We all know that wearing a backpack for an extended period can be painful but few of us realise that, in admittedly rare cases, a badly fitted pack can have real consequences. A backpack typically rests on our shoulders, with smaller schoolbag sized packs distributing the weight on to the upper trapezius muscles and larger trekking style backpacks using straps to pull tightly around the chest for stability while the weight is transferred to the pelvis via a sacral pad.
For adults it is always advisable to use a trekking style pack for heavier loads, think anything above 15kg, so that the weight is taken by the hips. A school bag should be sufficient for most school sized loads though the weight of text books, laptops, instruments and sports gear can be challenging to carry at some schools. Careful thought should be given as to what is required in each days load out.
Backpack palsy occurs very rarely, but it is a paralysis of the serratus anterior muscle. This muscle extends from the rib cage to the bottom tip of the shoulder blade and keeps the shoulder blade sitting flush against the rib cage. The resulting paralysis and loss of function of the serratus anterior muscle gives us the classic “winged appearance” of backpack palsy as shown in the image below.
This type of paralysis can occur when a backpack overloads our shoulder girdle, causing the shoulder blades to sag down dragging the collarbones with them. The collarbones will then compress the delicate long thoracic nerve against our rib cage and it is this nerve compression which causes the paralysis. It may be accompanied by some pain in the shoulder and may make it difficult for the sufferer to raise their arm above shoulder height but the most prominent sign of backpack palsy is the winging of the shoulder blade.
Interestingly backpack palsy is more common in soldiers than the general population and the Korean army has found that, amongst new recruits, men with lower body mass were more likely to develop a backpack palsy! Presumably a lower body mass correlates with lower muscle mass and these people are less resistant to the drag their loaded packs put on them.
How long function takes to return might vary and there are different treatment approaches available. A surgeon may be able to harvest a small piece of ligament to fix the shoulder blade back against the rib cage so it never moves upwards again however physical therapy is usually required after surgery.
The other treatment option is to go straight to a physical therapist who will generally be able to exercise the muscle back to normalcy over a period of about 8 weeks. In both cases however full recovery will likely take 6 – 12 months and this time period will depend on the degree of initial nerve damage.