The origin of the medial circumflex femoral artery: a meta-analysis and proposal of a new classification system

Search strategy

An extensive search of the major electronic databases (Pubmed, EMBASE, Scopus, ScienceDirect, Web of Science, SciELO, BIOSIS, and CNKI) was conducted through July 2015 in order to identify articles eligible for inclusion into the meta-analysis. To identify all potentially relevant anatomical data, a comprehensive search of all articles related to femoral circulation was performed. The following search terms were used: femoral head circulation, femoral head blood supply, femoral neck circulation, femoral neck blood supply, superior gluteal artery, inferior gluteal artery, medial femoral circumflex artery, lateral femoral circumflex artery, superficial femoral artery, deep femoral artery, retinacular arteries, extracapsular arterial ring of femoral neck, intracapsular arterial ring of femoral neck, arteries of the round ligament, posterior superior nutrient artery, posterior inferior nutrient artery, piriformis branch of the IGA, and profunda femoris. The authors did not set any date or language restrictions. Additionally, a broad search of the references of all relevant manuscripts was conducted to identify further eligible articles. Authors of the study strictly followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines (Supplemental Information 1).

Eligibility assessment

Eligibility for inclusion into the study was assessed by two reviewers (JV and MS). All studies reporting extractable data on the anatomy of the MCFA were included into the meta-analysis. The exclusion criteria for the meta-analysis included: (1) reviews, case reports, letters to the editor, conference abstracts, (2) reporting incomplete or non-extractable data, (3) studies on patients with congenital hip or femur pathologies, and (4) animal studies. All studies written in languages not spoken fluently by any of the authors, were translated by medical professionals, who are fluent in the original language of the publication and English. In the case of any inconsistencies or disagreements during the study selection process, all decisions were made by a consensus between all the reviewers, after consulting with the authors of the original study if possible.

Data extraction

Two reviewers (JV and MS) independently extracted all the eligible data from the studies included in the meta-analysis. Data on the sample size, year of study, type of study, geographical region, gender, side, prevalence of the various origins of the MCFA, and the mean distance of the MCFA originating from the DFA and the CFA to the mid-inguinal point (MIP) were extracted. As only some studies reported specific data on the different types of CFA origins of the MCFA and the different types of DFA origins of the MCFA, we extracted them separately for the purposes of analysis.

Authors of all articles containing inconsistent data were contacted by email for additional information when possible. Additionally, authors excluded from the analysis morphometric data (mean length) from studies on fetuses, due to the lack of comparability of such data with that obtained from adult samples.

Statistical analysis

Statistical analysis was performed by BMH, JV, and JR using MetaXL version 2.0 by EpiGear International Pty Ltd (Wilston, Queensland, Australia) to calculate multi-categorical pooled prevalence estimates for the various origins of the MCFA (Henry et al., 2015). The morphometric data was pooled into an analysis using Comprehensive Meta-Analysis version 3.0 by Biostat (Englewood, New Jersey, USA). All analyses were performed by using a random effects model.

The Chi² test and Higgins I² statistic were used to measure heterogeneity among the studies included in the meta-analysis. A Cochran’s Q p-value of <0.10 for the Chi² test was regarded as indicator of significant heterogeneity between studies (Higgins & Green, 2011). For Higgins I², values of 0–40% were considered as “might not be important”; 30–60% “might indicate moderate heterogeneity”; 50–90% “may indicate substantial heterogeneity”; and 75–100% “may represent considerable heterogeneity” (Higgins & Green, 2011).

To probe the sources of heterogeneity, subgroup analysis by type of study, geographical distribution, gender, and side (left vs. right) and/or a sensitivity analysis inclusive of studies with a number of lower limbs ≥100, was conducted. Confidence intervals were used to determine statistically significant differences between 2 or more groups. In the case of overlapping confidence intervals, the differences were regarded as statistically insignificant (Henry et al., 2015).

Establishment of a classification system

In order to establish a universally applicable classification system for the origin of MCFA, the authors set an a priori threshold level of a minimum 1% pooled prevalence of a variant in the overall analysis for it to be eligible for inclusion in the classification system. For any sub-variants not represented in the overall analysis, eligibility for inclusion was determined by multiplying the pooled prevalence of the particular sub-variant by the pooled prevalence of its main variant representative in the overall analysis. If the calculated value was ≥1%, it would be deemed eligible for inclusion as independent variant in the new classification. All variants below a pooled prevalence of ≤1% were considered as anomalies. For an anomaly to be included in the classification system, a threshold of ≥0.5% pooled prevalence in the overall analysis was set.

Study identification

The study identification process is summarized in Fig. 1. Major databases were extensively searched to initially identify 7,486 articles. A further 71 articles were added by searching the references of included articles. A total of 155 articles were assessed by full text for potential eligibility. One hundred and twenty-five articles were deemed ineligible for inclusion, and 38 articles were finally included into the meta-analysis.

Characteristics of included studies

The characteristics of included studies are summarized in Table 1. A total of 38 studies (n = 4,351 lower limbs) were included in the meta-analysis. The studies spanned from 1934 to 2015 and demonstrated a wide geographical distribution with studies hailing from North America, Europe, Asia and Africa. The type of study included in the meta-analysis was predominantly cadaveric, except for studies by Massoud & Fletcher (1997) and Gościcka, Gielecki & Zietek (1990) who used digital subtraction transfemoral aortogram and radiograms, respectively.

Origins of the medial circumflex femoral artery

Thirty-eight studies (n = 4,351 lower limbs) reported data on the prevalence of the various origins of the MCFA. After a thorough review of the literature, we identified eight different variants of MCFA origins (Fig. 2), with 6 different sub-variants of MCFA origins from the CFA (Fig. 3). The pooled results are reported in Table 2 (Supplemental Information 2). Our analysis demonstrated that the MCFA most commonly originates from the DFA, with a pooled prevalence of 64.6% (95% CI [58.0–71.5]). The second most common origin of the MCFA was from the CFA with a pooled prevalence of 32.2% (95% CI [25.9–39.1]), of which it originates as a single branch in 81.1% (95% CI [70.1–91.7]) of these cases (Table 3).

To probe the sources of heterogeneity, a sensitivity analysis was performed on 15 studies (n = 3,267 lower limbs) by limiting inclusion to studies with a sample size of 100 or more lower limbs (Table 2). Our results showed no significant deviations from the results of the overall analysis. Furthermore, subgroup analysis according to the geographical region was also performed (Table 2). Our results showed that the results were mostly consistent with our overall analysis, with all population subgroups demonstrating the MCFA originating from the DFA as the most common pattern of origin.

Origins of the medial circumflex femoral artery with respect to gender and side

Five studies (n = 894 lower limbs; 683 male and 211 female) reported the prevalence of the various origins of MCFA according to gender (Table 4). Our results showed that the prevalences of the various origins of MCFA are comparable in both sexes and consistent with our overall result. When the MCFA originated from the CFA, it usually originated as a single trunk in both males and females. This was consistent with the results of our overall analysis. Further results on the origins of the MCFA with respect to gender are presented in Tables 4 and 5.

Data on the prevalence of the various origins of the MCFA according to side were also extracted (Table 6). Our results showed that, like our overall analysis, the MCFA most commonly originated from the DFA. However, the prevalence of a DFA origin MCFA was slightly more common on the left side with a prevalence of 69.4% (95% CI [65.1–76.6]) versus the right side which had a prevalence of 62.4% (95% CI [55.2–72.2]). On the other hand, the MCFA originating from the CFA, which was the second most common origin, was more commonly found on the right side (34.6%) versus the left side (28.2%). However, due to overlapping confidence intervals, these differences were not statistically significant. Further results on the various origins of the MCFA according to side can be found in Tables 6 and 7.

Pooled mean distance of the medial circumflex femoral artery origin to the mid-inguinal point

A total of 4 studies (n = 149 lower limbs) reported data on the pooled mean distance of the MCFA originating from the DFA to the mid-inguinal point (MIP) (Table 8). Our results showed that the pooled mean distance was 50.14 mm (95% CI [42.50–57.78]). This was longer than the distance reported in the same 4 studies (n = 54 lower limbs) for the MCFA originating from the CFA to MIP, which has a pooled mean of only 30.58 mm (95% CI [21.52–39.20]).

New classification system for origin of the MCFA

After a thorough assessment of the results of the analysis, a new classification system for the origin of the MCFA was established and presented in Fig. 4. Five different types of variations that met the a priori thresholds were included in the classification: Type 1 (normal)—MCFA branching from the DFA; Type 2—MCFA branching from the CFA as a single trunk; Type 3—MCFA branching from the CFA with the DFA; Type 4—MCFA branching from the SFA; and Type 5—Anomalies (MCFA—A. Aplasia, B. Duplications). Although two distinct types of duplication patterns were identified, for the purposes of a clinically applicable classification system, all duplication patterns of MCFA origin are considered as on one type (5B).