Introduction

Patellar femoral instability (PFI) has multiple predisposing factors including acute trauma, ligamentous laxity, bony malalignment, or anatomical pathology. The primary objective of this systematic literature review was to determine if there is a threshold for axial plane alignment that triggers surgical correction in the published literature. The secondary objective was to determine the constellations of other anatomic PFI factors that might co-exist, and if so, determine the outcomes after surgery.

Methods

Using a predetermined search strategy, a systematic literature search of 10 major databases and grey literature resources was completed including Medline and Embase (via OVID), Cochrane Library, SPORTDiscus, Web of Science, Scopus, ClinicalTrials.gov, WHO ICTRP, and Global Index. Only studies reporting on instability with outcomes were included. Radiologic indications (valgus/torsional threshold for performing the osteotomy), additional procedures, outcomes, and complications were reported. Titles and abstracts were screened by two reviewers. If there was a discrepancy, a third reviewer was utilized. Full text manuscripts were then selected and extracted by three reviewers. The following variables were extracted: sex, age, indication, time from first dislocation, number of dislocations, previous surgery, surgery performed, operative level of correction, coronal and axial correction, trochlea dysplasia, axial measurement technique, recurrent instability, complications, and reoperations. The following pre-operative and post-operative variables were collected: tubercle-sulcus angle, femorotibial angle, tibial-tuberosity to trochlear groove distance, valgus, femoral anteversion, tibial torsion, J-sign, Kujala score, Lysholm score, and International Knee Documentation Committee (IKDC) score.

Results

A total of n=1132 abstracts and titles were screened by two reviewers yielding n=15 eligible studies. The main indications for subject inclusion in operative studies was tibial torsion greater than 30 degrees in seven studies (47%), femoral anteversion greater than 25 degrees in two studies (13%), and patella instability in six studies (40%). Two studies (13%) had no surgical correction but evaluated axial alignment. Following surgical intervention, one study (7%) reported improvements in tubercle-suclus angle, two studies (13%) reported improvements in femoral-tibial angle, four studies (27%) reported decreases in tibial torsion, seven studies (47%) reported increases in Kujala score, five studies (33%) reported increases in Lysholm, and four studies (27%) reported increases in IKDC. Nine studies (60%) commented on pre-operative femoral anteversion, but only one study compared pre- and post-operative values (observed a decrease in anteversion). Interestingly, only two studies (13%) reported cases of recurrent instability at follow up. Lastly, seven papers (47%) reported complications ranging from staple pain at incision site, deep vein thrombosis, limited flexion, and non-union of the osteotomy site.

Conclusion

This systematic review of the literature demonstrates a paucity of evidence to guide treatment of patients with recurrent PFI who have co-existing axial plane malalignment. Femoral internal torsion values of greater than 25 degrees and tibial external torsion values of greater than 30 degrees in patients with PFI appear to be a reasonable threshold to consider corrective osteotomy; however, it is clear that further research is required to determine a clear decision making pathway to achieve optimal clinical outcomes.