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Biomedical subjects

Cheng-Kung Cheng

Publications and source records attributed to Cheng-Kung Cheng.

At least 19 recordsLinked to original sources
PubMed2007

Fixed or mobile-bearing total knee arthroplasty.

Fixed and mobile-bearing in total knee arthroplasty are still discussed controversially. In this article, biomechanical and clinical aspects in both fixed and mobile-bearing designs were reviewed. In biomechanical aspect, the mobile-bearing design has proved to provide less tibiofemoral contact stresses under tibiofemoral malalignment conditions. It also provides less wear rate in in-vitro simulator test. Patients with posterior stabilized mobile-bearing knees had more axial tibiofemoral rotation than patients with posterior stabilized fixed-bearing knees during gait as well as in a deep knee-bend activity. However, in clinical aspect, the mid-term or long-term survivorship of mobile-bearing knees has no superiority over that of fixed-bearing knees. The theoretical advantages for mobile-bearing design to provide a long-term durability have not been demonstrated by any outcome studies. Finally, the fixed-bearing design with all-polyethylene tibial component is suggested for relatively inactive, elder people. The mobile-bearing design is suggested for younger or higher-demand patients due to the potential for reduced polyethylene wear and more normal kinematics response after joint replacement. For younger surgeon, the fixed-bearing design is suggested due to less demand for surgical technique. For experienced surgeon, one familiar surgical protocol and instrumentation is suggested rather than implant design, either fixed-bearing or mobile-bearing.

Journal Article↗
PubMed2007

Stress analysis of the anterior tibial post in posterior stabilized knee prostheses.

Recent retrieval studies have indicated a high incidence of polyethylene wear on the anterior tibial post caused by impingement. This study investigated the influences of post-cam design features and component alignment on the stress distribution in the anterior tibial post when subjected to the impingement loading. Two three-dimensional finite element models of posterior stabilized knee prostheses were constructed, one with flat on flat (FF) and another with curve on curve (CC) contact surfaces between anterior tibial post and femoral cam. The polyethylene insert was modeled with elastoplastic properties. Nine cases, three hyperextension angles (0 degrees , 5 degrees , and 10 degrees ) combined with three axial tibial rotations (0 degrees , 2.5 degrees , and 5 degrees ) simulating different component alignments were analyzed. A vertical compressive load of 2,000 N and an extension moment of 45 Nm were applied simultaneously. The FF model had larger stress increases than the CC model in both hyperextension and tibial rotation compared with the neutral position. The maximum increase for the FF model was 68% in peak contact stress, 125% in von Mises stress, and 58% in tensile stress in the extreme case of 10 degrees of hyperextension combined with 5 degrees of axial rotation. Stress concentration was found at the anterior corner of the post in the FF model; this was not found in the CC model. The curve on curve design can reduce edge loading on the tibial post, especially during axial tibiofemoral rotation.

Arthroplasty, Replacement, Knee↗
PubMed2007

The accuracy of posterior condylar angles measured by one MR image.

The posterior condylar axis is used to establish femoral rotational alignment during total knee arthroplasty. One magnetic resonance image or computed tomography image often is used to determine the posterior condylar angle. However, the bony landmarks for determining the posterior condylar angle are not always present or obvious. We hypothesized measuring the posterior condylar angle on one slice would be no different when compared with using superimposed images with bony landmarks accurately identified in one or more slices. We analyzed magnetic resonance images of 95 knees without any bone disorders. Only 20 knees had all four bony landmarks apparent on any single slice. We compared the posterior condylar angles measured from one slice in which the medial sulcus, lateral epicondyle, or both posterior condyles were accurately identified with the angle measured from superimposed images. The average posterior condylar angle in the remaining 75 knees measured from superimposed images was 4.27 degrees +/- 1.95 degrees, which was similar to the angle measured from one in which the lateral epicondyle was the most accurately identified (3.95 degrees +/- 1.93 degrees). However, the largest difference (-3.53 degrees and 4.29 degrees) between three-dimensional and two-dimensional posterior condylar angle measurements in the worse-case scenario was unacceptable in clinical practice. We could not confirm our hypothesis: using one two-dimensional image to measure the posterior condyle angle is not accurate enough to determine its three-dimensional angle.

Adult↗
PubMed2006

Journal of orthopaedic surgery and research editorial.

Journal of Orthopaedic Surgery and Research is an open access, online journal that aims to expeditiously publish clinical and basic research studies related to musculoskeletal issues in different cultural communities. It provides a platform for exchanges of new clinical and scientific information in the most precise and expeditious way to achieve dissemination of information and cross-fertilization of ideas. The open access nature of this journal allows articles to be universally and freely accessible via the Internet. This ensures a rapid and efficient communication of research findings. The journal welcomes all types of articles related to musculoskeletal issues. Its timely publication and high visibility are the two most important features that make this journal different from other traditional journals in the orthopaedic field.

Editorial↗
PubMed2006

Biomechanical comparison of instrumented posterior lumbar interbody fusion with one or two cages by finite element analysis.

STUDY DESIGN: Using finite element models to study the biomechanics of lumbar instrumented posterior lumbar interbody fusion (PLIF) with one or two cages. OBJECTIVE: Analyzing the biomechanics of instrumented PLIF with one or two cages as to evaluate whether a single cage is adequate for instrumented PLIF. SUMMARY OF BACKGROUND DATA: Implantation of a single cage in instrumented PLIF of lumbar spine is still controversial. METHODS: Three validated finite element models of L3-L5 lumbar segment were established [intact model (INT), one cage model (LS-1), and two cages model (LS-2)]. The available finite element program ANSYS 6.0 (Swanson Analysis System Inc., Houston, TX) was applied. To analyze the biomechanics of these models, 10 Nm flexion, extension, rotation, and lateral bending moment with 150 N of preload were respectively imposed on the superior surfaces of the L3. RESULTS: Compared with the INT model, the decrease of ROM in the LS-1 and LS-2 models were exaggerated from 0.67 degrees to 3.73 degrees and ranged from 37.2% to 86.1% in all motions. The mean subsidence was found to be slightly higher in the LS-1 model. Most of the cage dislodgement in both models was less than 0.03 mm. The mean dislodgement was slightly higher in the LS-1 model. The stress of cage was found to be high in the LS-2 model. The mean stress of screw was raised to 4.5% to 9.7% in the LS-1, which was higher than that in the LS-2 model. In general, stress of adjacent disc was more pronounced in the LS-2 model. The most stress distributed at the anterior portion of the adjacent disc, which could be used to interpret the clinical findings of the early adjacent disc degeneration. CONCLUSIONS: A single cage inserted in an instrumented PLIF gains approximate biomechanical stability, slight greater subsidence, and a slight increase in screw stress but less early degeneration in adjacent disc. Adjusting these factors, instrumented PLIF with one cage could be encouraged in clinical practice.

Biomechanical Phenomena↗
PubMed2006

Relationship of skin temperature to sympathetic dysfunction in diabetic at-risk feet.

The relationship of plantar skin temperature to diabetic neuropathy was studied using clinical, nerve conduction and autonomic evaluations. The sympathetic skin response (SSR) was found present in both feet of 25 control subjects and 29 (out of 69) diabetic patients (SSR+ group). For those diabetic patients absent with the SSR in both feet, 18 patients (at-risk group) had preulcerative skin lesions (dry and fissured skin) and 22 did not (SSR- group). The at-risk group showed significantly higher mean foot temperature (30.2+/-1.3 degrees Celsius) than the SSR- (27.9+/-1.7 degrees Celsius), the SSR+ (27.1+/-2.0 degrees Celsius) and the control group (26.8+/-1.8 degrees Celsius). The SSR- group had smaller temperature differences (7.2+/-1.7 degrees Celsius versus 8.6+/-1.6 degrees Celsius, p<0.05) and smaller normalized temperature (referencing to the forehead temperature) (0.19 versus 0.24, p<0.01) than the SSR+ group. Although the three diabetic groups had no significant differences in clinical and cardiovascular abnormalities, the at-risk group showed more nerve conduction abnormalities than the SSR- and SSR+ groups (55% versus 23% and 14%, p<0.02). This study indicated that the thermoregulatory sweating abnormality signified early sympathetic damage in diabetic feet. Assessing skin conditions and sudomotor activities should help identify small fiber neuropathy in diabetic patients with at-risk feet conditions.

Autonomic Nervous System Diseases↗
PubMed2006

Influence of post-cam design on stresses on posterior-stabilized tibial posts.

Polyethylene wear and fracture at the tibial post of posterior- stabilized knee prostheses are common complications. Analyzing the stresses on various designs of tibial posts should predict the risk of damage. The post-cam of knee prostheses generally are designed either as flat-on-flat or curve-on- curve contact surfaces. We investigated stress on such tibial posts using a finite element method. We applied a 500-N anteroposterior shear force to the knee at neutral contact and 10 degrees tibial internal rotation when the knee was flexed at 60 degrees , 90 degrees , 120 degrees , and 150 degrees . There was more stress during tibial rotation compared with during neutral contact. The greatest increments of maximum von Mises stress and contact stress in the flat-on-flat model were from 20.4 to 46.1 MPa (126.3%) and from 22.2 to 55.7 MPa (151%), respectively, whereas in the curve-on-curve design they were from 20.5 to 22.7 MPa (10.7%) and from 33.0 to 35.4 MPa (7.2%), respectively. Increased stress concentration at the tibial post occurred at increased flexion angles along with axial tibial rotation. The curve-on-curve design reduced stress concentration when the knee sustained an anteroposterior shear force with tibial rotation.

Finite Element Analysis↗
PubMed2006

Finite element analysis of the spondylolysis in lumbar spine.

Spondylolysis is a fracture of the bone lamina in the pars interarticularis and has a high risk of developing spondylolisthesis, as well as traction on the spinal cord and nerve root, leading to spinal disorders or low back pain when the lumbar spine is subjected to high external forces. Previous studies mostly investigated the mechanical changes of the endplate in spondylolysis. However, little attention has been focused on the entire structural changes that occur in spondylolysis. Therefore, the purpose of this study was to evaluate the biomechanical changes in posterior ligaments, disc, endplate, and pars interarticularis between the intact lumbar spine and spondylolysis. A total of three finite element models, namely the intact L2-L4 lumbar spine, lumbar spine with unilateral pars defect and with bilateral pars defect were established using a software ANSYS 6.0. A loading of 10 N.m in flexion, extension, left torsion, right torsion, left lateral bending, and right lateral bending respectively were imposed on the superior surface of the L2 body. The bottom of the L4 vertebral body was completely constrained. The finite element models estimated that the lumbar spine with a unilateral pars defect was able to maintain spinal stability as the intact lumbar spine, but the contralateral pars experienced greater stress. For the lumbar spine with a bilateral pars defect, the rotation angle, the vertebral body displacement, the disc stress, and the endplate stress, was increased more when compared to the intact lumbar spine under extension or torsion.

Adult↗
PubMed2005

Fatigue resistance analysis of tibial baseplate in total knee prosthesis--an in vitro biomechanical study.

BACKGROUND: Tibial baseplates were occasionally reported with clinical fatigue failures. This study postulated that tibial baseplate of a specific mobile bearing design with a uniform thickness across the baseplate offers more fatigue resistance than the fixed-bearing design. Tibial baseplates of a fixed bearing and a mobile bearing design were fatigue-tested in vitro to study their fatigue resistance. METHODS: Five samples of each design were tested under a sinusoidal loading between 90 N and 900 N at 30 Hz till failure or 10 million cycles. Experimental setup followed a standard published test method. Scanning electron microscope was used for inspecting the fracture surface of the failed baseplate. FINDINGS: Two baseplates of fixed bearing design failed before 10 million cycles. Fatigue crack advancement marks were visible on the fractured surface of the failed samples. The fractured cross-section showed that the failure started near the end of the fin, it was likely due to the stress concentration as stress singularity existed at a point of sudden geometrical change. Five mobile bearing baseplates passed the test. Design of the tibial baseplate without fin structure and with a uniform thickness across the whole baseplate could help reducing the incidence of fatigue failure. INTERPRETATION: The prosthesis survival rate was influenced by the long-term integrity of the metallic part of the prostheses such as the tibial baseplate. This study revealed that the tibial baseplate of a mobile bearing design with a uniform thickness provided better fatigue resistance than fixed bearing one. Standardized fatigue screening of the tibial baseplate was considered important in designing knee prostheses.

Biomechanical Phenomena↗
PubMed2005

Morphometrical measurements of resected surface of femurs in Chinese knees: correlation to the sizing of current femoral implants.

Morphometrical data were measured in the resected femurs of seventy Chinese patients who underwent total knee arthroplasties. Two measured parameters, the anterior-posterior length of the lateral condyle and the total width of the distal condyle, were compared to the anterior-posterior length and the medial-lateral width of five femoral implants currently used in Taiwan. Three implants (Duracon, NexGen and UKnee) have a larger medial-lateral width than the total width of the resected distal condyle for a given femoral implant anterior-posterior length. These implants tend to overhang the medial-lateral width of resected femurs from Chinese patients. In addition, one femoral implant (Duracon), which has previously been shown to be suitable for use in Caucasian patients, is not suitable in Chinese patients. Our results will allow manufacturers to design femoral implants better suited to Chinese patients.

Aged↗
PubMed2005

Thermal effects after anterior cruciate ligament shrinkage using radiofrequency technology: a porcine cadaver study.

The effects of thermal energy on an anterior cruciate ligament (ACL) are unknown. This study was undertaken to know the immediate and direct effects of thermocoagulation on normal ACL. Thermocoagulation was generated by monopolar radiofrequency (RF) at 67 degrees C and 40 W of energy and applied with use of a commercial jig in a porcine cadaveric model, and biomechanical and histological changes were evaluated immediately. Thermocoagulation caused significant shrinkage of ACL without immediate effects on ligament biomechanical properties, including stiffness and maximal failure force. However, histological analysis demonstrated a decrease in number of dense elongated cells and blood vessels within the epiligamentous tissue, loss of areolar spaces, decrement in the periodicity of collagen waveform, and shortening and pyknotic nuclear changes of cells within the fascicular region. RF-generated thermocoagulation resulted in ACL shortening with significant changes on histological findings but not on initial biomechanical properties.

Animals↗
PubMed2005

Polyethylene failure of the patellar component in New Jersey low-contact stress total knee arthroplasties.

In a postoperative 5- to 12-year follow-up study of 598 New Jersey low-contact stress total knee arthroplasties, 32 required revision. All retrieved patellar components were examined for polyethylene damage. These 32 cases had 3 types of failure: split rupture (7 cases), peripheral wear (21), and cantilevering breakage (4), respectively 75%, 64.3%, and 100% of which showed subluxation and/or tilting of the patellar component on the prerevision roentgenograms. Misalignment at the joint contact surfaces and rotational blockage of the mobile patellar component were considered the major causes of the failure. A design of a flatter metallic button (giving larger focal thickness of the polyethylene) and a dome-shaped polyethylene (reducing stress concentration at the pinnacle) may alleviate the failure driving mechanism should subluxation or tilting of the patellar component take place.

Arthroplasty, Replacement, Knee↗
PubMed2005

Failure analysis of broken pedicle screws on spinal instrumentation.

Revised spinal surgery is needed when there is a broken pedicle screw in the patient. This study investigated the pedicle screw breakage by conducting retrieval analyses of broken pedicle screws from 16 patients clinically and by performing stress analyses in the posterolateral fusion computationally using finite element (FE) models. Fracture surface of screws was studied by scanning electron microscope (SEM). The FE model of the posterolateral fusion with the screw showed that screws on the caudal side had larger axial stress than those on the cephalic side, supporting the clinical findings that 75% of the patients had the screw breakage on the caudal side. SEM fractography showed that all broken screws exhibited beach marks or striations on the fractured surface, indicating fatigue failure. Screws of patients with spinal fracture showed fatigue striations and final ductile fracture around the edge. Among the 16 patients who had broken pedicle screws 69% of them achieved bone union in the bone graft, showing that bone union in the bone graft did not warrant the prevention of screw breakage.

Adult↗
PubMed2005

The influence of mechanical properties of subchondral plate, femoral head and neck on dynamic stress distribution of the articular cartilage.

A few finite element models have addressed the dynamic juxtaarticular stress transmission but none focused the investigation on the combined influence of the individual moduli of the underlying bones, including the subchondral plate, the femoral head and the femoral neck of the proximal femur. A finite element model including the acetabulum and the proximal femur was analyzed with dynamic loadings to study the effects of mechanical property changes in the underlying bones of the proximal femur on the stress distribution in the cartilage at the hip joint. We found the stress distribution was most sensitive to the subchondral plate stiffening, while the overall stiffening of the underlying bones had mild effect on the shear stress on the cartilage surface (or at the subchondral bone/cartilage interface) and on the strain energy density in the cartilage. Our results indicate that the subchondral plate plays a predominant mechanical role in the initial degeneration of the cartilage. The results may offer a mechanical explanation as to why the cartilage failure is common in patients with osteoarthritis but rare in patients with osteoporosis.

Animals↗
PubMed2005

Biomechanical analysis of the disc adjacent to posterolateral fusion with laminectomy in lumbar spine.

OBJECTIVES: After posterolateral fusion with laminectomy for the degenerative lumbar spine, accelerated degeneration of the disc adjacent to the fusion mass has been clinically observed. Previous studies used a finite element model (FEM) to calculate the stress of the adjacent disc in the fused lumbar spine with spinal fixator and bone graft. However, little emphasis was placed on the simultaneous spinal fusion and decompression procedure. To investigate if the spinal decompression procedure in posterolateral fusion would increase stress significantly, the FEM was employed to estimate the stress concentration of the disc above the fusion mass in posterolateral fusion with laminectomy and hemilaminectomy. METHODS: Three FEMs of the lumbar spine were established: intact spine, posterolateral fusion with total laminectomy, and posterolateral fusion with hemilaminectomy (preserved partial lamina, spinous process, and supraspinous and interspinous ligaments). The posterolateral fusion added spinal fixator and bone graft between the transverse process. The L1 vertebral body was subjected to 10-Nm flexion, extension, torsion, and lateral bending. The bottom of the L5 vertebral body was fixed. RESULTS: In flexion, the stress on the adjacent disc in posterolateral fusion with laminectomy and hemilaminectomy respectively increased 90% and 21% over that of the intact spine. In posterolateral fusion with hemilaminectomy, the supraspinous and interspinous ligaments shared some external forces to alleviate the stress concentration of the adjacent disc. However, in extension, torsion, and lateral bending, these two fusion models had almost no change in range of motion and stress of adjacent disc. CONCLUSION: Posterolateral fusion with hemilaminectomy (preserved partial lamina, spinous process, and supraspinous and interspinous ligaments) was able to alleviate the stress concentration of the disc above the fusion mass in flexion.

Biomechanical Phenomena↗
PubMed2005

Assessing foot temperature using infrared thermography.

BACKGROUND: Previous reports recommended using skin temperature as a guide to monitor neuropathic feet during their rehabilitation course. However, the diagnostic usefulness was limited because of poor thermal measurement and procedures. The purpose of this study was to propose a standardized protocol to quantify foot temperature. METHODS: An infrared image system was used to measure skin temperature. The first experiment was conducted on 16 healthy volunteers to study temperature variation with respect to time. This study mapped out six subregions of anatomic interest over the sole, and average temperature values for each were studied. The second experiment was conducted on 62 diabetic patients, with and without sympathetic skin response (SSR), to study proposed sole temperature normalization with respect to forehead temperature for clinical diagnosis. RESULTS: In the first experiment, the temperature in each plantar subregion varied as a function of time. In the sole area, the highest temperature was noted in the arch region (29.3 +/- 0.9 degrees C). The toes had the lowest temperature value (26.2 +/- 1.2 degrees C) in all areas. Equilibrium was reached after 15 minutes for the mean plantar temperature (27.8 +/- 1.0 degrees C). In the second experiment, the diabetic patients without SSR had a slightly higher mean plantar temperature (27.6 +/- 1.8 degrees C) than those with SSR (26.8 +/- 2.2 degrees C), but the difference was not statistically significant (p > 0.05). The SSR-absent group (0.19) and the SSR-present group (0.24) had significant differences in their normalized temperatures as proposed (p < 0.05). CONCLUSIONS: The mean temperature of the entire plantar area was found to be more stable than the individual subregions, serving as a more practical indicator for thermoregulatory functions. The study also found that the overall mean plantar temperature stabilized after 15 minutes, and, thus, this time was recommended for clinical thermographic measurements. The normalized temperature may have more useful application than the plantar absolute temperature, as exemplified by the better correlation in diabetic feet. The mean plantar temperature, the wait time to start measurement, and the proposed normalization are believed to play important roles in neuropathic foot disorders.

Diabetes Mellitus↗
PubMed2004

Feasibility study of custom hip stem design based on X-ray films.

The hip stem design based upon X-ray films requires sufficient information in order to customize for the patient. If the errors are resulted from rotating angles, more X-ray films may carry out the solution. The present study aimed to realize the improvement of multiple X-ray films for hip stem design. Eight X-ray films were taken from a volunteer. The characteristic length of X-ray film was input into cosine function to derive the relative rotating angle of each X-ray film. The combinations of 2, 4, 6, and 8 X-ray films that included true AP view and lateral view were obtained to construct the corresponding stem. CT images were used to construct femur and stem model to verify the rotating angle of femur in each X-ray film. A quantitative comparison was made between the hip stems for the fill ratio, fit gap and contact area. The results showed that the markers on the body surface would result in error and were unable to provide reference to the rotating angle of femur. The contact area and fill ratio of the stems designed by 6 or 8 X-ray films would get closer to that by CT images. It is concluded that the rotation of the femur could be determined from the length of femoral neck as well as the distance between the tips of medial and lateral condyles. The use of 6 or more X-ray films for custom-made hip stem as a source of design is recommended in this study.

Feasibility Studies↗