Design, Validation, and Clinical Testing of a Novel Fastening Device for a Scoliosis Brace
Authors:   ,   University of Tennessee Health Science Center, Bateman Cody 
Published: January 2022

Each year, thirty thousand children in the US were put into a scoliosis brace. The primary function of scoliosis braces was to reduce and prevent progression of the spinal deformity as the patient grew by application of corrective forces to the spine. Straps, often made of Velcro, were attached to the back of the brace that applied forces to the spine when the straps were tightened. Braces were prescribed to be worn up to 23 hours a day. Studies have concluded that discomfort increased with increasing strap tension and pad pressure. They have also shown an increase in strap tension occurred during deep breathing and some daily activities which led to discomfort. Consequently, discomfort often led to poor user compliance and reduced brace wear hence decreasing treatment efficacy. Treatment efficacy also decreased due to a loss of strap tension activities of lying down. The overall goals were to develop a novel fastening device, or controlled tension unit (CTU), for a scoliosis brace that allowed the user to set the strap tension to the prescribed value as determined by the orthotist at the time of brace fitting and to maintain the prescribed strap tension during a variety of typical daily living activities. This device should ensure the corrective force capacity of the scoliosis brace was present and the occurrence of strap loosening and tension loss was minimized. In the end, three studies were carried out to design and validate the CTU devices. For Study One, the objective was to determine the force-displacement properties of the controlled tension devices alone. The materials used were: Controlled Tension Units (CTU), Robotic Testing Platform. The methods were as follows: The controlled tension units were mounted in a robotic testing platform that was programmed to displace the CTU device at a set speed (or rate of spring displacement) and measure the force response of the device. Three different speeds and spring tensions were tested. The results were as follows: The CTU were designed with desired load settings of 20N, 30N, and 40N which were confirmed. The units applied a relatively constant tension over a working range of 12.7mm and maintained a load tolerance within ±10%. The force output response and load tolerances were independent of the rate of spring displacement. In conclusion, CTU devices could be fabricated with selectable load settings that held a relatively constant tension throughout a desired range of displacement. For Study Two, the first objective was to validate that the CTU force output was maintained over a finite amount of brace gap opening and closing (as it related to the brace gap separation). The second objective was to evaluate the corrective force capacity and structural stiffness properties of a standard 3-strap brace using either Velcro straps or CTU devices as the fastening system. The materials used were: Controlled Tension Units, Standard (Velcro Strap) Brace, Standard (CTU) Brace, Robotic Testing Platform, Scoliosis Analog Model (SAM), Lab Tensiometers. The methods were as follows: Three brace configurations were tested: Native Standard Brace, Standard (CTU) Brace, and Standard (Velcro Strap) Brace. A low tension CTU (≈20N) was used for all tests. Throughout the movement, the reaction forces and strap tensions in the craniocaudal and mediolateral axes were continuously recorded. The results were as follows: The CTU devices provided a greater range of brace gap displacement compared to the Velcro straps. For the CTU devices, the strap tension was constant over the range of displacement and remained close to the tension value of the CTU device (approximately 20N). However, the tensiometer readings were significantly greater with the Velcro straps being greatest at the top strap and lowest at the bottom. In conclusion, CTU devices could be used to develop a more flexible dynamic brace that allowed for directional movement without compromising the corrective force capacity of the brace. Contrary to the Velcro straps, the CTU strap tension setting would remain present independent of the brace gap allowing for opportunities of deep breathing, increased range of movement, and/or improved brace force correction. For Study Three, the objective was to determine if CTU reduced discomfort while maintaining a constant strap tension. The materials used were: Standard (Velcro Strap) Brace, Standard (CTU) Brace, Portable Tensiometers. The methods were as follows: The discomfort, strap tension, and gap distance were evaluated during typical daily activities as well as the range of motion where applicable using the Standard (Velcro Strap) Brace and the Standard (CTU) Brace. Afterwards, a CTU Increase Test was performed in which the tension in each CTU fastener was incrementally increased until the patient experienced a greater level of discomfort than with the Velcro strap condition at the prescribed tension. In conclusion, CTU improved bracing in scoliosis by maintaining strap tension, improving brace flexibility, decreasing discomfort at similar strap tensions, or by achieving higher strap tensions without increasing discomfort. In conclusion, the CTU devices allowed the user to set the strap tension to the prescribed value as determined by the orthotist at the time of brace fitting and maintained the prescribed strap tension during a variety of typical daily living activities to ensure the corrective force capacity of the scoliosis brace was present and the occurrence of strap loosening and tension loss was minimized.