On Dec. 16, 2010, plaintiff Nathan Barker, 30, a milk delivery man visiting from Australia, was a front seat passenger in a 2001 Ford Explorer traveling on North Fairfax Avenue in Los Angeles. At approximately 6:30 p.m., while stopped for a red light at the intersection with Santa Monica Boulevard, the sport utility vehicle was rear-ended by a 2003 Mercedes C230 Coupe operated by Roxanna Aminirad. Barker claimed an injury to his lower back. Barker sued Roxanna Aminirad and the registered owner of the Mercedes, Mohsen Aminirad. Barker alleged that Roxanna Aminirad was negligent in her operation of the vehicle and that Mohsen Aminirad was vicariously liable for his daughter’s actions. Roxanna Aminirad admitted liability for the accident, and Mohsen Aminirad was dismissed from the action. The matter then proceeded to a trial on causation and damages., Barker was taken by ambulance to an emergency room with complaints of mild pain and instability in his lower back. He underwent X-rays (which were negative), was given ibuprofen for his sore back, and was released. Upon returning to Australia, Barker underwent roughly eight sessions of physical therapy and chiropractic care. In February 2011, Barker returned to the United States to study and was examined by an orthopedist in New Jersey for lower back pain. An MRI was recommended, which he underwent in Los Angeles in February 2011, and a 3- to 4-millimeter posterior disc herniation at L5-S1 was revealed. Barker did not treat again until November 2011, when he had an orthopedic evaluation. He then followed up with more physical therapy in Australia in March 2012, had three epidural injections in Los Angeles in April 2012, had a spine surgeon evaluation in August 2012, and underwent more physical therapy (six visits) starting in June 2013. In March 2014, Barker was re-examined due to ongoing pain and discomfort complaints, and he was recommended fusion surgery at L5-S1. Barker claimed his residual lower back pain and discomfort has restricted several physical activities/hobbies, including white water rafting, rugby, tennis, hiking, and biking. Thus, he sought recovery of $27,734.90 in past medical costs, $160,000 to $180,000 in future medical costs for the fusion surgery, and another $160,000 to $180,000 in future medical costs for a revision surgery in 20 years due to adjacent segment disease. Barker also sought recovery of $4.1 million to $4.8 million in damages for his past and future pain and suffering, which he alleged would continue for a life span of 43.6 years. Defense counsel argued that the accident only exacerbated a pre-existing lower back injury, which Barker suffered in 2001 due to his strenuous delivery job. Counsel contended that Barker received treatment for the prior injury from 2001 until 2003, and that Barker suffered no new injury from the subject accident. Defense counsel further argued that Barker’s treatment had been inconsistent. The defense’s biomechanical expert opined that the forces of the impact were insufficient and were less than what one would experience from riding a bumper car. However, the defense’s biomechanical expert was prohibited from testifying as to any potential mechanism of injury or lack thereof, to the forces required to injure a disc, or to the causation or lack of causation of Baker’s injury., and underwent more physical therapy (six visits) starting in June 2013. In March 2014, Barker was re-examined due to ongoing pain and discomfort complaints, and he was recommended fusion surgery at L5-S1. Barker claimed his residual lower back pain and discomfort has restricted several physical activities/hobbies, including white water rafting, rugby, tennis, hiking, and biking. Thus, he sought recovery of $27,734.90 in past medical costs, $160,000 to $180,000 in future medical costs for the fusion surgery, and another $160,000 to $180,000 in future medical costs for a revision surgery in 20 years due to adjacent segment disease. Barker also sought recovery of $4.1 million to $4.8 million in damages for his past and future pain and suffering, which he alleged would continue for a life span of 43.6 years. Defense counsel argued that the accident only exacerbated a pre-existing lower back injury, which Barker suffered in 2001 due to his strenuous delivery job. Counsel contended that Barker received treatment for the prior injury from 2001 until 2003, and that Barker suffered no new injury from the subject accident. Defense counsel further argued that Barker’s treatment had been inconsistent. The defense’s biomechanical expert opined that the forces of the impact were insufficient and were less than what one would experience from riding a bumper car. However, the defense’s biomechanical expert was prohibited from testifying as to any potential mechanism of injury or lack thereof, to the forces required to injure a disc, or to the causation or lack of causation of Baker’s injury.