CHAPTER SYNOPSIS

The role of allograft-prosthesis composites in revision hip arthroplasty is controversial. Allograft-prosthesis composites are indicated only in the most complex cases of severe femoral bone loss and are technically demanding and unforgiving procedures requiring prolonged surgical time and extensive and involved rehabilitation. Advantages include the potential for trochanteric and soft tissue attachment and healing as well as maintaining distal bone stock while restoring proximal bone stock.

IMPORTANT POINTS

• 1
  

  Allograft-prosthesis composites are technically involving procedures and should be reserved for centers with appropriate resources and suitable allograft availability.

  
  
• 2
  

  Younger patients who will likely need future revision procedures are able to tolerate the extended surgical time and are able to comply with prolonged, protected weight bearing and activity restrictions are the most ideal candidates.

  
  
• 3
  

  A megaprosthesis (“tumor prosthesis”) is the main alternative.

CLINICAL/SURGICAL PEARLS

• 1
  

  Careful preoperative planning, including availability of resources, equipment, and suitable allograft, is critical.

  
  
• 2
  

  A suitable backup procedure (and equipment) should be available.

  
  
• 3
  

  The native remaining proximal femur is maintained for bone stock.

  
  
• 4
  

  The allograft-prosthesis composite can be prepared on the back table while the host femur is being prepared.

  
  
• 5
  

  Antibiotic cement is used to affix the prosthesis to the allograft.

  
  
• 6
  

  The intact distal diaphysis is preserved to maintain future reconstruction options.

  
  
• 7
  

  The greater trochanter and abductors are reaffixed to the proximal allograft, and particulate graft is placed at the host-graft junction.

  
  
• 8
  

  Protected weight bearing and restricted activity are enforced until radiographic evidence of healing at the host-allograft junction is detected.

CLINICAL/SURGICAL PITFALLS

• 1
  

  Lack of attention to allograft-prosthesis composite length, anteversion of the prosthesis, and rotation of the composite at the host-allograft junction will result in major technical errors.

  
  
• 2
  

  Excessive drilling or cortical violation of the allograft can result in weakening and fracture.

  
  
• 3
  

  A distal step cut allows rotational control but can cause malrotation if done incorrectly and may be a stress riser for fracture.

  
  
• 4
  

  Cement within the host-graft junction will impair healing.

  
  
• 5
  

  Excessive diaphyseal preparation will reduce future reconstruction options.

OVERVIEW

Revision hip arthroplasty constitutes an increasing burden on hip arthroplasty surgeons and the economics of health care. A wide spectra of bone stock, prosthesis options, and surgical techniques all must be factored in to the decision-making pathway. To further complicate this, revision hip arthroplasty represents a multifactorial and complex balance among symptomatic relief, hip function, technically straightforward (reproducible) procedures, and longevity of the reconstruction all while maintaining options for future reconstructions.

It is not uncommon to see patients younger than 60 years old who have had multiple hip procedures, including osteotomy, arthroplasty, and revision arthroplasty. With each subsequent procedure the proximal femoral bone stock and subsequently reconstructive options become progressively more limited. When osteolysis, infection, and periprosthetic fracture are factored in, large, uncontained, and segmental femoral bone loss in relatively young patients is increasingly commonplace. This represents a major reconstruction challenge from a technical perspective. Ultimately, even a technically perfect complex revision procedure is likely not a permanent solution for these more active patients with more than 25 years of life expectancy.

The allograft-prosthesis composite (APC) is one of many reconstruction options available to the revision arthroplasty surgeon. As this chapter outlines, in cases of massive femoral bone loss it is one of only two available reconstruction options—the other being a megaprosthesis (“tumor prosthesis”). Because of the inherent drawbacks of bulk allograft and the technically demanding nature of APCs, the indications and benefits are controversial. APC is still discussed as a viable option because it offers the potential advantages of bone stock restoration, preservation of the distal diaphyseal bone for future reconstruction, and the ability to allow soft tissue repair and healing (especially of the abductor musculature).

Of note, APCs should be reserved for cases with extreme bone loss that offer no other realistic reconstruction option besides a megaprosthesis. In addition, this is not a technique for occasional use and ideally should be performed by surgeons (and at centers) who frequently do complex revisions and are comfortable working with structural allograft.

INDICATIONS AND CONTRAINDICATIONS

When discussing femoral revision, the extent of bone loss and remaining bone stock available for femoral stem fixation should be fully understood and evaluated. Several classification systems are available to guide this process. From the perspective of APCs, perhaps the most relevant system is shown in Table 37-1 . This classification system was developed by Gross et al, and primary prosthetic reconstruction is the technique of choice in the majority of cases (femoral bone loss of types I to IV). APCs are considered only during discussion of type V femoral defects ( Fig. 37-1 ), which constitute only a small percentage of all revision hip arthroplasty cases.

Example of type IV femoral defect before (left) and after (right) reconstruction with allograft-prosthesis composite.

(Reprinted from Blackley HR, Davis AM, Hutchison CR, et al: Proximal femoral allografts for reconstruction of bone stock in revision arthroplasty of the hip. A nine to fifteen-year follow-up, J Bone Joint Surg (Am) 83A(3):346-354, 2001.)

The ability to restore proximal bone stock while preserving distal diaphyseal bone for later fixation is an appealing potential advantage of APC. A younger patient who has a significant life expectancy and is more active is the appropriate candidate to consider for this reconstructive method. Because the patient is expected to need subsequent revision procedures, a healed proximal femoral allograft and an intact, unviolated distal diaphysis provide additional fixation options that would not be able with a megaprosthesis.

Ongoing infection is a contraindication to any definitive reconstruction, though an APC can be used for second-stage procedures after eradication of deep infection.

Patients should be placed on weight-bearing restrictions until evidence of radiographic healing is seen at the allograft-femoral junction. This usually is for at least 3 to 6 months. Patients who are not able to comply with these restrictions are at increased risk of mechanical failure and are probably better suited for prosthetic reconstruction. In addition, because of the technically demanding nature of the reconstruction, an APC requires a longer surgical time (3 to 6 hours) than a megaprosthesis and should be avoided in patients not able to tolerate this physiologically. Therefore an elderly, low-demand patient with numerous medical comorbidities and perioperative risk factors as well as a limited life expectancy is better suited for a megaprosthesis, which affords easier reconstruction, shorter surgical time, immediate weight bearing, and earlier functional recovery.

Type IV femoral bone loss, though uncommon overall, is more often encountered at specialty arthroplasty institutions that serve as referral centers. Apart from familiarity with the technical aspects of reconstruction, ready availability of a wide variety of structural allograft tissue is a prerequisite before considering this procedure.