Many back injured patients become depressed. Some would say that most become depressed. However, very few seek treatment for their depression.
Even if they were depressed prior to injury, and, again, there are data to support that pre-existing depression increases the risk of injury, there is a responsibility for treating the exacerbation of the depression caused by the injury. Once again, few of these patients would want/accept care even if offered especially if mental health care is not sanctioned by their family/community.
When in pain, the individual sleeps poorly, concentration is impaired, they eat out of boredom, they are irritable and very little of life is enjoyable to them. Anti-depressants have become an effective way of helping patients cope with pain.
Often antidepressants are sufficiently therapeutic that the patient can taper his/her narcotic pain medication (which itself can trigger depression).
Thus, antidepressants can be a very cost effective way of dealing with the painful residuals of work-injury.