Effects of social isolation associated with the COVID-19 pandemic on hip muscle strength, hip joint pain, and walking ability in patients with osteoarthritis of the hip joint

•Social isolation adversely affected patients with severe hip OA.•During the pandemic, SLR strength decreased in 25% of patients with severe hip OA.•More patients in the severe-OA group had increased hip joint pain.•Walkable distance decreased in more patients in the severe-OA group.•Fewer patients who received THA had decreased walking ability. To reduce the spread of the Sars-CoV-2 virus, governments in many countries adopted a social isolation strategy. However, social isolation may adversely affect people's health, e.g., by decreasing the muscle function of lower limbs. We recruited 118 patients who had undergone total hip arthroplasty (THA) and 87 patients with moderate to severe hip joint osteoarthritis (OA) and measured hip muscle strength, hip joint pain, and walking ability from before to one year after the start of the COVID-19 pandemic. During the pandemic, hip flexion (straight leg raise, SLR) strength decreased in 13.1% of patients in the post-THA group and 25.6% in the severe-OA group; in the severe-OA group, the decrease in SLR strength was mainly in patients aged 65 years and older. In addition, pain increased to mild or moderate and walkable distance decreased in more patients in the severe-OA group.