Hydrogel Injection Into Porcine Lumbar Intervertebral Disk Lacuna After Nucleus Discectomy Recovers Biomechanical Effects

Objective：Nucleus discectomy is a common surgery for disc degenerativediseases, especially for disc protrusion, however with changes of lumbar geometricstructure, which may lead to biomechanical differences. From this, injecting hydrogelas substitute of nucleus pulposus after discectomy partially restores the geometricstructure of degenerative discs. But whether injecting hydrogel can recoveroptimizing mechanical properties after discectomy, there is no research about thisquestion. By using the ex-vivo animal test, we investigated the mechanical propertiesof the functional lumbar spinal units (FSU) with or without hydrogel injection afternucleus discectomy.Methods：Three groups of six FSUs from each of Wuzhishan miniature pigswere randomized to normal group (respectively intact FSU), mimic group (withhydrogel injection after discectomy) and control group (without hydrogel injectionafter discectomy). All of the specimens were subjected to static and dynamiccompression loads sequentially, then time-displacement curves, mean storagemodulus, mean loss modulus and mean phase angles were worked out respectivelywith help of software.Results：(1)In the static unconfined compression test, mimic group have asimilar time-displacement curves with normal group, whereas this two groupscompared with control group show obvious statistical differences.(2)In the dynamiccompression test,the storage modulus and loss modulus under all frequencies, mimicgroup was greater than normal group and control group with significant differenceP<0.05, P<0.01,respectively),and normal group and control also had significantdifference(P<0.05); Phase angles had significant differences between each groupsunder0.5HZ,but had not significant differences under other frequencies.Conclusions: Injecting hydrogel after nucleus discectomy can better reserve normal lumbar structure as well as the biomechanical properties than simplediscectomy. However, hydrogel injection brings about other biomechanics changes,which needs more investigations.