The design of the rehabilitative functional hinged knee brace incorporates several fundamental physical principles central to its performance in supporting and stabilizing the knee joint. Hinge mechanics play an essential role in its operation. Ratchet hinges allow for precise control over the range of motion of the knee joint. They can be designed to permit movement in set increments, which is beneficial for rehabilitation purposes where gradual progression is essential. The locking feature of ratchet hinges ensures that the knee brace can maintain a specific angle during rehabilitation exercises. This prevents unwanted movement and provides stability, which is crucial for patients recovering from knee injuries or surgeries.
The principle of force distribution is also vital in the design. The brace uses the biomechanics of leverage to adjust the pressure exerted on the knee joint, particularly in the coronal plane. This adjustment helps redistribute load between the internal and external compartments of the knee, reducing stress on specific regions and relieving pain. The use of three-point and four-point force systems in the design, as in Figure 1, allows the brace to create a balance between the forces exerted on the thigh and calf, providing continuous pressure on the knee to stabilize and protect it from excessive movement, especially during weight-bearing activities. The force is applied using adjustable straps, where a larger surface area allows for greater leverage and more even force distribution. This design is particularly beneficial for post-injury recovery and preventing re-injury during daily activities or sports.
Figure 1: 3-point and 4-point force system
Compression is another critical factor in the design of polycentric knee braces. Compression is applied through the strategically placed straps, bands, or fabric panels surrounding the knee joint. It serves multiple purposes, including stabilizing the joint by compressing the soft tissues—such as muscles, tendons, and ligaments—to prevent excessive lateral or rotational movement. Compression also helps reduce swelling, a common issue after injury or surgery, by promoting fluid drainage and preventing excessive fluid accumulation. Additionally, compression improves blood flow around the knee, enhancing the delivery of oxygen and nutrients to injured tissues, supporting healing, and alleviating pain. Effective compression, designed to be snug without causing discomfort, improves proprioception and the body’s awareness of joint position and movement, which aids in balance and gait adjustments.
