Disc replacement adjacent to cervical fusion: a biomechanical comparison of hybrid construct versus two-level fusion.

STUDY DESIGN: A cadaveric biomechanical study. OBJECTIVE: To investigate the biomechanical behavior of the cervical spine after cervical total disc replacement (TDR) adjacent to a fusion as compared to a two-level fusion. SUMMARY OF BACKGROUND DATA: There are concerns regarding the biomechanical effects of cervical fusion on the mobile motion segments. Although previous biomechanical studies have demonstrated that cervical disc replacement normalizes adjacent segment motion, there is a little information regarding the function of a cervical disc replacement adjacent to an anterior cervical decompression and fusion, a potentially common clinical application. METHODS: Nine cadaveric cervical spines (C3-T1, age: 60.2 ± 3.5 years) were tested under load- and displacement-control testing. After intact testing, a simulated fusion was performed at C4-C5, followed by C6-C7. The simulated fusion was then reversed, and the response of TDR at C5-C6 was measured. A hybrid construct was then tested with the TDR either below or above a single-level fusion and contrasted with a simulated two-level fusion (C4-C6 and C5-C7). RESULTS: The external fixator device used to simulate fusion significantly reduced range of motion (ROM) at C4-C5 and C6-C7 by 74.7 ± 8.1% and 78.1 ± 11.5%, respectively (P < 0.05). Removal of the fusion construct restored the motion response of the spinal segments to their intact state. Arthroplasty performed at C5-C6 using the porous-coated motion disc prosthesis maintained the total flexion-extension ROM to the level of the intact controls when used as a stand-alone procedure or when implanted adjacent to a single-level fusion (P > 0.05). The location of the single-level fusion, whether above or below the arthroplasty, did not significantly affect the motion response of the arthroplasty in the hybrid construct. Performing a two-level fusion significantly increased the motion demands on the nonoperated segments as compared to a hybrid TDR-plus fusion construct when the spine was required to reach the same motion end points. The spine with a hybrid construct required significantly less extension moment than the spine with a two-level fusion to reach the same extension end point. CONCLUSION: The porous-coated motion cervical prosthesis restored the ROM of the treated level to the intact state. When the porous-coated motion prosthesis was used in a hybrid construct, the TDR response was not adversely affected. A hybrid construct seems to offer significant biomechanical advantages over two-level fusion in terms of reducing compensatory adjacent-level hypermobility and also loads required to achieve a predetermined ROM.

Coronal deformity correction in adolescent idiopathic scoliosis patients using the fulcrum-bending radiograph: a prospective comparative analysis of the proximal thoracic, main thoracic, and thoracolumbar/lumbar curves.

The aim of the prospective, comparative radiographic analysis was to determine the role of the fulcrum-bending radiograph (FBR) for the assessment of the proximal thoracic (PT), main thoracic (MT), and the thoracolumbar/lumbar (TL/L) curves in patients undergoing posterior spinal pedicle screw fixation and fusion for adolescent idiopathic scoliosis (AIS). The FBR demonstrated statistically better correction than other preoperative methods for the assessment of frontal plane correction of the MT curves. The fulcrum-bending correction index (FBCI) has been considered a superior method than the correction rate for comparing curve correction undergoing posterior spinal fusion because it accounts for the curve flexibility. However, their applicability to assess the PT and TL/L curves in AIS patients remains speculative. The relation between FBR and correction obtained by pedicle screws fixation is still unknown. Thirty-eight consecutive AIS patients who underwent pedicle screw fixation and posterior fusion were included in this study. The assessment of preoperative radiographs included standing posterior-anterior (PA), FBR, supine side-bending, and postoperative standing PA and lateral plain radiographs. The flexibility of the curve, as well as the FBCI, was calculated for all patients. Postoperatively, radiographs were assessed at immediate (i.e. 1 week), 3-month, 6-month, 12-month, and 2-year follow-up. Cobb angles were obtained from the PT, MT, and TL/L curves. The study consisted of 9 PT, 37 MT, and 12 TL/L curves, with a mean age of 15.1 years. The mean FBR flexibility of the PT, MT, and the TL/L curves was 42.6, 61.1, and 66.2%, respectively. The mean operative correction rates in the PT, MT, and TL/L curves were 43.4, 69.3, and 73.9%, respectively, and the mean FBCI was 103.8, 117.0, and 114.8%, respectively. Fulcrum-bending flexibility was positively correlated with the operative correction rate in PT, MT, and TL/L curves. Although the correction rate in MT and TL/L curves was higher than PT curves, the FBCI in PT, MT, and TL/L curves was not significantly different (p < 0.05). The FBR can be used to assist in the assessment of PT, MT, and TL/L curve corrections in AIS patients. When curve flexibility is taken into account by FBR, the ability of pedicle screws to correct PT, MT, and TL/L curves is the same.

Repeat use of human recombinant bone morphogenetic protein-2 for second level lumbar arthrodesis.

STUDY DESIGN: Prospective randomized controlled animal model. OBJECTIVE: The purpose of this study is to determine whether the readministration of human recombinant bone morphogenetic protein-2 (rhBMP-2) induces an immune response and inhibits successful fusion in repeat posterolateral spinal surgery. SUMMARY OF BACKGROUND DATA: Little research has been performed on the effectiveness or immunoreactivity of rhBMP-2 (Infuse, Medtronic, Memphis, TN) in the context of its reuse in posterolateral fusion spinal surgery at adjacent levels. METHODS: A total of 34 New Zealand White rabbits underwent posterior intertransverse process fusion with the use of rhBMP-2 delivered on an absorbable collagen sponge (rhBMP-2/ACS). Two rabbits were killed early leaving 32 total rabbits. Serologic studies (Type I bovine collagen and rhBMP-2 antibodies) were obtained at 2-week intervals throughout the experiment. At 10 weeks, posteroanterior radiographs confirmed solid fusion masses in all rabbits. The 32 rabbits were randomly separated into 2 groups of 16, and each group underwent an adjacent level, bilateral intertransverse process fusion with either rhBMP-2/ACS or iliac crest. RESULTS: There was no statistical difference in fusion rates with repeat use of rhBMP-2 (n = 15/16, 94%) or iliac crest (n = 11/16, 69%) (P = 0.17) at the adjacent level. Four rabbits (n = 4/32, 13%) developed rhBMP-2 antibodies. Of these 4 rabbits, 1 developed anti-rhBMP antibodies after the first exposure and 3 developed antibodies after the second surgery. Eight rabbits (n = 8/32, 25%) developed collagen antibodies with 7 rabbits developing antibodies after the first exposure and 1 rabbit developing antibodies after the second exposure. The development of antibodies did not effect fusion rates. No rabbit demonstrated evidence of a systemic or anaphylactic reaction to repeat exposure to rhBMP-2. CONCLUSION: rhBMP-2 appears to be successful in promoting intertransverse fusions when used in both primary and repeat fusion environments. The infrequent development of antibodies to rhBMP-2 after re-exposure occurs without a predictable time course suggesting that host immunologic variation may play a role. This animal study would tend to support early clinical data emerging on the reuse of BMP-2 for lumbar fusion, suggesting an acceptable fusion rate without a high incidence of complications.

A multicenter study to evaluate the safety and efficacy of a stand-alone anterior carbon I/F Cage for anterior lumbar interbody fusion: two-year results from a Food and Drug Administration investigational device exemption clinical trial.

STUDY DESIGN: Two-year prospective multicenter clinical trial. OBJECTIVE: To determine the safety and efficacy of the anterior I/F Cage in the primary treatment of single-level degenerative disc disease. SUMMARY OF BACKGROUND DATA: A carbon fiber-reinforced polymer cage was designed to replace the traditional allograft/autograft structural graft used in an anterior lumbar interbody fusion (ALIF). Although the outcomes of various types of ALIF cages have previously been reported, the safety and efficacy of the I/F cage are unknown. METHODS: Between June 2000 and June 2004, 112 patients were prospectively enrolled at 12 study sites for the current study. Efficacy was evaluated clinically and radiographically. "Patient success" was declared only when the following 4 criteria were present at final follow-up: (1) "clinical success": improvement of 15 points on Oswestry Disability Index, (2) absence of a new neurologic abnormality, (3) successful radiographic fusion, and (4) no subsequent secondary surgical intervention at 24-month follow-up. Safety was inferred by way of an objective summary of complications and adverse events, as reported at regular intervals throughout the course of the study. RESULTS: A total of 112 patients (mean age: 41.7 years) underwent a single-level ALIF procedure (L5-S1: 95 patients, L4-L5: 17 patients). The mean surgical time was 126 minutes, the mean estimated blood loss was 134 mL, and the mean duration of hospitalization was 3.3 days. There were 80 patients available for 24-month follow-up. Overall patient success was 25% (20/80). Clinical success was present in 46.3% (37/80), fusion success was 57.5% (46/80), and 87.5% of patients (70/80) avoided a subsequent secondary surgical intervention. Disc space height had significantly increased after surgery, and this increase was maintained at 2 years follow-up period. Complications and adverse events included the following: 8 infections (7.1%) (7 superficial, 1 deep), 2 vascular injuries (1.8%) (left common iliac vein), and 12 secondary surgical interventions (15%). CONCLUSION: This safety and efficacy study suggests that the anterior I/F Cage is a safe surgical option in the treatment of single-level lumbar degenerative disc disease. As a stand-alone construct, the I/F Cage yields suboptimal radiographic and clinical outcomes. Additional benefit may be gained from adjunctive posterior stabilization.

Percutaneous treatment of vertebral compression fractures: a meta-analysis of complications.

STUDY DESIGN AND OBJECTIVE: This study performs a meta-analysis to compare complication rates from vertebroplasty (VP) and kyphoplasty (KP). SUMMARY OF BACKGROUND DATA: Recently, the development of VP and balloon KP has been shown to provide symptomatic relief and restoration of sagittal alignment of vertebral compression fractures refractory to medical therapy. Complications in treatment of vertebral compression fractures are rare, however can be potentially devastating. Fortunately, clinical sequelae are rare; however, severe clinical complications from cement extravasation have been reported. METHODS: Using PubMed and Ovid, we performed a literature search for "kyphoplasty," "vertebroplasty," and "vertebral augmentation." This search was performed in December 2006. Case reports and reports not available in English were excluded. We categorized complications in 3 categories: (1) procedure-related complications, (2) medical complications, and (3) new vertebral fracture. Cement leakage, asymptomatic and symptomatic, and its locations were recorded. We performed a meta-analysis of complications of all studies. We then repeated the meta-analysis examining only prospective studies. We then used proportion analysis to determine statistical significance. We defined statistical significance as a P value less than 0.05. RESULTS: We identified 121 reports of KP and/or VP that specifically addressed complications. Of these studies, 33 addressed KP and 82 addressed VP (6 reports addressed complications of both). There were 29 reports in which the data appeared to be collected prospectively. Of these, 9 addressed KP and 21 addressed VP.VP was found to have a significantly increased rate of procedure-related complications than KP in the analysis of all studies and only prospective studies. VP also appears to have a significantly higher rate of symptomatic and asymptomatic cement leakage than KP (P < 0.05). The incidence of medical complications was significantly higher in the KP procedure; however, this difference was not observed when analyzing only prospective studies. The incidence of new fracture was significantly higher in the VP procedure; however, this was not observed when analyzing only prospective studies. CONCLUSION: VP and KP are 2 minimally invasive procedures that have been shown to be effective in the treatment of symptomatic vertebral compression fractures. Although the incidence of adverse events for both VP and KP are low, it appears that VP is associated with a statistically significant increased rate of procedure-related complications and cement extravasation (symptomatic and asymptomatic). Future prospective studies with large patient enrollment will be needed to further validate the finding of this meta-analysis.

Ulnar nerve palsy after elbow arthroscopy.

Reports of ulnar nerve injury as a result of elbow arthroscopy are rare in the literature. We report a case of ulnar nerve injury following arthroscopic debridement and retrograde drilling of the capitulum in a patient with symptomatic osteochondritis dissecans. The standard location of proximal medial portal placement is 2 cm proximal to the medial epicondyle at the level of the medial intermuscular septum. In this location, the ulnar nerve is protected from injury by the medial intermuscular septum. Extending this placement more proximally may negate this protection, leaving the nerve more susceptible to injury.

A biomechanical evaluation of an anatomical coracoclavicular ligament reconstruction.

BACKGROUND: Despite numerous surgical techniques described, there have been few studies evaluating the biomechanical performance of acromioclavicular joint reconstructions. PURPOSE: To compare a newly developed anatomical coracoclavicular ligament reconstruction with a modified Weaver-Dunn procedure and a recently described arthroscopic method using ultrastrong nonabsorbable suture material. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-two fresh-frozen cadaveric shoulders (72.8 +/- 13.4 years) were randomly assigned to 3 groups: arthroscopic reconstruction, anatomical coracoclavicular reconstruction, and a modified Weaver-Dunn procedure. Bone mineral density was obtained on all specimens. Specimens were tested to 70 N in 3 directions, anterior, posterior, and superior, comparing the intact to the reconstructed states. Superior cyclic loading at 70 N for 3000 cycles was then performed at a rate of 1 Hz, followed by a load to failure test (120 mm/min) to simulate physiologic states at the acromioclavicular joint. RESULTS: In comparison to the intact state, the modified Weaver-Dunn procedure had significantly (P < .05) greater laxity than the anatomical coracoclavicular reconstruction or the arthroscopic reconstruction. There were no significant differences in bone mineral density (g/cm(2)), load to failure, superior migration over 3000 cycles, or superior displacement. The anatomical coracoclavicular reconstruction had significantly less (P < .05) anterior and posterior translation than the modified Weaver-Dunn procedure. The arthroscopic reconstruction yielded significantly less anterior displacement (P < .05) than the modified Weaver-Dunn procedure. CONCLUSION: The anatomical coracoclavicular reconstruction has less anterior and posterior translation and more closely approximates the intact state, restoring function of the acromioclavicular and coracoclavicular ligaments. CLINICAL RELEVANCE: A more anatomical reconstruction using a free tendon graft of both the trapezoid and conoid ligaments may provide a stronger, permanent biologic solution for dislocation of the acromioclavicular joint. This reconstruction may minimize recurrent subluxation and residual pain and permit earlier rehabilitation.

Evaluation and management of acromioclavicular joint injuries.

The acromioclavicular joint is stabilized by the coracoclavicular and acromioclavicular ligaments and by the trapezius and deltoid muscles. Joint dislocation commonly results from a direct blow to the acromion. Injury types I through III are generally treated nonoperatively, whereas types IV through VI are treated operatively. Nonoperative protocols should always begin with ice and immobilization. Operative techniques include acromioclavicular ligament repair, dynamic transfer of the conjoined tendon, coracoclavicular ligament reconstruction, and coracoacromial ligament transfer. The goal with any injury type should always be full return to the patient's preinjury condition.