The scapholunate is an interosseous carpal ligament that provides stability to the proximal carpal row. It consists of dorsal, proximal and palmar segments that bridge the scaphoid and lunate. When the ligament complex tears, the scaphoid tends to flex while the lunate extends, creating translational and rotational instability between the two. Instability is generally defined as the inability to bear physiological loads with an associated loss of normal wrist alignment.
Injuries to the scapholunate, along with the resulting instability, are among the most common and significant ligament injuries. They often occur during sports when an athlete falls on an outstretched hand, for example. When not properly diagnosed and treated, they can lead to functional disabilities and progressive degenerative osteoarthritis. Although arthritis can occur even after surgical repair or reconstruction, early diagnosis and appropriate treatment may restore normal function and prevent further damage to the joint.
Mayo Clinic orthopedic surgeons James H. Dobyns, M.D., and Ronald L. Linscheid, M.D., were among the first to conceptualize and describe traumatic carpal instability in 1972. They introduced the defining terms "dorsal intercalated carpal instability" and "volar intercalated instability" and described other problems related to abnormal wrist motion.
Since then, carpal instability has continued to vex hand surgeons. Diagnosis can be difficult in early injuries, and the diagnostic gold standard remains wrist arthroscopy.
In the last few years, however, advances in the understanding of wrist biomechanics and kinematics have led to improvements in the early, noninvasive detection of abnormal joint motion. Through the collaborative efforts of Mayo Clinic radiologists, biomedical engineers, basic science specialists and hand surgeons, the role of 4-D computerized tomography (CT) imaging has shown promise for the noninvasive diagnosis of dynamic carpal instability, which can only be detected during joint motion.
"This state-of-the-art CT technology provides information about carpal motion in real time at velocities similar to those of activities of daily living," explains Sanjeev (Sanj) Kakar, M.D., an orthopedic surgeon at Mayo Clinic's campus in Rochester, Minnesota. "Three-D movies of the patient's wrist can be played back, allowing physicians to see and measure discrepancies in joint motion and altered carpal loading from these subtle ligament injuries."
Not only does 4-D CT technology allow earlier and better assessment of dynamic joint instabilities, it also helps locate the exact site of ligament injury.
"The team at Mayo is currently studying patients with scapholunate instability using this technology with the goal of precisely identifying which part of the ligament is injured and directing treatment to that area as opposed to a shotgun approach where one treatment suits all," Dr. Kakar says.
Building a better ligament
Management of scapholunate instability is both complex and controversial. Therapeutic options range from splinting and casting or arthroscopic treatment to ligament reconstruction using autograft tendons. Nearly 40 years after the seminal work of Drs. Dobyns and Linscheid, the results of surgery remain unpredictable.
Reconstruction presents special challenges for hand surgeons, and a number of techniques have been proposed to overcome them. But the problem of poor tissue regeneration continues to be a vexing one. So Mayo Clinic researchers, including Dr. Kakar, Andre J. van Wijnen, Ph.D,, and Michael J. Yaszemski, M.D., Ph.D., are experimenting with the use of scaffolds seeded with progenitor cells and growth factors to regenerate ligamentous tissue.
In a study published in the November 2015 issue of Tissue Engineering Part A, they describe the successful creation of a collagen-rich extracellular matrix using adipose tissue-derived human mesenchymal stem cells seeded on a composite polymer neoligament.
"We are trying to further optimize the scaffold, and final results are at least a few years away," Dr. Kakar says. "Although it requires a lot more research, scaffold technology has great potential for stem cell engineering and ligament regeneration."
For more information
Wagner ER, et al. Ligament tissue engineering using a novel porous polycaprolactone fumarate scaffold and adipose tissue-derived mesenchymal stem cells grown in platelet lysate. Tissue Engineering Part A. 2015;21:2703.