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Prevalence of Heterotopic Ossification Following Total Disc ReplacementA Prospective, Randomized Study of Two Hundred and Seventy-six Patients
P. Justin Tortolani, MD1; Bryan W. Cunningham2; MMech Eng2; Paul C. McAfee, MD1; Gwen A. Holsapple, BS2; Karen A. Adams, BS2
1 Scoliosis and Spine Center of Maryland, O'Dea Medical Arts Building, 7506 Osler Drive, Suite 104, Baltimore, MD 21204
2 Orthopaedic Research Laboratory, Union Memorial Hospital, 201 East University Parkway, Suite 781, Baltimore, MD 21218
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Disclosure: In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from DePuy Spine. In addition, one or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (DePuy Spine). Also, a commercial entity (DePuy Spine and the Orthopedic Spinal Research Fund) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at Scoliosis and Spine Center of Maryland, St. Joseph Medical Center, and the Orthopaedic Research Laboratory, Union Memorial Hospital, Baltimore, Maryland

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2007 Jan 01;89(1):82-88. doi: 10.2106/JBJS.F.00432
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Background: Despite reports of good clinical outcomes in patients treated with lumbar and cervical disc replacements, varying degrees of heterotopic bone have been observed around these devices. The purposes of the present study were to determine the prevalence of heterotopic ossification following lumbar disc replacement and to investigate whether heterotopic ossification results in loss of motion or negatively affects clinical outcome.

Methods: All preoperative and postoperative radiographs from a completed prospective, randomized, United States Food and Drug Administration-regulated trial comparing replacement with the CHARITÉ Artificial Disc with anterior interbody arthrodesis were analyzed. In each of 276 patients treated with disc replacement, heterotopic ossification was categorized with use of a validated 5-point radiographic classification system both preoperatively and at all protocol-specified follow-up intervals to two years. The range of motion on flexion and extension radiographs made preoperatively was compared with that on radiographs made two years postoperatively, and the motion was correlated with the presence or absence of heterotopic ossification. Similarly, validated clinical outcome measures were correlated with the presence or absence of heterotopic ossification at two years.

Results: The prevalence of heterotopic ossification in the 276 consecutive patients treated with lumbar disc replacement with the CHARITÉ Artificial Disc was 4.3%. There were four cases of Class-I heterotopic ossification and eight cases of Class-II heterotopic ossification. In five of the twelve patients, heterotopic bone was visible as early as six weeks postoperatively, and eleven of the twelve patients had evidence of heterotopic ossification by three months postoperatively. The postoperative range of motion exceeded the preoperative range in all of the patients with heterotopic ossification. With the numbers available, no difference in either the range of motion or the clinical outcome at twenty-four months postoperatively was found between the patients who had and those who did not have heterotopic ossification.

Conclusions: Heterotopic ossification is infrequent in patients treated with the CHARITÉ Artificial Disc, and it does not impact the range of motion or clinical outcome.

Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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