Indications for Medial Patellofemoral Ligament Reconstruction: A Systematic Review

Transcription

1 Original Article Indications for Medial Patellofemoral Ligament Reconstruction: A Systematic Review Marco Yeung, MD 1 Marie-Claude Leblanc, MD, FRCS(C) 1 Olufemi R. Ayeni, MD, MSc, FRCS(C) 1 Moin Khan, MD, MSc, FRCS(C) 1 Laurie A. Hiemstra, MD, PhD, FRCS(C) 2,3 Sarah Kerslake, MSc, BPhty 2,4 Devin Peterson, MD, FRCS(C) 1 1 Department of Surgery, McMaster University, Hamilton, Ontario, Canada 2 Banff Sport Medicine, Banff, Alberta, Canada 3 Department of Surgery, University of Calgary, Calgary, Alberta, Canada 4 Department of Physical Therapy, University of Alberta, Edmonton, Alberta, Canada Address for correspondence Devin Peterson, MD, FRCS(C), Department of Orthopaedic Surgery, McMaster University, Suite 4E11, 1200 Main Street West, Hamilton, Ontario L8N 3Z5, Canada ( dpeters@mcmaster.ca). J Knee Surg Abstract Keywords medial patellofemoral ligament (MPFL) patellofemoral instability patellofemoral dislocation The medial patellofemoral ligament (MPFL) plays a key role in lateral patellofemoral stability, and there has been significant clinical and research interest in MPFL reconstruction (MPFLR) in recent years. The primary objective of this systematic review of clinical studies is to investigate the reported indications for an isolated MPFLR and secondarily to examine some of the reasons reported for not performing an isolated MPFLR. A comprehensive search of the MEDLINE, EMBASE, PUBMED, and Cochrane databases was conducted to identify surgical studies investigating MPFLR. Study information including author, publication date, sample size, patient age, follow-up period, procedure performed, surgical indications and contraindications, and study design were extracted. The most common indication for isolated MPFLR was recurrent patellofemoral instability (82.1%). Common reasons given for not performing an isolated MPFLR included bony malalignment (51.8%), trochlear dysplasia (30.4%), and patella alta (23.2%). This systematic review identified recurrent patellofemoral instability as the primary indication for an isolated MPFLR; however, a large number of the studies did not provide clear criteria for when an isolated MPFLR should be performed. Similarly, there was significant variability in the reasons given for not performing an isolated MPFLR. Patellofemoral instability is reported as the second most common cause of traumatic knee hemarthrosis 1 and is commonly seen in young, active patients. 2,3 Complications following a primary patellofemoral dislocation include redislocation (15 49% 1,3 9 ), patellofemoral pain, 3,10 and patellofemoral osteoarthritis. 3,10 Subjective complaints of giving way, instability, decreased physical activity, diminished function, and reduced quality of life have also been described. 1,2,9,11 Furthermore, studies have shown that up to 55% of patients are unable to return to their previous level of physical activity. 7,8 A long-term study by Cofield and Bryan reported on 48 acute primary dislocations treated conservatively and followed for an average of 11 years. 12 Only 25% of patients reported being asymptomatic, with the remaining patients having complaints ranging from a conscious limitation of their activities to avoiding all vigorous sports. In 1997, Mäenpää et al reported results of a longterm study (13-year mean follow-up) on conservative treatment of acute patellar dislocation. 9 In 25% of cases, retropatellar crepitation was observed during physical examination, which was interpreted as a sign of cartilaginous degeneration. received March 1, 2015 accepted after revision August 23, 2015 Copyright by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) DOI /s ISSN

2 Recurrent patellofemoral dislocation is also a very complex problem with significant consequences including patellofemoral pain, patellofemoral osteoarthritis, decreased functional ability, and reduced quality of life. 1,3,4,8 11 The reported recurrence rate rises after recurrent dislocation, 4 6,8 with greater than 50% of patients reporting persistent instability symptoms. 1 Several studies have also demonstrated that greater than 50% of patients are dissatisfied following nonoperative treatment. 3,4,10,12 Nomura and Inoue conducted an arthroscopic study on 60 knees, confirming chondral damage following acute patellar dislocation (30 patients) and recurrent patellar instability (30 patients). 13 During the initial arthroscopy, 97% of patients in both cohorts demonstrated chondral damage of the patella. The trochlea was noted to be normal in 100% of the acute group, but only 90% of the recurrent group had a normal trochlea. The medial patellofemoral ligament (MPFL) plays a critical role in medial constraint for lateral patellofemoral stability, providing 50 to 60% of the soft tissue restraint prior to patellar engagement in the trochlear groove. 2,4 6,14,15 MPFL insufficiency is present in as many as 90% of acute patellar dislocations and up to 100% of recurrent cases. 3,15 Surgical stabilization has become an important and accepted modality in the management of patients with recurrent patellofemoral dislocation. Addressing MPFL insufficiency is a key component in the treatment algorithm of these individuals. 6,14,15 In 1992, Ellera Gomes first described anatomical MPFL reconstruction (MPFLR) for recurrent patellar dislocation. 16 In recent years, stabilization of the patellofemoral joint by addressing the medial soft tissue insufficiency through MPFLR has become a popular procedure, and studies have shown very high success rates One large single-center study of 193 patients with recurrent patellar instability treated with isolated MPFLR showed significant improvement in pre- and postoperative outcomes scores, with no recurrence of instability. 18 The popularity of MPFLR and the number of described techniques have increased exponentially; however, no single gold standard procedure has been established. 15 Another significant challenge of assessing the number of studies on MPFLR is the lack of consensus in the literature regarding the appropriate surgical indications for MPFLR, and no review to date has fully documented the spectrum of indications applied in clinical practice. The primary purpose of this systematic review of patellofemoral instability clinical studies is to investigate the reported indications for an isolated MPFLR. Second, this review will examine some of the reasons reported for not performing an isolated MPFLR. Methods Inclusion Criteria The inclusion criteria for this systematic review were as follows: (1) studies of human patients including all ages and both sexes, (2) clinical studies investigating the procedure of MPFLR either alone or associated with arthroscopic debridement and/or lateral release, and (3) studies published in English. Exclusion criteria were (1) review articles, (2) diagnostic studies, (3) case reports and studies with fewer than five patients, (4) studies involving MPFLR with concurrent MPFL repair, osteotomies, or trochleoplasties, and (5) studies investigating only skeletally immature patients. For simplicity, the term isolated MPFLR will be used throughout the remainder of this article to describe studies that performed MPFLR with or without arthroscopic debridement and/or lateral release, but excluded MPFL repair, osteotomies, or trochleoplasties. A title and abstract review to screen for eligible studies was completed in duplicate. A full-text review was then conducted, also in duplicate, and references were hand searched for other eligible studies. Any discrepancies regarding inclusion were resolved through discussion and consensus between reviewers (M. Y. and M. K.). Search Strategy Electronic databases (MEDLINE, EMBASE, PubMed, and Cochrane Library) were searched for MPFL studies from January 2000 to late April Given the rapid advancement of surgical techniques, the search was limited to the year 2000 to maintain surgical relevance. The search strategy used the following search terms: (1) MPFL or medial patellofemoral ligament, or patellofemoral ligament AND (2) reconstruction, surgical operation, or surgery. The Surgical Procedures, Operative (MeSH) subheading was also included in the MEDLINE search, and surgery, orthopedic surgery, and surgical technique subheadings were included in the EMBASE search. The results were uploaded to a bibliographic management database (RefWorks, version 2.0; Bethesda, MD). Data Collection Data were collected from the included studies by two reviewers (M. Y. and M.-C. L.). Abstracted information included the following data: title, author, year of publication, location of study, sample size of isolated MPFLRs, number of male and female patients, mean age, length of follow-up, level of evidence, technique of intervention studied, surgical indications, and reasons for study exclusion of an isolated MPFLR. Data Analysis All data abstracted from eligible studies were organized into a table (Microsoft Excel, Santa Rosa, CA). Descriptive statistics were calculated to reflect the frequency of outcome measures. Study quality was assessed in duplicate (by authors M. Y. and M.-C. L.). The quality assessment scoring for nonrandomized studies were performed using the methodological index for nonrandomized studies (MINORS) instrument. 20 The quality assessment scoring for randomized trials was performed using the Cochrane Collaboration s Risk of Bias tool. 21 The κ (kappa) statistic was used to examine interobserver agreement for study eligibility. On the basis of the guidelines of Landis and Koch, a κ of 0 to 0.2 represents slight agreement, 0.21 to 0.40 fair agreement, 0.41 to 0.60 moderate agreement, and 0.61 to 0.80 substantial agreement. A value above 0.80 is considered almost perfect agreement. 22

3 Citations identified on Ovid Search of Embase, Medline, Cochrane databases (n = 1029) Embase (n = 376) Medline (n = 286) PubMed (n = 314) Cochrane (n = 54) Duplicates removed (n = 549) Citations after duplicates removed (n = 480) Studies included after title and abstract review (n = 105) Studies included after full text review (n = 56) Excluded studies after title and abstract screen (n = 375) Nonpatellar instability studies (n = 47) Radiographic studies (n = 29) Cadaveric studies (n = 59) Review articles (n = 65) Case reports/case series <5 (n = 33) Technique articles (n = 39) Systematic reviews (n = 11) Periprosthetic studies (n = 16) Nonsurgical studies (n = 18) Other surgical techniques (n = 20) Further duplicates (n = 27) Letters/editorials (n = 8) Scientific/conference abstracts Excluded studies (n = 49) No isolated MPFL reconstruction (n = 19) Abstract/no full article (n = 10) Non-English (n = 15) Nonsurgical outcome study (n = 4) Open physes only (n = 1) Fig. 1 Summary of the literature search and inclusion/exclusion process. Results Study Identification The initial literature search produced 1,029 articles. Two independent reviewers (M. Y. and M. K.) performed a title and abstract search, and duplicates were removed, leaving 105 articles. The title and abstract search showed excellent agreement between reviewers (κ ¼ 0.896; 95% CI ). The full text article review produced 56 relevant articles ( Fig. 1) with excellent agreement between reviewers (κ ¼ 0.922; 95% CI ). Study Characteristics Our review identified 56 relevant articles investigating the surgical procedure of isolated MPFLR without concurrent MPFL repair, osteotomies, or trochleoplasties. All articles were published between the years 2000 and With regard to geographical distribution, 21 of the included studies were conducted in Europe, 20 studies were conducted in Asia, 10 studies were performed in North America, 4 studies were performed in South America, and 1 study was performed in Africa. The cumulative sample size for patients undergoing isolated MPFLR was 1,903. The pooled data showed a mean age of 23.6 years (ranging from the lowest mean age for an individual study of 14.2 years to the highest mean age of 32.5 years) ( Table 1). Fifty-one studies (91.1%) described the use of autograft reconstruction; 34 studies (60.7%) used semitendinosus tendon, 23 studies (41.1%) gracilis tendon, 4 studies (7.1%) quadriceps tendon, 3 studies (5.4%) patellar tendon, 2 studies

4 Table 1 Characteristics of included studies Study characteristic Quantity (percentage) Number of included studies 56 Sample size 1,903 Mean patient age of 23.6 y included studies Location of study Europe 21 (37.5%) Asia 20 (35.7%) North America 10 (17.9%) South America 4 (7.1%) Africa 1 (1.8%) Oceania 0 (0.0%) Grafts used Autografts used 51 studies (91.1%) Semitendinosus 34 studies (60.7%) tendon autograft Gracilis tendon autograft 23 studies (41.4%) Quadriceps tendon autograft 4 studies (7.1%) Patellar tendon autograft 3 studies (5.4%) Adductor magnus autograft 2 studies (3.6%) Iliotibial band autograft 1 study (1.8%) Allografts used 3 studies (5.4%) Semitendinosus 2studies(3.6%) tendon allograft Patellar tendon allograft 1 study (1.8%) Tibialis anterior allograft 1 study (1.8%) Synthetic grafts 3 studies (5.4%) Surgical techniques Arthroscopy 41 studies (73.2%) Lateral release 24 studies (42.9%) Level of Evidence Level I 2 studies (3.6%) Level II 2 studies (3.6%) Level III 9 studies (16.1%) Level IV 43 studies (76.8%) (3.6%) adductor magus tendon, and 1 study (1.8%) used the iliotibial band. Allograft use was described in three studies (5.4%); one used semitendinosus allografts, another used patellar tendon allograft, and the final study described the use of semitendinosus or tibialis anterior tendon allografts. Finally, artificial ligament grafts were used in three studies (5.4%). Study Quality The large majority of the 56 included studies were level IV evidence (43 studies, 76.8%), with the minority being level III (9 studies, 16.1%), level II (2 studies, 3.6%), and level I studies (2 studies, 3.6%) ( Table 1). The 47 noncomparative, nonrandomized studies included in this systematic review had a mean MINORS criteria score of 8.3/16. Of the seven comparative, nonrandomized studies included in this review, the mean MINORS criteria score was 12.6/24. The majority (49) of the studies did not report on the prospective calculation of the study size and the unbiased assessment of the study end point. Other reasons for low scores were inadequate inclusion of consecutive patients, inadequate prospective collection of data, and poor reporting of loss to follow-up. Two randomized studies were assessed with the Cochrane Collaboration s tool for assessing risk of bias in randomized trials. One study was assessed to have adequate sequence generation; incomplete outcome data were addressed and were free of selective reporting and other bias, but had inadequate blinding and unclear allocation concealment. 23 The second study had inadequate allocation sequence generation, allocation concealment and blinding, but incomplete outcome data was addressed and it was free of selective reporting and other bias. 17 Indications for Isolated Medial Patellofemoral Ligament Reconstruction Table 2 lists the indications for isolated MPFLR. Recurrent patellofemoral instability was the most common indication for performing an isolated MPFLR and was an indication in 46 of the 56 studies (82.1%). There was minimal differentiation of patellofemoral instability between dislocations and subluxations. In the studies that clearly described patellofemoral dislocation along with the number of dislocations, isolated MPFLR was indicated with a history of 2 or more patellar dislocations in 12 studies (21.4%) and a history of 3 or more patellofemoral dislocations in 3 studies (5.4%). A single dislocation was sometimes considered an indication for isolated MPFLR especially if there were ongoing symptoms of instability such as lateral subluxation (five studies, 8.9%) or if there was an associated osteochondral fracture (three studies, 5.4%). Failure of nonoperative management, such as bracing and physiotherapy, with persistent symptoms of patellofemoral instability was an indication for isolated MPFLR in 17 (30.4%) studies. Seven studies (12.5%) reported on duration of conservative treatment with a range from 3 to 9 months prior to MPFLR. There were several other indications for isolated MPFLR that were less clear and included symptomatic patellofemoral instability associated with pain (five studies, 8.9%), positive physical examination findings (nine studies, 16.1%), and positive imaging (five studies, 8.9%). In five studies (8.9%), patellofemoral instability without further description was cited as the surgical indication, and in four studies (7.1%) there was no indication as to why an isolated MPFLR was performed. Reasons for Not Performing an Isolated Medial Patellofemoral Ligament Reconstruction Table 3a and 3b outline the reasons provided in specific studies for not performing an isolated MPFLR. Table 3a summarizes reasons specific to risky anatomy.

5 Table 2 Indications for MPFL reconstruction in included studies Indications Number of studies Recurrent patellar instability 46 (82.1%) 17 19,24 66 Minimum two or more patellar dislocations 12 (21.4%) 17,32,33,37,40,44,45,50,51,53,59,60 Minimum three or more patellar dislocations 3 (5.4%) 25,26,42 Primary patellar dislocation a 11 (19.6%) 17 19,23,32,33,45,54,56,59,63 With ongoing instability symptoms 5 (8.9%) 17,18,32,33,45 Associated osteochondral fracture 3 (5.4%) 56,59,63 Loose osteochondral lesion 1 (1.8%) 35 Painful subluxation 5 (8.9%) 17,18,46,49,67 Patellar instability clinical examination a 9 (16.1%) 32,34,39 41,45,53,56,67 Excessive lateral mobility/laxity on examination 3 (5.4%) 41,45,53 Positive patellar apprehension 8 (14.3%) 32,34,39 41,45,56,67 Patellar instability CT/MRI 5 (8.9%) 17,23,32,41,60 MRI-defined MPFL injury 2 (3.6%) 23,41 Patellar instability not further specified 5 (8.9%) Participation in sports 2 (3.6%) 25,26 Failed conservative measures 17 (30.4%) 24 30,32,34,35,37,41,49,54,59,67,68 No indications 4 (7.1%) a Subcategory numbers do not necessarily add up as some studies are represented multiple times. Bony malalignment was the most common reason provided for not performing an isolated MPFLR (29 studies, 51.8%). An increased quadriceps angle (Q-angle) was often described as a reason not to perform an isolated MPFLR, and some of the studies provided specific angles. Two studies 24,31 (3.6%) used a Q-angle value of greater than 25 degrees, five studies 25,32 34,67 (8.9%) greater than 20 degrees, one study 26 (1.8%) greater than 20 degrees in females and greater than 17 degrees in males, and two studies 35,36 (3.6%) used a value of greater than 15 degrees. Unfortunately, none of the studies provided details on the exact method used to measure the Q-angle. Similarly, an increased tibial tubercle trochlear groove (TT-TG) distance was a common reason suggested for not doing an isolated MPFLR. Some of the specific measurements were reported; one study (1.8%) used a cutoff of greater than 22 mm, 37 seven studies 26,34,38 42 (12.5%) greater than 20 mm, one study 43 (1.8%) greater than 17 mm, and five studies 17,32,33,44,45 (8.9%) used a TT-TG distance greater than 15 mm. Other alignment issues were also stated as reasons to avoid an isolated MPFLR. Increased knee valgus was described including some specific angles; one study 67 (1.8%) used greater than 10 degrees, two studies 25,26 (3.6%) greater than 7 degrees, and two studies 17,41 (3.6%) considered greater than 5 degrees as a cutoff value. Excessive femoral anteversion (EFA) and excessive tibial torsion (ETT) were also suggested as reasons to avoid an isolated MPFLR. One study 17 (1.8%) used a cutoff for EFA of greater than 35 degrees and another study 41 used a cutoff of greater than 20 degrees. For ETT, one study 41 cited a cutoff of greater than 40 degrees, and another study 27 used a tibial rotational angle of greater than 8 degrees. The most frequent imaging used to measure the rotation was a computed tomography scan. Patella alta was often an identified reason for not performing an isolated MPFLR (13 studies, 23.2%). Several studies provided specific numbers; one study 31 (1.8%) used an Insall Salvati ratio of greater than 1.3 and five studies 25,26,32 34 (8.9%) an Insall Salvati ratio of greater than 1.2, and one study 42 (1.8%) used a Caton Deschamps index of greater than 1.35 and four studies 38 40,43 (7.1%) used a Caton Deschamps index of greater than 1.2 as a cutoff. Trochlear dysplasia and patellar dysplasia were both described as reasons not to perform an isolated MPFLR. The amount of trochlear dysplasia suggested varied, with three studies 17,32,33 (5.4%) describing trochlear-sulcus angles greater than 150 degrees and two studies 25,26 (3.6%) using a value of 145 degrees; two studies 26,44 (3.6%) described trochlea dysplasia greater or equal to Dejour classification grade B as an exclusion criteria for an isolated procedure, one study 41 (1.8%) trochlea dysplasia greater than grade B, four studies 18,28,42,46 (7.1%) simply described severe or highgrade trochlear dysplasia, and one study 47 (1.8%) used a trochlear boss height of greater than 4 mm. The most common outcome scores used in the reviewed papers included the Kujala, Tegner activity scale, Lysholm, International Knee Documentation Committee, and the Crosby Insall grading. Several additional outcome scores as well as paper-specific subjective outcome scores were also employed in a limited number of papers. Table 4 outlines the clinical outcomes of MPFLR when clearly reported in the included studies.

6 Table 3 Reasons for not performing an isolated MPFL reconstruction Reason for study exclusion Number of studies a. Related to risky anatomy Boney malalignment a 29 (51.8%) 17,24 27,29,31 45,54,61,66 69,72,73 Excessive femoral anteversion 3 (5.4%) 17,41,66 Increased knee valgus angle 8 (14.3%) 17,25,26,37,41,67,69,72 Increased Q-angle 12 (21.4%) 24 26,31 36,44,66,67 Excessive tibial torsion 3 (5.4%) 27,41,66 Increased TT-TG distance 15 (26.8%) 17,26,32 34,37 45,54 Abnormal pelvic geometry 1 (1.8%) 66 Abnormal hind foot position 1 (1.8%) 66 Dysplasias a 17 (30.4%) 17,18,25,26,28,32 34,37,41,42,44,46,47,54,55,66 Trochlear dysplasia 17 (30.4%) 17,18,25,26,28,32 34,37,41,42,44,46,47,54,55,66 Patellar dysplasia 2 (3.6%) 25,33 Patella alta 13 (23.2%) 25,26,31 34,38 40,42,43,54,68 Neurogenic abnormality 3 (5.4%) 23,36,47 General ligamentous laxity 2 (3.6%) 56,66 Contralateral patellar instability 2 (3.6%) 17,60 Obesity 2 (3.6%) 69,72 b. Unrelated to risky anatomy Patellofemoral arthrosis a 14 (25%) 23,28 30,32,34,38,41,42,44,47,51,53,64 Severe osteochondral lesion 6 (10.7%) 23,28,29,32,34,41 Patellofemoral arthritis 10 (17.9%) 30,32,38,41,42,44,47,51,53,64 Other ligamentous or meniscal injury 10 (17.9%) 17,23,25,26,32 34,42,60,64 Patellofemoral crepitus 2 (3.6%) 69,72 Associated fractures 1 (1.8%) 17 Inability to comply to treatment protocol 1 (1.8%) 23 Joint infection 1 (1.8%) 36 a Subcategory numbers do not necessarily add up as some studies are represented multiple times. Discussion The most consistent indication for performing an isolated MPFLR was recurrent patellofemoral instability (46 studies, 82.1%). Common reasons for not performing an isolated MPFLR were bony malalignment (29 studies, 51.8%), trochlear dysplasia (17 studies, 30.4%), and patella alta (13 studies, 23.2%). The significant disability associated with patellofemoral instability has led to the development of numerous soft tissue and bony patella stabilizing procedures. In recent years, stabilization of the patellofemoral joint by addressing the medial soft tissue insufficiency through MPFLR has become a popular procedure, and many studies have shown high success rates However, to maximize and standardize patient outcomes, it is critical that clear indications and contraindications exist for a particular procedure. Unfortunately, in this systematic review, a large number of the studies did not provide clear criteria for when an isolated MPFLR should be performed. This is possibly related to the retrospective nature of many of the studies where precise information pertaining to the surgical procedure may not have been available. There were also several studies whose primary focus was a particular surgical technique and as such overall indications for the surgery were not clearly specified. Another possible reason for the vagueness and variability of the information assessed in this review is the fact that surgical indications for MPFLR are currently evolving. This review assesses 56 cohort studies that examined the results of isolated MPFLR. Reporting a cohort such as this requires the presentation of a homogeneous group. The authors of these studies presented certain exclusion criteria representing some of the pathoanatomic features prevalent in patients with patellofemoral instability. On this basis, some studies precluded particular patients from the homogeneous group that had strong indications for an isolated MPFLR. Either these patients were felt to require additional procedure in combination with the MPFLR or it was felt that the predicted results of MPFLR in these patients were sufficiently different as to be not included in the analysis of the main

7 Table 4 Clinical outcomes of isolated medial patellofemoral ligament reconstruction in included studies Study Isolated MPFLR patients (no. of patients) Mean follow-up Recurrence of instability postsurgery Kujala scores IKDC scores Lysholm scores Tegner activity scale score (preop/ postop) Other measures Ahmad et al (2009) mo None 50/88 42/82 50/89 3.6/5.6 Berard et al (2014) a 39 3 y Berruto et al (2014) a mo Bitar et al (2012) mo None Christiansen et al (2008) mo 1 dislocation 3 sub inst 18 þ app 4.0 postop Csintalan et al (2014) 49 0 dislocations 6subluxations 76.3 postop 5.6 postop Deie et al (2011) y 0 dislocations 0subluxations 1 þ app 64/94.5 Dopirak et al (2008) a 8 42 mo Drez et al (2001) mo 0 dislocations 1subluxation 87.8 postop 6.42 postop Fulkerson 92.5 postop Ellera Gomes (2008) 12 NR None ADL scale 40/75 Ellera Gomes et al (2004) 15 min 5 y None reported 0 þ app Aglietti 4 postop, Crosby Insall 4 postop Fernandez et al (2005) a mo Fithian et al (2006) 83 NR 1 dislocation Gomes (2008) mo None ADL 50.1/72.8 (ST group), 50.6/72.7 (Add group) Goyal et al (2013) mo None 49.31/91.25 Han et al (2011) y 0 dislocations 0subluxations 7 sub inst 41.4/82.6 Cincinnati scores 50.6/88.7 Harle et al (2010) a 27 knees 41.7 mo Hinterwimmer et al (2013) mo None 92 postop 5 postop Insall score 95% excellent 89% satisfaction Hopper et al (2014) a 50 knees 31.3 mo Howells and Eldridge (2012) a 206 knees 16 mo Howells et al (2012) mo None 46.6/64.28 (hyper) 55.44/82.56 (nonhyper) 41.61/54.96 (hyper) 43.83/77.08 (nonhyper) 3.80/4.13 (hyper) 4.60/5.44 (nonhyper) OKS, WOMAC, Fulkerson, SF12 scores improved preop to postop in both groups (Continued)

8 Table 4 (Continued) Study Isolated MPFLR patients (no. of patients) Mean follow-up Recurrence of instability postsurgery Kujala scores IKDC scores Lysholm scores Tegner activity scale score (preop/ postop) Other measures Kodkani and Joshi (2012) 23 NR None reported Lim et al (2008) mo None 59.1/ / /6.80 Lippacher et al (2014) dislocations 5subluxations 5 þ app 66/ / /4 100% return to sport, 79.4% satisfied, VAS: 4/2, Activity Rating Scale: 6/3 Ma et al (2013) mo 0 þ app 54/87 3/5 Matsushita et al (2014) mo 0 dislocations 4 þ app 75.5/92.3 (Increased TT-TG) 67.8/92.1 (control) 79.5/94.7 (Increased TT-TG) 71.1/91.9 (control) Crosby Insall grading 47% excellent, 47% good (increased TT-TG), 40% excellent, 60% good (control) Matthews and Schranz (2010) mo None 87 postop 3/4 McCarthy et al (2013) a 15 NR Mikashima et al (2006) mo 1 þ app 30.5/ % return to sport Nomura et al (2000) y 1 dislocation/ subluxation 2 þ app Crosby Insall grading: 55% excellent, 41% good, 4% fair Nomura and Inoue (2006) y none 56.3/96.0 Crosby Insall grading: 66% excellent, 17% good, 17% fair Nomura et al (2007) y 2 dislocations or subluxations 63.2/94.2 Crosby Insall grading: 46% excellent, 42% good, 12% fair Ostermeier et al (2007) mo None 56/95 Panni et al (2011) mo None 56.7/ /88.1 Fulkerson: 59.2/90.1 Larsen: 12.4/17.1, 64% return to same level of sport, 87% satisfaction Parikh et al (2013) 151 knees recurrent instability Raghuveer and Mishra (2012) mo 1 sub inst 44.8/ % excellent, 20% good, 13% fair result Ronga et al (2009) y 3 dislocations 45/83 modified Cincinnati: 52/89, 9/28 return to same level of sport Schöttle et al (2005) mo 1 dislocation 2 þ app 45.86/ % excellent, 43% good, 29% fair result Servien et al (2011) a mo

9 Table 4 (Continued) Study Isolated MPFLR patients (no. of patients) Mean follow-up Recurrence of instability postsurgery Kujala scores IKDC scores Lysholm scores Tegner activity scale score (preop/ postop) Other measures Shafizadeh and Balke (2014) 48 min 6 mo None Siebold and Borbon (2012) 22 up to 2 y None Smith et al (2014) 30 NR 1 dislocation 65.4/ /77.7 VAS pain: 32.2/16.3 Song et al (2014) mo (med) 1 þ app 52.6/ / /5.0 Steensen et al (2005) mo None Tateishi et al (2011) 27 NR Not reported Thaunat and Erasmus (2007) y None 93 postop Toritsuka et al (2011) mo None 96 postop Crosby Insall grading 30% excellent, 70% good Wagner et al (2013) mo 1 dislocation 70/87 80% return to same level of activity Wang et al (2013) mo 3 dislocations (single bundle), 0 dislocations (double bundle) 57.35/80.46 (single bundle), 61.00/92.86 (double bundle) 80.8% good to excellent for single bundle, 95.5% good to excellent for double bundle Wang et al (2010) mo 0 dislocations 8 þ app 51.3/ % excellent, 25% good, 32.1% fair result Wang et al (2012) mo 0 dislocations 0subluxations 1 þ app 53.9/ /82.8 Watanabe et al (2008) 29 knees 4.3 y 8 þ app 70/92 Witoński et al (2013) 10 3 y 7 mo None 59.7/84.4 Improved scores from all aspects of KOOS and most aspects of SF36 from pre- to postop Zhou et al (2014) mo None 63.0/ % excellent, 31.25% good, 6.25% fair result Abbreviations: ADL, activities of daily living; Add, adductor; hyper, hypermobile group; IKDC, International Knee Documentation Committee Score; KOOS, Knee Injury and Osteoarthritis Outcome Score; med, median; min, minimum; mo, month; MPFLR, medial patellofemoral ligament reconstruction; no., number; NR, not reported; postop, postoperatively; preop, preoperatively; ST, semitendinosus; sub inst, subjective instability; TT-TG, tibial tubercle trochlear groove; VAS, visual analogue scale; y, year. Note: þ app ¼ positive apprehension. a Unable to extract data for isolated MPFLR.

10 cohort. Unfortunately, there was significant variability between the studies as to these exclusion criteria. Even the most commonly described exclusion criteria were present in fewer than 50% of studies. This may have occurred because the focus in the majority of these studies was to assess the result of MPFLR rather than discussing these risky anatomical characteristics as exclusions for an MPFLR. Some authors have adopted the philosophy that medial soft tissue insufficiency combined with bone abnormality necessitates a global approach 5,6,8,14 and there have been recommendations to address all possible associated patellar instability risk factors as a first line of treatment (e.g., medial soft-tissue deficiency, increased TT-TG distance, patella alta). 76 It was evident in this systematic review that there is a lack of consensus regarding the degree of malalignment or the severity of abnormality that precludes successful isolated MPFLR. One such controversial area is patellofemoral instability combined with associated trochlear dysplasia, which is one of the predominant factors in patellar instability, but the most difficult to address in surgery. In 1994, Dejour et al performed a radiologic assessment study of trochlear anatomy on 143 operated knees for symptomatic patellar instability compared with a normal control group. 77 These authors concluded that trochlear dysplasia was a constant feature of objective patellar instability. In 2006, Steiner et al studied isolated MPFLR in the setting of trochlear dysplasia and concluded that isolated MPFLR provide excellent long-term pain relief and functional return with prevention of redislocation; however, these authors failed to define the severity of trochlear dysplasia in their study cohort. 68 In 2013, Wagner et al studied patients with trochlea dysplasia and isolated MPFLR and concluded that addressing only ligamentous factors through MPFLR leads to satisfying clinical results and low redislocation rates in most cases, although they observed poor clinical outcomes in patients with a high degree of trochlear dysplasia. 48 The heterogeneity of the surgical techniques as well as the lack of consistency in reporting functional outcomes made indepth analysis of outcomes data meaningless. Recurrent instability postoperatively was also reported in various different ways; however, combined instability (dislocations and subluxations) post-mpflr ranged from 0 to 17% (excluding patients with a positive apprehension test as their only sign of instability). There were multiple strengths in this systematic review. A thorough search strategy using various keyword and subheading searches as well as a comprehensive search of multiple databases was undertaken. There were multiple reviewers involved in the process of title, abstract and full text reviews, and data abstraction of the studies, to ensure accuracy and minimize bias. The inclusion criteria also attempted to investigate isolated MPFLRs without other bony procedures to ensure that the indications that were analyzed were not related to associated procedures. Furthermore, the included articles were limited to a contemporary time period to ensure that the most relevant surgical indications were studied. The included studies were undertaken in multiple continents, potentially increasing the generalizability of the results. To our knowledge, this is the first systematic review to investigate surgical indications for isolated MPFLR. Despite the methodological strengths of this study, there were certain limitations. This study is limited by the methodological quality of the available included studies. The majority of the studies included in this systematic review are case series and are therefore of lower level on the hierarchy of evidence. The observational studies also had low MINORS scores. Of the studies with a comparison group, many were retrospective in nature. There is also possible expertise bias in reporting, as many of the papers were performed in high-volume centers. We did not discuss issues surrounding isolated MPFLR in patients with open growth plates as this is beyond the scope of this article. 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