by Erin Hatfield

PROVIDENCE, R.I. - There are certain things the medical community thinks it knows: Like how the bones in the wrist move and how to treat it when it's injured. Then along come researchers such as those from Brown Medical School/Rhode Island Hospital who make science reconsider previous knowledge.

Under a five-year study funded by the National Institutes of Health, researchers at Brown Medical School/Rhode Island Hospital are using a combination of computer tomography (CT), new reverse-engineering software, CAD/CAM solid modeling tools, and computer animations to study the human wrist in completely new ways. Early discoveries indicate that the wrist doesn't move in previously accepted manners, and widely practiced treatments of wrist injuries could be dramatically improved.

Living, breathing subjects

Current knowledge of wrist kinematics and pathologies is based on clinical experience and years of research using cadavers. Cadaver-based studies possess inherent limitations, namely the inability to simulate physical stress loads on the wrists and real injuries.

Joseph Crisco, director of the Orthopedic Bioengineering Laboratory at Brown Medical School/Rhode Island Hospital, and his colleagues are one of the first groups of researchers to gather data on wrist movement from live subjects. The process is non-invasive and uses data from CT scans of the human wrist through a full range of motion, revealing 3D images, which traditional X-rays do not.

Once the scan data is collected, it is exported to Mayo Foundation's Analyze software to extract the contours of the small bones present in the scans. Crisco and his team have developed programs that can generate point-cloud data from the extracted bone contours. The point-cloud data is imported into Geomagic Studio reverse-engineering software, where the data is turned into polygonal models and NURBS surfaces.

Crisco's group also combines scanned point-cloud data of varying resolutions to create the final 3D models of the wrist bones. The surfaces of the higher-resolution scans are automatically aligned within Geomagic Studio with corresponding point clouds from other positions and saved as new files. Using these files, the team creates accurate and easily viewed digital models of completed wrists in multiple positions.

"Without accurate digital models, we wouldn't be able to quantitatively study various wrist positions and motions," says Crisco.

Crisco's team then imports the digital wrist models into SolidWorks CAD/CAM software for additional fine-tuning. The final CAD data is output to a rapid prototyping machine, where physical models of the wrist are created. The models are extremely accurate, within two degrees of rotation and 0.2mm of dimension, and preserve the bone orientation of each wrist position.

Animation reveals complex motion

Brown Medical researchers also use the digital models to create 3D animations of wrist movement. Proprietary mathematical algorithms help the team fill in the gaps between scanned positions by calculating and predicting the range of motion - much like a flip-book animation. The animations help the researchers see, three dimensionally, how the relations between wrist positions play out in real life.

Based on the animations, Crisco has found that wrist motion and function are more complicated than previous theories indicate. Current descriptions of wrist motion suggest that the eight wrist bones move as three columns or two rows. Instead, Crisco has discovered that each bone has a separate pattern of motion that is associated with each unique direction of wrist motion.

"As we continue to prove our hypotheses correct," he says, "we are generating an understanding of the increasingly complicated motion of the carpal bones. Three-dimensional animations have been the only way for us to visualize these findings."

The potential to revolutionize treatment

The Brown Medical team is studying injured wrists as well as healthy ones to determine if current diagnosis and treatment methods can be improved. They are examining soft tissue injuries, such as scapholunate ligament tears, which are often the consequence of a fall on an outstretched hand. Current evaluations of ligament tears use X-rays to examine the gap between the scaphoid and lunate bones. If the gap between is wider than expected, a ligament tear is the most probable diagnosis.

"Our current findings indicate that altered 3D bone motion of the wrist - rather than X-rays - is a better indicator of ligament injuries," says Crisco.

"For fractures, we can use the auto-align function in Geomagic Studio to compare a fractured wrist with a normal wrist," he says. "With this method, we can better predict the orientation of fractured bones and better align them during surgical treatment."

Most joint surgeries do one of two things - either they limit motion through fusion, or restore normal motion through reconstruction to reduce pain and the progression of degenerative joint disease. With these surgeries the adjacent unfused joints can become abnormally strained with movement, leading to further pain and degeneration of otherwise healthy joints. The researchers want to use the scanning techniques to further study how fusion alters the motion of the healthy joints.

An entirely new knowledge base

Crisco's team at Brown Medical School/Rhode Island Hospital hopes the new method of visualizing wrist movement will help change current diagnosis and treatment practices.

"We are extremely excited about our research and findings," says Crisco. "Using CT scans and Geomagic Studio to create 3D models and animations, we are creating a new knowledge base of wrist movement. This knowledge will hopefully refine the way wrist injuries are diagnosed and treated, as well as serve as the definitive data basis for future studies."

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