Eur J Orthop Surg Traumatol (2007) 17:125–129 DOI 10.1007/s00590-006-0137-5

O R I G I N A L A RT I C L E

Posterior lumbar interbody fusion and segmental lumbar lordosis Rahul Kakkar Æ P. B. R. Sirigiri Æ A. Howieson Æ A. Siva Raman Æ R. J. Crawford

Received: 15 February 2006 / Accepted: 5 July 2006 / Published online: 11 August 2006 Ó Springer-Verlag 2006

Abstract Introduction The sagittal plane of body produces a convex curve anteriorly referred to as the lordotic curve. Malalignment of lordotic curve leads to low back disorders and lumbar spinal surgery has been known to cause this. This study was a retrospective analysis of the effects of posterior lumbar interbody fusion using cages on segmental lumbar lordosis. Materials and methods We conducted a retrospective study involving 27 patients of which 16 were females and 11 were males. All patients underwent single level posterior lumbar interbody fusion with insertion of non-wedged intervertebral cage and pedicle screw fixation. Intraoperatively, all patients had a change from knee chest position to prone to augment their lumbar lordosis. The minimum follow up was 2 years and fusion was achieved in 21 patients. Results Segmental lordotic angles increased from 15.2° to 20.6° at L4/5 level and from 17.8° to 24.5° at L5/S1 level, preoperative to postoperative, respectively (P < 0.01 at both levels). Conclusion Thus apparently, posterior lumbar interbody fusion with insertion of non-wedged intervertebral cage and pedicle screw fixation results in creation and maintenance of lumbar lordosis.

R. Kakkar Æ P. B. R. Sirigiri Æ A. Howieson Æ A. Siva Raman Æ R. J. Crawford Norfolk and Norwich University Hospital, Colney Lane, Norwich NR4 7UY, UK R. Kakkar (&) 55, Edwin Street, Daybrook, Nottingham NG5 6AX, UK e-mail: [email protected]

Keywords Lumbar spine Æ Interbody fusion Æ Cages Æ Pedicle screws Æ Lordosis

Arthrode`se intersomatique lombaire poste´rieure et lordose lombaire segmentaire

Re´sume´ Introduction Le plan sagittal des corps verte´braux produit une courbe convexe vers l’avant re´fe´re´e comme e´tant la lordose lombaire. Le mal alignement de cette lordose entraıˆne des de´sordres du bas du dos et la chirurgie lombaire est cense´e cre´er ces de´sordres. Cette e´tude est une analyse re´trospective des effets de l’arthrode`se intersomatique lombaire avec cages place´es par voie poste´rieure sur la lordose segmentaire lombaire. Mate´riels et me´thode Nous avons fait cette e´tude re´trospective chez 27 patients, soit 16 femmes et 11 hommes. Tous les patients furent ope´re´s par pose de cages intersomatiques non cune´iformes a` un seul niveau, associe´e a` une oste´osynthe`se avec vissage pe´diculaire. Pendant l’intervention tous les patients ont e´te´ de´place´s de la position genu-pectorale au procubitus afin d’augmenter leur lordose lombaire. Le recul moyen a e´te´ de deux ans et la fusion a e´te´ conside´re´e comme atteinte chez 21 patients. Re´sultats Les angles de lordose lombaire segmentaire ont augmente´ de 15.2° a` 20.6° en L4/5 et de 17.8° a` 24.5° en L5/S1 entre la mensuration pre´-ope´ratoire et la post-ope´ratoire (P < 0.01 aux deux niveaux). Conclusion On peut en de´duire qu’apparemment l’arthrode`se intersomatique par voie poste´rieure avec insertion de cages non cune´iformes et fixation par vissage pe´diculaire cre´e et maintient la lordose lombaire.

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Mots cle´s Rachis lombaire Æ Arthrode`se intersomatique Æ Cages Æ Vissage pe´diculaire Æ Lordose

Eur J Orthop Surg Traumatol (2007) 17:125–129

Sagittal malalignment has been implicated as the key cause of lower back dysfunction [5, 8, 10] and flatback syndrome [3, 18] after lumbar intervertebral fusions. Lumbar region is the major load bearing area of the spinal column and changes in the lordosis affect the sagittal balance of the patient. This is especially true in the L4/S1 segment, which has a disproportionate effect on the maintenance of lordosis as it accounts for about 67% of the lordotic angle [2, 15] and thus it becomes an important consideration during lower lumbar spine instrumentation. Loss of lordosis leads to a shortened paraspinal muscle lever arm, which requires greater forces to maintain the upright posture and thus leads to low back dysfunction and consequently, surgery for the low back disorders should try and achieve a normal sagittal balance by restoring lordosis [14, 15, 19]. The intervertebral cages are used to achieve immediate structural stability and to achieve a normal segmental lordosis [9, 13, 16]. Few studies have looked into the restoration and maintenance of lumbar lordosis following posterior lumbar interbody fusion [7]. This study was performed to assess the difference in lordotic angles, before and after posterior lumbar interbody fusion with the use of intervertebral cage and pedicle screws for a single level pathology in the lower lumbar spine and to determine if they actually contribute to a change in segmental lordosis.

tomy of the superior vertebra at the affected level was done after insertion of the pedicle screws (variable angle screws, Synthes). Discectomy was performed with curettage of the end plates. Morsellised graft from the removed lamina was inserted as bone graft with a transversely oriented intervertebral cage (Travios, Synthes) placed towards the front of the disc space. All the patients were then repositioned intraoperatively from knee chest to prone position, supported under the chest and pelvis to obtain further restoration of lordosis. The connecting rods were then applied to fix the pedicle screws in the lordotic position obtained. Remaining bone graft was then applied to the intertransverse area. Postoperatively the patients were allowed out of bed after 24–48 h with soft corset. All had postoperative neurological assessment and mobilised after check radiographs. The patients were followed up at regular intervals (6 weeks, 12 weeks, 6 months, 1 year and 2 years) and radiographs taken at 6 months, 12 months and 24 months to ascertain fusion status. Segmental lumbar lordosis was measured at each level by drawing lines parallel to the cephalad endplate and the caudad endplate. Perpendiculars were then dropped from these lines to intersect each other. This intersection angle was taken as the segmental lordotic angle. In case of L5/S1 measurement, the superior aspect of sacrum was used in the calculation (Fig. 1). These measurements were done on preoperative and the postoperative images by an independent observer. The measurements were taken from the PACS (computer software for radiology used in our institution) system preoperative, immediate postoperative, 1-year postoperative and 2-year postoperative periods, respectively.

Materials and methods

Results

We conducted a retrospective study involving 27 patients who had undergone posterior lumbar interbody fusion with non-wedged intervertebral cage (Travios, Synthes) and pedicle screw fixation between November 1999 and December 2003. All procedures were done by the same surgeon. The indication in all these patients was degenerative spondylolisthesis with symptoms of spinal stenosis at single level with axial back pain and bilateral radicular symptoms. There were 16 females and 11 males with an average age of 57 years (range 32–79 years). Sixteen patients presented with L4/5, ten with L5/S1, one with L3/4 spondylolisthesis. All procedures were done under general anaesthesia, prone on knee chest position with image intensifier guidance. Posterior lumbar decompression—complete laminec-

Fusion was said to have been achieved if there was evidence of bony trabeculae crossing the endplates and no lucencies were seen around the cage or the screws (Figs. 2, 3) According to these criteria, fusion was achieved in 21 of our patients at 2-year follow up and all of them were clinically improved. The six patients who were not fused radiologically did not have any clinical symptoms to warrant further surgical intervention. We had three dural tears and one deep infection, all of which subsided without consequences. The mean preoperative lordosis at L4/5 level was 15.2° and 20.6° postoperatively. Thus the mean change in lordosis was 5.4°. This change was statistically significant (P < 0.0039) using a paired t-test (Fig. 4).

Introduction

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Fig. 1 Measurement of segmental lordosis at L4/5 and L5/S1 levels

Mean preoperative segmental lordosis for L5/S1 level was 17.8° and 24.5° postoperatively with the mean change being 6.7°. This change was statistically significant as well (P < 0.0001) (Fig. 5). The results for all 27 patients are shown in Table 1. Discussion The goal of posterior spinal fusion in the lower lumbar spine should be only to achieve fusion but also to achieve normal lordosis as well. Goldstein et al. [7] and Godde et al. [6] gave conflicting results with regards to the maintenance of this lordosis as Goldstein et al. [7] stated that lumbar interbody fusion with threaded cages does not appear to have any clinically relevant effects on segmental lordosis. Godde et al. [6] on the other hand achieved a significant difference in the alignment after use of wedge-shaped cages. We concur with Godde et al. that intervertebral cages do have a significant role in the restoration of segmental lumbar lordosis in posterior lumbar fusions. The mean preoperative segmental lordotic angle at L4/5 level in our study was 15.2° and 17.8° at the L5/S1 level, which was not statistically significant. Gelb et al.

Fig. 2 Preoperative lateral radiograph showing L4/5 spondylolisthesis

[5] had found the mean preoperative angles at L4/5 and L5/S1 levels to be 24 ± 7° with Goldstein et al. [7] finding it to be 19° at both levels. This difference in lordotic angles can be attributed to various factors. First the average age of our patients was 57 years compared to the younger patients in other studies and it has been suggested that lumbar lordosis decreases as age increases [5, 12]. Second, people having lower lumbar disorders generally tend to have a lower lordosis as compared to the asymptomatic individuals and that they tend to lose their lordosis by the age of 40 years [5, 10]. Finally huge ranges of normal lordotic angles have been reported in the literature, possibly because of differences in measurement techniques [20]. Thus, our patient population could be part of a normal variation tending towards less lordosis. The change in segmental lordosis at both L4/5 and L5/S1 fused levels was significant at 2-year follow up in our study. This apparently indicates that cages help in the creation and maintenance of segmental lordosis. Godde et al. [6] had reported that wedge-shaped cages

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Eur J Orthop Surg Traumatol (2007) 17:125–129 30 25 20 15 10 5 0

preop

postop

Fig. 5 Comparison of pre- and postoperative segmental lordosis at L5/S1 level. Error bars indicate 1 SEM. Significant difference (P < 0.01)

sagittal alignment but that, they could be used to correct sagittal plane deformity as well [11]. We think that this statistically significant increase in the segmental lumbar lordosis is the factor responsible for the improvement in the clinical symptoms of our patients, even in the group of patients who did not achieve fusion as the recreation of lordosis puts them in a bio mechanically advantageous position and prevents the cantilever mode of failure of the fixed posterior rods.

Table 1 Patient details including pre- and postoperative lordotic angles and at follow up Fig. 3 Postoperative lateral radiograph showing increased lordosis after PLIF and cage insertion

significantly increase segmental lordosis whereas nonwedged cages actually lead to a decrease in the lordosis in the fused segments. Other studies [4, 11] reported that cages could not only be used to achieve normal

25 20 15 10 5 0 preop

postop

Fig. 4 Comparison of pre- and postoperative segmental lordosis at L4/5 level. Error bars indicate 1 SEM. Significant difference (P < 0.01)

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Patient Age Level Preoperative Postoperative Angle at Angle at (years) angle angle 1 year 2 years 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

38 41 60 44 57 55 58 35 69 50 50 64 67 38 64 79 70 68 61 72 68 65 32 41 50 79 55

L5/S1 L5/S1 L4/5 L4/5 L4/5 L5/S1 L5/S1 L4/5 L4/5 L5/S1 L5/S1 L3/4 L4/5 L5/S1 L4/5 L4/5 L4/5 L4/5 L4/5 L4/5 L5/S1 L4/5 L5/S1 L4/5 L4/5 L4/5 L5/S1

22 31 6 16 31 32 6 25 21.4 16 11.3 –7 –0.5 14.1 12 10 4 8 12 16 13 26.7 11.6 15 19 24 23

38 35 13 19 33 29.4 22 34 29 28 23.4 3.7 12.1 16.7 15 16.3 17 16.5 17 22.1 25 24 12 23 20.4 31 28.3

32 34 12.5 19 33 29.4 18 34 28 25 22.6 3.5 9.5 16 12.5 16 13.9 12 18.7 24.9 25 24 12 21 20.4 29.1 27.5

32 34 12 19 32.5 29 18 34 28 25 22 3 10 16 12 16 13 12 18 24 25 24 12 20.2 20 29.5 27

Eur J Orthop Surg Traumatol (2007) 17:125–129

But, we would also like to bring to attention that all our patients underwent intraoperative change of position from knee chest to prone before final fixation and that this fact should also be taken into consideration. Few studies have already emphasised the need for correct operative positioning in order to achieve lordosis [1, 17, 19]. Thus, the increase in segmental lordosis in our patients could have been either due to the cages alone or the effect of intraoperative change of position alone or to a combination of both. In conclusion we can say that posterior lumbar interbody fusion with the help of a cage apparently, does influence the sagittal balance of the lumbar spine and helps in recreation and maintenance of lordosis.

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