Could you be a metal head?

Dr Alan Kop

Image from RPH: Royal Pulse Magazine

Dr Alan Kop

Clare Varcoe, Feature writier

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Advances in 3D printing and titanium use in skull injury means you could be.

In Perth, 600 people a year need skull repairing surgery, and 68% is trauma-related, from either injury or sport. Research led by the Royal Perth Hospital and Sir Charles Gairdner Hospital has revealed that titanium plates are better than replacing bone in some patients with skull injuries.

Head injury accounts for the highest per cent of hospitalisation due to sport related injury, at 16%, is associated with the longest hospital stay, and costs an average of $5300 per patient.

Dr Alan Kop and his team at Royal Perth Hospital, are at the forefront of using titanium plates in cranioplasty patients, rather than bone.

The trial was partially funded by the Western Australian State Health Advisory Council and involved 64 patients.

The practice of cranioplasty dates as far back as the Incan empire, performed with both metal plates and pieces of bone – some of which didn’t belong to the patient.

The operation’s purpose is to both protect the brain and to ensure the cosmetic look of a regular shaped head by repairing a deformity or an indent in the skull. 32% of Cranioplasty operations in Perth are performed after a skull fragment is removed for surgery or stroke, and in these cases, surgeons must wait until swelling on the brain has gone down, which can take many weeks.

But the operation has always been associated with risk. Autologous procedures, using the patient’s own bone, has always been considered the best option; if the piece of bone is useable, it has always been used, as it is more accurate and better suited to the job.

At the Australasian Society of Biomaterials and Tissue Engineering annual conference, Dr Kop explained the criteria of the material used in cranioplasty: “it’s got to be resistant to infection, strong, flexible, and fit with the skull, so basically, bone.”

Bone has always been the better choice because it has been nearly impossible to make an accurate plate for the size of the hole and the size and shape of the patient’s head, but it is not always possible to use the patient’s bone. In the cases where trauma is the cause of skull damage, the fragment of bone that belonged to the hole is often shattered and unusable.

Occasionally, a bone graft can be carried out, but the quantity of bone is quite limited.

Another issue the surgeons have to deal with is resorption (a medical term short for reabsorbtion). In the study carried out by Dr Kop and his team, 50% of the patients who were implanted with bone tissue from their own bodies (autologous tissue) had resorption to a degree, and 10% were so severe that they needed to have a titanium plate anyway. Royal Perth’s study concluded that bone resorption is much higher in younger adults, compared to people over 40.

They found that 12% of patients had partial resorption that although didn’t require surgery effected the cosmetic look of the patients’ skulls severely enough that the surgery was considered a failure.

As well as that, the risk of infection is high. To keep the bone from deteriorating, it is stored between -40 and -80 degrees Celsius, double-wrapped in serialised plastic and stored in a designated freezer, but if the brain has swelling, the bone cannot be replaced until it has gone down, so it can often be 6 weeks before the cranioplasty operation is performed – that’s 6 weeks the bone fragment, the skull, and the brain are compromised.

Since 2011, 124 cranioplasty operations at Royal Perth have failed, most from infection.

Titanium is not the first metal to be used as an alternative to bone: gold was the most common metal used, especially in the Incan empire, however it is extremely soft, only slightly stronger than a figure nail, and nowhere near as strong as bone, so, although it meets the cosmetic needs of the operation, it does little to protect the brain.

Polymer mesh is also not suitable, although used to replace ligaments, cartilage, keratin, skin and hair, is one of the closest inorganic mesh to biological tissue, and dissolves harmlessly once the tissue it is fused to has repaired itself, it simply isn’t variable. Doctors at Royal Perth experimented with a combination of allogeneic mesenchymal stromal cells, ceramic granules and a polymer scaffold, however, Kop explains that at this stage, “its lack of rigidity means mesh is not palatable.”

With the invention of 3D printers, titanium plates have become more precise than bone, and can be made to perfectly fit the skull better than ever before. Titanium is strong, lightweight, non-corrosive, and keeps its shape under pressure or strain, making it able to protect the brain as well as bone does.

Royal Perth designs and creates 40 to 50 titanium plates per year: “Basically we start with a defect, then we use titanium tilings to fix the defect,” Dr Kop explained.

The cranioplasty operation is relatively easy, despite the infection risk, and only takes an hour to perform, both with bone and the titanium plate. However, the study suggests that this is the reason for infection: “the findings of this study would lend support to the hypothesis that surgical technique might be important.”

Prior to this study, in two hospitals in Western Australia where cranioplasties were performed, the operation was carried out by junior resisters rather than senior neurosurgeons, and the handling of surgical tools and implants: “can make maintenance of sterility difficult in inexperienced hands.”

Before the incision, the area is shaved, the head is scrubbed with antiseptic to minimise infection, and local anaesthetic is applied to the incision line, but the patient receives no general anaesthetic, and therefore is wake for the operation, a common practice for neuro surgery.

Despite the cost to manufacture the titanium plates, performing the cranioplasty exclusively with titanium over bone is more cost effective, because the cost for replacing the bone with titanium, and the cost of extending the patient’s stay in hospital and the longer rehabilitation of the 10% that experience bone resorption and need to have a titanium plate anyway greatly outweighs the price of exclusively carrying out titanium cranioplasty for every patient.

However, in children, bone is still favoured. Unless the defect is congenital, it often closes spontaneously, and cranioplasty isn’t required, and infection rate is lower in children.  Although ready-made titanium strips are often usable for children, where they aren’t in adults, bone in children can be re-implanted if removed after cranioplasty due to infection and reduces the need for a replacement.

Despite the preference for bone over titanium in children, the rate of bone reabsobtion is far higher, having been reported as high as 81.8% of paediatric cranioplasty has resulted in resorption.

Royal Perth Hospital will carry out another trial starting May 18, using 3D printed biomimetic ceramic scaffolds inoculated with mesenchymal stromal (bone) cells, as the next step from titanium. So far, ceramics have a limited use in regard to bone, but Royal Perth hopes to expand its use.

The base of the ceramic scaffold is designed so that the bone stem cells can form on the plate and eventually completely cover the deformity in bone, eliminating the need for titanium plates and using existing bone that is susceptible to resorption.

The trial is five years in the making and hopes to solve the problem of infection that comes with titanium and existing bone cranioplasty.

The stem cells are slow growing though and it will take 12 months until the bone grows over the ceramic plate, which is designed to dissolve at the same rate as bone growth.


For support for and information on brain and skull injury, contact the Brain Injury Association of WA, Headwest.

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Could you be a metal head?