Neuromuscular adaptations in older males and females with knee osteoarthritis during weight-bearing force control

BACKGROUND

Females exhibit significantly greater incidence, prevalence, and severity of osteoarthritis (OA) compared to males. Despite known biological, morphological, and functional differences between males and females, there has been little sex-related investigation into sex-specific biomechanical and neuromuscular responses to OA.

OBJECTIVE

To identify sex-related differences in OA-affected adults and within-sex differences between healthy and OA-affected adults' muscular activation patterns during lower limb loading.

METHODS

Thirty adults with OA and 36 controls completed a standing ground reaction force (GRF) matching protocol requiring participants to expose equal body weight to each leg and modulate horizontal GRFs while maintaining constant joint positions. Electromyography was plotted as a function of GRF direction to depict muscle activation patterns. Muscles were classified as a general joint stabilizer, specific joint stabilizer or moment actuator by quantifying activation patterns with a test of asymmetry, specificity index and mean direction of activity. Lower limb kinematics and kinetics were also recorded.

RESULTS

In general, muscle roles as it relates to joint stability did not differ between groups. Compared to controls, both males and females with OA demonstrated greater rectus femoris activity and reduced knee rotation moments. Females with OA had significantly greater biceps femoris and gastrocnemius activity during respective lateral, and anterior-medial loading directions compared to males with OA.

CONCLUSIONS

We identified fundamental differences in muscular stabilization strategies in older adults with OA as well as sex-related changes in neuromuscular function that may influence joint loading conditions and provide insight into the greater incidence of knee OA in females.

Muscle weakness causes joint degeneration in rabbits

OBJECTIVE

The objective of this study was to investigate the effects of botulinum toxin type-A (BTX-A) induced quadriceps weakness on micro-structural changes in knee cartilage of New Zealand White (NZW) rabbits.

DESIGN

Fifteen rabbits were divided randomly into an experimental and a sham control group. Each group received a unilateral single quadriceps muscle injection either with saline (sham control; n=4) or BTX-A (experimental; n=11).

RESULTS

BTX-A injection produced significant quadriceps muscle weakness (P<0.05) and loss of quadriceps muscle mass (P<0.05). Degenerative changes of the knee cartilage, assessed with the Mankin grading system, were the same for the injected and non-injected hind limbs of the experimental group animals. Sham injection had no effect on joint degeneration but all control animals showed some degenerative changes in the knee. Degenerative changes of the retro-patellar cartilage were more severe in the experimental compared to sham control group rabbits (P<0.05). The distal region of the retro-patellar cartilage was more degenerated than the proximal part in the experimental and control group rabbits (P<0.05). The Mankin grades for the tibiofemoral region were not significantly different between experimental and control group rabbits (P>0.05).

CONCLUSION

Quadriceps muscle weakness caused increased degeneration in the retro-patellar cartilage of NZW rabbits, providing evidence that muscle weakness might be a risk factor for the onset and progression of osteoarthritis (OA). Future work needs to delineate whether muscle weakness directly affects joint degeneration, or if changes in function and movement execution associated with muscle weakness are responsible for the increased rate of OA onset and progression observed here.

Considerations on Joint and Articular Cartilage Mechanics

When studying joint degeneration leading to osteoarthritis (OA), it seems imperative that local joint tissue loading is known during normal everyday movement and that the adaptive/degenerative effects of this loading are quantified systematically. Philosophically, we believe the best way to approach this problem is by studying joint degeneration and osteoarthritis in long-term experimental models and by representing diarthrodial joints and the associated tissues with accurate, geometric and structural, theoretical models. Here, we present selected examples of our work representing this approach. Experimentally, we demonstrate that the local loading of joints changes continuously in experimental models of OA, not only because of the changing external and internal loading, but also because of the continuous alterations in joint contact geometry and tissue mechanical properties. Furthermore, we show that single bouts of joint loading affect gene expression, and that gene expression, as well as subsequent joint degeneration is site-specific. In fact, opposing articular surfaces that are exposed to the same loading may degenerate at completely different rates. Finally, we propose a series of theoretical models of articular cartilage and contact mechanics, demonstrating that many of the anisotropic and inhomogeneous properties can be explained by structural elements and their orientation and volumetric concentration across the tissue.

Heterogeneity in patellofemoral cartilage adaptation to anterior cruciate ligament transection; chondrocyte shape and deformation with compression

OBJECTIVE

The purpose of this study was to determine if the opposing cartilages of the feline patellofemoral joint adapted differently to short-term anterior cruciate ligament transection (ACL-T) and if the magnitude of chondrocyte deformation upon tissue loading was altered under ACL-T conditions compared to contralateral controls. In situ static compression of physiological magnitude was applied to the feline patellofemoral cartilage 16 weeks post-ACL-T and cartilage and chondrocyte deformation were evaluated by histomorphometry.

DESIGN

Six adult cats were euthanized 16 weeks after unilateral ACL-T. A peak surface pressure of 9 MPa was applied to the fully intact patella and femoral groove cartilages. After in situ fixation under compression, sections from the centre of the indent and from an adjacent unloaded area of the cartilages were analysed. Chondrocyte shape, size, clustering and volumetric fraction were quantified.

RESULTS

Experimental patellar articular cartilage was thicker, contained larger chondrocytes that were more frequently arranged in clusters and had, on average, a larger chondrocyte volumetric fraction compared to contralateral controls. In contrast, the experimental femoral groove cartilage demonstrated little adaptation to ACL-T.

CONCLUSIONS

The patellar articular cartilage adapts to short-term ACL-T to a greater extent than femoral groove cartilage. We speculate that differences in the histological parameters of control tissues, such as cartilage thickness and the magnitude and depth distribution of chondrocyte shape, size and volumetric fraction may contribute to predisposing patellar cartilage, and not femoral groove cartilage, to adaptation after ACL-T.

Opposing cartilages in the patellofemoral joint adapt differently to long-term cruciate deficiency: chondrocyte deformation and reorientation with compression

OBJECTIVE

The purposes of this study were to quantify patellofemoral histology in the feline knee 67 months post-anterior cruciate ligament transection (ACL-T) and to apply an in situ static load of physiological magnitude to the articular cartilage and evaluate the resulting cartilage and chondrocyte deformation.

DESIGN

Six cats were sacrificed 67+/-6 months post-unilateral ACL-T. Static compression was applied to the cartilage surfaces of the patellofemoral joint using a cylindrical metal indentor. After fixation, full thickness osteochondral blocks were harvested and sections cut from not-indented and indented areas. Chondrocyte shape, orientation and volumetric fraction as well as cartilage thickness were evaluated.

RESULTS

Experimental and contralateral patellae were histologically different compared to normal with thickened cartilage, rounded superficial chondrocytes, and uneven proteoglycan staining throughout. In contrast, no differences were apparent in 10 of the 12 femoral groove samples. The structural reorganisation of the experimental patellae cartilage that occurred with load was also different compared to normal. Specifically, the indentation shape was deeper and had steeper sides and the realignment of deep zone cells at angles of 45 degrees and 135 degrees observed in normal cartilage was no longer apparent in the experimental tissue.

CONCLUSIONS

Two directly articulating cartilage surfaces of the feline patellofemoral joint have completely contrasting responses to long-term ACL-T. We speculate that this could be a result of the different nature of the loads experienced by the two surfaces (intermittent vs constant) and/or the differences in the histology and material properties of the two tissues in their normal state, and/or an inherent difference in the biological response capabilities of the articular cartilages.

An articular cartilage contact model based on real surface geometry

Abnormal, excessive stresses acting on articular joint surfaces are speculated to be one of the causes for joint degeneration. However, articular surface stresses have not been studied systematically, since it is technically difficult to measure in vivo contact areas and pressures in dynamic situations. Therefore, we implemented a numerical model of articular surface contact using accurate surface geometries. The model was developed for the cat patellofemoral joint. We demonstrated that small misalignments of the patella relative to the femur change the joint contact mechanics substantially for a given external load. These results suggest that misalignment might be studied as one of the factors causing articular cartilage disorder and joint degeneration.