Many hens will suffer from salpingitis which cause lash egg material to form inside the abdomen. Cancer is also common. Those can put pressure on the leg nerves causing lameness. When they still are walking, some develop a walk like a penguin, or prefer to sit a lot. I had a hen last year who stopped being able to stand without falling for about 5 weeks. She recovered, but a year later she died of salpingitis and cancer, and I found large masses in her lower abdomen.