In this case report, we describe a rare clinical situation of acute arterial thoracic outlet syndrome (TOS) after osteosynthesis, using an intramedullary Knowles pin, to treat nonunion of a midshaft clavicular fracture.
Postoperative radiographs revealed malpositioning of the Knowles pin [Figure 2]b, with intimal dissection of the left subclavian artery and high-grade stenosis  evident on computed tomography angiography [Figure 3].
8],, In our case, acute arterial TOS developed following revision osteosynthesis using an intramedullary Knowles pin and caused acute limb ischemia requiring immediate thrombolysis.
reported a case of clavicular nonunion complicated with venous and neurogenic TOS, in which bone union was achieved by revision osteosynthesis using a Knowles pin and an autogenous bone marrow graft.
To our knowledge, this is the first case to describe TOS as a complication of intramedullary fixation with a Knowles pin for nonunion of a clavicular fracture.
More recently Chu and associates reported on the healing of 77 of 78 clavicle fractures treated with a Knowles pin.
The technique is variable and may involve the use of K-wires, threaded screws, Knowles pins, Hagie pins, or elastic titanium nails.