Clinical And Mechanism Of Discogenic Low Back Pain

part1 Morphologic and relative factors analysis of discography in chroniclow back pain AbstractObjective: To evaluate the diagnostic effectiveness of discography in discogenic low back pain.Methods: 96 cases of chronic low back pain with or without radiated pain were enrolled in this study. All these cases received CT discography after a failed conservative treatment for at least 6 months. There were 42 males and 54 females; aging from 24 to 67 years old (46．4 on the average); Discographies were performed in 218 discs. They located at L2/3 in 6, L3/4 in 52, L4/5 in 76 and L5/S1 in 84．2 discs involved in 72 cases; 3 discs involved in 22 cases and 4 discs involved in 2 cases. 6 cases had previous lumbar surgery history before discography. According to Dallas Discogram Description (DDD) the positive discs were classified morphologically.Results: 56 cases (58．3%) were positive in discography, which was divided into 2 subgroups by ageing over or less than 50y. positive rate of the 2 subgroups were 33．3% and 66．6% respectively. 122 discs showed morphologic abnormality in which 62 (50．8%) were positive in discography, whereas all the positive discs showed evident morphologic abnormality. In the positive discs DDD annulus fibrous degeneration grade 1, 2, 3 account for 45．2%,35．5%,19．4% respectively, and in the negative discs those account for 30．0%,33．3%,36．7% respectively (P>0．25) . In the positive discs DDD annulus fibrous rupture grade 1, 2, 3 account for 32．3%, 67．7%, 0% respectively; and in the negative discs those account for 23．3%, 20．0%, 56．7% respectively, (P<0．005) . in the young group (<50y) DDD annulus fibrous degeneration grade 1, 2, 3 account for 51．3%, 33．3%, 15．4% respectively, DDD annulus fibrous rupture grade 1, 2, 3 account for 25．6%, 56．4%, 17．9% respectively, (P<0．005) . in the old group (≥50y) DDD annulus fibrous degeneration grade 1, 2, 3 account for 13．6%, 36．4%, 50．0% respectively; DDD annulus fibrous rupture grade 1, 2, 3 account for 13．6%, 40．9%, 45．5% respectively (P<0．005) . All 62 positive discs in 56 cases demonstrated more or less degenerative changes on MR (black discs), whereas none of the 96 normal discs on MR was positive in discography. A total of 16 high intensity zone (HIZ) was noted in these cases and 14 of them were positive in discography which accounts for 22．6% of all positive discs. The contrast volume injected into morphologically normal discs was averaged to 1．2±0．3ml.As to morphologically abnormal discs, discography positive: 3．2±1．4ml, discography negative: 3．4±1．8ml. No complication relative to discography was found in all the cases. Conclusion: (1) older LBP patients have a lower positive rate of discography despite more serious degenerative discs. (2) Inner layer disruption of annulus fibrous is the pathology of a positive discography. (3) MR intensity changes lack specificity in diagnosing discogenic pain. Additional discography is needed to identify the responsible disc. (4) The contrast volume injected into discs can be influenced by multiple factors which restricted its diagnostic value. Part 2 Pathology of discogenic low back painObjective: To compare the distribution of algesia nerve fibers and TNF-αbetween discography positive and negative discs.Methods: 15 discography positive discs (6 L4/5, 9 L5/S1) were incised during artificial lumbar disc replacement or anterior lumbar interbody fusion. These patients comprised of 8 males and 7 females and their age ranged from 33y to 69y (averaged 55y). The control group comprised of 12 dicography negative discs (3 L3/4, 4 L4/5, 5 L5/S1) from patients of chronic low back pain (4 males and 8 females). The discs were incised during discectomy or posterior lumbar interbody fusion. Their age ranged from 29y to 58y (averaged 47y). all the specimens were fixed with 10% formalkehyde and embedded with paraffin. Slices of 5μm were incised every 1mm and then HE stained. SP immuno-positive nerve fibers and TNF-αimmuno-positive cells were detected by means of immunohistochemistry. Quantitative morphological analysis was applied for account (20 fields were randomly selected in every slice, the average was calculated).Results: Degenerative changes were noted in all the specimens. Algesia nerve fibers accompanied by capillary were noted in inner layer of fibrous annulus and nucleus pulposus in most of the discs in both groups. But SP positive fibers were significantly more in discography positive group than in negative group. There was no obvious difference between distribution of TNF-αpositive macrophages in both groups.Conclusion: the significant different between distribution of algesia nerve fiber in discography positive and negative group indicates algesia nerve fiber infiltration may be the pathogenesis of discogenic low back pain. Part 3 Instant and fatigue biomechanical stability of anterior lumbarinterbody fusion (ALIF)Objective: To evaluate instant and fatigue biomechanical stability of anterior lumbar interbody fusion with a PEEK cage.Methods: 6 male human lumbar spines were collected; X-ray was performed toexclude pathology and obvious degenerative changes of the spines. Bone mineraldensities of these spines were identified as normal by LUNAR DPX-L X-ray BoneDensitometer. L4-S2 segment were prepared and embedded to clamps. 500 N ofpreloads was applied to specimens through longitudinal axis of the spine. Then thespecimens were tested on the following 3 modes in flexation, extension, lateralbending and torsion: (1) intact lumbar spine; (2) stand alone ALIF on L5/S1; (3) ALIFaugmented with pedicle screw system. Stability tests were performed instantly andafter 10,000 repetitive flexation-extension loads respectively.Results: Range of motion (ROM) of stand alone ALIF decreased 76．9%, 66．6%, 81．1% in flexation, extension and lateral bending respectively. Augmented with pediclescrew system further decreased ROM of ALIF by 93．9%, 90%, 86．6% in flexation,extension and lateral bending respectively. After 10,000 repetitive fiexation-extensionloads, no loosening or migration of cage or pedicle screws were noted.Conclusion: instant and fatigue stabilities of stand alone PEEK cage ALIF are allmuch better than intact lumbar spine. Pedicle screw system fixation can reinforcestability of ALIF significantly.Part 4 Relationship between discography pressure and outcome of anteriorlumbar interbody fusion for discogenic low back painObjective: To explore relationship between discography pressure and outcome of anterior lumbar interbody fusion (ALIF) for discogenic low back pain.Methods: From 2004．4 to 2006．6, 65 patients with chronic low back pain were identified as discogenic by pressure controlled discography, 22 cases of which received ALIF after failed conservative treatment for at least 6 months. The diagnostic criterion of discogenic low back pain include: (1) the pain of low back and lower limb is not accord with nerve roots; (2) course of pain persisted at least half a year; (3) MRI T2 weight showed black disk; (4) positive discography ( VAS≥50) with pressure no more than 500 KPa ; (5) articular process block to exclude pain derived from degeneration. The surgically treated patients aged 45 on the average (ranging form 25 to 67) . The treated discs located: 8 in L4,5, 12 in L5S1, 2 in both L4,5 and L5S1．22 cases received ALIF in 24 levels via retroperitoneal approach. The pressure as soon as accordant pain was initially induced was recorded during discography. Low pressure (pressure≤300KPa) in 10 cases and high pressure (pressure 300-500KPa) in 12 cases. 3 days postoperative the patients were allowed to leave bed with a brace, and thebrace should be used for 3 months.Results: all the cases were followed up for 18 months on the average (6-26 months),At the end of follow-up all the patients recovered normal social life and work withoutany symptoms. Disc height increased from 9．5 mm preoperatively to 13．5 mmpostoperatively. Surgery time averaged 90 min (70-120 min); blood loss averaged 220ml (100-400 ml). Low pressure group and high pressure group showed no significantdifferent in VAS, ODI, disc height, surgery time and blood loss preoperatively. At 6months follow up, VAS and ODI improve rate of low pressure group account for82．4% and 90．1% respectively; and which of high pressure group account for 71．7%and 80．6% respectively. No ileus, retrograde ejaculation nor artificial disc translationwas noticed during follow-up.Conclusion: ALIF provides satisfactory outcome for discogenic low back pain.Pressure controlled discography can increase diagnostic accuracy of discogenic lowback pain, and a positive discography on low pressure indicates better surgicaloutcome.