Resulting Knee Kinematics Research Articles

The superficial medial collateral ligament reconstruction of the knee: effect of altering graft length on knee kinematics and stability

The purpose of this study was to evaluate and compare the resulting knee kinematics and stability of an anatomic superficial MCL (sMCL) reconstruction and a non-anatomic sMCL reconstruction. In a cadaveric model, normal knee stability and kinematics were compared with sMCL deficient knees and with two experimental sMCL reconstructions. The first reconstruction (AnatRecon) attempted to anatomically reconstruct the sMCL. The second reconstruction (ShortRecon) used a shorter graft to mimic the effect of failing to reproduce the anatomic length of the sMCL. Changes in position of the femur with respect to the tibia were measured with an electromagnetic tracking system during simulated active knee extension and during passive knee stability testing in the sMCL intact knee, the sMCL deficient knee, and the two experimental reconstructions. Simulated active knee extension demonstrated a significant increase in external tibial rotation of ShortRecon compared to AnatRecon between 30° and 80° of knee flexion (mean difference <3.0° over the range of knee flexion angles; P < 0.008), and a significant increase in external tibial rotation of ShortRecon compared to the intact sMCL was found at 60° and 70° of knee flexion (mean difference <2.0°over the range of knee flexion angles; P < 0.008). Passive joint stability testing demonstrated that division of the sMCL produced approximately 6° of valgus laxity at 30° of knee flexion and increased external tibial rotation of approximately 5° at 30°, 9° at 60°, and 10° at 90° of knee flexion, respectively. AnatRecon restored normal knee kinematics and stability. Additionally, passive stability testing demonstrated a significant increase in external tibial rotation of ShortRecon compared to AnatRecon at 60° (mean difference = 3.7°; P < 0.05) and 90° of knee flexion (mean difference = 4.9°; P < 0.05). Anatomic reconstruction of the sMCL effectively restored knee kinematics and stability in the sMCL deficient knee. Altering the normal ligament length resulted in measurable changes in knee kinematics and stability. This study suggests that in cases of chronic valgus knee instability, anatomic sMCL reconstruction would provide better results than non-anatomic sMCL reconstruction.

Biomechanical comparison of three anatomic ACL reconstructions in a porcine model

Different tunnel configurations have been used for double-bundle (DB) anterior cruciate ligament (ACL) reconstruction. However, controversy still exists as to whether three-tunnel DB with double-femoral tunnels and single-tibial tunnel (2F-1T) or with single-femoral tunnel and double-tibial tunnels (1F-2T) better restores intact knee biomechanics than single-bundle (SB) ACL reconstruction. The purpose was to compare the knee kinematics and in situ force in the grafts among SB and two types of three-tunnel DB ACL reconstructions performed in an anatomic fashion. Twenty-four porcine knees were subjected to an 89-N anterior tibial load (simulated KT-1000 test) at 30°, 60°, and 90° of flexion and to a 4-Nm internal tibial torque and 7-Nm valgus torque (simulated pivot-shift test) at 30° and 60° of flexion. The resulting knee kinematics and in situ force in the ACL or replacement grafts were measured using a robotic system for (1) ACL-intact, (2) ACL-deficient, and (3) three ACL reconstructed knees: SB; DB 2F-1T; and DB 1F-2T. During the simulated pivot-shift test, the DB grafts more closely restored the in situ force in the intact ACL at low flexion angle than the SB graft. There were no significant differences in knee kinematics between SB and DB ACL reconstruction. The DB 2F-1T reconstruction did not show a significant difference in knee kinematics or in situ force when compared to the DB 1F-2T technique. The in situ force in the ACL is better restored with an anatomic three-tunnel DB reconstruction in response to the simulated pivot-shift test at low flexion angle when compared to an anatomic SB reconstruction. Both three-tunnel DB ACL reconstructions performed in an anatomic fashion had similar biomechanical behavior. As long as it is performed anatomically, DB ACL reconstruction could be better alternative than SB ACL reconstruction, no matter which three-tunnel procedure, 2F-1T or 1F-2T, is used.

Introducing a new staircase design to quantify healthy knee function during stair ascent and descent

The design, manufacture and validation of a new free standing staircase for motion analysis measurements are described in this paper. The errors in vertical force measurements introduced when the stairs interface with a force plate (FP) are less than 0.6%. The centre of pressure error introduced is less than 0.7 mm compared to the error from the FP. The challenges of introducing stair gait into a clinical trial with a limited number of FPs and time limitations for assessment sessions are addressed by introducing this cost effective solution. The staircase was used in a study to measure non-pathological knee function of 10 subjects performing stair ascent and descent. The resulting knee kinematics and knee joint moments are in agreement with previous studies. The kinematic and joint moment profiles provide a normative range, which will be useful in future studies for identifying alterations in joint function associated with pathology and intervention.

Double-bundle reconstruction cannot restore intact knee kinematics in the ACL/LCL-deficient knee

The aim of this study was to evaluate the effect of single-bundle (SB) and anatomic double-bundle (DB) anterior cruciate ligament (ACL) reconstruction on the resulting knee kinematics in a simulated clinical setting with ACL rupture and associated extra-articular damage to the lateral structures. It was hypothesized that anatomic DB ACL reconstruction restores the intact knee kinematics in ACL/LCL-deficient knees, whereas SB ACL reconstruction fails to restore the intact knee kinematics. Ten fresh-frozen human cadaver knees were subjected to anterior tibial load of 134 N (simulated KT 1000) and combined rotatory load of 10-Nm valgus and 4-Nm internal tibial torque (simulated pivot shift) using a robotic/UFS testing system. The resulting knee kinematics was determined for intact, ACL/LCL-deficient, SB ACL-reconstructed/LCL-deficient, and DB ACL-reconstructed/LCL-deficient knee. Statistical analysis was performed using a two-way ANOVA test with the level of significance set at P < 0.05. Under a simulated KT 1000 test, anterior tibial translation (ATT) following SB ACL reconstruction was statistically significant at 0 degrees , 30 degrees and 60 degrees of knee flexion when compared to the intact knee. ATT after DB ACL reconstruction showed no statistically significant difference from the intact knee; however, there was a significant difference in SB reconstruction at 0 degrees and 30 degrees of knee flexion. Under a simulated pivot shift test, both SB and DB ACL reconstruction failed to restore the intact knee kinematics. The results of the study did not support our initial hypothesis. Though DB reconstructions were significantly superior to SB reconstruction under simulated KT 1000 test, SB as well as DB reconstruction failed to restore the intact kinematics under simulated pivot shift loads. The clinical relevance of this study is that caution and precise preoperative diagnostics are needed to avoid failure of intra-articular ACL reconstruction if the extra-articular stabilizers are torn.

Effect of Tunnel-Graft Length on the Biomechanics of Anterior Cruciate Ligament-Reconstructed Knees

Background In anterior cruciate ligament (ACL) reconstruction using hamstring grafts, the graft can be looped, resulting in an increased graft diameter but reducing graft length within the tunnels. Hypothesis After 6 and 12 weeks, structural properties and knee kinematics after soft tissue ACL reconstruction with 15 mm within the femoral tunnel will be significantly inferior when compared with the properties of ACL reconstruction with 25 mm in the tunnel. Study Design Controlled laboratory study. Methods In an intra-articular goat model, 36 ACL reconstructions using an Achilles tendon split graft were performed with 15-mm (18 knees) and 25-mm (18 knees) graft length in the femoral tunnel. Animals were sacrificed 6 weeks and 12 weeks after surgery and knee kinematics was tested. In situ forces as well as the structural properties were determined and compared with those in an intact control group. Histologic analyses were performed in 2 animals in each group 6 and 12 weeks postoperatively. Statistical analysis was performed using a 2-factor analysis of variance test. Results Anterior cruciate ligament reconstructions with 15 mm resulted in significantly less anterior tibial translation after 6 weeks (P < .05) but not after 12 weeks. Kinematics after 12 weeks and in situ forces of the replacement grafts at both time points showed no statistically significant differences. Stiffness, ultimate failure load, and ultimate stress revealed no statistically significant differences between the 15-mm group and the 25-mm group. Conclusion The results suggest that there is no negative correlation between short graft length (15 mm) in the femoral tunnel and the resulting knee kinematics and structural properties. Clinical Relevance Various clinical scenarios exist in which the length of available graft that could be pulled into the bone tunnel (femoral or tibial) could be in question. To address this concern, this study showed that reducing the tendon graft length in the femoral bone tunnel from 25 mm to 15 mm did not have adverse affects in a goat model.

Double bundle revision of a malplaced single bundle vertical ACL reconstruction: ACL revision surgery using a two femoral tunnel technique

Several factors influence the outcome after ACL reconstruction. One of the most important factors influencing the resulting knee kinematics and subjective instability is femoral tunnel placement. Revision can be necessary if the femoral tunnel is drilled transtibial in the roof of femoral notch (mismatch). Double bundle reconstruction using two femoral tunnels and one tibial tunnel technique can be used in revision of a primary vertical ACL reconstruction. Case series (level of evidence III). ACL revision was performed in five patients complaining instability after primary transtibial ACL reconstruction. Clinical examination, X-ray and CT analysis were performed to evaluate objective knee laxity, tunnel placement and widening. In all patients a technique using two femoral tunnels in a two medial portal technique and one tibial tunnel was used. Patients were reevaluated at a follow up of 24 months. Preoperatively, pivot shift tests were 2+ in three and 1+ in the remaining two patients. Lachman test was found to be positive in all patients (4 patients, 2+ firm endpoint; 1 patient, 2+ soft endpoint). X-rays showed a femoral tunnel position at 11.30 (1 patient) and 12.00 o'clock (4 patients). In one patient significant tibial tunnel enlargement was to be found. At a follow up of 24 months, KT 1000 was <2 mm side to side difference and the pivot shift test was negative in all patients. Revision of a primary vertical ACL reconstruction can be safely performed using a double bundle reconstruction with two femoral tunnels in a two medial portal technique and one tibial tunnel technique. The femoral tunnel need to be located in the anatomic origin of the AM and PL bundle. Femoral tunnel placement in the notch of the intercondylar notch should be avoided. In these cases without significant tunnel enlargement, a primary double bundle revision with two femoral and one tibial tunnel can be performed.

Biomechanical Evaluation of Two Techniques for Double-Bundle Anterior Cruciate Ligament Reconstruction

Background This research was undertaken to determine whether there is a need for a second tibial tunnel in anatomic anterior cruciate ligament reconstruction. Hypothesis Anatomic two-bundle reconstruction with two tibial tunnels restores knee anterior tibial translation in response to 134 N and to 5-N·m internal tibial torque combined with 10-N·m valgus torque more closely to normal than does double-bundle reconstruction with one tibial tunnel. Study Design Controlled laboratory study. Methods Ten cadaveric knees were subjected to a 134-N anterior tibial load at 0°, 30°, 60°, and 90° and to 5-N·m internal tibial torque and 10-N·m valgus torque at 15° and 30°. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) anterior cruciate ligament–deficient, (3) double-bundle/one tibial tunnel, and (4) double-bundle/two tibial tunnels. Results Anterior tibial translation for the reconstruction with two tibial tunnels was significantly closer to that of the intact knee than was the reconstruction with one tibial tunnel at 0° and 30° of flexion (0° = 3.82 vs 6.0 mm, P < .05; 30° = 7.99 vs 11 mm, P < .05). The in situ force normalized to the intact anterior cruciate ligament for the reconstruction with two tibial tunnels was significantly higher than the in situ force of the reconstruction with one tibial tunnel (30° = 89 vs 82 N, P < .05). With a combined rotatory load, the anterior tibial translation of specimens with a tibial two-tunnel technique was significantly lower than that of specimens with one tunnel (0° = 5.7 vs 8.4 mm, P < .05; 30° = 7.5 vs 9.5 mm, P < .05). Conclusions Anatomic reconstruction with two tibial tunnels may produce a better biomechanical outcome, especially close to extension. Clinical Relevance At the time of initial fixation, there appears to be a small biomechanical advantage to the second tibial tunnel in the setting of two-bundle anterior cruciate ligament reconstruction.

The Role of the Anteromedial and Posterolateral Bundles of the Anterior Cruciate Ligament in Anterior Tibial Translation and Internal Rotation

Background A rupture of the entire fibers of the anterior cruciate ligament leads to knee instability due to increased anterior tibial translation and increased internal tibial rotation. The influence of isolated deficiency of the anteromedial or posterolateral bundle of the anterior cruciate ligament on the resulting knee kinematics have not yet been reported. Hypothesis Transection of the anteromedial bundle will lead to increased anterior tibial translation at 90°. Transection of the posterolateral bundle will show an increased anterior tibial translation as well as a combined rotatory instability at 30°. Study Design Controlled laboratory study. Methods Kinematics of the intact knee were determined in response to a 134-N anterior tibial load and a combined rotatory load of 10 N·m valgus and 4 N·m internal tibial rotation using a robotic/universal force moment sensor testing system. Subsequently, the fibers of the anteromedial and posterolateral bundle were resected in an alternating order and the new translation in response to the same external loading conditions measured. Statistical analysis was performed using a 2-way ANOVA test. Results Transection of the anteromedial bundle increased anterior tibial translation at 60° and 90° of knee flexion significantly. Isolated transsection of the posterolateral bundle increased anterior tibial translation in response to 134-N anterior load at 30° of knee flexion significantly and resulted in a significant increase in combined rotation at 0° and 30° in response to a combined rotatory load compared with the intact knee and isolated resection of the anteromedial bundle. Conclusion The anteromedial and posterolateral bundles stabilize the knee joint in response to anterior tibial loads and combined rotatory loads in a synergistic way. Clinical Relevance The results of the current study suggest that, from a biomechanical point of view, it may be beneficial to reconstruct both bundles of the anterior cruciate ligament to better restore normal anterior tibial translation and combined rotation.

Anterolateral rotational knee instability: role of posterolateral structures

The aim of this study was to determine the anterolateral rotational instability (ALRI) of the human knee after rupture of the anterior cruciate ligament (ACL) and after additional injury of the different components of the posterolateral structures (PLS). It was hypothesized that a transsection of the ACL will significantly increase the ALRI of the knee and furthermore that sectioning the PLS [lateral collateral ligament (LCL), popliteus complex (PC)] will additionally significantly increase the ALRI. Five human cadaveric knees were used for dissection to study the appearance and behaviour of the structures of the posterolateral corner under anterior tibial load. Ten fresh-frozen human cadaver knees were subjected to anterior tibial load of 134 N and combined rotatory load of 10 Nm valgus and 4 Nm internal tibial torque using a robotic/universal force moment sensor (UFS) testing system and the resulting knee kinematics were determined for intact, ACL-, LCL- and PC-deficient (popliteus tendon and popliteofibular ligament) knee. Statistical analyses were performed using a two-way ANOVA test with the level of significance set at P < 0.05. Sectioning the ACL significantly increased the anterior tibial translation (ATT) and internal tibial rotation under a combined rotatory load at 0 and 30 degrees flexion (P < 0.05). Sectioning the LCL further increased the ALRI significantly at 0 degrees , 30 degrees and 60 degrees of flexion (P < 0.05). Subsequent cutting of the PC increased the ATT under anterior tibial load (P < 0.05), but did not increase the ALRI (P > 0.05). The results of the current study confirm the concept that the rupture of the ACL is associated with ALRI. Current reconstruction techniques should focus on restoring the anterolateral rotational knee instability to the intact knee. Additional injury to the LCL further increases the anterior rotational instability significantly, while the PC is less important. Cautions should be taken when examining a patient with ACL rupture to diagnose injuries to the primary restraints of tibial rotation such as the LCL. If an additional extraarticular stabilisation technique is needed for severe ALRI, the technique should be able to restore the function of the LCL and not the PC.

In Situ Force in the Anterior Cruciate Ligament and Knee Kinematics in the Partially and Completely Posterolateral Corner Deficient Knee (SS-11)

In Situ Force in the Anterior Cruciate Ligament and Knee Kinematics in the Partially and Completely Posterolateral Corner Deficient Knee (SS-11)

Importance of Femoral Tunnel Placement in Double-Bundle Posterior Cruciate Ligament Reconstruction

Background Previous studies have identified the femoral attachment of the posterior cruciate ligament fibers as one of the primary determinants of fiber tension behavior. In addition, a double-bundle posterior cruciate ligament reconstruction has been shown to restore the intact knee kinematics more closely than does a single-bundle reconstruction. Hypothesis An anterior tunnel position in double-bundle posterior cruciate ligament reconstruction restores the biomechanics of the normal knee more closely than does a posterior tunnel position. Study Design Controlled laboratory study. Methods Kinematics and in situ forces of human knees after double-bundle posterior cruciate ligament reconstruction with 2 different femoral tunnel positions (anterior vs posterior) were evaluated using a robotic/universal force-moment sensor testing system. Within the same specimen, the resulting knee kinematics and in situ forces were compared. For statistical analysis, 2-way analysis of variance repeated measures were performed. Results The femoral tunnel position of the double-bundle hamstring graft had significant effect on the resulting posterior tibial displacement and in situ forces of the hamstring grafts. The anterior femoral tunnel position provided significantly less posterior tibial translation than did the posterior tunnel position. There was a tendency toward higher in situ forces of grafts fixed in the anterior tunnel when compared to the posterior position, but this difference was statistically not significant. Conclusion An anterior position of the bone tunnels in double-bundle posterior cruciate ligament reconstruction restores the normal knee kinematics more closely than does a posterior position of the tunnels. Clinical Relevance In double-bundle posterior cruciate ligament reconstruction, posterior placement of the tunnel should be avoided.

Knee Stability and Graft Function after Anterior Cruciate Ligament Reconstruction

Background Locations of femoral tunnels for anterior cruciate ligament replacement grafts remain a subject of debate. Hypothesis A lateral femoral tunnel placed at the insertion of the posterolateral bundle of the anterior cruciate ligament can restore knee function comparably to anatomical femoral tunnel placement. Study Design Controlled laboratory study. Methods Ten cadaveric knees were subjected to the following external loading conditions: (1) a 134-N anterior tibial load and (2) combined rotatory loads of 10-N.m valgus and 5-N.m internal tibial torques. Data on resulting knee kinematics and in situ force of the intact anterior cruciate ligament and anterior cruciate ligament graft were collected using a robotic/universal force-moment sensor testing system for (1) intact, (2) anterior cruciate ligament-deficient, (3) anatomical double-bundle reconstructed, and (4) laterally placed single-bundle reconstructed knees. Results In response to anterior tibial load, anterior tibial translation and in situ force in the graft were not significantly different between the 2 reconstructions except at high knee flexion. For example, at 90° of knee flexion, anterior tibial translation was 6.1 ± 2.3 mm for anatomical double-bundle reconstruction and 7.6 ± 2.6 mm for laterally placed single-bundle reconstruction (P < .05). In response to rotatory loads, there were no significant differences between the 2 reconstruction procedures (4.8 ± 2.4 mm vs 4.8 ± 3.0 mm in anterior tibial translation at 15° of knee flexion, P > .05). Conclusion Lateral tunnel placement can restore rotatory and anterior knee stability similarly to an anatomical reconstruction when the knee is near extension. However, the same is not true when the knee is at high flexion angles. Clinical Relevance To reproduce the complex function of the anterior cruciate ligament, reproducing both bundles of the anterior cruciate ligament may be necessary.

Effects of Increasing Tibial Slope on the Biomechanics of the Knee

Purpose To determine the effects of increasing anterior-posterior (A-P) tibial slope on knee kinematics and in situ forces in the cruciate ligaments. Methods Ten cadaveric knees were studied using a robotic testing system using three loading conditions: (1) 200 N axial compression; (2) 134 N A-P tibial load; and (3) combined 200 N axial and 134 N A-P loads. Resulting knee kinematics were determined before and after a 5-mm anterior opening wedge osteotomy. Resulting in situ forces in each cruciate ligament were determined. Results Tibial slope was increased from 8.8 ± 1.8 ° to 13.2 ± 2.1 °, causing an anterior shift in the resting position of the tibia relative to the femur up to 3.6 ± 1.4 mm. Under axial compression, the osteotomy caused a significant anterior tibial translation up to 1.9 ± 2.5 mm (90 °). Under A-P and combined loads, no differences were detected in A-P translation or in situ forces in the cruciates (intact versus osteotomy). Conclusions Results suggest that small increases in tibial slope do not affect A-P translations or in situ forces in the cruciate ligaments. However, increasing slope causes an anterior shift in tibial resting position that is accentuated under axial loads. This suggests that increasing tibial slope may be beneficial in reducing tibial sag in a PCL-deficient knee, whereas decreasing slope may be protective in an ACL-deficient knee.

Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction.

The focus of most anterior cruciate ligament reconstructions has been on replacing the anteromedial bundle and not the posterolateral bundle. Anatomic two-bundle reconstruction restores knee kinematics more closely to normal than does single-bundle reconstruction. Controlled laboratory study. Ten cadaveric knees were subjected to external loading conditions: 1) a 134-N anterior tibial load and 2) a combined rotatory load of 5-N x m internal tibial torque and 10-N x m valgus torque. Resulting knee kinematics and in situ force in the anterior cruciate ligament or replacement graft were determined by using a robotic/universal force-moment sensor testing system for 1) intact, 2) anterior cruciate ligament deficient, 3) single-bundle reconstructed, and 4) anatomically reconstructed knees. Anterior tibial translation for the anatomic reconstruction was significantly closer to that of the intact knee than was the single-bundle reconstruction. The in situ force normalized to the intact anterior cruciate ligament for the anatomic reconstruction was 97% +/- 9%, whereas the single-bundle reconstruction was only 89% +/- 13%. With a combined rotatory load, the normalized in situ force for the single-bundle and anatomic reconstructions at 30 degrees of flexion was 66% +/- 40%and 91% +/- 35%, respectively. Anatomic reconstruction may produce a better biomechanical outcome, especially during rotatory loads. Results may lead to the use of a two-bundle technique.

The effect of axial tibial torque on the function of the anterior cruciate ligament: A biomechanical study of a simulated pivot shift test

Purpose: Various techniques are used to produce the pivot shift phenomenon after anterior cruciate ligament (ACL) injury. In particular, the amount of applied axial tibial torque varies among examiners. Thus, the objective of this study was to determine the effect of the magnitude and direction of axial tibial torque in combination with valgus torque on the resulting knee kinematics during such a simulated pivot shift test. Type of Study: This was a biomechanical study that used cadaveric knees with the intact knee of the same specimen serving as a control. Methods: On 19 human cadaveric knees (age, 26 to 69 years), a constant 10-Nm valgus torque was applied at 15° of knee flexion. Then, internal and external tibial torque was applied incrementally from 0 to 10 Nm and the resulting kinematics of the ACL-intact and ACL-deficient knee, as well as the in situ force in the ACL, were measured using a robotic/universal force-moment sensor testing system. Results: In response to isolated valgus torque, the coupled anterior tibial translation for the ACL-intact and ACL-deficient knee was 1.6 ± 2.4 mm and 8.5 ± 4.7 mm, respectively; therefore the difference between the ACL-intact and ACL-deficient knee was 6.9 ± 3.4 mm. With an external tibial torque greater than 5 Nm, the tibia translated up to 4 mm posteriorly for both the ACL-intact and ACL-deficient knee. Whereas, internal tibial torque greater than 1.6 Nm caused a rapid increase in coupled anterior tibial translation up to 10.2 mm in the ACL-deficient knee, while causing only a gradual increase for the ACL-intact knee. With excessive internal torque of 10 Nm, the difference in coupled anterior tibial translation was only 4.4 ± 2.2 mm, suggesting a decrease in the sensitivity of the test. Correspondingly, the in situ force in the ACL under 10 Nm valgus tibial torque was 43 ± 17 N, and increased up to 87 ± 32 N as a 10-Nm internal torque was added. By applying a 3.3-Nm external tibial torque in addition to the 10-Nm valgus torque, the in situ force decreased to 21 ± 14 N. Conclusions: This study showed that a minimal amount of internal torque in combination with valgus torque may be a suitable way to elicit a pivot shift from an ACL-deficient knee.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 4 (April), 2002: pp 394–398

Significance of Changes in the Reference Position for Measurements of Tibial Translation and Diagnosis of Cruciate Ligament Deficiency

Measurements of tibial translation in response to an external load are used in clinical and laboratory settings to diagnose and characterize knee-ligament injuries. Before these measurements can be quantified, a reference position of the knee must be established (defined as the position of the knee with no external forces or moments applied). The objective of this study was to determine the effects of cruciate ligament deficiency on this reference position and on subsequent measurements of tibial translation and, in so doing, to establish a standard of kinematic measurement for future biomechanical studies. Thirty-six human cadaveric knees were studied with a robotic/universal force-moment sensor testing system. The reference positions of the intact and posterior cruciate ligament-deficient knees of 18 specimens were determined at full extension and at 30, 60, 90, and 120 degrees of flexion, and the remaining five-degree-of-freedom knee motion was unrestricted. Subsequently, under a 134-N anterior-posterior load, the resulting knee kinematics were measured with respect to the reference positions of the intact and posterior cruciate ligament-deficient knees. With posterior cruciate ligament deficiency, the reference position of the knee moved significantly in the posterior direction, reaching a maximal shift of 9.3 +/- 3.8 mm at 90 degrees of flexion. For the posterior cruciate ligament-deficient knee, posterior tibial translation ranged from 13.0 +/- 3.4 to 17.7 +/- 3.6 mm at 30 and 90 degrees, respectively, when measured with respect to the reference positions of the intact knee. When measured with respect to the reference positions of the posterior cruciate ligament-deficient knee, these values were significantly lower, ranging from 11.7 +/- 4.3 mm at 30 degrees of knee flexion to 8.4 +/- 4.8 mm at 90 degrees. A similar protocol was performed to study the effects of anterior cruciate ligament deficiency on 18 additional knees. With anterior cruciate ligament deficiency, only a very small anterior shift in the reference position was observed. Overall, this shift did not significantly affect measurements of tibial translation in the anterior cruciate ligament-deficient knee. Thus, when the tibial translation in the posterior cruciate ligament-injured knee is measured when the reference position of the intact knee is not available, errors can occur and the measurement may not completely reflect the significance of posterior cruciate ligament deficiency. However, there should be less corresponding error when measuring the tibial translation of the anterior cruciate ligament-injured knee because the shift in reference position with anterior cruciate ligament deficiency is too small to be significant. We therefore recommend that in the clinical setting, where the reference position of the knee changes with injury, comparison of total anterior-posterior translation with that of the uninjured knee can be a more reproducible and accurate measurement for assessing cruciate-ligament injury, especially in posterior cruciate ligament-injured knees. Similarly, in biomechanical testing where tibial translations are often reported for the ligament-deficient and reconstructed knees, a fixed reference position should be chosen when measuring knee kinematics. If such a standard is set, measurements of knee kinematics will more accurately reflect the altered condition of the knee and allow valid comparisons between studies.

Significance of changes in the reference position for measurements of tibial translation and diagnosis of cruciate ligament deficiency.

Measurements of tibial translation in response to an external load are used in clinical and laboratory settings to diagnose and characterize knee-ligament injuries. Before these measurements can be quantified, a reference position of the knee must be established (defined as the position of the knee with no external forces or moments applied). The objective of this study was to determine the effects of cruciate ligament deficiency on this reference position and on subsequent measurements of tibial translation and, in so doing, to establish a standard of kinematic measurement for future biomechanical studies. Thirty-six human cadaveric knees were studied with a robotic/universal force-moment sensor testing system. The reference positions of the intact and posterior cruciate ligament-deficient knees of 18 specimens were determined at full extension and at 30, 60, 90, and 120 degrees of flexion, and the remaining five-degree-of-freedom knee motion was unrestricted. Subsequently, under a 134-N anterior-posterior load, the resulting knee kinematics were measured with respect to the reference positions of the intact and posterior cruciate ligament-deficient knees. With posterior cruciate ligament deficiency, the reference position of the knee moved significantly in the posterior direction, reaching a maximal shift of 9.3 +/- 3.8 mm at 90 degrees of flexion. For the posterior cruciate ligament-deficient knee, posterior tibial translation ranged from 13.0 +/- 3.4 to 17.7 +/- 3.6 mm at 30 and 90 degrees, respectively, when measured with respect to the reference positions of the intact knee. When measured with respect to the reference positions of the posterior cruciate ligament-deficient knee, these values were significantly lower, ranging from 11.7 +/- 4.3 mm at 30 degrees of knee flexion to 8.4 +/- 4.8 mm at 90 degrees. A similar protocol was performed to study the effects of anterior cruciate ligament deficiency on 18 additional knees. With anterior cruciate ligament deficiency, only a very small anterior shift in the reference position was observed. Overall, this shift did not significantly affect measurements of tibial translation in the anterior cruciate ligament-deficient knee. Thus, when the tibial translation in the posterior cruciate ligament-injured knee is measured when the reference position of the intact knee is not available, errors can occur and the measurement may not completely reflect the significance of posterior cruciate ligament deficiency. However, there should be less corresponding error when measuring the tibial translation of the anterior cruciate ligament-injured knee because the shift in reference position with anterior cruciate ligament deficiency is too small to be significant. We therefore recommend that in the clinical setting, where the reference position of the knee changes with injury, comparison of total anterior-posterior translation with that of the uninjured knee can be a more reproducible and accurate measurement for assessing cruciate-ligament injury, especially in posterior cruciate ligament-injured knees. Similarly, in biomechanical testing where tibial translations are often reported for the ligament-deficient and reconstructed knees, a fixed reference position should be chosen when measuring knee kinematics. If such a standard is set, measurements of knee kinematics will more accurately reflect the altered condition of the knee and allow valid comparisons between studies.

Biomechanical analysis of a posterior cruciate ligament reconstruction. Deficiency of the posterolateral structures as a cause of graft failure.

We hypothesized that posterior cruciate ligament reconstructions are often compromised by associated injuries to the posterolateral structures. Therefore, we evaluated a posterior cruciate ligament reconstruction in isolated and combined injury models using a robotic/universal force-moment sensor testing system. The resulting knee kinematics and the in situ forces in the native and reconstructed posterior cruciate ligament were determined under four external loading conditions. In the isolated injury model, reconstruction reduced posterior tibial translation to within 1.5+/-1.3 to 2.4+/-1.4 mm of the intact knee at 30 degrees and 90 degrees under a 134-N posterior tibial load. In the combined injury model, deficiency of the posterolateral structures increased posterior tibial translation of the reconstructed knee by 6.0+/-2.7 mm at 30 degrees and 4.6+/-1.5 mm at 90 degrees of flexion. External rotation increased up to 14 degrees while varus rotation increased up to 7 degrees. In situ forces in the posterior cruciate ligament graft also increased significantly (by 22% to 150%) for all loading conditions. Our results demonstrate that a graft that restores knee kinematics for an isolated posterior cruciate ligament deficiency is rendered ineffective and may be overloaded if the posterolateral structures are deficient. Therefore, surgical reconstruction of both structures is recommended in the setting of a combined injury.

The effect of anterior cruciate ligament graft fixation site at the tibia on knee stability: Evaluation using a robotic testing system

Despite its current popularity and relative success, endoscopic reconstruction of the anterior cruciate ligament (ACL) using a bone-patellar tendon-bone (BPTB) graft has not yet been perfected. Using a recently developed robotic/UFS testing system, we assessed the overall stability of porcine knees following ACL reconstruction with different sites of tibial graft fixation—proximal, central, and distal. Testing of the intact knee was performed first to determine the normal anterior-posterior (A-P) displacements and in situ forces of the ACL under 110 N of anterior tibial loading at 30°, 60°, and 90° of knee flexion. The knee was then reconstructed with a BPTB autograft, and the distal end of the graft was fixed sequentially at three different locations in each specimen—proximal, central, distal. A-P testing was repeated for each fixation site, and the resulting knee kinematics and the in situ forces of the grafts were compared to the intact case. The site of tibial fixation was demonstrated to have a significant effect on the resulting anterior displacement and internal rotation of the tibia as well as the in situ forces of the graft. Proximal fixation produced the most stable knee (A-P displacements reduced to 120% of intact at 30° and 170% at 90°), becoming significantly less stable with more distal fixation. These results suggest that proximal graft fixation may provide the most acute stability of the reconstructed knee.