Orthopaedic measurements with computed radiography. Methodological development, accuracy, and radiation dose with special reference to the weight-bearing lower extremity and the dislocating patella

The overall aim of this study was to develop and evaluate a measurement system for computed radiography (CR) and Picture Archiving and Communication Systems (PACS), permitting measurements of long distances and angles in and between related images. The developed measurement system, which was based on the QUESTOR Precision Radiography (QPR) system, was applied to the weight-bearing knee with special reference to the dislocating patella. The QPR system modified for CR fulfilled the criteria for measuring the weight-bearing knee. The special measuring assistance tools that were developed were important for the implementation of CR and PACS, particularly in workstations programmed for musculoskeletal radiology. The energy imparted to the patient was reduced by 98% at the lowest exposure of the CR-system, compared with our conventional analogue method, without loss of diagnostic accuracy. The CR technique creates a possibility, to an extent not previously feasible, to differentiate the exposure parametres (and thus minimise the radiation dose to the patient) by carefully considering the purpose of the examination. A radiographic method for measuring the rotation of the femur and the tibia, the Q-angle, and the patellar translation was developed and applied to healthy volunteers. The introduced patellar variables have yielded new insights into the complex sequence of motions between the femur, tibia, and patella. The patients with a dislocating patella were subdivided into one "clean" group of spontaneous dislocations and one group with various traumas in the history, which thus resulted in two groups with distinct radiographic differences. The Q-angle was decreased in knees that had suffered dislocations, and the traditional surgical treatment with a further reduction of the Q-angle must be challenged. The use of clinical measurements of the Q-angle was not an optimal way to evaluate the mechanical alignment in the patellofemoral joint under physiological conditions. In this study, we have proved that the developed method for CR and PACS is a useful technique for measurements in and between related images, and is superior to the conventional analogue technique.     

Femorotibial rotation and the Q-angle related to the dislocating patella

PURPOSE: To compare the femorotibial rotation, the patellar translation, the hip-knee-ankle angle and the Q-angle in patients with a dislocation of the patella with those of healthy volunteers. Further, the clinically measured Q-angle was compared to that measured by radiography. MATERIAL AND METHODS: A system for measurement of patellar variables was previously developed and applied to 80 healthy volunteers. In the present study, 28 patients (20 women, 8 men) with dislocation of the patella were examined bilaterally. Fourteen patients had habitual dislocations (20 affected knees) and 14 patients traumatic dislocations (17 affected knees). In 20 patients the clinical Q-angle was measured bilaterally by an orthopaedic surgeon and in 9 of these patients also by a second independent orthopaedic surgeon. RESULTS: The most striking finding was that dislocating knees in both groups showed a smaller Q-angle than the healthy knees. Further, the habitual group showed greater relative rotation between the tibia and the femur and an increased patellar translation compared to the traumatic group and to the healthy volunteers. There was a poor correlation between clinical and radiographic measurements of the Q-angle and no correlation was found between two independent clinical measurements. CONCLUSION: Surgical operations aiming at decreasing the Q-angle should be challenged.     

ORTHOPAEDIC MEASUREMENTS WITH COMPUTED RADIOGRAPHY: Methodological development, accuracy, and radiation dose with special reference to the weight-bearing lower extremity and the dislocating patella

Sanfridsson J.: Orthopaedic measurements with computed radiography. Methodological development, accuracy, and radiation dose with special reference to the weight-bearing lower extremity and the dislocating patella. Lund 2001. ISBN 87-16-16449-0.The overall aim of this study was to develop and evaluate a measurement system for computed radiography () and Picture Archiving and Communication Systems (), permitting measurements of long distances and angles in and between related images. The developed measurement system, which was based on the QUESTOR Precision Radiography () system, was applied to the weight-bearing knee with special reference to the dislocating patella.The QPR system modified for CR fulfilled the criteria for measuring the weight-bearing knee.The special measuring assistance tools that were developed were important for the implementation of CR and PACS, particularly in workstations programmed for musculoskeletal radiology.The energy imparted to the patient was reduced by 98% at the lowest exposure of the CR-system, compared with our conventional analogue method, without loss of diagnostic accuracy. The CR technique creates a possibility, to an extent not previously feasible, to differentiate the exposure parametres (and thus minimise the radiation dose to the patient) by carefully considering the purpose of the examination.A radiographic method for measuring the rotation of the femur and the tibia, the , and the patellar translation was developed and applied to healthy volunteers. The introduced patellar variables have yielded new insights into the complex sequence of motions between the femur, tibia, and patella.The patients with a dislocating patella were subdivided into one "clean" group of spontaneous dislocations and one group with various traumas in the history, which thus resulted in two groups with distinct radiographic differences. The Q-angle was decreased in knees that had suffered dislocations, and the traditional surgical treatment with a further reduction of the Q-angle must be challenged.The use of clinical measurements of the Q-angle was not an optimal way to evaluate the mechanical alignment in the patellofemoral joint under physiological conditions.In this study, we have proved that the developed method for CR and PACS is a useful technique for measurements in and between related images, and is superior to the conventional analogue technique ( ).     

Fluoroscopic validation of electrogoniometrically measured femorotibial translation in healthy and ACL deficient subjects

Equipment which measure femorotibial motions indirectly by using a patellar pad are reported to have errors caused by deformation of soft tissues and slippage of the device. For the purpose of validation, the tibial translation in relation to the femur per degree of knee extension was estimated from the slope coefficients of the flexion-displacement curve, obtained by both fluoroscopic and electrogoniometric tests, in the knee of the dominant limb in healthy subjects and in both knees of patients with unilateral anterior cruciate ligament (ACL) deficiency. In addition, the anterior and posterior static knee laxity limits and the tibial resting position were evaluated. Within all knee groups, the tibia moved posteriorly in relation to the femur during extension. The measured movement was similar both with the electrogoniometer and with fluoroscopy thereby indicating that sagittal plane knee translation measurements with the CA-4000 electrogoniometer are reliable and in good agreement with the X-ray measurements, even though the measurements were made separately. The ACL injured knees showed approximately 20% smaller posterior movement of tibia in relation to femur per degree change of knee extension than the non-injured or control knees (p < 0.05) and a more anterior resting position of the tibia relative to femur as compared to the contralateral healthy knee during knee laxity testing (p = 0.002).     

The relationship between quadriceps angle and tibial tuberosity–trochlear groove distance in patients with patellar instability

Purpose

The quadriceps angle (Q-angle) represents the angle between the vector of action of the quadriceps and the patellar tendon. An increased Q-angle has been associated with an increased risk of patellar instability, although there is disagreement on its reliability and validity as it is affected by the position of the limb and contraction of the quadriceps. Tibial tuberosity?Ctrochlear groove distance (TT?CTG) is ascertained by axial CT scanning, with an increased value associated with patellar instability. This study aimed to determine whether the Q-angle correlates with the TT?CTG distance in patients with patellar instability.

Methods

Q-angles were measured in 34 knees that had previously undergone CT scanning for assessment of patellar instability. Measurements were made with the patient supine, the knee extended and the lower limbs in neutral rotation with the quadriceps relaxed and contracted. TT?CTG distance was measured on CT scanning in an identical position.

Results

Of the 34 knees measured, 24 had symptoms of patellar instability, and 10 were normal. A significant negative correlation between relaxed Q-angle and TT?CTG in all knees was demonstrated (p?=?0.028). In symptomatic knees, contracted Q-angle also demonstrated a significant negative correlation with TT?CTG (p?=?0.037).

Conclusions

If TT?CTG distance is regarded as the gold standard measurement, Q-angle is not a reliable indicator of patellar instability. There is a clear need to develop methods to more fully characterise the knee and factors contributing to patellar instability.

Level of evidence

II.     

Sonography of the medial and lateral tendons and ligaments of the knee: the use of bony landmarks as an easy method for identification

OBJECTIVE: Our purpose was to describe the use of bony landmarks in the evaluation of the medial and lateral ligaments and tendons of the knee on sonography and to evaluate the value of this approach in healthy volunteers. MATERIALS AND METHODS: Anatomic slices obtained in cadaveric specimens were inspected for the presence of bony landmarks on the medial and lateral aspects of the knee. Then sonography was performed on 40 knees of 20 healthy volunteers by two musculoskeletal radiologists who independently rated the visualization of bony landmarks and adjacent ligaments and tendons on a 5-point grading scale. RESULTS: Bony landmarks on the lateral aspect of the knee include Gerdy's tubercle on the tibia and the sulcus for the popliteal tendon on the femur. Landmarks on the medial aspect of the knee include the medial epicondyle on the femur and the sulcus for the semimembranosus tendon on the tibia. Visualization of all landmarks was rated in the good to excellent range, and agreement between observers ranged from 92.5% to 100%. CONCLUSION: Bony landmarks can be identified in healthy adults on the medial and lateral aspects of the knee and may serve as reference points for identification of most medial and lateral tendons and ligaments.     

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.     

Variations in kinematics and function following patellar stabilization including tibial tuberosity realignment

Purpose

The current study was performed to characterize the influence of patellar stabilization procedures on patellofemoral and tibiofemoral dynamic motion.

Methods

Six knees were evaluated pre-operatively and 1 year or longer following stabilization via tibial tuberosity realignment, with simultaneous medial patellofemoral ligament reconstruction performed for five knees. Knees were imaged during extension against gravity using a dynamic CT scanner. Models representing each knee at several positions of extension were reconstructed from the images. Local coordinate systems were created within one femur, patella and tibia for each knee, with shape matching of the bones used to transfer the coordinate axes to the other models. The patellar lateral shift and tilt and tibial external rotation were quantified based on the reference axes and interpolated to flexion angles from 5° to 40°. Pre-operative and post-operative data were compared with the paired t tests.

Results

Surgical realignment significantly decreased the average patellar lateral shift and tilt at low flexion angles. At 5°, surgical realignment decreased the average lateral shift from 15.5 (6.3) to 8.5 (4.7) mm and decreased the average lateral tilt from 20.8 (9.4)° to 13.8 (6.4)°. The changes were statistically significant (p < 0.05) at 5° and 10° of flexion, as well as 20° for lateral shift. The average tibial external rotation also increased significantly at 30° and 40° following surgery.

Conclusion

Patellar stabilization including a component of tuberosity realignment reduces patellar lateral shift and tilt at low flexion angles, but the long-term influence of increased tibial external rotation on tibiofemoral function is currently unknown.

Level of evidence

Prospective comparative study, Level II.     

The effect of knee position on the reproducibility of measurements taken from stress films: a comparison of four measurement methods

We evaluated the accuracy of four different means of radiographic measurement of anteroposterior translation in the knee joint. The tests were performed in normal knees, in knees lacking the anterior cruciate ligament, and in knees lacking both anterior and posterior cruciate ligaments; the knees were obtained from cadavers. It is difficult to define landmarks and to perform exact measurements, and we sought to determine which of the four methods is the most accurate. In particular, we examined the effect of various degrees of rotation and flexion on the positional relationships of the landmarks of the tibia and the femur. Received: 25 July 1998/Accepted: 17 December 1999     

In vivo kinematics of early-stage osteoarthritic knees during pivot and squat activities

Kinematic changes have been shown to accompany severe knee osteoarthritis, but no studies have analyzed early-stage osteoarthritic knee kinematics in the transverse plane during functional activities. The purpose of this study was to analyze kinematics of early-stage osteoarthritic knees using model registration techniques. Fifteen early-stage osteoarthritic knees from eight females with a mean age of 52 years old (range, 43–57 years old) were involved in this study. A radiologist confirmed with plain radiographs that knees had Kellgren-Lawrence grade-1 or −2 arthritic changes. Fluoroscopic images of squat and pivot activities were recorded for each subject. Three-dimensional surface models of the distal femur and proximal tibia were created from CT images, and anatomic coordinate systems were embedded in each model. The three-dimensional position and orientation of the femur and the tibia were determined using model-image registration techniques, and tibial anteroposterior translation and internal/external rotation relative to the femur were calculated. The contact points of the medial and lateral femoral condyle were also computed. Compared to healthy knees, osteoarthritic knees showed lateral contact points that were significantly shifted anteriorly in both pivot (P < 0.001) and squat (P = 0.001) activities and greater tibial external rotation in pivot activity (P = 0.007). The medial contact point location was similar to healthy knees, but the amount of anteroposterior translation was smaller (P < 0.001). These kinematic changes might change stress distributions in the medial compartment during weight-bearing activities. The changes in kinematics possibly have some influence on initiation or progression of knee osteoarthritis.     

Roles of ACL remnants in knee stability

Purpose

This study evaluated knee laxity in anterior tibial translation and rotation following removal of anterior cruciate ligament (ACL) remnants using a computer navigation system.

Methods

This prospective study included 50 knees undergoing primary ACL reconstruction using a navigation system. ACL remnants were classified into four morphologic types: Type 1, bridging between the roof of the intercondylar notch and tibia; Type 2, bridging between the posterior cruciate ligament and tibia; Type 3, bridging between the anatomical insertions of the ACL on the lateral wall of the femoral condyle and the tibia; and Type 4, no bridging of ACL remnants. Anterior tibial translation and rotatory laxity were measured before and after remnant resection using a navigation system at 30°, 60°, and 90° of knee flexion. The amount of change in anterior tibial translation and rotatory laxity of each type was compared among the types.

Results

The different morphologic types of ACL remnants were as follows: Type 1, 15 knees; Type 2, 9 knees; Type 3, 6 knees; and Type 4, 20 knees. The amount of change in anterior tibial translation and rotatory laxity at 30° knee flexion in Type 3 was significantly larger than in the other types. There were no significant differences in either tibial translation or rotatory laxity at 60° and 90° knee flexion among the types.

Conclusions

In Type 3, ACL remnants contributed to anteroposterior and rotatory knee laxity evaluated at 30° knee flexion. The bridging point of the remnants is important to knee laxity. The Type 3 remnant should be preserved as much as possible when ACL reconstruction surgery is performed.

Level of evidence

Prognostic study, Level II.     

The in vivo assessment of tibial motion in the transverse plane in anterior cruciate ligament-reconstructed knees.

Twenty-one knees with acutely injured anterior cruciate ligaments were reconstructed with patellar tendon autografts. Eight of the knees had concomitant medial ligament injuries that were not addressed surgically. Follow-up evaluation (average, 25 months) included computed tomography measurements to analyze transverse-plane laxity in both translation and rotation. These measurements were performed with the patient's leg in a load cell device that stabilizes the distal femur and applies known anterior translational force to the proximal tibia at approximately 20 degrees of flexion. A torque apparatus was used to apply internal and external rotational torque to the leg. Images of the tibial plateau in neutral, internal, and external rotation were performed, with and without an anterior translational force. Both knees of each patient were tested and categorized as group I (anterior cruciate ligament-reconstructed) or group II (uninjured). Translation as measured by computed tomography averaged 1 mm side-to-side difference. Internal rotation averaged 8.7 degrees in group I knees and 10.8 degrees in group II knees. External rotation averaged 9.1 degrees in group I knees and 7.4 degrees in group II knees. The eight knees with concomitant medial ligament injuries were analyzed separately; external rotation without anterior load in group I was 9.5 degrees, compared with 5 degrees in group II. This difference was significant (P < 0.01).     

Medial sixth of the patellar tendon at the tibial attachment is useful for the anterior reference in rotational alignment of the tibial component

Purpose

The anteroposterior (AP) axis connecting the middle of the posterior cruciate ligament to the medial border of the patellar tendon at its attachment has been introduced as a reproducible and reliable reference perpendicular to the surgical epicondylar axis in healthy knees. A recent literature has reported that the AP axis of the tibia is, on average, almost perpendicular to the surgical epicondylar axis also in varus and valgus knees and can be used as a tibial rotational reference to minimize the risk for rotational mismatch between the femoral and tibial components in total knee arthroplasty (TKA). However, it is difficult to identify the AP axis after tibial resection. The purpose of the current study was to determine a modified AP axis that runs parallel to the AP axis and passes through the centre of the cut surface in osteoarthritic knees.

Methods

Preoperative computed tomography scans on 30 varus and 30 valgus knees undergoing TKA were studied using a three-dimensional software. The modified AP axis that runs parallel to the AP axis and passes through the centre of the cut surface was drawn. We investigated where the modified AP axis crossed the patellar tendon at its tibial attachment.

Results

The modified AP axis passed through the medial 1/6 of the patellar tendon (4 mm from medial edge) at its attachment in both varus and valgus knees.

Conclusions

The AP axis of the tibia is useful as a tibial rotational reference in cutting the proximal tibia, but it is difficult to identify the AP axis after tibial resection. The clinical relevance of this study is that medial 1/6 of the patellar tendon at its attachment would be a useful landmark in aligning the tibial component.

Level of evidence

IV.     

Bone mineral density of the proximal tibia relates to axial torsion in the lower limb

This study sought to determine the relationship between bone mineral density distribution in the proximal tibia and tibial and femoral torsions, hip-knee-ankle angle, hip rotation index (internal-external rotation), knee abduction moments, and the foot progression angle. Simple linear regression found that the hip rotation index (r=-0.59, p<0.001), tibial torsion (r=-0.41, p=0.004), and knee abduction moments (r=0.39, p=0.005) were significantly related to medial-lateral BMD ratio for all subjects. The three variables were then studied together to determine their relationship to the bone mineral distribution in the proximal tibia using multiple linear regression (r=0.80, p<0.001). These findings suggest that higher medial knee joint loads, loss of internal rotation of the hip, and internal tibial torsion may lead to increased medial versus lateral BMD of the proximal tibia of healthy knees. Similar bone distribution patterns are found in knees with osteoarthritis; therefore, we suggest these may be risk factors.     

MRI of knee osteonecrosis in children with leukemia and lymphoma: Part 2, clinical and imaging patterns

OBJECTIVE: This aim of this study was to explore the relationship between MRI findings and clinical symptoms of knee osteonecrosis in children and to determine the significance of this relationship. Such information is important for early diagnosis of this frequent complication and for choosing an appropriate treatment strategy. MATERIALS AND METHODS: Osteonecrotic lesion size and location were determined in a retrospective analysis of MR images of the knee obtained in our institution during the past 10 years. Association between MRI findings and clinical symptoms expressed by the knee scores was tested for a subgroup of our patient population who had clinical evaluation of the knees in the orthopedic clinic within 6 weeks of their MRI studies. RESULTS: In 80% of patients, osteonecrosis was bilateral. Lesions were distributed as follows: femur and tibia, 66% of the knees; femur alone, 26%; and tibia alone, 8%. Clinical symptoms of knee osteonecrosis were associated with lesions involving the articular surface of the distal femur, large lesions, and involvement of any part of the tibia. MR images showed milder osteonecrosis in patients who were less than 10 years old at the time of primary diagnosis. CONCLUSION: Osteonecrosis affecting the knees of children treated for leukemia and lymphoma is mostly asymptomatic. Children who are 10 years old or older have signs of more advanced osteonecrosis. Clinical symptoms often lag MRI presentation and may develop late in the course of the disease. Routine MRI evaluation is recommended for timely diagnosis of treatment-induced osteonecrosis.     

Longitudinal in vivo reproducibility of cartilage volume and surface in osteoarthritis of the knee

Objective The aim of this study was to evaluate the longitudinal reproducibility of cartilage volume and surface area measurements in moderate osteoarthritis (OA) of the knee. Materials and methods We analysed 5 MRI (GE 1.5T, sagittal 3D SPGR) data sets of patients with osteoarthritis (OA) of the knee (Kellgren Lawrence grade I–II). Two scans were performed: one baseline scan and one follow-up scan 3 months later (96 ± 10 days). For segmentation, 3D Slicer 2.5 software was used. Two segmentations were performed by two readers independently who were blinded to the scan dates. Tibial and femoral cartilage volume and surface were determined. Longitudinal and cross-sectional precision errors were calculated using the standard deviation (SD) and coefficient of variation (CV%=100×[SD/mean]) from the repeated measurements in each patient. The in vivo reproducibility was then calculated as the root mean square of these individual reproducibility errors. Results The cross-sectional root mean squared coefficient of variation (RMSE-CV) was 1.2, 2.2 and 2.4% for surface area measurements (femur, medial and lateral tibia respectively) and 1.4, 1.8 and 1.3% for the corresponding cartilage volumes. Longitudinal RMSE-CV was 3.3, 3.1 and 3.7% for the surface area measurements (femur, medial and lateral tibia respectively) and 2.3, 3.3 and 2.4% for femur, medial and lateral tibia cartilage volumes. Conclusion The longitudinal in vivo reproducibility of cartilage surface and volume measurements in the knee using this segmentation method is excellent. To the best of our knowledge we measured, for the first time, the longitudinal reproducibility of cartilage volume and surface area in participants with mild to moderate OA.     

The position of the tibia tubercle in 0°–90° flexion: comparing patients with patella dislocation to healthy volunteers

Purpose

The aim of this study was to measure the tibia tubercle trochlea groove distance (TT–TG) as a function of knee flexion. Our hypothesis was that there is a different pattern in healthy volunteers and patients with patella instability (PFI).

Methods

Thirty-six knees of 30 patients with at least one dislocation of the patella and 30 knees of 30 healthy volunteers as control group were analysed with magnetic resonance imaging by three different observers. The TT–TG was measured in steps of 15° between 0° and 90° of knee flexion. Furthermore, the alignment of the leg (MA), the femur torsion (FTor) and the tibia torsion (TTor) was calculated.

Results

The TT–TG was higher in patients compared to volunteers and in extension compared to flexion. This difference was statistically significant (p < 0.05). Most of the patients with a TT–TG above 20 mm in extension showed a high decrease in flexion to normal values. In some patients, this compensating mechanism fails. MA, FTor and TTor were not different in patients and control group (n.s.).

Conclusion

The TT–TG distance is dynamic and decreased significantly during flexion in knees with PFI and healthy volunteers. However, there were a small number of patients in the PFI group where this compensation mechanism did not work. Therefore, the decision to perform a tibia tubercle osteotomy should not be based on one single measurement in extension or 30° of knee flexion.

Level of evidence

II.     

髌股疼痛综合征患者髌骨运动轨迹的动态CT研究

目的 应用320排动态容积CT描述髌股疼痛综合征患者在膝关节屈曲运动中的动态髌骨轨迹,为髌股疼痛综合征的临床诊断及治疗方案的选择提供理论依据.方法 随机选择济南军区总医院2010年3月～2011年2月间资料完整确诊髌股疼痛综合征的女性患者24例（32膝）为实验组,年龄18～46岁,平均年龄31.1岁;随机选择健康女性13例（26膝）为对照组,年龄19～45岁,平均年龄32.1岁.应用320排动态容积CT检查：股四头肌等长收缩状态下自主屈曲膝关节,在膝关节屈曲0°～120°范围内间隔15°依次垂直髌骨进行动态CT扫描.应用Vitrea 2.1软件进行图像后处理,获得膝关节三维重建图像,测量髌骨运动轨迹参数：髌骨倾斜、髌骨移位和髌骨旋转.所有计数资料以均数和标准差描述,应用SPSS 16.0软件进行两样本均数t检验,P≤0.05有显著性意义.结果 15°～45°范围内两组的髌骨倾斜有显著性差异,P＜0.001;膝关节屈曲15°～45 °范围内两组的髌骨中心外移有显著性差异,P＜0.001;15°～120°范围内两组的髌骨旋转有显著性差异,P＜0.001.结论 膝关节屈曲15°～45°范围内髌股疼痛综合征患者的髌骨轨迹最具临床诊断、治疗意义.     

Evaluation of the patellofemoral joint with kinematic MR fluoroscopy

OBJECTIVE: The aim of this study was to evaluate the diagnostic effectiveness of kinematic magnetic resonance fluoroscopy (KMRF) on patients with patellofemoral incongruency. MATERIALA AND METHODS: 17 patients (20 knees) and 10 healthy volunteers (20 knees), all men (mean age 29.4 years, S.D. 9, range 16-50), were included to our study. Only male subjects were studied because of potential biomechanical differences between sexes. KMRF was used to perform kinematic MR imaging of patellar alignment and tracking in 10 healthy subjects and 17 patients with a provisional clinical diagnosis of abnormal patellofemoral joints. The patellofemoral joints were examined with the knee in different angles of active flexion. At each knee position, real time kinematic and axial MRF image was used to focus on the sagittal plane, followed by an axial image focused through the middle of the patella. Three angles were measured: patellar tilt angle (PTA), sulcus angle (SA) and congruence angle (CA). RESULTS: Five patterns of malalignment were identified and studied. Two patellofemoral joints were normal, 10 had lateralization of the patella, 2 had patellar tilt, 2 had lateralization and patellar tilt (i.e. excessive lateral pressure syndrome) and 4 had medialization of the patella. CONCLUSION: KMRF is an effective method in evaluating patellofemoral incongruency. Short time duration of investigation, ability to get nearly real time images, suitable temporal contrast resolution and investigation from very different angles of knee are important advantages of the method.