Desmoplastic Fibroma of the Distal Femur in a Young Man: A Rare Case Report Introduction Of all the primary bone tumors, desmoplastic fibroma (DFB) is a relatively rare entity [1, 2]. The reported incidence in literature ranges from 0.06% to 0.3%. DFB is a benign but locally aggressive tumor with border line activity with no site, sex, or age predilection. Like its soft-tissue counterpart, DFB is notorious for its recurrence. One study [2] refers the recurrence rate being as high as 42%. Cortical destruction and soft-tissue spread portend a more aggressive presentation [3]. Treatment varies from aggressive curettage to wide excision during index surgery to amputations or radical excision and distal femoral replacement with prosthesis [4]. Literature review shows that a pre-operative diagnosis of DFB is as a rule never made and therefore appropriateness of surgical excision during the index procedure can always be debated [5]. We report a case of DFB of the distal femur treated by a novel technique using extended curettage, adjuvant phenol application, and bone cement with plate fixation. All laboratory investigations were within normal limits. The core biopsy was non- conclusive. Curetted material from the lesion obtained intraoperatively revealed a mesenchymal neoplasm of the bone, of mild- to-moderate cellularity. It was composed of A 24-year-old young male presented with a history of the left knee and lower thigh pain and swelling for the past 4 months. The pain started acutely, without any history of trauma, and progressed over the past 4 months. For the past month, he was unable to weight bear on the left lower limb, and there were no constitutional symptoms. There was a moderately large and tender swelling present over the lower medial left thigh with painful knee movements. Case Report Clinical presentation Imaging Laboratories and tissue diagnosis On plain radiographs, a large destructive osteolytic lesion involving the distal femur with breakage of the medial cortex was seen (Fig. 1). Magnetic resonance imaging revealed a large heterogeneous altered signal in the lower diaphysis and metaphysis of the distal femur, with an asymmetrical expansion of the involved bone. Case Report: A 24-year-old male presented with swelling around with DFB the left distal femur presented with pain for 4 months which progressed in severity and led to inability to bear weight. On clinical examination, he had a tender discrete swelling over the medial aspect of the left distal femur. Radiographic examination showed an eccentric lytic lesion in the metaphyseoepiphyseal region of the left distal femur. An extended curettage using phenol (10%) as adjuvant therapy was performed. The cavity was packed with bone cement and the distal femur was fixed by spanning the lytic lesion with a distal femoral locking plate. At months follow-up, he reported complete resolution of symptoms, and on examination, he had pain free and full range of motion, without any signs of recurrence. Keywords: Desmoplastic fibroma, benign bone tumors, surgery, knee, femur. Introduction: Lytic lesions in the distal femur in a mature skeleton though a common presentation for various tumors, desmoplastic fibroma (DFB) of bone is a rare occurrence. Review of the literature shows its incidence of 0.06% to 0.3%. In the majority of reported cases, the diagnosis has been obtained on histopathological examination. Treatment varies from aggressive curettage to amputations. We describe a novel surgical technique for dealing such lesions. Conclusion: An effort should be made to obtain a pre-operative histopathological diagnosis of the tumor type. In cases of equivocal findings, a diagnosis of DFB of the bone should be considered. Extended curettage, phenol ablation, and bone cement with plate augmentation offer an effective treatment modality in the treatment of DFB. Abstract Case Report Journal of 2020 September-December; 6(3) Bone and Soft Tissue Tumors : 2-4 | Suresh Babu¹, Abhishek Vaish¹, Raju Vaishya¹ which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) © 2020 by Journal of Bone and Soft Tissue Tumors | Available on www.jbstjournal.com | doi:10.13107/jbst.2020.v06i03.030 Dr. Suresh Babu, E-mail: yssureshbabu@gmail.com 1 Department of Orthopaedics and Joint Replacement Surgery, Indrparastha Apollo Hospitals, New Delhi, India. Address of Correspondence Department of Orthopaedics and Joint Replacement Surgery, Indrparastha Apollo Hospitals, Sarita Vihar, New Delhi - 110 076, India. Dr. Abhishek Vaish Journal of Bone and Soft Tissue Tumors Volume 6 Issue 3 Sep-Dec 2020 Page 2-4 2| | | | | Dr. Raju Vaishya Dr. Suresh Babu