Effect of intermittent cyclic preloads on the response of articular cartilage explants to an excessive level of unconfined compression

Post-traumatic Osteoarthritis in Rabbits Following Traumatic Injury and Surgical Reconstruction of the Knee

Post-traumatic osteoarthritis (PTOA) of the knee is often attributed to anterior cruciate ligament (ACL) and meniscus injury. The development of PTOA, however, does not seem to depend on whether or not the damaged ACL is reconstructed. There has been a need to develop animal models to study the mechanisms of PTOA following reconstruction of a traumatized knee. Eighteen rabbits underwent closed-joint trauma to produce ACL rupture and meniscus damage. Then, for the first time, the traumatized knee was surgically repaired in this animal model. Upon euthanasia at 1-, 3- or 6-month post-trauma, joint stability, cartilage morphology and mechanical properties, as well as histology of the cartilage and subchondral bone were evaluated. Trauma-induced knee injury involved 72% mid-substance ACL rupture, 28% partial ACL tear and 56% concurrent medial meniscal damage. ACL reconstruction effectively restored joint stability by reducing joint laxity to a level similar to that in the contralateral intact knee. Compared to their contralateral controls, reconstructed limbs showed osteoarthritic changes to the cartilage and subchondral bone as early as 1-month post-trauma. The degeneration progressed over time up to 6-month. Overall, the medial compartments had more tissue damage than their corresponding lateral counterparts. Damage patterns to the ACL, the frequency of observed concurrent meniscal injury, and reductions in cartilage integrity and health were consistent with clinical observations of human patients who undergo ACL injury and reconstruction. Thus, we believe the combined closed-joint injury and surgical repair lapine model of PTOA, being first-ever and clinically relevant, shows promise to evaluate well-targeted therapeutics and other interventions for this chronic disease.

Biomechanical loading of the porcine femorotibial joint during maximal movements: An exploratory, ex vivo study

Thus far, there is a lack of scientific investigation regarding the hypothesis that biomechanical factors contribute to the cross-species pathogenesis of osteochondrosis (OC). Therefore, the aim of this pilot study was to investigate whether high (peak) pressures occur in the porcine femorotibial (FT) joint. In this experimental, ex vivo study, the right hind limbs of seven weaned piglets were subjected to maximal joint excursions, as a priori radiologically estimated. Subsequently, the intra-articular pressures were measured using sensors placed in both the medial and the lateral compartments of the FT joint. The overall highest individual peak pressure was found in the lateral FT joint during maximal extension (2611 kPa; group mean ± standard deviation (SD) 982.3 ± 988.2 kPa). In the medial FT joint, the highest individual peak pressure was found during maximal adduction (1481 kPa; group mean ± SD 664.9 ± 393.2 kPa). Moreover, nearly 30% of the ex vivo peak pressures were above published thresholds for cartilage catabolism (>500 kPa/0.5 MPa), but not for interfering with cell viability (>5 MPa). In conclusion, this ex vivo study on FT joint pressures in weaned piglets showed that FT joint movements at maximal excursions are related to concomitant internal peak joint pressures. More studies should be performed to evaluate the possible biomechanical relation of these observations with osteochondrosis, which would allow the design of preventive measures in the pig industry, to avoid extreme limb movements and concomitant joint peak pressures in vivo.

Hemiarthroplasties: the choice of prosthetic material causes different levels of damage in the articular cartilage

BACKGROUND

Hemiarthroplasty has clear advantages over alternative procedures and is used in 20% of all shoulder joint replacements. Because of cartilage wear, the clinical outcome of hemiarthroplasty is unreliable and controversial. This paper suggests that the optimal choice of prosthetic material may reduce cartilage degeneration and improve the reliability of the procedure. The specific objectives were to assess 3 materials and assess how the severity of arthritis might affect the choice of prosthetic material.

METHODS

A CoCr alloy, an AL₂O₃ ceramic, and a polycarbonate urethane polymer (PCU) were mechanically tested against 5 levels of human osteoarthritic cartilage (from intact to severely arthritic, n = 45). A high friction coefficient, a decrease in Young's modulus, an increase in permeability, a decrease in relaxation time, an increase in surface roughness, and a disrupted appearance of the cartilage after testing were used as measures of cartilage damage. The biomaterial that caused minimal cartilage damage was defined as superior.

RESULTS

The CoCr caused the most damage. This was followed by the AL₂O₃ ceramic, whereas the PCU caused the least amount of damage. Although the degree of arthritis had an effect on the results, it did not change the trend that CoCr performed worst and PCU the best.

DISCUSSION AND CONCLUSION

This study indicates that ceramic implants may be a better choice than metals, and the articulating surface should be as smooth as possible. Although our results indicate that the degree of arthritis should not affect the choice of prosthetic material, this suggestion needs to be further investigated.

Development of a Cartilage Shear-Damage Model to Investigate the Impact of Surface Injury on Chondrocytes and Extracellular Matrix Wear

Background Many i n vitro damage models investigate progression of cartilage degradation after a supraphysiologic, compressive impact at the surface and do not model shear-induced damage processes. Models also neglect the response to uninterrupted tribological stress after damage. It was hypothesized that shear-induced removal of the superficial zone would accelerate matrix degradation when damage was followed by continued load and articulation. Methods Bovine cartilage underwent a 5-day test. Shear-damaged samples experienced 2 days of damage induction with articulation against polyethylene and then continued articulation against cartilage (CoC), articulation against metal (MoC), or rest as free-swelling control (FSC). Surface-intact samples were randomized to CoC, MoC, or FSC for the entire 5-day test. Samples were evaluated for chondrocyte viability, GAG (glycosaminoglycan) release (matrix wear surrogate), and histological integrity. Results Shear induction wore away the superficial zone. Damaged samples began continued articulation with collagen matrix disruption and increased cell death compared to intact samples. In spite of the damaged surface, these samples did not exhibit higher GAG release than intact samples articulating against the same counterface ( P = 0.782), contrary to our hypothesis. Differences in GAG release were found to be due to tribological testing against metal ( P = 0.003). Conclusion Shear-induced damage lowers chondrocyte viability and affects extracellular matrix integrity. Continued motion of either cartilage or metal against damaged surfaces did not increase wear compared with intact samples. We conjecture that favorable reorganization of the surface collagen fibers during articulation protected the underlying matrix. This finding suggests a potential window for clinical interventions to slow matrix degradation after traumatic incidents.

Cartilage and chondrocyte response to extreme muscular loading and impact loading: Can in vivo pre-load decrease impact-induced cell death?

BACKGROUND

Impact loading causes cartilage damage and cell death. Pre-loading prior to impact loading may protect cartilage and chondrocytes. However, there is no systematic evidence and understanding of the effects of pre-load strategies on cartilage damage and chondrocyte death. This study aimed at determining the effects of the pre-load history on impact-induced chondrocyte death in an intact joint.

METHODS

Patellofemoral joints from 42 rabbits were loaded by controlled quadriceps muscle contractions and an external impacter. Two extreme muscular loading conditions were used: (i) a short-duration, high intensity, static muscle contraction, and (ii) a long-duration, low-intensity, cyclic muscle loading protocol. A 5-Joule centrally-oriented, gravity-accelerated impact load was applied to the joints. Chondrocyte viability was quantified following the muscular loading protocols, following application of the isolated impact loads, and following application of the impact loads that were preceded by the muscular pre-loads. Joint contact pressures were measured for all loading conditions by a pressure-sensitive film.

FINDINGS

Comparing to cartilage injured by impact loading alone, cartilage pre-loaded by static, maximal intensity, short-term muscle loads had lower cell death, while cartilage pre-loaded by repetitive, low-intensity, long-term muscular loads has higher cell death. The locations of peak joint contact pressures were not strongly correlated with the locations of greatest cell death occurrence.

INTERPRETATION

Static, high intensity, short muscular pre-load protected cells from impact injury, whereas repetitive, low intensity, prolonged muscular pre-loading to the point of muscular fatigue left the chondrocytes vulnerable to injury. However, cell death seems to be unrelated to the peak joint pressures.

Calcium signaling as a novel method to optimize the biosynthetic response of chondrocytes to dynamic mechanical loading

Chondrocyte sensitization and desensitization to mechanical stimuli are complex phenomena that have not been fully described. In this study, we investigated the temporal response of chondrocytes to dynamic mechanical loading and whether changes in calcium signaling could be used a predictor of the biosynthetic response. Cell-seeded agarose gels pre-incubated with an intracellular [Formula: see text] dye (Fluo-4) were subjected to dynamic compressive loading under varying conditions (amplitude and duration). Induced changes in Ca(2+) signaling were determined by confocal imaging and matrix biosynthesis by radioisotope incorporation. It was observed that chondrocytes required a minimum amount of stimulation in order to elicit an anabolic response and they quickly became insensitive to the imposed stimulus. The response appeared to be amplitude dependent and could be predicted by measuring resultant changes in Ca(2+) signaling. A positive correlation between Ca(2+) signaling and matrix synthesis was achieved when changes in Ca(2+) signaling was expressed as a relative number of cells experiencing multiple transients. In addition, these changes in Ca(2+) signaling were effective at determining optimal recovery period between successive applications of intermittent mechanical loading, in which full mechanosensitivity was achieved when [Formula: see text] signaling was allowed to return to baseline (control) levels. The use of Ca(2+) signaling to predict the effectiveness of a particular mechanical stimulus as well as to determine optimal refractory periods appears to be advantageous over empirical-based approaches. Future work will investigate the process of Ca(2+) ion sequestration into intracellular stores to elucidate potential desensitization mechanisms to dynamic mechanical loading.

Subphysiological compressive loading reduces apoptosis following acute impact injury in a porcine cartilage model

BACKGROUND

Acute cartilage injuries induce cell death and are associated with an increased incidence of osteoarthritis development later in life. The objective of this study was to investigate the effect of posttraumatic cyclic compressive loading on chondrocyte viability and apoptosis in porcine articular cartilage plugs.

HYPOTHESIS

Compressive loading of acutely injured cartilage can maintain chondrocyte viability by reducing apoptosis after a traumatic impact injury.

STUDY DESIGN

In vitro controlled laboratory study.

LEVEL OF EVIDENCE

Level 5.

METHODS

Each experiment compared 4 test groups: control, impact, impact with compressive loading (either 0.5 or 0.8 MPa), and no impact but compressive loading (n = 15 per group). Flat, full-thickness articular cartilage plugs were harvested from the trochlear region of porcine knees. A drop tower was utilized to introduce an impact injury. The articular plugs were subjected to two 30-minute cycles of either 0.5 or 0.8 MPa of dynamic loading. Cell viability, apoptosis, and gene expression of samples were evaluated 24 hours postimpaction.

RESULTS

Cell viability staining showed that 0.5 MPa of dynamic compressive loading increased cell viability compared with the impact group. Apoptotic analysis revealed a decrease in apoptotic expression in the group with 0.5 MPa of dynamic compressive loading compared with the impact group. Significantly higher caspase 3 and lower collagen II expressions were observed in impacted samples without compressive loading, compared with those with. Compressive loading of nonimpacted samples significantly increased collagen II and decreased caspase 3 expressions.

CONCLUSION

In this porcine in vitro model, dynamic compressive loading at subphysiological levels immediately following impact injury decreases apoptotic expression, thereby maintaining chondrocyte viability.

CLINICAL RELEVANCE

Therapeutic exercises could be designed to deliver subphysiological loading to the injured cartilage, thereby minimizing injury.

The acute effect of bipolar radiofrequency energy thermal chondroplasty on intrinsic biomechanical properties and thickness of chondromalacic human articular cartilage

Radio frequency energy (RFE) thermal chondroplasty has been a widely-utilized method of cartilage debridement in the past. Little is known regarding its effect on tissue mechanics. This study investigated the acute biomechanical effects of bipolar RFE treatment on human chondromalacic cartilage. Articular cartilage specimens were extracted (n = 50) from femoral condyle samples of patients undergoing total knee arthroplasty. Chondromalacia was graded with the Outerbridge classification system. Tissue thicknesses were measured using a needle punch test. Specimens underwent pretreatment load-relaxation testing using a spherical indenter. Bipolar RFE treatment was applied for 45 s and the indentation protocol was repeated. Structural properties were derived from the force-time data. Mechanical properties were derived using a fibril-reinforced biphasic cartilage model. Statistics were performed using repeated measures ANOVA. Cartilage thickness decreased after RFE treatment from a mean of 2.61 mm to 2.20 mm in Grade II, II-III, and III specimens (P < 0.001 each). Peak force increased after RFE treatment from a mean of 3.91 N to 4.91 N in Grade II and III specimens (P = 0.002 and P = 0.003, respectively). Equilibrium force increased after RFE treatment from a mean of 0.236 N to 0.457 N (P < 0.001 each grade). Time constant decreased after RFE treatment from a mean of 0.392 to 0.234 (P < 0.001 for each grade). Matrix modulus increased in all specimens following RFE treatment from a mean 259.12 kPa to 523.36 kPa (P < 0.001 each grade). Collagen fibril modulus decreased in Grade II and II-III specimens from 60.50 MPa to 42.04 MPa (P < 0.001 and P = 0.005, respectively). Tissue permeability decreased in Grade II and III specimens from 2.04 ∗10(-15) m(4)/Ns to 0.91 ∗10(-15) m(4)/Ns (P < 0.001 and P = 0.009, respectively). RFE treatment decreased thickness, time constant, fibril modulus, permeability, but increased peak force, equilibrium force, and matrix modulus. While resistance to shear and tension could be compromised due to removal of the superficial layer and decreased fibril modulus, RFE treatment increases matrix modulus and decreases tissue permeability which may restore the load- bearing capacity of the cartilage.

High levels of glucosamine-chondroitin sulfate can alter the cyclic preload and acute overload responses of chondral explants

A recent study by our laboratory showed that 14 days of low intensity, intermittent cyclic preloading of chondral explants elevated the concentration of proteoglycans (PGs) to cause a mechanical stiffening of the explants prior to an acute overload and limit the extent of tissue damage. Longer term loading to 21 days resulted in tissue degradation prior to the acute traumatic event and excessive damage from an acute overload. Previous studies by others showed that bathing chondral explants in a supplement of glucosamine-chondroitin sulfate (glcN-CS) upregulated the synthesis of tissue PGs, particularly in stressed tissue, and the supplement served as an anti-inflammatory agent. Our current hypothesis was that the supplementation of culture media with a high concentration of glcN-CS would upregulate the production of tissue PG and limit or mitigate long-term degradation of chondral explants under cyclic preloading and limit tissue damage in an acute overload. We showed that, in the presence of supplement, cyclic preloading significantly increased tissue PG content and matrix modulus by about 65 and 300%, respectively, at 21 days, resulting in a reduction of matrix damage and cell death following an acute overload. These data show a biological action of high concentrations of this supplement and its effect on the mechanical properties in this in vitro model.