J. Anat. (1985), 143, pp. 149-159 149 With 3 figures Printed in Great Britain Third trochanter incidence and metric trait covariation in the human femur SCOTT LOZANOFF*, PAUL W. SCIULLIt AND KIM N. SCHNEIDERt *Department ofAnatomy, Ohio State University, Columbus, Ohio, 43210 U.S.A. tDepartment ofAnthropology, Ohio State University, Columbus, Ohio, 43210 and $Department ofAnthropology, Wichita State University, Wichita, Kansas, 67820 U.S.A. (Accepted 21 March 1985) INTRODUCTION The third trochanter is a rounded bony projection which may be present along the superior border of the gluteal tuberosity of the femur (Houze, 1883; Hrdlicka, 1937) and functions to provide an attachment area for the ascending tendon of the gluteus maximus. This skeletal variant, when present, occurs as an oblong, rounded or conical bony elevation which may be continuous with the gluteal ridge and is mani- fested as a distinct femoral entity (Torok, 1886; Hrdlicka, 1937). Third trochanter frequencies commonly are utilised in batteries of infracranial nonmetric traits for quantitative studies of population affinities (Finnegan, 1974, 1978; Sciulli, Lozanoff & Schneider, 1984). However, factors governing the aetiology and expression of the third trochanter as well as other postcranial nonmetric skeletal traits are not well delineated. The phenotypic development and expression of discontinuous skeletal traits originally were considered to be controlled largely by genetic factors (Berry & Berry, 1967). However, Gruineberg (1963) recognised that the expression of nonmetric skeletal variants was partially dependent on generalised or local size variation. Recent studies indicate the significance ofvarious biological and environmental factors such as age, sex, nutritional status or side dependence influencing the manifestation of certain nonmetric traits in both experimental non-human samples (Howe & Parsons, 1967; Truslove, 1976; Dahinten & Pucciarelli, 1981, 1983) and human populations (Ossenberg, 1970; Corruccini, 1974; Perizonius, 1979). Local mechanical factors also represent potent sources ofepigenetic information which influence the incidence and expression ofdiscontinuous variants (Moss & Moss-Salentijn, 1978; Moss, 1981). A general mechanism of nonmetric trait transmission and expression for both cranial and infracranial traits remains obscure. Utilising a prehistoric human skeletal population, Cheverud, Buikstra & Twichell (1979) show that both general and local size and shape variation of the cranium are correlated with the incidence of many nonmetric traits. They find that cranial metric parameters and nonmetric trait incidence correlate with cranial size and shape. Cheverud et al. (1979) suggest that * Present address: Department of Orthodontics, University of British Columbia, Vancouver, British Columbia, V6T 1Z7 Canada, t Reprint requests to Dr Sciulli. 150 S. LOZANOFF, P. W. SCIULLI AND K. N. SCHNEIDER soft tissue development within the functional spaces of the cranium determines epigenetic trait expression. Cheverud & Buikstra (1981 a; 1982) have shown that a moderate to high heritability of many cranial nonmetric traits exists in a naturally occurring mendelian rhesus population. These authors find genetic correlations among cranial nonmetric traits even when phenotypic correlations are low, and suggest that skeletal traits arise from localised genetically controlled developmental processes in the cranium (Cheverud & Buikstra, 1981b). They hypothesise that growth of the bony cranium and the expression of nonmetric traits are secondary to the development of soft tissue anatomical structures of the head. It is appropriate to extend this model to infracranial discrete trait manifestation, and to analyse third trochanter expression within the context of femoral variation. A relationship between third trochanter incidence and a specific femoral morphology implies that this discrete trait shares a common developmental basis with size and/or shape components of femoral development and growth. By extension, the third trochanter would thus appear to possess a high information content with respect to underlying hereditary factors among human populations. The purpose of this study is to determine whether the incidence of the third trochanter is associated with a specific metric and/or shape pattern displayed by the human femur. MATERIALS AND METHODS The experimental sample consisted of 60 left femora (30 male, 30 female) randomly selected from three prehistoric Ohio Valley skeletal populations. Twenty femora were from the Fort Ancient, Anderson Village site (c. A.D. 1250). A second group of twenty femora represented the Adena sites of Sidner, McMurray and Galbreath (c. 200 B.C.-A.D. 0). The third group of twenty long bones were from the Glacial Kame sites of Straton-Wallace, Kirian-Treglia, Boose and Clifford Williams (c. 950 B.C.). The Adena and Glacial Kame samples have been tested for homogeneity and satisfactorily meet the statistical requirements for pooling cranial metric, cranial nonmetric and infracranial metric data (Sciulli et al. 1984; Sciulli & Schneider, 1985). The total sample was constructed so that one group of thirty male and female femora expressed a third trochanter (n = 15 male, 15 female with incidence (1) of a third trochanter) and a second group consisting of an equivalent number of sexed long bones lacked this trait (n = 15 male, 15 female without incidence (0) of a third trochanter). The third trochanter was considered to be present only if a distinct conical elevation was separate from the gluteal ridge. This classification was dis- tinguished from that of a gluteal tuberosity and a fossa hypotrochanterica in that a separated elevation from the gluteal ridge was required. Femora were only from skeletons that included a well preserved pelvis, allowing accurate sexing (Phenice, 1967). Ten measurements represented each femur (Fig. 1). Randomly selected femora were measured on two succeeding days in order to assess the significance of observer error. Values were subjected to a univariate analysis of variance (ANOVA) and variation within samples was significantly greater than that between measurements (P > 0-82). Therefore, slight variation introduced as a result of unavoidable incon- sistencies in measurement was insiginificant compared to that existing within samples. Original variables were sorted according to main effects and interactions, (i.e. sex, incidence, sex*incidence), and respective covariance matrices were tested for equi- Third trochanter incidence 151 7. n s Fig. 1. Linear measurements utilised in this study. Total femoral length (LEN), k-m; mid-shaft circumference (CIR), n; transverse midshaft width (TVM), g; anterior to posterior mid-shaft width(APM),j; transverse proximaldiaphyseal width (TVP), d-e; anterior to posterior proximal diaphyseal width (APP), h-i; distance from the lesser trochanter to the most superior point of the greater trochanter (LGT), e-a; distance from the lesser trochanter to the most inferior point along the superior border of the femoral neck (LNK), e-b; distance from the lesser trochanter to the most medial point of the femoral head (LHD), e-c; and distance from the most medial point of the femoral head to the most lateral point on the greater trochanter (PWD), f-c. valence. Covariance matrices of sorted variables determined not to be significantly different were subjected to a multivariate analysis ofvariance (MANOVA) in order to delineate an overall test for sex effects, incidence effects and their interactions as well as an ANOVA for individual variables. These variables were then subjected to a principal component analysis (covariance matrix) in order to establish dimensional relationships among femora. Covariance matrices of sorted variables which were different were subjected to a principal component analysis separately. Principal component scores of sorted groups were checked qualitatively for normality according to the method outlined by Johnson & Wichern (1982), i.e. eigenvector scores for original variables for the first 152 S. LOZANOFF, P. W. SCIULLI AND K. N. SCHNEIDER Table 1. The source of variation (SOURCE), dependent variables and the probability associated with an F value (PR) for ANO VA For abbreviations, see Figure 1. Source Dependent Sex*incidence variables Sex PR PR TVP 0-0001 0-8988 APP 0-0002 0-0995 TVM 0-0002 0-2526 APM 0-0001 0-5051 LEN 0-0001 0-4186 CIR 0-0001 0-3419 PWD 0-0001 0-1501 LHD 0.0001 0-5496 LNK 0-0001 0-3245 LGT 0.0001 0-1830 and last principal components were plotted against their normal distribution prob- ability values. Normality was assumed if the scatterplots appeared reasonably elliptical. Thus covariability of respective sorted variables was considered to differ rather than group means. Eigenvectors for sorted variables were compared quali- tatively in order to delineate differing patterns of covariability. RESULTS Covariance matrices of variables sorted by gender were not significantly different (x2 = 48-2, P < 0-73) and a pooled covariance matrix was used for the MANOVA. Similarly, the sex*incidence interaction covariance matrices were equivalent (x2 = 118, P < 0-10), and a pooled covariance matrix was used. Covariance matrices of variables sorted by incidence were significantly different (x2 = 77-43, P < 0-02) and were analysed separately utilising principal component analysis. ANO VA and MANO VA for sex, sex*incidence The results of the univariate analysis of variance are given in Table 1. The effects due to sex were highly significant