Biomedical subjects

Kai-Nan An

Publications and source records attributed to Kai-Nan An.

At least 19 recordsLinked to original sources

PubMed2007

Gliding characteristics of flexor tendon and tenosynovium in carpal tunnel syndrome: a pilot study.

The characteristic pathological finding in carpal tunnel syndrome (CTS) is noninflammatory fibrosis of the synovium. How this fibrosis might affect tendon function, if at all, is unknown. The subsynovial connective tissue (SSCT) lies between the flexor tendons and the visceral synovium (VS) of the ulnar tenosynovial bursa. Fibrosis of the SSCT may well affect its gliding characteristics. To investigate this possibility, the relative motion of the flexor tendon and VS was observed during finger flexion in patients undergoing carpal tunnel surgery, and for comparison in hands without CTS, in an in vitro cadaver model. We used a camera to document the gliding motion of the middle finger flexor digitorum superficialis (FDS III) tendon and SSCT in three patients with CTS during carpal tunnel release and compared this with simulated active flexion in three cadavers with no antemortem history of CTS. The data were digitized with the use of Analyze Software (Biomedical Imaging Resource, Mayo Clinic, Rochester, MN). In the CTS patients, the SSCT moved en bloc with the tendon, whereas, in the controls the SSCT moved smoothly and separately from the tendon. The ratio of VS to tendon motion was higher for the patients than in the cadaver controls. These findings suggest that in patients with CTS the synovial fibrosis has altered the gliding characteristics of the SSCT. The alterations in the gliding characteristics of the SSCT may affect the ability of the tendons in the carpal tunnel to glide independently from each other, or from the nearby median nerve. These abnormal tendon mechanics may play a role in the etiology of CTS.

Aged↗

PubMed2007

Gliding characteristics between flexor tendons and surrounding tissues in the carpal tunnel: a biomechanical cadaver study.

The purpose of this study was to investigate the gliding characteristics of flexor tendons within the carpal tunnel with varied wrist positions and tendon motion styles, which may help us to understand the relationship between carpal tunnel syndrome (CTS) and repetitive hand motion. Eight fresh human cadaveric wrists and hands were used. The peak (PGR) and mean (MGR) gliding resistance of the middle finger flexor digitorum superficialis tendon were measured with the wrist in 0, 30, and 60 degrees of flexion and extension. While moving all three fingers together, the PGR at 60 degrees flexion was significantly higher than that at 0, 30, or 60 degrees extension. While moving the middle finger alone, the PGR at 60 and 30 degrees flexion was significantly higher than the PGR at 60 degrees extension. The PGR moving the middle finger FDS alone was significantly greater than that for all three digits moving together in 0, 30, and 60 degrees flexion. Differential finger motion with wrist flexion elevated the tendon gliding resistance in the carpal tunnel, which may be relevant in considering the possible role of wrist position and activity in the etiology of CTS.

Biomechanical Phenomena↗

PubMed2006

The number of screws, bone quality, and friction coefficient affect acetabular cup stability.

One of the major causes of loosening of cementless acetabular cup implants is insufficient initial stability. This study used three-dimensional finite element models of the pelvis and acetabular components to investigate the effects of the number of screws, bone quality, and friction coefficient of the acetabular cup on the initial stability under normal walking. A commercially available hemispherical acetabular cup with five screw holes was used as the default model. The stiffness of the pelvis and the friction coefficient of the cup were systematically varied, within a realistic range, to assess the initial stability of the acetabular cup. The simulations showed that the inserted screws provide only a localized reduction in the relative micromotion between the cup and pelvis therefore inserting several screw closed together might not be useful. Changes in the pelvic stiffness have a non-linear effect on the initial stability of acetabular cup and the subchondral bone provides good support for fixation of the cementless cup. The friction coefficient of the acetabular cup plays a limited role, comparing with the factor of bone quality, in resisting relative micromotion in the cup-pelvis interface.

Alloys↗

PubMed2006

The effect of glenoid component size on the stability of total shoulder arthroplasty.

Frequently, during the course of total shoulder arthroplasty, the measurement of the patient's native glenoid is between the available prosthetic glenoid sizes. Technically, it may be easier for the surgeon to implant a smaller glenoid component. Currently, there is no information regarding the difference in joint stability by use of glenoid components of different sizes. Stability ratio measurements were performed by use of a multiaxis testing machine with 3 different glenoid sizes (small, medium, and large) and compared by use of analysis of variance and the Tukey HSD test. Changes in the size of the glenoid component were found to have a significant effect on the stability ratio. At a load of 50 N, the stability ratio increased by 18% from the small to the medium glenoid component and by 15% from the medium to the large glenoid in the superoinferior axis. In the anteroposterior axis, the stability ratio increased by 17% from small to medium and by 10% from medium to large. The results from this study indicate a modest increase in stability when one chooses the larger of the 2 glenoid components.

Arthroplasty, Replacement↗

PubMed2006

Effect of curing time and concentration for a chemical treatment that improves surface gliding for extrasynovial tendon grafts in vitro.

The purpose of this study was to evaluate whether treatment time and concentration of these reagents have an effect on the resulting gliding resistance. Forty peroneus longus (PL) tendons were used, from 20 adult mongrel dogs, along with the A2 pulley obtained from the ipsilateral hind paw. After the baseline gliding resistance was measured, the PL tendons were treated with one of three concentrations of hyaluronic acid (HA) and 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) or N-hydroxysuccinimide (NHS) mixed with 10% gelatin for various times (5, 30, and 60 min). Tendon friction was measured over 1000 cycles of simulated flexion/extension motion. Gliding resistance of the untreated PL tendons had no significant difference among the groups. After surface treatment with low concentration of HA and EDC/NHS for 5-min cure, the gliding resistance was similar to that of the untreated PL tendon and significantly higher than its 30- and 60-min treatment. For the rest of high concentration of HA and EDC/NHS groups, the gliding resistance was lower than that of untreated PL tendon. However, there was no significant difference among the timing points. It is possible to optimize the effect of surface treatment on friction and durability by regulating cure time and concentration of reagents in a canine extrasynovial tendon in vitro.

Animals↗

PubMed2006

Tendon excursion and gliding: clinical impacts from humble concepts.

As integral components of the musculoskeletal system, the primary function is transmission of muscle forces to the skeletal system. Proper excursion and gliding of the tendon determine the efficiency of this function. Studies of the tendon excursion and gliding based on two simple mechanical concepts have resulted in several significant clinical implications.

Biomechanical Phenomena↗

PubMed2006

The relation between micromotion and screw fixation in acetabular cup.

One of the major causes inducing loosening in the cementless acetabular cup implanting is its insufficient initial stability. In this study, three-dimensional finite element models of the pelvis and acetabular components were developed to investigate the relationship between relative micromotion, initial stability, and screw fixation under six daily activity loadings. A commercial available hemispheric cup with five screw holes was used as the target acetabular cup. The simulation results showed that if screws were placed closed together, when the screw number increased from 1 to 5, the peak micromotion decreased less than 14%, from 126.5 to 108.8 microm, while the stable region, micromotion less than 28 microm, enlarged only by 40%, from 46.1% to 64.7%. However, if the screw could be placed near the cup rim, a single rim screw, 202.1 microm micromotion, could provide better stability than that of four dome screws, 209.6 microm micromotion, placed closed together. To conclude, multiple cup screws should be placed near cup rim and as separate as possible to enlarge the stable region and reduce the peak micromotion between cup and acetabulum.

Acetabulum↗

PubMed2006

Effects of screw eccentricity on the initial stability of the acetabular cup.

One of the major failure modes of cementless acetabular components is the loosening of the acetabular cup, which is mostly attributable to insufficient initial stability. A hemispherical cup with a porous coating which is inserted with press-fit fixation and secured with several screws is one of the most widely used approaches. Many studies have found that bone screws are very helpful aids for cup fixation, but the optimal surgical technique for inserting screws has not been clearly reported. In this study, hemispherical cups were fixed into blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity (a 1-mm offset and angular eccentricities of 15 degrees and 25 degrees ) on the initial stability of the acetabular cup were evaluated. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing (i.e., with no eccentricity). An angular eccentricity of 15 degrees did not affect the cup stability for fixation with one or two screws. However, the presence of 25 degrees of angular eccentricity significantly reduced the stability of the cup, while 1 mm of offset eccentricity produced an even greater impact.

Acetabulum↗

PubMed2006

TGFbeta inducible early gene-1 knockout mice display defects in bone strength and microarchitecture.

TGFbeta inducible early gene-1 (TIEG) is a member of the Sp/Krüppel-like transcription factor family originally cloned from human osteoblasts. We have previously demonstrated that TIEG plays a role in the expression of important osteoblast marker genes and in the maturation/differentiation of osteoblasts. To elucidate the function of TIEG in skeletal development and maintenance, we have generated a TIEG knockout (KO) mouse. Three-point bending tests demonstrated that the femurs of TIEG KO mice are significantly weaker than those of wild-type animals. pQCT analysis of tibias revealed significant decreases in bone content, density and size in KO animals compared to wild-type mice. Micro-CT analysis of the femoral head and vertebrae revealed increases in femoral head trabecular separation and decreases in cortical bone thickness and vertebral bone volume in KO mice relative to wild-type controls. In addition, electron microscopy indicated a significant decrease in osteocyte number in the femurs of KO mice. Taken together, these data demonstrate that the bones of TIEG KO mice display an osteopenic phenotype with significantly weaker bones and reduced amounts of cortical and trabecular bone. In summary, an important role for TIEG in skeletal development and/or homeostasis is indicated.

Animals↗

PubMed2006

Age-dependent changes in the mechanical properties of tail tendons in TGF-beta inducible early gene-1 knockout mice.

The purpose of this study is to investigate age-dependent changes in the architecture and mechanical properties of tendon in TGF-beta inducible early gene-1 (TIEG) knockout mice. Wild-type and TIEG knockout mice, aged 1, 2, and 15 mo, were used. The mechanical properties of tail tendons isolated from these mice were determined using uniaxial tensile ramp (0.05 mm/s) and relaxation (5 mm/s) tests, with a strain of 10%. Mechanical parameters (Young's modulus from the ramp test; fast and static stresses from the relaxation test) were measured and recorded. The structure of the tail tendon fascicle was characterized by transmission electron microscopy. The results of the mechanical testing revealed no significant difference between the knockout and wild-type groups at 1 or 15 mo of age. However, the fascicles of the knockout mice at 3 mo of age exhibited decreased fast and static stresses compared with those of the wild-type mice. Electron microscopy revealed an increase in fibril size in the knockout mouse tendons relative to wild-type controls at 1 and 3 mo of age. These data indicate an important role for TIEG in tendon microarchitecture and strength in adult mice.

Aging↗

PubMed2006

Effect of hyaluronic acid on the excursion resistance of tendon graft: a biomechanical in vitro study in a modified human model.

BACKGROUND: Adhesion between the tendon and tendon sheath after flexor tendon graft inhibits restoration of excursion and strength of the grafted tendons, so post-operative finger function is occasionally unsatisfactory. Early setting rehabilitation is one important factor to prevent the adhesion, and another factor may be a lubricant. We considered the possibility of utilizing hyaluronic acid as a lubricant. The goal of this study is to investigate the in vitro effect of hyaluronic acid on tendon excursion resistance against a digital pulley in a modified human model. METHODS: The excursion resistance between grafted intrasynovial and extrasynovial tendons and A2 pulley were evaluated, and compared before and after soaking in 10 mg/ml hyaluronic acid. FINDINGS: The resistance increased after extrasynovial tendon graft, and then it decreased after soaking hyaluronic acid solution. INTERPRETATION: The evidence we collected suggests that some style of administration of the hyaluronic acid might reduce the excursion resistance in the tendon-pulley unit, facilitating post-operative rehabilitation and limiting adhesion, after tendon graft and possibly improve the clinical outcome of flexor tendon graft.

Adjuvants, Immunologic↗

PubMed2006

Sagittal plane motion in the human lumbar spine: comparison of the in vitro quasistatic neutral zone and dynamic motion parameters.

BACKGROUND: Disabling low back pain is often attributed to clinical instability but defining instability is problematic. The most common parameter used to characterize instability in the lab is the neutral zone which is measured with a quasi-static technique. But, it cannot be measured from continuous motion data. Our goal was to describe the relationship between the quasi-static neutral zone and dynamic motion parameters that might reflect laxity about the neutral position. We also sought to determine if dynamic parameters were correlated with disc degeneration. METHODS: Fifteen cadaveric lumbar motion segments were tested with both quasi-static and dynamic (continuous load) methods. Quasi-static range of motion and neutral zone were compared with dynamic range of motion, hysteresis loop width, and two parameters derived from the hysteresis data: transitional zone size and slope. Degeneration was graded macroscopically. FINDINGS: Neutral zone size was moderately correlated with hysteresis loop width (r=0.69) and strongly correlated with the transitional zone slope (r=-0.80). Degenerative grade had a significant effect on dynamic range of motion and transitional zone size and slope with differences found between grade 1 (normal) discs and higher grades. Only transitional zone slope was different between grades 1 and 2. INTERPRETATION: The transitional zone slope (representing the neutral region stiffness) had the strongest correlation with neutral zone and could best detect lower grades of degeneration. The transitional zone slope might be a useful parameter in dynamic studies investigating the association between degeneration and motion segment behavior.

Adult↗

PubMed2006

A probabilistic model of glenohumeral external rotation strength for healthy normals and rotator cuff tear cases.

The reigning paradigm of musculoskeletal modeling is to construct deterministic models from parameters of an "average" subject and make predictions for muscle forces and joint torques with this model. This approach is limited because it does not perform well for outliers, and it does not model the effects of population parameter variability. The purpose of this study was to simulate variability in musculoskeletal parameters on glenohumeral external rotation strength in healthy normals, and in rotator cuff tear case using a Monte Carlo model. The goal was to determine if variability in musculoskeletal parameters could quantifiably explain variability in glenohumeral external rotation strength. Multivariate Gamma distributions for musculoskeletal architecture and moment arm were constructed from empirical data. Gamma distributions of measured joint strength were constructed. Parameters were sampled from the distributions and input to the model to predict muscle forces and joint torques. The model predicted measured joint torques for healthy normals, subjects with supraspinatus tears, and subjects with infraspinatus-supraspinatus tears with small error. Muscle forces for the three conditions were predicted and compared. Variability in measured torques can be explained by differences in parameter variability.

Computer Simulation↗

PubMed2006

Comparison of rectoanal axial forces in health and functional defecatory disorders.

Anal manometry measures circumferential pressures but not axial forces that are responsible for defecation and contribute to fecal continence. Our aims were to investigate these mechanisms by measuring axial rectoanal forces with an intrarectal sphere or a latex balloon fixed at 8, 6, or 4 cm from the anal verge and connected to axial force and displacement transducers. Rectoanal forces and rectal pressures within a latex balloon were measured at baseline (i.e., at rest) and during maneuvers (i.e., squeeze, simulated evacuation, and a Valsalva maneuver) in 12 asymptomatic women and 12 women with symptoms of difficult defecation. Anal resting and squeeze pressures were also assessed by manometry and were similar in control patients and experimental patients. At rest, axial rectoanal forces were directed inward and increased as the device approached the anal verge. Control patients augmented this inward force when they squeezed and exerted an outward force during simulated expulsion and a Valsalva maneuver. The force change during maneuvers was also affected by device location and was highest at 4 cm from the verge. In experimental patients, the force at rest and the change in force during all maneuvers was lower than in control patients. The rectal pressure during a Valsalva maneuver was also lower in experimental patients than in control patients, suggestive of impaired propulsion. In conclusion, a subset of women with defecatory symptoms had weaker axial forces not only during expulsion but also during a Valsalva maneuver and when they squeezed (i.e., contracted) their pelvic floor muscles, suggestive of generalized pelvic floor weakness.

Adult↗

PubMed2006

Determination of thigh muscle stiffness using magnetic resonance elastography.

PURPOSE: To measure the elastic properties of the vastus lateralis (VL), vastus medialis (VM), and sartorius (Sr) muscles using magnetic resonance elastography (MRE). MATERIALS AND METHODS: To obtain a normative database of the aforementioned muscles, oblique scan directions were prescribed passing through each muscle. Shear waves were induced into the muscles using pneumatic and mechanical drivers at 90 and 120 Hz, respectively. These drivers were attached to the distal end of the right thigh with the knee flexed at 30 degrees . The foot was placed in a footplate containing MR-compatible load cells to record the force during a contraction (10% and 20% of the maximum voluntary contraction). RESULTS: The shear moduli measured at rest in the VL (N = 12), VM (N = 14), and Sr (N = 13) were 3.73 +/- 0.85 kPa, 3.91 +/- 1.15 kPa, and 7.53 +/- 1.63 kPa, respectively. The stiffness of both vasti increased with the level of contraction, while the stiffness of the Sr remained the same. CONCLUSION: The MRE technique was able to approximate the stiffness of different thigh muscles. Furthermore, the wave length was sensitive to the morphology (unipennate or longitudinal) and fiber composition (type I or II) in each muscle.

Adult↗

PubMed2006

Effect of wrist and ulna head position on gliding resistance of the extensor digitorum minimi and extensor digitorum communis III tendons: a cadaver study.

While attrition from sharp bony surfaces is the most common cause of extensor digiti minimi (EDM) tendon rupture, the etiology of other cases of spontaneous EDM tendon rupture is still unknown. Friction within the compartment may play a role, especially with ulna dislocation. The purpose of this study was to compare gliding resistance of the EDM tendon with that of a tendon which rarely ruptures spontaneously, the extensor digitorum communis of the middle finger (EDC III) tendon, under various wrist and ulna head positions. Eight fresh frozen cadavers were used. Gliding resistance between the tendon and its sheath in each compartment was measured in five different wrist positions and three different ulna head positions. Gliding resistance of the EDM tendon (0.13 +/- 0.03 N) was significantly greater than the EDC III tendon (0.09 +/- 0.03 N) (p < 0.05). For the EDM tendon, the gliding resistance in ulnar deviation or pronation was higher than the gliding resistance in neutral, radial deviation, or supination (p < 0.05), and the gliding resistance with ulnar lengthening (over 6 mm) or dorsal ulnar dislocation (over 9 mm) was higher than in neutral ulnar head positioning. For the EDC III tendon, the gliding resistance in ulnar deviation was significantly higher than the gliding resistance in neutral, radial deviation, or supination, or dorsal dislocation with ulnar lengthening (p < 0.05). Wrist ulnar deviation, ulnar dorsal dislocation (over 9 mm), and ulnar lengthening (over 6 mm) increased the gliding resistance of the EDM tendon. In patients at risk for EDM rupture, such as those with rheumatoid arthritis or distal radioulnar joint osteoarthritis, avoiding such positions may be advantageous.

Aged↗

PubMed2006

Nerve endings of the wrist joint: a preliminary report of the dorsal radiocarpal ligament.

As part of an investigation of the articular nerve ending populations in the wrist joint capsule associated with the anterior and posterior interosseous nerves, this study addresses the nerve ending population in the dorsal radiocarpal ligament. The ligaments were harvested from four wrists of two fresh cadavers within 12 h of death. Tissues were fixed, cryostat sectioned, and processed for fluorescence immunohistochemistry using antibody to protein gene product 9.5 (PGP 9.5), a general or pan neuronal marker, and a secondary antibody conjugated to a fluorescent tag (Alexa Fluor 488). The sections were evaluated with a confocal laser microscope and an image analyzer. Labeled nerve endings were mapped, measured, and categorized. Type I (Ruffini-like ending), Type III (Golgi-like tendon organ) and Type IV (noncorpuscular) nerve endings could be identified in all four DRC ligaments, with Types I and IV dominating. These receptors were distributed primarily over the superficial two thirds of the ligament (>80%), and near the bony attachments (>70%). The dorsal radiocarpal ligament has a rich sensory innervation from the posterior interosseous nerve terminating in nerve endings located in the superficial two-thirds of the ligaments, primarily near bony attachment sites.

Aged↗

PubMed2006

Optimization of surface modifications of extrasynovial tendon to improve its gliding ability in a canine model in vitro.

Previous studies have shown that the carboxyl groups in hyaluronic acid (HA) could be activated by 1-ethy 1-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) to form intermediate O-acylisoureas, which can chemically bind to exposed amino groups on the tendon surface, leading to improved gliding ability. However, the optimal ratio and concentrations of the components in this chemical mixture were not investigated. The purpose of this study was to optimize the constituents of this tissue engineering approach to tendon surface modification, to reduce friction and improve durability. Peroneus longus (PL) tendons (n=40) were harvested from adult mongrel dogs along with the A2 pulley obtained from the ipsilateral hind paw. After the gliding resistance of the normal PL tendon was measured, the tendons were treated under varying concentrations of HA (0.5, 1, and 2%) and EDC/NHS (0.05, 0.25, and 1%) mixed with a 10% gelatin. Tendon friction was measured for 1000 cycles of simulated flexion/extension motion. Following testing, the residual HA on the tendon surface was evaluated by immunohistochemisty. The gliding resistance of the untreated PL tendons had a mean value of 0.087+/-0.021 N. After surface treatment, there was no significant difference in friction due to HA concentration alone, but the concentration of EDC/NHS and the interaction between HA concentration and EDC/NHS concentration had a significant effect on friction. Regardless of HA concentration, the friction after 1000 cycles was significantly decreased in preparations which included a 1% concentration of EDC/NHS. The tendons with lower gliding resistance presented a smoother surface on light microscopy and maintained more residual HA on the tendon surface. By varying the relative concentrations of HA, EDC, and NHS it is possible to optimize the effect of surface treatment on friction and durability in a canine extrasynovial tendon in vitro.

Animals↗