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 Table of Contents  
ORIGINAL ARTICLES
Year : 2022  |  Volume : 37  |  Issue : 2  |  Page : 59-69

Magnetic resonance imaging evaluation of patients with anterior knee pain: A prospective observational study


1 Department of Radiodiagnosis and Imaging, Institute of Medical Sciences, Banaras Hindu University, Varanasi, India
2 Department of Orthopedics, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Date of Submission24-May-2022
Date of Acceptance06-Sep-2022
Date of Web Publication19-Oct-2022

Correspondence Address:
Rahul Patel
Department of Orthopedics, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jbjd.jbjd_10_22

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  Abstract 

Anterior knee pain (AKP) is one of the most common clinical conditions related to knee pathology among the athletes and young adults. The identification of pain provoking factor is crucial for the better outcome of the treatment. Many patients with AKP have disabling pain and significant disability, but the physical signs and radiological findings are unremarkable. Its aetiology is still not fully understood, but there are some major factors that can be attributed to its aetiology. Accurate diagnosis of the condition is needed before any decision regarding its management is undertaken. Diagnosis is usually suspected clinically and is confirmed by imaging. Although, radiography, ultrasonography, computed tomography scan and magnetic resonance imaging (MRI) are the available modalities for the evaluation of AKP, MRI is considered the gold standard for pain imaging and can provide important information regarding individually tailored treatment. The present study is a prospective descriptive compilation of the role of available imaging modalities, particularly MRI in the evaluation of different pathological conditions related to AKP. The present study demonstrated that patellofemoral instability was a major cause for origin of AKP.

Keywords: Anterior knee pain, anterior knee pain in young, MRI evaluation in anterior knee pain


How to cite this article:
Ojha R, Patel R, Kumar I, Bhardwaj V, Verma A, Shukla RC. Magnetic resonance imaging evaluation of patients with anterior knee pain: A prospective observational study. J Bone Joint Dis 2022;37:59-69

How to cite this URL:
Ojha R, Patel R, Kumar I, Bhardwaj V, Verma A, Shukla RC. Magnetic resonance imaging evaluation of patients with anterior knee pain: A prospective observational study. J Bone Joint Dis [serial online] 2022 [cited 2022 Nov 29];37:59-69. Available from: http://www.jbjd.in/text.asp?2022/37/2/59/358790




  Introduction Top


Anterior knee pain (AKP) is one of the most common clinical condition related to knee pathology among the athletes and young adults.[1] The AKP patient presented as knee pain, insidious onset and without obvious trauma, although there is an associated factor that may explain the clinical presentation. The identification of pain provoking factor is crucial for the better outcome of the treatment. therefore, a proper clinical history is important. A careful clinical history and physical evaluation along with imaging studies are important to concluding an accurate diagnosis, which will be help in developing an appropriate therapeutic program.

Assessment of the psychological state of patients with AKP is also important. Numerous misconceptions are there among the patients with regard to this condition. Many patients with AKP have disabling pain and significant disability, but the physical signs and radiological findings are unremarkable. Nevertheless, psychological factors are not directly responsible for the pain, although they may modulate it.[2],[3] Moreover, it has been shown that young female adults with long-standing AKP demonstrated impaired conditioned pain modulation.[4]

Its aetiology is still not fully understood, but there three major factors that can be attributed to its aetiology:

  1. Quadriceps muscle imbalance


  2. Lower extremity malalignment


  3. Increased physical activity.


Patient usually complaints of mild to moderate pain on going uphill, climbing stairs, or after vigorous exercise.

Lateral pain indicates iliotibial band syndrome or nerve injury from previous surgery. Pain on medial side indicates recurrent stretching of a medial retinaculum plicae. Retro-patellar pain indicates stress of the subchondral bone causing articular cartilage damage. Superior pain indicates quadriceps tendinopathy. inferior pain may be due to fat pad irritation or patella tendinopathy.

The history and physical examination, complemented by imaging studies, are helpful in defining as precisely as possible the origin of the patient’s complaint.

The present study is a prospective descriptive compilation of the role of available imaging modalities, particularly magnetic resonance imaging in evaluation of different pathological conditions related to anterior knee pain. On the hypothesis that some patients with AKP would have anatomical lesion or abnormal knee joint geometry on MRI, we have examined the prevalence and types of abnormal MRI findings of patients with atraumatic AKP as a single symptom. To explore the geometric characteristics of the PF joint, we have performed subgroup comparisons among the AKP groups.


  Materials and Methods Top


This Prospective observational study “Imaging in Anterior Knee Pain” was carried out from 2015 to JULY 2017 on 30 patients. Majority of the referred cases were those who had clinical features raising the suspicion of Anterior Knee Pain. Cases were recruited from patients attending Orthopedics department for anterior knee pain complaints. Full history was taken especially about any previous operative procedure, any drug allergy or any absolute contraindication for MRI.

Inclusion criteria

  • Patients presenting with anterior knee pain complaints with or without other associated symptoms.


  • Patients with history of knee dislocation


  • Evaluation of patients

  • Clinical history was elicited from the patients or guardians.


  • Clinical records were evaluated to look for any relevant investigation and for any previous operative procedure.


  • Consent of the patients/guardians was obtained before any imaging procedure was carried out on patients who participated in the study.


  • Exclusion criteria

  • Patients who had previous knee surgical interventions.


  • Patients with history of inflammatory knee disease such as gout or rheumatoid arthritis.


  • Patients with history of traumatic knee injuries.


  • Any absolute contraindication for MRI such as ferromagnetic implants, pacemaker, aneurysm clips.


  • Patients who were claustrophobic.


  • Equipments

    Patients presenting with anterior knee pain, referred for imaging were evaluated by Digital radiography, USG and MRI.

  • Digital radiography: FCR Capsula XL II (fuji-film)


  • USG: the ultrasound machine used was Diagnostic Ultrasound, iU22 (Philips Medical System, California, United States).


  • MRI: 1.5 Tesla Superconducting magnet (MAGNETOM AVANTO, Siemens Medical System, Erlangen-Germany) equipped with surface coils.


  • Once the patient fulfilled the inclusion criteria for this study, he/she was briefed about the procedure. Written and informed consent was taken before the relevant imaging.

    Patient positioning

    MRI: Patients were made to lie in supine position with knees in the neutral position.

    Protocol

    Digital radiography: True AP view, Lateral view and Sunrise view

    Knee USG: Various structures were imaged in following sequence:

    • ➢ Quadriceps tendon, Patellar tendon, Suprapatellar bursa, Medial and lateral menisci, Hyaline articular cartilage and Hoffa’s fat pad


    Knee MRI

  • Coil: 8- Channel knee coil


  • Image orientation: field of view (25cm), 3- to 4-mm-thick slices and matrix, 300 x 512 in three imaging planes: (1) coronal (2) axial, and (3) sagittal


  • Pulse sequences:


  • For standard knee MRI -

  • T1W Sagittal and coronal


  • T2W Coronal and Axial


  • Proton density Sagittal and Coronal with fat suppression


  • Images were analyzed on off-line work-station of Magnetom Avanto, and printed on laser images for pertinent observations.

    Statistical analysis

    The statistical analysis was done using statistical software SPSS for windows (version 16). Chi-square test was used for non-parametric variables. Student’s t test was used for comparing two groups and one-way ANOVA test was used for multiple group comparison. P-value < 0.05 was stated as statistically significant.

    Observations

    The present study “IMAGING IN ANTERIOR KNEE PAIN” was undertaken in Department of Radiodiagnosis, Institute of Medical Sciences, Banaras Hindu University, Varanasi and completed the study on 30 cases between July 2015 to July 2017. After obtaining detailed clinical history and physical examination, imaging was performed. The present study is a prospective observational study on patients having symptoms of anterior knee pain and imaged for eliciting different pathologies related to anterior knee pain

    Age distribution in present study

    Among the 30 cases, there were 7 cases in the 11–20 years age group, 11 cases in the 21–30 years age group, 9 cases in 31–40 years age group and 3 cases with more than 40 years age.

    Gender distribution in present study

    Among the 30 cases, there were 13 male and 17 female patients included in study.

    The most common category of clinical symptoms and/or physical sign of patients was – Typical clinical symptoms with patellofemoral crepitus or pain on manipulation of patella (n=13). Diffuse anterior knee pain as single symptom was least common group (n=6) [Table 1].
    Table 1: Incidence rate of clinical categories

    Click here to view


    Distribution of pathologies noted on imaging

    In the present study, the most common pathology was trochlear dysplasia followed by patella alta and chondromalacia patellae.

    Imaging pathologies [[Table 2]]

    PATELLA ALTA: Incidence of patella alta as depicted by study (n=30)

    In present study, 15 cases of patella alta were diagnosed. So, incidence was 50%. It was second most common pathology found in our study. Patella alta was diagnosed with help of Insall-salvati ratio, if it was > 1.3. Mean value of I-S ratio in patients with patella alta was 1.36.
    Table 2: Incidences of various pathologies elicited in present study (n=30)

    Click here to view


    PATELLAR SUBLUXATION: Incidence of Patellar subluxation as depicted by study (n=30)

    In present study, 10 cases of patellar subluxation were diagnosed; hence incidence 33.3%.

    LATERALLY INCLINED PATELLA: Incidence of laterally inclined patella of as depicted by study (n=30)

    8 cases of laterally inclined patella were diagnosed with incidence of 26.75. It was demonstrated with help of patellar tilt angle. When patellar tilt was less than 80, patella was categorized as laterally inclined.

    TROCHELAR DYSPLASIA: Incidence of trochlear dysplasia of as depicted by study (n=30)

    Total 17 cases of trochlear dysplasia were diagnosed with incidence of 56.7%. It was most common abnormality found in our study. It was diagnosed with help of measurement of sulcus angle and sulcus depth. Cases were categorized as of Trochlear dysplasia if sulcus angle was > 1440 and / or sulcus depth was < 3mm.

    Sulcus depth

    Sulcus depth was measured and 8 cases measured sulcus depth <3 mm with incidence of 26.7% and rest 22 measured with sulcus depth >3mm.

    Chondromalacia patellae

    Incidence of chondromalacia patella of as depicted by study (n=30)

    Chondromalacia patellae (patellar chondral lesions) was present in 11 cases with incidence of 36.7%.

    Femoral condyle cartilage lesion

    Femoral condyle cartilage lesions were present in 4 cases. These lesions were not present isolated, rather it was present with patellar chondral lesions.

    Medial plica

    Medial plica was demonstrated in 11 cases with incidence of 36.7%.

    Ligament/Meniscal tear

    Ligament/meniscal tears were present in 7 cases as associated finding with incidence of 23.3%.

    Synovial effusion

    Synovial effusion was present in 12 cases as an associated finding with incidence of 40%.

    Hoffa’s fat pad edema

    Hoffa’s fat pad edema was present in 9 cases with incidence of 30%.

    Out of 11 cases with medial plica, 10 showed presence of trochlear dysplasia. Significant statistical association was found in between both. Therefore, patients with trochlear dysplasia have more incidence of medial plica.

    Out of 11 cases of chondromalacia patellae, 10 cases were associated with trochlear dysplasia. Therefore, patients with trochlear dysplasia have high incidences of patellar chondral lesions.

    Statistically, significant association was found in between patellar subluxation and patellar tilt.


      Discussion Top


    Anterior knee pain is one of the commonest conditions that are encountered in Orthopedic out-patient department. Accurate diagnosis of the condition is needed before any decision regarding its management is undertaken. Diagnosis is usually suspected clinically and is confirmed by imaging.

    The various imaging modalities used are Radiography, Ultrasonography, Computed tomography scan and Magnetic Resonance Imaging. Though MR imaging is said to be the gold standard for pain imaging. Present study included 30 patients who were suspected of having complaints of Anterior Knee Pain and were referred for imaging.

    Epidemiological interpretation

    Subjects of present study belonged to the age range of 12 to 47 years with mean age of 27 years. Maximum patients were young adults falling in the age range of 21–30 years [Table 1]. In our study, 56.7% of subjects were females and 43.3% were males.

    Devereaux & Lachmann(1984), In their study, also showed that Anterior Knee Pain (AKP), or AKP syndrome, is a very common and challenging condition, particularly in the young active population.[5] Anterior Knee Pain among adolescents is thought to result from submaximal, repetitive, tensile stresses acting on the immature junction of the patellar tendon, tibial tubercle, and tibia, if there is excess load on patella tendon, particularly if there are insufficient rest periods which is commonly seen in people participating in sports activities. AKP is differentially distributed across genders, with greater prevalence in females than males.

    Boling et al, found that females were 2.23 times more likely to develop AKP than males.[6] In present study also, incidence of AKP was 1.3 times more in females than males. Females are at a higher risk of joint pain and injury due to increased flexibility, and possible ligament laxity or muscle weakness.[7]

    Clinico-pathological interpretation

    In the present study, subjects were categorized in three groups on basis of clinical history and physical examination.

    Maximum patients (n=13) were of group- “Typical clinical symptoms with patellofemoral crepitus or pain on manipulation of patella”, followed by group (n=11) “Typical clinical symptoms without patellofemoral crepitus or pain on manipulation of patella”, and group (n=6) “Diffuse anterior pain as single symptom”.

    Typical clinical symptoms of AKP syndrome are dull pain in the anterior aspect of the knee that worsens when climbing stairs, sitting with the knees flexed, and rising from a sitting position. Extending the knee against resistance may also cause pain, and there may also be catching or locking and giving-way sensations (Sanchis-Alfonso, Vicente, 2011).[8]

    Niskanen, et al (2001) suggested that patellofemoral crepitus is one of the signs most indicative of patellar chondral lesions.[9]

    Anterior knee pain pathologies

    Patella alta

    Patella alta, [Figure 1] was the second commonest patellofemoral joint morphological abnormality as detected in the present study, and it was seen in 50% of our study subjects.
    Figure 1: Patella alta diagnosed by high Insall-Salvati ratio (1.36) calculated as the ratio of the patellar tendon length to the maximal diagonal length of the patella

    Click here to view


    Present study is also supported by data of various studies like Steensen et al (2015) showing patella alta incidence of 60%,[10]48% by Neyret et al (2002)[11] and 53.25 by Kohltiz et al (2013).[12] Souza et al (2013)[13] reported in his results prevalence of 53% for patella alta among his study group.

    Mean values for Install Salvati index were 1.27 in our study, and our results were comparable to several studies whose results were 1.26 (Charles MD et al, 2013)[14] and 1.23 (Escala et al, 2006).[15]

    Study done by T. Luyckx et al (2009)[16] indicated that there is a biomechanical reason for anterior knee pain in patients with patella alta. Patellofemoral contact force depends on patellar height. The maximum patellofemoral contact area gradually increases with increasing patellar height. The maximum patellofemoral contact area gradually increases with increasing patellar height. A higher patellofemoral contact force causes more deformation of the articulating surface, resulting in an increases contact area and symptoms of anterior knee pain.

    Because patella alta is frequently associated with patellar dislocation and subluxation, this condition should be assessed when a patient with anterior knee pain is evaluated (Fulkerson JP et al., 2004).[17] Patella alta also is associated with chondromalacia patella and therefore may contribute to anterior knee pain, although the relationship between such cartilage defects and anterior knee pain is not entirely clear (Chrisman OD et al., 1986).[18]

    Patella alta is the most consistent anatomic feature of patellar instability, which allows excessive lateral motion by reducing the articular contact between the patella and trochlea at a given angle of flexion. Mechanical modeling experiments have shown that because patella alta causes a delay in patellofemoral articular contact, maximal contact force and contact pressure between the patella and trochlea are abnormally increased. These factors likely account for the association between patella alta and articular cartilage abnormalities as well as patellar malalignment and instability.

    Trochlear dysplasia

    Trochlear dysplasia is a geometric abnormality in the shape and depth of the trochlear groove, defined by a shallow trochlea, a low medial-to-lateral trochlear facetal ratio or an abnormal sulcus angle.

    Trochlear dysplasia was the commonest patellofemoral joint abnormality found in the present study, and it was found in 56.7% of the study subjects. Our results are comparable to study done by Steensen et al (2015)[10] and Kohlitz et al (2013)[12] who found out an incidence of 68.3% and 66% in the study respectively.

    We examined for Trochlear dysplasia by measuring the sulcus angle and sulcus depth [Figure 2]. Their mean values have shown wide variability in between subjects in several studies provided by the literature, however most studies resulted in significant statistical difference. We found mean values of sulcus angle and sulcus depth of 150 and 2.4mm in our study group which is supported by mean values of 148.50 and 4.0mm from study of Charles et al (2013).[14]
    Figure 2: Trochlear dysplasia. (a) axial T2W image of a patient with high Sulcus angle (1490). (b) Sulcal depth of 3.5 mm. Sulcal depth is measured using three lines connecting the distance between the floor of the trochlear and a tangential line connecting the most anterior points of the medial (m) and lateral facet (l) and the posterior most point of sulcus (s). Sulcal depth is calculated as (m+l)/2-s

    Click here to view


    Dejour H et al (1990)[19] concluded in their study that a dysplastic trochlea can lead to abnormal patellar tracking, chronic patellar dislocation and to an abnormal distribution of loading, which increase the risk for anterior knee pain.

    Based on these results, AKP appears to arise mainly from abnormalities in the PF joint or extensor mechanism, or subtle changes in the articular geometry. The sulcus angle is reportedly associated with Patellofemoral instability; the larger the angle the more unstable the knee (Diederichs et al., 2010).[20] Notably, in this study the cartilaginous sulcus angle was meaningful in the evaluation of AKP patients on MR images, but not the bony sulcus angle, which is traditionally well investigated, indicating that the cartilaginous articular geometry could substitute for bony articular geometry with more accurate prediction.

    Chondromalacia patella

    In present study, we found 11 cases of chondromalacia patella with percentage incidence of 36.75. Chondromalacia patella, which is one of the major causes of chronic anterior knee pain, is characterized by the softening or breakdown of the patellar cartilage and is frequently associated with decreased quality of life. There is evidence of a relationship between AKP and patellofemoral pathology.

    In a case control study done by Joensen AM et al (2001)[21] using magnetic resonance imaging (MRI), demonstrated that a higher proportion of chondral lesions were found in athletes with AKP than in pain free matched controls.

    Arthroscopy is the standard modality for diagnosing chondromalacia patella but is a highly invasive procedure, and surgical treatment of chondromalacia patella is only indicated in a small minority of patients. Magnetic resonance imaging (MRI) help can visualize joint structure directly and noninvasively and is recognized as a valid, accurate, and reproducible tool to measure articular cartilage lesions.

    Several authors have reported that the sensitivity of MRI is considerably higher for detecting severe (Grade 3 or 4) cartilage defects [Figure 3].
    Figure 3: T2 weighted axial MR image showing chondromalacia patella as indicated by thinning of articular cartilage of lateral patellar facet with underlying bony changes (white arrow)

    Click here to view


    Patients with anterior knee pain (AKP) have revealed a high prevalence of lesions of the articular cartilage of the patella (Kannus, Natri, Paakkala, Jrvinen,1999).[22] Therefore, these lesions are considered important. However, previous studies have not been able to show an association between articular cartilage lesions and AKP, mainly because these studies have not included both persons with and without AKP. This is important, as post-mortem studies have indicated that the prevalence of articular cartilage lesions is also high among persons with no symptoms of knee disease (Stougird, 1975).

    Medial plica

    The occurrence of medial plicae within subjects differs markedly between studies and ranges between 19% and 70% (Dupont, 1997).[23]

    Studies have reported high incidences of plica within athletes who repeatedly flex their knees during sports such as rowing, swimming, cycling and running (Dupont, 1997).[23] It is proposed that each flexion / extension creates small microtraumas resulting in synovitis, effusion and pain.

    Medial plica starts from the suprapatellar plica or medial joint wall, the oblique moves along the wall, and ends on the level of the infrapatellar fat pad (Pinar H, 1988).[24] Plica has a flexible structure, glide on the femur condyles, and are generally asymptomatic. However, after inflammations, that frequently occur due to trauma, the elasticity of the thickened plica degenerates, and it may induce cartilage damage in progressive cases. Apart from trauma, chronic effusions can also cause the plica to thicken. Plica syndrome is generally found in youths and is more frequently encountered in females (Pinar H, 1988).[24]

    Typically, history of anterior knee pain developing after a blunt trauma on the knee and effusion are present. The pain is intermittent, manifests with activity, and wears off with rest. In the diagnosis of medial plica [Figure 4] the sensitivity of dynamic ultrasonography (US) and magnetic resonance imaging (MRI) is quite high (90% and 95% respectively); whereas the gold standard is arthroscopic evaluation (Al Hadithy N et al., 2011).[25]
    Figure 4: T2 weighted axial magnetic resonance image showing thick medial plica (black arrow) associated with joint effusion (*)

    Click here to view


    Hoffa’s fat pad edema

    In present study, Hoffa’s fat pad edema was present in 9 cases out of 30 with incidence of 30%. The present study is in agreement with the study done by Subhawong et al (2010)[26] in which, Twenty-five of 50 patients (50%) exhibited edema like T2 hyperintense signal in the superolateral portion of Hoff’as fat pad. Hoffa’s infrapatellar fat pad is one of three anterior fat pads of the knee, the other two being the anterior suprapatellar (quadriceps) and posterior suprapatellar (prefemoral) fat pads.

    The infrapatellar fat pad is an intracapsular structure and plays a role in stabilizing the patella in extremes of flexion and extension (Bohnsack M et al., 2005).[27] Superior to inferior, it extends from the patella to the anterior menisci and tibial periosteum and anterior to posterior, from the patella tendon to the synovial lining of the knee. Superoposteriorly, it extends to the cartilage overlying the anterior aspect of the distal femur (Saddik D et al., 2004).[28]

    Hoffa (Hoffa A., 1904) first recognized chronic impingement of the fat pad between the femur and tibia in 1904. The impingement manifests as fat pad enlargement and increased T2 signal (Jacobson JA et al., 1997).[29] A second form of impingement, which is clinically more common but radiologically more subtle, occurs at the superolateral portion of the fat pad between the patellar tendon and lateral femoral condyle and results in high t2 signal intensity related to edema [Figure 5]. It is this signal abnormality in superolateral Hoffa’s fat pad that has recently been suggested as a secondary sign of patellofemoral mal-tracking.
    Figure 5: T2 weighted fat-saturated sagittal magnetic resonance image demonstrating hyperintense edema in superior aspect of Hoffa’s fat pad (black arrow)

    Click here to view


    The statistically significant association in our study between Hoffa’s fat pad edema and patella alta is in accordance with these theories and previous studies (Chung CB et al., 2001).[30]

    The edema signal observed in the superolateral portion of Hoffa’s fat pad is the result of abnormal friction and mechanical impingement of the fat pad between the lateral femoral condyle and the patellar tendon, as previously postulated by Chung et al (2001).[30]

    A similar phenomenon occurring at the level of the superior pole of the patella maybe responsible for the association of superolateral Hoffa’s fat pad edema and pre-femoral fat pad edema, which has received little attention in the radiologic literature.

    Patellar subluxation

    In present study, patellar subluxation was seen in 10 out of 30 patients with incidence of 33.3%. Patellar subluxation is a condition, where the apex of the patella is not sliding centrally down the trochlea groove. This can be assessed using dynamic MRI (McNally EG et al, 2000).[31] The measurement of patellar subluxation [Figure 6] from dynamic MRI scans, based on a cine-loop of sequential axial images, is semi-quantitative and has been shown to be reproducible and reliable. There is an established relationship between increasing subluxation and worsening pain. O’Donnell et al (2005)[32] found an association between pain and subluxation in asymptomatic volunteers and patients with anterior knee pain. In an asymptomatic group, 91% had no or mild subluxation, 95% had moderate subluxation and no subjects had severe subluxation; in contrast in the group with anterior knee pain 17% had moderate subluxation and 7% had severe subluxation.
    Figure 6: T2 weighted axial magnetic resonance image showing lateral patellar subluxation (4.31 mm) associated with mild joint effusion

    Click here to view


    During knee flexion, subluxation of the patella lead to abnormal stresses being transferred through surrounding soft tissue, the cartilage and subchondral bone. These factors may contribute to anterior knee pain (Fulkerson JP, 1994).[33] The causes of patellofemoral subluxation are highly likely to be multi-factorial. Although certain aberrant anatomical features are known to contribute to subluxation, to date there have been no studies that have attempted to identify which anatomical features are the most relevant.

    Laterally inclined patella

    In present study, 8 out of 30 patients had laterally inclined patella with incidence of 26.7%. Study done by Powders CM (2000), shown that women with patellofemoral pain had significantly greater lateral patella inclination compared to healthy controls. Similarly, in the study done by Tanamas et al (2010),[34] they demonstrated that the patellar tilt angle which assesses the inclination of the patella relative to the orientation of the femur, was associated with knee pain.

    In particular, a more medially inclined patella (an increased lateral condyle-patella angle) was associated with reduced knee pain scores, and this was more pronounced in the obese subjects. They, also demonstrated that a more medially inclined patella [Figure 7] was associated with increased medial patella cartilage volume. In contrast, a recent radiographic study found that a more laterally inclined patella (an increase in the lateral patella tilt angle) was associated with an increase in the medial patellofemoral joint space (Hunter DJ et al, 2007).[35] This was regarded as protective of medial joint space narrowing progression, thereby presuming it to be advantageous to the patellofemoral joint. However, when the patella is laterally inclined, the radio-graphic patellofemoral joint space will intuitively be widened medially, without necessarily being associated with increased cartilage volume.
    Figure 7: T2 weighted axial magnetic resonance image showing laterally inclined patella with patellar tilt angle <80

    Click here to view


    Joint effusion

    Joint effusion was seen as associated finding in the present study. Joint effusion was present in 12 cases out of 30 subjects with incidence of 40%.

    Knee joint effusion is typical finding after patellar dislocation and will be seen in most patients, especially when imaging is performed immediately after the event (Sanders TG et al, 2006).[36] The amount of effusion decreases with time. The presence of effusion is not specific and may also be associated with other conditions. The amount of hyperintense fluid depicted with T2 weighted sequences can be amount of joint fluid present. Joint effusion is defined as a fluid depth of more than 4mm in the suprapatellar recess on midline sagittal images and more than 10 mm in the lateral recess on lateral sagittal images. If hemorrhage is present, fluid-fluid levels will be seen as a result of sedimentation of blood components, which may have intermediate or low T2 signal intensity, depending on the age of the effusion. Effusion is often absent in patients with habitual dislocations. Because such patients have considerable instability, re-dislocation rarely causes new injury to the lax medial stabilizers.

    Ligaments and meniscal tears

    Besides, synovial joint effusion, ligaments and meniscal tears were also an associated findings. Ligaments and meniscal tears comprised least proportion of anterior knee pain pathologies and had incidence of 23.3%. Many previous studies have reported a weak association between meniscus also damage and anterior knee pain (Englund M et al, 2008). The presence of meniscal damage was not associated with the development of knee pain symptoms in 15 months follow up among young and middle age patients with anterior knee pain (Kemp MA et al, 2011).[37]

    Association of trochlear dysplasia and medial plica

    Out of 11 cases with medial plica, 10 showed presence of trochlear dysplasia [Table 3]. Significant statistical association was found in between both. Medial plica was more frequently seen in the group with trochlear dysplasia (P<0.001). So, detailed evaluation in terms of medial plica is necessary in patients with trochlear dysplasia.
    Table 3: Trochlear dysplasia Vs Medial plica, as observed in present study

    Click here to view


    Kang et al indicated the correlation of the presence of abnormal geometry and/or medial plica in the patellofemoral joint with anterior knee pain in a study conducted among young male soldiers with atraumatic anterior knee pain. In addition to the results of Kang et al, it was evident in our study that the ratio of trochlear dysplasia affected the prevalence of medial plica. When trochlear dysplasia was taken into consideration, the prevalence of medial plica was found to be statistically high in the group with dysplasia. It can be considered that the prevalence of medial plica is higher in societies where the prevalence of trochlear dysplasia is high.

    Nakayama A et al (2011)[38] demonstrated in their study that as the type of trochlear dysplasia advances, the prevalence of thicker and shelf shaped plica also increases.

    Association of chondromalacia patella with trochlear dysplasia

    In the present study, there was significant statistical agreement in between chondromalacia patella and trochlear dysplasia. Out of 11 cases of chondromalacia patella, 10 cases had patellar chondral lesions [Table 4]. Numerous studies have analyzed the influence of patellofemoral malalignment on patellofemoral instability (Biedert RM et al, 2011).
    Table 4: Trochlear dysplasia Vs CMP as observed in present study

    Click here to view


    However, there is only few literature about the correlation of patellofemoral malalignment and patellar cartilage defects. Moreover, in most of these studies, a clear definition of the subject group and/or the control group is missing. Yang et al (2009)[39] for example aimed to identify variations in patellofemoral anatomy and congruency that predispose to cartilage lesions of the patellofemoral joint in 111 patients who underwent knee arthroscopy because of symptomatic cartilage lesions of the PFJ. Patients with isolated meniscus rupture and no history of anterior knee pain served as the control group. The authors found that the patella lateral facet width, patella lateral facet ratio, sulcus depth, lateral patella displacement, patella epicondylar axis and congruence angle were associated with patellofemoral cartilage defects. However, several factors limit the validity of their study. The chondral defect varied from focal defects to diffuse defects in terms of advanced patellofemoral osteoarthritis, resulting in a very heterogeneous patient group.

    J. Mehl et al (2014)[40] demonstrated that patients with isolated grade III and IV cartilage defects of the patella show distinct geometric differences of the patellofemoral joint when compared to a control group of patients without patellar cartilage defects. In particular, a flat and shallow trochlea, trochlea dysplasia and patella alta seem to contribute to the development of patellar cartilage defects.

    Association of patellar subluxation and laterally inclined patella

    In the present study, significant association was found in between patellar subluxation and laterally inclined patella [Table 5].
    Table 5: Patellar subluxation Vs Patellar tilt as observed in the present study

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    In patellofemoral subluxation, dislocation, and pain syndromes, the precipitating event is generally considered to be generated by excessive lateral translation of the patella (Post WR, 1999).[41]

    A conglomerate of imaging modalities were utilised in the present study to demonstrate various structural abnormalities in patients with anterior knee pain. The point that emerged from results in this study with contemporary literature, indicates towards the utility of MRI for the purpose. This modality presumed earlier to be a problem-solving tool, appears to have now take a certain stage with the other modalities being primarily supportive in nature.


      Summary and Conclusion Top


    The present prospective observational study attempted to determine the role of imaging modalities particularly MRI in patients with anterior knee pain, analyzed over 30 patients. Key findings of this data set indicate:

    Maximum number of patients affected with anterior knee pain belong to the age group of 21 to 30 years. 56.7% of subjects of this study were females, approximately 1.3 times more than males.

    Majority of patients (43.3%) had complaints of typical clinical symptoms with patellofemoral crepitus or pain on manipulation of patella.

    The present study demonstrated that patellofemoral instability was a major cause for origin of anterior knee pain.

    In the present study, most common detected pathology was trochlear dysplasia, followed by patella alta and chondromalacia patella.

    Abnormal morphology of the femoral trochlea, referred as trochlear dysplasia had highest incidence of 56.75 in patients of anterior knee pain.

    Second most common pathology was patella alta with percentage incidence of 50%.

    Third most common causes in incidence wise were chondromalacia patella and medial plica. Both had incidences of 36.7%. Other predisposing factors for patellofemoral instability were laterally inclined patella and patellar subluxation. Laterally inclined patella had incidence of 26.7% and Patellar subluxation had 33.3% incidence. Abnormal signal intensity in Hoffa’s fat pad was present in 30% cases. Associated synovial effusion was present in 40% cases, while meniscal tears were associated in 23.3% cases.

    The observations in present study reveal significant association in between incidence of trochlear dysplasia and medial plica. Out of 11 cases with medial plica, 10 had trochlear dysplasia.

    Trochlear dysplasia was also associated with chondromalacia patella. The patients with trochlear dysplasia had high incidence of patellar chondral lesions. Out of 11 cases with chondromalacia patella, 10 had trochlear dysplasia.

    In the present study, significant association was found in between patellar subluxation and laterally inclined patella.

    In the present study, it could be deciphered that MRI was useful in quantitative measuring of the predisposing factors contributing to Anterior Knee Pain. MR imaging contributed to the diagnosis of different anatomic variants, ligamentous injuries and chondral lesions that predispose to instability, and guide the orthopedic surgeons in selecting the most optimal treatment.

    Financial support and sponsorship

    Nil.

    Conflicts of interest

    There are no conflicts of interest.



     
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        Figures

      [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
     
     
        Tables

      [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



     

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