The Biomechanical Effects of Simulated Radioscapholunate Fusion With Distal Scaphoidectomy, 4-Corner Fusion With Complete Scaphoidectomy, and Proximal Row Carpectomy Compared to the Native Wrist.

PURPOSE: To determine the effect of simulated radioscapholunate fusion with distal scaphoid excision (RSLF+DSE), 4-corner fusion with scaphoidectomy (4-CF), and proximal row carpectomy (PRC) on the wrist's range of motion (ROM), contact pressure, and contact force in a cadaveric model. METHODS: Ten freshly frozen cadaveric wrists were tested under 4 sequential conditions: native wrist, RSLF+DSE, 4-CF, and PRC. The simulated fusions were performed using two 1.6-mm Kirschner wires. The ROM in the flexion-extension and radioulnar deviation planes was evaluated. Contact area, contact pressure, and contact force were measured at the scaphocapitolunate joint for the RSLF+DSE simulation and radiocarpal joint for the 4-CF and PRC simulations. Mechanical testing was performed using a 35-N uniaxial load and pressure-sensitive film. RESULTS: The RSLF+DSE and 4-CF groups had a decreased wrist arc ROM compared with the native wrist. The PRC group had a greater wrist arc ROM compared with the RSLF+DSE and 4-CF groups, but compared to the native wrist, it demonstrated a mildly decreased wrist arc ROM. The carpal pressure and contact force were significantly increased in the RSLF+DSE, 4-CF, and PRC groups compared with those in the native wrist. The RSLF+DSE group had the smallest increase in the carpal pressure and contact force, whereas the PRC group had the greatest increase. CONCLUSIONS: Our study validates previous findings that PRC is motion-conserving but has the greatest contact force, whereas RSLF-DSE and 4-CF may cause a decrease in the ROM but have lower contact forces. CLINICAL RELEVANCE: Understanding the underlying native wrist biomechanics and alterations following different surgical treatments may assist hand surgeons in their clinical decision making for the treatment of stage II scapholunate advanced collapse.

Aging Decreases the Ultimate Tensile Strength of Bone-Patellar Tendon-Bone Allografts.

PURPOSE: The purpose of this study was to determine whether aging imparts a clinically significant effect on the (1) mechanism of graft failure and (2) structural, material, and viscoelastic properties of patellar tendon allografts by evaluating these properties in younger donors (≤30 years of age) and older donors (>50 years of age). METHODS: A total of 34 younger (≤30 years of age) and 34 older (>50 years of age) nonirradiated, whole bone-tendon-bone allografts were prepared for testing by isolating the central third of the patellar tendon using a double-bladed 10-mm width scalpel under a 10-N load to ensure uniformity of harvest. Bone blocks were potted in polymethylmethacrylate within custom molds. Tendon length and cross-sectional area were measured using an area micrometer. A mechanical loading system was used to precondition the grafts for 100 cycles with a load between 50 N and 250 N (1 Hz). A creep load (500 N) was then applied at a rate of 100 mm/min (10 minutes). Grafts were allowed to recover at 1 N (10 minutes), followed by pull-to-failure at a rate of 100% strain per second. Mechanisms of failure (midsubstance vs avulsion) were noted and the structural, material, and viscoelastic properties calculated and compared between groups. RESULTS: There were 33 (97%) midsubstance tears in the younger group and 28 (82%) in the older group (P = .034). Younger grafts showed greater ultimate load to failure (1,782 N [1,533, 2,032] vs 1,319 N [1,103, 1,533]) (P = .006) and ultimate tensile stress (37.4 MPa [32.4, 42.4] vs 27.5 MPa [22.9, 32.0]) (P = .006). There were no significant differences in displacement (P = .595), stiffness (P = .950), strain (P = .783), elastic modulus (P = .114), creep displacement (P = .881), and creep strain (P = .614). CONCLUSIONS: This in vitro study suggests that aging weakens the bone-tendon junction and decreases the ultimate tensile strength of patellar tendon allografts. However, aging did not affect the displacement, strain, stiffness, elastic modulus, creep displacement, or creep strain of patellar tendon allografts. CLINICAL RELEVANCE: Surgeons should be aware that patellar tendon allografts from donors >50 years of age have a lower ultimate tensile stress than donors ≤30 years of age.

The Biomechanical Effects of Augmentation With Flat Braided Suture on Dorsal Intercarpal Ligament Capsulodesis for Scapholunate Instability.

PURPOSE: Selecting treatment for scapholunate (SL) instability is notoriously difficult. Many methods of reconstruction have been described, but no procedure demonstrates clear superiority. New methods proposed use internal bracing (IB) with suture anchors and flat braided suture (FBS), alone or as an augmentation with tendon autograft for SL ligament injuries. Our goal was to use computed tomography (CT) to analyze alignment of the SL joint after 3 different modes of fixation of SL instability: after reconstruction with IB incorporating either tendon autograft or the dorsal intercarpal ligament (DICL), or DICL capsulodesis without FBS. METHODS: Ten fresh-frozen, matched-pair, forearm-to-hand specimens were used. Serial sectioning of the SL stabilizing ligaments was performed and the SL interval was measured with CT. We reconstructed the SL ligament with DICL capsulodesis alone (DICL) or with IB augmented with either tendon autograft (IB plus T) or DICL (DICL plus IB). The SL interval was measured with CT. Specimens underwent 500 weighted cycles on a jig and were reimaged. Differences in SL interval after repair and cycling were compared. RESULTS: Dorsal intercarpal ligament capsulodesis augmented with IB best maintained the SL interval before and after cycling. Dorsal intercarpal ligament capsulodesis alone was inferior to DICL plus IB and IB plus T both before and after cycling. CONCLUSIONS: Dorsal intercarpal ligament capsulodesis augmented with IB appears to maintain better SL joint reduction than IB with tendon autograft. CLINICAL RELEVANCE: This work serves as a necessary step for further study of the biomechanical strength and clinical application of FBS technology in the reconstruction of SL instability. Flat braided suture augmentation of DICL capsulodesis may provide another option to consider for reconstruction of SL instability.

Compressive fatigue and endurance of juvenile bovine articular cartilage explants.

Articular cartilage is an enduring tissue. For most individuals, articular cartilage facilitates a lifetime of pain-free ambulation, supporting millions of loading cycles from activities of daily living. Although early studies into osteoarthritis focused on the role of mechanical fatigue in articular cartilage degeneration, much is still unknown regarding its strength and endurance characteristics. The compressive strength of juvenile, bovine articular cartilage explants was determined to be loading rate-dependent, reaching a maximum strength of 29.5 ±â€¯4.8 MPa at a strain rate of 0.10 %/sec. The fatigue and endurance properties of articular cartilage were characterized utilizing a material testing system, as well as a custom, validated instrument termed the two degrees-of-freedom endurance meter (endurometer). These instruments characterized fatigue in articular cartilage explants at loading levels ranging from 10 to 80 % strength (%S), up to 100,000 cycles. Cartilage explants displayed characteristics of fatigue - fatigue life increased as the loading magnitude decreased. All explants failed within 14,000 cycles at loading levels between 50 and 80 %S. At 10 and 20 %S, all explants endured 100,000 loading cycles. There was no significant difference in equilibrium compressive modulus between run-out explants and unloaded controls, although the pooled modulus increased in response to testing. Histological staining and biochemical assays revealed no material changes in collagen, sulfated glycosaminoglycan, or hydration content between unloaded controls and explants cyclically loaded to run-out. These results suggest articular cartilage may have a putative endurance limit of 20 %S (5.86 MPa), with implications for articular cartilage biomechanics and mechanobiology.

The Effect of Radioscapholunate Fusion With and Without Distal Scaphoid and Triquetrum Excision on Capitolunate Contact Pressures.

PURPOSE: To determine the effects of motion-increasing modifications to radioscapholunate (RSL) arthrodesis on capitolunate contact pressure in cadaveric wrist specimens. METHODS: Ten fresh-frozen cadaveric wrists were dissected of all superficial soft tissue, potted in polymethyl-methacrylate, and the carpus exposed via a ligament-sparing capsulotomy. An RSL arthrodesis was simulated using 2 2.4-mm distal radius plates with locking screws. The distal scaphoid pole and triquetrum were removed with an osteotome and rongeur, respectively. Contact area, pressure, and force were measured in the capitolunate joint during the application of a 35-N uniaxial load using pressure-sensitive film. Measurements were obtained before and after simulated RSL fusion, following distal scaphoidectomy and after triquetrectomy. RESULTS: The combination of RSL fusion with distal scaphoid excision (DSE) increased contact forces in the capitolunate joint by 50% over controls. An RSL fusion, and RSL fusion with DSE and triquetrum excision (TE), exhibited intermediate levels of contact force between controls and RSL fusion with DSE. Capitolunate contact pressures were similar between all experimental groups. Contact area in the capitolunate joint increased by 43% after RSL fusion with DSE over intact specimen controls. Lastly, contact area in wrists with RSL fusion, and RSL fusion with DSE and TE, were elevated, but not significantly different from intact controls. CONCLUSIONS: A DSE performed at the time of RSL fusion results in increased midcarpal joint contact force and area, with resultant contact pressures unchanged. Triquetrectomy, which has been previously shown to improve range of motion, did not increase contact forces in the capitolunate joint. CLINICAL RELEVANCE: If a surgeon is contemplating performing an RSL arthrodesis with DSE, we recommend adding a triquetrectomy to improve motion because this does not add to the potentially deleterious effects of increased midcarpal contact force.

Modulation of Superficial Zone Protein/Lubricin/PRG4 by Kartogenin and Transforming Growth Factor-ß1 in Surface Zone Chondrocytes in Bovine Articular Cartilage.

OBJECTIVE: Superficial zone protein (SZP)/lubricin/PRG4 functions as a boundary lubricant in articular cartilage to decrease friction and wear. As articular cartilage lubrication is critical for normal joint function, the accumulation of SZP at the surface of cartilage is important for joint homeostasis. Recently, a heterocyclic compound called kartogenin (KGN) was found to induce chondrogenic differentiation and enhance mRNA expression of lubricin. The objective of this study was to determine whether KGN can stimulate synthesis of SZP in superficial zone, articular chondrocytes. DESIGN: We investigated the effects of KGN and transforming growth factor-ß1 (TGF-ß1) on articular cartilage and synovium of the bovine knee joint by evaluating SZP secretion by enzyme-linked immunosorbent assay analysis. Monolayer, micromass, and explant cultures of articular cartilage, and monolayer culture of synoviocytes, were treated with KGN. SZP accumulation in the medium was evaluated and mRNA expression was measured through quantitative polymerase chain reaction. RESULTS: TGF-ß1 stimulated SZP secretion by superficial zone chondrocytes in monolayer, explant, and micromass cultures as expected. In addition, SZP secretion was inhibited by IL-1ß in explant cultures, and enhanced by TGF-ß1 in synoviocyte monolayer cultures. Although KGN elicited a 1.2-fold increase in SZP mRNA expression in combination with TGF-ß1, KGN neither stimulated any significant increases in SZP synthesis nor prevented catabolic decreases in SZP production from IL-1ß. CONCLUSIONS: These data suggest that the chondrogenic effects of KGN depend on cellular phenotype and differentiation status, as KGN did not alter SZP synthesis in differentiated, superficial zone articular chondrocytes.

Superficial Zone Extracellular Matrix Extracts Enhance Boundary Lubrication of Self-Assembled Articular Cartilage.

OBJECTIVE: Previous work has shown that increasing the production of boundary lubricant, superficial zone protein (SZP), did not reduce the friction coefficient of self-assembled articular cartilage constructs and was possibly due to poor retention of the lubricant. The aim of this investigation was to reduce the friction coefficient of self-assembled articular cartilage constructs through enhancing SZP retention by the exogenous addition of extracellular matrix (ECM) extracted from the superficial zone of native articular cartilage. DESIGN: Superficial zone cartilage was shaved from juvenile bovine femoral condyles using a dermatome, minced finely with razor blades, extracted with 4 M guanidine-hydrochloride, buffer exchanged with culture medium, and added directly to the culture medium of self-assembled articular cartilage constructs at low (10 µg/mL) and high (100 µg/mL) concentrations for 4 weeks. Biochemical and biomechanical properties were determined at the conclusion of 4 weeks culture. RESULTS: ECM treatment increased compressive and tensile stiffness of self-assembled articular cartilage constructs and decreased the friction coefficient. Glycosaminoglycan content decreased and collagen content increased significantly in self-assembled constructs by the ECM treatment. CONCLUSIONS: Friction coefficients of self-assembled articular cartilage constructs were reduced by adding extracted superficial zone ECM into the culture medium of self-assembled articular cartilage constructs.

The distribution of superficial zone protein (SZP)/lubricin/PRG4 and boundary mode frictional properties of the bovine diarthrodial joint.

The diarthrodial, knee joint is a remarkably efficient bearing system; articulating cartilage surfaces provide nearly frictionless performance with minimal wear. The low friction properties of the cartilage surfaces are due in part to the boundary lubricant, superficial zone protein (SZP); also known as lubricin or proteoglycan 4 (PRG4). In previous work, SZP localization and cartilage friction were examined across the femoral condyles. Studies in the literature have also individually investigated the other tissues that comprise the human knee and four-legged animal stifle joint, such as the meniscus or patella. However, comparisons between individual studies are limited due to the variable testing conditions employed. Friction is a system property that is dependent on the opposing articulating surface, entraining speed, and loading. A cross-comparison of the frictional properties and SZP localization across the knee/stifle joint tissues utilizing a common testing configuration is therefore needed. The objective of this investigation was to determine the friction coefficient and SZP localization of the tissues comprising the three compartments of the bovine stifle joint: patella, patellofemoral groove, femoral condyles, meniscus, tibial plateau, and anterior cruciate ligament. The boundary mode coefficient of friction was greater in tissues of the patellofemoral compartment than the lateral and medial tibiofemoral compartments. SZP immunolocalization followed this trend with reduced depth of staining and intensity in the patella and patellofemoral groove compared to the femoral condyles and tibial plateau. These results illustrate the important role of SZP in reducing friction in the tissues and compartments of the knee/stifle joint.

Stimulation of the superficial zone protein and lubrication in the articular cartilage by human platelet-rich plasma.

BACKGROUND: Platelet-rich plasma (PRP) contains high concentrations of autologous growth factors that originate from platelets. Intra-articular injections of PRP have the potential to ameliorate the symptoms of osteoarthritis in the knee. Superficial zone protein (SZP) is a boundary lubricant in articular cartilage and plays an important role in reducing friction and wear and therefore is critical in cartilage homeostasis. PURPOSE: To determine if PRP influences the production of SZP from human joint-derived cells and to evaluate the lubricating properties of PRP on normal bovine articular cartilage. STUDY DESIGN: Controlled laboratory study. METHODS: Cells were isolated from articular cartilage, synovium, and the anterior cruciate ligament (ACL) from 12 patients undergoing ACL reconstruction. The concentrations of SZP in PRP and culture media were measured by enzyme-linked immunosorbent assay. Cellular proliferation was quantified by determination of cell numbers. The lubrication properties of PRP from healthy volunteers on bovine articular cartilage were investigated using a pin-on-disk tribometer. RESULTS: In general, PRP stimulated proliferation in cells derived from articular cartilage, synovium, and ACL. It also significantly enhanced SZP secretion from synovium- and cartilage-derived cells. An unexpected finding was the presence of SZP in PRP (2.89 ± 1.23 µg/mL before activation and 3.02 ± 1.32 µg/mL after activation). In addition, under boundary mode conditions consisting of high loads and low sliding speeds, nonactivated and thrombin-activated PRP decreased the friction coefficient (µ = 0.012 and µ = 0.015, respectively) compared with saline (µ = 0.047, P < .004) and high molecular weight hyaluronan (µ = 0.080, P < .006). The friction coefficient of the cartilage with PRP was on par with that of synovial fluid. CONCLUSION: PRP significantly stimulates cell proliferation and SZP secretion by articular cartilage and synovium of the human knee joint. Furthermore, PRP contains endogenous SZP and, in a functional bioassay, lubricates bovine articular cartilage explants. CLINICAL RELEVANCE: These findings provide evidence to explain the biochemical and biomechanical mechanisms underlying the efficacy of PRP treatment for osteoarthritis or damage in the knee joint.

Surface zone articular chondrocytes modulate the bulk and surface mechanical properties of the tissue-engineered cartilage.

The central hypothesis of functional tissue engineering is that an engineered construct can serve as a viable replacement tissue in vivo by replicating the structure and function of native tissue. In the case of articular cartilage, this requires the reproduction of the bulk mechanical and surface lubrication properties of native hyaline cartilage. Cartilage tissue engineering has primarily focused on achieving the bulk mechanical properties of native cartilage such as the compressive aggregate modulus and tensile strength. A scaffold-free self-assembling process has been developed that produces engineered cartilage with compressive properties approaching native tissue levels. Thus, the next step in this process is to begin addressing the friction coefficient and wear properties of these engineered constructs. The superficial zone protein (SZP), also known as lubricin or PRG4, is a boundary mode lubricant that is synthesized by surface zone (SZ) articular chondrocytes. Under conditions of high loading and low sliding speeds, SZP reduces friction and wear at the articular surface. The objective of this investigation was to determine whether increasing the proportion of SZ chondrocytes in cartilage constructs, in the absence of external stimuli such as growth factors and mechanical loading, would enhance the secretion of SZP and improve their frictional properties. In this study, cartilage constructs were engineered through a self-assembling process with varying ratios of SZ and middle zone (MZ) chondrocytes (SZ:MZ): 0:100, 25:75, 50:50, 75:25, and 100:0. Constructs containing different ratios of SZ and MZ chondrocytes did not significantly differ in the glycosaminoglycan composition or compressive aggregate modulus. In contrast, tensile properties and collagen content were enhanced in nearly all constructs containing greater amounts of SZ chondrocytes. Increasing the proportion of SZ chondrocytes had the hypothesized effect of improving the synthesis and secretion of SZP. However, increasing the SZ chondrocyte fraction did not significantly reduce the friction coefficient. These results demonstrate that additional factors, such as SZP-binding macromolecules, surface roughness, and adhesion, need to be examined to modulate the lubrication properties of engineered cartilage.

Transforming growth factor ß-induced superficial zone protein accumulation in the surface zone of articular cartilage is dependent on the cytoskeleton.

The phenotype of articular chondrocytes is dependent on the cytoskeleton, specifically the actin microfilament architecture. Articular chondrocytes in monolayer culture undergo dedifferentiation and assume a fibroblastic phenotype. This process can be reversed by altering the actin cytoskeleton by treatment with cytochalasin. Whereas dedifferentiation has been studied on chondrocytes isolated from the whole cartilage, the effects of cytoskeletal alteration on specific zones of cells such as superficial zone chondrocytes are not known. Chondrocytes from the superficial zone secrete superficial zone protein (SZP), a lubricating proteoglycan that reduces the coefficient of friction of articular cartilage. A better understanding of this phenomenon may be useful in elucidating chondrocyte dedifferentiation in monolayer and accumulation of the cartilage lubricant SZP, with an eye toward tissue engineering functional articular cartilage. In this investigation, the effects of cytoskeletal modulation on the ability of superficial zone chondrocytes to secrete SZP were examined. Primary superficial zone chondrocytes were cultured in monolayer and treated with a combination of cytoskeleton modifying reagents and transforming growth factor ß (TGFß) 1, a critical regulator of SZP production. Whereas cytochalasin D maintains the articular chondrocyte phenotype, the hallmark of the superficial zone chondrocyte, SZP, was inhibited in the presence of TGFß1. A decrease in TGFß1-induced SZP accumulation was also observed when the microtubule cytoskeleton was modified using paclitaxel. These effects of actin and microtubule alteration were confirmed through the application of jasplakinolide and colchicine, respectively. As Rho GTPases regulate actin organization and microtubule polymerization, we hypothesized that the cytoskeleton is critical for TGFß-induced SZP accumulation. TGFß-mediated SZP accumulation was inhibited by small molecule inhibitors ML141 (Cdc42), NSC23766 (Rac1), and Y27632 (Rho effector Rho Kinase). On the other hand, lysophosphatidic acid, an upstream activator of Rho, increased SZP synthesis in response to TGFß1. These results suggest that SZP production is dependent on the functional cytoskeleton, and Rho GTPases contribute to SZP accumulation by modulating the actions of TGFß.

Engineering lubrication in articular cartilage.

Despite continuous progress toward tissue engineering of functional articular cartilage, significant challenges still remain. Advances in morphogens, stem cells, and scaffolds have resulted in enhancement of the bulk mechanical properties of engineered constructs, but little attention has been paid to the surface mechanical properties. In the near future, engineered tissues will be able to withstand and support the physiological compressive and tensile forces in weight-bearing synovial joints such as the knee. However, there is an increasing realization that these tissue-engineered cartilage constructs will fail without the optimal frictional and wear properties present in native articular cartilage. These characteristics are critical to smooth, pain-free joint articulation and a long-lasting, durable cartilage surface. To achieve optimal tribological properties, engineered cartilage therapies will need to incorporate approaches and methods for functional lubrication. Steady progress in cartilage lubrication in native tissues has pushed the pendulum and warranted a shift in the articular cartilage tissue-engineering paradigm. Engineered tissues should be designed and developed to possess both tribological and mechanical properties mirroring natural cartilage. In this article, an overview of the biology and engineering of articular cartilage structure and cartilage lubrication will be presented. Salient progress in lubrication treatments such as tribosupplementation, pharmacological, and cell-based therapies will be covered. Finally, frictional assays such as the pin-on-disk tribometer will be addressed. Knowledge related to the elements of cartilage lubrication has progressed and, thus, an opportune moment is provided to leverage these advances at a critical step in the development of mechanically and tribologically robust, biomimetic tissue-engineered cartilage. This article is intended to serve as the first stepping stone toward future studies in functional tissue engineering of articular cartilage that begins to explore and incorporate methods of lubrication.