The use of fusion mass screws in revision spinal deformity surgery.

STUDY DESIGN: To report the use of a posterior based 'fusion mass screw' (FMS) as a primary or salvage fixation point in a revision spinal deformity following a previous posterior spinal fusion (PSF). Our experience of this technique in a case report and the clinical and radiological results are reported. OBJECTIVES: To describe the technique and uses of the FMS as a primary/salvage fixation point in osteotomies in previously arthrodesed spinal deformity surgery. Obtaining fixation points to correct and stabilize a spinal deformity with coronal and sagittal imbalance in a previously arthrodesed spine during revision surgery can be challenging. Several alternate pedicle fixation techniques and laminar screw techniques have been described in the literature. However, there is no description of these techniques in the presence of a spinal fusion with distorted anatomy. A pedicle screw placed coronally across a thick posterior fusion mass can provide an alternate method of fixation in these cases with complex anatomy. METHODS: Two cases of complex spinal deformity and corrective spinal osteotomies using fusion mass screws (FMSs) placed coronally across the posterior fusion mass are described. The first case is an 8-year-old patient with Marfan's syndrome who developed a crank shaft phenomenon and severe thoracolumbar kyphoscoliosis following a previous PSF. The second case is a 53-year-old patient with coronal imbalance following PSF as a child using Harrington instrumentation who developed distal degeneration with stenosis in her remaining mobile segments. Both patients underwent vertebral column resection and osteotomy closure plus stabilisation using FMS. The clinical and radiological results and technique for insertion of the FMS are described. CONCLUSION: In this report, we present a novel method of using posterior FMSs to achieve fixation and correction in cases of revision deformity surgery with difficult anatomy. While we feel pedicle screws are the gold standard in deformity correction, knowledge of alternatives such as the FMS can allow surgeons to achieve stable constructs when faced with challenging situations.

Comparison of three types of lumbar osteotomy for ankylosing spondylitis: a case series and evolution of a safe technique for instrumented reduction.

INTRODUCTION: The principles of correction of thoraco-lumbar kyphotic deformity (TKLD) in ankylosing spondylitis (AS) are essentially centred on lordosing osteotomies such as pedicle subtraction closing wedge osteotomy (CWO), polysegmental posterior lumbar wedge osteotomies (PWO) and Smith Peterson's open wedge osteotomy (OWO) of the lumbar spine. There have been no studies that compared the results of the three osteotomies performed by a single surgeon with a long-term follow-up. MATERIALS AND METHODS: A retrospective review of 31 patients with AS was performed: 12 patients underwent CWO, 10 had OWO, and 9 had PWO. Radiographic assessment was performed at 6, 12, 24, and 52 weeks and annually thereafter. Clinical assessment included blood loss, intensive care unit (ICU) stay, and surgical time recordings. All patients were assessed clinically at regular intervals and outcome measures recorded included Oswestry Disability Index (ODI), Visual Analogue Score (VAS) for pain, and SRS-22 (recorded in 23 patients). RESULTS: The mean age at surgery was 54.7 years (40-74 years) and mean duration of symptoms was 3 years (range, 5-8 years). Mean follow-up was 5 years (range, 2-10 years). There was no statistically significant difference between the three techniques with regard to mean duration of surgery and ICU stay. The mean duration of surgery was 7 h (range, 4-9 h) (OWO cases had shorter period than CWO and PWO cases, and the longest period was for CWO cases). The mean ICU stay was 3 days (range, 2-20 days) (the period of stay was shorter in general for OWO and slightly longer for CWO and PWO). Blood loss was expressed as percentage of estimated blood volume (EBV). The mean blood loss in PWO was 23 ± 15.4% (range, 9-36%), CWO was 28 ± 4.5% (range, 12-40%) and in OWO was 15 ± 11% (range, 13-99%). Mean correction of kyphosis was 38° (range, 25°-49°) with CWO, 28° with OWO (range, 24°-38°) and 30° with PWO (range, 28°-40°). In comparison to preoperative scores, statistically significant improvement was noted in all three groups in the postoperative period with regard to ODI, VAS and SRS-22 (p = 0.001, Wilcoxon signed-rank test). CONCLUSION: Better radiographic correction was noted in the CWO and PWO groups, although this was associated with increased blood loss, multiple levels of instrumentation, and increased surgical time compared to OWO. A new safe technique of instrumentation using temporary malleable rods to prevent sagittal translation during the reduction manoeuvre is also described.

Scoliosis in Duchenne's muscular dystrophy: a changing trend in surgical management : a historical surgical outcome study comparing sublaminar, hybrid and pedicle screw instrumentation systems.

A non-randomised retrospective study to compare the results of surgical correction of scoliosis in Duchenne's muscular dystrophy (DMD) patients using three different instrumentation systems-Sublaminar instrumentation system (Group A), a hybrid of sublaminar and pedicle screw systems (Group B) and pedicle screw system alone (Group C). Between 1993 and 2003, 43 patients with DMD underwent posterior spinal fusion and instrumentation. Group A (n = 19) had sublaminar instrumentation system, Group B (n = 13) had a hybrid construct and Group C (n = 11) was treated with pedicle system. The mean blood loss in Group A was 4.1 l, 3.2 l in Group B and 2.5 l in Group C. Average operating times in Group A, B and C were 300, 274 and 234 min, respectively. Mean pre-operative, post-operative and final Cobb angle in Group A was 50.05 +/- 15.46 degrees , 15.68 +/- 11.23 degrees and 21.57 +/- 11.63 degrees , Group B was 17.76 +/- 8.50 degrees , 3.61 +/- 2.53 degrees and 6.69 +/- 4.19 degrees and Group C was 25.81 +/- 9.94 degrees , 5.45 +/- 3.88 degrees , 8.90 +/- 5.82 degrees , respectively. Flexibility index or the potential correction calculated from bending radiographs were 60 +/- 6.33, 70 +/- 4.65 and 67 +/- 6.79% for Group A, Group B and Group C respectively. The percentage correction achieved was 72.5 +/- 14.5% in Group A, 82 +/- 6% in Group B and 82 +/- 8% in Group C. The difference between percentage correction achieved and the flexibility index was 12.45 +/- 8.22, 12.05 +/- 1.3 and 15.00 +/- 1.21% in Group A, B and C, respectively The percentage loss of correction in Cobb angles at final follow-up in Group A, B and C was 12.5 +/- 3.5, 16.5 +/- 1. and 12.5 +/- 2.5%, respectively. Complications seen in Group A were three cases of wound infection and two cases of implant failure; Group B had a single case of implant failure and Group C had one patient with wound infection and one case with a partial screw pull out. Early surgery and smaller curve corrections appears to be the current trend in the management of scoliosis in DMD. This has been possible due to early curve detection and surgery thus having the advantage of less post-operative respiratory complications and stay in paediatric intensive care. Also, early surgery avoids development of pelvic deformity and extension of instrumentation to the pelvis thereby reducing blood loss. This trend reflects the advent of newer and safer instrumentation systems, advanced techniques in anaesthesia and cord monitoring. Sublaminar instrumentation system group had increased operating times and blood loss compared to both the hybrid and pedicle screw instrumentation systems due to increased bleeding from epidural vessels and pelvic instrumentation. Overall, the three instrumentation constructs appear to provide and maintain an optimal degree of correction at medium to long term follow up but the advantages of lesser blood loss and surgical time without the need for pelvic fixation seem to swing the verdict in favour of the pedicle screw system.

Spontaneous kyphotic collapse followed by autostabilisation secondary to cervical osteomyelitis in an intravenous drug abuser.

There is a high risk of cervical osteomyelitis in intravenous drug abusers due to the use of jugular veins for administration of drugs. Here described is a case of rapid vertebral body destruction at two levels leading to a progressive kyphotic deformity followed by autofusion, secondary to cervical osteomyelitis. The case report goes on to hypothesise about the unique manner of progression of untreated cervical osteomyelitis with a rapid onset of kyphotic deformity and associated severe bone destruction in an intravenous drug abuser. Due to the high incidence of osteomyelitis in intravenous drug abusers, there should be a low threshold to investigate for this condition and early magnetic resonance imaging is vital. It alerts the treating spine surgeon to the fact that early immobilisation is crucial in these cases to prevent a severe impending deformity that can be surgically challenging.

Multilevel vertebral osteomyelitis and facet joint infection following epidural catheterisation.

We report a case of multilevel vertebral osteomyelitis with facet joint infection after epidural catheterisation. Back pain relating to regional anaesthetic techniques is common and usually self-limiting. However, it is essential to consider infection in any differential diagnosis. Prolonged use of these regional anaesthetics post-operatively makes the possibility of infection more likely. The microbiology of spine infection resulting from direct spread is not well documented but the few cases reported suggest a wide range of causative organisms. For this reason in cases of spinal infection resulting from epidural catheterisation every effort should be made to obtain a direct tissue sample for pathogen identification and one should not simply rely on blood cultures or nonspecific empirical antimicrobials. Delays in commencing appropriate antimicrobials may result in considerable morbidity.

V-Y vertebral body osteotomy for the treatment of fixed sagittal plane spinal deformity.

BACKGROUND CONTEXT: Fixed sagittal plane imbalance (FSI) has traditionally been corrected by either opening or closing wedge osteotomies or vertebral column resections. These methods involve multiple vertebrae and have been associated with limited degrees of correction and/or neurovascular compromise. PURPOSE: We describe a new V-Y vertebral osteotomy (VYO) that involves a single vertebra, allowing for correction of all three columns in a safer fashion. STUDY DESIGN: A prospective assessment of the degree of correction pre- and post-VYO in a tertiary spinal center. PATIENT SAMPLE: Ten consecutive patients presenting with sagittal plane imbalance were enrolled in this study. OUTCOME MEASURES: Outcomes were assessed with pre- (preop) and postoperative (postop) outcome questionnaires (Oswestry Disability Index [ODI] and Scoliosis Research Society-24) and radiography. METHODS: Ten patients underwent VYO at L3 with varying levels of instrumentation. The procedure involves a V-shaped osteotomy in the sagittal plane, sparing the anterior 50% of the body, the apex of which is then converted to a Y shape, and the osteotomy closed. RESULTS: Patients were followed for a mean of 36 months (24-48 months). The procedure led to significant improvements in sagittal balance, lumbar lordosis, thoracic kyphosis, coronal balance, sacral inclination, and pelvic incidence. The average degree of correction achieved was 44.58°±6.19° (mean±standard deviation). The mean blood loss was 1,287±350 mL and the operative time was 220±24 minutes. The mean preop ODI was 72% (range 58%-85%) and postop ODI averaged 22% (range 10%-30%). The mean preop SRS-24 score was 30.1 and postop was 101. CONCLUSIONS: The VYO provides a safe correction of up to 45° at a single osteotomy site in FSI patients. It involves an isolated posterior approach and is recommended for corrections below the region of the conus.

Do quantitative magnetic resonance imaging parameters correlate with the clinical presentation and functional outcomes after surgery in cervical spondylotic myelopathy? A prospective multicenter study.

STUDY DESIGN: A prospective multicenter cohort study. OBJECTIVE: To establish the relationship between preoperative quantitative magnetic resonance imaging (MRI) parameters and clinical presentation and postoperative outcomes in patients with cervical spondylotic myelopathy. SUMMARY OF BACKGROUND DATA: Correlation of magnetic resonance imaging with clinical presentation and outcomes in cervical spondylotic myelopathy is poorly understood. METHODS: A total of 134 magnetic resonance imaging scans were reviewed from 12 sites across North America. The transverse area (TA) of the spinal cord at the site of maximal compression was computed, and spinal cord signal intensity (SI) changes on T1-/T2-weighted imaging (WI) were evaluated. Detailed clinical assessments--neurological signs, symptoms, Nurick grade, modified Japanese Orthopaedic Association, segmental-tract score, and long-tract score of modified Japanese Orthopaedic Association, 30-m walk test, Short-Form 36 questionnaire, and neck disability index were performed at admission, 6 months, and 12 months postoperatively. RESULTS: The total number of neurological signs in a patient correlated with TA (P = 0.01) and SI changes on T1-/T2WI (P = 0.05). Pre- and postoperative Nurick grade (P = 0.03, P = 0.02), modified Japanese Orthopaedic Association score (P = 0.005, P = 0.001), segmental-tract score (P = 0.05, P = 0.006), and long-tract score (P = 0.006, P = 0.002), 30-m walk test (P = 0.002, P = 0.01) correlated with TA. There was no significant difference in pre- and postoperative clinical scores in patients with/without SI changes. Patients with severe cord compression showed SI changes on T1-/T2WI more frequently (r =-0.27, r =-0.38). Pyramidal signs--plantar response, Hoffmann reflex and hyper-reflexia correlated with TA (P = 0.003, P = 0.0004, P = 0.024, respectively) and SI changes on T1/T2WI (P = 0.02). CONCLUSION: TA closely mirrors the clinical presentation of cervical spondylotic myelopathy and may be used in predicting surgical outcomes. Pyramidal signs correlated with TA and/or SI changes on T1-/T2WI. The total number of neurological signs in a patient correlated with TA. There was no significant relationship between TA, age and duration of symptoms. LEVEL OF EVIDENCE: 3.

Assessment of spinal cord compression by magnetic resonance imaging--can it predict surgical outcomes in degenerative compressive myelopathy? A systematic review.

STUDY DESIGN: Systematic review. OBJECTIVE: We sought to conduct a systematic review to examine the role of magnetic resonance imaging in predicting outcomes after surgery and to evaluate the evidence currently available critically. SUMMARY OF BACKGROUND DATA: Degenerative compressive myelopathy is a common clinical problem associated with adverse health outcomes. Although a number of studies have investigated the association between preoperative magnetic resonance imaging characteristics and outcomes after surgery for degenerative compressive myelopathy, the conclusions of these studies have often yielded differing results. METHODS: Articles examining the predictive value of magnetic resonance imaging were obtained from MEDLINE, EMBASE, and PubMed databases (1980-2011). Thirty publications that met the inclusion criteria were reviewed. Two reviewers independently assessed each study regarding the level of evidence (using the criteria proposed by Sackett) and methodological quality based on revised Cochrane quality assessment checklist. RESULTS: Three excellent, 1 good, and 10 poor quality studies assessed cord compression--transverse area (4), compression ratio (5), and anteroposterior diameter (1). Relationship between signal intensity (SI) changes and surgical outcomes were reviewed by 28 studies--8 excellent, 9 good, and 13 poor quality studies. SI changes within the spinal cord included the presence of SI on T2-weighted image (WI) (17), area of SI on T2WI (8), degree of SI on T2WI (5), presence of SI on both T1-/T2WI (2), SI ratio on T2WI (2), and the position of SI on T2WI (1). CONCLUSION: Based on a combination of excellent and good quality studies, transverse area correlates with recovery ratio but not with postoperative functional score assessed by Japanese Orthopaedic Association/modified Japanese Orthopaedic Association scores. SI changes defined by (1) its presence on T2WI, (2) its extent (focal or multisegmental), (3) its brightness, and (4) its presence on both T1-/T2WI can predict surgical outcomes in degenerative compressive myelopathy.

Predictors of surgical outcome in cervical spondylotic myelopathy.

STUDY DESIGN: Prospective study. OBJECTIVE: To determine whether magnetic resonance imaging and clinical and demographic findings in patients with cervical spondylotic myelopathy (CSM) were independently associated with baseline functional scores and whether these were also predictive of postoperative functional outcomes. SUMMARY OF BACKGROUND DATA: There are considerable limitations in current literature that prevent making formal recommendations regarding the use of clinical and radiological prognostic factors in patients with CSM. METHODS: This prospective study included 65 consecutive patients with CSM treated in a tertiary referral center. The modified Japanese Orthopaedic Association (mJOA) scale was used to quantify disability at admission and at 12-month follow-up. Age, sex, duration of symptoms, severity of myelopathy, spinal column alignment, surgical technique, levels of compression, anteroposterior diameter and transverse area at the site of maximal cord compression, and magnetic resonance imaging signal intensity changes were assessed. Data were analyzed using Spearman rank correlation test, analysis of variance, Mann-Whitney U test, and stepwise multivariate regression. RESULTS: Higher baseline mJOA scores were associated with younger age (P = 0.0002), shorter duration of symptoms (P = 0.03), and greater transverse area (P = 0.02). Better recovery ratio was associated with younger age (P = 0.005) and higher baseline mJOA score (P = 0.003). Greater changes in mJOA score were associated with higher baseline mJOA score (P < 0.0001). Using multivariate analysis, the functional outcomes after surgery were best predicted by baseline mJOA score and age of patient. CONCLUSION: Age and baseline mJOA scores were highly predictive of outcome for patients undergoing surgical treatment of CSM. The degree of spinal cord compression and patterns of signal intensity changes on T1/T2 weighted images were not independently predictive of outcome, but it was found to correlate with the functional status at the time of presentation and age of the patient. The duration of symptoms correlated well with preoperative functional status but did not seem to affect the postoperative outcome.

Predictors of treatment outcomes in geriatric patients with odontoid fractures: AOSpine North America multi-centre prospective GOF study.

STUDY DESIGN: Multicenter prospective cohort study. OBJECTIVE: To identify patient and treatment characteristics associated with treatment success or failure in the management of odontoid fractures. SUMMARY OF BACKGROUND DATA: Odontoid fractures are the most common cervical spine fractures in the elderly and represent a significant management challenge with widely divergent views regarding operative versus nonoperative management. METHODS: A total of 159 patients 65 years and older with radiographically confirmed type II odontoid fractures were enrolled at 10 sites in the United States and 1 site in Canada between January 2006 and May 2009. Subjects were followed at 6 and 12 months post-initial treatment with Neck Disability Index and SF-36v2 scores. Final treatment outcome was classified as failure or success. Treatment failure was defined as death by any cause, decline in Neck Disability Index by more than 9.5 absolute points, or occurrence of a major treatment-related complication. Baseline characteristics between the groups were compared using t test for the continuous variables and χ2 test for the categorical variables. Baseline characteristics associated with treatment outcomes were identified by multiple logistic stepwise regression analysis. RESULTS: A total of 101 (63.5%) patients were treated surgically and 58 (36.5%) conservatively. Forty-four (27.7%) patients had a successful outcome and 86 (54.1%) had a treatment failure; for 29 patients (18.2%), treatment status could not be determined (3 withdrew; 26 were lost to follow-up). Twenty-nine (18.2%) patients expired before the 12-month follow-up. Follow-up information was available for 103 of 127 surviving (81.1%) patients. Twelve-month SF-36v2 scores were worse in the failure group. The characteristics associated with treatment failure were older age (odds ratio [OR] = 1.08 for each year of age); initial nonsurgical treatment (OR = 3.09); male sex (OR = 4.33), and baseline neurological system comorbidity (OR = 4.13). CONCLUSION: Older age, initial nonsurgical treatment, and male sex are associated with failure of treatment in patients with geriatric odontoid fractures.

Reliability of quantitative magnetic resonance imaging methods in the assessment of spinal canal stenosis and cord compression in cervical myelopathy.

STUDY DESIGN: Prospective, blinded reliability study of quantitative magnetic resonance imaging (MRI) measures in patients with cervical myelopathy. OBJECTIVE: To assess the intra- and interobserver reliability of commonly used quantitative MRI measures such as transverse area (TA) of spinal cord, compression ratio (CR), maximum canal compromise (MCC), and maximum spinal cord compression (MSCC). SUMMARY OF BACKGROUND DATA: There is no consensus on an optimal quantitative MRI method(s) in assessing canal stenosis and cord compression. METHODS: Seven surgeons performed measurements on 17 digital MR images, on 4 separate occasions. The degree of stenosis was evaluated by measuring TA and CR on axial T2, MCC, and MSCC on midsagittal T1- and T2-weighted MRI sequences, respectively. Statistical analyses included repeated-measures analysis of variance and intraclass correlation coefficients (ICCs). RESULTS: The mean ± SD for intraobserver ICC was 0.88 ± 0.1 for MCC, 0.76 ± 0.08 for MSCC, 0.92 ± 0.07 for TA, and 0.82 ± 0.13 for CR. In addition, the interobserver ICC was 0.75 ± 0.04 for MCC, 0.79 ± 0.09 for MSCC, 0.80 ± 0.05 for CR, and 0.86 ± 0.03 for TA. Higher degree of canal compromise (MCC) was associated with lower modified version of Japanese Orthopaedic Association Scale score (P = 0.05). Also, a strong association was found between MSCC and lower modified version of Japanese Orthopaedic Association Scale score, greater number of steps, and longer walking time (P < 0.05). CONCLUSION: All 4 measurement techniques demonstrated a good to moderately high degree of intra- and interobserver reliability. Highest reliability was noted in the assessment of T2-weighted sequences and axial MRI. Our results show that the measurements of MCC, MSCC, and CR are sufficiently reliable and correlate well with clinical severity of cervical myelopathy.

A safe controlled instrumented reduction technique for cervical osteotomy in ankylosing spondylitis.

STUDY DESIGN: A retrospective review of clinical and radiologic outcome in 13 consecutive patients with Ankylosing Spondylitis (AS) who underwent cervical osteotomy for correction of fixed cervicothoracic kyphotic deformity (CTKD) using an innovative technique. OBJECTIVE: To report further refinements to an existing technique for instrumented reduction of cervical osteotomy and assess the safety and efficacy of this procedure in 13 patients. SUMMARY OF BACKGROUND DATA: Cervical osteotomy in AS has been used for correction of CTKD, but is associated with significant risks. We have previously reported a novel technique to perform this procedure safely. Even with this technique, there was a small risk of subluxation, and this risk has been further reduced with our new technique. METHODS: Between 1993 and 2008, the senior author (SMHM) performed cervical osteotomy for severe CTKD in 13 AS patients. There were 11 male and two female patients, the average age being 56 (40-74) years. The main surgical indication was restricted frontal visual field. The average symptom duration was 2.7 (1-5) years. All patients had a general anesthetic and underwent cervical osteotomy and instrumentation from C3 to T5 in prone position. RESULTS: The average duration of surgery was 4.7 (3-6.5) hours. The calculated blood loss was 1938 mL (1000-3600). The mean follow-up period was 6.5 (1.5-16) years. The mean preoperative chin brow vertical angle was found to be 54° (20°-70°). After surgery, this improved to 7° (2°-12°). The preoperative kyphotic angle measured was 19.2° (14°-28°). This improved after surgery to -34° (-21° to -39°). There were no instances of a neurologic deficit. At a mean follow-up of 6.5 years (18 months-6 yr), no instances of loss of correction or implant failure were noted. CONCLUSION: This innovative new technique provides for a safe, controlled reduction for cervical osteotomy for fixed cervicothoracic kyphosis in AS. The technique reliably renders rigid immobilization that obviates the risk of intra- and postoperative junctional subluxation, eliminates the need for postoperative halo-vest immobilization, and achieves satisfactory fusion.

A new three-stage spinal shortening procedure for reduction of severe adolescent isthmic spondylolisthesis: a case series with medium- to long-term follow-up.

STUDY DESIGN: A case series of eight consecutive patients with severe (Meyerding Grade ≥ 3) adolescent isthmic spondylolisthesis (SAIS) who underwent reduction and stabilization by using a new surgical technique. OBJECTIVE: To report the results of a safe three-stage spinal shortening procedure in a single operative session in eight patients with SAIS. SUMMARY OF BACKGROUND DATA: The treatment of SAIS is controversial and the opinion continues to remain divided between in situ fusion and reduction followed by stabilization. We reported a new surgical technique to facilitate safe reduction and stabilization of SAIS and the results in eight adolescents are presented. METHODS: Eight patients with Meyerding Grade III (2), IV (5), and V(1) were operated between 2000 and 2006 for SAIS. The back/leg pain duration was 13.7 months and average age at surgery was 14.75 years. The slip angle (SA), percentage slip (%S), sacral inclination (SI), lumbar lordosis (LL), pelvic incidence (PI), and sagittal balance were measured and the Oswestry Disability Index (ODI) and visual analog scale pain score were used as outcome measures. All patients underwent posterior decompression with sacral dome osteotomy, anterior transperitoneal L5/S1 discectomy, and posterior reduction and instrumented circumferential fusion in a single operative session. RESULTS: The average follow-up was 6 years. The mean preoperative degree of slip was 86%, which improved to 5% (r 1-17%, spondyloptosis case 32%) postoperatively. The mean L5 SA, SI, and LL preoperatively were 48°, 34°, and -72°, respectively, and postoperatively improved to 43° and -47°, respectively. The sagittal balance was 55 and 34 mm pre- and postoperatively, respectively. Near anatomical reduction was achieved in seven patients. No implant failures or revisions to date. The mean ODI improved to 6% from 56% and visual analog scale from 8 to 1, postoperatively. CONCLUSION: This safe 3-stage procedure assists sudden reduction and circumferential fusion of SAIS without any neurologic deficit and excellent clinicoradiologic outcome restoring normal lumbosacral biomechanics.

2009 ISSLS Prize Winner: What influence does sustained mechanical load have on diffusion in the human intervertebral disc?: an in vivo study using serial postcontrast magnetic resonance imaging.

STUDY DESIGN: An in vivo study of the effects of mechanical loading on transport of small solutes into normal human lumbar intervertebral discs (IVD) using serial postcontrast magnetic resonance imaging (MRI). OBJECTIVE: To investigate the influence of a sustained mechanical load on diffusion of small solutes in and out of the normal IVD. SUMMARY OF BACKGROUND DATA: Diffusion is an important source of disc nutrition and the in vivo effects of load on diffusion in human IVD remains unknown. METHODS: Forty normal lumbar discs (on MRI) in 8 healthy volunteers were subjected to serial post contrast (Gadoteridol) 3 Tesla MRI in 2 phases. In phase 1 (control), volunteers were scanned at different time points--precontrast and 1.5, 3, 4.5, 6, and 7.5 hours postcontrast injection. In phase 2, 1 month later, the same volunteers were subjected to sustained supine loading for 4.5 hours. MRI scans were performed precontrast (preload) and postcontrast (postloading) at 1.5, 3, and 4.5 hours. Their spines were then unloaded and recovery scans performed at 6 and 7.5 hours postcontrast. In house software was used to analyze images. RESULTS: Repeated-measures ANOVA and pairwise comparisons at different time points in the central region of the loaded disc (LD) compared to the unloaded discs (UD) revealed significantly lower signal intensity ratios (P1.5h:P3h:P4.5h<0.001:<0.001:<0.002) indicating reduction in transport rates for the LDs. Signal intensity ratios continued to rise in LD for 3 hours into recovery phase,whereas UD at the same time point showed a decrease (mean +/- SD = 0.08 +/- 0.08 vs. -0.21 +/- 0.03). CONCLUSION: Sustained supine creep loading (50% body weight) for 4.5 hours retards transport of small solutes into the center of human IVD and it required 3 hours of accelerated diffusion in recovery state for LD to catch-up with diffusion in UD. The study supports the theory that sustained mechanical loading impairs diffusion of nutrients entering the disc and quite possibly accelerates disc degeneration.