BackgroundOne potential mechanism for early superficial cartilage wear in normal joints is alteration of the lubricant content and quality of synovial fluid. The purpose of this study was to determine if the concentration and quality of the lubricant, hyaluronan, in synovial fluid: (1) was similar in left and right knees; (2) exhibited similar age-associated trends, whether collected postmortem or antemortem; and (3) varied with age and grade of joint degeneration.MethodsHuman synovial fluid of donors (23–91 years) without osteoarthritis was analyzed for the concentrations of protein, hyaluronan, and hyaluronan in the molecular weight ranges of 2.5–7 MDa, 1–2.5 MDa, 0.5–1 MDa, and 0.03–0.5 MDa. Similarity of data between left and right knees was assessed by reduced major axis regression, paired t-test, and Bland-Altman analysis. The effect of antemortem versus postmortem collection on biochemical properties was assessed for age-matched samples by unpaired t-test. The relationships between age, joint grade, and each biochemical component were assessed by regression analysis.ResultsJoint grade and the concentrations of protein, hyaluronan, and hyaluronan in the molecular weight ranges of 2.5–7 MDa, 1–2.5 MDa, and 0.5–1 MDa in human synovial fluid showed good agreement between left and right knees and were similar between age-matched patient and cadaver knee joints. There was an age-associated decrease in overall joint grade (–15 %/decade) and concentrations of hyaluronan (–10.5 %/decade), and hyaluronan in the molecular weight ranges of 2.5–7 MDa (–9.4 %/decade), 1–2.5 MDa (–11.3 %/decade), 0.5–1 MDa (–12.5 %/decade), and 0.03–0.5 MDa (–13.0 %/decade). Hyaluronan concentration and quality was more strongly associated with age than with joint grade.ConclusionsThe age-related increase in cartilage wear in non-osteoarthritic joints may be related to the altered hyaluronan content and quality of synovial fluid.

Background Osteochondral allograft (OCA) transplantation is an effective treatment for defects in the medial femoral condyle (MFC), but the procedure is limited by a shortage of grafts. Lateral femoral condyles (LFCs) differ in geometry from MFCs but may be a suitable graft source. The difference between articular surface locations of the knee can be evaluated with μCT imaging and 3D image analysis. Hypothesis/Purpose We tested the hypothesis that LFC OCAs inserted into MFC lesions can provide a cartilage surface match comparable to those provided by MFC allografts by comparing the surgical placement of human MFC and LFC allografts into MFC defects ex-vivo. Study Design Controlled laboratory study Methods 20 MFC and 10 LFC were divided into three groups, 10 MFC recipients (MFCr), 10 MFC donors (MFCd) and 10 LFC donors (LFCd). A 20 mm defect was created in the weight-bearing portion of the MFCr. Two grafts, one MFCd and one LFCd, were implanted sequentially into each MFCr recipient condyle. Images of the MFCr using a Skyscan 1076 μCT at 18 μm voxel size were acquired and analyzed to compare the surface contours of the original recipient site with the MFCd- and LFCd-repaired sites. 3D transformations were defined to localize the defect site in the three scans of each MFCr condyle. Vertical heights from each cartilage surface voxel to a plane were determined to delineate the contour of each image. Vertical deviations from each voxel of the graft cartilage surface, relative to the intact recipient cartilage surface, were calculated and assessed as root mean square deviation (sRMS), percent graft area that was proud, sunk, and within the “acceptable” (±1.00mm) distance. The effect of repair (with MFC versus with LFC) on each of the surface match parameters (ARMS, Aacc, A unacc,proud, Aunacc,sunk, hRMS, hacc, h unacc,proud, and hunacc,sunk,) is presented as mean±StDev and was assessed by t-test. Percentage data were arcsin transformed before statistical testing. An alpha level of 0.05 was used to conclude if variations were statistically significant. Results MFCr defects were filled using both orthotopic MFCd and non-orthotopic LFCd. Registered μCT images of the MFCr illustrate the cartilage surface contour in the sagittal and coronal planes, in the original intact condyle as well as after OCA repairs. Specimen-specific surface color-maps for the MFCr after implant of the MFCd and after implant of LFCd were generally similar with some deviation near the edges. On average, the MFCr site exhibited a typical contour, and the MFCd and LFCd were slightly elevated. Both types of OCA, MFCd and LFCd, matched well, with overall height deviations of 0.63mm and 0.0.47 for area and stepoff, respectively, with no difference between MFCd and LFCd (p=0.92 and p=0.57, respectively) and acceptable deviation based on area (87.6% overall) and stepoff (96.7% overall) with no significant difference between MFCd and LFCd (p=0.87 and p=0.22, respectively). A small portion of the implant was proud, (12.1% of area and 2.6% of circumf...

Synovial fluid (SF) is a viscous ultrafiltrate of plasma that lubricates articulating joint motion. During acute trauma and certain cartilage repair procedures, blood is introduced into the joint and mixes with variable amounts of SF. The hypothesis of this study was that the dilution of blood with SF alters the rheological properties of the blood and the mechanical properties of the clot formed. The objectives were to determine the composition (solid fraction, protein content), coagulation (fibrin polymerization time, torsional strength), and mechanical (stiffness, permeability) properties of mixtures of blood with 10% or 50%SF. While the initial stages of coagulation of blood were not markedly affected by the presence of the SF, dilution with SF altered the coagulation torque profile over time, decreased the final clot structure mechanical stiffness (42-90% decrease), and increased the fluid permeability of the clots (41-to 468-fold). Compared to diluting blood with PBS, SF had a smaller effect on the mechanical properties of the clot, possibly due to the presence of high molecular weight hyaluronan. These properties of blood/SF mixtures may facilitate an understanding of the repair environment in the joint and of mechanisms of cartilage repair. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J. Orthop. Res. 29: 240-246, 2011 Keywords: blood rheology; synovial fluid; hemarthrosis; TEG; cartilage repair Synovial fluid (SF) is a viscous ultrafiltrate of plasma that lubricates articulating joint motion. SF contains several lubricant molecules, including high molecular weight hyaluronan (HA, ∼2-10 MDa, ∼1-4 mg/mL) [1][2][3] and proteoglycan 4 (PRG4, also called lubricin or SZP, ∼0.05-0.5 mg/mL).4 Articular cartilage, lubricated by SF, normally provides a low-friction, low-wear, loadbearing surface on the ends of bones, in part through the ability of cartilage to facilitate fluid pressurization during load bearing. 5 Focal defects in cartilage due to trauma, and less localized degradation common in osteoarthritis (OA), increase the local strain in cartilage near the defects, 6 while deficiencies in lubricating molecules increase the friction generated between cartilage surfaces during boundary lubrication. 7,8 During acute trauma, advanced stage OA, and bone marrow stimulation cartilage repair procedures, blood is introduced into the joint and mixes with variable amounts of SF, creating the conditions in the joint when repair is initiated. Hemarthosis, or bleeding into the joint, can occur during traumatic events, such as intra-articular fracture and ACL rupture, as well as in advanced OA. Although evidence exists that hemarthrosis may lead to cartilage erosion 9 and decreased matrix synthesis, 10 certain cartilage repair procedures used to treat focal defects, such as microfracture, 11 encourage hemarthrosis through subchondral penetrations as a source of hematopoietic stem cells for repair. Whole blood entering the intra-articular space mixes with SF, or is diluted with sal...

Objectives The residence time of hyaluronan (HA) in the synovial fluid (SF) of knee joints was investigated using the rabbit anterior cruciate ligament transection (ACLT) model. The aims were to assess at 7 and 28 days after surgery for non-operated (NonOp), ACLT, and SHAM groups: 1) HA molecular mass (Mr) distribution in SF, 2) endogenous replenishment of HA after saline washout, 3) HA residence times in SF, and 4) synovium and subsynovium cellularity. Methods Adult NZW rabbits underwent ACLT or SHAM surgeries on one hind limb, while each contralateral limb was a NonOp control. At 7 or 28d after surgery, joints were aspirated for SF, lavaged with saline, injected with saline or polydisperse HA, and sampled over 8hrs. Fluid samples were analyzed for HA concentration and Mr distribution to calculate HA residence times. Results HA Mr-distributions showed 1) loss of high-Mr HA at day 7, and a shift towards a lower-Mr HA distribution at day 28, 2) endogenous replenishment of high-Mr HA after washout, and 3) Mr-dependent HA loss, particularly at day 7 after ACLT. The residence time of HA decreased with Mr (~27hrs for 7000–2500kDa to ~7hrs for 250–50kDa) and at day 7 after ACLT (~70% decrease). The subsynovium of ACLT joints contained 4) increased cellularity and neovascularization at 7 and 28 days. Conclusions The residence time of HA in SF is transiently decreased after ACLT, suggesting a biophysical transport mechanism for the altered SF composition post-injury or during inflammation.