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Current Reviews in Musculoskeletal Medicine logoLink to Current Reviews in Musculoskeletal Medicine
. 2023 Apr 18;16(7):255–262. doi: 10.1007/s12178-023-09836-0

Patellofemoral Instability in the Pediatric Population

Prushoth Vivekanantha 1,✉, Dan Cohen 2, Devin Peterson 2, Darren de SA 2
PMCID: PMC10356699  PMID: 37071284

Abstract

Purpose of Review

This review focuses on the etiology, diagnosis, and management of patellar instability in pediatric patients.

Recent Findings

Radiological outcomes such as tibial-tubercle to trochlear groove (TT-TG) distance used in diagnosis are subject to factors of influence such as femoral anteversion and knee flexion angle, and new measure such as tibial-tubercle to posterior cruciate ligament distance as well as TT-TG/trochlear width (TT-TG/TW) are under investigation. To prevent recurrent instability, surgical intervention for acute patellar dislocations may be advantageous compared to conservative management.

Summary

Patellar instability is a common pathology found in pediatric cohorts. Diagnosis can be performed via a combination of history, physical examination maneuvers, and radiological risk factors such as patella alta, patellar tilt, trochlear dysplasia, and elevated TT-TG distances. Current literature advocates the usage of additional radiological measures to TT-TG such as TT-TG/TW, especially as TT-TG varies with age in younger patients. Recent literature potentially suggests the utilization of surgical procedures such as MPFL reconstruction or repair for acute dislocations in the hope of preventing recurrent instability. Special indications for pediatric patients include osteochondral fracture identification to help prevent patellofemoral osteoarthritis. A comprehensive workup and understanding of current literature can aid clinicians in aiming to prevent recurrent patellar dislocation in pediatric patients.

Keywords: Patella, Pediatrics, Dislocation, Instability

Introduction

Acute patellar dislocation is a common knee injury within the pediatric population [1], and up to 40% of these patients can develop chronic patellofemoral instability (PFI) overtime [2]. PFI is defined as recurrent patellar subluxation or dislocation in relation to the trochlea of the femur, with dislocation almost always occurring laterally [3]. PFI is more common in adolescent females and the incidence ranges from 5.8 to 29/100,000 in the 10–17-year age group [4]. The incidence of primary patellar dislocations is increasing with the increase in the number of adolescent athletes involved in intense sports [4]. Adolescents are at increased risk due to changes in ligamentous laxity and lower extremity mechanics during a period of rapid skeletal maturation and growth [5].

This manuscript aims to provide an overview on the current understandings of the diagnosis, classification, and management of PFI in the pediatric patient.

Anatomy

The patellofemoral joint consists of the posterior surface of the patella and the trochlear surface of the distal anterior femur [6]. During flexion, the contact between the patella and the trochlear groove increases, distributing joint forces over a greater area, allowing protection from routine high compressive forces [6]. The greatest potential for instability is at full extension, where the trochlear groove is more shallow distally, resulting in decreased stability of the patella [6].

The medial patellofemoral ligament (MPFL) is a structure that plays a critical role in stabilizing the patella between 0 and 30 degrees of knee flexion [7]. The MPFL is a triangular band with its base on the superior half of the patella, with the tip of the triangle attaching onto the epiphysis of the femur in children, distal to the growth plate [7]. The MPFL is taut during extension of the knee and relaxed during flexion. Rupture of this ligament is often commonly seen in patellar dislocation, and reconstruction of this ligament may be indicated [7].

Etiology and Risk Factors

There are four main anatomical risk factors for PFI in the pediatric patient: elevated TT-TG distance, patella alta, trochlear dysplasia, and patellar tilt [8]. However, other risk factors include decreased age, open physes, and MPFL laxity and injury [9, 10••].

Elevated TT-TG Distance

Measurements of PFI include assessment of the tibial tubercle to TT-TG distance, Q angle, patellar tilt, patella alta, and the congruence angle [9]. The Q angle is defined as the angle between the line connecting the anterior superior iliac spine and center of patella, and the line connecting the center of the patella to the tibial tubercle [9]. A recent meta-analysis reported that pediatric patients with recurrent PFI had a significantly higher TT-TG distance of 15.5 mm compared to controls who had a mean TT-TG distance of 9.4 mm (p < 0.01) [9]. This is consistent with guidelines suggesting that TT-TG values over 15 mm may be a possible risk factor for PFI [2]. However, another study found that elevated TT-TG distance was not an isolated instability risk factor for lateral PFI, and instead often co-occurred with other risk factors [9].

Patella Alta

Patella alta occurs when the patella is relatively high to the trochlear groove, and is defined as a Caton-Deschamps Index (CDI) greater than 1.2 [11]. The Insall-Salvati ratio, defined as the ratio between patellar tendon length and patella length, can also be used with values greater than 1.2 indicating patella alta. A recent literature review reported that correcting patella alta, regardless of ancillary procedures performed, resulted in improvement in patellofemoral stability [11].

Trochlear Dysplasia

A recent meta-analysis found that more than 50% of included patients with PFI had a form of trochlear dysplasia (types A, B, C, D) as per Dejour’s classification. The sulcus angle can be used to describe severity of trochlear dysplasia, and is defined as the angle between medial and lateral trochlear facets [9]. It was also noted that the weighted bony sulcus angle of 150.2° was significantly higher (p < 0.01) in patients with PFI than a bony sulcus angle of 140.4° for controls who did not have PFI [9]. These results correspond with 145° being a threshold sulcus angle value for predicting PFI [12]. Type A consists of preserved trochlear morphology with a moderately shallow trochlea while type B consists of a flat or convex trochlea. Type C consists of asymmetrical trochlear facets with a convex and hypoplastic lateral and medial facet respectively and type D consists of asymmetrical trochlear facets with a hypoplastic medial facet and a cliff pattern [12].

Patella Tilt

A prospective consecutive series found that patellar tilt had an exact odds ratio of 97.79 and was significant for predicting PFI (p < 0.01), with a threshold value of 20° being considered pathological [12].

Classification

There are three main classification systems for pediatric PFI that have been reported in the literature.

Dejour et al. [8] classified patellar instability into three categories:

  1. Major patellar instability: more than one document dislocation

  2. Objective patellar instability: one documented dislocation and associated anatomic abnormality (elevated TT-TG, patellar alta, patellar tilt, trochlear dysplasia)

  3. Potential patellar instability: patellar pain with associated radiographic abnormalities

This was followed by Chotel et al. [7] who created their own classification system. They proposed five categories:

  1. Congenital dislocation: Patients have short, externally rotated quadriceps leading to fixed knee flexion, an irreducible patella, and genu valgum. The trochlea is often flat and the patella is often hypoplastic.

  2. Permanent dislocation: Patients often dislocate before the age of 5 and antalgic gait is often present.

  3. Habitual dislocation with knee flexion: Patients have short vastus lateralis muscles that causes the patella to dislocate at variable angles of knee flexion. Challenges are experienced with running and jumping activities.

  4. Habitual dislocation during knee extension: Most of the articulation of the patellofemoral joint is preserved until the knee is near full extension where the patella laterally dislocates.

  5. Recurrent dislocation: This is the most common type of PFI and instability is associated with certain sporting events in female adolescents.

Parikh et al. [13] proposed a comprehensive classification to include all forms of patellar dislocation:

  1. Type I: First time patellar dislocation that is associated with (IA) or without (IA) osteochondral fractures, typically of the medial aspect of the patella. Type IA is often associated with traumatic injury, whereas type IB is often associated with atraumatic injury or trivial trauma such as walking down the steps or pivoting maneuvers.

  2. Type II: The most common type of PFI, characterized by recurrent subluxations of the patellofemoral joint (IIA) or recurrent dislocations (IIB). This often occurs in female adolescents.

  3. Type III: Type IIIA is classified by patellar dislocation with the application of a varus force against the patella, whereas type IIIB is classified by dislocation with each flexion/extension cycle of the knee.

  4. Type IV: Permanent patellar dislocation with the absence of articulation at the patellofemoral joint indicates type IV PFI. Type IVA is reducible whereas type IVB is irreducible.

Patients with neuromuscular disorders or connective tissues can present with syndromic PFI which can vary from type I to IV. Female adolescents with Ehlers-Danlos syndrome have hypermobile joints, and can present with type I or type II PFI, which can progress to more severe stages with an absence of management. Patients with Down syndrome often have hypotonia and can present with type III PFI due to poor muscle restraint [13]. Since 2016, there have not been any new updates with regard to classification systems for PFI [14].

Diagnosis and Radiographic Evaluation

History

Clinical assessment should begin with a detailed history that encompasses age, sex, activity level of patient, and relevant family history. Age of first dislocation as well as mechanism of injury should be determined if the patient presents with recurrent dislocations [15].

Physical Examination

After general inspection, the Beighton scale assessing laxity of the ligaments can be performed, with scores of six or more indicating ligament laxity [16].Assessment for the presence of a “J sign” can also be performed while the patient is seated and asked to flex and then extend their knee. Notable excessive lateral translation of the patella during extension is classified as a positive “J sign” [17]. The Moving Patellar Apprehension Test is described to have 88.4% specificity and 100% sensitivity, and can be performed by taking the knee from full extension into flexion with a lateral force on the patella. This is followed by a medial force applied to the lateral patella with concurrent flexion and extension of the patella. A positive test is indicated by pain, apprehension, and quadriceps contraction upon lateral force application and relief of symptoms upon medial force application [18]. Another physical exam maneuver includes palpation over the medial femoral epicondyle, the attachment side of the MPFL; tenderness over this area indicates possible injury to the MPFL [19].

Imaging

In a prospective study analyzing pediatric patients with PFI and their magnetic resonance imaging (MRI) data, 17% of patients had patella alta, patellar tilt, elevated TT-TG distances, and trochlear dysplasia, 27% had three of the four risk factors, 35% had two of the four risk factors, and 17% had one [12]. This suggests that in this patient population, it is advantageous to incorporate a combination of the major radiographic risk factors while diagnosing patients. The Patellar Instability Severity Score was developed by taking these factors into consideration for a maximum score of seven points [20]. Patients who scored above four points had a significantly higher likelihood of suffering recurrent dislocations than those who scored three or lower (p = 0.0064) [20]. Patellar alta via CDI can be measured on radiograph by taking the ratio between the anterosuperior aspect of the tibial tubercle to the posterior pole of the patellar articular surface and the patellar articular surface length [21]. Additionally, sulcus angle can be measured via radiograph, MRI, or computed tomography (CT) with a Merchant view.

In the skeletally immature cohort, CT has shown to produce larger measurements for TT-TG compared to MRI, with a mean difference of 2–4 mm between both imaging modalities [22]. TT-TG can be plotted as a function of subject age in years, with non-linear regression modeling showing that TT-TG increases with age [23]. However, recently, there has been debate over the usage of TT-TG in the context of patellar instability [24]. TT-TG is influenced by factors such as knee flexion, femoral anteversion, and patient size, impacting the reproducibility of measurements [25]. This has led to the recent investigation of other radiological measures that predict lateralization of the tibial tubercle. Tibial tubercle to posterior-cruciate ligament (TT-PCL) distance is free of influence from femoral anatomy unlike TT-TG. However, several recent studies have shown that TT-TG has better discriminatory power than TT-PCL at predicting patellar instability [26–28, 29•, 30•]. A recent study investigated the predictive capacity for patellar instability of TT-TG normalized to trochlear width (TT-TG/TW) and found that TT-TG/TW was significantly more discriminative than TT-TG with high sensitivity and specificity [31, 32]. Future studies investigating the usage of TT-TG/TW for pediatric populations can help determine if orthopedic surgeons should shift towards using this marker for patellar instability.

Conservative Management and Surgical Indications

Conservative management is the most common initial treatment for acute first-time patellar dislocations in the absence of osteochondral injury [5]. A recent review on the management of pediatric patellar instability describes a combination of physical therapy, activity modification, strength training, and brace wear [5]. If pain, effusions, and apprehension persist, and the patient is unable to return to sport, operative treatment can be considered [5]. Typically, patients managed non-operatively should aim to obtain full range of motion by 6 weeks and can return to sport anywhere from 6 weeks to 3 months ( 32).

Recent literature suggests that surgical intervention for primary patellar dislocations may be more advantageous [33•], especially as 49% of patients who are treated non-surgically will develop recurrent instability [34]. A recent meta-analysis found that pooled mean redislocation rates were lower in patients who underwent MPFL repair compared to those who underwent rehabilitation. Additionally, there was less anterior knee pain in the surgical group [33•]. Another recent systematic review and meta-analysis specifically looked at surgical versus non-surgical intervention for primary patellar dislocation in the pediatric population [35••]. Redislocation rate was found to be significantly lower in the surgical group (38.4%) as opposed to the non-surgical group (43.1%) in the meta-analysis; however, self-reported knee function was found to be significantly worse within 10 years post-treatment [35••].

For adolescent patients who are suffering from PFI and require surgical intervention, recent literature advocates for the use of MPFL reconstruction as opposed to MPFL repair in first-time and repeat dislocators. A retrospective review from 2019 found that the overall rate of redislocation in patients with recurrent instability was significantly higher in the repair group compared to the reconstruction group (36.9 vs 6.3%, p = 0.01), with no significant difference in self-reported knee function or return to activity [36]. Another case series found similar results in that MPFL reconstruction was associated with significantly lower recurrent instability than MPFL repair in adolescents after first-time dislocation (10.0 vs 58.7%, p < 0.001) [37•]. They also found a significantly lower rate of secondary procedures and a faster return of the sports in the MPFL reconstruction group [37•].

A recent systematic review and meta-analysis in 2022 compared MPFL reconstruction and concomitant MPFL reconstruction and tibial-tubercle osteotomy (TTO) in patients with TT-TG distances greater than 15 mm [38••]. It was reported that isolated MPFL reconstruction led to similar postoperative anterior knee pain, and similar re-dislocation rates compared to MPFL reconstruction and TTO [38••]. Distal alignment procedures have the potential to add to surgical morbidity and increase recovery time in patients [39]. Additionally, in the pediatric population, it is essential that children reach skeletal maturity and physeal closure before considering TTO as a treatment option [34].

Senior Author’s Preferred Surgical Technique for Recurrent PFI

An initial examination under anesthesia to look at medial and lateral patella movement and tilt is performed. This is followed by an evaluation with a diagnostic knee arthroscopy using standard anteromedial and anterolateral portals that is performed to ensure that there are no loose bodies or osteochondral lesions that require removal or fixation. We subsequently proceed with the graft using either an autograft or allograft tendon as chosen by the surgeon after careful consideration of the patients Beighton score and other physical examination/patient factors. A 2-cm longitudinal incision is made over the anteromedial aspect of the patella and dissection done to the patella. Two suture anchors are then placed in the proximal half of the patella 1 cm apart. Another skin incision is then made over the medial femoral epicondyle with a guide pin passed through Schottle’s point under radiographic guidance. Specific to the pediatric population with open physes, careful radiographic assessment is performed to ensure that this starting point is distal the femoral physis [40]. The proximal femoral cortex is then drilled overtop of the guide pin to a diameter equal to the graft diameter with the remainder of the femoral tunnel drilled to 4.5 mm. Importantly, the drill is aimed slightly distal in order to avoid any damage to the distal femoral physis, if still open. The two free ends of the graft are then each tied down to the previously placed suture anchors in the patella while the remainder of the graft is shuttled through the second and third layers of tissue and fixed in the femoral tunnel using a bioabsorbable interference screw.

Other Surgical Technique Considerations

A systematic review found that autograft quadriceps tendon provided low rates of recurrent instability and could potentially be an alternative to hamstring autograft options for MPFL reconstruction [41••]. Potential advantages of the quadriceps tendon include increased structural similarity to the native MPFL, and similar loads to failure [41••]. It was also noted that high fixation (45–90 degrees) angles of grafts in MPFL reconstruction did not show any significant difference in Kujala scores than low (0–30 degrees) fixation angles of grafts [42]. One retrospective study found that anchor-screw fixation did not result in statistically significant differences in recurrent dislocation rates or Kujala scores than those who underwent suture fixation in pediatric patients [43•]. These results were also reflected in another study that found improvements in Kujala scores when using a guide pin to ensure maintenance of the distal femoral physis, followed by bioabsorbable interference screw used to secure the graft to the medial condyle of the femur [40]. Another retrospective case series found that soft tissue femoral fixation via suture anchors resulted in improved functional scores via Kujala, Lille femoro-patellar instability, and Tegner scores [44].

Outcomes and Complications

MPFL reconstruction tends to have high patient satisfaction with good functional results. A recent article found that 88.2% of included patients said they were either satisfied or extremely satisfied with their results, and 11.8% suffered from redislocation [45]. A recent systematic review published prognostic factors for outcomes that influence MPFL reconstruction [46••]. Longer times from injury to surgery were associated with greater redislocation rates, as well as lower Kujala scores, while gender had no significant association with surgical outcomes [46••]. With regard to complications, malposition of the femoral tunnel is the most commonly reported cause of MPFL reconstruction failure, followed by unaddressed trochlear dysplasia, and patellar fracture [47]. Malposition included being too proximal and anterior on the femoral fixation point, often due to technical error without using fluoroscope guidance [47]. Complications of MPFL reconstruction include patellofemoral pain and arthrofibrosis [48, 49].

Special Considerations for Pediatrics

Osteochondral Fractures

Osteochondral fractures are common occurrences in pediatric patients and often occur in the knee joint [50]. Surgical intervention is indicated in this population to either excise or reduce and fix the displaced fracture, and stabilization procedures of the patella can be performed concomitantly [51]. A recent study proposed that fragments that are smaller than 1cm2 could be excised or left in place if stable, and fragments that are larger than 1cm2 can be qualified for fixation [52, 53]. Without early surgical intervention, there is a risk of loss of articular cartilage and early onset patellofemoral osteoarthritis [54]. Despite controversy on the method of osteochondral fracture fixation, a recent report outlined that bioabsorbable nails are safe, provide good fracture healing, and result in low rates of repeat instability [55•].

Return to Sport

The most up-to-date criteria for return to play after PFI treated nonoperatively or operatively was developed by the International Society of Arthoscopy, Knee Surgery, and Orthopaedic Sports Medicine (ISAKOS) meeting in 2013. If the pediatric patient has complete radiographic healing of bone if bone surgery is performed, an absence of knee effusion, appropriate core strength and endurance, completed neuromuscular and proprioceptive training, limb symmetry index greater than 85% on hop tests, demonstrated a psychological readiness to sport (Single Assessment Numerical Evaluation score greater than 80), full or near full range of motion, and demonstrates adequate performance during sport-specific drills as well as adequate control during dynamic movements, then they can be cleared to play [56]. There is still a lack of specific data on rehabilitation and return to sport in pediatric cohorts due to varying procedures and forms of patellar instability [56]. Additionally, pediatric cohorts tend to have an increased lack of physical therapy compliance, worse neuromuscular control than adults, and increased participation in sporting activities that are high risk for reinjury [5]. It is important that surgeons counsel patients on modifying their activity while setting goals that are realistic on the journey to return to sport [5].

Conclusions

PFI is a common pathology found in pediatric cohorts. Diagnosis can be performed via a combination of history, physical examination maneuvers, and radiological risk factors such as patella alta, patellar tilt, trochlear dysplasia, and elevated TT-TG distances. Current literature advocates the usage of additional radiological measures to TT-TG such as TT-TG/TW, especially as TT-TG varies with age in younger patients. Recent literature potentially suggests the utilization of surgical procedures such as MPFL reconstruction or repair for acute dislocations in the hope of preventing recurrent instability. Special indications for pediatric patients include osteochondral fracture identification and management to help prevent patellofemoral osteoarthritis. A comprehensive workup and understanding of current literature can aid clinicians in aiming to prevent patellofemoral redislocation in adolescent patients.

Declarations

Conflict of Interest

Prushoth Vivekanantha declares that he has no conflict of interest.

Dr. Dan Cohen declares that he has no conflicts of interest.

Dr. Devin Peterson declares that he has no conflicts of interest.

Dr. Darren de SA is an advisory board member for Heron Therapeutics, a consultant for L.E.K Consulting, Atheneum Partners, and Stryker. He is a speaker for Bureau Member (Conmed Linatec) and a working group member for Pendopharm.

Human and Animal Rights and Informed Consent

This article does not contain any studies with human or animal subjects performed by any of the authors.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Contributor Information

Prushoth Vivekanantha, Email: prushoth.vivekanantha@medportal.ca.

Dan Cohen, Email: dan.cohen@medportal.ca.

Devin Peterson, Email: petersd@hhsc.ca.

Darren de SA, Email: darren.desa@medportal.ca.

References

Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance

  • 1.Nwachukwu BU, So C, Schairer WW, Green DW, Dodwell ER. Surgical versus conservative management of acute patellar dislocation in children and adolescents: a systematic review. Knee Surg Sports Traumatol Arthrosc. 2016;24(3):760–767. doi: 10.1007/s00167-015-3948-2. [DOI] [PubMed] [Google Scholar]
  • 2.Popkin CA, Bayomy AF, Trupia EP, Chan CM, Redler LH. Patellar instability in the skeletally immature. Curr Rev Musculoskelet Med. 2018;11(2):172–181. doi: 10.1007/s12178-018-9472-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Khormaee S, Kramer DE, Yen YM, Heyworth BE. Evaluation and management of patellar instability in pediatric and adolescent athletes. Sports Health. 2015;7(2):115–123. doi: 10.1177/1941738114543073. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Dejour DH, Mesnard G, Giovannetti de Sanctis E. Updated treatment guidelines for patellar instability: “un menu à la carte.” J Exp Orthop 2021:8:109. [DOI] [PMC free article] [PubMed]
  • 5.Vellios EE, Trivellas M, Arshi A, Beck JJ. Recurrent patellofemoral instability in the pediatric patient: management and pitfalls. Curr Rev Musculoskelet Med. 2020;13(1):58–68. doi: 10.1007/s12178-020-09607-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Loudon JK. Biomechanics and pathomechanics of the patellofemoral joint. Int J Sports Phys Ther. 2016;11(6):820–830. [PMC free article] [PubMed] [Google Scholar]
  • 7.Chotel F, Bérard J, Raux S. Patellar instability in children and adolescents. Orthop Traumatol Surg Res. 2014;100(1 Suppl):S125–137. doi: 10.1016/j.otsr.2013.06.014. [DOI] [PubMed] [Google Scholar]
  • 8.Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19–26. doi: 10.1007/BF01552649. [DOI] [PubMed] [Google Scholar]
  • 9.Barzan M, Maine S, Modenese L, Lloyd DG, Carty CP. Patellofemoral joint alignment is a major risk factor for recurrent patellar dislocation in children and adolescents: a systematic review. J ISAKOS. 2018;3(4):287–297. doi: 10.1136/jisakos-2017-000189. [DOI] [Google Scholar]
  • 10.•• Familiari F, Cetik RM, Huri G. Patellar instability in pediatric patients: review of the literature. Osteology 2021:1(4):197–208. Recent review of literature that outlines the factors that put patients at risk for patellar instability in pediatric patients.
  • 11.Tan SHS, Ngiam EHK, Lim JY, Lim AKS, Hui JH. Surgical management of patella alta in patellofemoral instability: a systematic review and meta-analysis. Orthop J Sports Med. 2021;9(4):2325967121999642. doi: 10.1177/2325967121999642. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Askenberger M, Janarv PM, Finnbogason T, Arendt EA. Morphology and anatomic patellar instability risk factors in first-time traumatic lateral patellar dislocations: a prospective magnetic resonance imaging study in skeletally immature children. Am J Sports Med. 2017;45(1):50–58. doi: 10.1177/0363546516663498. [DOI] [PubMed] [Google Scholar]
  • 13.Parikh SN, Lykissas MG. Classification of lateral patellar instability in children and adolescents. Orthop Clin North Am. 2016;47(1):145–152. doi: 10.1016/j.ocl.2015.08.016. [DOI] [PubMed] [Google Scholar]
  • 14.Wolfe S, Varacallo M, Thomas JD, Carroll JJ, Kahwaji CI. Patellar instability. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022. [PubMed]
  • 15.Dennis ER, Gruber S, Marmor WA, Stein BES. Evaluation and management of patellar instability. Ann Jt. 2022;7:2. doi: 10.21037/aoj-2020-02. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Beighton P, Solomon L, Soskolne CL. Articular mobility in an African population. Ann Rheum Dis. 1973;32(5):413–418. doi: 10.1136/ard.32.5.413. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Post WR. Clinical evaluation of patients with patellofemoral disorders. Arthrosc. 1999;15(8):841–851. doi: 10.1053/ar.1999.v15.015084. [DOI] [PubMed] [Google Scholar]
  • 18.Ahmad CS, McCarthy M, Gomez JA, Shubin Stein BE. The moving patellar apprehension test for lateral patellar instability. Am J Sports Med. 2009;37(4):791–796. doi: 10.1177/0363546508328113. [DOI] [PubMed] [Google Scholar]
  • 19.Bassett FH. Acute dislocation of the patella, osteochondral fractures, and injuries to the extensor mechanism of the knee. Instr Course Lect. 1976;25:40–49. [Google Scholar]
  • 20.Balcarek P, Oberthür S, Hopfensitz S, Frosch S, Walde TA, Wachowski MM, et al. Which patellae are likely to redislocate? Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2308–2314. doi: 10.1007/s00167-013-2650-5. [DOI] [PubMed] [Google Scholar]
  • 21.Orellana KJ, Batley MG, Lawrence JTR, Nguyen JC, Williams BA. Radiographic evaluation of pediatric patients with patellofemoral instability. Curr Rev Musculoskelet Med. 2022;15(5):411–426. doi: 10.1007/s12178-022-09780-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Dai WL, Zhang H, Zhou AG, Zhang G, Zhang J. Discoid lateral meniscus. J Knee Surg. 2017;30(9):854–862. doi: 10.1055/s-0036-1598021. [DOI] [PubMed] [Google Scholar]
  • 23.Dickens AJ, Morrell NT, Doering A, Tandberg D, Treme G. Tibial tubercle-trochlear groove distance: defining normal in a pediatric population. J Bone Joint Surg Am. 2014;96(4):318–324. doi: 10.2106/JBJS.M.00688. [DOI] [PubMed] [Google Scholar]
  • 24.Matsushita T, Kuroda R, Oka S, Matsumoto T, Takayama K, Kurosaka M. Clinical outcomes of medial patellofemoral ligament reconstruction in patients with an increased tibial tuberosity-trochlear groove distance. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2438–2444. doi: 10.1007/s00167-014-2919-3. [DOI] [PubMed] [Google Scholar]
  • 25.Heidenreich MJ, Camp CL, Dahm DL, Stuart MJ, Levy BA, Krych AJ. The contribution of the tibial tubercle to patellar instability: analysis of tibial tubercle-trochlear groove (TT-TG) and tibial tubercle-posterior cruciate ligament (TT-PCL) distances. Knee Surg Sports Traumatol Arthrosc. 2017;25(8):2347–2351. doi: 10.1007/s00167-015-3715-4. [DOI] [PubMed] [Google Scholar]
  • 26.Friedman MV, Hillen TJ, Misra S, Hildebolt CF, Rubin DA. Quantitative variable assessment of patellar instability: an MRI-based study. Am J Roentgenol. 2020;215(5):1163–1170. doi: 10.2214/AJR.19.22556. [DOI] [PubMed] [Google Scholar]
  • 27.Su P, Jian N, Mao B, Zhang Z, Li J, Fu W. Defining the role of TT-TG and TT-PCL in the diagnosis of lateralization of the Tibial tubercle in recurrent patellar dislocation. BMC Musculoskelet Disord. 2021;22(1):52. doi: 10.1186/s12891-020-03900-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Tensho K, Shimodaira H, Akaoka Y, Koyama S, Hatanaka D, Ikegami S, et al. Lateralization of the tibial tubercle in recurrent patellar dislocation: verification using multiple methods to evaluate the tibial tubercle. J Bone Joint Surg Am. 2018;100(9):e58. doi: 10.2106/JBJS.17.00863. [DOI] [PubMed] [Google Scholar]
  • 29. • Xu Z, Zhang H, Yan W, Qiu M, Zhang J, Zhou A. Validating the role of tibial tubercle-posterior cruciate ligament distance and tibial tubercle-trochlear groove distance measured by magnetic resonance imaging in patients with patellar dislocation: a diagnostic study. Arthroscopy 2021:37(1):234–42. Recent report that advocates for the use of TT-TG over TT-PCL for patellar instability diagnosis. [DOI] [PubMed]
  • 30. • Xu Z, Zhao P, Song Y, Wang H, Zhou A, Yu JK. Reliability of the tibial tubercle-roman arch distance for evaluating tibial tubercle malposition and predicting patellar dislocation via magnetic resonance imaging. Orthop J Sports Med. 2022:10(8):23259671221118560. Another report that advocates for the use of TT-TG over TT-PCL for patellar instability diagnosis. [DOI] [PMC free article] [PubMed]
  • 31.Su P, Hu H, Li S, Xu T, Li J, Fu W. Tibial tubercle-trochlear groove/trochlear width is the optimal indicator for diagnosing a lateralized tibial tubercle in recurrent patellar dislocation requiring surgical stabilization. Arthrosc. 2022;38(4):1288–1298. doi: 10.1016/j.arthro.2021.11.030. [DOI] [PubMed] [Google Scholar]
  • 32.Ménétrey J, Putman S, Gard S. Return to sport after patellar dislocation or following surgery for patellofemoral instability. Knee Surg Sports Traumatol Arthrosc. 2014;22(10):2320–2326. doi: 10.1007/s00167-014-3172-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.• Le N, Blackman B, Zakharia A, Cohen D, de Sa D. MPFL repair after acute first-time patellar dislocation results in lower redislocation rates and less knee pain compared to rehabilitation: a systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc 2022: 10.1007/s00167-022-07222-w. Recent systematic review and meta-analysis comparing MPFL repair and rehabilitation for first-time patellar dislocations. [DOI] [PubMed]
  • 34.Redler LH, Wright ML. Surgical management of patellofemoral instability in the skeletally immature patient. J Am Acad Orthop Surg. 2018;26(19):e405–e415. doi: 10.5435/JAAOS-D-17-00255. [DOI] [PubMed] [Google Scholar]
  • 35.•• Zhang K, Jiang H, Li J, Fu W. Comparison between surgical and nonsurgical treatment for primary patellar dislocations in adolescents: a systematic review and meta-analysis of comparative studies. Orthop J Sports Med. 2020;8(9):2325967120946446. Recent systematic review and meta-anyalysis that found that redislocation rates were lower in surgical groups compared to non-surgical groups in adolescents. [DOI] [PMC free article] [PubMed]
  • 36.Puzzitiello RN, Waterman B, Agarwalla A, Zuke W, Cole BJ, Verma NN, et al. Primary medial patellofemoral ligament repair versus reconstruction: rates and risk factors for instability recurrence in a young, active patient population. Arthrosc. 2019;35(10):2909–2915. doi: 10.1016/j.arthro.2019.05.007. [DOI] [PubMed] [Google Scholar]
  • 37.• Gurusamy P, Pedowitz JM, Carroll AN, Johnson K, Chambers HG, Edmonds EW, et al. Medial patellofemoral ligament reconstruction for adolescents with acute first-time patellar dislocation with an associated loose body. Am J Sports Med. 2021;49(8):2159–64. Level IV that found MPFL reconstruction was associated with better clinical outcomes than MPFL repair in adolescents, in terms of return to sport rates, redislocation rates, and reoperation rates. [DOI] [PubMed]
  • 38.•• Vivekanantha P, Kahlon H, Cohen D, de Sa D. Isolated medial patellofemoral ligament reconstruction results in similar postoperative outcomes as medial patellofemoral ligament reconstruction and tibial-tubercle osteotomy: a systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc 2022: 10.1007/s00167-022-07186-x. Recent systematic review that found that isolated MPFLR showed similar postoperative anterior knee pain and dislocation rates to MPFLR + TTO. [DOI] [PubMed]
  • 39.Erickson BJ, Nguyen J, Gasik K, Gruber S, Brady J, Shubin Stein BE. Isolated medial patellofemoral ligament reconstruction for patellar instability regardless of tibial tubercle-trochlear groove distance and patellar height: outcomes at 1 and 2 years. Am J Sports Med. 2019;47(6):1331–1337. doi: 10.1177/0363546519835800. [DOI] [PubMed] [Google Scholar]
  • 40.Nelitz M, Dreyhaupt J, Williams SRM. Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents using a pedicled quadriceps tendon graft shows favourable results at a minimum of 2-year follow-up. Knee Surg Sports Traumatol Arthrosc. 2018;26(4):1210–1215. doi: 10.1007/s00167-017-4597-4. [DOI] [PubMed] [Google Scholar]
  • 41.•• Olotu O, Siddiqui A, Peterson D, de Sa D. The superficial “Swing-Down” quadriceps tendon autograft is a viable option for medial patellofemoral ligament reconstruction: a systematic review. Arthrosc 2021:37(10):3187–97. Recent systematic showing that the quadriceps tendon is an alternative graft option to the hamstrings tendon in MPFLR. [DOI] [PubMed]
  • 42.Patel NK, de Sa D, Vaswani R, Kay J, Musahl V, Lesniak BP. Knee flexion angle during graft fixation for medial patellofemoral ligament reconstruction: a systematic review of outcomes and complications. Arthrosc. 2019;35(6):1893–1904. doi: 10.1016/j.arthro.2018.11.071. [DOI] [PubMed] [Google Scholar]
  • 43.• Zampieri A, Girardin C, Hocquet B, Coursier R, Fournier A, Martin C, et al. Patellar dislocation recurrence after pediatric MPFL reconstruction: bone tunnels and soft tissues versus suture anchors and interference screw. Orthop Traumatol Surg Res 2022:14;103515. There was no difference between fixation strategies in pediatric patients for MPFLR. [DOI] [PubMed]
  • 44.Bremond N, Prima R, Rabattu PY, Accadbled F, Chotel F, Konkel M, et al. Isolated MPFL reconstruction with soft tissue femoral fixation technique in 54 skeletally immature patients: clinical outcomes at 2 years follow-up. A French multicenter retrospective study. Orthop Traumatol Surg Res. 2022;103530. 10.1016/j.otsr.2022.103530. [DOI] [PubMed]
  • 45.Gondolfo R, Emanuele HS, Guerreiro JPF, Queiroz A de O, Danieli MV. Clinical results of medial patellofemoral ligament reconstruction. Acta Ortop Bras. 2022:30(3):e241172. [DOI] [PMC free article] [PubMed]
  • 46.•• Migliorini F, Eschweiler J, Betsch M, Knobe M, Tingart M, Maffulli N. Prognostic factors for isolated medial patellofemoral ligament reconstruction: a systematic review. Surgeon 2022:20(4):e112–21. A recent systematic review that found that longer times from injury to surgery is a risk factor for lower Kujala scores and increased redislocation rates from MPFLR. [DOI] [PubMed]
  • 47.Walker M, Maini L, Kay J, Siddiqui A, Almasri M, de Sa D. Femoral tunnel malposition is the most common indication for revision medial patellofemoral ligament reconstruction with promising early outcomes following revision reconstruction: a systematic review. Knee Surg Sports Traumatol Arthrosc. 2022;30(4):1352–1361. doi: 10.1007/s00167-021-06603-x. [DOI] [PubMed] [Google Scholar]
  • 48.Zimmermann F, Milinkovic DD, Börtlein J, Balcarek P. Revision surgery for failed medial patellofemoral ligament reconstruction results in better disease-specific outcome scores when performed for recurrent instability than for patellofemoral pain or limited range of motion. Knee Surg Sports Traumatol Arthrosc. 2022;30(5):1718–1724. doi: 10.1007/s00167-021-06734-1. [DOI] [PubMed] [Google Scholar]
  • 49.Schmiesing A, Engelking M, Agel J, Arendt EA. Distalization of the tibial tubercle for patellar stabilization combined with medial patellofemoral ligament reconstruction: length of distalization or residual patella alta and its effect on outcome. Am J Sports Med. 2022;50(6):1627–1634. doi: 10.1177/03635465221089979. [DOI] [PubMed] [Google Scholar]
  • 50.Cordunianu MA, Antoniac I, Niculescu M, Paltanea G, Raiciu AD, Dura H, et al. Treatment of knee osteochondral fractures. Healthcare 2022:10(6):1061. [DOI] [PMC free article] [PubMed]
  • 51.Lee BJ, Christino MA, Daniels AH, Hulstyn MJ, Eberson CP. Adolescent patellar osteochondral fracture following patellar dislocation. Knee Surg Sports Traumatol Arthrosc. 2013;21(8):1856–1861. doi: 10.1007/s00167-012-2179-z. [DOI] [PubMed] [Google Scholar]
  • 52.Brophy RH, Wojahn RD, Lamplot JD. Cartilage restoration techniques for the patellofemoral joint. J Am Acad Orthop Surg. 2017;25(5):321–329. doi: 10.5435/JAAOS-D-15-00447. [DOI] [PubMed] [Google Scholar]
  • 53.Felus J, Kowalczyk B, Starmach M, Wyrobek L. Osteochondral fractures in acute patellar dislocations in adolescents: midterm results of surgical treatment. Orthop J Sports Med. 2022;10(7):23259671221107610. doi: 10.1177/23259671221107608. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 54.Vollnberg B, Koehlitz T, Jung T, Scheffler S, Hoburg A, Khandker D, et al. Prevalence of cartilage lesions and early osteoarthritis in patients with patellar dislocation. Eur Radiol. 2012;22(11):2347–2356. doi: 10.1007/s00330-012-2493-3. [DOI] [PubMed] [Google Scholar]
  • 55.• Aitchison AH, Hidalgo Perea S, Schlichte LM, Green DW. Medial patellofemoral ligament reconstruction with simultaneous osteochondral fracture fixation is an effective treatment for adolescent patellar dislocation with osteochondral fractures. J Child Orthop 2022:16(5):393–400. Level IV study that showed that bioabsorbable nails are safe to provide fracture healing for osteochondral fixation, resulting in lower rates of redislocation. [DOI] [PMC free article] [PubMed]
  • 56.Sherman SL, Deasis DP, Garrone AJ, Voss EE, Oliver HA. Return to play after patellar stabilization. Curr Rev Musculoskelet Med. 2018;11(2):280–284. doi: 10.1007/s12178-018-9484-1. [DOI] [PMC free article] [PubMed] [Google Scholar]

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