Under the direction of Dr. Daniel Mass, the Hand and Upper Extremity Research Laboratory has focused on the biology of flexor tendon healing and the biomechanics of flexor tendon repair techniques. Recently, the lab has expanded its focus to look at other aspects of biomechanics of upper extremity to include the basilar joint and the elbow.

The Biology of Flexor Tendons

Twenty years ago, Dr. Mass started studying the biology of flexor tendons. He cultured human flexor tendon tenocytes and discovered they were part of the flexor tendon healing process. He developed a special tensiometer to study the strength of flexor tendon healing and began stimulating tendon healing by adding growth factors. He is now investigating this in an in vivo rabbit model in a combined effort with Drs. Rex Haydon and Tong-Chuan He.

Flexor Tendon Biomechanics

Drs. Mass and Phillips have used the tensiometer to study the flexor tendon biomechanics. They developed a model for studying flexor tendon repair and pulley system using cadaver hands. This differs from other models, which pull on the tendon linearly. Since the tendons do not see normal frictional rubs against tendon sheaths in these models, it is not physiologic.

This past year, he was able to compare the strength of four different strand repairs. While the modified Becker and Cruciate repairs were equally strong and allowed early active motion, the Cruciate required less work for flexion. This research finding has changed his recommended repair technique in the clinical setting.

Dr. Mass has also initiated a study on the energy to flex three different silastic MP implants. While each are used clinically and resist millions of bending motions, they have previously only been studied for their center of rotation and ease of extension. Patients with rheumatoid arthritis who require these joint replacements have weak muscles, particularly the intrinsic muscles that flex the MP joints. By studying the energy required for flexion, Dr. Mass hopes to determine which of the three implants is the easiest to flex and which will thus work best for patients.

Biomechanics of the Hand, Wrist and Elbow

Using a three-dimensional electromagnetic digitizing system and software developed by Dr. Louis Draganich in prior studies of the knee joint, Drs. Draganich and Mass have been investigating the biomechanics of the thumb, fingers, wrist and elbow. Recently, their work on the effects of the adductor pollicis and abductor pollicis brevis on thumb metacarpophalangeal joint laxity before and after ulnar collateral ligament reconstruction has been published in the Journal of Hand Surgery. Their other investigations include:

• Best pulley site for opposition transfers affecting the metacarpalphalangeal joint
• Effects of the radial and ulnar collateral ligaments on laxity of the trapeziometacarpal joint
• Best tendon transfers for correcting claw deformity and restoring flexion of the metacarpalphalangeal joints and extension of the proximal interphalangeal joints of the fingers
• Anatomic study of the coronoid process of the elbow
• Effects of the type-II coronoid fracture on the three-dimensional ulnohumeral laxity of the elbow. 

For more information about these studies, please click here.

Biomechanics of the Ankle

Drs. Louis Draganich and Brian Toolan are currently investigating the effects of corrective orthoses and surgical reconstruction on acquired flatfoot deformity, which alters the contact characteristics of the ankle joint. Our prior biomechanical investigation demonstrated that the valgus deformity of the hindfoot shifts the location of articulation posterolaterally, increases pressure and decreases the contact area within the ankle. These changes may explain the pattern of articular degeneration and angulation observed in a longstanding adult acquired flatfoot. Corrective orthoses and surgical reconstruction have been employed to realign the pes planovalgus foot. However, the effects of these treatments on tibiotalar contact characteristics are unknown. We theorized that both interventions would restore the contact characteristics to the intact condition. Specifically, we hypothesized that the location of tibiotalar contact, the mean contact area, mean pressure and peak pressure of the ankle to return to the intact state when the flatfoot was realigned with either an orthosis or an osteotomy. We would interpret this anticipated normalization of the contact characteristics as beneficial to the prevention of pantalar disease in an adult acquired flatfoot.