The effects of trochlear groove geometry on patellofemoral joint stability-a computer model study

Influence of Articular Geometry and Tibial Tubercle Location on Patellofemoral Kinematics and Contact Mechanics

Trochlear groove geometry and the location of the tibial tubercle, where the patellar tendon inserts, have both been associated with patellofemoral instability and can be modified surgically. Although their effects on patellofemoral biomechanics have been investigated individually, the interaction between the two is unclear. The authors' aim was to use statistical shape modeling and musculoskeletal simulation to examine the effect of patellofemoral geometry on the relationship between tibial tubercle location and patellofemoral function. A statistical shape model was used to generate new knee geometries with trochlear grooves ranging from shallow to deep. A Monte Carlo approach was used to create 750 knee models by randomly selecting a geometry and randomly translating the tibial tubercle medially/laterally and anteriorly. Each knee model was incorporated into a musculoskeletal model, and an overground walking trial was simulated. Knees with shallow trochlear geometry were more sensitive to tubercle medialization with greater changes in lateral patella position (-3.0 mm/cm medialization shallow vs -0.6 mm/cm deep) and cartilage contact pressure (-0.51 MPa/cm medialization shallow vs 0.04 MPa/cm deep). However, knees with deep trochlear geometry experienced greater increases in medial cartilage contact pressure with medialization. This modeling framework has the potential to aid in surgical decision making.

Mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint using in vivo laxity tests

BACKGROUND

The purpose of this study was to propose a methodology for mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint (PFJ) of living individuals.

METHOD

PFJ laxity tests were performed on a healthy volunteer using a specially designed loading apparatus under biplane fluoroscopy. A three-dimensional (3D) parametric model of the PFJ was developed in the framework of the rigid body spring model using the geometrical data acquired from the subject's computed tomography and magnetic resonance images. The stiffness and pre-strains of the medial and lateral PFJ ligaments were characterized using a two-step optimization procedure which minimized the deviation between the model predictions and the calibration test results. Sensitivity analyses were performed to investigate the effect of mechanical properties of the non-characterized model components on the characterization procedure and its results.

RESULTS

The overall findings indicate that the proposed methodology is applicable and can improve the model predictions effectively. For the subject under study, ligament characterization reduced the root mean square of the deviations between the patellar shift and tilt predicted by the model and obtained experimentally for the validation laxity test (from 6.2 mm to 0.5 mm, and from 8.4° to 1.5°, respectively) and passive knee flexion test (from 1.4 mm to 0.3 mm, and from 2.3° to 1.3°, respectively). The non-characterized mechanical properties were found to have a minimal effect on the characterization procedure and its results.

CONCLUSION

The proposed methodology can help in developing truly patient-specific models of the PFJ, to be used for personalized preplanning of the clinical interventions.

Anteroposterior distance between the tibial tuberosity and trochlear groove in patients with patellar instability

BACKGROUND

Our objective was to describe a measurement to assess sagittal tibial tuberosity (TT)-trochlear groove (TG) distance and to compare this between asymptomatic (control) patients and patients with symptomatic patellar instability.

METHODS

We compared static CT images of 22 fully extended knees of patients with symptomatic patellar instability with images of 22 asymptomatic knees. TT-TG distance was measured to quantify lateralization of the TT, and anteroposterior TT-TG distance was used to quantify the sagittal distance between these two points. Lateral trochlear inclination, sulcus angle, and trochlear depth were measured. Groups were compared using paired t tests (alpha = 0.05). Correlations of anteroposterior TT-TG distance with lateral trochlear inclination, sulcus angle, and trochlear depth were assessed using linear and multivariate regression.

RESULTS

Mean TT-TG distances were 19.9 ± 4.4 mm (symptomatic) and 16.8 ± 5.5 mm (control) (mean ± std deviation) (P = 0.002). Mean anteroposterior TT-TG distances were 8.3 ± 7.8 mm (symptomatic) and -0.5 ± 4.6 mm (control) (P < 0.0001). The symptomatic group had greater measurements of trochlear dysplasia, with lower lateral trochlear inclination, greater sulcus angle, and lower trochlear depth (all P < 0.0001). Anteroposterior TT-TG distance and trochlear depth were strongly negatively correlated (r = 0.62, R² = 0.39, P < 0.0001).

CONCLUSIONS

In asymptomatic patients, the anteroposterior TT-TG distance was -0.5 mm, indicating that the TG and TT were nearly in the same coronal plane. In patients with symptomatic patellar instability, the TG was almost nine millimeters anterior, and this distance correlated with measurements of trochlear dysplasia.

LEVEL OF EVIDENCE

III, case control study.

The effect of articular geometry features identified using statistical shape modelling on knee biomechanics

Articular geometry in the knee varies widely among people which has implications for risk of injury and pathology. The goals of this work were to develop a framework to systematically vary geometry in a multibody knee model and to use this framework to investigate the effect of morphological features on dynamic knee kinematics and contact mechanics. A statistical shape model of the tibiofemoral and patellofemoral joints was created from magnetic resonance images of 14 asymptomatic knees. The shape model was then used to generate 37 unique multibody knee models based on -3 to +3 standard deviations of the scores for the first six principal components identified. Each multibody model was then incorporated into a lower extremity musculoskeletal model and the Concurrent Optimization of Muscle Activations and Kinematics (COMAK) routine was used to simulate knee mechanics for overground walking. Changes in articular geometry affected knee function, resulting in differences up to 17° in orientation, 8 mm in translation, 0.7 BW in contact force, and 2.0 MPa in mean cartilage contact pressure. Understanding the relationship between shape and function in a joint could provide insight into the mechanisms behind injury and pathology and the variability in response to treatment.

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.

The use of rapid prototyped implants to simulate knee joint abnormalities for in vitro testing: A validation study with replica implants of the native trochlea

To investigate the biomechanical effect of skeletal knee joint abnormalities, the authors propose to implant pathologically shaped rapid prototyped implants in cadaver knee specimens. This new method was validated by replacing the native trochlea by a replica implant on four cadaver knees with the aid of cadaver-specific guiding instruments. The accuracy of the guiding instruments was assessed by measuring the rotational errors of the cutting planes (on average 3.01° in extension and 1.18° in external/internal rotation). During a squat and open chain simulation, the patella showed small differences in its articulation with the native trochlea and the replica trochlea, which could partially be explained by the rotational errors of the implants. This study concludes that this method is valid to investigate the effect of knee joint abnormalities with a replica implant as a control condition to account for the influence of material properties and rotational errors of the implant.

Subject-specific analysis of joint contact mechanics: application to the study of osteoarthritis and surgical planning

Advances in computational mechanics, constitutive modeling, and techniques for subject-specific modeling have opened the door to patient-specific simulation of the relationships between joint mechanics and osteoarthritis (OA), as well as patient-specific preoperative planning. This article reviews the application of computational biomechanics to the simulation of joint contact mechanics as relevant to the study of OA. This review begins with background regarding OA and the mechanical causes of OA in the context of simulations of joint mechanics. The broad range of technical considerations in creating validated subject-specific whole joint models is discussed. The types of computational models available for the study of joint mechanics are reviewed. The types of constitutive models that are available for articular cartilage are reviewed, with special attention to choosing an appropriate constitutive model for the application at hand. Issues related to model generation are discussed, including acquisition of model geometry from volumetric image data and specific considerations for acquisition of computed tomography and magnetic resonance imaging data. Approaches to model validation are reviewed. The areas of parametric analysis, factorial design, and probabilistic analysis are reviewed in the context of simulations of joint contact mechanics. Following the review of technical considerations, the article details insights that have been obtained from computational models of joint mechanics for normal joints; patient populations; the study of specific aspects of joint mechanics relevant to OA, such as congruency and instability; and preoperative planning. Finally, future directions for research and application are summarized.

A detailed and validated three dimensional dynamic model of the patellofemoral joint

A detailed 3D anatomical model of the patellofemoral joint was developed to study the tracking, force, contact and stability characteristics of the joint. The quadriceps was considered to include six components represented by 15 force vectors. The patellar tendon was modeled using four bundles of viscoelastic tensile elements. Each of the lateral and medial retinaculum was modeled by a three-bundle nonlinear spring. The femur and patella were considered as rigid bodies with their articular cartilage layers represented by an isotropic viscoelastic material. The geometrical and tracking data needed for model simulation, as well as validation of its results, were obtained from an in vivo experiment, involving MR imaging of a normal knee while performing isometric leg press against a constant 140 N force. The model was formulated within the framework of a rigid body spring model and solved using forth-order Runge-Kutta, for knee flexion angles between zero and 50 degrees. Results indicated a good agreement between the model predictions for patellar tracking and the experimental results with RMS deviations of about 2 mm for translations (less than 0.7 mm for patellar mediolateral shift), and 4 degrees for rotations (less than 3 degrees for patellar tilt). The contact pattern predicted by the model was also consistent with the results of the experiment and the literature. The joint contact force increased linearly with progressive knee flexion from 80 N to 210 N. The medial retinaculum experienced a peak force of 18 N at full extension that decreased with knee flexion and disappeared entirely at 20 degrees flexion. Analysis of the patellar time response to the quadriceps contraction suggested that the muscle activation most affected the patellar shift and tilt. These results are consistent with the recent observations in the literature concerning the significance of retinaculum and quadriceps in the patellar stability.

Relationship between the trochlear groove angle and patellar cartilage morphology defined by 3D spoiled gradient-echo imaging

OBJECTIVE

To examine whether the femoral trochlear groove angle (TGA) is a determinant of the patellar cartilage volume and patellar cartilage damage.

MATERIALS AND METHODS

Patellar cartilage was evaluated by MR imaging in 66 patients (22 males and 44 females) with knee pain. Fat-suppressed 3D spoiled gradient-echo images were used to calculate the cartilage volume and to grade the cartilage damage. The proximal and distal TGAs were measured from axial PD-weighted FSE MR images with fat suppression.

RESULTS

For every increase in the TGA at the distal femur, the patellar cartilage volume was significantly increased by 6.07 × 10(-3) cm(3) (95% CI: 1.27 × 10(-3), 10.9 × 10(-3)) after adjustment for age, gender, and patellar bone volume (P < 0.05). The MR grade of medial patellar cartilage damage progressed as the distal TGA became narrower, although there was no significant correlation between the distal TGA and the MR grading of patellar cartilage damage.

CONCLUSION

A more flattened distal TGA was associated with increased patellar cartilage volume. However, there was no association between TGA and patellar cartilage defects.

What activities do patients with patellar instability perceive makes their patella unstable?

Patellar instability is a disabling musculoskeletal condition. Whilst previous texts have suggested that twisting activities may cause patients to experience instability symptoms, no studies have assessed which activities are related to the patient's perceived instability. The purpose of this study was to determine which activities and with what frequency patients with patellar instability symptoms, perceive their patella to be unstable. Ninety patients referred because of recurrent patellar instability were asked to assess the frequency with which they perceived patellar instability for 19 everyday and sporting activities. The results indicated that sporting and multi-directional twisting activities were more frequently related to patellar instability symptoms, compared to lower energy, uni-planar activities. Females and those without a family history of patellar instability reported more frequent patellar instability symptoms, compared to males, or those with a family history of this disorder. Further study is now recommended to determine whether these results reflect that of patients with milder subluxation disorders, and whether factors such as hypermobility have an impact on perceived patellar instability for this patient group.

Gracilis tendon transfer associated with distal alignment for patella alta with recurrent dislocations: an original surgical technique

Many surgical techniques for the medial patellofemoral ligament have recently been suggested, all of which included problems identifying the femoral anchorage point and determining the proper extent of knee flexion for the transplant. P. Burdin proposed a different and original approach consisting in performing a gracilis muscle transfer to the medial edge of the patella, thus obtaining progressive tension of the transfer during knee flexion by means of the myotatic reflex. We report the results herein. We retrospectively assessed 17 knees treated for patellofemoral instability using this technique. Two cases presented subjective patellofemoral instability and 15 presented objective patellofemoral instability. The patients' mean age was 17.4 years (range, 8-47 years) during the first episode of dislocation. Two cases of instability were secondary to advanced neuromuscular disease. Two knees had already undergone two stabilization attempts. Fifteen knees presented trochlear dysplasia (four stage A, eight stage B, and three stage C). The mean age at surgery was 28.2 years (range, 16-47 years). In 15 cases, the gracilis transfer was associated with lowering the anterior tibial tuberosity (mean, 10mm). No patellar fracture occurred. A persistent sensory deficit of the anterior branch of the internal saphenous nerve was observed in 15 cases. One knee remained painful and retained subjective instability; total knee arthroplasty was performed 3 years after the intervention. The mean follow-up at revision was 5.5 years (range, 1.5-16.5 years). No recurrence of dislocation was reported. Eight cases retained subjective instability. The SF-36 and IKDC scores were good or excellent in 12 cases and the KOOS was good or excellent in 13 cases. Radiologically, patellar tilt persisted in six cases out of 14, translation persisted in two cases out of 14, and secondary patella baja was observed in one. Medial patellofemoral osteoarthritis was observed in five cases: one case IWANO stage I and four cases IWANO stage II. These satisfactory results seem stable over time and were acquired using a simple procedure with reduced morbidity, making it possible to avoid significant displacement of the anterior tibial tuberosity and stabilize the extensor apparatus. It can also be hoped that the onset of secondary patellofemoral osteoarthritis, undoubtedly inevitable, has been delayed.

Patellar maltracking correlates with vastus medialis activation delay in patellofemoral pain patients

BACKGROUND

Delayed onset of vastus medialis (VM) activity compared with vastus lateralis activity is a reported cause for patellofemoral pain. The delayed onset of VM activity in patellofemoral pain patients likely causes an imbalance in muscle forces and lateral maltracking of the patella; however, evidence relating VM activation delay to patellar maltracking is sparse. The aim of this study was to investigate the relationship between VM activation delay and patellar maltracking measures in pain-free controls and patellofemoral pain patients.

HYPOTHESIS

Patellar tilt and bisect offset, measures of patellar tracking, correlate with VM activation delay in patellofemoral pain patients classified as maltrackers.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Vasti muscle activations were recorded in pain-free (n = 15) and patellofemoral pain (n = 40) participants during walking and jogging. All participants were scanned in an open-configuration magnetic resonance scanner in an upright weightbearing position to acquire the position of the patella with respect to the femur. Patellar tilt and bisect offset were measured, and patellofemoral pain participants were classified into normal tracking and maltracking groups.

RESULTS

Correlations between VM activation delay and patellar maltracking measures were statistically significant in only the patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset (R(2) = .89, P < .001, with patellar tilt during walking; R(2) = .75, P = .012, with bisect offset during jogging). There were no differences between the means of activation delays in pain-free and all patellofemoral pain participants during walking (P = .516) or jogging (P = .731).

CONCLUSION

There was a relationship between VM activation delay and patellar maltracking in the subgroup of patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset.

CLINICAL RELEVANCE

A clinical intervention such as VM retraining may be effective in only a subset of patellofemoral pain participants-namely, those with excessive tilt and excessive bisect offset measures. The results highlight the importance of appropriate classification of patellofemoral pain patients before selection of a clinical intervention.

Relationship between three-dimensional geometry of the trochlear groove and in vivo patellar tracking during weight-bearing knee flexion

It is widely recognized that the tracking of patella is strongly influenced by the geometry of the trochlear groove. Nonetheless, quantitative baseline data regarding correlation between the three-dimensional geometry of the trochlear groove and patellar tracking under in vivo weight-bearing conditions are not available. A combined magnetic resonance and dual fluoroscopic imaging technique, coupled with multivariate regression analysis, was used to quantify the relationship between trochlear groove geometry (sulcus location, bisector angle, and coronal plane angle) and in vivo patellar tracking (shift, tilt, and rotation) during weight-bearing knee flexion. The results showed that in the transverse plane, patellar shift was strongly correlated (correlation coefficient R=0.86, p<0.001) to mediolateral location of the trochlear sulcus (raw regression coefficient β(raw)=0.62) and the trochlear bisector angle (β(raw)=0.31). Similarly, patellar tilt showed a significant association with the trochlear bisector angle (R=0.45, p<0.001, and β(raw)=0.60). However, in the coronal plane patellar rotation was poorly correlated with its matching geometric parameter, namely, the coronal plane angle of the trochlea (R=0.26, p=0.01, β(raw)=0.08). The geometry of the trochlear groove in the transverse plane of the femur had significant effect on the transverse plane motion of the patella (patellar shift and tilt) under in vivo weight-bearing conditions. However, patellar rotation in the coronal plane was weakly correlated with the trochlear geometry.

The role of trochlear dysplasia in patellofemoral instability

Trochlear dysplasia is characterized by abnormal trochlear morphology and a shallow groove. It is associated with recurrent patellar dislocation, but it is unclear whether the dysplasia is congenital, the result of lateral tracking and chronic instability, or caused by a combination of factors. Lateral radiographs elucidate the crossing sign and characteristic trochlear prominence. Recurrent patellofemoral instability is multifactorial, and each component must be considered in determining treatment. Managing other factors associated with recurrent instability may compensate for a deficient trochlea and provide stability. Medial patellofemoral ligament reconstruction is recommended for patellofemoral instability in the presence of trochlear dysplasia in patients without patella alta or increased tibial tubercle-trochlear groove distance. Trochleoplasty should be reserved for severe dysplasia in which patellofemoral stability cannot otherwise be obtained.

Analysis of the patellofemoral region on MRI: association of abnormal trochlear morphology with severe cartilage defects

OBJECTIVE

The objective of our study was to assess patellofemoral measurements on MRI and to correlate the measurements with different grades of cartilage defect.

MATERIALS AND METHODS

Axial and sagittal MR images of 100 patients with various pathologic knee conditions were analyzed. The patients were divided into two age groups: < 40 years and > or = 40 years. Patellar measurements of facet asymmetry, the patella-to-patellar tendon ratio, and the amount of patellotrochlear cartilage overlap were obtained in each subject. Similarly, trochlear measurements of the ventral trochlear prominence, trochlear depth, facet asymmetry, sulcus angle, and lateral inclination were obtained. Axial and sagittal MR images were reviewed to grade the severity of focal cartilage defects in the patellofemoral region on the basis of the depth of the lesion. Measurements in knees without a chondral defect were compared with knees with mild and severe chondral defects.

RESULTS

There was a statistically significant difference in the trochlear measurements of the ventral prominence (p = 0.012), trochlear depth (p = 0.001), sulcus angle (p = 0.208), and lateral inclination (p = 0.154) between normal knees and knees with severe cartilage defects in patients younger than 40 years. No significant difference was seen in the patellar measurements between normal knees and knees with severe cartilage defects.

CONCLUSION

There is an association between abnormal trochlear morphology and severe patellofemoral cartilage defects in patients younger than 40 years.

Review article: Patellar instability after total knee arthroplasty

Patellar instability after total knee arthroplasty (TKA) is a serious complication that impairs functional outcome and may lead to revision surgery. Its aetiology can be related to the surgical technique and component positioning, extensor mechanism imbalance, and other causes. After TKA, the presence of anterior knee pain, especially during stressful activities, is indicative of patellar instability. Diagnosis can be made by radiological evaluation of the patella position, alignment, and component fixation. Main treatment options include revision of the TKA components (in case of malposition) and lateral retinacular release with or without a proximal or distal realignment (in case of soft-tissue imbalance).

Baseline articular contact stress levels predict incident symptomatic knee osteoarthritis development in the MOST cohort

We studied whether contact stress estimates from knee magnetic resonance images (MRI) predict the development of incident symptomatic tibiofemoral osteoarthritis (OA) 15 months later in an at-risk cohort. This nested case-control study was conducted within a cohort of 3,026 adults, age 50 to 79 years. Thirty cases with incident symptomatic tibiofemoral OA by their 15 month follow-up visit were randomly selected and matched with 30 control subjects. Symptomatic tibiofemoral OA was defined as daily knee pain/stiffness and Kellgren-Lawrence Grade > or =2 on weight bearing, fixed-flexion radiographs. Tibiofemoral geometry was segmented on baseline knee MRI, and contact stresses were estimated using discrete element analysis. Linear mixed models for repeated measures were used to examine the association between articular contact stress and case/control status. No significant intergroup differences were found for age, sex, BMI, weight, height, or limb alignment. However, the maximum articular contact stress was 0.54 +/- 0.77 MPa (mean +/- SD) higher in incident OA cases compared to that in control knees (p = 0.0007). The interaction between case-control status and contact stress was significant above 3.20 MPa (p < 0.0001). The presence of differences in estimated contact stress 15 months prior to incidence suggests a biomechanical mechanism for symptomatic tibiofemoral OA and supports the ability to identify risk by subject-specific biomechanical modeling.

A rigid body spring model to investigate the lateral shift - restraining force behavior of the patella

Patellar lateral stability was studied using a 2D transverse plane model with deformable articular surfaces. Quadriceps muscles and patellar tendon were considered as strings with predefined forces and lateral and medial retinaculum as tensile springs. Deformation behavior of articular cartilage was modeled by a set of compression springs perpendicular to articular surfaces, based on rigid body spring model method (RBSM). Patellar lateral stability was investigated using restraining force method (the external force required to cause up to 10 mm lateral displacement on patella). The results were in good agreement with experimental reports for normal joint, vastus lateralis and vastus medialis relieved. Small changes in the femoral trochlear groove geometry provided significant variation in patellar stability. Simulation of different surgical treatments showed that the tibial tubercle medialization is the most effective procedure for patellar subluxation and dislocation disorders.