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
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).
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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