Technical variation of trans-articular sacroiliac joint (SIJ) fusion using three screws considering the effects of sacral dysplasia in patients with non-traumatic SIJ pain.

BACKGROUND: This study evaluated the technical adequacy of trans-articular sacroiliac joint (SIJ) fusion using three screws for non-traumatic SIJ pain, considering different grades of sacral dysplasia. METHODS: Cadaveric CT data of unilateral sacropelvic complexes for 72 individuals (53.4 ± 8.4 years) were selected. A 3D model was reformatted into the plain lateral radiograph to mark the articular surface of the SIJ. Subjects were classified into dysplastic (DYS) and non-dysplastic sacrum (NDS) groups. Proximal (PS), middle (MS), and distal screws (DS) with 10-mm diameter were virtually introduced to the iliac bone and the SIJ on the lateral image with a 5-mm safety margin. On a corresponding axial image, each screw was advanced vertically to the sagittal plane with the same safety margin. The entry points for each screw to the endplate of S1 (S2) and to the corresponding anterior sacral margin on the lateral image were measured, along with the maximal screw lengths on the axial image. Whether each screw passed through the SIJ was determined. Different types of sacral dysplasia and screws were compared statistically. RESULTS: Thirty-eight (26.4%) cases were DYS, and 106 (73.6%) were NDS. The entry points of all screws were significantly more distal in DYS than in NDS groups. The PS and MS screw lengths differed significantly between the 2 groups. Incidences of short sacral fixation (< 10 mm) were significantly higher for the DS in both NDS (38.7%) and DYS (39.5%) groups. Incidences of screw pass were lowest for the MS in both NDS (43.4%) and DYS (47.4%) groups. CONCLUSIONS: Sacral dysplasia locates the SIJ more distally and therefore affects the entry point locations and screw lengths for all screws in trans-articular SIJ fusion, compared with a non-dysplastic sacrum. Moreover, three-screw fixation risks the development of unstable DS fixation and a high extra-articular fixation rate in MS.

Correction to: Clinical and radiological outcomes of unilateral biportal endoscopic lumbar interbody fusion (ULIF) compared with conventional posterior lumbar interbody fusion (PLIF): 1-year follow-up.

The original publication of this article has incorrect presentation of one of the author names. Instead of Sangu-Kyu Son, it should have been Sang-Kyu Son.

Clinical and radiological outcomes of unilateral biportal endoscopic lumbar interbody fusion (ULIF) compared with conventional posterior lumbar interbody fusion (PLIF): 1-year follow-up.

This study retrospectively compared clinical and radiological outcomes of unilateral biportal endoscopic lumbar interbody fusion (ULIF) to those of conventional posterior lumbar interbody fusion (PLIF). Seventy-one ULIF (age, 68 ± 8 years) and 70 PLIF (66 ± 9 years) patients for one lumbosacral segment followed more than 1 year were selected. Parameters for surgical techniques (operation time, whether transfused), clinical results [visual analogue scale (VAS) for back and leg pain, Oswestry disability index (ODI)], surgical complications (dural tear, nerve root injury, infection), and radiological results (cage subsidence, screw loosening, fusion) between the two groups were compared. The PLIF group demonstrated a significantly shorter operation time and more transfusions done than the ULIF group. The VAS for leg pain in both groups and for back pain in the ULIF group significantly improved at 1 week, while the VAS for back pain in the PLIF group significantly improved at 1 year. ODI scores improved at 1 year in both groups. Complication rates were not significantly different between groups. Fusion rates with definite and probable grades were not significantly different between groups. However, the ULIF group had significantly (P = 0.013) fewer cases of definite fusion and more cases of probable fusion [43 (74.1%) and 15 (25.9%) cases, respectively] than the PLIF group [58 (92.1%) and 5 (7.9%) cases, respectively]. ULIF is less invasive while just as effective as conventional PLIF in improving clinical outcomes and obtaining fusion. However, ULIF has a longer operation time than PLIF and requires further development to improve the fusion grade.

Changes of spinopelvic parameters in different positions.

INTRODUCTION: To observe changes of spinopelvic parameters and the presence of pelvic incidence (PI) variation in different positions, and the accuracy of PI compared with CT scan. MATERIALS AND METHODS: Patients with standing whole-spine radiograph, CT scan of the pelvic bone, and MRI of the lumbar spine done within a few days were included. The pelvic [pelvic tilt (PT), sacral slope (SS), and PI] and spinal [lumbar lordosis (LL)] parameters were measured by two different observers. RESULTS: The PIs from radiograph were significantly greater than those from CT in both observers. By adopting the upper limit of the confidence interval and the agreement of two observers on grouping, patients were categorized into two subgroups (SG1, with less PI change; SG2, with higher PI change). The PT and LL values decreased, whereas SS increased significantly from standing to supine positions in SG1. Significantly decreased PT and PI from standing to supine were observed in SG2. All pelvic parameters and the sagittal vertical axis on radiograph, and the LL amount on MRI were significantly greater in SG2 than in SG1. CONCLUSIONS: Majority of patients demonstrated alignment changes of unchanged PI with decreased PT and LL, and increased SS from standing to supine; however, decreased PT and PI and fixed SS and LL were also demonstrated. Patients with higher PI change have high values in three pelvic parameters and sagittal vertical axis, and fixed LL.

Depth of Pleural Effusion in Thoracentesis: Comparison of Lateral, Posterolateral and Posterior Approaches in the Supine Position.

BACKGROUND: In patients who have difficulty sitting, thoracentesis is attempted in a supine position via lateral approach. Recently, a new table has been designed for supine thoracentesis. This table has gaps that allow access to the posterolateral and posterior hemithorax. OBJECTIVES: To compare important safety-related parameters between lateral, posterolateral, and posterior approaches in supine thoracentesis. MATERIALS AND METHODS: First, two cadavers were placed supine on a table featuring gaps allowing access to the posterolateral and posterior hemithorax. Water was administered with sonographic measurement of the depth of pleural effusion (DPE) at the mid-axillary and posterior axillary line. Second, CT images were analyzed in 25 consecutive patients (32 free-shifting, moderate-to-large effusions; mean, 668 (146 - 2020 mL). DPE, craniocaudal distance that effusion can be visualized (CCD), and presence of passive atelectasis at each of the lateral, posterolateral, and posterior routes was assessed. RESULTS: In each cadaver, DPE in the posterolateral route was greater than that in the lateral route (P = 0.002, P < 0.001). The amount of pleural fluid enough to spread DPE to higher than 1 cm at the posterior axillary line was less than half the amount at the mid-axillary line (500 mL vs. 1,100 mL; 800 mL vs. 1700 mL). CT showed that the DPEs and CCDs of posterolateral and posterior routes were greater than those of the lateral route (P < 0.001). In thirteen effusions (40.6%), DPE was greater than 1 cm in both posterolateral and posterior routes but less than 1 cm in the lateral route. Frequencies of passive atelectasis in posterolateral and posterior routes (81.3% and 90.6%) were higher (P < 0.001) than that in the lateral route (28.1%). CONCLUSION: Safety-related parameters of posterolateral and posterior approaches in supine thoracentesis are far better than that of the conventional lateral approach.

Entry zone of iliac screw fixation to maintain proper entry width and screw length.

PURPOSE: To evaluate the entry zone of iliac screw fixation to maintain proper entry width and screw length. METHODS: Computed tomography images of pelvic bones from 90 human cadavers were reconstructed into 3-dimensional models. In each model, a sectional image crossing the posterior superior iliac spine (PSIS) and anterior inferior iliac spine (AIIS) and consecutive sectional images up to 20 mm superiorly and inferiorly from the PSIS with 1-mm intervals aiming the AIIS were obtained. One virtual iliac screw with 10-mm diameter was introduced onto the PSIS at the middle and at the lateral and medial 1/4 points on the prominence of the posterior iliac spine. The entry width of the bony prominence and the corresponding maximal screw length available were evaluated for each entry point. RESULTS: The entry width was smallest on the inferior 20 mm (4.7 ± 3.0 mm) and gradually increased up to the superior 10 mm (19.1 ± 3.9 mm) sectional images. The maximal screw length was smallest on the superior 20 mm (76.7 ± 39.7 mm) and gradually increased down to the inferior 10 mm (112.3 ± 15.1 mm) sectional images. The maximal screw lengths were significantly greatest at the most medial point and smallest at the most lateral point on the superior 20- and 10-mm sectional images and at the PSIS. CONCLUSIONS: The iliac screw fixation entry zone to maintain proper screw length and entry width is outlined from 20 mm superiorly to 10 mm inferiorly from the PSIS and is located more medially from the prominence of the posterior iliac spine.

Topographical anatomy of the anterior cervical approach for c2-3 level.

PURPOSE: To develop a clinically relevant anterior cervical approach (ACA) to the C2-3 level. METHODS: Frequently encountered nerves [hypoglossal (HyN), internal (ISLN) and external superior laryngeal nerves (ESLN)] and vessels [lingual (LiA), superior laryngeal (SLA) and superior thyroid arteries (STA)] in the field of high ACA and the anatomic spatial markers [submandibular gland (SMG); sling for digastrics muscle (SDG); hyoid bone (HyB), and thyroid cartilage (ThC)] were evaluated using 18 fresh cadavers. The vertical distance of each structure at the carotid sheath and larynx and each disc for cervical level were measured from the suprasternal notch. RESULTS: The cervical levels of SDG, SMG and HyB were mostly C3 and that of ThC was C5. The vertical locations of HyN and LiA were not significantly different and the levels corresponded to C2. The levels for ISLN and ESLN were C3 at carotid and C4 and C5 at larynx sides, respectively. The vertical locations of ISLN and HyN were significantly different at carotid (p = 0.001) and larynx (p < 0.001) sides. The vertical locations and cervical levels of SLA and STA at carotid and larynx sides were not significantly different with those of ISLN and ESLN, respectively. The HyN traversed C2 with accompanying LiA. The ISLN passed C3 and C4 from carotid to larynx sides and accompanied SLA. CONCLUSIONS: The C2-3 level can be exposed through the space between the HyN and the ISLN by retracting the LiA superiorly, the SLA inferiorly, the HyB medially, and the carotid sheath laterally.

An in vivo kinematic comparison of dynamic lumbar stabilization to lumbar discectomy and posterior lumbar fusion using radiostereometric analysis.

BACKGROUND: Biomechanical studies have shown that dynamic stabilization restores the neutral zone and stabilizes the motion segment. Unfortunately, there are limitations to clinical measurement of lumbar motion segments when using routine radiographs. Radiostereometric analysis is a 3-dimensional technique and can measure the spinal motion segment more accurately than techniques using plain film radiographs. The purpose of this study was measure and compare the range of motion after dynamic stabilization, posterior lumbar fusion (PLF), and lumbar discectomy. METHODS: Four patients who underwent lumbar decompression and dynamic stabilization (Dynesys; Zimmer Spine, Inc., Warsaw, Indiana) for treatment of lumbar spondylosis were compared with 4 patients with a similar diagnosis who were treated by PLF and pedicle screw fixation (PLF group) and 8 patients who had undergone lumbar microdiscectomy (discectomy group) for treatment of radiculopathy. During the surgical procedure, 3 to 5 tantalum beads were placed into each of the operative segments. The patients were followed up postoperatively at 1 month, 1 year, and 2 years. At each follow-up time point, segmental motions (flexion, extension, and total sagittal range of motion [SROM]) were measured by radiostereometric analysis. RESULTS: Flexion, extension, and SROM measured 1.0° ± 0.9°, 1.5° ± 1.3°, and 2.3° ± 1.2°, respectively, in the Dynesys group; 1.0° ± 0.6°, 1.1° ± 0.9°, and 1.5° ± 0.6°, respectively, in the PLF group; and 2.9° ± 2.4°, 2.3° ± 1.5°, and 4.7° ± 2.2°, respectively, in the discectomy group. No significant difference in motion was seen between the Dynesys and PLF groups or between the Dynesys and discectomy groups in extension. Significant differences in motions were seen between the PLF and discectomy groups and between the Dynesys and discectomy groups in flexion (P = .007) and SROM (P = .002). There was no significant change in the measured motions over time. CONCLUSIONS: In this study a significantly lower amount of motion was seen after dynamic stabilization and PLF when compared with discectomy. A future study with a larger cohort is necessary to examine what effect, if any, these motions have on clinical outcomes.

A novel method of screw placement for extremely small thoracic pedicles in scoliosis.

STUDY DESIGN: A retrospective clinical study. OBJECTIVE: To introduce a novel method of pedicle screw placement for extremely small thoracic pedicles in scoliosis and evaluate the safety and accuracy of the method. SUMMARY OF BACKGROUND DATA: Few studies have provided technical guidelines for screw placement in patients with extremely small thoracic pedicles in scoliosis. METHODS: In a severely rotated scoliotic spine, thoracic pedicle screw placement is challenging, and particularly more so for extremely small pedicles with a diameter less than 2 mm. The authors introduced a novel method of screw placement for these small pedicles: "medial margin targeting method."The C-arm fluoroscope is rotated until a true PA image of the rotated vertebral body is acquired and both pedicle shadows are symmetrically visualized en face. In extremely small pedicles, pedicle shadows appear as long, slender ellipses or lines. An imaginary pedicle outline is presumed with the elliptical or linear shadows being the medial margin of the pedicle. The entry point of a screw can be made at the 10-o'clock or 2-o'clock position on the presumed pedicle outline, and the screw can be safely inserted targeting the presumed medial margin with caution not to penetrate the medial cortex using the guidance of a true PA image. This is a kind of extrapedicular screw placement method.The safety and accuracy of this method were evaluated in 97 patients with scoliosis who had undergone posterior correction and instrumentation using postoperative computed tomography scans. A total of 1634 pedicle screws were inserted into thoracic pedicles, 128 of them (7.8%) being extremely small pedicles with a diameter less than 2 mm. RESULTS: Among 128 extremely small thoracic pedicles with a diameter less than 2 mm, one screw (0.8%) violated the medial cortex and 22 screws (17.6%) violated the anterior cortex of the vertebral body. No screws violated the lateral cortex of the pedicle-rib unit. There were no complications associated with screw misplacement. CONCLUSION: In scoliosis patients with extremely small thoracic pedicles, our pedicle screw placement method targeting the presumed medial margin in a true PA C-arm image allows easy application with accuracy and safety, which would not possible by any other method described so far.

Laminar closure after classic Hirabayashi open-door laminoplasty.

STUDY DESIGN: Prospective analysis of preoperative and postoperative radiological data. OBJECTIVE: To assess the incidence and extent of laminar closure after Hirabayashi open-door laminoplasty, as determined by multi-detector computed tomography (CT), and to investigate the influence of this phenomenon on spinal cord compression, as shown by magnetic resonance imaging (MRI). SUMMARY OF BACKGROUND DATA: Although laminar closure occurs after laminoplasty, little is known about its progression or its effect on restenosis of the spinal canal. METHODS: Thirty-five patients (132 laminae) underwent classic Hirabayashi laminoplasty and were followed for at least 12 months. Multi-detector CT was performed preoperatively, at 1 week, or less, and 6 months after surgery. At each level, the anteroposterior (AP) diameter of the spinal canal and the angle of the opened lamina were measured. MRI was performed preoperatively and 1 year after surgery to evaluate the severity of cord compression based on a six-grade classification system. RESULTS: The mean AP diameter and the mean opening angle increased immediately after surgery (P <0.05 each) and decreased 6 months after surgery (P < 0.0001 each), with the AP diameter and opening angle decreasing by 9.4% and 10.2%, respectively. CT at 6 months showed fusion of the hinge in 91% of opened laminae. Segments with high-grade cord compression (grade ≥3) at 1 year showed greater decreases in AP diameter and opening angle (P < 0.05). CONCLUSION: After classic Hirabayashi open-door laminoplasty, opened laminae showed reclosure at 6 months, with approximately 10% decrease in AP diameter and opening angle. Postoperative lamina closure was associated with recurrent spinal cord compression, suggesting the need for other augmenting techniques that keep the laminae opened.

Under-recognized soft-tissue structures inferior and lateral to the head of the clavicle: Anatomy with computed tomography correlation.

This study was undertaken to provide an anatomical explanation for two soft-tissue structures anecdotally found on axial computed tomography (CT) scan, which are inferior (SI) and lateral (SL) to the head of the clavicle and adjacent to the sternoclavicular joint (SCJ). Three sets of cryosection images were reviewed to identify the anatomical structures corresponding to SI and SL. To demonstrate that SI and/or SL communicate with the SCJ cavity in the living, 312 consecutive chest CT scans were assessed for coexistence of SCJ and SI/SL air. To prove that under-recognition of SI and SL is due to the use of thick-section CT scan, another 50 consecutive chest CT scans were evaluated: visibility of SI and SL, and continuity between them on thick (5 mm)-section images were compared with those on thin (0.75 mm)-section images. The anterior portions of SI and SL were extensions from the SCJ cavity in the cryosection images, with the articular cartilage and disc occupying variable volumes of SI. The posterior portions of the SI and SL corresponded to the thyroid strap muscles. Air was present in 1 SI, 6 SLs, and 10 SCJs. Four of five patients with SI or SL air had coexisting SCJ air. Thick sections provided significantly poor visibility of SI and SL and continuity compared with thin-section images. SI and SL are constant shadows on thin-section CT scan, and their anterior and posterior portions represent extensions of the SCJ cavity and the strap muscles, respectively. The use of thick sections may be responsible for the under-recognition of SI and SL on CT scan.

Radiostereometric analysis of postoperative motion after application of dynesys dynamic posterior stabilization system for treatment of degenerative spondylolisthesis.

STUDY DESIGN: Prospective case series OBJECTIVE: This was designed to precisely measure motion after posterior dynamic stabilization using Dynesys instrumentation. SUMMARY OF BACKGROUND DATA: The Dynesys posterior dynamic stabilization system, which stabilizes the spinal segment while potentially decreasing the risk of adjacent segment disease, is undergoing evaluation by the US Food and Drug Administration for treatment of degenerative spondylolisthesis without fusion. Evaluation of adjacent segment disease requires precise characterization of motion on the surgical level. Unfortunately, routine clinical radiographic techniques are imprecise and unreliable for full characterization of spinal segment motion. Radiostereometric analysis, which is very precise and reliable for in vivo measurement of motion, was used to examine spinal segment motion after dynamic stabilization with Dynesys. METHODS: Six patients (age 59+/-7 y) underwent posterior decompression followed by posterior stabilization using Dynesys instrumentation (4 one-level, 2 two-levels). Three to 5 tantalum beads were placed in each vertebral body. Postoperative biplanar radiographs were obtained in flexion, extension, right, and left lateral bending, and 3-dimensional reconstruction was performed using radiostereometric analysis at 3, 6, 12, and 24 months postoperatively. The translations and rotations of the superior vertebral body were measured relative to the inferior vertebral body. RESULTS: Over the 24-month follow-up period, mean flexion, extension, left, and right lateral bending of the motion segments were noted to be 1.0 degrees, 2.4 degrees, 0.6 degrees, and 0.6 degrees or less, respectively. There were no statistically significant changes in the degree of motion. During follow-up, no significant changes in neutral position of the device were noted in any of the 3 planes, and minimal translation was noted in the postoperative period. CONCLUSIONS: The Dynesys dynamic instrumentation system seems to stabilize degenerative spondylolisthesis. As expected in the degenerative lumbar spine, the segmental motion of the implanted level in this study was limited and considerably less than normal spinal motion.

Comparison of Cobb technique, quantitative motion analysis, and radiostereometric analysis in measurement of segmental range of motions after lumbar total disc arthroplasty.

STUDY DESIGN: Prospective clinical study. OBJECTIVE: To compare the amount of segmental motion in the sagittal plane after lumbar total disc arthroplasty (TDA) measured by using the Cobb technique, quantitative motion analysis (QMA), and radiostereometric analysis (RSA). SUMMARY OF BACKGROUND DATA: The aim of TDA is preservation of motion and therefore essential to properly quantify the motion. Clinically, segmental motion is measured by using the Cobb technique, which involves either the endplates or the implant as radiographic landmarks. This technique has been reported to have large intraobserver and interobserver variability. QMA and RSA are in vivo techniques that can measure the segmental motion with accuracy, but have not been compared with each other or compared with the Cobb technique in the literature. METHODS: Ten patients (6 males and 4 females, 47 + or - 7 y) with lumbar disc degeneration were surgically treated with ProDisc-L (Synthes Inc). Intraoperatively, tantalum beads were inserted into each vertebra and patients were followed postoperatively at 1 month, 1 year, and 2 years. At each follow-up time-point, biplanar flexion/extension radiographs were obtained and sagittal range of motion (ROM) of the index level was calculated by using the RSA technique. Clinical flexion/extension radiographs were also obtained and the sagittal ROM at the same level was calculated by using a modified Cobb technique. The clinical films were additionally analyzed by Medical Metrics for sagittal ROM using QMA. The results of the 3 measurement techniques were statistically analyzed and compared in pairwise fashion. RESULTS: A significant difference (P = 0.02) was observed between the Cobb technique (5.9 + or - 4.9) and RSA (3.5 + or - 2.4). A trend (P = 0.069) was also seen between QMA (5.7 + or - 4.7) and RSA. On paired-samples correlation, a significantly high correlation was seen between Cobb technique and QMA (r = 0.868, P < 0.001). A larger variability was seen when using the Cobb technique or QMA in comparison to the RSA. CONCLUSIONS: Sagittal ROM after TDA was similar between QMA and digital Cobb technique. A larger variability was seen between these techniques and RSA.

Lower trunk kinematics and muscle activity during different types of tennis serves.

BACKGROUND: To better understand the underlying mechanisms involved in trunk motion during a tennis serve, this study aimed to examine the (1) relative motion of the middle and lower trunk and (2) lower trunk muscle activity during three different types of tennis serves - flat, topspin, and slice. METHODS: Tennis serves performed by 11 advanced (AV) and 8 advanced intermediate (AI) male tennis players were videorecorded with markers placed on the back of the subject used to estimate the anatomical joint (AJ) angles between the middle and lower trunk for four trunk motions (extension, left lateral flexion, and left and right twisting). Surface electromyographic (EMG) techniques were used to monitor the left and right rectus abdominis (LRA and RRA), external oblique (LEO and REO), internal oblique (LIO and RIO), and erector spinae (LES and RES). The maximal AJ angles for different trunk motions during a serve and the average EMG levels for different muscles during different phases (ascending and descending windup, acceleration, and follow-through) of a tennis serve were evaluated. RESULTS: The repeated measures Skill x Serve Type x Trunk Motion ANOVA for maximal AJ angle indicated no significant main effects for serve type or skill level. However, the AV group had significantly smaller extension (p = 0.018) and greater left lateral flexion (p = 0.038) angles than the AI group. The repeated measures Skill x Serve Type x Phase MANOVA revealed significant phase main effects in all muscles (p < 0.001) and the average EMG of the AV group for LRA was significantly higher than that of the AI group (p = 0.008). All muscles showed their highest EMG values during the acceleration phase. LRA and LEO muscles also exhibited high activations during the descending windup phase, and RES muscle was very active during the follow-through phase. CONCLUSION: Subjects in the AI group may be more susceptible to back injury than the AV group because of the significantly greater trunk hyperextension, and relatively large lumbar spinal loads are expected during the acceleration phase because of the hyperextension posture and profound front-back and bilateral co-activations in lower trunk muscles.

Correlation of radiostereometric measured cervical range of motion with clinical radiographic findings after anterior cervical discectomy and fusion.

STUDY DESIGN: Prospective clinical study. OBJECTIVE: To evaluate the correlation between clinical radiographic findings and sagittal range of motion (ROM) measured using radiostereometric analysis (RSA) after anterior cervical discectomy and fusion (ACDF). SUMMARY OF BACKGROUND DATA: Evaluation of fusion after ACDF continues to be difficult. Radiographic films including flexion/extension views are routinely used for this purpose. Unfortunately, routine radiographs are insensitive in demonstrating pseudarthrosis. RSA is an accurate technique that can be used in evaluation of segmental motion in vivo and can potentially be used in evaluation of spinal fusion. METHODS: Sixteen patients who underwent multi-level ACDF were enrolled in this study. The procedure was performed in the routine fashion; cervical plates were utilized in each case. Intraoperatively, 3 to 5 tantalum beads were inserted into each vertebral body. At the 1-year follow-up period, sagittal ROM of the operated segments was measured with RSA. In addition, each segment was clinically evaluated for evidence of radiographic fusion by using a 3-point grading system (fused, uncertain, pseudarthrosis) and by measuring the interspinous widening on flexion/extension films. The correlation between the radiographic findings and RSA measured sagittal ROM was evaluated. RESULTS: Fourteen 2-level and two 3-level procedures representing 31 motion segments were analyzed. The average sagittal ROM of all segments as measured by RSA was 1.3 +/- 1.4 degrees . The sagittal ROM of the segments with less than 2 mm of interspinous widening on clinical flexion/extension radiographs was measured at 1.1 degrees +/- 1.0 degrees with RSA, whereas the sagittal ROM of the segments with greater than 2 mm of interspinous widening was measured at 3.4 degrees +/- 2.9 degrees ; a significant correlation was noted between the 2-point grading method and the sagittal ROM (Pearson coefficient, r = 0.504, P = 0.004). Using the 3-point grading system, there were 20 levels graded as fused (0.8 degrees +/- 0.9 degrees ), 6 levels were graded as uncertain (1.7 degrees +/- 1.0 degrees ), and 4 levels were graded as pseudarthrosis (3.5 degrees +/- 2.7 degrees ). The pseudarthrosis group showed significantly greater motion than the fusion group (P = 0.005); a significant correlation was noted between the 3-point grading method and the sagittal ROM (Pearson coefficient, r = 0.561, P = 0.001). CONCLUSION: In this study, we evaluated the utility of RSA in evaluating segmental motion after ACDF and demonstrated a significant difference between segments that demonstrated radiographic evidence of fusion when compared with segments that demonstrated evidence of pseudarthrosis. RSA appears to be a quantitative technique capable of assisting in the evaluation of fusion.

Twelve-Month Follow-up of Lumbar Spine Range of Motion Following Intervertebral Disc Replacement Using Radiostereometric Analysis.

BACKGROUND: Many clinical studies have focused on clinical pain scores and less on kinematics following intervertebral disc replacement. Although flexion and extension of the motion segment can be measured on lateral X-rays, measuring lateral bending and axial rotation of the device is extremely difficult on plain radiography. This study was designed to measure, using radiostereometric analysis (RSA), the postoperative range of motion of the spinal segment following placement of ProDisc-L interbody device (Synthes Spine, West Chester, Pennsylvania). METHODS: Twelve patients (15 discs) with a ProDisc-L intervertebral disc replacement were followed postoperatively at 1.5, 3, 6, and 12 months with both clinical and RSA examinations. For follow-up RSA analysis, 4 to 5 tantalum beads were inserted into the vertebrae adjacent to the surgical level during surgery. Standing biplanar films were collected during follow-up, and the ranges of motion (ROM) (sagittal and coronal bending) of the adjacent vertebrae were determined by RSA. RESULTS: Based on the clinical surveys, this group of patients had similar outcomes compared to larger clinical populations. The flexion/extension ROM with the disc replacement averaged 2.5° at 6 weeks and increased over the follow-up period to 6.6° at 6 months. The lateral bending ROM with the disc replacement remained consistent over the 4 time points and averaged 3.0°. The motion at the level of the L4-5 vertebrae following disc replacement was greater across all time points than the motion at the L5-S1 level for both sagittal (5.9° versus 2.1°) and coronal (4.2° versus 0.6°) bending. CONCLUSIONS: In this study, the amount of RSA-measured segmental flexion/extension ROM for those with disc replacement was similar to other studies using plain radiography. In lateral bending, the amount of motion with disc replacement was less than the typical 6°-16° reported for normal ROM. CLINICAL RELEVANCE: This is the first published study evaluating the in vivo kinematics of artificial disc replacement using RSA.

Measurement of paradoxical and coupled motions following lumbar total disc replacement.

BACKGROUND: Maintenance of segmental motion following lumbar total disc replacement (LTDR) is one of the theoretical advantages of spinal arthroplasty. This in vivo study examined paradoxical and coupled motions during sagittal plane movements following disc arthroplasty and compared these motions with those measured following lumbar discectomy. METHODS: Ten patients following LTDR using ProDisc-L (Synthes, Inc., West Chester, Pennsylvania) and 8 patients following lumbar discectomy (LD) were enrolled. At 1-month, 1-year and 2-year postoperative time-points, patients performed flexion/extension starting from a neutral position, and the intervertebral rotations were determined with radiostereometric analysis. The amount of intended and coupled motion was compared in each group and at each postoperative time. The frequency of paradoxical motion was compared between the 2 groups, and the effects of intended motion, operative-level, number of levels, and postoperative time-point were examined. RESULTS: The intended and coupled motions following LTDR and LD did not change over time and did not differ from each other for the flexion and total sagittal movements. The sagittal range of motion (ROM) of LTDR was significantly smaller than that of LD in extension (-0.6° ± 1.1° vs -2.2° ± 1.6°). LTDR exhibited a significantly higher rate of paradoxical motion when compared to LD (26.4% vs 6.7%). In LTDR, the rate of paradoxical motion at 1 month (40%) was significantly higher than at 1-year (21.1%) or at 2-year (25.0%). The presence of paradoxical motion was significantly less frequent at L4-5 (19.2%) when compared to L5-S1 (31.3%) or L2-3 (36.4%). CONCLUSION: The overall sagittal ROM of LTDR was 3.5° ± 2.4° and not significantly different than LD. The current study did not demonstrate a difference in coupled motions between LTDR and LD. The rate of paradoxical motion was significantly higher in LTDR than in LD. In LTDR, there was a significantly lower rate of paradoxical motion seen at L4-5 and significantly higher rate seen in the earlier postoperative period. LEVEL OF EVIDENCE: Prospective cohort study with good follow-up (level 1b).

Reliability of a technique for determining sagittal knee geometry from lateral knee radiographs.

The purposes of this study were to describe an analytical technique for determining selected 2-dimensional geometric characteristics of a knee joint using lateral knee radiographs and to examine the inter- and intra-analyst reliability of this technique. Five lateral knee radiographs of different knee flexion angles (25-85 degrees at intervals of 15 degrees ) were obtained from five subjects. Two graduate and five undergraduate students with knowledge of knee anatomy served as the analysts and were asked to identify certain landmarks from the radiographs. The coordinates of these landmarks were used to determine the effective moment arm of the quadriceps force, patellar tendon length, patella height, patellar mechanism and patellar tendon angles, and tibiofemoral and patellofemoral joint spaces. For each radiograph, intraclass correlation coefficients (ICCs) were computed for combinations of 2-7 analysts. Using all seven analysts, the ICCs ranged from 0.9967 to 0.9985 for different radiographs. When fewer analysts were used, the average ICCs were 0.9975 (6 analysts), 0.9974 (5 analysts), 0.9974 (4 analysts), 0.9974 (3 analysts), and 0.9973 (2 analysts). Four of the analysts re-analyzed the radiographs 2-3months after the initial analyses. Intra-analyst ICCs ranged from 0.9842 to 0.9999. Overall, the high ICC values indicate excellent inter- and intra-analyst reliability. The proposed technique is reliable and may be used for both clinical and research purposes. The relatively small reductions in ICCs when fewer analysts were used suggest that a single experienced analyst is sufficient for clinical assessment. However, 2-3 analysts are recommended for research purposes.

Characterization of a developing lumbar arthrodesis in a sheep model with quantitative instability.

BACKGROUND CONTEXT: Mechanical forces have been considered responsible for stress shielding an arthrodesis, but the biology of a developing lumbar fusion has not been well characterized. PURPOSE: A large animal model was used to test the hypothesis that mechanical forces modify the biological processes involved in a developing bony fusion. STUDY DESIGN: Lumbar fusion was performed in an ovine model using custom instrumentation that permitted a controlled degree of anterior-posterior translation after surgery. Fusion sites were evaluated by radiography, microradiography, histology and histomorphometry at time points that corresponded with predicted early and later stages of bone healing. METHODS: Fourteen skeletally mature ewes underwent lumbar spinal fusion under general anesthesia. In the control (stable) group, the spine was rigidly fixed with a cage anteriorly and pedicle screws posteriorly. In the experimental (unstable) group, the spine was destabilized by an annulectomy (with no anterior implant) and custom pedicle screws that allowed 2 mm of anterior-posterior translation. Animals were euthanized 6 and 12 weeks after surgery. RESULTS: Radiographs confirmed that the fusion mass had not fully consolidated at either time point. Microradiographs revealed a trend toward increased bone formation at 6 weeks in the stable case as compared with the unstable, but by 12 weeks, this trend had reversed (p=.03). Intramembranous bone formation was the primary mechanism of healing near the transverse process in animals with both stable and unstable fixation. In the area between the two transverse processes, new bone formation occurred primarily through endochondral ossification. At 12 weeks, the stable case had significantly more cartilage formed (p=.023) but less newly formed bone (p=.07) as compared with the quantitatively unstable. CONCLUSIONS: This clinically realistic animal model allowed characterization of the biology of the developing arthrodesis before fusion. Under stable or unstable conditions, endochondral ossification was the predominant mechanism of new bone formation within the intertransverse process region. This finding, which contrasts with previous reports from small animal models of spine fusion, may reflect a difference in biology that results from the increased size of the intertransverse space in sheep as compared with small animals. Interestingly, mechanical instability increased the formation of new bone within this region, but not at the transverse process. Endochondral ossification therefore appears to respond to mechanical factors in the fusion site. The ovine model shows promise as an alternative to the rabbit model and may provide a more stringent test for potential new surgical and nonsurgical strategies for spine fusion.