Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

88. Revision Total Hip Arthroplasty With Acetabular Bone Loss: Antiprotrusio Cage

Matthew S. Austin, James J. Purtill, and Brian A. Klatt

DEFINITION

images Acetabular bone deficiency may occur primarily (eg, dysplasia, inflammatory arthritis, seronegative arthropathy) or secondarily (eg, aseptic or septic loosening of acetabular components, osteolysis, trauma, iatrogenic loss during removal of well-fixed components).

images The use of antiprotrusio cages is indicated in situations where an uncemented porous-coated acetabular component will not gain reliable initial stability.

ANATOMY

images The confluence of the ilium, the ischium, and the pubis forms the hemispherically-shaped acetabulum, each contributing to the anterior and posterior walls and columns.

images Surgical landmarks include the anterior and posterior walls, dome, and medial wall “teardrop.”

images The acetabulum is normally oriented with 45 degrees of inclination and 15 degrees of anteversion relative to the pelvic plane.

PATHOGENESIS

images Acetabular bone deficiency may occur primarily due to dysplasia. This type of deficiency usually does not require the use of an antiprotrusio cage.

images Certain conditions (eg, rheumatoid arthritis, juvenile rheumatoid arthritis, anklylosing spondylitis, Paget disease) may predispose to acetabular protrusio but usually do not require the use of an antiprotrusio cage.

images The antiprotrusio cage is used most often in cases of secondary bone stock deficiency so massive that the use of a cementless press-fit acetabular component is precluded.

NATURAL HISTORY

images The natural history of massive acetabular bone defects that would require an antiprotrusio cage is not known. Patients usually require revision surgery to return to functional activities.

PATIENT HISTORY AND PHYSICAL FINDINGS

images The history should be directed to determine whether the source of pain is extrinsic or intrinsic.

images The patient's pain may be extrinsic (eg, lumbar radiculopathy, intrapelvic pathology), in which case revision surgery may fail to relieve pain completely.

images Pain usually, but not always, is located in the groin.

images Infection always must be assessed with careful questioning about previous infections, fevers, chills, wound drainage, and pain at rest.

images Start-up pain is a characteristic indication of loosening.

images Medical comorbidities must be assessed to determine the presence of any that may compromise the outcome of the surgery or place the patient at increased risk of complications.

images The skin should be inspected visually for placement of prior incisions and signs of infection.

images The appropriate incision for the surgical approach must be used with an adequate (6 cm) skin bridge.

IMAGING AND OTHER DIAGNOSTIC STUDIES

images Plain radiographs, including AP of the pelvis and AP and true lateral of the hip should be obtained to classify bone loss and to adequately preoperatively plan (FIG 1).

images CT scans may be used to assess the remaining bone stock.

images This is especially important in cases of superior or posterior bone loss that may require allograft reconstruction.

images The CT scan can help determine the need to have allograft bone available to reconstruct the defect and may help to dictate the approach if a posterior column reconstruction or plating is necessary.

images CT scans with intravascular contrast are useful in situations in which a prior implant is medial to Kohler's line and proximity of the implant to the vessels and intra-abdominal contents is unknown.

images Erythrocyte sedimentation rate and C-reactive protein are useful screening tools to detect infection.

images Aspiration of the hip to assess for infection is valuable if either the erythrocyte sedimentation rate, C-reactive protein, or clinical suspicion is elevated.

images Nuclear medicine studies such as technetium Tc 99 methylene diphosphonate in combination with gallium citrate, indium 111–labeled leukocyte scans, positron emission tomographic scans with 18Ffluorodeoxyglucose (PET-FDG), and sulfur colloid scans may help differentiate aseptic from septic loosening.

DIFFERENTIAL DIAGNOSIS

images The following conditions may contribute to pain and may be the cause of continued pain after the surgery:

images Lumbar radiculopathy

images Spinal stenosis

images Sacroiliac degenerative joint disease

images Intra-abdominal pathology

images Intrapelvic pathology

images Neuropathy

images Meralgia paresthetica

images Complex regional pain syndrome

images Vascular claudication

images Primary bone tumors

images Metastasis

NONOPERATIVE MANAGEMENT

images Nonoperative management of severe acetabular bone loss is reserved for those patients for whom surgical management is contraindicated. These include patients with substantial medical comorbidities and patients with active infection.

images

FIG 1 • AP radiograph of the hip demonstrates medial migration of the acetabular cup with significant loss of acetabular bone stock.

SURGICAL MANAGEMENT

images Surgical management begins with preoperative planning.

images The radiographs are assessed and it is determined whether the defect can be reconstructed with a cementless acetabular component or will require an antiprotrusio cage.

images The surgical approach is planned.

images If posterior column plating is anticipated, a posterior approach is indicated.

images If this is not required, a direct lateral or posterior approach may be used, according to the surgeon's preference.

images The acetabulum is exposed, bone loss is assessed, and the determination as to the appropriate reconstructive choice is made.

Preoperative Planning

images Planning for the antiprotrusio cage begins with appropriate radiographs.

images The radiographs allow for classification of the defect and aid in planning for the reconstruction.

images We have found the Paprosky classification to be helpful in defining bone deficiency and in predicting the method of reconstruction3 (FIG 2).

images Paprosky type 1 acetabular defects have minimal bone loss and usually can be reconstructed using just a cementless component.

images Type 2A defects have an intact superior rim, and the acetabulum is oval in shape. The anterior and posterior columns are intact. The implant has migrated less than 2 cm. These defects may be reconstructed with so-called “jumbo” cups or cementless reconstruction with additional bone grafting or trabecular metal augments. The socket also may be placed in a more superior position to attain greater contact with host bone.

images Type 2B defects are similar to type 2A defects, with the exception of loss of the superior rim. The implant has migrated less than 2 cm. The superior rim can be reconstructed with an uncemented socket in association with bone grafting or trabecular metal augments.

images Type 2C defects involve medial bone loss with intact anterior and posterior columns. The medial bone loss may be reconstructed with bone graft or trabecular metal augments.

images Type 3A defects generally migrate more than 2 cm superolaterally. The medial wall and ischium usually are still present, but damaged. These defects can be reconstructed with bone grafting or trabecular metal augments and an uncemented socket.

images Type 3B defects generally migrate more than 2 cm superomedially. There is loss of the teardrop and severe damage to the ischium. Pelvic discontinuity should be suspected. These defects can be recontructed with bulk allograft, trabecular metal, antiprotrusio cage, or a combination. Posterior column plating may be needed in cases of acute discontinuity. If this is a possibility, then a posterior approach should be selected.

images Pelvic discontinuity should be suspected if a fracture is noted that involves both the anterior and posterior columns, the inferior hemipelvis has migrated medial to the superior hemipelvis, or the inferior hemipelvis is rotated in relation to the superior hemipelvis.

images Large posterior column defects may predispose to cage failure, and reconstruction of the defect should be included in preoperative planning.

images An appropriate device should be selected.

images

FIG 2 • Preoperative radiographs of a patient with severe acetabular bone loss due to superior and medial migration of construct as well as pelvic discontinuity (Paprosky type 3B defect). An AP radiograph of the pelvis (A), an AP view of the hip (B), and a frog-leg lateral view of the hip (C) are obtained. Occasionally more specialized views of the pelvis, such as the Judet view, may be necessary to assess integrity of the acetabular columns.

images The flanges should be malleable to allow the cage to be shaped to the bone.

images The implant must have sufficient strength.

images We believe that an inferior flange that gains fixation in or on the ischium is superior to a hook that gains fixation on the teardrop.

Positioning

images The patient is positioned according to surgeon preference, as dictated by the surgical approach. The hip should be draped in such a fashion as to allow wide surgical exposure.

Approach

images The surgeon should select a posterior approach if he or she anticipates the need for posterior column plating or reconstruction. Otherwise, the surgeon should select the approach that is most familiar and comfortable.

images A trochanteric ostetomy, either conventional or extended, may improve exposure of the acetabulum and pelvis.

images Exposure of the sciatic nerve (posterior approach) is left to the judgment of the surgeon.

TECHNIQUES

ACETABULAR EXPOSURE

images  The acetabulum is exposed, and the failed construct and any soft tissue that interferes with visualization should be retracted or removed (TECH FIG 1A–E).

images  The anterior and posterior walls/columns, superior dome/rim, medial wall, teardrop, and ischium are identified, and bone loss is noted (TECH FIG 1F–H).

images

TECH FIG 1 • Acetabular exposure. A. The acetabulum after exposure with a direct lateral (modified Hardinge) approach in the supine position. B. The polyethylene cup is removed. C. Unstable cage construct is removed in one piece with cement. D,E. Failed construct after removal. Once all material is removed, the acetabular landmarks are clearly exposed and evaluated: teardrop (F), posterior column (G), superior dome/rim (H).

INTRAOPERATIVE DETERMINATION OF RECONSTRUCTIVE TECHNIQUE

images  The remaining bone stock is assessed and corroborated with the preoperative assessment of bone loss.

images Paprosky types 1, 2A, 2B, 2C, and 3A defects usually can be reconstructed with an uncemented acetabular component with or without bone grafting or trabecular metal augments.

images All acetabuli, especially Paprosky type 3B defects, should be tested for pelvic discontinuity.

images  If a pelvic discontinuity exists (TECH FIG 2), the surgeon may then elect to use an antiprotrusio cage with or without posterior column plating or additional bone grafting.

images Alternatively, the surgeon may elect to distract the discontinuity with an uncemented socket and bridge the defect in this manner.

images  The acetabulum should be assessed for the remaining bone's ability to support an uncemented component. To support an uncemented cup, the remaining bone stock should allow for at least partial inherent stability of the reamer or trial.

images Reamers or trials that are inherently unstable may not be appropriate for cementless reconstruction.

images  The reamers are not used initally to shape the acetabulum but, rather, are used to assess the ability of the remaining bone to support a socket.

images  If it is determined that the remaining bone stock cannot support a socket, then an antiprotrusio cage should be used.

images

TECH FIG 2 • Intraoperative determination of reconstructive technique. A large central defect is visible where the cage was removed. Pelvic discontinuity is demonstrated (arrow) with a fracture of the posterior column.

BONE PREPARATION

images  The ilium must be exposed with care to avoid the superior gluteal neurovascular bundle (TECH FIG 3A).

images  The size of the defect can be assessed with a standard acetabular reamer. The reamer can then be used to remove small amounts of bone that may prevent complete seating of the cage (TECH FIG 3B).

images It should not be necessary to remove significant bone, because the indication for use of this device is severe bone loss.

images  The outer diameter of the reamer that best fits the acetabulum determines the outer diameter of the cage.

images The trial cage or the actual implant can be used to determine the removal of small amounts of bone that interfere with complete seating of the cage (TECH FIG 3C).

images

TECH FIG 3 • Bone preparation. A. The ilium is exposed. B. Minimal reaming is performed to allow the cage to seat. C. A trial cage is seated to determine whether the actual cage will seat. Small amounts of bone that interfere are removed.

BONE GRAFT AND TRABECULAR METAL AUGMENTATION

images  The cage may not be stable in situations with severe superior dome or posterior bone loss.

images It may be necessary to augment the acetabulum with either structural or particulate bone graft (TECH FIG 4) or trabecular metal to provide the cage with support.

images Severe superior dome or posterior wall or column bone loss may be reconstructed with structural allograft fashioned from a distal femur, proximal tibia, or acetabular allograft.

images  Trabecular metal acetabular components can be used in the cup–cage construct.

images It may be necessary to support the trabecular metal acetabular component with a cage if native host–bone contact is less than 50%. This technique is beyond the scope of this chapter.

images

TECH FIG 4 • Bone graft and trabecular metal augmentation. A. Allograft cancellous bone is placed into the prepared acetabulum. B. Large reamer is used in reverse to crush and distribute the graft.

CAGE IMPLANTATION

images  The ischial flange can be placed on or in the ischium (TECH FIG 5A,B).

images The advantage of placing the flange on the ischium is that screws can be used to fix the cage to the ischium (TECH FIG 5C,D).

images The advantage of blade-plating the flange in the ischium is avoidance of the sciatic nerve (TECH FIG 5E).

images Both methods allow for stable fixation.

images  The cage is shaped to the contour of the ilium and ischium while allowing for seating of the socket portion of the cage into the remaining acetabulum. Usually the ischial flange must be bent laterally to follow the contour of the ischium.

images  The ischial flange is fixed to or in the ischium using the surgeon's preferred method.

images

images

TECH FIG 5 • Cage implantation. A. The cage is shown in the orientation in which it will be inserted. B. Cage being inserted. C,D. Screw fixation to ischium. E. Blade plate fixation of the ishium flange. F,G. Screw fixation to the ileum. H. Cement pressurization. I. Cement after pressurization. J,K. Cup cemented in place. L. Polyethylene liner placed into cup.

images  The socket portion of the cage must be fully seated within the acetabulum to maximize the stability of the construct.

images  The flange must be contoured to the ilium to minimize cage motion. Usually this requires the flange to be bent medially with some rotation.

images  Once the cage is appropriately contoured to the ischium, ileum, and acetabulum and fixed to the ischium, it is fixed with screws through the dome of the cage.

images Fixation usually can be obtained in the posterior and anterior columns, with care to stay within the recognized safe zones.

images  Additional screws should then be passed through the superior flange into the ilium (TECH FIG 5F,G). The number of screws is limited by the amount of bone that can safely provide fixation.

images  A polyethylene liner is then cemented into the cage construct.

images The cement is placed in the socket and pressurized (TECH FIG 5HK).

images A liner designed for cementation or a liner appropriately modified for cementation is then cemented into place in the appropriate position (TECH FIG 5L).

images A 2-mm cement mantle is desirable.

images Care must be taken not to leave large areas of the liner uncovered.

images

images

images

FIG 3 • Postoperative radiographs are taken to verify the position of the cage.

POSTOPERATIVE CARE

images Radiographs are taken to confirm appropriate cage positioning (FIG 3). Intraoperative radiographs may be beneficial to confirm cage positioning prior to final fixation of the device.

images The patient is allowed protected weight bearing as tolerated if bone augmentation was not necessary.

images The patient is restricted to toe-touch weight bearing for 6 to 12 weeks if bone augmentation was necessary. He or she is then allowed to increase weight bearing progressively on a schedule that is individualized to each patient.

OUTCOMES

images The survivorship of antiprotrusio cages has been acceptable in shortto mid-term follow-up.

images However, because most of these devices cannot achieve biologic fixation, it is assumed that they will loosen over time, although one series reported 92% survivorship at 21 years.4

images Other series have shown 100% survivorship at 7.3 years5 and 93.4% survivorship at 10.9 years.2

images The success of these devices also will depend on the environment in which they are placed.

images Most surgeons in North America are selectively using these devices in cases of severe acetabular deficiency in which a press-fit uncemented socket is not appropriate. This may predispose these devices to failure.

images A recent report on the use of the cage in the setting of discontinuity revealed a 31% revision rate at 46 months.1

COMPLICATIONS

images The use of antiprotrusio cages is accompanied by the complications inherent to significant revision surgery:

images Blood loss

images Infection

images Neurovascular injury

images Construct failure

images Anesthetic and medical complications

REFERENCES

1. Paprosky WG, Sporer S, O'Rourke MR. The treatment of pelvic discontinuity with acetabular cages. Clin Orthop Relat Res 2006;453:183–187.

2. Pieringer H, Auersperg V, Bohler N. Reconstruction of severe acetabular bone-deficiency: the Burch-Schneider antiprotrusio cage in primary and revision total hip arthroplasty. J Arthroplasty 2006; 21:489–496.

3. Sporer SM, Paprosky WG, O'Rourke M. Managing bone loss in acetabular revision. J Bone Joint Surg Am 2005;87A:1620–1630.

4. Wachtl SW, Jung M, Jakob RP, et al. The Burch-Schneider antiprotrusio cage in acetabular revision surgery: a mean follow-up of 12 years. J Arthroplasty 2000;15(8):959–963.

5. Winter E, Piert M, Volkmann R, et al. Allogeneic cancellous bone graft and a Burch-Schneider ring for acetabular reconstruction in revision hip arthroplasty. J Bone Joint Surg Am 2001;83A:862–867.



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