Relative Surface Velocity of the Tibiofemoral Joint and Its Relation to the Development of Osteoarthritis After Joint Injury

Exogenous Collagen Crosslinking is Highly Detrimental to Articular Cartilage Lubrication

Healthy articular cartilage is a remarkable bearing material optimized for near-frictionless joint articulation. Because its limited self-repair capacity renders it susceptible to osteoarthritis (OA), approaches to reinforce or rebuild degenerative cartilage are of significant interest. While exogenous collagen crosslinking (CXL) treatments improve cartilage's mechanical properties and increase its resistance to enzymatic degradation, their effects on cartilage lubrication remain less clear. Here, we examined how the collagen crosslinking agents genipin (GP) and glutaraldehyde (GTA) impact cartilage lubrication using the convergent stationary contact area (cSCA) configuration. Unlike classical configurations, the cSCA sustains biofidelic kinetic friction coefficients (μk) via superposition of interstitial and hydrodynamic pressurization (i.e., tribological rehydration). As expected, glutaraldehyde- and genipin-mediated CXL increased cartilage's tensile and compressive moduli. Although net tribological rehydration was retained after CXL, GP or GTA treatment drastically elevated μk. Both healthy and "OA-like" cartilage (generated via enzymatic digestion) sustained remarkably low μk in saline- (≤0.02) and synovial fluid-lubricated contacts (≤0.006). After CXL, μk increased up to 30-fold, reaching values associated with marked chondrocyte death in vitro. These results demonstrate that mechanical properties (i.e., stiffness) are necessary, but not sufficient, metrics of cartilage function. Furthermore, the marked impairment in lubrication suggests that CXL-mediated stiffening is ill-suited to cartilage preservation or joint resurfacing.

Enzymatic digestion does not compromise sliding-mediated cartilage lubrication

Articular cartilage's remarkable low-friction properties are essential to joint function. In osteoarthritis (OA), cartilage degeneration (e.g., proteoglycan loss and collagen damage) decreases tissue modulus and increases permeability. Although these changes impair lubrication in fully depressurized and slowly slid cartilage, new evidence suggests such relationships may not hold under biofidelic sliding conditions more representative of those encountered in vivo. Our recent studies using the convergent stationary contact area (cSCA) configuration demonstrate that articulation (i.e., sliding) generates interfacial hydrodynamic pressures capable of replenishing cartilage interstitial fluid/pressure lost to compressive loading through a mechanism termed tribological rehydration. This fluid recovery sustains in vivo-like kinetic friction coefficients (µk<0.02 in PBS and <0.005 in synovial fluid) with little sensitivity to mechanical properties in healthy tissue. However, the tribomechanical function of compromised cartilage under biofidelic sliding conditions remains unknown. Here, we investigated the effects of OA-like changes in cartilage mechanical properties, modeled via enzymatic digestion of mature bovine cartilage, on its tribomechanical function during cSCA sliding. We found no differences in sliding-driven tribological rehydration behaviors or µk between naïve and digested cSCA cartilage (in PBS or synovial fluid). This suggests that OA-like cartilage retains sufficient functional properties to support naïve-like fluid recovery and lubrication under biofidelic sliding conditions. However, OA-like cartilage accumulated greater total tissue strains due to elevated strain accrual during initial load application. Together, these results suggest that elevated total tissue strains-as opposed to activity-mediated strains or friction-driven wear-might be the key biomechanical mediator of OA pathology in cartilage. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) decreases cartilage's modulus and increases its permeability. While these changes compromise frictional performance in benchtop testing under low fluid load support (FLS) conditions, whether such observations hold under sliding conditions that better represent the joints' dynamic FLS conditions in vivo is unclear. Here, we leveraged biofidelic benchtop sliding experiments-that is, those mimicking joints' native sliding environment-to examine how OA-like changes in mechanical properties effect cartilage's natural lubrication. We found no differences in sliding-mediated fluid recovery or kinetic friction behaviors between naïve and OA-like cartilage. However, OA-like cartilage experienced greater strain accumulation during load application, suggesting that elevated tissue strains (not friction-driven wear) may be the primary biomechanical mediator of OA pathology.

Osteoarthritis as an Umbrella Term for Different Subsets of Humans Undergoing Joint Degeneration: The Need to Address the Differences to Develop Effective Conservative Treatments and Prevention Strategies

Osteoarthritis (OA) of joints such as the knee and hip are very prevalent, and the number of individuals affected is expected to continue to rise. Currently, conservative treatments after OA diagnosis consist of a series of increasingly invasive interventions as the degeneration and pain increase, leading very often to joint replacement surgery. Most interventions are focused on alleviating pain, and there are no interventions currently available that stop and reverse OA-associated joint damage. For many decades OA was considered a disease of cartilage, but it is now considered a disease of the whole multi-tissue joint. As pain is the usual presenting symptom, for most patients, it is not known when the disease process was initiated and what the basis was for the initiation. The exception is post-traumatic OA which results from an overt injury to the joint that elevates the risk for OA development. This scenario leads to very long wait lists for joint replacement surgery in many jurisdictions. One aspect of why progress has been so slow in addressing the needs of patients is that OA has been used as an umbrella term that does not recognize that joint degeneration may arise from a variety of mechanistic causes that likely need separate analysis to identify interventions unique to each subtype (post-traumatic, metabolic, post-menopausal, growth and maturation associated). A second aspect of the slow pace of progress is that the bulk of research in the area is focused on post-traumatic OA (PTOA) in preclinical models that likely are not clearly relevant to human OA. That is, only ~12% of human OA is due to PTOA, but the bulk of studies investigate PTOA in rodents. Thus, much of the research community is failing the patient population affected by OA. A third aspect is that conservative treatment platforms are not specific to each OA subset, nor are they integrated into a coherent fashion for most patients. This review will discuss the literature relevant to the issues mentioned above and propose some of the directions that will be required going forward to enhance the impact of the research enterprise to affect patient outcomes.

Vertical Drop Jump Biomechanics of Patients With a 3- to 10-Year History of Youth Sport-Related Anterior Cruciate Ligament Reconstruction

Background

A better understanding of movement biomechanics after anterior cruciate ligament reconstruction (ACLR) could inform injury prevention, knee injury rehabilitation, and osteoarthritis prevention strategies.

Purpose

To investigate differences in vertical drop jump (VDJ) biomechanics between patients with a 3- to 10-year history of youth sport-related ACLR and uninjured peers of a similar age, sex, and sport.

Study Design

Cross-sectional study. Level of evidence III.

Methods

Lower limb kinematics and bilateral ground-reaction forces (GRFs) were recorded for participants performing 10 VDJs. Joint angles and GRF data were analyzed, and statistical analysis was performed using 2 multivariate models. Dependent variables included sagittal (ankle, knee, and hip) and coronal (knee and hip) angles at initial contact and maximum knee flexion, the rate of change of coronal knee angles (35%-90% of the support phase; ie, slopes of linear regression lines), and vertical and mediolateral GRFs (normalized to body weight [BW]). Fixed effects included group, sex, and time since injury. Participant clusters, defined by sex and sport, were considered as random effects.

Results

Participants included 48 patients with a history of ACLR and 48 uninjured age-, sex-, and sport-matched controls (median age, 22 years [range, 18-26 years]; 67% female). Patients with ACLR demonstrated steeper negative coronal knee angle slopes (β = -0.04 deg/% [95% CI, -0.07 to -0.00 deg/%]; P = .025). A longer time since injury was associated with reduced knee flexion (β = -0.2° [95% CI, -0.3° to -0.0°]; P = .014) and hip flexion (β = -0.1° [95% CI, -0.2° to -0.0°]; P = .018). Regardless of ACLR history, women displayed greater knee valgus at initial contact (β = 2.1° [95% CI, 0.4° to 3.8°]; P = .017), greater coronal knee angle slopes (β = 0.05 deg/% [95% CI, 0.02 to 0.09 deg/%]; P = .004), and larger vertical GRFs (landing: β = -0.34 BW [95% CI, -0.61 to -0.07 BW]; P = .014) (pushoff: β = -0.20 BW [95% CI, -0.32 to -0.08 BW]; P = .001).

Conclusion

Women and patients with a 3- to 10-year history of ACLR demonstrated VDJ biomechanics that may be associated with knee motion control challenges.

Clinical Relevance

It is important to consider knee motion control during activities such as VDJs when developing injury prevention and rehabilitation interventions aimed at improving joint health after youth sport-related ACLR.

The instrumented sheep knee to elucidate insights into osteoarthritis development and progression: A sensitive and reproducible platform for integrated research efforts

BACKGROUND

Osteoarthritis of the knee is a very common condition that has been difficult to treat. The majority of cases are considered idiopathic. Much research effort remains focused on biology rather than the biomechanics of such joints. Some new methods were developed and validated to better appreciate the subtleties of the biomechanical integrity of joints, and how changes in biomechanics can contribute to osteoarthritis.

METHODS

Over the past 15 years our lab has enhanced the sensitivity of the assessment of knee biomechanics of an instrumented, trained large animal model (sheep) of osteoarthritis and integrated the findings with biological and histological assessments. These new methods include gait analysis before and after injury followed by robotic validation post-sacrifice, and more recently using Fibre Bragg Grating sensors to detect alterations in cartilage stresses.

RESULTS

A review of the findings obtained with this model are presented. The findings indicate that sheep, like humans, exhibit individual characteristics. They also indicate that joint kinetics, rather than kinematics may better define the alterations induced by injury. With the addition of Fibre Bragg Grating sensors, it has been possible to measure with good accuracy, alterations to cartilage stresses following a controlled knee injury.

INTERPRETATION

Using this model as Proof of Concept, this sheep system can now be viewed as a sensitive platform to address many questions related to risk for development of idiopathic osteoarthritis of the human knee, the efficacy of potential interventions to correct biomechanical disruptions, and how joint biomechanics and biology are integrated during aging.

Gait biomechanics: A clinically relevant outcome measure for preclinical research of musculoskeletal trauma

Traumatic injuries to the musculoskeletal system are the most prevalent of those suffered by United States Military Service members and accounts for two-thirds of initial hospital costs to the Department of Defense. These combat-related wounds often leave survivors with life-long disability and represent a significant impediment to the readiness of the fighting force. There are immense opportunities for the field of tissue engineering and regenerative medicine (TE/RM) to address these musculoskeletal injuries through regeneration of damaged tissues as a means to restore limb functionality and improve quality of life for affected individuals. Indeed, investigators have made promising advancements in the treatment for these injuries by utilizing small and large preclinical animal models to validate therapeutic efficacy of next-generation TE/RM-based technologies. Importantly, utilization of a comprehensive suite of functional outcome measures, particularly those designed to mimic data collected within the clinical setting, is critical for successful translation and implementation of these therapeutics. To that end, the objective of this review is to emphasize the clinical relevance and application of gait biomechanics as a functional outcome measure for preclinical research studies evaluating the efficacy of TE/RM therapies to treat traumatic musculoskeletal injuries. Specifically, common musculoskeletal injuries sustained by service members-including volumetric muscle loss, post-traumatic osteoarthritis, and composite tissue injuries-are examined as case examples to highlight the use of gait biomechanics as an outcome measure using small and large preclinical animal models.

Comparative Tribology: Articulation-induced rehydration of cartilage across species

Articular cartilage is a robust tissue that facilitates load distribution and wear-free articulation in diarthrodial joints. These biomechanical capabilities are fundamentally tied to tissue hydration, whereby high interstitial fluid pressures and fluid load support facilitate the maintenance of low tissue strains and frictions. Our recent ex vivo studies of cartilage sliding biomechanics using the convergent stationary contact area (cSCA) configuration, first introduced by Dowson and colleagues, unexpectedly demonstrated that sliding alone can promote recovery of interstitial pressure and lubrication lost to static compression through a mechanism termed 'tribological rehydration.' Although exclusively examined in bovine stifle cartilage to date, we hypothesized that tribological rehydration, i.e., the ability to recover/modulate tissue strains and lubrication through sliding, is a universal behavior of articular cartilage. This study aimed to establish if, and to what extent, sliding-induced tribological rehydration is conserved in articular cartilage across a number of preclinical animal species/models and diarthrodial joints. Using a comparative approach, we found that articular cartilage from equine, bovine, ovine, and caprine stifles, and porcine stifle, hip, and tarsal joints all exhibited remarkably consistent sliding speed-dependent compression/strain recovery and lubrication behaviors under matched contact stresses (0.25 MPa). All cartilage specimens tested supported robust, tribological rehydration during high-speed sliding (>30 mm/s), which as a result of competitive recovery of interstitial lubrication, promoted remarkable decreases in kinetic friction during continuous sliding. The conservation of tribological rehydration across mammalian quadruped articular cartilage suggests that sliding-induced recovery of interstitial hydration represents an important tissue adaptation and largely understudied contributor to the biomechanics of cartilage and joints.