Compressive strength of interbody cages in the lumbar spine: the effect of cage shape, posterior instrumentation and bone density

One goal of interbody fusion is to increase the height of the degenerated disc space. Interbody cages in particular have been promoted with the claim that they can maintain the disc space better than other methods. There are many factors that can affect the disc height maintenance, including graft or cage design, the quality of the surrounding bone and the presence of supplementary posterior fixation. The present study is an in vitro biomechanical investigation of the compressive behaviour of three different interbody cage designs in a human cadaveric model. The effect of bone density and posterior instrumentation were assessed. Thirty-six lumbar functional spinal units were instrumented with one of three interbody cages: (1) a porous titanium implant with endplate fit (Stratec), (2) a porous, rectangular carbon-fibre implant (Brantigan) and (3) a porous, cylindrical threaded implant (Ray). Posterior instrumentation (USS) was applied to half of the specimens. All specimens were subjected to axial compression displacement until failure. Correlations between both the failure load and the load at 3 mm displacement with the bone density measurements were observed. Neither the cage design nor the presence of posterior instrumentation had a significant effect on the failure load. The loads at 3 mm were slightly less for the Stratec cage, implying lower axial stiffness, but were not different with posterior instrumentation. The large range of observed failure loads overlaps the potential in vivo compressive loads, implying that failure of the bone-implant interface may occur clinically. Preoperative measurements of bone density may be an effective tool to predict settling around interbody cages.

Little-known Swiss contributions to the description, diagnosis, and surgery of lumbar disc disease before the Mixter and Barr era

The understanding of lumbar spine pathologies made substantial progress at the turn of the twentieth century. The authors review the original publication of Otto Veraguth in 1929 reporting on the successful resection of a herniated lumbar disc, published exclusively in the German language. His early report is put into the historical context, and its impact on the understanding of pathologies of the intervertebral disc (IVD) is estimated. The Swiss surgeon and Nobel Prize laureate Emil Theodor Kocher was among the first physicians to describe the traumatic rupture of the IVD in 1896. As early as 1909 Oppenheim and Krause published 2 case reports on surgery for a herniated lumbar disc. Goldthwait was the first physician to delineate the etiopathogenes is between annulus rupture, symptoms of sciatica, and neurological signs in his publication of 1911. Further publications by Middleton and Teacher in 1911 and Schmorl in 1929 added to the understanding of lumbar spinal pathologies. In 1929, the Swiss neurologist Veraguth (surgery performed by Hans Brun) and the American neurosurgeon Walter Edward Dandy both published their early experiences with the surgical therapy of a herniated lumbar disc. Veraguth's contribution, however, has not been appreciated internationally to date. The causal relationship between lumbar disc pathology and sciatica remained uncertain for some years to come. The causal relationship was not confirmed until Mixter and Barr's landmark paper in 1934 describing the association of sciatica and lumbar disc herniation, after which the surgical treatment became increasingly popular. Veraguth was among the first physicians to report on the clinical course of a patient with successful resection of a herniated lumbar disc. His observations should be acknowledged in view of the limited experience and literature on this ailment at that time.