The present study provides evidence that implants with osteoconductive and osteoinductive properties can reduce the risk of SSI and the rate of explantations after CP compared to allogenic materials (PMMA). There was no difference in surgery-related complications between the two implant types in our study.
The optimal timing of CP to minimize complications has yet to be established. Some favor early (within 12 weeks) and ultra-early (within 4 weeks) CP [11, 19, 23] Early CP has been associated with lower infection rates and lower probability of developing hydrocephalus, although some authors reported that timing had no influence and have observed similar SSI numbers [17, 23]. In our study, CP was performed at 122.2±96.37 days after DC. The time span did not differ between both groups. Continued research will show if the timing of CP should be adapted to the chosen implant material.
Titanium-enhanced biocompatible CaP implants comprise a ceramic compound containing monetite, β-calcium pyrophosphate (PPi), β-tricalcium phosphate, and brushite . These ceramics have chemical resemblance to the osteoconductive and osteoinductive elements in native bone. While osteointegration has been defined as load-bearing integration without loosening, osteoconduction facilitates bone growth on a particular surface  and osteoinduction encompasses processes leading to the differentiation of undifferentiated osteoprogenitor cells to osteoblasts [22, 25].
Gene expression analysis in bioactive CaP implants has detected osteoblastic activity and bone formation at nine months after CP [12, 13]. In large animal models, bioactive ceramics are better promotors of bone formation, remodeling, and osteointegration than titanium implants . We found that the integration of the bioactive ceramic implant as seen in one patient after explantation proved superior to PMMA implants. This observation adds proof to the previously published in vitro and animal data. Only one patient required explantation of the bioactive ceramic implant. Osteointegration is also observed with PMMA in animal models . However, it is much less pronounced and matter of ongoing research using different porosities and additives such as strontium containing borate bioactive glass to improve upon this property [6, 10].
Much is yet to be learned about the safety and efficacy of bioactive CaP, among others, as CP implant materials. Despite the early paucity in literature, PEEK CP seems to be associated with lower post-operative complication rates compared to autografts, and with lower implant failure rates compared with titanium mesh implants [28, 34]. Previous studies indicate that infection and complication rates in CP with bone cement are substantially higher, while titanium-based implants impair follow-up imaging, and that ceramics and PMMA have similar complication profiles but differences in cost and availability . We observed no statistically significant difference in postsurgical complications such as hemorrhage, CSF fistulas and seizures. However, the necessity for explanation of PMMA implants was higher in the entire cohort, as well as in a subgroup analysis with a given 1 year follow-up. As there is currently no other published literature comparing bioactive CaP implants with alloplastic materials, it remains to be seen how these implants will ultimately reduce complication and implant failure rates and improve clinical outcomes . Prospective clinical trials in this field are difficult to establish due to a tremendous variability of techniques and applied materials. However prospective registries (e.g. German Cranial Reconstruction Registry) bear the potential of longitudinal multicentric analyses with homogenous datasets [14, 31].
In contrast to alloplastic implants, surgical dissection of ceramic implants was much difficult due to substantial integration with the surrounding tissue [12, 13]. Extensive adhesions necessitated sharp dissection from the covering skin flap. This seems to further support the potential for improved implant stability and reduced probability of dislocation. It is also of note that despite contamination of the atrophic skin dehiscence, no bacterial contamination was found on the underlying ceramic implant. Implant-associated infections involve biofilms that are challenging to eradicate . Despite biofilm-active antibiotic therapy, implant removal is necessary in most cases . It is possible that antimicrobial treatment will be more effective in bioactive implants. Strong osteointegrative properties also relate to vascularization and soft tissue coverage, and an excellent soft tissue coverage due to robust osteointegration, promotion of vascularization, and tissue ingrowth via multiple interconnected spaces should facilitate improved wound healing, prevention of atrophy, and, with them reduced risk of SSI .
There was no difference in rates of post-surgical complications such as epidural hematoma or seizures. This is not unexpected, as the main osteointegrative, osteoconductive and osteoinductive advantages of the novel bioactive compound come to bear over time without immediate impact on the post-surgical course [12, 13]. As always, caution is a prime requirement when drawing conclusions from results in small patient groups. Further research will show if these promising results can be confirmed. Although follow-up in the present study was adequate, late implant-associated infections are known [14, 19]. More extended follow-up periods should determine whether bioactive CaP implants retain their advantages regarding infection and clarify the treatment strategies.