LASER MICROGROOVING AND NANOFIBER MEMBRANE APPLICATION FOR TOTAL KNEE REPLACEMENT IMPLANTS USING A CAPRINE MODEL

Abstract

Aseptic loosening is a well-recognized phenomenon in cementless total knee replacement (TKR) and often carries severe consequences for the patient. We recently developed and tested in vitro a novel strategy for enhancing osseointegration and acute mechanical stability of orthopedic implants that employ laser-induced microgroove (LIM) and nanofiber membrane (NFM) applications at the bone-implant interface. We report herein investigation of the approach with results from a pilot study employing three skeletally mature female Spanish cross goats (~4y, 35-45kg) receiving cementless TKR with a commercially available implant system (Biomedrix® Canine Total Knee). Pre-operative radiographs were taken to ensure limb normality and to select the appropriately sized implants for each goat. With the animal under general anesthesia and the limb properly prepped for aseptic surgery, the stifle was approached, and osteotomies of the proximal tibia and distal femur performed in preparation for implantation of the tibial (TT) and femoral (FT) trays. For one goat, the arthroplasty implant surfaces were unaltered from the manufacturer's mirrorpolished (MP) condition. For the other two goats, the TT bonecontact surface was laser-micro grooved (150 μm depth, 200 μm width, 200 μm spacing) prior to sterilization and then implanted with (LIM/NFM) or without (LIM) an intermediate (surfaceapplied) polycaprolactone (PCL) nanofiber mesh (50x50mm, electrospun, aligned, unidirectional, 10 μm thickness). Following surgery, animals received appropriate analgesic therapy and rehabilitative care to maximize animal comfort, function, and quality of life while limiting the risk of major complications. Post-operative monitoring included assessment of mentation, vital signs, pain level, digestive function (weight, appetite, rumen contractions, feed intake, fecal output), and limb status (usage, range of motion, muscular volume). By the study's end (12 wks), all animals had recovered a pre-surgery range of motion in the operated knee and exhibited typical bony changes on radiographic follow-up. At necropsy following humane euthanasia, no gross instability of TKR components was observed. Histomorphometric analysis of explanted bone-TT constructs showed the increased new bone surface area in the LIM-NFM sample (0.49 mm2) compared with the MP sample (0.03 mm2), suggesting that microgrooves and/or PCL nanofiber coating may improve the clinical performance of the implant. A finite element analysis (FEA) model was developed to explore the impact of surface micro grooving to the mechanical stimuli at the bone-implant interface to supplement the in vivo studies. The three-dimensional geometry of the tibia was scanned using computed tomography and imported into a proprietary (MIMICS®) software to construct the solid models for finite element micro-strain analyses.