Page 216 - Reconstructive Techniques in Musculoskeletal Tumor Surgery

Chapter 11
1.2 Aseptic loosening
Aseptic loosening is one of the major modes of failure for endoprosthetic reconstructions in orthopaedic oncology, especially for reconstructions around the knee57, 58. The high risk of loosening for knee replacements has been ascribed to several factors, including the torque acting on the stem-bone interfaces59, 60. As opposed to knee replacements, reconstructions of polyaxial joints allow for a certain degree of movement between prosthetic parts and therefore, less torque acts on these stem-bone interfaces. Irrespective of the limited torque acting on pelvic implants, we found that three of 19 patients (16%) had aseptic loosening of their uncemented porous-coated pedestal cup endoprosthesis10. Although the reported incidence of loosening is closely correlated with duration of follow- up, and results are therefore di cult to compare, previous authors reported comparable rates of loosening for saddle (12%) and hemipelvic prostheses (16%)17, 61. Factors that contribute to the risk of loosening of pelvic implants include the high mechanical stresses as a result of great resection length and extensive soft tissue dissection. Moreover, because of the at morphology of the ilium, there is limited initial contact between the implant and cortical bone.
In keeping with results reported for reconstructions of the appendicular skeleton, it was hypothesized that hydroxyapatite (HA) coating of the iliac stem would stimulate bony ongrowth and thus reduce the risk of loosening62. In our study on reconstructions with the LUMiC prosthesis, we found that two patients with uncemented HA-coated iliac stem (2/45, 4%) experienced loosening. Further analysis showed that both patients had inadequate primary xation of the stem (one due to an intraoperative fracture, one due to xation in a previous structural allograft), while primary stability is a prerequisite for ingrowth of HA-coated implants63. An alternative modern pelvic implant, the “ice-cream cone prosthesis” (Stanmore Implants Worldwide, United Kingdom), relies on a combination of HA- coating and bone cement for stem xation39. Cement may be useful to obtain adequate primary stability and thus allow for bony ingrowth in the HA-coating. On the other hand, cement fragmentation and foreign body reaction to wear debris may result in late periprosthetic osteolysis and loosening64. Excellent results have been reported for tumor implants with hybrid xation, although the number of patients included and follow-up were limited in the studies on pelvic reconstructions39, 65-68.
Other advantages of cementing are that it allows for immediate weight- bearing, especially in case of extensive bony destruction, and the possibility to add
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