chool hallways are filled with backpacks adorned with familiar cartoon faces, dangling clips and designer logos. But hidden beneath the popular characters and trendy colors is a health problem that has become a burden on school kids across the nation.

Designed to distribute the weight of the load across some of the body’s strongest muscles, backpacks, when used correctly, can be a good way for your child to carry the necessities of the school day. But improperly used backpacks may injure your child’s muscles and joints, leading to severe back, neck and shoulder pain, as well as posture problems.

More than 21,000 backpack-related injuries are treated at hospital emergency rooms, doctors’ offices and clinics each year.

“Despite their potential problems, backpacks are an excellent tool for students when used properly,” says Dr. Sue Hubbard, a pediatrician on the medical staff at Children’s and assistant clinical professor of pediatrics at UT Southwestern. “Prior to purchase, parents should consider the bag’s construction and functionality more than its appearance or popularity.” Here are some tips to help you take a proactive approach to backpack safety:

• Urge your child to tell you about pain or discomfort that may be caused by a heavy backpack.
• Talk to the school about lightening the load.
• Make sure the school allows students to stop at their lockers throughout the day.
• Consider buying a second set of textbooks for your student to keep at home.

According to the American Academy of Pediatrics, parents should consider the following when selecting a backpack for their child:

• Wide, padded shoulder straps — Narrow straps can dig into shoulders. This can cause pain and restrict circulation.
• Two shoulder straps — Backpacks with one shoulder strap that runs across the body cannot distribute weight evenly.
• Padded back — A padded back protects against sharp edges on objects inside the pack and increases comfort.
• Waist strap — A waist strap can distribute the weight of a heavy load more evenly.
• Lightweight backpack — The backpack itself should not add much weight to the load.
• Rolling backpack — This type of backpack may be a good choice for students who must tote a heavy load. Remember that rolling backpacks still must be carried up stairs.

Students should follow these guidelines to prevent injury:

• Always use both shoulder straps — Slinging a backpack over one shoulder can strain muscles and may increase curvature of the spine.
• Tighten the straps so that the pack is close to the body — The straps should hold the pack two inches above the waist.
• Pack light — The backpack should never weigh more than 10 to 20 percent of total body weight.
• Organize the backpack — Pack heavier items closest to the center of the back, and use all of the bag’s compartments to evenly distribute the weight.
• Use lockers — Stop often at school lockers if possible, and do not carry all of the books needed for the day.
• Bend using both knees — Do not bend over at the waist when wearing or lifting a heavy backpack.
• Exercise — Strengthen the muscles used to carry the backpack. Ask your pediatrician for advice.

• Change in posture when wearing the backpack.
• Struggling when putting on or removing the backpack.
• Pain when wearing the backpack.
• Shoulder numbness or red marks.