Intratendinous pressure changes in the Achilles tendon during stretching and eccentric loading: Implications for Achilles tendinopathy.

Mechanical overload is considered the main cause of Achilles tendinopathy. In addition to tensile loads, it is believed that the Achilles tendon may also be exposed to compressive loads. However, data on intratendinous pressures are lacking, and consequently, their role in the pathophysiology of tendinopathy is still under debate. Therefore, we aimed to evaluate the intratendinous pressure changes in the Achilles tendon during stretching and eccentric loading. Twelve pairs of human cadaveric legs were mounted in a testing rig, and a miniature pressure catheter was placed through ultrasound-guided insertion in four different regions of the Achilles tendon: the insertion (superficial and deep layers), mid-portion, and proximal portion. Intratendinous pressure was measured during three simulated loading conditions: a bent-knee calf stretch, a straight-knee calf stretch, and an eccentric heel-drop. It was found that the intratendinous pressure increased exponentially in both the insertion and mid-portion regions of the Achilles tendon during each loading condition (p < 0.001). The highest pressures were consistently found in the deep insertion region (p < 0.001) and during the eccentric heel-drop (p < 0.001). Pressures in the mid-portion were also significantly higher than in the proximal portion (p < 0.001). These observations offer novel insights and support a role for compression in the pathophysiology of Achilles tendinopathy by demonstrating high intratendinous pressures at regions where Achilles tendinopathy typically occurs. To what extent managing intratendinous pressure might be successful in patients with Achilles tendinopathy by, for example, avoiding excessive stretching, modifying exercise therapy, and offering heel lifts requires further investigation.

Intratendinous pressure of the Achilles tendon during exercise is related to the degree of tendon torsion.

Torsion of the Achilles tendon (AT) enhances tensile strength, but a high degree of torsion might also be a risk factor for Achilles tendinopathy, due to greater internal compression exerted during tensile loading. However, evidence supporting the grounds for this assumption is lacking. Hence, we aimed to investigate the impact of AT torsion type on intratendinous pressure. Eighteen human fresh frozen cadaveric legs were mounted in a testing rig and a miniature pressure catheter was placed through ultrasound-guided insertion in the midportion region of the AT. Intratendinous pressure was measured during a simulated straight-knee calf stretch and eccentric heel drop. The AT was then carefully dissected and classified into Type I (least), Type II (moderate), and Type III (extreme) torsion. Of the ATs examined, nine were found to have Type I torsion (50%), nine Type II (50%), and none Type III. It was found that the intratendinous pressure of the AT increased exponentially with ankle dorsiflexion during both exercises (p < 0.001) and that this increase was greater in ATs with Type II torsion than Type I torsion (p < 0.05). This study provides the first biomechanical data to support the hypothesis that in athletes with a high degree of torsion in the AT, the midportion area will experience more internal compression during exercise, for example, calf stretching and eccentric heel drops. Whether this phenomenon is also associated with an elevated risk for Achilles tendinopathy needs further prospective investigation.

The Definition of the Tibial Sagittal Plane and the Paradox of Imageless Navigation and Robotics: A Cadaveric Study.

BACKGROUND: The accuracy, precision, and repeatability by which the tibial sagittal plane can be found with imageless technology is currently unknown. The purpose of this study was to identify any differences between imageless and image-based technology to define the sagittal plane of the tibia. METHODS: A computed tomography (CT) was obtained of 18 cadavers with the knee fully extended. The surgical trans-epicondylar axis and several tibial rotation references were acquired on the CT scan. After a medial parapatellar approach, the same anatomical landmarks were acquired in vivo. In the horizontal plane, the angle between the surgical trans-epicondylar axis and the tibial rotational axes was assessed. RESULTS: Highest accuracy was found for posterior cruciate ligament (PCL)-anterior cruciate ligament (ACL, -1.48°, standard deviation [SD] 13.64; imageless), tibial medial condyle (TMC)-tibial lateral condyle (TLC, 1.72°, SD 4.24; image-based), the ACL-medial border of tibial tuberosity (MTT, -2.89°, SD 18.86; image-based). Highest precision was acquired with image-based technology: TMC-TLC (SD 4.24), PCL-ACL (SD 5.86), and PCL-medial third of tibial tuberosity (M3TT, SD 7.10). Excellent intraobserver and interobserver correlation coefficients were observed with image-based technology: PCL-MTT, anterior medial condyle (AMC)-anterior lateral condyle (ALC), and TMC-TLC (Intraobserver and interobserver correlation coefficients 0.90-0.98). CONCLUSION: The tibial sagittal plane could be defined with highest accuracy, precision, and repeatability on a preoperative CT. Imageless methodology lacked the precision and repeatability of image-based technology. With the current pursuit of high accuracy and precision in total knee arthroplasty, the reference frame used to quantify implant position should be highly accurate and precise as well. LEVEL OF EVIDENCE: IV, Case Series.

Joint Track Machine Learning: An Autonomous Method of Measuring Total Knee Arthroplasty Kinematics From Single-Plane X-Ray Images.

BACKGROUND: Dynamic radiographic measurements of 3-dimensional (3-D) total knee arthroplasty (TKA) kinematics have provided important information for implant design and surgical technique for over 30 years. However, current methods of measuring TKA kinematics are too cumbersome, inaccurate, or time-consuming for practical clinical application. Even state-of-the-art techniques require human-supervision to obtain clinically reliable kinematics. Eliminating human supervision could potentially make this technology practical for clinical use. METHODS: We demonstrate a fully autonomous pipeline for quantifying 3D-TKA kinematics from single-plane radiographic imaging. First, a convolutional neural network (CNN) segmented the femoral and tibial implants from the image. Second, those segmented images were compared to precomputed shape libraries for initial pose estimates. Lastly, a numerical optimization routine aligned 3D implant contours and fluoroscopic images to obtain the final implant poses. RESULTS: The autonomous technique reliably produces kinematic measurements comparable to human-supervised measures, with root-mean-squared differences of less than 0.7 mm and 4° for our test data, and 0.8 mm and 1.7° for external validation studies. CONCLUSION: A fully autonomous method to measure 3D-TKA kinematics from single-plane radiographic images produces results equivalent to a human-supervised method, and may soon make it practical to perform these measurements in a clinical setting.

Muscle loaded stability reflects ligament-based stability in TKA: a cadaveric study.

PURPOSE: This paper aims at evaluating the effects of muscle load on knee kinematics and stability after TKA and second at evaluating the effect of TKA surgery on knee kinematics and stability; and third, at correlating the stability in passive conditions and the stability in active, muscle loaded conditions. METHODS: Fourteen fresh frozen cadaveric knee specimens were tested under passive and active condition with and without external loads involving a varus/valgus and internal/external rotational torque before and after TKA surgery using two in-house developed and previously validated test setups. RESULTS: Introduction of muscle force resulted in increased valgus (0.98°) and internal rotation of the femur (4.64°). TKA surgery also affected the neutral path kinematics, resulting in more varus (1.25°) and external rotation of the femur (5.22°). All laxities were significantly reduced by the introduction of the muscle load and after implantation of the TKA. The presence of the implant significantly affects the active varus/valgus laxity. This contrasts with the rotational laxity, in which case the passive laxity is the main determinant for the active laxity. For the varus/valgus laxity, the passive laxity is also a significant predictor of the active laxity. CONCLUSION: Knee stability is clearly affected by the presence of muscle load. This points to the relevance of appropriate rehabilitation with focus on avoiding muscular atrophy. At the same time, the functional, muscle loaded stability strongly relates to the passive, ligament-based stability. It remains therefore important to assess knee stability at the time of surgery, since the passive laxity is the only predictor for functional stability in the operating theatre. LEVEL OF EVIDENCE: Case series, Level IV.

The contralateral knee is a good predictor for determining normal knee stability: a cadaveric study.

PURPOSE: The goal is to evaluate contralateral knee joint laxity and ascertain whether or not contralateral symmetry is observable. Secondary, a validation of a knee laxity testing rig is provided. METHODS: Seven pairs of cadaveric knee specimens have been tested under passive conditions with and without external loads, involving a varus/valgus and an external/internal rotational torque and an anteroposterior shear force. RESULTS: Through the range of motion, the width of the varus/valgus laxity, internal/external laxity and anterior/posterior laxity for the medial and lateral compartment show no significant differences between left and right leg. These findings allow us to validate the setup, especially for relative values of laxity based on anatomical measures and knee joint biomechanics. CONCLUSION: A multidirectional laxity symmetry has been demonstrated for the intact knee and its contralateral knee in passive conditions as in an anesthetized patient. The passive laxity evaluation setup has been validated. Our work furthermore demonstrated a pronounced difference in anteroposterior mobility between the medial and lateral compartment of the knee, with a more stable medial side and more mobile lateral side. CLINICAL RELEVANCE: The contralateral knee can be used as reference for determining optimal knee laxity peri-operatively in total knee replacement and ligament reconstruction. LEVEL OF EVIDENCE: Level IV, Case series.

Elevated fluid and glycosaminoglycan content in the Achilles tendon contribute to higher intratendinous pressures: Implications for Achilles tendinopathy.

BACKGROUND: Tendinopathy alters the compositional properties of the Achilles tendon by increasing fluid and glycosaminoglycan content. It has been speculated that these changes may affect intratendinous pressure, but the extent of this relationship remains unclear. Therefore, we aimed to investigate the impact of elevated fluid and glycosaminoglycan content on Achilles tendon intratendinous pressure and to determine whether hyaluronidase (HYAL) therapy can intervene in this potential relationship. METHODS: Twenty paired fresh-frozen cadaveric Achilles tendons were mounted in a tensile-testing machine and loaded up to 5% strain. Intratendinous resting (at 0% strain) and dynamic pressure (at 5% strain) were assessed using the microcapillary infusion technique. First, intratendinous pressure was measured under native conditions before and after infusion of 2 mL physiological saline. Next, 80 mg of glycosaminoglycans were administered bilaterally to the paired tendons. The right tendons were additionally treated with 1500 units of HYAL. Finally, both groups were retested, and the glycosaminoglycan content was analyzed. RESULTS: It was found that both elevated fluid and glycosaminoglycan content resulted in higher intratendinous resting and dynamic pressures (p < 0.001). HYAL treatment induced a 2.3-fold reduction in glycosaminoglycan content (p = 0.002) and restored intratendinous pressures. CONCLUSION: The results of this study demonstrated that elevated fluid and glycosaminoglycan content in Achilles tendinopathy contribute to increased intratendinous resting and dynamic pressures, which can be explained by the associated increased volume and reduced permeability of the tendon matrix, respectively. HYAL degrades glycosaminoglycans sufficiently to lower intratendinous pressures and may, therefore, serve as a promising treatment.

Effect of iliotibial band and gastrocnemius activation on knee kinematics.

BACKGROUND: This paper aimed to evaluate the effects of iliotibial band (ITB) activation and gastrocnemius activation on knee kinematics and stability. A quantitative analysis needs to determine the effect of ITB and gastrocnemius activation in each of the six degrees of freedom of the knee joint. METHODS: Four cadaveric knee specimens were tested during squat motions with physiological loads. The quadriceps and hamstring muscles were activated in each situation. The ITB was intermittently activated using an actuator and a cable pulley system. The gastrocnemius was activated anatomically as part of the triceps surae complex together with the soleus and the plantaris muscle. During the squat motion, the Achilles tendon has increased tension which induced muscle activation in the calf muscles thus creating the activated situation. RESULTS: Introduction of the ITB resulted in a reduced laxity width during extension and an external tibial rotation (2.4°). The femur shifted less posterior in the lateral compartment when the ITB was activated. Activation of gastrocnemius as part of the calf muscles led to an increased laxity width. CONCLUSIONS: Knee stability and knee joint kinematics are affected significantly by the activation of the ITB and the gastrocnemius as part of the triceps surae complex. This points to the importance of muscles and stabilizing tissue structures such as the ITB in the evaluation of knee joint kinematics both in vitro and in vivo.

Knee kinematics during staircase descent.

The goal was to evaluate tibiofemoral knee joint kinematics during stair descent, by simulating the full stair descent motion in vitro. The knee joint kinematics were evaluated for two types of knee implants: bi-cruciate retaining and bi-cruciate stabilized. It was hypothesized that the bi-cruciate retaining implant better approximates native kinematics. The in vitro study included 20 specimens which were tested during a full stair descent with physiological muscle forces in a dynamic knee rig. Laxity envelopes were measured by applying external loading conditions in varus/valgus and internal/external direction. The laxity results show that both implants are capable of mimicking the native internal/external-laxity during the controlled lowering phase. The kinematic results show that the bi-cruciate retaining implant tends to approximate the native condition better compared to bi-cruciate stabilized implant. This is valid for the internal/external rotation and the anteroposterior translation during all phases of the stair descent, and for the compression-distraction of the knee joint during swing and controlled lowering phase. The results show a better approximation of the native kinematics by the bi-cruciate retaining knee implant compared to the bi-cruciate stabilized knee implant for internal/external rotation and anteroposterior translation. Whether this will result in better patient outcomes remains to be investigated.

Accuracy of intraoperative bone registration and stereotactic boundary reconstruction during total knee arthroplasty surgery.

BACKGROUND: The intraoperative registration of the bones play a crucial role in image-based computer-assisted knee arthroplasty to achieve accurate implant placement and to create reliable stereotactic bone boundaries for robot-assisted surgical systems. METHOD: This study assessed the intraoperative registration accuracy on six intact fresh frozen cadavers. RESULTS: Rotational errors around the mechanical axis were the largest, with a standard deviation of 1.2° and outliers up to 3.7°. The mean translational errors were lower than 1 mm, with outliers up to 1.5 mm. These errors were amplified to 2 mm for the registration-based reconstruction of the posterior bone surface at the resection levels. CONCLUSION: Given the cumulative behaviour of surgical errors, registration errors can affect the final implant positioning. Furthermore, inaccuracies in the reconstructed bone boundary directly affect the virtual stereotactic boundaries used in robotic-assisted surgery and can result in an incomplete resection or inadvertent soft tissue damage.

Fractional-order PID design: Towards transition from state-of-art to state-of-use.

This paper presents a new tuning method for fractional-order (FO)PID controllers to simplify current tuning and make FOPID controllers more convenient for industry, i.e. facilitate transition from state-of-art to state-of-use. The number of tuning parameters is reduced from five to three based on popular specification settings for PID controllers without the need for reduced process models which introduce modeling errors. A test batch of 133 simulated processes and two real-life processes are used to test the presented method. A comparative study between the new method and the established CRONE controller, quantifies the performance. The conclusion states that the new method gives fractional controllers with similar performances as the current methods but with a significantly decreased tuning complexity making FOPID controllers more acceptable to industry.