Fueling the debate: Are outcomes better after posterior lumbar interbody fusion (PLIF) or after posterolateral fusion (PLF) in adult patients with low-grade adult isthmic spondylolisthesis?

STUDY
DESIGN: Retrospective cohort study. CLINICAL QUESTION: Do more adult patients affected by low grade isthmic spondylolisthesis have significant clinical and radiological improvement following posterior lumbar interbody fusion (PLIF) than those who receive posterolateral fusion (PLF)?
METHODS: One hundred and fourteen patients affected by adult low grade isthmic spondylolisthesis, treated with posterior lumbar interbody fusion or posterolateral fusion, were reviewed. Clinical outcome was assessed by means of the questionnaires ODI, RMDQ and VAS. Radiographic evaluation included CT, MRI, and x-rays. The results were analyzed using the Student t-test.
RESULTS: The two groups were similar with respect to demographic and surgical characteristics. At an average follow-up of 62.1 months, 71 patients were completely reviewed. Mean ODI, RMDQ and VAS scores didn't show statistically significant differences. Fusion rate was similar between the two groups (97% in PLIF group, 95% in PLF group). Major complications occurred in 5 of 71 patients reviewed (7%): one in the PLIF group (3.6%), four in the PLF group (9.3%). Pseudarthrosis occurred in one case in the PLIF group (3,6%) and in two cases in PLF group (4.6%).
CONCLUSIONS: In our series, there does not appear to be a clear advantage of posterior lumbar interbody fusion (PLIF) over posterolateral fusion (PLF) in terms of clinical and radiological outcome for treatment of adult low grade isthmic spondylolisthesis.

Study Rationale and Context

The choice of correct surgical treatment of adult low-grade isthmic spondylolisthesis remains a topic of debate. Many studies in the literature analyze clinical and radiological outcome of different fusion techniques by various approaches, including posterolateral fusion (PLF) and lumbar interbody fusion, but considerable controversies regarding what is the “gold standard” approach still exist.1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16

Clinical Question

Do more adult patients affected by low grade isthmic spondylolisthesis have significant clinical and radiological improvement following posterior lumbar interbody fusion (PLIF) than those who receive posterolateral fusion (PLF)?

Methods

Retrospective cohort study.

All adult patients who had undergone posterior lumbar interbody fusion (PLIF) (Figs. 2, 3) or posterolateral fusion (PLF) (Fig. 4) for low grade isthmic spondylolisthesis (Meyerding grade 1 or 2) between February 2003 and April 2005, and who had a minimum of 4 years of follow-up.

Fig. 2

Posterior lumbar interbody fusion for low grade isthmic spondylolisthesis, 3 and 15 months after surgery. Note the segmental sagittal alignement (kyphosis) that could compromise long term clinical and radiographic outcome (risk of negative effect on adjacent disc).

Fig. 3

CT scan 15 months after surgery.

Fig. 4

Posterolateral fusion for low grade isthmic spondylolisthesis. Note the postoperative disc height gain that could compromise fusion.

Previous spine surgery, age less than 40 years, etiology other than isthmic, high-grade spondylolisthesis, concomitant conditions which could compromise outcomes.

(Fig. 1)

Fig. 1

Patient sampling and selection

One-hundred-and-fourteen consecutive patients met the inclusion criteria, and were divided into two groups, according to the surgical treatment they received: PLIF group (posterior lumbar interbody fusion) and PLF group (posterolateral fusion) (Table 1). Patients were evaluated preoperatively, postoperatively and at final follow-up.

Table 1

Characteristics of intervention groups

	PLIF group		PLF group
	All enrolledN = 47	Patients at follow-upN = 28	All enrolledN = 67	Patients at follow-upN = 43
Age, years (mean ±SD)	54.8 ±8.6	55.1 ±9.2	51.6 ±8.6	49.3 ±7.4
	n (%)	n (%)	n (%)	n (%)
Female gender	25 (53.2)	14 (50.0)	39 (58.2)	24 (55.8)
Spondylolisthesis grade I	21 (44.7)	12 (42.9)	28 (41.8)	16 (37.2)
Spondylolisthesis grade II	26 (55.3)	16 (57.1)	39 (58.2)	28 (65.1)
L3–4 spondylolisthesis	3 (6.4)	2 (7.1)	0 (0)	0 (0)
L4–5 spondylolisthesis	16 (34.0)	14 (50.0)	25 (37.3)	14 (32.6)
L5–S1 spondylolisthesis	28 (59.6)	12 (42.9)	42 (62.7)	29 (67.4)
1 level fusion	30 (63.8)	19 (67.9)	50 (74.6)	32 (74.4)
2 level fusion	13 (27.7)	7 (25.0)	16 (23.9)	11 (25.6)
3 or more level fusion	4 (8.5)	2 (7.1)	1 (1.5)	0 (0)

At the time of surgery all patients complained of low back and leg pain.

Posterior pedicle screw instrumentation alone was used as support to fusion in the PLF group. Carbon fiber, titanium and peek cages were added in the PLIF group. A laminectomy was performed in all cases. All patients received allograft bone and autograft bone obtained from decompression.

Demographic, preoperative, perioperative and postoperative data were collected.

Clinical outcome was assessed by means of the Oswestry disability index (ODI), Roland Morris Disability Questionnaire (RMDQ) and visual analogue scale (VAS), for back and leg pain respectively, filled in by patients preoperatively and at last follow-up.

Radiographic evaluation included preoperative CT (performed to assess the isthmic nature of the lesion) and MRI of the lumbar spine, as well as standing plain and functional films with flexion and extension views before and after surgery and during the follow-up, when requested. Fusion was defined as radiographic evidence of bone bridging, the absence of lucency around the implant, and no motion during functional films.

Overall complications were noted. Major complications were those that needed revision surgery or resulted in permanent neurological deficit.

The results were analyzed using the Student t-test. Results are expressed as the mean (range), with a P-value of < 0.5 considered as being statistically significant.

The two groups were similar with respect to demographic and surgical characteristics (Table 1).

At an average follow-up of 62.1 months (range 51–78), 71 patients (62.3%), 28 (59.6%) of the PLIF group and 43 (64.2%) of the PLF group, were completely reviewed.

Clinical outcome. Both techniques ensured improvement of clinical outcome, without statistically significant differences between the two groups (P > .05). Unsatisfactory clinical results were achieved in four patients (14.3%) in the PLIF group and in eight patients in the PLF group (18.6%) (Table 2).

Table 2

Clinical outcome

	PLIF group				PLF group
	Baseline	Follow-up	Percent change	Within group P-value*		Baseline	Follow-up	Percent change	Within group P-value*	Between group P-value†
ODI (mean % ±SD)	53.2 ± 18.8	25.6 ± 18.1	57.7 ± 24.4	<.05	52.1 + 19.0	24.5 + 18.3	59.2 + 24.9	<.05	>.05
RMDQ	13.9 ± 6.1	7.2 ± 6.2	57.3 ± 26.5	<.05	13.4 ± 6.2	6.9 ± 6.3	58.3 ± 27.4	<.05	>.05
VAS “leg score”	7.4 ± 1.4	4.1 ± 2.8	49.3 ± 30.0	<.05	7.6 ± 1.4	3.5 ± 3.2	58.5 ± 33.6	<.05	>.05
VAS “back score”	7.7 ± 1.3	3.0 ± 2.0	62.8 ± 21.8	<.05	7.8 ± 1.3	3.8 ± 2.7	55.3 ± 29.1	<.05	>.05
Persistent low-back pain (%)	100%	14.3%	n.a.	n.a.	100%	18.6%	n.a.	n.a.	n.a.
Persistent sciatica	100%	3.6%	n.a.	n.a.	100%	11.6%	n.a.	n.a.	n.a.

P-value associated with change from baseline to follow-up in each treatment group

P-value comparing change in baseline to follow-up between PLIF and PLF groups

Radiologic outcome. The x-rays performed at final follow-up showed a fusion rate of 97% in the PLIF group, 95% in the PLF group, without statistically significant differences (P > .05).

Complications. Complications requiring revision surgery occurred in 5 of 71 patients reviewed (7%), one in the PLIF group (3.6%) and four in the PLF group (9.3%). Pseudarthrosis occurred in one case in the PLIF Group, in two cases in the PLF group (Table 3).

Table 3

Major complications requiring revision surgery

	PLIF group(n = 28)n (%)	PLF group(n = 43)n (%)
Major complications, n (%)
Revision surgery	1 (3.6)*	4 (9.3)†
Pseudarthrosis	1 (3.6)	2 (4.6)

Revision due to pseudarthrosis

Two revisions due to pseudarthrosis

Results

More information on complications is available in the web appendix at .

In our series, there does not appear to be a clear advantage of posterior lumbar interbody fusion over posterolateral fusion in terms of clinical and radiological outcome.

A higher incidence of complications requiring surgical revision (9.3% versus 3.6%) was found in the PLF group. Pseudarthrosis occurred in one case in the PLIF group (3.6%) and in two cases in the PLF group (4.6%).

Despite nerve root manipulation required to insert the cages into the intervertebral space, in our series we found only one case of sciatica at last follow-up in the PLIF group.

Limitations. The present series should be interpreted in the context of its limitations, including the retrospective nature of the review, the fact that patients were not randomized between posterior lumbar interbody fusion and posterolateral fusion, the low follow-up rate and the small sample size.

In case of adult low grade isthmic spondylolisthesis, posterior lumbar interbody fusion doesn't seem to provide advantages in terms of mechanical stability and fusion rate (pseudarthrosis incidence: 3.6% verses 4.6%).

In our series, both treatments ensured good clinical results, without statistically significant differences between the two techniques.