Tibiofemoral kinematics of the anterior cruciate ligament (ACL)-deficient weightbearing, living knee employing vertical access open "interventional" multiple resonance imaging

BACKGROUND: Our current understanding of tibiofemoral kinematics in the anterior cruciate ligament (ACL)-deficient knee is very limited. Using vertical open-access MRI, it is possible to accurately analyze tibiofemoral motion in patients with isolated rupture of the ACL. STUDY: Prospective cohort study. PURPOSE: To assess if ACL rupture alters normal knee weightbearing kinematics. METHODS: Tibiofemoral motion was assessed through the arc of flexion from 0 degrees to 90 degrees in 10 patients with isolated rupture of the ACL in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. RESULTS: In the lateral compartment of the knee, the tibial plateau is persistently subluxed anteriorly throughout the arc of flexion from 0 degrees to 90 degrees (flexion facet center to posterior tibial cortex distance of 15.8 mm +/- 2.9 in ACL-deficient knees compared to 21.4 mm +/- 1.4 in normal knees at 0 degrees extension, P <.0001) when compared to normal knees. The medial tibiofemoral relationship is unchanged compared to normal knees. CONCLUSION: Rupture of the ACL changes tibiofemoral kinematics producing anterior subluxation of the lateral tibial plateau. CLINICAL SIGNIFICANCE: Altered kinematics may explain, at least in part, the increased incidence of secondary osteoarthritis in patients with ACL rupture.     

Tibiofemoral kinematics following successful anterior cruciate ligament reconstruction using dynamic multiple resonance imaging

BACKGROUND: The aim of anterior cruciate ligament reconstruction is to reduce excess joint laxity, hoping to restore normal tibiofemoral kinematics and therefore improve joint stability. It remains unclear if successful ACL reconstruction restores normal tibiofemoral kinematics and whether it is this that is associated with a good result. STUDY: Case series. PURPOSE: To assess the kinematics of the anterior cruciate ligament-reconstructed knee using open-access MRI. METHODS: Tibiofemoral motion was assessed using open-access MRI, weightbearing through the arc of flexion from 0 degrees to 90 degrees in 10 patients with isolated reconstruction of the anterior cruciate ligament (hamstring autograft) in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. Sagittal laxity was also assessed by performing the Lachman test while the knees were scanned dynamically using open-access MRI. RESULTS: The amount of excursion between the tibial and femoral joint surfaces was similar between the normal and reconstructed knees, but the relationship of tibia to femur was always different for each position of knee flexion assessed-the lateral tibia being about 5 mm more anterior in the anterior cruciate ligament-reconstructed knees. This anterior tibial position is statistically significantly different at 0 degrees (P <.0006), 20 degrees (P =.0004), 45 degrees (P =.002), and 90 degrees of flexion (P <.006). Anteroposterior laxity was similar between normal and anterior cruciate ligament-reconstructed knees. CONCLUSION: Anterior cruciate ligament reconstruction reduces sagittal laxity to within normal limits but does not restore normal tibiofemoral kinematics despite a successful outcome.     

In vivo kinematics of the knee after anterior cruciate ligament reconstruction: a clinical and functional evaluation

BACKGROUND: Recent follow-up studies have reported a high incidence of joint degeneration in patients with anterior cruciate ligament reconstruction. Abnormal kinematics after anterior cruciate ligament reconstruction have been thought to contribute to the degeneration. HYPOTHESIS: Anterior cruciate ligament reconstruction, which was designed to restore anterior knee laxity under anterior tibial loads, does not reproduce knee kinematics under in vivo physiological loading conditions. STUDY DESIGN: Controlled laboratory study. METHODS: Both knees of 7 patients with complete unilateral rupture of the anterior cruciate ligament were magnetic resonance imaged, and 3D models were constructed from these images. The anterior cruciate ligament of the injured knee was arthroscopically reconstructed using a bone-patellar tendon-bone autograft. Three months after surgery, the kinematics of the intact contralateral and reconstructed knees were measured using a dual-orthogonal fluoroscopic system while the subjects performed a single-legged weightbearing lunge. The anterior laxity of both knees was measured using a KT-1000 arthrometer. RESULTS: The anterior laxity of the reconstructed knee as measured with the arthrometer was similar to that of the intact contralateral knee. However, under weightbearing conditions, there was a statistically significant increase in anterior translation of the reconstructed knee compared with the intact knee at full extension (approximately 2.9 mm) and 15 degrees (approximately 2.2 mm) of flexion. In addition, there was a mean increase in external tibial rotation of the anterior cruciate ligament-reconstructed knee beyond 30 degrees of flexion (approximately 2 degrees at 30 degrees of flexion), although no statistical significance was detected. CONCLUSION: The data demonstrate that although anterior laxity was restored during KT-1000 arthrometer testing, anterior cruciate ligament reconstruction did not restore normal knee kinematics under weightbearing loading conditions. CLINICAL RELEVANCE: Future reconstruction techniques should aim to restore function of the knee under physiological loading conditions.     

The biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads

BACKGROUND: The effectiveness of posterior cruciate ligament reconstruction in restoring normal kinematics under physiologic loading is unknown. HYPOTHESIS: Posterior cruciate ligament reconstruction does not restore normal knee kinematics under muscle loading. STUDY DESIGN: In vitro biomechanical study. METHODS: Kinematics of knees with an intact, resected, and reconstructed posterior cruciate ligament were measured by a robotic testing system under simulated muscle loads. Anteroposterior tibial translation and internal-external tibial rotation were measured at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under posterior drawer loading, quadriceps muscle loading, and combined quadriceps and hamstring muscle loading. RESULTS: Reconstruction reduced the additional posterior tibial translation caused by ligament deficiency at all flexion angles tested under posterior drawer loading. Ligament deficiency increased external rotation and posterior translation at angles higher than 60 degrees of flexion when simulated muscle loading was applied. Posterior cruciate ligament reconstruction reduced the posterior translation and external rotation observed in posterior cruciate ligament-deficient knees at higher flexion angles, but differences were not significant. CONCLUSION: Under physiologic loading conditions, posterior cruciate ligament reconstruction does not restore six degree of freedom knee kinematics. Clinical Relevance: Abnormal knee kinematics may lead to development of long-term knee arthrosis.     

Dynamic instability during stair descent in isolated PCL-deficient knees: what affects abnormal posterior translation of the tibia in PCL-deficient knees?

Posterior cruciate ligament (PCL)-deficient patients usually display few functional disabilities during activities of daily living (ADL), even in the presence of significant objective knee laxity. This suggests that the magnitude of posterior instability occurring in ADL (dynamic instability) does not parallel the knee laxity detected in clinical examinations. The present study analyzed kinematics of the knee joint during stair descent in 14 isolated PCL-deficient patients and ten healthy volunteers using fluoroscopy. Factors influencing dynamic instability were investigated. In addition, magnitude of posterior tibial translation occurring during stair descent was measured and compared with static knee laxity measured on posterior stress radiography. Increased posterior tibial translation was observed in early swing phase (52.5 ± 5.6%) in PCL-deficient knees compared with normal knees (48.2 ± 8.6%). Almost the same magnitude of posterior instability was observed at early swing phase during stair descent using fluoroscopy and on posterior stress radiography. These results indicate that in PCL-deficient patients, posterior instability does not occur when weight is loaded onto the knee, but occurs when weight-bearing is released during stair descent.     

Anatomical posterior cruciate ligament transplantation: a biomechanical analysis

BACKGROUND: Although current techniques of posterior cruciate ligament reconstruction may successfully stabilize the posterior cruciate ligament-deficient knee, no studies have demonstrated restoration of intact-knee kinematics. HYPOTHESIS: Posterior cruciate ligament transplantation will successfully restore posterior stability and kinematics to the posterior cruciate ligament-deficient knee. STUDY DESIGN: Controlled laboratory study. METHODS: Seven pairs (donor/recipient) of size-matched cadaveric knees underwent a novel technique for posterior cruciate ligament transplantation. The grafts were fixed at the femoral origin and tibial insertion using an inlay technique with rigid fixation. The knees were tested in the intact (intact group), posterior cruciate ligament-deficient (deficient group), and posterior cruciate ligament-transplanted (transplant group) states. A 3-dimensional electromagnetic tracking system during an active knee extension and passive knee flexion maneuver was used to quantify kinematics, specifically looking at femoral rollback. KT ligament arthrometry was used to quantify posterior stability at the quadriceps neutral angle (70 degrees ). RESULTS: For femoral rollback, the intact versus deficient groups was significantly different (P = .045) as was deficient versus transplant groups (P = .008) but not intact versus transplant groups. Similar differences were noted with the measurements of posterior stability (P < .001). Total posterior laxity between the intact versus deficient groups was significantly different (means, 1.32 mm vs 11.1 mm; P < .0001), as was deficient versus transplant groups (means, 11.1 mm vs 2.04 mm; P < .126) but not intact versus transplant groups. CONCLUSION: In a posterior cruciate ligament-deficient cadaveric model, we demonstrated the technical feasibility and efficacy of posterior cruciate ligament transplantation for restoring femoral rollback and posterior stability at the quadriceps neutral angle. CLINICAL RELEVANCE: Future studies in posterior cruciate ligament reconstruction should not only address stability but also restoration of normal knee kinematics in assessing the success of a given technique.     

Kinematics of the posterior cruciate ligament/posterolateral corner-injured knee after reconstruction by single- and double-bundle intra-articular grafts

BACKGROUND: Single- and double-bundle reconstructions have been proposed for the knee after combined posterior cruciate ligament/posterolateral corner injuries. HYPOTHESIS: The double-bundle posterior cruciate ligament reconstruction is superior to the single-bundle posterior cruciate ligament reconstruction with regard to restoration of normal knee kinematics to the posterior cruciate ligament/posterolateral corner-sectioned knee. STUDY DESIGN: Controlled laboratory study. METHODS: Kinematics of 8 fresh-frozen, cadaveric human knees were determined in the following conditions: intact, sectioned posterior cruciate ligament/posterolateral corner, single anterolateral bundle posterior cruciate reconstruction, and double-bundle posterior cruciate reconstruction. RESULTS: The sectioned knee demonstrated a posterior shift of the tibial neutral position and the abnormal posterior, varus, and external rotation laxities used clinically to define a combined posterior cruciate ligament/posterolateral corner injury. Both reconstructions restored the posterior laxity to levels that were not statistically different from those seen in the intact knee, but the double-bundle reconstruction more closely mimicked the posterior laxity profile of the intact knee, having statistically lower posterior laxities than did the single-bundle reconstruction at 30 degrees, 60 degrees, and 90 degrees of flexion (P < .05, analysis of variance, HSD test). The resting position of the tibia after double-bundle reconstruction trended to be anteriorly subluxated relative to its position for the intact knee at flexion angles of 30 degrees and greater (P <.05, paired t test). Neither technique corrected the abnormal varus or external rotation laxities. CONCLUSION: With either single- or double-bundle reconstructions, additional posterolateral reconstruction is recommended to correct the external rotation laxity. CLINICAL RELEVANCE: Knowledge of the kinematics of the combined posterior cruciate ligament/posterolateral corner-injured knee is important in the proper diagnosis of the injury and in the selection of the appropriate surgical reconstruction.     

The effect of posterior cruciate ligament reconstruction on patellofemoral contact pressures in the knee joint under simulated muscle loads

BACKGROUND: The mechanism of cartilage degeneration in the patellofemoral joint (PFJ) and medial compartment of the knee following posterior cruciate ligament (PCL) injury remains unclear. PCL reconstruction has been recommended to restore kinematics and prevent long-term degeneration. The effect of current reconstruction techniques on PFJ contact pressures is unknown. PURPOSE: To measure PFJ contact pressures after PCL deficiency and reconstruction. METHOD: Eight cadaveric knees were tested with the PCL intact, deficient, and reconstructed. Contact pressures were measured at 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under simulated muscle loads. Knee kinematics were measured by a robotic testing system, and the PFJ contact pressures were measured using a thin film transducer. A single bundle achilles tendon allograft was used in the reconstruction. RESULTS: PCL deficiency significantly increased the peak contact pressures measured in the PFJ relative to the intact knee under both an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Reconstruction did not significantly reduce the increased contact pressures observed in the PCL-deficient knee. CONCLUSION: The elevated contact pressures observed in the PCL-deficient knee and reconstructed knee might contribute to the long-term degeneration observed in both the non-operatively treated and PCL-reconstructed knees.     

A biomechanical analysis of joint contact forces in the posterior cruciate deficient knee

The approach to the posterior cruciate deficient knee is controversial. The purpose of this study is to document the biomechanical changes in the static cadaveric knee model with simulated physiological loads. Nine fresh cadaveric knees from young donors (aged under 45 years) were mounted on a materials testing machine. Loading was carried out at 0°, 30° and 60° to 1.5 kN with low-pressure sensitive Prescale film (Fuji; Tokyo, Japan) inserted through arthrotomies into the medial and lateral compartments. Computerized analysis of the imprints on the film was then carried out. Tests were then repeated after cutting the posterior cruciate ligament (PCL). Results demonstrate a statistically significant posterior subluxation of the tibia on the femur at 60° flexion. This causes a significant increase in contact pressure and pressure concentration on the medial compartment of the knee after cutting the PCL. This may help explain the long-term degenerative changes observed in the medial femoral condyle after cutting the PCL.     

A comparison of modified Larson and ‘anatomic’ posterolateral corner reconstructions in knees with combined PCL and posterolateral corner deficiency

Different methods to reconstruct damaged posterolateral structures are available, but there has been little work studying their relative performance in combined PCL plus posterolateral corner (PLC) deficiency. We hypothesized that an ‘anatomic’ reconstruction with three graft bundles crossing the joint line would restore knee laxity closer to normal than a modified two-bundle Larson reconstruction. In a controlled laboratory study, the kinematics of cadaveric knees were measured electromagnetically with posterior drawer, external rotation, or varus rotation loads applied, with the knee at sequential stages: intact, PCL-deficient; PCL plus PLC-deficient; modified Larson reconstruction; anatomic PLC reconstruction. The graft bundles were tensioned sequentially to restore specific degrees of freedom to intact values of laxity at specific angles of knee flexion. A significant difference was not found between the two reconstructions. Both reconstructions restored external rotation and varus laxity to normal. Both restored posterior drawer to that caused by isolated PCL deficiency, but did not restore posterior laxity to normal. It was concluded that, with appropriate graft tensioning, both PLC reconstructions could restore both external rotation and varus laxity to normal, but not posterior drawer. The three-stranded anatomical reconstruction did not perform better than the modified two-strand Larson technique. Both of these isolated PLC reconstructions in knees with combined PCL plus PLC deficiency restored the knees to the laxity condition of an isolated PCL-deficiency, they could not reduce posterior drawer to normal.     

Posterior cruciate ligament recess and normal posterior capsular insertional anatomy: MR imaging of cadaveric knees

PURPOSE: To analyze the normal pattern of fluid accumulation adjacent to the posterior cruciate ligament and anatomic variations of joint capsule insertion sites in the posterosuperior corner of the human knee by using magnetic resonance (MR) imaging in cadaveric specimens. MATERIALS AND METHODS: Fourteen fresh cadaveric knees (obtained and used according to institutional guidelines, with informed consent from relatives of the deceased) from 11 men and three women (six left knees, eight right knees; age range, 70-82 years at time of death; mean age, 76 years +/- 4.4 [standard deviation]) were studied with high-spatial-resolution MR imaging performed before and after intraarticular injection of 35-45 mL gadopentetate dimeglumine. MR images were evaluated by two readers in consensus, with emphasis on location of fluid posterior to the posterior cruciate ligament, communication of that fluid with the medial or lateral compartment of the knee, and the relation of fluid to surrounding structures. Readers also were asked to measure, in the sagittal plane, the distance between the posterior capsular insertion sites and the femoral physeal scar. For anatomic analysis, cadaveric specimens were sectioned in 3-mm-thick slices in the sagittal plane that approximated the sections acquired at MR imaging. RESULTS: In all 14 cadaveric specimens, MR arthrographic images showed a fluid collection behind the posterior cruciate ligament (in the posterior cruciate ligament recess), a finding not evident on images obtained prior to contrast material injection. The recess was distended during flexion, and it communicated only with the medial femorotibial compartment in all cases. Posterior to the posterior cruciate ligament recess, a fat pad was observed in all specimens. Incomplete joint capsule was seen behind the fat pad in seven specimens. Joint capsule insertion was at the level of the femoral physeal scar or between it and a point 15 mm above it. CONCLUSION: The posterior cruciate ligament recess has specific characteristics that allow its identification: communication with the medial compartment of the knee and absence of the adjacent joint capsule.     

In vivo function of the posterior cruciate ligament during weightbearing knee flexion

BACKGROUND: Current knowledge of posterior cruciate ligament function is mainly based on in vitro cadaveric studies. There are few studies on the in vivo function of the posterior cruciate ligament. The objective of the study was to quantify the multidimensional deformation of the posterior cruciate ligament. HYPOTHESIS: During in vivo weightbearing flexion, the posterior cruciate ligament undergoes complex 3-dimensional deformations, including elongation, twist, and changes in orientation. STUDY DESIGN: In vivo biomechanical study. METHODS: Magnetic resonance images of 5 human knees were used to create 3-dimensional computer models of each subject's knee, including the insertion areas of the posterior cruciate ligament. Orthogonal fluoroscopic images of each subject's knee were acquired as a quasi-static lunge was performed. The images and computer models were used to reproduce the in vivo motion of the knee. The relative motion of the femoral and tibial insertions was described in terms of elongation, twist, elevation (the angle between the tibial plateau and posterior cruciate ligament, measured in the sagittal plane), and deviation (mediolateral orientation, measured in plane of tibial plateau). RESULTS: The length of the posterior cruciate ligament increased significantly with increasing flexion. It twisted almost 80 degrees as the knee flexed from 0 degrees to 90 degrees . The elevation angle remained relatively constant at 50 degrees . The deviation angle was medially oriented by 20 degrees at full extension, then decreased to approximately 10 degrees at 30 degrees through 90 degrees of flexion. CONCLUSION: The posterior cruciate ligament undergoes a complex twisting motion as it elongates with flexion. CLINICAL RELEVANCE: During reconstruction, the tunnels and graft may need to be placed such that the multidimensional deformation of the intact posterior cruciate ligament is reproduced.     

Anatomic reconstruction of the posterior cruciate ligament after multiligament knee injuries. A combination of the tibial-inlay and two-femoral-tunnel techniques

BACKGROUND: Neither operative nor nonoperative treatment of posterior cruciate ligament rupture after multiligament knee injuries have shown very favorable outcomes. HYPOTHESIS: Reconstruction of the posterior cruciate ligament by combining the tibial-inlay and two-femoral-tunnel techniques will result in improved stability and functional outcomes. STUDY DESIGN: Prospective cohort study. METHODS: Twenty-nine patients with 30 posterior cruciate ligament ruptures and multiligament knee injuries treated with the combined technique were evaluated with clinical, radiographic, and functional outcome measures. RESULTS: All patients had a clinical examination result indicating joint stability (0 or 1+) at an average follow-up of 25 months (range, 15 to 39). Twenty-three knees had no laxity, and seven had 1+ laxity. The KT-2000 arthrometer data documented less than 0.5 mm of side-to-side mean difference for both posterior displacement and total anterior-posterior displacement at both 30 degrees and 70 degrees of knee flexion. Knee range of motion was a mean extension of 1 degrees (range, 0 degrees to 10 degrees ) and a mean flexion of 124 degrees (range, 75 degrees to 145 degrees ). Mean Lysholm knee score was 89.4. CONCLUSIONS: Reconstruction with a combination tibial-inlay and two-femoral-tunnel technique provides good results after multiligament knee injuries. All patients had a stable posterior cruciate ligament at most recent clinical follow-up, and 77% had no laxity at all.     

The effect of anterior cruciate ligament reconstruction on knee joint kinematics under simulated muscle loads

BACKGROUND: Numerous studies have investigated anterior stability of the knee during the anterior drawer test after anterior cruciate ligament reconstruction. Few studies have evaluated anterior cruciate ligament reconstruction under physiological loads. PURPOSE: To determine whether anterior cruciate ligament reconstruction reproduced knee motion under simulated muscle loads. STUDY DESIGN: Controlled laboratory study. METHODS: Eight human cadaveric knees were tested with the anterior cruciate ligament intact, transected, and reconstructed (using a bone-patellar tendon-bone graft) on a robotic testing system. Tibial translation and rotation were measured at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion under anterior drawer loading (130 N), quadriceps muscle loading (400 N), and combined quadriceps and hamstring muscle loading (400 N and 200 N, respectively). Repeated-measures analysis of variance and the Student-Newman-Keuls test were used to detect statistically significant differences between knee states. RESULTS: Anterior cruciate ligament reconstruction resulted in a clinically satisfactory anterior tibial translation. The anterior tibial translation of the reconstructed knee was 1.93 mm larger than the intact knee at 30 degrees of flexion under anterior load. Anterior cruciate ligament reconstruction overconstrained tibial rotation, causing significantly less internal tibial rotation in the reconstructed knee at low flexion angles (0 degrees-30 degrees) under muscle loads (P < .05). At 30 degrees of flexion, under muscle loads, the tibia of the reconstructed knee was 1.9 degrees externally rotated compared to the intact knee. CONCLUSIONS: Anterior cruciate ligament reconstruction may not restore the rotational kinematics of the intact knee under muscle loads, even though anterior tibial translation was restored to a clinically satisfactory level under anterior drawer loads. These data suggest that reproducing anterior stability under anterior tibial loads may not ensure that knee joint kinematics is restored under physiological loading conditions. CLINICAL RELEVANCE: Decreased internal rotation of the knee after anterior cruciate ligament reconstruction may lead to increased patellofemoral joint contact pressures. Future anterior cruciate ligament reconstruction techniques should aim at restoring 3-dimensional knee kinematics under physiological loads.     

Measurement of posterior tibial translation in the posterior cruciate ligament-reconstructed knee: significance of the shift in the reference position

BACKGROUND: The measurement of anterior or posterior tibial translation depends on the existence of a repeatable and accurate reference position of the knee from which the corresponding translation is measured. HYPOTHESIS: Clinical measurements of posterior tibial translation alone do not accurately reflect the laxity of posterior cruciate ligament-reconstructed knees. STUDY DESIGN: Controlled laboratory study. METHODS: Ten human cadaveric knees were tested by using a robotic/universal force-moment sensor testing system. The reference positions and the resulting kinematics in response to a 134-N anterior-posterior tibial load were determined for the intact and reconstructed knees. Posterior cruciate ligament reconstruction was performed with the graft tensioned and fixed at two different positions: 1) 90 degrees of knee flexion with a 134-N anterior tibial load and 2) full extension with no load. RESULTS: Posterior cruciate ligament reconstruction with graft fixation at full extension with no load resulted in anterior shift of the reference position by 1.5 to 3.2 mm. The reconstruction resulted in an overconstrained knee with significantly decreased total anterior-posterior translation of 2.6 to 3.2 mm. However, the posterior tibial translation measured was not significantly different from that of the intact knee. Posterior cruciate ligament reconstruction with graft fixation performed at 90 degrees of flexion with a 134-N anterior tibial load resulted in kinematics similar to those of the intact knee. CONCLUSION: Posterior tibial translations that are measured clinically can be misleading because the reference position of the knee can be shifted significantly after posterior cruciate ligament reconstruction. Clinical Relevance: The measurement of total anterior-posterior translation may be a more accurate way to assess kinematics of the reconstructed knee.     

Intraarticular anterior cruciate ligament graft placement on the average most isometric line on the femur. Does it reproducibly restore knee kinematics?

In the past, there has been a plausible hypothesis that anterior cruciate ligament graft placement at isometric sites, such that the tibial and femoral attachment sites remain equidistant from each other throughout knee range of motion, would increase the likelihood of a satisfactory outcome. For a given tibial placement we wanted to determine whether placing the graft on the average of the most isometric femoral line, a fixed distance from the outlet of the intercondylar notch, would return normal laxity to all knees. The three-dimensional kinematics of seven cadaveric knees were measured for angles from full extension to 90 degrees of flexion at 15 degrees increments. Physiologic levels of quadriceps muscle forces were applied to the intact knee, after transection of the anterior cruciate ligament, and after ligament reconstruction with a patellar tendon graft. On average, the reconstruction was found to return anterior-posterior translation, internal-external rotation, and varus-valgus rotation to levels not significantly different from those of the intact knee. However, the ranges of the translation and rotations were large. Placing the graft on the average most isometric femoral line did not restore knee laxity to normal in all knees. This supports the need to customize graft placement in each knee at the time of surgery.     

Injuries to the posterior cruciate ligament of the knee

The posterior cruciate ligament (PCL) is the strongest ligament about the knee and is approximately twice as strong as the anterior cruciate ligament. Its main function is to prevent the posterior dislocation of the tibia in relation to the femur, providing 95% of the strength to resist the tibial posterior displacement. Along with the anterior cruciate ligament (ACL) the PCL controls the passive 'screw home' mechanism of the knee in terminal knee extension. It also provides mechanical support for the collateral ligaments during valgus or varus stress of the knee. PCL ruptures are uncommon apparently due to its strong fibre structure. The most frequent injury mechanism in isolated PCL tears is a direct blow on the anterior tibia with the knee flexed thus driving the tibia posteriorly. Automobile accidents (in which the knee hits the dashboard) and soccer injuries (in which an athlete receives a blow to the anterior surface of the tibia during knee flexion) characteristically produce this type of injury. In other PCL injury mechanisms (hyperextension, hyperflexion or rotational injuries with associated valgum/varum stress), other knee structures are also often damaged. The most characteristic diagnostic finding in a knee with a PCL rupture is the 'posterior sag sign' meaning the apparent disappearance of the tibial tubercle in lateral inspection when the knee is flexed 90 degrees. This is due to gravity-assisted posterior displacement of the tibia in relation to the femur. A positive posterior drawer test performed at 90 degrees of flexion and a knee hyperextension sign are sensitive but nonspecific tests. False negative findings are frequent, especially in acute cases. If necessary, the clinical diagnosis of the PCL tear can be verified by magnetic resonance imaging, examination under anaesthesia, arthroscopy, or a combination of these modalities. If a PCL avulsion fragment has been dislocated, surgical treatment is recommended. In isolated, complete midsubstance tears of the PCL the majority of the recent studies recommend conservative treatment, since abnormal residual posterior laxity1 in most of these knees is consistent with functional stability and minimal symptoms. This has been the case even in athletes. In isolated PCL tears, the outcome seems to depend more on the muscular (quadriceps) status of the knee than on the amount of residual posterior laxity. Therefore, the conservative treatment protocol emphasises intensive quadriceps exercises, and only a short (under 2 weeks) immobilisation period followed by early controlled activities and early weightbearing.(ABSTRACT TRUNCATED AT 400 WORDS)     

Kinematics and laxity of the knee joint after anterior cruciate ligament reconstruction: pre- and postoperative radiostereometric studies

BACKGROUND: Injury of the anterior cruciate ligament changes the kinematics of the knee joint. In studies of cadaveric knees, investigators have examined the effect of anterior cruciate ligament reconstruction on knee kinematics, but the effect on dynamic knee motion is not known. HYPOTHESIS: Reconstruction of the anterior cruciate ligament restores knee kinematics to normal. STUDY DESIGN: Prospective cohort study. METHODS: Nine patients were examined preoperatively and 1 year after reconstruction. Continuous radiostereometric exposures were performed at a speed of two to four exposures per second while the patients ascended an 8-cm high platform. Tibial rotation and tibial and femoral translation were measured with radiostereometric analysis. RESULTS: Tibial rotation and tibial and femoral translation were not significantly different after anterior cruciate ligament reconstruction compared with preoperative measurements. A radiostereometric evaluation of anterior knee laxity revealed restoration to within 1 mm of that on the uninjured side. Further evaluation of knee function using the Lysholm score, the Tegner activity level score, the International Knee Documentation Committee evaluation system score, and measurements of laxity using the KT-1000 arthrometer revealed significant improvements after reconstruction. CONCLUSION: Kinematics of the anterior cruciate ligament injured knee did not change significantly after ligament reconstruction, but the functional results were satisfactory and knee laxity was diminished.     

The role of the medial collateral ligament and posteromedial capsule in controlling knee laxity

BACKGROUND: The medial aspect of the knee has a complex capsular structure; the biomechanical roles of specific structures are not well understood. HYPOTHESIS: The 3 strong stabilizing structures, the superficial and deep medial collateral ligaments and the posteromedial capsule, make distinct contributions to controlling tibiofemoral laxity. STUDY DESIGN: Controlled laboratory study. METHODS: Changes in knee laxity under anterior-posterior drawer, valgus, and internal-external rotation loads were found by sequential cutting in 18 cadaveric knees. Three cutting sequences allowed the roles of the 3 structures to be seen in isolation and in combination. Some force contributions were also calculated. RESULTS: The posteromedial capsule controlled valgus, internal rotation, and posterior drawer in extension, resisting 42% of a 150-N drawer force when the tibia was in internal rotation. The superficial collateral ligament controlled valgus at all angles and was dominant from 30 degrees to 90 degrees of flexion, plus internal rotation in flexion. The deep collateral ligament controlled tibial anterior drawer of the flexed and externally rotated knee and was a secondary restraint to valgus. CONCLUSION: Distinct roles in controlling tibiofemoral laxity have been found for these structures that vary according to knee flexion and tibial rotation. CLINICAL RELEVANCE: The restraining functions demonstrated provide new information about knee stabilization, which may allow better evaluation of structural damage at the medial aspect of the knee.     

Comparing in vivo kinematics of unicondylar and bi-unicondylar knee replacements

Preserving both cruciate ligaments in unicondylar knee arthroplasty likely provides more normal knee mechanics and contributes to enhanced patient function. It follows that preserving both cruciate ligaments with total knee arthroplasty should provide functional benefit compared to arthroplasty sacrificing one or both cruciates. The purpose of this study was to compare knee kinematics in patients with optimally functioning cruciate-preserving medial unicondylar and bi-unicondylar arthroplasty to determine if knee motions differed. Eight consenting patients with seven medial unicondylar and five bi-unicondylar arthroplasties were studied using lateral fluoroscopy during treadmill gait, stair stepping, and maximum flexion activities. Patient-specific geometric models based on CT and CAD data were used for shape matching to determine the three-dimensional knee kinematics. Tibiofemoral contact locations were computed for the replaced compartments. Maximum flexion in kneeling was 135°±14° for unicondylar knees and 123°±14° for bi-unicondylar knees (p=0.22). For 0°–30° flexion during the stair activity, the medial condyle translated posterior 3.5±2.5 mm in unicondylar knees and 4.7±1.9 mm in bi-unicondylar knees (p>0.05). Lateral posterior translation was 5.0±2.3 mm in bi-unicondylar knees for 0°–30° flexion. From heel-strike to mid-stance phase, there was little tibial rotation, but unicondylar knees showed 1.5±1.6 mm posterior translation of the medial condyle, while bi-unicondylar knees showed 5.1±2.2 mm (p<<0.05). The bi-unicondylar knees showed 3.8±3.4 mm posterior lateral condylar translation. Preserving both cruciate ligaments in knee arthroplasty appears to maintain some basic features of normal knee kinematics. Knees with bi-unicondylar arthroplasty showed kinematics closer to motions observed in total knee arthroplasty, slightly less weight-bearing flexion, and greater dynamic laxity in gait than unicondylar knees. Despite kinematic differences, knees with unicondylar and bi-unicondylar arthroplasty can provide excellent functional outcomes in appropriately selected patients.