Posterior instability near extension is related to clinical disability in isolated posterior cruciate ligament deficient patients

The purpose of this study is to evaluate the relationship between the magnitude of knee laxity and posterior instability at different knee flexion angles and clinical disability in isolated posterior cruciate ligament (PCL) deficient patients. Knee laxity at 20° and 70° of knee flexion were evaluated using KT-2000 arthrometer, and the posterior instability at 20°, 45° and 90° of flexion were evaluated using stress radiography. We assessed the differences in the knee laxity and the tibial translation between isolated PCL deficient knees and normal knees, and between the patients with giving-way during activities of daily living (ADL) and without giving-way. There were statistical differences in the knee laxity and the tibial translation at all knee flexion angles between the PCL deficient knees and normal knees. The magnitude of the knee laxity at 20° of flexion measured with KT-2000 arthrometer was significantly larger in the patients with giving-way than those in the patients without giving-way although there was no significant difference in the tibial translation at 70° between the two groups. The tibial translation in both medial and lateral compartments at 20° and 45° measured with stress radiography were significantly larger in the patients with giving-way than those in the patients without giving-way although there was not significant difference at 90° between the two groups. These results suggested that the magnitude of the knee laxity and the posterior tibial translation at shallow knee flexion angles would be related to giving-way during ADL in isolated PCL deficient patients.     

Anatomic double-bundle ACL reconstruction restricts knee extension in knees with hyperextension

Purpose

Double-bundle ACL reconstruction has been demonstrated to be at least as effective as single-bundle reconstruction in terms of restoring knee rotational and translational stability. Until now, the influence on knees with hyperextension has not been evaluated. It was the purpose of this study to evaluate whether double-bundle ACL reconstruction restricts extension in hyperextendable knees.

Methods

Hamstring tendon reconstructions of 10 human cadaveric knees with the ability of hyperextension (age: 48 ± 14 years) were performed as single bundle (SB) on one side and double bundle (DB) on the other side. A surgical navigation system (BrainLab, Germany) was used to assess the kinematics of each knee at the intact and reconstructed state. A difference with regard to the anterior-to-posterior translation (AP) and rotational stability at 30° of knee flexion, 90° of flexion and the hyperextension capability of each specimen was analysed.

Results

The difference in AP translation before and after the reconstruction was not significantly different in 30° and 90° of flexion (n.s). Both single- and double-bundle reconstructions restored the preoperative kinematics at 30° and 90° of knee flexion (n.s). The knee extension was 4° ± 1.8° with the intact ACL and 4° ± 1.7° after reconstruction in the SB group (n.s). The knee extension was 5° of hyperextension ± 1.1° with the intact ACL and 0° ± 0.4° after reconstruction in the DB group; the limitation of the extension was significantly larger in this group (p = 0.013).

Conclusion

Both single- and double-bundle ACL reconstruction techniques are capable of restoring knee anteroposterior and rotational stability. Double-bundle reconstructions significantly reduce knee extension in knees with hyperextension capability. Care must be taken when using double-bundle techniques in patients with knee hyperextension as this procedure may limit the knee extension after double-bundle ACL reconstruction.     

Comparison of stability and kinematics of the natural knee versus a PS TKA with a ‘third condyle’

Purpose

The goal of this study was to compare the kinematics of knees before and after total knee arthroplasty (TKA) that relies on an inter-condylar ‘third condyle’. The hypothesis was that the ‘third condyle’ provides sufficient flexion stability and induces a close to normal femoral rollback, thus granting natural joint kinematics.

Methods

Intra-operative navigation data were collected from 29 consecutive cases that received a cemented TKA (HLS Noetos, Tornier SA, France) designed with an inter-condylar ‘third condyle’ that engages within the tibial insert beyond 35° flexion. Operations were guided by a non-image-based system (BLU-IGS, Orthokey Italia srl, Italy) that recorded relative femoral and tibial positions in native and implanted knees during: passive range of motion, anterior drawer test at 90° flexion, and varus–valgus stress tests at full extension and at 30° flexion.

Results

The total internal tibial rotation during flexion was similar for native (8.2 ± 4.2°) and implanted knees (8.0 ± 5.4°). The lateral femoral condyle was more posterior in implanted knees (1.2 ± 9.4 mm) than in native knees (9.5 ± 3.6 mm) throughout early flexion (p < 0.01), but this difference diminished beyond 100° flexion (n.s.). The implanted knees did not exhibit paradoxical external tibial rotation. Varus–valgus laxity in full extension was lower for implanted knees than for native knees (p = 0.0221), but at 30° flexion was almost identical for both native and implanted knees. Anteroposterior laxity was similar in implanted and native knees.

Conclusions

The ‘third condyle’ TKA provides similar anteroposterior and mediolateral stability to the natural knee. This feature granted an adequate balance between laxity and constraint to reproduce natural joint kinematics, including smooth femoral rollback, without causing paradoxical external tibial rotation.

Level of evidence

Comparative study, Level III.     

Patient function after a posterior stabilizing total knee arthroplasty: cam–post engagement and knee kinematics

Even though posterior substituting total knee arthroplasty has been widely used in surgery, how the cam–post mechanism (posterior substituting mechanism) affects knee joint kinematics and function in patients is not known. The objective of the present study was to investigate posterior femoral translation, internal tibial rotation, tibiofemoral contact, and cam–post engagement of total knee arthroplasty patients during in vivo weight-bearing flexion. Twenty-four knees with a PS TKA were investigated while performing a single leg weight-bearing lunge from full extension to maximum flexion as images were recorded using a dual fluoroscopic system. The in vivo knee position at each targeted flexion angle was reproduced using 3D TKA models and the fluoroscopic images. The kinematics of the knee was measured from the series of the total knee arthroplasty models. The cam–post engagement was determined when the surface model of the femoral cam overlapped with that of the tibial post. The mean maximum flexion angle for all the subjects was 112.5 ± 13.1°. The mean flexion angle where cam–post engagement was observed was 91.1 ± 10.9°. The femur moved anteriorly from 0° to 30° and posteriorly through the rest of the flexion range. The internal tibial rotation increased approximately 6° from full extension to 90° of flexion and decreased slightly with further flexion. Both the medial and lateral contact point moved posteriorly from 0° to 30°, remained relatively constant from 30° to 90°, and then moved further posterior from 90° to maximum flexion. The in vivo cam–post engagement corresponded to increased posterior translation and reduced internal tibial rotation at high flexion of the posterior substituting total knee arthroplasty. The initial cam–post engagement was also mildly correlated with the maximum flexion angle of the knee (R = 0.51, p = 0.019). A later cam–post engagement might indicate an environment conducive to greater flexion. If the factors that affect cam–post engagement timing can be established, proper manipulation of those factors may improve the function of the knee after posterior substituting total knee arthroplasty.     

Bicruciate substituting total knee replacement: how effective are the added kinematic constraints in vivo?

Purpose

The Journey bicruciate substituting (BCS) TKR was designed to restore normal knee kinematics. It has two cam-post mechanisms which substitute for the ACL and PCL. The aim of this study was to undertake a comprehensive study of the Journey BCS kinematics in vivo to assess the function of the cam-post mechanisms and their effect on functional kinematics and compared to the kinematics of a group of normal knees.

Methods

The kinematics of 10 Journey BCS were assessed fluoroscopically during step-up and lunge exercises, and were compared to those of 20 normal knees. The fluoroscopic images were used to determine relative implant orientation using a 2D to 3D reconstruction method. The determined relative tibio-femoral orientations allowed for cam-post engagement and tibio-femoral contact points to be determined. Functional kinematics were assessed using the patella tendon angle (PTA) and the patella flexion angle (PFA) relationship with the knee flexion angle (KFA).

Results

The average maximum flexion achieved by the Journey was 124.7°. Both cam mechanisms engaged: The anterior cam during extension at 12.6° and the posterior cam in flexion at 45.4°. During flexion, the contacts points on the tibia moved posteriorly with no paradoxical anterior translation. The PTA/KFA relationships of the Journey implant group for both the step-up and lunge exercises were broadly similar in terms of trend to those established for the normal knee but the PTA between 10° KFA and 140° KFA were significantly (P?Conclusion The Journey BCS showed no paradoxical anterior movement and sufficient posterior femoral roll back which corresponded with the engagement of the anterior and posterior cam-post mechanisms. Trends shown by the PTA/KFA and PFA/KFA kinematic profiles observed for the Journey group were more normal than those seen with other designs of TKR. However, despite being more close to normal than other implants, the Journey group showed a different kinematic profile to that of the normal knees, which is most likely due to the femur being too far posterior relative to the tibia.

Level of evidence

Case–control study, retrospective, comparative study, Level III.     

Patellofemoral kinematics during deep knee flexion after total knee replacement: a computational simulation

Purpose

Actions requiring deep knee flexion, such as kneeling and squatting, are challenging to perform after total knee replacement (TKR), though many manufactures emphasize that their knee prostheses could safely achieve high flexion. Little is known about the patellofemoral kinematics during deep flexion. This study aimed to track the movement of the patella during kneeling and squatting through dynamic computational simulation.

Methods

A validated knee model was used to analyse the patellar kinematics after TKR, including shifting, tilting and rotation. The data were captured from full extension to 135° of knee flexion. For kneeling, an anterior force of 500 N was applied perpendicularly on the tibial tubercle as the knee flexed from 90° to 135°. For squatting, a ground reaction force was applied through the tibia from full extension to 135° of flexion.

Results

This study found that patellar shifting and rotation in kneeling were similar to those while squatting. However, during kneeling, the patella had a greater medial tilt and showed signs of abrupt patellar tilt owning to an external force being concentrated on the tibial tubercle.

Conclusions

In terms of squatting and kneeling movements, the latter is a more strenuous action for the patellofemoral joint after TKR due to the high forces acting on the tibial tubercle. It is suggested that overweight patients or those requiring high flexion should try to avoid kneeling to reduce the risk of the polyethylene wear. Further modification of trochlear geometry may be required to accommodate abrupt changes in patellar tilting.

Level of evidence

II.     

Patellofemoral contact pressure following high tibial osteotomy: a cadaveric study

Patella infera is a known complication of high tibial osteotomy (HTO) that can cause anterior knee pain due to excessive stresses associated with abnormal patellofemoral (PF) joint biomechanics. However, the translation of these abnormal biomechanics to native cartilage pressure has not been explored. The present study was designed to compare the PF contact pressures of three different HTOs in a human cadaveric model of valgus tibiofemoral correction. Nine fresh cadaveric knees underwent (1) medial opening wedge (OWHTO) with a proximal tuberosity osteotomy (PTO), (2) OWHTO with a distal tuberosity osteotomy (DTO), and (3) a lateral closing wedge (CWHTO). The specimens were mounted in a custom knee simulation rig, with muscle forces being simulated using a pulley system and weights. The PF contact pressure was recorded using an electronic pressure sensor at 15°, 30°, 60°, 90°, and 120° of knee flexion, with results of the intact knees obtained as relative control. Compared to the intact knee, the DTO OWHTO and CWHTO did not significantly (P > 0.05) influence PF pressure at any flexion angle. On the other hand, PTO OWHTO lead to a significant elevation in PF cartilage pressure at 30° (P < 0.05), 60° (P < 0.005), and 90° (P < 0.0005) knee flexion. We conclude from these results that DTO OWHTO maintains normal joint biomechanics and has no significant effect on PF cartilage pressure. In patients who complain of pre-existing anterior knee pain, DTO OWHTO or CWHTO should be considered.     

Reconstructing the anterolateral ligament does not decrease rotational knee laxity in ACL-reconstructed knees

Purpose

Little is known about the anterolateral ligament’s (ALL) influence on knee laxity. The purpose of this study was to investigate rotational knee laxity against a pure axial rotational stress using radiostereometric analysis (RSA) after cutting and reconstructing both the anterior cruciate ligament (ACL) and the ALL.

Methods

Eight human donor legs were positioned and stereoradiographically recorded at 0°, 30° and 60° of knee flexion using a motorised fixture, while an internally rotating force of 4 Nm was applied to the foot. Anterior–posterior and rotational laxity were investigated for knees with intact ligaments and compared with those observed after successive ACL and ALL resection and reconstruction.

Results

After cutting the ALL in ACL-deficient knees, the internal rotation was increased in all three knee flexion angles, 0° (p?=?0.04), 30° (p?=?0.03) and 60° (p?<?0.01) by 1.0°, 1.6° and 2.5°, respectively. However, no decrease in laxity was found after reconstructing the ALL in ACL-reconstructed knees.

Conclusions

The ALL was confirmed as a stabiliser of internal rotation in ACL-deficient knees. However, reconstructing the ALL using a gracilis autograft tendon did not decrease the internal rotation laxity in the ACL-reconstructed knee. Based on the results of this study, we do not recommend reconstructing the ALL in ACL-reconstructed knees to decrease internal knee laxity.

     

Effects of four different surgical approaches on intra-operative joint gap in posterior-stabilized total knee arthroplasty

Purpose

The effects of surgical approaches and patellar positions on joint gap measurement during total knee arthroplasty (TKA) remain unclear. We hypothesized that joint gap changes with different knee flexion angles would not be consistent within four different approaches and two different patellar positions.

Methods

This study enrolled 80 knees undergoing posterior-stabilized TKA. For 60 varus knees, parapatellar, midvastus, and subvastus approaches were used in 20 knees each. For 20 valgus knees, a lateral subvastus approach was used. Component gap length and inclination were measured intra-operatively using a specific tensor device under 40 lb with the patella reduced or shifted laterally, at 0°, 45°, 90°, and 135° of knee flexion.

Results

Mean gap lengths at 45° and 90° of knee flexion were significantly larger with the parapatellar approach than with midvastus or lateral subvastus approaches (P < 0.05). Regarding gap inclination, varus angle increased linearly through the entire arc of flexion in all four approaches. When the patella was shifted laterally, gap lengths at 45°, 90°, and 135° were significantly reduced compared with those for the patella reduced in the subvastus approach, whereas gap length was constant in the parapatellar approach, regardless of patellar position.

Conclusion

Joint gap kinematics was not consistent within four different approaches and two different patellar positions. Relatively large gaps at 45° and 90° were unique features for the parapatellar approach. Surgeons should be aware that the flexion gap is reduced when the patella is shifted laterally in vastus medialis-preserving approaches such as the subvastus approach.

Level of evidence

II.     

Patella-tibial transfixation for posterior cruciate ligament repair and reconstruction: a biomechanical analysis

The posterior cruciate ligament (PCL) restricts posterior translation of the tibia on the femur. Because flexion of the knee increases tension on the PCL, the knee is usually immobilized in extension after PCL repair or reconstruction. Patella-tibial transfixation (olecranization), however, has been proposed to reduce the tension on the PCL without requiring immobilization of the knee. The objective of this study was: (1) to evaluate the distribution of strain in the anterolateral and posterior oblique fiber bundles of the PCLs in eight cadaveric knees before and after olecranization and (2) to measure the patellofemoral contact pressures at various degrees of knee flexion. Olecranization significantly (P < 0.05) reduced the strain on the anterolateral fiber bundles of the PCL at 15°–45° of flexion. No significant strain reduction was observed in the posterior oblique fiber bundles. Patellofemoral contact pressures measured from digitized Fuji sensitive film indicated significantly increased contact pressures (P < 0.05) following olecranization from 0°–60° of knee flexion. Increased parapatellar soft tissue tightness limited knee flexion to 90° and patella lift-off occurred at 75°. Although olecranization of the patella does reduce strain on the intact PCL within a selected range of motion, the beneficial effect of allowing early motion may be negated by the potentially harmful effects imposed upon the patellofemoral articular cartilage by increased contact pressures. Received: 20 December 1996 Accepted: 24 June 1997     

Roles of ACL remnants in knee stability

Purpose

This study evaluated knee laxity in anterior tibial translation and rotation following removal of anterior cruciate ligament (ACL) remnants using a computer navigation system.

Methods

This prospective study included 50 knees undergoing primary ACL reconstruction using a navigation system. ACL remnants were classified into four morphologic types: Type 1, bridging between the roof of the intercondylar notch and tibia; Type 2, bridging between the posterior cruciate ligament and tibia; Type 3, bridging between the anatomical insertions of the ACL on the lateral wall of the femoral condyle and the tibia; and Type 4, no bridging of ACL remnants. Anterior tibial translation and rotatory laxity were measured before and after remnant resection using a navigation system at 30°, 60°, and 90° of knee flexion. The amount of change in anterior tibial translation and rotatory laxity of each type was compared among the types.

Results

The different morphologic types of ACL remnants were as follows: Type 1, 15 knees; Type 2, 9 knees; Type 3, 6 knees; and Type 4, 20 knees. The amount of change in anterior tibial translation and rotatory laxity at 30° knee flexion in Type 3 was significantly larger than in the other types. There were no significant differences in either tibial translation or rotatory laxity at 60° and 90° knee flexion among the types.

Conclusions

In Type 3, ACL remnants contributed to anteroposterior and rotatory knee laxity evaluated at 30° knee flexion. The bridging point of the remnants is important to knee laxity. The Type 3 remnant should be preserved as much as possible when ACL reconstruction surgery is performed.

Level of evidence

Prognostic study, Level II.     

Reproducibility of joint space width and the intermargin distance measurements in patients with medial osteoarthritis of the knee in various degrees of flexion

Objective  This study tested the variability and reproducibility of measurements of the joint space width (JSW) and intermargin distance (IMD) of the medial tibial plateau in specific positions of knee flexion in osteoarthritic knees in order to evaluate the most useful knee angle for radiographic measurements. Design  Radiographs from 56 knees with osteoarthritis from 46 patients were taken with the knees in conventional full extension and 15°, 30°, and 45° of flexion with weight bearing. Three orthopedic surgeons independently measured the JSW and IMD at the narrowest point and the midpoint of medial tibial plateau using a computer-assisted method. Results  The JSW and IMD were smallest at 15° flexion, both measured at the narrowest point and the midpoint of the medial compartment. Reproducibility of the IMD at the midpoint was better than at the narrowest point for all four flexion angles. Conclusion  Measurements of the medial JSW and IMD are smallest at 15° of knee flexion indicating that radiographs should be obtained at this angle in order to best demonstrate the extent of osteoarthritis.     

Ligament releases do not lead to increased postoperative varus-valgus laxity in flexion and extension: a prospective clinical study in 49 TKR patients

This prospective study investigated whether ligament releases necessary during total knee replacement (TKR) led to a higher varus-valgus laxity during intraoperative examination after implantation of the prosthesis and after 6 months. The laxity values of TKR patients were also compared to healthy controls. Varus-valgus laxity was assessed intra- and postoperatively in extension and 70° flexion in 49 patients undergoing TKR, implanted using a balanced gap technique. Knees were catalogued according to ligament releases performed during surgery. Postoperative varus-valgus laxity and laxity after 6 months had not increased following release of the posteromedial capsule, iliotibial tract, and the superficial medial collateral ligament. The obtained postoperative laxity compares well with a healthy equally aged control group. It can be concluded that the balanced gap technique results in stable knees and that releases can safely be performed to achieve neutral leg alignment without causing postoperative laxity.     

Anteroposterior and rotational stability in fixed and mobile bearing unicondylar knee arthroplasty: a cadaveric study using the robotic force sensor system

Purpose

Different bearing designs in unicondylar knee arthroplasty (UKA) have been developed in order to influence the rate of polyethylene wear. Increased anteroposterior translation and rotation after UKA has been hypothesized due to changes in joint surface geometry. The mobile bearing design was expected to show increased anteroposterior translation compared to the fixed bearing and biconcave bearing design.

Methods

Six human cadaver knees were used for the tests. Anteroposterior and rotational knee stability was analysed in 0°, 30°, 60°, 90° and 120° of knee flexion using a robotic testing system (KR 125, KUKA Robots Augsburg, Germany). Three forces and moments were measured in a Cartesian coordinate system with a resolution of 1.0 N and 0.1 Nm.

Results

There was no difference between the native knees and the knees after UKA in AP translation and rotation in all knee flexion angles. The factor knee flexion angle had a significant impact on the anterior translation when the type of bearing was neglected (p ≤ 0.015).

Conclusion

This study shows that the natural knee stability in AP translation and rotation can be preserved in UKA. The preserved knee stability in different planes after UKA underlines the advantage of UKA when surgery is required in osteoarthritic changes of the medial compartment.     

The position of the tibia tubercle in 0°–90° flexion: comparing patients with patella dislocation to healthy volunteers

Purpose

The aim of this study was to measure the tibia tubercle trochlea groove distance (TT–TG) as a function of knee flexion. Our hypothesis was that there is a different pattern in healthy volunteers and patients with patella instability (PFI).

Methods

Thirty-six knees of 30 patients with at least one dislocation of the patella and 30 knees of 30 healthy volunteers as control group were analysed with magnetic resonance imaging by three different observers. The TT–TG was measured in steps of 15° between 0° and 90° of knee flexion. Furthermore, the alignment of the leg (MA), the femur torsion (FTor) and the tibia torsion (TTor) was calculated.

Results

The TT–TG was higher in patients compared to volunteers and in extension compared to flexion. This difference was statistically significant (p < 0.05). Most of the patients with a TT–TG above 20 mm in extension showed a high decrease in flexion to normal values. In some patients, this compensating mechanism fails. MA, FTor and TTor were not different in patients and control group (n.s.).

Conclusion

The TT–TG distance is dynamic and decreased significantly during flexion in knees with PFI and healthy volunteers. However, there were a small number of patients in the PFI group where this compensation mechanism did not work. Therefore, the decision to perform a tibia tubercle osteotomy should not be based on one single measurement in extension or 30° of knee flexion.

Level of evidence

II.     

Intraoperative evaluation of total knee replacement: kinematic assessment with a navigation system

Interest in the kinematics of reconstructed knees has increased since it was shown that the alteration of knee motion could lead to abnormal wear and damage to soft tissues. We performed intraoperative kinematic measurements using a navigation system to study knee kinematics before and after posterior substituting rotating platform total knee arthroplasty (TKA). We verified intraoperatively (1) if varus/valgus (VV) laxity and anterior/posterior (AP) laxity were restored after TKA; (2) if TKA induced abnormal femoral rollback; and (3) how tibial axial rotation was influenced by TKA throughout the range of flexion. We found that TKA improved alignment in preoperative osteoarthritic varus knees which became neutral after surgery and maintained a neutral alignment in neutral knees. The VV stability at 0° was restored while AP laxity at 90° significantly increased after TKA. Following TKA, the femur had an abnormal anterior translation up to 60° of flexion, followed by a small rollback of 12 ± 5 mm. TKA influenced the tibia rotation pattern during flexion, but not the total amount of internal/external rotation throughout whole range of flexion, which was preserved after TKA (6° ± 5°). This study showed that the protocol proposed might be useful to adjust knee stability at time zero and that knee kinematic outcome during total knee replacement can be monitored by a navigation system.     

Far anteromedial portal technique for posterolateral femoral tunnel drilling in anatomic double-bundle anterior cruciate ligament reconstruction: a cadaveric study

Purpose

To identify the relationship between knee flexion angle and femoral tunnel length, as well as the exit points of guidewires, when using a far anteromedial portal technique for posterolateral femoral tunnel drilling in double-bundle anterior cruciate ligament reconstruction.

Methods

Using the far anteromedial portal technique in 8 cadaveric knees, femoral tunnel drilling for the posterolateral bundle was performed at 3 knee flexion angles: 90°, 110° and 130°. We measured the femoral tunnel length and the distances from each guidewire to the closest relevant structures.

Results

The mean tunnel length at 90° knee flexion (25.8 ± 1.8 mm) was significantly shorter than the length at 110° and 130° knee flexion (32.1 ± 2.6 and 33.1 ± 2.5 mm, respectively). The average distance between the exit point of the guidewire and the posterior articular cartilage of the lateral femoral condyle was the shortest at 90° knee flexion (3.3 ± 2.2 mm). The distance between the guidewire and the centre of the origin of the lateral collateral ligament was the shortest at 130° knee flexion (8.0 ± 1.8 mm). The guidewires penetrated the origin of the lateral gastrocnemius tendon in 2 cases at 110° knee flexion and in 1 case each at 90° and 130° knee flexion.

Conclusions

When using the far anteromedial portal technique, more than 110° knee flexion is desirable to achieve ideal femoral tunnel length and avoid articular cartilage injury. In addition, the risk of damage to the origin of the lateral collateral ligament increases when the knee flexion angle increases to 130°. A knee flexion angle between 110° and 120° was recommended when using the far anteromedial portal technique.     

Effects of sectioning the posterolateral structures on knee kinematics and in situ forces in the posterior cruciate ligament

The objective of this study was to determine the effects of sectioning the posterolateral structures (PLS) on knee kinematics and in situ forces in the posterior cruciate ligament (PCL) in response to external and simulated muscle loads. Ten human cadaveric knees were tested using a robotic/universal force-moment sensor testing system. The knees were subjected to three loading conditions: (a) 134-N posterior tibial load, (b) 5-Nm external tibial torque, and (c) isolated hamstring load (40 N biceps/40 N semimembranosus). The knee kinematics and in situ forces in the PCL for the intact and PLS-deficient knee conditions were determined at full extension, 30°, 60°, 90°, and 120° of knee flexion. Under posterior tibial loading posterior tibial translation with PLS deficiency increased significantly at all flexion angles by 5.5 ± 1.5 mm to 0.8 ± 1.2 mm at full extension and 90°, respectively. The corresponding in situ forces in the PCL increased by 17–¶19 N at full extension and 30° of knee flexion. Under the external tibial torque, external tibial rotation increased significantly with PLS deficiency by 15.1 ± 1.6° at 30° of flexion to 7.7 ± 3.5° at 90°, with the in situ forces in the PCL increasing by 15–90 N. The largest increase occurred at 60° to 120° of knee flexion, representing forces two to six times of those in the intact knee. Under the simulated hamstring load, posterior tibial translation and external tibial and varus rotations also increased significantly at all knee flexion angles with PLS deficiency, but this was not so for the in situ forces in the PCL. Our data suggest that injuries to the PLS put the PCL and other soft tissue structures at increased risk of injury due to increased knee motion and the elevated in situ forces in the PCL.     

Graft tension of the posterior cruciate ligament using a finite element model

Purpose

The aim of the study was to analyse the change in length and tension of the reconstructed single-bundle posterior cruciate ligament (PCL) with three different femoral tunnels at different knee flexion angles by use of three-dimensional finite element method.

Methods

The right knees of 12 male subjects were scanned with a high-resolution computed tomography scanner at four different knee flexion angles (0°, 45°, 90° and 135°). Three types of single-bundle PCL reconstruction were then conducted in a 90° flexion model: femoral tunnels were created in anterolateral (AL), central and posteromedial (PM) regions of the footprint. Length versus flexion curves and tension versus flexion curves were generated.

Results

Between 0° and 90° of knee flexion, changes in length and tension in the PM grafts were not significant. Whereas the lengths and tension of the AL and central grafts significantly increased in the same flexion range. The length and tension of the PM grafts at 135° of knee flexion were significantly higher than those at 90° of knee flexion, whereas the AL and the central grafts showed only slight length changes beyond 90° of flexion. However, the tension of the AL graft increased significantly beyond 90° of flexion.

Conclusions

Changes in the graft length, and tension were generally affected by different femoral tunnels and knee flexion angles. In groups with the AL and PM single-bundle reconstruction, the graft tension increased beyond 90° of knee flexion when the graft is tensioned at 90° of flexion. These data suggest that final fixation angle at 90° for the AL or PM graft would induce graft overtension in high knee flexion of 135°. Whereas central graft which is fixed in 90° of flexion is desirable in terms of prevention of graft overtension. Because the graft tension within it was relatively constant beyond 90° of flexion.     

A computerized analysis of femoral condyle radii in ACL intact and contralateral ACL reconstructed knees using 3D CT

The bony geometry of the distal femoral condyles may have a significant influence on knee joint kinematics. The aim of this study was to analyze the relationship between the size of the medial and lateral femoral condyles in different planes. Seventy-four three-dimensional (3D) CT reconstructions of 37 patients with ACL intact and contralateral ACL reconstructed knees were used and the data were imported into a graphical software program. The radii of the medial and lateral femoral condyles were analyzed in the sagittal, coronal, and axial planes by digitally reconstructed circular arcs along the bony condylar profiles marked with multiple digital surface points. Intra- and interobserver testing was performed. In the intact knees the average sagittal radius of the distal medial and lateral femoral condyles was similar. There was a significant difference between the radii of the distal medial femoral condyles compared to lateral femoral condyles in the coronal plane (22.4 vs. 27.8 mm, P < 0.001) as well as between the radii of the medial femoral condyles in the axial plane in 90° knee flexion compared to the lateral femoral condyles (21.3 vs. 18.3 mm, P < 0.001). The average radius of the medial femoral condyles was significantly smaller in extension compared to 90° of flexion (21.2 vs. 22.4 mm, P = 0.05) and the average radius of the lateral femoral condyles was significantly larger in extension compared to 90° of flexion (27.8 vs. 18.3 mm, P < 0.001). The 37 ACL reconstructed knees demonstrated similar radii in all three planes when compared to the intact knees without any significant difference. The described method of assessing the architecture of the distal femoral condyles is non-invasive, reproducible, and provides reliable geometric parameters necessary for the 3D reconstruction of the femoral geometry in vivo. The radii of the FC were similar in the sagittal planes but demonstrate a significant asymmetry in the axial and coronal planes. The average radius of the lateral femoral condyles was significantly larger in extension whereas the radius of the medial femoral condyles was significantly larger in flexion. We did not find any significant difference in the shape of the femoral condyles in ACL intact and contralateral ACL reconstructed knees indicating that the geometry of the femoral condyles might not influence the injury mechanism of ACL rupture. The asymmetry between the femoral condyles may be considered when designing new anatomical femoral components in knee arthroplasty.