OBJECTIVETo analyze the risk factors of heterotopic (HO) ossification after total lumbar disc replacement and probe the preventive strategies for it.

METHODSThe radiographs and clinical data of 78 discs in 65 patients who received artificial lumbar disc replacement (ADR) from April 1998 to December 2003 were analyzed retrospectively by two radiologists and one orthopaedic surgeon and then postoperative HO were graded according to McAfee system. The bony formations in disc spaces, time of HO were found, and range of motion (ROM) of the operated levels were measured on radiographic films. In addition, the risk factors such as preoperative peri-annulus ossification, bony endplates injuries, and subsided or mal-position of the prostheses were also analyzed by Logistic regression analysis.

RESULTSPostoperative HO was found in 10 spaces of 9 cases. Class I of HO were occurred in 7 patients at means 2.1 years postoperatively with normal range of motion preserved. Three of them turned into class II or III with 10 degrees of mean ROM in the following 2.5 years. Another 2 (2/9) cases with preoperative peri-annulus ossification had bridging trabecular bone (class III) between the endplates and 9 degrees of ROM 2 years after surgery, then turned into class IV at 6 years with 0 degrees and 4 degrees of motion in the operated levels. As the risk factors of HO, preoperative annulus ossification (2 cases), bony endplates injuries (5 cases), mal-positioned prostheses (2 cases) and subsided prostheses (2 cases) were found simultaneity with significant positive relation to HO occurred (P < 0.05).

CONCLUSIONSFactors such as preoperative ossification of annulus, endplate injuries, prosthesis subsided and mal-position would have higher risks to have HO occurred after ADR, but ROM of most affected levels are preserved. Strict control indication and avoid all above risk factors can prevent HO occurring effectively.