Stem Management of Postoperative Hematomas The Cemented Stem

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Mar 10, 2016 | Posted by in Reconstructive surgery | Comments Off on Jumbo Cups

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