Studies of acetabular reconstruction with use of cement and bulk bone graft have demonstrated increasing rates of cup failure in patients with dysplastic hips seven years after total hip arthroplasty. Comparable data on the long-term results of bulk bone-grafting done in conjunction with cementless implants are limited. The aim of this study was to review the clinical and radiographic results of autologous bulk bone-grafting in conjunction with a cementless cup.
From 1987 to 1992, forty-seven patients (forty women and seven men, with an average age of 50.4 years) who had developmental dysplasia of the hip underwent fifty-six total hip arthroplasties and received a structural graft in combination with a cementless Harris-Galante type-I cup. All patients were followed prospectively. In fifty-five hips, implant migration was measured with single-image radiographic analysis.
After an average duration (and standard deviation) of 10.2 ± 2.9 years, three patients (four hips) had died. In the surviving patients, four implants had been revised and two had radiographic evidence of loosening. With use of revision and loosening as end points, the eleven-year survival rates were 91.6% and 88.9%, respectively. Of the fifty implants that had no loosening, fourteen had measurable cup migration, thirty-five had no migration, and one implant could not be measured. All migrations but one were progressive. With loosening used as the end point, the survival rate at eleven years was 100% for the implants with no migration; however, the survival rate for the cups that had migrated was 69.3% (p = 0.0012).
The eleven-year survival rate for the spherical press-fit cups in combination with bulk bone-grafting is satisfactory, given the complexity of these reconstructions. However, the difference between the survival of the implants that had migrated and those that had not was significant. We expect that the thirteen implants with progressive acetabular migration at the time of the latest follow-up are at risk for loosening, which will increase the revision rate for this series in the coming years.
Under optimal circumstances, a large structural acetabular graft will be incorporated only at its margins. In cemented cups, the construct of bulk graft and cup may fail when the graft collapses. However, in uncemented acetabular reconstruction, bone-grafting plays a different role. Structural bone-grafting is used to achieve a stable situation until definite osseointegration has occurred. In addition to the primary stability of the bone graft construct (the cup, additional screws, and the three-dimensional surface structure of the cup), the placement of the construct against autologous host bone is essential for obtaining secure osseointegration. Therefore, if broader support on autologous bone can be achieved in total hip arthroplasty in patients with developmental dysplasia of the hip, an elevated hip center may be accepted even in combination with a structural bone graft.
A high-quality anteroposterior pelvic overview radiograph (Fig. 1) is essential for preoperative planning and templating. For cup placement, the ideal position is in the true acetabulum as far medial as possible and good support from autologous bone should be planned. The resulting acetabular osseous defect can be estimated. Also, extensive resection of the femoral neck should be planned in order to provide a stronger graft. Often a preoperative drawing can be helpful (Fig. 2).
Perioperative prophylaxis with antibiotics is achieved with 2 g of cefazolin administered intravenously. All patients are placed in the supine position, and the operation is performed through a transgluteal approach, which permits continuous monitoring of the position of the pelvis. The patient is placed flat to one side of the table so that the soft tissues of the buttocks can fall posteriorly, and the hip is flexed approximately 30° (Fig. 3). In patients in whom extensive lengthening may be anticipated, it is useful to excise the capsule completely. Relocation of the hip is facilitated in patients with developmental dysplasia of the hip when the maximum neck resection possible is used. After removal of the femoral head, the acetabulum is exposed with use of Hohmann retractors.
Often the depth of the acetabulum is hidden by a large overhanging osteophyte (Fig. 4). Excision of the osteophyte with use of chisels may be helpful. The best landmark for the identification of the true acetabulum is the acetabular teardrop (Köhler teardrop), which can be identified by the overlying fat pad. The first reamer is targeted at 90° to the horizontal axis of the body to medialize the cup as far as possible by reaching the internal cortex of the pelvis (Figs. 5 and 6). After removal of the overhanging osteophyte, the underlying bone may be very soft. Especially with new reamers, the preparation should be performed step-wise without too much effort. Care also should be taken not to weaken a thin anterior wall. The position of the reamer is then changed to the desired cup position, which will give the surgeon a first impression of the portion of the cup that will remain uncovered by bone. Use of the acetabular reamers in ascending series may result in a mild elevation and lateralization because of the shape of the anterior and posterior walls. This should be accepted since it will result in broader coverage with autologous bone. Reaming is continued until the anteroposterior diameter of the acetabulum is reached. Depending on the quality of bone, only line-to-line reaming may be possible. With the last reamer, the position of the cup may be simulated (Fig. 7). The remaining acetabular defect is exposed, and the outer cortex of the ilium is freed of soft tissue for a short distance cephalad to the upper limit of the defect. When sclerotic bone is encountered, it may be perforated by small drill-holes or with a small chisel.
All grades of developmental dysplasia of the hip, in which >20% of the cup remains uncovered by bone when the cup is in an ideal position.
When limb-lengthening of >3 cm is anticipated, an additional femoral shortening procedure or a trochanteric osteotomy may be considered.
Primary and secondary osteoporosis
A history of irradiation to the affected hip
Complete collapse of the femoral head
Inadequate planning can result in missing instruments, inappropriate implants, or unexpected leg-lengthening.
Care must be taken not to drop the graft on the floor.
The graft must be seated well. This may require reshaping of femoral neck cortex.
Graft fracture can be avoided by predrilling the screw-holes.
Damage of the graft by the acetabular reamer can be avoided by first using a small oscillating saw or a high-speed burr to prepare the acetabulum.
Dislocation can be avoided by using an elevated liner and a 32-mm head.
Instead of the original cups, a multiple-hole cup design is currently used with a 32-mm elevated cross-linked polyethylene liner and a 32-mm alumina femoral head (Biolox; CeramTec, Plochingen, Germany). The original malleolar-type screws have been replaced by cannulated self-tapping 5-mm titanium malleolar screws.
The preparation of the graft may be challenging because of its complex three-dimensional shape. The femoral head should be cleared of all osteophytes and soft tissue (Fig. 8). The biggest danger is that the graft may fall on the floor during manipulation; therefore, an extra table should be provided and one experienced assistant should hold the graft with a strong bone clamp. New medium-sized saw blades should be used to shape the graft.
Our technique follows four steps:
Step 1: At an angle of about 120°, two cuts are made along the inside of the cortex of the femoral neck to the depth of the head-neck junction (Fig. 9).
Step 4: The short side of the L-shaped graft is trimmed in a triangular form to remove the remaining cortical bone. After this cut, only cancellous bone is left to face into the acetabulum (Figs. 16, 17, and 18).
The autograft is then positioned into the defect so that the long side of the “L” is positioned laterally, and its inner aspect slides along the outer cortex of the ilium (Fig. 19). If the graft is not seated completely, the anterior and posterior parts of the neck may be trimmed a little to allow an optimum fit. The autograft is then pressed against the ilium with a sharp-tipped bone impactor (Fig. 20) and is provisionally fixed with two (threaded) Kirschner wires (Fig. 21). In the case of a weak autograft and a sclerotic defect, predrilling with a long 2.0-mm drill may be helpful. In the original technique, two AO cortical or malleolar screws as long as possible, with or without washers, were used for the final fixation. Depending on the stability of the fixation, it is not necessary that the screws gain purchase of the inner table of the ilium. To avoid placing screws that are too long, intraoperative fluoroscopy with an image-intensifier may be helpful. During drilling for those screws, the autograft has to be stabilized with the sharp-tipped bone impactor. Currently, we use 5.0-mm cannulated titanium malleolar screws to facilitate this step (Figs. 22 and 23).
The acetabulum and the graft are then reamed with the last acetabular reamers (Fig. 24).
Especially in soft bone before reaming, trimming of the cancellous part of the graft with a small saw blade or a high-speed burr may prevent the graft from getting damaged by a jammed reamer (Fig. 25). Bone-graft slurry from the acetabular reaming is used to fill in the gaps (Fig. 26).
The hemispherical acetabular cup is seated with a limited or minimum press-fit depending on the quality of bone and the size of the graft (Fig. 27). Currently, multiplehole cups are used to allow more options for screw fixation and to improve visualization during seating of the cup. The cup is then secured with use of at least two cortical or cancellous screws. In soft bone, the use of a tap is recommended. However, care must be taken not to break the tap against the malleolar screws of the graft.
The graft fixation screws are tightened once more after definitive placement of the cup. Marginal osteophytes are resected. After lavage of the implant, the polyethylene liner is inserted in the locking mechanism. Since hips with developmental dysplasia have a tendency to dislocate, a 10° elevated liner is used in all patients with an anticipated leg-lengthening of up to 1.0 cm (Fig. 28). With large grafts, portions of the front and back of the cup may be uncovered. Where it is appropriate, the gaps can be filled with bone-graft slurry. Also the back side of the structural graft can be palpated, and bone-graft slurry may be used to fill in here. In the original technique, conventional polyethylene liners were combined with 32-mm alumina heads (Fig. 29). Currently, 32-mm highly-cross-linked polyethylene liners are used in combination with 32-mm alumina heads.
Postoperative mobilization commences on day 1. Over the ensuing twelve weeks, partial weight-bearing of up to 20 kg with use of two lower-arm walking supports is recommended.
DISCLOSURE: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (CeramTec AG, Finance and Accounting Department, D-73207 Plochingen/Zimmer Germany GmbH, D-79100 Freiburg) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Department of Orthopaedics, Würzburg University, Würzburg, Germany
The original scientific article in which the surgical technique was presented was published in JBJS Vol. 88-A, pp. 387-394, February 2006
- Copyright © 2007 by The Journal of Bone and Joint Surgery, Incorporated
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