Chen and Chmell Journal of Medical Case Reports 2011, 5:453 http://www.jmedicalcasereports.com/content/5/1/453 C A S E R E P O R T JOURNAL OF MEDICAL CASE REPORTS Open Access Heterotopic ossification after patellar tendon repair in a man with trisomy 8 mosaicism: a case report and literature review Austin Chen* and Samuel Chmell Abstract Introduction: Heterotopic ossification is the abnormal formation of lamellar bone in soft tissue. Its presence jeopardizes functional outcome, impairs rehabilitation and increases costs due to subsequent surgical interventions. Case presentation: We present a case of a 32-year-old African-American man with trisomy 8 mosaicism who developed severe heterotopic ossification of his right extensor mechanism subsequent to repair of a patellar tendon rupture. Conclusion: To the best of our knowledge there are no prior reports of heterotopic ossification as a complication of patellar tendon repair. This case may suggest an association between trisomy 8 mosaicism and increased risk of heterotopic ossification. Introduction Heterotopic ossification (HO) is most commonly asso- ciated with musculoskeletal trauma, central nervous sys- tem disorders or injuries, severe burns, and elective surgery such as total hip arthroplasty [1]. The clinical signs of HO include increased joint stiffness, limited range of motion, warmth, swelling and erythema. Although its etiology is still unclear, important contri- buting factors include hypercalcemia, tissue hypoxia, alterations in sympathetic nerve activity, prolonged immobilization and imbalance between parathyroid hor- mone and calcitonin [2]. The overexpression of bone morphogenetic proteins (BMPs), among other systemic and local factors, also appears to play an important role in the pathophysiology of HO [2]. HO occurs in 3-90% of lower limb joint replacement cases, though only 3-7% is clinically significant based on the Brooker Classifica- tion of HO (Grades 3 and 4) [3,4]. HO can also be her- editary; similar to fibrodysplasia ossificans progressiva, progressive osseous heteroplasia, and Albright’s heredi- tary osteodystrophy [3]. Complete somatic trisomy 8 is rarely compatible with life and often results in miscarriage [5]. Trisomy 8 * Correspondence: achen9@uic.edu Department of Orthopedic Surgery, University of Illinois at Chicago, 835 S Wolcott Avenue, M/C 844 Chicago, IL 60612, USA mosaicism (T8M), on the other hand, is a form of tris- omy 8 in which some of the body’s cells have three copies of chromosome 8 while other cells still possess the normal two copies. T8M is an uncommon diagnosis affecting only one in every 25,000-50,000 live births. The timing and particular cell lineages in which nondis- junction occurs determine which tissues and cells are affected. Therefore, T8M can present with a wide range of clinical manifestations and extremely variable pheno- type [6]. Some of the common musculoskeletal features of T8M include joint contractures, long and narrow thorax with wide sloping ribs, hypoplastic glenoid cav- ities, symmetrical widening of the clavicles, abnormal sternum, narrow pelvis and hip dysplasia [5-8]. Case presentation Our patient is a 32-year-old African-American man with a history of T8M syndrome documented by chro- mosomal analyses at an outside hospital. His syndrome is characterized by dysmorphic facial features including saddle nose deformity and a large forehead as well as mild mental retardation. He presented to our clinic with complaints of right knee pain and inability to completely extend his right knee after injuring it sev- eral months ago. On examination of his right knee he was able to achieve full extension passively but was © 2011 Chen and Chmell; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.