Pathogenesis of osteoarthritis-like changes in the joints of mice deficient in type IX collagen.

OBJECTIVE: To examine the pathogenetic mechanisms of osteoarthritis (OA)-like changes in Col9a1-/- mice, which are deficient in type IX collagen. METHODS: Knee joints and temporomandibular joints (TMJs) from Col9a1-/- mice and their wild-type (Col9a1+/+) littermates were examined by light microscopy. Immunohistochemical staining was performed to examine the expression of matrix metalloproteinase 3 (MMP-3) and MMP-13, degraded type II collagen, and the discoidin domain receptor 2 (DDR-2) in knee joints. Cartilage mechanics were also evaluated for compressive properties by microindentation testing of the tibial plateau and for tensile properties by osmotic loading of the femoral condyle. RESULTS: Histologic analysis showed age-dependent OA-like changes in the knee and TMJs of Col9a1-/- mice starting at the age of 3 months. At the age of 6 months, enhanced proteoglycan degradation was observed in the articular cartilage of the knee and TMJs of the mutant mice. The expression of MMP-13 and DDR-2 protein and the amount of degraded type II collagen were higher in the knee joints of Col9a1-/- mice than in their wild-type littermates at the age of 6 months. Changes in cartilage mechanics were observed in the femoral and tibial plateaus of Col9a1-/- mice at 6 months, including a decrease in the compressive modulus and uniaxial modulus. At 3 and 6 months of age, tibial cartilage in Col9a1-/- mice was found to be more permeable to fluid flow, with an associated compromise in the fluid pressurization mechanism of load support. All of these changes occurred only at medial sites. CONCLUSION: Lack of type IX collagen in Col9a1-/- mice results in age-dependent OA-like changes in the knee joints and TMJs.

Osteoarthritis-like changes and decreased mechanical function of articular cartilage in the joints of mice with the chondrodysplasia gene (cho).

OBJECTIVE: To investigate whether heterozygosity for a loss-of-function mutation in the gene encoding the alpha1 chain of type XI collagen (Col11a1) in mice (chondrodysplasia, cho) causes osteoarthritis (OA), and to understand the biochemical and biomechanical effects of this mutation on articular cartilage in knee and temporomandibular (TM) joints. METHODS: Articular cartilage from the knee and TM joints of mice heterozygous for cho (cho/+) and their wild-type littermates (+/+) was examined. The morphologic properties of cartilage were evaluated, and collagen fibrils were examined by transmission electron microscopy. Immunohistochemical staining was performed to examine the protein expression levels of matrix metalloproteinase 3 (MMP-3) and MMP-13 in knee joints. In 6-month-old animals, fixed-charge density was determined using a semiquantitative histochemical method, and tensile stiffness was determined using an osmotic loading technique. RESULTS: The diameter of collagen fibrils in articular cartilage of knee joints from heterozygous cho/+ mice was increased relative to that in control cartilage, and histologic analysis showed OA-like degenerative changes in knee and TM joints, starting at age 3 months. The changes became more severe with aging. At 3 months, protein expression for MMP-3 was increased in knee joints from cho/+ mice. At 6 months, protein expression for MMP-13 was higher in knee joints from cho/+ mice than in joints from their wild-type littermates, and negative fixed-charge density was significantly decreased. Moreover, tensile stiffness in articular cartilage of knee joints from cho/+ mice was moderately reduced and was inversely correlated with the increase in articular cartilage degeneration. CONCLUSION: Heterozygosity for a loss-of-function mutation in Col11a1 results in the development of OA in the knee and TM joints of cho/+ mice. Morphologic and biochemical evidence of OA appears to precede significant mechanical changes, suggesting that the cho mutation leads to OA through a mechanism that does not initially involve mechanical factors.

Development of tensile strength during distraction osteogenesis in a rat model.

These studies were designed to determine the reliability of in vitro tensile testing to measure the temporal development of regenerate bone strength in rats during limb lengthening (distraction osteogenesis, DO). External fixators were placed on the right tibiae of 36 virus-free, 400-450 g male Sprague Dawley rats, and osteotomies (n = 33) were performed. Distraction was initiated the following morning (0 day latency) at 0.4 mm/day and continued to day 20. The 8 mm gap was allowed to consolidate for up to 50 days (day 70 postop). Contralateral unoperated and operated (fixator only) controls were included. On days 20, 30, 50 and 70 postop, the rats were anesthetized, and their tibiae were radiographed prior to undergoing sacrifice for histological or tensile analysis. On day 70, an additional group was tested by three-point bending. Radiodensity measurements demonstrated progressive mineralization of the DO gap, and histology confirmed typical intramembranous ossification of collagen bundles oriented parallel to the distraction force. Tensile stiffness increased significantly between days 20 and 30 postop, this increase correlated with initial radiographic and histologic bridging of the DO gap. Energy to failure and ultimate tensile strength increased progressively to day 70. At day 70, the force to failure for three-point bending was 65% of control tibiae. In conclusion, in vitro tensile testing provides a reliable method to test the development of structural integrity during the early stages of DO. Therefore, the biomechanical effects of postulated modulators of bone repair can be measured during early stages (bone formation, bridging, early consolidation) of DO in a rat model.

Analysis of a biodegradable composite for bone healing.

A degradable L-PLA/calcium carbonate composite made of interconnecting phases was examined. This structure was used both to slow the degradation rate and to reduce the brittleness of the ceramic. Both in vitro and in vivo degradation studies were performed. Samples were incubated in buffered saline or placed in the dorsum of rats for 0, 1, or 4 weeks. Mechanical testing was performed on both groups, volume fraction of each component was determined for in vitro samples, and histology was performed on in vivo samples. Failure load, tensile strength, and elastic modulus significantly decreased during the 1st week for both groups. Continued decreases were seen at 4 weeks for in vitro samples but not for in vivo. Failure strain and tensile strength decreased only for in vitro specimens. PLA fraction significantly decreased during the 1st week and then stabilized. Histology showed that tissue ingrowth occurred at 4 weeks. The decrease in mechanical properties was probably a result of the decreased PLA fraction. The stabilization and even a slight increase in tensile strength and failure strain in the in vivo samples was probably due to the tissue ingrowth forming an implant-tissue composite.

Simulated lateral ankle ligamentous injury. Change in ankle stability.

The effect of simulated ankle ligamentous injury on ankle-subtalar joint complex laxity was studied. Thirty-six intact ankles were loaded in inversion-eversion and anterior-posterior directions. Motions of the talus and calcaneus were measured with respect to the tibia. Ankles were tested at neutral, 15 degrees of dorsiflexion, and 15 degrees of plantar flexion. In all the specimens the anterior talofibular ligament was sectioned and then the calcaneofibular ligament was sectioned; testing was then repeated. With sectioning of the anterior talofibular ligament, motion increased primarily in dorsiflexion with both anterior-posterior and inversion-eversion loading. This increase was primarily caused by a large increase in subtalar motion. Additional sectioning of the calcaneofibular ligament produced little change in ankle subtalar joint motion except in dorsiflexion. Clinically, these findings show that if an anterior-posterior drawer test shows less laxity in dorsiflexion than in neutral and greater laxity than the contralateral asymptomatic side, then an isolated anterior talofibular ligamentous tear exists. Similarly, laxity in 15 degrees of dorsiflexion and in neutral suggests calcaneofibular ligament disruption. During inversion-eversion loading, the increase in ankle-subtalar joint complex rotation with calcaneofibular ligament sectioning occurred primarily in the ankle joint, implying that the calcaneofibular ligament constrains the talus through the calcaneus. Therefore, a talar tilt on stress radiographs demonstrates a torn calcaneofibular ligament.

Biomechanical comparison of reconstruction techniques in simulated lateral ankle ligament injury.

Eighteen intact ankles were loaded with inversion-eversion and anterior-posterior forces, and motions of the talus and calcaneus were measured. Ankles were tested in neutral, 15 degrees of dorsiflexion, and 15 degrees of plantar flexion. The anterior talofibular ligament was then sectioned and testing was repeated. In half the specimens the calcaneofibular ligament was also sectioned followed by repeat testing. The Evans, Watson-Jones, and Chrisman-Snook procedures were performed on each ankle and testing was repeated. With inversion-eversion loading, only the Chrisman-Snook reconstruction resulted in a significantly more stable ankle joint complex than in the anterior talofibular ligament cut ankles. All three reconstructions increased ankle stability over the anterior talofibular and calcaneofibular ligament cut state. With anterior-posterior loading, all reconstructions resulted in a significantly more stable ankle joint complex than the anterior talofibular ligament cut ankles. The Evans and Chrisman-Snook procedures resulted in more stability than the anterior talofibular and calcaneofibular ligament cut ankles. There was no difference in subtalar joint motion with inversion-eversion loading among ankles with the anterior talofibular ligament cut and those with any of the reconstructions. For the anterior talofibular and calcaneofibular ligament cut ankles, subtalar joint motion was similar to that in intact ankles after each reconstruction. All three reconstructions resulted in ankles with significantly less subtalar joint motion with anterior-posterior loading than ankles with the anterior talofibular ligament cut or with the anterior talofibular and calcaneofibular ligaments cut. The Chrisman-Snook procedure resulted in ankles with significantly less motion than intact ankles.

Biomechanical analysis of patellar tendon allografts as a function of donor age.

We evaluated the biomechanical properties of patellar tendon allografts from donors aged 18 to 55 years. Bone-patellar tendon-bone complexes were harvested from acceptable donors and processed. Fat and soft tissue were removed, and the tendons were sectioned lengthwise leaving the central third. Area measurements were taken, and mechanical testing was performed. Specimens were pulled to failure at a rate of 10% of the initial length per second. The force at failure, tensile stress, modulus of elasticity, and percent elongation were determined for each specimen. There was no significant correlation (P > 0.05) between age and any of the mechanical properties. Load at failure ranged from 2110 to 4650 N, with a mean of 3424 N. Regression analysis showed slightly decreasing tensile stress with increasing age, but the correlation was not significant. It appears that patellar tendon allografts from donors up to age 55 have similar mechanical properties.

Pullout strength of fixation screws from polymethylmethacrylate bone cement.

Polymethylmethacrylate bone cement is often used to fill voids and increase the strength of osteoporotic and pathological bone. However, it is unclear as to which method of cement augmentation provides optimal screw fixation. This study was conducted to determine which of the current cement augmentation techniques provides the strongest construct when used in association with orthopaedic fixation screws. Pullout strength was determined for screws placed in sawbones with no cement, soft cement, doughy cement and hard cement after drilling and tapping. All cement-screw constructs were significantly stronger than the no cement group. Screws placed in doughy cement had a significantly higher pullout force than those placed in hard cement. Pullout strength of screws placed in soft cement was intermediate between the other cement techniques but not significantly different from either group.

Initial stability of porous coated acetabular implants. The effect of screw placement, screw tightness, defect type, and oversize implants.

The effects of screw location, screw tightness, acetabular bony defects, and implant size on the initial stability of porous coated acetabular implants was studied in vitro using 12 fresh frozen cadaver pelves. The fixation of porous coated acetabular implants was compared following fixation with either rim or center screws. Implants were tested first under axial and torsional stress. Then, either a peripheral or central bony defect was created in the acetabulum and testing was repeated in a similar fashion. Rim screws were noted to significantly improve the initial fixation of implants in intact acetabula and in acetabula with central bony defects. It was also shown that the tightness of the screws is an important factor affecting the strength of fixation. Although bony defects compromise the fixation of implants, specimens with central defects were very stable, particularly when tested with axial load. Acetabula with peripheral defects lost significant stability. The use of larger implants in acetabula with bony defects was shown to increase bony coverage and the overall implant stability.

Retention and strength of silicone-rubber catheters. A report of five cases of retention and analysis of catheter strength.

Five patients had a silicone-rubber catheter that broke during attempted removal. Mechanical testing was performed to determine the tensile strength of silicone-rubber as well as of polyvinyl chloride catheters. Silicone-rubber catheters were found to have a low tensile strength. The pull-out force of ten indwelling silicone-rubber catheters was also measured. The pullout force measured from a patient who had a cast was close to 40 per cent of the strength of the silicone-rubber catheters.

A biomechanical evaluation of an intramedullary fixation device for intertrochanteric fractures.

The strength and stability of an intramedullary device when used to fix intertrochanteric fractures were determined and compared with the dynamic hip screw (DHS). A standard four-part osteotomy was created in eight paired fresh frozen human cadaver femurs. The intramedullary fixation device and a DHS were implanted in each pair member, and mechanical testing was performed. Micromotion was measured during cyclic loading to determine implant stability, and then the specimens were loaded to failure. The intramedullary fixation device had significantly greater stability in cyclic loading than the DHS and required more than twice the force for failure. For patients with osteoporosis, this device may be a useful alternative to standard sliding nail systems.