Article
The bony anatomy of the radius and ulna: A Computed Tomography study for implant design and related research
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Authors
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Henry Pretorius
- Stellenbosh University, Tygerberg Hospital, Bellville, South Africa
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Marilize Burger
- Stellenbosh University, Tygerberg Hospital, Bellville, South Africa
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Nabeela Adam
- Stellenbosh University, Tygerberg Hospital, Bellville, South Africa
| Published: | February 6, 2020 |
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Outline
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Objectives/Interrogation: CT scans where utilized to measure multiple anatomical dimensions of the radius and ulna in a reproducible manner. Intramedullary fixation for length unstable forearm fractures could render favorable results and this information could aid in optimizing the size and design of these devises.
The specific objectives of the study will be to evaluate the radius and ulna structurally, especially the radius curvature and the canal diameters of both bones. This may aid with future implant design and for current implant modification. No current comparable descriptive or comparative studies are available in the literature.
Methods: We retrospectively looked at 100 CT forearm scans with unaffected radius and ulnas. We measured the length, radius of curvature, canal width and head measurement in both plains.
Results and Conclusions: The length of the radius shows a mean of 238 mm.The mean curvature will be an arc with a radius of 558.27 mm. The radial head diameter in two planes are 23.84 and 23.24 respectively. The canal size shows a mean of 5.48 mm. Radial inclination, radial styloid length and volar tilt show a mean of 21.57deg, 10.47mm and 12.8deg respectively. The maximum distal radius height 20.56mm. The length of the ulna shows a mean of 259.7 mm. The ulna head diameter in two plains show means of 19.48 and 16.76 mm respectively. The canal size in the ulna shows mean of 5.28. Radial length predicts ulna length, and both radius and ulnar length predict radius curvature. Radial head diameter predicts radial length and ulna head diameter predicts ulna length. Radial canal maximum diameter predicts ulnar canal minimum diameter.
This anatomical measurements will aid with implant design and ranges. Radius: Implant length of 230-240 mm cover 95% of patients. Radius curvature can be set at the mean for most forearms at 558mm and this would correct the arc within 19 mm for 95% of the patients. A 4 mm rod diameter will pass through most radial medullary canals. The distal height of the radius allows adequate space for the 6mm nail locking block.
Ulna: The ulna is consistently 20 mm longer than the radius which has prosthesis design implications. The ulnar nail should be longer than the radius range and anatomical bend of 12 deg.The proximal ulna entry point will accommodate a 6 mm reamer. The ulnar shaft will easily accommodate a nail diameter of 4 mm.
