The Effect of an Interspinous Process Implant on Facet Loading During Extension

Abstract

Study Design. Facet loading parameters of lumbar cadaver spines were measured during extension before and after placement of an interspinous process implant.Objective. The study was undertaken to quantify the influence of an interspinous implant on facet loading at the implanted and adjacent levels during extension.Summary of Background Data. Facet loading is increased during extension and decreased during flexion. Previous studies have demonstrated that interspinous process decompression relieves disc pressure at the implanted level and does not alter disc pressure at the adjacent levels. Facet joints are believed to play a key role in back pain, especially in patients with collapsed discs and increased motion segment mobility resulting in increased facet loading.Methods. Seven cadaver spines (L2-L5) were loaded to 15 Nm of extension and 700 N compression with and without an interspinous process implant (X STOP) placed between the L3-L4 spinous processes. Pressure-sensitive film was placed in the facet joints of the implanted and adjacent levels. After loading, the film was digitally analyzed for peak pressure, average pressure, contact area, and force. These values were compared between the intact and implanted specimens at the adjacent and implanted levels using a paired t test (P Ͻ 0.05).Results. The implant significantly reduced the mean peak pressure, average pressure, contact area, and force at the implanted level. The mean peak pressure, average pressure, contact area, and force at the adjacent levels were not significantly different between the intact and implanted specimens with the exception of contact area at the L2-L3 level.Conclusions. Interspinous process decompression will unlikely cause adjacent level facet pain or accelerated facet joint degeneration. Furthermore, pain induced from pressure originating in the facets and/or posterior anulus of the lumbar spine may be relieved by interspinous process decompression. Clinical results from patients with a component of lower back pain suggest that this is a valid conclusion.Key words: facet joint, neurogenic intermittent claudication, lumbar, back pain, interspinous process decompression. Spine 2005;30:903-907Although the precise etiology of lower back pain (LBP) lacks a general consensus, there is general agreement that the facet joints must be considered when studying its pathology. 1-7 The lifetime incidence of LBP is estimated to be between 60% and 90% with 15% to 40% of chronic LBP caused by the lumbar facet joints. 8 -10 Although clinically difficult to diagnose, facet specific back pain is exacerbated by hyperextension and lessened in a recumbent position or flexion. 1,6,8 During extension, loading of the facet joints is increased, resulting in compression of the nerve root and central canals and deformation of the joint capsule. 6,9 It is believed that the deformation of the joint capsule is the source of pain as it stimulates nociceptors of the capsule. 8,11 The capsule surrounding the facet joint has been shown to be well innervated by aff...

An anatomic study of the interspinous space of the lumbosacral spine

“…Basic science has provided some insights into the treatment mechanism of these implants. Lumbar cadaveric studies have shown that at the implanted level the disc and facet joints are unloaded [13] [15], and narrowing of the spinal canal and intervertebral foramen is prevented in extension [8]. Position magnetic resonance imaging of the lumbar spine pre-and post-in vivo implantation has shown L5-S1 9 9 1-20 3.4 Table 2 Moderate to high inter-rater reliability was established for each measure with an ICC ranging from 0.5 to 0.9 using a two-way random effect model with agreement and single-rater reliability significantly improved spinal vertebral canal and intervertebral foramen spaces at the implanted level [10,11].…”

Biomechanical effect of different lumbar interspinous implants on flexibility and intradiscal pressure

“…This emphasizes the need to use specific forceps meanwhile supplied by the distributers of Only a few reports of in vitro flexibility tests of interspinous implants are available in the literature for comparison. Most data about the biomechanical behavior of interspinous implants were gathered using the X-Stop [7,11,17]. Lindsey et al [7] could show for example, that the ROM in flexion-extension was significantly reduced at the instrumented level, whereas there was no significant effect for the other directions.…”

Does Wallis implant reduce adjacent segment degeneration above lumbosacral instrumented fusion?

“…In our series, Wallis implant controlled the ROM of the cephalad not fused vertebra and restored the DH at this segment without reduction of the global lumbar lordosis and sagittal balance until the latest observation 60 months after index surgery. Using an MRI-based classification, some investigators inserted the Wallis implant to treat disc degeneration grades II-IV [33,62]. In our study, we used the Wallis implant also in patients with UCLA I and II degeneration in the segment cephalad to instrumentation.…”