Comparison of allograft and polyetheretherketone (PEEK) cage subsidence rates in anterior cervical discectomy and fusion (ACDF).

Structural allografts and PEEK cages are commonly used interbody fusion devices in ACDF. The subsidence rates of these two spacers have not yet been directly compared. The primary aim of this study was to compare the subsidence rate of allograft and PEEK cage in ACDF. The secondary aim was to determine if the presence of subsidence affects the clinical outcome. We reviewed 67 cases (117 levels) of ACDF with either structural allograft or PEEK cages. There were 85 levels (48 cases) with PEEK and 32 levels (19 cases) with allograft spacers. Anterior and posterior disc heights at each operative level were measured at immediate and 6months post-op. Subsidence was defined as a decrease in anterior or posterior disc heights >2mm. NDI of the subsidence (SG) and non-subsidence group (NSG) were recorded. Chi-square test was used to analyze subsidence rates. T-test was used to analyze clinical outcomes (α=0.05). There was no statistically significant difference between subsidence rates of the PEEK (29%; 25/85) and allograft group (28%; 9/32) (p=0.69). Overall mean subsidence was 2.3±1.7mm anteriorly and 2.6±1.2mm posteriorly. Mean NDI improvement was 11.7 (from 47.1 to 35.4; average follow-up: 12mos) for the SG and 14.0 (from 45.8 to 31.8; average follow-up: 13mos) for the NSG (p=0.74). Subsidence rate does not seem to be affected by the use of either PEEK or allograft as spacers in ACDF. Furthermore, subsidence alone does not seem to be predictive of clinical outcomes of ACDF.

Radiographic Comparison of Lateral Lumbar Interbody Fusion Versus Traditional Fusion Approaches: Analysis of Sagittal Contour Change.

BACKGROUND: Lateral approach to lumbar fusion has been gaining popularity in recent years. With increasing awareness of the significance of sagittal balance restoration in spinal surgery, it is important to investigate the potential of this relatively new approach in correcting sagittal deformities in comparison to conventional approaches. The aim of this study was to evaluate sagittal contour changes seen in lateral lumbar interbody fusion and compare them with radiographic changes in traditional approaches to lumbar fusion. METHODS: Lumbar fusion procedures from January 2008 to December 2009 were reviewed. Four approaches were compared: anterior lumbar interbody fusion (ALIF), lateral lumbar interbody fusion (LLIF), transforaminal interbody fusion (TLIF) and posterior spinal fusion (PSF). Standing pre-operative and 6-week post-operative radiographs were measured in terms of operative level, suprajacent and subjacent level, and regional lumbar lordosis (L1-S1) as well as operative level anterior (ADH) and posterior disc heights (PDH). T-test was used to analyze differences between and within different approaches (α=0.05). RESULTS: A total of 147 patients underwent lumbar fusion at 212 levels. Mean operative level segmental lordosis change after each procedure is as follows: ALIF 3.8 ± 6.6° (p < 0.01); LLIF 3.2 ± 3.6° (p<0.01); TLIF 1.9 ± 3.9° (p<0.01); and PSF 0.7 ± 2.9° (p =0.13). Overall lumbar lordosis change after each procedure is as follows: ALIF 4.2 ± 5.8° (p < 0.01); LLIF 2.5 ± 4.1° (p<0.01); TLIF 2.1 ± 6.0 (p = 0.02); PSF -0.5 ± 6.2° (p = 0.66). There were no significant changes in the supradjcent and subjacent level lordosis in all approaches except in ALIF where a significant decrease in supradjecent level lordosis was seen. Mean ADH and PDH significantly increased for all approaches except in PSF where PDH decreased post-operatively. CONCLUSION: LLIF has the ability to improve sagittal contour as well as other interbody approaches and is superior to posterioronly approach in disc height restoration. However, ALIF provides the greatest amount of segmental and overall lumbar lordosis correction. LEVEL OF EVIDENCE: This is a Level III study. CLINICAL RELEVANCE: Regional lordosis correction may be effectively achieved with LLIF. This approach is a good addition to a surgeon's armamentarium in maintenance or restoration of normal lumbar sagittal alignment.

Comparison of open and percutaneous lumbar pedicle screw revision rate using 3-D image guidance and intraoperative CT.

Complications arising from a malpositioned screw can be both devastating and costly. The incidence of neurologic injury secondary to a malpositioned screw is reported to be as high as 7% to 12%. The advancement of image-guided technology has allowed surgeons to place screws more accurately and confirm correct placement prior to leaving the operating room. Only a small number of studies have examined image-guided pedicle screw accuracy in terms of intraoperative revision and reoperation rates. The purpose of this study was to determine the intraoperative revision and return to surgery rates for navigated lumbar pedicle screws and to compare navigated open and percutaneous techniques. The authors reviewed 199 cases of 3-dimensional image-guided lumbar pedicle screw instrumentation from November 2006 to December 2011. Screw or K-wire removal, repositioning, or eventual abandonment of insertion were noted. Chi-square test was used to determine statistical significance in rates between the 2 groups (alpha=0.05). The authors also noted return to surgery secondary to complications from a malpositioned screw. The overall intraoperative revision rate of navigated lumbar pedicle screws was 4.6%. There were significantly more revisions in the percutaneously inserted screws (7.5%) than with the open technique (2.7%) (P=.0004). If K-wire revisions are excluded, there was no statistically significant difference in intraoperative revision rates between the percutaneous and open groups (2.1% vs 2.7%, respectively) (P=.0004). No patients underwent reoperation for a malpositioned screw. This technology has virtually eliminated the need for reoperation for screw malposition. It may suggest a more cost-effective way of preventing neurovascular injuries and revision surgeries.

New generation intraoperative three-dimensional imaging (O-arm) in 100 spine surgeries: does it change the surgical procedure?

The O-arm (Medtronic Sofamor Danek, Inc., Memphis, TN, USA), an intraoperative CT scan imaging system, may provide high-quality imaging information to the surgeon. To our knowledge, its impact on spine surgery has not been studied. We reviewed 100 consecutive spine surgical procedures which utilized the new generation mobile intraoperative CT imaging system (O-arm). The most common diagnoses were degenerative conditions (disk disease, spondylolisthesis, stenosis and acquired kyphosis), seen in 49 patients. The most common indication for imaging was spinal instrumentation in 81 patients (74 utilized pedicle screws). In 52 (70%) of these, the O-arm was used to assess screw position after placement; in 22 (30%), it was coupled with Stealth navigation (Medtronic Sofamor Danek, Inc.) to guide screw placement. Another indication was to assess adequacy of spinal decompression in 38 patients; in 19 (50%) of these, intrathecal contrast material was used to obtain an intraoperative CT myelogram. In 20 patients O-arm findings led to direct surgeon intervention in the form of screw removal/repositioning (n=13), further decompression (n=6), interbody spacer repositioning (n=1), and removal of kyphoplasty trocar (n=1). In 20% of spine surgeries, the procedure was changed based on O-arm imaging findings. We found the O-arm to be useful for assessment of instrumentation position, adequacy of spinal decompression, and confirmation of balloon containment and cement filling in kyphoplasty. When used with navigation for image-guided surgery, it obviated the need for registration.

Neck-shoulder crossover: how often do neck and shoulder pathology masquerade as each other?

Cases of consecutive new patients seen at orthopedic spine and shoulder clinics were reviewed. Four percent of spine patients had significant shoulder pathology, and 3.6% of shoulder patients had significant spine pathology. Identification of the correct pain generator is a prerequisite for effective treatment in patients with neck and/or shoulder problems. However, distinguishing between the two can be difficult. Relative frequencies of how often one is mistaken for the other have not been well established. Six hundred ninety-four new patients were seen at the orthopedic shoulder clinic (n = 452) or spine clinic (n = 242) at an academic institution during a 2-year period. One hundred seven patients had previous shoulder surgery, and 39 had previous neck surgery. The 548 patients (shoulder clinic, 345; spine clinic, 203) who had no previous surgery were reviewed with respect to workup performed, final diagnosis, subsequent operative procedures, and incidence of referral from the shoulder clinic to the spine clinic and vice versa. Among the patients seen at the shoulder clinic, 325 (94.2%) had shoulder pathology, 6 (1.7%) had neck but no shoulder pathology, 6 (1.7%) had shoulder and neck pathology, and 8 (2.3%) had an unidentifiable cause of pain. Of the 12 patients with neck pathology, none underwent neck surgery. Among the patients seen at the spine clinic, 182 (89.7%) had neck pathology, 5 (2.5%) had shoulder but no neck pathology, 3 (1.5%) had neck and shoulder pathology, and 13 (6.4%) had an unidentifiable cause of pain. Of the 8 patients with shoulder pathology, 1 (12.5%) underwent shoulder surgery. Our analysis suggests that for patients who present to a shoulder surgeon's clinic for shoulder pain, 3.6% will turn out to have neck pathology. For patients who present to a spine surgeon's clinic for neck pain, 4% may turn out to have shoulder pathology. Thus, approximately 1 in 25 patients seen at a surgeon's clinic for a presumed shoulder or neck problem may exhibit neck-shoulder crossover, in which pathology in one may be mistaken for or coexist with the other.

Comparison of cranial facet joint violation rates between open and percutaneous pedicle screw placement using intraoperative 3-D CT (O-arm) computer navigation.

STUDY DESIGN: Retrospective study comparing cranial facet joint violation rates of open and percutaneous pedicle screws inserted using 3-dimensional image-guidance. OBJECTIVE: To determine the rate of cranial facet joint violation in intraoperative computed tomography (CT) image-guided lumbar pedicle screw instrumentation and compare facet joint violation rates between CT image-guided open and percutaneous techniques. SUMMARY OF BACKGROUND DATA: Facet joint violation by pedicle screws can potentially result in a higher rate of adjacent segment degeneration. Reported cranial facet joint violation rates range from 7% to 100%. Intraoperative image-guidance, which has enhanced pedicle screw placement accuracy, may aid in avoiding impingement of the cranial facet joints. METHODS: We reviewed 188 cases of 3-dimensional image-guided lumbar pedicle screw instrumentation from November 2006 to December 2011. The cranial screws of each construct were graded by 3 reviewers according to the Seo classification (0 = no impingement; 1 = screw head in contact/suspected to be in contact with joint; 2 = screw clearly invaded the joint) on intraoperative axial CT images. If there was a difference in evaluation, a consensus was reached to arrive at a single grade. The χ2 test was used to determine significance between the open and percutaneous group (α = 0.05). RESULTS: A total of 370 screws (245 open, 125 percutaneous) were graded. Overall facet joint violation rate was 18.9% (grade 1 = 16.2%, grade 2 = 2.7%). Open technique (grade 1 = 22.4%, grade 2 = 4.1%) had a significantly higher violation rate than percutaneous technique (grade 1 = 4%, grade 2 = 0%) (P < 0.0001). There is a trend of an increasing likelihood of facet joint violation from L1 to L5. CONCLUSION: The use of intraoperative CT image-guidance in lumbar pedicle screw placement resulted in a facet joint violation rate at the lower end of the reported range in literature. The percutaneous technique has a significantly lower facet violation rate than the open technique. LEVEL OF EVIDENCE: 4.

Segmental lumbar sagittal correction after bilateral transforaminal lumbar interbody fusion.

OBJECT: In this paper the authors sought to determine the segmental lumbar sagittal contour change after bilateral transforaminal lumbar interbody fusion (TLIF). METHODS: Between March 2007 and October 2010, 42 consecutive patients (57 levels) underwent bilateral TLIF. Standard preoperative and 6-week postoperative standing lumbar spine radiographs were examined. Preoperative and postoperative segmental lordosis was determined by manual measurements using the Cobb method. The difference between the preoperative and postoperative values were calculated and analyzed for statistical significance. RESULTS: The mean preoperative segmental alignment was 8.1°. The mean postoperative alignment was 15.3°, with a mean correction of 7.2° per segment. The largest gain in lordosis was obtained at the L5-S1 level (10.1°). There was a significant difference between the preoperative and postoperative values (p = 5 × 10(-9)). There was no significant difference in mean segmental correction between levels. Improvement in lordosis was higher in multilevel fusions (9.8°) than in single-level fusions (5.2°) (p = 0.047). There was an inverse correlation between preoperative sagittal lordosis measurement and change in lordosis (r = -0.599). CONCLUSIONS: A significant improvement in lumbar lordosis can be gained by preforming bilateral facetectomies in TLIF with posterior compression. This procedure provides an additional option to a spine surgeon's armamentarium in dealing with significant lumbar sagittal plane deformities.

Intraoperative 3-dimensional imaging (O-arm) for assessment of pedicle screw position: Does it prevent unacceptable screw placement?

BACKGROUND: Pedicle screws are biomechanically superior over other spinal fixation devices. When improperly positioned, they lose this advantage and put adjacent structures at risk. Accurate placement is therefore critical. Postoperative computed tomography (CT) scans are the imaging gold standard and have shown malposition rates ranging from 2% to 41%. The O-arm (Medtronic Navigation, Louisville, Colorado) is an intraoperative CT scanner that may allow intervention for malpositioned screws while patients are still in the operating room. However, this has not yet been shown in clinical studies. The primary objective of this study was to assess the usefulness of the O-arm for evaluating pedicle screw position by answering the following question: What is the rate of intraoperative pedicle screw revision brought about by O-arm imaging information? A secondary question was also addressed: What is the rate of unacceptable thoracic and lumbar pedicle screw placement as assessed by intraoperative O-arm imaging? METHODS: This is a case series of consecutive patients who have undergone spine surgery for which an intraoperative 3-dimensional (3D) CT scan was used to assess pedicle screw position. The study comprised 602 pedicle screws (235 thoracic and 367 lumbar/sacral) placed in 76 patients, and intraoperative 3D (O-arm) imaging was obtained to assess screw position. Action taken at the time of surgery based on imaging information was noted. An independent review of all scans was also conducted, and all screws were graded as either optimal (no breach), acceptable (breach ≤2 mm), or unacceptable (breach >2 mm). The rate of pedicle screw revision, as detected by intraoperative 3D CT scan, was determined. RESULTS: On the basis of 3D imaging information, 17 of 602 screws (2.8%) in 14 of 76 cases (18.4%) were revised at the time of surgery. On independent review of multiplanar images, 11 screws (1.8%) were found to be unacceptable, 32 (5.3%) were acceptable, and 559 (92.9%) were optimal. All unacceptable screws were revised to an optimal or acceptable position, and an additional 6 acceptable screws were revised to an optimal position. Thus, by the end of the cases, none of the 602 pedicle screws in the 76 surgical procedures was in an unacceptable position. CONCLUSION: The new-generation intraoperative 3D imaging system (O-arm) is a useful tool that allows more accurate assessment of pedicle screw position than plain radiographs or fluoroscopy alone. It prompted intraoperative repositioning of 2.8% of pedicle screws in our series. Most importantly, it allowed identification and revision of all unacceptably placed pedicle screws without the need for reoperation.

Validity of surgeon perception of navigated pedicle screw position: a cadaveric study.

STUDY DESIGN: Human Cadaveric Experimental Study. OBJECTIVE: To determine the validity of surgeon perception of pedicle screw position inserted using intraoperative three-dimensional (O-arm) image-guided screw insertion. SUMMARY OF BACKGROUND DATA: A surgeon's ability to detect pedicle wall violations intraoperatively is crucial for optimal pedicle screw placement. Accuracy of use of a probe or sound to assess pedicle breach is not optimal and may require experience. Intraoperative navigation has been shown to improve screw placement accuracy. It has not been shown, however, whether navigation in combination with screw tract palpation can further increase the surgeon's ability to detect a pedicle breach in pedicle screw placement in the cervical, thoracic, and lumbosacral spine. METHODS: Four hundred eighteen screws were inserted using three-dimensional image guidance transpedicularly from C2 to S1 in 10 fresh frozen cadavers. Screw tracts were created using navigation and then probed. After probing, the surgeon stated whether he perceived that the screw would be in, out laterally, or out medially. After screw insertion for all the levels, open dissection was then performed to determine the actual pedicle screw position. The surgeon's perception of screw position was compared to the dissection results. RESULTS: The overall specificity, sensitivity, positive predictive value, and negative predictive value of the surgeon perception of pedicle screw position were 87%, 80%, 78% and 88%, respectively. Accuracy of surgeon perception of pedicle screw position was significantly less than in the cervical spine when compared with thoracic and lumbosacral spine. CONCLUSION: Surgeon perception of a navigated pedicle screw position is accurate in the thoracic and lumbar spine. Detection of pedicle screw violations by surgeon perception in the cervical spine is less accurate and does not reliably lead to accurate screw placement.

Optimizing iliac screw fixation: a biomechanical study on screw length, trajectory, and diameter.

OBJECT: The authors performed a study to determine the optimal iliac screw size, length, and trajectory that produce the highest insertional torques. METHODS: Ten fresh cadavers were used and 7.5 × 140-mm and 9.5 × 140-mm iliac screws were placed using 3D image guidance in a randomized fashion in 1 of 2 trajectories. The screws were inserted from the posterior superior iliac spine (PSIS) to either 1) supraacetabular bone or 2) the anterior inferior iliac spine (AIIS). Insertional torque was measured for each full revolution, and the concomitant depth for each torque measurement was recorded. Insertional torque was correlated with detailed bony anatomy. RESULTS: There was no difference in mean peak insertional torque between the 2 trajectories (25.6 ± 16.4 in-lb [supraacetabular], 26.3 ± 18.2 lb-in [AIIS]; p = 0.8). However, there was a difference between the 2 screw diameters (21.1 ± 10.9 lb-in [7.5-mm-diameter screw], 33.7 ± 19.4 lb-in [9.5-mm-diameter screw]; p = 0.0003). The greatest mean peak insertional torques were observed at depths greater than 80 mm (12.7 ± 9.6 lb-in [≤ 80 mm], 23.7 ± 15.7 lb-in [> 80 mm]; p = 2.6 × 10(-7)). Insertional torque peaks correlated with engagement of the lateral iliac cortex and the superior iliac fossa. CONCLUSIONS: Although the trajectory had no effect on insertional torque, increased torques are achievable by placing larger-diameter and longer screws in proximity to bony landmarks, most of which are at distances greater 80 mm from the entry point at the PSIS. Iliac screws longer than those commonly used in clinical practice can be safely and accurately placed using image guidance, and reproducible screw paths can be achieved.