Patellar Tracking Research Articles

To Resurface the Patella or Not? Better Assessments Needed to Address the Benefits for Total Knee Replacement

Low-friction metal-on-polyethylene primary total knee arthroplasty has been utilized for forty years, and anterior knee pain has been an issue for all of that time. The first implants either ignored the patellofemoral joint or even compromised it by means of a transverse metal bar that joined the medial and lateral condylar femoral components. Anterior knee pain was common, developing in 40% to 58% of patients1. As a result, attempts were made to address the patellofemoral joint in the design of future total knee arthroplasties. The first initiative was to add an anterior flange to the femoral component, and this was followed shortly by the addition of a polyethylene resurfacing button to the articular surface of the patella that articulated with the anterior flange of the femoral component2. The prevalence of anterior knee pain was greatly reduced by these changes, but it was not completely eliminated. Since that time, continued patellofemoral-related changes have been made, such as a move to specific right and left femoral components, closer replication of normal patellar tracking, and deepening of the patellar groove in the femoral component3. Despite these improvements, consensus was not reached with regard to how to deal with the patellofemoral joint during total knee arthroplasty. Complications …

Effects of medial patellofemoral ligament reconstruction on patellar tracking

Medial patellofemoral ligament (MPFL) reconstruction has been performed to treat recurrent patellar dislocation. However, the effects on patellar tracking have not been well documented, particularly in patients. The purpose of this study is to compare patellar tracking pattern and chondral status at MPFL reconstruction with those at second-look arthroscopy. Between 1999 and 2008, 71 patients with recurrent patellar dislocation underwent MPFL reconstruction using a double-looped semitendinosus tendon. Of these, 25 knees in 24 patients underwent second-look arthroscopy (at 6-26 months after initial surgery), forming the subject for the present study. No other surgical procedures such as tibial tuberosity transfer, lateral release, or osteotomy were performed in any patients. To assess the patellar tracking pattern, the position of the patella on femoral groove was evaluated arthroscopically during passive knee motion through lateral suprapatellar portal. Before MPFL reconstruction, the patella in all patients was shifted laterally throughout the entire range of knee motion. Immediately after MPFL reconstruction, patellar malalignment was corrected in all cases. On second-look arthroscopy, two different patellar tracking patterns were observed. In 9 knees, the patella was located on the center of the femoral groove throughout the range of motion. Meanwhile, in the remaining 16 knees, the patella was shifted laterally at knee extension and migrated to the center of femoral groove with increased knee flexion. No significant deteriorations in chondral status were seen on second-look arthroscopy. The present study revealed that not all improved patellar trackings after MPFL reconstruction remained intact at follow-up. Chondral status in patellofemoral joint was not aggravated by MPFL reconstruction. Therapeutic studies, Level IV.

The role of the medial ligamentous structures on patellar tracking during knee flexion

The influence of the medial patellar ligamentous structures on patellar tracking has rarely been studied. Thus the main purpose of this cadaveric biomechanical study was to determine the influence of the medial patellofemoral (MPFL), medial patellomeniscal (MPML) and medial patellotibial (MPTL) ligaments on the three-dimensional patellar tracking during knee flexion. This study was conducted using a validated cadaveric optoelectronic protocol for analysis of patellar kinematics. For each cadaveric knee study, four successive acquisitions were performed; first was studied patellar tracking in healthy knees, then the junction between MPFL and vastus medialis obliquus (VMO) was sectioned, the MPFL was released at its patellar attachment and finally was released the insertion of the MPML and MPTL. In this study, the MPFL accounts for 50-60% of the medial stabilization forces of the lateral patellar shift during patellar engagement in the femoral trochlea. This work confirm and clarify the role of the MPFL as the primary stabilizer of the patella during the initial 30° of knee flexion. Moreover, this study shows no significant results regarding the stabilizing action of the VMO on the patella during knee flexion. This in vitro study, conducted with an experimental protocol previously validated in the literature, helps quantify the actions of the MPFL, the VMO, and the MPML/MPTL respectively, and identify areas of joint motion where these structures have the most significant influence. This confirms the importance of reconstruction in the treatment of chronic patellar instability. During its reconstruction, care should be taken to adjust the MPFL balance during the initial 20°-30° of flexion.

Arthroscopic Medial Retinacular Imbrication for the Treatment of Recurrent Patellar Instability: A Simple and All-Inside Technique

Proximal soft tissue realignment is the main surgical intervention for recurrent patellar instability. In recent years, all-inside arthroscopic procedures or mini-open surgeries have replaced traditional surgeries, which have more associated morbidity and poor cosmetic results. This article describes a simple and all-inside arthroscopic technique for the operative treatment of recurrent patellar instability. Using 2 epidural needles in several steps and no accessory portals required, the medial patellar retinaculum is imbricated to the desired tension. The combination of lateral release and medial retinacular placation obviously improves the patellar tracking compared with preoperatively.

Inferior Dislocation of Patella after a Total Knee Replacement—A Case Report

Acute inferior dislocation of the patella is rare but has been documented. However, there has been no published report of inferior dislocation of the patella following a total knee replacement (TKR). A 62-year-old man underwent a posterior cruciate retaining TKR Anatomic Graduated Component (AGC) (Biomet, Warsaw, IN) without patellar resurfacing. Perioperative events were unremarkable. The patient presented a year later with an acutely painful locked knee at 60 degrees flexion. Physical examination and radiographs confirmed an inferior dislocation of the patella due to interlocking of superior pole patellar osteophytes on the anterior edge of the intercondylar box of the femoral component. Closed reduction under anesthesia failed and open reduction with debridement of the osteophytes resulted in excellent patellar tracking and a good functional result without any recurrence. Surgeons need to be aware of this rare complication of acute locked knee following TKR which may require open reduction. Also, the debridement of the osteophytes or even a resurfacing of the patella may be a more definitive solution to such patellofemoral problems.

La luxation de la rotule au cours d’une arthroplastie totale de genou est-elle déterminante sur l’ajustement de l’espace prothétique et l’équilibrage des parties molles ?

Summary Introduction Assessment of soft-tissue balance by the gap technique in Total Knee Arthroplasty (TKA) impacts femoral component rotation positioning. Proper femoral component rotation is a critical factor in TKA, both for adequate patellar tracking and in achieving a symmetrical flexion gap. Soft tissue balance assessment and gap measurements are performed at 90° flexion and with the patella everted in conventional TKA; during MIS-TKA, this step is performed with the patella in situ. We therefore investigated intra-operative joint gap parameters at 90° flexion with and without patellar eversion during conventional TKA, so as to better understand the influence of this intraoperative patellar position factor on final ligament balance. Hypothesis Conducting TKA without patellar eversion increases both gap size and gap inclination. Materials and methods Twenty-four osteoarthritic knees were included in the study. Joint gap size and inclination were measured intraoperatively on a knee in 90° flexion, with and without patellar eversion. Results The joint gap with patella in situ (17.0 ± 3.4 mm) was significantly greater than with patellar eversion (15.4 ± 3.0 mm), as was gap inclination at 90° flexion with the patella in situ (4.9 ± 3.1°) compared to with patellar eversion (4.0 ± 2.9°). Discussion The flexion gap inclination obtained without patellar eversion was steeper than with patellar eversion. This induced more externally rotated femoral positioning in absence of patellar eversion. These results ought to be taken into account by surgeons considering switching from conventional to MIS-TKA. Level of evidence Level II. Prospective randomized study.

Average 7-Year Survivorship and Clinical Results of a Newer Primary Posterior Stabilized Total Knee Arthroplasty

We evaluated the average 7-year survivorship and clinical results of a newer primary posterior stabilized total knee arthroplasty (TKA). The modifications in this design included a deeper patellar sulcus aimed at reducing contact stresses, improving patellar tracking, and achieving greater maximum flexion. A consecutive group of 137 patients (171 knees) who underwent TKAs using the Optetrak PS knee prosthesis between October 1997 and March 2004 were followed for an average of 6.8years (range 4.0-11.5years). Preoperative range of motion (ROM) and Knee Society scores were obtained and compared to that of the patients' most recent follow-up. Manipulation under anesthesia (MUA) and revision of the implant for any reason were considered endpoints for Kaplan-Meier survival analysis of all knees. Twenty-one knees (12.3%) underwent MUA. Three knees (1.8%) underwent revision, resulting in a 97.2% survival at a mean 10years follow-up. Pain scores and ROM significantly improved after surgery (from preoperative average of 5.3 and 105° respectively to 44.6 and 120° postoperatively). These findings suggest that this posterior stabilized knee design is both a safe and effective option for patients undergoing primary TKA.

The effect of femoral component rotation on the kinematics of the tibiofemoral and patellofemoral joints after total knee arthroplasty

Complications after total knee arthroplasty (TKA) often involve the patellofemoral joint, and problems with patellar maltracking or lateral instability have sometimes been addressed by external rotation of the femoral component. This work sought to measure the changes of knee kinematics caused by TKA and then to optimise the restoration of both the patellofemoral and tibiofemoral joint kinematics, by variation of femoral component internal-external rotation. The kinematics of the patella and tibia were measured in eight cadaveric knees during active extension motion. This was repeated with the knee intact, with a Genesis II TKA in the standard position (3° of external rotation) and with the femoral component at ±5° rotation from there. Both patellar and tibial motions were significantly different from normal with the standard TKA rotation, with 3° tibial abduction at 90° flexion and reversal of the screw-home from 5° external rotation to 6° internal rotation. The patella was shifted medially 6mm in flexion and tilted 7° more laterally near extension. Femoral rotation to address one abnormality caused increased abnormality in other degrees of freedom. Internal and then external rotation of 5° caused tibial abduction and then adduction of 5° at 90° flexion. These femoral rotations also caused increased patellar lateral tilt of 4° with femoral external rotation and decreased tilt by 4° with internal rotation. Thus, correction of tibial abduction in flexion, by external rotation of the femoral component, worsened the patellar lateral tilt near extension. It was concluded that femoral rotation alone could not restore all aspects of both patellar and tibial kinematics to normal with this specific implant. The clinical relevance of this is that it appears to be inadvisable to reposition the femoral component, in an attempt to improve patellar tracking, if that repositioning may then cause abnormal tibiofemoral kinematics. Further, the pattern of patellar tracking, with the type of TKA used in this study, could not be adjusted to normal by femoral component rotation.

Quantitative analysis of patellar tracking for screening of lateral patellar instability in adolescent population

BackgroundThe incidence of lateral patellar dislocation becomes higher with increased participation in sports activities in adolescence. A screening test to diagnose asymptomatic lateral patellar instability could be useful for prevention...

반 쪼그려 앉기(Semi-Squat) 운동 시 무릎뼈 주행(Tracking)과 Q-각도 분석

Closed kinematic chain exercises such as squatting have been widely indicated for knee rehabilitation in patients with patellofemoral disorders such as osteoarthritis and patellofemoral pain. Patellofemoral disorders are thought to be associated with abnormal patellar kinematics. In addition, the Q-angle may be undervalued in patients with patellofemoral pain and a laterally displaced patella. The purpose of this study was to assess patellar kinematics and the Q-angle during double-leg semi-squat and wall-slide semi-squat exercises. In this study, 28 asymptomatic subjects(16 male, 12 female) were assessed. Patellar tilt, patellar spin, and Q-angle were recorded using a motion analysis system during double-leg semi-squat and wall-slide semi-squat exercises. The Q-angle and patellar tilt were significantly increased, whereas patellar spin was significantly decreased, at <TEX>$45^{\circ}$</TEX> of knee flexion compared with <TEX>$0^{\circ}$</TEX>. No differences were observed for the Q-angle, patellar tilt, and patellar spin during double-leg semi-squat and wall-slide semi-squat exercises. However, a significant interaction was observed between squat type and knee angle for patellar spin. We found that the patella is laterally tilted during semi-squat exercises and that there was no difference in patellar tracking between knee flexion during double-leg semi-squat and wall-slide semi-squat exercises.

Is patella eversion during total knee arthroplasty crucial for gap adjustment and soft-tissue balancing?

Assessment of soft-tissue balance by the gap technique in Total Knee Arthroplasty (TKA) impacts femoral component rotation positioning. Proper femoral component rotation is a critical factor in TKA, both for adequate patellar tracking and in achieving a symmetrical flexion gap. Soft tissue balance assessment and gap measurements are performed at 90° flexion and with the patella everted in conventional TKA; during MIS-TKA, this step is performed with the patella in situ. We therefore investigated intraoperative joint gap parameters at 90° flexion with and without patellar eversion during conventional TKA, so as to better understand the influence of this intraoperative patellar position factor on final ligament balance. Conducting TKA without patellar eversion increases both gap size and gap inclination. Twenty-four osteoarthritic knees were included in the study. Joint gap size and inclination were measured intraoperatively on a knee in 90° flexion, with and without patellar eversion. The joint gap with patella in situ (17.0±3.4 mm) was significantly greater than with patellar eversion (15.4±3.0 mm), as was gap inclination at 90° flexion with the patella in situ (4.9±3.1°) compared to with patellar eversion (4.0±2.9°). The flexion gap inclination obtained without patellar eversion was steeper than with patellar eversion. This induced more externally rotated femoral positioning in absence of patellar eversion. These results ought to be taken into account by surgeons considering switching from conventional to MIS-TKA.

Femoral component rotation after balanced gap total knee replacement is not a predictor for postoperative patella position

Femoral component rotation is believed to be one of the factors influencing patellar tracking behavior. With the balanced gap implantation technique, the rotation of the femoral component can vary as it is guided by the ligaments. This study investigated whether femoral component rotation influenced patella position after primary total knee replacement (TKR). In this prospective cohort study, a primary TKR was implanted in 49 patients using a balanced gap technique and a CT-free navigation system. Femoral component rotation was measured using the navigation data of the distal femur cut, referenced from the posterior condyles. At the 2-year follow-up, lateral patellar tilt and patellar displacement were measured on axial patella radiographs. Logistic regression analysis on femoral component rotation and preoperative patella position was conducted to identify predictors for postoperative patellar tilt and displacement. Femoral component rotation that varied between -3 and 12° exorotation was not a predictor for postoperative tilt and displacement. Only preoperative displacement significantly predicted patella displacement. Although the balanced gap implantation technique resulted in a wide inter-patient variability for femoral component rotation, this variable rotation was not found to be associated with abnormal patellar position. Preoperative displacement results in a higher risk at a postoperatively displaced patella. The balanced gap technique can safely be used without an elevated risk for patella malposition.

A national survey of the physiotherapy management of patients following first-time patellar dislocation

Objectives The purpose of this study was to determine how musculoskeletal physiotherapists in acute National Health Service (NHS) hospitals manage patients following a first time patellar dislocation. Design National survey study. Setting All NHS acute hospitals with an accident and emergency and/or an orthopaedic department were surveyed. Participants 306 institutions were surveyed. Interventions Each institution was sent a 14 question self-administered questionnaire pertaining to the assessment, treatment, evaluation and outcome of patients following a first time patellar dislocation. After 3 weeks, all non-respondents were sent a reminder letter. After a further 3 weeks, those who had not responded by this time were sent a final reminder and copy of the questionnaire. Results The survey response rate was 59%. The respondents indicated that first-time patellar dislocation was not a common musculoskeletal disorder managed by NHS physiotherapists, constituting an average of 2% of caseloads. The results suggested that physiotherapists most commonly assess for reduced quadriceps or VMO capacity, gait, patellar tracking and glide, and knee effusion when examining patients following a first-time patellar dislocation. The most common treatments adopted are reassurance, behaviour modification followed by proprioceptive, knee mobility, quadriceps and specific VMO exercises. Conclusions Generic lower limb assessment and treatment strategies are widely used to manage this patient group. Given the previous paucity in this literature, further study is now recommended to assess the efficacy of these interventions to provide UK physiotherapists with an evidence-base to justify their management strategies.

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

The purpose of this in vitro study was to investigate the influence of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral pressure. A dynamic muscle-loaded knee squat was simulated on eight knee specimens with an upright knee simulator while measuring tibiofemoral joint kinematics and patellofemoral pressure distribution. The quadriceps muscle was attached to three actuators simulating the three main extensor muscles, and five different quadriceps loading patterns were tested. Tibial axial and varus-valgus-rotation are affected most while changing quadriceps loading patterns from lateral to medial. Higher internal tibial rotation is associated with higher medial muscle load compared to the symmetrical loading condition. Contact force, contact area and maximum peak pressure rise with increasing flexion angles. Accentuating the vastus lateralis muscle induces a significant reduction in patellofemoral contact force and a 30% diminished contact area at 90° of flexion. Strengthening the vastus medialis muscle leads to increased internal tibial rotation, thus optimizing patella tracking by lowering the Q-angle. In contrast, weakness of the vastus medialis muscle causes decreased tibial internal rotation and is associated with lower patellofemoral contact pressure and contact area. Vastus medialis exercise is advisable to improve patella tracking but may not be recommended in patients with disorders due to increased patellofemoral contact pressure.

An initial study of tracking movement of normal patellar using volume scan on sensation 320 CT

Objective To evaluate the diagnostic value of tracking movement of normal patellar using volume scan on sensation 320 CT. Method Data of dynamic scans of 30 knees was collected using the motor function of 320 CT and retrospectively analyzed. The data of movement of the patellorfemoral joint was obtained during flexion (from 0° to 120°) within 10-sec by 320 CT from all volunteers. The 3D coordinate of the center of patella was recorded to investigate the dispose relation of patellofemoral joint.Result With the knee angle changed from 0° to 90°, the patella moved rapidly along the Y-axis direction ( sagittal plane) down about (53.87 ± 0. 45 ) mm, and then entered the plateau phase with little change.When the knee flexion reached 10°-30° ,the patellar movement along the X-axis reached the largest range of (2. 31 ±0. 52)-(3.36 ± 0. 43 ) mm, and subsequently moved to the opposite lateral direction with the maximum about (8. 53 ± 0. 44 ) mm at 120°. In the Z axis, the track initially showed plateau, and then presented a rapidly downward trend after 30°. The patellar tracking is like an outward arc during the whole knee flexion. Conclusion The motor functional imaging of 320 CT can pinpoint the patelar tracking in a fast, painless way. Key words: Patella; Tracking movement; Tomography,X-ray computed

Total Diz Artroplastisinde Midvastus Yaklaşımına Karşılık Medial Parapatellar Yaklaşım: Erken Fonksiyonel Sonuçların Karşılaştırılması

Objective: The purpose of this study was to compare the early outcomes of total knee arthroplasty (TKA) using midvastus (MV) versus medial parapatellar (MPP) approaches on both knees. Material and Methods: Fifty two consecutive patients (104 knees) who underwent single-stage bilateral TKA performed by two surgeons between August 2004 and December 2007 were evaluated retrospectively at a minimum follow-up duration of two years. Patients were divided into two groups. In the MV group, consisted of 27 patients, a midvastus approach was performed on both knees. Besides, in the MPP group, consisted of 25 patients, a medial parapatellar approach was performed on both knees. Results: Mean follow-up duration was 40.2 months (27-66 months) and 42.3 months (25-61 months) for the MV and MPP groups, respectively. The Knee Society Clinical Rating System (knee and function score), the range of motion, patellofemoral pain questionnaire, patient satisfaction questionnaire and radiography were used for the evaluation of both groups. Lateral retinacular release (LRR) was performed on four knees in the MPP group whereas it was not used in the MV group. There was a significant difference between the two groups with regard to the rate of LRR (p= 0.034). Axial radiographs revealed that six patellas in the MPP group, but only one in the MV group exhibited lateral displacement postoperatively (p= 0.039). Conclusion: The preservation of normal patellar tracking is important for TKA. In this study, the midvastus approach required significantly less LRR as compared to the medial parapatellar approach.

Patellofemoral kinematics in mobile-bearing and fixed-bearing posterior stabilised total knee replacements: a cadaveric study

The aim was to compare the patellar kinematics in the normal knee, fixed-bearing (FB) and mobile-bearing total knee replacement (MB-TKR). The hypothesis that a mobile-bearing TKR has a more natural patellar movement was tested. Computer navigation was used to track the patella in nine whole lower extremities in the natural knee and in the same knee with a posterior stabilised FB-TKR and a posterior stabilised MB-TKR from 0° to 90° flexion. The form and position of the trochlea in the natural knee and the patellar groove of the TKR femoral component was also analysed. There were no differences between the FB and MB-TKRs. But the patella in the TKRs at flexion angles of more than 50° had a more medial tilt compared to the natural knee. The patella of the natural knee tended to rotate externally with flexion, this was not seen in both TKR types. There were no significant differences in absolute mediolateral translation nor in translation relative to the patellar groove. During flexion, the patella lost contact with its groove earlier in the TKRs. The radius of the patellar groove of the femoral component was larger. The groove extended more superiorly and less far posteriorly, it was also positioned further laterally compared to the natural knee. There are subtle kinematic differences in patellar tracking between the natural knee and a TKR presumably due to differences in the shape and position of the patellar groove. There are no kinematic differences in patellar movement between the FB- and MB-TKR.

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.

Differences in patellofemoral kinematics between weight‐bearing and non‐weight‐bearing conditions in patients with patellofemoral pain

Patellar maltracking is thought to be one source of patellofemoral pain. Measurements of patellar tracking are frequently obtained during non-weight-bearing knee extension; however, pain typically arises during highly loaded activities, such as squatting, stair climbing, and running. It is unclear whether patellofemoral joint kinematics during lightly loaded tasks replicate patellofemoral joint motion during weight-bearing activities. The purpose of this study was to: evaluate differences between upright, weight-bearing and supine, non-weight-bearing joint kinematics in patients with patellofemoral pain; and evaluate whether the kinematics in subjects with maltracking respond differently to weight-bearing than those in nonmaltrackers. We used real-time magnetic resonance imaging to visualize the patellofemoral joint during dynamic knee extension from 30° to 0° of knee flexion during two conditions: upright, weight-bearing and supine, non-weight-bearing. We compared patellofemoral kinematics measured from the images. The patella translated more laterally during the supine task compared to the weight-bearing task for knee flexion angles between 0° and 5° (p = 0.001). The kinematics of the maltrackers responded differently to joint loading than those of the non-maltrackers. In subjects with excessive lateral patellar translation, the patella translated more laterally during upright, weight-bearing knee extension for knee flexion angles between 25° and 30° (p = 0.001). However, in subjects with normal patellar translation, the patella translated more laterally during supine, non-weight-bearing knee extension near full extension (p = 0.001). These results suggest that patellofemoral kinematics measured during supine, unloaded tasks do not accurately represent the joint motion during weight-bearing activities.

Case Report: Quantitative MRI of Tibial Tubercle Transfer During Active Quadriceps Contraction

The evaluation of distal transfer procedures relies primarily on qualitative clinical findings. Although quantitative MRI measurements provide an objective supplement to qualitative clinical findings, an association between qualitative clinical findings and quantitative patellofemoral indices has yet to be established. A 21-year-old man presented with frequent episodes of patellar dislocation. Clinical and radiographic findings identified the patient as a candidate for realignment. MR images were obtained with the quadriceps contracted at 30° flexion and in full extension preoperatively and postoperatively. The procedure eliminated the clinical J-sign, defined as lateral movement of the patella over the lateral femoral condyle during active leg extension, which was confirmed quantitatively using established patellofemoral indices in conjunction with MRI. Movement of the patellofemoral joint is complex and dependent on many factors, including skeletal geometry, dynamic muscle action, and soft tissue restraints. Therefore, proper clinical and radiographic evaluation of patellar tracking requires observation during active quadriceps contraction. However, it is unclear whether there is any association between quantitative radiographic indices and qualitative clinical assessment during active quadriceps contraction. We believe objective measurements are valuable in determining the radiographic assessment of patellar realignment procedures. Lateral patellar edge appears to quantify the clinical J-sign. The association between radiographic medialization of the patella and clinical improvement postoperatively in this patient warrants additional investigation in a larger group of patients with longer followup.