The information provided here is not a replacement for a doctor. You shouldn't use it for the purpose of self-diagnosing or self-medicating but rather so you can have a more informed discussion with a professional TCM practitioner.
Because it is a herb specifically indicated to treat bone contracture as can be seen on Garden Balsam Stem's page.
Garden Balsam Stems is a Cool herb that tastes Bitter and Pungent. It targets the Spleen, the Kidney and the Liver.
Its main actions are: Invigorates Blood and removes Blood Stagnation. Clear Toxic-Heat, cools the Blood and relieves pain. Drains Damp-Heat. Dispels Wind-Damp and relaxes the muscle and sinews.
Trauma Bruising Swellings Sores Burns Carbuncles Acute jaundice Hepatitis Arthritis Arthralgia