We report a consecutive series of 200 patients who underwent Dynesys flexible stabilisation in the management of intractable lower back pain.
Group 1 - Cases where implantation was used as an adjunct to other procedures including decompression, discectomy, or posterior lumbar interbody fusion. (32 male, 36 female, Mean age 56years (range 31–85)). Group 2 - Patients with back pain and/or sciatica in which no other procedure was used. (65 male 67 female, Mean age 58years (range 27–86)) All patients were profiled prospectively using the Oswestry Disability Index (ODI), SF36 and Visual Analogue Scale (VAS). Patients were reviewed post-operatively using the same measures at 3, 6 &
12 months, and yearly thereafter. Follow-up was 95% at 2 to 5 years.
Group 2 – Mean ODI fell from 49 pre-op to 28 at four years Similar trends were observed in both groups with a fall in VAS and improvement in SF36.
Fixation was at one level in 14, two levels in 23, and three or four levels in 6 patients. Thirty-seven had Dyne-sys fixation alone and six had additional procedures at the same operation. Complications included facet fracture (1), broken pedicle screw (1), apparent screw loosening (1) and discitis (1). At average follow-up of eight months (range 2–14 months), the average Oswestry disability score had fallen from 52 to 32 and the visual analogue pain score from 7.5 to 1.7. 65% of patients were pleased or better with their result.
Wet foam was used as bone substitute, this is an open cell foam that is fairly fragile but has the benefit of being constant and is cheap and readily available. This foam is not desired to have cancellous bone characteristics but is useful in observing the relative effect of adding these pegs. Two different settings in vivo were mimicked: that of a tibial tray and pegs resting fully on cancellous bone, in which case a central vertical force was applied, and that of the tray resting on the cortex on one side with a lateral vertical force applied over the other side in both the proud and flush setting (2&
4 pegs respectively). The investigation was undertaken using a home made system allowing a crude estimate of the forces producing initial subsidence, which was identified by initial fracture of the foam, and total subsidence which was identified as total failure of the foam. Each test was carried out three times. Controls were carried out on the tray with no pegs and on the pegs individually before attaching these to the tray and repeating the tests for each design.
The mean lateral vertical force for total subsidence with pegs mounted on the foam side was 12.3 kg (11.5–13 ± 0–76) for the short pegs, 13.5 kg (12–15.5 ± 1.8) for the medium pegs and 13.83 kg (12–15.5 ± 1.7) for the long pegs. Again no definite initial subsidence force could be identified.