Rates of Bone Flap Resorption and Fusion 1 Year Following Craniotomy – a Volumetric Analysis

Introduction: Bone flap resorption is a well-established phenomenon in the craniectomy setting. Few studies have assessed rates of bone resorption and fusion in the craniotomy setting. The aim of the present study was to assess rates of resorption and fusion in bone flaps 1 year following craniotomy using volumetric analysis.

Methods: Patients with computed tomography (CT) scans available in the first postoperative week and at 1-year (11-13 months) follow-up were included. Postoperative and 1-year follow-up CT scans were automatically aligned using the lambda, bregma, and left and right jugal points as fiducials. 360° radial slices around the circumference of the kerf were reconstructed. Bone volume was measured with a threshold of 500 Hounsfield units in four zones: inner bone flap; outer bone flap; peripheral bone; burr hole. Extent of bony fusion was estimated through the assessment of extent of kerf bridging.

Results: A total 13 consecutive patients with high quality bone CT scans were analyzed. 6 patients (46.1%) were female, the mean age was 59.8 years (SD=16.5). Indications for craniotomy were tumor (6 patients), vascular (4 patients), infectious (1 patient) and trauma (3 patients). The mean rate of fusion across these patients was 23.5%. Bone resorption was observed in the inner flap in 6 patients, in the outer flap in 5 patients, peripheral bone in 4 patients and around the burr hole in 5 patients. No patients reported cerebrospinal fluid leaks, surgical site infection, implant migration, or flap revision surgery. All bone flaps were fixed using titanium plates and screws, 2 patients reported pain associated with their fixation hardware.

Conclusion : Bone resorption and lack of fusion is a consideration not only in the craniectomy setting but also in the craniotomy setting. Future efforts on improving bone flap fixation to prevent bone resorption and improve rates of fusion are required.