The clinical relevance of instrumented testing for ACL insufficiency. Experience with the UCLA clinical knee testing apparatus

An instrumented clinical testing device developed at UCLA records a continuous anteroposterior force versus displacement curve of the tibia with respect to the femur at 20 degrees of flexion. Laxity and stiffness are calculated from the response curve. With this device, 95% of normal knees have an anterior laxity less than 7.5 mm and a side-to-side difference less than 2 mm. In contrast, an anterior cruciate ligament (ACL) absent knee has a mean anterior laxity of 10 mm and a mean side-to-side difference of 5 mm. In a small group of patients with an intraarticular ACL substitution using the medial or lateral one-third of the patellar tendon, laxity and stiffness of the injured knees were returned to within the normal range and remained constant three years after surgery. In a group of 76 patients treated with ACL substitution using the torn meniscus, 51% of the patients still had an anterior laxity outside the normal range 3.5 years after surgery. In a preliminary study of 19 patients receiving a Gore-Tex synthetic ACL substitution, 55% of the patients still had a side-to-side difference greater than 2 mm two years after the procedure. These studies illustrate the advantages of impartial, objective measurements of knee stability. Laxity and stiffness values can supplement, but never replace, a thorough patient examination and patient history. As sports medicine matures as a scientific discipline, improved instrumented test devices may ultimately provide a standardized means for reporting knee stability parameters.     

Anterior-posterior stiffness and laxity of the knee after major ligament reconstruction

We recorded anterior-posterior force-versus-displacement curves at 20 and 90 degrees of flexion preoperatively and three years after major ligament reconstruction in patients with documented absence of the anterior cruciate ligament. Patients who had an extracapsular stabilization procedure alone showed no significant changes in laxity or stiffness of the injured knee in either position of flexion. Those who underwent reconstruction of the absent anterior cruciate ligament utilizing the middle or medial one-third of the patellar ligament in addition to the extracapsular procedure showed a significant decrease in anterior laxity and increase in anterior stiffness of the injured knee at 20 degrees of flexion. These changes in stability were not observed at 90 degrees of flexion. Six patients with a cruciate substitution had improved laxity and stiffness values at one year postoperatively which were unchanged at three years. At three-year follow-up the increases in activity scores, decreased feelings of giving-way and pain, and elimination of the pivot shift were comparable in both groups of patients.     

Objective anterior cruciate ligament testing

We examined subjects with the Stryker knee laxity tester as part of the clinical examination to determine its usefulness in evaluating the anterior cruciate ligament. We measured 123 athletes with no history of knee injury, as well as 30 patients with ACL injury proven by arthroscopy, and 11 injured patients with intact ACL at arthroscopy. We recorded anterior and posterior tibial displacement at 20 degrees of knee flexion and 20 lbs force in each direction. Anterior laxity and side to side difference correlated with ACL injury; posterior and total AP laxity did not. In normal subjects, mean anterior laxity was 2.5 mm. Only 8% of normal knees had anterior laxity of 5 mm or more. Ten percent of normal subjects had a side to side difference of 2 mm or more. In ACL tears, mean laxity was 8.1 mm, with 94% measuring 5 mm or more. Of the subjects, 89% with unilateral ACL injury had an increase of 2 mm or more on the injured side. Ten of ten acute ACL tears were detected by these criteria, with no false positives. In injured knees with intact ACL, measurements did not differ significantly from normal. We found the objective knee laxity measurement to be a useful complement to clinical knee examination.     

Three-dimensional instability of the anterior cruciate deficient knee

Using roentgen stereophotogrammetry we have recorded the three-dimensional movements of the knee during an anteroposterior laxity test in 36 patients with torn anterior cruciate ligaments and in three cadaver knees. At 30 degrees of knee flexion and before loads were applied the tibia occupied a more laterally rotated position if the anterior cruciate ligament had been injured. When the tibia was pulled anteriorly knees with cruciate deficiency rotated more laterally and were more abducted than normal knees. Posterior traction induced lateral rotation in the injured knee and medial rotation in the intact one. Precise knowledge of the three-dimensional instability of the anterior cruciate deficient knee may be important when the laxity is evaluated only in relation to one of the three cardinal axes.     

The late course of acute partial anterior cruciate ligament tears. A nine to 15-year follow-up evaluation.

Twenty-two patients had an acute anterior cruciate ligament (ACL) tear. Nineteen patients were treated conservatively, except for associated injuries. In three patients, a reinsertion of the torn portion of the ACL was done surgically. All patients were reexamined after nine to 15 years with special emphasis on stability testing; this was done manually and with instruments. Knee function score and activity level were also measured. Standing roentgenograms with the knee in slight flexion were taken as well. At follow-up examination, none of the patients had needed ACL reconstruction. Knee function was good, with a mean Lysholm score of 93 points. Patients had changed activities from recreational team sports to light individual sports. Manual laxity values were similar to the values obtained at the time of initial injury. A 1-mm sagittal laxity increase was found on the injured knee with the Stryker laxity tester. Slight signs for osteoarthrosis were found in more than half of the knees, mainly in cases with chondral fractures or meniscectomy. In general, conservative treatment had a good long-term prognosis.     

Measurement of anterior instability of the knee. A new apparatus for clinical testing

We have developed an apparatus to measure the anteroposterior stability of the knee to forces of up to 250 N, applied at 20 degrees of flexion. We measured anterior laxity at 200 N, anterior stiffness at 50 N and total laxity at +/- 200 N. A study of cadaveric knees revealed that the soft tissues surrounding the bones had a significant influence on the force-displacement curve, and emphasised that differences between injured and normal pairs of knees are much more important than the absolute values of the parameters. In 61 normal volunteers we found no significant left to right differences in anterior laxity at 200 N and anterior stiffness at 50 N. In 92 patients with unilateral anterior cruciate deficiency there were significant differences (p less than 0.0005) in anterior laxity, anterior stiffness and total laxity, the injured-normal differences averaging 6.7 mm, 1.3 N/mm, and 8.1 mm respectively.     

Functional medical ligament balancing in total knee arthroplasty

Function of the anterior and posterior oblique portions of the medial collateral ligament and the posterior capsule in flexion and extension was evaluated in eight knee specimens after posterior cruciate retaining total knee arthroplasty. The posterior oblique portion of the medial collateral ligament was released subperiosteally in four specimens, and the anterior portion was released in four specimens. The medial posterior capsule was released in each group, then the remaining portion of the medial collateral ligament was released. Release of the posterior oblique portion produced moderate laxity at full extension and at 30 degrees flexion, and posterior capsule release produced additional laxity in full extension. Release of the anterior portion produced major laxity at 60 degrees and 90 degrees flexion. Complete medial collateral ligament release increased laxity significantly in both groups in flexion and extension. This rationale was tested in a clinical study of 82 knees (76 patients) in which 62 (76%) required medial collateral ligament release to correct varus deformity during posterior cruciate retaining total knee arthroplasty. Twenty-two knees (35.5%) were tight medially in extension only, and were corrected by releasing the posterior oblique portion. Thirty-one knees (50%) were tight medially in flexion only, and were corrected by releasing the anterior portion. Nine knees (14.5%) were tight medially in flexion and extension and required complete medial collateral ligament release, but three knees (4.8%) remained tight in extension and required medial posterior capsule release to correct flexion contracture and medial ligament contracture. Seventeen (27%) had partial posterior cruciate ligament release to correct excessive rollback of the femoral component on the tibial surface.     

Arthroscopic medial meniscectomy on stable knees

We reviewed 74 partial medial meniscectomies in 57 patients with stable knees, to assess the long-term functional and radiological outcome. The International Knee Documentation Committee score and the residual laxity were assessed in both knees. At the time of surgery the mean age of the patients was 36 +/- 11 years and the mean follow-up was 12 +/- 1 years. All had a limited medial meniscectomy. The anterior cruciate ligament was intact in all cases. The meniscal tear was vertical in 95% and complex in 5%. The posterior part of the meniscus was removed in 99%. A peripheral rim was preserved in all cases. After 12 years 95% of the patients were satisfied or very satisfied with their knee(s). Objectively, 57% had grade A function and 43% were grade B. The outcome correlated only with the presence of anterior knee pain at final follow-up. In the 49 cases of arthroscopic meniscectomy for which there was a contralateral normal knee there was narrowing of the 'joint-space' in 16% of the operated knees. There was no correlation between this and other parameters such as age or different meniscal pathologies.     

MRI analysis of in vivo meniscal and tibiofemoral kinematics in ACL-deficient and normal knees.

The objectives of this study were to analyze simultaneously meniscal and tibiofemoral kinematics in healthy volunteers and anterior cruciate ligament (ACL)-deficient patients under axial load-bearing conditions using magnetic resonance imaging (MRI). Ten healthy volunteers and eight ACL-deficient patients were examined with a high-field, closed MRI system. For each group, both knees were imaged at full extension and partial flexion ( approximately 45 degrees ) with a 125N compressive load applied to the foot. Anteroposterior and medial/lateral femoral and meniscal translations were analyzed following three-dimensional, landmark-matching registration. Interobserver and intraobserver reproducibilities were less than 0.8 mm for femoral translation for image processing and data analysis. The position of the femur relative to the tibia in the ACL-deficient knee was 2.6 mm posterior to that of the contralateral, normal knee at extension. During flexion from 0 degrees to 45 degrees , the femur in ACL-deficient knees translated 4.3 mm anteriorly, whereas no significant translation occurred in uninjured knees. The contact area centroid on the tibia in ACL-deficient knees at extension was posterior to that of uninjured knees. Consequently, significantly less posterior translation of the contact centroid occurred in the medial tibial condyle in ACL-deficient knees during flexion. Meniscal translation, however, was nearly the same in both groups. Axial load-bearing MRI is a noninvasive and reproducible method for evaluating tibiofemoral and meniscal kinematics. The results demonstrated that ACL deficiency led to significant changes in bone kinematics, but negligible changes in the movement of the menisci. These results help explain the increased risk of meniscal tears and osteoarthritis in chronic ACL deficient knees.     

Instrumented testing for evaluation of sagittal knee laxity

Seventy-one patients with untreated ruptures of the anterior cruciate ligament of at least four years' duration had their knee laxity examined with a laxity testing device. Twenty of the 71 patients were tested by two examiners independently. Another 30 patients without previous knee injury were chosen as a reference group and tested. Patients with anterior cruciate-deficient knees had significantly increased anterior and total laxity. If the testing procedure was altered, the laxity changed. Thus, an increase of knee flexion from 15 degrees to 25 degrees resulted in an increased anterior laxity. Changes in the amount and placement of the tibial load also affected laxity. Inter-examiner reproducibility was high if a standardized testing procedure was followed. Sensitivity was 92% if the difference in total laxity between involved and uninvolved knees was determined with a high tibial load (180 N), whereas specificity was 70%. Therefore, the laxity tester has disadvantages as a diagnostic tool, but it is still valuable for evaluation of anterior cruciate ligament ruptures and their treatment.     

Radiographic analysis of low contact stress meniscal bearing total knee replacements

BACKGROUND: Meniscal bearing total knee replacements were developed to decrease the contact stresses on polyethylene and to reduce polyethylene wear. The kinematics of meniscal bearing knee replacements is poorly understood. The present study was designed to evaluate, with radiographic analyses, the motion of the meniscal bearings and the femoral rollback of the Low Contact Stress meniscal bearing knee replacement during knee flexion. METHODS: Eighty-one Low Contact Stress meniscal bearing total knee replacements in seventy-six male patients were assessed on fluoroscopically centered lateral radiographs made with the knee in full extension and in full flexion at an average of six years (range, twenty-four to 147 months) after the operation. The distance and direction of motion of the meniscal bearings and the center contact position of the femoral condyles were measured. Knee evaluations were performed with use of the Knee Society rating system. RESULTS: The average range of motion of the knees, measured on lateral radiographs, was 90 degrees (range, 45 degrees to 136 degrees). As they moved from terminal extension to terminal flexion, thirty-nine knees (48%) exhibited anterior motion of both bearings and sixteen (20%) demonstrated posterior motion of both bearings. Ten knees (12%) had reciprocal motion of the two bearings (one bearing moving anteriorly and one bearing moving posteriorly) with flexion, nine knees (11%) had motion of only one bearing, and seven knees (9%) had no motion of either bearing. When moving from full extension to full flexion, eighteen knees (22%) demonstrated femoral rollback, six knees (7%) showed no change in the position of femoral contact, and fifty-seven knees (70%) exhibited anterior sliding of the femoral condyles. Flexion of the knees demonstrating femoral rollback averaged 104 degrees (range, 76 degrees to 128 degrees), and flexion of the knees demonstrating anterior sliding averaged 94 degrees (range, 45 degrees to 125 degrees). The difference was significant (p = 0.03). According to the Knee Society rating system, the average clinical score for the entire group was 76 points (range, 27 to 100 points) and the average functional score for the entire group was 72 points (range, 30 to 100 points). The average clinical score was 79 points (range, 27 to 98 points) for the knees that exhibited anterior sliding of the femoral condyles and 87 points (range, 52 to 100 points) for those exhibiting femoral rollback (p = 0.09). The average functional scores were 64 points (range, 30 to 100 points) and 72 points (range, 45 to 100 points), respectively (p = 0.15). CONCLUSIONS: Radiographic analysis of meniscal bearing total knee replacements demonstrated an average anterior motion of both the medial and the lateral meniscal bearing of 4.7 mm (range, 1 to 14 mm) in thirty-nine knees (48%) as they moved from terminal extension to terminal flexion. Sixty-three knees (78%) demonstrated no femoral rollback as they were flexed. Knees with anterior sliding of the condyles had a significantly smaller average range of flexion (p = 0.03) and a lower average Knee Society score than did knees demonstrating femoral rollback. We believe that lack of rollback indicates a functional insufficiency of the posterior cruciate ligament.     

Importance of the medial meniscus in the anterior cruciate ligament-deficient knee.

The incidence of meniscal tears in the chronically anterior cruciate ligament-deficient knee is increased, particularly in the medial meniscus because it performs an important function in limiting knee motion. We evaluated the role of the medial meniscus in stabilizing the anterior cruciate ligament-deficient knee and hypothesized that the resultant force in the meniscus is significantly elevated in the anterior cruciate ligament-deficient knee. To test this hypothesis, we employed a robotic/universal force-moment sensor testing system to determine the increase in the resultant force in the human medial meniscus in response to an anterior tibial load following transection of the anterior cruciate ligament. We also measured changes in the kinematics of the knee in multiple degrees of freedom following medial meniscectomy in the anterior cruciate ligament-deficient knee. In response to a 134-N anterior tibial load, the resultant force in the medial meniscus of the anterior cruciate ligament-deficient knee increased significantly compared with that in the meniscus of the intact knee; it increased by a minimum of 10.1 N (52%) at full knee extension to a maximum of 50.2 N (197%) at 60 degrees of flexion. Medial meniscectomy in the anterior cruciate ligament-deficient knee also caused a significant increase in anterior tibial translation in response to the anterior tibial load, ranging from an increase of 2.2 mm at full knee extension to 5.8 mm at 60 degrees of flexion. Conversely, coupled internal tibial rotation in response to the load decreased significantly, ranging from a decrease of 2.5 degrees at 15 degrees of knee flexion to 4.7 degrees at 60 degrees of flexion. Our data confirm the hypothesis that the resultant force in the medial meniscus is significantly greater in the anterior cruciate ligament-deficient knee than in the intact knee when the knee is subjected to anterior tibial loads. This indicates that the demand on the medial meniscus in resisting anterior tibial loads is increased in the anterior cruciate ligament-deficient knee compared with in the intact knee, suggesting a mechanism for the increased incidence of medial meniscal tears observed in chronically anterior cruciate ligament-deficient patients. The large changes in kinematics due to medial meniscectomy in the anterior cruciate ligament-deficient knee confirm the important role of the medial meniscus in controlling knee stability. These findings suggest that the reduction of resultant force in the meniscus may be a further motive for reconstructing the anterior cruciate ligament, with the goal of preserving meniscal integrity.     

Incidence and mechanism of the pivot shift. An in vitro study.

The aim of this study was to determine the incidence and mechanism of the pivot shift phenomenon in the normal and anterior cruciate ligament transected knee in vitro. Fifteen knees were tested under a range of valgus moments and iliotibial tract tensions when intact and after anterior cruciate ligament transection. Knee kinematics were measured and described in terms of tibial rotation as the knee flexed. Eight knees pivoted after anterior cruciate ligament transection. The mean pivot shift motion was an external tibial rotation of 17 degrees (+/- 11 degrees standard deviation) over a range of 27 degrees (+/- 24 degrees) knee flexion, at a mean flexion angle of 56 degrees (+/- 27 degrees). Clinically, this corresponds to a reduction of an anteriorly subluxed lateral tibial plateau as the knee flexes. When intact, pivoting and nonpivoting knees had similar anteroposterior laxity, but after anterior cruciate ligament transection, the pivoting group had significantly greater laxity. The loading required to elicit the pivot shift was critical and variable between knees, which raises questions about comparing clinicians' techniques and results in assessing the buckling instability attributable to anterior cruciate ligament injury.     

Return of motion after simultaneous repair of displaced bucket-handle meniscal tears and anterior cruciate ligament reconstruction.

Patients with displaced bucket-handle (DBH) meniscal tears in anterior cruciate ligament (ACL)-deficient knees are prone to flexion contracture following meniscal repair and simultaneous ACL reconstruction. It has been suggested that ACL reconstruction be delayed until full range of motion has returned after the meniscal repair. A retrospective analysis was performed comparing the return of extension in patients undergoing simultaneous ACL reconstruction and repair of DBH tears (group A) versus a control group of patients with non-DBH tears (group B). Age, sex, body mass index, duration of time from injury to surgery, and preoperative extension were also compared between groups and evaluated for their significance as risk factors. Patients in group A achieved recovery to -5 degrees and 0 degrees of extension 22% and 35% more slowly, respectively, when compared with group B. These differences were not statistically significant. Female patients tended to heal more rapidly in both groups. We conclude that a one-stage procedure is sufficient in allowing patients with DBH tears in ACL-deficient knees to regain a functional knee to within 5 degrees of full extension.     

Primary repair plus intra-articular iliotibial band augmentation in the treatment of an acute anterior cruciate ligament rupture

Between September 1987 and November 1989, we treated 90 consecutive patients with an acute anterior cruciate ligament (ACL) rupture with the multiple suture technique and iliotibial band augmentation. Seventy of these patients were re-examined 2 to 5 years after the operation (mean 3.5 years), the examination consisting of a questionnaire, clinical examination, laxity tests with the KSS machine (Acufex), radiological examination and isokinetic muscle strength testing (Cybex 6000). There were 32 men and 38 women (mean age 34 years). The injury was sustained in sports in 44 (63%) cases, and the sports most frequently involved were downhill skiing (18 cases), soccer (9 cases) and volleyball (5 cases). Of the injuries, 38 were isolated ACL ruptures and 31, ACL ruptures combined with a medial CL rupture. In 9 cases, an additional meniscus injury and in one case an additional posterior CL - lateral CL rupture was found. At the follow-up, 55 patients (79%) were satisfied with the end result, and according to our objective functional criteria 55 (79%) had an excellent or good outcome. According to the Lysholm score, 53 (76%) patients were excellent or good ( 82 points). In the Lachman test, 29 knees (41%) were completely stable. The Lachman test was mildy positive in 40 knees (57%) (36 had 1+ laxity and 4, 2+ laxity), and one patient had 3+ laxity with a hard end-point. Similarly, the anterior drawer test was negative in 53 knees (76%); and the other 17 (24%) had mild laxity (16 had 1+ laxity and 1, 2+ laxity). The total anterior-posterior laxity measured with the KSS averaged 9.7 ± 3.5 mm in the injured knee and 7.3 + 3.0 mm in the uninjured knee (the laxity measured at a knee angle of 20° of flexion). Corresponding values at a knee angle of 90° of flexion were 6.1 ± 2.4 mm and 4.7 ± 1.9 mm, respectively. The pivot shift test was negative in 62 patients (89%) and l+ positive in the remaining 8 patients (11%). Fifty-eight patients (83%) had full knee extension and 40 patients (57%), full knee flexion. Compared with the uninjured knee, the operated knees showed an average 14% strength deficit in isokinetic knee extension and 6% deficit in flexion at the speed of 60°/s. At the speed of 180°/s, the corresponding deficits were 8% and 4%, respectively. Of the 44 patients who were active in sport before the injury, 40 (91%) were able to return to sports. A flexion deficit of 5° or more was associated with thigh muscle atrophy (P < 0.05) and quadriceps weakness, both at the slow speed (P < 0.05) and high speed (P < 0.001) of the isokinetic movement. In conclusion, in an acute rupture of the ACL, primary repair of the ligament with intraarticular iliotibial band augmentation seems to be a good method to restore the functional capacity of the injured knee.     

Instrumented measurements of laxity in patients who have a Gore-Tex anterior cruciate-ligament substitute

Twenty patients who had substitution of the anterior cruciate ligament with a Gore-Tex synthetic ligament were evaluated preoperatively and postoperatively with the University of California at Los Angeles instrumented clinical-testing apparatus, which records anterior-posterior force versus displacement-response curves of the tibia with respect to the femur at 20 degrees of flexion of the knee. The mean age of the patients was thirty-three years (range, nineteen to fifty-four years). The duration of follow-up ranged from twenty-four to forty-four months (mean, thirty-one months). The mean preoperative difference in anterior laxity between the injured knee and the normal knee (4.5 millimeters with neutral rotation of the foot) was unchanged two years after the operation; at that time, all patients had an anterior laxity of the injured knee of more than eight millimeters, and 90 per cent had a difference in anterior laxity of more than two millimeters between sides. The mean values for anterior stiffness at fifty and 100 newtons of anterior force were unchanged after the operation, remaining at 40 to 50 per cent of normal levels. At 200 newtons, or 20.4 kilograms (forty-five pounds) of anterior force, the mean stiffness of the involved knee was 11 to 17 per cent greater than that of the normal knee. Clinically, there were improvements in both subjective and objective knee-rating scores. All but four patients had a reduction of at least one grade in the pivot-shift score; in thirteen, the pivot-shift sign was eliminated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fifteen-year follow-up of arthroscopic partial meniscectomy

From an original pool of 283 patients, 146 patients who had undergone arthroscopic partial meniscectomy an average of 14.7 years before were followed-up. Lysholm score, Tegner activity level, satisfaction index on a scale of 1 to 10, and standing anteroposterior and flexion weight-bearing radiographs of both knees, were obtained. A physical examination was performed on each knee emphasizing motion, swelling, and ligament evaluation. Radiographs were graded for degenerative changes for each knee. Each knee joint space was also measured in millimeters and compared, operative knee with unoperated knee. The unoperated knee had no injuries or surgeries and was used as a control. Patients were 83% male and 17% female; 78% had undergone medial meniscectomies, 19% lateral, and 3% both. There were 88% good and excellent results in anterior cruciate liagment—stable knees. The radiographic grade side-to-side difference showed the operative knee to be only a 0.23 grade worse than the nonoperative knee. Age at the time of meniscectomy was not found to be a factor. Male patients had better radiographic results than female patients, but not better functional scores. Medial meniscus and lateral meniscus results were not significantly different. Knees with a femoral-tibial anatomic alignment of >0° valgus compared with ≤0° and that had undergone medial meniscectomy had significantly better radiographic results. Patients with anterior cruciate ligament tears and meniscectomy did significantly poorer than stable knees with meniscectomy in regards to radiographic grade change, Lysholm, satisfaction index, Tegner level, and medial joint space narrowing.     

Effect of tension and placement of a prosthetic anterior cruciate ligament on the anteroposterior laxity of the knee.

We wished to determine the optimal tension required to restore normal joint laxity to anterior cruciate ligament (ACL)-deficient knees using a braided polyethylene ACL prosthesis (PACL). In 10 cadaveric specimens, we measured the anteroposterior (AP) laxity of the intact knee at 10 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. The ACL was then removed and replaced with the PACL using tunnel-tunnel (T-T) and "over-the-top" (OTT) placement techniques. In both positions, the PACL was initially tensioned to 0, 9, 18, and 27 N with the knee flexed to 30 degrees. AP joint laxity was then measured at each flexion angle. With an increase in initial tension, there was a corresponding decrease in AP laxity. At 30 degrees and 90 degrees of flexion, AP laxity was not significantly different from normal using T-T placement and an initial tension of 0 N. At 90 degrees of flexion, AP laxity was not significantly different from normal using OTT placement at 0 or 9 N of initial tension. For both positions, all other tension levels and flexion angles constrained AP laxity. No laxity differences were detected between the OTT and T-T positions at any flexion angle. The variability in AP laxity of the T-T position was significantly greater than OTT. With a 150-N anterior shear force applied to the proximal tibia, the maximum tensions developed in the PACL were not significantly different between the two positions except at 90 degrees. The results suggest that implantation of the PACL is best performed using OTT positioning with an initial tension of 0 N applied at 30 degrees of knee flexion.     

Knee stability in posterior cruciate ligament retaining total knee arthroplasty

Anteroposterior knee laxity was evaluated in 14 patients (19 knees) who had posterior cruciate ligament retaining total knee arthroplasty using the Miller Galante I prosthesis. The followup ranged from 87 to 118 months (average, 105.9 months), and the measurements were done using the KT-2000 arthrometer. The mean anteroposterior displacement with the knees with Miller Galante I prostheses was 10.1 mm at 30 degrees flexion and 8.1 mm at 75 degrees flexion. In the 15 knees with Miller Galante I prostheses with flexion greater than 90 degrees, seven had less stability at 75 degrees than at 30 degrees flexion. These knees were considered to have a nonfunctional posterior cruciate ligament, and they had a worse Knee Society score (81.1) than did the other eight knees with Miller Galante I prostheses (89.9). There were four knees in which the flexion was less than 90 degrees. In this study, approximately half of the knees with posterior cruciate ligament retaining total knee arthroplasty did not have good anteroposterior stability in flexion an average of 9 years after surgery.     

Knee instability after injury to the anterior cruciate ligament. Quantification of the Lachman test

We have measured anterior and posterior displacement in 563 normal knees and 487 knees with chronic deficiency of the anterior cruciate ligament (ACL). We performed stress radiography using a simple apparatus which maintained the knee at 20 degrees of flexion while a 9 kg load was applied. There was no significant difference in posterior translation dependent on the condition of the ACL. Measurement of anterior translation in the medial compartment proved to be more reliable than in the lateral compartment for the diagnosis of rupture of the ACL, with better specificity, sensitivity and predictive values. We have classified anterior laxity based on the differential anterior translation of the medial compartment and identified four grades in each of which we can further distinguish four subgrades for laxity of the lateral compartment. Within each of these subgroups, either internal or external rotation may dominate and sometimes there is a major translation of both compartments. Radiological evaluation of displacement of the knee in 20 degrees of flexion provides conclusive evidence of rupture of the ACL. A detailed study of pathological displacement is the basis for a classification of laxity. It is then possible to decide for each type of laxity, the surgical treatment which is specifically adapted to the lesion, and to define a reference value for judging outcome.