Beyond the average fit in cranioplasty: comparing pre-formed mesh and 3D-printed patient-specific implants

A defect in the craniomaxillofacial skeleton is far more than a medical diagnosis. Whether caused by sudden trauma, the removal of a tumor or a congenital diagnosis, the loss of this essential part represents a profound disruption to a person’s life. It is a challenge that extends deep beneath the skin, affecting not only physical function but the very essence of human identity. The goal of surgery is not merely to fill a void; it is to restore wholeness and return the patient's life back to normal.

From a patient's perspective, the ability to chew, to speak clearly, or to feel the simple security of a protected brain can be compromised. Though it's an everyday function, the loss of these abilities can lead to loss of self-esteem that goes beyond the function itself.

From craniomaxillofacial surgeon, oral and maxillofacial surgeon and neurosurgeon, this reality presents a much burden and responsibilities. The first responsibility is technical: to reconstruct the defect in a way that is structurally sound, protects vital organs like the brain, and restores critical functions. The second is aesthetic: to restore the natural contours and symmetry of the face, an outcome that is crucial for the patient's psychological recovery and social reintegration. The final result is often subjective and has historically been highly dependent on the surgeon's individual experience and artistry.

The conventional approach: a pre-formed, one-size-fits-many solution

A pre-formed craniomaxillofacial implant is typically a sheet, a plate or mesh made from a biocompatible material, most commonly commercially pure titanium or a titanium alloy like Ti6Al4V. They are available in a variety of standardised thicknesses, ranging from a very malleable 0.3 mm to a more rigid 1.0 mm or more, to offer surgeons a choice between strength and flexibility.

The core principle behind this technology is the “average fit”. Manufacturers create these meshes or plates by analysing a large compilation of adult CT scans to develop a series of pre-contoured shapes that represent the "best possible 'average' fit" for common cranial defects. These standard shapes are designed to correspond to specific, routine neurosurgical approaches, such as the bifrontal (across the forehead) or parietal (on the side of the head) regions. The result is a catalogue of off-the-shelf implants intended to provide a starting point for reconstruction.

The term "pre-formed" can be misleading, as it suggests a ready-to-use product. In reality, the standardised implant is rarely a perfect match for the unique anatomy of an individual patient. The surgeon must manually bend, cut, and contour the generic mesh to the specific contours of the patient's bone defect, which is time-consuming. The surgeon must also repeatedly test the fit, make adjustments, and secure the adapted mesh with a significant number of titanium screws. The extensive time required for this manual adaptation is a direct cause of longer surgeries. This increased time under anesthesia not only elevates direct hospital costs related to operating room staff and facility usage but is also a well-established risk factor for post-operative complications, most notably surgical site infections.

Furthermore, the imperfect fit that often results from manual bending can lead to a cascade of suboptimal outcomes. Clinical studies have shown that pre-formed meshes frequently fail to cover the entire defect, leaving persistent gaps and creating visible asymmetries [1,2]. In many cases, surgeons often need to use a large number of fixation screws—an average of 15 in one study, compared to just 6 for a custom implant [1] —which can increase the risk of the implant being palpable and causing patient discomfort.

Therefore, the seemingly lower upfront cost of a standardized implant can be deceptive, as it often leads to a series of hidden clinical and financial costs downstream, including the potential need for revision surgeries to correct poor cosmetic or functional results. The "average" solution, while functional, places a heavy burden on the surgeon and can leave the patient with a result that is merely adequate rather than truly restorative.

The personalised approach: the 3D-printed, one-size-fits-one solution

In contrast to the one-size-fits-many of conventional implants, this approach has been driven by advancements in digital imaging, computer-aided design (CAD), and additive manufacturing (3D printing). This approach enables the creation of patient-specific implants (PSIs), devices designed and fabricated for just one patient. The journey of patient-specific implant begins with data, where a high-resolution computed tomography (CT) or magnetic resonance imaging (MRI) scan of the patient is performed. In a collaborative process, the surgeon and specialised design engineer work together to create a design of the one-size-fits-one-patient implant. Once the design is approved by the surgeon, a medical-grade 3D printed implant is fabricated by the process called additive manufacturing [3].

By resolving every design challenge, validating the implant's strength, and planning the precise fit digitally, the process transforms the nature of the surgery itself. It shifts the operation from a procedure of improvisation and manual adaptation to one of precise, predictable execution. The precision achieved before surgery has a direct impact on efficiency during surgery, significantly reducing operating time and improving cosmetic outcomes.

References:

[1] Policicchio D, Casu G, Dipellegrini G, Doda A, Muggianu G, Boccaletti R. Comparison of two different titanium cranioplasty methods: Custom-made titanium prostheses versus precurved titanium mesh. Surg Neurol Int. 2020 Jun 13;11:148. doi: 10.25259/SNI_35_2020

[2] Kim YC, Lee SJ, Woo SH, Yang S, Choi JW. A Comparative Study of Titanium Cranioplasty for Extensive Calvarial Bone Defects: Three-Dimensionally Printed Titanium Implants Versus Premolded Titanium Mesh. Ann Plast Surg. 2023 Oct 1;91(4):446-455. doi: 10.1097/SAP.0000000000003663

[3] Moiduddin K, Darwish S, Al-Ahmari A, ElWatidy S, Mohammad A, Ameen W. Structural and mechanical characterization of custom design cranial implant created using additive manufacturing. Electronic Journal of Biotechnology. 2017 Sep; 29: 22-31. Doi: https://doi.org/10.1016/j.ejbt.2017.06.005