Introduction

The medial patellofemoral ligament (MPFL) is the primary stabiliser against lateral patellar translation, providing between 53 and 67% of the medial soft tissue restraint [2, 3, 6, 11, 27]. It lies deep to the vastus medialis muscle, and attaches from the posterior part of the medial epicondyle, to the superomedial patella, the under-surface of the vastus medialis, and the quadriceps tendon [1, 36]. Anatomically, the MPFL acts as a passive check rein in preventing the patella from extreme lateral displacement [1, 12, 24, 37].

It has been suggested that in the majority of patellar dislocation cases the MPFL is disrupted [15, 25, 33, 34]. Not surprisingly, it has also been estimated that the redislocation rate after primary patellar dislocation managed non-operatively is 15–44% [3, 40]. Accordingly, several authors over the past decade have suggested that repair or reconstruction of the MPFL may be advocated to reduce this high incidence of recurrent dislocation [3, 22, 38].

A variety of different surgical techniques for MPFL reconstruction have been described, harvesting various different soft tissues to form the graft. These have included using the adductor magnus [10, 39], quadriceps tendon [3, 38] and semitendinosus [13, 23], in addition to the use of a mesh-type artificial ligament by Nomura et al. [24].

Although various case series of such patients have been published, reconstruction of the MPFL is not widely performed [19]. Furthermore, on a preliminary literature search, no studies have collectively evaluated the clinical or radiological outcomes following MPFL using a formal systematic review design. Accordingly, we undertook this systematic review of the literature to determine whether MPFL reconstruction is a suitable procedure, in respect to clinical and radiological outcomes, for patients with patellar instability. We also assessed the quality of the evidence-base on which such findings are presently based.

Methodology

The research question was: What are the clinical and radiological outcomes following MPFL reconstruction for patellar instability?

Inclusion and exclusion criteria

The inclusion criteria were:

  • Clinical papers reporting the outcome following MPFL reconstruction, with or without secondary surgery such as lateral release, tibial tubericle transfers or medial reefing.

  • Allograft or autograft ligament reconstructions.

  • Open or arthroscopic reconstructions.

  • Full text, English language publications.

  • Male or female subjects, of any age.

The exclusion criteria included:

  • Single-subject case reports, editorials, comments, letters, guidelines, protocols, abstracts and review papers. Review papers were excluded to allow each research methodology to be critically appraised using the original publication. The reference lists of such papers could be examined for further citations.

  • Open repairs of the MPFL rather than reconstruction.

  • Papers with insufficient detail pertaining to patient history, indications for surgery, surgical intervention, outcome measurement or results.

  • Non-English language papers.

  • Unpublished material such as theses and dissertations.

  • Animal and cadaver studies.

Search strategy

A search of the electronic databases AMED, British Nursing Index, CINAHL, the Cochrane database, EMBASE, ovid Medline, Physiotherapy Evidence Database (PEDro), PsycINFO, Pubmed and Zetoc was performed from their inception to May 2007. Key terms searched as key words included: patellar dislocation; patella dislocation; patellar subluxation; patella subluxation; patellar instability; patella instability AND reconstruction AND MPFL. A hand-search was undertaken of the specialist journals: The Knee (1994–May 2007), American Journal of Sports Medicine (1986–May 2007), British Journal of Sports Medicine (1986–May 2007), and the British and American editions of the Journal of Bone and Joint Surgery (1986–May 2007).

Three reviewers (TS, JW, NR) independently examined titles and abstracts from all identified papers to assess their appropriateness to the research question. Full manuscripts were ordered of those articles which adhered to the selection criteria. The reference lists of these papers were scrutinised to identify any possible additional publications not found through the electronic or hand-searches. The same three independent reviewers again assessed the full texts of the identified papers against the selection criteria. Any disagreement between the three reviewers with respect to article inclusion or exclusion was resolved through discussion until consensus was met.

Data extraction and assessment

The data extracted from each paper included the study design, sample size, population characteristics including indication for surgery, age, gender; surgical procedure; outcome measures; results; follow-up period; and any pertinent methodological limitations noted during critical appraisal. The methodological quality of each paper was assessed using the scoring system developed by the Critical Appraisal Skills Programme [8]. The CASP tool was chosen as it was an appropriate format with which to assess the methodology of the observational study designs recovered from the literature search. It was also chosen as it is a widely used critical appraisal tool, which has been employed in previous systematic reviews to assess the methodological quality of clinical studies [31]. The same three reviewers independently assessed each paper using this tool. If any disagreements arose regarding the appraisal, these were resolved through discussion until a consensus was met.

The final papers included in the review are summarised as Table 1.

Table 1 Summary of paper included in the review
Full size table

Results

Papers

The search strategy is summarised as Fig. 1. In total 351 citations were initially identified by the electronic search. Twenty-five articles were identified through the hand search. Titles and abstracts of these citations were assessed against the selection criteria, providing 31 papers that appeared relevant. Full manuscripts of these papers were ordered. In addition six papers were identified after scrutinizing the reference lists of each of these manuscripts. All ordered articles were again examined against the selection criteria; nine articles still adhered to these criteria. Two papers were initially included by Deie et al. [9, 10]. On analysis, it emerged that Deie et al. [10] included the patients reviewed in their earlier publication. Accordingly, the earlier paper was excluded. Eight papers were therefore included in this review. No disagreements arose between the reviewers on the inclusion of these articles. The results of these included papers are presented below.

Fig. 1
figure 1

A QUORUM statement flow-diagram

Full size image

Cases

All eight papers were case series designs, published between 2000 and 2006. In total 186 MPFL reconstructions were included in the review, performed on 174 different patients: 56 males and 118 females. When assessed collectively, the mean age was 24.0 years. This ranged from 6 [10] to 52 years [13]. Three papers acknowledged the duration between primary dislocation to surgery for their subjects [13, 23, 24]. When analysed, the majority of patients had chronic symptoms pre-operatively with a mean duration from initial dislocation to surgery of 6.5 years, ranging from 7 days [13] to 37 years [13].

The most common indications for a MPFL reconstruction in the papers reviewed were failure of conservative treatment [7, 19, 24, 39], recurrent dislocation or persistent instability [10, 13, 19, 23, 24, 35, 39] and a positive apprehension test [7, 19, 35].

As demonstrated in Table 1, the surgical procedures undertaken in the eight papers varied considerably. Various different graft types were employed. A number of authors harvested a semitendinosis graft to reconstruct the MPFL [10, 13, 19, 23, 35] whilst Drez et al. [13] also used gracilis or fascia lata. Steiner et al. [39] used adductor magnus or quadriceps muscle to form their grafts, whereas Cossey and Paterson [7] harvested medial retinaculum. In contrast, Nomura et al. [24] used a mesh-type artificial ligament. For a more detailed description of the different surgical techniques adopted, the reader is advised to examine Table 1 and the specific articles.

In addition to the patient’s MPFL reconstruction, three papers noted that secondary knee surgery procedures were also undertaken. All patients in Cossey and Paterson’s [7] series had a tibial tuberosity transfer and lateral release in addition to their MPFL reconstruction; a tibial tuberosity transfer was also performed in eight of Schöttle et al.’s [35] sample; Deie et al. [10] performed a vastus medialis advancement and lateral release in 43 knees, whilst the remaining four in this study only received a vastus medialis advancement in addition to their MPFL reconstruction. Nomura and Inoue [23] performed a lateral release in three patients, whilst in Nomura et al.’s [24] series ten underwent this procedure as well as their MPFL reconstruction.

None of the papers assessed provided details regarding the rehabilitation programmes provided for their MPFL reconstruction patients. Similarly, no papers discussed which conservative treatments had been trialled with their samples pre-operatively.

The findings from the papers included in this review are presented by individual outcome, to clearly evaluate the clinical and radiological outcomes following a MPFL reconstruction.

Recurrence of dislocation or subluxation

The prevention of recurrent patellar dislocation or subluxation is one of the main considerations for undertaking this operation [17]. Six of the papers reviewed assessed this outcome post-operatively in their samples [7, 10, 13, 23, 24, 39]. Nomura and Inoue [23] and Cossey and Paterson [7] stated that none of their patients reported recurrent patellar dislocation or subluxation post-operatively, whilst Nomura et al. [24] and Drez et al. [13] each reported one patient in each of their samples (24 and 15 respectively) who presented with a re-dislocation or subluxation when followed-up. Deie et al. [10] reported that four patients presented at follow-up with patellar subluxations post-operatively.

Subjective assessment

A number of papers subjectively assessed patient satisfaction of this procedure [13, 19, 35, 39]. Drez et al. [13] and Schöttle et al. [35] used the same four questions to determine subjective response. Drez et al. [13] reported that ten subjects reported excellent results, three good results and one patient reported a poor outcome. Similarly Schöttle et al. [35] recorded eight patients had excellent scores, five patients with a good outcome and two patients with fair results. Both Steiner et al. [39] and Gomes et al. [19] asked whether their patients were satisfied with their outcome. Steiner et al. [39] found that 33 patients were satisfied with their outcome, and would have the operation again. Gomes et al. [19] reported that 13 patients were satisfied with their outcome, whilst 2 were not.

Outcome scale scores

A wide variety of outcome scales were used to assess functional and clinical outcome; these are presented as Table 2. The most commonly used score was the Kujala patellofemoral disorder score [20].

Table 2 The findings of outcome scale scores assessed by the paper included in this review
Full size table

Complication

Post-operative complications were assessed in five papers. Nomura and Inoue [23] acknowledged that no post-operative complications were noted in their sample. Post-operative knee stiffness was a complication acknowledged in Drez et al.’s [13] paper, with one patient developing arthrofibrosis. Nomura et al. [24] reported that one of their subjects developed a post-operative haemoarthrosis. Drez et al. [13] noted that one of their patients developed a wound dehiscence, whilst Nomura et al. [24] and Cossey and Paterson [7] each acknowledged that one subject from their cohort presented with a minor wound infection post-operatively. Steiner et al. [39] presented a patient who had a post-operative haematoma, and one patient who presented with graft advancement. Finally, pain caused by implants was a complication noted in three papers [7, 24, 39]. Nomura et al. [24] reported 11 patients (41%) presented with pain from the staple fixation site, Steiner et al. [39] reported one patient complained of pain from a screw at the medial epicondyle, and Cossey and Paterson [7] reported one patient had pain from a tibial tuberosity transfer screw; both screws were removed.

Radiological outcomes

A number of factors were radiologically assessed to determine the outcome of MPFL reconstructions. Cossey and Paterson [7], Deie et al. [10], Drez et al. [13], Nomura et al. [24] and Nomura and Inoue [23] assessed congruence angle. Deie et al. [10], Drez et al. [13], Nomura et al. [24] and Nomura and Inoue [23] reported that this figure improved following a MPFL reconstruction in their subjects, whilst Cossey and Paterson [7] simply provided their sample’s average post-operative congruence angle of 6.62°. Sulcus angle was assessed by Nomura and Inoue [23] and Cossey and Paterson [7]. Nomura and Inoue [23] reported that this improved post-operatively. Although Cossey and Paterson [7] documented that their average post-operative sulcus angle was 140.1°, they did not state how this compared to pre-operative values.

Lateral patellofemoral angle was assessed by in two papers [7, 13]. Drez et al. [13] reported that this angle improved post-operatively, whilst Cossey and Paterson [7] again only reported post-operative figures, acknowledging that their sample’s average lateral patellofemoral angle was 2°. Patellar tilt angle was assessed in two papers [10,35]. Schöttle et al. [35] commented that this has significantly decreased post-operatively, whilst Deie et al. [10] described that the patellar tilt angle was within normal limits following a MPFL reconstruction in their subjects.

Radiological patellar height was assessed in Nomura et al. [24] and Nomura and Inoue’s [23] papers. Both reported that this figure significantly improved post-operatively.

The Blackburne–Peel ratio and Caton ratios were assessed in three of the papers reviewed [7, 13, 35]. Schöttle et al. [35] reported that their subject’s Caton ratio improved from 1.14 pre-operatively to 1.04 post-operatively. Drez et al. [13] commented that there was no difference in Blackburne–Peel ratios from pre- to post-operatively in their subjects. Cossey and Paterson [7] described that their average Blackburne–Peel ratio was 0.94, and did not comment on whether this changed following surgery.

Finally, Deie et al. [10] acknowledged that there was no radiological difference in lateral shift or medial or lateral stress shift ratios from pre- to post-operatively in their sample.

Clinical examination

A variety of clinical measures were used to determine outcomes following a MPFL reconstruction in the papers reviewed. The most frequently used test was the apprehension test. Three papers reported that all their subjects presented with negative apprehension tests post-operatively [7, 13, 38]. In contrast, three patients (20) in Schöttle et al.’s [35] study, two (7%) in Nomura et al. [24] and one patient (6%) in Gomes et al. [19] paper presented with a positive apprehension test post-operatively. Patellofemoral joint crepitus was documented in Drez et al. [13], Gomes et al. [19] and Schöttle et al.’s [35] studies. Whilst Schöttle et al. [35] stated that none of their sample presented with patellofemoral joint crepitus on review, ten patients (67%) of Drez et al.’s [13] sample and ten subjects (63%) of Gomes et al.’s [19] paper presented with this post-operatively.

Subjects Q-angle was assessed in two studies [13, 23]. The average Q-angle in Drez et al.’s [13] subjects was 12.8°, (range 10–20°); whilst the average value in Nomura and Inoue’s [23] paper was 20.2° (range 15–25°).

Patellofemoral joint tenderness on palpation was assessed in Gomes et al. [19], Drez et al. [13] and Schöttle et al.’s [35] paper. Although Schöttle et al. [35] reported that none of their subjects presented with this variable, both Drez et al. [13] and Gomes et al. [19] reported that one subject in each of their papers reported patellofemoral joint tenderness on post-operative palpation. Anterior knee pain was assessed in two papers [19, 23]. Gomes et al. [19] found that none of their subjects presented with this condition on examination, whereas four patients in Nomura and Inoue’s [23] case series exhibited anterior knee pain symptoms.

Manual medial hypomobility was assessed in Drez et al. [13], Nomura and Inoue [23] and Schöttle et al.’s [35] papers. Nomura and Inoue [23] presented two subjects with medial hypomobility of their patella, Drez et al. [13] reported one patient, whilst Schöttle et al. [35] reported that none of their sample presented with this outcome post-operatively.

Knee range of movement was unfortunately only assessed in four papers [13, 24, 23]. Only end of range knee flexion was limited in three of these papers [13, 24, 23]. Full extension was regained in all subjects. Drez et al. [13] reported that four patients had reduced knee flexion, whilst Nomura and Inoue [23] and Nomura et al. [24] presented only a single case of reduced knee flexion.

Quadriceps atrophy was only assessed in Drez et al.’s [13] paper, using thigh circumference measurements. They reported that nine patients presented with quadriceps atrophy.

The patellofemoral compression test was assessed in two papers [19, 35]. Both papers reported that no patients presented with a positive painful response on compression test. Patellar tracking and tilt was assessed in Gomes et al. [19] paper. These authors reported that none of their patients presented with abnormal patellar tracking or excessive tilt when clinically examined post-operatively.

Methodological assessment

Table 3 presents the results of the CASP review. This demonstrated that there were numerous short-comings within the literature. A notable limitation exhibited in all but Nomura and Inoue’s [23] paper, was that the studies failed to ask a research question. As a consequence, according to the CASP criteria, it was not possible to determine how appropriate each study’s designs were, as it was unclear whether each design would be applicable for the research question. In many studies, it was also difficult to determine whether subject recruitment was appropriate since all the studies poorly described subject demographics or characteristics, or how they were selected, and whether they were consecutive or randomly allocated to the study [19, 23, 24, 35, 39].

Table 3 A summary of the CASP guidelines results
Full size table

A considerable strength in the studies reviewed was that all studies clearly described the surgical intervention performed and clearly stated which outcome measure was used. Although the CASP criteria suggest that each study should indicate whether they used validated or reliable outcomes, the studies did not clearly describe this. Nonetheless the majority of outcome scores used such as the Lysholm, Fulkerson and Kujala scores have been shown to be valid and reliable for patients with patellar instability [28].

There were a number of confounding factors which may have had a considerable impact on patient’s outcomes following MPFL reconstruction. These include syndromes such as Ehlers-Danlos, Down’s, Rubinstein-Taybi or hypermobility [4, 16, 21, 26]. Although Deie et al. [10] stated that patients with Ehlers-Danlos or Down’s syndrome were excluded; they did not mention whether hypermobile patients were included. Furthermore, the remaining papers did not acknowledge whether these factors were accounted for during subject selection. A strength of the literature was that all papers allocated an adequate time to allow the outcomes of their surgical intervention to be assessed, with no paper assessing outcomes less than 23 months on average. Similarly, with the exception of Deie et al. [10] and Drez et al. [13], all papers followed-up over 80% of their sample on the final assessment.

Although all but Cossey and Paterson [7] and Gomes et al. [19] assessed outcome using inferential statistics, none of the papers presented confidence interval data to determine how precise their statistical results were. Finally, because all the papers did not clearly define their samples, how they were recruited, or take account of confounding variables, it remained difficult to determine whether the findings could have been influenced by major bias, whilst making it difficult to make generalisations or interpret the findings in relation to current clinical practice.

Discussion

The aim of this review was to determine if MPFL reconstruction is an appropriate procedure for patients with patellar instability. Eight studies were deemed appropriate for this review. Following an appraisal of these papers, it would appear that a MPFL reconstruction may provide favourable clinical and radiological outcomes for patients with patellar instability. However, following a critical appraisal of these papers, a number of methodological limitations were found. These included poorly detailing subject recruitment or post-operative characteristics, not controlling for confounding factors, not presenting confidence interval data on analysis, and recruiting small sample sizes since none of the papers performed a power calculation to determine the likelihood of Type II errors [30].

It may be prudent to raise a number of issues which may have impacted on this review’s findings. One such factor was that there was some variation within the literature in grafts used, and the addition of other surgical procedures to the MPFL reconstruction was exhibited in three papers. These variables may have had an influence on the final results presented. This was a consideration during the design phase of our systematic review, but excluding papers which presented secondary surgery to the MPFL reconstruction, would have greatly reduced the data available for review, and possible external validity by not reflecting clinical practice [29].

The methodological design of the studies appeared appropriate, as a case series design would be capable of capturing changes in outcomes following this procedure. A prospective study design may have been more applicable, detailing whether consecutive patients were recruited, and following their outcomes at a series of time points. This would have improved the rigour of the study methodology [29] and a consideration when designing future studies on this topic.

The findings from these studies may be generalisable to the MPFL population. As acknowledged in the results section, the number of MPFL reconstruction patients in the papers reviewed was 174, where the majority (118) were female. This is representative of the patellar instability population [18], permitting a degree of generalisation from these results. The collective mean age of the patients was 24 years old (range 6–52), which corresponds to the typical patient who undergoes this orthopaedic procedure [18].

This review indicated that of the six papers, including 155 knees, which evaluated the post-operative recurrence of patellar dislocation or subluxation [7, 10, 13, 23, 24, 39], only six patients reported post-operative patellar dislocation or subluxation. Of these, four patients originated from Deie et al.’s [10] study. This may suggest that there may have been either sampling or surgical differences between this study and the others reviewed; a further consideration when considering the clinical application of this review.

The most common indication for MPFL reconstruction amongst the papers reviewed was failure of conservative treatment [7, 19, 24, 39]. Nonetheless, no paper specified what conservative treatments were undertaken and how long these were trialled for, a limitation in the presentation of these papers. Furthermore, all the studies evaluated, poorly documented their post-operative rehabilitation. Accordingly variations in this management may have influenced the surgical results when comparing each of the eight studies. It is recommended that future reports on the outcomes of MPFL should document the post-operative rehabilitation programme used, to allow the reader to determine whether this had an influence on patient’s functional and post-operative results.

In addition to reviewing this topic further, addressing the plethora of methodological limitations which have been highlighted, a number of other areas of further study are recommended. One such area includes determining whether post-operative outcome is influenced by the duration between primary patellar dislocation and surgery, to evaluate whether acute reconstructions are beneficial or detrimental to outcome. In addition, a well controlled and standardised comparison of different surgical techniques is indicated, to assess whether a specific graft or technique is superior to the others. Although the studies in this review adopted reasonable follow-up periods, further study could be undertaken to follow-up these patients over a longer period, to determine whether their patellar stability altered over time or if complications develop; an important evaluation for this relatively modern procedure. Similarly, little is also known on the optimal rehabilitation of this group of patients, a further area for investigation.

It is anticipated that over the next few years, as the MPFL reconstruction gains recognition, more case series and reported outcomes following this procedure will be presented. Accordingly, a repeat of this review may be indicated to compare the findings from this paper to future studies, as surgical technique and rehabilitation develop and evolve. In addition, once more cases are presented, a larger sample than the 186 can be accumulated for analysis, to provide greater weight behind any statements made from this review.

It is necessary to give consideration to a number of factors that could have impacted upon the findings of this systematic review. Firstly, the selection criteria excluded unpublished material such as university thesis, protocols, guidelines, or grey literature. Although, this was undertaken to ensure that the material reviewed had been through a peer-review process to attempt to maintain quality, it also permitted the potential for that publication bias may have influenced this review’s results [32]. Secondly, the search strategy used was based on a computer search. Colville-Stewart [5] acknowledged that computer searches may omit some articles, and consequently, limiting the scope of this review. To address this, the reference lists of each manuscript ordered and a hand-search of pertinent journals was performed. Non-English language articles were excluded. This was done due to the costs which translation may have required. Nonetheless, it may have limited the breadth of literature. Subsequently, further review assessing the literature published in other languages may be recommended, to compare against the findings of this review. As acknowledged, there were important differences between papers, most notably in surgical technique, outcome measurements, cohort’s duration from injury to surgery, and post-operative rehabilitation. Due to this heterogeneity, this topic could not have statistically assessed the papers collectively using a meta-analysis design, which may have allowed the reader to make greater generalisations on the review’s findings [29]. Furthermore, Egger et al. [14] suggested that formal meta-analysis is not recommended for systematic review of observational study designs.

Conclusion

It would appear that the literature suggests that a MPFL reconstruction may provide favourable clinical and radiological outcomes for patients with patellar instability. However, a critical appraisal of the papers reviewed highlighted a number of methodological limitations which meant that any conclusions made from these papers should be interpreted with caution. Further study is recommended to address the methodological weaknesses identified, potentially in the form of a prospective study. As MPFL reconstruction gains recognition, and as surgical technique and rehabilitation develop over the next few years, it is felt that a repeat of this literature review may be indicated to allow us to state with greater confidence, what the clinical or radiological outcomes are following a MPFL reconstruction.

Conflict of interest: None declared. Ethical approval not required. No funds were provided.