Knees are among the most used body parts in physically demanding professions or jobs that have workers perform repetitive actions. As a result they are exposed to more pressure than they normally would. For instance, you may not think it but operating a motor vehicle, particularly one that transports passengers or cargo over a long distance day in and day out can put strain a lot of strain on the knees.
As an employer, it is in your best interest to keep your workers in good health. Since knee injuries can happen at the workplace from time to time, the best way to do this is through avoiding them altogether through precautions like a DOT physical. After all, prevention is better than cure.