Biomechanics of the patello-femoral joint. Part I: A study of the contact and the congruity of the patello-femoral compartment and movement of the patella

Sesamoid bones also show functional adaptation in their microanatomy-The example of the patella in Perissodactyla

The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no "compensation" of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint.

Rehabilitation Variability Following Femoral Condyle and Patellofemoral Microfracture Surgery of the Knee

OBJECTIVE

To assess the variability of postoperative rehabilitation protocols used by orthopedic surgery residency programs for microfracture of femoral condyle and patellofemoral lesions of the knee.

DESIGN

Online postoperative microfracture rehabilitation protocols from US orthopedic programs and the scientific literature were reviewed. A custom scoring rubric was developed to analyze each protocol for the presence of discrete rehabilitation modalities and the timing of each intervention.

RESULTS

A total of 18 programs (11.6%) from 155 US academic orthopedic programs' published online protocols and a total of 44 protocols were analyzed. Seventeen protocols (56.7%) recommended immediate postoperative bracing for femoral condyle lesions and 17 (89.5%) recommended immediate postoperative bracing for patellofemoral lesions. The average time to permitting weight-bearing as tolerated (WBAT) was 6.1 weeks (range, 0-8) for femoral condyle lesions and 3.7 weeks (range, 0-8 weeks) for patellofemoral lesions. There was considerable variation in the inclusion and timing of strength, proprioception, agility, and pivoting exercises. For femoral condyle lesions, 10 protocols (33.3%) recommended functional testing prior to return to sport at an average of 23.3 weeks postoperatively (range, 12-32 weeks). For patellofemoral lesions, 4 protocols (20.0%) recommended functional testing for return to sport at an average of 21.0 weeks postoperatively (range, 12-32 weeks).

CONCLUSION

A minority of US academic orthopedic programs publish microfracture rehabilitation protocols online. Among the protocols currently available, there is significant variability in the inclusion of specific rehabilitation components and timing of many modalities. Evidence-based standardization of elements of postoperative rehabilitation may help improve patient care and subsequent outcomes.

Function of the Distal Part of the Vastus Medialis Muscle as a Generator of Knee Extension Twitch Torque

The distal part of the vastus medialis (VM) (VM obliquus: VMO) muscle acts as the medial stabilizer of the patella. However, it has been known to facilitate VMO contraction during training of the quadriceps femoris muscle in knee joint rehabilitation. This study aimed to examine the contribution degree of VMO as a knee joint extension torque generator. Sixteen healthy male volunteers participated in this study. Electrical muscle stimulation (EMS) was performed on VMO at 60° knee angle for 20 min to induce muscle fatigue. Knee extension twitch torques (TT) at 90° and 30° knee angle evoked by femoral nerve stimulation were measured before and after EMS. Although each TT at 90° and 30° knee angle significantly decreased after EMS, the decreased TT rate in both joint angles showed no significant difference. Our results show that VMO might contribute to the generation of the knee joint torque at the same level in the range from flexion to extension. Therefore, it was suggested that the facilitating the neural drive for VMO is important during the quadriceps femoris muscle strengthening exercise.

Dose and Recovery Response of Patellofemoral Cartilage Deformations to Running

Background:

Running is a common recreational activity that provides many health benefits. However, it remains unclear how patellofemoral cartilage is affected by varied running distances and how long it takes the cartilage to recover to its baseline state after exercise.

Hypothesis:

We hypothesized that patellofemoral cartilage thickness would decrease immediately after exercise and return to its baseline thickness by the following morning in asymptomatic male runners. We further hypothesized that we would observe a significant distance-related dose response, with larger compressive strains (defined here as the mean change in cartilage thickness measured immediately after exercise, divided by the pre-exercise cartilage thickness) observed immediately after 10-mile runs compared with 3-mile runs.

Study Design:

Descriptive laboratory study.

Methods:

Eight asymptomatic male participants underwent magnetic resonance imaging of their dominant knee before, immediately after, and 24 hours after running 3 and 10 miles at a self-selected pace (on separate visits).

Results:

Mean patellar cartilage thicknesses measured before exercise and after the 24-hour recovery period were significantly greater than the thicknesses measured immediately after both the 3- and 10-mile runs (P < .001). This relationship was not observed in trochlear cartilage. Mean patellar cartilage compressive strains were significantly greater after 10-mile runs compared with 3-mile runs (8% vs 5%; P = .01).

Conclusion:

Patellar cartilage thickness decreased immediately after running and returned to its baseline thickness within 24 hours of running up to 10 miles. Furthermore, patellar cartilage compressive strains were dose-dependent immediately after exercise.

Clinical Relevance:

These findings provide critical baseline data for understanding patellofemoral cartilage biomechanics in asymptomatic male runners that may be used to optimize exercise protocols and investigations targeting those with running-induced patellofemoral pain.

Dynamic Intra-articular Space Variation in Clicking TMJs

During mandibular movement, the geometric relationships of the articular surfaces in the temporomandibular joint (TMJ) change, so that the disc undergoes different stress concentrations with respect to time and position. In this study, we compared the intra-articular space variations of 13 clicking and 15 asymptomatic TMJs for jaw opening/closing. Magnetic resonance imaging and jaw tracking were combined to display the motion of the whole condyle within the fossa. In clicking TMJs, the mediolateral spread s of the stress-field trajectories was 2.4 ± 1.0 mm ( smax = 4.9 ± 2.1 mm) with an aspect ratio a/h of 2.5 ± 1.6, both significantly greater than in controls (p < 0.05). The stress-field trajectories of the controls coincided during opening/closing ( s = 0.9 ± 0.2 mm, smax = 1.8 ± 0.8 mm, a/h = 1.6 ± 0.3). Clicking TMJs showed much less coincident stress-field paths and much “flatter” stress-fields than controls during jaw opening/closing.

Validation of a method for combining biplanar radiography and magnetic resonance imaging to estimate knee cartilage contact

Combining accurate bone kinematics data from biplane radiography with cartilage models from magnetic resonance imaging, it is possible to estimate tibiofemoral cartilage contact area and centroid location. Proper validation of such estimates, however, has not been performed under loading conditions approximating functional tasks, such as gait, squatting, and stair descent. The goal of this study was to perform an in vitro validation to resolve the accuracy of cartilage contact estimations in comparison to a laser scanning gold standard. Results demonstrated acceptable reliability and accuracy for both contact area and centroid location estimates. Root mean square errors in contact area averaged 8.4% and 4.4% of the medial and lateral compartmental areas, respectively. Modified Sorensen-Dice agreement scores of contact regions averaged 0.81 ± 0.07 for medial and 0.83 ± 0.07 for lateral compartments. These validated methods have applications for in vivo assessment of a variety of patient populations and physical activities, and may lead to greater understanding of the relationships between knee cartilage function, effects of joint injury and treatment, and the development of osteoarthritis.

In vivo kinematics of the extensor mechanism of the knee during deep flexion

While various factors have been assumed to affect knee joint biomechanics, few data have been reported on the function of the extensor mechanism in deep flexion of the knee. This study analyzed the patellofemoral joint contact kinematics and the ratio of the quadriceps and patellar tendon forces in living subjects when they performed a single leg lunge up to 150 deg of flexion. The data revealed that in the proximal-distal direction, the patellofemoral articular contact points were in the central one-third of the patellar cartilage. Beyond 90 deg of flexion, the contact points moved towards the medial-lateral edges of the patellar surface. At low flexion angles, the patellar tendon and quadriceps force ratio was approximately 1.0 but reduced to about 0.7 after 60 deg of knee flexion, implying that the patella tendon carries lower loads than the quadriceps. These data may be valuable for improvement of contemporary surgical treatments of diseased knees that are aimed to achieve deep knee flexion.

Validation of an MRI-based method to assess patellofemoral joint contact areas in loaded knee flexion in vivo

PURPOSE

To develop and validate short axial and sagittal MRI scans (<1min) to assess in vivo patellofemoral contact areas in loaded knee flexion.

MATERIALS AND METHODS

Contact area was assessed in four cadaver knee specimens from axial and sagittal scans using two contact area extraction techniques (delineation and intersection) and three calculation techniques (slice thickness multiplication, linear interpolation, and spline interpolation). Error was expressed as the mean absolute and percentage difference from a dye staining-based reference standard. Intrareader and intrasubject repeatability, expressed as the mean standard deviation, was determined.

RESULTS

Contact area assessments from the sagittal MRI scans using the delineation and slice thickness multiplication technique had the smallest error (47.7 ± 38.1 mm(2) or 10.7%). The intrareader repeatability from assessments using the sagittal scans was smaller than those using the axial scans when the delineation method was used (<9.4 ± 4.3 mm(2) and <15.4 ± 14.1 mm(2) , respectively). The intrasubject repeatability of the assessment from the sagittal scan was less than 39.9 ± 23.0 mm(2) .

CONCLUSION

This protocol yields assessments of contact area in less than 1 minute that have errors similar to those made using scans many times longer and can be used in series with kinematic scans to carry out simultaneous assessments in vivo to study patellofemoral joint disease.

Rehabilitation following Microfracture of the Knee

Postoperative rehabilitation programs following articular cartilage repair procedures will vary greatly among patients and need to be individualized based on the nature of the lesion, the unique characteristics of the patient, and the type and detail of each surgical procedure. These programs are based on knowledge of the basic science, anatomy, and biomechanics of articular cartilage as well as the biological course of healing following surgery. The goal is to restore full function in each patient as quickly as possible by facilitating a healing response without overloading the healing articular cartilage. The purpose of this article is to overview the principles of rehabilitation following microfracture procedures of the knee.

In vivo movement analysis of the patella using a three-dimensional computer model

We used three-dimensional movement analysis by computer modelling of knee flexion from 0° to 50° in 14 knees in 12 patients with recurrent patellar dislocation and in 15 knees in ten normal control subjects to compare the in vivo three-dimensional movement of the patella. Flexion, tilt and spin of the patella were described in terms of rotation angles from 0°. The location of the patella and the tibial tubercle were evaluated using parameters expressed as percentage patellar shift and percentage tubercle shift. Patellar inclination to the femur was also measured and patellofemoral contact was qualitatively and quantitatively analysed.

The patients had greater values of spin from 20° to 50°, while there were no statistically significant differences in flexion and tilt. The patients also had greater percentage patellar shift from 0° to 50°, percentage tubercle shift at 0° and 10° and patellar inclination from 0° to 50° with a smaller oval-shaped contact area from 20° to 50° moving downwards on the lateral facet.

Patellar movement analysis using a three-dimensional computer model is useful to clearly demonstrate differences between patients with recurrent dislocation of the patella and normal control subjects.

The measurement of patellar alignment in patellofemoral pain syndrome: are we confusing assumptions with evidence?

Patellofemoral pain syndrome is one of the most common orthopaedic complaints presenting to physical therapists. Although its etiology is uncertain, the cause is most often considered to be malalignment or lateral tracking of the patella. Consequently, measurement of patellar alignment has come to be accepted as an integral part of the examination of patellofemoral pain syndrome. Various measurement techniques exist, both clinical and radiological, and these have been frequently used in the diagnosis and treatment of the condition. As a corollary, the widespread use of such measurements has also lent weight to the theory that patellar malalignment is one of the primary causes of patellofemorai pain syndrome. However, an analysis of the literature reveals that the vast majority of these measurement procedures lack the appropriate scientific qualities to be considered acceptable measurement tools, including questionable reliability and validity, and an absence of appropriate normative data and a gold standard. This paper assesses the evidence for the usefulness of the most commonly used measures of patellar alignment and concludes that many of the beliefs of the clinical community with regard to the existence and measurement of patellar malalignment in patellofemoral pain syndrome may be based largely on assumptions and not on evidence.

Rehabilitation and Nonoperative Treatment of Patellar Instability

Patellofemoral instability can be a difficult condition for clinicians to manage. Differentiation needs to be made as to whether the problem is an acute injury where a traumatic incident has usually precipitated the dislocation or whether the problem is a recurrent instability where the patellofemoral joint is unstable during everyday activities. This review defines instability, discusses the factors affecting instability, and provides assessment procedures and nonoperative intervention strategies for the clinician.

Current concepts in the rehabilitation following articular cartilage repair procedures in the knee

Postoperative rehabilitation programs following articular cartilage repair procedures will vary greatly among patients and need to be individualized based on the nature of the lesion, the unique characteristics of the patient, and the type and detail of each surgical procedure. These programs are based on knowledge of the basic science, anatomy, and biomechanics of articular cartilage as well as the biological course of healing following surgery. The goal is to restore full function in each patient as quickly as possible by facilitating a healing response without overloading the healing articular cartilage. The purpose of this paper is to overview the principles of rehabilitation following articular cartilage repair procedures. Furthermore, specific rehabilitation guidelines for debridement, abrasion chondroplasty, microfracture, osteochondral autograft transplantation, and autologous chondrocyte implantation will be presented based upon our current understanding of the biological healing response postoperatively.

Modeling of Temporomandibular Joint Function Using MRI and Jaw-Tracking Technologies – Mechanics

The study of mechanics of the temporomandibular joint (TMJ) is important because its dysfunction and breakdown could be, at least partially, of mechanical origin. The incongruity of the articular surfaces of the TMJ is compensated by a fibrocartilaginous articular disc. Its dislocation and failure seem to be closely related to the development of osteoarthritis of the TMJ. The analysis of mandibular kinematics permits the detection and assessment of irregularities of TMJ function due to internal obstacles such as a displaced articular disc. Furthermore, the measurement of the dynamic relationship between the articular surfaces of the TMJ is useful to determine the strains undergone by the disc that if too high might compromise its integrity. The development of our research in TMJ mechanics has evolved from the acquisition of the traces of single mandibular points to an accurate and compact description of mandibular motion, in which the mechanical advantage of jaw muscles, and forces and torques acting on the jaw are considered as well. The combination of three-dimensional software models of TMJ anatomies obtained from MRI and jaw tracking with six degrees of freedom permits a subject-specific dynamic analysis of the intra-articular space, providing insight into individual disc deformation during function and TMJ loading. Studies performed with this system indicate that both TMJs are loaded during chewing, the balancing more so than the working joint. In fact, during chewing, the intra-articular distance is smaller for hard than for soft food, on closing than on opening, on the balancing than on the working side. This last finding is confirmed by static biting experiments, in which the condyle-fossa distance decreases more on the side contralateral to the bite force, depending on its magnitude. Also studies on the dynamics of compression areas indicate that plowing can occur through the disc during function, especially mediolaterally, due to stress field translation. This effect might contribute to cartilage wear and fatigue also because the disc is weaker mediolaterally. Further data indicate that the lateral area of the disc is mostly exposed to a higher mechanical energy density. This will be more intensively investigated using finite element method.

In vivo assessment of patellofemoral joint contact area in individuals who are pain free

Magnetic resonance imaging was used to quantify in vivo patellofemoral joint contact area and to determine if contact area is affected by quadriceps muscle contraction. Ten subjects without pain (six women, four men) had their right patellofemoral joint imaged. Cartilage-enhanced, axial plane images were obtained at 0 degrees, 20 degrees, 40 degrees, and 60 degrees knee flexion under quadriceps loaded (contracted) and quadriceps unloaded (relaxed) conditions. Medial and lateral facet contact area measurements were obtained on each image, and then summed across all images in a series to yield facet contact area measurements for each knee angle. Total contact area was computed as the sum of medial and lateral facet contact areas. Consistent with in vitro studies, progressive increases in patellofemoral joint contact area were observed from 0 degrees to 60 degrees knee flexion. The lateral facet comprised a greater percentage of total contact area compared with the medial facet at each knee flexion angle, suggesting increased load-bearing potential. Quadriceps contraction did not affect patellofemoral joint contact area indicating that the addition of a compressive load to the joint did not alter the area of the load-bearing surfaces. In vivo assessment of patellofemoral joint contact area could provide insight into mechanisms of patellofemoral joint disorders.

Patellar tracking during simulated quadriceps contraction

The current study compared patella tracking during simulated concentric and eccentric quadriceps contractions in 12 knees from cadavers using a three-dimensional electromagnetic tracking system. The patella shifted (translated) and tilted medially during approximately the initial 22 degrees tibiofemoral flexion. The patella then shifted and tilted laterally for the remaining arc of tibiofemoral flexion (90 degrees). At 90 degrees tibiofemoral flexion, the patella had an orientation of lateral patella shift and lateral patella tilt. Patella shift was significantly more lateral between 40 degrees and 70 degrees tibiofemoral flexion during concentric quadriceps action than during eccentric contraction. Patella tilt was significantly more lateral between 45 degrees and 55 degrees tibiofemoral flexion during concentric quadriceps contraction than during eccentric action. No other significant differences were seen between the quadriceps contraction conditions. The current study supports the hypothesis that patellar instability is most likely a result of various anatomic and physiologic factors causing a failure of the extensor mechanism to deliver the patella into the femoral sulcus and that a patellar dislocation rarely would occur in a normal knee.

Measurement of patellar tracking: assessment and analysis of the literature

Patellar tracking is defined as the motion of the patella relative to the femur or femoral groove on knee flexion and extension. Abnormalities of tracking (maltracking) are thought to relate to many disorders of the patellofemoral joint and may be defined easily or may be extremely difficult to observe. Accurate measurement of patellar tracking, and definition of normal tracking, have not been achieved yet in experimental conditions or in clinical conditions. Such information would be valuable in the diagnosis and treatment of patellofemoral disorders. In the current report, the literature is reviewed critically with an emphasis on methodology and results. The reporting of patellar tracking is affected significantly by basic definitions of coordinate systems and reference points. The method of muscle loading, range, and direction of knee motion, use of static or dynamic measurement techniques, and tibial rotation also will affect the results obtained. The accuracy of the equipment used is important as differences in tracking may be small. Comparison between existing studies is difficult because of differences in methodology. There is general agreement that the patella translates medially in early knee flexion and then translates laterally. Regarding patellar tilt, results are less consistent, especially in vivo and the results for patellar rotation are highly variable.

Patellofemoral stress during walking in persons with and without patellofemoral pain

OBJECTIVE

To determine whether individuals with patellofemoral pain (PFP) demonstrate elevated patellofemoral joint (PFJ) stress compared with pain-free controls during free and fast walking.

DESIGN

A cross-sectional study utilizing an experimental and a control group.

BACKGROUND

Although the cause of PFJ pathology is believed to be related to elevated joint stress (force per unit area), this hypothesis has not been adequately tested and causative mechanisms have not been clearly defined.

METHODS

Ten subjects with a diagnosis of PFP and 10 subjects without pain participated. All subjects completed two phases of data collection: 1) magnetic resonance imaging (MRI) assessment to determine PFJ contact area and 2) comprehensive gait analysis during self-selected free and fast walking velocities. Data obtained from both phases were required as input variables into a biomechanical model to quantify PFJ stress.

RESULTS

On the average, PFJ stress was significantly greater in subjects with PFP compared with control subjects during level walking. The observed increase in PFJ stress in the PFP group was attributed to a significant reduction in PFJ contact area, as the PFJ reaction forces were similar between groups.

CONCLUSION

Our results are consistent with the hypothesis that increased patellofemoral joint stress may be a predisposing factor with respect to development of PFP. Clinically, these findings indicate that treatments designed to increase the area of contact between the patella and the femur may be beneficial in reducing the PFJ stress during functional activities.

RELEVANCE

Patellofemoral pain affects about 25% of the population, yet its etiology is unknown. Knowledge of the biomechanical factors contributing to patellofemoral joint pain may improve treatment techniques and guide development of prevention strategies.

Correlation of patellar tracking pattern with trochlear and retropatellar surface topographies

The study was aimed to test the hypothesis that in the knee extension range 100 to 30 deg, the patellar "out-of-plane" tracking pattern is controlled by the passive restraint provided by the topographic interaction of the patellofemoral contacting surfaces. The out-of-plane tracking pattern, i.e., the pattern of patellar displacements not in the plane of knee extension/flexion, consists of translation in the medial-lateral direction, and rotations about the anterior-posterior axis (spin) and the proximal-distal axis (tilt). Using 15 fresh-frozen knees subjected to extensor moment magnitudes comparable to those in the "static-lifting" activity (foot-ground reaction = 334 N), the patellar displacements were measured using a calibrated six-degree-of-freedom electromechanical goniometer. The topographies of the trochlear and retropatellar surfaces were then measured using a calibrated traveling dial-gage arrangement and the same coordinate system used for the displacement measurements. Three indices were defined to quantify particular natural features of the three-dimensional topographies that are expected to control the patellar displacements. Correlation of the indices with their corresponding displacements showed that topographic interaction was significant in the control of all three displacements. However, for patellar spin, unlike for the other two displacements, the direction of the active quadriceps tension vector was also a significant controlling factor. Patellar medial-lateral translation was found to be controlled dominantly by the trochlear topography, while retropatellar topography also had a significant role in the control of the other two displacements.

Contact area of the trapeziometacarpal joint

Eighteen cadaver hands were studied to determine the contact area of the trapeziometacarpal joint by using silicone rubber casts. Casting material was introduced into the trapeziometacarpal joint during several motions of the thumb and the contact location was observed. The ratios of the contact area to the total joint area were calculated. The contact locations in opposition were the radial, volar, and ulnar segments of the trapezium and the dorsal, radial, and volar segments of the metacarpal. On average, 53% of the trapezium was in contact with 53% of the metacarpal in opposition, while 28% of the trapezium was in contact with 28% of the metacarpal in palmar abduction and 25% of the trapezium was in contact with 25% of the metacarpal in radial abduction. The contact area was the largest in opposition. The trapeziometacarpal joint is stable in opposition and facilitates a strong pinch.

In vitro measurement of the tracking pattern of the human patella

This study sought to determine whether a general pattern describing the three-dimensional tracking characteristics of the human patella could be established, and if not, then to determine the extent and nature of interspecimen variations in the characteristics in a normal population. Using 32 fresh-frozen knees subjected to extensor moment magnitudes similar to those in "static-lifting" and "leg-raising against resistance" maneuvers, patellar displacements were measured in the knee extension range 120 to 0 deg. For static-lifting, a constant foot-floor reaction of 334 N was applied. For leg-raising, a constant net quadriceps tension of 668 N was used throughout the extension range. Measurements were taken with a calibrated six-degree-of-freedom electromechanical goniometer and a displacement coordinate system referenced to the geometry of individual specimens. The three patellar displacements in the plane of knee extension/flexion (extension rotation, and anterior and proximal translations) consistently demonstrated the same pattern in the entire knee extension range with an average coefficient of variation of 13 percent. For knee angles greater than 45 deg, the three other displacements (medial-lateral translation, and rotations about the anterior--posterior and proximal--distal axes) followed a general pattern. However, for knee angles less than 45 deg, these displacements differed considerably between specimens for each loading condition, both in terms of magnitude (average coefficient of variation: 70 percent), and direction.

Influence of lateral release on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty

The influence of lateral release of retinaculum on patellofemoral kinematics and contact characteristics after total knee arthroplasty was investigated in vitro. Lateral release altered the patellar tracking in patellar flexion, rotation, tilting, and translation. The contact force was decreased at high flexion angles. The contact area was slightly decreased and the contact region shifted laterally on the patellar button and medially on the femoral component at most of the flexion angles. The results suggest that the lateral release in total knee arthroplasty can change some patellar tracking and patellofemoral joint contact characteristics.

Anatomic alignment of the patellar groove

The variability in alignment of the natural patellar groove was determined about various anatomic axes of the femur, using 3 plane radiographs and electronic digitization. After the patellar groove was identified and marked on 15 anatomic specimen femurs, radiographs were taken in the coronal, sagittal, and transverse planes so that principal anatomic axes could be outlined. Through electronic digitization, a 3-dimensional representation of the patellar groove was constructed about the distal anatomic axis, mechanical axis, transepicondylar axes, and transcondylar axes. Regarding these 4 principal anatomic axes, the variability in orientation of the patellar groove was profound in both coronal and transverse planes, typically involving a range of 11 degrees to 16 degrees about the mean. The average orientation most closely approximated the perpendicular to the transepicondylar axis in the coronal plane; however, the range varied extensively. None of the anatomic axes tested proved reliable as a reference axis for proper position of the patellar groove, and this study shows that the orientation of the natural patellar groove is more variable than previously suspected. The failure of femoral components to accommodate this variability may explain many complications associated with the patellar component in total knee arthroplasty.

Influence of patellar thickness on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty

Although total knee arthroplasty (TKA) has become a very common procedure, patellar problems remain a major cause of disability. Patellar thickness is one of the most challenging factors. The influence of patellar thickness on patellofemoral kinematics and contact characteristics following TKA was investigated. Seven unembalmed whole-lower-extremity cadaveric specimens were used. The kinematics was measured with a magnetic tracking device (3Space Tracker System, Polhemus Navigation Sciences Division, Colchester, VT). Contact area was calculated from the kinematic data and the digitized joint surface geometrics based on a theoretical method. The patellofemoral joint contact force was measured directly using a uniaxial force transducer. Kinematically, the influence of patellar thickness on patellar flexion, rotation, and proximodistal shift was not significant. Orthopaedic surgeons are often challenged by derangement of the patellofemoral joint, especially following TKA. It is commonly assumed that restoration of overall patellar thickness is most desirable. A thin patella can reduce the contact force, but it also poses the potential risks of stress fracture and anteroposterior instability. Increasing patellar thickness might be expected to increase the effective quadriceps moment arm at low flexion angles of the knee, but potentially reduces the range of motion of the knee and predisposes to patellar subluxation. Either a thicker or a thinner patella had a smaller contact area than intact and normal-thickness patella. Therefore, the surgical technique of patellar resurfacing during TKA should attempt to reproduce the original patellar thickness.

The biomechanics of the human patella during passive knee flexion

The fundamental objectives of patello-femoral joint biomechanics include the determination of its kinematics and of its dynamics, as a function of given control parameters like knee flexion or applied muscle forces. On the one hand, patellar tracking provides quantitative information about the joint's stability under given loading conditions, whereas patellar force analyses can typically indicate pathological stress distributions associated for instance with abnormal tracking. The determination of this information becomes especially relevant when facing the problem of evaluating surgical procedures in terms of standard (i.e. non-pathological) knee functionality. Classical examples of such procedures include total knee replacement (TKR) and elevation of the tibial tubercle (Maquet's procedure). Following this perspective, the current study was oriented toward an accurate and reliable determination of the human patella biomechanics during passive knee flexion. To this end, a comprehensive three-dimensional computer model, based on the finite element method, was developed for analyzing articular biomechanics. Unlike previously published studies on patello-femoral biomechanics, this model simultaneously computed the joint's kinematics, associated tendinous and ligamentous forces, articular contact pressures and stresses occurring in the joint during its motion. The components constituting the joint (i.e. bone, cartilage, tendons) were modeled using objective forms of non-linear elastic materials laws. A unilateral contact law allowing for large slip between the patella and the femur was implemented using an augmented Lagrangian formulation. Patellar kinematics computed for two knee specimens were close to equivalent experimental ones (average deviations below 0.5 degrees for the rotations and below 0.5 mm for the translations) and provided validation of the model on a specimen by specimen basis. The ratio between the quadriceps pulling force and the patellar tendon force was less than unity throughout the considered knee flexion range (30-150 degrees), with a minimum near 90 degrees of flexion for both specimens. The contact patterns evolved from the distal part of the retropatellar articular surface to the proximal pole during progressive flexion. The lateral facet bore more pressure than the medial one, with corresponding higher stresses (hydrostatic) in the lateral compartment of the patella. The forces acting on the patella were part of the problem unknowns, thus leading to more realistic loadings for the stress analysis, which was especially important when considering the wide range of variations of the contact pressure acting on the patella during knee flexion.

Patellar tracking measurement in the normal knee

Eleven fresh frozen cadaveric knee specimens were mounted in a knee kinematics test device, and normal patellar movements were evaluated with use of an external device for direct measurement of patellar movements. The effects of four different measurement conditions were assessed through alteration of one condition and determination of its effect on patellar kinematics with the use of six specimens. The four conditions included (a) change of the measuring axis from an axis parallel to the central axis of the femur (femoral axis) to one parallel to the central axis of the tibia (tibial axis), (b) rotation of the femoral axis internally 6 degrees, (c) change of the direction of the quadriceps force from parallel to the mechanical line of the lower extremity to a direction parallel to the femoral shaft, and (d) increase of the magnitude of the quadriceps force from 111 to 500 N. During knee flexion, the patella shifted laterally after a slight initial medial shift, tilted laterally from midflexion to 90 degrees, and gradually rotated medially. The patellar shift relative to the tibial axis appeared to be more medial than the shift measured relative to the femoral axis; the discrepancy was caused by the valgus position of the tibia relative to the femur. Changing the rotational angle of the femoral axis artificially changed the patellar position. Varying the direction of the quadriceps within the narrow range and increasing the quadriceps force did not affect patellar movements.(ABSTRACT TRUNCATED AT 250 WORDS)

A three-dimensional anatomical model of the human patello-femoral joint, for the determination of patello-femoral motions and contact characteristics

The object of this study is to develop a three-dimensional mathematical model of the patello-femoral joint, which is modelled as two rigid bodies representing a moving patella and a fixed femur. Two-point contact was assumed between the femur and patella at the medial and lateral sides and in the analysis, the femoral and patellar articular surfaces were mathematically represented using Coons' bicubic surface patches. Model equations include six equilibrium equations and eleven constraints: six contact conditions, four geometric compatibility conditions, and the condition of a rigid patellar ligament; the model required the solution of a system of 17 nonlinear equations in 17 unknowns, its response describing the six-degrees-of-freedom patellar motions and the forces acting on the patella. Patellar motions are described by six motion parameters representing the translations and rotations of the patella with respect to the femur. The forces acting on the patella include the medial and lateral component of patello-femoral contact and the patellar ligament force, all of which were represented as ratios to the quadriceps tendon force. The model response also includes the locations of the medial and lateral contact points on the femur and the patella. A graphical display of its response was produced in order to visualize better the motion of the components of the extensor mechanism. Model calculations show good agreement with experimental results available from the literature. The patella was found to move distally and posteriorly on the femoral condyles as the knee was flexed from full extension. Results indicate that the relative orientation of the patellar ligament with respect to the patella remains unchanged during this motion. The model also predicts a patellar flexion which always lagged knee flexion. Our calculations show that as the angle of knee flexion increased, the lateral contact point moved distally on the femur without moving significantly either medially or laterally. The medial contact point also moved distally on the femur but moved medially from full extension to about 40 degrees of knee flexion, then laterally as the knee flexion angle increased. The lateral contact point on the patella did not change significantly in the medial and lateral direction as the knee was flexed; however, this point moved proximally toward the basis of the patella with knee flexion. The medial contact point also moved proximally on the patella with knee flexion, and in a similar manner the medial contact point on the patella moved distally with flexion from full extension to about 40 degrees of flexion.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of tibial rotations on patellar tracking and patello-femoral contact areas

The object of this study is to determine the effect of tibial rotations on the three-dimensional patello-femoral motions and contact areas during a physiological loading condition, the knee-extension exercise. A commercially available device, the 3-SPACE digitizer and tracker system, was used to collect the motion data, utilizing cadaveric human lower limbs as well as the geometric measurements describing the articular surfaces at the patello-femoral joint. It was found that tibial rotations caused statistically significant differences, at the 0.05 level, in patellar tilt, patellar rotation and patellar medial-lateral shift. It was also found that while the magnitude of the total contact area at a given knee flexion angle did not change significantly with tibial rotations, medial and lateral components of the total contact areas were affected by tibial rotations. Medical femoral contact areas increased with internal tibial rotations at all flexion angles; lateral femoral contact areas increased with external tibial rotations at all flexion angles. This correlates well with the kinematic data since it was found that the patella shifted medially with internal tibial rotations at all flexion angles, and titled more medially near full-extension causing an increase in the medial contact areas and a decrease in the lateral contact areas.

In vivo tracking of the human patella

The purpose of this study was to describe the dynamic, in vivo, three-dimensional tracking pattern of the patella for one normal male subject. Intracortical pins were inserted into the patella, tibia, and femur. The subject performed seated and squatting knee flexion/extension, and maximum voluntary quadriceps contractions. In addition, the vastus medialis oblique was subjected to maximal electrical stimulation. Motions of the markers attached to the intracortical pins were analyzed using an automated video system. Patellar and tibial motions were determined relative to a femoral reference system. While the tibia flexed 50 degrees from full extension (seated condition), the patella flexed 30.3 degrees, tilted laterally 10.3 degrees, and shifted laterally 8.6 mm. In general, these results show qualitative agreement with the data collected from cadaveric specimens [van Kampen and Huiskes, J. orthop. Res. 8, 372-382 (1990)]. The differences present may reflect different passive constraints to patellar motions, and different relative loading of the individual quadriceps components, in our study compared to the cadaveric study. Only small differences were found between patellar motions in the seated and squatting conditions. Differences in patellar displacements produced by (1) maximal electrical stimulation of the vastus medialis oblique, and (2) maximum voluntary quadriceps contraction, at 30 degrees knee flexion and full extension, may reflect the dominant influence of passive constraints, and the vastus lateralis, on normal patellar motions. Further in vivo study of patellar tracking seems warranted to evaluate surgical and conservative interventions for patellofemoral disorders.

The three-dimensional tracking pattern of the human patella

A study was undertaken to provide data on the three-dimensional tracking pattern of the patella, relative to the femur, in human knee-joint specimens. For this purpose, a highly accurate roentgen stereophotogrammetric analysis (RSA) method was applied. The three-dimensional motion patterns of the tibia and the patella were measured and represented in terms of three translations and three rotations each, during knee flexion in neutral (unloaded), endorotated, and exorotated pathways. We found that the patella displays complex but consistent three-dimensional motion patterns during flexion, which include flexion rotation, medial rotation, wavering tilt, and a lateral shift relative to the femur. The motion patterns are very much affected by tibial rotations accompanying flexion.

Elbow joint contact study: comparison of techniques

Elucidation of the contact areas between joint surfaces is important to both prosthetic design and the understanding of degeneration of articular cartilage. Numerous experimental methods are available to study joint contact, including cartilage staining, joint space casting, and pressure sensitive film techniques. This study attempts to compare the ability of each experimental technique to determine elbow joint contact. The silicone casting technique appears to be the best method to study joint contact area. The effects of magnitude and orientation of applied forces on the elbow joint contact patterns are studied.

Biomechanics of the patello-femoral joint. Part II: A study of the effect of simulated femoro-tibial varus deformity on the congruity of the patello-femoral compartment and movement of the patella

This paper investigates the effect of different degrees of varus deformity on the pattern of contact, congruence of the patello-femoral joint, and movement of the patella. Varus deformity of 5, 10, and 15 degrees was imposed on the same cadaveric knee specimen used in the study reported in Part I (Fujikawa, Seedhom, Wright, 1983). This was done by high tibial osteotomy and the introduction of a wooden wedge of the appropriate thickness to effect the deformity. It was found that the contact gradually shifted to the medial side of the knee, and the congruence of the patello-femoral compartment was gradually destroyed as the degree of varus deformity increased to 15 degrees, although the effect of 5 degrees of varus deformity was minimal.

Clinically, contact is shifted to the lateral side of the knee with varus deformity, but this is invariably associated with lateral tibial rotation. This rotation explains the difference between the results of the varus deformity imposed on cadaveric knees and those observed clinically. It is proposed that an adverse change in the congruence of the knee will occur after a sudden correction by high tibial osteotomy, just as that occurring in the normal cadaveric knee after imposing a sudden varus deformity, and therefore it may be useful to consider performing the correction at an early stage of the deformity.

The effect of the varus deformity on the movement of the patella is also described.