Foreign body reaction to hydroxyapatite after anterior cervical discectomy with fusion

Abstract

Dear Editor, The surgical management of cervical disc herniation has greatly evolved over the last century. Shortly after the anterior cervical approach and fusion with a horseshoe bone graft [5], the interbody fusion using autologous iliac bone was described [2], and recent studies have highlighted the morbidity associated with these autografts [3, 8, 9], mainly donor site morbidity and limited supply. Consequently, the use of allograft or synthetic materials for fusion has been increasing. Nevertheless, the fusion rates are similar for the three methods, with synthetic materials averting the pain of autograft bone sourcing and being less expensive than allograft bone use [1, 7]. We are reporting an unexpected complication following the use of phosphocalcic hydroxylapatite after anterior cervical discectomy with fusion. A 68-year-old man with type 2 diabetes mellitus, came to the out–patient clinic of our department complaining of decreased strength on the right limbs. He presented with a right hemiparesis (grade 2) and hemihyposthesia, with ipsilateral gait disturbance; no changes in muscle stretch reflexes were elicited and the Babinsky sign was present on the right side only. The cervical spine MRI revealed right paramedian C4-C5 cervical disc extrusion, with upward and downward migration, and compression of the spine cord. The patient was submitted to surgery: anterior cervical C4-C5 discectomy; fusion with cage filled with autologous bone and hydroxyapatite, and fixation with an anterior plate (over C4 and C5). He recovered motor function, being discharged 48 h later with grade 4 muscle strength and the ability to use the right hand in activities of daily living. However, he was readmitted at 15 days postoperatively with a paraparesis and paraesthesias in both forearms and hands. The MRI showed spinal cord compression at C4-C5 and upward migration of the cage into the C4 vertebral body. He was reoperated and the anterior plate and screws were removed. We did a C4 corpectomy, dissection and excision of epidural tissue and fusion with mesh filled with autologous bone and anterior plate between C3 and C5, with fixed screws over both vertebral bodies. The epidural tissue was sent for microbiology and for histopathology analysis. The patient was treated empirically with a high dose of flucloxacilin for an eventual empyema, and was discharged with partial recovery of autonomous gait with orthosthasis, and no paraesthesies. The microbiological evaluation was negative but neuropathology revealed a foreign body reaction with calcium-positive material surrounded by giant-multinucleated cells (Fig. 1). The patient was followed in the immunoallergy out-patient clinic in order to test hypersensivity to hydroxyapatite, which was negative. At 4 weeks after reoperation, the patient showed a J. P. Lavrador : S. Livraghi Department of Neurosurgery, Hospital de Santa Maria, CHLN, Lisbon, Portugal