Page 223 - Reconstructive Techniques in Musculoskeletal Tumor Surgery

rates in one study on VFGs114. Nevertheless, initial stability is an important concern in VFG reconstructions, especially when reconstructing large defects in heavy adults. VFGs however have the potential of hypertrophic growth; although patients will have to accept a long period of partial weight-bearing, gradual increase in weight-bearing may result in a durable construct of living bone. Interposition of a joint-sparing implant is another promising technique for reconstruction of intercalary long-bone defects, and allows for early weight-bearing117. Modern additive manufacturing techniques may be used to produce patient-speci c joint- sparing implants with optimal three-dimensional t. Future comparative studies are needed to de nitively determine what is the best technique for reconstruction of (large) intercalary defects.
2.3 Structural failure
For endoprostheses, structural complications can be divided into (1) implant breakage or wear, and (2) periprosthetic osseous fractures. Breakage of stems is rare, occurring in approximately 2% of knee endoprostheses57, 118. Obvious risk factors for stem fractures include greater resection length and the use of small- diameter stems58, 118. Failure of the polyethylene and PEEK-OPTIMA (Invibio Ltd, Thornton-Cleveleys, United Kingdom) locking mechanisms has been a particular concern for the MUTARS system119. With the introduction of a metal-on-metal locking mechanism, the risk of structural failure has been eradicated. In vitro studies and close follow-up of patients are indicated to assess the amount of wear debris released, the risk of adverse reactions, and thus the long-term safety of these locking mechanisms.
Periprosthetic fractures can be divided into intraoperative crack fractures without displacement and ‘true’ (or late) periprosthetic fractures. The occurrence of intraoperative crack fractures is associated with the use of uncemented press- t stems120. As they generally require little or no further surgical treatment and mostly heal uneventfully58, 121, we do not consider this a contraindication for the use of uncemented stems. Management of late periprosthetic fractures, on the other hand, is problematic, but their incidence is low69. These fractures are presumably associated with periprosthetic osteolysis (bone resorption) and aseptic loosening of implants122. The occurrence of resorption has been ascribed to stress shielding; if osseointegration of the stem occurs over a longer trajectory, stresses in the outer cortex are reduced, and resorption may occur69. To reduce the low-stress region in the outer cortex, Blunn et al suggested that the region of HA-coating should
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General discussion
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