Design and development of an improved intramedullary telescopic implant for osteogenesis imperfecta patients

Abstract

Osteogenesis Imperfecta (OI) or “brittle bone disease” is a group of genetic disorders, caused by the collagen deficiency in connective tissues. The collagen deficiency in bones results in low bone mass and reduced bone strength, leading to bone deformity and susceptibility to fractures. Although it has been classified as a rare disease, still it is the most common disorder in bone etiology. OI has a prevalence of 1/10,000 to 1/20,000 and varies geographically. Unfortunately, an effective cure to the disorder is still not found. Strengthening of bone through external means, therefore, is a common way to prevent fracture. The most popular method is to insert an intramedullary implant (in particular, a telescoping nail as most of the patients are children). However, it is observed that standard implants often fail due to factors such as overloading, loss of fixation, stress fractures and lack of rotational stiffness. The failure of implant leads to additional surgical procedure for the patient. Moreover, replacement of implant and treatment expenses are also a financial burden on the family. Hence, the current work focuses on the development of an economical and improved subject-specific implant. As there is very little data and knowledge in the existing literature about the physiological loading on the long bones of lower limb for type IV OI patients. Clinical gait analysis was performed to investigate the variations in spatio-temporal, kinematics, and kinetic data obtained from type IV OI subjects and age-matched healthy subjects. Results showed the velocity, stride length, and step length were significantly short for OI subjects compared to age-matched healthy subjects. The kinematic data showed the variations of ankle, knee and hip angles throughout the gait cycle. Similarly, kinetic data revealed the variation of ground reaction forces, joint forces and moments, and ankle push-off power for both OI and age-matched healthy subjects. Musculoskeletal modeling was performed using OpenSim, to calculate the muscle forces acting on the femoral bone. The subject-specific data from clinical gait analysis was used as an input for the musculoskeletal modeling. Based on the knowledge of physiological loadings, a recipe for the development of an improved subject-specific implant was proposed, which may overcome the issues such as overloading and rotational instability. In addition, possible manufacturing processes have been suggested, and cost-effectiveness is compared. A hybrid manufacturing process is proposed which may reduce the cost of a subject-specific implant. In summary, these findings proposed a new method of fracture risk assessment and management of fracture in OI bone due to its fragile nature. This work also proposed a simplified method for the calculation of loading acting on the long bones of the lower limb, which can be utilized for the design of an implant. The proposed hybrid manufacturing process results in the economical subject-specific implant for enhancing the quality of life for these patients.