RESTORATION OF FEMORAL BONE STOCK

IN REVISION TOTAL HIP ARTHROPLASTY

 

Carolyn R. Hutchison BSc, MD, Med, FRCS(C)

Assistant Professor

University of Toronto

Division of Orthopaedic Surgery

Mount Sinai Hospital

Toronto, Ontario

 

The loss of femoral bone stock presents a significant problem in revision total hip arthroplasty. Many options are available for reconstruction. The key points that must be kept in mind are:

 

  1. When pre-operatively planning for revision THA with insufficient bone stock, REMEMBER: the extent of bone loss is determined by the bone that will be remaining after the existing implant has been removed. This is often underestimated on radiographs.
  2. If you avoid compromising the bone stock in the distal femur, you will have more options remaining for future revisions.
  3. No matter which option you select, the goal is to obtain a stable implant.

 

Classification of Bone Loss:

 

*    Contained/intraluminal                        Impaction grafting

 

*    Uncontained

*    noncircumferential                     Cortical strut grafts

*    circumferential                          Proximal femoral allograft

(Best method for restoring bone loss)

 

Impaction Grafting:

 

Indications: The indications for impaction grafting are in evolution. Long term outcomes are not well established. For this reason the indications and contraindications remain to be clarified. Presently, satisfactory results have been obtained with mechanical failure of femoral stems without significant bone loss and contained osteolysis with some cortical thinning.

 

Technique: If at all possible a greater trochanteric osteotomy should be avoided in the surgical approach. The bone graft size should measure > 5 mm. The packing of bone graft into the canal must be tight. The cement must be very liquid when inserted. Most importantly, the implant-bone construct must be stable.

 

Complications: The two most common complications include excessive subsidence and femoral fracture (intra- & post-operatively).

 

Cortical Strut Allografts:

 

Indications: Cortical strut grafts are used to restore uncontained non-circumferential defects, bypass stress-risers, stabilize a proximal femoral allograft–host junction and fix periprosthetic fractures.

 

Technique: These struts are made from fibula or hemi cylinders of diaphyseal bone. They are fixed to host bone with cerclage wires. Dahl-Miles cables should not be used. Autograft bone should be placed at the ends of the strut to promote union.

 

Results: Fifty-two patients with uncontained non-circumferential femoral defects were reconstructed using cortical strut allografts. The allografts were irradiated and deep frozen. The mean age was 65. The average follow-up was 4.8 years (1.6-10years). Time to union averaged 10 months. The union rate was 96%. There were no graft fractures. There was a decrease in strut length of 8%. The Harris Hip Scores improved from 39 pre-operatively to 66 post-operatively. Six of the fifty-two patients had re-revisions, however, none of the revisions were done for reasons related to the allograft.

 

Proximal Femoral Allografts:

 

Indications: The primary indications for using a proximal femoral allograft are for uncontained circumferential bone loss. These include periprosthetic fractures in association with osteolysis, severe osteolysis with a very thin cortex that is structurally unsound and distally well-fixed femoral components with proximal stress shielding.

 

Technique: The surgical approach most commonly used is a greater trochanteric slide. This is a variation of a posterior approach. In performing this approach, the distal aspect of the cut must be distal to the origin of vastus lateralis. The greater trochanter is reflected anteriorly attached to the soft tissue sleeve. During closure it is important to reattach the trochanter in the posterior position. This is anatomically correct and the attached muscle action will then prevent posterior disclocation. If the greater trochanter is reattached anteriorly, contraction of the gluteus medius and minimus will force the femoral head posteriorly.

 

Mainatin as much of the thickness of the allograft as possible in order to minimize the threat of periosteal resorption. Do not make drill holes into the allograft. The femoral implant must be cemented into the allograft but not into the host bone.

 

Management of the allograft-host junction is critical to stabilizing the reconstruction. The following steps will help to stabilize the junction: 1) Use a step cut or oblique cut to control rotation, 2) Wrap host bone around the junction and 3) Secure the junction with strut allografts and cerclage wires.

 

Results: Sixty-five proximal femoral allografts followed for a minimum of 5 years and an average of 9 years, had a success rate of 85%.

 

Complications: The most frequent complication was greater trochanter nonunion (43%). This did not affect the health status measures or results. The trochanteric slide decreases the chance for greater trochanteric escape, however, we have yet to see whether there is an increase in the union rate. Allograft resorption is not seen on the endosteal surface but can be seen focally on the periosteal surface. None of the allografts have required reoperation due to resorption. The additional complications are infection (4%), nerve injury (1.3%), host-graft nonunion (4%) and dislocation (4%). The risk of dislocation is higher if the femoral component alone is revised and decreased if the acetabulum is revised at the same operation.

 

Summary:

  1. Anticipate more bone loss than is evident on radiographs.
  2. Avoid compromising the bone stock in the distal femur.
  3. Ensure implant stability
  4. Align patient and surgeon expectations

 

References:

 

  1. Duncan CP, Bourne RB (ed). The Orthopaedic Clinics of North America: Management of Bone Loss During Revision Hip or Knee Replacement, April 1998.

 

  1. Haddad FS, Garbuz DS, Masri BA, Duncan CP, Hutchison CR, Gross AE. Femoral Bone Loss in Patients Managed with Revision Hip Replacement: Results of Circumferential Allograft Replacement, JBJS 81-A(3):420-436, 1999.

 

  1. Steinberg ME, Garino JP. Revision Total Hip Arthoplasty, Lippincott Williams & Wilkins, Philadelphia 1999.

 

  1. Villar RN, Gross AE, McMinn D (ed). Revision Hip Arthroplasty: A Practical Approach to Bone Stock Loss. Reed Educational and Professional Publishing Ltd, Oxford 1997.

 

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