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General Review

Treatment of Primary Acute Patellar Dislocation

Systematic Review and Quantitative Synthesis of the Literature

Longo, Umile Giuseppe MD, MSc, PhD; Ciuffreda, Mauro MD; Locher, Joel MD; Berton, Alessandra MD; Salvatore, Giuseppe MD; Denaro, Vincenzo MD

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Clinical Journal of Sport Medicine: November 2017 - Volume 27 - Issue 6 - p 511-523
doi: 10.1097/JSM.0000000000000410
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Primary acute patellar dislocations account for 3% of all traumatic knee lesions and represent the second most frequent cause of traumatic hemarthrosis of the knee after anterior cruciate ligament tears.1–7 Subjects under 20 years of age, involved in sports activity, are at greater risk of acute traumatic patellar dislocation.8,9 Patellar dislocations are typically caused by a twisting motion of the knee, a sudden lateral cut, or a direct impact that knocks the patella out of the joint.10 About 93% of traumatic patellar dislocations occur during flexion and valgus movement of the knee without direct contact.9 Patellar dislocations are mainly lateral, whereas medial dislocations are exclusively iatrogenic. Intra-articular dislocations have been reported, but they are rare.11 Patients commonly complain about a slipping sensation, intense pain, and secondary effusion. According to Sillanpaa et al,9 hemarthrosis, medial patellar wing fracture, and medial patellofemoral ligament (MPFL) lesion occur in almost all patients after a traumatic patellar dislocation, and osteochondral fracture can be observed in 25% of cases.

Long-term consequences of primary acute patellar dislocation include recurrent dislocations, patellar instability, cartilage injury, pain, limitation of activities of daily living, and patellofemoral osteoarthritis.11 The risk of redislocation increases by 6 times in patients with a history of contralateral patellar dislocation. If 2 dislocations occur, the risk of redislocation has been reported to be up to 50% or even higher if the MPFL is injured.9 Predisposing factors for recurrent dislocations are femoral anteversion, external tibial torsion, genu valgum, patellar dysplasia, trochlear dysplasia, patella alta, vastus medialis obliquus atrophy, pes planus, and generalized hyperlaxity.12

The management of primary acute patellar dislocation aims to reduce the risk of redislocation and painful subluxation and to prevent osteoarthritis. The conservative management of primary acute patellar dislocation is favored by several teams.13,14 Rest and immobilization of the knee in 20° of flexion is suggested for 2 to 3 weeks to control pain and approximate the 2 extremities of the MPFL. As soon as pain allows it, weight-bearing and mobilization are recommended. A brace can be used to stabilize the patella.15 Closed-chain exercises and passive mobilization are suggested to reinforce muscles and proprioception.16 However, the incidence of recurrent patellar instability after conservative treatment ranges from 15% to 40% of cases.12 Several surgical procedures to address primary acute patellar dislocation have been described,14,17–34 including medial reefing, extensor mechanism realignment and MPFL reconstruction.35 In recent years, the number of medical centers performing reconstruction of the MPFL has doubled, reporting favorable functional outcomes and improved complication and failure profiles.36 However, the role of surgery for primary acute patellar dislocation is still debated.

The aim of this study was to evaluate clinical outcomes, rate of redislocation, and complications after conservative and surgical treatment of primary acute patellar dislocation. We hypothesized that surgical treatment leads to lower rate of redislocation and better clinical outcomes in the short–medium follow-up. However, clinical outcomes of patients treated conservatively will be as good as those of surgical patients in the long-term follow-up.


We performed a systematic review of the literature according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.37 The flowchart of literature search is shown in Figure 1. A comprehensive search of PubMed, Medline, CINAHL, Cochrane, Embase, and Google Scholar databases was performed using various combinations of the following keywords: “patella,” “dislocation,” “treatment,” “acute,” “primary.” Three independent reviewers (U.G.L., M.C., and J.L.) separately conducted the search. All journals were considered, and all relevant studies were analyzed. To qualify for the study, an article had to be published in a peer-reviewed journal. All articles were initially screened for relevance by title and abstract, excluding articles without an abstract, and obtaining the full-text article if the abstract did not allow the investigators to assess the defined inclusion and exclusion criteria. The same investigators (U.G.L., M.C., and J.L.) separately reviewed the abstract of each publication and then performed a close reading of all papers and extracted data to minimize selection bias and errors. A cross-reference research of the selected articles was also performed to obtain other relevant articles for the study. We selected articles published from inception of databases to February 5, 2016. Given the linguistic capabilities of the authors, articles in English, French, Spanish, German, or Italian were included. We included articles about conservative and/or surgical treatment of primary acute patellar dislocation that reported information about outcomes, rate of redislocation, and complications. Missing data pertinent to these parameters warranted exclusion from this systematic review. Literature reviews, case reports, studies on animals, cadavers or in vitro, biomechanical reports, technical notes, letters to editors, and instructional courses were excluded.

PRISMA 2009 flow diagram.

Finally, to avoid bias, the selected articles, the relative list of references, and the articles excluded from the study were reviewed, assessed, and discussed by all the authors, and if there was disagreement among investigators regarding the inclusion and exclusion criteria, the senior investigator (V.D.) made the final decision. According to the Oxford centre of evidence-based medicine, level I to IV articles were found in the literature and included in our study.

The following data were independently extracted by all the investigators: demographics, chondral defects and soft tissue lesions, clinical scores for the outcome measurement, type of management recurrence of instability, and complications.

We performed a quantitative synthesis to compare the rate of recurrence in patients undergoing conservative or surgical treatment. We used Review Manager (RevMan, version 5.3 for Windows; Cochrane Information Management System) to assess the magnitude of treatment effect. We assessed an I2 index as a measure of heterogeneity for the main analysis. An I2 value represents the percentage of total variation across studies, which is caused by heterogeneity rather than by chance. We considered a low I2 value as 25% or lower and a high I2 value as 75% or higher.

Categorical variable data were reported as frequency with percentage. Continuous variable data were reported as mean value with a range between minimum and maximum values. In all studies, P < 0.5 was considered statistically significant.

Quality Assessment

The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system38,39 was used to assess the quality of evidence. It was used to establish the quality of evidence through 4 factors: study design, study quality, consistency, and directness. The quality of evidence is classified as high, moderate, or low according to factors that include the study design, the consistency of the results, and the directness of the evidence.


The literature and cross-reference research resulted in a total of 1271 references, 1229 of which were rejected because of off-topic abstracts, failure to fulfill the inclusion criteria, or both (Figure 1). After reading the remaining full-text articles, 18 articles were excluded for the following reasons: insufficient details, uncertain diagnosis and outcome measures, inclusion of patients with chronic patellar dislocation, and report of mixed results. Finally, 24 articles describing the management of patients with primary acute patellar dislocation were included. An exclusively surgical approach was used in 5 studies,21,22,25,34,40 an exclusively conservative approach was used in 2 studies,40,41 and both approaches were used in 17 studies.14,17–20,23,24,26,28–33,42–44 The conservative approach was always the immobilization of the affected knee; details of the surgical techniques are reported in Table 2.


A total of 2134 knees in 2086 patients were included, with an average age at dislocation of 20.3 years ranging from 830 to 7419 years (Table 1). Patients were assessed at follow-up for an average time of 69.9 months ranging from 024 to 26 years.41

TABLE 1-a:
Details of Included Studies
TABLE 1-b:
Details of Included Studies

Chondral Defects and Soft Tissue Lesions

Nine of 24 studies14,21,25,26,31–34,42,44,45 reported chondral lesions, with 1014 knees analyzed. The most frequent lesions were chondral defect of the patellar joint surface in 226 knees (22.2%); Chondral defect of the femoral joint surface was detected in 103 knees (10.1%).

Soft tissue lesions were reported in 3 of 21 of the included studies21,34,45 (Table 1), describing 481 knees. Medial patellofemoral ligament lesions were diagnosed in 111 (23%) knees, meniscus tears in 5 (0.1%) knees, and anterior cruciate ligament tears in 3 (0.06%) knees.

Outcome Measurements

Several outcome measures were reported in the included studies (Table 2). The most frequently reported score was the Kujula score used in 1118,19,25,26,28,29,32,33,41–43 of 24 studies. The mean Kujula score was 82.4 in patients undergoing conservative treatment and 87.9 in patients undergoing surgical treatment. Results from the included studies were divided into 2 groups: group A, short–medium follow-up term18,19,25,29,40,42 (less than 5 years); group B, long-term follow-up26,28,33,43 (more than 5 years). The average Kujula score in group A was 75.6 for patients treated conservatively and 88.7 for patients undergoing surgical treatment; instead in group B, the average Kujula score was 87.5 for patients treated conservatively and 86.6 for patients undergoing surgical treatment.

TABLE 2-a:
Type of Treatment and Percentage of Recurrence
TABLE 2-b:
Type of Treatment and Percentage of Recurrence
TABLE 2-c:
Type of Treatment and Percentage of Recurrence
TABLE 2-d:
Type of Treatment and Percentage of Recurrence
TABLE 2-e:
Type of Treatment and Percentage of Recurrence

Other less consistently reported scoring systems were the Lysholm score used in 4 studies14,22,25,44 with an average score of 86.2 and 85.8 for patients undergoing conservative and surgical treatment, respectively, the Hughston visual analog score used in 3 studies,28,43,44 and the Cincinnati Knee Rating17 used only in 1 study.28

Recurrent Instability and Complications

Redislocations were reported in 23 studies with 1524 knees. The overall rate of recurrence was 32.2% (492/1524) (Table 2). A total of 349 of 883 (39.5%) knees undergoing conservative treatment experienced new dislocation events,14,17–20,23,24,26,28–33,40–44 whereas the overall occurrence of redislocation was reported in 143 of 641 (22.3%) knees undergoing surgical procedure.14,17–26,28–34,42–44

A quantitative synthesis including studies that compared conservative and surgical management was performed.14,17–19,23,24,26,28–33,42–44 The rate of recurrence was significantly lower in the surgical group (25%) than in the conservative group (36.4%) (odds ratio, 0.53; 95% confidence interval, 0.40-0.70; P < 0.00001). A moderate heterogeneity (I2 = 26%) was found across studies (Figure 2).

Quantitative synthesis of 2 types of treatment: surgery versus conservative treatment.

Complications were reported in 5 studies.30,32,34,44,45 The overall complication rate was 6.5% (29 of 441 knees) in the surgical management group: superficial or deep wound infections in 12 knees; wound hematomas in 9 knees; deep venous thrombosis in 3 knees; peroneal palsy, osteoarthrosis, dermatitis of surgical dressing, paresis of the sciatic nerve, and bum injury on the insensible anterior skin in 1 knee. No complications were reported for patients treated conservatively.

Quality Assessment

The quality of the evidence within the topic is “low” according to GRADE (Figure 3).

GRADE. Summary of findings.


The main finding of this review is that surgical treatment of primary acute patellar dislocation lead to significantly lower rate of redislocation compared to conservative treatment (odds ratio, 12.71; 95% confidence interval,49 0.11-0.57; P = 0.0009). The rate of redislocation was 36.4% in the conservative group and 25% in the surgical group. These results agree with previous studies that reported 13% to 52% rate of redislocation after conservative treatment and 10% to 30% rate of redislocation after surgical procedures.11,46

The success of a treatment for primary patellar dislocation requires investigation beyond the incidence of recurrent dislocations, as patients can experience residual symptoms of instability limiting their quality of life.50 In the short–medium follow-up, patients undergoing surgical treatment reported better clinical outcome measures than patients treated conservatively (Kujala score 88.7 vs 75.6). However, in the long-term follow-up, results of patients treated conservatively were as good as those of surgical patients (Kujala score 87.5 vs 86.6).

Complications have been described only for patients undergoing surgical treatment. Five studies30,32,34,44,45 included in this review reported an overall complication rate of 6.7%. The most common complications were superficial wound infections and wound hematomas. Deep venous thrombosis, peroneal palsy, osteoarthrosis, and dermatitis of surgical dressing were also reported.

Primary acute patellar dislocation usually results in chondral defect and damage to soft tissues surrounding the patellofemoral joint. Although the nature and extent of damage are variable, some injury patterns have been found frequently. In this systematic review, a chondral defect of the patellar joint surface was found in 26.5% of knees, whereas a chondral defect of the femoral joint was detected in 15% of knees. A rupture of MPFL was diagnosed in 23% of knees. The MPFL is considered the most important medial restraining structure against patellar lateralization, but also patello-meniscal and patello-tibial ligaments and the superficial medial retinaculum contribute to patellar stability.11,47,51 Computed tomography (CT) and MRI are important in the decision-making process to precisely determine involved structures,48 hemarthrosis, osteochondral lesions of the medial patellar facet, bone edema of the medial patellar facet and lateral femoral condyle, and the anterolateral part of the lateral femoral condyle.52,53

Only low quality of evidence for primary acute patellar dislocation has been reported in literature.11 Studies were at risk of bias because they had weaknesses such as sample size, randomization, and lack of blinding. This represents the main limitation of the present study. Therefore, available data must be interpreted with caution. Future studies should accomplish blinding of interventions, perform concealed allocation, and use blinded outcome measurements because these would improve the quality and validity of their results.

A further limitation of the included studies was the heterogeneous distribution of predisposing factors in treatment groups. Recurrent patellar dislocation is associated with abnormalities of knee anatomy and soft-tissue integrity that predispose to patellar instability. Multiple anatomic factors and substantial intersubject variation have been recently described in the majority of patients with recurrent dislocation.54,55 Optimal treatment should be individualized to address specific anatomic factors that contribute to patellar instability.56,57 Moreover, it was not possible to compare efficacy of different surgical interventions for primary acute patellar dislocation because results of different procedures were not reported separately and surgical techniques were not always adequately described in the studies. In addition, limited data on cost-effectiveness of the included treatments were available. This information is indispensable for the decision-making process of care providers. Indeed, surgery should be more expensive than conservative treatment in the short term, but it should be more cost-effective than conservative treatments with a shorter patient sick leave.


Surgical treatment of primary acute patellar dislocation leads to significantly lower rate of redislocation and provides better short–medium clinical outcomes; whereas in the long-term follow-up, results of patients treated conservatively were as good as those of surgical patients. Unfortunately, the overall quality of the body of evidence is low. Further randomized controlled trials, describing anatomical abnormalities and soft-tissue integrity that may influence the choice of treatment, are needed.


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knee; patella; treatment; dislocation; primary; acute

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