Changes in Neuroforaminal Dimensions with Two-Level Axial Lumbar Interbody Fusion at L4-S1 with Graduated Distraction through the Implant

PURPOSE: The goal of this study was to evaluate the number of complications requiring reoperation for symptomatic failed fusion and hyper responsive compressive fluid collections. STUDY DESIGN/SETTING: Retrospective cohort study/one large orthopaedic surgery private practice associated with a tertiary referral spine center. PATIENT SAMPLE: 1158. OUTCOMEMEASURES: Complications related to rhBMP were defined as reoperation secondary to failed symptomatic fusion, hyper reaction resulting in compressive fluid collections, hyper formation of bone resulting in neural compression, and infections. METHODS: During a 7-year period of time (2002–2009), all patients undergoing lumbar posterolateral fusion utilizing of rhBMP-2 (INFUSE) were retrospectively evaluated within a large orthopaedic surgery private practice. Patient demographics, comorbidities, number of levels, and types of bone void filler (BVF) were analyzed. Complications related to rhBMP were defined as reoperation secondary to failed symptomatic fusion, hyper reaction resulting in compressive fluid collections, hyper formation of bone resulting in neural compression, and infections. RESULTS: 1158 consecutive patients were evaluated with 468 (40.4%) males and 690 (59.6%) females. Average age was 59.2 yo and BMI was 30.7 kg/m. Number of levels fused was: 1 (414, 35.8%), 2 (469, 40.5%), 3 (162, 14.0%), 4 (70, 6.0%), 5 (19, 1.6%), 6 (11, 0.9%), 7 (7, 0.6%), 8 (4, 0.3%), and 9 (2, 0.2%). Complications including add on stenosis requiring reoperation were 117/1158 (10.1%): Seroma with acute neural compression 32 (2.8%), excess bone formation with delayed neural compression 4 (0.3%), infection requiring debridement 26 (2.2%), and symptomatic nonunion requiring redo fusion and instrumentation 41 (3.5%). Nonunion was not related to smoking, number of levels fused, or age. There was an increased risk for nonunion in male patients and patients with previous BMP exposition. All nonunions were successfully treated with redo surgical instrumentation and rhBMP application. Seroma formation was not associated with interbody fusion, gender, BMI or comorbidities and was associated with acute exacerbation of radicular pain and transient neural involvement of varying degrees. The incidence of seroma formation was significantly higher in patients with higher doses of rhBMP-2 (p5.050) and especially in patients with more than 12 mg rhBMP-2 (c50.025). Bone reformation at the laminectomy and foraminotomy sites occurred in a delayed fashion associated with a solid union, progressive worsening of radicular pain, and were successfully treated with repeat neural decompression only. CONCLUSIONS: rhBMP-2 is a reliable adjunct for bone induction in posterolateral lumbar fusions. Complication rates using rhBMP-2 are low and do not exceed complication rates using iliac crest bone graft. A higher rate of seroma formation and infection occurs with increasing rhBMP-2 dose. Therefore, further studies concerning rhBMP-2 dosage are warranted. FDA DEVICE/DRUG STATUS: rhBMP-2: Investigational/Not approved.