Luo, Zong-Ping

Shear wave elastography (SWE) is a powerful method for the diagnosis of tissue disorders or degeneration based on tissue elasticity. In SWE application, it was recognized that the wave speed depends not only on the tissue elasticity but also on the structural shape, leading to different theoretical models. For liver, skin and myocardium, the appropriate theoretical model is known to be shear wave, Rayleigh wave and Lamb wave theory, respectively. Therefore, appropriate theoretical model should be adopted for the proper application of SWE. In this study, we verify these theoretical models in gelatin samples of different thicknesses, using experimental and numerical SWE tests. The results indicate that the wave speed was influenced by the ratio of the wavelength and sample thickness and the measurement region. Based on these results, the selection of theoretical model could be divided into three cases, and the appropriate theoretical model can be selected accordingly.

Background: One factor believed to contribute to the development of hallux valgus is an abnormality in collagen structure and makeup of the medial collateral ligament (MCL) of the first metatarsophalangeal joint (MTPJ). We hypothesized that the mechanical properties of the MCL in feet with hallux valgus are significantly different from those in normal feet and that these differences may be related to alterations in the type or distribution of collagen fibers at the interface between the MCL and the bone. Materials and Methods: Seven normal fresh-frozen cadaver feet were compared to four cadaver feet that had hallux valgus deformities. The MCL mechanical properties, structure of collagen fibers, and content proportion of type I and type III collagen were determined. Results: The load-deformation and stress-strain curves were curvilinear with three regions: laxity, toe, and linear regions. Laxity of the MCL in feet with hallux valgus was significantly larger than that of normal feet ( p = 0.022). Stiffness and tensile modulus in the toe region in feet with hallux valgus were significantly smaller than those in normal feet ( p = 0.004); however, stiffness and tensile modulus in the linear region were not significantly different. The MCL collagen fibrils in the feet with hallux valgus had a more wavy distribution than the fibrils in the normal feet. Conclusions: In general, strong staining for collagen III and to a lesser extent, collagen I was observed at the interface between the MCL and bone in the feet with hallux valgus but not in the normal feet. These results indicate that the abnormal mechanical properties of the MCL in feet with hallux valgus may be related to differences in the organization of collagen I and collagen III fibrils.

Background: It is necessary to have an understanding of ankle and hindfoot motion and stability to accurately diagnosis and treat ankle-hindfoot disorders. Methods: We devised an ankle ligament testing apparatus to more critically determine ankle stability in all planes with a constant rotational force applied (inversion, eversion, internal rotation, external rotation) throughout the range of sagittal plane motion in 13 cadaver specimens. Three-dimensional kinematics were determined with a magnetic tracking device. Results: With inversion force applied, calcanealtibial inversion was greatest in maximal plantarflexion (mean 22.1 ± 6.0 degrees) and gradually decreased with dorsiflexion, which indicated that the ankle had the most inversion instability in plantarflexion. With eversion force applied, calcaneal-tibial eversion gradually increased with increasing dorsiflexion to 12.7 ± 7.4 degrees indicating that the most eversion instability was in dorsiflexion. With internal rotation force applied, calcaneal-tibial internal rotation from plantarflexion to neutral ankle position increased. With external rotation force application, external rotation from neutral to maximal dorsiflexion increased. Conclusions: Ankle laxity was not constant but varied depending on the plantarflexion-dorsiflexion position and the direction of the applied force. The degree of ankle laxity was greater with inversion and internal rotation torque. Variation in laxity between specimens was observed, consistent with previous reports. These data indicate that the ankle is less stable in plantarflexion when inversion and internal rotation forces are applied. This may explain why the lateral ankle ligaments are most prone to injury in this position. The ankle was less stable in dorsiflexion when eversion and external rotation forces were applied. This is consistent with the observation that deltoid ligament injuries occur in the neutral to dorsiflexion position. The study demonstrates the importance of examining patients with suspected ankle ligament injuries in several ankle positions. The ankle testing device has potential application for in vivo testing of patients with suspected ankle ligament instability.

Eleven fresh-frozen cadaver foot specimens were tested to define changes in tarsal alignment associated with flatfoot, or pes planus, a common clinical problem. The three-dimensional position of four bones (talus, calcaneus, navicular, and first metatarsal) relative to the fixed tibia was determined with a magnetic tracking system in the intact foot and flatfoot conditions. In the flatfoot, the average metatarsal-to-talar position difference was 11.7° ± 4.4° in abduction ( P < 0.0001), 10.4° ± 3.6° in dorsiflexion ( P < 0.0001), and 10.9° ± 6.0° in eversion ( P < 0.0001) compared with the intact foot. The average calcaneal-to-talar position difference was 2.2° ± 2.6° in abduction ( P = 0.0171) and 2.7° ± 2.0° in eversion ( P = 0.0012) compared with the intact foot. The average navicular-to-talar position difference was 13.6° ± 5.0° in abduction ( P < 0.0001), 10.5° ± 6.6° in dorsiflexion ( P = 0.0004), and 8.1° ± 3.8° in eversion ( P < 0.0001) compared with normal. The average talar-to-tibial position difference was −8.2° ± 3.2° in dorsiflexion ( P < 0.001) compared with the intact foot. The average arch height difference was 6.0 ± 2.7 mm ( P < 0.0001) less than the normal condition. The deformity associated with flatfoot is complex and occurs in multiple joints and in all three planes. An understanding of the normal and pathologic (flatfoot) conditions is necessary to surgically restore appropriate alignment and function in hindfoot reconstruction operations.

A major limitation of operations commonly performed for acquired flatfoot is inadequate correction of alignment. The authors defined the efficacy of two operations, deltoid ligament reconstruction and flexor digitorum longus tendon transfer, for treatment of posterior tibial tendon dysfunction with flatfoot deformity. Twelve fresh-frozen foot specimens were used. A flatfoot deformity was created, and, to simulate the midstance phase of gait, loads were applied axially to the plantar surface of the foot and to appropriate tendons. Foot position improved substantially after deltoid ligament reconstruction but not after flexor digitorum longus tendon transfer. The average increase in arch height after deltoid ligament reconstruction was 10.3 ± 8.9 mm and after flexor digitorum longus tendon transfer, −0.6 ± 2.0 mm. Mean arch height after deltoid ligament reconstruction was 2.2 ± 1.7 mm less than intact arch height and, after flexor digitorum longus tendon transfer, 13.2 ± 9.0 mm less than intact arch height. Improvement in metatarsal-talar, calcaneal-talar, and talar-tibial positions was significantly greater after deltoid ligament reconstruction than after flexor digitorum longus tendon transfer. Although the authors do not advocate clinical use, the deltoid ligament reconstruction was more effective than flexor digitorum longus tendon transfer in restoring arch alignment in flatfoot.

Ligaments surrounding the hindfoot joints play an important role in hindfoot stability. This in vitro study investigated anatomical and biomechanical characteristics of nine major ligamentous structures, including length and orientation at neutral position and physiological elongation with the foot in five different positions relative to the neutral position. The results showed that ligament elongation depended on the ligament length, orientation in neutral position, and movement of bones to which they were attached.

We studied six fresh frozen cadaver feet to define the three-dimensional motion of the hallux proximal phalanx in relation to the first metatarsal and to describe the contact features of the first metatarsophalangeal joint. Six tendons to the hallux were loaded to simulate dynamic loading of the hallux. A magnetic tracking system was used to monitor the three-dimensional movement of the proximal phalanx while the toe position was changed from a neutral position to full extension by adjusting the tendon loads. The average surface area was 0.38 ± 0.08 cm 2 in the neutral position; it decreased with toe extension and was the lowest (0.04 ± 0.03 cm 2 ) at the full extension position. Contact distribution of the proximal phalanx did not change substantially throughout the arc of motion. However, for the metatarsal articular surface, the contact distribution shifted dorsally with increasing degrees of extension. These data are consistent with the observation that chondral erosions associated with hallux rigidus and degenerative arthritis initially affect the dorsal articular surface of the metatarsal, and implant arthroplasty often fails from component loading dorsally. The current technique of determining joint contact characteristics is applicable not only for the first metatarsophalangeal joint but also other joints that have not been studied because of shortcomings with more conventional methods.

There is very little data addressing cartilage response to tensile forces, and no literature attempts to correlate compressive with tensile modalities. Our hypothesis was that the cyclic compression and tension modulate chondrocyte matrix proteoglycan synthetic response differently. Porcine chondrocytes cultured to confluence on a flexible membrane were subjected to cyclic compression (Group A: 13 KPa at 1 Hz) or tension (Group C: 10% strain at 1 Hz) for 16 or 32 h; while controls not subjected to any force were kept (Group B). The chondrocytes were then stained with alcian blue and stained areas quantified with confocal microscopy and image processing software. Two-factor ANOVA with post-hoc tests (Scheffe and Bonferroni) statistical analysis were used. Proteoglycan staining covered 46% (range 28%–61%) and 39% (range 26%–49%) of the surface area following 32 and 16 h of compression respectively, 23% (range 15%–49%) for control, and 19% (range 10%–29%) and 16% (range 9%–25%) following 16 and 32 h tension respectively. Proteoglycan content following all compressions was significantly greater than with cyclic tension or control (p < 0.0001). Our data demonstrate that chondrocytes cultured in vitro respond to compression distinctly different from tension and that it is highly sensitive to mechanical loading, with rapid adaptation to its mechanical environment. These results imply that cartilage grown in culture, with the intention of transplantation, may structurally benefit from an environment of cyclic loading at higher frequencies.

Background: We performed a laboratory-based study of the ankle-hindfoot complex in normal cadaveric ankles with simulated lateral ankle ligament injuries, utilizing an ankle stability testing device. The ankle stability testing device distinguished between intact, injury to anterior talofibular ligament (ATFL) and combined injury to ATFL and calcaneofibular ligament (CFL). Materials and Methods: Ankles were tested in an ankle stability testing device, with a specified inversion torque applied through the range of sagittal plane motion, then internal rotation torque applied through the entire range of sagittal plane motion. Three-dimensional motion of the calcaneus and talus in relation to the tibia were determined with a magnetic tracking system. The specimens were tested in the intact condition, then after sectioning the ATFL, then the CFL. Results: Upon sectioning the ATFL, there was a significant increase in the internal rotation motion at the tibiotalar joint. Subsequent sectioning of the CFL did not significantly increase ankle-hindfoot internal rotation, but it did significantly increase the motion in inversion testing. This increase occurred primarily at the tibiotalar level. Conclusion: The isolated ATFL injury was clearly distinguished from the intact condition by increased talar-tibial internal rotation, but not inversion. The more severe combined ATFL/CFL injury was distinguished from the ATFL injury condition with inversion torque. Clinical Relevance: Inversion torque may disclose combined ATFL/CFL injury, and internal rotation torque may be the key to distinguish isolated ATFL and combined ATFL/CFL injuries.

This study evaluated the effects of soft tissue integrity on patellar tracking and patellofemoral joint force after total knee arthroplasty. The results indicate that partial dissection of the soft tissue integrity in the in vitro biomechanical studies of the patellofemoral joint can alter patellar tracking and joint force significantly, leading to improper conclusions.