An instrument for inducing continuous passive motion after fracture of the tibial plateau in rabbits

Abstract

Objective To design and develop intelligent rehabilitation equipment for administering continuous passive motion (CPM) of a rabbit′s knee joint after tibial plateau fracture. Methods The equipment constructed had three main parts: the core machinery, electronic control and a control program designed based on bionics principles. Twenty six-month-old New Zealand White male rabbits were randomly divided into sedentary (SED) and CPM groups after their knees had been fractured. The rabbits in the CPM group were given 30 min of early joint rehabilitation once a day for 4 weeks using the CPM equipment, while those in the SED group were kept in their cages and allowed free activity without any special exercise program. The body weight, range of motion and swelling of the affected knee joint were measured before the fracture and on the 3rd, 7th, 14th, 21st and 28th days after the fracture. On the 28th day after the fracture the pathological structure of the articular cartilage on the operative side was observed under a light microscope. Results The equipment ran safely and reliably, and drove the rabbits to move synchronously. It could accurately and conveniently adjust the knee flexion angle, movement speed and movement time. The intelligence of the equipment met the experimental requirements. On the 3rd day after the operation the average range of motion in the joints of both groups had changed significantly compared to that before the fracture. On the 28th day after the fracture the average degree of swelling and range of motion in the CPM group were significantly different from those of the SED group. On the 28th day, deformity and the smoothness of the fracture line in the CPM group were superior to those in the SED group. Moreover, the dominant tissues in the defect area of the CPM group were mainly hyaline cartilage while those in the SED group were mainly repair fibrocartilage. The defect area and its adjacent articular cartilages, chondrocyte regeneration and arrangement, layers of cells and subchondral tidal line recovery of the CPM group were better than in the SED group on average. Conclusion The equipment for knee joint manipulation is convenient to use, reliable and effective for the early rehabilitation of tibial plateau fracture, at least in rabbits. It promotes remodeling of the fracture and cartilage repair after tibial plateau fracture, and also improves range of motion in the knee and reduces swelling. Key words: Passive motion; Tibial plateau fracture; Rehabilitation equipment