Practicability for robot-aided measurement of knee stability in-vivo

Background

For the analysis of different treatments concerning anterior cruciate ligament (ACL) rupture, objective methods for the quantification of knee stability are needed. Therefore, a new method for in-vivo stability measurement using a robotic testing system should be developed and evaluated.

Methods

A new experimental setting was developed using a KUKA robot and a custom-made chair for the positioning and fixation of the participants. The tibia was connected to the robot via a Vacoped shoe and magnetic buttons, providing adequate safety. Anterior tibial translation and internal tibial rotation were measured on both legs of 40 healthy human subjects at 30°, 60° and 90° of flexion, applying anterior forces of 80 N and internal torques of 4 Nm, respectively.

Results

While the mean differences between the right and left leg measured for anterior tibial translation were within an acceptable range (<1.5 mm), the absolute values were substantially large (38–40.5 mm). For mean internal tibial rotation, between 17.5 and 20° were measured at the different sides and flexion angles, with a maximal difference of 0.75°. High reproducibility of the measurements could be demonstrated for both, anterior tibial translation (ICC(3,1) = 0.97) and internal tibial rotation (ICC(3,1) = 0.94).

Conclusions

Excellent results were achieved for internal tibial rotation, almost reproducing current in-vitro studies, but too large anterior tibial translation was measured due to soft-tissue compression. Therefore, high potential for the analysis of ACL related treatments concerning rotational stability is seen for the proposed method, but further optimization is necessary to enhance this method for the reliable measurement of anterior tibial translation.

Robot-aided in vitro measurement of patellar stability with consideration to the influence of muscle loading

Background

Anterior knee pain is often associated with patellar maltracking and instability. However, objective measurement of patellar stability under clinical and experimental conditions is difficult, and muscular activity influences the results. In the present study, a new experimental setting for in vitro measurement of patellar stability was developed and the mediolateral force–displacement behavior of the native knee analyzed with special emphasis on patellar tilt and muscle loading.

Methods

In the new experimental setup, two established testing methods were combined: an upright knee simulator for positioning and loading of the knee specimens, and an industry robot for mediolateral patellar displacement. A minimally invasive coupling and force control mechanism enabled unconstrained motion of the patella as well as measurement of patellar motion in all six degrees of freedom via an external ultrasonic motion-tracking system. Lateral and medial patellar displacement were measured on seven fresh-frozen human knee specimens in six flexion angles with varying muscle force levels, muscle force distributions, and displacement forces.

Results

Substantial repeatability was achieved for patellar shift (ICC(3,1) = 0.67) and tilt (ICC(3,1) = 0.75). Patellar lateral and medial shift decreased slightly with increasing flexion angle. Additional measurement of patellar tilt provided interesting insights into the different displacement mechanisms in lateral and medial directions. For lateral displacement, the patella tilted in the same (lateral) direction, and tilted in the opposite direction (again laterally) for medial displacement. With regard to asymmetric muscle loading, a significant influence (p < 0.03, up to 5 mm shift and 8° tilt) was found for lateral displacement and a reasonable relationship between muscle and patellar force, whereas no effect was visible in the medial direction.

Conclusion

The developed experimental setup delivered reproducible results and was found to be an excellent testing method for the in vitro analysis of patellar stability and future investigation of surgical techniques for patellar stabilization and total knee arthroplasty. We demonstrated a significant influence of asymmetric quadriceps loading on patellar stability. In particular, increased force application on the vastus lateralis muscle led to a clear increase of lateral patellar displacement.

Simulation of in vivo dynamics during robot assisted joint movement

Background

Robots are very useful tools in orthopedic research. They can provide force/torque controlled specimen motion with high repeatability and precision. A method to analyze dissipative energy outcome in an entire joint was developed in our group. In a previous study, a sheep knee was flexed while axial load remained constant during the measurement of dissipated energy. We intend to apply this method for the investigation of osteoarthritis. Additionally, the method should be improved by simulation of in vivo knee dynamics. Thus, a new biomechanical testing tool will be developed for analyzing in vitro joint properties after different treatments.

Methods

Discretization of passive knee flexion was used to construct a complex flexion movement by a robot and simulate altering axial load similar to in vivo sheep knee dynamics described in a previous experimental study.

Results

The robot applied an in vivo like axial force profile with high reproducibility during the corresponding knee flexion (total standard deviation of 0.025 body weight (BW)). A total residual error between the in vivo and simulated axial force was 0.16 BW. Posterior-anterior and medio-lateral forces were detected by the robot as a backlash of joint structures. Their curve forms were similar to curve forms of corresponding in vivo measured forces, but in contrast to the axial force, they showed higher total standard deviation of 0.118 and 0.203 BW and higher total residual error of 0.79 and 0.21 BW for posterior-anterior and medio-lateral forces respectively.

Conclusions

We developed and evaluated an algorithm for the robotic simulation of complex in vivo joint dynamics using a joint specimen. This should be a new biomechanical testing tool for analyzing joint properties after different treatments.

Status of the diagnostics development for the first operation phase of the stellarator Wendelstein 7-X

An overview of the diagnostics which are essential for the first operational phase of Wendelstein 7-X and the set of diagnostics expected to be ready for operation at this time are presented. The ongoing investigations of how to cope with high levels of stray Electron Cyclotron Resonance Heating (ECRH) radiation in the ultraviolet (UV)/visible/infrared (IR) optical diagnostics are described.

Changes in dissipated energy and contact pressure after osteochondral graft transplantation

Osteochondral autologous transplantation is frequently used to repair small cartilage defects. Incongruence between the osteochondral graft surface and the adjacent cartilage leads to changed friction and contact pressure. The present study wanted to analyze the differences between intact and surgically treated cartilage surface in respect to contact pressure and frictional characteristic (dissipated energy). Six ovine carpometacarpal joints were used in the present study. Dissipated energy during instrumentally controlled joint movement as well as static contact pressure were measured in different cartilage states (intact, defect, deep-, flush-, high-implanted osteochondral graft and cartilage failure simulation on a high-implanted graft). The best contact area restoration was observed after the flush implantation. However, the dissipated energy measurements did not reveal an advantage of the flush implantation compared to the defect and deep-implanted graft states. The high-implanted graft was associated with a significant increase of the mean contact pressure and decrease of the contact area but the dissipated energy was on the level of intact cartilage in contrast to other treatments where the dissipated energy was significantly higher as in the intact state. However the cartilage failure simulation on the high-implanted graft showed the highest increase of the dissipated energy.

Cartilage surface characterization by frictional dissipated energy during axially loaded knee flexion--an in vitro sheep model

Cartilage defects and osteoarthritis (OA) have an increasing incidence in the aging population. A wide range of treatment options are available. The introduction of each new treatment requires controlled, evidence based, histological and biomechanical studies to identify potential benefits. Especially for the biomechanical testing there is a lack of established methods which combine a physiologic testing environment of complete joints with the possibility of body-weight simulation. The current in-vitro study presents a new method for the measurement of friction properties of cartilage on cartilage in its individual joint environment including the synovial fluid. Seven sheep knee joints were cyclically flexed and extended under constant axial load with intact joint capsule using a 6° of freedom robotic system. During the cyclic motion, the flexion angle and the respective torque were recorded and the dissipated energy was calculated. Different mechanically induced cartilage defect sizes (16 mm², 50 mm², 200 mm²) were examined and compared to the intact situation at varying levels of the axial load. The introduced setup could significantly distinguish between most of the defect sizes for all load levels above 200 N. For these higher load levels, a high reproducibility was achieved (coefficient of variation between 4% and 17%). The proposed method simulates a natural environment for the analysis of cartilage on cartilage friction properties and is able to differentiate between different cartilage defect sizes. Therefore, it is considered as an innovative method for the testing of new treatment options for cartilage defects.

Dissipated energy as a method to characterize the cartilage damage in large animal joints: an in vitro testing model

Several quantitative methods for the in vitro characterization of cartilage quality are available. However, only a few of these methods allow surgical cartilage manipulations and the subsequent analysis of the friction properties of complete joints. This study introduces an alternative approach to the characterization of the friction properties of entire joint surfaces using the dissipated energy during motion of the joint surfaces. Seven sheep wrist joints obtained post mortem were proximally and distally fixed to a material testing machine. With the exception of the carpometacarpal articulation surface, all joint articulations were fixed with 'Kirschner' wires. Three cartilage defects were simulated with a surgically introduced groove (16 mm(2), 32 mm(2), 300 mm(2)) and compared to intact cartilage without an artificial defect. The mean dissipated energy per cycle was calculated from the hysteresis curve during ten torsional motion cycles (±10°) under constant axial preload (100-900 N). A significant increase in dissipated energy was observed with increasing cartilage defect size and axial load (p<0.001). At lower load levels, the intact and 16 mm(2) defect showed a similar dissipated energy (p>0.073), while all other defect conditions were significantly different (p=0.015). All defect sizes were significantly different (p=0.049) at 900 N axial load. We conclude that the method introduced here could be an alternative for the study of cartilage damage, and further applications based on the principles of this method could be developed for the evaluation of different cartilage treatments.

1.2 French stone retrieval baskets further enhance irrigation flow in flexible ureterorenoscopy

Ureterorenoscopy (URS) has revolutionized upper urinary tract stone therapy. However, the size of the working channel and the stone baskets limit irrigation flow as well as vision. This study determined further improvements of irrigation flow, deflection capacities and impairments of breaking resistance in a new 1.2 French (F) ultra-miniaturized basket. Irrigation measurements were performed in semirigid URS (semiURS, working channel 5F) and in flexible URS (flexURS, 3.6F) in 0°, 90° and 270° deflection with 1.2F, 1.8F, 1.9F and 2.2F baskets and compared with empty channel. Breaking strength of 1.2F, 1.8F and 1.9F baskets were evaluated using a material testing machine. Tested baskets affected irrigation in semiURS and flexURS (p < 0.05). Mean ± SEM (standard error of the mean) for semiURS flow rates counted 197.1 ± 2.0, 140.9 ± 1.6, 111.1 ± 1.5, 98.0 ± 1.3 and 77.1 ± 0.9 ml/min for empty channel, 1.2F, 1.8F, 1.9F and 2.2F baskets (p < 0.05). Using unbent flexURS flow rates of 44.2 ± 0.4, 20.4 ± 0.2, 5.9 ± 0.1, 5.4 ± 0.1 and 1.5 ± 0.1 ml/min for empty channel, 1.2F, 1.8F, 1.9F and 2.2F baskets, were observed (p < 0.05). The 1.2F versus 2.2F basket showed a 13.6-fold increase in flexURS irrigation (p < 0.05), while only the 2.2F basket reduced deflection by 20.3 %. The breaking strength decreased with a reduced basket size (1.2F: 6.4 ± 0.46 vs. 1.8F: 16.8 ± 2.79 vs. 1.9F: 32.2 ± 2.74 N, p < 0.05). Ultra-miniaturized baskets of 1.2F ensured a sufficient irrigation flow as needed for high quality vision in URS stone management. However, miniaturization of the 1.2F basket resulted in a reduced breaking strength compared with larger sized devices which in turn may hamper stone removal by an increased vulnerability.

The influence of asymmetric quadriceps loading on patellar tracking--an in vitro study

BACKGROUND

In patients with anterior knee pain and patellar instability, a specific training of the quadriceps muscle - especially the vastus medialis - is often recommended, although the practicability is discussed controversially and the proof of a measurable clinical effect is difficult. Therefore, this in vitro study investigates the influence of asymmetric muscle loading on the motion of the human patella.

METHODS

Seven human knee specimens were tested in a specially developed knee simulator. During simulated weight-bearing knee flexion, the kinematics of tibia, femur and patella were measured using an ultrasound motion capture system. The quadriceps forces were controlled to achieve a constant ankle force over the whole flexion range which is assumed to represent almost physiological loading. Three different force distributions of the quadriceps were tested - a central, equally distributed load as well as mainly lateral and medial loads.

RESULTS

A significant influence of different quadriceps force distributions was found for patellar tilt around a proximodistal axis (up to 1.7°) and patellar rotation around an anteroposterior axis (up to 3.8°) with respect to the femur. Interestingly, the patellar mediolateral shift was influenced only marginally (<1.5mm).

CONCLUSIONS

Specific muscle training might help patients with patellofemoral pain and cartilage damage by a slight modification of the kinematics, but we could show that even highly asymmetric quadriceps loads only led to a small alteration of the mediolateral shift in case of a physiologic anatomy of the trochlear groove.

Phosphorylation of wild-type and mutant phenotypes of p53 by an associated protein-kinase

Immunopurified mutant mouse p53 from transformed cells is known to be tightly associated with a protein kinase which phosphorylates p53 in an in vitro kinase reaction. Wild-type p53 from a non-transformed cell line was not associated with a protein kinase whereas immunopurified wild-type p53 from a transformed cell line was tightly associated with a protein kinase which phosphorylated p53. In order to compare wild-type and mutant p53 in the same cellular environment both forms were cloned in a baculovirus expression system and in in vitro transcription/translation vectors and both p53 proteins were expressed in the two systems. Wild-type and mutant p53 from baculovirus infected insect cells were tightly associated with a protein kinase which phosphorylates p53. In contrast, immunopurified wild-type and mutant p53 from an in vitro transcription/translation reaction were not associated with a protein kinase but could be phosphorylated by added casein kinase II. Thus, in the present paper we demonstrate that the association of p53 with a protein kinase and the in vitro phosphorylation of p53 seems to depend on the surrounding cellular environment.

[Hereditary variants of primary hyperparathyroidism--MEN1, MEN2, HPT-JT, FHH, FIHPT]

OBJECTIVE

The challenge in diagnosing primary hyperparathyroidism (HPT) is to detect hereditary cases before first surgery. About 5% of cases are hereditary and integral component of multiple endocrine neoplasia type 1 and 2 (MEN1/MEN2), hyperparathyroidism-jaw tumor syndrome (HPT-JT), familial hypocalciuric hypercalcemia (FHH), and familial isolated hyperparathyroidism (FIHPT). Aim of this study was to evaluate similarities and differences in hereditary varieties of HPT.

PATIENTS

80 patients with hereditary HPT were evaluated in a retrospective analysis between 1980 and 2010 concerning clinical findings, family history, therapy, biochemical and molecular-genetic findings and follow-up.

RESULTS

80 patients with hereditary HPT are described, 52 belonged to MEN1, 15 to MEN2, 7 to HPT-JT, 4 to FHH and 2 to FIHPT kindreds. Penetrance of HPT was highest in MEN1 (85%), followed by HPT-JT (64%), FHH (28.5%), and MEN2 (8%). Youngest age at diagnosis of HPT was 7 and 16 years in the MEN2/HPT-JT group. Serum Calcium was highest in the HPT-JT group (3.6 mM), recurrencies of HPT were highest in the MEN1 group (40.5%). Parathyroid cancer solely occurred in the HPT-JT group. In single cases HPT occurs in FHH.

CONCLUSION

Among the different varieties of hereditary HPT MEN1-HPT is most frequent and carries the utmost recurrence rate. Early diagnosis of HPT-JT syndrome is important because of the occurrence of parathyroid cancer. Single cases of HPT in FHH are described. Preoperative diagnosis of hereditary HPT has therapeutic consequences concerning extent of surgery and implications concerning patient and family care.

ERβ-specific agonists and genistein inhibit proliferation and induce apoptosis in the large and small intestine

Epidemiological data indicate that intake of estrogens and isoflavones may be beneficial for the prevention of colorectal cancer (CRC). Based on this data, the aim of the study was to investigate estrogen receptor (ER) subtype-specific effects on intestinal homeostasis. Ovariectomized (OVX) female Wistar rats were either treated with 17β-estradiol (4 μg/kg body wt/day) (E2), an ERα-specific agonist (ALPHA) (10 μg/kg body wt/day), an ERβ-specific agonist (BETA) (100 μg/kg body wt/day) or genistein (GEN) (10 mg/kg body wt/day) for three weeks. Vehicle-treated OVX and SHAM animals and those cotreated with BETA and the pure antiestrogen Fulvestrant (ICI 182780) (100 μg/kg body wt/day and 3 mg/kg body wt/day) served as controls. GEN and BETA treatment but not E2 and ALPHA administration reduced proliferation in ileal and colonic mucosa cells. The rate of apoptosis in the small intestine and colon was increased by treatment with BETA and GEN, but not by E2. BETA induced antiproliferative and proapoptotic activity also in SHAM animals. The effects were antagonized by the pure antiestrogen Fulvestrant. Polymerase chain reaction gene array analysis revealed that BETA resulted in the downregulation of the oncogene transformation-related protein 63 (p63). Our data indicate that activation of the ERβ by specific ERβ agonists and GEN induces antiproliferative and proapoptotic effects in the intestinal tract. This observation can be taken as an indication that intake of GEN and specific ERβ agonists may protect the ileal and colonic epithelium from tumor development via modulation of tissue homeostasis.

Are commonly recommended dosages for vitamin D supplementation too low? Vitamin D status and effects of supplementation on serum 25-hydroxyvitamin D levels--an observational study during clinical practice conditions

Vitamin D deficiency is associated with increased fracture risk. The observational study aimed to investigate vitamin D status and supplementation in ambulatory patients. Only 20% of patients had optimal serum 25-hydroxyvitamin D [25(OH)D] levels. Commonly recommended dosages were insufficient to achieve clinically relevant increase of 25(OH)D levels. Higher dosages were safe and effective under clinical practice conditions.

INTRODUCTION

Vitamin D deficiency is associated with adverse health outcome. The study aimed to investigate vitamin D status and supplementation in ambulatory patients.

METHODS

Nine hundred seventy-five women and 188 men were evaluated for bone status from January 2008 to August 2008 within an observational study; 104 patients (n = 70 osteoporosis) received follow-up after 3 months. Dosage of vitamin D supplementation was documented and serum 25(OH)D and parathyroid hormone (PTH) determined.

RESULTS

In all patients (age, 60.4 ± 14.1 years), distribution of 25(OH)D was 56.3 ± 22.3 nmol/L (normal range, 52-182 nmol/L) and PTH 53.8 ± 67.5 ng/L (normal range, 11-43 ng/L). The proportion of patients with 25(OH)D < 25, 25 to <50, 50 to <75, ≥75 nmol/L was 7.5%, 33.3%, 38.9% and 20.2% in the total group and 20.1%, 38.5%, 30.8%, 10.6% at baseline in the follow-up group, respectively. After 3 months, 3.9% had still 25(OH)D < 25 nmol/L; only 12.5% achieved 25(OH)D ≥ 75 nmol/L. In osteoporosis patients, 25(OH)D increased more in those taking ≥1,500 (median, 3,000) IU vitamin D per day (33.1 ± 14.7 nmol/L) compared with ≤1,000 (median, 800) IU/day (10.6 ± 20.0 nmol/L) (p < 0.0008). PTH decreased more in patients taking ≥1,500 IU/day (-13.2 ± 15.2 ng/L) compared with ≤1,000 IU/day (-7.6 ± 19.2 ng/L; p = 0.29). 25(OH)D was negatively correlated to PTH (r = -0.49, p < 0.0001). An increase of 25(OH)D ≥ 75 nmol/L resulted in normalised PTH.

CONCLUSION

Supplementation with higher vitamin D dosages (2,000-3,000 IU/day) is required to achieve a relevant increase of 25(OH)D and normalisation of PTH.