Cartilage defects in the knee are often seen in young and active patients. There is a need for effective joint preserving treatments in patients suffering from cartilage defects, as untreated defects often lead to osteoarthritis. Within the last two decades, tissue engineering based techniques using a wide variety of polymers, cell sources, and signaling molecules have been evaluated. We start this review with basic background information on cartilage structure, its intrinsic repair, and an overview of the cartilage repair treatments from a historical perspective. Next, we thoroughly discuss polymer construct components and their current use in commercially available constructs. Finally, we provide an in-depth discussion about construct considerations such as degradation rates, cell sources, mechanical properties, joint homeostasis, and non-degradable/hybrid resurfacing techniques. As future prospects in cartilage repair, we foresee developments in three areas: first, further optimization of degradable scaffolds towards more biomimetic grafts and improved joint environment. Second, we predict that patient-specific non-degradable resurfacing implants will become increasingly applied and will provide a feasible treatment for older patients or failed regenerative treatments. Third, we foresee an increase of interest in hybrid construct, which combines degradable with non-degradable materials.

Loss of sagittal alignment and balance in adult spinal deformity can cause severe pain, disability and progressive neurological deficit. When conservative

Focal knee resurfacing implants (FKRIs) are intended to treat cartilage defects in middle‐aged patients. Most FKRIs are metal‐based, which hampers follow‐up of the joint using magnetic resonance imaging and potentially leads to damage of the opposing cartilage. The purpose of this study was to develop a nondegradable thermoplastic polyurethane (TPU) FKRI and investigate its osseointegration. Different surface roughness modifications and biphasic calcium phosphate (BCP) coating densities were first tested in vitro on TPU discs. The in vivo osseointegration of BCP‐coated TPU implants was subsequently compared to uncoated TPU implants and the titanium bottom layer of metal control implants in a caprine model. Implants were implanted bilaterally in stifle joints and animals were followed for 12 weeks, after which the bone‐to‐implant contact area (BIC) was assessed. Additionally, 18F‐sodium‐fluoride (18F‐NaF) positron emission tomography PET/CT‐scans were obtained at 3 and 12 weeks to visualize the bone metabolism over time. The BIC was significantly higher for the BCP‐coated TPU implants compared to the uncoated TPU implants (p = .03), and did not significantly differ from titanium (p = .68). Similar 18F‐NaF tracer uptake patterns were observed between 3 and 12 weeks for the BCP‐coated TPU and titanium implants, but not for the uncoated implants. TPU FKRIs with surface modifications could provide the answer to the drawbacks of metal FKRIs.

Growth-guidance constructs are an alternative to growing rods for the surgical treatment of early onset scoliosis (EOS). Constructs containing ultra-high molecular weight polyethylene (UHMWPE) sublaminar tape have been proposed as an improvement to the traditional Luque trolley. Ideally, a certain minimum number of levels is instrumented, thus offering the best balance between providing adequate spinal fixation and minimizing surgical exposure and spinal mobility reduction. The objective of the current study was to validate a parametric FE model of the thoracolumbar spine including its ability to predict the biomechanical effects of varying the number of levels instrumented with UHMWPE sublaminar tape in a growth-guidance construct for EOS correction. In a first step, the material properties of the L4-L5 segment in the model were calibrated relative to literature data. Next, whole thoracolumbar spine behavior was verified relative to literature data as well. Subsequently, rods, screws, and sublaminar tape were implemented in the model and a simulation of a previously performed in vitro experiment, in which the range of motion (ROM) of porcine spine segments was measured for different tape configurations, was performed. Good agreement between in vitro and FE-results was found for the changes in ROM before and after instrumentation. Good agreement for changes in ROM was obtained when varying the number of instrumented levels as well, indicating that the model can be a useful tool to evaluate the effects of construct composition variations. The present study was limited by the fact that only normal spine curvatures were analyzed and the fact that results of porcine spine experiments were compared to results of human FE models. Nevertheless, the good agreement in results, even at a detailed level, supports the idea that the model can ultimately be used as a pre-operative planning tool to evaluate different construct designs. The FE model of the thoracolumbar spine was successfully validated and was able to capture the biomechanical effect of construct component variations.