Twenty-nine studies (n=1,181) were included in the review: 8 RCTs (n=385) and 21 observational studies (n=796).
Four of the 8 RCTs were described as high quality. With the exception of 1 RCT that scored only 1 point; the remaining trials scored 4 or 5 points out of a possible 11. Of the 5 uncontrolled cohort studies included in the analysis only, two were considered to be of a high quality; the remaining studies scored either 5 or 7 points out of a possible 17. Ten of the 21 observational studies failed to clearly identify consecutive patient selection.
Best surgical treatment (8 RCTs, n=385).
Four RCTs (n=169) compared PLF with or without instrumentation, but found no additional benefits of using instrumentation. A 'best evidence analysis' compared fusion rates in the 2 high-quality RCTs (n=115) and found non significant differences in both studies which favoured the non-instrumented group (78% non-instrumented versus 65% instrumented; and 84% non-instrumented versus 73% instrumented). A further 3 RCTs (n=105) found no significant differences when PLF was compared with modifications of PLF including the addition of anterior interbody fusion (1 RCT), decompression (1 RCT) and bone graft substitute (1 RCT). One low-quality RCT (n=111; quality score 1) reported that PLF was superior to exercise.
Outcome after surgical techniques (21 observational studies, n=796).
Twenty-four patient groups were included in the analysis: 15 PLF groups, 5 anterior interbody fusion groups, 2 posterior interbody fusion groups, 1 posterolateral endoscopic foraminal decompression group and 1 unspecified treatment group.
The proportion of participants achieving good or excellent clinical outcomes in the PLF groups ranged from 60 to 98%, and fusion rates varied from 81 to 100%. For the anterior interbody fusion groups, good or excellent clinical outcomes ranged from 85 to 94% and fusion rates from 47 to 90%. For posterior interbody fusion groups, good or excellent clinical outcomes were reported to be 45% and fusion rates 80% and 95%. For posterolateral endoscopic foraminal decompression, 79% of the participants achieved a good or excellent clinical outcome; the fusion rate was not reported.
Three PLF studies reported an average reduction of the listhesis of 12.3% and an average loss of reduction at follow-up of 5.9%. One PLF study reported that reduction was maintained at follow-up. Data for pre-operative lordotic angles varied considerably.
Eighteen studies (including RCTs) reported complications. Complications rates varied between studies but, overall, the rates were lower for PLF than for anterior interbody fusion and posterior interbody fusion (12%, 16% and 24%, respectively). Complications varied and included neurological complications, instrument failure and infections. Eight types of instrument failures (in 388 patients) were reported for PLF. Adjacent segment failures were not reported in any of the studies.