Collagen 1 gel may improve the regenerative capacity of minced adult and preosteoarthritic cartilage.

PURPOSE: Minced cartilage implantation (MCI) is an evolving technique for the treatment of osteochondral lesions. It was hypothesised that mincing of cartilage may affect chondrocyte viability and phenotype and that embedding in collagen 1 gel results in an improved outcome. The objective of this study was to evaluate the impact of cartilage mincing and whether collagen 1 gel mediates beneficial effects on the chondrocyte phenotype and viability. METHODS: Human cartilage samples from 11 patients undergoing total knee arthroplasty were collected and minced according to the MCI protocol. Minced cartilage was cultured for 1 week with and without embedding in collagen 1 gel and was compared with unminced cartilage flakes as control. Quantitative reverse transcription-PCR and immunohistochemical staining for the chondrocyte marker genes SOX9, COL2, ACAN, COL10 and MMP13 were used to examine the chondrocyte phenotype. Cell death was assessed by the terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. RESULTS: Increased chondrocyte cell death of cultured cartilage after mincing was observed. Chondrocytes from minced cartilage exhibited significantly decreased expression and protein levels of homeostatic and hypertrophic chondrocyte markers. Embedding in collagen 1 gel showed no positive effect on viability. However, remarkable is the increased expression of ACAN and the preserved protein level of SOX9 in the collagen 1-embedded minced cartilage. CONCLUSIONS: This study shows that the mincing of cartilage leads to increased chondrocyte death and decreased expression of chondrocyte phenotypic marker genes after 7 days. The use of collagen 1 gel may improve the stability of the phenotype, which needs to be further elucidated. LEVEL OF EVIDENCE: Level III (therapeutic).

Quantitative imaging of bone remodeling in patients with a unicompartmental joint unloading knee implant (ATLAS Knee System)-effect of metal artifacts on a SPECT-CT-based quantification.

BACKGROUND: SPECT-CT using radiolabeled phosphonates is considered a standard for assessing bone metabolism (e.g., in patients with osteoarthritis of knee joints). However, SPECT can be influenced by metal artifacts in CT caused by endoprostheses affecting attenuation correction. The current study examined the effects of metal artifacts in CT of a specific endoprosthesis design on quantitative hybrid SPECT-CT imaging. The implant was positioned inside a phantom homogenously filled with activity (955 MBq 99mTc). CT imaging was performed for different X-ray tube currents (I = 10, 40, 125 mA) and table pitches (p = 0.562 and 1.375). X-ray tube voltage (U = 120 kVp) and primary collimation (16 × 0.625 mm) were kept constant for all scans. The CT reconstruction was performed with five different reconstruction kernels (slice thickness, 1.25 mm and 3.75 mm, each 512 × 512 matrix). Effects from metal artifacts were analyzed for different CT scans and reconstruction protocols. ROI analysis of CT and SPECT data was performed for two slice positions/volumes representing the typical locations for target structures relative to the prosthesis (e.g., femur and tibia). A reference region (homogenous activity concentration without influence from metal artifacts) was analyzed for comparison. RESULTS: Significant effects caused by CT metal artifacts on attenuation-corrected SPECT were observed for the different slice positions, reconstructed slice thicknesses of CT data, and pitch and CT-reconstruction kernels used (all, p < 0.0001). Based on the optimization, a set of three protocols was identified minimizing the effect of CT metal artifacts on SPECT data. Regarding the reference region, the activity concentration in the anatomically correlated volume was underestimated by 8.9-10.1%. A slight inhomogeneity of the reconstructed activity concentration was detected inside the regions with a median up to 0.81% (p < 0.0001). Using an X-ray tube current of 40 mA showed the best result, balancing quantification and CT exposure. CONCLUSION: The results of this study demonstrate the need for the evaluation of SPECT-CT protocols in prosthesis imaging. Phantom experiments demonstrated the possibility for quantitative SPECT-CT of bone turnover in a specific prosthesis design. Meanwhile, a systematic bias caused by metal implants on quantitative SPECT data has to be considered.

Screw Track Osteolysis in the Cementless Total Knee Replacement Design.

BACKGROUND: There is a paucity of reports on osteolysis associated with tibial screw fixation in cementless total knee arthroplasty (TKA), and the pathophysiology is not clear. This study aimed to describe the pathology related to screw track osteolysis around the tibia in cementless TKA. METHODS: The study cohort comprised 100 revised cementless TKAs with tibial screw fixation. Screw track osteolysis and various screw angles were analyzed radiologically. Tissue samples from the joint capsule and the osteolytic cavity were investigated for metal/polyethylene wear. The type of tissue response was determined using immunohistochemistry. Retrieved tibial polyethylene inserts were analyzed for screw hole impression and mode of wear. Tissue metal content was measured by inductively coupled plasma optical emission spectrometry. Electrochemical reactions between the tibial tray and the cancellous screws were investigated. RESULTS: Radiological analysis showed screw track osteolysis predominantly at the medial aspect of the tibial component, and the severity of osteolysis positively correlated with smaller medial proximal tibial screw angles. Osteolysis was associated with high titanium concentrations but not with polyethylene particles. An open circuit potential between the screw and the tibial base plate was measured. Necrosis, osteolytic cyst formation and macrophages, T and B cells, and dendritic cells were present. CONCLUSION: The present study highlights the risk for screw track osteolysis in cementless TKA with screw fixation. Our data collectively suggest that titanium wear may contribute to screw track osteolysis in the cementless TKA design. The contribution of screw angles is difficult to prove.