Patellofemoral kinematics during knee flexion-extension: an in vitro study

Objective quantification of trochlear dysplasia: Assessment of the difference in morphology between control and chronic patellofemoral instability patients

BACKGROUND

Trochlear dysplasia is an important risk factor associated with patellofemoral instability, but it remains difficult to classify with consistency. Currently there is no objective way to quantify the dysplasia. The purpose of this study is to define and quantify objectively the trochlear morphology by volume and length via computed tomography (CT).

METHODS

One-hundred control patients (136 knees) were retrospectively reviewed and compared to 36 consecutive patients (72 knees) who were treated surgically for recurrent patellar instability and known trochlear dysplasia based on a lateral radiograph. Trochlear morphology was analyzed from a pre-operative CT and data presented as trochlear sulcus volume trochlear length. To determine where along the trochlear length dysplasia is most variable, the trochlear length was radiographically divided into thirds, volume was quantified along that section and compared to control trochlear.

RESULTS

A significant difference in trochlear morphology exists between cohorts, volume (1.98 vs 3.77cm³) and length (31.97 vs 34.66mm) (p<0.05). However, there appears to be a gender based difference in trochlea morphology. The trochlea volumetric analysis between the female cohorts (L: 2.02cm³ vs. 2.94cm³, R: 1.95cm³ vs. 2.93cm³) demonstrated significantly less volume in instability patients (p<0.001). The proximal third of the trochlear contributed the majority of dysplasia difference determined by comparing mean trochlear volume, 95% of the difference. This difference decreased in distal sections, 53% and 32% respectively.

CONCLUSION

This reproducible technique can be used to quantify the trochlea morphology, in order to describe the severity of a dysplasia.

Analysis of the moment arms and kinematics of ostrich (Struthio camelus) double patellar sesamoids

The patella ("kneecap") is a biomechanically important feature of the tendinous insertion of the knee extensor muscles, able to alter the moment arm lengths between its input and output tendons, and so modify the mechanical advantage of the knee extensor muscle. However, patellar gearing function is little-explored outside of humans, and the patella is often simplified or ignored in biomechanical models. Here, we investigate patellar gearing and kinematics in the ostrich-frequently used as an animal analogue to human bipedal locomotion and unusual in its possession of two patellae at the knee joint. We use x-ray reconstruction of moving morphology (XROMM) techniques to capture the kinematics of the patellae in an adult ostrich cadaver, passively manipulated in flexion-extension. Moment arm ratios between the input and output tendons of each patella are calculated from kinematically determined centers of patellofemoral joint rotation. Both patellae are found to decrease the mechanical advantage of the extensor muscle-tendon complex, decreasing the tendon output force for a given muscle input force, but potentially increasing the relative speed of knee extension. Mechanically and kinematically, the proximal patella behaves similarly to the single patella of most other species, whereas the distal patella has properties of both a fixed retroarticular process and a moving sesamoid. It is still not clear why ostriches possess two patellae, but we suggest that the configuration in ostriches benefits their rapid locomotion and provides tendon protection.

Patella morphological alteration after patella instability in growing rabbits

Background

The shape of the patella has been considered to be a predisposing factor resulting in patellar instability, but the effects of abnormal patella position during its development are unclear. The present study evaluated patellar morphological changes after patella instability and evaluated the influence of patellar instability on the patella shape.

Methods

Twenty rabbits that were 2 months old were included in the study. The left knee of each rabbit, defined as the experimental group (N = 20 knees/group), underwent a medial soft tissue restraint release. The right knee of each rabbit, defined as the control group (N = 20 knees/group), did not undergo any surgical procedures. A CT scan was performed on each knee before surgery and 6 months post-surgery to measure the transverse diameter, thickness, Wiberg index, and Wiberg angle for analysis of the patellar morphological changes. Cross-specimen examination was conducted to evaluate the differences between the experimental group and the control group.

Results

The four indices remained the same between the two groups before surgery. However, 6 months after surgery, the mean transverse diameter of the patellae in the experimental group was significantly longer than that in the control group (P < 0.001), while the mean thickness in the experimental group was not significantly greater than that in the control group (P = 0.314), resulting in a flattened shape. The Wiberg indices were not significantly different between the two groups. However, the mean Wiberg angle was higher in the experimental group than in the control group (P < 0.001), which resulted in a flattened articular surface of the patella.

Conclusion

The sectional shape and articular surface of the patella became more flattened after patella instability in this study, which indicates that patella dysplasia could be caused by patella instability. Clinically, early intervention for adolescent patients with patella instability is important.

Relationship between the Patellar Ridge and the Femoral Trochlea in the Patellar Tracking

OBJECTIVE

To investigate the anatomic morphology of the patellar ridge and how it matches the femoral trochlea in patellar tracking.

METHOD

We selected 40 volunteers, 20 males (age, 28 ± 5 years) and 20 female (age, 27 ± 6 years), who were completely asymptomatic with normal knee structures. We measured the right or left legs of volunteers, and the region from the distal femur to the tibial tuberosity was scanned by computed tomography (CT) with flexion at 0°, 30°, 60°, and 90°. CT data was reconstructed using image analysis software (Mimics). Variables such as the angle between the patellar ridge and patellar long axis, the tibial external rotation angle, as well as the best matching position between the patellar ridge and femoral trochlea at different knee flexion angles were measured. A single experienced orthopedic surgeon performed all the measurements, and the surgeon was blinded to the subject identifying information. We analyzed the differences between the various angles using a one-way analysis of variance. The differences between genders were analyzed using the t test.

RESULTS

The intraclass correlation coefficient (ICC) values were greater than 0.81 for all measurements, and the ICC value is almost in perfect agreement. The angle between the patellar ridge and the patellar long axis was 11.13° ± 4.1°. The angle in male participants was 10.87° ± 4.5° and it was 12.09° ± 3.7° in female participants. There were significant differences between each angle (0°, 30°, 60°, and 90°). The angles between the patellar ridge and femoral trochlear groove did not greatly increase with the knee flexion. The tibial internal rotation angle also showed a gradually increase at knee flexion of 0°-60°, and a gradually decrease at 60°-90°. The best-fit point between the patellar ridge and femoral trochlear groove gradually increased along with the knee flexion. There were no significant differences between male and female participants at all angles ( P < 0.05).

CONCLUSION

The anatomic morphology of the patellar ridge allows better matching between the patellar ridge and femoral trochlea during knee flexion, which is an important mechanism for the regulation of patellar tracking.

Fatigue injury risk in anterior cruciate ligament of target side knee during golf swing

A golf-related ACL injury can be linked with excessive golf play or practice because such over-use by repetitive golf swing motions can increase damage accumulation to the ACL bundles. In this study, joint angular rotations, forces, and moments, as well as the forces and strains on the ACL of the target-side knee joint, were investigated for ten professional golfers using the multi-body lower extremity model. The fatigue life of the ACL was also predicted by assuming the estimated ACL force as a cyclic load. The ACL force and strain reached their maximum values within a short time just after ball-impact in the follow-through phase. The smaller knee flexion, higher internal tibial rotation, increase of the joint compressive force and knee abduction moment in the follow-through phase were shown as to lead an increased ACL loading. The number of cycles to fatigue failure (fatigue life) in the ACL might be several thousands. It is suggested that the excessive training or practice of swing motion without enough rest may be one of factors to lead to damage or injury in the ACL by the fatigue failure. The present technology can provide fundamental information to understand and prevent the ACL injury for golf players.

Variations in medial-lateral hamstring force and force ratio influence tibiofemoral kinematics

A change in hamstring strength and activation is typically seen after injuries or invasive surgeries such as anterior cruciate reconstruction or total knee replacement. While many studies have investigated the influence of isometric increases in hamstring load on knee joint kinematics, few have quantified the change in kinematics due to a variation in medial to lateral hamstring force ratio. This study examined the changes in knee joint kinematics on eight cadaveric knees during an open-chain deep knee bend for six different loading configurations: five loaded hamstring configurations that varied the ratio of a total load of 175 N between the semimembranosus and biceps femoris and one with no loads on the hamstring. The anterior-posterior translation of the medial and lateral femoral condyles' lowest points along proximal-distal axis of the tibia, the axial rotation of the tibia, and the quadriceps load were measured at each flexion angle. Unloading the hamstring shifted the medial and lateral lowest points posteriorly and increased tibial internal rotation. The influence of unloading hamstrings on quadriceps load was small in early flexion and increased with knee flexion. The loading configuration with the highest lateral hamstrings force resulted in the most posterior translation of the medial lowest point, most anterior translation of the lateral lowest point, and the highest tibial external rotation of the five loading configurations. As the medial hamstring force ratio increased, the medial lowest point shifted anteriorly, the lateral lowest point shifted posteriorly, and the tibia rotated more internally. The results of this study, demonstrate that variation in medial-lateral hamstrings force and force ratio influence tibiofemoral transverse kinematics and quadriceps loads required to extend the knee. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1707-1715, 2016.

Changes in the orientation of knee functional flexion axis during passive flexion and extension movements in navigated total knee arthroplasty

PURPOSE

Recently, the functional flexion axis has been considered to provide a proper rotational alignment of the femoral component in total knee arthroplasty. Several factors could influence the identification of the functional flexion axis. The purpose of this study was to analyse the estimation of the functional flexion axis by separately focusing on passive flexion and extension movements and specifically assessing its orientation compared to the transepicondylar axis, in both the axial plane and the frontal plane.

METHODS

Anatomical and kinematic acquisitions were performed using a commercial navigation system on 79 patients undergoing total knee arthroplasty with cruciate substituting prosthesis design. The functional flexion axis was estimated from passive movements, between 0° and 120° of flexion and back. Intra-observer agreement and reliability, internal-external rotation and the angle with the surgical transepicondylar axis, in axial and frontal planes, were separately analysed for flexion and extension, in pre- and post-implant conditions.

RESULTS

The analysis of reliability and agreement showed good results. The identification of the functional flexion axis showed statistically significant differences both in relation to flexion and extension and to pre- and post-implant conditions, both in frontal plane and in axial plane. The analysis of internal-external rotation confirmed these differences in kinematics (p < 0.05, between 25° and 35° of flexion).

CONCLUSIONS

The identification of the functional flexion axis changed in relation to passive flexion and extension movements, above all in frontal plane, while it resulted more stable and reliable in axial plane. These findings supported the possible clinical application of the functional flexion axis in the surgical practice by implementing navigated procedures. However, further analyses are required to better understand the factors affecting the identification of the functional flexion axis.

LEVEL OF EVIDENCE

IV.

A new classification system of patellar instability and patellar maltracking

To date there is no classification of patellar dislocations considering clinical and radiological pathologies. As a result many studies mingle the dislocation's underlying pathologies, so that there are no consistent therapy recommendations. It is this article's objective to introduce a patellar dislocation classification based on the current literature to allow for the application of a structured diagnosis and treatment algorithm. The classification is based on instability criteria as well as on clinical and radiological analyses of maltracking and on loss of patellar tracking. There are five types of patellar instability and maltracking. The rare type 1 is a simple (traumatic) patellar dislocation without maltracking and instability with a low risk of redislocation. Type 2 has a high risk of redislocation after primary dislocation; there is no maltracking. Here, a stabilising operation (in most cases MPFL reconstruction) is indicated and sufficient. Type 3 shows both instability and maltracking. Maltracking is mainly caused by: (a) soft tissue contracture, (b) patella alta, (c) pathological tibial tuberosity-trochlea groove distance, (d) valgus deviations and (e) torsional deformities. Stabilisation by means of isolated MPFL reconstruction is not sufficient in these types and additional osseous corrective surgeries are required to achieve physiological patellar tracking and to prevent redislocation. Type 4 features a highly unstable "floating patella" with complete loss of tracking caused by severe trochlear dysplasia. Therapy of choice is trochleoplasty, and if necessary combined with bony and soft-tissue procedures. Type 5 shows a patellar maltracking without instability. Maltracking can only be fixed by means of corrective osteotomy. The classification is referenced to current literature and each type is introduced by a case example. The resulting treatment consequence is also presented.

In vivo kinematics of healthy male knees during squat and golf swing using image-matching techniques

PURPOSE

Participation in specific activities requires complex ranges of knee movements and activity-dependent kinematics. The purpose of this study was to investigate dynamic knee kinematics during squat and golf swing using image-matching techniques.

METHODS

Five healthy males performed squats and golf swings under periodic X-ray images at 10 frames per second. We analyzed the in vivo three-dimensional kinematic parameters of subjects' knees, namely the tibiofemoral flexion angle, anteroposterior (AP) translation, and internal-external rotation, using serial X-ray images and computed tomography-derived, digitally reconstructed radiographs.

RESULTS

During squat from 0° to 140° of flexion, the femur moved about 25 mm posteriorly and rotated 19° externally relative to the tibia. Screw-home movement near extension, bicondylar rollback between 20° and 120° of flexion, and medial pivot motion at further flexion were observed. During golf swing, the leading and trailing knees (the left and right knees respectively in the right-handed golfer) showed approximately five millimeters and four millimeters of AP translation with 18° and 26° of axial rotation, respectively. A central pivot motion from set-up to top of the backswing, lateral pivot motion from top to ball impact, and medial pivot motion from impact to the end of follow-through were observed.

CONCLUSIONS

The medial pivot motion was not always recognized during both activities, but a large range of axial rotation with bilateral condylar AP translations occurs during golf swing. This finding has important implications regarding the amount of acceptable AP translation and axial rotation at low flexion in replaced knees.

LEVEL OF EVIDENCE

IV.

Influence of posterior lateral femoral condyle geometry on patellar dislocation

INTRODUCTION

Patellar instability is a condition with multifactorial aetiology, potentially involving soft tissue characteristics, the bony anatomy of the patella, femur and tibia, and alignment of the lower limb. The shape of the distal femur and patellofemoral joint has been frequently studied using plain orthogonal and skyline radiographs. We investigated a possible contribution of hypoplasia of the lateral femoral condyle in the axial plane to patellar instability.

METHODS

The geometry of the distal femur and alignment of the lower limb on plain radiographs and MRI scans in 25 young adult patients with patellar instability was measured, and compared to a control group of 75 age-matched patients. Measurements were validated by intra-observer and inter-observer reliability studies, and multivariate analysis was used to compare the groups. Cases with and without high Beighton score or knee hyperextension were also compared.

RESULTS

The anatomical posterior condylar angle, anterior condylar angle and sulcus angle on axial MRI scans showed insignificant differences between groups. The Blackburne-Peel ratio, anatomical femoro-tibial angle and femoral joint angle showed significant differences between groups, but not the tibial plateau angle. There was a significant correlation between posterior condylar angle and valgus knee alignment. In cases with joint hypermobility, femoral joint angle was significantly increased and posterior condylar angle was significantly decreased.

CONCLUSIONS

Multiplanar hypoplasia of the lateral femoral condyle resulting in a valgus knee is a risk factor for patellar instability in young patients without osteoarthritis or joint hypermobility. Isolated posterior lateral condyle hypoplasia appears to be unrelated to patellar instability.

Statistical modeling to characterize relationships between knee anatomy and kinematics

The mechanics of the knee are complex and dependent on the shape of the articular surfaces and their relative alignment. Insight into how anatomy relates to kinematics can establish biomechanical norms, support the diagnosis and treatment of various pathologies (e.g., patellar maltracking) and inform implant design. Prior studies have used correlations to identify anatomical measures related to specific motions. The objective of this study was to describe relationships between knee anatomy and tibiofemoral (TF) and patellofemoral (PF) kinematics using a statistical shape and function modeling approach. A principal component (PC) analysis was performed on a 20-specimen dataset consisting of shape of the bone and cartilage for the femur, tibia and patella derived from imaging and six-degree-of-freedom TF and PF kinematics from cadaveric testing during a simulated squat. The PC modes characterized links between anatomy and kinematics; the first mode captured scaling and shape changes in the condylar radii and their influence on TF anterior-posterior translation, internal-external rotation, and the location of the femoral lowest point. Subsequent modes described relations in patella shape and alta/baja alignment impacting PF kinematics. The complex interactions described with the data-driven statistical approach provide insight into knee mechanics that is useful clinically and in implant design.

Sequential 3D analysis of patellofemoral kinematics from biplanar x-rays: In vitro validation protocol

BACKGROUND

Developing criteria for assessing patellofemoral kinematics is crucial to understand, evaluate, and monitor patellofemoral function. The objective of this study was to assess a sequential 3D analysis method based on biplanar radiographs, using an in vitro protocol.

HYPOTHESIS

Biplanar radiography combined with novel 3D reconstruction methods provides a reliable evaluation of patellofemoral function, without previous imaging.

MATERIAL AND METHODS

Eight cadaver specimens were studied during knee flexion cycles from 0° to 60° induced by an in vitro simulator. The protocol was validated by investigating sequential and continuous motion using an optoelectronic system, evaluating measurement accuracy and reproducibility using metallic beads embedded in the patella, and comparing the 3D patellar geometry to computed tomography (CT) images.

RESULTS

The differences in position between the sequential and continuous kinematic analyses were less than 1mm and 1°. The protocol proved reliable for tracking several components of knee movements, including patellar translations, flexion, and tilt. In this analysis, uncertainty was less than 2 mm for translations and less than 3° for rotations, except rotation in the coronal plane. For patellar tilt, uncertainty was 5°. Mean difference in geometry was 0.49 mm.

DISCUSSION

Sequential analysis results are consistent with continuous kinematics. This analysis method provides patellar position parameters without requiring previous CT or magnetic resonance imaging. A clinical study may deserve consideration to identify patellofemoral kinematic profiles and position criteria in vivo.

LEVEL OF EVIDENCE

IV, experimental study.

Simulation of varying femoral attachment sites of medial patellofemoral ligament using a musculoskeletal multi-body model

The medial patellofemoral ligament (MPFL) is a key structure in the treatment of habitual and traumatic patellofemoral instability. However, there exists little knowledge about its behaviour during deep knee flexion after femoral refixation. Since improper femoral attachment sites may lead to unnatural length change patterns in the ligament and consequently to osteoarthritis due to pathological femoro-patellar contact pressure, the understanding of the patella kinematics and MPFL behaviour is crucial.

The purpose of this numerical study was to compute the six-degree-of-freedom motion pattern of the human patella during deep knee flexion for systematic analysis of varying landmarks for the femoral attachment in medial patellofemoral ligament reconstruction surgery by means of multibody simulation.

Therefore, based on a previously presented musculoskeletal model [1] the dynamic pathways of the patella were computed. Then, the spatial motion was approximated by rheonomic polynomials and exploited for systematic evaluation of the MPFL length change patterns. Hence, 16 femoral attachment points at a radius of 5 mm and 10 mm around the radiographic centre point [2] were defined and the absolute length changes were recorded during deep knee flexion to 120 degree.

This approach allows for a systematic evaluation of numerous MPFL attachment sites while exploiting the physiological patella kinematics. The patella kinematics including shift, flexion, tilt and rotation as well as the MPFL length change patterns were consistent to in vitro and in vivo data in the literature [3–7] and therefore indicate validity of the numerical approach. The parameter study on the femoral attachment site should enable to determine the most isometric point and non-isometric variations corresponding to patellofemoral instability, arthritis or high graft load.

Does patellofemoral geometry in TKA affect patellar position in mid-flexion?

PURPOSE

This study aimed to compare the position of the patella at 90° of flexion before and after implantation of two TKA models with identical tibiofemoral geometry but different trochlear and patellar designs. The hypothesis was that the design with the deeper 'anatomic' trochlea could produce more natural patellar positions.

METHODS

Intra-operative navigation data were collected from 22 consecutive cases that received two TKA designs (9 HLS Noetos(®) and 13 HLS KneeTec(®)). Both implants were cemented postero-stabilised TKAs with mobile tibial inserts and patellar resurfacing. Operations were guided by a non-image-based system that recorded relative femoral, tibial and patellar positions pre- and post-operatively.

RESULTS

The two groups exhibited little difference in femoral internal-external rotation and anterior-posterior translation during knee flexion. The two groups exhibited significant differences in patellar position at 90° of flexion. Post-operatively, the patella was similarly shifted medially relative to the femur (Noetos 6.9 mm, KneeTec 6.0 mm, n.s.). Patellar flexion was equivalent in native knees (Noetos 18.3°, KneeTec 20.5°, n.s.), but in implanted knees, it was considerably different (Noetos 6.3°, KneeTec 23.5°, p = 0.031).

CONCLUSIONS

The present study compared intra-operative navigation data from two patient series that received TKA implants with identical tibiofemoral articular geometry but different patellofemoral designs. The results confirm that tibiofemoral kinematics are unchanged, but that patellar positions at 90° of flexion offer greater mechanical advantage to the quadriceps using the KneeTec than using the Noetos. The findings raise awareness of influence of patellofemoral geometry on mid-flexion kinematics and help surgeons select the most suitable implant for patients with weak quadriceps muscles or with history of patellar instability.

LEVEL OF EVIDENCE

Comparative study, Level III.

The effects of squatting with visual feedback on the muscle activation of the vastus medialis oblique and the vastus lateralis in young adults with an increased quadriceps angle

[Purpose] The purpose of this study was to identify the effects of performing squat exercises with visual feedback on the activation of the vastus medialis oblique (VMO) and vastus lateralis (VL) muscles in young adults with an increased quadriceps angle (Q-angle). [Subjects] This study used a motion analysis program (Dartfish, Switzerland) to select 20 young adults with an increased Q-angle, who were then divided into a squat group that received visual feedback (VSG, n=10) and a squat group that received no visual feedback (SG, n=10). [Methods] The intensity of exercises was increased every two weeks over a six-week exercise period in both groups. A visual marker was attached to the patella of the subjects in the VSG, and they then performed squat exercises with a maximum of 90° of knee flexion within a route marked on a mirror. The SG performed squat exercises with a maximum 90° of knee flexion without attaching a visual feedback device. [Results] Analysis of the muscle activation due to 90° squat exercises indicated that both groups had statistically significant increases in activation of the VL. The VSG exhibited statistically significant increases in activation of the VMO. [Conclusion] This study confirmed that squat exercises with visual feedback are effective in activation of the VMO and VL muscles. The findings are meaningful in terms of preventing the occurrence of patellofemoral pain.

Sagittal plane evaluation of patellofemoral movement in patellofemoral pain patients with no evidence of maltracking

PURPOSE

The cause of abnormal patellar kinematics in patients with patellofemoral pain remains unclear. Many patients who develop patellofemoral pain symptoms do not exhibit evidence of maltracking. In these patients, sagittal plane evaluation of patellofemoral movement should be performed.

METHODS

Knee radiographs were obtained for forty healthy volunteers and thirty patients at 0°, 30°, 60°, 90° and 120° of flexion in a standing weight-bearing position. The degree of active patellar movement was measured by a newly developed technique called "patellar motion angle". Three independent examiners sequentially performed all of the measurements under identical conditions.

RESULTS

A significant decrease in the patellar motion angle was found during deep knee flexion from 90° to 120° in the patient group compared to the volunteer group (mean 18.5° ± 5.8° and 23.6° ± 6.2°, respectively) (P = 0.001). From 0° to 90° of knee flexion, no significant differences in the patellar motion angle were found between the two groups.

CONCLUSION

Sagittal plane patellofemoral joint kinematics is an area of interest in the study of the mechanical factors associated with patellofemoral pain. This study demonstrated a decrease in patellar movement during deep knee bending activity in patients with patellofemoral pain.

LEVEL OF EVIDENCE

Therapeutic study, Level II.

Effects of patellofemoral overstuffing on knee flexion and patellar kinematics following total knee arthroplasty: a cadaveric study

PURPOSE

The purpose of this study was to test the hypothesis that overstuffing the patellofemoral joint during total knee arthroplasty (TKA) would decrease passive knee flexion and alter patellar kinematics during knee flexion.

METHODS

Ten cadaveric knees were implanted with cruciate-retaining TKAs, and the patellofemoral joint was overstuffed in 2-mm increments with custom-augmented patellar prostheses (+2 mm through +8 mm). Changes to knee flexion, patellar shift, tilt and rotation were measured with an imageless optical-tracking computer navigation system.

RESULTS

Knee flexion decreased an average 1.2° with each additional 2 mm of patellar thickness. Compared with control TKA (+0 mm), no significant decrease in knee flexion was detected until the patellofemoral joint was overstuffed with the +8-mm patellar prosthesis. Kinematic tracking data showed significantly greater lateral shift of patella with the +6- and +8-mm prostheses and significantly greater lateral tilt with the +8-mm prosthesis. Overstuffing had no appreciable effect on patellar rotation.

CONCLUSIONS

Passive knee flexion after TKA is significantly reduced when overstuffing the patellofemoral joint by +8 mm, and patellofemoral kinematics are altered when overstuffing the joint by +6 mm. These results demonstrate the relatively modest effects of patellofemoral overstuffing on knee flexion and patellar tracking kinematics after TKA.

The effect of coordinate system variation on in vivo patellofemoral kinematic measures

BACKGROUND

The use of different coordinate system definitions for the patella leads to difficulties in comparing kinematic results between studies. The purpose of this work was to establish the effect of using a range of coordinate system definitions to quantify patellar kinematics. Additionally, intra- and inter-investigator repeatabilities of the digitization of anatomic landmarks on the patella were determined.

METHODS

Four different patellar coordinate system definitions were applied using digitisations in two and three dimensions and a single femoral coordinate system was used for comparison. Intra-investigator variability was established by having one investigator digitize the patellar landmarks of three subjects on five separate occasions. Inter-investigator variability was quantified by having five participants digitize the same landmarks on the same three subjects. Patellofemoral kinematics were quantified for ten subjects, at six angles of tibiofemoral flexion, using MRI.

RESULTS

As a result of changes in the patellar coordinate system, differences of up to 11.5° in flexion, 5.0° in spin, and 27.3° in tilt were observed in the resultant rotations for the same motion, illustrating the importance of standardizing the coordinate system definition.

CONCLUSIONS

To minimize errors due to variability while still maintaining physiologically sensible kinematic angles, a coordinate system based upon an intermediate flexion axis between the most medial and lateral points on the patella, and a superiorly-directed long axis located between the most proximal and distal points on the patella, with an origin at the centre of the most proximal, distal, medial, and lateral points on the patella is recommended.

CLINICAL RELEVANCE

The recommended anatomic coordinate frame may be employed in the calculation of dynamic in vivo patellar kinematics when used in combination with any method that reliably quantifies patellar motion.

Mapping of the femoral trochlea in a newborn population: an ultrasonographic study

BACKGROUND

The anatomy of the femoral trochlea is of vital importance to the stability of the patellofemoral joint. Knowing the characteristics of the femoral trochlea in newborns might prove useful when considering the predisposing factors to patellar instability.

PURPOSE

To define the normal anatomy and the natural variances of the femoral trochlea in a newborn population as well as evaluation of ultrasonography as a method of imaging.

MATERIAL AND METHODS

The femoral trochlea of both knees of 174 newborns (82 girls and 92 boys) was examined using ultrasonography within 3 days after birth. For evaluation of the repeatability of the method, a separate population of 40 newborns was examined by two examiners.

RESULTS

The sulcus angle (SA) and Trochlear Index (TI) proved to be the most reliable and reproducible parameters. The overall mean SA was 148° (SD 5.6). An angle of more than 159° was defined as dysplastic, and 17 of the knees were categorized in this group. The overall mean TI was 2.21 (SD 0.05). A value of less than 2.11 was defined as dysplastic and 11 of the newborns fell into this category.

CONCLUSION

As a method of visualizing the newborn femoral trochlea and the position of the patella, ultrasonography is a reliable tool and might be of vital importance. In a further perspective, knowledge of the anatomy of a normal versus a dysplastic newborn trochlea renders it possible to study the predisposing factors to patellar instability and methods of treatment. Our results indicate that dysplasia of the femoral trochlea may be congenital.

[Operative therapy of isolated patellofemoral arthritis. Biomechanics as a guide]

BACKGROUND

The treatment of patellofemoral arthritis places high demands on orthopedists. The exact analysis of the underlying pathobiomechanical relationships is the basis for every therapy decision.

METHODS

Soft tissue procedures, such as medial patellofemoral ligament (MPFL) reconstruction for stabilization and bone interventions for alignment optimization (e.g. tuberosity transfer and corrective osteotomy) can play a role in treatment. In cases of advanced patellofemoral arthrosis these interventions can be used as well as in combination with partial joint replacement. For the choice of implant the use of anatomical prosthesis types is recommended because with these components the number of additional procedures can be reduced.

CONCLUSION

The success of patellofemoral prosthetics depends mainly on the recognition of biomechanical deviations. If these can be corrected the risk of implant failure can be reduced.

Patellar instability

Patellar instability is a common injury that can result in significant limitations of activity and long-term arthritis. There is a high risk of recurrence in patients and operative management is often indicated. Advances in the understanding of patellofemoral anatomy, such as knowledge about the medial patellofemoral ligament, tibial tubercle-trochlear groove distance, and trochlear dysplasia may allow improved surgical management of patellar instability. However, techniques such as MPFL reconstruction are technically demanding and may result in significant complication. The role of trochleoplasty remains unclear.

Effect of medial-lateral malpositioning of the femoral component in total knee arthroplasty on anterior knee pain at greater than 8 years of follow-up

BACKGROUND

The trochlea is often medialized after total knee arthroplasty (TKA) resulting in abnormal patellar tracking, which may lead to anterior knee pain. However, due to the difference in shape of the natural trochlea and the patellar groove of the femoral component, a medialization of the femoral component of 5 mm results in an equal patellar position at 0-30° of flexion. We tested the hypothesis that more medialization of the trochlea results in a higher VAS pain score and lower Kujala anterior knee pain score at midterm follow-up.

METHODS

During surgery a special instrument was used to measure the mediolateral position of the natural trochlea and the prosthetic groove in 61 patients between 2004 and 2005. Patient reported outcome measures were used to investigate the clinical results (NRS-pain, NRS-satisfaction, KOOS-PS and Kujala knee score).

RESULTS

In total 40 patients were included. The mean follow-up was 8.8 years. A medialization of ≥5 mm resulted in a significantly lower NRS-pain (0.2 vs. 1.4; p=0.004) and higher NRS-satisfaction (9.6 vs. 8.2; p=0.045). Overall clinical results were good; KOOS-PS was 33.9 and Kujala knee score was 72.1.

CONCLUSIONS

The present study showed that a more medial position may result in a better postoperative outcome, which can probably be explained by the non-physiological lateral orientation of the trochlear groove in TKA designs.

LEVEL OF EVIDENCE

Level III.

A validated cadaveric model of trochlear dysplasia

PURPOSE

Despite the high prevalence of trochlear dysplasia among patients with patellar instability, it is not well studied and is infrequently addressed surgically. The lack of a validated cadaveric model of trochlear dysplasia may be a contributing factor. The goal of this study was to develop a simple, reproducible, and realistic cadaveric model of trochlear dysplasia by surgically modifying cadaveric femora with normal anatomy and then to validate this model through the use of mechanical and fluoroscopic measurements.

METHODS

The floor of the trochlear groove was surgically elevated using an inflatable bone tamp in eight cadaveric femora. The trochlear depth (TD) was measured with a custom-designed measuring device, and radiographic markers of dysplasia (sulcus angle, crossing sign, and prominence) were assessed before and after surgical modification.

RESULTS

The average TD was 3.6±1.4, 4.6±1.1, and 5.1±1.0 mm prior to reverse trochleoplasty (RT) and 1.0±1.8, 2.3±1.3, and 3.3±2.5 mm following RT at 0°, 20°, and 40° of flexion, respectively. These direct measurements of TD were confirmed with fluoroscopy. The sulcus angle averaged 141° prior to RT and 157° after RT. The average prominence across all specimens was 3.3±0.7 mm before RT, and 5.5±1.5 mm after RT. Finally, the crossing sign was found to be absent in all knees prior to RT and present in 7 of the 8 after RT.

CONCLUSIONS

The results of this study show that elevation of the trochlear floor with an inflatable bone tamp can reproducibly create a simulated dysplastic trochlea. This model may be useful in biomechanical studies of treatments for patellofemoral instability.

The effect of ground tilt on the lower extremity muscle activity of stroke patients performing squat exercises

[Purpose] The purpose of this study was to determine the effect of ground tilt on the lower extremity muscle activity of stroke patients performing squat exercises. [Subjects] Fifteen hemiparetic patients volunteered to participate in this study. [Methods] The subjects performed squat exercises at three different ground tilt angles: 15° plantar flexion, a neutral position, and 15° dorsiflexion. A surface electromyogram (sEMG) was used to record the electromyographic activities of the leg extensor muscle in the vastus lateralis (VL), vastus medialis (VM), gastrocnemius lateralis (GL), and gastrocnemius medialis (GM). The sEMG activity was analyzed using a one-way repeated measures ANOVA and a post hoc Bonferroni correction. [Results] The results of this study are summarized as follows. Significant differences were noted for the VL and the GL when the angle of the ankle joint was between the 15° plantar flexion and neutral positions during squat exercises involving the VL and when the angle of the ankle joint was between the neutral position and 15° dorsiflexion during squat exercises involving the VM. [Conclusion] In this study, sEMG showed that the VL and GL changed significantly during squat exercises according to the ground tilt angle of hemiparetic patients. Therefore, squat exercises with different ground tilt angles can be used to improve VL and GL strength.

Tibio-femoral and patello-femoral joint kinematics during navigated total knee arthroplasty with patellar resurfacing

PURPOSE

In total knee arthroplasty, surgical navigation systems provide tibio-femoral joint (TFJ) tracking for relevant bone preparation, disregarding the patello-femoral joint (PFJ). Therefore, the important intra-operative assessment of the effect of component positioning, including the patella, on the kinematics of these two joints is not available. The objective of this study is to explore in vivo whether accurate tracking of the patella can result in a more physiological TFJ and PFJ kinematics during surgery.

METHODS

Ten patients underwent navigated knee replacement with patellar resurfacing. A secondary system was used to track patellar motion and PFJ kinematics using a special tracker. Patellar resection plane position and orientation were recorded using an instrumented probe. During all surgical steps, PFJ kinematics was measured in addition to TFJ kinematics.

RESULTS

Abnormal PFJ motion patterns were observed pre-operatively at the impaired knee. Patellar resection plane orientation on sagittal and transverse planes of 3.9° ± 9.0° and 0.4° ± 4.1° was found. A good restoration of both TFJ and PFJ kinematics was observed in all replaced knees after resurfacing, in particular the rotations in the three anatomical planes and medio-lateral patellar translation.

CONCLUSIONS

Patella tracking results in nearly physiological TFJ and PFJ kinematics in navigated knee arthroplasty with resurfacing. The intra-operative availability also of PFJ kinematics can support the positioning not only of the patellar component in case of resurfacing, but also of femoral and tibial components.

Patellar instability

Patella instability can cause significant pain and functional limitations. Several factors can predispose to patella instability, such as ligamentous laxity, increased anterior TT-TG distance, patella alta, and trochlear dysplasia. Acquired factors include MPFL injury or abnormal quadriceps function. In many cases, first-time dislocation can successfully be managed with physical therapy and other nonoperative management; however, more than one dislocation significantly increases the chance of recurrence. Surgical management can improve stability, but should be tailored to the injuries and anatomic risk factors for recurrent dislocation. Isolated lateral release is not supported by current literature and increases the risk of iatrogenic medial instability. Medial repair is usually reserved for patients with largely normal anatomy. MPFL reconstruction can successfully stabilize patients with medial soft tissue injury but is a technically demanding procedure with a high complication rate and risks of pain and arthrosis. Tibial tubercle osteotomy can address bony malalignment and also unload certain articular cartilage lesions while improving stability. Trochleoplasty may be indicated in individuals with a severely dysplastic trochlea that cannot otherwise be stabilized. A combination of procedures may be necessary to fully address the multiple factors involved in causing pain, loss of function, and risk of recurrence in patients with patellar instability.

Trochlear dysplasia and the role of trochleoplasty

The diagnosis and treatment of chronic patellar instability caused by trochlear dysplasia can be challenging. A dysplastic trochlea leads to biomechanical and kinematic changes that often require surgical correction when symptomatic. In the past, trochlear dysplasia was classified using the 4-part Dejour classification system. More recently, new classification systems have been proposed. Future studies are needed to investigate long-term outcomes after trochleoplasty.

No difference in patellar tracking between symmetrical and asymmetrical femoral component designs in TKA

PURPOSE

Poor knee extension function after total knee arthroplasty (TKA) is associated with factors including articular geometry and alignment. Femoral trochlear geometry has evolved from symmetrical to become more prominent proximal-laterally, with the groove aligned proximal-lateral to distal-medial. This study in vitro tested the hypothesis that a modern asymmetrical prosthesis would restore patellar tracking and stability to more natural behaviour than an older symmetrical prosthesis.

METHODS

Six knees had their patellar tracking measured optically during active knee extension. Medial-lateral force versus displacement stability was measured at fixed angles of knee flexion. The measurements were repeated after inserting each of the symmetrical and asymmetrical TKAs.

RESULTS

Significant differences of patellar lateral displacement stability, compared to normal, were not found at any angle of knee flexion. The patella tracked medial-laterally within 2.5 mm of the natural path with both TKAs. However, for both TKAs near knee extension, the patella was tilted laterally by approximately 6° and was also flexed approximately 8° more than in the natural knee.

CONCLUSION

The hypothesis was not supported: The more anatomical component design did not provide more anatomical patellar kinematics and stability.

Sectioning the medial patellofemoral ligament alters patellofemoral joint kinematics and contact mechanics

Medial patellofemoral ligament (MPFL) disruption may alter patellofemoral joint (PFJ) kinematics and contact mechanics, potentially causing pain and joint degeneration. In this controlled laboratory study, we investigated the hypothesis that MPFL transection would change patellar tracking and PFJ contact pressures and increase the distance between the attachment points of the MPFL. Eight fresh frozen dissected cadaveric knees were mounted in a rig with the quadriceps and ITB loaded to 205 N. An optical tracking system measured joint kinematics, and pressure sensitive film between the patella and trochlea measured PFJ contact pressures. Length patterns of the distance between the femoral and patellar attachments of the MPFL were measured using a suture led to a linear displacement transducer. Measurements were repeated with the MPFL intact and following MPFL transection. A significant increase in the distance between the patellar and femoral MPFL attachment points was noted following transection (p < 0.05). MPFL transection resulted in significantly increased lateral translation and lateral tilt of the patella in early flexion (p < 0.05). Peak and mean medial PFJ contact pressures were significantly reduced and peak lateral contact pressures significantly elevated in early knee flexion following MPFL transection (p < 0.05). MPFL transection resulted in significant alterations to PFJ tracking and contact pressures, which may affect articular cartilage health.

The influence of medial patellofemoral ligament on patellofemoral joint kinematics and patellar stability

PURPOSE

Retinacular restraints have a critical role in patellar tracking, limiting the movement of the patella in the trochlear groove. The medial patellofemoral ligament (MPFL) is probably the main stabilizer against lateral displacement; few studies are focused on MPFL role on patellofemoral kinematics and patellar stability. The main goal of this in vitro study was to analyse the influence of the MPFL on the kinematics of the patellofemoral joint and patellar stability.

METHODS

Using a non-image-based navigation system, kinematics and anatomical data of six fresh-frozen specimens were collected. A passive flexion-extension from 0° to 90° and static acquisitions at 0°, 30°, 60° and 90°, with and without 25 N of lateral load, were performed with intact and resected MPFL with a 60 N axial force applied to the isolated quadriceps tendon. Patellar tilt and shift were analysed.

RESULTS

The MPFL intact state showed a shift in medial direction during the first degrees of knee flexion-that disappeared in MPFL resected condition-followed by a lateral shift, similar to that of MPFL resected condition. Tilt analysis showed that patella rotated laterally until 85° of knee flexion for intact MPFL condition and until 70° for resected MPFL condition and after rotated medially. Static tests showed that patellar stability was significantly affected by MPFL resected condition in particular at 30° and 60°.

CONCLUSIONS

The MPFL has an aponeurotic nature. It works as a restraint during motion, with an active role under high stress on lateral side, but with a small contribution during neutral knee flexion. Its biomechanical behaviour under loading conditions should be kept into account when performing surgical reconstruction of this ligamentous structure.

Physiological sagittal plane patellar kinematics during dynamic deep knee flexion

PURPOSE

Lateral radiographic views can be easily taken and have reveal considerable information about the patella. The purpose of this study was to obtain sagittal plane patellar kinematics data through the entire range of knee flexion under weight-bearing conditions.

METHODS

Patellar flexion angles relative to the femur and tibia and anterior-posterior and proximal-distal translations of the patella relative to the femur and tibia were measured from 0 to 165° knee flexion in nine healthy knees using dynamic radiographic images.

RESULTS

The patella flexed relative to the femur and tibia by two thirds times and one third times the knee flexion angle, respectively. The patella translated in an arc relative to the femur and tibia as the knee flexed. In early flexion, the superior and centroid points translated anteriorly and then the patella translated posteriorly relative to the femur. All three points of the patella translated posteriorly relative to the tibia during a full range of flexion. An average of four and three millimetres proximal patellar translation relative to the tibia was demonstrated from 0 to 20° and 140 to 160° knee flexion, respectively.

CONCLUSIONS

Physiological sagittal plane patellar kinematics, including patellar flexion angles and translations relative to the femur and tibia, showed generally similar patterns for each subject. Measurements of dynamic radiographic images under weight-bearing activities may enhance the opportunity to identify patellar pathological conditions.

Non-invasive measurement of the patellofemoral movements during knee extension-flexion: a validation study

BACKGROUND

This study compared the difference between patellofemoral kinematics derived simultaneously from patellar bone pin and skin sensors during full range of tibiofemoral joint movement.

METHODS

Movements at the tibiofemoral and patellofemoral joints during passive full extension-flexion of the knees in three un-embalmed human cadavers were studied with four electromagnetic tracking sensors at a sampling rate of 30 Hz. A total of four sensors were attached on distal femur, proximal tibia, the surface of a tailor-made patella mold and at the tip of a plastic bone pin planted in the patellar body through a window on the mold. Paired-sample Wilcoxon signed rank test was used to compare peak motions computed from different sensors. The correlation of the movement-time curves derived from different sensors was tested by coefficient of multiple correlations (CMC) in different sections of tibiofemoral joint range.

RESULTS

Peak motions detected by skin sensor for patellar lateral tilt (p=0.045), distal translation (p=0.021), lateral shift (p=0.032), and anterior-posterior shift of patella (p=0.03 and 0.01 respectively) were higher than that by the bone pin sensor. The overall CMC values for anterior-posterior translation and medial-lateral shift were lower than movements in other planes of movement. The CMC values in initial range were higher than that in the middle and end range in all planes of movement.

CONCLUSIONS

Patellofemoral kinematics derived from skin sensors may not be representative of the underlying patellar motion. Kinematics reported from the skin sensors should be carefully interpreted.

In vivo patellar tracking and patellofemoral cartilage contacts during dynamic stair ascending

The knowledge of normal patellar tracking is essential for understanding the knee joint function and for diagnosis of patellar instabilities. This paper investigated the patellar tracking and patellofemoral joint contact locations during a stair ascending activity using a validated dual-fluoroscopic imaging system. The results showed that the patellar flexion angle decreased from 41.9° to 7.5° with knee extension during stair ascending. During first 80% of the activity, the patella shifted medially about 3.9 mm and then slightly shifted laterally during the last 20% of the ascending activity. Anterior translation of 13 mm of the patella was measured at the early 80% of the activity and the patella slightly moved posteriorly by about 2mm at the last 20% of the activity. The path of cartilage contact points was slightly lateral on the cartilage surfaces of patella and femur. On the patellar cartilage surface, the cartilage contact locations were about 2mm laterally from heel strike to 60% of the stair ascending activity and moved laterally and reached 5.3mm at full extension. However, the cartilage contact locations were relatively constant on the femoral cartilage surface (∼5mm lateral). The patellar tracking pattern was consistent with the patellofemoral cartilage contact location pattern. These data could provide baseline knowledge for understanding of normal physiology of the patellofemoral joint and can be used as a reference for clinical evaluation of patellofemoral disorders.

PATELLA TRACKING WITH PERIPATELLAR SOFT TISSUE STABILIZERS AS A FUNCTION OF DYNAMIC SUBJECT-SPECIFIC KNEE FLEXION

Musculoskeletal modeling has found wide application in joint biomechanics investigations. This technique has been improved by incorporating subject-specific skeletal elements and passive patellofemoral stabilizers in a dynamic analysis. After trochlear engagement, the volunteers' patellae displaced laterally, whereas tilt was subject specific. Comparison of the tilt and mediolateral position values to in vivo MRI values at 30° knee flexion showed a mean accuracy of 84.4% and 96.9%, respectively. Medial patellofemoral ligament tension decreased with knee flexion, while the patellar tendon–quadriceps tendon ratio ranged from 0.4 to 1.2. The patellofemoral contact load–quadriceps tendon load ratio ranged from 0.7 to 1.3, whereas the mediolateral load component–resultant load ratio ranged from 0 to 0.4. Three validated subject-specific musculoskeletal models facilitated the analysis of patellofemoral biomechanics: Subject-specific patella tracking and passive stabilizer response was analyzed as a function of dynamic knee flexion.

Familial association of femoral trochlear dysplasia with recurrent bilateral patellar dislocation

Femoral trochlear dysplasia is an anatomic deformity that predisposes patients to patellar instability, including patellar subluxation and dislocation, and can lead to severe patellofemoral joint degeneration if left untreated. Femoral trochlear dysplasia leading to recurrent bilateral patellar dislocation has rarely been reported as having a familial association. Orthopedic surgeons who encounter patients presenting with chronic patellar instability with no underlying disease or syndrome should be aware of the presence of femoral trochlear dysplasia leading to recurrent bilateral patellar dislocation. Although femoral trochlear dysplasia remains uncommon, the presence of bilateral recurrent patellar dislocation in multiple members of the same family is highly suggestive of genetic inheritance.This article describes 3 patients from 1 family who presented with femoral trochlear dysplasia leading to recurrent bilateral patellar dislocation. To our knowledge, this is the second article to describe a familial form of femoral trochlear dysplasia associated with recurrent bilateral patellar dislocation and is the first article in English. A lower threshold for screening and early intervention for symptomatic family members may be indicated to prevent the long-term effects of chronic patellar subluxation, dislocation, and patellofemoral arthritis.

MRI of weight bearing and movement

Conventional, static magnetic resonance imaging (MRI) is able to provide a vast amount of information regarding the anatomy and pathology of the musculoskeletal system. However, patients, especially those whose pain is position dependent or elucidated by movement, may benefit from more advanced imaging techniques that allow for the acquisition of functional information. This manuscript reviews a variety of advancements in MRI techniques that are used to image the musculoskeletal system dynamically, while in motion or under load. The methodologies, advantages and drawbacks of stress MRI, cine-phase contrast MRI and real-time MRI are discussed as each has helped to advance the field by providing a scientific basis for understanding normal and pathological musculoskeletal anatomy and function. Advancements in dynamic MR imaging will certainly lead to improvements in the understanding, prevention, diagnosis and treatment of musculoskeletal disorders. It is difficult to anticipate that dynamic MRI will replace conventional MRI, however, dynamic MRI may provide additional valuable information to findings of conventional MRI.

Patellar chondral defects: a review of a challenging entity

PURPOSE

The aim of this study was to perform a review of the management of patellar cartilage defects, identify prognostic factors for better clinical outcomes, and propose a treatment algorithm of this challenging entity.

METHODS

We conducted a review of multiple databases, evaluating the clinical outcomes after patellar cartilage lesion treatment. Because of the heterogeneity of data, a meta-analysis could not be performed.

RESULTS

Twelve studies were identified for inclusion. Based on the clinical outcomes of these studies, a treatment algorithm was proposed. The clinical outcomes after patellar cartilage defects repair depend on the location and size of the articular defect, the age of the patient, the successful reconstruction of the patellar ridge, the repair of extensor mechanism malalignment, and the coexistence of chondromalacia.

CONCLUSION

The optimal treatment for cartilaginous defects of the patella is still elusive. More prospective studies are needed, in order to identify which techniques are cost-effective especially on a long-term basis.

Value of the tibial tuberosity-trochlear groove distance in patellar instability in the young athlete

BACKGROUND

A lateralized tibial tubercle may be a relevant anatomic factor in patients with patellar instability and can be used as an indication for a distal realignment procedure. However, parameter values for the tibial tuberosity-trochlear groove (TT-TG) distance in the young patient have not been defined. It also remains to be determined how this parameter contributes to patellar instability in the growing knee joint.

PURPOSE

The purpose of this study was to evaluate the value of the TT-TG distance in patellar instability in the young athlete.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Knee magnetic resonance images were collected from 109 patients with lateral patellar instability and from 136 control subjects. Student t test and multiple logistic regression analysis were used to compare the absolute and relative values of the TT-TG distance between patients and controls. The relative value was defined as the ratio between the TT-TG distance and the total width of the distal femur.

RESULTS

The TT-TG distance (absolute and relative to femur width) differed significantly between patients with patellar dislocation and the control group (both P < .01). The TT-TG distances were on average 4 mm larger in patients with patellar dislocation; TT-TG distance divided by femur width was on average 5% larger in patients with patellar dislocation. Multiple logistic regression analysis confirmed the TT-TG distance as a significant risk factor for patellar dislocation (P = .04), but showed no significant interaction with patient age or femur width (P = .95 and P = .15, respectively).

CONCLUSION

A lateralized tibial tubercle is a relevant anatomic factor in the young athlete and in the adult patient with lateral patellar instability. Its parameter values and its influence on patellar dislocation are independent of patient age and should therefore be evaluated as in adults.

The effect of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral contact pressure during simulated partial weight-bearing knee flexion

PURPOSE

The purpose of this in vitro study was to investigate the influence of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral pressure.

METHODS

A dynamic muscle-loaded knee squat was simulated on eight knee specimens with an upright knee simulator while measuring tibiofemoral joint kinematics and patellofemoral pressure distribution. The quadriceps muscle was attached to three actuators simulating the three main extensor muscles, and five different quadriceps loading patterns were tested.

RESULTS

Tibial axial and varus-valgus-rotation are affected most while changing quadriceps loading patterns from lateral to medial. Higher internal tibial rotation is associated with higher medial muscle load compared to the symmetrical loading condition. Contact force, contact area and maximum peak pressure rise with increasing flexion angles. Accentuating the vastus lateralis muscle induces a significant reduction in patellofemoral contact force and a 30% diminished contact area at 90° of flexion.

CONCLUSION

Strengthening the vastus medialis muscle leads to increased internal tibial rotation, thus optimizing patella tracking by lowering the Q-angle. In contrast, weakness of the vastus medialis muscle causes decreased tibial internal rotation and is associated with lower patellofemoral contact pressure and contact area. Vastus medialis exercise is advisable to improve patella tracking but may not be recommended in patients with disorders due to increased patellofemoral contact pressure.

Computationally efficient finite element evaluation of natural patellofemoral mechanics

Finite element methods have been applied to evaluate in vivo joint behavior, new devices, and surgical techniques but have typically been applied to a small or single subject cohort. Anatomic variability necessitates the use of many subject-specific models or probabilistic methods in order to adequately evaluate a device or procedure for a population. However, a fully deformable finite element model can be computationally expensive, prohibiting large multisubject or probabilistic analyses. The aim of this study was to develop a group of subject-specific models of the patellofemoral joint and evaluate trade-offs in analysis time and accuracy with fully deformable and rigid body articular cartilage representations. Finite element models of eight subjects were used to tune a pressure-overclosure relationship during a simulated deep flexion cycle. Patellofemoral kinematics and contact mechanics were evaluated and compared between a fully deformable and a rigid body analysis. Additional eight subjects were used to determine the validity of the rigid body pressure-overclosure relationship as a subject-independent parameter. There was good agreement in predicted kinematics and contact mechanics between deformable and rigid analyses for both the tuned and test groups. Root mean square differences in kinematics were less than 0.5 deg and 0.2 mm for both groups throughout flexion. Differences in contact area and peak and average contact pressures averaged 5.4%, 9.6%, and 3.8%, respectively, for the tuned group and 6.9%, 13.1%, and 6.4%, respectively, for the test group, with no significant differences between the two groups. There was a 95% reduction in computational time with the rigid body analysis as compared with the deformable analysis. The tuned pressure-overclosure relationship derived from the patellofemoral analysis was also applied to tibiofemoral (TF) articular cartilage in a group of eight subjects. Differences in contact area and peak and average contact pressures averaged 8.3%, 11.2%, and 5.7% between rigid and deformable analyses in the tibiofemoral joint. As statistical, probabilistic, and optimization techniques can require hundreds to thousands of analyses, a viable platform is crucial to component evaluation or clinical applications. The computationally efficient rigid body platform described in this study may be integrated with statistical and probabilistic methods and has potential clinical application in understanding in vivo joint mechanics on a subject-specific or population basis.

Comparison of patellar bone strain in the natural and implanted knee during simulated deep flexion

Instances of anterior knee pain and patellar fracture are significant complications following total knee replacement (TKR). Bone strain measured in the patella can provide an indication of patellar fracture risk and may also be related to anterior knee pain. The objective of this study was to develop subject-specific finite element models of the patellofemoral (PF) joint including density-mapped material properties to gain insight into the patellar bone strain distribution in the natural and implanted knee. In eight subjects, the volume of bone experiencing strains >0.5% in the implanted condition was ∼200% larger, on average, than the natural condition. An inverse relationship with a correlation of -0.74 was established between postoperative bone volume and strain in the implanted specimens, suggesting that patellar geometry may be a useful indicator of postoperative strain. Comparing strains between regions (superior, inferior, medial, and lateral), it was found that although highly strained bone was evenly distributed between medial and lateral regions in the natural case, the implanted specimens demonstrated significantly larger volumes of highly strained bone medially as a result of substantially lower modulus bone in the medial compartment. Understanding distributions of PF strain may aid in preoperative identification of those patients at risk for patellar fracture or anterior knee pain, guidance regarding altered component placement for at-risk patients, and design of components considering the implications of PF load transfer and patellar strain distribution.

Anatomy of lateral patellar instability: trochlear dysplasia and tibial tubercle-trochlear groove distance is more pronounced in women who dislocate the patella

BACKGROUND

A trend toward young women being at greatest risk for primary and recurrent dislocation of the patella is evident in the current literature. However, a causative factor is missing, and differences in the anatomical risk factors between men and women are less defined.

PURPOSE

To identify differences between the sexes in the anatomy of lateral patellar instability.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Knee magnetic resonance images were collected from 100 patients treated for lateral patellar instability. Images were obtained from 157 patients without patellar instability who served as controls. Using 2-way analyses of variance, the influence of patellar dislocation, gender, and their interaction were analyzed with regard to sulcus angle, trochlear depth, trochlear asymmetry, patellar height, and the tibial tubercle-trochlear groove (TT-TG) distance. Mechanisms of injury of first-time dislocations were divided into high-risk, low-risk, and no-risk pivoting activities and direct hits.

RESULTS

For all response variables, a significant effect was observed for the incidence of patellar dislocation (all P < .01). In addition, sulcus angle, trochlear asymmetry, and trochlear depth depended significantly on gender (all P < .01) but patellar height did not (P = .13). A significant interaction between patellar dislocation and gender was observed for the TT-TG distance (P = .02). The mean difference in TT-TG distance between study and control groups was 4.1 mm for women (P < .01) and 1.6 mm for men (P = .05). Low-risk and no-risk pivoting injuries were most common in women, whereas first-time dislocations in men occurred mostly during high-risk pivoting activities (P < .01).

CONCLUSION

The data from this study indicate that trochlear dysplasia and the TT-TG distance is more prominent in women who dislocate the patella. Both factors might contribute to an increased risk of lateral patellar instability in the female patient as illustrated by the fact that dislocations occurred most often during low-risk or no-risk pivoting activities in women.