Introduction and importanceColorectal cancer rarely metastasizes to the bones, and if so, metastasis usually occurs in the axial skeleton. We encountered a rare case of a metastatic lesion to the right ulna arising from colonic adenocarcinoma that was treated by resection of the proximal ulna and radial neck-to-humerus trochlea transposition to salvage the limb.Case presentationA 60-year-old man previously diagnosed with colonic adenocarcinoma presented with a single bony metastatic lesion in the right proximal ulna and was referred to our clinic for assessment. After five sessions of systemic therapy, the lesion continued to grow, causing diffuse swelling and loss of elbow range of motion. Local x-rays revealed extensive destruction of the proximal ulna and soft tissue component, with subluxation of the radial head. Magnetic resonance imaging showed an extensive lesion involving the proximal half of the ulna and a large soft tissue component. After restaging, only this metastatic lesion was found. Amputation was offered to the patient for wide margin resection, but the patient refused; therefore, we performed resection of the proximal ulna, debulking of soft tissue, and radial neck-to-humerus trochlea transposition to salvage the limb.Clinical discussionDue to the rarity of the location, no clinical standard exists regarding the surgical treatment. Radial neck-to-humerus trochlea transposition is a valid surgical reconstruction technique to salvage the limb and preserve the hand function.ConclusionRadial neck-to-humerus trochlea transposition is an alternative elbow reconstruction technique after proximal ulna resection in cases where other options are not ideal or contraindicated. Long-term studies are recommended to assess different surgical options for treating and reconstructing proximal ulnar tumors.