Floor plan - 2013 Annual Meeting - American Association for Hand ...

Partial Ulnar Head Resurfacing Implant Arthroplasty
Institution where the work was prepared: University of Iowa, Iowa City, IA, USA
Danielle A. Conaway, MD; Brian D. Adams; University of Iowa
Although complete implant replacement of the distal ulna has become a popular and accepted procedure, in many cases it sacrifices
normal portions of a distal ulna and important soft tissue attachments. Consequences of resecting unaffected portions of the distal ulna
include a higher risk of distal radioulnar joint instability, implant prominence, soft tissue irritation, and ulnocarpal instability. To minimize
the resection and to optimize the functional result of implant arthroplasty of the distal ulna for the treatment of distal radioulnar arthritis,
a partial ulnar head replacement was developed, which only replaces the articular surfaces. The implant allows retention of the ulnar
neck, ulnar styloid, extensor carpi ulnaris grove, ulnocarpal ligament attachments, extensor carpi ulnaris sheath, and the triangular fibrocartilage
complex attachments to the ulnar styloid. It is intended for patients who have good skeletal alignment and functioning soft
tissue stabilizers surrounding the distal ulna. To assess the design's replication of the natural anatomy, a study was performed on 10
cadavers. A number of radiographic parameters were compared between the natural state of the distal ulna and the state after implantation.
In addition, the results of the first 10 patients treated by 3 surgeons were reviewed to assess its clinical efficacy. Plain radiographs
demonstrated a good match (within 7%) between the size and shape of the natural ulna and the implant, as well as ulnar variance, ulnar
offset, and ulnar height at the distal radioulnar joint. Distal radioulnar joint stability was maintained by subjective assessment, and there
was no loss of forearm rotation. Of the 10 clinical patients, 7 were treated for osteoarthritis and 3 for posttraumatic arthritis. In a retrospective
chart review at an average 6 month follow up, there were no intraoperative or postoperative complications. Pain relief was satisfactory
in all, though none were pain free. Motion was improved in all, with all patients achieving at least 75 degrees of pronation and
65 degrees of supination. Wrist flexion and extension was unaffected. There were no cases of distal radioulnar joint instability. In conclusion,
this preliminary report suggests that surface, ìconservativeî, implant replacement of the distal ulna may offer advantages over
complete distal ulna replacement in selected patients.
Dynamic (4D) Computed Tomography of the Wrist : Proof of Feasibility in a Cadaveric Model
Institution where the work was prepared: Mayo Clinic College of Medicine, Rochester, MN, USA
Shian Chao Tay, MBBS, FRCS, FAMS1; Andrew N. Primak, PhD2; Joel G. Fletcher, MD2; Bernhard Schmidt, PhD3;
Kimberly K. Amrami, MD1; Cynthia H. McCollough, PhD1; Richard A. Berger, MD, PhD4; (1)Mayo Clinic, (2)Mayo Clinic
College of Medicine, (3)Siemens Medical Solutions, (4)Mayo Clinic Foundation
PURPOSE:
High resolution real-time 3D imaging of the moving wrist may provide novel insights into the pathophysiology of dynamic joint instability.
The purpose of this work was to assess the feasibility of using retrospectively-gated spiral computed tomography to perform
dynamic (4D) imaging of the moving wrist joint.
METHODS:
A cadaver forearm from below the elbow was mounted on a motion simulator which performed periodic radioulnar deviation of the
wrist at 30 cycles per minute. An electronic trigger from the simulator provided the "electrocardiogram" (ECG) signal required for gated
reconstructions. The wrist was scanned on a 64-slice CT scanner (Sensation 64, Siemens Medical Solutions) using a retrospectively-gated
CT protocol with a special low pitch of 0.1 provided by the manufacturer. Scanning was performed from the distal radius and ulna to
the proximal metacarpals to ensure adequate coverage of the carpal bones. The first condition scanned was during periodic radioulnar
deviation and was designated the 4D condition. The second scan served as a control where the wrist was precisely moved to four
designated static positions and scanned. This control scan was designated the 3D condition. Both the 4D and 3D images were then
compared by two blinded observers for image quality and presence of artifacts. The displacement of the distal pole of the scaphoid
during radioulnar deviation was also calculated from the dynamic 4D phase after appropriate image segmentation and thresholding.
RESULTS:
Image quality of 4D images was rated by both observers to be excellent at the extremes of radial and ulnar deviation (end-motion phases).
Mid-motion phases were rated by both observers to be fair due to the presence of motion and band artifacts. However, in all phases,
carpal joint spaces remain well resolved. The centroid of the distal pole of the scaphoid was found to undergo a displacement magnitude
of 12.4 mm.
CONCLUSION:
In conclusion, a method using retrospectively-gated CT for dynamic 4D imaging in the wrist is feasible. In the near future, this may provide
hand surgeons a new diagnostic tool in which dynamic carpal instabilities can be assessed.
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