Different Patellar Indices and Their Role in Decision-Making: An MRI-Based Study

Abstract

Magnetic resonance imaging (MRI) of knee has become the integral part of knee evaluation, hence any MRI based study adds more value if it helps in the decision-making process, especially for surgery in treating patellofemoral pain. We tried to determine normal patellar indices using knee MR images and the correlation between them and also compared the results with different ethnic population. We analyzed the prospectively collected MR images of 117 knees/patients, and Insall–Salvati (IS) index, modified IS index, patellotrochlear (PT) index, and patellophyseal (PP) index were calculated. Two standard deviations from the mean were used to define the normal and abnormal patellar position. Cohen's kappa values were used to assess the agreement between the indices and the correlation between them was analyzed using Pearson's correlation. The mean values for IS index, modified IS index, PT index, and PP index were 1.00, 1.53, 0.40, and 0.58, respectively. There was very good agreement between PT index and PP index. There was weak correlation between all the indices except the one between PT and PP indices which had a strong negative correlation. Based on commonly used methodology, there were 4% of asymptomatic patients who were outside the standardized cut-off values and different indices classified different knees as abnormal. This indicates patellar position should be one among the many other factors, not as a sole factor when making a surgical decision in patellofemoral pain. We also noted that the indices compared fairly with other populations. Further research is needed to determine the clinical applicability of these indices.

Keywords

patella - knee - patellofemoral pain - patellotrochlear index - patellophyseal index - MRI knee

Publication History

Received: 16 February 2019

Accepted: 10 November 2019

Article published online:
08 January 2020

• References

• 1 Kannus PA. Long patellar tendon: radiographic sign of patellofemoral pain syndrome--a prospective study. Radiology 1992; 185 (03) 859-863
• 2 Lancourt JE, Cristini JA. Patella alta and patella infera. Their etiological role in patellar dislocation, chondromalacia, and apophysitis of the tibial tubercle. J Bone Joint Surg Am 1975; 57 (08) 1112-1115
• 3 Karadimas JE, Piscopakis N, Syrmalis L. Patella alta and chondromalacia. Int Orthop 1981; 5 (04) 247-249
• 4 Insall J, Goldberg V, Salvati E. Recurrent dislocation and the high-riding patella. Clin Orthop Relat Res 1972; 88 (88) 67-69
• 5 Insall J, Salvati E. Patella position in the normal knee joint. Radiology 1971; 101 (01) 101-104
• 6 Blackburne JS, Peel TE. A new method of measuring patellar height. J Bone Joint Surg Br 1977; 59 (02) 241-242
• 7 Caton J, Deschamps G, Chambat P, Lerat JL, Dejour H. [Patella infera. Apropos of 128 cases]. Rev Chir Orthop Repar Appar Mot 1982; 68 (05) 317-325
• 8 Grelsamer RP, Meadows S. The modified Insall-Salvati ratio for assessment of patellar height. Clin Orthop Relat Res 1992; (282) 170-176
• 9 Miller TT, Staron RB, Feldman F. Patellar height on sagittal MR imaging of the knee. AJR Am J Roentgenol 1996; 167 (02) 339-341
• 10 Biedert RM, Albrecht S. The patellotrochlear index: a new index for assessing patellar height. Knee Surg Sports Traumatol Arthrosc 2006; 14 (08) 707-712
• 11 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 (05) 1361-1366
• 12 Leung YF, Wai YL, Leung YC. Patella alta in southern China. A new method of measurement. Int Orthop 1996; 20 (05) 305-310
• 13 Upadhyay S, Raza HKT, Srivastava P. Position of the patella in adults in central India: evaluation of the Insall-Salvati ratio. J Orthop Surg (Hong Kong) 2013; 21 (01) 23-27
• 14 Phillips CL, Silver DA, Schranz PJ, Mandalia V. The measurement of patellar height: a review of the methods of imaging. J Bone Joint Surg Br 2010; 92 (08) 1045-1053
• 15 Shabshin N, Schweitzer ME, Morrison WB, Parker L. MRI criteria for patella alta and baja. Skeletal Radiol 2004; 33 (08) 445-450
• 16 Endo Y, Schweitzer ME, Bordalo-Rodrigues M, Rokito AS, Babb JS. MRI quantitative morphologic analysis of patellofemoral region: lack of correlation with chondromalacia patellae at surgery. AJR Am J Roentgenol 2007; 189 (05) 1165-1168
• 17 Dowd GS, Bentley G. Radiographic assessment in patellar instability and chondromalacia patellae. J Bone Joint Surg Br 1986; 68 (02) 297-300
• 18 Altman DG. Practical Statistics for Medical Research. London, England: Chapman and Hall/CRC; 1991: 40
• 19 Hinkle DE, Wiersma W, Jurs SG. Applied Statistics for the Behavioral Sciences. 5th ed. Boston, MA: Houghton Mifflin; 2003