The presented prospective patient series shows a new bone remodeling technique that relies on the properties ascribed to the ceramic bone substitute composite used [
17]. The immediate pain relief, full weight-bearing recovery, bone consolidation and incorporation as well as the structural bone integrity and durability demonstrated in the study indicate that the material can provide a safe and effective long-term solution for the treatment of benign bone tumors. Of special interest is the ability of percutaneous transcortical injection under fluoroscopy in patients with juvenile cysts, which is enabled by mixing the ceramic powder composition with the water soluble radiocontrast agent iohexol.
An interesting observation was that the epithelium of unicameral cysts did not require complete removal since multiple scratching with the needle tip was sufficient to allow fresh bone to come in contact with the ceramic implant and provide full remodeling to bone. Another observation was that in spite of incomplete filling complete or almost complete healing was attained, which indicates that the material or the procedure triggers a bone healing process beyond that facilitated by the material itself [
19].
The biphasic ceramic bone substitute is designed to remodel in tune with the natural bone remodeling process. Due to the microporosity of the cured calcium sulfate component an immediate flow of tissue fluids with nutrients and growth factors is allowed so to penetrate the implant. That in turn promotes osteoclasts and macrophages to enter the material and create macropores resulting in a widespread ingrowth of early bone [
17]. The end result seems to be full transformation and remodeling into mature bone after 9–12 months [
13,
15,
17]. In a previous study on a composite bone graft substitute similarly consisting of calcium sulfate and hydroxyapatite (Schindler et al.) the graft material was still present after two years, whereas in the current study a CT-confirmed complete bone remodeling was demonstrated on X-ray after one year in all but one patient. One explanation for the faster remodeling in the present study might be a more favorable proportion of calcium sulfate to hydroxyapatite (CaS/HA = 60 to 40 %) compared to that used in the study by Schindler and co-workers [
21] where the graft material consisted of somewhat inverted proportion of 35 to 65 %. Reasonably fast remodeling has also been described with composite calcium phosphate based products [
11,
22].
It has been reported that products consisting of pure calcium sulfate have a tendency to quickly dissolve [
12] which, together with a low pH [
23], leads to a high frequency of long term drainage [
8] and subsequent wound complications [
9]. Also, products mainly based on calcium phosphate cements have been reported to cause adverse and sometimes painful soft tissue reactions [
24,
25]. The product used in the study presents with a neutral pH [
17] and once implanted a passive precipitation of endogenous hydroxyapatite takes places on the implant surface [
26], which seems to extend the gradual resorption of the calcium sulfate component over months [
13] allowing the cement to resist immediate dissolution and be actively degraded and replaced by ingrowing bone that eventually remodels to form trabeculae [
18,
27]. These two product differences (pH and composition) might partly explain: 1) the absence of prolonged post-operative drainage and/or late wound complications, 2) the rapid and reliable remodeling to bone [
15]. The minimal invasive technique might also have contributed to the absence of adverse reactions due to less leakage into the soft tissue. Although the actual prospective study presents with favorable results, it must be emphasized that it is a rather small and non-controlled study which requires repeated and larger trials to confirm the findings.