## 1 Introduction  
The hip joint is one of the largest weight-bearing joints in the body and is commonly affected by arthritis after the knee joint. Among hip arthritis, degenerative osteoarthritis is the most common form of arthritis. It can occur when the joint is deformed or damaged due to congenital or acquired disease or trauma or when it appears with age without a specific cause. The global incidence rate of hip osteoarthritis (OA) has increased from 740,000 to 1.58 million between 1990 and 2019. This trend is likely to continue due to the rapid aging of the world population, increased lifespan, and prevalence of arthritis and obesity [1]. Thus, the importance of early treatment and continuous disease management is essential.  
OA in hip joints induces pain in the gait process, thus limiting the range of movement. While pain and weakened muscles cause abnormal gait on the affected side, the non-affected side also shows an abnormal gait caused by compensatory motions in other joints. From these, hip OA patients have a slower gait speed when compared to healthy subjects. The stride length of the affected side is shortened, the stance duration is lengthened, and the swing duration is quickened. When comparing the patient's affected and non-affected sides, the stance duration of the affected side was shorter. Thus, although there is no severe problem in classifying the difference in gait pattern between hip OA patients and healthy subjects, the current methods for evaluation or diagnosis still give patients a high burden.  
When diagnosing such hip OA in general, medical doctors ask the patient about the onset of symptoms, progression pattern, and medical history. Then, they request the patient to walk in various postures along a line to record the gait pattern based on human observation. Existing methods for diagnosing degenerative hip arthritis include the gait in various motions. For example, the squat test can be used to see the patient's ability to squat, and the hip flexion and hip scour tests can be used to test the range of motion of the hip and knee [2]. In addition, the TUG test is an abbreviation of the time up to the test. It is an evaluation that measures exercise ability and static and dynamic balance ability when walking for 6 m [3]. However, according to studies, when comparing affected and non-affected sides, the results of swing duration and step length were inconsistent.  
Patients may have different gait patterns despite the same hip OA. For example, some studies reported the existence of different gait patterns in patients with the same disease for hereditary spastic paraparesis. Furthermore, these existing methods are problematic because they can continuously cause pain during diagnosis. It causes pain continuously, even while examining people with pain. Despite the same patient with hip OA, it is possible to show a different gait pattern according to the pain symptom at that time. That means deciding on the kinematic solution with measured angles and angular velocities seems complicated.  
Suppose hip OA could be diagnosed with only a one-step gait. This would be is excellent for both patients and medical doctors because it would not only reduce the diagnosis time but also decrease the burden on the patient dramatically. Thus, we aimed to propose a method to recognize the abnormality of the hip OA patient with a one-step gait pattern based on a dynamic time warping (DTW) algorithm through three directional ground reaction forces (GRFs).