Orthopaedic Surgery and Rehabilitation

Biomechanical Research
 

    Under the direction of Daniel Mass, M.D., 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. In doing this, he cultured human flexor tendon tenocytes and discovered that they were able to participate in the flexor tendon healing process. He then developed a special tensiometer in order to study the strength of flexor tendon healing. Using the tensiometer as a measure of healing, he started to stimulate tendon healing by adding growth factors. This is going to now be taken back into an in vivo rabbit model when we combine our efforts 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 have developed a model for studying the flexor tendon repair and pulley system within the human hand using cadaver hands. This is different than all the other models, which pull on the tendon linearly. The tendons do not see the normal frictional rubs against the tendon sheaths in these models and therefore is not physiologic. This past year, he was able to compare the strength of the four different described four strand repairs. While the modified Becker and the Cruciate repairs were equally strong, and allowed early active motion, the Cruciate required less work for flexion so that he has changed his recommended repair technique in the clinical setting. Dr. Mass 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 very 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, therefore, which will work best for patients. A negative study would also provide important information.

Biomechanics of the Hand and Wrist and Elbow

Investigation of the best pulley site for opposition transfers
    The abductor pollicis brevis, opponens pollicis, and the radial head of the flexor pollicis brevis muscles are supplied by the motor branch of the median nerve and work together as the thenar muscle unit to create opposition about the carpometacarpal joint (CMC). Restoration of opposition following median nerve damage has been attempted by use of tendon transfers. The purpose of this cadaveric study is to determine which tendon transfer pulley site best replicates normal thumb opposition as assessed by CMC joint kinematics.

Investigation of the effects of the radial and ulnar collateral ligaments on laxity of the trapeziometacarpal joint
    Osteoarthritis of the TMC joint affects as many as 18% of post-menopausal women and 5% of middle-aged men. Ligamentous laxity, resulting in abnormal thumb kinematics and, in particular, abnormal dorsal translation, is a proposed mechanism in the development of degenerative joint disease in the TMC joint. However, there is controversy as to which of two ligaments, the dorsoradial ligament (DRL) or the volar oblique ligament (VOL), is most important in stabilizing the CMC joint. In a preliminary study, we found different roles for these two ligaments in lateral pinch, although both ligaments appear important to limiting abnormal dorsal translation of the metacarpal. We hypothesized that the DRL and VOL each contribute to preventing dorsal translation of the TMC joint during lateral pinch.

Investigation of tendon transfers for correcting claw deformity and restoring flexion of the metacarpalphalangeal joints and extension of the proximal interphalangeal joints of the fingers
    Traumatic lesions and compressive neuropathies of the ulnar nerve lead to numerous sensory and motor deficits in the hand including intrinsic muscle paralysis. Clawing of the fingers, grasp weakness, and abnormal grasping patterns are common clinical presentations of intrinsic muscle paralysis. Surgical approaches to intrinsic muscle paralysis have included nerve transpositions, static corrections, and tendon transfers. Nerve transpositions are not usually recommended for ulnar nerve lesions above the elbow. Static corrections are usually only recommended for patients with multiple paralyses in which no muscle can be selected for tendon transfer. Tendon transfers, therefore, are generally considered to be the best treatment option for standard patients with intrinsic muscle paralysis. The goal of tendon transfer surgery is two-fold; 1) To identify the tendon transfer that best corrects claw deformity and 2) that returns normal MCP flexion and PIP extension for proper grip strength and kinematics.

Anatomic study of the coronoid process of the elbow
    Coronoid injuries are classified according to the size of the coronoid fracture. However, standardized measurements of the coronoid process have not been previously reported. The purpose of this study was to provide a detailed and comprehensive anatomic description of the coronoid process, with specific focus on coronoid height, coronoid width, and olecranon-coronoid angle.

Investigation of the effects of the type-II coronoid fracture on the three-dimensional ulnohumeral laxity of the elbow
    Coronoid fractures have been classified by Regan and Morrey as type-I (0-25% bone fragment lost), type-II (25-50%), and type-III (50-100%). Although posterior displacement of the ulna with respect to the humerus has been examined in elbows with isolated coronoid fractures, such fractures are rare and are usually associated with lateral or medial ligamentous disruption, or both. We hypothesized that the three-dimensional ulnohumeral laxity of type-II fractures would not be significantly different from the intact elbow, but would be significantly less than when the type-II fracture is combined with one or more of radial head insufficiency, LCLC disruption, or MCLC disruption.

Dr. Draganich and Dr. Brian Toolan are currently investigating the effects of corrective orthoses and surgical reconstruction on acquired flatfoot deformity.   Flatfoot deformity 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.

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Last update:  January 10, 2010