The sesamoids of the feet in humans: a systematic review and meta-analysis

The prevalence and distribution of the sesamoid bones in the feet has been reported in the literature with a high degree of variability. This systematic review aims to provide a better estimate of the frequency of the sesamoids of the foot and their association with variables such as ancestry, gender, and side. Thirty-seven studies met the inclusion criteria and were submitted for meta-analyses, sensitivity analyses and proportion difference tests, whenever possible. At the metatarsophalangeal (MTP) joint of the hallux, sesamoids were nearly always present. At the interphalangeal (IP) joint, the pooled true estimates of large-sampled studies were: (1) an overall prevalence of 22.4 %, (2) a cadaveric rate at 71.6 %, and (3) a radiological rate (based on X-ray images) of 21.1 %. The pooled partition frequencies of the hallucal medial and lateral sesamoids were 10.7 and 1.3 %, respectively. Bipartism was the most frequent partition type (92 %), followed by tripartism (7.5 %) and quadripartism (0.5 %). Middle Eastern ancestry was associated with significantly lower hallucal partition rate (P < 0.0001) and African ancestry with significantly lower prevalence of the IP sesamoid than all other ethnicities (P < 0.001). Feet with a hallux valgus deformity seemed to be associated with significantly higher rate of partition of the medial sesamoid (odds ratio = 3) than that of the normal feet. The respective values of the pooled true prevalence in adults at the MTP joint for the 2nd, 3rd, 4th and 5th toes were 1.9, 0.32, 0.9 and 13 %, respectively. There was a significantly higher prevalence of tibial sesamoids vs lateral sesamoids, with pooled odds ratio of 34.7, 8, 4.8, and 2.27, respectively. Partition was found in around 10 % of the sesamoids of the 5th MTP joint; no partition was noted in the other toes. For most 2nd-5th MTP joints, European ancestry showed the highest frequency whereas African ancestry showed the lowest; Middle Eastern ancestry was in between. No sesamoids were found at the 4th proximal IP joint and at the 4th and 5th distal IP joints. No sesamoids were found at any IP joint in the feet of Middle Eastern and African populations. The pooled rates of the IP sesamoids of the second and third toes in European populations were 1.2 % for the 2nd proximal, 0.33 % for the second distal and 0.6 % for both IP joints of the third toe. This anatomical meta-analysis yielded results that are likely to be more accurate regarding the rates of the sesamoids in the foot, their laterality and partition. It also provided solid evidence for the genetic basis of the frequency distribution among the different populations.