I run into that term often, mine refers to upper extremities. We code what caused the "double crush" - usually a nerve compression. So, without seeing your MD's note I couldn't say, but maybe the article below will be helpful:
J Am Acad Orthop Surg. 2015 Sep;23(9):558-62. doi: 10.5435/JAAOS-D-14-00176.
Double Crush Syndrome.
Kane PM, Daniels AH, Akelman E.
Abstract
Double crush syndrome is a distinct compression at two or more locations along the course of a peripheral nerve that can coexist and synergistically increase symptom intensity. In addition, dissatisfaction after treatment at one site may be the result of persistent pathology at another site along a peripheral nerve. Double crush syndrome is a controversial diagnosis; some scientists and surgeons believe it is an illness construction that may do more harm than good because it emphasizes an objective pathophysiologic explanation for unexplained symptoms, disability, and dissatisfaction that may be more psychosocially mediated. However, peripheral neuropathy may coexist with compressive neuropathy and contribute to suboptimal outcomes following nerve decompression. To better manage patients' expectations, treating practitioners should be aware of the possibility of concomitant cervical radiculopathy and carpal tunnel syndrome, as well as the presence of underlying systemic neuropathy.