Unicameral Bone Cysts (UBC) are benign lesions with poorly understood etiology. They may resolve spontaneously typically after pathologic fracture and with advancing age; however they can be recalcitrant even after puberty.

Treatment is needed in symptomatic patients depending on size, location and fracture or threatened fracture.

Aneurysmal Bone Cysts (ABC) are neoplasias typically containing USP6-rearrangements. Good results and spontaneous healing can be achieved by injection of alcoholic solutions. However, often additional measures are needed for restitution of the bony defect.

We wish to communicate a minimally invasive technique to induce healing of these persistent cystic bone defects injecting the highly viscous paste of Grafton^â DBF Putty (demineralised allogenic bone containing fibers) mixed with autologous bone marrow (BM), using the Kyphon^â Cement Delivering System (Medtronic) resulting in a high rate of bone regeneration.

Eight consecutive patients with symptomatic large UBC (humerus, pelvis, femur, calcaneus, Table 1), recurrent after different procedures, were treated since 2016 by the technique presented. Five patients with ABC (pubic bone, femoral neck, tibia, Table 2) not showing bone remodeling at a minimum follow-up of 3 months after inactivation by Aethoxysclerol 3% were treated accordingly. Biopsies taken at filling with Grafton^â DBF Putty in these cases proved no remnants of pathologic tissue. Further details of the otherwise healthy patients aged 15 to 27 years are given in Table 1 and Table 2.

Two 8G Jamshidi needles CareFusion^â are inserted under fluoroscopy or computer tomography (CT) to have 2 portals—one for injection, the other for “ventilation”. After aspiration of the cystic fluid content radio opaque dye (Iopamiro^â) is injected to document its distribution within the cavity and to exclude extraosseous leakage as described in detail by Rougraff and Kling [1]. Grafton^â DBF Putty (3 to 40 cc) was mixed with bone marrow aspirate in the relation of about 2:1 to 1:1 (Table 1, Table 2). Bone marrow aspirate (each sample maximally 5 cc) is taken from various pelvic locations to provide sufficient osteoblastic progenitor cells [2]. The bone marrow aspirate is mixed with DBF and this highly viscous paste is then injected using the Kyphon^â Cement Delivering System providing the well controlled high pressure under image intensifier control (CT in special locations) of the extrusion of the contrast dye through the ventilation needle (Figure 1 and Figure 2).

There was sufficient incorporation/restitution of bone in 11 patients at a minimum follow-up time of 8 months. In 2 patients a second intervention (1 UBC at 5 years, 1 ABC at 2 years following the first one) was successful. No patients

DBF—Grafton^â DBF Putty, DBM—Demineralized Bone Matrix, BM—Bone Marrow aspirate. Volume calculated based on the radii of an elliptoid body: a × b × c × d × π × 4/3.

DBF—Grafton^â DBF Putty, DBM—Demineralized Bone Matrix, BM—Bone Marrow Aspirate. Volume calculated based on the radii of an elliptoid body: a × b × c × d × π × 4/3.

suffered fractures and all are pain free at present. Images of selected cases of UBCs und ABCs are presented in Figures 2-6; imaging findings at follow-up are given in Table 1 and Table 2.

No adverse reactions to the DBF/BM implant or complications related to technical aspects and the application system were observed.

The cause of UBC (synonymously used for juvenile bone cysts or simple bone cysts) is poorly understood. Initially UBC was treated mostly by extensive curettage and bone transfer [3]. Since the introduction of intracystic Corticosteroid-Injection by Scaglietti et al. [4] less invasive methods are now mostly used; among them are intramedullary nailing and steroid injection [5], injection of bioabsorbable bone cement [6] and artificial bone substitutes [7]. However, so far there is no evidence to determine the best method for treatment [8]. One randomized trial comparing intralesional bone marrow and steroid injections showed superiority of the latter [9].

Good results with the injection of Demineralized Bone Matrix (DBM) mixed with autologous bone marrow aspirate into UBCs were first reported by Rougraff and Kling [1] and confirmed by several studies, e.g. Cho et al. [10] and Gundle et al. [11].

Grafton^â DBF Putty was used in our patients because of its superior osteoinductivity and osteoconductivity compared to DBM [12] [13] [14].

ABCs are lesions unrelated to UBC exhibiting USP6-rearrangement, a marker involved in the development and spontaneous regression of neoplastic processes [15]. We add our cases of ABC in this study as we use the same treatment principles as in UBC if the standard treatment with Aethoxysclerol and recently augmented by surgiflo [16] has successfully inactivated the process, but no new bone formation shows up after at least 4 months.

The Kyphon^â Cement Delivering System developed for the injection of cement in kyphoplasty proved to be a useful device to inject the pasty mixture of DBF/BM under well controlled pressure.

Drawbacks of this study are the lacking of a control group and the still relatively short f/u.

The technique of percutaneous treatment of inactive cysts appears to be effective, minimally invasive and may be considered as a primary choice instead of large open procedures. The use of Grafton^â DBF Putty with higher osteoinductive and osteoconductive potential appears to enhance the good results achieved so far with DBM. The minimally invasive injection of the highly viscous paste needs an application system as provided by the Kyphon^â Cement Delivering System (Medtronic). The presented system has been useful in other bone defects, e.g. after radiofrequency ablation and cystic degenerative changes of fibrous dysplasia.

The patients were informed that data from their case would be submitted for publication, and informed consent was obtained.

We gratefully acknowledge the collaboration with Jorge J. Herrero, Sales and Therapy Manager Interventional and Biologics, who has drawn our attention to Grafton^â DBF Putty and the Kyphon^â Cement Delivering System as well as for the assistance in the surgical interventions.

The authors declare no conflict of interest regarding the publication of this paper.

No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this article.

Exner, G.U. and Schai, P.A. (2020) Treatment of Unicameral and Aneurysmal Bone Cysts by Minimally Invasive Percutaneous Injection of Grafton^â DBF Putty Using the Kyphon^â Cement Delivery System. Open Journal of Orthopedics, 10, 143-151. https://doi.org/10.4236/ojo.2020.107016