title: Neuroforaminal chondrocyte metaplasia and clustering associated with recombinant bone morphogenetic protein-2 usage in transforaminal lumbar interbody fusion.
abstract: BACKGROUND
  Recombinant human bone morphogenetic protein-2 (rhBMP-2) is commonly used to augment posterior and interbody spinal fusion techniques and has many reported side effects. Neuroforaminal heterotopic ossification (HO) is a known cause of postoperative leg pain, but the pathohistologic composition of this material is not well understood.
  
  
  OBJECTIVE
  The purpose of this article was to report the histologic composition of a case of HO and lumbar radiculopathy after transforaminal lumbar interbody fusion with rhBMP-2.
  
  
  METHODS
  This is a case report.
  
  
  METHODS
  This is a single patient case report.
  
  
  METHODS
  The outcomes considered were physician-recorded clinical, physiological, and functional measures.
  
  
  METHODS
  A retrospective review of a single patient was performed. Clinical, radiographic, and pathologic specimens were reviewed and are reported.
  
  
  RESULTS
  A 69-year-old woman presented with low back pain and right leg radicular pain associated with L4-L5 stenosis and a recurrent facet cyst. After attempted nonsurgical care, she underwent an L4-L5 revision decompression with interbody and posterolateral fusions including off-label rhBMP-2. Postoperatively, her symptoms resolved for approximately 7 months but then returned in association with right L4-L5 foraminal HO. The ectopic tissue was notably larger than suggested by preoperative computed tomographic scan. It was decompressed, which then improved her symptoms. Histologic examination of the specimen revealed three discrete tissue types: a nonspecific fibrovascular stroma; immature osteoid and woven bone; and chondrocyte metaplasia with chondrocyte clustering.
  
  
  CONCLUSIONS
  Neuroforaminal HO formation is a reported side effect associated with the off-label use of rhBMP-2 for posterior lumbar interbody fusion. The mechanism of formation and the composition of this material are not well understood but may involve a chondrocyte differentiation pathway.
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Christensen
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA.
authors.forename: Prokopis
authors.initials: P
authors.lastname: Annis
authors.affiliation: Department of Orthopaedics, University of Utah, 590 Wakara Way, Salt Lake City, UT 84108, USA.
authors.forename: Justin B
authors.initials: JB
authors.lastname: Hohl
authors.affiliation: Department of Orthopaedic Surgery, Northwestern University School of Medicine, 676 N St Clair St, Suite 1350, Chicago, IL 60611, USA. Electronic address: alpesh.patel@northwestern.edu.
authors.forename: Alpesh A
authors.initials: AA
authors.lastname: Patel
mesh_terms: D000368:Aged; D055396:Bone Morphogenetic Protein 2 / Q000009:adverse effects* / Q000627:therapeutic use; D019902:Chondrocytes / Q000473:pathology*; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000209:etiology / Q000473:pathology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008679:Metaplasia / Q000139:chemically induced / Q000473:pathology; D056687:Off-Label Use; D009999:Ossification, Heterotopic / Q000139:chemically induced* / Q000473:pathology; D011994:Recombinant Proteins / Q000009:adverse effects / Q000627:therapeutic use; D012008:Recurrence; D013123:Spinal Fusion / Q000009:adverse effects* / Q000379:methods; D016212:Transforming Growth Factor beta / Q000009:adverse effects* / Q000627:therapeutic use
chemical_list: D055396:Bone Morphogenetic Protein 2; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2
keywords: BMP-2; Chondrocyte metaplasia; Complication; Heterotopic bone; Radiculopathy; TLIF