Gender difference in the modified Insall-Salvati ratio in a black Kenyan population

Abstract

The patellar tendon (PT) is part of the extensor mechanism of the knee attaching to the apex of the patella and tibial tuberosity. Gender differences of the PT have been described in terms of response to tensile forces. This response may be influenced by the patella height. An index for assessment of patellar height is the modified Insall-Salvati ratio. This ratio is used to classify the patella as either high riding (alta) or low riding (baja). Patella alta has been correlated to chronic patellar tendinopathy. Patellar tendinopathy is more common in males (6:1). The hypothesis of the study was that males would have a higher ratio and there was an expectation of more cases of patella alta among males. One hundred and two pairs of patellar tendons (58 male, 44 female) were thus obtained by simple random sampling from postmortem specimens at the Kenyatta National Hospital and Nairobi City mortuary. All the patellar tendons and patella bones were used to study the modified Insall-Salvati ratio, using a digital vernier caliper. This ratio was determined by dividing the length of the posterior lamina of the patellar tendon with the maximum diagonal length of the patella. The mean of the modified Insall-Salvati ratio for the right was 1.201 +/- 0.0901 in females and 1.1275 +/- 0.133 in males, p=0.001. The mean of the modified Insall-Salvati ratio for the left was 1.206 +/- 0.085 in females and 1.132 +/- 0.123 in males, p=0.001. Therefore, using the cut off value of 2.0, no cases of patella alta were observed. The modified Insall- Salvati ratio was thus observed to be higher in females in the Kenyan population. This observation of disparity between the expected and the observed results is confounding yet similar and consistent with previous findings in other populations. Research on the prevalence of patellar tendinopathy in the Kenyan population and radiological determination of the modified Insall-Salvati ratio is recommended.

Keywords: Modified Insall-Salvati ratio, black Kenyan population