Chondral and Soft Tissue Injuries Associated to Acute Patellar Dislocation: A Systematic Review

Introduction: Chondral and soft tissue injuries can be associated with first time patellar dislocation, but it is unclear how common they are, and which tissues are affected. A systematic review of the literature was performed to investigate the frequency, location, and extent of chondral and medial patellofemoral ligament (MPFL) injuries in patients following first time patellar dislocation. Methods: This systematic review was conducted according to the PRISMA guidelines. PubMed, Google Scholar, Embase, and Web of Science databases were accessed in November 2021. All the published clinical studies reporting the frequency, location, and extent of soft tissue lesions following first time patellar dislocation were accessed. Studies reporting data on habitual, congenital, or recurrent patellofemoral instability were excluded. Results: Data from 42 articles (2254 patients, mean age 21.6 ± 7.3 years) were retrieved. Ninety-eight percent of patients who experienced first time patellar dislocation demonstrated MPFL rupture at MRI. Forty-eight percent of MPFL ruptures were located at the patellar side, 34% at the femoral insertion site, and 18% in the midportion. Eighty-five percent of patients showed signs of patellar chondral damage at MRI, and trochlear chondral injuries were evidenced in 47% of patients. Intra-articular loose bodies were observed in 11.5% of patients. At arthroscopy, the medial facet and the crest of the patella more commonly exhibited chondral lesions than the lateral facet and femoral trochlea. Conclusions: Most patients suffer chondral damage and MPFL tears following after a first time patellar dislocation.

The frequency, location, and extent of chondral injuries, along with the rate of medio patellofemoral ligament (MPFL) tears following first time patellar dislocation are un-Life 2021, 11, 1360 2 of 12 clear [14][15][16][17][18]. Soft tissue injuries can occur during reduction of the patellar dislocation [19][20][21]. Pathoanatomical factors predisposing to patellofemoral instability can be demonstrated in most patients with patellar chondral defects [22,23]. If left untreated, chondral defects lead to persistent pain, limiting daily living activities, and may induce premature osteoarthritis in the long term [24][25][26][27]. The MPFL is the most important restraint to the lateral displacement of the patella during the first 30 degrees of flexion; thus, if left untreated, MPFL tears can increase joint instability and consequently the risk of redislocation [28][29][30][31]. Better characterization of soft tissue injury patterns in patients following first time patellar dislocation may assist in establishing proper treatment. A systematic review of the literature was performed to investigate the frequency, location, and extent of chondral injuries and MPFL tears in patients after first time patellar dislocation. We hypothesized that most patients following first time patellar dislocation demonstrate chondral and MPFL damages.

Search Strategy
This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [32]. The literature search was guided by the following points: • Problem: first time patellar dislocation; • Outcome: soft tissue injuries.

Literature Search
Two authors (**;**) independently performed the literature search in November 2021. PubMed and Google Scholar were accessed. Embase and Web of Science were also accessed to identify further articles. The following keywords were used in combination: patella, dislocation, acute, instability, soft tissue, chondral, cartilage, lesion, osteochondral, injury, loose body, ligament, tear, muscle injury, tendon tear, ACL, PCL, MCL, meniscus, MRI, arthroscopy, medial patellofemoral ligament, MPFL, damage, insertion, rupture, Outerbridge, International Cartilage Repair Society, ICRS. The same authors performed the screening of the resulting titles in a separate fashion, accessing the full-text of the articles of interest. A cross-reference of the bibliographies was also performed. Disagreements were resolved by a third author (**).

Eligibility Criteria
All the published clinical studies which reported the frequency, location, and extent of chondral injuries and MPFL ruptures following first time patellar dislocations were accessed. Given the authors language capabilities, articles in English, German, Italian, French, and Spanish were eligible. Level I to IV of evidence, according to Oxford Centre of Evidence-Based Medicine [33], were considered. Reviews, technical notes, comments, letters, editorials, protocols, and guidelines were not eligible, nor were biomechanical, animal, and cadaveric studies. Studies reporting data on habitual, congenital, or recurrent patellofemoral instability were excluded. Studies involving patients who underwent previous patellofemoral surgical procedures were also not eligible. Only articles reporting quantitative data under the outcomes of interest were considered for inclusion.

Outcomes of Interest
Data extraction was performed by two authors (**;**). Study generalities were collected: author, year, journal, study design, number of patients. MRI findings were retrieved: rate of free loose bodies, rate, extent, and location of MPFL, trochlear, and patellar chondral injuries. Arthroscopy findings were also collected: location and extent of trochlear and patellar chondral injuries. The MRI findings were evaluated using the Outerbridge classification [34], whereas the International Cartilage Repair Society (ICRS) [35] was used for the arthroscopic findings.

Methodology Quality Assessment
Two authors (**;**) independently performed the methodological quality assessment using the PEDro Score. PEDro is an 11-item scale designed for rating methodological quality of the included studies. These items evaluated the eligibility criteria, allocation and blinding procedures, the length of the follow-up, the intention-to-treat and betweengroup analyses, point estimates, and variability. Items were scored either as present (1) or absent (0). Mean values of 6/11 were considered satisfactory.

Statistical Analysis
For the statistical analysis, IBM SPSS (Chicago, IL, USA) software version 25 was used. For continuous variables, the Shapiro-Wilk test was performed to investigate data distribution. For normal data, mean and standard deviation were calculated. For nonparametric data, median and interquartile range were calculated. Dichotomic data was evaluated as follow: Number o f patients reporting the event Number o f patients included in the study × 100 (1)

Search Result
The literature search resulted in 1549 articles. Of these, 839 were excluded as duplicates. Another 560 were not eligible due to not matching the topic (n = 250), study design (n = 201), recurrent, congenital, or habitual patellofemoral instability (n = 103), language limitation (n = 4), and uncertain results (n = 2). This left 150 articles for inclusion. A further 108 articles were excluded because of lack of quantitative data under the outcomes of interest. Finally, 42 articles were considered for analysis ( Figure 1). chondral injuries. Arthroscopy findings were also collected: location and extent of trochlear and patellar chondral injuries. The MRI findings were evaluated using the Outerbridge classification [34], whereas the International Cartilage Repair Society (ICRS) [35] was used for the arthroscopic findings.

Methodology Quality Assessment
Two authors (**;**) independently performed the methodological quality assessment using the PEDro Score. PEDro is an 11-item scale designed for rating methodological quality of the included studies. These items evaluated the eligibility criteria, allocation and blinding procedures, the length of the follow-up, the intention-to-treat and betweengroup analyses, point estimates, and variability. Items were scored either as present (1) or absent (0). Mean values of 6/11 were considered satisfactory.

Statistical Analysis
For the statistical analysis, IBM SPSS (Chicago, IL, USA) software version 25 was used. For continuous variables, the Shapiro-Wilk test was performed to investigate data distribution. For normal data, mean and standard deviation were calculated. For nonparametric data, median and interquartile range were calculated. Dichotomic data was evaluated as follow:

Search Result
The literature search resulted in 1549 articles. Of these, 839 were excluded as duplicates. Another 560 were not eligible due to not matching the topic (n = 250), study design (n = 201), recurrent, congenital, or habitual patellofemoral instability (n = 103), language limitation (n = 4), and uncertain results (n = 2). This left 150 articles for inclusion. A further 108 articles were excluded because of lack of quantitative data under the outcomes of interest. Finally, 42 articles were considered for analysis ( Figure 1).

Methodological Quality Assessment
The adequate baseline comparability, length of the follow-up, and outcome measure reliability were the most important strengths of this study. The most important limitations evidenced by the PEDro score were the lack of randomization and blinding, along with the high risk of bias during allocation concealment. In conclusion, the PEDro score resulted in 6.6/11, attesting to the acceptable quality of the methodological assessment (Table 1).

Arthroscopic Findings
Ten studies (236 patients) [15,37,[50][51][52]55,60,63,[66][67][68] evaluated the chondral lesions arthroscopically using the IRCS (Table 3). In the lateral patellar facet, 2.8% of lesions were grade I lesions, 2.8% grade II, 2.8% grade III, but none were grade IV. In the medial patellar facet, 2.8% of lesions were grade I, 18.3% grade II, 15.5% grade III, and 29.6% were grade IV. In the median crest, 7.0% of lesions were grade I, 19.7% grade II, 8.5% grade III, and 18.3% grade IV. In the trochlea, 9.7% of lesions were grade I, 13.9% were grade II, 3.2% were grade III, but none were grade IV. These results are shown in greater detail in Table 4. According to the main findings of the present systematic review, 98% of patients who experienced first time patellar dislocation demonstrated MPFL rupture at MRI. This rupture is more frequent at the patellar site (48%), whereas femoral (34%) and midportion (18.2%) tears are less common. Eighty-five percent of patients following patellar dislocation reported signs of patellar chondral damage at MRI, whereas 47% demonstrated trochlear chondral injuries. Arthroscopic findings evidenced that the medial chondral facet and median crest of the patella were affected more commonly by advanced chondral injuries than the lateral patellar facet and femoral trochlea. Loose bodies were observed in 11.5% of patients.
Given the multifactorial aetiology along with the juvenile onset, the management of patellar dislocation can be challenging [88,89]. Primary patellar dislocations are typically managed conservatively, and surgery is reserved for patients with recurrent patellar dislocations or demonstrating loose bodies or osteochondral defects [13,26,90]. The rate of redislocation after conservative management ranges from 15% to 71% [28,29,62,[91][92][93][94][95][96][97][98][99]. Conservative treatments included braces, cryotherapy, physiotherapy, and long periods of absence from sports [26,27]. Previous clinical studies comparing surgical versus conservative management for first patellofemoral dislocations suggest that patients may benefit from prompt surgery immediately after the first acute patellar dislocation [86,[100][101][102][103][104][105][106][107][108]. In a recent meta-analysis including 654 patients, immediate surgery was compared to conservative management for acute patellar dislocation [31]. At a mean of 54 months follow-up, the risk of redislocation was 2.44 folds greater in the conservative group, along with a 10% worse Kujala score [31]. If left untreated, patellofemoral instability can result in anterior knee pain, persistent instability sensation, and remarkable reduction in quality of life [109][110][111]. Therefore, a growing tendency to surgically treat the first patellar dislocation has been evidenced [112,113]. Moreover, isolated reconstruction of the MPFL shows excellent results and patient satisfaction, together with a very low rate of complications and failure [114]. Indeed, centres performing MPFL reconstruction have doubled in the last decades [115]. Concluding, patients may benefit from prompt surgical intervention to repair soft tissue injuries and restore patellar tracking, preventing further redislocations. An MRI should be considered in all the patients following patellar dislocation to evaluate soft tissue injuries.
The present investigation has certain limitations. The retrospective design and the relatively short length of follow-up in most available studies represents important limitations. Most of the included studies were case series or case reports, which lead to an increased risk of selection and allocation biases, negatively impacting the conclusions of the present systematic review. A formal control group was missing in most studies. Elias et al. [40] included a control group of consecutive knee MR imaging examinations performed for various indications. A control group of patients suffering recurrent patellar dislocations were used in two studies [55,69]. Sanders et al. [61] matched their patients with a cohort of patients who did not experience a previous patellar dislocation. No study took advantages from blinding methods, increasing the risk of detection and performance biases. The primary aim of most studies was not to report the rate of soft tissue injuries, which could represent an important source of bias. Most of the authors referred to "MPFL rupture" without clarifying the extent (partial or total tears). Given these limitations, results from the present study must be interpreted with caution. Future studies should validate these results in larger scale investigations.

Conclusions
Almost all patients following first time patellar dislocation presented chondral damages and MPFL rupture.