Psychologist Kimberley Wilson and Dr Xand van Tulleken continue their journey around the human body, asking what our insides can reveal about our lives and the world around us. The knee is one of the most complicated joints in the human body, but also one of the most prone to failure. In this episode, Kimberly shares the story of someone with a rare genetic disorder that results in poorly developed kneecaps, while drilling into the gory detail of knee replacements. Later, Xand explores osteoarthritis and the exciting research that could change how we think about joint injury. Producer: James Tindale Researcher: Leonie Thomas Executive Producer: Robert Nicholson A Whistledown production for BBC Radio 4