Intact Knee Research Articles

The Role of Fibers Within the Tibial Attachment of the Anterior Cruciate Ligament in Restraining Tibial Displacement

To evaluate the load-bearing functions of the fibers of the anterior cruciate ligament (ACL) tibial attachment in restraining tibial anterior translation, internal rotation, and combined anterior and internal rotation laxities in a simulated pivot-shift test. Twelve knees were tested using a robot. Laxities tested were: anterior tibial translation (ATT), internal rotation (IR), and coupled translations and rotations during a simulated pivot-shift. The kinematics of the intact knee was replayed after sequentially transecting 9 segments of the ACL attachment and fibers entering the lateral gutter, measuring their contributions to restraining laxity. The center of effort (COE) of the ACL force transmitted to the tibia was calculated. A blinded anatomic analysis identified the densest fiber area in the attachment of the ACL and thus its centroid (center of area). This centroid was compared with the biomechanical COE. The anteromedial tibial fibers were the primary restraint of ATT (84% across 0° to 90° flexion) and IR (61%) during isolated and coupled displacements, except for the pivot-shift and ATT in extension. The lateral gutter resisted 28% of IR at 90° flexion. The anteromedial fibers showed significantly greater restraint of simulated pivot-shift rotations than the central and posterior fibers (P < .05). No significant differences (all <2mm) were found between the anatomic centroid of the C-shaped attachment and the COE under most loadings. The peripheral anteromedial fibers were the most important area of the ACL tibial attachment in the restraint of tibial anterior translation and internal rotation during isolated and coupled displacements. These mechanical results matched the C-shaped anteromedial attachment of the dense collagen fibers of the ACL. The most important fibers in restraining tibial displacements attach to the C-shaped anteromedial area of the native ACL tibial attachment. This finding provides an objective rationale for ACL graft position to enable it to reproduce the physiological path of load transmission for tibial restraint.

Biomechanical Assessment of a Distally Fixed Lateral Extra-articular Augmentation Procedure in the Treatment of Anterolateral Rotational Laxity of the Knee

Background: Most lateral extra-articular tenodesis (LET) procedures rely on passing a strip of the iliotibial band (ITB) under the fibular (lateral) collateral ligament and fixing it proximally to the femur. The Ellison procedure is a distally fixed lateral extra-articular augmentation procedure with no proximal fixation of the ITB. It has the potential advantages of maintaining a dynamic element of control of knee rotation and avoiding the possibility of overconstraint. Hypothesis: The modified Ellison procedure would restore native knee kinematics after sectioning of the anterolateral capsule, and closure of the ITB defect would decrease rotational laxity of the knee. Study Design: Controlled laboratory study. Methods: Twelve fresh-frozen cadaveric knees were tested in a 6 degrees of freedom robotic system through 0° to 90° of knee flexion to assess anteroposterior, internal rotation (IR), and external rotation laxities. A simulated pivot shift (SPS) was performed at 0°, 15°, 30°, and 45° of flexion. Kinematic testing was performed in the intact knee and anterolateral capsule–injured knee and after the modified Ellison procedure, with and without closure of the ITB defect. A novel pulley system was used to load the ITB at 30 N for all testing states. Statistical analysis used repeated measures analyses of variance and paired t tests with Bonferroni adjustments. Results: Sectioning of the anterolateral capsule increased anterior drawer and IR during isolated displacement and with the SPS (mean increase, 2° of IR; P < .05). The modified Ellison procedure reduced both isolated and coupled IR as compared with the sectioned state (P < .05). During isolated testing, IR was reduced close to that of the intact state with the modified Ellison procedure, except at 30° of knee flexion, when it was slightly overconstrained. During the SPS, IR with the closed modified Ellison was less than that in the intact state at 15° and 30° of flexion. No significant differences in knee kinematics were seen between the ITB defect open and closed. Conclusion: A distally fixed lateral augmentation procedure can closely restore knee laxities to native values in an anterolateral capsule–sectioned knee. Although the modified Ellison did result in overconstraint to isolated IR and coupled IR during SPS, this occurred only in the early range of knee flexion. Closure of the ITB defect had no effect on knee kinematics. Clinical Relevance: A distally fixed lateral extra-articular augmentation procedure provides an alternative to a proximally fixed LET and can reduce anterolateral laxity in the anterolateral capsule–injured knee and restore kinematics close to the intact state.

Mid- to long-term function and implant survival of ACL reconstruction and medial Oxford UKR

PurposeThe purpose of this study was to describe mid- to long-term outcomes of anterior cruciate ligament (ACL) reconstruction with simultaneous or staged medial unicompartmental knee replacement (UKR), and compare outcomes between (1) young patients aged younger than 55 at surgery and those older, (2) those with long-term follow-up greater than 10 years, (3) cemented and cementless UKR, and (4) compare outcomes to those with an intact ACL. Patients and methodsWe identified knees with staged or simultaneous ACL reconstruction and medial UKR from a prospectively followed designer UKR cohort, and describe mean Oxford Knee Score (OKS), mean Tegner activity score and Kaplan–Meier survival estimates. We matched these knees to ACL-intact knees. ResultsSeventy-six consecutive UKR with staged or simultaneous ACL reconstruction were identified with mean six-year follow-up (range 1–15). There was significant improvement in OKS and Tegner score with surgery. At most recent follow-up, OKS was 41.0 (range 11 to 48), and Tegner score 3.6 (0 to 8). There were three revisions occurring at a mean of five years post-operatively. The five-, 10- and 15-year survival estimates were 97% (95% confidence interval [CI] 93–100), 92% (83–100), and 92% (83–100). There was no difference in functional scores or implant survival in young patients, those with long-term follow-up (>10 years), those with cementless fixation, or when compared to ACL intact knees. ConclusionThese results demonstrate excellent mid- to long-term function and survival of selected patients who have undergone ACL reconstruction and medial UKR. Their outcome was similar to those with intact ACLs.

Small Lateral Meniscus Tears Propagate and are Detrimental to Knee Kinematics and Contact Forces

Aims and Objectives: To quantify propagation of small vertical lateral meniscus tears located in the posterior horn during simulated cyclic cutting maneuvers on a robotic testing system and the resulting changes in knee kinematics and forces. Materials and Methods: 14 fresh-frozen human cadaveric knees (mean age: 74.8 ± 14.4) were mounted onto a 6-DOF robotic testing system. Knees with osteoarthritis greater than grade II were excluded. A small vertical tear in the posterior horn of the lateral meniscus medial to the popliteus tendon was created via a posterior arthrotomy. Tear length was measured with a custom-made device (accuracy 0.2 mm, inter-rater reliability 0.914). In 6 specimens, the ACL was resected arthroscopically, whereas in 8 knees the ACL was left intact. 10Nm valgus and 5Nm external rotation moment combined with 250N of axial compression were applied while the knees were continuously flexed from full extension to 90° of flexion for 500 cycles. Meniscus tear length was measured after each 100 cycles. After the measurements, the posterior capsule and skin were closed in a standardized fashion. Knee kinematics, the in situ force in the ACL, the resultant force in the lateral meniscus, and bony contact forces at the tibiofemoral joint were calculated at 30°, 60°, and 90° of knee flexion. A repeated measures ANOVA was used to compared the outcome parameters between knee states (p &lt; 0.05). Results: In intact knees, small vertical lateral meniscus tears propagated significantly from baseline to 100, 200, 300, 400, and 500 cycles (all p &lt; 0.001). This corresponds to a tear propagation of 28.7% ± 5.4%. Similarly, in ACL deficient knees meniscus tear propagation was significant throughout all sets of cycles (p = 0.001). This corresponds to a tear propagation of 26.1% ± 8.3%. While in intact knees, external tibial rotation was significantly increased by up to 45.5% after meniscus tear propagation, knee kinematics were not significantly affected in ACL deficient knees (NS). The resultant forces in the lateral meniscus increased with tear propagation in the intact knees by up to 54.1%. Likewise, the resultant forces in the lateral meniscus increased in the ACL deficient knees by up to 116.5% (p &lt; 0.05). In intact knees, bony contact forces at the tibiofemoral joint increased with meniscus tear propagation by up to 91.9% (p &lt; 0.05), which was comparable to ACL deficient knees. Conclusion: The data of this study suggest, that small vertical lateral meniscus tears propagate significantly regardless of the integrity of the ACL and after only 100 cycles of knee loading. The findings of the current robotic study are in contrast to recent clinical studies that found that small, vertical and stable tears in the posterior horn of the lateral meniscus could be left in situ. However, based on the current data, such tears do propagate over time regardless of the integrity of the ACL, which might alter knee kinematics and resultant forces in the lateral meniscus as well as bony contact forces at the tibiofemoral joint.

Effect of Meniscal Ramp Lesion Repair on Knee Kinematics, ACL In-Situ Forces and Bony Contact Forces – A Biomechanical Study

Aims and Objectives: While recent studies showed that all inside meniscal ramp repair is able to restore knee kinematics, the effects of ramp repairs on ACL in-situ forces and bony contact forces is still unclear. Therefore, the purpose of this study is to determine the effect of ramp lesion repair on knee kinematics, the ACL-ISF and bony contact forces using a 6-degree-of-freedom (DOF) robotic testing system. It was hypothesized that ramp repair will restore kinematics, ACL-ISF and bony contact forces comparably to the forces of the intact knee. Materials and Methods: Nine fresh-frozen human cadaveric knee specimens were tested using a 6-degree-of-freedom robotic testing system (FRS2010) to continuously flex the knee from full extension to 90° and apply continuous loading conditions: 1) 90 N of anterior force, 2) 5 Nm of external rotation torque, 3) 134 N anterior force + 200 N compression force, 4) 4 Nm external rotation torque + 200 N compression force, 5) 4 Nm internal rotation torque + 200 N compression force. Loading conditions were applied to the intact knee, a knee with an arthroscopically induced 25 mm ramp lesion, and a knee with an all-inside repaired ramp lesion. ACL in-situ forces, medial compartment bony contact forces and lateral compartment bony contact forces were quantified. Repeated measure ANOVAs were performed to compare knee states at each flexion angle (p&lt;0.05). Results: In response to all loading conditions, no differences with respect to kinematics, ACL in-situ forces, and bony contact forces between the intact state and the ramp lesion state were detected. However, compared to the intact state, ramp lesion repair significantly reduced anterior translation in flexion angles from full extension to 40° in response to 5 N anterior force (p &lt; 0.05). In addition, a significant decrease in the ACL in-situ forces after ramp repair was detected only for higher flexion angles when 4 Nm external rotation torque combined with 200 N compression force (p &lt; 0.05) and when 4 Nm internal rotation torque combined with 200 N compression force were applied (p &lt; 0.05). Conclusion: In this biomechanical study, ramp lesions did not significantly affect knee biomechanics. Care must be taken to avoid potential overconstraint when performing all-inside ramp lesion repairs. From biomechanical time-zero perspective, it is debatable if stable ramp lesions need to be addressed surgically. As stable ramp lesions do not significantly change knee biomechanics, the indications for ramp lesion repair may be limited.

Electronic and atomic structure of subchondral femoral bone in intact and osteoarthritic knee compartments

In the work we suggest an answer to the question: how is the local electronic and atomic structure as well as molecular architecture of bone tissue distorted in case of skeletal pathology? X-ray diffraction and photoelectron spectroscopy techniques are applied to medial and lateral condyles of the femoral bone resected during total knee arthroplasty in patients with medial compartmental knee osteoarthritis (OA). The measured data are examined and discussed. It is shown that the skeletal pathology affects local electronic and atomic structure of mineral matrix in bone. For the first time the site-dependent changes in cristallinity, binding energies and chemical composition of the intact and OA damaged areas of femur-saw-cuts are investigated. Specifically, in the sclerotic area crystallinity of the subchondral bone tissue increases, the binding energies of the Ca and P 2p core levels demonstrate opposite shifts and the widths of the core−1 photoelectron lines are maximal. The results show perspectives for development of novel approaches to medical imaging and diagnosis of bone tissue at the subcellular level.

STUDY ON MECHANICAL PROPERTIES OF TOTAL KNEE ARTICULAR CARTILAGE UNDER DIFFERENT LOADING RATES

Knee joint is the main weight bearing tissue of human body, also it is one of the prone parts of the clinical disease. Under different sports conditions, knee joint was loaded at different forms. In this study, the changes of average contact pressure, peak contact pressure, contact area and pressure-sharing regions were researched using the intact and defect pig knee joints under different loading rates and loads, including fast rates and large loads. These data were measured and recorded by usage of the sensor plate that placed between the unilateral meniscus and the femur cartilage during loading process. As for the intact cartilage samples, the average contact pressure and peak contact pressure of the femur cartilage increase with the loading rate, while the contact area is contrast to it. As for defect cartilage samples, it not only emerged stress concentration on the edge of the defect and pressure distribution in joint cavity was different with intact cartilage samples, but also the main bearing region was transferred from the femur cartilage-meniscus contact area to the femur cartilage-tibial cartilage contact area at different loading forms. In different loading stages, the pressure-sharing regions between the cartilage and the meniscus also changes. Different loading rates, different loads and defects will change the mechanical states of the knee joint. In loading forms, the mechanical condition may cause or aggravate damnification of the knee joint cartilage. Therefore, this study is beneficial for promoting and perfecting the research of mechanical properties of knee joint cartilage and provides a theoretical basis for the prevention and treatment of knee cartilage injury.

Lateral Posterior Tibial Slope in Male and Female Athletes Sustaining Contact Versus Noncontact Anterior Cruciate Ligament Tears: A Prospective Study

Background: Lateral posterior tibial slope (PTS) has been identified as a risk factor for primary anterior cruciate ligament (ACL) tears. Purpose/Hypothesis: The purpose was to prospectively determine if there was a difference in lateral PTS between male and female athletes sustaining contact ACL tears as compared with a group of sex-, age-, and activity-matched athletes who sustained noncontact ACL tears. It was hypothesized that there would be no difference in degree of lateral PTS between contact and noncontact mechanisms among patients sustaining primary ACL tears in sports. Study Design: Cohort study; Level of evidence, 3. Methods: Data from patients who underwent primary ACL reconstruction without posterior cruciate ligament injury between 2016 and 2018 by a single surgeon were prospectively analyzed. Measurements of lateral PTS were performed on magnetic resonance imaging. Mean values of lateral PTS were compared between the ACL tear groups. Additionally, a group of patients with intact knee ligaments were matched to patients with ACL tears to serve as controls. Results: A total of 245 patients had complete primary ACL tears during the inclusion period. Of these, 56 (23%) reported a contact mechanism of injury at the time of ACL tear, and 56 patients who sustained noncontact ACL tears were matched to the contact ACL tear group. There were no significant differences in sex (P≥ .999), age (P = .990), or body mass index (P = .450) between the patient groups. The mean lateral PTS was 9.1°± 2.9° for the ACL contact and 9.9°± 3.0° for the ACL noncontact group (P = .180). There was a significant difference in mean lateral PTS between the ACL tear groups (noncontact and contact: 9.5°± 3.0°) and matched control group (5.6°± 1.9°, P = .0001). Conclusion: The lateral PTS was significantly increased among patients with contact and noncontact ACL tears as compared with controls. However, there were no differences in lateral PTS between patients who sustained contact and noncontact ACL tears. Lateral PTS measured on magnetic resonance imaging does not appear to be predictive of the mechanism of injury type among patients who sustain a contact or noncontact primary ACL tear.

Development of a pre-clinical experimental simulation model of the natural porcine knee with appropriate ligamentous constraints.

A robust and stratified pre-clinical natural knee model, which has the capability to more appropriately simulate the biomechanical environment in vivo, will deliver more efficient and reliable assessment of soft tissue interventions before clinical studies. In order to simulate the biomechanical function of the natural knee without the natural ligaments in place, there is a requirement to develop appropriate spring constraints for the natural knee model. Therefore, this study was to investigate the effect of spring constraints on the function and output of the natural porcine knee model, and determine the spring constraint which most closely replicated the function of the natural ligaments. Two linear compression springs with stiffnesses of 9 N/mm (spring-9) and 20 N/mm (spring-20) were set at different free lengths in the anterior-posterior (A/P) axis in a natural knee simulator. The kinematic (A/P displacement) and tribological properties (shear force) output of the simulator were compared at different spring settings. The most appropriate spring setting was determined by comparing the A/P displacement and shear force output at different spring settings with those of the all ligaments model. Spring-9 with a free length of 4 mm showed the minimal difference (-0.03±0.68 mm) in A/P displacement output and spring-20 with a free length of 5 mm showed the minimal difference (-0.10±0.73 mm) in A/P displacement output compared to the all ligament control. There was no statistical difference between the two minimal differences either in A/P displacement or in shear force (paired t-test, p = 0.58, and p = 0.68 respectively) when both spring settings matched most closely to the A/P kinematics of the intact knee. This indicated that both conditions were appropriate spring constraints settings in the A/P direction for the natural porcine knee model.

Comparison of the use of a laximeter and a triaxial accelerometer for Anterolateral ligament injury diagnosis in ACL deficient knee

Objectives: The objective of this study was to compare the use of a laximeter and a triaxial accelerometer, for Anterolateral ligament injury diagnosis of in ACL deficient knee. We hypothesized that a triaxial accelerometer was more effective than a laximeter. Methods: A total of 11 cadaver knees were studied according to a new conservative dissection protocol without damage to the lateral structures. A GnRB® laximeter (Genourob, France) was used to determine anterior tibial translation (AP) of the tibia. Simultaneously, a KiRA® triaxial accelerometer (Kinetic Rapid Assessment) (OrthoKey, Italy) was used to determine two parameters: the AP translation and the Pivot Shift (PS). For each knee, 5 conditions were successively applied: intact knee (intact), knee with ALL (ALLsec) isolated section, knee with ALL and ACL section (ALL + ACLsec). Results: For the laximeter, the ACL and ALL sections led to a significant AP translation increase: + 2.1 mm for the ACL section, and + 0.9 mm for the ALL section. This difference was significant regardless of the level of force applied (p &lt;0.05). For the triaxial accelerometer, the ACL and the ALL sections led to a significant AP translation increase: + 2.8 mm for ACL, and + 1.5 mm for ALL section. In contrast, for the PS, the increase was more consistent. There was a multiplier factor between the ACLsec condition and the ACL + ALLsec condition comparable to that between the intact condition and the ACLsec condition (P&gt; 0.05). Conclusion: Whatever the device, the AP translation difference induced by the ALL injury, of the order of mm, remains too small to make the diagnosis of an ALL injury. The evaluation of the AP translation is therefore not a relevant to diagnostic an ALL injury. With greater increase, the evaluation of the rotatory laxity, through the PS test, is more relevant. In current practice, there is no clinical interest to use a laximeter or accelerometer on AP translation assessment to diagnosis an ALL injury in a deficient ACL knee. On the other hand, the use of a triaxial accelerometer to quantify the lateral tibial plateau acceleration in the pivot shift test appears to be relevant for detecting an ALL injury on a deficient ACL knee. These findings help provide clinical guidelines for more effective objective measures to diagnose ALL injury, and determine the most effective management for each patient.

The use of a hydrogel implant in the repair of osteochondral defects of the knee: A biomechanical evaluation of restoration of native contact pressures in cadaver knees

BackgroundOsteochondral injuries have been treated by a variety of methods, each having its own drawbacks. The purpose of this study was to determine the biomechanical feasibility of using a hydrogel implant replacement for an osteochondral core defect. The hypothesis of this study was that the contact pressure of the native knee can be recreated with the use of a hydrogel implant. MethodsSix cadaver knees were tested in a knee simulator while contact pressures were measured on the tibial plateau. Pressure data was collected in the intact knee, after coring of the condyle and after insertion of a hydrogel implant. Following 1000 gait cycles of fatigue testing, each knee was taken through axial loading indentation testing where the stiffness of the in situ implant was compared to the contralateral condyle. FindingsWhile coring significantly reduced the peak pressure at the coring site from 1.8 MPa in the intact knee to 0.0 MPa after coring, implant insertion significantly increased it to 1.2 MPa. There was no significant difference in the peak pressures or the average pressures at the hole location between the intact knee and following implant insertion. After fatigue testing, no macroscopic loosening or implant damage was observed. Based on indentation testing, the stiffness of the medial condyle, 157 N/mm, was significantly less than the lateral condyle, 696 N/mm. InterpretationThe insertion of the hydrogel implant was able to achieve restoration of contact pressures in the knee supporting the viability of hydrogel implants in the treatment of osteochondral lesions of the knee.

Design and biomechanical characteristics of porous meniscal implant structures using triply periodic minimal surfaces

BackgroundArtificial meniscal implants can be used to replace a severely injured meniscus after meniscectomy and restore the normal functionality of a knee joint. The aim of this paper was to design porous meniscal implants and assess their biomechanical properties.MethodsFinite element simulations were conducted on eight different cases including intact healthy knees, knee joints with solid meniscal implants, and knee joints with meniscal implants with two types of triply periodic minimal surfaces. Compression stresses, shear stresses, and characteristics of stress concentrated areas were evaluated using an axial compressive load of 1150 N and an anterior load of 350 N.ResultsCompared to the solid meniscal implant, the proposed porous meniscal implant produced lower levels of compression and shear stresses on the cartilage, which facilitated the cartilage to retain a semilunar characteristic similar to the natural meniscus. Moreover, both compression and shear stresses on the artificial cartilage were found to be sensitive to the pore properties of the meniscal implant. The meniscal implants with primitive surfaces (porosity: 41%) showed a better performance in disseminating stresses within the knee joint.ConclusionThe present commercial meniscal implant has the problem of equivalent biomechanical properties compared to natural menisci. The main advantage of the proposed porous structure is that it can be used to prevent excessive compression and shear stresses on the articular cartilages. This structure has advantages both in terms of mechanics and printability, which can be beneficial for future clinical applications.

BIOMECHANICAL COMPARISON OF ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION TECHNIQUES USING A NOVEL ROBOTICALLY SIMULATED PIVOT SHIFT: A CADAVERIC STUDY

INTRODUCTION: The robotically simulated clinical pivot shift (PS), a dynamic loading profile based on measurement of loads applied by a surgeon, was developed as a more robust test for detecting kinematic changes for evaluating ACL reconstructions [2]. Two ACL reconstruction techniques were evaluated in this study: the all-epiphyseal (AE) and over-the-top (OTT). These techniques are used exclusively in the pediatric population in lieu of traditional techniques so as not to disrupt the epiphyseal in growing patients. Both techniques’ effectiveness in restoring intact knee kinematics has been examined previously in a cadaveric study, concluding that both techniques provide anterior and rotational stability, but no conclusions were made as to which technique provided more stability [1]. This study aimed to use the simulated clinical PS to assess anterior and rotational stability provided by the AE and OTT surgical techniques. METHODS: Six fresh-frozen, cadaveric legs were transected mid-femur and mid-tibia and mounted to the Universal Musculoskeletal Simulator capable of real-time force feedback using simVITROTM software. Four surgical conditions were tested: Intact knee, deficient ACL, AE reconstruction and OTT reconstruction. The AE and OTT reconstruction order was randomized. For each surgical condition, three tests were performed: Anterior drawer (134 N anterior, 20 N compression) at 0, 15, 30, 60, and 90° of flexion Rotary loads (5 Nm internal rotation torque, 10 Nm valgus torque, 20 N compression) at 5, 15, and 30° of flexion Simulated clinical PS test [2] For each specimen, the kinematics from the intact knee for each respective test was subtracted from the kinematics of the three remaining surgical conditions to acquire kinematic response relative to the intact knee. Relative anterior tibial translation (ATT) and internal tibial rotation (ITR) were reported at each tested flexion angle for the Anterior Drawer and Rotary Loads tests and for the flexion angle initiating the shift in the simulated clinical PS test. This angle was at the peak ATT and corresponded to the start of the shift. Paired t-tests were used to determine significance (p&lt;0.05). In one specimen the simulated clinical PS could not induce a shift, even in the deficient state, and thus was excluded from the analysis. RESULTS: Figure 1A displays the ATT and ITR for the simulated clinical PS at the flexion angle initiating the shift. Neither surgery restored intact knee kinematics. OTT exhibited 4.2 mm more ATT compared to AE (p=0.021) and 7.2° more ITR (p=0.015). OTT had no significant kinematic difference compared to the deficient ACL. Figure 1B displays the ATT for the Anterior Drawer test. The AE surgery significantly reduced ATT compared to deficient at flexion angles of 0, 15 and 30°. No significant difference between OTT and deficient was established. Figure 1C and 1D display the ATT and ITR (respectively) for the Rotary Loads test. Neither surgery restored intact knee kinematics nor significantly reduced ATT or ITR compared to the other surgery, agreeing with previous work with similar loading conditions[1]. DISCUSSION: The all-epiphyseal technique, though unable to restore native kinematics, showed significantly improved stability (4.2 mm ATT, 7.2° ITR) compared to the over-the-top technique when tested with a robotically simulated clinical pivot shift. Analysis of the Anterior Drawer and Rotary Loads tests did not detect significant differences in these surgical techniques, and are in agreement with a previous study which utilized similar loading conditions [1]. Limitations of our study include the small sample size, and the removal of one of the specimens. More work is needed on refining the loading profile to ensure it is able to induce a pivot shift in all specimens. While there is still room for improvement, it is currently still more effective than Rotary Loads, especially in its ability to detect rotational instabilities. The results from our study agree with previous studies [1, 2] in that the Rotary Loads test does not induce large rotational changes amongst ACL surgical states. It also does not provide additional information compared to the Anterior Drawer test for measuring anterior laxity. It is our recommendation that the Rotary Loads test be replaced by the simulated clinical PS when comparing biomechanical advantages of ACL reconstruction techniques in in vitro testing. SIGNIFICANCE: This study provides evidence that the novel robotically simulated clinical pivot shift is a more robust test for detecting kinematic changes when evaluating ACL reconstructions compared to the traditional Anterior Drawer and Rotary Loads tests. It also provides evidence that the All-Epiphyseal technique for reconstructing the ACL restores native kinematics better than the Over-the-Top technique. REFERENCES: [1] McCarthy et al., Am J Sports Med. 41,6: 1330-1339,2013 [2] Colbrunn et al., Pro ASME SBC, SCC2013-14288, 2013

ANTERIOR CRUCIATE LIGAMENT SECTIONING ALTERS CENTER OF PRESSURE WITHIN THE TIBIOFEMORAL JOINT: AN IN VITRO STUDY

Anterior cruciate ligament (ACL) injuries often lead to secondary injuries, joint degradation, and were linked to osteoarthritis. There is little known about how ACL rupture affects the loading and contact characteristics within the tibiofemoral joint. The objective of this study was to evaluate changes in tibiofemoral joint contact pressure and center of pressure (COP) during dynamic motion before and after ACL sectioning in vitro. Six intact cadaveric knees were manipulated through three full cycles of motion ranging from 30∘ to 120∘ of flexion in a custom-built device. A pressure sensor inserted in the tibiofemoral joint measured contact pressure of the medial and lateral compartments as well as COP characteristics of the whole joint before and after the ACL was sectioned. There was a significant decrease in lateral-compartment peak pressure, medial and lateral mean pressure, and total contact area after the ACL was sectioned. In both intact and ACL deficient knees, a posterior-lateral shift in COP was observed during flexion and a medial-anterior shift when returning to extension. Plotting the COP trajectory through the flexion-extension cycle resulted in a distinct hysteresis curve due to the viscoelastic soft tissue properties. Following sectioning, the COP trajectory had a diminished area compared to the intact condition. The diminished area of contact pressure may be more problematic than the overall magnitude when the integrity of the ACL is compromised. The centralized pressure distribution to a smaller surface area over time may cause focal damage to the cartilage leading to osteoarthritis.

Patellofemoral kinematic characteristics in anterior cruciate ligament deficiency and reconstruction

BackgroundIt is very important to dynamically evaluate the functional outcome in the knee after anterior cruciate ligament (ACL) reconstruction under physiological weight bearing. The objective of the current study is that we would like to compare the patellofemoral joint kinematics in three ACL status: ACL intact, ACL deficiency, ACL reconstruction.MethodsTwenty patients with unilateral ACL deficient knees were recruited as preoperative group. Six months after ACL reconstruction, these ten subjects were included as postoperative subjects. Ten normal subjects with healthy knees as the control group. Each subject was asked to walk up a custom set of stairs and a single-plane fluoroscopic imaging system was used to determine the 6DOF kinematics of the injured knees, ACL reconstructed knees, and intact knees.ResultsACL deficient knees showed reduced patellar flexion angle and reduced distal patellar translation during knee flexion. ACL reconstructed knees showed abnormal patellofemoral joint kinematics compared to ACL intact and ACL deficient knees, exhibiting increased patellar external rotation, lateral tilt, lateral translation during knee flexion.ConclusionThese findings imply that some alterations persist after ACL deficiency and ACL reconstruction. These abnormal changes will be the onset of degeneration in patellofemoral joint even if the ACL is reconstructed in a way that restores the clinical anteroposterior stability of the knee. Some biomechanical changes should be made to improve the outcome of intervention especially in surgical treatment like ACL reconstruction.

Development of a Mechanistic Hypothesis Linking Compensatory Biomechanics and Stepping Asymmetry during Gait of Transfemoral Amputees.

Objective Gait asymmetry is a common adaptation observed in lower-extremity amputees, but the underlying mechanisms that explain this gait behavior remain unclear for amputees that use above-knee prostheses. Our objective was to develop a working hypothesis to explain chronic stepping asymmetry in otherwise healthy amputees that use above-knee prostheses. Methods Two amputees (both through-knee; one with microprocessor knee, one with hydraulic knee) and fourteen control subjects participated. 3D kinematics and kinetics were acquired at normal, fast, and slow walking speeds. Data were analyzed for the push-off and collision limbs during a double support phase. We examined gait parameters to identify the stepping asymmetry then examined the external work rate (centre of mass) and internal (joint) power profiles to formulate a working hypothesis to mechanistically explain the observed stepping asymmetry. Results Stepping asymmetry at all three gait speeds in amputees was characterized by increased stance phase duration of the intact limb versus relatively normal stance phase duration for the prosthesis limb. The prosthesis limb contributed very little to positive and negative work during the double support phase of gait. To compensate, the intact leg at heel strike first provided aid to the deficient prosthetic ankle/foot during its push-off by doing positive work with the intact knee, which caused a delayed stance phase pattern. The resulting delay in toe-off of the intact limb then facilitated the energy transfer from the more robust intact push-off limb to the weaker colliding prosthesis side. This strategy was observed for both amputees. Conclusions There is a sound scientific rationale for a mechanistic hypothesis that stepping asymmetry in amputee participants is a result of a motor adaptation that is both facilitating the lower-leg trajectory enforced by the prosthesis while compensating for the lack of work done by the prosthesis, the cost of which is increased energy expenditure of the intact knee and both hips.

Determining the change in length of the anterolateral ligament during knee motion: A three-dimensional optoelectronic analysis

BackgroundThe variation of the anterolateral ligament (ALL) length during knee motion is still unclear, and the knee position in which a reconstruction graft should be tensioned remains controversial. The objective of this study was to determine the variation of the ALL length during knee motion using a three-dimensional optoelectronic system. MethodsKinematic analyses of 20 cadaveric knees were performed using a Motion Analysis® system. The variability of the measurements made during the five acquisition cycles was studied. Reliability was evaluated by two separate measurement sessions, with complete system reinstallation, using different cadavers and a new operator. The ALL length was analysed from extension to full flexion in three rotational conditions. FindingsWhen analysing the reliability of the five cycles, 82% of the measurements we found to have an Intra Class Correlation (ICC) >0.85. The reproducibility of inter-sessional measures by different operators and different cadavers was either good (ICC >0.75) or excellent (ICC >0.85). The ALL length was maximum in full internal rotation with the knee at 25° of flexion. InterpretationThis three-dimensional optoelectronic protocol allowed us to analyse the variation of the ALL length during intact knee motion with good reliability and the required accuracy to analyse this variable. The maximal length and highest tension of the ALL was reported at 25° of knee flexion in internal rotation, suggesting this as the optimal position for the knee joint when tensioning an ALL reconstruction.

Biomimetic proteoglycans can molecularly engineer early osteoarthritic cartilage in vivo.

Biomimetic proteoglycans (BPGs) have the potential to treat osteoarthritis (OA) given that these molecules mimic the structure and properties of natural proteoglycans, which are significantly reduced in OA. We examined the effects of BPGs injected into the intra-articular space in an in vivo OA rabbit knee model and evaluated the effect on histological response, joint friction, and BPG distribution and retention. Rabbits underwent ACL transection to create an arthritic state after 5 weeks. OA rabbits were treated with BPGs or Euflexxa® (hyaluronic acid) intra-articular injections. Non-OA rabbits were injected similarly with BPGs; contralateral joints served as controls. The progression of OA and response to injections were evaluated using Mankin and gross grading systems indicating that mild OA was achieved in operated joints. The coefficient of friction (COF) of the intact knee joints were measured using a custom pendulum friction apparatus, showing that OA joints and OA + Euflexxa® joints demonstrated increased COF than non-operated controls, while BPG-injected non-OA and OA + BPGs were not significantly different from non-OA controls. Injected fluorescently labeled BPGs demonstrated that BPGs diffused into cartilage with localization in the pericellular region. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:403-411, 2019.

Exercise in Persons with Unilateral Lower-Limb Amputation and Contralateral Limb Knee Injury: A Pilot Study

Introduction Exercise habits and return to exercise in individuals with lower-limb amputation (LLA) have been reported in up to 11% to 61% of individuals with amputation, but it is unclear if these individuals meet American College of Sports Medicine (ACSM) exercise guidelines and if there are any negative consequences associated with exercise. This pilot study investigated the exercise habits of individuals with unilateral nonvascular LLA to ascertain adherence to ACSM exercise guidelines and any relationships to contralateral (intact)-limb limb knee injuries. Methods A telephone survey was conducted with 25 individuals (n = 7, female) 22 to 90 years of age (M = 47) with nonvascular unilateral LLAs (2 transmetatarsal/Syme [TM], 13 transtibial [TT], 7 transfemoral [TF], 3 hip disarticulation [HD]) from a university hospital population. Weekly reported exercise before and after amputation (including type, frequency, duration and intensity, based on talk test correlating to intensity) as well as any history of intact-limb knee injuries was obtained. Data were analyzed using χ2 and one-way analysis of variance tests. Results Sixty-eight percent met the recommended ACSM guidelines for cardiorespiratory (CR) exercise before amputation and 48% of individuals met CR guidelines after amputation, and, of those, 41.7% reported sustaining intact-limb knee injuries (there were no injuries in those not meeting CR guidelines; P = 0.009). Respondents who met CR guidelines were at significantly higher risk of knee injury (P = 0.05). Also, those engaged in greater than moderate intensity CR exercise had significantly higher rates of intact knee injury compared with those exercising at low or moderate intensities (P = 0.01). Conclusions This pilot study suggests that engaging in an exercise routine at greater than moderate intensity may significantly increase the risk of intact-limb knee injury in individuals with unilateral LLAs. A larger study involving more subjects would be beneficial in clarifying the risk of knee injury from exercise in patients with amputation.

Pre-Clinical Translation of Second Harmonic Microscopy of Meniscal and Articular Cartilage Using a Prototype Nonlinear Microendoscope.

Previous studies using nonlinear microscopy have demonstrated that osteoarthritis (OA) is characterized by the gradual replacement of Type II collagen with Type I collagen. The objective of this study was to develop a prototype nonlinear laser scanning microendoscope capable of resolving the structural differences of collagen in various orthopaedically relevant cartilaginous surfaces. The current prototype developed a miniaturized femtosecond laser scanning instrument, mounted on an articulated positioning system, capable of both conventional arthroscopy and second-harmonic laser-scanning microscopy. Its optical system includes a multi-resolution optical system using a gradient index objective lens and a customized multi-purpose fiber optic sheath to maximize the collection of backscattered photons or provide joint capsule illumination. The stability and suitability of the prototype arthroscope to approach and image cartilage were evaluated through preliminary testing on fresh, minimally processed, and partially intact porcine knee joints. Image quality was sufficient to distinguish between hyaline cartilage and fibrocartilage through unique Type I and Type II collagen-specific characteristics. Imaging the meniscus revealed that the system was able to visualize differences in the collagen arrangement between the superficial and lamellar layers. Such detailed in vivo imaging of the cartilage surfaces could obviate the need to perform biopsies for ex vivo histological analysis in the future, and provide an alternative to conventional external imaging to characterize and diagnose progressive and degenerative cartilage diseases such as OA. Moreover, this system is readily customizable and may provide a suitable and modular platform for developing additional tools utilizing femtosecond lasers for tissue cutting within the familiar confines of two or three portal arthroscopy techniques.