A new in vivo technique for determination of 3D kinematics and contact areas of the patello-femoral and tibio-femoral joint

Patellofemoral pain syndrome assessed by Lysholm score, radiological and biorheometric measurements

INTRODUCTION

The aim of In this study was to verify the relationship among clinical indicators of patellofemoral pain syndrome (PFPS) and the results of modifying radiological investigation. Previous research suggests that there is a poor association between them. Therefore we have employed a technique for the functional evaluation of PFPS based on measuring the stiffness of the knee joint during passive flexion (biorheometry).

METHOD

The correlation between clinical examination and a standardized Lysholm score, radiological and biorheometric measures was investigated in the 28 knee joints of 14 subjects exhibiting clinical features of PFPS. A modified axial radiological projection of the patellofemoral articulation in 90° of flexion provided the parameters quantifying the anatomical - morphological arrangement of the patellofemoral joint. The biorheometric properties of the knee were evaluated using a custom made measuring apparatus during passive flexion and extension of the knee.

RESULTS

Our results confirm that the link between the clinical findings and the X-ray imaging examinations was not evident. On the contrary, the biorheometric examination proved to correlate well with the clinical symptoms of PFPS. Parameters were identified which can characterize the biorheograms of people suffering PFPS.

CONCLUSIONS

Analysis of the relationship among the clinical, radiological and biorheometric examinations leads to the recommendation that biorheometric examination is an effective method for the objective assessment of PFPS.

Associations between the morphological parameters of proximal tibiofibular joint (PTFJ) and changes in tibiofemoral joint structures in patients with knee osteoarthritis

Background

To describe the longitudinal associations between the morphological parameters of proximal tibiofibular joint (PTFJ) and joint structural changes in tibiofemoral compartments in patients with knee osteoarthritis (OA).

Methods

The participants were selected from the Vitamin D Effects on Osteoarthritis (VIDEO) study. PTFJ morphological parameters were measured on coronal and sagittal MRI. The contacting area (S) of PTFJ and its projection areas onto the horizontal (load-bearing area, Sτ), sagittal (lateral stress-bolstering area, Sφ), and coronal plane (posterior stress-bolstering area, Sυ) were assessed. Knee structural abnormalities, including cartilage defects, bone marrow lesions (BMLs), and cartilage volume, were evaluated at baseline and after 2 years. Log binominal regression models and linear regression models were used to assess the associations between PTFJ morphological parameters and osteoarthritic structural changes.

Results

In the longitudinal analyses, the S (RR: 1.45) and Sτ (RR: 1.55) of PTFJ were significantly and positively associated with an increase in medial tibial (MT) cartilage defects. The Sτ (β: − 0.07), Sυ (β: − 0.07), and S (β: − 0.06) of PTFJ were significantly and negatively associated with changes in MT cartilage volume. The Sτ (RR: 1.55) of PTFJ was positively associated with an increase in MT BMLs, and Sφ (RR: 0.35) was negatively associated with an increase in medial femoral BMLs.

Conclusions

This longitudinal study suggests that higher load-bearing area of PTFJ could be a risk factor for structural changes in medial tibiofemoral (MTF) compartment in knee OA.

Trial registration

Clinicaltrials.gov Identifier: NCT01176344

Anzctr.org.au Identifier: ACTRN12610000495022

Date of registration: 7 May 2010

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-022-02719-8.

Arthroscopic lateral retinacular release improves patello-femoral and femoro-tibial kinematics in patients with isolated lateral retinacular tightness

PURPOSE

Arthroscopic lateral retinacular release (LRR) has long been considered the gold standard for the treatment for anterior knee pain caused by lateral retinacular tightness (LRT). However, one-third of patients experience continuous pain postoperatively, which is thought to be related to persistent maltracking of the patella and altered femoro-tibial kinematics. Therefore, the aim of the present study was to simultaneously assess femoro-tibial and patello-femoral kinematics and identify the influence of arthroscopic LRR.

METHODS

Sixteen healthy volunteers and 12 patients with unilateral, isolated LRT were prospectively included. Open MRI scans with and without isometric quadriceps contraction were performed in 0°, 30° and 90° of knee flexion preoperatively and at 12 months after surgery. Patellar shift, tilt angle, patello-femoral contact area and magnitude of femoro-tibial rotation were calculated by digital image processing.

RESULTS

Postoperatively, patellar shift was significantly reduced at 90° of knee flexion compared to preoperative values. The postoperative patellar tilt angle was found to be significantly smaller at 30° of knee flexion compared to that preoperatively. Isometric muscle contractions did not considerably influence patellar shift or tilt in either group. The patello-femoral contact area increased after LRR over the full range of motion (ROM), with significant changes at 0° and 90°. Regarding femoro-tibial kinematics, significantly increased femoral internal rotation at 0° was observed in the patient group preoperatively, whereas the magnitude of rotation at 90° of knee flexion was comparable to that of healthy individuals. The pathologically increased femoral internal rotation at 30° without muscular activity could be significantly decreased by LRR. With isometric quadriceps contraction no considerable improvement of femoral internal rotation could be achieved by LRR at 30° of knee flexion.

CONCLUSIONS

Patello-femoral and femoro-tibial joint kinematics could be improved, making LRR a viable surgical option in carefully selected patients with isolated LRT. However, pathologically increased femoral internal rotation during early knee flexion remained unaffected by LRR and thus potentially accounts for persistent pain.

LEVEL OF EVIDENCE

II.

Reliability of tibiofemoral contact area and centroid location in upright, open MRI

BACKGROUND

Imaging cannot be performed during natural weightbearing in biomechanical studies using conventional closed-bore MRI, which has necessitated simulating weightbearing load on the joint. Upright, open MRI (UO-MRI) allows for joint imaging during natural weightbearing and may have the potential to better characterize the biomechanical effect of tibiofemoral pathology involving soft tissues. However open MRI scanners have lower field strengths than closed-bore scanners, which limits the image quality that can be obtained. Thus, there is a need to establish the reliability of measurements in upright weightbearing postures obtained using UO-MRI.

METHODS

Knees of five participants with prior anterior cruciate ligament (ACL) rupture were scanned standing in a 0.5 T upright open MRI scanner using a 3D DESS sequence. Manual segmentation of cartilage regions in contact was performed and centroids of these contact areas were automatically determined for the medial and lateral tibiofemoral compartments. Inter-rater, test-retest, and intra-rater reliability were determined and quantified using intra-class correlation (ICC_3,1), standard error of measurement (SEM), and smallest detectable change with 95% confidence (SDC₉₅). Accuracy was assessed by using a high-resolution 7 T MRI as a reference.

RESULTS

Contact area and centroid location reliability (inter-rater, test-retest, and intra-rater) for sagittal scans in the medial compartment had ICC_3,1 values from 0.95-0.99 and 0.98-0.99 respectively. In the lateral compartment, contact area and centroid location reliability ICC_3,1 values ranged from 0.83-0.91 and 0.95-1.00 respectively. The smallest detectable change in contact area was 1.28% in the medial compartment and 0.95% in the lateral compartment. Contact area and centroid location reliability for coronal scans in the medial compartment had ICC_3,1 values from 0.90-0.98 and 0.98-1.00 respectively, and in the lateral compartment ICC_3,1 ranged from 0.76-0.94 and 0.93-1.00 respectively. The smallest detectable change in contact area was 0.65% in the medial compartment and 1.41% in the lateral compartment. Contact area was accurate to within a mean absolute error of 11.0 mm².

CONCLUSIONS

Knee contact area and contact centroid location can be assessed in upright weightbearing MRI with good to excellent reliability. The lower field strength used in upright, weightbearing MRI does not compromise the reliability of tibiofemoral contact area and centroid location measures.

Application of the Chinese Aircraft-shaped Sleeve system in the treatment of tibial shaft fractures using a suprapatellar approach for tibial intramedullary nailing: a randomised controlled trial

Background

The use of the suprapatellar approach for intramedullary nailing has recently become popular for the treatment of tibial fractures. This study aimed to investigate the effectiveness of using the Chinese Aircraft-shaped Sleeve (CASS) system on the clinical outcomes of tibial intermedullary nailing using a suprapatellar approach for the treatment of tibial fractures in a cohort of adult Chinese patients.

Methods

Magnetic resonance images (MRI) of the knee joints of 212 healthy adults with normal lower limb function from May 2011 to May 2015 were obtained from a level I Chinese regional trauma centre. Sixty inpatients at the same trauma centre who underwent treatment for tibial shaft fractures from June 2015 to June 2018 were enrolled. Tibial intramedullary nailing fixation of tibial shaft fractures via the suprapatellar approach was performed with either a CASS system or a conventional sleeve. The measurements of patellofemoral joint anatomy, the surgical time, the assessments of the patellofemoral joint cartilage conditions, and information of residual debris based on arthroscopic analysis were subsequently collected.

Results

The mean patellar angle (PA), sulcus angle (SA), sulcus width (SW) and sulcus depth (SD) were 135.40 ± 6.20°, 142.37 ± 5.33°, 33.37 ± 2.73 mm, and 4.29 ± 0.63 mm, respectively. The surgical time until entry reaming commencement and the irrigation time were significantly lower in the CASS group (P < 0.001). The difference in cartilage damage rate between groups was statistically significant (P = 0.031); the difference in residual debris conditions was not statistically significant (P = 0.1967).

Conclusion

The use of the CASS system could improve clinical outcomes of intramedullary nailing via suprapatellar approach for patients with a small patellofemoral joint space.

Trabecular bone patterning in the hominoid distal femur

BACKGROUND

In addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.

METHODS

Micro-computed tomography scans of Homo sapiens (n = 11), Pan troglodytes (n = 18), Gorilla gorilla (n = 14) and Pongo sp. (n = 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.

RESULTS

Results indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles in Pan and higher BV/TV and anisotropy in the posteroinferior region in Homo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separating Gorilla from the other apes.

DISCUSSION

The trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, and Homo was not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.

Impact of Simulated Knee Injuries on the Patellofemoral and Tibiofemoral Kinematics Investigated with an Electromagnetic Tracking Approach: A Cadaver Study

Purpose

The purpose of this study was to evaluate the approach of using an electromagnetic tracking (EMT) system for measuring the effects of stepwise, simulated knee injuries on patellofemoral (PF) and tibiofemoral (TF) kinematics.

Methods

Three cadaver knees were placed in a motion rig. EMT sensors were mounted on the patella, the medial/lateral femoral epicondyles, the tibial condyle, and the tibial tuberosity (TT). After determining the motion of an intact knee, three injuries were simulated and the resulting bony motion was tracked.

Results

Starting with the intact knee fully extended (0° flexion) and bending it to approximately 20°, the patella shifted slightly in the medial direction. Then, while bending the knee to the flexed position (90° flexion), the patella shifted progressively more laterally. After transecting the anterior cruciate ligament (ACL), the base of the medial menisci (MM) at the pars intermedia, and the medial collateral ligament (MCL), individual changes were observed. For example, the medial femoral epicondyle displayed a medial lift-off in all knees.

Conclusion

We demonstrated that our EMT approach is an acceptable method to accurately measure PF joint motion. This method could also enable visualization and in-depth analysis of in vivo patellar function in total knee arthroplasty, if it is established for routine clinical use.

Sagittal plane tilting deformity of the patellofemoral joint: a new concept in patients with chondromalacia patella

PURPOSE

The aims of this study were to evaluate sagittal plane alignment in patients with chondromalacia patella via magnetic resonance imaging (MRI), analyse the relationships between the location of the patellar cartilaginous lesions and sagittal alignment and finally investigate the relationships between the sagittal plane malalignment and patellofemoral loadings using by finite element analysis.

METHODS

Fifty-one patients who were diagnosed with isolated modified Outerbridge grade 3-4 patellar chondromalacia based on MRI evaluation and 51 control subjects were evaluated. Chondromalacia patella patients were divided into three subgroups according to the chondral lesion location as superior, middle and inferior. The patella-patellar tendon angle (P-PT) was used for evaluation of sagittal alignment of patellofemoral joint. Each subgroup was compared with control group by using P-PT angle. To investigate the biomechanical effects of sagittal plane malpositioning on patellofemoral joint, bone models were created at 30°, 60° and 90° knee flexion by using mean P-PT angles, which obtained from patients with chondromalacia patellae and control subjects. The total loading and contact area values of the patellofemoral joints were investigated by finite element analysis.

RESULTS

The mean age of all participants was 52.9 ± 8.2 years. The mean P-PT angle was significantly lower in chondromalacia group (142.1° ± 3.6°) compared to control group (144.5° ± 5.3°) (p = 0.008). Chondral lesions were located in superior, middle and inferior zones in 16, 20 and 15 patients, respectively. The mean P-PT angles in patients with superior (141.8 ± 2.7) and inferior subgroups (139.2 ± 2.3) were significantly lower than the values in the control group (p < 0.05). The contact area values were detected higher in models with chondromalacia than in the control models at the same flexion degrees. There were increased loadings at 30° and 90° flexions in the sagittal patellar tilt models.

CONCLUSION

This study revealed that sagittal plain malpositioning of the patellofemoral joint might be related to chondromalacia, especially in the presence of lesions in the upper and lower part of the patella. This condition leads to supraphysiological loadings on the patellofemoral joint. Sagittal patellar tilt should be considered in the evaluation and management of patellar cartilage defects. Taking sagittal plane malalignment into consideration in patellofemoral joint evaluation will enable us to design new physical and surgical modalities.

LEVEL OF EVIDENCE

IV.

Statistical shape modeling predicts patellar bone geometry to enable stereo-radiographic kinematic tracking

Complications in the patellofemoral (PF) joint of patients with total knee replacements include patellar subluxation and dislocation, and remain a cause for revision. Kinematic measurements to assess these complications and evaluate implant designs require the accuracy of dynamic stereo-radiographic systems with 3D-2D registration techniques. While tibiofemoral kinematics are typically derived by tracking metallic implants, PF kinematic measurements are difficult as the patellar implant is radiotransparent and a representation of the resected patella bone requires either pre-surgical imaging and precise implant placement or post-surgical imaging. Statistical shape models (SSMs), used to characterize anatomic variation, provide an alternative means to obtain the representation of the resected patella for use in kinematic tracking. Using a virtual platform of a stereo-radiographic system, the objectives of this study were to evaluate the ability of an SSM to predict subject-specific 3D implanted patellar geometries from simulated 2D image profiles, and to formulate an effective data collection methodology for PF kinematics by considering accuracy for a variety of patient pose scenarios. An SSM of the patella was developed for 50 subjects and a leave-one-out approach compared SSM-predicted and actual geometries; average 3D errors were 0.45±0.07mm (mean±standard deviation), which is comparable to the accuracy of traditional segmentation. Further, initial imaging of the patella in five unique stereo radiographic perspectives yielded the most accurate representation. The ability to predict the remaining patellar geometry of the implanted PF joint with radiographic images and SSM, instead of CT, can reduce radiation exposure and streamline in vivo kinematic evaluations.

Does leg predomination affect the measurement of vasti muscle activity during single leg squatting? A reliability study

INTRODUCTION

Although measuring vasti muscle activity may reveal whether pain relief is associated with altering this parameter during functional activities in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring VMO/VL amplitude. The aim of the present study was to examine the effect of leg predomination on reliability testing of the VMO/VL amplitude measurement during single leg squatting in healthy subjects.

METHODS

Using an electromyography (EMG) unit, the ratio amplitudes of VMO and VL muscles of ten healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from two silver-silver surface electrodes placed over the muscle bellies of the VMO and VL. This procedure was performed on the both right and left legs, during three separate single leg squats from a neutral position to a depth of approximately 30° of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week's interval. The amplitude of VMO and VL were then calculated using root mean square (RMS).

RESULTS

There was no significant difference between the VMO/VL amplitude mean values of paired test of right (mean, SD of 0.85, 0.10) and left knees (mean, SD of 0.82, 0.10) (p > 0.05). The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of VMO/VL amplitude measurements on both knees. The ICC (intra class correlation coefficient) values during within and between sessions tests showed the high reliability of these measurements on both knees.

CONCLUSION

The high reliability of VMO/VL amplitude measurements on both dominant and non-dominant legs of healthy subjects suggests that the VMO/VL amplitude measurement would not be influenced by the leg predomination during single leg squatting.

The influence of knee alignment on lower extremity kinetics during squats

The squat is an assessment of lower extremity alignment during movement, however there is little information regarding altered joint kinetics during poorly performed squats. The purpose of this study was to examine changes in joint kinetics and power from altered knee alignment during a squat. Thirty participants completed squats while displacing the knee medially, anteriorly, and with neutral alignment (control). Sagittal and frontal plane torques at the ankle, knee, and hip were altered in the descending and ascending phase of the squat in both the medial and anterior malaligned squat compared to the control squat. Ankle and trunk power increased and hip power decreased in the medial malaligned squat compared to the control squat. Ankle, knee, and trunk power increased and hip power decreased in the anterior malaligned squat compared to the control squat. Changes in joint torques and power during malaligned squats suggest that altered knee alignment increases ankle and trunk involvement to execute the movement. Increased anterior knee excursion during squatting may also lead to persistent altered loading of the ankle and knee. Sports medicine professionals using the squat for quadriceps strengthening must consider knee alignment to reduce ankle and trunk involvement during the movement.

The influence of component alignment on patellar kinematics in total knee arthroplasty

BACKGROUND AND PURPOSE

Postoperative anterior knee pain is one of the most frequent complications after total knee arthroplasty (TKA). Changes in patellar kinematics after TKA relative to the preoperative arthritic knee are not well understood. We compared the patellar kinematics preoperatively with the kinematics after ligament-balanced navigated TKA.

PATIENTS AND METHODS

We measured patellar tracking before and after ligament-balanced TKA in 40 consecutive patients using computer navigation. Furthermore, the influences of different femoral and tibial component alignment on patellar kinematics were analyzed using generalized linear models.

RESULTS

After TKA, the patellae shifted statistically significantly more laterally between 30° and 60°. The lateral tilt increased at 90° of flexion whereas the epicondylar distance decreased between 45° and 75° of flexion. Sagittal component alignment, but not rotational component alignment, had a significant influence on patellar kinematics.

INTERPRETATION

There are major differences in patellar kinematics between the preoperative arthritic knee and the knee after TKA. Combined sagittal component alignment in particular appears to have a major effect on patellar kinematics. Surgeons should be especially aware of altering preoperative sagittal alignment until the possible clinical relevance has been investigated.

Opening wedge high tibial osteotomy: plate position and biomechanics of the medial tibial plateau

PURPOSE

To ascertain whether changing position and size of the spacer may modify the load and displacement of the tibial plateau when performing an opening wedge high tibial osteotomy.

METHODS

Fifteen sawbones tibia models were used. In the axial plane, the anterior, medial, and posterior thirds of the tibial plateau were marked, and the medial and posterior thirds were called "point 1" and "point 2", respectively. A 7.5-mm-stainless steel indenter was used to apply the load over these two points: the load applied to point 1 simulated the load to that site when the knee was extended, and the load to point 2 simulated the load to the same area when the knee was flexed. Maximum load (N) and displacement (mm) were calculated.

RESULTS

The system was shown to withstand higher loads with less displacement when the plate was posterior than it could do with the plate in the middle position. Significant differences were also found when comparing the anterior and middle position of the plate with the greatest displacement when the plate was anterior. The differences were increased when comparing the anterior and posterior positions of the plate. No statistical differences (n.s.) were found when using different spacers. The maximum stiffness was achieved if the plate was posterior and in point 1 indenter position, in which the force vector stands on the points of the lateral and medial supports (Fμ = 198.8 ± 61.5 N). The lowest stiffness was observed when the plate was anterior, and the force was applied to point 2 (Fμ = 29.7 ± 5.1 N).

CONCLUSIONS

Application of the plate in a more posterior position provides greater stability.

Validation of an anatomical coordinate system for clinical evaluation of the knee joint in upright and closed MRI

A computerized method to automatically and spatially align joint axes of in vivo knee scans was established and compared to a fixed reference system implanted in a cadaver model. These computational methods to generate geometric models from static MRI images with an automatic coordinate system fitting proved consistent and accurate to reproduce joint motion in multiple scan positions. Two MRI platforms, upright and closed, were used to scan a phantom cadaver knee to create a three-dimensional, geometric model. The knee was subsequently scanned in several positions of knee bending in a custom made fixture. Reference markers fixed to the bone were tracked by an external infrared camera system as well as by direct segmentation from scanned images. Anatomical coordinate systems were automatically fitted to the segmented bone model and the transformations of joint position were compared to the reference marker coordinate systems. The tracked translation and rotation measurements of the automatic coordinate system were found to be below root mean square errors of 0.8 mm and 0.7°. In conclusion, the precision of the translation and rotational tracking is found to be sensitive to the scanning modality, albeit in upright or closed MRI, but still within comparative measures to previously performed studies. The potential to use segmented bone models for patient joint analysis could vastly improve clinical evaluation of disorders of the knee with continual application in future three-dimensional computations.

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.

Acute cartilage loading responses after an in vivo squatting exercise in people with doubtful to mild knee osteoarthritis: a case-control study

BACKGROUND

The effects of exercise on osteoarthritic cartilage remain elusive.

OBJECTIVE

The objective of this study was to investigate the effect of dynamic in vivo squatting exercise on the magnitude and spatial pattern of acute cartilage responses in people with tibiofemoral osteoarthritis (ie, Kellgren-Lawrence grades 1 and 2).

DESIGN

This investigation was a case-control study.

METHODS

Eighteen people with radiographic signs of doubtful to mild medial tibiofemoral osteoarthritis were compared with 18 people who were middle-aged and healthy (controls). Three-dimensional magnetic resonance imaging was used to monitor deformation and recovery on the basis of 3-dimensional cartilage volume calculations (ie, total volume and volumes in anterior, central, and posterior subregions) before and after a 30-repetition squatting exercise. Three-dimensional volumes were estimated after semiautomatic segmentation and were calculated at 4 time points (1 before and 3 after scans). Scans obtained after the exercise were separated by 15-minute intervals.

RESULTS

In both groups, significant deformation was noted in the medial compartment (-3.4% for the femur and -3.2% for the tibia in people with osteoarthritis versus -2.8% for the femur and -3.8% for the tibia in people in the control group). People with osteoarthritis had significant deformation in the lateral femur (-3.9%) and a tendency toward significant deformation in the lateral tibia (-3.1%). From 15 minutes after exercise cessation onward, volume changes were no longer significantly different from the baseline. At all time points, no significant between-group differences were revealed for volume changes. People with osteoarthritis showed a tendency toward slower recovery preceded by larger deformations in entire cartilage plates and subregions. Spatial subregional deformation patterns were similar between groups.

LIMITATIONS

Generalizability is limited to people with doubtful to mild osteoarthritis and low levels of pain.

CONCLUSIONS

Tibiofemoral cartilage deformation appeared similar in magnitude and spatial pattern in people who were middle-aged and either had or did not have tibiofemoral osteoarthritis (ie, Kellgren-Lawrence grades 1 and 2). Restoration of volumes required a 15-minute recovery, especially in the presence of osteoarthritic cartilage degeneration.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation and progression of osteoarthritis. However, our understanding of which mechanical parameters are most important, and what their impact is on the disease, is limited by the challenge of measuring the most important mechanical quantities in living subjects. Consequently, comprehensive statements cannot be made about how mechanics should be modified to prevent, slow or arrest osteoarthritis. Our current understanding is based largely on studies of deviations from normal mechanics caused by malalignment, injury, and deformity. Some treatments for osteoarthritis focus on correcting mechanics, but there appears to be scope for more mechanically based interventions.

Tibiofemoral and patellofemoral joint 3D-kinematics in patients with posterior cruciate ligament deficiency compared to healthy volunteers

BACKGROUND

The posterior cruciate ligament (PCL) plays an important role in maintaining physiological kinematics and function of the knee joint. To date mainly in-vitro models or combined magnetic resonance and fluoroscopic systems have been used for quantifying the importance of the PCL. We hypothesized, that both tibiofemoral and patellofemoral kinematic patterns are changed in PCL-deficient knees, which is increased by isometric muscle flexion. Therefore the aim of this study was to simultaneously investigate tibiofemoral and patellofemoral 3D kinematics in patients suffering from PCL deficiency during different knee flexion angles and under neuromuscular activation.

METHODS

We enrolled 12 patients with isolated PCL-insufficiency as well as 20 healthy volunteers. Sagittal MR-images of the knee joint were acquired in different positions of the knee joint (0°, 30°, 90° flexion, with and without flexing isometric muscle activity) on a 0.2 Tesla open MR-scanner. After segmentation of the patella, femur and tibia local coordinate systems were established to define the spatial position of these structures in relation to each other.

RESULTS

At full extension and 30° flexion no significant difference was observed in PCL-deficient knee joints neither for tibiofemoral nor for patellofemoral kinematics. At 90° flexion the femur of PCL-deficient patients was positioned significantly more anteriorly in relation to the tibia and both, the patellar tilt and the patellar shift to the lateral side, significantly increased compared to healthy knee joints. While no significant effect of isometric flexing muscle activity was observed in healthy individuals, in PCL-deficient knee joints an increased paradoxical anterior translation of the femur was observed at 90° flexion compared to the status of muscle relaxation.

CONCLUSIONS

Significant changes in tibiofemoral and patellofemoral joint kinematics occur in patients with isolated PCL-insufficiency above 30 degrees of flexion compared to healthy volunteers. Since this could be one reasonable mechanism in the development of osteoarthritis (OA) our results might help to understand the long-term development of tibiofemoral and/or patellofemoral OA in PCL-insufficient knee joints.

Lateral patellar facetectomy had improved clinical results in patients with patellar-retaining total knee arthroplasty

To evaluate the functional outcome of a partial lateral facetectomy in patellar-retaining total knee arthroplasty (TKA), we retrospectively analyzed 63 knees of 59 patients who underwent TKA for primary knee osteoarthritis with (32 knees of 30 patients, group 1) or without (31 knees of 29 patients, group 2) patellar facetectomy from September 2005 to July 2007. All cases were followed up for a minimum of 36 months. Although there was no significant differences between the 2 groups in preoperative patellar score, Western Ontario and McMaster Universities score, knee and function scores, postoperatively, group 1 showed more significant improvements in the scores and fewer lateral patellar osteophytes in radiographs than group 2. A partial lateral facetectomy is an effective way to improve the function of patellar-retaining TKA in patients with primary osteoarthritis.

A comparison of tibiofemoral and patellofemoral alignment during a neutral and valgus single leg squat: an MRI study

BACKGROUND

The etiology of anterior knee pain is not well understood. Recently, excessive hip adduction and internal rotation have been cited as possible factors. However, how these altered hip mechanics affect the patellofemoral joint is still unclear.

OBJECTIVE

To compare the three-dimensional tibiofemoral and patellofemoral alignment between a neutral squat and one performed with increased hip adduction and internal rotation. We aimed to examine the relationships between the three-dimensional tibiofemoral and patellofemoral alignment during a neutral and valgus squat. Finally, we aimed to determine the relationship between two-dimensional and three-dimensional measures of patellofemoral alignment.

METHODS

10 healthy subjects were recruited for this study. Knee and patellar kinematics in a neutral squat and one performed with hip adduction and internal rotation were measured using a open, upright, magnetic resonance imaging unit. Both single leg squats were performed at 30° of knee flexion.

RESULTS

There was a significant correlation between knee external rotation and lateral patellar translation, and between knee abduction and lateral patellar translation. Moderate relationships were found between the 2D and 3D measures but these were not statistically significant.

CONCLUSION

The valgus squat resulted in greater knee external rotation in all subjects. Although mean patellar mechanics were not different in the valgus squat, lateral patellar translation increased as knee external rotation increased. Lastly, 2D measures of patellofemoral alignment only provide moderately fair surrogates for 3D measures.

Does leg predomination affect the measurement of patellofemoral joint reaction force (PFJRF) during single leg squatting?: a reliability study

INTRODUCTION

Although measuring patellofemoral joint reaction forces (PFJRF) may provide reliable evidence for conservative treatments to correct probable malalignment in subjects with patellofemoral pain syndrome (PFPS), it may be necessary to determine whether the inherent properties of the dominant leg influences the reliability of measuring PFJRF. The aim of the present study was to examine the effect of leg predomination on reliability testing of the PFJRF measurement during single leg squatting in healthy subjects.

METHODS

Using a motion analysis system and one force plate, PFJRF of 10 healthy subjects with a right dominant leg was assessed during single leg squatting. Data was collected from superficial markers taped to selected landmarks. This procedure was performed on the both right and left legs, during three separate single leg squats from a neutral position to a depth of approximately 30° of knee flexion. Subjects were then asked to repeat the test procedure after a minimum of a week's interval. The PFJRF was calculated using a biomechanical model of the patellofemoral joint.

RESULTS

There was significant difference between the PFJRF mean values of paired test of right (mean, SD of 1887.7, 325.1 N) and left knees (mean, SD of 2022.6, 270.5 N) (p < 0.05). The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of PFJRF measurements on both knees. The ICC (intra class correlation coefficient) values during within and between sessions tests showed the high reliability of these measurements on both knees.

CONCLUSION

The high reliability of PFJRF measurements on both dominant and non-dominant legs of healthy subjects suggests that the PFJRF measurement would not be influenced by the leg predomination during single leg squatting.

Patellar resurfacing in total knee arthroplasty: does design matter? A meta-analysis of 7075 cases

BACKGROUND

Patellar resurfacing in total knee arthroplasty remains controversial. The aim of this study was to compare outcomes following total knee arthroplasty with patellar resurfacing with those following total knee arthroplasty without patellar resurfacing. We also sought to identify any correlation between outcomes and prosthetic design.

METHODS

Eighteen Level-I randomized controlled trials with a cumulative sample size of 7075 knees (3463 in the resurfacing group and 3612 in the non-resurfacing group) satisfied the inclusion criteria. In the primary analysis, patellar resurfacing total knee arthroplasty was compared with non-resurfacing total knee arthroplasty, with use of reoperation rates, incidence of anterior knee pain, and functional scores as outcome measures. The secondary analysis focused on comparing patella-friendly and non-patella-friendly total knee arthroplasty designs with regard to the same three outcome measures.

RESULTS

No significant differences were found between the resurfacing and non-resurfacing groups with regard to the incidence of anterior knee pain. A higher rate of reoperations was observed in the non-resurfacing group. Analysis of homogeneous data comparing patella-friendly with non-patella-friendly total knee arthroplasty designs demonstrated no differences in the incidence of reoperations.

CONCLUSIONS

No evidence was found to suggest that either patellar resurfacing or the prosthetic design affects the clinical outcome of a total knee arthroplasty. The higher incidence of reoperations in the non-resurfacing group may be attributed to the fact that secondary patellar resurfacing adds a surgical option for the treatment of anterior knee pain following total knee arthroplasty, thus artificially increasing the rate of reoperations in the non-resurfacing group.

The effect of a patellar brace on three-dimensional patellar kinematics in patients with lateral patellofemoral osteoarthritis

OBJECTIVE

Patellar bracing is a mechanical treatment strategy for patellofemoral osteoarthritis (OA) that aims to unload the lateral compartment of the joint by translating the patella medially. Our objective was to determine whether a patellar brace can correct patellar kinematics in patients with patellofemoral OA.

DESIGN

We assessed the effect of a patellar brace on three-dimensional patellar kinematics (flexion, spin and tilt; proximal, lateral and anterior translation) at sequential, static knee postures, using a validated magnetic resonance imaging (MRI)-based method, in 19 patients with radiographic lateral patellofemoral OA. Differences in kinematics between unbraced and braced conditions were assessed in the unloaded and loaded knee (15% bodyweight load) using hierarchical linear random-effects models. Random slope and quadratic terms were included in the model when significant (P<0.05).

RESULTS

Bracing with load caused the patellae to translate 0.46 mm medially (P<0.001), tilt 1.17° medially (P<0.001), spin 0.62° externally (P=0.012) and translate 1.09 mm distally (P<0.001) and 0.47 mm anteriorly (P<0.001) over the range of knee flexion angles studied. Bracing also caused the patellae to extend in early angles of knee flexion (P<0.001). The brace caused similar trends for the unloaded condition, though magnitudes of the changes varied.

CONCLUSION

Bracing changed patellar kinematics, but these changes did not appear large enough to be clinically meaningful because no reduction in pain was observed in the parent study.

Assessing the accuracy and precision of musculoskeletal motion tracking using cine-PC MRI on a 3.0T platform

The rising cost of musculoskeletal pathology, disease, and injury creates a pressing need for accurate and reliable methods to quantify 3D musculoskeletal motion, fostering a renewed interest in this area over the past few years. To date, cine-phase contrast (PC) MRI remains the only technique capable of non-invasively tracking in vivo 3D musculoskeletal motion during volitional activity, but current scan times are long on the 1.5T MR platform (∼ 2.5 min or 75 movement cycles). With the clinical availability of higher field strength magnets (3.0T) that have increased signal-to-noise ratios, it is likely that scan times can be reduced while improving accuracy. Therefore, the purpose of this study is to validate cine-PC MRI on a 3.0T platform, in terms of accuracy, precision, and subject-repeatability, and to determine if scan time could be minimized. On the 3.0T platform it is possible to limit scan time to 2 min, with sub-millimeter accuracy (<0.33 mm/0.97°), excellent technique precision (<0.18°), and strong subject-repeatability (<0.73 mm/1.10°). This represents reduction in imaging time by 25% (42 s), a 50% improvement in accuracy, and a 72% improvement in technique precision over the original 1.5T platform. Scan time can be reduced to 1 min (30 movement cycles), but the improvements in accuracy are not as large.

Standardized cartilage biopsies from the intercondylar notch for autologous chondrocyte implantation (ACI)

Autologous chondrocyte implantation (ACI) is an established therapy for the treatment of cartilage defects across the knee joint. Even though different techniques for initial biopsy have been described, the exact location, depth, and volume of the biopsy are chosen individually by the treating surgeon. This study evaluated 252 consecutive cartilage biopsies taken from the intercondylar notch with a standardized hollow cylinder system for the isolation and in vitro cultivation of human chondrocytes assigned to ACI. All biopsies were assessed for weight of total cartilage obtained, cartilage biopsy weight per cylinder, biopsy cylinder quality, and initial cell count after digestive cellular isolation as well as cell vitality. Parameters were correlated with individual patient parameters. Mean patient age was 35.1 years (median 35.9; range 14.7-56.4). Adequate amounts of cartilage assigned to chondrocyte in vitro cultivation could be harvested in all cases. The mean overall biopsy weight averaged 75.5 mg (SD +/- 44.9) and could be identified as main factor for initial cell number (mean 1.05E+05; SD +/- 7.44E+04). No correlation was found between the initial cell count and patient age (correlation coefficient r = 0.005) or grade of joint degeneration (r = 0.040). Concerning cell viability, a total of 4.4% (SD + 3.0) of the chondrocytes harvested were apoptotic. Cartilage biopsies from the intercondylar notch using a standardized hollow cylinder system provides a reliable, safe, and successful method to obtain articular cartilage for further in vitro cultivation of articular chondrocytes to achieve autologous chondrocyte transplantation.

The effect of load magnitude on three-dimensional patellar kinematics in vivo

Studies of three-dimensional patellar kinematics done with little or no applied load may not accurately reflect kinematics at physiological load levels, and may provide different results to those acquired with greater applied loads or in physiologic weightbearing. We report the effect of load magnitude on three-dimensional patellar kinematics (flexion, spin and tilt; proximal, lateral and anterior translation) using a validated, sequential static, MRI-based method. Ten healthy subjects loaded their study knee to 0% (no load), 15% and 30% bodyweight (BW) using a custom designed loading rig. Differences between loading levels were determined as a function of knee flexion for each kinematic parameter using linear hierarchical random-effects models. Quadratic and random slope terms were included in the models when significant. We found that the patellae flexed less with knee flexion at 30% BW load compared to 0% BW load (p<0.001) and 15% BW (p=0.004) load. The patellae showed a slight medial tilt with knee flexion at 30% BW load which was significantly less than the medial tilt seen at 0% BW load (p=0.017) and 15% BW load (p=0.043) with knee flexion. Small but statistically significant differences were also observed for proximal and anterior translation; the patellae were in a more proximal and posterior position at 30% BW load than at 0% BW load (p=0.010 and p=0.005, respectively) and 15% BW load (p<0.001 and p=0.029, respectively). Since differences in three-dimensional patellar kinematics were observed between loading levels, magnitudes of prescribed loads must be considered when designing studies and comparing results between studies.

Measuring patellar height using the lateral active flexion radiograph: Effect of total knee implant design

Patellar position during knee flexion was studied in 41 patients with bicruciate substituting (BCS), 41 patients with posterior cruciate retaining (CR) and 41 patients with posterior stabilized (PS) TKA's. The perpendicular height of the patella above the tibial tubercle was compared to the length of the patellar tendon on maximum flexion lateral radiographs. BCS knees had greater active flexion compared to PS and CR knees (BCS=124+/-9.8, PS=112+/-9.5, CR=110+/-10.9). In flexion, apparent patella infera (API) or the height of the patella above the tibial tubercle was 3.5% lower than the patellar tendon length for BCS knees, 1.7% lower in PS knees and 0.5% lower in CR knees. API in PS and BCS knees correlated with active knee flexion, but not in CR knees. Our findings indicate that an apparent inferior position of the patella occurs in BCS knees during deep flexion which is not caused by significant patellar ligament shortening or joint line elevation, but associated with normal posterior rollback of the femur.

EOS orthopaedic imaging system to study patellofemoral kinematics: assessment of uncertainty

BACKGROUND

Accurate knowledge of knee joint kinematics, especially patellofemoral joint kinematics,is essential for prosthetic evaluation so as to further improve total knee arthroplasty performances. Improving the evaluation of the functioning of the extensor apparatus appears,in this respect, particularly important in this optimization effort.

OBJECTIVES

The aim of this study was to propose a new experimental setup for the analysis of knee joint kinematics and to validate its relevance in terms of accuracy and uncertainty.The technique developed herein combines 3D reconstruction imaging with the use of a motion capture system.

MATERIAL AND METHODS

Eight pairs of fresh-frozen cadaver specimens with no evidence of previous knee surgery were studied using a new test rig where the femur remains fixed and the tibia is free to rotate. The flexion-extension cycles were executed using computer-controlled traction of the quadriceps tendon combined with an antagonist force applied to the distal part of the tibia. Knee joint kinematics were tracked using an optoelectronic motion capture system after a preliminary stage of data acquisition of bone geometry and markers position. This stage was carried out using a new digital stereophotogrammetric system, EOS, combined with specific 3D reconstruction software that also determined the coordinate system used in the kinematic analysis. The resulting uncertainty was assessed as was its impact on the estimated kinematics.

RESULTS

Test results on eight knees validated the setup designed for the analysis of knee joint kinematics during the flexion-extension cycle. More specifically, the statistical results show that measurement uncertainty for rotations and translations remains below 0.4 and 1.8 mm,respectively, for the tibia and 0.4 and 1.2 mm for the patella (+/- 2 S.D. for all four measurements).

DISCUSSION

The combination of 3D imaging and motion capture enables the proposed method to track the real-time motion of any bone segment during knee flexion-extension cycle. In particular,the new test rig introduced in this paper allows in vitro measurements of the patello femoral and tibiofemoral kinematics with a good level of accuracy. Moreover, this personalized experimental analysis can provide a more objective approach to the evaluation of knee implants as well as the validation of the finite-elements-based models of the patellofemoral joint.

Three-dimensional in vivo patellofemoral kinematics and contact area of anterior cruciate ligament-deficient and -reconstructed subjects using magnetic resonance imaging

PURPOSE

The purpose of this study was to test whether (1) the 3-dimensional in vivo patellofemoral kinematics and patellofemoral contact area of anterior cruciate ligament (ACL)-deficient knees are different from those of normal, contralateral knees and (2) ACL reconstruction restores in vivo patellofemoral kinematics and contact area.

METHODS

Ten ACL-deficient knees and twelve ACL-reconstructed knees, as well as the contralateral uninjured knees, were tested. Magnetic resonance imaging was performed at full extension and 40 degrees of flexion under simulated partial weight-bearing conditions. Six-degrees of freedom patellofemoral kinematics, patellofemoral contact area, and contact location were analyzed by use of magnetic resonance image-based 3-dimensional patellofemoral knee models.

RESULTS

The patella in the ACL-deficient knees underwent significantly more lateral tilt during flexion (P < .05) and tended to translate more laterally (P = .083) than the patella in contralateral knees. After ACL reconstruction, no kinematic parameters were significantly different from those in contralateral knees. The patellofemoral contact areas of ACL-deficient knees at both the extended and flexed positions (37 +/- 22 mm(2) and 357 +/- 53 mm(2), respectively) were significantly smaller than those of contralateral knees (78 +/- 45 mm(2) and 437 +/- 119 mm(2), respectively) (P < .05). After reconstruction, the patellofemoral contact area of ACL-reconstructed knees in the extended position (86 +/- 41 mm(2)) was significantly larger (P < .05) than that of contralateral knees (50 +/- 34 mm(2)), but no difference was detected in the flexed position. Reproducibility of all patellofemoral kinematic parameters, contact centroid translation, and contact area showed coefficients of variation of less than 6.8%.

CONCLUSIONS

ACL injuries alter patellofemoral kinematics including patellar tilt and patellar lateral translation, but ACL reconstruction with hamstring or allograft restores altered patellar tilt. ACL injuries reduce the patellofemoral contact area at both the extended and flexed positions, but ACL reconstruction enlarges the patellofemoral contact area at extension and restores the normal contact area at low angles of flexion.

LEVEL OF EVIDENCE

Level III, case-control study.

The effect of volume sub-sampling on motion estimation of joints via MR imaging

The technique of three-dimensional imaging is being explored as a means of better understanding the morphology and kinematics of the foot and ankle. To capture information about the dynamic nature of the joint, MRI pulse sequences are used to rapidly acquire single-slice kinematic images, which are then used to track the motion of the bone or other tissues. This approach cannot capture true 3D motion information. On the other hand, full 3D acquisitions are time consuming. A more time-efficient alternative to this method that may give accurate 3D motion information may be to use select MRI slices, instead of full resolution 3D models, that may be just enough to capture the vital information needed to track motion. This was tested by removing slices from already acquired full kinematic MRI datasets and progressively removing slices to determine up to what level data can be eliminated and still achieve accurate motion tracking. We evaluated the ability of the reduced data set in tracking motion in terms of both volume overlap and actual motion estimated, and compared these with the results from the full resolution data. We based our analysis of accuracy on the ability to transform the reduced images from one position of the foot to another. In tracking the motion of the bones of the tarsal joints, we were able to reduce the number of slices to about 25% of the full data set while maintaining an accurate representation of motion within about 0.5mm of translation and 0.5 degrees of rotation of the motion estimated from full data.

The measurement of joint mechanics and their role in osteoarthritis genesis and progression

Mechanics play a role in the initiation, progression, and successful treatment of osteoarthritis. However, we don't yet know enough about which specific mechanical parameters are most important and what their impact is on the disease process to make comprehensive statements about how mechanics should be modified to prevent, slow, or arrest the disease process. The objectives of this review are (1) to summarize methods for assessing joint mechanics and their relative merits and limitations, (2) to describe current evidence for the role of mechanics in osteoarthritis initiation and progression, and (3) to describe some current treatment approaches that focus on modifying joint mechanics.

Accuracy of biplane x-ray imaging combined with model-based tracking for measuring in-vivo patellofemoral joint motion

BACKGROUND

Accurately measuring in-vivo motion of the knee's patellofemoral (PF) joint is challenging. Conventional measurement techniques have largely been unable to accurately measure three-dimensional, in-vivo motion of the patella during dynamic activities. The purpose of this study was to assess the accuracy of a new model-based technique for measuring PF joint motion.

METHODS

To assess the accuracy of this technique, we implanted tantalum beads into the femur and patella of three cadaveric knee specimens and then recorded dynamic biplane radiographic images while manually flexing and extending the specimen. The position of the femur and patella were measured from the biplane images using both the model-based tracking system and a validated dynamic radiostereometric analysis (RSA) technique. Model-based tracking was compared to dynamic RSA by computing measures of bias, precision, and overall dynamic accuracy of four clinically-relevant kinematic parameters (patellar shift, flexion, tilt, and rotation).

RESULTS

The model-based tracking technique results were in excellent agreement with the RSA technique. Overall dynamic accuracy indicated errors of less than 0.395 mm for patellar shift, 0.875 degrees for flexion, 0.863 degrees for tilt, and 0.877 degrees for rotation.

CONCLUSION

This model-based tracking technique is a non-invasive method for accurately measuring dynamic PF joint motion under in-vivo conditions. The technique is sufficiently accurate in measuring clinically relevant changes in PF joint motion following conservative or surgical treatment.

In vivo patellar tracking: clinical motions and patellofemoral indices

Patellar tracking during in vivo weightbearing knee function is not well understood. This study investigated patellar tracking of eight subjects during a full range of weightbearing flexion using magnetic resonance imaging and dual orthogonal fluoroscopy. The data were reported using a clinical description based on patellar and femoral joint coordinate systems and using patellar indices based on geometrical features of the femur and patella. The mean patellar shift was within 3 mm over the entire range of flexion. The patella tilted laterally from 0 degrees to 75 degrees, and then tilted medially beyond 75 degrees of flexion. The mean tilt was within 6 degrees. Similarly, the mean patellar rotation was small at early flexion, and the mean total excursion of patellar rotation was about 8 degrees. The patellofemoral indices showed that the mean sulcus angle and congruence angle varied within 8 degrees over the entire flexion range. The mean lateral patellar displacement was within 6 mm. A consistent decrease in lateral patellar tilt and an increase in lateral patellofemoral angle were observed with knee flexion. In conclusion, patellar motion is relatively small with respect to the femur during in vivo weightbearing knee flexion. These data may provide baseline knowledge for understanding normal patellar tracking.

The management of recurrent patellar dislocation

Acute and chronic trauma, chronic abnormal joint loading conditions, and hemarthroses have been implicated in the development of degenerative joint disease. Patellar instability with acute and recurrent patellar dislocation provides all of these ingredients. This article describes an approach to the treatment of recurrent patellar instability that considers the unique features and expectations of the patient rather than using a generic algorithm.

Fully automated computer algorithm for calculating articular contact points with application to knee biomechanics

A fully automated computer algorithm for calculating the articular contact points between two bone surface models is presented. The algorithm requires the bone surface models and their relative positions as inputs in order to resolve the articular contact path. In the case of surface model overlap due to measurement errors or as a solution of an optimization procedure, the result is a volumetric estimation of the space confined between the two surfaces. The algorithm is based on attaching a grid of lines to one bone surface model and calculating the intersecting points of each of the lines in the grid with both bone surface models. The contact points are then determined as the closest points between the surfaces along the lines in the grid. The same contact points are used to evaluate any volume that is confined between two overlapping surface models. The algorithm is ideal for use in biomechanical studies, simulations of joint motion, and optimizations that require an iterative process to determine contact path and relative bone position. The algorithm is applied to a Sawbones knee model that is moved from flexion to extension while being tracked by an optical tracking system. The contact path of the two bones is generated and an example of calculating bone impingement is provided.

The effect of the design of the femoral component on the conformity of the patellofemoral joint in total knee replacement

One of the most controversial issues in total knee replacement is whether or not to resurface the patella. In order to determine the effects of different designs of femoral component on the conformity of the patellofemoral joint, five different knee prostheses were investigated. These were Low Contact Stress, the Miller-Galante II, the NexGen, the Porous-Coated Anatomic, and the Total Condylar prostheses. Three-dimensional models of the prostheses and a native patella were developed and assessed by computer. The conformity of the curvature of the five different prosthetic femoral components to their corresponding patellar implants and to the native patella at different angles of flexion was assessed by measuring the angles of intersection of tangential lines. The Total Condylar prosthesis had the lowest conformity with the native patella (mean 8.58 degrees ; 0.14 degrees to 29.9 degrees ) and with its own patellar component (mean 11.36 degrees ; 0.55 degrees to 39.19 degrees ). In the other four prostheses, the conformity was better (mean 2.25 degrees ; 0.02 degrees to 10.52 degrees ) when articulated with the corresponding patellar component. The Porous-Coated Anatomic femoral component showed better conformity (mean 6.51 degrees ; 0.07 degrees to 9.89 degrees ) than the Miller-Galante II prosthesis (mean 11.20 degrees ; 5.80 degrees to 16.72 degrees ) when tested with the native patella. Although the Nexgen prosthesis had less conformity with the native patella at a low angle of flexion, this improved at mid (mean 3.57 degrees ; 1.40 degrees to 4.56 degrees ) or high angles of flexion (mean 4.54 degrees ; 0.91 degrees to 9.39 degrees ), respectively. The Low Contact Stress femoral component had the best conformity with the native patella (mean 2.39 degrees ; 0.04 degrees to 4.56 degrees ). There was no significant difference (p > 0.208) between the conformity when tested with the native patella or its own patellar component at any angle of flexion. The geometry of the anterior flange of a femoral component affects the conformity of the patellofemoral joint when articulating with the native patella. A more anatomical design of femoral component is preferable if the surgeon decides not to resurface the patella at the time of operation.

Effect of variability in anatomical landmark location on knee kinematic description

Small variability associated with identifying and locating anatomical landmarks on the knee has the potential to affect the joint coordinate systems and reported kinematic descriptions. The objectives of this study were to develop an approach to quantify the effect of landmark location variability on both tibiofemoral and patellofemoral kinematics and to identify the critical landmarks and associated degrees of freedom that most affected the kinematic measures. The commonly used three-cylindric open-chain kinematic description utilized measured rigid body kinematics from a cadaveric specimen during simulated gait. A probabilistic analysis was performed with 11 anatomical landmarks to predict the variability in each kinematic. The model predicted the absolute kinematic bounds and offset kinematic bounds, emphasizing profile shape, for each kinematic over the gait cycle, as well as the range of motion. Standard deviations of up to 2 mm were assumed for the anatomical landmark locations and resulted in significant variability in clinically relevant absolute kinematic parameters of up to 6.5 degrees and 4.4 mm for tibiofemoral and 7.6 degrees and 6.5 mm for patellofemoral kinematics. The location of the femoral epicondylar prominences had the greatest effect on both the tibiofemoral and patellofemoral kinematic descriptions. A quantitative understanding of the potential changes in kinematic description caused by anatomical landmark variability is important not only to the accuracy of kinematic gait studies and the evaluation of total knee arthroplasty implant performance, but also may impact component placement decision-making in computer-assisted surgery.

Patellar tracking during total knee arthroplasty: an in vitro feasibility study

Abnormal patellar tracking results in patello-femoral (PF) joint disorders and frequently in failure of total knee arthroplasty (TKA). It is fundamental to assess this tracking intra-operatively, i.e. since the implantation of the femoral and tibial components. The aim of this study was to assess the feasibility of three-dimensional anatomical-based patellar tracking intra-operatively in standard TKA. A surgical navigation system was utilized to test the new technique in-vitro. An original tracking device and a reference frame were designed and an articular convention for the description of PF joint kinematics was adopted. Six fresh-frozen amputated legs were analyzed with the new technique. Landmark digitations were used to define anatomical reference frames for the femur, tibia, and patella. Five trials of passive flexion were performed with 100 N force on the quadriceps, before and after standard knee arthroplasty. Patellar flexion, tilt, rotation and shift were calculated in addition to standard tibio-femoral (TF) joint kinematics. An intra-specimen repeatable path of motion over repetitions and a coupled path of motion throughout the flexion-extension cycle were observed in all intact knees, both at the TF and PF joints. Replication of the original PF motion in the intact knee was not fully accomplished in the replaced knee. These results revealed the feasibility and the necessity of patellar tracking during TKA. By monitoring intra-operatively also the PF kinematics, the surgeon has a more complete prediction of the performance of the final implant and therefore a valuable support for the most critical surgical decisions.

Knieprothesenkinematik

Until now it remains less clear to what extent the different types of endoprostheses can simulate the physiological motion pattern of the knee joint. The aim of this study was to present fluoroscopy and functional MRI as well as the results of these in vivo imaging techniques for TKA kinematics. Videofluoroscopy is a dynamic investigation, analyzing the subjects under fluoroscopic surveillance during different activities. Three-dimensional (3D) kinematics were recovered from the two-dimensional fluoroscopic images using a model-fitting technique. Kinematic analysis with functional MRI was performed in an open MR system at different flexion angles with external loads being applied during imaging. Femoropatellar and femorotibial 3D kinematics were analyzed by image postprocessing. The findings in healthy knees obtained with functional MRI under static conditions are in good agreement with the fluoroscopic outcome under dynamic conditions. In all investigated TKA in the mean an increased external rotated position of the femur relative to the tibia was observed at full extension, while the amount of external rotation during knee flexion was decreased. Although there was great variability among the individuals, differences were observed between the TKA-groups (e.g. posterior stabilized vs PCL retaining). Significant changes of femorotibial and femoropatellar kinematics were found in TKA compared to healthy knees, which may lead to early aseptic loosening or increased polyethylene wear The presented techniques and results allow for advanced in vivo diagnostics and may help to improve the design of TKA and to enhance the long-term performance.