Stem fracture after total facet replacement in the lumbar spine: a report of two cases and review of the literature.

BACKGROUND CONTEXT A randomized controlled multicenter investigational device exemption clinical trial comparing the total facet arthroplasty system (TFAS) (Archus Orthopedics, Redmond, WA, USA) with posterior fusion was discontinued because of financial reasons. To our knowledge, no clinical outcomes or complications have yet been presented for the TFAS, and no device-related complications have been reported for any other lumbar facet replacement system. PURPOSE To report and discuss two cases of stem fracture after total facet replacement in the lumbar spine. STUDY DESIGN Case report and literature review. PATIENT SAMPLE A 55-year-old man with a body mass index (BMI) of 40 underwent total facet replacement at L4-L5 for Grade 1 spondylolisthesis with stenosis. After 9 months of pain relief, he experienced gradually increasing pain and radiographs showed a broken stem. A 60-year-old woman with a BMI of 31 underwent total facet replacement at L4-L5 for Grade 1 spondylolisthesis with stenosis. She experienced stem fracture 27 months postoperatively. OUTCOME MEASURES Visual analog scale for pain, Oswestry Disability Index for function, and computed tomography and X-ray for imaging. RESULTS After TFAS stem breakage, both patients underwent interbody fusion through a transpsoas approach and have done well over 24- and 12-month follow-up periods, respectively. CONCLUSIONS These are the first cases of stem fracture reported after total facet replacement in the lumbar spine. Biomechanics of TFAS stem breakage may be similar to those of pedicle screw breakage, including fatigue and three-point bending stress. Further biomechanical studies and failure analyses however are needed for adequate understanding to improve the biomechanics of dynamic pedicle-based devices.