***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: STUDY DESIGN A prospect i ve study of 87 patients who underwent unilateral or bilateral pedicle screw fixation .  OBJECTIVES To determine whether unilateral pedicle screw fixation is comparable with bilateral fixation in one- or two-segment lumbar spinal fusion . SUMMARY OF BACKGROUND DATA Clinical results for unilateral variable screw placement instrumentation in isolated L4-L5 fusion have been reported to be as good as those for bilateral instrumentation . However , unilateral instrumentation may not be recommended for multilevel fusion . METHODS Eighty-seven patients were assigned to either unilateral ( n = 47 ) or bilateral ( n = 40 ) pedicle screw instrumentation groups  . Two kinds of pedicle screw system ( Moss Miami , DePuy , Warsaw , IN , and Steffee VSP , AcroMed , Clevel and , OH ) were used . Operating time , blood loss , duration of hospital stay , clinical outcomes , fusion rates , complication rates , and medical expenses were studied and tested with independent sample t test and chi2 test . RESULTS There were no significant differences between the two groups in blood loss , clinical ly satisfactory results , fusion rate , and complication rate . There were significant differences in duration of operating time , duration of hospital stay , and medical expenses . The number of fusion segments or kinds of instrumentation did not affect the fusion rate or clinical outcomes . CONCLUSIONS Unilateral pedicle screw fixation was as effective as bilateral pedicle screw fixation in lumbar spinal fusion independent of the number of fusion segments ( one or two segments ) or pedicle screw systems . Based on the results of this study , unilateral fixation could be used in two-segment lumbar spinal fusion OBJECT Many surgeons currently prefer to use transforaminal lumbar interbody fusion ( TLIF ) , placing 1 unilateral pedicle screw ( PS ) and 1 cage . However , no study has examined whether unilateral fixation improves surgical outcome . The authors conducted a prospect i ve r and omized controlled trial with a minimum 2-year follow-up to analyze TLIF outcomes for 2 techniques : placement of a unilateral PS and a cage compared with placement of bilateral PSs and 2 cages . METHODS Fifty patients with degenerative spondylolisthesis undergoing single-level TLIF were r and omly assigned to receive either unilateral or bilateral fixation . Parameters compared between the groups were surgical invasiveness , severity of intermittent claudication , pre- and postoperative visual analog scale ( VAS ) scores ( from 0 to 10 for back pain , lower-extremity pain , and lower-extremity numbness ) , postoperative disability scores for lumbar spinal disorders ( Japanese Orthopaedic Association Back Pain Evaluation Question naire [ JOABPEQ ] ) , and fusion rates . RESULTS The mean operative time for TLIF was significantly ( p = 0.05 ) shorter and mean estimated blood loss was significantly lower in the unilateral than in the bilateral group . Intermittent claudication improved in response to each technique , but there was no significant intergroup difference . The unilateral group had a nonsignificant tendency toward less improvement in VAS score for back pain ( 1.5 vs 3.7 for the bilateral group ) and exhibited significantly less improvement in VAS score for lower-extremity pain ( 2.1 vs 5.1 , respectively ) and numbness ( 1.7 vs 4.4 ) . There were no significant differences between the groups in postsurgical scores for all 5 items of the JOABPEQ . The fusion rates were 87.5 % ( 21 of 24 patients ) in the unilateral group and 95.7 % ( 22 of 23 ) in the bilateral group . CONCLUSIONS Transforaminal lumbar interbody fusion involving unilateral PS fixation and a single-cage technique is less invasive than a 2-cage technique and bilateral fixation , and it improved patients ' symptoms . However , it result ed in less improvement in back pain , lower-extremity pain , and lower-extremity numbness . When considering unilateral PS fixation and a single cage , the surgeon should be aware of the potential limitations of this technique . Clinical trial registration no. : UMIN000007833 ( UMIN ) Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more Study design Prospect i ve observational cohort study . Objective Comparison of clinical and radiological outcomes of  single-level open versus minimally invasive ( MIS ) transforaminal lumbar interbody fusion ( TLIF )  at 6 months and 2-year follow-up . Summary of background data There is recognition that more data are required to ascertain the benefits and risks of MIS vis-a-vis open TLIF . This study aims to report on one of the largest currently available series comparing the clinical and radiological outcomes of the two procedures with a minimum follow-up of 2 years . Methods From January 2002 to March 2008 , 144 single-level open and MIS TLIF were performed at our centre , with 72 patients in each group . Clinical outcomes were based on patient-reported outcome measures recorded at the Orthopaedic Diagnostic Centre by independent assessors before surgery , at 6 months and 2 years post-operatively . These were visual analogue scores ( VAS ) for back and leg pain , Oswestry disability index ( ODI ) , short form-36 ( SF-36 ) , North American Spine Society ( NASS ) scores for neurogenic symptoms , returning to full function , and patient rating of the overall result of surgery . Radiological fusion based on the Bridwell grading system was also assessed at 6 months and 2 years post-operatively by independent assessors . Results In terms of demographics , the two groups were similar in terms of patient sample size , age , gender , body mass index ( BMI ) , spinal levels operated , and all the clinical outcome measures ( p > 0.05 ) . Perioperative analysis revealed that MIS cases have comparable operative duration ( open : 181.8 min , MIS : 166.4 min , p > 0.05 ) , longer fluoroscopic time ( open : 17.6 s , MIS : 49.0 s , p < 0.05 ) , less intra-operative blood loss ( open : 447.4 ml , MIS : 50.6 ml , p < 0.05 ) and no post-operative drainage ( open : 528.9 ml , MIS : 0 ml , p < 0.05 ) . MIS patients needed less morphine ( open : 33.5 mg , MIS : 3.4 mg , p < 0.05 ) and were able to ambulate ( open : 3.4 days , MIS : 1.2 days , p < 0.05 ) and be discharged from hospital earlier ( open : 6.8 days , MIS : 3.2 days , p < 0.05).At 6 months , clinical outcome analysis showed both groups improving significantly ( > 50.0 % ) and similarly in terms of VAS , ODI , SF-36 , return to full function and patient rating ( p > 0.05 ) . Radiological analysis showed similar grade 1 fusion rates ( open : 52.2 % , MIS : 59.4 % , p > 0.05 ) with small percentage of patients developing asymptomatic cage migration ( open : 8.7 % , MIS : 5.8 % , p > 0.05 ) . One major complication ( open : myocardial infa rct ion , MIS : screw malpositioning requiring subsequent revision ) and two minor complications in each group ( open : pneumonia and post-surgery anemia , MIS : incidental durotomy and pneumonia ) were noted . At 2 years , continued improvements were observed in both groups as compared to the preoperative state ( p > 0.05 ) , with 50.8 % of open and 58 % of MIS TLIF patients returning to full function ( p > 0.05 ) . Almost all patients have Grade 1 fusion ( open : 98.5 % , MIS : 97.0 % , p > 0.05 ) with minimal new cage migration ( open : 1.4 % , MIS : 0 % , p > 0.05 ) . Conclusions MIS TLIF is a safe option for lumbar fusion , and when compared to open TLIF , has similar operative duration , good clinical and radiological outcomes , with additional significant benefits of less perioperative blood loss and pain , earlier rehabilitation , and a shorter hospitalization OBJECT Clinical and radiographic results were assessed to determine the clinical outcomes and fusion rate in eight consecutive patients selected for minimally invasive transforaminal lumbar interbody fusion ( TLIF ) in which a percutaneous pedicle screw system was used unilaterally . METHODS Eight patients underwent one-level , minimally invasive TLIF  in which a percutaneous pedicle screw system was used only on the side where facets were removed for interbody access . Clinical , economic , functional , and radiographic data were recorded preoperatively and at 6 months postoperatively . The mean 6-month change in the modified Prolo Scale score was 7 , and osseous interbody bridging assessed on coronal and sagittal computerized tomography studies was seen in all patients . CONCLUSIONS The use of unilateral percutaneous pedicle screw instrumentation for the minimally invasive TLIF procedure provides excellent clinical results and is an option in selected patients OBJECTIVE To compare the clinical effects of unilateral pedicle screw fixation ( uni-PS ) assisted by Quadrant system and bilateral pedicle screw fixation ( bi-PS ) for the treatment of lumbar degenerative diseases . METHODS From October 2008 to October 2010,102 patients with lower back pain , unilateral lower limb radiating pain or paraesthesia were treated with pedicle screw fixation and lumbar interbody fusion .  There were 67 males and 35 females with an average age of 51.5 years ranging from 34 to 69 years . The patients were r and omly divided into two groups ( group A and group B ) according to the internal fixation type . The patients of group A ( n=50 ) underwent with minimally transforaminal lumbar interbody fusion ( TLIF ) and unilateral pedicle screw fixation with one single cage placement assisted by Quadrant system ; and the patients of group B ( n = 52 ) underwent with posterior lumbar interbody fusion ( PLIF ) and bilateral pedicle screw fixation with one single cage placement . There were no significant differences between two groups in general information ( P > 0.05 ) . VAS score and ODI score system were used to evaluate the preoperative and postoperative pain and function recovery . Operative time , volume of blood loss , fusion rate and complication rate were compared and analyzed by statistical test . RESULTS All the patients were followed up from 12 to 21 months with an average of 18.2 months . In the group A , operative time and volume of blood loss were ( 87.6 + /- 25.5 ) min and ( 105.7 + /- 27.2 ) ml , respectively ; VAS score of low back pain and leg pain , ODI score decreased respectively from preoperative 7.2 + /- 1.4 , 7.9 + /- 1.1 , 42.2 + /- 11.8 to 3.2 + /- 0.6 , 3.0 + /- 0.7,15.6 + /- 2.3 at one month after operation ; the fusion rate was 96.0 % ( 48/50 ) and the complication rate was 4.00 % ( 2/50 ) . In the group B , operative time and volume of blood loss were ( 160.3 + /- 20.5 ) min and ( 220.6 + /- 25.5 ) ml , respectively ; VAS score of low back pain and leg pain , ODI score decreased respectively from preoperative 7.3 + /- 1.1 , 8.1 + /- 0.9 , 43.1 + /- 12.0 to 3.3 + /- 0.4 , 3.2 + /- 0.3 , 14.9 + /- 2.6 ; the fusion rate was 96.2 % ( 50/52 ) and the compli- cation rate was 5.77 % ( 3/52 ) . There were no statistically significant differences between the two groups in fusion rate , complication rate , VAS pain and ODI score . Whereas the operative time and blood loss in group A were significantly lower than that of group B. CONCLUSION Minimally invasive unilateral pedicle screw fixation is a safe and feasible method for the treatment of lumbar degenerative diseases . It is as effective as the bilateral fixation in lumbar spinal fusion . In addition , it has the advantages of short operative time , less volume of blood loss , high fusion rate , etc Purpose To compare the clinical and radiological outcomes of unilateral versus bilateral instrumented in two-level degenerative lumbar diseases after minimally invasive transforaminal lumbar interbody fusion ( MITLIF ) . Methods We conducted a prospect i ve cohort study of 74 patients , who underwent unilateral or bilateral instrumented in two-level MITLIF for degenerative lumbar diseases from May 2010 to June 2012 . There were 35 patients in group A undergoing unilateral pedicle screw fixation and 39 patients in group B undergoing bilateral pedicle screw fixation .  Demographic data and clinical characteristics were compared between the two groups before surgery 
    Output:
    
Conclusions Based on this systematic review and meta- analysis , the unilateral fixation in TLIF may achieve a similar clinical outcome and reduce blood loss and operative time when compared with that in bilateral fixation .
However , the unilateral fixation may produce lower fusion rate and more cage migration than bilateral fixation in