There are a variety of complications the stem from trauma. First of all, there is an increased risk for a blood clot (known as a deep venous thrombosis). This can present in an area of hardness - sometimes described as a "cord" on the back of the leg. An ultrasound can be done to evaluate this.
If the area is hot, the an infection of the skin is a possibility. If this is the case, then antibiotics should be considered.
If those two diseases have been ruled out, the certainly scar tissue can present as hardened skin.
In any case, I would suggest having a physician evaluate the area because of the possibility of a blood clot or infection.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.