Pius Wong

The influence of muscle load on tibiofemoral knee kinematics

A comparative kinematics study was conducted on six cadaver limbs, comparing tibiofemoral kinematics in five conditions: unloaded, under a constant 130 N ankle load with a variable quadriceps load, with and without a simultaneous constant 50 N medial and lateral hamstrings load. Kinematics were described as translation of the projected centers of the medial (MFT) and lateral femoral condyles (LFT) in the horizontal plane of the tibia, and tibial axial rotation (TR) as a function of flexion angle. In passive conditions, the tibia rotated internally with increasing flexion to an average of −16° (range: −12/−20°, SD = 3.0°). Between 0 and 40° flexion, the medial condyle translated forwards 4 mm (range: 0.8/5.5 mm, SD = 2.5 mm), followed by a gradual posterior translation, totaling −9 mm (range: −5.8/−18.5 mm, SD = 4.9 mm) between 40–140° flexion. The lateral femoral condyle translated posteriorly with increasing flexion completing −25 mm (range: −22.6 to −28.2 mm, SD = 2.5 mm). Dynamic, loaded measurements simulating a deep knee bend were carried out in a knee rig. Under a fixed ankle load of 130 N and variable quadriceps loading, tibial rotation was inverted, mean TR = 4.7° (range: −3.3°/11.8° SD = 5.4°), MFT = −0.5 mm (range: = −4.3/2.4 mm, SD = 2.4 mm), LFT = 3.3 mm (range: = −3.6/10.6 mm, SD = 5.1 mm). Compared to the passive condition, all these excursions were significantly different (p ≤ 0.015). Adding medial and lateral hamstrings force of 50 N each reduced TR, MFT, and LFT significantly compared to the passive condition. In general, loading the knee with hamstrings and quadriceps reduces rotation and translation compared to the passive condition. Lateral hamstring action is more influential on knee kinematics than medial hamstrings action.

How Isometric Are the Medial Patellofemoral, Superficial Medial Collateral, and Lateral Collateral Ligaments of the Knee?

Background Ligament isometry is a cornerstone in the description of normal knee function and thorough knowledge is mandatory for successful repair of torn ligaments. Purpose This study was undertaken to validate a novel experimental model for the study of ligament strains and to determine the length changes in the superficial medial collateral, lateral collateral, and medial patellofemoral ligaments. Study Design Descriptive laboratory study. Methods Passive motions and loaded squats of 12 cadaveric specimens were performed while controlling ankle load and optically tracking the motion of the bones. Preexperiment and postexperiment computed axial tomography scans allow the transformation of rigid body motion to relative motion of relevant anatomic landmarks on the femur, tibia, and patella. Results The superficial medial collateral ligament is a near-isometric ligament with a strain of less than 2%. The ligament is a little more slack in midflexion (30° to 50°) and in deep flexion, but length changes are not significant (P > .05). The lateral collateral ligament behaves near isometric (<2% strain) from 0° to 70° of knee flexion. Cartilage compression in a loaded environment relieves tension from the collateral ligaments (P < .05). The medial patellofemoral ligament is nonisometric. The cranial part of the medial patellofemoral ligament is most taut at full extension, while the caudal part is most taut at 30° of knee flexion. Conclusion Ligament insertion sites on the femur, patella, and fibula can be derived from computed axial tomography scans. The described model allows the study of dynamic ligament behavior. The superficial medial collateral ligament is a near-isometric ligament with no significant length changes. The medial patellofemoral ligament behaves differently in its cranial and caudal parts. Clinical Relevance In knees with chronic medial collateral ligament insufficiency, isometric repair of the superficial medial collateral ligament can be attempted. A medial patellofemoral ligament reconstruction with a double fixation on the medial patellar border is supported. The cranial bundle should be tightened at full extension and the caudal bundle at 30° of knee flexion.

Can medio-lateral baseplate position and load sharing induce asymptomatic local bone resorption of the proximal tibia? A finite element study

BackgroundAsymptomatic local bone resorption of the tibia under the baseplate can occasionally be observed after total knee arthroplasty (TKA). Its occurrence is not well documented, and so far no explanation is available. We report the incidence of this finding in our practice, and investigate whether it can be attributed to specific mechanical factors.MethodsThe postoperative radiographs of 500 consecutive TKA patients were analyzed to determine the occurrence of local medial bone resorption under the baseplate. Based on these cases, a 3D FE model was developed. Cemented and cementless technique, seven positions of the baseplate and eleven load sharing conditions were considered. The average VonMises stress was evaluated in the bone-baseplate interface, and the medial and lateral periprosthetic region.ResultsSixteen cases with local bone resorption were identified. In each, bone loss became apparent at 3 months post-op and did not increase after one year. None of these cases were symptomatic and infection screening was negative for all. The FE analysis demonstrated an influence of baseplate positioning, and also of load sharing, on stresses. The average stress in the medial periprosthetic region showed a non linear decrease when the prosthetic baseplate was shifted laterally. Shifting the component medially increased the stress on the medial periprosthetic region, but did not significantly unload the lateral side. The presence of a cement layer decreases the stresses.ConclusionLocal bone resorption of the proximal tibia can occur after TKA and might be attributed to a stress shielding effect. This FE study shows that the medial periprosthetic region of the tibia is more sensitive than the lateral region to mediolateral positioning of the baseplate. Medial cortical support of the tibial baseplate is important for normal stress transfer to the underlying bone. The absence of medial cortical support of the tibial baseplate may lead to local bone resorption at the proximal tibia, as a result of the stress shielding effect. The presence of a complete layer of cement can reduce stress shielding, though. Despite the fact that the local bone resorption is asymptomatic and non-progressive, surgeons should be aware of this phenomenon in their interpretation of follow-up radiographs.

Range of motion and repeatability of knee kinematics for 11 clinically relevant motor tasks.

Standard gait analysis reports knee joint rotations in the three anatomical planes without addressing their different levels of reliability. Most clinical studies also restrict analysis to knee flexion-extension, because knee abduction-adduction and axial rotation are small with respect to the corresponding amount of measurement artefact. This study analyses a set of 11 motor tasks, in order to identify those that are adequately repeatable and that can induce greater motion at the knee than walking. Ten volunteers (mean ± SD age: 29 ± 9 years) each underwent three motion analysis sessions on different days with a standard gait analysis system and protocol. In each session they performed normal walking, walking with sidestep and crossover turns, ascent onto and descent off a step, descent with sidestep and crossover turns, chair rise, mild and deep squats, and lunge. Range and repeatability of motions in the three anatomical planes were compared by ANOVA. The sidestep turns showed a range of axial rotation significantly larger than that in walking (about 8°), while maintaining similar levels of repeatability. Ascent, chair rise, squat, and lunge showed greater flexion ranges than walking; among these, ascent was the most repeatable. The results show that turning increases knee axial rotation in young subjects significantly. Further, squats and lunges, currently of large interest in orthopaedics and sports research, have smaller repeatability, likely accounted for to the smaller constraints than in the traditional motor tasks.

Can CT-based patient-matched instrumentation achieve consistent rotational alignment in knee arthroplasty?

PurposeLong-term success of contemporary total knee replacements relies to a large extent on proper implant alignment. This study was undertaken to test whether specimen-matched cutting blocks based on computed axial tomography (CT) scans could provide accurate rotational alignment of the femoral component.MethodsCT scans of five fresh frozen full leg cadaver specimens, equipped with infrared reflective markers, were used to produce a specimen-matched femoral cutting block. Using those blocks, the bone cuts were made to implant a bi-compartmental femoral component. Rotational alignment of the components in the horizontal plane was determined using an optical measurement system and compared with all relevant rotational reference axes identified on the CT scans.ResultsAverage rotational alignment for the bi-compartmental component in the horizontal plane was 1.9° (range 0°–6.3°; standard deviation 2.6°). One specimen that showed the highest deviation from the planned alignment also featured a completely degraded medial articular surface.ConclusionsThe CT-based specimen-matched cutting blocks achieved good rotational alignment accuracy except for one specimen with badly damaged cartilage. In such cases, imaging techniques that visualize the cartilage layer might be more suitable to design cutting blocks, as they will provide a better fit and increased surface support.

Age-related changes in kinematics of the knee joint during deep squat

Researchers frequently use the deep knee squat as a motor task in order to evaluate the kinematic performance after total knee arthroplasty. Many authors reported about the kinematics of a normal squatting motion, however, little is known on what the influence of aging is. Twenty-two healthy volunteers in various age groups (range 21-75 years) performed a deep knee squat activity while undergoing motion analysis using an optical tracking system. The influence of aging was evaluated with respect to kinematics of the trunk, hip, knee and ankle joints. Older subjects required significantly more time to perform a deep squat, especially during the descending phase. They also had more knee abduction and delayed peak knee flexion. Older subjects were slower in descend than ascend during the squat. Although older subjects had a trend towards less maximal flexion and less internal rotation of the knee compared to younger subjects, this difference was not significant. Older subjects also showed a trend towards more forward leaning of the trunk, resulting in increased hip flexion and anterior thoracic tilt. This study confirmed that some aspects of squat kinematics vary significantly with age, and that the basic methodology employed here can successfully detect these age-related trends. Older subjects had more abduction of the knee joint, and this may indicate the load distribution of the medial and lateral condyles could be different amongst ages. Age-matched control data are therefore required whenever the performance of an implant is evaluated during a deep knee squat.

A new spacer-guided, PCL balancing technique for cruciate-retaining total knee replacement

AbstractPurpose The goal of this study was to investigate whether a new posterior cruciate ligament (PCL) balancing approach with a spacer technique during total knee arthroplasty (TKA) reproduced the correct tibiofemoral contact point (CP) location. It was hypothesized that it should be possible to adequately balance the PCL with this geometrical technique, obtaining correct position and stability of the medial femoral condyle, independent of insert shape. MethodsNine fresh-frozen full-leg cadaver specimens were used. After native testing, prototype components of a new PCL-retaining implant were implanted using navigation and a bone-referencing technique. After finishing the bone cuts, the spacer technique was used to ascertain balancing of the PCL and the tibial cut was corrected if necessary. Passive and squat motions were performed before and after TKA using a dynamic knee simulator while tibiofemoral kinematics were recorded using six infrared cameras. CPs (native and implant) were calculated as the projections of the femoral condylar centres on the horizontal plane of the tibia.ResultsThe spacer technique resulted in correct PCL balancing in all specimens. The kinematic patterns of native and replaced knees showed no statistically significant differences in passive and squat motions. The medial CP after TKA was at the same position as in the native knee. No paradoxical sliding forward was seen after TKA, supporting our hypothesis.ConclusionsThe spacer technique can be applied by surgeons during PCL-retaining TKA and will lead to good PCL balancing, indicated by a correct CP, no lift-off in flexion and no posterior sag.

An in-vitro study of human knee kinematics: natural vs. replaced joint

Cadaver specimens mounted on a knee simulator combined with motion tracking devices have been used for the kinematics study of the human knee. The results of these studies have shown that the classical four bar linkage model of the knee is not adequate. This obviously has repercussions for the design of knee implants. They should at least permit normal kinematic behavior to prevent abnormal loads on the soft tissues and on other joints of the leg. Studies where implant kinematics can be compared to kinematics of the natural knee of the same specimen are very rare, though. In this project, the kinematics of six fresh frozen human cadaver knees in the natural state and after replacement of the knee joint with a bi-cruciate stabilizing implant were evaluated using a knee simulator and stereophotogrammetry. Before testing, frames with reflective markers were fixed to the femur and tibia. Then, a CT scan was made and the images were processed to identify anatomical landmarks and their position with respect to the reflective markers. Thus, an anatomically relevant coordinate system could be defined for each bone. During a squat, the motion of the markers was continuously measured. Several load conditions were considered for each specimen. The data obtained enabled us to calculate the motion of the femur and tibia with respect to each other and present that in clinically relevant terms. After testing, a second CT scan was made to check the position of the implant with respect to the original articular surfaces and also for a control of the position of the marker frames. The results show that kinematics of the natural knee joint are more variable than expected. The knee replacement, on the other hand, produces a consistent kinematics pattern in all the specimens.

Determination of In Vivo Three-Dimensional Lower Limb Kinematics for Simulation of High-Flexion Squats

In vitro and numerical simulations of the knee require reasonable kinematic and load inputs and boundary conditions, in order to help ensure their clinical relevance. However, previous simulations of high-flexion squats often have applied loads and motions that possibly oversimplify the true knee kinematics. This study aimed to improve future simulations of squatting by obtaining three-dimensional squat kinematics from a cohort of healthy adults. Seventeen subjects (age range 24-75) underwent motion capture sessions using a standard, systematic clinical procedure. Joint positions were normalized versus femur and tibia segment lengths, and ground reaction forces were normalized versus body weight. Range of motion and velocity decreased with age. The ankle was more anterior to the hip with decreasing hip height. Dynamic squat kinematics were reported.