Surgical management of patellofemoral instability. I. Imaging considerations

  • Neeraj PurohitEmail author
  • Nicholas Hancock
  • Asif Saifuddin
Review Article


The patellofemoral joint is a complex joint that relies on both bone and soft tissues for its stability. Dysfunction of the patellofemoral joint, whether pain or instability, is a common cause of medial consultation. Thorough clinical and imaging assessment is important for managing these patients, who may require a combination of a bony and soft tissue surgical procedure. Trochlear dysplasia, a cause of anterior knee pain and patellar instability, has been classified using conventional radiography. Radiographic signs on a lateral projection, such as the “double contour” sign and the “crossing sign”, can alert the radiologist to the grade of trochlear dysplasia. Magnetic resonance imaging (MRI) is the gold standard for accurately assessing the soft tissue around the patellofemoral joint, such as the medial patellofemoral ligament and the medial and lateral patella retinacula, especially in the context of a transient patella dislocation. Risk factors for patellofemoral instability, such as patella alta, an increased tibial tubercle to trochlear groove distance and trochlear dysplasia, can all be assessed on MRI. Advanced imaging techniques such as dynamic MRI and CT are able to demonstrate patellar maltracking. These techniques can also be employed to reliably assess the outcomes of treatment. In this article, we review the normal and abnormal pre-operative imaging findings of the knee extensor mechanism in relation to patellofemoral joint instability. This review provides a useful tool for the reporting radiologist and highlights the imaging findings that are of relevance to the orthopaedic surgeon.


Knee Extensor mechanism Patellofemoral Instability Pre-operative assessment Post-operative assessment 


Compliance with ethical standards

Conflicts of interest

The authors declare that they have no conflicts of interest.


  1. 1.
    Shih Y-F, Bull AMJ, Amis AA. The cartilaginous and osseous geometry of the femoral trochlear groove. Knee Surg Sports Traumatol Arthrosc. 2004;12(4):300–6.CrossRefGoogle Scholar
  2. 2.
    Chaitow L, DeLany J. The knee. In: Clinical application of neuromuscular techniques, vol 2. 2011. p. 447–501.Google Scholar
  3. 3.
    Dejour H, Walch G, Neyret P, Adeleine P. [Dysplasia of the femoral trochlea]. Rev Chir Orthop Reparatrice Appar Mot. 1990;76(1):45–54.PubMedGoogle Scholar
  4. 4.
    Wiberg G. Roentgenographs and anatomic studies on the femoropatellar joint: with special reference to chondromalacia patellae. Acta Orthop Scand. 1941;12(1–4):319–410.Google Scholar
  5. 5.
    Post WR, Fithian DC. Patellofemoral instability: a consensus statement from the AOSSM/PFF patellofemoral instability workshop. Orthop J Sport Med. 2018;6(1):232596711775035.CrossRefGoogle Scholar
  6. 6.
    Dietrich TJ, Fucentese SF, Pfirrmann CWA. Imaging of individual anatomical risk factors for patellar instability. Semin Musculoskelet Radiol. 2016;20(1):65–73.CrossRefGoogle Scholar
  7. 7.
    Goh JC, Lee PY, Bose K. A cadaver study of the function of the oblique part of vastus medialis. J Bone Jt Surg Br. 1995;77(2):225–31.CrossRefGoogle Scholar
  8. 8.
    Krebs C, Tranovich M, Andrews K, Ebraheim N. The medial patellofemoral ligament: review of the literature. J Orthop. 2018;15(2):596–9.CrossRefGoogle Scholar
  9. 9.
    Loeb AE, Tanaka MJ. The medial patellofemoral complex. Curr Rev Musculoskelet Med. 2018;11(2):201–8.CrossRefGoogle Scholar
  10. 10.
    Desio SM, Burks RT, Bachus KN. Soft tissue restraints to lateral patellar translation in the human knee. Am J Sports Med. 1998;26(1):59–65.CrossRefGoogle Scholar
  11. 11.
    Senavongse W, Amis AA. The effects of articular, retinacular, or muscular deficiencies on patellofemoral joint stability. J Bone Joint Surg Br. 2005;87(4):577–82.CrossRefGoogle Scholar
  12. 12.
    Patel VV, Hall K, Ries M, Lindsey C, Ozhinsky E, Lu Y, et al. Magnetic resonance imaging of patellofemoral kinematics with weight-bearing. J Bone Joint Surg Am. 2003;85–A(12):2419–24.CrossRefGoogle Scholar
  13. 13.
    Huberti HH, Hayes WC. Patellofemoral contact pressures. The influence of q-angle and tendofemoral contact. J Bone Joint Surg Am. 1984;66(5):715–24.CrossRefGoogle Scholar
  14. 14.
    Geenen E, Molenaers G, Martens M. Patella alta in patellofemoral instability. Acta Orthop Belg. 1989;55(3):387–93.PubMedGoogle Scholar
  15. 15.
    Luyckx T, Didden K, Vandenneucker H, Labey L, Innocenti B, Bellemans J. Is there a biomechanical explanation for anterior knee pain in patients with patella alta? Influence of patellar height on patellofemoral contact force, contact area and contact pressure. J Bone Joint Surg (Br). 2009;91:344–50.CrossRefGoogle Scholar
  16. 16.
    Köhlitz T, Scheffler S, Jung T, Hoburg A, Vollnberg B, Wiener E, et al. Prevalence and patterns of anatomical risk factors in patients after patellar dislocation: a case control study using MRI. Eur Radiol. 2013;23(4):1067–74.CrossRefGoogle Scholar
  17. 17.
    Diederichs G, Issever AS, Scheffler S. MR imaging of patellar instability: injury patterns and assessment of risk factors. Radiographics. 2010;30(4):961–81.CrossRefGoogle Scholar
  18. 18.
    Nolan JE, Schottel PC, Endres NK. Trochleoplasty: indications and technique. Curr Rev Musculoskelet Med. 2018;11(2):231–40.CrossRefGoogle Scholar
  19. 19.
    Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19–26.CrossRefGoogle Scholar
  20. 20.
    Batailler C, Neyret P. Trochlear dysplasia: imaging and treatment options. EFORT Open Rev. 2018;3(5):240–7.
  21. 21.
    LaPrade RF, Cram TR, James EW, Rasmussen MT. Trochlear dysplasia and the role of trochleoplasty. Clin Sports Med. 2014;33(3):531–45.CrossRefGoogle Scholar
  22. 22.
    Insall J, Salvati E. Patella position in the normal knee joint. Radiology. 1971;101(1):101–4.CrossRefGoogle Scholar
  23. 23.
    Caton J, Deschamps G, Chambat P, Lerat JL, Dejour H. Patella infera. Apropos of 128 cases. Rev Chir Orthop Reparatrice Appar Mot. 1982;68(5):317–25.PubMedGoogle Scholar
  24. 24.
    Grelsamer RP, Proctor CS, Bazos AN. Evaluation of patellar shape in the sagittal plane. A clinical analysis. Am J Sports Med. 1994;22(1):61–6.CrossRefGoogle Scholar
  25. 25.
    Grelsamer RP, Meadows S. The modified Insall-Salvati ratio for assessment of patellar height. Clin Orthop Relat Res. 1992;(282):170–6.Google Scholar
  26. 26.
    Brattstroem H. Shape of the intercondylar groove normally and in recurrent dislocation of patella. A clinical and X-ray-anatomical investigation. Acta Orthop Scand Suppl. 1964;68:1–148.CrossRefGoogle Scholar
  27. 27.
    Biedert RM, Warnke K. Correlation between the Q angle and the patella position: a clinical and axial computed tomography evaluation. Arch Orthop Trauma Surg. 2001;121(6):346–9.CrossRefGoogle Scholar
  28. 28.
    Goutallier D, Bernageau J, Lecudonnec B. The measurement of the tibial tuberosity. Patella groove distanced technique and results (author’s transl). Rev Chir Orthop Reparatrice Appar Mot. 1978;64(5):423–8.Google Scholar
  29. 29.
    Camp CL, Stuart MJ, Krych AJ, Levy BA, Bond JR, Collins MS, et al. CT and MRI measurements of tibial tubercle-trochlear groove distances are not equivalent in patients with patellar instability. Am J Sports Med. 2013;41(8):1835–40.CrossRefGoogle Scholar
  30. 30.
    Anley CM, Morris G V., Saithna A, James SL, Snow M. Defining the role of the tibial tubercle-trochlear groove and tibial tubercle-posterior cruciate ligament distances in the work-up of patients with patellofemoral disorders. Am J Sports Med. 2015;40(5):1119–25.Google Scholar
  31. 31.
    Thakkar RS, Del Grande F, Wadhwa V, Chalian M, Andreisek G, Carrino JA, et al. Patellar instability: CT and MRI measurements and their correlation with internal derangement findings. Knee Surg Sports Traumatol Arthrosc. 2016;24(9):3021–8.CrossRefGoogle Scholar
  32. 32.
    Seitlinger G, Scheurecker G, Högler R, Labey L, Innocenti B, Hofmann S. Tibial tubercle-posterior cruciate ligament distance: a new measurement to define the position of the tibial tubercle in patients with patellar dislocation. Am J Sports Med. 2012;40(5):1119–25.CrossRefGoogle Scholar
  33. 33.
    Tscholl PM, Antoniadis A, Dietrich TJ, Koch PP, Fucentese SF. The tibial–tubercle trochlear groove distance in patients with trochlear dysplasia: the influence of the proximally flat trochlea. Knee Surg Sport Traumatol Arthrosc. 2016;24(9):2741–7.CrossRefGoogle Scholar
  34. 34.
    Miller T, Staron RB, Feldman F. Patellar height on sagittal MR imaging of the knee. Am J Roentgenol. 1996;167(2):339–41.CrossRefGoogle Scholar
  35. 35.
    Shabshin N, Schweitzer M, Morrison W, Parker L. MRI criteria for patella alta and baja. Skeletal Radiol. 2004;33(8):445-50.CrossRefGoogle Scholar
  36. 36.
    Biedert RM, Albrecht S. The patellotrochlear index: a new index for assessing patellar height. Knee Surg Sport Traumatol Arthrosc. 2006;14(8):707–12.CrossRefGoogle Scholar
  37. 37.
    Ali SA, Helmer R, Terk MR. Patella alta: lack of correlation between patellotrochlear cartilage congruence and commonly used patellar height ratios. AJR Am J Roentgenol. 2009;193(5):1361–6.CrossRefGoogle Scholar
  38. 38.
    Dejour D, Ferrua P, Ntagiopoulos PG, Radier C, Hulet C, Rémy F, et al. The introduction of a new MRI index to evaluate sagittal patellofemoral engagement. Orthop Traumatol Surg Res. 2013;99(8):S391–8.CrossRefGoogle Scholar
  39. 39.
    Chhabra A, Subhawong TK, Carrino JA. A systematised MRI approach to evaluating the patellofemoral joint. Skeletal Radiol. 2011;40(4):375–87.CrossRefGoogle Scholar
  40. 40.
    Shellock FG, Mink JH, Deutsch AL, Fox JM. Patellar tracking abnormalities: clinical experience with kinematic MR imaging in 130 patients. Radiology. 1989;172(3):799–804.CrossRefGoogle Scholar
  41. 41.
    McNally EG, Ostlere SJ, Pal C, Phillips A, Reid H, Dodd C. Assessment of patellar maltracking using combined static and dynamic MRI. Eur Radiol. 2000;10(7):1051–5.CrossRefGoogle Scholar
  42. 42.
    Fascia, D, Amiras, D, Hohnen, A, Wambeek N. Realtime dynamic CT of the patellofemoral joint: a new approach to the old problem of patellar maltracking. In: Radiological Society of North America Scientific Assembly and Annual Meeting. Chicago IL.; 2014. Available from:
  43. 43.
    Xue Z, Song G, Liu X, Zhang H, Wu G, Qian Y, et al. Excessive lateral patellar translation on axial computed tomography indicates positive patellar J sign. Knee Surg Sport Traumatol Arthrosc. 2018;26(12):3620-3625.CrossRefGoogle Scholar
  44. 44.
    Pfirrmann CWA, Zanetti M, Romero J, Hodler J. Femoral trochlear dysplasia: MR findings. Radiology. 2000;216(3):858–64.CrossRefGoogle Scholar
  45. 45.
    Carrillon Y, Abidi H, Dejour D, Fantino O, Moyen B, Tran-Minh VA. Patellar instability: assessment on MR images by measuring the lateral trochlear inclination—initial experience. Radiology. 2000;216(2):582–5.CrossRefGoogle Scholar
  46. 46.
    Biedert RM, Netzer P, Gal I, Sigg A, Tscholl PM. The lateral condyle index: a new index for assessing the length of the lateral articular trochlea as predisposing factor for patellar instability. Int Orthop. 2011;35(9):1327–31.CrossRefGoogle Scholar
  47. 47.
    Yi M, Hong SH, Choi JY, Yoo HJ, Kang Y, Park J, et al. Femoral trochlear groove morphometry assessed on oblique coronal MR images. Am J Roentgenol. 2015;205(6):1260–8.CrossRefGoogle Scholar
  48. 48.
    Nelitz M, Lippacher S, Reichel H, Dornacher D. Evaluation of trochlear dysplasia using MRI: correlation between the classification system of Dejour and objective parameters of trochlear dysplasia. Knee Surg Sport Traumatol Arthrosc. 2014;22(1):120–7.CrossRefGoogle Scholar
  49. 49.
    MacKay JW, Godley KC, Toms AP, Donell ST. Trochlear boss height measurement: a comparison of radiographs and MRI. Knee. 2014;21(6):1052–7.CrossRefGoogle Scholar

Copyright information

© ISS 2018

Authors and Affiliations

  • Neeraj Purohit
    • 1
    Email author
  • Nicholas Hancock
    • 2
  • Asif Saifuddin
    • 3
  1. 1.Department of RadiologyUniversity Hospital Southampton NHS Foundation TrustSouthamptonUK
  2. 2.Department of Trauma and OrthopaedicsUniversity Hospital Southampton NHS Foundation TrustSouthamptonUK
  3. 3.Department of RadiologyThe Royal National Orthopaedic Hospital NHS TrustStanmoreUK

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