Thermal mirror buckling in freestanding graphene locally controlled by scanning tunnelling microscopy.

Knowledge of and control over the curvature of ripples in freestanding graphene are desirable for fabricating and designing flexible electronic devices, and recent progress in these pursuits has been achieved using several advanced techniques such as scanning tunnelling microscopy. The electrostatic forces induced through a bias voltage (or gate voltage) were used to manipulate the interaction of freestanding graphene with a tip (substrate). Such forces can cause large movements and sudden changes in curvature through mirror buckling. Here we explore an alternative mechanism, thermal load, to control the curvature of graphene. We demonstrate thermal mirror buckling of graphene by scanning tunnelling microscopy and large-scale molecular dynamic simulations. The negative thermal expansion coefficient of graphene is an essential ingredient in explaining the observed effects. This new control mechanism represents a fundamental advance in understanding the influence of temperature gradients on the dynamics of freestanding graphene and future applications with electro-thermal-mechanical nanodevices.

Unusual ultra-low-frequency fluctuations in freestanding graphene.

Intrinsic ripples in freestanding graphene have been exceedingly difficult to study. Individual ripple geometry was recently imaged using scanning tunnelling microscopy, but these measurements are limited to static configurations. Thermally-activated flexural phonon modes should generate dynamic changes in curvature. Here we show how to track the vertical movement of a one-square-angstrom region of freestanding graphene using scanning tunnelling microscopy, thereby allowing measurement of the out-of-plane time trajectory and fluctuations over long time periods. We also present a model from elasticity theory to explain the very-low-frequency oscillations. Unexpectedly, we sometimes detect a sudden colossal jump, which we interpret as due to mirror buckling. This innovative technique provides a much needed atomic-scale probe for the time-dependent behaviours of intrinsic ripples. The discovery of this novel progenitor represents a fundamental advance in the use of scanning tunnelling microscopy, which together with the application of a thermal load provides a low-frequency nano-resonator.

High tibial osteotomy and ligament reconstruction in varus angulated, anterior cruciate ligament-deficient knees. A two- to seven-year follow-up study.

We assessed short-term treatment results of younger patients with varus malalignment and chronic anterior cruciate ligament deficiency. Forty-one patients (mean, 32 years; range, 16 to 47) underwent a high tibial osteotomy. Because of giving way symptoms, 14 also had a lateral iliotibial band extraarticular procedure at the time of the osteotomy and 16 had an intraarticular anterior cruciate ligament allograft reconstruction after the osteotomy. All returned for followup (mean, 58 months; range, 23 to 86), which included KT-1000 arthrometer testing and evaluation by our knee rating system. Statistically significant (P < 0.05) improvements were found in the mean overall rating scores for pain, swelling, and giving way. Preoperatively, 30 (73%) had pain with activities of daily living or with any sports activity; 11 (27%) could perform only light sports activities without pain. At followup, 32 patients (78%) had no pain with activities of daily living or light sports. Ten of 15 patients with advanced medial tibiofemoral arthrosis (subchondral bone exposure) had significant improvements in symptoms. Patient satisfaction was high: 88% stated they would undergo the procedure again and 78% felt their knee condition was improved. Patients who had the allograft reconstruction had significantly lower (P < 0.05) anterior-posterior displacements at followup than those who had the extraarticular procedure. We concluded that osteotomy should be performed early in the disease process for younger athletes who experience symptoms with activity. It may be unrealistic, however, to expect continuation of sports beyond light recreational, given the joint arthrosis that is usually present and the high in vivo joint loadings with athletes. Anterior cruciate ligament reconstruction should be considered when giving way previously occurred and the patient plans to resume athletics. However, patients with advanced arthrosis can avoid anterior cruciate ligament surgery by reducing athletic activities.

The effect of a ligament-augmentation device on allograft reconstructions for chronic ruptures of the anterior cruciate ligament.

A prospective study was performed to determine the effect of a combination of a ligament-augmentation device with a bone-patellar ligament-bone allograft for the treatment of chronic rupture of the anterior cruciate ligament. One hundred and fifteen knees in 110 patients were divided into two groups. Group BLB consisted of sixty-six knees in sixty-four patients who were managed with a bone-patellar ligament-bone allograft only, and Group BLB-LAD consisted of forty-nine knees in forty-six patients who were managed with both the allograft and a ligament-augmentation device. Preoperatively, there were no statistically significant differences between the two groups with regard to fifteen variables. All patients were managed with the same postoperative program of immediate motion and rehabilitation of the knee. All patients returned for evaluation at a mean of thirty-four months (range, twenty-three to fifty-three months) postoperatively. The results were evaluated with a comprehensive rating system that assessed twenty factors. Both of these procedures significantly decreased functional limitations and symptoms and improved the level of sports activity and the over-all score. However, the use of the ligament-augmentation device did not improve the efficacy of the reconstruction with regard to any of the individual variables that were assessed or in terms of the over-all score. All but one of the patients regained an arc of 0 to 135 degrees of motion. Although the augmentation device reduced anterior-posterior displacement effectively for the first twenty weeks postoperatively (p less than 0.05), there was no difference between the groups in terms of the percentage of knees that had abnormal displacement at the latest follow-up. A new classification system was developed to determine rates of failure. The over-all rate of failure was 28 per cent (thirty-two) of the 115 knees: 29 per cent (nineteen) of the sixty-six knees in Group BLB and 27 per cent (thirteen) of the forty-nine knees in Group BLB-LAD. The difference between the two groups was not statistically significant. The addition of the ligament-augmentation device did not improve the results of allograft reconstruction in the treatment of chronic rupture of the anterior cruciate ligament. The use of either an allograft alone or an allograft combined with a ligament-augmentation device did not reduce the amount of anterior-posterior displacement satisfactorily in all of the knees.

The early treatment of motion complications after reconstruction of the anterior cruciate ligament.

The use of active and passive knee motion in the immediate postoperative period and a treatment plan for early postoperative limitations in knee motion has proven highly effective in restoring motion after anterior cruciate ligament (ACL) reconstruction. Of 207 knees, 189 (91%) regained a full range of motion of 0 degrees-135 degrees. The remaining 18 knees (9%) did not regain motion as rapidly as the others and were placed in an early postoperative phased treatment program. Six knees had serial extension casts, nine had early gentle manipulation under anesthesia, and three had arthroscopic lysis of intraarticular adhesions and scar tissue. Fourteen of these 18 knees regained a full range of knee motion. Two of the remaining four knees lacked 5 degrees of full extension, whereas the other two, in patients who had failed to follow medical advice and the rehabilitation program, had permanent and significant limitation of motion. The incidence of postoperative motion problems was related to the extent of the surgical procedure. The incidence was 4% in patients who had only ACL reconstruction, 10% in cases in which added lateral extraarticular procedure had been done, 12% where a meniscus repair had been done, and 23% where a medial collateral ligament repair was done.

Abnormal lower limb symmetry determined by function hop tests after anterior cruciate ligament rupture.

This study assessed the sensitivity of four different types of one-legged hop tests. The goal was to determine alterations in lower limb function in ACL deficient knees. Regression analyses were conducted between limb symmetry as measured by the hop tests and muscle strength, symptoms, and self-assessed function. In 67 patients, 50% had abnormal limb symmetry scores on a single hop test. When the results of two hop tests were calculated, the percent of abnormal scores increased to 62%. The percentage of normal scores indicated that these hop tests had a low sensitivity rate. However, the high specificity and low false-positive rates allow the tests to be used to confirm suspected defects in lower limb function. Statistical trends were noted between abnormal limb symmetry on the hop tests and low velocity quadriceps isokinetic test results.

The effect of an extra-articular procedure on allograft reconstructions for chronic ruptures of the anterior cruciate ligament.

A study was performed on the effect of the addition of an extra-articular procedure involving tenodesis of the iliotibial band to a reconstruction with a bone-patellar ligament-bone allograft for the treatment of chronic rupture of the anterior cruciate ligament. One hundred and four patients were divided into two groups for comparison: Group 1 (sixty-four patients) was treated with only an intra-articular replacement with an allograft and Group 2 (forty patients), with both an intra-articular replacement with an allograft and the extra-articular procedure. Preoperatively, there were no statistically significant differences between the two groups in terms of twenty variables, including body weight, level of activity, anterior-posterior displacements, number of previous operations, and duration of follow-up. All of the patients returned for follow-up evaluation twenty-three to fifty-four months (mean, thirty-five months) postoperatively. All were treated with the same postoperative program of immediate motion of the knee and rehabilitation. The results were evaluated with the use of a comprehensive subjective and objective system that rated the twenty factors. Both procedures proved to be effective in decreasing functional limitations and symptoms and in improving the level of sports activity and the over-all scores. The results in Group 2 were significantly better than those in Group 1, as measured with tests done with the KT-1000 arthrometer (p less than 0.01) and with regard to the level of sports activity (p less than 0.05) and the over-all scores (p less than 0.01). There was no postoperative difference between the two groups in terms of the results on pivot-shift or isokinetic testing, patellofemoral crepitus, functional limitations, or symptoms. The program of rehabilitation effectively restored 0 to 135 degrees of motion to all but four knees, which lacked 5 degrees of extension at the most recent follow-up. The over-all rate of failure for both groups was 11 per cent. However, the rate of failure was 16 per cent (ten of sixty-four knees) in Group 1 and only 3 per cent (one of forty knees) in Group 2. This difference was significant (p less than 0.05). The extra-articular procedure appeared to provide support to the healing intra-articular allograft by reducing deleterious forces and tibial displacements, and to restore the secondary restraints provided by the lateral iliotibial band. The results suggest that the combination of the procedures is of value in young, athletically active people who have chronic rupture of the anterior cruciate ligament.(ABSTRACT TRUNCATED AT 400 WORDS)

The assessment of work-related activities and limitations in knee disorders.

The success of knee treatment programs and surgery must be assessed, in part, by both the ability to return patients to work and the documentation of any work-related limitations. Existing occupational rating scales do not rate, in a valid manner, the effect of altered knee function on work activities. We performed a prospective randomized clinical trial in which two different occupational rating systems were tested on 50 patients. One system used job titles and an arbitrary numeric scale for rating occupations; the other used specific criteria for rating job functions according to the intensity, frequency, and duration of certain tasks. The results showed that an effective and valid rating format should consist of five specific objectives: 1) evaluation of different knee functions that typically occur in the work environment; 2) evaluation of work activities separately from sports activities; 3) detection of patients who may have remained at an occupation but who have significantly modified work activities because of knee symptoms; 4) identification of patients who continue to work despite experiencing moderate to severe symptoms; and 5) identification of patients whose work activities decrease because of nonknee-related factors. Furthermore, the results showed that an effective rating system should identify common data reduction errors that can bias the results in analyzing knee-related occupational limitations. The rating system developed circumvents the bias introduced by these anomalies. This system, if adopted by other researchers, would allow for the comparison of treatment results among studies.

Bone-patellar ligament-bone and fascia lata allografts for reconstruction of the anterior cruciate ligament.

A prospective study was performed of the first forty-seven consecutive patients who had repair of a ruptured anterior cruciate ligament and replacement with an allograft. Patients who had a rupture of another ligament were excluded, to provide a homogeneous group. Twenty-two patients received a fascia lata allograft and twenty-five patients received a bone-patellar ligament-bone allograft. All patients were enrolled in an exercise program to facilitate motion of the knee immediately after the operation, and all patients returned for postoperative evaluation (mean, forty months; range, twenty-five to sixty-seven months). The results were based on a comprehensive subjective and objective rating system, which assessed twenty factors. On testing with the KT-1000 arthrometer, 69 per cent of the patients had less than three millimeters of increased anterior-posterior displacement of the knee that had been operated on compared with the contralateral knee, 26 per cent had three to five millimeters, and 5 per cent had more than five millimeters. The knees that had a bone-patellar ligament-bone allograft had significantly lower values for anterior-posterior displacement than did those that had a fascia lata allograft (p less than 0.05). Just one patient, the only one in whom the fascia lata graft failed, had giving-way. There were no infections, and there was no evidence of rejection of the allograft or documented transmission of disease at the time of writing. A strict rating system was used. Eighteen patients (38 per cent) had an excellent result, twenty-four (51 per cent) had a good result, and five (11 per cent) had a fair or poor result. Motion of the knee immediately postoperatively was not deleterious to the allograft, and, because limitations of motion were identified and treated in the early postoperative period, full motion (0 to 135 degrees) was restored in all knees.

Quantitative assessment of functional limitations in normal and anterior cruciate ligament-deficient knees.

The purpose of this study was to evaluate the effectiveness of five hopping, jumping, and cutting-type (shuttle run) tests in determining lower extremity functional limitations in anterior cruciate ligament- (ACL) deficient knees. Ninety-three normal subjects were tested. No statistical significance was found between right and left lower limb scores (limb symmetry index) as related to sports activity level, gender, or dominant side. This allowed an overall symmetry index score to be established for the population as a whole. An 85% symmetry index score was found in more than 90% of the normal population for the one-legged hop for distance test and the one-legged timed hop test. Thirty-five patients with ACL-deficient knees were tested. The patients also had KT-1000 and Cybex testing and completed questionnaires rating symptoms, sports activity levels, and sports functional limitations. The cutting-type tests and the vertical jump test did not detect functional limitations in a reliable manner. In the one-legged hop tests, 50% of the patients performed normally, however, all reported giving-way episodes with sports, indicating a lack of sensitivity of these tests in defining functional limitations. Patients with abnormal one-legged hop test scores were considered at serious risk for giving way and limitations during sports activities. Statistically significant relationships were found among abnormal scores on the one-legged hop-type tests and (1) self-assessed difficulty with pivoting, cutting, and twisting, (2) quadriceps weakness (Cybex), and (3) patellofemoral compression pain.

A rationale for assessing sports activity levels and limitations in knee disorders.

Existing published knee rating systems that assess sports participation, knee function, and subjective symptomatology following ligamentous surgical procedures were analyzed. Major errors in questionnaire design and data reduction have led to invalid conclusions. A questionnaire containing a minimum set of rating criteria was formulated to validly assess athletic participation before and after treatment or surgery. Select questions and a data reduction format were established to assess the intensity of sports participation, changes in sports participation, the variables that produced the changes, self-assessed functional limitations, and the ability to participate in different types of sports. A clinical trial of the questionnaire was performed on 59 patients. An interview conducted upon completion of the questionnaire enabled the authors to detect difficulties or inconsistencies in the responses to the questions. The design format described in this report forms the basis for a subjective evaluation of ligamentous surgery. A standard format for analysis of sports participation and knee function is proposed to aid investigators in comparing variations in clinical results.