Surgical Options for Femoral Reconstruction

CHAPTER 46 Surgical Options for Femoral Reconstruction


Allograft-Prosthesis Composites



Petros J. Boscainos, Catherine F. Kellett, Allan E. Gross



CHAPTER OUTLINE



Key Points 344

Indications, Contraindications, and Pitfalls 345

Preoperative Planning 345

Technique 346
Preparation of the Allograft 346

Revision Surgical Technique 347

Perioperative Management 349

Results 349

Complications 352



KEY POINTS



image The most important factor that determines the technique and the outcome of revision hip arthroplasty is bone stock.

image The allograft-prosthesis composite is a viable solution that provides pain relief, function, and a stable implant and does not compromise the distal host canal, facilitating further revision surgery.

image Initial stability is obtained with apposition of the allograft on the host bone through a step-cut or oblique osteotomy supplemented with wires and strut grafts.

image Long-term stability is achieved by union at the allograft-host junction; using the host proximal bone with its soft-tissue attachments as a biologic envelope around the junction promotes union.

image Union is usually achieved in 6 to 10 weeks.

Bone stock is the paramount factor that determines the appropriate technique in addressing a failing total hip arthroplasty, provides reference to the complexity of the revision procedure, and gives an indication of the expected outcome.1 The degree of bone loss is associated with the number of revision hip operations, and because younger patients are having hip arthroplasty surgery, this problem is expected to become more prevalent.


Several classification systems are used to evaluate femoral bone loss.1–3 The system that we use has five types. We have modified this system since its original publication (Table 46-1)4 and use proximal femoral allografts in types 4 and 5. With the current implant designs, we use proximal femoral allografts in femoral defects extending 8 cm or more into the femoral diaphysis. Tumor prosthesis can be used as an alternative in selected patients.


TABLE 46-1 GROSS CLASSIFICATION OF FEMORAL BONE STOCK





































Gross Classification Type of Defect Treatment Alternatives
Type 1 No significant bone loss Conventional cemented or uncemented femoral component
Type 2 Contained (cavitary) bone loss Proximally porous-coated implant
Extensively porous-coated implants for ingrowth
Extensively grit-blasted titanium implants for ongrowth
Impaction grafting with a cemented component
Modular implants for proximal or extensive ingrowth or ongrowth
Long-stemmed cemented implants
Type 3 Segmental (full circumferential) bone loss from the proximal femur that is less than 5 cm in length and involves the calcar and the lesser trochanter but does not extend into the diaphysis As in type 2, with a calcar replacement option
Type 4 Segmental (full circumferential) bone loss of greater than 8 cm in length extending into the diaphysis Allograft-prosthesis composite or tumor prosthesis
Type 5 As in type 4, with the addition of a periprosthetic fracture Allograft-prosthesis composite or tumor prosthesis

The tumor or megaprosthesis has the advantages of being modular, being available off the shelf, and carrying no possibility of disease transmission. Operating time for implanting such components is usually less than for proximal femoral allograft reconstruction. The disadvantages of tumor prostheses are that host bone or muscle cannot be effectively reattached, they do not restore bone stock, and they violate the distal host canal with cement or a porous-coated stem, rendering further revision surgery even more difficult.


A proximal femoral allograft, on the other hand, allows bone and muscle attachment. The reattachment of the greater trochanter in particular reduces the risk of dislocation and improves function. With an appropriate technique the distal canal is not violated, and this facilitates further revision surgery. A solid union at the graft-host junction augments the existing bone stock, which is important in young patients. The allograft-prosthesis composite disadvantages are the potential for disease transmission and the possibility of a poor result because of biologic complications including resorption, fracture, and host graft nonunion.



INDICATIONS, CONTRAINDICATIONS, AND PITFALLS


Proximal femoral allografts in the form of allograft-prosthesis composites are indicated in hip joint reconstruction surgery either in revision total hip replacement or after tumor resection. In revision hip arthroplasty performed at our institution, full circumferential structural femoral allograft-prosthesis composites have been used in uncontained segmental femoral defects that extend for more than 8 cm into the femoral diaphysis, especially if adequate distal stabilization cannot be achieved. Another indication is the presence of Vancouver type B3 periprosthetic femoral fractures5 with significant loss of bone stock rendering the distal fixation of a long, uncemented femoral stem at least difficult, if not impossible. Proximal femoral allograft is a useful technique, particularly in young patients, because it preserves distal bone stock and potentially improves the proximal bone stock to facilitate future reconstruction.


Active infection is a contraindication to the use of proximal femoral allografts in a single-stage revision surgery. However, we have successfully used allograft-prosthesis composites in a second-stage reconstruction surgery in patients with negative infection markers and frozen sections.


Patients with malignancies may benefit more from tumor implants because of the detrimental effects of chemotherapy and radiotherapy on allograft host healing. Also, extensive resection of muscle and bone, including the greater trochanter, makes reattachment of muscle and bone irrelevant. In addition, patients with multiple comorbidities, limited life expectancy, or need for fast mobilization benefit from a tumor prosthesis, as it does not require an extended non–weight-bearing period.


Problems with the proximal femoral allograft may occur if the allograft is cut too short. The final allograft length should be determined intraoperatively after multiple trials. Reaming of the allograft or placement of metal plates and screws may weaken the allograft and may result in fractures or in late allograft-prosthesis composite failures. Allowing cement to flow distal to the allograft-host junction has a number of deleterious effects: adequate pressurization and interdigitation at the allograft-cement interface is not achieved; the interface at the allograft-host junction is compromised and nonunion is probable; and the distal femur is violated, rendering possible further revision surgery more complicated. We recommend the preparation of the allograft-prosthesis composite on a separate table. A relatively small-diameter stem has to be chosen, as with this technique there is no need for distal press fit. A large-diameter stem may require reaming of the allograft in order to achieve an adequately thick cement mantle. Reaming the allograft weakens its mechanical properties and thus is not recommended. Finally, preserving the shell of the proximal femur with its soft-tissue attachments and wrapping it around the host-graft junction are expected to enhance union.



PREOPERATIVE PLANNING


Preoperative planning will determine the level of deficient proximal femur, the approximate length and diameter of allograft required, and the correct size of the femoral component. For this purpose an anteroposterior (AP) pelvic radiograph, AP and lateral radiographs of the involved femur, and a lateral view of the involved hip are necessary. Further imaging may be required to address possible acetabulum revision issues (Fig. 46-1).


image

FIGURE 46-1 Preoperative radiograph. Severe osteolysis of the femur with periprosthetic femoral fracture.


It is prudent to order an allograft that is longer than estimated. The diameter of the host femur and allograft should be approximately equal. This would ensure a good fit at the level of the allograft-host junction. It is best not to have an allograft with a significantly wider diameter than that of the host as this may prevent or delay union or may result in poor stability of the construct. Usually the allograft’s diameter is smaller than that of the host femur because of lysis and cavitation. This is not disadvantageous, as the allograft can be telescoped into the host femur for 1 cm or 2 cm, which enhances union and stability. It is important for the allograft canal to accommodate the implant to be used and also to allow at least a 2-mm thick cement mantle after reaming and broaching. Radiographs of the allograft with a known magnification rate are therefore important for preoperative planning, as is a template of the femoral implant. Allografts are usually imaged in their sterile packaging. Any preoperative leg length discrepancy should be measured and taken into account during templating.



TECHNIQUE



Preparation of the Allograft


The allograft used in this procedure is stored at −70° C and in our institution is irradiated with 2.5 Mrad. Graft preparation is performed on a separate surgical table by a second surgical team while the surgical exposure is being performed by the operating surgeon. We recommend using fresh frozen allograft from an American Association of Tissue Banks–accredited tissue bank. The larger banks process the bone in bactericidal and virucidal solutions before the bone is deep frozen. Some banks provide irradiated bone, which is 10% to 20% weaker, depending on the dose.6

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Mar 10, 2016 | Posted by in Reconstructive surgery | Comments Off on Surgical Options for Femoral Reconstruction

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