Surgicaloutcomes ofmini-open Wiltse approach and conventional open approach in patients with single-segment thoracolumbar fractures withoutneurologic injury

Haijun Li,Lei Yang,Hao Xie,Lipeng Yu,Haifeng Wei,Xiaojian Cao,?

1Department of Orthopaedics,the First Affiliated Hospital of Nanjing Medical University,Nanjing,Jiangsu 210029,China;

2Department of Orthopaedics,the Second Affiliated Hospital of Nanjing Medical University,Nanjing,Jiangsu,China;

3Department of Radiology,Taizhou Peopleˊs Hospital affiliated to Nantong University,Taizhou,Jiangsu,China.

Surgicaloutcomes ofmini-open Wiltse approach and conventional open approach in patients with single-segment thoracolumbar fractures withoutneurologic injury

Haijun Li1,Lei Yang1,Hao Xie2,Lipeng Yu1,Haifeng Wei3,Xiaojian Cao1,?

1Department of Orthopaedics,the First Affiliated Hospital of Nanjing Medical University,Nanjing,Jiangsu 210029,China;

2Department of Orthopaedics,the Second Affiliated Hospital of Nanjing Medical University,Nanjing,Jiangsu,China;

3Department of Radiology,Taizhou Peopleˊs Hospital affiliated to Nantong University,Taizhou,Jiangsu,China.

Thisstudy aimed to introduce a novelmini-open pedicle screw fixation technique via Wiltse approach,and compared itwith the traditionalposterior open method.A totalof 72 cases of single-segmentthoracolumbarfractures withoutneurologic injury underwentpedicle screw fixation via two differentapproaches.Among them,37 patients were treated using posterioropen surgery,and 35 patients received mini-open operation via Wiltse approach.Crew placement accuracy rate,operative time,blood loss,postoperative drainage,postoperative hospitalization time, radiation exposure time,postoperative improvementin R value,Cobbˊs angle and visualanalog scale(VAS)scores of the two methods were compared.There were no significant differences in the accuracy rate of pedicle screw placement,radiation exposure and postoperative R value and Cobbˊs angle improvementbetween the two groups. However,the mini-open method had obvious advantages over the conventional open method in operative time, blood loss,postoperative drainage,postoperative hospitalization time,and postoperative improvementin VAS. The mini-open pedicle screw technique could be applied in treatment of single-segment thoracolumbar fracture without neurologic injury and had advantages of less tissue trauma,short operative and rehabilitative time on the premise of guaranteed accuracy rate and no increased radiation exposure.

thoracolumbar fracture,pedicle screw,Mini-open,Wiltse approach,minimally invasive

Introduction

The thoracolumbar spine is one of the most common areasforspinalfractures[1,2].Fortreatmentofcaseswith neurological injuries,internal fixation after decompression has been widely accepted.The choice of treatment in the absence of a neurological deficit depends on the Thoracolumbar Injury Classification and Severity Score(TLICS)scores[3,4].However,for patients with thoracolumbar biomechanical changes as a result of a certain degree of spinal deformity, low back pain and even neurological symptoms may occur over time,which may seriously jeopardize their work and daily life.Therefore,some scholars advocate early surgical treatment,even for stable thoracolumbar fractures(TLICS:score≤3)[5,6].

In the conventional open posterior pedicle screw fixation with posterior midline incision,detachmentof the paraspinalmuscles may be required to reduce softtissue ischemia,alleviate dysfunction ofthe paraspinal muscles and relieve chronic pain[7-10].In addition,this open approach may be disadvantaged by prolonged operative time,increased intraoperative bleeding and delayed functional rehabilitation[11].All these problems appear to defeatour originalintention of surgical treatment.With the advantage of no paraspinal muscle stripping,the percutaneous pedicle screw placementtechnique is attracting increasing attention as itbrings a multitude of benefits including less bleeding, lower infection risk,lower incidence of postoperative pain,shorter rehabilitative time and reduced hospitalization time[12-20].It is also worth mentioning that the incidences of both postoperative intractable low back pain and muscle atrophy are also significantly reduced[12,16,21-24].

Although percutaneous pedicle screw fixation is a mature technique,itstillrequiresspecialized equipments and long learning curve[25]before implementation.High incidence ofscrew malposition[26,27]and large doses of radiation exposure[28,29]have caused a sluggish evolution.

In this study,we described a novelmini-open pedicle screw fixation technique via Wiltse approach forsinglesegmentthoracolumbar fractures and compared the reliability and safety ofthis approach with the conventionalposterioropen method.

Patients and methods

Patients

The clinical data of 72 cases of single-segment thoracolumbarfractures withoutneurologic injury were reviewed.Among them,35 cases(21 males and 14 females)from the mini-open group underwentpedicle screw internalfixation via Wiltse approach.Thirty-seven cases(23 males and 14 females)received conventional open surgeries via the posterior midline approach.The inclusion criteria were as follows:patients with singlesegmentthoracolumbar vertebralfractures classified as A1,A2,A3 or B1 type according to the AO classification,aged from 16 to 65 years,patients had fresh fracturesand were treated surgically within 10 daysafter the injury,TLICS score≥4 and load-sharing score＜7. The exclusion criteria were as follows:patients with neurologicalinjury,spinal anatomical variations or vertebraldeformity,a history ofneurologicaldysfunction or mentalillness,significantsurgicalcontraindications, osteoporosis[dual-energy X-ray absorptiometry(DEXA) examination,T value≤-2.5],and patients who refused to sign informed consent.

Surgical methods

For the conventional posterior open approach,we firstly performed a posterior midline incision at the targetsegmentand striped the paraspinalmuscle along the spinous process and the vertebrallamina.Then,the facet joints and roots of the transverse process were exposed by an automatic retractor.The entry pointwas determined based on anatomicallandmarks according to the AO method.

Forpedicle screw internalfixation via Wiltse approach, body positioning and anesthesia were performed the same asforpatientsreceiving the conventionalposterior open approach.Manipulative reduction was performed to correctthe kyphosis ofthe fractured vertebralbody before routine sterilization.Positions offoursmallincisionswere accurately determined by thelocatorand C-arm (Fig.1A).Then,dissection wasperformed tillthe outer edge of the facet joints was reached through the intermuscularplane between the multifidus and the longissimus muscles after four 1.5-2.0-centimeter-long incisions were made(Fig.1B).With the help of mini-retractor designed by ourselves,the pedicle entry point was exposed clearly(Fig.2).The determination ofthe entry pointwas also based on the anatomicallandmarks usingthe same method as the conventionalopen group.The guide wire was inserted perpendicular to the corresponding supraspinalligament[30],and then C-arm was performed to check whether the guide wire was in the pedicle before pedicle screw placement.If the guide wire was in a satisfactory position,the pedicle screw could be inserted;otherwise,position ofthe guide wire should be adjusted.Likewise,afterthe procedure ofrod installation and distraction for restoration,positions of pedicle screwsand heightofthe fractured vertebraewere confirmed using C-arm again.

Fig.1 Location of four small incisions.A:Four small incisions can be accurately determined by the locator and C-arm.B:Four 1.5-2.0-centimeter-long incisions are made with reference to the locator.

Fig.2Self-designed mini-retractor.With the help of the mini-retractor,the pedicle entry point is exposed clearly and the determination of the entry point is based on the anatomical landmarks using the same method as in the conventional open group.

Study parameters

The study parameters included operative time from the firstskin incision to skin suture,estimated blood loss,postoperative drainage,postoperative hospital stays,X-ray exposure time,which was automatically accumulated by C-arm machine,R value,Cobbˊs angle, visualanalog scale(VAS)scores,postoperative complications,and accuracy rate of screws.Blood loss was carefully measured by weighing the sponges and determining the volume of shed blood in the suction bottle.The volume of postoperative drainage was estimated by weighing wound dressings in the mini-open group as drainage tube placement was notrequired and was estimated by blood volume in the drainage bag and wound dressings in the open group.Hospital stay was calculated from the first postoperative day to the discharge day.R value was determined by the following formula:

The mean height of the fractured vertebral body/the mean height of upper and lower adjacent vertebral bodies×100%

Cobbˊs angle was delineated on lateral radiographs as the angle of the verticalline to the upper endplate of the upper adjacent vertebralbody and lower endplate of the lower adjacent vertebralbody.VAS was evaluated preoperatively,three days and one week postoperatively.Positions of pedicle screws were assessed by a single-blinded,independent and boardcertified spine surgeon according to postoperative CT scans within one week after surgery.Screw which was extrapedicular or breached the front edge of the vertebral body,inferio r or superior endplate was regarded as a failure.

Table 1 Patient data and clinical outcomes in two groups(mean±SD)

Statistical analysis

All continuous data were presented as mean± standard deviation(SD)and allcategoricaldata as percentages or numbers.Statisticalanalyses for comparisons between groups were performed using the unpaired Studentˊs t-test,Χ2 test,or non-parametric Kruskal-Wallistest.P＜0.05 wasconsidered statistically significant.Statisticalanalysis was done using SPSS 20.0(SPSS,Chicago,IL,USA).

Results

Accuracy rate of pedicle screw placement

Among all the pedicle screws,both groups required no intraoperative adjustment.No complications such as spinal cord,nerve root or blood vessel injuries occurred.In the open group,according to postoperative CT image,two screws broke through the medial cortex of the pedicle;two broke through the lateral cortex; one broke through the front cortex of the vertebral body.No screw broke through vertebral endplates. The accuracy rate of pedicle screw placement was 96.6%.In the mini-open group:five pedicle screws broke through the lateral cortex of pedicle;one broke through the frontcortex ofthe vertebralbody;no screw broke through the vertebralendplate.The accuracy rate was 95.7%.There was no significantdifference in the accuracy rate of pedicle screw placement between the two groups(Table 1).

Surgical outcomes

There were significantdifferences in operative time (P=0.018),blood loss(P＜0.001),postoperative drainage(P＜0.001)and postoperative hospitalization time(P＜0.001)between the two groups(Table 1). The results showed that the mini-open method had obvious advantages in these aspects compared with the conventionalopen method.There were no significantdifferences in R value and Cobbˊs angle between the two groups before and after surgery(P＞0.05, Table 2).But in either group,operation brought significantimprovementcompared with preoperative data (P＜0.001,Table 3).No significantdifferences were found in improvement of R value and Cobbˊs angle between the two groups(P＞0.05,Table 2).

Preoperative VAS for the two groups showed no significant difference(P＞0.05).In general,VAS forboth groups showed significantimprovementcompared with preoperative value(P＜0.01).However, the degree of this improvement between the two groups was not the same.The results showed thatthe mini-open method had greater improvement in VAS scores at postoperative day 3 and 7(P＜0.01)than the open approach(Table 4).

Table 2 Comparison of R value and Cobbˊs angle between the two groups(mean±SD)

Table3 Comparison between preoperative and postoperative Rvalue and Cobbˊs angle in the two groups(mean±SD)

Discussion

In 1968,Wiltse[31]first described the paraspinal sacrospinalis-splitting approach between the multifidus and the longissimus which was associated with less bleeding and tissue dissection compared with the single midline incision approach[32-34].Drawbacks including extensive stripping ofthe paraspinalmuscle, electrical-burn damage from electricknife and prolonged mechanicalcompression by automatic retractor could be effectively avoided in the procedure of entry point exposure through the mini-open method via Wiltse approach.The mini-open approach had rapid recovery with slight pain and markedly shorter hospitalization time compared with the traditionalopen approach.All patients from the mini-open group were mobile with the protection of the waistbrace 24 hours aftersurgery and discharged afteran average of3.4 days postoperatively.However,for those patients who underwent the open surgery,the drainage tubeswere removed on postoperative day 2,the mean postoperative hospitalstay was 9.1 days,and activity was permitted atleasttwo weeks aftersurgery.

The conventionalopen method had advantage over the mini-open technique in exposure of pedicle screw entry point based on clear anatomical landmarks. However,the operation time in the open group was prolonged,which may be due to more soft tissue dissection and skin suture.Smooth surgicalprocedure of the mini-open group was another important reason. Foursmallincisionswere rapidly located by the locator with few X-ray exposure(Fig.1A);Two separated blunthook teeth of the retractor which were confirmed suitable for varied local bone structures played an important role in preventing muscles slipping away (Fig.2).Aimed by the self-designed retractor,the entry point could also be easily exposed and determined based on the anatomicallandmarks identical to the open approach.With intactcoverage of the sarcolemma,muscle creep could be effectively avoided in muscle dissection if only the approach was strictly along the muscle gap.Especially for segments of L4 and L5,muscle gaps were absolutely clear and the sarcolemmas were relatively hypertrophic[35].

Radiation exposure in pedicle screw placementhas always been the focus of attention,and the risk of long-term low-doses X-ray remains unclear[29].In our research,determination of pedicle screw entry point in the two groups both required C-arm assistance. For the reason given above,there was no obvious difference in X-ray exposure(9.2±2.1 seconds for the open group vs.9.6±2.2 seconds forthe mini-open group)between the two groups.Namely,the mini-open approach did not increase radiation exposure in the operation.

The mini-open technique is similar to the open metho d in restoration o f vertebral body height, improvement of Cobbˊs angle and accuracy rate of screw placement.There were no cases of spinalcord, nerve orvesselinjury in both groups.Study limitations included lack of long-term follow-up in such as postoperative loss ofthe vertebralheight.However,the only distinction between the two groups was the surgical approach.In aspects of fixation method and pedicle screw type,the two techniques were the same. Therefore,we can infer thatthe mini-open approach was similar to the open method in postoperative loss ofvertebralheightin long-term follow-up.

The biggest current limitation of the mini-open approach is that it is not suitable for posterior lami-nectomy and posterolateral fusion.Therefore,the inclusion criteria was strictly limited to cases of single segmentthoracolumbarvertebralfractures classified as A1,A2,A3 or B1 type according to AO classification. Additionally,the patientˊs load-sharing score(spinal load scoring system)must be less than seven points to ensure the security of only posterior fixation for thoracolumbar fractures.Narrow indication is the drawback of this technique.

Table 4 VAS scores of the two groups(mean±SD)

In conclusion,compared with the traditional open posterior surgery,the mini-open surgery via Wiltse approach has the following advantages on the premise of no increased radiation exposure,less bleeding, shorter operative time,less postoperative pain and tissue trauma,and shorter rehabilitative and hospitalization time.Therefore,itis reliable in treating cases of thoracolumbarfractures withoutneurologicaldamage.

Acknowledgement

This work was supported by the National Natural Science Foundation of China(Grant No.30973058, 81171694,and 81371968);the Program for Development of Innovative Research Team in the First Affiliated Hospital of NJMU(No.IRT-015),and A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions. This study was approved by Ethical Committee of the First Affiliated Hospital of Nanjing Medical University.The clinicltrails.gov number is‘‘ChiCTROCC-10001133’’,and written informed consent were obtained from allpatients.

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?Corresponding author:Prof.Xiaojian Cao,Department of Orthopaedics,the First Affiliated Hospital of Nanjing Medical University,300 Guangzhou Road,Nanjing,Jiangsu 210029,China, Tel/Fax:86-013002505801/86-25-83724440,E-mail:xiaojiancao@gmail.com.

Received 01 June 2014,Revised 27 Octorber 2014,Accepted 19 December 2014,Epub 16 January 2015

The authors reported no conflict of interests.

?2015 by the Journal of Biomedical Research.All rights reserved.

10.7555/JBR.29.20140083