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3D-printed splint for mallet finger injury
affected by mallet finger, the only joint with a for washing. The top section of the splint extends to
degree of freedom. the proximal interphalangeal joint. This allows the
Using Autodesk Inventor Software and the user some flexion of the finger without hindering
measurements, the patient-specific splint is recovery. A benefit of using topology optimization
designed. As shown in Figure 4, a constraint was (TO) is that areas of the finger and finger pad
designed at the rear of the splint to prevent leeway in remain exposed, so a person can still feel and get
the splint when being worn. When the user clenches sensation through the finger when performing
their fist, without this material removed, the skin of everyday tasks such as writing with a pen or using
their middle phalanx finger can push into the back of their toothbrush. This is opposed to a molded splint
the splint dislodging its correct position. The stack that is fully enclosed, which makes the finger
splint is designed with an open ventilation section become less functional for the recovery period. The
above the fingernail to allow some airflow to reduce maximum pressure load calculated from the distal
interphalangeal joint, simulating the maximum
sweat when being worn and to allow limited access force a person could generate in their index finger
solely from the flexion of the distal interphalangeal
joint, was applied to the rim of the finger splint.
This was chosen because the finger “pad” section
of the splint is a large space that will be optimized
in all topology-optimized splints. Because of this,
the area and geometry in that section changed for
each splint. By applying the pressure load to the rim
Figure 3. The seven measurements required to of the splint, it was a consistent way to compare all
create a personalized finger splint computer-aided splints.
drawing model. 2.2 3D Printing patient-specific finger splint

A number of materials could potentially be used
in FDM having the properties required to match
and exceed those of the current hand-molded
thermoplastic splints. These materials include
poly-lactic-acid (PLA), acrylonitrile-butadiene-
styrene, polyamide, thermoplastic polyurethane,
polycarbonates, polystyrene, and poly-ether-
ether-ketone. Environmental considerations were
considered as the use of this product is highly
personal; it cannot be passed onto the next patient,
so it must be disposed of after treatment. The
non-recyclability of casts and splints causes large
amounts of waste. In fact, in the US, according
to the National Ambulatory Medical Care Survey
and American Academy of Orthopaedics, 2.4%
of the population experiences some fracture ,
[31]
producing an average of 670,000 kg of waste per
year [17,32] . However, PLA being derived from natural
sources, corn, beet, and cassava among others, is
Figure 4. Geometry of a sample 100% mass biodegradable. Because of this, PLA splints can be
design according to a patient’s finger. composted after their 6 – 8 weeks use, rather than

20 International Journal of Bioprinting (2020)–Volume 6, Issue 2