Hip and femur fracture treatments require expert surgical skills and an implant shape that closely matches the patient’s anatomy when inserted into the canal of the thigh bone, called the femur.
IHBI’s Dr Beat Schmutz is an expert in implant shape design and optimisation and understands the pressure to get it right, as the implants need to fit a global patient population with a
wide range of bone shapes and sizes. ‘This is a very complex process that has to take into account clinical and regulatory requirements, anatomical patient variabilities and logistical and commercial factors,’ he says.
Dr Schmutz has worked with product development groups from global orthopaedics company and industry partner DePuy Synthes (DPS), part of Johnson & Johnson, in the US and Switzerland on the design and validation of new implant shapes for the development of two nails. The first, the TFN-ADVANCED (TFNA) Proximal Femur Nailing System has been in use in surgery since 2015, while the Femoral Recon Nail (FRN) has been used since June 2018.
The work builds on a collaboration with DPS stretching back 10 years and involving IHBI input from Professor Michael Schuetz and members of the Trauma Research Group in the development of several implants for fracture treatment. Under the leadership of Dr Schmutz, the research associated with nail fit has attracted awards at four international conferences, notably the prestigious Wilhelm-Roux Prize at the 2009 Annual Meeting of the German Society for Orthopaedics and Trauma in Berlin.
Factors that determine differences in bone properties such as shape and size include age, gender and ethnicity. Older people are likely to have weaker bones and signs of bowing, while
women commonly have smaller bones. Ethnicity is linked to differences in bone curvature and length, in part based on a person’s height.
Surgeons have several implant options, with each nail similar in shape but having varying lengths, diameters and different angles for hip screw fixation.
More than 1.6 million people sustain a hip fracture globally every year and an estimated 6.3 per cent of patients undergoing surgical treatment require revision surgery. Revision surgery is
a second surgery that takes place if the original implant fails and needs to be replaced.
‘Fracture treatment with a nail inserted into the femur is highly effective, with successful outcomes for the majority of patients,’ Dr Schmutz says. ‘However, there are studies that show certain design elements of the nails sometimes lead to complications during or after surgery.’
Dr Schmutz says there have been reports of misfits between a patient’s anatomy and nail designs, leading to complications such as the nail tip impinging on, or protruding from, the
internal bone surface. While impingement often results in knee pain, nails that protrude require revision surgery.
Traditionally, design validation of the nail shapes involves surgically implanting nails in the lab using anatomical specimens, and the fit being assessed using 2D x-ray images. However, the images generated contain distortion and do not necessarily indicate the true fit between the nail and the bone.
Dr Schmutz has overcome the limitations through use of a customised nail fit tool, using computer graphical 3D modelling, developed in collaboration with Professor Schuetz. The software that drives the nail fit tool was developed at IHBI as part of Jayani Amarathunga’s PhD project, under the supervision of Dr Schmutz, Professor Schuetz and Professor Prasad
An important consideration has been the nail’s radius of curvature (ROC), the bend in the nail that enables it to fit the natural bow of the patient’s femur when inserted. Dr Schmutz conducted 3D computer graphical anatomy studies in collaboration with DPS, showing that a 1.0m ROC nail would more closely match the average anatomy of the target patient populations than the present 1.5 m ROC nails. ‘This helps to reduce nail tip impingement in the canal,’ he says.
‘Using our nail fit tool along with 3D bone and nail models, we have been able to contribute to the development of anatomically better fitting nails for an age and ethnically diverse patient population. This would not have been possible with traditional methods.’
Institute of Health and Biomedical Innovation (IHBI)
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