Knee Signature System Research Articles

Knee Stability Controlled by Hamstrings and Functional Knee Brace

The purpose of this study was to determine the effectiveness of an off-the-shelf functional knee brace on preventing anterior tibial translation in anterior cruciate ligament-deficient knees (ACL-d) with greater than 6 mm of side-to-side difference, and the effect of a 50% maximal voluntary hamstring contraction on knee joint laxity. A therapist experienced in using the Knee Signature System (KSS) screened 14 patients who had been diagnosed arthroscopically with ACL deficiency. Nine patients (8 men, 1 woman; mean age, 32.9 years; mean mass, 75 kg; mean height, 177 cm) met the inclusion criteria. All participants were 240 ± 42 days post injury. Participants in the study were tested with no brace, with brace, and 50% maximal voluntary contraction (MVC) of the hamstrings. The uninjured limb was tested only in the unbraced condition. Repeated measures ANOVA (p ≤ .05) and a Bonferroni post hoc analysis was used to detect specific differences between conditions. Results indicate that a 50% hamstring contraction provided better control of anterior tibial displacement than a functional knee brace under the same loading conditions, but a brace may contribute significantly to reducing anterior displacement when the hamstring force is not sufficient.

Correlates of knee laxity change in early rehabilitation after anterior cruciate ligament reconstruction.

Factors other than ligament graft length (knee ROM, knee swelling, initial knee laxity) may need to be accounted for in interpreting changes in knee laxity during rehabilitation following anterior cruciate ligament reconstruction (ACLR) surgery. Twenty-three patients recovering from ACLR surgery (16 M, 7 F, age mean = 30) were tested at 2 and 6 weeks after ACLR with knee laxity measured using th Knee Signature System arthrometer, passive ROM with a standard goniometer and swelling by measuring knee circumference at the mid-patella level using a cloth measuring tape. Spearman correlation coefficients (in parentheses) were calculated using rankings of the change in the injured minus uninjured knee laxity as the dependent variable and the following independent variables: pre-test injured minus uninjured knee laxity (ranked; -0.457; statistically significant two-tailed P < 0.05); change in injured knee maximum extension relative to the uninjured side (ranked; 0.127); change in injured knee maximum flexion relative to the uninjured side (unranked; -0.073); and change in the injured minus uninjured knee girth (unranked; -0.159). These results indicate that consideration should be given to the patient's knee laxity at the start of intervention when using changes in laxity to guide rehabilitation after ACLR.

Instrumented measurement of anterior-posterior translation in knees with chronic anterior cruciate ligament tear.

Anteroposterior translation of the knee joint was measured with a Knee Signature System device on 12 women and 14 men with a unilateral, chronic, isolated, anterior cruciate ligament (ACL) tear. A control group with stable knees consisted of 10 women and 10 men. Anterior translation at 178 N load of the uninjured knees was 8.0 mm (+/-2.2 mm) and in knees with an ACL tear, 14.2 mm (+/-4.2 mm). Corresponding values for anteroposterior translation were 12.1 mm (+/-2.5 mm) and 19.3 mm (+/-4.9 mm), respectively. A difference of 3 mm or more in anteroposterior translation at 178 N load between injured and uninjured knees indicated an ACL tear with 85% specificity and 88% sensitivity.

Instrumented measurement of anterior-posterior laxity of the knee joint after tibial plateau fracture

The Knee Signature System (KSS) was used to measure anterior-posterior laxity of the knees of 34 patients who had an old tibial plateau fracture. The mean total tibial translation with respect to the femur was 9.8 (range 3.1–19.5) mm in the injured knees and 7.5 (range 3.1–14.2) mm in the uninjured knees ( P < 0.01). A side-to-side difference (injured versus uninjured knee) to 3 mm or more was found in 13 knees (38%). Neither mode of treatment nor extent of residual displacement of the condyles had any correlation with the sagittal translation. Because complete rupture of cruciate ligaments in association with tibial plateau fracture has been proven to be uncommon and changes in bony configuration did not affect the result, the abnormal tibial translation was left to be a consequence of stretching of the ligaments increasing multi-dimensional instability of the knee joint. The phenomenon was found more pronounced in older patients whose tolerance of ligaments and other soft tissues against stretching forces is decreased. Therefore, when using the KSS device, a side-to-side difference of 3 mm or more in sagittal translation of the tibia with respect to the femur is not always an indication of anterior cruciate ligament deficiency, when such differences are found in patients with an old tibial plateau fracture.

Instrumented Examination of Knee Laxity in Patients With Anterior Cruciate Deficiency: A Comparison of the KT-2000, Knee Signature System, and Genucom

Knee ligament arthrometers are used during rehabilitation to assess changes in knee laxity after anterior cruciate ligament injury. This study investigated the reliability and error associated with measurements of knee laxity using three different instrumented devices: the KT-2000, the Knee Signature System (KSS), and the Genucom Knee Analysis System to aid in the interpretation of instrumented laxity measurements during rehabilitation. Ten subjects with unilateral anterior cruciate deficiency were examined by two testers on two separate days. Measurement error was calculated as the minimum difference required to assume a true change in laxity between two measurements (p < 0.05). Between-day reliability was relatively high for both the KSS and the KT-2000 (.95 and .83, respectively) but substantially lower for the Genucom (.22). Intertester reliability was slightly lower for the KT-2000 and the KSS (.92 and .78, respectively) and slightly higher but still low for the Genucom (.27). When monitoring changes in anterior laxity of an anterior-cruciate-deficient knee, the following error values were determined to be needed in order to assume a true difference between successive measurements: KT-2000, 2.0 mm; KSS, 4.2 mm; and Genucom, 5.9 mm. The results of this study suggest that measurements of anterior laxity taken by a single examiner using the KT-2000 provide the most reliable measurements.

Prospective Preoperative Evaluation of Anterior Cruciate Ligament Instability of the Knee Joint and Results of Reconstruction With Patellar Ligament

Of 54 patients with chronic (n = 49) or acute (n = 5) anterior cruciate ligament instability, 52 were evaluated after mean 16 months' follow-up interval after open (n = 18) or arthroscopic assisted (n = 36) bone-tendon-bone patellar ligament reconstruction. Preoperative Knee Signature System side-to-side difference in anterior displacement decreased from 7.9 mm to 3.5 min at follow-up evaluation (p < 0.0001). An objectively satisfactory limit of 5 mm in side-to-side difference was achieved in 73% of the patients. At follow-up evaluation, there was a positive pivot shift sign in eight knees (one definite and seven trace). Average Lysholm knee scores improved from 69 to 83. The only significant difference between the arthroscopic assisted and open groups was smaller side-to-side anterior displacement difference in the arthroscopic group (2.2 mm versus 4.8 mm, p = 0.002). Results suggest that more accurate and isometric placement of the graft is possible with the arthroscopic-assisted technique.

An in vivo comparison of anterior tibial translation and strain in the anteromedial band of the anterior cruciate ligament

The objective of this in vivo study was to determine if strain in the anteromedial band (AMB) of the anterior cruciate ligament (ACL) may be predicted by an external measurement of anterior tibial-femoral translation. A Hall effect strain transducer was implanted on the AMB of five human subjects with normal intact ACLs. AMB strain was then measured during anterior shear loading of the tibia relative to the femur, with the knee flexed to 30 and 90°, simulating the loads applied in the Lachman and anterior drawer tests, respectively. The Knee Signature System, a commercially available arthrometer, was used to simultaneously measure anterior tibial translation relative to the femur. The resulting AMB strains and translations during anterior shear loading of the tibia with respect to the femur at 30 and 90° were compared using a regression analysis to determine if AMB strain could be predicted from a measure of anterior tibiofemoral translation at either flexion angle. AMB strain at 150 N anterior shear load at 30° flexion (3.0%) was significantly greater than that at 150 N anterior shear load at 90° flexion (0.9%). During anterior shear loading at 30° flexion, AMB strain correlated with anterior tibial translation ( r 2 = 0.59). However, there was no significant correlation between AMB strain and anterior tibial translation for anterior shear loading at 90° flexion ( r 2 = 0.002). Therefore, AMB strain was not accurately predicted from an external measurement of tibial displacement at 90° in this experiment.

The effects of pad placement and angular velocity on tibial displacement during isokinetic exercise.

The purpose of this study was to compare the effects of proximal single resistance pad placement (PSPP) and distal single pad placement (DSPP) on tibial displacement during isokinetic exercise on anterior cruciate ligament (ACL)-deficient knees. This study is important to the clinician because it documents tibial displacement during open chain isokinetic knee extension exercise at various isokinetic speeds. In addition, this study documents the range of motion where the greatest amount of anterior tibial displacement occurs. The anterior displacement of the tibia was recorded by a computerized knee laxity testing device during isokinetic exercise. Data were collected from 12 ACL-deficient knees. Each subject was tested on an OSI Knee Signature System for quantifiable tibial displacement during a Lachman's test, anterior drawer test, and active vs. passive knee extension. Following this, each subject was tested on a Biodex isokinetic dynamometer at isokinetic velocities of 60, 180, and 300 degrees/sec with the computerized knee laxity testing device in place. Pad placement consisted of distal single pad placement, which is 1 inch proximal to the medial malleolus, and proximal single pad placement, which is 3 inches proximal to the DSPP location. The testing procedure was standardized, and peak torque was monitored to ensure consistent maximal effort throughout the study. The results indicated that PSPP resulted in less anterior tibial displacement at all three test speeds. The peak anterior tibial displacement occurred in a range from 30 to 15 degrees of knee flexion at both pad placements and all three test speeds.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Versus Instrumented Knee Testing on Autopsy Specimens

The accuracy, reliability, and reproducibility of the Genucom Knee Analysis System and Knee Signature System (KSS) for anteroposterior knee laxity evaluations were compared. The devices detected the same relative change in laxity between normal and anterior cruciate ligament-deficient specimens during Lachman and drawer testing; however, the absolute values differed. In a clinical study, two examiners performed three independent Lachman and drawer tests using the Genucom, KSS, and a subjective clinical examination on ten patients. The Genucom demonstrated interexaminer differences during the Lachman test. The clinical examination proved to be more reliable than either instrumented device for both Lachman and drawer testing. The intraexaminer variability of the Genucom and KSS was large, with the average 95% confidence limits about the mean for the Genucom and KSS equal to +/- 4.2 and +/- 2.8 mm, respectively. These findings question the accuracy, reliability, and reproducibility of the instrumented methods.

The Knee Signature System: a preliminary report

SummaryThis paper reports on the early results obtained using the Acufex Knee Signature System (KSS) to study ligament laxity.

Suture of the torn anterior cruciate ligament. 5-year follow-up of 60 cases using an instrumental stability test.

60 patients were examined 5 (2-9) years after simple suture of acute rupture of the anterior cruciate ligament. In the follow-up the patients were examined clinically and by instrumental testing of stability (Acufex Knee Signature System). 10 knees had had a ligament reconstruction during the follow-up period, 28 knees were stable, and 22 unstable. By the Lysholm knee-score, function was rated excellent or good in both stable and unstable knees and the Tegner activity score dropped insignificantly. A positive correlation was found between the measured laxity and the clinical tests. Instrumental stability testing seems to be a reliable supplementary tool in the diagnosis of anterior cruciate ligament insufficiency. Ligament repair by simple suture was not better than reported results on conservative treatment.

Reproducibility of the Knee Signature System

To assess trial-to-trial, installation-to-installation, and day-to-day effects of the Knee Signature System, we studied anterior/posterior translation measurements in six normal subjects. The protocol consisted of testing both knees on 6 days with three installations per day and three trials per installation. We recorded anterior, posterior, and total anterior/posterior translation at +/- 20 and +/- 40 pounds of force at 30 degrees of flexion. Additionally, after measuring anterior/posterior translation during passive knee extension, active extension, and active extension with 15 pounds of weight at the ankle, we calculated the difference in anterior translation at 30 degrees of flexion between each of these three conditions. We analyzed the size of the effects and computed 90% confidence limits using analysis of variance. Means and 90% confidence limits for total anterior/posterior translation measured at +/- 20 pounds of force were: right knee, 6.8 +/- 2.3; left knee, 8.2 +/- 2.0; and right/left difference, 1.5 +/- 2.7 mm. Left knee translation means were significantly greater than right knee means in all tests. Day-to-day effects, while statistically significant for right and left knee measurements, showed no significant effects for right/left differences. Trial-to-trial and installation-to-installation effects were not significant for any parameter. Right/left differences during knee extension testing were smaller than for the stress test, measuring 0.1 mm or less, but confidence limits were larger, being +/- 3.7 mm for active extension-passive knee extension, +/- 1.5 mm for 15 pounds of weight at the ankle-active extension, and +/- 4.6 mm for 15 pounds of weight at the ankle-passive knee extension. Active extension produced 6.3 mm more anterior translation at 30 degrees of flexion than passive extension.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo measurement of anterior tibial translation using continuous passive motion devices

Early motion protocols following anterior cruciate reconstruction often use continuous passive motion devices. There is concern that these devices may induce undesired anterior translation of the tibia and resulting graft stretching or rupture. This study measured the amount of anterior tibial translation that occurred during one cycle in 10 different brands of continuous passive motion devices. Five patients with ACL deficient knees participated in this study. Anterior translation was recorded by using an electrogoniometer with four degrees of freedom (Knee Signature System). Anterior translation measurements were also recorded for a 20 pound Lachman test in these same five patients using the Knee Signature System. Two of the devices showed anterior translation measurements that approached the recorded 20 pound Lachman values. These two devices had a high calf bar for the primary support of the leg. The results indicate that, when using a continuous passive motion device for early postoperative management of the reconstructed ACL in a patient, use of a calf-supporting type of continuous passive motion could induce an undesired strain of the healing graft.

Assessing the limits of knee motion

Ten patients were examined clinically by 11 experienced knee surgeons and with three measurement devices (Genucom, Knee Signature System, and KT-1000). Nine of the 10 patients examined had sustained documented intraarticular ligament disruptions including eight ACL disruptions and five posterior cruciate ligament disruptions. The eight patients with ACL injuries had undergone reconstructive surgery. The clinical examination test sequence was performed as described by the International Knee Documentation Committee. Testing results were reported as estimated degrees of angulation or millimeters of displacement. Testing results were divided into two groups based on the index minus nonindex knee difference. Eighteen displacement tests were performed on each knee by each examiner. The index minus nonindex knee difference was greater than 3 mm in 16% of the tests. Only 1 of the 198 displacement tests performed on the subject who did not have a ligament disruption was recorded as an index minus nonindex difference greater than 3 mm. There was appreciable difference between measurements recorded by different examiners, particularly anterior/posterior measurements in patients who had sustained combined anterior and posterior cruciate ligament injuries. There is a need to rigorously evaluate limits of motion tests that are used to develop treatment plans and report the results of ligament surgery.

Measurement of anterior-posterior displacement of the knee. A comparison of the results with instrumented devices and with clinical examination.

Thirteen subjects who had normal knees and fifteen patients who had a chronic rupture of the anterior cruciate ligament were tested in order to compare the measurements of tibiofemoral displacement as recorded by four commercial devices: the Acufex knee-signature system, the Genucom knee-analysis system, the Medmetric KT-1000 arthrometer, and the Stryker knee-laxity tester. Anterior and posterior displacement were measured at forces of eighty-nine newtons (twenty pounds) and 133 newtons (thirty pounds). We found significant differences in reproducibility of measurement among the devices. The Acufex, Medmetric, and Stryker devices had more reproducible measurements, and they could be used to identify 80 to 90 per cent of the normal subjects and anterior cruciate-deficient patients. The Genucom device had poorer reproducibility of measurement, and it tended to register greater differences in displacement between the right and left knees of normal subjects.