3D analysis of the distal ulna with regard to the design of a new ulnar head prosthesis

Abstract

Study design A retrospective, single center, data analysis. Objective Persistent pain and instability are common complications after distal ulnar head arthroplasty. One main reason may be the insufficient representation of the anatomical structures with the prosthesis. Some anatomical structures are neglected such as the ulnar head offset and the ulnar torsion which consequently influences the wrist biomechanics. Methods CT scans of the ulnae of forty healthy and asymptomatic patients were analyzed in a three-dimensional surface calculation program. In the best fit principle, cylinders were fitted into the medullary canal of the distal ulna and the ulnar head to determine their size. The distance between the central axes of the two cylinders was measured, which corresponds to the ulnar offset, and also their rotational orientation was measured, which corresponds to the ulnar torsion. Results The mean medullary canal diameter was 5.8 mm (±0.8), and the ulnar head diameter was 15.8 mm (±1.5). The distance between the two cylinder axes was 3.89 mm (±0.78). The orientation of this offset was at an average of 8.63° (±15.28) of supination, reaching from 23° pronation to 32° supination. Conclusion With these findings, a novel ulnar head prosthesis should have different available stem and head sizes but also have an existing but variable offset between these two elements. A preoperative three-dimensional analysis is due to the high variation of offset orientation highly recommended. These findings might help to better represent the patients natural wrist anatomy in the case of an ulnar head arthroplasty. Level of Evidence III.

Quantification of Malalignment and Corrective Osteotomies in Patients With Malunion After Elastic Stable Intramedullary Nailing of Pediatric Forearm Fractures

“…Additionally, the rotation of both forearm bones is subject to scatter within the population, with the ulna varying by >50°. 13 , 17 Landmarks that appear to be easily detected on conventional x-rays and are commonly used for rotational evaluation, such as the bicipital tuberosity or the radial styloid, may only be used to a very limited extent because of high natural variation among the population. 17 As a result, examining the rotational displacement of the fragments using conventional x-ray images is extremely difficult and likely has an underestimated rate of inaccuracy.…”

“…1 ). 13 On the basis of the generated data, a complete design of individualized bone surface contact drilling and sawing guides was created and 3D printed for the surgical intervention (Medacta International). Finally, the osteotomies were performed by two expert hand surgeons ( Fig.…”