• challenges
• clinical decision-making
• individualized treatment strategies
• recurrent patellar dislocation
• surgical strategies

• Ligaments
• Operative procedures
• Patellar dislocation
• Patellofemoral joint

• Humans
• Patellofemoral Joint/surgery
• Patellofemoral Joint/physiopathology
• Joint Instability/surgery
• Patellar Dislocation/surgery
• Recurrence

The surgical approach for patellar instability usually refers to reconstruction of the medial patellofemoral ligament associated with an osteotomy of the tibial tuberosity or a trochleoplasty when required. The medial patellotibial ligament and the medial patellomeniscal ligament are secondary stabilizers of the patella. Despite this, both the medial patellotibial and patellofemoral ligaments aid in patellar rotation and tilt when the knee is flexed beyond 45°. The medial patellotibial ligament plays a particularly important role in the final stages of stretching in extension and between 40 degrees to 90 degrees of flexion. The clinical relevance and surgical indications for medial patellotibial ligament reconstruction associated with medial patellofemoral ligament reconstruction are still controversial. This editorial explores the surgical indications and clinical results for medial patellotibial ligament reconstruction to improve readers’ understanding of this technique, especially because reported clinical outcomes have remained sparse.

• Medial patellotibial ligament
• Patellar instability
• Reconstruction
• Surgical

• arthroscopic reduction
• arthroscopic surgery
• irreducible
• lateral patellar dislocation
• locked patellar dislocation
• mpfl

• anterior cruciate ligament reconstruction
• knee arthrofibrosis
• knee ligaments, ACL
• manipulation under anesthesia
• medial patellofemoral ligament reconstruction
• pediatric sports medicine

• Kujala score
• Lysholm score
• Medial patellofemoral ligament reconstruction
• Recurrent instability
• Tegner score
• Tibial tubercle osteotomy

• Humans
• Osteotomy/methods
• Joint Instability/surgery
• Tibia/surgery
• Patellofemoral Joint/surgery
• Treatment Outcome
• Plastic Surgery Procedures/methods
• Adult
• Patellar Dislocation/surgery
• Young Adult
• Patellar Ligament/surgery
• Adolescent
• Ligaments, Articular/surgery
• Recurrence

• MPFL
• bibliometric analysis
• knee
• medial patellofemoral ligament
• most cited articles
• patella
• reconstruction

• dislocation
• instability
• medial patellofemoral ligament
• patella
• reconstruction
• repair

• T32 AR056950 NIAMS NIH HHS
• National Institute of Arthritis and Musculoskeletal and Skin Diseases

• Humans
• Patellofemoral Joint/surgery
• Femur
• Joint Instability/diagnosis
• Joint Instability/surgery
• Patellar Dislocation
• Ligaments, Articular

• MPFL reconstruction
• acute patella dislocation
• medial patellofemoral ligament
• synthetic graft

• Humans
• Patellofemoral Joint/surgery
• Joint Instability/surgery
• Knee Joint/surgery
• Patellar Dislocation/surgery
• Ligaments, Articular/injuries
• Ligaments, Articular/surgery

• Medial patellofemoral ligament reconstruction
• Medial patellotibial ligament
• Patella instability
• patella dislocation

• Joint instability
• Knee surgery
• Patella
• Patellofemoral joint

• Humans
• Adolescent
• Joint Instability/surgery
• Patellofemoral Joint/surgery
• Retrospective Studies
• Joint Dislocations
• Ligaments, Articular/surgery
• Risk Factors

• MPFL
• autografts
• patellofemoral instability
• recurrent
• return to sport

• Dislocation
• MPFL
• Management
• Patella
• Repair

• Dislocation
• MPFL
• Management
• Patella

To systematically review the literature to evaluate the biomechanical properties of the interference screw (IS) versus suture anchor (SA) techniques for patellar and femoral fixation of medial patellofemoral ligament (MPFL) reconstruction.

A systematic review was performed by searching PubMed, the Cochrane library, and Embase using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to identify studies that analyzed the biomechanical properties of IS and SA techniques for MPFL reconstruction. The search phrase implemented was “medial patellofemoral ligament reconstruction biomechanics.” Evaluated outcomes included ultimate load to failure (N), stiffness (N/mm), and mode of failure. Forest plots were created for statistical analysis and heterogeneity was assessed via I² statistic.

Six studies met inclusion criteria, including a total of 108 cadaveric specimens, for MPFL patellar fixation, and 3 studies met inclusion criteria, including a total of 50 cadaveric specimens, for MPFL femoral fixation. Pooled analysis from 5 studies reporting on stiffness for MPFL patellar fixation revealed a statistically significant difference in favor of IS compared with SA (P = .007). Pooled analysis from 3 studies reporting on ultimate load to failure of femoral fixation revealed a statistically significant difference in favor of IS compared with SA (P = .043).

The use of IS was associated with a greater stiffness compared with the use of SA in MPFL patellar fixation, but there was no difference in load to failure between IS and SA. The use of IS was associated with a greater load to failure compared with the use of SA in MPFL femoral fixation, but there was no difference in stiffness between IS and SA.

There have been multiple individual biomechanical studies conducted comparing IS and SA fixation for MPFL patellar and femoral fixation; however, they have yielded conflicting results, with small sample sizes. Pooling the data from these studies in a meta-analysis may allow for more meaningful biomechanical data to coincide with the existing, albeit scarce, clinical data, this may help to inform clinical decision making for surgeons managing these injuries.

• Nursing
• Patellofemoral
• Reconstruction
• Value

To determine whether conventional logistic regression or machine learning algorithms were more precise in identifying the risk factors for unplanned overnight admission after medial patellofemoral ligament (MPFL) reconstruction.

A retrospective review of the prospectively collected National Surgical Quality Improvement Program database was performed to identify patients who underwent outpatient MPFL reconstruction from 2006–2018. Patients admitted overnight were identified as those with length of stay of 1 or more days. Models were generated using random forest, extreme gradient boosting, adaptive boosting, or elastic net penalized logistic regression, and an additional model was produced as a weighted ensemble of the 4 final algorithms. The predictive capacity of these models was compared to that of logistic regression.

Of the 1307 patients identified, 221 (16.9%) required at least one overnight stay after MPFL reconstruction. Multivariate logistic regression found the following variables to be predictors of inpatient admission: age (odds ratio [OR] = 1.03 [95% confidence interval {CI} 1.02-1.04]; P <.001), spinal anesthesia (OR = 3.42 [95% CI 1.98-6.08]; P < .001), American Society of Anesthesiologists (ASA) class 3/4 (OR = 1.96 [95% CI 1.25-3.06]; P < .001), history of chronic obstructive pulmonary disease (COPD) (OR = 6.44 [95% CI 1.58-26.17]; P = .02), and body mass index (BMI) (OR = 1.03 [95% CI 1.01-1.05]; P < .001). The ensemble model achieved the best performance based on discrimination assessed via internal validation (area under the curve = 0.722). The variables determined most important by the ensemble model were increasing BMI, increasing age, ASA class, anesthesia, smoking, hypertension, lateral release, and history of COPD.

An internally validated machine learning algorithm outperformed logistic regression modeling in predicting the need for unplanned overnight hospitalization after MPFL reconstruction. In this model, the most significant risk factors for admission were age, BMI, ASA class, smoking status, hypertension, lateral release, and history of COPD. This tool can be deployed to augment provider assessment to identify high-risk candidates and appropriately set postoperative expectations for patients.

Identifying and mitigating patient risk factors to prevent adverse surgical outcomes and hospitalizations is one of our primary goals. There may be a key role for machine learning algorithms to help successfully and efficiently risk stratify patients to decrease costs, appropriately set postoperative expectations, and increase the quality of delivered care.

Patellar instability is a common multifactorial disease in orthopedics, which seriously affects the quality of life. Because of the unified pathogeny, diagnosis and treatment, patellar instability has gradually attracted the interest of more scholars these years, resulting in an explosive growth in the research output. This study aims to summarize the knowledge structure and development trend in the field from the perspective of bibliometrics.

The data of articles and reviews on patellar instability was extracted from the Web of Science database. The Microsoft Excel, R-bibliometrix, CiteSpace, VOSviewer, Pajek software are comprehensively used to scientifically analyze the data quantitatively and qualitatively.

Totally, 2,155 papers were identified, mainly from North America, Western Europe and East Asia. Until December 31, 2021, the United States has contributed the most articles (1,828) and the highest total citations (17,931). Hospital for Special Surgery and professor Andrew A Amis are the most prolific institutions and the most influential authors respectively. Through the analysis of citations and keywords based on a large number of literatures, “medial patellofemoral ligament construction”, “tibial tubercle-trochlear groove (TT-TG) distance”, “epidemiological prevalence”, “multifactor analysis of etiology, clinical outcome and radiographic landmarks “ were identified to be the most promising research directions.

This is the first bibliometric study to comprehensively summarize the research trend and development of patellar instability. The result of our research provides the updated perspective for scholars to understand the key information in this field, and promote future research to a great extent.

There is disagreement regarding the description of the patellofemoral ligaments (PFLs), considered by some authors as capsular thickening and by others as independent ligaments. It was hypothesised that the PFLs and retinacula are structures with different histological features. The aim of this study was to describe the stabilising structures of the patella in detail and to determine if the PFLs and retinacula are different and separable structures from a macroscopic, microscopic and imaging viewpoint. An anatomical study was performed on eight knees from five cadavers (mean age, 56.2 years; range, 35–63 years), and a histological study was conducted on specimens from nine patients having a mean age of 65 years (range 35–84 years) who had undergone surgical knee procedures. The imaging study was based on 100 MRIs (96 patients). The mean age was 46 years (range 16–88), and the study analysed the capsular-ligamentous structures. In the medial compartment, the layers and structures were as follows: superficial layer, medial retinaculum; intermediate layer, Medial Collateral Ligament (MCL), Posterior Oblique Ligament (POL) and Medial Patellofemoral Ligament (MPFL); deep layer, deep part of the MCL and joint capsule. In the lateral compartment, the layers and structures were the following: superficial layer, lateral retinaculum; intermediate layer, Lateral Collateral Ligament (LCL) and Lateral Patellofemoral Ligament (LPFL); deep layer, joint capsule. All of the knees examined presented a clearly distinguishable MPFL and LPFL separable from the capsular layer. Histological study: there was a higher density of nerve fibres in retinacula compared to ligaments (p = 0.0034) and a higher content of elastic fibres in retinacula (p < 0.0005). In imaging, there was no difference between medial and lateral retinaculum thickness (p > 0.05). In conclusion, both the lateral and medial compartment can be described using the three-layer scheme. PFLs and retinacula are separate structures both macroscopically and according to imaging analysis. The retinacula respond to their specific function with a higher nerve fibre content and higher number of elastic fibres compared to the ligaments.

• Adolescent
• Adult
• Aged
• Aged, 80 and over
• Cadaver
• Humans
• Knee Joint/physiology
• Ligaments, Articular/diagnostic imaging
• Magnetic Resonance Imaging
• Middle Aged
• Young Adult

• Knee
• MPFL reconstruction
• Patella dislocation
• Patella instability
• Stabilization

• Extensor mechanism
• Patella
• Patellofemoral instability
• Pediatric
• Recurrent dislocation

Femoral-sided graft fixation in medial patellofemoral ligament (MPFL) reconstruction is commonly performed using an interference screw (IS). However, the IS method is associated with several clinical disadvantages that may be ameliorated by the use of suture anchors (SAs) for femoral fixation.

To compare the load to failure and stiffness of SAs versus an IS for the femoral fixation of a semitendinosus autograft in MPFL reconstruction.

Controlled laboratory study.

Based on a priori power analysis, a total of 6 matched pairs of cadaveric knees were included. Specimens in each pair were randomly assigned to receive either SA or IS fixation. After an appropriate reconstruction procedure, the looped end of the MPFL graft was pulled laterally at a rate of 6 mm/s until construct failure. The best-fit slope of the load-displacement curve was then used to calculate the stiffness (N/mm) in a post hoc fashion. A paired t test was used to compare the mean load to failure and the mean stiffness between groups.

No significant difference in load to failure was observed between the IS and the SA fixation groups (294.0 ± 61.1 vs 250.0 ± 55.9; P = .352), although the mean stiffness was significantly higher in IS specimens (34.5 ± 9.6 vs 14.7 ± 1.2; P = .004). All IS reconstructions failed by graft pullout from the femoral tunnel, whereas 5 of the 6 SA reconstructions failed by anchor pullout.

In this biomechanical study using a cadaveric model of MPFL reconstruction, SA femoral fixation was not significantly different from IS fixation in terms of load to failure. The mean load-to-failure values for both reconstruction techniques were greater than the literature-reported values for the native MPFL.

These results suggest that SAs are a biomechanically viable alternative for femoral-sided graft fixation in MPFL reconstruction.

• biomechanics
• cadaveric
• femoral fixation
• interference screw
• medial patellofemoral ligament
• suture anchor

• athlete
• knee
• medial patellofemoral ligament
• patella
• return to play
• systematic review

• citations
• level of evidence
• medial patellofemoral ligament
• methodological quality
• patellar dislocation
• patellar instability
• trochleoplasty

• MPFL
• MPTL
• Medial patellofemoral ligament reconstruction
• Medial patellotibial ligament reconstruction
• Patellar dislocation reconstruction

• Female
• Humans
• Joint Instability/surgery
• Ligaments, Articular/surgery
• Male
• Orthopedic Procedures/methods
• Patella/surgery
• Patellar Dislocation/surgery
• Patellofemoral Joint/surgery
• Plastic Surgery Procedures/methods
• Tibia/surgery
• Treatment Outcome

To compare the clinical utility of tibial tubercle-midepicondyle (TT-ME) and tibial tubercle-trochlear groove (TT-TG) distances in predicting the risk for recurrent instability after isolated MPFL reconstruction.

A consecutive series of patients with recurrent patellar dislocation who underwent isolated MPFL reconstruction made up the study population. The patients were followed for a minimum of 2 years. In assessment of surgical outcome, the patient was deemed to exhibit “postoperative recurrent patellar instability” when ≥1 of the following 3 conditions was identified: redislocation, positive apprehension sign, and positive J-sign (manifestation of abnormal patellar tracking). As for radiological parameters for position of the tibial tubercle, TT-ME distance (transverse distance between the tibial tubercle and midpoint of the transepicondylar line) and TT-TG distance were measured on axial computed tomography images. The clinical utility as a factor to predict the outcome of MPFL reconstruction was compared between the 2 distances using receiver operating characteristic (ROC) analysis. In addition, various radiological indices potentially influencing the surgical outcome were subjected to multivariable logistic regression analysis.

We examined 38 knees in 38 patients with a mean age at surgery of 17.6 years. Postoperative recurrent patellar instability was encountered in 8 of the 38 knees. The ROC curve analysis showed the TT-ME distance to be a significantly better indicator in predicting surgical outcome than the TT-TG distance (P = .001). The univariate analysis for radiological factors demonstrated that the TT-ME distance was significantly associated with postoperative recurrent patellar instability (odds ratio 1.42, P = .012) whereas all other factors including the TT-TG distance did not correlate with recurrent instability. The multivariable logistic regression analysis revealed that only the TT-ME distance was significantly associated with recurrent instability (P = .035).

Analysis of our patient population undergoing isolated MPFL reconstruction showed that the TT-ME distance was a significantly better indicator than the TT-TG distance to predict the risk for recurrent instability after isolated MPFL reconstruction performed for patellar instability.

Level IV, therapeutic case series.

• Knee
• MPFL
• MPTL
• Medial patella femoral ligament
• Patella dislocation

• Adolescent
• Adult
• Female
• Humans
• Joint Instability/diagnostic imaging
• Joint Instability/surgery
• Ligaments, Articular/diagnostic imaging
• Ligaments, Articular/surgery
• Male
• Patella/diagnostic imaging
• Patella/surgery
• Patellar Dislocation/diagnostic imaging
• Patellar Dislocation/surgery
• Patellofemoral Joint/diagnostic imaging
• Patellofemoral Joint/surgery
• Plastic Surgery Procedures
• Tissue Fixation
• Young Adult

• mpfl
• mpflr
• patello-femoral instability
• patellar dislocation
• mpfl reconstruction

• Humans
• Joint Instability/diagnosis
• Joint Instability/surgery
• Ligaments, Articular/surgery
• Orthopedic Procedures/methods
• Patellofemoral Joint
• Treatment Outcome

• Biomechanical
• Double-bundle
• Knee kinematics
• MPFL
• Patella
• Patellofemoral

• Finite element model
• MPFL reconstruction
• Patellar cartilage degeneration after MPFL reconstruction
• Patellar contact pressure

The purpose of this study is to review the use of an allograft or autograft in medial patellofemoral ligament (MPFL) reconstruction.

Various electronic databases were searched for relevant articles published from January 2000 to September 2017 that evaluated clinical outcomes of MPFL reconstruction using an autograft or allograft. Data search, extraction, analysis, and quality assessments were performed based on Cochrane Collaboration guidelines.

The study of 21 autografts and one allograft was included in this review. Although direct comparative studies were unavailable, the Kujala score and subjective results were reported in the majority of these studies. While the use of an autograft for MPFL reconstruction yielded satisfactory clinical outcomes with few perioperative complications, no new outcome has been drawn from the use of allografts.

Although many studies have shown favorable clinical results for MPFL reconstruction using an autograft, the clinical results of MPFL reconstruction using an allograft have not yet been sufficient to achieve meaningful clinical results due to low levels of evidence. Direct comparisons were not conducted because there were very few studies on allografts; thus, further research in this area should be performed in the future.

The online version of this article (10.1186/s43019-019-0008-0) contains supplementary material, which is available to authorized users.

• Allograft
• Autograft
• Knee
• Medial patellofemoral ligament
• Patellar instability
• Systematic review

Surgical treatment of young patients with recurrent lateral patella dislocation (RLDP) is often recommended because of loss of knee function that compromises their level of activity or even their daily life functioning. This situation is comparable to young patients with an anterior cruciate ligament (ACL) rupture. The purpose of this study was therefore to explore the time from injury to surgery and the pre-operative symptoms and knee function of young RLPD patients scheduled for stabilizing surgery and compare this group to age and sex-matched ACL-deficient patients.

Forty-seven patients with unilateral RLPD listed for isolated medial patellofemoral ligament reconstruction were included in the study (RLPD-group). This group was compared to an age, sex and BMI matched ACL patient group obtained from the Norwegian knee ligament registry (ACL-group) for the following outcome measures: the knee injury and osteoarthritis outcome score (KOOS) assessed on the day of surgery and time from injury to surgery.

The RLPD-group scored significantly lower than the ACL-group for the three KOOS subscales “Pain” (73.6 vs. 79.8, p < 0.05), “Symptoms” (71.7 vs. 79.3, p < 0.05) and “ADL” (84.7 vs 89.5, p < 0.05). The lowest KOOS values were found for Sports/Recreation (53.5 vs. 51.3, p = 0.65) and Quality of life (37.6 vs. 36.7, p = 0.81). The average time from primary injury to surgery was 6 months for the ACL group and 31 months for the RLPD group.

RLPD affected knee function as much as ACL deficiency, and was associated with more pain. Still the RLDP patients waited on average 5 times longer for surgery.

The patients with RLPD consisted of patients who were examined for possible recruitment for a concurrent prospective randomized controlled trial comparing conservative treatment and isolated surgical medial patellofemoral ligament (MPFL) reconstruction (Clinical trials no: NCT02263807, October 2014).

• Comparative study
• Indication for surgery
• Patella dislocation
• Symptoms and function evaluation
• Time to surgery
• Young adults and adolescents

Currently, there is uncertainty regarding the long-term outcome of medial patellofemoral ligament reconstructions (MPFLr). Our objectives were: (1) to develop a parametric model of the patellofemoral joint (PFJ) enabling us to simulate different surgical techniques for MPFLr; (2) to determine the negative effects on the PFJ associated with each technique, which could be related to long-term deterioration of the PFJ.

A finite element model of the PFJ was created based on CT data from 24 knees with chronic lateral patellar instability. Patella contact pressure and maximum MPFL-graft stress at five angles of knee flexion (0, 30, 60, 90 and 120°) were analysed in three types of MPFLr: anatomic, non-anatomic with physiometric behaviour, and non-anatomic with non-physiometric behaviour.

An increase in patella contact pressure was observed at 0 and 30° of knee flexion after both anatomic and non-anatomic MPFLr with physiometric behaviour. In both reconstructions, the ligament was tense between 0 and 30° of knee flexion, but at 60, 90 and 120°, it had no tension. In the third reconstruction, the behaviour was completely the opposite.

A parametric model of the PFJ enables us to evaluate different types of MPFLr throughout the full range of motion of the knee, regarding the effect on the patellofemoral contact pressure, as well as the kinematic behaviour of the MPFL-graft and the maximum MPFL-graft stress.

The online version of this article (10.1186/s40634-019-0200-x) contains supplementary material, which is available to authorized users.

• Finite element methodology
• MPFL reconstruction
• MPFL-stress
• Medial patellofemoral ligament
• Patellofemoral contact pressure
• Patellofemoral joint

• biomechanics
• elongation
• fluoroscopy
• in vivo
• isometry
• length changes
• medial patellofemoral ligament

• Beighton
• Gracilis
• MPFL
• MPTL
• Marx
• Tegner

• Clinical outcomes
• Ligament reconstruction
• MPTL
• MTPL reconstruction
• Medial patellotibial ligament
• Medial patellotibial ligament reconstruction
• Patellar dislocation
• Patellar instability
• Patellar ligaments
• Surgical treatment patellar instability
• Systematic review