Sensor Testing System Research Articles

Hill-Sachs Defects and Repair Using Osteoarticular Allograft Transplantation

Background Humeral head defects have been associated with failed anterior shoulder instability repairs. Quantitative data are required to determine (1) the critical defect size for consideration of surgical repair and (2) the ability of proposed repair techniques to restore normal joint function. Hypotheses Increasing defect size will decrease stability and anterior translation before dislocation. Stability will decrease in shoulder positions where the defect is oriented in line with the anterior glenoid. Osteoarticular repair will restore joint stability to intact shoulder level. Study design Controlled laboratory study. Methods A robotic/universal force-moment sensor testing system was used to apply joint compression (22 N) and an anterior load (40 N) to cadaveric shoulders (n = 9) with all soft tissues removed (intact) at joint orientations with 60° of glenohumeral abduction and 0° and 60° of external rotation. Four posterolateral osteoarticular defects were created (12.5%, 25.0%, 37.5%, and 50.0% defect) followed by an osteoarticular allograft transplantation (repair). The loading protocol was repeated in each shoulder state for both joint orientations. The anterior translation and stability ratio (anterior load/compressive load) were recorded before dislocation. Results All shoulders dislocated at 60° of external rotation with all sizes of defects. At 0° of external rotation, shoulders with the 12.5% to 37.5% defects did not dislocate, and only 2 shoulders with the 50.0% defect dislocated. At 60° of external rotation, the 25.0% defect and 37.5% defect had significantly less anterior translation before dislocation, as compared with the intact (P < .05), both of which became similar to the intact after repair (P > .05). The stability ratio at 60° of external rotation significantly decreased in the 25.0% and 37.5% defects, as compared with the intact (P < .05), representing a 25% and 40% decrease in stability ratio. The stability ratio became similar to intact after repair (P > .05). Conclusion The size and orientation of the defect has important contributions to glenohumeral joint function. Increasing defect size required less anterior translation before dislocation and decreased the stability ratio, thereby increasing the risk of recurrent instability. Clinical Relevance Defects as small as 12.5% of the humeral head have biomechanical consequences that may affect joint stability. In addition, shoulders with large osteoarticular defects (37.5% or 50.0%) may benefit from osteoarticular allograft transplantation to restore shoulder stability.

Evaluation of Knee Stability with Use of a Robotic System

In our research center, we have developed and utilized a novel robotic/universal force-moment sensor testing system to gain quantitative data on multiple-degree-of-freedom kinematics of the knee simultaneously with data on the in situ forces in normal and repaired soft tissues. In particular, we have investigated the complex interaction of the anteromedial and posterolateral bundles of the anterior cruciate ligament as well as several key biomechanical variables in anterior cruciate ligament reconstruction, such as graft selection and femoral tunnel placement (both of which impact knee stability). For example, both the bone-patellar tendon-bone and quadrupled hamstrings tendon autografts restored anterior stability but were insufficient in gaining rotatory stability. In a follow-up study, we have shown that a more laterally placed graft was beneficial and could improve these outcomes. Such findings led to additional investigation in which the biomechanical advantages of double-bundle anterior cruciate ligament reconstruction were demonstrated. However, a more laterally placed autograft at the femoral insertion of the posterolateral bundle also worked well, especially when the knee was nearly at full extension (a position in which the anterior cruciate ligament is needed most). At present, we are moving forward by obtaining in vivo kinematics data and then repeating those kinematics exactly to obtain new data with use of the robotic/universal force-moment sensor testing system in order to gain further insight regarding the function of the anterior cruciate ligament and anterior cruciate ligament replacement grafts in vivo. In parallel, we are developing a mathematical model of the knee and validating the computational model with experimental data. The combined approach will yield new and relevant information, including the stress and strain distribution in the anterior cruciate ligament and anterior cruciate ligament grafts. This will facilitate a better understanding of the function of the anterior cruciate ligament and a scientifically based design of surgical procedures and postoperative rehabilitation protocols that will lead to better patient outcomes.

Tension patterns of the anteromedial and posterolateral grafts in a double‐bundle anterior cruciate ligament reconstruction

The two functional bundles of the anterior cruciate ligament (ACL), namely, the anteromedial (AM) and posterolateral (PL) bundles, must work in concert to control displacement of the tibia relative to the femur for complex motions. Thus, the replacement graft(s) for a torn ACL should possess similar tension patterns. The objective of the study was to examine whether a double-bundle ACL reconstruction with the semitendinosus-gracilis autografts could replicate the tension patterns of those for the intact ACL under controlled in vitro loading conditions. By means of a robotic/universal force moment sensor (UFS) testing system, the in situ force vectors (both magnitude and direction) for the AM and PL bundles of the ACL, as well as their respective replacement grafts, were determined and compared on nine human cadaveric knees. It was found that double-bundle ACL reconstruction could closely replicate the in situ force vectors. Under a 134-N anterior tibial load, the resultant force vectors for the intact ACL and the reconstructed ACL had a difference of 5 to 11 N (p > 0.05) in magnitude and 1 to 13 degrees (p > 0.05) in direction. Whereas, under combined rotatory loads of 10-N-m valgus and 5-N-m internal tibial torques, the corresponding differences were 10 to 16 N and 4 degrees to 11 degrees, respectively. Again, there were no statistically significant differences except at 30 degrees of flexion where the force vector for the AM graft had a 15 degrees (p < 0.05) lower elevation angle than did the AM bundle.

Intercondylar roof impingement pressure after anterior cruciate ligament reconstruction in a porcine model

Anterior cruciate ligament (ACL) graft impingement against the intercondylar roof has been postulated, but not thoroughly investigated. The roof impingement pressure changes with different tibial and femoral tunnel positions in ACL reconstruction. Anterior tibial translation is also affected by the tunnel positions of ACL reconstruction. The study design included a controlled laboratory study. In 15 pig knees, the impingement pressure between ACL and intercondylar roof was measured using pressure sensitive film before and after ACL single bundle reconstruction. ACL reconstructions were performed in each knee with two different tibial and femoral tunnel position combinations: (1) tibial antero-medial (AM) tunnel to femoral AM tunnel (AM to AM) and (2) tibial postero-lateral (PL) tunnel to femoral High-AM tunnel (PL to High-AM). Anterior tibial translation (ATT) was evaluated after each ACL reconstruction using robotic/universal force-moment sensor testing system. Neither the AM to AM nor the PL to High-AM ACL reconstruction groups showed significant difference when compared with intact ACL in roof impingement pressure. The AM to AM group had a significantly higher failure load than PL to High-AM group. This study showed how different tunnel placements affect the ACL-roof impingement pressure and anterior-posterior laxity in ACL reconstruction. Anatomical ACL reconstruction does not cause roof impingement and it has a biomechanical advantage in ATT when compared with non-anatomical ACL reconstructions in the pig knee. There is no intercondylar roof impingement after anatomical single bundle ACL reconstruction.

Anatomical and Nonanatomical Double-Bundle Anterior Cruciate Ligament Reconstruction

Background Studies have suggested that double-bundle anterior cruciate ligament reconstruction may restore intact knee kinematics better than single-bundle anterior cruciate ligament reconstruction. Although the tunnel position of the femoral anteromedial bundle is well established, the effects of different posterolateral bundle positions on knee kinematics are unknown. Hypothesis Double-bundle anterior cruciate ligament reconstruction with an anatomical (shallow) femoral posterolateral bundle tunnel placement will restore knee kinematics more closely than will a nonanatomical (deep) femoral posterolateral bundle tunnel position. Study Design Controlled laboratory study. Methods In 12 human cadaveric knees, the kinematics of the intact knee, anterior cruciate ligament-deficient knee, and double-bundle anterior cruciate ligament-reconstructed knees with nonanatomical femoral posterolateral tunnel placement and anatomical posterolateral bundle placement were determined in response to a 134-N anterior tibial load and a combined rotatory load of 10 Nm valgus and 4 Nm internal tibial rotation using a robotic/universal force moment sensor testing system. Statistical analyses were performed using a 2-way analysis of variance test. Results Double-bundle anterior cruciate ligament reconstruction with nonanatomical posterolateral bundle placement showed significantly higher anterior tibial translation under anterior tibial and combined rotatory load than did the intact knee at 0° and 30° of knee flexion (P < .05). Reconstruction with an anatomical posterolateral tunnel placement restored the intact knee kinematics and showed significantly lower anterior tibial translation under anterior tibial and combined rotatory load when compared with reconstruction with nonanatomical posterolateral placement (P < .05). Conclusion Double-bundle anterior cruciate ligament reconstruction using the anatomical posterolateral bundle tunnel position restores the intact knee kinematics. A nonanatomical posterolateral bundle position results in rotatory instability. Clinical Relevance Double-bundle anterior cruciate ligament reconstruction should be performed using anatomical tunnel placement of the anteromedial and posterolateral bundles. Nonanatomical double-bundle reconstruction may fail to show any clinical superiority to single-bundle reconstruction and should be avoided.

The Role of the Posterior Oblique Ligament in Controlling Posterior Tibial Translation in the Posterior Cruciate Ligament-Deficient Knee

Background Posterior cruciate ligament injuries are often associated with injuries to other structures. The role of the posteromedial structures of the knee in these injuries has received little attention. Hypothesis The posterior oblique ligament is an important restraint to posterior tibial translation in the posterior cruciate ligament–deficient knee. Study Design Controlled laboratory study. Methods Kinematic studies were performed on 10 cadaveric knees to test 3 external loading conditions at 0°, 30°, 60°, and 90° of flexion (134 N posterior tibial load, 10 N·m valgus rotation, and 5 N·m internal rotation). Resulting posterior tibial translation was determined by using a robotic/universal force-moment sensor testing system for (1) intact, (2) posterior cruciate ligament–deficient, (3) posterior cruciate ligament/superficial medial collateral ligament–deficient, (4) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament–deficient, and (5) posterior cruciate ligament/superficial medial collateral ligament/deep medial collateral ligament/posterior oblique ligament/posteromedial capsule–deficient knee. Results When both the superficial medial collateral ligament and deep medial collateral ligament were cut in the posterior cruciate ligament–deficient knee, posterior tibial translation did not increase significantly at any flexion grade under all external loading conditions (P > .05). Additional cutting of the posterior oblique ligament increased posterior tibial translation significantly at 0°, 30°, 60°, and 90° of flexion under posterior tibial load and at all flexion angles tested under valgus or internal tibial load (P < .05). Additional cutting of the posteromedial capsule increased posterior tibial translation only at 0° and 30° in response to a valgus and internal tibial load (P < .05). Conclusion The posterior oblique ligament and posteromedial capsule have a significant role in the prevention of additional posterior tibial translation in the knee with posterior cruciate ligament injury. Clinical Relevance The posterior oblique ligament should be addressed in the patient with combined injuries to the posterior cruciate ligament and the posteromedial structures.

Importance of Tibial Slope for Stability of the Posterior Cruciate Ligament—Deficient Knee

Background Previous studies have shown that increasing tibial slope can shift the resting position of the tibia anteriorly. As a result, sagittal osteotomies that alter slope have recently been proposed for treatment of posterior cruciate ligament (PCL) injuries. Hypotheses Increasing tibial slope with an osteotomy shifts the resting position anteriorly in a PCL-deficient knee, thereby partially reducing the posterior tibial “sag” associated with PCL injury. This shift in resting position from the increased slope causes a decrease in posterior tibial translation compared with the PCL-deficient knee in response to posterior tibial and axial compressive loads. Study Design Controlled laboratory study. Methods Three knee conditions were tested with a robotic universal force-moment sensor testing system: intact, PCL-deficient, and PCL-deficient with increased tibial slope. Tibial slope was increased via a 5-mm anterior opening wedge osteotomy. Three external loading conditions were applied to each knee condition at 0°, 30°, 60°, 90°, and 120° of knee flexion: (1) 134-N anterior-posterior (A-P) tibial load, (2) 200-N axial compressive load, and (3) combined 134-N A-P and 200-N axial loads. For each loading condition, kinematics of the intact knee were recorded for the remaining 5 degrees of freedom (ie, A-P, medial-lateral, and proximal-distal translations, internal-external and varus-valgus rotations). Results Posterior cruciate ligament deficiency resulted in a posterior shift of the tibial resting position to 8.4 ± 2.6 mm at 90° compared with the intact knee. After osteotomy, tibial slope increased from 9.2° ± 1.0° in the intact knee to 13.8° ± 0.9°. This increase in slope reduced the posterior sag of the PCL-deficient knee, shifting the resting position anteriorly to 4.0 ± 2.0 mm at 90°. Under a 200-N axial compressive load with the osteotomy, an additional increase in anterior tibial translation to 2.7 ± 1.7 mm at 30° was observed. Under a 134-N A-P load, the osteotomy did not significantly affect total A-P translation when compared with the PCL-deficient knee. However, because of the anterior shift in resting position, there was a relative decrease in posterior tibial translation and increase in anterior tibial translation. Conclusion Increasing tibial slope in a PCL-deficient knee reduces tibial sag by shifting the resting position of the tibia anteriorly. This sag is even further reduced when the knee is subjected to axial compressive loads. Clinical Relevance These data suggest that increasing tibial slope may be beneficial for patients with PCL-deficient knees.

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Introduction: Osteoarticular lesions of the humeral head are often observed after shoulder dislocations. 1 Matsen F.A. et al. The shoulder. 1994 Google Scholar The presence of such lesions could contribute to changes in position of the humeral head with respect to the glenoid. These alterations in the position of the humerus may lead to joint subluxation and the development of osteoarthritis. 2 Hawkins R.J. et al. JBJS. 1990; 72: 1193-1197 PubMed Google Scholar The objective of this study was to determine the effects of osteoarticular lesions on the position of the humeral head during the application of a compressive force to the humerus. Methods: Nine fresh-frozen cadaveric shoulders were dissected free of all skin and musculature except for the coracoacromial ligament and labrum. (Intact joint.) The humerus and scapula were then potted in epoxy putty and fixed within a robotic/universal force-moment sensor (UFS) testing system. 3 Debski R.E. et al. J Orthop Res. 1999; 17: 769-776 Crossref PubMed Scopus (82) Google Scholar The joint was initially oriented in the testing system at 60° of glenohumeral abduction and 0° of external rotation. A 22 N joint compressive force was applied to the humerus while minimizing the forces in the orthogonal directions to center the humeral head within the glenoid cavity. The joint orientation was held constant during application of the compressive force. This protocol was then repeated after the joint was moved to 60° of glenohumeral abduction and 60° of external rotation. Three osteoarticular lesions on the posterolateral side of the humeral head were subsequently created to simulate an injury that would occur during joint dislocation at 60° of glenohumeral abduction and 60° of external rotation. The size of each lesion was approximately 12.5% (Lesion 1), 25% (Lesion 2), and 27.5% (Lesion 3) of the humeral head diameter and was created using an oscillating bone saw. The compressive force was applied again to the shoulders at 60° glenohumeral abduction and both external rotation angles in each lesion state. The position of the humerus was recorded for each joint orientation following application of the compressive force. The change in the position of the humerus for each lesion state was then calculated and paired t-tests were used to determine significant differences between the position of the humerus for the intact joint and each lesion state (p<0.05). Results: No significant changes in joint position were found for all lesion states at 0° external rotation (less than 1 mm for each direction; p>0.05). The largest changes in position compared to the intact joint were found for Lesion 2 and 3 at 60° external rotation. The position of the humerus for Lesion 2 shifted 1.3±1.4 mm and 2.5±1.6 mm in the medial and posterior directions, respectively. The position of the humerus for Lesion 3 shifted 1.8±1.1 mm and 1.9±1.5 mm in the medial and posterior directions, respectively. These changes in position were statistically significant (p<0.05). No significant changes in joint position were found for Lesion 1 with the humerus shifting by less than 1 mm in all directions. Discussion: This study evaluated the effect of osteoarticular lesions on the position of the humeral head with respect to the glenoid. A significant effect was found when the size of the lesion was greater than 25% of the humeral head diameter (Lesions 2 and 3). However, smaller lesions did not affect bony contact between the humeral head and glenoid, and consequently the position of the humerus. In addition, the change in position was dependent on the location of the lesion and orientation of the joint. These altered joint positions could contribute to abnormal joint contact and the development of osteoarthritis. 2 Hawkins R.J. et al. JBJS. 1990; 72: 1193-1197 PubMed Google Scholar In the future, the effect of the lesions on the contact forces and forces in the glenohumeral capsule will be examined. If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use). If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use).

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.

Differences in Torsional Joint Stiffness of the Knee between Genders

Background In many sports, female athletes have a higher incidence of anterior cruciate ligament injury than do male athletes. Among many risk factors, the lower rotatory joint stiffness of female knees has been suggested for the increased rate of anterior cruciate ligament injuries. Hypothesis In response to combined rotatory loads, female knees have significantly lower torsional joint stiffness and higher rotatory joint laxity than do male knees at low flexion angles, despite the fact that no such gender differences would be found in response to an anterior tibial load. Study Design Comparative laboratory study. Methods Joint kinematics of 82 human cadaveric knees (38 female, 44 male) in response to (1) combined rotatory loads of 10 N·m valgus and ±5 N·m internal tibial torques and (2) a 134-N anterior-posterior tibial load were measured using a robotic/universal force-moment sensor testing system. Results In response to combined rotatory loads, female knees had as much as 25% lower torsional joint stiffness (female: 0.79 N·m/deg; 95% confidence interval, 0.67-0.91; male: 1.06 N·m/deg; 95% confidence interval, 0.95-1.17) and up to 35% higher rotatory joint laxity (female: 26.2°; 95% confidence interval, 24.5°-27.9°; male: 20.5°; 95% confidence interval, 18.8°-22.2°) than did male knees (P < .05), whereas there were no gender differences in response to the anterior tibial load (P > .05). Conclusion Female knees had lower torsional joint stiffness and higher rotatory joint laxity than did male knees in response to combined rotatory loads. Clinical Relevance Larger axial rotations of female knees in response to rotatory loads may affect the distribution of forces in soft tissues and the function of muscles that provide knee stability. Control algorithms used during the biomechanical testing of cadaveric knees and computational knee models might need to be gender specific.

Effect of the iliotibial band on knee biomechanics during a simulated pivot shift test

The purpose of this study was to evaluate the effect of the iliotibial band (ITB) on the kinematics of anterior cruciate ligament (ACL) intact and deficient knees and also on the in situ force in the ACL during a simulated pivot shift test. A combination of 10 N-m valgus and 5 N-m internal tibial torques was applied to 10 human cadaveric knees at 15 degrees, 30 degrees, 45 degrees, and 60 degrees of flexion using a robotic/universal force-moment sensor testing system. ITB forces of 0, 22, 44, and 88 N were also applied. An 88 N ITB force significantly decreased coupled anterior tibial translation of ACL deficient knees by 32%-45% at high flexion angles, but did not have a significant effect at low flexion angles. Further, an 88 N ITB force significantly decreased in situ forces in the ACL at all flexion angles by 23%-40%. These results indicate that during the pivot shift test, the ITB can improve tibial reduction at high flexion angles while not affecting subluxation at low flexion angles. Additionally, the action of the ITB as an ACL agonist suggests that its use as an ACL graft might hinder knee stability in response to rotatory load.

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.

Joint kinematics and in situ forces after single bundle PCL reconstruction: a graft placed at the center of the femoral attachment does not restore normal posterior laxity

Femoral tunnel placement has a great influence on the clinical outcome after PCL reconstruction. Using a robotic/universal force moment sensor (UFS) testing system, we examined joint kinematics and in situ forces of human knees following soft-tissue single bundle PCL reconstruction fixed at the center of the femoral attachment. Posterior tibial translation significantly increased at all flexion angles after transsection of the posterior cruciate ligament (p<0.05). PCL reconstruction resulted in significantly less posterior tibial translation at all flexion angles when compared to the PCL deficient knee (p<0.05). The differences in the in situ force between the intact ligament and the reconstructed graft were statistical significant (p<0.05). Single bundle PCL reconstruction with a soft-tissue graft fixed at the center of the femoral attachment is able to reduce the posterior tibial translation significantly. However, it cannot restore kinematics of the intact knee and in situ forces of the intact PCL.

Biomechanics of Initial Tibial Fixation in Posterior Cruciate Ligament Reconstruction

Clinical success of posterior cruciate ligament (PCL) reconstruction continues to lag behind that of its anterior counterpart. The tibial site of PCL graft fixation has been a focus of recent research. This study examined the effect of combined distal and proximal tibial fixation on the ability of a transtibial PCL reconstruction to restore intact knee kinematics and in situ forces of the intact PCL. Biomechanical study. Ten human cadaveric knees were tested. A 134-N posterior tibial load was applied using a robotic/universal force moment sensor testing system at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of knee flexion. Each knee was tested under 4 conditions: intact, PCL-deficient, single-bundle transtibial reconstruction with distal tibial fixation, and single-bundle transtibial reconstruction with combined distal and proximal tibial fixation. Knee kinematics in 5 degrees of freedom for each condition were recorded and in situ forces of the intact PCL and the PCL grafts were determined. Reconstruction with combined fixation resulted in significantly less posterior tibial translation than reconstruction with distal fixation at 30 degrees, 90 degrees, and 120 degrees (P < .05), and restored intact knee kinematics at 90 degrees and 120 degrees (P > .05). Reconstruction with combined fixation more closely restored intact PCL in situ forces at 90 degrees (P < .05). Transtibial reconstruction with combined fixation more closely restores intact knee kinematics and in situ forces in the PCL at initial fixation than does reconstruction with distal tibial fixation. The improved kinematics and in situ forces seen with the combined fixation may be attributed to decreased functional graft length and increased stiffness of the PCL graft. Combined tibial fixation may provide a more stable reconstruction at initial fixation.

The Effectiveness of Reconstruction of the Anterior Cruciate Ligament Using the Novel Knot/Press-Fit Technique

Background A variety of fixation devices are used for anterior cruciate ligament reconstruction with hamstring tendon grafts. These devices increase costs and can present artifacts in magnetic resonance imaging as well as complications in revision surgery. Therefore, a novel knot/press-fit technique that requires no implantable devices has been introduced. Null Hypothesis The knot/press-fit technique restores knee kinematics as well as the more commonly used EndoButton CL fixation and has similar biomechanical properties as other devices published in the literature. Study Design Controlled laboratory study. Methods Eight fresh-frozen cadaveric knees (52 ± 7 years) were tested using a robotic/universal force-moment sensor testing system. The knee kinematics of the intact, anterior cruciate ligament-deficient, EndoButton-reconstructed, and knot/pressfit-reconstructed knee in response to both a 134-N anterior tibial load and a combined rotatory load at multiple knee flexion angles was determined. Differences between the 4 knee states were evaluated with a 2-factor repeated-measures analysis of variance (P <. 05). To determine the stiffness and strength of the knot/press-fit fixation, the femur-graft-tibia complex was tested in uniaxial tension. Results In response to an anterior tibial load, the anterior tibial translation for the knot/press-fit reconstruction was found to be not significantly different from that of the intact anterior cruciate ligament as well as that of the EndoButton reconstruction (P >. 05). In response to a combined rotatory load, neither reconstruction procedure could effectively reduce the coupled anterior tibial translation to that of the intact knee, and no significant difference between the 2 reconstructions could be detected (P >. 05). The stiffness of the knot/press-fit complex was found to be 37.8 ± 9.6 N/mm, and the load at failure was 540 ± 97.7 N, which is equal to other devices published in the literature. Clinical Relevance The experiment suggests that the knot/press-fit technique may be a reliable alternative for the femoral fixation of hamstring tendon grafts.

Varying Femoral Tunnels between the Anatomical Footprint and Isometric Positions

Background Knee kinematics and in situ forces resulting from anterior cruciate ligament reconstructions with 2 femoral tunnel positions were evaluated. Hypothesis A graft placed inside the anatomical footprint of the anterior cruciate ligament will restore knee function better than a graft placed at a position for best graft isometry. Study Design Controlled laboratory study. Methods Ten cadaveric knees were tested in response to a 134-N anterior load and a combined 10-N·m valgus and 5-N·m internal rotation load. A robotic universal force-moment sensor testing system was used to apply loads, and resulting kinematics were recorded. An active surgical robot system was used for positioning tunnels in 2 locations in the femoral notch: inside the anatomical footprint of the anterior cruciate ligament and a position for best graft isometry. The same quadrupled hamstring tendon graft was used for both tunnel positions. The 2 loading conditions were applied. Results At 30° of knee flexion, anterior tibial translation in response to the anterior load for the intact knee was 9.8 ± 3.1 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 13.8 ± 4.6 mm; position 2: 16.6 ± 3.7 mm; P <. 05). There was a significant difference between the 2 tunnel positions. At the same flexion angle, the anterior tibial translation in response to the combined load for the intact knee was 7.7 ± 4.0 mm. Both femoral tunnel positions resulted in significantly higher anterior tibial translation (position 1: 10.4 ± 5.5 mm; position 2: 12.0 ± 5.2 mm; P <. 05), with a significant difference between the tunnel positions. Conclusion Neither femoral tunnel position restores normal kinematics of the intact knee. A femoral tunnel position inside the anatomical footprint of the anterior cruciate ligament results in knee kinematics closer to the intact knee than does a tunnel position located for best graft isometry. Clinical Relevance Anatomical femoral tunnel position is important in reproducing function of the anterior cruciate ligament.

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.

Experimental and Computational Modeling of Joint and Ligament Mechanics

Quantitative data on the mechanics of diarthrodial joints and the function of ligaments are needed to better understand injury mechanisms, improve surgical procedures, and develop improved rehabilitation protocols. Therefore, experimental and computational approaches have been developed to determine joint kinematics and the in-situ forces in ligaments and their replacement grafts using human cadaveric knee and shoulder joints. A robotic/universal force-moment sensor testing system is used in our research center for the evaluation of a wide variety of external loading conditions to study the function of ligaments and their replacements; it has the potential to reproduce in-vivo joint motions in a cadaver knee. Two types of computational models have also been developed: a rigid body spring model and a displacement controlled spring model. These computational models are designed to complement and enhance experimental studies so that more complex loading conditions can be examined and the stresses and strains in the soft tissues can be calculated. In the future, this combined approach will improve our understanding of these joints and soft tissues during in-vivo activities and serve as a tool to aid surgical planning and development of rehabilitation protocols.