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local antibiotics. Therefore, cemented implants may be preferable for patients with radiotherapy or those at high risk of developing postoperative deep infection39. We prefer uncemented xation with HA-coated stems for patients with a reasonable prognosis and su cient bone quality, mainly because these implants are at a lower risk of loosening once bony ongrowth has taken place58, 69.
1.3 Structural failure
Structural failure is common for pelvic allograft reconstruction, either due to primary fracture or due to graft resorption15, 70. Saddle prostheses also frequently fail due to structural complications, including prosthetic dissociation and fractures of the remnant ilium38. With modern endoprosthetic production quality and design, implant fractures are rare; no structural implant failures were reported in recent studies on the pedestal cup, LUMiC and ice-cream cone endoprostheses10, 39, 40. Periprosthetic iliac fractures, however, still occur. Two types of iliac fractures should be distinguished. First, intraoperative crack fractures, which cause minimal displacement and generally heal without major interventions10, 40. Obvious risk factors for intraoperative fractures include the use of uncemented press- t iliac stems, poor bone quality, and revision procedures; in these cases, extra caution is warranted71. And second, postoperative fractures of the iliac wing. The saddle prosthesis has been associated with a substantial risk of fracture of the remnant iliac wing, in addition to the risk of cranial migration of the saddle component (up to 7%)17, 22, 34, 72, 73. A possible explanation for these structural failures lies in the fact that the saddle prosthesis anchors laterally from the natural femorosacral weight- bearing axis, where the anteroposterior dimension of the ilium is limited and the iliac cortices are thin; therefore, adequate supportive bone stock is lacking17, 34, 35, 38, 74, 75. Consequently, more cranial migration has been reported when larger resection of the iliac wing is required17, 35. Cranial migration of the implant in turn causes limb length discrepancy and recurrent dislocations, compromising function of the a ected side34. Moreover, the eccentric position of the arti cial hip center allows only limited range of motion76. Several more modern implants, including the Mark II saddle (Link, Hamburg, Germany) and the PAR prosthesis (Stryker Howmedica, NJ, USA), still have these unfavorable features37, 72.
Conversely, so-called “stemmed acetabular” or “inverted ice-cream cone” prostheses anchor in the medial ilium, adjacent to the sacroiliac joint10, 39, 40. There, a thick bar of bone extends from the sacroiliac joint down to the acetabulum, along the natural weight-bearing axis. This allows the implant to be seated well
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General discussion
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