6 Cone R. Patella Alta and Baja. In eight of 17 patients, the mechanism of injury was a patellar tendon tear (n = 1) or valgus hyperextension (n = 7). A sliver of fluid undermines a moderately thickened and scarred MPFL at the medial femoral condyle attachment consistent with a chronic partial stripping tear (arrowheads). The patella remains laterally subluxed and tilted, and the patient has an abnormally shallow trochlear groove (line). Bull NYU Hosp Jt Dis 67:2229, Dupuy DE, Hangen DH, Zachazewski JE, Boland AL, Palmer W (1997) Kinematic CT of the patellofemoral joint. It runs obliquely and transversely and inserts on the patella and the patellar tendon, and is composed of two layers. Findings typically associated with acute lateral patellar dislocation were also assessed and recorded (present or absent) including characteristic bone bruises and osteochondral injuries involving the patella, lateral trochlear facet, and lateral femoral condyle. Google Scholar, Miller TT, Staron RB, Feldman F (1996) Patellar height on sagittal MR imaging of the knee. Discussion. Radiology 216:582585, Ward SR, Terk MR, Powers CM (2007) Patella alta: association with patellofemoral alignment and changes in contact area during weight-bearing. The MPFL plays a significant role in the stabilization of the medial aspect of the patella.Especially during the early stages of knee flexion, the MPFL is a critical component in patellar tracking and stability within the trochlear groove. The decreased patellar contact area decreases stability particularly in shallow degrees of flexion and thus predisposes to lateral patellar subluxation. As a common knee injury, patellar dislocation has a mean annual incidence of 5.8 in 100,000 people and is more prevalent in women. The distance from the tibial tubercle to the trochlear groove (TT-TG) provides a quantitative evaluation of excessive lateralization of the tibial tuberosity.7, (10a) Axial image of the knee with superimposition of the tibial tubercle from another slice (yellow outline). 0000070933 00000 n 0000192215 00000 n 0000212094 00000 n Soft tissue changes may include effusion, thickening or disruption of the MPFL, and retinacular complex and regional edema. Lateral Patellar Dislocation. a Normal trochlea. AJR Am J Roentgenol 195:13671373, Jarraya M, Diaz LE, Roemer FW, Arndt WF, Goud AR, Guermazi A (2018) MRI findings consistent with peripatellar fat pad impingement: how much related to patellofemoral maltracking? a Sagittal PD knee MRI showing the method of assessing the InsallSalvati index, calculated as the ratio of the patellar tendon length at its inner aspect (white dashed line) to the greatest diagonal length of the patella (white line). (1a) A single fat-suppressed proton density-weighted coronal image is provided. Failure to identify or treat injury to the patellar retinaculum is associated with recurrent patellar instability and contributes to significant morbidity. The lateral trochlear articular surface is usually more prominent than its medial portion. We confirm that this article is not under consideration for publication elsewhere and that the authors did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors. The lateral retinaculum is a ligament that helps hold your patella, or kneecap, in place. Magnetic Resonance Cholangiopancreatography MRI PREMIUM Digestive system Illustrations PREMIUM CT axial male abdomen and pelvis CT PREMIUM CT peritoneal cavity CT PREMIUM MRI female pelvis MRI PREMIUM Female pelvis Med Sci Sports Exerc 35:20432047, Steiner T, Parker RD (2009) Patella: subluxation and dislocation. Subluxation and dislocation: recurrent. The rectus femoris (RF), vastus lateralis (VL), and lateral retinaculum (LR) are also indicated. Treatment is nonoperative with physical therapy focusing on quadriceps stretching and strengthening. Concave impaction deformity of the inferomedial patella is a specific sign of prior LPD. Adjunctive treatments such as knee aspiration and patellar stabilizing braces have been proposed to decrease swelling and enable early range of motion; however, there is no conclusive evidence for their use [71]. The latter distinction is important to recognize among both radiologists and surgeons. b Axial MRI at the level of the tibial tuberosity. VMO dysplasia may play a role in patellofemoral instability. (Figs.1-A 1-A also and1-B). Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella Injury to the medial retinaculum, MPFL, and VMO may be identified at MR imaging after acute LPD. AJR Am J Roentgenol 169:211215, Buchner M, Baudendistel B, Sabo D, Schmitt H (2005) Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Methods: We compared 361 treated cases of aneurysm occlusion after subarachnoid hemorrhage from 1997 to 2003 with 281 cases from 2006 to 2014. Radiology. The patellofemoral joint has two primary functions; firstly, it acts as an anatomic pulley to provide mechanical advantage for the extensor mechanism and, secondly, to reduce friction between the extensor mechanism and the femur. official website and that any information you provide is encrypted 8 Lippacher S, Dejour S, Elsharkawi M, et al. J Bone Joint Surg Am Volume 90:27512762, Dixit S, Deu RS (2017) Nonoperative treatment of patellar instability. In either case, careful search for possible displaced osteochondral fragments is necessary, as surgery is often indicated in such patients. The trochlear depth is calculated by measuring the mean of the maximum anteroposterior (AP) distance of the medial and lateral femoral condyles minus the distance between the deepest point of the trochlear groove and the line paralleling the posterior femoral condyles surfaces (Fig. PMID: 9168713. Acute patellar dislocation (APD) is a common injury in children, accounting for up to 16% of acute knee hemarthroses. Trochlear depth=[(a+b)/2]c, Lateral trochlear inclination measurement on axial MRI. Patellar tilt assessment. Radiology 225:736743, Kirsch MD, Fitzgerald SW, Friedman H, Rogers LF (1993) Transient lateral patellar dislocation: diagnosis with MR imaging. Methods MRI studies taken at one imaging site between January, 2007 to January, 2008 with the final diagnosis of patella . Edema is also present medially in the region of the MPFL and medial retinaculum (arrowheads). The lateral retinaculum appears as a hyperechoic band originating from the iliotibial band and the vastus lateralis muscle. Recent literature does not encourage the use of lateral release, since this can increase patellar instability. Advantages of CT over MRI include the reduced cost, larger gantry diameter allowing to fit larger patients, faster acquisition with less potential for claustrophobia, fewer absolute and relative contraindications related to implanted devices, and better cortical bone definition. Imaging plays a vital role in detecting not only the secondary damage but also subtle early features that can raise the suspicion for the presence of this entity. 3). The conditions are presented anatomicallyanterior, lateral, medial, or posteriorwith common etiologies, history and physical exam findings, and diagnosis and treatment options for each (see Table, page 28). Radiology 216:858864, Biedert RM, Tscholl PM (2017) Patella alta: a comprehensive review of current knowledge. Jibri, Z., Jamieson, P., Rakhra, K.S. Rev Bras Ortop 46:160164, LeGrand AB, Greis PE, Dobbs RE, Burks RT (2007) MPFL reconstruction. 2012 Feb;41(2):137-48. doi: 10.1007/s00256-011-1291-3. It is composed of Lockwood's ligament (inferior suspensory ligament), the lateral extension or horn of the levator aponeurosis, the continuations of the pretarsal and preseptal muscles, and the check ligament of the lateral rectus muscle. Lateral release and medial imbrication on their own are generally insufficient, but can be used to augment an MPFL repair or reconstruction or, if there is osseous misalignment, used in conjunction with a bony procedure particularly if there is recurrent instability or demonstrable lateral patellar tilt [73,74,75,76,77,78]. A ratio equal or more than 1.2 indicates patella alta [35] (Fig. CAS There is agreement, however, that the MPFL is almost always injured with lateral patellar dislocations4. An association has been demonstrated between patellofemoral cartilage damage and patellar maltracking. Knee Surg Sports Traumatol Arthrosc 2:1926, Jaquith BP, Parikh SN (2017) Predictors of recurrent patellar instability in children and adolescents after first-time dislocation. Medial retinacular complex injury in acute patellar dislocation: MR findings and surgical implications. AJR Am J Roentgenol 1997; 168:1493-1499. Several methods have been used to assess patella alta. On T2-weighted MR images, sprain is depicted as thickening of retinaculum with signal intensity signifying edema and hemorrhage (Fig. Privacy Clipboard, Search History, and several other advanced features are temporarily unavailable. It is the angle between a line tangential to the subchondral bone of the posterior aspect of the femoral condyles and a line along the lateral trochlear facet subchondral bone (Fig. [Google Scholar] 6. Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr 2001; 25:957-962. (8a) A more posterior coronal T1-weighted image also demonstrates the intimate relationship of the VMO and MPFL. It is therefore recommended that radiologists include measurement of TT-TG in reports on patients who undergo MRI for patellar instability. Features that may predispose to patellar dislocation and/or patellar maltracking and can be evaluated with CT include patellar and trochlear morphology and the alignment between the two structures. 9). Trochleoplasty is rarely performed in this country and is reserved for significant dysplasias or when other surgical options have been insufficient in restoring patellofemoral stability. (28a) A sagittal proton density-weighted image demonstrates the typical hardware location in a patient status post medialization of the tibial tuberosity (arrow). Check for errors and try again. The mechanism is commonly a non-contact twisting injury of the lower extremity with the knee extended and external rotation of the foot and is perceived as the knee giving way. The patella will often self-reduce by reflexic contraction of the quadriceps muscles. Each of the mentioned assessment methods of patella alta has its own advantages and limitations. Incidence and concomitant chondral injuries in a consecutive cohort of primary traumatic patellar dislocations examined with sub-acute MRI. Insights into Imaging By altering the insertion point of the patellar tendon, these procedures affect the timing and position of patellar engagement in the trochlea and have the ability to biomechanically offload damaged distal articular cartilage, thereby reducing pain and increasing stability simultaneously. Prior lateral patellar dislocation: MR imaging findings. The injuries involved the medial retinacular ligament in 16 of 17 patients and the medial and lateral retinacular ligament in one patient. From this insertion, it extends posteriorly to blend with the lateral margin of the knee capsule and inferior surface of the lateral tibial condyle 1,2. 21 Patellar dislocation not only has a high recurrence rate 51 but also readily causes articular cartilage damage, osteochondral fractures, and patellofemoral arthritis, which can ultimately lead to motor dysfunction and pain. AJR Am J Roentgenol 179:11591166, Zhang GY, Zheng L, Ding HY, Li EM, Sun BS, Shi H (2015) Evaluation of medial patellofemoral ligament tears after acute lateral patellar dislocation: comparison of high-frequency ultrasound and MR. Eur Radiol 25:274281, Tecklenburg K, Dejour D, Hoser C, Fink C (2006) Bony and cartilaginous anatomy of the patellofemoral joint. In: West RV, Colvin AC (eds) The patellofemoral joint in the athlete. Clin Orthop Relat Res 144:1626, Elias DA, White LM, Fithian DC (2002) Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. It is the angle between a line tangential to the subchondral bone of the posterior aspect of the femoral condyles and a line along the lateral trochlear facet. (20a) A fat-suppressed proton density-weighted sagittal image in a patient following patellar dislocation reveals an osteochondral injury with a chondral defect (arrows) at the lateral weightbearing surface of the lateral femoral condyle, a finding seen in only 5% of patients. Arthroscopy 32:929943, Dejour D, Saggin P (2010) The sulcus deepening trochleoplastythe Lyons procedure. Sports Med Arthrosc Rev 15:7277, Mikashima Y, Kimura M, Kobayashi Y, Miyawaki M, Tomatsu T (2006) Clinical results of isolated reconstruction of the medial patellofemoral ligament for recurrent dislocation and subluxation of the patella. (7a) A coronal T1-weighted image at the level of the patella demonstrates blending of fibers of the VMO with the MPFL superiorly. Patellar maltracking: an update on the diagnosis and treatment strategies, https://doi.org/10.1186/s13244-019-0755-1, http://creativecommons.org/licenses/by/4.0/. Open Orthop J. Jumping. Note the edema in the superolateral aspect of Hoffas fat pad (arrow). However, the use of this method is not widespread. Elsevier, Philadelphia, Buckens CF, Saris DB (2010) Reconstruction of the medial patellofemoral ligament for treatment of patellofemoral instability: a systematic review. Pedersen ME, DaCambra MP, Jibri Z, Dhillon S, Jen H, Jomha NM. From 10 to 20 of flexion, the patella engages the trochlear groove with the contact area being the inferior most portion of the medial and lateral facets. It has been suggested that fat impingement occurs between the lateral femoral condyle and the posterior aspect of the patellar tendon [54]. Nonoperative treatment is generally recommended in first time dislocators unless there are MRI findings of severe predisposing dysplasia and the presence of a chondral or osteochondral body. Anatomical and radiology atlas of the abdomen and pelvis based on anatomical diagrams and cross-sectional CT and MRI imaging. (23a) In this patient with recurrent patellofemoral dislocations, there are findings of subchondral degeneration (arrow) from recurrent impaction and chondral shearing injuries to the inferolateral femoral condyle. Int Orthop 34:311316, Donell ST, Joseph G, Hing CB, Marshall TJ (2006) Modified Dejour trochleoplasty for severe dysplasia: operative technique and early clinical results. Isacsson A, Olsson O, Englund M, Frobell RB. Because of the transient and brief nature of lateral patellar dislocations, the diagnosis is frequently unrecognized by both patients and clinicians. HHS Vulnerability Disclosure, Help The deep layer of the lateral retinaculum contains thickenings that form ligaments providing stabilizing support to the patella. Analysis with magnetic resonance imaging. 1 Pain is often described as medial because of soft tissue injuries that occur to the medial retinaculum and/or MPFL. (4a) This 3D graphic view of the medial knee with the crural fascia and sartorius (S) muscle incised and reflected demonstrates the main medial contributors to patellar stability. CT of both knees in 20 flexion demonstrating bilateral shallow trochlear groove (arrows) compatible with dysplasia and bilateral lateral patellar subluxation and lateral tilt. A bone bruise at the anterolateral aspect of the lateral femoral condyle is also apparent (arrowheads). Yu JS, Goodwin D, Salonen D, Pathria MN, Resnick D, Dardani M, Schweitzer M. AJR Am J Roentgenol. The MPFL is attached to the region of the adductor tubercle or medial femoral epicondyle extending deep to the vastus medialis obliquus (VMO) and attaching to the superior two thirds of the patella [52]. Lateral patellar compression syndrome is the improper tracking of the patella in the trochlear groove generally caused by a tight lateral retinaculum. This results in a slightly superolateral direction of pull on the patella by the quadriceps. Another study noted an association between abnormal trochlear morphology and high-grade patellofemoral cartilage damage [58]. Transient lateral patellar dislocation. Patellar tendon lateral femoral condyle friction syndrome is one of several entities that result in anterior knee pain and in which abnormalities of the patellar fat pads are found on MR imaging. [Crossref] Harvinder Bedi, John Marzo. As the knee joint ranges from extension to flexion, the articular surface area of the patella is in contact with the femur changes. Medial patellar. 28 The average annual incidence for patellar dislocation injuries ranged between 5.8 and 7.0 per 100,000 person-years in the civilian population, and up to 29 per 100,000 person-years in the 10-17 year age . ANTERIOR KNEE PAIN Usually, young individuals, particularly women, suffer the consequences of this disorder [2]. The medial patellofemoral ligament (MPFL) is a condensation of the medial capsule of the knee joint. Quinn described the MRI findings following acute patellar dislocation as contusion or impaction of the medial patellar facet and lateral femoral condyle, along with injury of the medial retinaculum and/or medial patellofemoral ligament (MPFL) (Quinn, 1993). 2011;39(8):1756-1761. Evaluate the TCO of your PACS download >, 750 Old Hickory Blvd, Suite 1-260Brentwood, TN 37027, Focus on Musculoskeletal and Neurological MRI, https://radsource.us/patella-alta-and-baja/, The Anterior Meniscofemoral Ligament of the Medial Meniscus. The knee then was flexed 30, 60, 90, and 120, and the transducer recorded changes in tension within the lateral patellofemoral . At the time the article was last revised Joel Hng had Less commonly, a direct laterally or medially orientated blow to the patella can precipitate dislocation. Axial PDFS left knee MR image, demonstrating the method used for the measurement of trochlear depth. Am J Sports Med 2009 37: 2355-2362. 30 Correctly diagnosing APD can be difficult as the displaced patella usually relocates spontaneously, with fewer than 10% of patients presenting with fixed lateral dislocation. Springer Nature. Manage cookies/Do not sell my data we use in the preference centre. Characterization of the type of medial restraint injury is crucial for surgical planning. Thawait SK, Soldatos T, Thawait GK, Cosgarea AJ, Carrino JA, Chhabra A. Skeletal Radiol. 23,29,37 The causative factors of . A newer method to assess for patella alta is the patellotrochlear index (PTI), which is measured in the midsagital MRI as the ratio of the length of trochlear cartilage engaged with the patella to the patellar cartilage length [36]. MRI and CT are superior modalities in looking for predisposing factors associated with patellar maltracking [26,27,28]. There is edema of the medial patella and of the lateral femoral condyle (arrow), consistent with bone contusion due to recent lateral patellar dislocation. It is a ratio between the patellar tendon length (along the inner surface of the tendon) and the diagonal patellar height [27]. Cochrane Database Syst Rev 2:CD008106, Woo R, Busch MT (1998) Management of patellar instability in children. Background Lateral Patella dislocations are common injuries seen in the active and young adult populations. The radiograph can also be useful in detecting osseous morphologic features associated with patellar maltracking such as patella alta and trochlear dysplasia [24, 25]. It has been shown that damage to the medial patellar stabilizers including medial patellar retinaculum and the medial patellofemoral ligament (MPFL) injuries are prevalent in 70100% of cases of lateral patellar dislocation [5, 27, 49,50,51]. On MRI, impingement is usually manifested as high signal intensity within the superolateral aspect of the infrapatellar fat pad on fluid-sensitive sequences (edema) (Fig. 1 Lance E, Deutsch AL, Mink JH. However, it lacks sensitivity with 40% of sizable osteochondral lesions being missed on initial presentation after patellar dislocation [16]. However, patellofemoral tracking is a dynamic process with the spatial relationship between the articular surfaces varying depending on the position of the knee joint [57, 64]. A generalized physical examination assessing ligamentous laxity and rotational profile of the lower extremity is critical. In a series of 474 patients with anterior knee pain, patellar tilt or subluxation was present in 40% of the cases on axial MRI [46]. Normal TD > 5.2mm. Current Concepts Regarding Patellofemoral Trochlear Dysplasia. In these patients, a triad of findings that included focal impaction injuries involving the lateral femoral condyle, osteochondral injuries of the medial patellar facet, and injuries of the medial retinacular ligament were seen. b Trochlear dysplasia (9 inclination), Facet asymmetry assessment for trochlear dysplasia on axial MRI. Patellar tilt can also be assessed using the patellofemoral angle (PFA). Reconstruction of the medial patellofemoral ligament for treatment of patellar instability. This injury has been described in conjunction with numerous sports activities, particularly snow skiing. PubMed Am J Sports Med. The most common trochleoplasty procedure described is a combination of lateral trochlear osteotomy and bone graft to heighten the lateral trochlea. MRI and operative studies have revealed that it is almost . Some controversy exists regarding whether female gender is a definite risk factor for patellar instability with certain studies identifying a 33% increased likelihood of first-time dislocation as well as three times high re-dislocation rates than males, whereas others have found roughly equal rates [2, 12,13,14]. Patellar maltracking occurs as a result of an imbalance in the dynamic relationship between the patella and trochlea. Objective: This prospective study is designed to detect changes in the treatment of ruptured intracranial aneurysms over a period of 17 years. For first-time dislocators without intra-articular loose bodies or chondral injury, a trial of nonoperative therapy is indicated. Traumatic lateral patellar dislocation is a common injury among young, athletic individuals and is generally transient in nature. Int J Sports Med 29:359365, Smith TO, Walker J, Russell N (2007) Outcomes of medial patellofemoral ligament reconstruction for patellar instability: a systematic review. Google Scholar, Pfirrmann CW, Zanetti M, Romero J, Hodler J (2000) Femoral trochlear dysplasia: MR findings. Before Biomechanical evaluation of lateral patellar dislocations. Magnetic resonance imaging (MRI) is a vital tool in evaluating the potential cause(s) of anterior knee pain due to the complexity of the structure and biomechanics of the knee. AJR Am J Roentgenol 194:721727, Kalichman L, Zhang Y, Niu J et al (2007) The association between patellar alignment and patellofemoral joint osteoarthritis features--an MRI study. Bone bruise in acute traumatic patellardislocation: volumetric magnetic resonance imaging analysis with follow-up mean of 12 months. 20,61 This is attributable to a medial retinacular injury, specifically, avulsion or tearing of the medial patellofemoral ligament. no financial relationships to ineligible companies to disclose. Am J Sports Med 33:220230, Nikku R, Nietosvaara Y, Aalto K, Kallio PE (2005) Operative treatment of primary patellar dislocation does not improve medium-term outcome: a 7-year follow-up report and risk analysis of 127 randomized patients. The axial proton density-weighted image reveals a large osteochondral shearing injury involving the mid to medial patella (arrowheads). Early diagnosis is essential, as chronic maltracking will lead to patellofemoral cartilage damage and osteoarthritis [3]. J Knee Surg 19:307316, Gonaives MB, Jnior LH, Soares LF, Gonaives TJ, Dos Santos RL, Pereira ML (2011) Medial patellofemoral ligament reconstruction to treat recurrent patellar dislocation. A facet ratio of < 40% indicates dysplasia. The adductor magnus tendon (AT) attaches to the adductor tubercle, which lies posterior and superior to the femoral attachment of the MPFL. Lateral patellar dislocation results in bone contusion at the medial patella and along the lateral aspect of the lateral femoral condyle. The lateral patellar retinaculum can also be assessed in this position. Patellar dislocation most commonly results from a twisting motion, with the knee in flexion and the femur rotating internally on a fixed foot (valgus-flexion-external rotation) 1. {"url":"/signup-modal-props.json?lang=us"}, Moodaley P, Hng J, Hacking C, et al. It is therefore helpful in surgical planning. 1). If the lateral retinaculum tendon is tight enough to pull the patella out of the trochlear groove, a lateral release procedure can loosen the tissue and correct the patellar malalignment. TT-TG assessment has its own limitations. MRI is the imaging modality of choice in the assessment of patellar maltracking, as a virtue of what it can reveal (Table1). . Similar 2-year results in 125 randomized patients. The lateral patellar retinaculum is a fibrous expansion comprising of superficial and deep layers. AJR Am J Roentgenol 187:13321337, White BJ, Sherman OH (2009) Patellofemoral instability. Prevalence of Lateral Patellofemoral Maltracking and Associated Complications in Patients with Osgood Schlatter Disease. The medial patellar retinaculum is part of the anterior third of the medial joint capsule. Trauma itself rarely causes patellofemoral dislocations without predisposing factors such as trochlear dysplasia, patella alta and lateralization of the tibial tuberosity. By using this website, you agree to our Axial PDFS MR image showing MPFL disruption (open arrow) and trochlear dysplasia (arrowheads). The two features are associated with patellar maltracking. On the other hand, the PTI is significantly altered with knee flexion [37]. The TT-TG distance can be influenced by the degree of knee flexion (reduces with flexion), and it is also smaller upon weight bearing [41]. A buckle transducer was clamped on the lateral patellofemoral ligament and the transducer was calibrated to zero with the knee at full extension. 9 Lippacher S, Dejour S, Elsharkawi M, et al. From the inside of the knee the lateral retinaculum is incised, from the inside, allowing the kneecap to untilit itself. is a term coined for anatomic characteristics that lead to an increased Q angle and an exacerbation of patellofemoral dysplasia. TT-TG is a reflection of the clinically measured Q angle. Evaluation of both of these soft tissue structures is critical when one examines a MRI following lateral patellar dislocation, as the extent of soft-tissue injury influences the use of operative repair. Acta Orthop Belg 72:6571, Panagopoulos A, van Niekerk L, Triantafillopoulos IK (2008) MPFL reconstruction for recurrent patella dislocation: a new surgical technique and review of the literature. Clin Biomech (Bristol, Avon) 19:10401047, Horton MG, Hall TL (1989) Quadriceps femoris muscle angle: normal values and relationships with gender and selected skeletal measures. TT-TG distance of more than 20mm is believed to be nearly always associated with patellar instability [27]. A typical bone bruise is seen within the anterolateral aspect of the lateral femoral condyle (asterisk). Observer Agreement on the Dejour Trochlear Dysplasia Classification: A comparison of true lateral radiographs and axial magnetic resonance images. Stretching this ligament keeps the patella in place and the ligament healthy. Acta Orthop 76:699704, Nikku R, Nietosvaara Y, Kallio PE, Aalto K, Michelsson JE (1997) Operative versus closed treatment of primary dislocation of the patella. https://doi.org/10.1186/s13244-019-0755-1, DOI: https://doi.org/10.1186/s13244-019-0755-1. PFA of 0 or if it opens medially (negative value) is considered abnormal indicating lateral patellar tilt [27, 48].
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