The 10 causes of the most serious workplace accidents cost employers more than $58 billion in annual medical costs and lost wage payments, according to the latest Liberty Mutual Workplace Safety Index.

Of those, the top five injury causes account for 68.9% of the total cost burden, totaling $40 billion, according to the index. The index also found that U.S. businesses spend more than $1 billion dollars a week on serious, nonfatal workplace injuries.

The Liberty Mutual Workplace Safety Index is based on information from Liberty Mutual, the U.S. Bureau of Labor Statistics and the National Academy of Social Insurance. Injury data is analyzed to determine which events caused employees to miss more than five days of work. The index then ranks those events by total workers compensation costs, which include medical and lost-wage payments.

Overexertion involving outside sources, such as handling objects, continues to rank first among the leading causes of disabling injuries. This category includes injuries related to lifting, pushing, pulling, holding, carrying or throwing objects. Overexertion costs businesses $13.30 billion in direct costs and accounts for 22.7% of the overall national burden.

“Falls on same level" ranks second, with direct costs of $10.58 billion, and accounts for 18.1% of the total injury burden while “falls to a lower level" ranks third at $6.26 billion and 10.7% of the burden.

Being hit by objects ranks fourth at $5.61 billion and accounts for 9.6% while other exertions or bodily reactions, which include bending, reaching, twisting, climbing, crawling, kneeling, sitting, standing, walking, and running, rank fifth at $4.71 billion and 8% of the total injury burden.

The remaining injury causes ranked 6 to 10 on the list account for 20.1% of the total direct cost of disabling injuries. These injury causes include roadway incidents involving motorized land vehicles, slips or trips without falling, struck against object or equipment, caught in or compressed by equipment or objects and repetitive motions involving microtasks.

“Understanding the top risks in the workplace is the first step in better protecting employees and the bottom line," says Jamie Merendino, Liberty Mutual general manager, risk control services. “The Liberty Mutual Workplace Safety Index gives companies a critical starting point, letting them partner with insurers, brokers and agents to understand what causes their most serious injuries and what can be done to improve workplace safety."

Will Jones is IA editor-in-chief.