Early detection of knee osteoarthritis (OA) is critical for possible preventive treatment, such as weight loss, physical activity and sports advice and restoring biomechanics, to postpone total knee arthroplasty (TKA). Specific biomarkers for prognosis and early diagnosis of OA are lacking. Therefore, in this study, we analyzed the lipid profiles of different tissue types within Hoffa's fat pad (HFP) of OA and cartilage defect (CD) patients, using matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI). The HFP has already been shown to play an important role in the inflammatory process in OA by prostaglandin release. Additionally, MALDI-MSI allows us to investigate on tissue lipid distribution at molecular level, which makes it a promising tool for the detection of disease specific biomarkers for OA development.

Samples of HFP were obtained of patients undergoing surgical treatment for OA (n=3) (TKA) or CD (n=3) (cartilage repair). In all cases, tissue was obtained without patient harm. HFP samples were washed in phosphate buffered saline (PBS) and snap-frozen directly after surgical dissection to remove redundant blood contamination and to prevent as much tissue degradation as possible. Tissue sections were cut at 15 µm thickness in a cryostat (Leica Microsystems, Wetzlar) and deposited on indium tin oxide glass slides. Norharmane (Sigma-Aldrich) matrix was sublimed onto the tissue using the HTX Sublimator (HTX Technologies, Chapel Hill). µMALDI-MSI was performed using Synapt G2Si (Waters) at 50 µm resolution in positive ion mode. MS/MS fragmentation was performed for lipid identification. Data were processed with in-house Tricks for MATLAB and analyzed using principle component analysis (PCA) and verlan

OA and CD HFP specific lipid profiles were revealed by MALDI-MSI followed by PCA and DA. With these analyses we were able to distinguish different tissue types within HFP of different patient groups. Further discriminant analysis showed HFP intra-tissue heterogeneity with characteristic lipid profiles specific for connective and adipose tissues, but also for synovial tissue and blood vessels, revealing the high molecular complexity of this tissue. As expected, lipid signals were lower at the site of the connective tissue, compared to the adipose tissue. In particular, tri-acyl glycerol, di-acyl glycerol, sphingomyelin and phosphocholine species were differently abundant in the adipose tissue of HFP of OA compared to CD.

To our knowledge, this is the first study comparing lipid profiles in HFP of OA patients with CD patients using MALDI-MSI. Our results show different lipid profiles between OA and CD patients, as well as intra-tissue heterogeneity within HFP, rendering MALDI-MSI as a useful technology for OA biomarker discovery. Future research will focus on expanding the number of subjects and the improvement of lipid detection signals.

Surgical microfracture is considered a first line treatment for talar osteochondral defects. Pain reduction, functional improvement and patient satisfaction are described to be 61–86% in both primary and secondary osteochondral defects. However, limited research is available whether improvement of the surgical technique is possible. We do know that the current rigid awls and drills limit the access to all locations in human joints and increase the risk of heat necrosis of bone. Application of a flexible water jet instrument to drill the microfracture holes can improve the reachability of the defect without inducing thermal damage. The aim of this study is to determine whether water jet drilling is a safe alternative compared to conventional microfracture awls by studying potential side effects and perioperative complications, as well as the quality of cartilage repair tissue in a caprine model. 6 mm diameter talar chondral defects were created bilaterally in 6 goats (12 samples). One defect in each goat was treated with microfracture holes created with conventional awls. The contralateral defect was treated with holes created with 5 second water jet bursts at a pressure of 50 MPa. The pressure was generated with a custom-made setup using an air compressor connected to a 300 litre accumulator that powered an air driven high-pressure pump (P160 Resato, Roden, The Netherlands, www.resato.com). Postoperative complications were recorded. After 24 weeks, analyses were performed using the ICRS macroscopic score and the modified O'Driscoll histological score. Wilcoxon ranked sum tests were used to assess significant differences between the two instrument groups using each goat as its own control (p ≤ 0.05). One postoperative complication was signs of a prolonged wound healing with swelling and reluctance to weight bearing starting two days after surgery on the water jet side. Antibiotics were administered which resolved the symptoms. The median total ICRS score for the tali treated with water jets was 9,5 (range: 6–12) and 9 (range 2–11) for Observer 1 and 2 respectively; and for the tali treated conventionally this was 9,5 (range 5–11) and 9 range (2–10). The median total Modified O'Driscoll score for the tali treated with water jets was 15 (range: 7–17) and 13 (range: 3–20) for Observer 1 and 2 respectively; and for the tali treated conventionally was 13 (range: 11–21) and 15 (range: 9–20). No differences were found in complication rate or repair tissue quality between the two techniques. The results suggest that water jet drilling can be a safe alternative for conventional microfracture treatment. Future research and development will include the design of an arthroscopic prototype of the water jet drill. The focus will be on stability in nozzle positioning and minimized sterile saline consumption to further the decrease the risk of soft tissue damage.

The incidence of osteoarthritis (OA) is increasing in our younger population. OA development early in life is often related to cartilage damage, caused by (sport) injury or trauma. Detection of early knee OA is therefore crucial to target early treatment. However, early markers for OA prognosis or diagnosis are lacking. Hoffa's fat pad (HFP) is an emerging source for knee biomarkers, as it is easily accessible and shows important interaction with the homeostasis of the knee. In this study, we used Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) as a first approach. MALDI-MSI allows the study of tissue-specific molecular distributions. Therefore, we used MALDI-MSI to analyze the lipid profiles in the HFP of three patients with OA and three patients undergoing cartilage regenerative treatment. We demonstrate that the lipid profile of patients with OA is different from patients with cartilage defects.

HFP of each patient were snap frozen directly after surgical resection and cryosectioned at 15 μm. Each slide was sublimed with Norharmane matrix and analyzed by MALDI-MSI in positive and negative ion modes at a lateral resolution of 50 μm on a RapifleX Tissue Typer. The difference between patient groups were analyzed using principle component analysis and linear discriminant analysis. Lipid identifications were obtained on an Orbitrap Elite™ Hybrid Ion Trap-Orbitrap Mass Spectrometer in data dependent acquisition mode and analyzed using Lipostar software.

Linear discriminant analysis showed a specific lipid profile for each group (variance 33.94%). Score projections revealed a differential lipid spatial distribution of OA patients compared to cartilage defect patients. Among the lipids that differed significantly, for instance, the m/z 760.59 [M+H]⁺ was associated to osteoarthritis and identified as glycerophospholipid (PC 34:1), a main component of biological membranes. Additionally, the samples were found to be intra-tissue heterogeneous, with molecular profiles found in adipose-, connective- and synovial tissue.

These results suggest that lipid profiles in HFP could be useful for early OA detection. However, intra-tissue heterogeneity in HFP should be recognized when using HFP as a biomarker source.

PURPOSE

Osteochondral talar defects (OCDs) are sometimes located so far posteriorly that they may not be accessible by anterior arthroscopy, even with the ankle joint in full plantar flexion, because the talar dome is covered by the tibial plafond. It was hypothesized that computed tomography (CT) of the ankle in full plantar flexion could be useful for preoperative planning. The dual purpose of this study was, firstly, to test whether CT of the ankle joint in full plantar flexion is a reliable tool for the preoperative planning of anterior ankle arthroscopy for OCDs, and, secondly, to determine the area of the talar dome that can be reached by anterior ankle arthroscopy.