What is implied in the following lines: "Quackenbush was studying me to to see if he could detect a limp. But I knew that [he] would never detect my trouble"?

Gene's guilt over Finny was so great that he felt he should manifest some pain. He wanted to distance himself from Quakenbush and draw in closer with Finny and his pain. Having an injury, real or imaginary, somehow appeased his guilt over Finny.