Page 222 - Reconstructive Techniques in Musculoskeletal Tumor Surgery

Chapter 11
2.2 Aseptic loosening and graft-host nonunion
As discussed in paragraph 1.2, endoprostheses around the knee were notorious for the risk of aseptic loosening. With the introduction of hydroxyapatite (HA) coating for uncemented implants and HA collars for cemented implants, the risk of failure due to aseptic loosening decreased from 25-40% to approximately 5% at 10 years follow-up for primary implants58, 65, 66. The risk of loosening has been ascribed to a number of factors, including the torque acting on the stems59, 60. Endoprostheses of the knee originally had a xed hinge without rotational freedom, which resulted in excessive stress transfer at the implant-bone or cement-bone interface112. Modern hinges allow for a certain degree of axial rotation, thereby theoretically reducing mechanical stress at the interface and thus lowering the risk of loosening. Clinical studies that compared outcomes of xed and rotating hinges concluded that rotating hinges appeared to reduce the risk of loosening65, 66, although results may have been biased by concomitant modi cations in endoprosthetic design (including the introduction of HA coating and collars) and increasing surgical experience.
Whereas the incidence of type 2 failure of endoprostheses has greatly been reduced during recent decades, graft-host nonunion is still among the main complications for allograft reconstructions. Even though the risk of reconstruction failure is limited (5-7%), up to 40% of patients require operative intervention to facilitate union33, 113. We demonstrated that plate xation and cortical contact at the junction are important prognostic factors in union of allograft-host junctions. Although the number of patients included in our study on allograft-host junctions was limited, we found that all junctions with plate xation and radiographic cortical continuity on the rst postoperative radiograph united without further surgical intervention. These results shine new light on the dilemma whether to use an allograft or a vascularized bular graft (VFG) for reconstruction of intercalary defects.
The superior biological potential of VFGs is one of the reasons why some surgeons prefer to use a VFG114. However, if the risk of nonunion of allograft-host junctions can be eliminated, there presumably is no advantage of using a VFG over an allograft for defects with a length of less than eight to 10 centimeters. A virtual bone bank system and computer-assisted surgery may prove useful to obtain superior t between host bone and the allograft115, 116. For larger defects, VFGs may be preferable because of the increased risk of complications in large allograft reconstructions113. Reconstruction length was not associated with complication
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