Question: Jamie is a 53-year-old male, who is 175cm tall, weighs 100kg, and has a waist circumference of 98cm. He lives in Queensland, and travels to work each day to the office where he works as a regional manager within a manufacturing organisation. Jamie experiences constant soreness and stiffness in his left knee, and it sometimes feels like it might 'give way'. Jamie blames an old knee injury, which he says ended his rugby career; it transpires that Jamie suffered tears to his meniscus and anterior cruciate ligament at age 45.
In attempt to manage his knee-pain, Jamie has been prescribed pain medication that contains codeine, known as Panadeine Forte. Medication that contains codeine has a potential risk of constipation. Remember that the focus of this question is on anatomy and physiology, and not specifically on details of the medication. Focus on Jamie's potential constipation. Where appropriate, consider all elements of Jamie's case when answering this question.