Revision Acetabulum Treatment Options: The Use of Cages

Paul E. Beaulé, M.D., FRCSC
Associate Professor
Head of Adult Reconstruction, The Ottawa Hospital
University of Ottawa
Ottawa, ON

The most common indication for cage reconstruction is limited host bone contact (less than 50%) and pelvic discontinuity. The majority of these deficiencies fall into Paprosky type III and IV.  The surgical technique of cage reconstruction has not focused on restoring normal hip anatomy. The majority of the surgical technique focuses on placing the cage on intact host bone; as the main role of the cage should be to protect the graft from mechanical overload during its revascularization phase. Udomkiat and associates reported clinical and radiographic short-term results of three different metallic reconstruction devices (Burch-Schneider, Ganz, and Muller) with an overall mechanical failure rate, at an average of 4.6 years, of 17%. The Burch-Schneider cage had less favourable biomechanical characteristics than the other devices - abduction angles of 70.7 ± 12.6 and elevated hip centres of 16.6 ± 12.5 mm. In general, the surgical technique, particularly with the Burch-Schneider cage, focused on stabilizing the implant on host bone with large deficiencies leading to superior and lateral placement of the hip centre and increased joint reaction forces. Doehring and associates have demonstrated that with a 25 - mm displacement of the hip centre, the joint reaction force increases by 29% (~7.5-8.0x body weight). Consequently, the cage is at high risk of fatigue failure. In contrast, Kerboull and associates reported a ten-year follow-up survivorship rate of 92.1 ± 5% for on type III and IV deficiencies. The biomechanical parameters were more favourable, with a device abduction angle of 38.7 ± 7.6.

Surgical Technique
The surgical principles for using a ring hook cage are the following: 1) reconstruction of the anatomic hip centre with the inferior hook, using the teardrop as a landmark; 2) device and cup abduction angles of 45°; 3) structural allograft reconstruction around the device not compromising the first two principles (Figure 1). Left and right implants are useful in order to optimize anteversion. Standard anteroposterior pelvis and Judet views are used to determine the amount of acetabular deficiency (Figure 2). The opposite hip is templated to determine the size of the ring and the hip centre of rotation of the operative extremity. Structural (femoral heads) and particulate allograft sources are made available at the time of surgery. An extended posterior approach is most commonly used with a trochanteric slide osteotomy as needed.

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1A
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1B















Figure 1A: 44-year-old female 12 years post left total hip replacement for arthritis secondary to hip dysplasia presenting with a failed acetabular component.

Figure 1B: One year post revision surgery with cage reconstruction (Gap Cup®, Stryker, Allendale, NJ) and structural femoral allograft.

With the inferior hook in the obturator foramen, the cage is placed in the defect to determine the placement and orientation of the structural bone graft. Careful debridement and blunt dissection is used during these manoeuvres. The device should not be contoured to the deficiency. This would inadvertently lead to vertical, superior, and lateral placement, especially with large, combined defects. In the presence of pelvic discontinuity (transverse acetabular non union), plating of the posterior column should be bone (Figure 3). Structural graft (femoral head) is usually placed on the superior rim of the acetabulum and in other areas as necessary. The plate extension from the cup can be contoured and reduced in size as necessary. Usually, the last three holes are removed to prevent excessive abductor muscle dissection and superior gluteal nerve injury. After the structural allograft is contoured, focusing on superior dome placement, and the cavitary defects are filled with particulate allograft, the cage is placed. The first step is to place the inferior hook under the teardrop and lever down into the allograft. The screw hole closest to the graft is filled first using 4.5mm screws to maximally compress the allograft and avoid excessive cage abduction. With larger deficiencies to the ilium, screws may need to be placed in the plate extension holes through the allograft into host bone. Finally, a liner either all polyethylene or mono block cobalt chrome component are cemented with a two millimetre mantle. Patients are restricted in weight-bearing for up to three months.
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Figure 2: 55-year-old female with rheumatoid arthritis presenting with failed acetabular components of both hips with left side also showing a pelvic discontinuity on Judet Oblique views.

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Figure 3: Eighteen months post bilateral revision surgery staged six months in between. Note plating of the posterior column on the left side.

References

  1. Berry D.J., Muller M.E: Revision Arthroplasty using an anti-protrusio cage for massive acetabular bone deficiency. J Bone Joint Surg 74B:711-715, 1992.
  2. Hamadouche M., Antoniades J.T., Kerboull M., Beaulé P.E.: Reinforcement rings with hook in acetabular reconstruction. Operative Techniques in Orthopaedics 14:121-129, 2004.
  3. Doehring T.C., Rubash H.E., Shelley F.J., et al: Effect of superrio and superolateral relocations of the hip center on hip joint forces: An experimental and analytical model. J Arthroplasty 11:693-703, 1996.
  4. Kerboull M., Hamadouche M., Kerboull L: The Kerboull reinforcement acetabular reinforcement device in major acetabular reconstructions. Clin Orthop 378:155-168, 2000.
  5. Paprosky W.G., Perona P.G., Lawrence J.M.: Acetabular defect classification and surgical reconstruction in revision arthroplasty. J Arthroplasty 9:33-44, 1994.
  6. Udomkiat P., Dorr L.D., Won Y.-Y., et al: Technical factors for success with metal ring acetabular reconstruction. J Arthroplasty 16:961-969, 2001.

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