How the Tenodesis Grasp Supports Daily Hand Function

For individuals with limited hand function due to spinal cord injuries, the ability to grasp and release objects can be significantly affected. The tenodesis grasp is a biomechanical mechanism that enables functional hand movement without active finger control, benefiting those with certain levels of paralysis.

Anatomy of Wrist and Finger Tendons

The coordination of wrist and finger tendons plays a fundamental role in hand movement, particularly in tenodesis grasp. These tendons, composed of dense connective tissue, link muscles and bones, transmitting force to facilitate motion. The flexor tendons, including the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS), run along the palmar side of the hand, enabling finger flexion when the wrist extends. Conversely, the extensor tendons, such as the extensor digitorum communis (EDC), extend the fingers when the wrist flexes. This reciprocal relationship is central to passive grasping movements in individuals using tenodesis.

Encasing these tendons are synovial sheaths, which reduce friction and allow smooth movement. Specialized structures like the flexor and extensor retinacula anchor the tendons, preventing bowstringing and ensuring efficient force transmission. The flexor retinaculum, forming the roof of the carpal tunnel, secures the flexor tendons, while the extensor retinaculum stabilizes the extensor tendons. Disruptions to these structures, whether from injury or neurological impairment, can alter tendon mechanics and affect functional hand use.

The interaction between tendons and wrist position is particularly relevant for individuals with spinal cord injuries. When the wrist extends, passive tension in the flexor tendons increases, causing the fingers to curl into a grasping position. This biomechanical effect results from tendon elasticity and length-tension relationships, which dictate how tendons respond to joint positioning. The degree of passive finger flexion during wrist extension depends on tendon stiffness, muscle tone, and joint integrity, all of which influence the effectiveness of tenodesis grasp in daily activities.

Biomechanics of the Tenodesis Effect

The tenodesis effect arises from the interplay between wrist position and passive finger movement, driven by the length-tension properties of the flexor and extensor tendons. When the wrist extends, the flexor tendons experience passive tension, causing the fingers to flex without active muscular control. Because these tendons cross multiple joints, their length adjusts as the wrist moves, redistributing tension. The opposite occurs when the wrist flexes—passive tension shifts to the extensor tendons, leading to finger extension. This motion allows individuals with limited voluntary finger movement to manipulate objects through controlled wrist positioning.

Several factors influence the effectiveness of this grasp, including tendon stiffness, muscle tone, and joint stability. Higher tendon stiffness enhances the tenodesis effect, as reduced slack results in more pronounced finger flexion. Conversely, excessive laxity diminishes grasping force, sometimes requiring orthotic support. Muscle tone, particularly in individuals with spinal cord injuries, can alter tendon tension, either exaggerating or weakening the tenodesis response.

Joint stability also plays a role. Proper wrist and finger joint alignment ensures efficient force transmission from tendons to digits. Conditions such as ligamentous laxity or joint contractures can reduce passive grasping effectiveness. Rehabilitation strategies like stretching and splinting can improve joint positioning and enhance tenodesis function. Wrist extension angles also impact finger flexion, with research suggesting that 30 to 45 degrees of wrist extension maximizes grip strength while maintaining a functional range of motion.

Role of Spinal Cord Segments

The tenodesis grasp depends on the integrity of specific spinal cord segments, particularly those controlling wrist extension. In cervical spinal cord injuries, the level of injury determines which muscle groups remain functional, directly influencing the ability to use tenodesis. The wrist extensors, primarily controlled by the C6 and C7 spinal nerve roots, generate the wrist movement necessary to trigger passive finger flexion. When these segments remain intact while lower motor pathways are impaired, individuals can use wrist extension as a substitute for active grip, increasing independence in daily tasks.

C6-level injuries often preserve function in the extensor carpi radialis longus and brevis, enabling controlled wrist extension. This movement creates the passive finger flexion required for tenodesis, but the absence of active finger flexors means grip strength depends entirely on tendon tension. At the C7 level, partial function of the triceps brachii improves arm stability, enhancing wrist positioning control. While C7 does not directly contribute to tenodesis, its role in elbow extension allows for better force application. C8 involvement may restore some voluntary finger movement, reducing reliance on tenodesis while still benefiting from its mechanical assistance.

Neurological factors also affect grasp effectiveness. Muscle tone, influenced by upper motor neuron activity, varies among individuals with spinal cord injuries, sometimes leading to spasticity or hypertonicity that alters tendon tension. Rehabilitation strategies, including neuromuscular re-education and targeted stretching, aim to optimize wrist extension without excessive rigidity or laxity. Studies indicate that individuals with C6 injuries who undergo structured therapy, including passive range-of-motion exercises and functional training, improve tenodesis efficiency over time, reinforcing the role of spinal cord segment integrity in functional recovery.

Functional Use in Daily Tasks

The tenodesis grasp enables individuals with limited hand function to perform essential daily activities by leveraging passive finger flexion through wrist extension. This mechanism allows for controlled object manipulation without requiring active grip strength, making tasks such as eating, writing, and dressing more manageable. Holding a utensil, for instance, becomes possible by extending the wrist to create a firm grasp around the handle, while controlled release is achieved by allowing the wrist to flex. Similarly, picking up lightweight objects like a toothbrush or phone follows the same principle, with wrist movement dictating grip and release.

Beyond basic tasks, tenodesis supports more complex activities requiring sustained grasping. Many individuals use adaptive strategies, such as positioning items against a stable surface before engaging the grasp. This enhances efficiency when handling larger objects like water bottles or clothing. Occupational therapists emphasize wrist extension training to strengthen the grasping effect, helping individuals refine grip pressure. Studies suggest that consistent practice improves coordination, leading to greater functional independence.

Specialized Equipment for Enhanced Grasp

Specialized equipment enhances functional independence by optimizing grip strength, improving object control, and reducing wrist strain. Assistive devices complement the passive grasp mechanism, allowing users to perform tasks more efficiently while minimizing fatigue. These tools range from simple adaptive utensils to advanced orthotic systems that stabilize the hand and wrist for improved precision. Many devices are customized to accommodate variations in tenodesis effectiveness, ensuring that individuals with different levels of spinal cord injury can maximize hand function.

Wrist-driven orthoses, often called tenodesis splints, support wrist extension while reinforcing finger flexion, amplifying the natural tenodesis effect. Common models, such as the wrist-hand orthosis (WHO), use a rigid frame to maintain proper alignment, improving grip consistency and endurance. Research shows that individuals using tenodesis splints experience notable improvements in holding and manipulating objects, particularly during extended activities like writing or using electronic devices. Adaptive gloves with embedded tension bands provide an alternative by increasing resistance during grasping motions, helping individuals with weaker tenodesis function maintain grip.

Beyond mechanical aids, advancements in neuroprosthetics offer innovative solutions for improving tenodesis grasp. Functional electrical stimulation (FES) systems use controlled electrical impulses to activate wrist and finger muscles, supplementing natural biomechanics. Studies indicate that FES-assisted grasping significantly improves hand function in individuals with incomplete spinal cord injuries, offering a promising avenue for rehabilitation. Additionally, 3D-printed adaptive tools, such as custom utensil holders and grip-enhancing attachments, provide cost-effective solutions tailored to individual needs. These innovations make daily activities easier, reinforcing the role of specialized equipment in optimizing tenodesis grasp for long-term functional independence.