Robotic Testing System Research Articles

Adaptation of a clinical fixation device for biomechanical testing of the lumbar spine

In-vitro biomechanical testing is widely performed for characterizing the load-displacement characteristics of intact, injured, degenerated, and surgically repaired osteoligamentous spine specimens. Traditional specimen fixture devices offer an unspecified rigidity of fixation, while varying in the associated amounts and reversibility of damage to and “coverage” of a specimen – factors that can limit surgical access to structures of interest during testing as well as preclude the possibility of testing certain segments of a specimen. Therefore, the objective of this study was to develop a specimen fixture system for spine biomechanical testing that uses components of clinically available spinal fixation hardware and determine whether the new system provides sufficient rigidity for spine biomechanical testing. Custom testing blocks were mounted into a robotic testing system and the angular deflection of the upper fixture was measured indirectly using linear variable differential transformers. The fixture system had an overall stiffness 37.0, 16.7 and 13.3 times greater than a typical human functional spine unit for the flexion/extension, axial rotation and lateral bending directions respectively – sufficient rigidity for biomechanical testing. Fixture motion when mounted to a lumbar spine specimen revealed average motion of 0.6, 0.6, and 1.5° in each direction. This specimen fixture method causes only minimal damage to a specimen, permits testing of all levels of a specimen, and provides for surgical access during testing.

A Novel Graft Fixation Technique for Anterior Cruciate Ligament Reconstruction Using Hamstring Tendon Grafts

This study evaluated the biomechanical efficacy of single-tunnel double-bundle anterior cruciate ligament (ACL) reconstruction technique. The graft construct is achieved using a novel fixation device that splits an ACL (SPACL) graft into two bundles, recreating the anteromedial (AM) and posterolateral (PL) bundles for ACL reconstruction. A pullout strength test of the SPACL was performed using a 7-mm bovine digital extensor tendon graft. The capability in restoration of knee kinematics after SPACL reconstruction was investigated using cadaveric human knees on a robotic testing system under an anterior tibial load of 134 N and a simulated quadriceps load of 400 N. The data indicated that the SPACL graft has a pullout strength of 823.7±172.3 N. Under the 134 N anterior tibial load, the anteroposterior joint laxity had increased constraint using the SPACL reconstruction but not significantly (p > 0.05) at all selected flexion angles. Under the 400 N quadriceps load, no significant differences were observed between the anterior tibial translation of intact knee and SPACL conditions at all selected flexion angles, but the SPACL graft induced a significant increase in external tibial rotation compared to the intact knee condition at all selected flexion angles with a maximal external rotation of −3.20 deg ±3.6 deg at 90 deg flexion. These data showed that the SPACL technique is equivalent or superior to existing ACL reconstruction techniques in restoration of knee laxity and kinematics. The new SPACL reconstruction technique could provide a valuable alternation to contemporary ACL reconstruction surgery by more closely recreating native ACL kinematics.

The Role of Extra-Articular Tenodesis in Combined ACL and Anterolateral Capsular Injury.

The "gold standard" treatment of anterolateral capsular injuries in anterior cruciate ligament (ACL)-deficient knees has not been determined. The purpose of this study was to determine the effects of ACL reconstruction and extra-articular reconstruction on joint motion in the ACL-deficient knee and in the combined ACL and anterolateral capsule-deficient knee. An anterior tibial load of 134 N and internal tibial torque of 7 Nm were applied to 7 fresh-frozen cadaveric knees using a robotic testing system continuously throughout the range of flexion. The resulting joint motion was recorded for 6 knee states: intact, ACL-deficient, ACL-reconstructed, combined ACL and anterolateral capsule-deficient, ACL-reconstructed + anterolateral capsule-deficient, and ACL-reconstructed + extra-articular tenodesis. Anterior tibial translation of the ACL-reconstructed + anterolateral capsule-deficient knee in response to an anterior tibial load was restored to that of the intact knee at all knee-flexion angles (p > 0.05). However, for this knee state, internal tibial rotation in response to internal tibial torque was not restored to that of the intact knee at 60° or 90° of knee flexion (p < 0.05). For the knee state of ACL-reconstructed + extra-articular tenodesis, internal rotation in response to internal tibial torque was restored to the motion of the intact knee at each of the tested knee-flexion angles (p > 0.05). Compared with the intact knee, 2 of 7 specimens showed decreased internal tibial rotation with ACL reconstruction + extra-articular tenodesis. In this study, an extra-articular tenodesis was necessary to restore rotatory knee stability in response to internal tibial torque in a combined ACL and anterolateral capsule-deficient knee. The amount of rotatory knee instability should be carefully assessed to avoid over-constraint of the knee in these combined ligament-reconstruction procedures. On the basis of our findings, the surgical procedure needs to be personalized depending on the amount of rotatory knee instability in the injured knee and the amount of rotation in the contralateral knee.

Graft Fixation Sequence in One-Stage Anterior Cruciate Ligament and Posterior Cruciate Ligament Reconstruction

According to the results of this study, the best fixation sequence for combined ACL/PCL reconstruction is when the ACL graft fixed first at close to full extension followed by the PCL graft fixation. There is no consensus regarding the best protocol for the sequence of graft tensioning and fixation in one-stage reconstruction of combined anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). This study sought to determine the effect of ACL/PCL graft tensioning and fixation protocol on knee biomechanics. It is hypothesized that the sequence to best restore intact knee kinematics and the intact tibial position will be the ACL graft fixed first at close to full extension and the PCL graft fixed second with the knee flexed. Twelve fresh-frozen mature porcine hind limbs (n=12) were used. The knees were tested using a robotic testing system with a universal force-moment sensor. One-stage, combined anatomic single bundle (SB) ACL and PCL reconstructions were performed with and 8 mm grafts from bovine extensor tendon. The knee states tested were: (1) intact ACL and intact PCL, (2) deficient ACL and deficient PCL, and (3) one-stage ACL and PCL reconstruction. Five fixation sequences were performed in each knee in a randomized order: (1) PCL fixed 1st at 30° and ACL fixed 2nd at 30° (Recon 1), (2) PCL fixed 1st at 90° and ACL fixed 2nd at 30° (Recon 2), (3) ACL fixed 1st at 30° and PCL fixed 2nd at 30° (Recon 3), (4) ACL fixed 1st at 30° and PCL fixed 2nd at 90° (Recon 4) and (5) ACL and PCL fixed simultaneously at 30° (Recon 5). Both grafts were tensioned to 40 N. Two external loading conditions were tested: an 89 N anterior tibial and a posterior tibial load at 30° (full extension in the porcine knee). A 3-dimensional digitizer was used to measure the anterior-posterior (A-P) shift of the tibia in each of the reconstructed knee positions from the intact knee position in the unloaded knee. Data was analyzed using one-way repeated measures ANOVA, and statistical significance was set at p<0.05. None of the reconstructions restored the range of A-P translation to that of the intact knee at 30° of flexion, where the A-P translation is the sum of the anterior tibial translation (ATT) and posterior tibial translation (PTT). The mean A-P translation was: 7.9 ±1.3 mm at intact ACL and PCL, 16.4 ± 3.7 mm at deficient ACL and PCL, 12.3 ± 2.2 mm at Recon 1, 12.1 ± 3.2 mm at Recon 2, 12.8 ± 3.3 mm at Recon 3, 13.5 ± 2.6 mm at Recon 4, and 13.1 ± 2.6 mm at Recon 5. The mean anterior shift was: 2.69 ± 1.41 mm in Recon 1, 2.73 ± 2.88 mm in Recon 2, 0.05 ± 0.60 mm in Recon 3, 0.44 ± 1.27 mm in Recon 4, and 1.02 ± 1.39 mm in Recon 5. From the results of this study, if the PCL graft is fixed first the tibia will shift anteriorly regardless of flexion angle of the knee. However, while the knee is at full extension (30° in the porcine knee), fixation of the ACL graft first only causes a smaller shift of the tibia. Thus, the ACL graft should be fixed first while the knee is at full extension, and then the PCL graft can be fixed at either a low or high flexion angle. While fixation of the ACL graft first at 30° of flexion does not cause a large shift of the tibia, the A-P translation is not restored by any of the five fixation sequences.

Significant Increases in Sagittal Translation and Transverse Rotation of the Fibula Occur with Sequential Disruption of the Syndesmosis

This study demonstrates that significant fibular motion occurs with isolated AITFL disruption and only minimally increases with sequential PITFL and IOM transection. Clinical diagnostic protocol should be expanded to evaluate beyond ML translation of the fibula and account for sagittal and rotational displacements as well. Injury to the Anterior inferior tibiofibular ligament (AITFL), Posterior inferior tibiofibular ligament (PITFL) and Interosseus membrane (IOM) predicts residual symptoms in ankle sprains. Limited kinematic knowledge of the tibiofibular joint results in missed diagnosis and poor clinical outcomes. Lateral fibular displacement on radiologic assessment signifies syndesmotic disruption which dictates operative management. Previous studies demonstrated that fibular motion is multiplanar after injury. The purpose of this study is to determine increases in fibular motion with sequential syndesmotic injury and the contribution of the AITFL. Five fresh-frozen human cadaveric tibial plateau-to-toe specimens with a mean age of 58 years (range 38-73 years) were tested using a 6-degree-of-freedom robotic testing system. The tibia and calcaneus were rigidly fixed. The subtalar joint was fused. The full fibular length was maintained and fibular motion was unconstrained. A 5Nm external rotation moment and 5Nm inversion moment were applied to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. The motion of the fibula was tracked by a 3D optical tracking system. Outcome variables included fibular medial-lateral (ML) translation, anterior-posterior (AP) translation, and external rotation (ER) during each max moment and flexion angle in the following conditions: 1) intact ankle, 2) AITFL transected, 3) PITFL and IOM transected. Statistical analysis included an ANOVA with a post-hoc Tukey analysis to compare the changes in fibular motion between the intact and injury models at each applied moment and flexion angle (*p<0.05). The only significant differences in fibular motion were during the 5Nm inversion moment. The posterior translation of the fibula was significantly greater with AITFL injury compared to the intact ankle at 15° and 30° plantarflexion. Significant increases in posterior translation between the intact ankle and AITFL, PITFL, and IOM injury exists at 0°, 15°, and 30° plantarflexion. No significant motion differences were observed between the AITFL injury and combined injury at any condition. When comparing the intact ankle and combined injury, significant increases in ER exist at 0° and 30° plantarflexion and 10° dorsiflexion. The only significant difference in ER between the intact ankle and AITFL injury exists at 0° plantarflexion. The data from this study showed that transecting the AITFL resulted in the largest increases fibular motion with only minimal further fibular displacement with transection of the PITFL and IOM. Total syndesmotic disruption creates significant fibular motion compared to the intact ankle but, a significant portion of the displacement of the fibula already occurs after isolated AITFL injury. A previous study demonstrated no measureable fibular ML displacement with syndesmosis injury but this was not supported by the current findings. This study utilized a novel setup with unconstrained motion in a full length, intact fibula. Basing clinical syndesmotic stability on ML translation alone could underestimate sagittal and rotation instability in AITFL injuries. Evaluating fibular AP translation and ER are not part of current standard diagnostic protocols. Physicians may consider more aggressive treatment of isolated AITFL injuries.

Anterior-Posterior Translation and Axial Rotation of the Fibula are Significantly Increased with Sequential Disruption of the Syndesmosis

Category: Ankle, Sports, Trauma Introduction/Purpose: Injury to the Anterior inferior tibiofibular ligament (AITFL), Posterior inferior tibiofibular ligament (PITFL) and Interosseus membrane (IOM) predicts residual symptoms in ankle sprains. Limited kinematic knowledge of the tibiofibular joint results in missed diagnosis and poor clinical outcomes. Lateral fibular displacement on radiologic assessment signifies syndesmotic disruption which dictates operative management. Previous studies demonstrated that fibular motion is multiplanar after injury. The objective of this study is to determine increases in fibular motion with sequential syndesmotic injury and the contribution of the AITFL. Methods: Five fresh-frozen human cadaveric tibial plateau-to-toe specimens with a mean age of 58 years (range 38-73 years) were tested using a 6-degree-of-freedom robotic testing system. The tibia and calcaneus were rigidly fixed. The subtalar joint was fused. The full fibular length was maintained and fibular motion was unconstrained. A 5 Nm external rotation and 5 Nm inversion moment were applied to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. The motion of the fibula was tracked by a 3D optical tracking system. Outcome variables included fibular medial-lateral (ML) translation, anterior-posterior (AP) translation, and external rotation (ER) during each applied moment and flexion angle in the following conditions: 1) intact ankle, 2) AITFL transected, 3) PITFL and IOM transected. Statistical analysis included an ANOVA with a post-hoc Tukey analysis to compare the changes in fibular motion between the intact and injury models at each applied moment and flexion angle (*p&lt;0.05). Results: The only significant differences in fibular motion were during the 5 Nm inversion moment. The posterior translation of the fibula was significantly greater with AITFL injury compared to the intact ankle at 15° and 30° plantarflexion. Significant increases in posterior translation between the intact ankle and AITFL, PITFL, and IOM injury existed at 0°, 15°, and 30° plantarflexion. No significant motion differences were observed between the AITFL injury and combined injury at any condition. When comparing the intact ankle and combined injury, significant increases in ER existed at 0° and 30° plantarflexion and 10° dorsiflexion. The only significant difference in ER between the intact ankle and AITFL injury existed at 0° plantarflexion. Conclusion: This study showed that transecting the AITFL resulted in the largest increases in fibular motion with only minimal further increases after complete syndesmotic injury. Fibular displacement was primarily in the sagittal plane. This study utilized a novel setup with unconstrained motion in a full length, intact fibula. Measuring ML translation alone could underestimate sagittal and rotational instability of the syndesmosis in AITFL injuries. Evaluating fibular AP translation and ER are not part of current standard diagnostic protocols. Physicians may consider more aggressive treatment of isolated AITFL injuries.

Restoration of Tibiofibular Kinematics with a Tricortical Screw or Suture Button Fixation After Syndesmotic Ankle Injuries

Category: Ankle, Sports, Trauma Introduction/Purpose: Anterior inferior tibiofibular ligament (AITFL), Posterior inferior tibiofibular ligament (PITFL) and Interosseous membrane (IOM) disruption is a predictive measure of residual symptoms after ankle injury. In unstable injuries, the syndesmosis is treated operatively with cortical screw fixation or a suture button apparatus. Biomechanical analyses of suture button versus cortical screw fixation methods show contradicting results regarding suture button integrity and maintenance of fixation. The objective of this study is to quantify tibiofibular joint motion in syndesmotic screw and suture button fixation models compared to the intact ankle. Methods: Five fresh-frozen human cadaveric specimens (mean age 58 yrs.; range 38-73 yrs.) were tested using a 6-degree-of- freedom robotic testing system. The tibia and calcaneus were rigidly fixed to the robotic manipulator and the subtalar joint was fused. The full fibular length was maintained and fibular motion was unconstrained. Fibular motion with respect to the tibia was tracked by a 3D optical tracking system. A 5 Nm external rotation moment and 5 Nm inversion moment were applied to the ankle at 0°, 15°, and 30° plantarflexion and 10° dorsiflexion. Outcome variables included fibular medial-lateral (ML) translation, anterior-posterior (AP) translation, and external rotation (ER) in the following states: 1) intact ankle, 2) AITFL transected, 3) PITFL and IOM transected, 4) 3.5 mm cannulated tricortical screw fixation, 5) suture button fixation. An ANOVA with a post-hoc Tukey analysis was performed for statistical analysis (*p&lt;0.05). Results: Significant differences in fibular motion were only during the inversion moment. Fibular posterior translation was significantly higher with complete syndesmosis injury compared to the intact ankle at 0°, 15°, and 30° plantarflexion and the tricortical screw at 15° and 30°. Significantly higher fibular posterior translation was observed with the suture button compared to the intact ankle at 15° and 30 plantarflexion and to the tricortical screw at 15°. ER was significantly increased with complete injury compared to the tricortical screw at 0° and 30° plantarflexion. The suture button demonstrated significantly greater ER at 0° plantarflexion and 10° dorsiflexion compared to the intact ankle. The only significant difference in ML translation exists between the tricortical screw and complete injury at 30° plantarflexion. Conclusion: The suture button did not restore physiologic motion of the syndesmosis. It only restored fibular ML translation. Significant differences in AP translation and ER persisted compared to the intact ankle. The tricortical screw restored fibular motion in all planes. No significant differences were observed compared to the intact ankle. These findings are consistent with previous studies. This study utilized a novel setup to measure unconstrained motion in a full length, intact fibula. Physicians should evaluate AP translation and ER as critical fibular motions when reconstructing the syndesmosis with suture button fixation.

In situ force in the anterior cruciate ligament, the lateral collateral ligament, and the anterolateral capsule complex during a simulated pivot shift test.

The role of the anterolateral capsule complex in knee rotatory stability remains controversial. Therefore, the objective of this study was to determine the in situ forces in the anterior cruciate ligament (ACL), the anterolateral capsule, the lateral collateral ligament (LCL), and the forces transmitted between each region of the anterolateral capsule in response to a simulated pivot shift test. A robotic testing system applied a simulated pivot shift test continuously from full extension to 90° of flexion to intact cadaveric knees (n = 7). To determine the magnitude of the in situ forces, kinematics of the intact knee were replayed in position control mode after the following procedures were performed: (i) ACL transection; (ii) capsule separation; (iii) anterolateral capsule transection; and (iii) LCL transection. A repeated measures ANOVA was performed to compare in situ forces between each knee state (*p < 0.05). The in situ force in the ACL was significantly greater than the forces transmitted between each region of the anterolateral capsule at 5° and 15° of flexion but significantly lower at 60°, 75°, and 90° of flexion. This study demonstrated that the ACL is the primary rotatory stabilizer at low flexion angles during a simulated pivot shift test in the intact knee, but the anterolateral capsule plays an important secondary role at flexion angles greater than 60°. Furthermore, the contribution of the "anterolateral ligament" to rotatory knee stability in this study was negligible during a simulated pivot shift test. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:847-853, 2018.

Anatomic and non-anatomic anterior cruciate ligament posterolateral bundle augmentation affects graft function.

The purpose of this study is to compare knee laxity and graft function (tissue force) between anatomic and non-anatomic posterolateral (PL) bundle augmentation. Twelve (n=12) fresh-frozen mature, unpaired porcine knees were tested using a robotic testing system. Four knee states were compared: (a) intact anterior cruciate ligament (ACL), (b) deficient PL and intermediate bundles, (c) anatomic PL augmentation, and (d) non-anatomic PL augmentation. Anterior tibial translation (ATT), internal rotation (IR) and external rotation (ER), and the in situ tissue force were measured under an 89.0-N anterior tibial load and 4.0-Nm internal and external tibial torques. Both anatomic and non-anatomic PL augmentation restored the ER, IR, and ATT of the intact knee at all knee flexion angles (n.s.). Both anatomic and non-anatomic PL augmentation restored the in situ tissue force of the ACL during ER and IR loading and ATT loading at all knee flexion angles except at 60° of knee flexion, where the non-anatomic PL augmentation did not restore the in situ tissue force of the ACL during external rotation loading and the anatomic PL augmentation did not restore the in situ tissue force of the ACL during IR loading. Furthermore, there were no differences in ATT, IR, ER, and in situ tissue force under anterior tibial loading, IR and ER loading between the two reconstruction groups. There were no significant differences between anatomic and non-anatomic PL augmentation using the porcine knee model.

A Novel Implant System for Unloading the Medial Compartment of the Knee by Lateral Displacement of the Iliotibial Band.

Background:Medial knee osteoarthritis (OA) typically occurs with excessive mechanical load within the medial compartment, resulting in degeneration of the articular cartilage.Purpose:A novel extracapsular implant (Latella Knee Implant) has been developed to unload the medial compartment of the knee. The implant displaces the iliotibial band (ITB) over the lateral femoral condyle, thereby increasing its effective moment arm, resulting in a transfer of load from the medial compartment to the lateral compartment of the knee. A cadaveric study was performed to evaluate the effect of altering the moment arm of the ITB on knee biomechanics.Study Design:Controlled laboratory study.Methods:A 6-degrees-of-freedom robotic testing system was utilized to measure medial and lateral compartment loads in 8 fresh-frozen cadaveric knees at various ITB loads and knee flexion angles. Measurements were made with and without the implant in place. The system measured the compartment forces at flexion angles between 0° and 30° under 3 simulated loading conditions (300 N quadriceps, 100 N hamstrings, and [1] 0 N ITB, [2] 50 N ITB, [3] 100 N ITB).Results:Lateral displacement of the ITB between 15 and 20 mm resulted in medial compartment unloading between 34% and 65%.Conclusion:Unloading the medial compartment with this novel implant has the potential to address the treatment gap for patients with medial knee OA.Clinical Relevance:Currently, there exists a treatment gap for patients with medial compartment OA who have exhausted conservative management but whose disease and symptoms do not warrant more invasive surgical procedures. An extracapsular implant to unload the medial compartment could fill this treatment gap by providing patients and surgeons with a less invasive option for early to mid-stage OA. Unloading the medial compartment may alleviate pain and improve function, allowing patients with early-stage medial OA to remain active longer prior to considering more invasive options such as arthroplasty.

Biomechanical evaluation of knee endpoint during anterior tibial loading: Implication for physical exams

BackgroundPhysical exams that apply anterior tibial loads are typically used to evaluate knees with anterior cruciate ligament (ACL) injuries. The amount of anterior tibial translation that occurs during these exams can be difficult to assess due to a “soft” endpoint. Therefore, the objective of this study is to determine the biomechanical characteristics of the endpoint for the intact and ACL deficient knee using quantitative criteria. MethodsEight porcine knees were tested using a robotic testing system. An 89N anterior tibial load was applied to the intact and ACL deficient knee at 30°, 45°, 60° and 75° of flexion. The stiffness of the toe and linear regions was determined from the load–translation curve. The width of the transition region was defined by the distance between the points where the best-fit lines used to define the stiffness of the toe and linear regions diverged from the load–translation curve. ResultsStiffness of the toe and linear regions significantly decreased after transecting the ACL at all flexion angles (71–85% and 38–62%, respectively). Width of the transition region was significantly increased in the ACL deficient knee at all flexion angles (approximately four to five times and four to nine times, respectively). ConclusionsThe novel quantitative criteria developed in this study have the potential to be deployed in clinical practice by coupling them with data from knee arthrometers that are commonly used in clinical practice. Thus, additional information from the load–translation curve can be provided to improve the diagnosis of ACL injury.

In Situ SEM Torsion Test of Metallic Glass Microwires Based on Micro Robotic Manipulation.

Microwires, such as metallic, semiconductor, and polymer microwires and carbon fibers, have stimulated great interest due to their importance in various structural and functional applications. Particularly, metallic glass (MG) microwires, because of their amorphous atoms arrangement, have some unique mechanical properties compared with traditional metals. Despite the fact that substantial research efforts have been made on the mechanical characterizations of metallic glass microwires under tension or flexural bending, the mechanical properties of microwires under torsional loading have not been well studied, mainly due to the experimental difficulties, such as the detection of torsion angle, quantitative measurement of the torsional load, and the alignment between the specimen and torque meter. In this work, we implemented the in situ SEM torsion tests of individual La50Al30Ni20 metallic glass (MG) microwires successfully based on a self-developed micro robotic mechanical testing system. Unprecedented details, such as the revolving vein-pattern along the torsion direction on MG microwires fracture surface, were revealed. Our platform could provide critical insights into understanding the deformation mechanisms of other microwires under torsional loading and can even be further used for robotic micromanufacturing.

The Anterolateral Capsule of the Knee Behaves Like a Sheet of Fibrous Tissue

Background: The function of the anterolateral capsule of the knee has not been clearly defined. However, the contribution of this region of the capsule to knee stability in comparison with other anterolateral structures can be determined by the relative force that each structure carries during loading of the knee. Purpose/Hypothesis: The purpose of this study was to determine the forces in the anterolateral structures of the intact and anterior cruciate ligament (ACL)–deficient knee in response to an anterior tibial load and internal tibial torque. It was hypothesized that the anterolateral capsule would not function like a traditional ligament (ie, transmitting forces only along its longitudinal axis). Study Design: Controlled laboratory study. Methods: Loads (134-N anterior tibial load and 7-N·m internal tibial torque) were applied continuously during flexion to 7 fresh-frozen cadaveric knees in the intact and ACL-deficient state using a robotic testing system. The lateral collateral ligament (LCL) and the anterolateral capsule were separated from the surrounding tissue and from each other. This was done by performing 3 vertical incisions: lateral to the LCL, medial to the LCL, and lateral to the Gerdy tubercle. Attachments of the LCL and anterolateral capsule were detached from the underlying tissue (ie, meniscus), leaving the insertions and origins intact. The force distribution in the anterolateral capsule, ACL, and LCL was then determined at 30°, 60°, and 90° of knee flexion using the principle of superposition. Results: In the intact knee, the force in the ACL in response to an anterior tibial load was greater than that in the other structures (P < .001). However, in response to an internal tibial torque, no significant differences were found between the ACL, LCL, and forces transmitted between each region of the anterolateral capsule after capsule separation. The anterolateral capsule experienced smaller forces (~50% less) compared with the other structures (P = .048). For the ACL-deficient knee in response to an anterior tibial load, the force transmitted between each region of the anterolateral capsule was 434% greater than was the force in the anterolateral capsule (P < .001) and 54% greater than the force in the LCL (P = .036) at 30° of flexion. In response to an internal tibial torque at 30°, 60°, or 90° of knee flexion, no significant differences were found between the force transmitted between each region of the anterolateral capsule and the LCL. The force in the anterolateral capsule was significantly smaller than that in the other structures at all knee flexion angles for both loading conditions (P = .004 for anterior tibial load and P = .04 for internal tibial torque). Conclusion: The anterolateral capsule carries negligible forces in the longitudinal direction, and the forces transmitted between regions of the capsule were similar to the forces carried by the other structures at the knee, suggesting that it does not function as a traditional ligament. Thus, the anterolateral capsule should be considered a sheet of tissue. Clinical Relevance: Surgical repair techniques for the anterolateral capsule should restore the ability of the tissue to transmit forces between adjacent regions of the capsule rather than along its longitudinal axis.

The effect of anterior cruciate ligament graft rotation on knee biomechanics.

The purpose of this study was to evaluate the effects on knee biomechanics of rotating the distal end of the bone-patellar tendon graft 90° in anatomic single-bundle (SB) anterior cruciate ligament (ACL) reconstruction with a porcine model. Twenty (n=20) porcine knees were evaluated using a robotic testing system. Two groups and three knee states were compared: (1) intact ACL, (2) deficient ACL and (3) anatomic SB ACL reconstruction with (a) non-rotated graft or (b) rotated graft (anatomic external fibre rotation). Anterior tibial translation (ATT), internal (IR) and external rotation (ER) and the in situ tissue force were measured under an 89-N anterior tibial (AT) load and 4-Nm internal and external tibial torques. A significant difference from the intact ACL was found in ATT at 60° and 90° of knee flexion for rotated and non-rotated graft reconstructions (p<0.05). There was a significant difference in the in situ force from the intact ACL with AT loading for rotated and non-rotated graft reconstructions at 60° and 90° of knee flexion (p<0.05). Under IR loading, the in situ force was significantly different from the intact ACL at 30° and 60° of knee flexion for rotated and non-rotated graft reconstructions (p<0.05). There were no significant differences in ATT, IR, ER and the in situ force between rotated and non-rotated reconstructions. Graft rotation can be used with anatomic SB ACL reconstruction and not have a deleterious effect on knee anterior and rotational biomechanics. This study has clinical relevance in regard to the use of graft rotation to better reproduce the native ACL fibre orientation in ACL reconstruction.

Biomechanical Evaluation of the Transpedicular Nucleotomy with Intact Anulus Fibrosus

Introduction Mechanical loading represents a crucial part of intervertebral disc (IVD) homeostasis. However, traditional regenerative strategies require violation of the annulus fibrosus (AF) resulting in significant alteration of joint mechanics. The transpedicular nucleotomy represents a suitable method to create a cavity into the nucleus polposus (NP), as a model to study IVD regeneration with intact AF. The aim is to study how the transpedicular tunnel (TT) and the novel mechanical nucleotomy affects the biomechanics of the NP. Material and Methods 60 ovine lumbar FSUs (L1-L6) randomly assigned to 5 groups: Control; TT; TT + polymethylmethacrylate (PMMA), to repair the bone tunnel; Nucleotomy; Nucleotomy + PMMA. The robotic spine testing system consists of a robotic manipulator (Staubli RX90) and a six-axis load cell (JR3 Inc.). Flexion/extension, lateral bending and axial rotation were evaluated under adaptive displacement control. Axial compression was applied for 15 cycles of preconditioning followed by 1 hour of constant compression. Viscoelastic properties were determined. Results TT has minimal effects on rotational biomechanics. The nucleotomy increases ROM and NZ displacement width while decreasing NZ stiffness. TT + PMMA has small effects in terms of ROM. Nucleotomy + PMMA brings ROM back to the control, increases NZ stiffness and decreases NZ displacement width. The nucleotomy tends to increase the rate of early creep. TT reduces early and late damping. The use of PMMA increased late elastic damping (S2) and reduced viscous damping (η2) culminating in faster resolution of creep. Conclusion Biomechanical properties of NP are crucial for IVD repair. TT does not affect rotational stability. Mechanical changes that occur with nucleotomy are similar to those characteristics of early degeneration. These findings confirm that the NP is crucial for segmental stability in physiologic rotations.

Practicability for robot-aided measurement of knee stability in-vivo

BackgroundFor the analysis of different treatments concerning anterior cruciate ligament (ACL) rupture, objective methods for the quantification of knee stability are needed. Therefore, a new method for in-vivo stability measurement using a robotic testing system should be developed and evaluated.MethodsA new experimental setting was developed using a KUKA robot and a custom-made chair for the positioning and fixation of the participants. The tibia was connected to the robot via a Vacoped shoe and magnetic buttons, providing adequate safety. Anterior tibial translation and internal tibial rotation were measured on both legs of 40 healthy human subjects at 30°, 60° and 90° of flexion, applying anterior forces of 80 N and internal torques of 4 Nm, respectively.ResultsWhile the mean differences between the right and left leg measured for anterior tibial translation were within an acceptable range (<1.5 mm), the absolute values were substantially large (38–40.5 mm). For mean internal tibial rotation, between 17.5 and 20° were measured at the different sides and flexion angles, with a maximal difference of 0.75°. High reproducibility of the measurements could be demonstrated for both, anterior tibial translation (ICC(3,1) = 0.97) and internal tibial rotation (ICC(3,1) = 0.94).ConclusionsExcellent results were achieved for internal tibial rotation, almost reproducing current in-vitro studies, but too large anterior tibial translation was measured due to soft-tissue compression. Therefore, high potential for the analysis of ACL related treatments concerning rotational stability is seen for the proposed method, but further optimization is necessary to enhance this method for the reliable measurement of anterior tibial translation.

A Comprehensive Specimen-Specific Multiscale Data Set for Anatomical and Mechanical Characterization of the Tibiofemoral Joint.

Understanding of tibiofemoral joint mechanics at multiple spatial scales is essential for developing effective preventive measures and treatments for both pathology and injury management. Currently, there is a distinct lack of specimen-specific biomechanical data at multiple spatial scales, e.g., joint, tissue, and cell scales. Comprehensive multiscale data may improve the understanding of the relationship between biomechanical and anatomical markers across various scales. Furthermore, specimen-specific multiscale data for the tibiofemoral joint may assist development and validation of specimen-specific computational models that may be useful for more thorough analyses of the biomechanical behavior of the joint. This study describes an aggregation of procedures for acquisition of multiscale anatomical and biomechanical data for the tibiofemoral joint. Magnetic resonance imaging was used to acquire anatomical morphology at the joint scale. A robotic testing system was used to quantify joint level biomechanical response under various loading scenarios. Tissue level material properties were obtained from the same specimen for the femoral and tibial articular cartilage, medial and lateral menisci, anterior and posterior cruciate ligaments, and medial and lateral collateral ligaments. Histology data were also obtained for all tissue types to measure specimen-specific cell scale information, e.g., cellular distribution. This study is the first of its kind to establish a comprehensive multiscale data set for a musculoskeletal joint and the presented data collection approach can be used as a general template to guide acquisition of specimen-specific comprehensive multiscale data for musculoskeletal joints.

Robotic axial lower leg testing: repeatability and reproducibility.

PurposeThe purpose of this study was to determine the test–retest reliability and the repeatability over multiple days of a robotic testing device when used to measure laxity of the lower leg during a simulated dial test.MethodsTen healthy subjects were evaluated using an instrumented robotic lower leg testing system over 4 days. Three testing cycles were performed each day. Each leg was rotated into external and then internal rotation by servomotors until a torque threshold of 5.65 N m was reached. Load–deformation curves were generated from torque and rotation data. Both average-measure and single-measure intraclass correlation coefficients (ICC) were compared across the curves. ICC scores were also compared for features of the curves including: maximum external rotation at −5.65 N m of torque, maximum internal rotation at 5.65 N m of torque, rotation at torque 0, compliance (slope of load–deformation curve) at torque 0, endpoint compliance in external rotation, endpoint compliance in internal rotation, and play at torque 0. Play at torque 0 was defined as the width of the hysteresis curve at torque 0.ResultsAverage-measure ICC scores and test–retest scores were >0.95 along the entire load–deformation curve except around zero torque. ICC scores at maximum internal and external rotation ranged from 0.87 to 0.99 across the left and right knees. ICC scores for the other features of the curves ranged from 0.61 to 0.98. The standard error of the mean ranged from 0.0497 to 1.1712.ConclusionsThe robotic testing device in this study proved to be reliable for testing a subject multiple times both within the same day and over multiple days. These findings suggest that the device can provide a level of reliability in rotational testing that allows for clinical use of test results. Objective laxity data can improve consistency and accuracy in diagnosing knee injuries and may enable more effective treatment.

Single-bundle ACL reconstruction with and without extra-articular reconstruction: evaluation with robotic lower leg rotation testing and patient satisfaction scores.

PurposeThe purpose of this study was to compare the biomechanical characteristics and patient outcomes after either isolated intraarticular ACL reconstruction or intraarticular reconstruction with lateral extra-articular tenodesis. In addition, we aimed to evaluate biomechanical parameters of the entire uninjured, contralateral knee as a baseline during the analysis.MethodsEighteen patients were evaluated at an average of 9.3 years after ACL reconstruction. Twelve patients had an intraarticular reconstruction (BTB), and six had an additional lateral extraarticular procedure (BTB/EAR). Patients were selected for the additional procedure by the operating surgeon based on clinical and radiological criteria. At the time of review, each patient was assessed using subjective patient questionnaires, manual laxity testing, and instrumented laxity testing. Each knee was also evaluated using a robotic lower leg axial rotation testing system. This system measured maximum internal and external rotations at 5.65 Nm of applied torque and generated load deformation curves and compliance data. Pointwise statistical comparisons within each group and between groups were performed using the appropriate paired or unpaired t test. Features were extracted from each load deformation curve for comparative analysis.ResultsThere were no significant differences between the two groups with respect to the patient satisfaction scores or to laxity testing (manual or instrumented). Robotic testing results for within-group comparisons demonstrated a significant reduction in maximum external rotation (8.77°) in the reconstructed leg when compared to the healthy leg (p < 0.05) in the BTB/EAR group, with a non-significant change in internal rotation. The slope of the curve at maximum internal rotation was also significantly greater in the reconstructed legs for the BTB/EAR group (p < 0.05), indicating reduced endpoint compliance or a harder endpoint. Finally, the leg that received the extra-articular tenodesis had a trend towards a reduced total leg axial rotation. Conversely, patients in the BTB group demonstrated no significant differences between their legs. For between-group comparisons, there was a significant increase in maximum internal rotation in the healthy legs in the BTB/EAR group compared with the healthy legs in the BTB group (p < 0.05). If the injured/reconstructed legs were compared, the significant difference at maximum internal rotation disappeared (p < 0.10). Similarly, the healthy legs in patients in the BTB/EAR group had a significantly more compliant or softer endpoint in internal rotation, greater maximum internal rotation, and more internal rotation at torque 0 in their healthy legs compared with the healthy legs in the BTB group (p < 0.05). These same differences were not noted in the reconstructed knees. The only identifiable significant difference between the injured/reconstructed legs was rotation at 0 torque (p < 0.05).ConclusionsIn this group of patients who were at an average of 9 years from surgery, the addition of a lateral extra-articular reconstruction to a standard bone–tendon–bone intraarticular ACL reconstruction does reduces internal rotation of the tibia with respect to the femur when compared to intraarticular reconstruction alone. It appears that the selection process for inclusion into the BTB/EAR group included an increase in total axial rotation of the healthy knee during the examination along with a decrease in endpoint stiffness at maximum internal rotation.Level of evidenceII.

Novel technique for evaluation of knee function continuously through the range of flexion

Previous research has utilized robots to examine joint kinematics and in situ forces in response to loads applied at discrete flexion angles (static method). Recently, studies have applied loads continuously throughout flexion (continuous flexion method). However, the joint kinematics resulting from each of these methods have not been directly compared. Therefore, the objective of this study was to utilize a robotic testing system to compare kinematics and in situ forces of porcine knees in response to 89N of anterior tibial load and 4Nm of internal tibial torque between the static method (loads applied at 30°, 45°, 60°, and 75° of flexion) and the continuous flexion method (measured continuously from 30–75° of flexion) for both the anterior cruciate ligament (ACL) intact and ACL deficient (ACLD) knees. When anterior tibial load was applied the average differences in anterior tibial translation between the two methods for the intact state was 0.5±0.0mm and for the ACLD state was 0.3±0.2mm. The difference in the in situ forces in the ACL was 1.6±0.9N. When internal tibial torque was applied the average differences in the resultant internal tibial rotation for the intact state was 0.9±0.4° and for the ACLD state was 1.0±0.5°. The difference in the in situ forces in the ACL was 3.3±2.0N. Both methods are equally efficient in detecting significant differences (p<0.05) between intact and ACL deficient knee states. The continuous flexion method was also shown to be more efficient than the static method and provides continuous data on knee function throughout the range of motion.