Reconstruction of Acetabular Bone Defects in Primary Total Hip Replacement Using Bone Graft
Introduction
Primary total hip replacement (THR) is a highly successful operation to relieve pain from a degenerative hip. Bone defects can be encountered both in the femur and acetabulum, but they are most common in the acetabulum. Reconstruction of anatomy is required to appropriately site the acetabular prosthesis, to restore the center of rotation, offset, leg length, and to achieve a well-functioning hip replacement with good long-term survival. Bone defects can be reconstructed using a number of techniques, using either cemented or uncemented components. In this chapter, we describe our preferred technique, which is reconstruction of the defect using femoral head autograft and fixation using cemented components.
Classification
A variety of classification systems are described for the classification of acetabular defects. These have mainly been developed for classification of defects in the revision setting. We find it useful to consider the AAOS classification.1 In the primary hip arthroplasty, the majority of defects are either Segmental (Type I), Cavitatory (Type II), or Mixed (Type III) defects. Pelvic discontinuity (Type IV) is rarely encountered in the primary setting. However, pelvic discontinuity secondary to acetabular fractures is addressed elsewhere in the book.
Table 27.1: Grading of protrusio acetabuli
| Grade | Men | Women |
|---|---|---|
| I | 3-8 mm | 6-11 mm |
| II | 8-13 mm | 12-17 mm |
| III | >13 mm with fragmentation | >17 mm with fragmentation |
Table 27.2: The classification of DDH5
| Type |
|---|
| A – Dysplastic hip The femoral head is contained within the original acetabulum |
| B – Low dislocation The lower lip of the false acetabulum contacts the upper lip of the true acetabulum |
| C – High dislocation No contact between the true and false acetabulum |
Approach
There are several approaches which can be used to satisfactorily expose the acetabulum to reconstruct defects. When considering which approach to use, it is important that the position of the defect is considered. The surgeon must ensure that the selected approach will facilitate adequate exposure of the defect. Our preferred approach is to use either a trochanteric osteotomy approach or a posterior approach. Both achieve good circumferential exposure of the acetabulum. The exception is in cases with a large posterior wall or column defect in which we prefer to use a posterior approach. The use of a trochanteric osteotomy is advantageous in the revision setting, when it allows excellent visualization of the femoral canal. The principles of these approaches are described elsewhere in this book.
Preoperative Planning
The main factors to consider during preoperative planning are: The nature of the defect (segmental or cavitatory), the size of the defect, bone graft required (autograft or supplementary allograft or synthetic graft), prosthesis required, component position, and leg length. In the majority of cases, we use standard cemented component for both the femoral and acetabular component. If we are using a structural graft, this usually only requires a single 6.5 mm partially threaded cancellous screw for fixation. Occasionally supplementary fixation is required with 3.5 mm reconstruction plates, but this is uncommon in the primary setting. In patients with a dysplastic hip, with a high hip center, it is important to consider the lengthening that will occur during the procedure. It is our experience that 5 cm of lengthening can be achieved without causing a sciatic nerve palsy.
Principles
Our general working principle is to reconstruct bone defects with bone. We accept there are a number of described alternatives in which satisfactory results have been described. Primary acetabular bone defects often occur in patients presenting for THR at a young age, for example, with degeneration secondary to DDH or trauma. A significant proportion of these patients will require revision surgery. We believe that it is preferable to reconstruct bone defects with bone, so that should the acetabular component require revision in the future, the size of the acetabular defect is minimized, and the bone anatomy has been restored. We believe that this is a favorable approach compared to using large uncemented implants, which often require additional bone removal to achieve satisfactory fixation. A prerequisite to the success of this philosophy is that a long lasting construct can be achieved, in which the grafted bone incorporates with the patient’s bone. It is our experience that this can be achieved in the majority of cases.
Illustrative Case
The shape and position of the reconstructed acetabulum can be checked with a cup sizer, the graft gently washed, and the cement mixed. Whilst the cement is mixed a hydrogen peroxide soaked thin swab wrapped over the impactor is pressed onto the bone to minimize bleeding onto the bone bed prior to cementation. The cement is then pressurized onto the prepared acetabulum in a standard fashion, and the acetabular component positioned. We have found that a stable construct is achieved and the bone reliably incorporates.
Technique
PROTRUSIO ACETABULI
The first challenge in a protrusio case is that the femoral head is often entrapped within the acetabulum. It is frequently necessary to cut the femoral neck in situ. The femoral head can then be divided into segments with an osteotome and removed to expose the acetabulum. Another important consideration, particularly when using a posterior approach, is the proximity of the sciatic nerve to the acetabulum. Because the femur is displaced medially by the deformity, the sciatic nerve is often very close to the posterior wall and could easily be damaged.
In most primary cases there is some medial wall bone, even if this is very thin. Once the acetabulum has been adequately exposed, soft tissue can be removed using a curette. A serrated ring curette is a useful tool for this. Care should be taken on the medial surface, particularly if the bone is very thin, or indeed there is no medial wall. A reamer may carefully be used to remove remaining acetabular cartilage or fibrous tissue from the superior acetabulum and anterior and posterior walls. We advise against reaming medially. If there is a medial wall defect the underlying fibrous membrane is often thick and stiff enough to impact bone directly onto. If there is a very thin or flexible membrane a slice of femoral head bone can be used to help contain the morcellized graft. Alternatively, mesh can be used, although we have found that this is rarely required.
Once the acetabulum has been exposed and prepared for grafting, attention is turned to preparing the graft. If there is a trained assistant surgeon, the graft can be prepared whilst the acetabulum is being prepared to receive the graft.
The initial stage of preparing the femoral head is to remove remaining cartilage and soft tissue. This can be performed, holding the femoral head in a trochanter holding clamp, or a proprietary femoral head vice. The next stage is to prepare “morcels” of bone to impact into the acetabulum. This can be done by hand with a bone nibbler or using a bone mill.
If preparing the graft by hand, it is helpful to clamp the head in a vice and cut it into slices. These slices can then be cut onto “croutons” using a large bone nibbler.
The alternative technique is to use a bone mill. The advantage of using a mill is that it is quicker. The disadvantage is that special equipment is required, and smaller sized bone chips are generally prepared.
Once the bone morcels have been prepared, the graft is washed. This helps to remove blood, fat, and protein from the graft and enhances the mechanical stability of the impacted graft, and leaves a drier bed to cement onto.
The graft is now ready to impact into the defect. It is advantageous to ensure that the scrub nurse has the bone cement available and ready to mix at this stage. This minimizes the time at the end of impaction so that the time for blood to accumulate in the impacted bone bed is minimized. It is also useful to select an appropriately sized flanged polyethylene acetabular component at this stage and cut the flange to fit the acetabular rim, again to minimize the time between impaction and cementing. The cup size should be selected to allow for adequate depth of impacted bone and a sufficient cement mantle.
The bone morcels are then inserted into the acetabulum. A simple spoon is useful to insert the bone into the acetabulum and to position the graft before impaction. An appropriately sized acetabular impactor is then used to impact the graft with firm strikes with a hammer. Approximately 8-10 strikes are required to sufficiently impact the bone and stabilize the graft. The process is repeated until the defect has been adequately reconstructed.
At the end of the impaction process, a stable bed of bone should have been achieved which has an appearance similar to a cobblestone pathway.
DEVELOPMENTAL HIP DYSPLASIA
Dysplasia of the acetabulum is a spectrum from mild acetabular dysplasia to a high dislocation. High dislocations are complex to reconstruct because of the extent of the deficiency of the acetabulum, in addition to issues surrounding leg length, soft tissue tension, and potential sciatic nerve damage. The reconstruction of the acetabular defect is considered in this chapter. The main defect is inadequate coverage of the acetabulum (essentially a segmental defect).
A number of techniques have been reported for reconstructing the acetabulum, from cement alone to use of a graft with a reinforcement ring, uncemented sockets below a graft, impaction grafting below a rim mesh, and a cemented socket below a roof structural autograft.
It is our preference to reconstruct the roof of the acetabulum using the patient’s own femoral head as a structural autograft, screwed into the defect.
Once the hip has been exposed, and the head removed, the true acetabulum is exposed. Soft tissue is removed, and the floor of the true acetabulum exposed. The roof defect is then prepared, removing soft tissue to expose a bleeding bone bed. The defect is usually the same size and shape as the femoral head that has been sitting within it. The femoral head is then prepared so that it will “jam” into the roof defect. It is not necessary at this stage to prepare the inferior aspect of the graft, that will be supporting the socket, as this can be prepared once the graft is fixed into position. The graft is held into position, and the direction of the drill estimated. It is desired to site the screw compressing the graft onto the ilium, with the screw passing towards the sacroiliac joint, between the inner and outer table of the ilium. We find that if the graft is fashioned to fit correctly a single 6.5 mm partially threaded screw with a washer is usually sufficient to secure the graft. Occasionally two screws are required. Once the graft has been secured, a reamer is used to fashion the under surface of the graft. It may be necessary to impact a small amount of morcellized bone under the structural graft. An acetabular cup can then be cemented into position in the standard fashion. We prefer to use a 22 mm inside diameter cup as it is often necessary to use a small outside diameter acetabular component (e.g. 38 mm).
POST-TRAUMATIC ACETABULAR DEFECTS
Post-traumatic acetabular defects can occur after acetabular fractures treated nonoperatively. As with other defects, these may be segmental or cavitatory or mixed, and the principles of reconstruction are as described above. Good results using this technique have previously been reported from our institution and others.
 |
 |
 |
F
 |
 |
 |
 |
 |
 |
 |
Figure 27.7: An example of a bone mill. Note there are often size options. Large fragments are prepared for impaction grafting of the acetabulum
The alternative technique is to use a bone mill (Fig. 27.7). The advantage of using a mill is that it is quicker. The disadvantage is that special equipment is required, and smaller sized bone chips are generally prepared.
Once the bone morcels have been prepared, the graft is washed. This helps to remove blood, fat and protein from the graft, and enhances the mechanical stability of the impacted graft, and leaves a drier bed to cement onto.
The graft is now ready to impact into the defect. It is advantageous to ensure that the scrub nurse has the bone cement available and ready to mix at this stage. This minimizes the time at the end of impaction, so that the time for blood to accumulate in the impacted bone bed is minimized. It is also useful to select an appropriately sized flanged polyethylene acetabular component at his stage and cut the flange to fit the acetabular rim, again to minimize the time between impaction and cementing. The cup size should be selected to allow for adequate depth of impacted bone and a sufficient cement mantle.
27
 |
 |
Reconstruction of Acetabular Bone Defects in Primary Total Hip Replacement Using Bone Graft
Figure 27.8: Morcellized bone being impacted into the acetabulum
 |
 |
 |
 |
 |
 |
Figures 27.12A to C: (A) Preoperative radiograph of a patient with DDH. (B) Initial post op radiograph showing structural allograft held with a single screw (C) 5 years post THR the structural graft has remodelled and incorporated to the host bone
 |
 |
Total Hip Arthroplasty
Figures 27.14A and B: (A) A large acetabular defect from a previous acetabular fracture (B) The acetabulum was reconstructed with impaction bone grafting and cemented components
 |
 |
References
-
D’Antonio JA, Capello WN, et al. Classification and management of acetabular abnormalities in total hip arthroplasty. Clin Orthop Relat Res 1989;243:126-37.
-
Sotelo-Garza A, Charnley J. The results of Charnley arthroplasty of hip performed for protrusio acetabuli. Clin Orthop Relat Res 1978;132:12-8.
Reconstruction of Acetabular Bone Defects in Primary Total Hip Replacement Using Bone Graft
-
Edelstein G, Murphy WA. Protrusio acetabuli: Radiographic appearance in arthritis and other conditions. Arthritis Rheum 1983;26(12):1511-6.
-
Crowe JF, Mani VJ, et al. Total hip replacement in congenital dislocation and dysplasia of the hip. J Bone Joint Surg Am 1979;61(1):15-23.
-
Hartofilakidis G, Stamos K, et al. Low friction arthroplasty for old untreated congenital dislocation of the hip. J Bone Joint Surg Br 1988;70(2):182-6.
-
Slooff TJ, Huiskes R, et al. Bone grafting in total hip replacement for acetabular protrusion. Acta Orthop Scand 1984;55(6):593-6.
-
Spence DJ, Diamond OJ, et al. Sciatic nerve palsy following total hip arthroplasty. British Hip Society Annual Scientific Meeting, Torquay, 2011.
-
Bobak P, Wroblewski BM, et al. Charnley low-friction arthroplasty with an autograft of the femoral head for developmental dysplasia of the hip. The 10 to 15-year results. J Bone Joint Surg Br 2000;82(4):508-11.