Cranial Sutures as a Cause of Osseointegration Failure in Bone-Anchored Implants : Case Reports

This report discusses 2 clinical cases where the failure of osseointegration in bone-anchored implants may be associated with their placement directly in cranial sutures. The increasing shift toward minimally invasive surgical techniques for implant placement, such as the minimally invasive Ponto surgery (MIPS) and the punch technique, raises concerns about the risk of inadvertently positioning implants on cranial sutures, which can lead to the failure of osseointegration. In the first case, the Ponto (Oticon) implant and abutment were placed using MIPS. Two months post-operation, minimal movement was observed until the implant was significantly displaced, necessitating its removal. A subsequent computed tomography (CT) scan revealed that the implant had been placed in the asterion. The second case involved a Bone Anchored Hearing Aid (BAHA-Cochlear) implant and abutment inserted via a punch and drill technique. Early mobilization of the abutment was observed, progressively worsening until the implant was removed 2 months post-operation. A CT scan showed that the implant was located at the parieto-occipital suture. These cases highlight a potential complication of minimally invasive implant surgery, suggesting that blind placement could elevate the risk of implant failure due to interference with cranial sutures. This underscores the importance of enhancing surgical precision and pre-operative planning with imaging.


Introduction
2][3] These prostheses are typically mounted on an abutment fixed to a boneanchored implant.5][6][7][8] Nevertheless, failures in osseointegration, ranging from 0 to 18% with implant extrusion, still occur. 2,9,10Two cases are reported where control CT scans showed the implants had been placed on a cranial suture, potentially explaining the failures.

Case Presentation
The first case involves a 47-year-old female with probable congenital right-sided deafness.A 1-month trial with a headband demonstrated significant subjective benefits from bone conduction device rehabilitation.A Ponto implant (Oticon Medical, Smorum, Denmark) BHX 4 mm pre-mounted on a 12 mm abutment was placed under local anesthesia using the Minimally Invasive Ponto Surgery (MIPS) technique.There was no postoperative pain or infections.Given good healing, the external processor was mounted onto the abutment 1 month and 10 days post-surgery.The patient experienced sensations of abutment mobility and "bone noise" when turning her head.Two months postoperatively, the implant mobilized and had to be removed.A subsequent cranial CT scan showed that the implant had been placed in the asterion (Figure 1).
The second case involves a 41-year-old female with bilateral moderate conductive hearing loss, predominantly on the left side, due to bilateral acquired stenosis of the external auditory canals.A headband trial of bone conduction fitting was highly successful subjectively.A BAHA implant (Cochlear, Sydney, Australia) BA300 3 mm mounted on a 10 mm abutment B-ENT 2024 was placed under local anesthesia using a minimally invasive punch and drill technique.There was no postoperative pain or infections.However, slight pillar mobility was noted 1 month postoperatively.Fitting of the external processor was not permitted, and the condition worsened, leading to implant removal 2 months postoperatively.A subsequent cranial CT scan revealed that the implant had been placed on the parietooccipital suture (Figure 2).
Informed consent was obtained from the 2 patients who agreed to participate for the purpose of case report writing.

Discussion
First of all, it should be stressed that these 2 clinical cases do not allow for definitive conclusions or recommendations.They merely suggest some warnings.
These clinical cases suggest that minimally invasive surgery without visualization of the bone insertion area might increase the risk of accidental placement on a cranial suture, leading to osseointegration failure.This is also a consideration for techniques involving incisions, as dissection is performed above the periosteum layer, and if the periosteum is only removed over a diameter of 4 mm, it may obscure the suture from view.In practice, the periosteal stripping is often more extensive in the case of a technique with an incision (12-15 mm), which facilitates the analysis of the drilling point and the avoidance of any potential suture.
The development of minimally invasive techniques for placing bone-anchored implants has advantages such as reducing the risk of bleeding, pain, infection, or healing complications and cosmetic sequelae, in addition to shortening the operative time. 4,8But, this comes at the expense of blind surgery concerning the precise implant placement on the cranial bone.Ideally, the implantation site should have good bone quality, with a thickness over 3 mm, and avoid not only diploic cranial vessels but also mastoid cells and cranial sutures. 11Poor quality of the implantation site (irregular surface) is frequently reported in cases of implant loss. 10Cranial sutures are therefore areas to avoid for implantation.However, avoiding these becomes more challenging with minimally invasive surgery, especially in the absence of pre-operative planning (measurements made on a cranial CT scan).7][8] In 2 studies, the extrusion rates with MIPS (12.1% and 15.2%) were higher than those with a linear incision (3.3%), although the difference was not statistically significant (P = .19and P = .12). 6,7The implant stability quotient was significantly lower after MIPS, with no clear association observed between the initial implant stability quotient and implant loss. 6,7Moreover, the majority of implant loss circumstances with MIPS were similar to those in our 2 cases (spontaneous loss or minor trauma). 7A recent meta-analysis could not compare implant loss rates, but raw data showed a difference unfavorable to punch techniques, although the significance of this difference could not be established. 8her explanations for failure should be considered in cases of minimally invasive surgery, especially in the absence of placement on a suture.It is possible that the drilling of the hole is

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We report 2 cases of osseointegration failure in boneanchored implants, likely related to the placement of the implants on a cranial suture.

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To our knowledge, no cases of this type have ever been described.

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We recommend surgeons identify cranial sutures via preoperative CT scans before surgery.not perfectly perpendicular to the bone plane or that the irrigation of the drilling site is less abundant, leading to bone cellular burns that could compromise healing.
The use of surgical radionavigation or augmented reality techniques could optimize implant placement. 11,12However, this would come at the cost of significantly increasing the operational procedure burden (duration, anesthesia, etc.), which we believe is rarely justified.
Without necessarily using surgical radionavigation, we encourage preoperative planning if a cranial CT scan is available for the patient (often done as part of the etiological or anatomical assessment).However, the risk-benefit ratio does not seem favorable for performing (or repeating) a CT scan in children to identify the position of sutures, as these radiological examinations may increase the risk of cancer (central nervous system tumors and leukemia). 13,14e placement of a bone-anchored implant on a cranial suture may promote lack of osseointegration and early implant failure.Blind minimally invasive surgery, especially in the absence of pre-operative planning, inherently increases the risk of accidentally positioning the implant on a cranial suture, thereby leading to osseointegration failure.Before proceeding with minimally invasive implant placement, we recommend that surgeons identify cranial sutures using a preoperative CT scan.An alternative is to use an incision technique, which more often allows avoiding implant placement on a suture.
Informed Consent: Informed consent was obtained from the patients who agreed to take part in the study.

Declaration of Interests:
The authors have no conflict of interest to declare.

Funding:
The authors declared that this study has received no financial support.

Figure 1 .
Figure 1.Volumetric cranial CT scan (A) with magnification (B) on the area of interest (dotted rectangle) showing the implantation site (arrow) at the asterion, as well as its position relative to the soft tissues (C) with a distance of 55 mm from the external auditory canal.

Figure 2 .
Figure 2. Volumetric cranial CT scan (A) with magnification (B) on the area of interest (dotted rectangle) showing the implantation site (arrow) at the parieto-occipital suture, as well as its position relative to the soft tissues (C) with a distance of 55 mm from the external auditory canal.