Radiographic Assessment of Instability of the Knee Due to Rupture of the Anterior Cruciate Ligament

Transcription

1 ( opyright 1991 by The Journal of Bone and Join: Surgery, Incorporated Radiographic Assessment of Instability of the Knee Due to Rupture of the Anterior Cruciate Ligament A QUADRICEPS-CONTRACTION TECHNIQUE* BY JONATHAN L. FRANKLIN, M.D.t, THOMAS D. ROSENBERG, M.D.t, LONNIE E. PAULOS, M.D4, AND E. PAUL FRANCE, PH.D.1, SALT LAKE CITY, UTAH From the Salt Lake City Knee and Sports Medicine Clinic, Salt Lake City ABSTRACT: We compared the results of a radiographic technique for the measurement of instability of the knee with those obtained with a KT-1000 arthrometer. The study was conducted on both knees of sixty patients who had a ruptured anterior-cruciate ligament in one knee, as well as in ten control subjects. The radiographic technique included the examination of a true lateral radiograph, made while the knee was in full extension and the quadriceps was maximally contracted, with a 66.7-newton downward force produced by a 6.8- kilogram weight suspended from the ankle. As demonstrated by both techniques, the maximum difference between the displacements of the right and left knees in the control subjects was 2.5 millimeters and the mean difference between the displacements in the two knees in the patients was 7.5 millimeters. In fourteen of the sixty knees in which the ligament was ruptured, the injury was acute. The forward translation of the medial side in these fourteen knees was compared with that in the forty-six knees in which the injury was chronic. The mean difference in the displacernent of the medial side in the right and left knees was 3.5 millimeters in the fourteen patients who had an acute injury and 5.0 millimeters in the forty-six patients who had a chronic injury. Thirteen of the sixty patients had disruption of the posteromedial corner of the injured knee, and the translation ofthe medial side in these knees was significantly increased compared with that in the intact knees of the same patients. The radiographic technique was as accurate as the KT-1000 arthrometer in the diagnosis of unilateral rupture of the anterior cruciate ligament. The quadricepscontraction radiographic technique is an accurate and simple method for diagnosis. In recent years, rupture ofthe anteriorcruciate ligament has been recognized more commonly and treated more ag- * No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject ofthis article. No funds were received in support of this study. t Ballard Orthopedic and Fracture Clinic, 1801 NW. Market Street, #403, Seattle, Washington Salt Lake City Knee and Sports Medicine Clinic, Suite 206, 359 8th Avenue, Salt Lake City, Utah gressively. However, in most centers, the diagnosis is still made on the basis of clinical findings. It is important that the decision of whether or not the rupture should be treated operatively be made on the basis of both functional and objective criteria. Arthrometers were introduced because of the limitations that are inherent in clinical examination. However, concerns regarding the accuracy of the currently available arthrometers have led to the development of techniques in which stress radiographs are made while external forces are applied68 4 or while the patient contracts the muscles3. The advantages of the radiographic techniques compared with the use of instrumented arthrometers are that there is no soft-tissue interposition, which may vary appreciably in different patients, and that they do not depend on the position of the patella. Also, radiographic techniques do not necessitate the use of special instrumentation or a technician trained to operate it. DeJour et al. described a technique in which a radiograph is made with the knee in full extension during an isometric contraction of the quadriceps, with a seven-kuogram weight on the ankle. They stated that the anterior subluxation of the tibia produced by this maneuver was the same on the medial and lateral sides of the knee; therefore, they used only the measurements on the medial side. However, they also showed that when the anterior cruciate hgament had been ruptured, anterior subluxation of the medial side of the knee was significantly greater than it was in knees in which the anterior cruciate ligament was intact. This subluxation was even greater after a medial meniscectomy. However, Deiour et al. did not correlate their findings with those determined by clinical examination or by use of instrumented arthrometers. The goal of our study was to establish the differences between sides in normal subjects with our quadriceps-contraction radiographic technique and to compare the results with those obtained with the KT arthrometer (Med- Metric, San Diego, California) with respect to the diagnosis of rupture of the anterior cruciate ligament. In addition, the amounts of anterior translation (subluxation) of the medial and lateral sides of the knees were measured radiographically, in an attempt to assess the value of the method for the determination of damage to the secondary restraints and VOL. 73-A, NO. 3. MARCH

2 366 J. L. FRANKLIN, 1. D. ROSENBERG, L. E. PAULOS, AND E. P. FRANCE for the assessment of rotational instability. Materials and Methods Sixty patients who were seen consecutively in the Salt Lake City Knee and Sports Medicine Clinic because of either an acute or a chronic unilateral rupture of the anterior cruciate ligament were tested. There were fifteen female patients and forty-five male patients, and the average age was 30.5 years (range, fourteen to fifty-three years). All of the ruptures of the anterior cruciate ligament were diagnosed on the basis of a grade-3 result on the Lachman test 3 and a positive pivot-shift sign. If these specific clinical criteria were met, the diagnosis of rupture of the anterior cruciate ligament was assumed to be correct. The diagnosis was also confirmed with arthroscopy in thirty of the sixty patients. No patient had a history of injury to the opposite knee. Five men and five women who had no history of injury to the knee or of an operative procedure on the knee were chosen as control subjects. Their average age was 29.2 years (range, twenty-two to forty-two years). Both knees of all of the individuals in the study were evaluated with physical examination, a KT-l000 arthrometer, and radiographs made with the quadriceps-contraction technique. Of the sixty patients who had a unilateral rupture of the anterior cruciate ligament, fourteen had an acute injury (time from injury to evaluation, two months or less) and forty-six, a chronic injury (time from injury to evaluation, more than two months). Twenty patients had, in addition, arthroscopic evidence of a peripheral tear of the medial meniscus, and nine had arthroscopic evidence of an intact medial meniscus. Thirteen patients had disruption of the socalled posteromedial corner complex, as demonstrated by an external-rotation pivot-shift test and anterior drawer test. These three subgroups were analyzed with the rest of the sixty patients, as well as separately. The radiographic technique that was used in this study involves a standardized cross-table lateral radiograph including the distal end of the femur and the proximal end of the tibia, with the x-ray beam centered on the joint line. The focal point-to-film distance is one meter, and the cassette is always placed on the medial side of the knee. The knee that is being tested is supported on a 30-degree wedge (knee-bolster), and a force of 66.7 newtons is produced by a 6.8-kilogram (fifteen-pound) weight suspended from the ankle. When the technician is ready to make the radiograph, the patient is instructed to straighten the knee as much as possible and to hold this position for the duration of the exposure. For each radiograph, the technician positions the patient in such a way that when the knee is fully extended, a true lateral radiograph of the distal end of the femur is made. It is imperative that the rotation be the same for both knees and that the radiographs of the two knees be cornparable. Before the radiograph is made, a radiopaque marker is placed on the anterior surface of the knee to determine the amount of magnification, which is calculated as a percentage of the true dimensions. For example, a true dimension of ten centimeters that measures eleven centimeters on the radiograph represents a magnification of 10 per cent. The magnification of the radiographs ranged from 9 to 1 1 per cent. After the radiographs are made, they are compared to ensure that the rotation is the same for both limbs. This is determined by a check of the relative positions of the postenor aspects of the femoral condyles on the two radiographs. If the positions are not the same, new radiographs are made. To make the measurements on the radiographs, the plane of the tibia! joint surface is identified on the radiograph of each knee (Fig. 1). A fine line is drawn with a pencil, as accurately as possible, along the subchondral plate of the medial tibia! plateau. When the observer is in doubt as to the exact location of the subchondral plate on one or both radiographs, a particular procedure is followed to make sure that the lines for the tibial joint surfaces of the two knees are identical: on the radiograph on which the subchondral plate (the joint surface) can be identified, or seems more identifiable, a line is drawn that passes along the plate. The radiographs of the two tibiae (right and left) are then superimposed (with the unmarked radiograph on top) so that the outlines of the metaphyses match exactly. The line along the joint surface is then drawn on the unmarked radiograph so that the two joint-surface lines coincide. Since rupture of the anterior cruciate ligament is diagnosed by comparison of the translations of the tibiae as seen on both radiographs, it is more important that the lines representing the joint lines be drawn in the same way on both radiographs than that the exact amounts of posterior declination of the tibial condylar surfaces be reproduced by the lines drawn on the radiographs. Once the tibial joint surfaces have been located by the lines, the posterior margins of the medial and lateral tibial condyles are identified and marked (Figs. 2 and 3). These osseous landmarks are easily identified, since the lateral tibial condyle is narrow and pointed and its outline is continuous with that of the lateral tibial eminence (Fig. 2). The medial tibial condyle is larger and squarer, and its posterior surface is flat (Fig. 3). The positions ofthe posterior margins of the medial and lateral tibial condyles in the sagittal plane are then established by lines drawn perpendicular to the tibialjoint lines, so that these lines pass through the posterior margins of the tibial condyles (Fig. 4). Once this has been done, the posterior margins of the medial and lateral femoral condyles are identified. The lateral femora! condyle is easily distinguished from the medial femoral condyle because it is larger and has a higher trochlear ridge anteriorly, as well as an indentation in its articular surface (the condylopatellar sulcus) (Fig. 5). The medial femoral condyle has no such sulcus, is smaller, and has a lower trochlear ridge anteriorly (Fig. 6). The final step is measurement of the horizontal distances of the posterior margins of the medial and lateral femoral condyles from the perpendicular lines that were drawn through the posterior margins ofthe medial and lateral tibia! condyles (Fig. 7). For each knee, the horizontal distance of either the THE JOURNAL OF BONE AND JOINT SURGERY

3 RADIOGRAPHIC ASSESSMENT OF INSTABILITY OF THE KNEE 367 FIG. 1 FIG. 2 Fig. 1: The joint line of the tibia is marked by a fine line drawn along the subchondral plate of the medial tibial condyle. The lines that were actually used for the measurements were made with a sharp pencil and were finer than those shown. Fig. 2: The posterior margin of the lateral tibial condyle and its continuation to the tibial eminence are marked by a line drawn along the margin. medial or the lateral femoral condyle from the corresponding medial or lateral perpendicular line that was drawn from the tibia (whichever distance is larger) is used as the value for the tibial displacement in that knee. A positive value is recorded when the posterior margin of the tibial condyle is anterior to that of the femoral condyle, and a negative value is recorded when the posterior margin of the tibial condyle is posterior to that of the corresponding femoral condyle. In this study, the measurements were made by one examiner (J. L. F.) and were recorded to the nearest one-half mihlimeter. The reproducibility of this technique was tested by three orthopaedists who made the measurements on the radiographs of ten patients in the series who were chosen according to the alphabetical order of their last names. Each orthopaedist made lines and measurements on each pair of radiographs. The values were recorded and then all markings were removed with an alcohol-soaked swab so that the next orthopaedist could make lines and measurements without being influenced by previous markings. The values that had been obtained independently by the three orthopaedists were compared with F ratio tests. There was no significant difference between the values, and the precision value for all of these measurements was found to be 1.2 ± 0.6 millimeter. In addition to the tests for reproducibility, accuracy was tested by having three examiners independently make measurements on ten radiographs on which the lines had already been drawn by one examiner (J. L. F.). Each cxaminer recorded values independently. The accuracy of these measurements was found to be 0.05 ± 0.03 millimeter, a level that easily justified the use of measurements to the nearest one-half millimeter in this series. Differences between the radiographic displacements in the right and left knees of each subject were recorded and compared with the differences in the same subject as determined with the KT arthrometer. The KT-l000 manual maximum measurements were made as described by Daniel et al. An attempt was also made to determine rotational instability with the quadriceps-contraction radiographic technique. This was done by comparison of the translations of FIG. 3 FIG. 4 Fig. 3: The posterior margin and posterosuperior surface of the medial tibial condyle are marked by a line. Fig. 4: Lines that are perpendicular to the Joint line and pass through the posterior margins of the medial and lateral tibial condyles are drawn. VOL. 73-A, NO. 3, MARCH 1991

4 368 J. L. FRANKLIN, 1. D. ROSENBERG, L. E. PAULOS, AND E. P. FRANCE FIG. 5 FIG. 6 Fig. 5: The lateral femoral condyle is outlined by a line drawn along its subchondral cortex. Note the condylopatellar sulcus and the high condylar ridge anteriorly that identify this condyle. Fig. 6: The medial femoral condyle is marked by a broken line drawn along its subchondral cortex. The condylopatellar sulcus and the low condylar ridge anteriorly. which are the characteristics of this condyle, are absent. the medial side of the knees in the previously described subgroups of patients. The KT arthrometer was employed by a physical therapist who had been trained in the use of this device according to previously described methods2. The significance of the differences was analyzed with the Student t test. Probability values of less than 0.05 were considered significant. Results In the ten control subjects, the values for tibial displacement varied considerably. The measurements on the lateral sides ofthe twenty knees ranged from - 3 millimeters (tibial condyle three millimeters posterior to the corresponding femoral condyle) to four millimeters (tibial condyle four millimeters anterior to the corresponding femoral condyle). The values on the medial side of the knees ranged from to seven millimeters. However, when the right and left knees of each of the control subjects were compared, the difference between the values for the medial sides of the right and left knees of each subject was quite small (range, zero to two millimeters), as was the difference between the values for the lateral sides (range, zero to 2.5 millimeters). Similarly, in the control subjects, measurements of anterior displacement with the KT arthrometer showed wide differences in the amounts of displacement (range, six to thirteen millimeters). However, the maximum difference between the two knees of any one subject was small (range, 0.5 to 2.5 millimeters). With the radiographic technique, the mean difference between the anterior displacements (on the medial or lateral side, whichever was larger) in the two knees of each subject was 1.5 millimeters (standard deviation, 0.5 millimeter). When the KT-l000 arthrometer was used, the mean difference was 1.0 millimeter (standard deviation, 0.5 millimeter). In the sixty patients who had a unilateral rupture of the anterior cruciate ligament, we determined the displacement of the lateral and medial sides of the involved and uninvolved knees. In the sixty normal extremities, the mean displacement of the lateral side was 2.0 ± 4.0 millimeters and that of the medial side was 1.0 ± 3.5 millimeters. In contrast, in the sixty knees in which the anterior cruciate ligament was ruptured, the mean translation of the lateral side was 8.5 ± 4.0 millimeters and that of the medial side was 5.5 ± 4.0 millimeters. The mean anterior displacement of the lateral side was 6.5 ± 4.5 millimeters more in the knees in which the anterior cruciate ligament was ruptured than in the uninvolved knees ofthe same patients. Similarly, the mean translation of the medial side was 4.5 ± 3.5 millimeters more in the involved knees than in the uninvolved knees of the same patients. This difference was significant (p < 0.00!). In thirty-seven patients, the translation in the involved knee was greater on the medial side than on the lateral side, and in twenty-two patients, it was greater on the lateral side. In the one remaining patient, the medial and lateral translations in the involved knee were the same. In the sixty patients, the anterior translation averaged 7.5 ± 4.0 milhimeters more in the involved knee than in the intact knee. FIG. 7 The positions of the medial and lateral tibial condyles in the sagittal plane, with respect to the corresponding femoral condyles, are determined as shown. THE JOURNAL OF BONE AND JOINT SURGERY

5 RADIOGRAPHIC ASSESSMENT OF INSTABILITY OF THE KNEE 369 In the sixty patients, measurements with the KT-l000 arthrometer showed a mean anterior displacement of 8.5 ± 2.0 millimeters in the uninvolved knees and 16.0 ± 2.5 millimeters in the involved knees, a significant difference of 7.5 millimeters (p < 0.001). No significant difference was found between the results obtained with the radiographic technique and those obtained with the KT-l000 arthrometer (p > 0.10). Fourteen patients who had an acute rupture (two months or less between injury and evaluation) ofthe anterior cruciate ligament were evaluated with the other patients but also as a separate group. In this group, the translations of the lateral side of the involved and uninvolved knees differed by a mean of 6.0 ± 2.0 millimeters and the translations of the medial side of the involved and uninvolved knees, by a mean of 3.5 ± 2.5 millimeters. When the side (medial or lateral) that demonstrated the most translation was considered, the radiographic measurements showed a mean anterior translation of 6.5 ± 2.0 millimeters in the fourteen involved knees. In only three of these knees was the translation greater on the medial than on the lateral side. In the forty-six patients who had a chronic tear of the anterior cruciate ligament, the mean difference between the translations of the lateral sides of the involved and uninvolved knees was 6.5 ± 5.0 millimeters, and the mean difference between the translations of the medial sides of the two knees was 5.0 ± 4.0 millimeters. When the side on which the translation was greater was considered, the mean difference between the translations of the involved and uninvolved knees was 8.0 ± 4.0 millimeters. There was a trend toward greater laxity in the forty-six knees in which the injury was chronic compared with the fourteen knees in which it was acute, but the difference was not significant (p > 0.10). Measurements with the KT-l000 arthrometer showed that the mean difference between the anterior displacement of the injured and the uninjured knees was 7.0 ± 2.5 muhimeters in the fourteen patients who had an acute injury and 7.5 ± 2.5 millimeters in the forty-six patients who had a chronic rupture. As was the case with the radiographic technique, these arthrometric data indicate a trend toward increased laxity in the knees in which the injury was chronic, but the difference was not significant (p > 0.10). In the twenty patients who had an arthroscopically documented peripheral tear of the medial meniscus and the seven patients who had had a media! meniscectomy, the mean difference between the translations of the medial sides of the intact and injured knees was 5.0 ± 3.5 millimeters, compared with 4.5 ± 3.0 millimeters in the nine patients in whom arthroscopy had shown the medial meniscus to be intact. In these thirty-six patients, the translation of the medial side of the knees in which there was a lesion of the medial meniscus was not significantly different from that in the knees in which there was no such lesion (p > 0.10). The thirteen patients who had clinical evidence of disruption of the posteromedial corner also were evaluated separately. External-rotation pivot-shift tests of the involved knees showed increases in the displacements of the tibia of one grade or more, compared with the displacements that were demonstrated by internal-rotation pivot-shift tests. Similarly, anterior drawer tests, performed with the knee in 90 degrees of flexion and the tibia in internal, external, or neutral rotation, showed that the anterior displacement of the tibia was greater by one grade or more when the tibia was externally rotated. In the thirteen patients who had disruption of the posteromedial corner, radiographic measurements showed that the translations of the medial side of the involved knees exceeded those of the uninvolved knees by a mean of 6.5 ± 4.5 millimeters. In the other forty-seven patients, the clinical examinations showed no evidence of increased anteromedial laxity in the involved knees. In addition, in these forty-seven patients, the radiographic technique demonstrated that the mean difference between the translations of the medial sides of the involved and uninvolved knees was 4.0 ± 3.5 millimeters, which was significantly different from the value in the patients who had disruption of the posteromedial corner (p < 0.05). Discussion For a quadriceps-contraction radiographic technique to be useful for the diagnosis of ruptures of the anterior cruciate ligament, it must be determined (1) whether osseous landmarks that are reliably identifiable and can be used to determine accurately the amount of translation of the tibia are visible on lateral radiographs of the knee, (2) how much flexion of the knee will lead to the most accurate and reproducible measurements oftibial translation, (3) how much anterior shear force should be applied to the tibia, and (4) how translation of the tibia can be measured in a clinically feasible and accurate way. Previous reports on radiographic stress tests of stability of the knee have discussed different femoral and tibial landmarks68 14, with the best perhaps being those described by Hooper. On the basis of his description and our observations of radiographs and skeletons, we identified the distinct landmarks on lateral radiographs that we have discussed. These anatomical landmarks were located in all 120 knees of the sixty patients and all twenty knees of the ten control subjects in this study. Therefore, these landmarks seem satisfactory as reference points for the measurements. In a few patients, the plane of the tibia! joint surface (subchondra! plate) could not be identified clearly, and the described superimposition technique was used. With regard to the amount that the knee should be flexed during a quadriceps-contraction test, it is much easier to perform the test with the knee in full extension, since the patient can contract the quadriceps muscle maximally and need not attempt to maintain a specific amount of flexion. In the quadriceps-contraction radiographic test described by Deiour et a!., in which the knee was fully extended rather than flexed 20 degrees, the authors were able to distinguish between knees in which the anterior cruciate ligament was ruptured and those in which it was not. In their 161 patients VOL. 73-A, NO. 3, MARCH 1991

6 370 J. L. FRANKLIN, T. D. ROSENBERG, L. E. PAULOS, AND E. P. FRANCE who had unilateral rupture of the anterior cruciate ligament, the anterior translation of the tibia on the injured side was increased an average of 6.5 millimeters compared with the translation on the uninjured side. In a study of the biomechanics of the knee, Grood et al. measured anterior translation of the tibia during active extension of the knee, with and without a weight on the ankle. When the anterior cruciate ligament was intact, the anterior displacement reached a maximum at approximately 45 degrees of flexion of the knee and then decreased as full extension was approached. When the anterior cruciate hgament was deficient, the anterior displacement of the tibia continued to increase as the amount of flexion decreased and the knee moved toward full extension. This was even more dramatic when a downward force of newtons was applied to the ankle by a 3.2-kilogram (seven-pound) weight. This finding suggests that deficiency of the anterior cruciate ligament should be tested with the knee in full extension since, in knees in which the anterior cruciate ligament is deficient, anterior translation is maximum when full extension is reached and, in intact knees, translation decreases near full extension. Yasuda and Sasaki 7 8 calculated the anterior shear forces on the tibia during isometric contractions of the quadriceps at angles of flexion of the knee ranging from 5 to 90 degrees. They found the greatest shear force at 5 degrees of flexion, at which angle it was 14 per cent of the total force exerted by the quadriceps. At 15 and 30 degrees of flexion, the shear forces decreased to 9 and 4 per cent. The findings suggest that quadriceps-contraction tests performed with the knee in nearly full extension may create more anterior shear force on the tibia than tests that are performed with the knee in more flexion. Therefore, tests for laxity due to deficiency of the anterior cruciate ligament are likely to be more effective when they are performed with the knee extended. Henning et al. implanted strain-gauges in two patients who had a partial tear of the anterior cruciate ligament. They found that, with the knee in full extension and an 89.0-newton force applied at the ankle with a 9. 1-kilogram (twenty-pound) weight, an isometric contraction of the quadriceps produced an anterior shear force equivalent to those produced during Lachman tests performed with the examiner exerting a pull of newtons (equivalent to the force applied by a 36.3-kilogram [eighty-pound] weight). In one of the two patients, the strain in the anterior cruciate ligament was higher with the knee at 0 degrees than when it was flexed 22 degrees. Again, this finding suggests that full extension is the most appropriate position in which to test for rupture of the anterior cruciate ligament. Thus, we believe that, with the knee fully extended, the quadriceps-contraction radiographic test is easier to perform, deficiency of the anterior cruciate ligament is mdicated more accurately, and the maximum anterior shear force on the tibia is produced. Using the direct measurements of our ten control subjects as well as data from anthropomorphic table&6, we addressed the third issue that had to be resolved before the merits of the radiographic technique could be determined: how much anterior shear force (as calculated on the tibiae in the plane of the joint line [the tibial plateaus]) is produced by contraction of the quadriceps with the knee in full extension and a 6.8-kilogram (fifteen-pound) weight applied at the anide. The largest control subject was a 188-centimeter (seventy-four-inch) tall man who weighed 102 kilograms (225 pounds), and the smallest was a 152-centimeter (sixty-inch) tall woman who weighed forty-four kilograms (ninety-seven pounds). Despite the different sizes of the ten control subjects, the anterior shear forces that were directed along the planes of the joint lines of the tibiae did not vary as much as might have been expected. The mean force was ± 28.5 newtons (34.8 ± 6.4 pounds), quite similar to the force that is ordinarily used during passive arthrometric tests. Daniel et al. found that the maximum pull that two of them could exert individually, using the KT-l000 arthrometer, was between 133 and 178 newtons (equivalent to the force applied by weights of 13.6 and kilograms [thirty and forty pounds]). As previously noted, Henning et al. found that, with the knee flexed 0 degrees and eighty-nine newtons of force applied to the ankle with a 9. 1-kilogram (twenty-pound) weight, the anterior shear force produced by an isometric contraction of the quadriceps was equal to the anterior force applied during a Lachman test performed with a pull of 356 newtons (the equivalent of the force produced by suspension of a 36.3-kilogram Leighty-pound] weight from the ankle). Yasuda and Sasaki 7 8 calculated that the anterior shear force on the tibia during an isometric contraction of the quadriceps with the knee in 5 degrees of flexion was equivalent to 14 per cent of the force being generated by the quadriceps during contraction. Grood et al. measured the force of the quadriceps directly, using a cadaver model, and found that this force was 700 newtons at 0 degrees of flexion with a 3.2-kilogram (seven-pound) weight suspended from the ankle. Fourteen per cent of this 700-newton force is ninety-eight newtons. These data suggest that when a 66.7-newton force is applied to the ankle with a fifteen-pound (6.8-kilogram) weight, contraction of the quadriceps produces 133 to 178 newtons (thirty to forty pounds) of anterior force on the tibia. This force is similar to that used in other tests. From our findings, it seems likely that this amount of force is sufficient to differentiate between knees in which the antenor cruciate ligament is ruptured and intact knees on the basis of the relative amounts of anterior displacement. To deal with the fourth factor - the best way to measure tibial translation - we reviewed the previously described techniques. For most of these techniques, the periosteal surface of the posterior cortex of the tibia is used as a reference point 6 8. However, as described by Hooper, tibial translation should be measured along the plane of the joint line, since the joint line slopes posteriorly and the tibia subluxates along this line when the anterior cruciate higament is ruptured. ThE JOURNAL OF BONE AND JOINT SURGERY

7 RADIOGRAPHIC ASSESSMENT OF INSTABILITY OF THE KNEE >12 mm Displacement FIG. 8-A Distribution of patients according to the amount of tibial displacement, as determined by the quadriceps-contraction radiographic technique. The displacement of either the medial or the lateral side was used, depending on which was larger. Displacement of only three millimeters was found in both the intact knees and the injured knees. In the present study, the quadriceps-contraction radiographic technique differentiated between knees in which the anterior cruciate was ruptured and normal knees. In no control subject was the difference between sides four rnilhimeters or more, and in no patient was it less than three millimeters (Fig. 8-A). Of all seventy people who were tested (ten control subjects and sixty patients), one control subject and two patients had a difference between sides of exactly three millimeters. In the other nine control subjects, the difference was two millimeters or less, and in the other fifty-nine patients, the difference was four millimeters or more. Therefore, when the radiographic technique was used, the zone of overlap (the so-called gray zone) was narrow (Fig. 8-A). Evaluation of the same subjects with the KT-l000 arthrometer also differentiated the knees in which the anterior cruciate was ruptured from the normal knees (Fig. 8-B). However, for all of the ten control subjects and for five of the sixty patients, the differences between sides ranged from one to three millimeters. Therefore, the zone of overlapping displacements was broader when the KT-l000 arthrometer was used (one to three millimeters) than when the radiographic technique was used (three millimeters only). Recently, in a prospective study, Anderson and Lipscomb reported that measurements with the KT-l000 arthrometer indicated the correct diagnosis in 75 per cent of fifty patients who had been suspected of having a rupture of the anterior cruciate ligament before they were operated on. In our study, the radiographic technique was more accurate than the KT-l000 arthrometer for the diagnosis of a torn anterior cruciate ligament, assuming that the diagnoses were correct in all sixty patients. (In thirty patients, the diagnosis was confirmed with arthroscopy; in the remaining thirty, it was based on clinical findings only.) C It >12 mm Displacement FIG. 8-B Distribution of patients according to the amount of tibial displacement, as measured with the KT-l000 arthrometer. Displacements of one to three millimeters were found in both the intact knees and the injured knees. VOL. 73-A, NO. 3, MARCH 1991

8 372 J. L. FRANKLIN, T. D. ROSENBERG, L. E. PAULOS, AND E. P. FRANCE There was less anterior translation of the tibia in the patients who had an acute injury than in those who had a chronic injury. This difference was especially apparent with respect to the translations of the medial sides of the knees, which averaged 3.5 millimeters (range, one to 9.5 milhimeters) in the knees in which the injury was acute compared with 5.0 millimeters (range, to 18.5 millimeters) in the knees in which the injury was chronic. However, the difference was not statistically significant. These findings suggest that, in the knees in which the rupture was chronic, the secondary restraints had stretched out or the so-called break-stop mechanism of the medial meniscus and the posterior oblique ligament had been injured. The value of the quadriceps-contraction radiographic technique for evaluation of the competency of the posteromedia! corner was assessed in a subgroup of twenty-one patients in whom a previous open medial meniscectomy had been performed or a peripheral detachment of the medial meniscus had been documented at arthroscopy. The translations of the medial side of the tibia, as determined radiographically, were quite similar to the translations in the patients who had an intact medial meniscus. This finding was surprising, since it has been shown that anterior translation increases after total. However, Shoemaker and Markolf pointed out that it was in unloaded knees that the anterior translation increased after medial meniscectomy. When the quadriceps-contraction radiographic technique is used, the knee is loaded, which may explain why we did not find any difference in the knees of our patients. However, the amount of remaining meniscal tissue could not be documented in these knees, and the remaining portion of the meniscus might have been responsible for the lack of difference. We also attempted to assess the value ofthe quadricepscontraction radiographic test for the determination of rotational instability. As demonstrated by a positive result on external-rotation anterior-drawer and pivot-shift tests, thirteen of the patients in our investigation had increased anterior laxity of the involved knee, which suggests that the posteromedial corner complex was. The radiographic technique also showed increased anterior laxity in the medial side of the knee in these thirteen patients. The mean difference between the rotations of the medial side of the involved and uninvolved knees was 6.5 ± 4.5 milhimeters, whereas in the other forty-seven patients, the mean difference was 4.0 ± 3.5 millimeters. The difference between the two groups ofpatients was significant (p < 0.05). These findings suggest that the radiographic technique may demonstrate rotatory instability and permit gradation of the amounts of laxity. The quadriceps-contraction radiographic technique is an accurate way to diagnose rupture of the anterior cruciate ligament. The results compare favorably with those obtained with the KT-1000 arthrometer. The technique is simple, not affected by the amount of soft tissue, and not dependent on the position of the patella, as are most arthrometric techniques. Neither special, expensive instrumentation nor a specially trained technician is necessary. Also, the measurements are made while the joint is loaded, simulating the clinical situation. Whether the technique will permit grading of laxity and of rotational instability remains to be determined by further investigation. References 1. ANDERSON, A. F., and LIPSCOMB, A. B. : Preoperative Instrumented Testing of Anterior and Posterior Knee Laxity. Am. J. Sports Med., 17: , DANIEL, D. M. ; STONE, M. L. ; SACHS, R. ; and MALCOM, L. : Instrumented Measurement of Anterior Knee Laxity in Patients with Acute Anterior Cruciate Ligament Disruption. Am. J. Sports Med., 13: , , DEJOUR, H.; WALCH, 0.; CHAMBAT, P.; and RANGER, P.: Active Subluxation in Extension. Am. J. Knee Surg., 1: , , GROOD, E. S.; SUNTAY, W. J. ; NOYES, F. R. ; and BUTLER, D. L.: Biomechanics of the Knee-Extension Exercise. Effect of Cutting the Anterior Cruciate Ligament. J. Bone and Joint Surg., 66-A: , June , HENNING, C. E. ; LYNCH, M. A. ; and GLICK, K. R., JR. : An in Vivo Strain Gage Study of Elongation of the Anterior Cruciate Ligament. Am. J, Sports Med., 13: 22-26, HOOPER, 0. J.: Radiological Assessment of Anterior Cruciate Ligament Deficiency. A New Technique. J. Bone and Joint Surg., 68-B(2): , IVERSEN, B. F. ; S rurup, JENS; JACOBSEN, KLAUS; and ANDERSEN, JENS: Implications of Muscular Defense in Testing for the Anterior Drawer Sign in the Knee. A Stress Radiographic Investigation. Am. J. Sports Med., 17: , JAKOB, R. P.; STAuBLI, H. U. ; and DELAND, J. T.: Grading the Pivot Shift. Objective Tests with Implications for Treatment. J. Bone and Joint Surg., 69-B(2): , LEVY, I. M.; TORZILLI, P. A. ; and WARREN, R. F. : The Effect of Medial Meniscectomy on Anterior-Posterior Motion of the Knee. J. Bone and Joint Surg., 64-A: , July MULLER, WERNER: The Knee: Form, Function and Ligament Reconstruction. Berlin, Springer, PAULOS, L. E. ; ROSENBERG, T. D. ; and PARKER, R. D. : The Medial Knee Ligaments: Pathomechanics and Surgical Repair with Emphasis on the External-Rotation Pivot-Shift Test. Tech. Orthop., 2(2): 37-46, SHOEMAKER, S. C., and MARKOLF, K. L. : The Role of the Meniscus in the Anterior-Posterior Stability of the Loaded Anterior Cruciate-Deficient Knee. Effects of Partial versus Total Excision. J. Bone and Joint Surg., 68-A: 71-79, Jan TORG, J. S.; CONRAD, WAYNE; and KALEN, VICKIE: Clinical Diagnosis of Anterior Cruciate Ligament Instability in the Athlete. Am. J. Sports Med., 4: 84-93, T0RzILLI, P. A. ; GREENBERG, R. L. ; and INSALL, JOHN: An in Vivo Biomechanical Evaluation of Anterior-Posterior Motion of the Knee. Roentgenographic Measurement Technique, Stress Machine, and Stable Population. J. Bone and Joint Surg., 63-A: , July TORZILLI, P. A. ; GREENBERG, R. L. ; HooD, R. W. ; PAVLOV, HELENE; and INSALL, J. N. : Measurement of Anterior-Posterior Motion of the Knee in Injured Patients Using a Biomechanical Stress Technique. J. Bone and Joint Surg., 66-A: , Dec WINTER, D. A. : Biomechanics of Human Movement. New York, Wiley, YASUDA, KAZUNORI, and SASAIU, TETSUTO: Muscle Exercise after Anterior Cruciate Ligament Reconstruction. Biomechanics of the Simultaneous Isometric Contraction Method of the Quadriceps and the Hamstrings. Clin. Orthop., 220: , YASUDA, KAZUNORI, and SASAKI, TETSUTO: Exercise after Anterior Cruciate Ligament Reconstruction. The Force Exerted on the Tibia by the Separate Isometric Contractions of the Quadriceps or the Hamstrings. Clin. Orthop., 220: , ThE JOURNAL OF BONE AND JOINT SURGERY