J. Anat. (1985), 143, pp. 149-159 149 With 3 figures Printed in Great Britain

Third incidence and metric trait covariation in the human 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 of the femur (Houze, 1883; Hrdlicka, 1937) and functions to provide an attachment area for the ascending tendon of the . 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 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 to the most superior point of the (LGT), e-a; distance from the lesser trochanter to the most inferior point along the superior border of the (LNK), e-b; distance from the lesser trochanter to the most medial point of the (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 for all parameters, indicating overall dimorphism between sexes. Effects due to sex*incidence interaction revealed no significant differences suggesting that femoral dimensions of male and female long bones, where incidence = 1, are not significantly different from one another or from those corre- sponding sexed femora lacking this trait. The overall tests of the main effects and their interaction showed that effects due to sex were highly significant for all parameters, again indicating marked sexual dimorphism (Wilks' lambda = 0-3058, P < 0-0001). Sex*incidence effects were not significant (Wilks' lambda = 0-7434, P < 0-76). Principal component analysis Femoral parameters and coefficients along principal components I, II and III are listed in Table 2. Principal component scores for individuals sorted according to sex* incidence are plotted in Figure 2. Principal component I appeared to represent mainly a size component and accounted for 90 % ofthe observed variation (Table 2). Femoral parameters expanded at a consistent rate indicative of a general increase in size (Rao, Third trochanter incidence 153 Table 2. Femoral metric parameters and eigenvector loadings for principal components I-III For abbreviations, see Figure 1. Parameter I II III TVP 0-0662 0-0058 0.0081 APP 0-0459 0-0946 0-2317 LEN 0-8862 -0-4207 -0-1550 TVM 0-0452 -0-0097 0-1054 APM 0-0625 0-0766 0-2276 CIR 0-1761 0-1076 0-6188 PWD 0-1914 0-1135 0-3806 LHD 0-2653 0-6851 -0-5174 LNK 0-1732 0-3420 0-1393 LGT 0-1841 0-4441 0-2106 (%) Variance 0.90 0-04 0-03

Table 3. Parameters and eigenvector loadings along principal component Ifor femora lacking a third trochanter (incidence = 0) and femora displaying a third trochanter (incidence = 1) For abbreviations, see Figure 1.

Incidence = 0 Incidence = 1 Parameter I II I II TVP 0-0670 0-0281 0-0658 0-0475 APP 0-0425 -0-0658 0-0477 0-1664 LEN 0-8817 0-3336 0-8912 -0-4391 TVM 0-0464 0-0233 0-0421 0-0290 APM 0-0686 -0-0148 0-0526 0.1901 CIR 0-1884 0-0813 0-1557 0-4199 PWD 0-2084 0-0729 0-1644 0-2568 LHD 0-2599 -0-8257 0-2792 0-4668 LNK 0-1666 -0-2878 0-1842 0-2777 LGT 0-1879 -0-3259 0-1775 0-4505 (%) Variance 0-90 0-04 0-88 0-06

1964). Loadings on the second eigenvector were either positive or negative which indicated the relative contribution of each parameter to the respective component. Hence, principal component 1I represented a shape component and accounted for 4 % ofthe variation (Table 2). The dimensional relationship contrasted an increasing proximal diaphyseal breadth and height with a decreasing femoral length. The shape relationship described by principal component III accounted for approximately 3 % ofthe variability and contrasted a decreasing femoral neck length and total femoral length, with an increasing mid-diaphyseal circumference and proximal diaphyseal breadth (Table 2). Two dimensional plots of principal component scores for variables sorted by sex*incidence indicated that male femora were larger than corresponding female long bones (Fig. 2). Male and female femora maintained similar shape dimensions in relation to both proximal diaphyseal shaft robusticity and femoral neck morpho- logy (Fig. 2, Table 2, parameter II). No substantial difference in proximal diaphyseal 6 ANA 143 154 S. LOZANOFF, P. W. SCIULLI AND K. N. SCHNEIDER 5-

0 4- a 0 3- * 0 0 .) o 1 a. O°* IJ 2- 0 0O 0. 0 o 0 0 a 0 O0 oao 0 *° 1- 0 * eo A * 0 0 0a 0 a 1 2 3 4 5 PC I

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0 4. 0 00 0 3- * 0 * 0 C.)u 00 o o 0 a· * 0 2 o O 0 o 0 1. B

.

1 2 3 4 5 PC I Fig. 2(A-B). Distribution of eigenvector scores of females (0) and males (O) lacking a third trochanter and females (@) and males (1) displaying a third trochanter. (A) Coefficients along the first (PC I) and second (PC II) principal components. (B) Coefficients along the first (PC I) and third (PC III) principal components. robusticity contrasting with mid-diaphyseal circumference occurred among indivi- duals (Table 2, parameter III). The two dimensional plots of principal components scores for sorted variables reflected a high degree of dispersion with mean values showing approximate equivalence (Fig. 2A, B). Although males tended to be generally larger than females, femoral shape reflected general homogeneity regardless of sex and third trochanter incidence. Covariance matrices sorted by incidence were significantly different and were tested for normality (Fig. 3). The scatterplots appeared to be elliptical for the variables where incidence = 0 when principal component I scores and principal component X Third trochanter incidence 155

4- x XX/ I I II 3- 0 II Z 2 L C)

1- A

1 2 3 Normal probability 5

x x "1 3 z

0 2

0a B

1 2 3 4 5 Normal probability Fig. 3(A-B). Distribution of individual eigenvector scores (PC score) along principal com- ponents I and X plotted against respective normal distribution probability values. (A) Femora lacking a third trochanter (INC = 0). (B) Femora displaying a third trochanter (INC = 1). scores were plotted against their normal distribution probability scores (Fig. 3). The scatterplot for variables where incidence = 1 was similarly elliptical for both principal component I values and principal component X scores plotted against their normal distribution values as seen in Figure 3. Variables sorted according to incidence were subjected to a principal com- ponent analysis separately and the generated eigenvector loadings for principal components I and II are given in Table 3. Comparison of eigenvectors for vari- ables sorted according to third trochanter incidence indicated that principal com- ponent I represented mainly a size component Principal component II described a decrease in proximal diaphyseal breadth with an increase in total femoral length for variables where incidence = 0 (Table 3). This same component contrasted an increase in proximal diaphyseal breadth and mid-diaphyseal circumference with decrease in femoral length for variables where incidence = 1 (Table 3), although 6-2 156 S. LOZANOFF, P. W. SCIULLI AND K. N. SCHNEIDER eigenvector loadings were small. This suggested that a third trochanter occurred when the femur maintained a robust proximal diaphysis and a short length, while femora lacking this trait were longer and maintained a more gracile proximal diaphysis. DISCUSSION Marked sexual dimorphism exists between sample femora indicating that the metric traits utilised here are very useful in discriminating between female and male femora. The specific size and shape profiles which characterise sexed long bones correspond in general with the descriptions of Van Gervan (1972). He found that male femora differ from female femora primarily in terms of overall size as well as by shape differences which are related to neck length/proximal shaft robusticity versus collo-diaphyseal angle. However, the linear measurements which describe the shape ofthe proximal femoral shaft in this study do not differentiate male from female femora. Covariance matrices sorted according to third trochanter incidence are unequal indicating that covariate dispersion is useful in discriminating between the morpho- logical patterns of femora with and without third trochanter expression. Several authors have shown that unequal covariance structure can indicate morphological heterogeneity (Jolicoeur & Mosimann, 1960; Reyment, 1962; Uytterschaut & Wilmink, 1983) and in some cases indicate greater biological significance than generalised mean differences (Corruccini, 1974). Heterogeneity of covariance indi- cates in this study that the third trochanter is associated with short robust femora. Interestingly, this same relationship is observed in femora (Hrdlicka, 1937; Trinkaus, 1976). Kate (1962, 1966) similarly reports that those East Indian long bones maintaining a third trochanter are short and display platymeria, although his study associates third trochanter incidence with gracile femora. Increased mechanical stress exerted on the lower extremity is distributed along the lateral femoral shaft, particularly in the subtrochanteric region of the posterior diaphysis (Amtmann, 1971; Rybicki, Simonen & Weis, 1972). Trinkaus (1976) indicates that the increased mechanical stress exerted on the lower limb during elevated levels of physical activity results in increased diaphyseal mass and robusticity in Neanderthal femora. Hence, the third trochanter may function to provide increased skeletal mass as a reinforcement mechanism for the proximal diaphysis in response to increased ground reaction force. Expression of the third trochanter also may be affected by mechanical stress exerted by the gluteus maximus. The gluteal muscle functions to decrease limb speed during the late swing and heel strike phases of locomotion (Lovejoy, 1973). The third trochanter may serve to increase attachment surface area for the gluteal musculature thereby providing greater efficiency of contracture. Gluteus maximus function may exert a mechanical loading on the third trochanter thereby altering surface morphology. The presence of bony crests, ridges and tuber- osities are directly correlated to the function of contiguous muscle activity (Doyle, 1977; Moss & Moss-Salentijn, 1978). Furthermore, Ljunggren (1976) has shown that the quadriceps femoris serves an important regulatory role in determining size and shape of the tibial tuberosity. Hence, we suggest that elevated activity of the gluteus maximus could affect proximal femoral diaphyseal morphology. Gluteus maximus function may act as a mechanism in determining the specific expression of the third trochanter. Third trochanter incidence 157 The third trochanter possesses genotypic and phenotypic attributes which prove well suited for nonmetric distance analyses among human populations. This infra- cranial trait is observed on immature femora indicating that this skeletal feature has a genetic component (Hrdlidka, 1937; Saunders, 1978; P. Sciulli, personal observa- tion). Furthermore, third trochanter expression is not associated with sex and age dependency, occurs bilaterally, and side to side dimorphism is not significant (Finnegan, 1978). Saunders (1978) notes, however, that gluteal tuberosity hyper- trophy may obscure third trochanter observation in older individuals. The specific expression of this trait is influenced by physical activity of the lower limb and therefore may provide information concerning specific environmental stimuli exerted on past populations. The third trochanter is associated with short robust femora as determined by this study and represents an important feature for de- scribing a general morphological pattern of the human diaphysis in a given popula- tion. Hence, the third trochanter should prove useful when included in batteries of nonmetric traits for discrimination among human populations.

SUMMARY The relationship between third trochanter incidence and femoral metric trait covariation has been investigated in a group of 60 left human femora. The experi- mental sample was constructed so that one group consisted of 15 male and 15 female femora which displayed a third trochanter and a second group consisted of an equal number ofsexed long bones which lacked this trait. A battery often femoral measurements was sorted according to main effects and interactions and respective covariance matrices were tested for equivalence. Covariance matrices of sorted variables determined not to be significantly different were initially subjected to both ANOVA and MANOVA and subsequently to a principal component analysis. Covariance matrices determined to be significantly different were subjected to a principal component analysis separately. Results of this study indicate that third trochanter incidence is associated with short femora displaying robust proximal diaphyses. The gluteus maximus muscle may act as a primary factor governing third trochanter expression. Further, this infracranial discrete trait appears well suited for human taxonomy studies. We would like to thank the Instruction and Research Computing Center, Ohio State University, for providing computing funds and Beth Koway for providing the excellent illustrations. We would also like to acknowledge Shelly R. Saunders, William W. Baden, Michael Finnegan and John A. Negulesco for their critical comments on earlier versions ofthis paper. We appreciate the cooperation ofBradley Baker and Martha Potter-Otto of the Ohio Historical Society for allowing us access to the skeletal material in their care.

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