New insights into the function of the vastus medialis with clinical implications

PURPOSE: To investigate the gross anatomy of the distal portion of the quadriceps, and to compare the relative contributions of the vastus medialis oblique (VMO) and vastus lateralis (VL) during dynamic weight-bearing conditions. METHODS: Dissection was carried out on 10 cadavers by a longitudinal incision from the anterior superior iliac spine to the patella and completed with upper and lower transverse cuts to reinvestigate the gross anatomy and innervation patterns of the quadriceps femoris. A biomechanical test of knee kinematics was conducted on 10 healthy male volunteers. Maximal isometric force, squat jump, and drop movement jump exercises were performed on a force plate and filmed using a Saga-3 3D system, and surface EMG activity was recorded for the VMO and the VL. RESULTS: The oblique fibers of the vastus medialis (VM) are not only attached to the medial border of the patella, but they also have a small region of direct continuity with the patellar tendon. Furthermore, VMO fibers in the middle and proximal thirds of the thigh attached to vastus intermedius, whereas distally, the fibers were independent. Both parts of the VM (proximal and distal) had independent motor points. During jumping exercises, the VMO and VL were activated in a coordinated manner in a squat jump using both legs. However, in a single-leg squat jump (which challenged the stability of the knee joint more acutely), VMO activation was higher during landing. CONCLUSION: VMO activity was pronounced during the weight-bearing conditions, with increased medial and lateral knee movements. This suggests that the VM should not be considered simply as a knee extensor or as a muscle whose main role is to maintain normal patellar tracking.     

In vivo and noninvasive load sharing among the vasti in patellar malalignment

PURPOSE: It is not clear how the knee extension torque is distributed quantitatively among the lateral and medial vasti in patellofemoral pain (PFP) patients with patellar malalignment, which was investigated in vivo and noninvasively in ten PFP patients and eleven controls. We hypothesized that the vastus medialis oblique (VMO) and vastus medialis longus (VML) of PFP patients contribute less to knee extension than that in controls. METHODS: Electrical stimulation was used to activate each vastus component selectively. The relationship between the knee extension torque generated by each individual vastus component and the corresponding compound muscle action potential (M-wave) was established over different contraction levels, which was used to calibrate the corresponding voluntary EMG signal and determine torque ratios of VMO/VL (vastus lateralis), VMO/VML, VML/VL and (VMO+VML)NL during voluntary isometric knee extension. RESULTS: The VMO and VML of PFP patients contributed significantly less to knee extension than their counterparts in controls. The combination of VMO and VML generated comparable amount of extension torque as the VL in the controls, while it produced significantly lower extension torque than that of the VL in the PFP patients. In addition, the VMO/VL was lower than VMO/VML and VML/VL in both PFP and control groups. CONCLUSIONS: Compared to controls, the VMO and VML in the PFP patients contributed significantly less to the knee extension torque. The approach can be used to investigate load sharing among quadriceps muscles in vivo and noninvasively, in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.     

Quantification of patellar tracking using kinematic MRI

The purpose of this study was to describe a method to quantify dynamic patellar tracking using kinematic MRI (KMRI). Twelve normal females and three patients with patellofemoral pain participated. Imaging was performed with a 1.5-T/64-MHz MR system using a fast spoiled gradient-recalled acquisition in the steady state (GRASS) pulse sequence. A nonferromagnetic positioning device permitted active, bilateral knee extension against resistance (15% bwt) from 45° knee flexion to full extension. Subjects were instructed to extend their knees at a rate of 9° per second, which allowed images to be obtained at 45°, 36°, 27°, 18°, 9°, and 0°. All images were assessed for medial/lateral patellar displacement, patellar tilt, and sulcus angle using a computer-aided system. Normal patellar motion was characterized by medial movement from 45° to 18°, followed by a reversal toward lateral displacement from 18° to full extension. The results for patellar tilt revealed a tendency toward decreasing lateral tilt as the knee extended. Sulcus angle measurements indicated that the patella was moving to a more shallow portion of the trochlear groove (superiorly) during extension.     

Kinematic CT and MR imaging of the patellofemoral joint

Anterior knee pain is a frequently encountered orthopedic symptom and is often associated with patellofemoral malalignment, which may cause chondromalacia of the patella. The difficulty in determining the patellar position between 0 ° and 30 ° of knee flexion with a conventional axial radiographic examination is well known. The introduction of computed tomography (CT) and magnetic resonance (MR) imaging for the diagnosis of knee joint abnormalities has enabled assessment of the patellar position in this critical range. More recently, emphasis has been placed on dynamic visualization of patellar motion to detect an abnormal tracking pattern. The important influence of the quadriceps muscle on the patellar tracking pattern is well known and has been examined during active knee extension by the use of ultrafast CT, and motion-triggered and ultrafast MR imaging. This article provides an overview of the current status of kinematic CT and MR imaging in the diagnosis of patellofemoral alignment, its clinical implications, and future directions. Received: 6 April 1998; Revision received: 22 July 1998; Accepted: 27 July 1998     

Active patellar tracking measurement: a novel device using ultrasound

BACKGROUND: Many patients suffer patellar instability that may relate to transient patellar tracking abnormalities. OBJECTIVE: To develop and test a technique to measure dynamic patellar tracking. STUDY DESIGN: Controlled laboratory and in vivo study. METHOD: A functional knee brace was modified to allow an ultrasound transducer to be mounted laterally to the femur, following the path of the patella during knee movement. An ultrasound system was used to measure patellar mediolateral position parallel to the femoral transepicondylar axis. Ten subjects with no patellar instability were studied to obtain patellar tracking and accuracy data. RESULTS: The interobserver and intraobserver reproducibility ranged from 0.2 +/- 0.1 mm to 1.0 +/- 0.5 mm. The accuracy of the ultrasound measurement was checked against magnetic resonance imaging and was 0.6 +/- 1.9 mm. The patella moved medially then laterally from extension to flexion when sitting. Squatting and stepping produced a more lateral path, without the initial medial translation. The patella was more lateral during knee extension than during flexion. CONCLUSIONS: This novel method for measurement of dynamic patellar mediolateral tracking was found to have good intraobserver and interobserver reproducibility, and the measurements matched closely with those obtained from magnetic resonance imaging reconstructions of static patellar positions. Some preliminary data for tracking in 3 activities were obtained from 10 normal knees.     

Effect of bracing on patellar kinematics in patients with patellofemoral joint pain

PURPOSE: Bracing is commonly used to correct patellar malalignment syndromes. However, there are little objective data documenting the effect of such supports on patellofemoral joint relationships. The purpose of this study was to assess the effectiveness of an elastic patellofemoral sleeve brace in altering patellar tracking in subjects with patellofemoral pain. METHODS: Ten female subjects (12 patellofemoral joints) between the ages of 17 and 46 participated in this study. All subjects had a diagnosis of patellofemoral pain and demonstrated lateral patellar tracking based on magnetic resonance imaging (MRI) assessment. Each subject underwent kinematic MRI of the patellofemoral joint through a range of 45 to 0 degrees of knee flexion against a resistance of 15% body weight. Imaging was performed with and without a patellofemoral joint brace (Bauerfeind Genutrain P3 brace, Atlanta, GA). Measurement of medial/lateral patellar displacement, medial/lateral patellar tilt, and the depth of the trochlear groove (sulcus angle) were obtained with midpatellar image sections at 45, 36, 27, 18, 9 and 0 degrees of knee flexion. RESULTS: No statistically significant differences in medial/lateral patellar displacement or tilt were found between braced and unbraced trials across all knee flexion angles (P < 0.05). A small but statistically significant increase in sulcus angle was found across all knee flexion angles with the braced trials (P > 0.05). CONCLUSIONS: These results do not support the hypothesis that the brace used in this study corrects patellar tracking patterns in subjects with patellofemoral pain. However, the increased sulcus angle indicates a change in patella position within the trochlea. It is possible that the clinical improvements seen with bracing may be the result of subtle differences in joint mechanics and not gross changes in alignment.     

Long patellar tendon: radiographic sign of patellofemoral pain syndrome--a prospective study.

The position of the patella was studied prospectively in both knees of 45 consecutive patients (21 male and 24 female patients aged 16-48 years who were competitive [n = 17] or recreational [n = 28] athletes) who had unilateral patellofemoral pain syndrome without symptoms or signs of patellar instability at initial examination. In each knee, standardized anteroposterior, lateral, and tangential radiographs were obtained and six indexes of patellar position (the ratio of the patellar tendon to the greatest diagonal length of the patella, sulcus angles, lateral patellofemoral angle, lateral patellar displacement, patellofemoral index, and knee angle) were measured. When healthy and affected knees were compared, high riding of the patella due to long patellar tendon (patella alta) was the only definite finding in the affected knees. The shape of the intercondylar sulcus and the mediolateral position of the patella were identical in both knees, providing no evidence for patellofemoral incongruence or lateral patellar tilt. Results of this study strongly suggest that idiopathic retropatellar pain is closely associated with patella alta.     

Decreased ratios of lateral to medial patellofemoral forces and pressures after lateral retinacular release and gender knees in total knee arthroplasty

Purpose

To demonstrate that lateral to medial patellofemoral force and pressure ratios could be a surrogate marker of retinacular tension and patellar tracking.

Methods

The patellofemoral forces of six knees from three fresh-frozen half-body female cadavers were evaluated with a capacitive sensor under simulated operative conditions in six staged clinical scenarios: native knees, knee arthroplasty without patellar resurfacing, resurfaced knee and patella, resurfaced knee and patella with lateral release, gender-specific knee arthroplasty with patella resurfacing, and gender-specific knee arthroplasty with lateral release. Maximum force and peak pressure were simultaneously recorded during three to four ranges of motion. Average values were compared between lateral and medial patellofemoral compartments as an objective measure of patellar tracking for the different settings.

Results

Significant differences in lateral and medial force and pressure differentials were seen in most scenarios despite clinically normal patellar tracking. Lateral to medial ratios of maximum force and peak pressure significantly increased after TKA (2.9, 2.1) and after patella resurfacing (2.8, 2.6) compared to the native knee (1.6, 1.8). Addition of a lateral release in resurfaced knees decreased the ratio of lateral to medial patellofemoral forces and pressures as did gender knee arthroplasty (1.5 and 1.1, 2 and 1.3, respectively). Pressure and force values most closely resembled the native knee in the resurfaced knee/resurfaced patella with lateral release and in the gender knee arthroplasty scenarios.

Conclusions

Use of lateral to medial patellofemoral force ratios as a surrogate objective marker for patellar tracking was validated in this study by decreasing ratios observed after lateral release in TKA and with gender-specific implants.     

Dynamic measurement of patellofemoral kinematics and contact pressure after lateral retinacular release: an in vitro study

The purpose of this study was to investigate the influence of lateral retinacular release and medial and lateral retinacular deficiency on patellofemoral position and retropatellar contact pressure. Human knee specimens (n = 8, mean age = 65 SD 7 years, all male) were tested in a kinematic knee-simulating machine. During simulation of an isokinetic knee extension cycle from 120° to full extension, a hydraulic cylinder applied sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The position of the patella was measured using an ultrasound based motion analysis system (CMS 100^®, Zebris). The amount of patellofemoral contact pressure and its pressure distribution was measured using a pressure sensitive film (Tekscan^®, Boston). Patellar position and contact pressure were first investigated in intact knee conditions, after a lateral retinacular release and a release of the medial and lateral retinaculum. After lateral retinacular release the patella continuously moved from a significant medialised position at flexion (P = 0.01) to a lateralised position (P = 0.02) at full knee extension compared to intact conditions, the centre of patellofemoral contact pressure was significantly medialised (0.04) between 120° and 60° knee flexion. Patellofemoral contact pressure did not change significantly. In the deficient knee conditions the patella moved on a significant lateralised track (P = 0.04) through the entire extension cycle with a lateralised centre of patellofemoral pressure (P = 0.04) with a trend (P = 0.08) towards increased patellofemoral pressure. The results suggest that lateral retinacular release did not inevitably stabilise or medialise patellar tracking through the entire knee extension cycle, but could decrease pressure on the lateral patellar facet in knee flexion. Therefore lateral retinacular release should be considered carefully in cases of patellar instability.     

Effect of the vastus medialis obliquus on the patellofemoral joint

In this study, the effect of dynamic stabilizers on the patellofemoral (PF) joint was investigated in normal volunteers (group I) and in patients with patellar pain (group II) or instability (group III) by using computed tomography (CT) analysis and integrated electromyography (iEMG) of the quadriceps muscle. Nine subjects (16 knees) from group I, 10 patients (12 knees) from group II and 8 patients (12 knees) from group III were included in the study. CT scans of the PF joint with quadriceps contracted (QC) and uncontracted (QU) and iEMG of vastus medialis obliquus (VMO), vastus lateralis (VL) and rectus femoris (RF) were obtained with the aid of a specially designed jig at 0°, 15°, 30° and 45° of knee flexion. The same muscle contraction pattern simulating closed kinetic chain exercise was used for both CT and iEMG. The difference between the congruence angles (CA) and tilt angles (PTA) in QC and QU positions and VMO:VL ratio from the iEMG were calculated separately for each flexion angle. CA was increased in all groups with quadriceps contraction at 0° and 15° of flexion. PTA was decreased in group I and increased in groups II and III with quadriceps contraction at the same flexion angles. This difference was statistically significant in group III at 0° and 15° of flexion. Quadriceps contraction did not affect the patellar position significantly even in the instability group at 45° of flexion. In all flexion angles the balanced VMO:VL activity ratio was observed only in group I. In the other goups, VL activity was higher than VMO activity except at 45° of flexion. These findings do not support the hypothesis of dominant centralizing effect of VMO on the patella in extension, but the effect of the VMO may be more clearly demonstrated by measuring PTA in both QC and QU positions. Received: 30 December 1996 Accepted: 22 August 1997     

Shape and size of the medial patellofemoral ligament for the best surgical reconstruction: a human cadaveric study

Purpose

The aim of this study was to investigate the shape and the attachments of the medial patellofemoral ligament (MPFL) in cadaver specimens to determine an anatomical basis for the best MPFL reconstruction.

Methods

Twenty fresh-frozen knees were used. Dissection protocol implied performing dissections from within the knee joint. We investigated the shape and the attachments between the MPFL and the quadriceps tendon, the patellar and femur insertions, and all the other relationships with the medial soft tissues of the knee.

Results

The distal fibers of MPFL were interdigitated with the deep layer of the medial retinaculum. All isolated ligament had a sail-like shape with the patellar side bigger than the femoral side. The femoral insertion, distinct both from medial epicondyle and adductor tubercle, was located at 9.5 mm (range 4–22) distal and anterior respect to adductor tubercle and proximal and posterior to epicondyle. The medial third of the thickness of patella was involved in the insertion. The proximal third of the patella is always involved in the MPFL attachment; in 45 % of the cases, it was extended to the medial third and in one case, an extension at the distal third was found. Additionally in 35 % (7 cases), it extended to the quadriceps tendon and it were inconstantly attached at the vastus medialis obliques (VMO) tendon and at the vastus intermedius (VI) tendon in an aponeurotic structure.

Conclusions

The MPFL is a distinct structure that goes from patella to femur with a sail-like shape; its patellar insertion, that mostly occur via an aponeurosis tissue with VMO and VI, is at the proximal third of the patella but it may extend in some cases to the medial third patella or to the quadriceps tendon, or very rarely to the distal third of the patella. In the femoral side, the MPFL is inserted in its own site, in most cases distinct both from epicondyle and adductor tubercle, located on average at a 9.5 mm distance distally and anteriorly in respect to the adductor tubercle. Its lower margin was difficult to define. Given the importance of this structure, it must be reconstructed as anatomically as possible in its insertion and in its shape. Many attempts have been made to make functional reconstructions with less than excellent results.     

The effects of patellar taping on patellofemoral incongruence. A computed tomography study

Patellar taping for the purpose of patellar medialization is a nonoperative rehabilitation technique used in the treatment of patellofemoral pain. Despite early reports of excellent success rates, the indications for this treatment and its efficacy on patellofemoral pain are unclear. The present computed tomography study was undertaken to evaluate the effect of patellar taping on patellofemoral incongruence. Sixteen female patients (age range, 16 to 25 years) with anterior knee pain related to patellofemoral incongruence underwent computed tomography examination with their quadriceps muscles relaxed and contracted both before and after patellar taping. Patellar lateralization was measured as lateral patellar displacement, and patellar tilt was measured as lateral patellar angle. Patellar taping did not significantly affect patellofemoral lateralization or tilt. The results of this study do not support the use of this method for passive correction of patellofemoral incongruence. Although patellar taping may well be effective in controlling anterior knee pain during physical therapy, it does not do so by medializing the patella.     

Computed tomography of the normal patellofemoral joint

Radiographic assessment of the patellofemoral joint (PFJ) is problematic because conventional views are cumbersome, difficult to standardize, and not reliable for displaying this joint with flexion of the knee less than about 30 degrees. We used computed tomography (CT) to obtain conveniently a direct transaxial view of the PFJ in ten normal human volunteers at different 0 degree, 20 degrees, and 45 degrees of knee flexion and during both contraction and relaxation of the quadriceps muscle. From the CT images we measured femoral trochlear angle, patellar centralization, femoral trochlear depth, and patella tilt angle. In full extension, with the quadriceps muscle relaxed, 19 of 20 knees showed the patella well centered in the femoral trochlear groove. The tilt and centralization of the patella were largely unchanged at 20 and 45 degrees of knee flexion with quadriceps contraction. CT appears to be an optimal method of studying the PFJ. The normal relationships described in this report can be the basis for evaluating patients with known or suspicious history of recurrent subluxation or dislocation of the patella.     

The effect of reconstruction of the medial patellofemoral ligament on patellar tracking

We evaluated patellar tracking in six cadaveric knees with the medial restraints intact and then sectioned to determine their contribution to lateral translation of the patella with and without a lateral force on the patella. The medial patellofemoral ligament was then reconstructed with a gracilis tendon graft and patellar tracking was again evaluated. The knees were extended using a materials testing machine, and patellar tracking was measured with a position sensing system. With no lateral force applied to the patella, patellar tracking was unaffected by the presence or absence of the medial restraints or by reconstruction of the medial patellofemoral ligament. With a lateral force applied to the patella, patellar tracking was changed significantly by the loss of the medial restraints. Normal patellar tracking was substantially restored by reconstruction of the medial patellofemoral ligament.     

Patellofemoral Instability in Children: Imaging Findings and Therapeutic Approaches

Patellofemoral instability (PFI) is common in pediatric knee injuries. PFI results from loss of balance in the dynamic relationship of the patella in the femoral trochlear groove. Patellar lateral dislocation, which is at the extreme of the PFI, results from medial stabilizer injury and leads to the patella hitting the lateral femoral condyle. Multiple contributing factors to PFI have been described, including anatomical variants and altered biomechanics. Femoral condyle dysplasia is a major risk factor for PFI. Medial stabilizer injury contributes to PFI by creating an imbalance in dynamic vectors of the patella. Increased Q angle, femoral anteversion, and lateral insertion of the patellar tendon are additional contributing factors that affect dynamic vectors on the patella. An imbalance in the dynamics results in patellofemoral malalignment, which can be recognized by the presence of patella alta, patellar lateral tilt, and lateral subluxation. Dynamic cross-sectional images are useful for in vivo tracking of the patella in patients with PFI. Therapeutic approaches aim to restore normal patellofemoral dynamics and prevent persistent PFI. In this article, the imaging findings of PFI, including risk factors and characteristic findings of acute lateral patellar dislocation, are reviewed. Non-surgical and surgical approaches to PFI in pediatric patients are discussed.     

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Patellar thickness and lateral retinacular release affects patellofemoral kinematics in total knee arthroplasty

Purpose

To study the effect of increasing patellar thickness (overstuffing) on patellofemoral kinematics in total knee arthroplasty and whether subsequent lateral retinacular release would restore the change in kinematics.

Methods

The quadriceps of eight fresh-frozen knees were loaded on a custom-made jig. Kinematic data were recorded using an optical tracking device for the native knee, following total knee arthroplasty (TKA), then with patellar thicknesses from ?2 to +4 mm, during knee extension motion. Staged lateral retinacular releases were performed to examine the restoration of normal patellar kinematics.

Results

Compared to the native knee, TKA led to significant changes in patellofemoral kinematics, with significant increases in lateral shift, tilt and rotation. When patellar composite thickness was increased, the patella tilted further laterally. Lateral release partly corrected this lateral tilt but caused abnormal tibial external rotation. With complete release of the lateral retinaculum and capsule, the patella with an increased thickness of 4 mm remained more laterally tilted compared to the TKA with normal patellar thickness between 45° and 55° knee flexion and from 75° onwards. This was on average by 2.4° ± 2.9° (p < 0.05) and 2.°9 ± 3.0° (p < 0.01), respectively. Before the release, for those flexion ranges, the patella was tilted laterally by 4.7° ± 3.2° and 5.4° ± 2.7° more than in the TKA with matched patellar thickness.

Conclusion

Patellar thickness affects patellofemoral kinematics after TKA. Although lateral tilt was partly corrected by lateral retinacular release, this affected the tibiofemoral kinematics.

Level of evidence

IV.     

Patellar tracking abnormalities: clinical experience with kinematic MR imaging in 130 patients

A kinematic magnetic resonance (MR) imaging technique for assessment of malalignment of the patella, involving the acquisition of multiple sequential axial images of the patellofemoral joint during the early increments of passive knee flexion, was used to evaluate 130 patients (235 symptomatic patellofemoral joints) showing clinical evidence of having patellar tracking abnormalities. Twenty-three of the patellofemoral joints had undergone previous surgical procedures for patellar realignment. In addition, 14 (28 patellofemoral joints) asymptomatic control subjects were studied. Normal patellar tracking was observed in all of the asymptomatic subjects and in 43 (17%) of the 260 patellofemoral joints in the patient population, 18 (7%) of which were symptomatic. Sixty-nine (26%) of the patellofemoral joints had lateral subluxation of the patella, 106 (41%) had medial subluxation of the patella, 21 (8%) had excessive lateral pressure syndrome, 19 (7%) had lateral-to-medial subluxation of the patella, and two (1%) had dislocation of the patella. Of the 235 patellofemoral joints with suspected abnormalities, 217 (93%) had patellar malalignment. Of the 23 patellofemoral joints that had undergone prior surgery, 20 (87%) had abnormal patellar tracking. Thirteen of 14 (93%) patellofemoral joints that had undergone a prior arthroscopic lateral retinacular release had a medially displaced patella.     

The effect of bracing on patella alignment and patellofemoral joint contact area

PURPOSE: To examine the influence of two patellofemoral braces on pain response, patellar alignment, and patellofemoral joint contact area in persons with patellofemoral pain. METHODS: Fifteen women between the ages of 18 and 45 yr with a diagnosis of patellofemoral pain participated. After the assessment of pain response using a visual analog scale, subjects underwent axial plane magnetic resonance imaging of patellofemoral joint at 0 degrees, 20 degrees, 40 degrees, and 60 degrees of knee flexion. Imaging was done with the knee extensors contracted (25% body weight) under three conditions: 1) no brace, 2) On-Track brace, and 3) Patellar Tracking Orthosis (PTO). Measures of mediolateral patellar displacement and tilt and medial and lateral facet contact area were obtained from the magnetic resonance images. RESULTS: On average, the On-Track brace reduced symptoms by 50%, whereas the PTO reduced pain by 44%. When averaged across all knee flexion angles, the PTO and the On-Track brace significantly increased total patellofemoral joint contact area by 52.0 mm (21%) and 59.3 mm (24%), respectively, when compared with the no-brace condition. Bracing had no influence on lateral patellar tilt; however, small but significant changes in lateral patellar displacement were observed. CONCLUSION: Large changes in pain and contact area occurred without sizable changes in patellar alignment. The results of this study suggest that changes in patellar alignment by itself may not be responsible for pain alleviation after patellar bracing.     

Effect of patellar brace on patellofemoral relationships

The effect of patellar brace on patellofemoral relationships was analyzed using magnetic resonance imaging in 17 knees with patellar subluxation or dislocation. Images were produced in 0° and 20° knee flexions without the patellar brace, with patellar brace and with patellar brace after 1 h of walking. In knee extension, the patellar brace had an unfavorable effect on lateral patellar tilt, but decreased the tilt in 20° knee flexion. The excessive lateral patellar displacement was alleviated in both knee flexion angles. The corrected position was still apparent after physical exercise. Isometric quadriceps muscle contraction increased the displacement. These results suggest a positive stabilizing effect of the brace in patients with patellar instability.