Abstract
Purpose
To evaluate medieval and postmedieval Dutch skeletal collections for signs of cam impingent.
Methods
The medieval collections from Alkmaar Paardenmarkt and Klaaskinderkerke and the postmedieval period from Middenbeemster were studied. Standard osteological methods for sex and age estimation were used. From digital photographs of the femora, the apparent neck shaft angle, true neck shaft angle, angles of version and inclination, and the α and β angles of Nötzli were measured with ImageJ software.
Results
The time spans were ~1448 to 1573 for Alkmaar Paardenmarkt, ~1286 to 1573 for Klaaskinderkerke, and 1615 to 1866 for Middenbeemster. Femora exhibiting signs of trauma, disease, or poor preservation were excluded. There were 116 individuals (186 femora) available for study: 21 individuals (35 femora) from Alkmaar Paardenmarkt, 38 individuals (52 femora) from Klaaskinderkerke, and 57 individuals (99 femora) from Middenbeemster. There were 104 male and 68 female femora (sex not known in 14). Using an α angle of ≥50°, ≥55°, and ≥60°, the prevalence of cam deformity was 25%, 16%, and 10%, respectively. The cam deformity prevalence (α ≥ 50°) was higher in the medieval group (39%) than the postmedieval group (13%) (P < .001) and in male individuals (35%) compared with females (9%) (P < .001). The prevalence of cam deformity was 46% in Klaaskinderkerke, 29% in the Alkmaar Paardenmarkt, and 13% in the Middenbeemster collection (P < .001). There were no differences by laterality, paired/unpaired femora, or individual/comingled burials. The prevalence of cam deformity correlated with the physical activities of the individuals. The highest prevalence was in the Klaaskinderkerke (46%) collection and soldiers (62%) from the Alkmaar Paardenmarkt collection. With increasing urbanization and a concomitant decrease in self‐sufficiency, the prevalence dropped to 13% in the Middenbeemster collection.
Conclusions
Cam deformities that correlate with physical activity levels were found in historical Dutch skeletal specimens.
Clinical Relevance
Cam deformity is considered an adaptive response to modern athletic activity. Evaluation of historical specimens will provide a fuller understanding of this condition by revealing whether cam deformity was present in historical skeletal specimens.
Femoracetabular impingement (FAI) is a known cause of hip osteoarthritis. It consists of cam, pincer, and mixed impingement types. 1 , 2 Most authors believe that the cam deformity is a response to stress during the pubertal growth spurt of the proximal femoral physis. 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 Most authors mention athletic activity as the cause of this stress to the proximal femoral physis. 10 , 11 , 12 Anterior pelvic tilt may also lead to a cam deformity 13 or a secondary effect of spinopelvic fixation, 14 although this is controversial. 15 This raises the question: is the cam deformity an adaptive response to modern‐day athletics or did it exist before? To answer this question, the prevalence of cam deformity in archeological specimens is needed. The large volume of FAI literature contains minimal archeological information. There are 3 archaeological population studies of cam FAI. A study from Tombos (present‐day northern Sudan) (1400‐656 BCE) found cam deformity in 7%. 16 Another study found cam deformity present in 5% of a Neolithic sample from Iran and 7% from medieval Poland. 17 A third study of 249 Native Americans in northern Ohio (Libben site—8th‐11th centuries) 18 found no cam deformity lesions. There are also 2 case reports of cam impingement in ancient humans: a 30‐ to 50‐year‐old Neolithic (10,000‐2000 BCE) male from Switzerland 19 and a Roman male from the necropolis of Castel Malnome (1st and 2nd century CE). 20 , 21 To further explore this question, we wished to study other populations from pre‐19th century times. Several skeletal collections from The Netherlands 22 , 23 , 24 exist and are available for study. Three are from the medieval (1200‐1600 CE) and postmedieval (1600‐1850 CE) periods. Alkmaar Paardenmarkt (Alkmaar Horsemarket—English) and Klaaskinderkerke (church of the children of Klaas—English) are from the medieval period and the Middenbeemster (middle Beemster—English) from the postmedieval period. The purpose of this study was to evaluate medieval and postmedieval Dutch skeletal collections for signs of cam deformity. We hypothesized that cam deformity did exist in medieval/postmedieval Dutch people.
METHODS
Specimens
Ethical approval for this study was granted by the Faculty of Archaeology, Leiden University. The time spans for these interred individuals are ~1286 to 1573 for Klaaskinderkerke, ~1448 to 1573 for Alkmaar Paardenmarkt, and ~1615 to 1866 for Middenbeemster. Their geographic locations are shown in Figure 1. The femora were reviewed for completeness and preservation, striving to find as many complete, well‐preserved femora as possible. Femora exhibiting signs of trauma, disease, or poor preservation were excluded.
FIGURE 1.
A modern map of the Netherlands showing the locations of the 3 sites.
Methodology
Sex and age were determined using standard osteological methods. 25 , 26 , 27 Sex was categorized as male, female, and indeterminate. Age (in years) was categorized as early young adult (18‐25 yr), late young adult (26‐35 yr), middle adult (36‐49 yr), and old adult (≥50 yr).
Digital photographs of the femora were taken as previously described. 18 , 28 , 29 From these photographs, the apparent neck shaft angle, true neck shaft angle, angles of version and inclination, and the α and β angles of Nötzli 29 , 30 were measured using Image J software (National Institutes of Health, Baltimore, Maryland) (Figure 2). All photographs and measurements were made by a single author, a graduate student in anthropology (N.B.), after formal instruction and review by the 2 senior orthopaedic surgeon authors (D.C., R.T.L.). This review consisted of 3 rounds of the student preparing the photographs and sending them to the senior orthopaedic surgeons for comments. After the third review, there were no further concerns from the senior orthopaedic surgeons.
FIGURE 2.
Showing angular measurement methodology made on an archeological sample. This right femur is from a female in the Alkmaar Paaredenmarkt collection who was middle adult age (36‐49 years). Further explanation on measurement techniques can be found in Toogood et al. 30 (A) Apparent neck shaft angle (ANSA). The femur is placed directly on the table surface, resting on the posterior aspects of the femoral condyles and the greater/lesser trochanters. The camera is perpendicular to the table surface and centered over the intertrochanteric region. Lines bisecting the femoral shaft and femoral neck are drawn; the ANSA is the angle between these 2 lines. (B) True neck shaft angle (TNSA). Here, the femur and camera are positioned the same as in (A), except that the femur is rotated along the femoral shaft such that the axis of the femoral neck is parallel to the table surface. The TNSA is the angle between the lines bisecting the femoral shaft and neck. (C) Version angle. The femur is positioned as in (A). The camera is perpendicular to and at the surface level of the table. The camera points directly down the femoral shaft from superior to inferior. A line bisects the femoral neck and head; another line is drawn at the table surface; the angle between these 2 lines is the angle of version. (D) Inclination, α and β angles. The camera is positioned as in (C), but the femur is abducted so the anteroposterior femoral neck axis is parallel with the table edge and camera. The inclination angle is between the surface table line and the line bisecting the femoral neck and head. The α and β angles of Notzli are also measured using this view.
Statistical Analysis
Continuous data are reported as the average ± 1 standard deviation, and categorical variables as frequencies and percentages. Differences between groups of continuous data were determined by nonparametric tests (Kruskal Wallis, Mann‐Whitney U test). Differences between categorical variables were determined by the Fisher's exact test for 2 × 2 analyses and the Pearson's chi‐square test for greater than 2 × 2 analyses. A P < .05 was considered statistically significant.
RESULTS
A total of 186 femora in 116 individuals (70 paired femora and 46 single femora; 94 were right and 92 left) were included (Table 1). From the Alkmaar Pardenmarkt cemeteries, 44 femora were in the collection and 35 were adequate for study, with all exclusions due to poor preservation. From the Klaaskinderkerke cemetery, 139 femora were in the collection and 52 were adequate for study; 6 were excluded as being skeletally immature, 8 had pathological conditions, and 73 were excluded due to poor preservation. From the Middenbeemster collection, 274 femora were in the collection and 99 were adequate for study. All of the Middenbeemster exclusions were due to poor preservation. Thus, 186 femora were of acceptable quality: 21 individuals with 35 femora from Alkmaar Paardenmarkt, 38 individuals with 52 femora from Klaaskinderkerke, and 57 individuals with 99 femora from Middenbeemster. The medieval group had fewer females (26% vs 45%) (P < .001). There was no difference in laterality between the medieval and postmedieval groups. The medieval group had more commingled and consequently unpaired femora. The medieval group consisted of younger individuals, with 12% of the older adults in the medieval group and 88% in the postmedieval group (P < .001). All individuals for whom the age and sex could not be determined were from the medieval group.
TABLE 1.
Demographic Data for the 186 Femora
| Total | Site | Era | ||||||
|---|---|---|---|---|---|---|---|---|
| KK | AP | MB | P Value | Medieval (KK + AP) | Postmedieval (MB) | P Value | ||
| All | 186 | 52 (28) | 35 (19) | 99 (53) | ‐ | 87 (47) | 99 (53) | ‐ |
| Sex | ||||||||
| Female | 68 | 11 (16) | 12 (18) | 45 (66) | <.001 | 23 (34) | 45 (66) | <.001 |
| Male | 104 | 28 (27) | 22 (21) | 54 (52) | .15* | 50 (48) | 54 (52) | |
| Undetermined | 14 | 13 (93) | 1 (7) | 0 (0) | 14 (100) | 0 (0) | ||
| Laterality | ||||||||
| Left | 92 | 23 (25) | 15 (16) | 53 (58) | .49 | 39 (41) | 53 (58) | .24 |
| Right | 94 | 29 (31) | 19 (20) | 46 (49) | 48 (51) | 46 (49) | ||
| Commingled burial | ||||||||
| No | 173 | 39 (23) | 35 (20) | 99 (57) | <.001 | 74 (43) | 99 (57) | |
| Yes | 13 | 13 (100) | 0 (0) | 0 (0) | 13 (100) | 0 (0) | ||
| Age | ||||||||
| EYU | 42 | 4 (10) | 12 (29) | 26 (62) | <.001 | 16 (38) | 26 (62) | <.001 |
| LYU | 67 | 21 (31) | 17 (25) | 29 (43) | 38 (57) | 29 (43) | ||
| MA | 47 | 11 (23) | 6 (13) | 30 (64) | 17 (36) | 30 (64) | ||
| OA | 16 | 2 (13) | 0 (0) | 14 (88) | 2 (12) | 14 (88) | ||
| AU | 14 | 14 (100) | 0 (0) | 0 (0) | 14 (100) | 0 (0) | ||
| Paired individual | 0 | |||||||
| No | 46 | 24 (52) | 7 (15) | 15 (33) | <.001 | 31 (67) | 15 (33) | .002 |
| Yes | 140 | 28 (20) | 28 (20) | 84 (60) | 56 (40) | 84 (60) | ||
Note: The raw numbers are shown with row percentages in parentheses.
AP, Alkmaar Paardenmarkt; AU, adult age unknown; EYU, early young adult; KK, Klaaskinderkerke; LYU, late young adult; MA, middle adult; MB, Middenbeemster; OA, old adult.
P value excluding the undetermined sex.
The angular measurements (Table 2) showed significant differences between the medieval and postmedieval groups only for the α and β angles. The average α angle was 49° ± 10° and 45° ± 8° in the medieval and postmedieval groups, respectively (P = .011). The average β angle was 45° ± 7° and 41° ± 5° in the medieval and postmedieval groups, respectively (P ≤ .001). The distribution of the α angle for the 3 different sites is shown in Figure 3.
TABLE 2.
Angular Measurements for the 186 Femora
| Measurement (°) | Total | AP | KK | MB | P Value | Medieval (AP + KK) | Postmedieval (MB) | P Value |
|---|---|---|---|---|---|---|---|---|
| Apparent neck shaft angle | 126 ± 7 | 125 ± 8 | 127 ± 5 | 126 ± 7 | .399 | 126 ± 6 | 126 ± 7 | .582 |
| True neck shaft angle | 125 ± 6 | 123 ± 6 | 126 ± 5 | 124 ± 6 | .234 | 125 ± 6 | 124 ± 6 | .811 |
| Version | 15 ± 9 | 13 ± 8 | 16 ± 8 | 15 ± 9 | .644 | 15 ± 8 | 15 ± 9 | .897 |
| Inclination | 12 ± 9 | 10 ± 10 | 14 ± 8 | 12 ± 9 | .0497 | 12 ± 9 | 12 ± 9 | .646 |
| α Angle | 48 ± 9 | 45 ± 7 | 52 ± 10 | 45 ± 8 | <.001 | 49 ± 10 | 45 ± 8 | .011 |
| β Angle | 43 ± 7 | 46 ± 7 | 44 ± 7 | 41 ± 5 | <.001 | 45 ± 7 | 41 ± 5 | <.001 |
Note: Measurements are given as average ± 1 SD.
AP, Alkmaar Paardenmarkt; KK, Klaaskinderkerke; MB, Middenbeemster.
FIGURE 3.
Distribution of the α angle between the 3 collections using the normal distribution.
The α angle used to define a cam lesion varies, 31 with ≥50°, 18 , 32 , 33 , 34 ≥55°, 35 , 36 , 37 , 38 , 39 and ≥60° 40 , 41 , 42 being used. The overall prevalence of cam deformity (Table 3) using the 3 α angle thresholds of ≥50°, ≥55°, and ≥60° was 25%, 16%, and 10%, respectively. There were no differences by laterality, paired/unpaired femora, or individual/comingled burials. The prevalence was higher in the medieval group (39%, 24%, and 14%) than the postmedieval group (13%, 9%, and 7%). The prevalence for each specific group was highest in the Klaaskinderkerke group (46%, 33%, and 19%), followed by the Alkmaar Paardenmarkt (29%, 11%, and 6%) and Middenbeemster groups (13%, 9%, and 7%). Cam deformity was more common in males (35%, 16%, and 14%) than females (9%, 3%, and 3%). See Table 3 for P values. Two examples of cam deformity are shown in Figures 4 and 5.
TABLE 3.
The Prevalence of Cam Deformity by α Angle Cutoff Criteria
| Variable | ≥50° Cutoff | ≥55° Cutoff | ≥60° Cutoff | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Cam Absent | Cam Present | P Value | Cam Absent | Cam Present | P Value | Cam Absent | Cam Present | P Value | |
| All | 139 (75) | 47 (25) | ‐ | 156 (84) | 30 (16) | ‐ | 167 (90) | 19 (10) | ‐ |
| Sex | |||||||||
| Female | 62 (91) | 6 (9) | <.001 | 66 (97) | 2 (3) | <.001 | 66 (97) | 2 (3) | .045 |
| Male | 68 (65) | 36 (35) | <.001* | 81 (86) | 23 (14) | <.001* | 89 (86) | 15 (14) | .017* |
| Undetermined | 9 (64) | 5 (36) | 9 (86) | 5 (14) | 12 (86) | 2 (14) | |||
| Laterality | |||||||||
| Left | 72 (78) | 20 (22) | .313 | 76 (83) | 16 (17) | .693 | 83 (90) | 9 (10) | 1.0 |
| Right | 67 (718) | 27 (29) | 80 (85) | 14 (15) | 84 (89) | 10 (11) | |||
| Burial | |||||||||
| Not comingled | 131 (76) | 42 (24) | .319 | 148 (86) | 25 (14) | .039 | 156 (90) | 17 (10) | .626 |
| Comingled | 8 (62) | 5 (38) | 8 (62) | 5 (38) | 11 (85) | 2 (15) | |||
| Paired individual | |||||||||
| No | 33 (72) | 13 (28) | .696 | 34 (74) | 12 (26) | .040 | 40 (87) | 6 (13) | .574 |
| Yes | 106 (76) | 34 (24) | 122 (87) | 18 (13) | 127 (91) | 13 (9) | |||
| Age of individual | |||||||||
| EYU | 37 (88) | 5 (12) | .044 | 40 (95) | 2 (5) | .001 | 41 (98) | 1 (2) | .010 |
| LYU | 46 (69) | 21 (31) | 56 (84) | 11 (16) | 60 (90) | 7 (10) | |||
| MA | 38 (81) | 9 (19) | 42 (89) | 5 (11) | 44 (94) | 3 (6) | |||
| OA | 10 (63) | 6 (38) | 10 (63) | 6 (37) | 11 (69) | 5 (31) | |||
| AU | 8 (57) | 6 (43) | 8 (57) | 6 (43) | 11 (79) | 3 (21) | |||
| Site | |||||||||
| AP | 25 (71) | 10 (29) | <.001 | 31 (89) | 4 (11) | <.001 | 33 (94) | 2 (6) | .040 |
| KK | 28 (54) | 24 (46) | 35 (67) | 17 (33) | 42 (81) | 10 (19) | |||
| MB | 86 (87) | 13 (13) | 90 (91) | 9 (9) | 92 (93) | 7 (7) | |||
| Era | |||||||||
| Medieval | 53 (61) | 34 (39) | <.001 | 66 (76) | 21 (24) | .009 | 75 (86) | 12 (14) | .151 |
| Postmedieval | 86 (87) | 13 (13) | 90 (91) | 9 (9) | 92 (93) | 7 (7) | |||
Note: The raw numbers are shown with row percentages in parentheses.
AP, Alkmaar Paardenmarkt; AU, adult age unknown; EYU, early young adult; KK, Klaaskinderkerke; LYU, late young adult; MA, middle adult; MB, Middenbeemster; OA, old adult.
P value excluding the undetermined sex.
FIGURE 4.
This late young adult male from the medieval Klaaskinderkerke site showed a large cam lesion of the left femur. (A) The inclination view with α angle of 75°. (B) The anterior view showing the large cam lesion (yellow arrow).
FIGURE 5.
A middle adult male right femur from the medieval Klaaskinderkerke site. (A) There was a cam lesion of the right femur, with the inclination view having an α angle of 69°. (B) The anterior superior aspect of the acetabular rim shows significant erosion and loss of the anterior acetabular rim (yellow arrow).
Further analyses between the male and female cohorts (Table 4) showed that there was a gradual decrease in the prevalence from the oldest to most recent of the skeletal collections for males (Figure 6A) but not for females (Figure 6B). The prevalence for females was consistently low for all the collections over time. See Table 4 for P values.
TABLE 4.
The Prevalence of Cam Deformity by α Angle Cutoff Criteria Between Males and Females
| Variable | ≥50° Cutoff | ≥55° Cutoff | ≥60° Cutoff | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Cam Absent | Cam Present | P Value | Cam Absent | Cam Present | P Value | Cam Absent | Cam Present | P Value | |
| Male | |||||||||
| Site | |||||||||
| AP | 13 (59) | 9 (41) | <.001 | 18 (82) | 4 (18) | .007 | 20 (91) | 2 (9) | .045 |
| KK | 10 (35) | 18 (65) | 47 (57) | 7 (43) | 20 (71) | 8 (29) | |||
| MB | 45 (83) | 9 (17) | 47 (87) | 7 (13) | 49 (91) | 5 (9) | |||
| Era | |||||||||
| Medieval | 23 (46) | 27 (54) | <.001 | 34 (68) | 16 (32) | .032 | 40 (80) | 10 (20) | .164 |
| Postmedieval | 45 (83) | 9 (17) | 47 (87) | 7 (13) | 49 (91) | 5 (9) | |||
| Paired individual | |||||||||
| No | 9 (60) | 6 (40) | .770 | 9 (60) | 6 (40) | .093 | 12 (80) | 3 (20) | .451 |
| Yes | 59 (66) | 30 (34) | 72 (81) | 17 (19) | 77 (87) | 12 (13) | |||
| Laterality | |||||||||
| Left | 33 (67) | 16 (33) | .837 | 37 (75) | 12 (25) | 42 (86) | 7 (14) | 1.0 | |
| Right | 35 (64) | 20 (36) | 44 (80) | 11 (20) | .640 | 47)85) | 8 (15) | ||
| Female | |||||||||
| Site | |||||||||
| AP | 11 (92) | 1 (8) | 1.0 | 12 (100) | 0 (0) | .591 | 12 (100) | 0 (0) | .591 |
| KK | 10 (91) | 1 (9) | 11 (100) | 0 (0) | 11 (100) | 0 (0) | |||
| MB | 41 (91) | 4 (9) | 43 (96) | 2 (4) | 43 (96) | 2 (4) | |||
| Era | |||||||||
| Medieval | 21 (91) | 2 (9) | 1.0 | 23 (100) | 0 (0) | .546 | 23 (100) | 0 (0) | .546 |
| Postmedieval | 41 (91) | 4 (9) | 43 (96) | 2 (4) | 43 (96) | 2 (4) | |||
| Paired individual | |||||||||
| No | 15 (88) | 2 (12) | .635 | 16 (94) | 1 (6) | .440 | 16 (94) | 1 (6) | .440 |
| Yes | 47 (92) | 4 (8) | 50 (98) | 1 (2) | 50 (98) | 1 (2) | |||
| Laterality | |||||||||
| Left | 36 (97) | 1 (3) | 36 (97) | 1 (3) | 1.0 | 36 (97) | 1 (3) | 1.0 | |
| Right | 26 (84) | 5 (16) | .085 | 30 (97) | 1 (3) | 30 (97) | 1 (3) | ||
Note: The raw numbers are shown with row percentages in parentheses.
AP, Alkmaar Paardenmarkt; KK, Klaaskinderkerke; MB, Middenbeemster.
FIGURE 6.
The prevalence of cam deformity for the 3 different skeletal collection for (A) males and (B) females. The collections are arranged on the x‐axis from the oldest to the most recent, with the dates of existence for the cities from which the skeletal collections were obtained shown on the x‐axis labels.
DISCUSSION
The prevalence of cam deformity (α angle ≥ 50°) in these Dutch collections was 25%, 39% in the medieval cohort and 13% in the postmedieval cohort, showing that cam deformity is not a unique product of modern lifestyle and affirming our hypothesis. This 25% prevalence is greater than the 7% from Tombos 16 and the 7% from medieval Poland 17 for archeological collections. There are several possible explanations for this finding. One is that it may simply represent the increase in α angles seen over the last 17 centuries. 43 However, the 2 medieval samples, the one from Poland 17 and this study, are from similar times, as is the Libben 18 population (8th‐11th centuries CE), which found no cam FAI. These differences likely reflect variations in genetic patterns 44 and activity levels.
There was higher prevalence of cam deformity in males compared with females, consistent with modern studies. 45 , 46 , 47 , 48 , 49 Archeological findings are similar. Musielak et al. 17 found a 1.3% prevalence of cam in females and 15.3% in males from medieval Poland. Coon et al. 16 noted 9 cam lesions: 6 were in males and 3 in females.
The etiology of the primary cam deformity is likely an adaptation to increased proximal femoral physeal loading during puberty. 3 , 4 , 5 , 6 , 7 , 8 Today, this is usually from sporting activities. 10 , 11 , 12 , 50 The odds ratio of a cam lesion in athletes at 23 years of age, compared with nonathletes, is higher in power sports athletes (basketball, cheerleading, football, gymnastics, soccer, and volleyball) (odds ratio = 2.93, P = .046) but not when compared with non–power sport athletes (wrestling, baseball, cross country and track/field, softball, tennis) (odds ratio = 1.93, P = .32). 31 However, large stresses across the hip are not limited to sporting activities but are also present with any heavy physical activity, including farming 51 and military activity. 52 Farming and military activity is germane to this study as discussed below.
Differences between these 3 Dutch collections in cam deformity prevalence are easily explained when considering the geographical and sociopolitical aspects of the Netherlands. The Netherlands was not a coherent and united country historically, with significant past military conflict. 53 Geographically, the Netherlands is located on an extension of the Lower Rhine plain where the river meets the sea and is surrounded by low mountains to the south and southeast. This low, flat landscape is dominated by both rivers and the sea, making it vulnerable to water‐related erosion. Parts of the coastal region have amassed elevated sand deposits over the ages offering natural barriers against the water. Alteration and management of this landscape to make it livable began in the Middle Ages and continue to the present. 53
Each of the excavations is unique regarding these geographical/sociopolitical aspects. The excavation at Alkmaar Paardenmarkt focused on the Minderbroederklooster cemetery (Franciscan monastery—English) dating from 1448 until 1574. The Alkmaar Paardenmarkt skeletal collection contains both citizens from Alkmaar as well as soldiers that perished during the 1573 Siege of Alkmaar. The excavation associated with the Franciscan monastery yielded 189 burials belonging to the local population. Additionally, there were 2 mass graves containing the remains of 22 soldiers (S404) and 9 other individuals (S403) who died during the Siege. The mass grave of the soldiers (S404) was included whereas the S403 grave could not be included due to poor quality.
The village of Klaaskinderkerke, located in Zeeland (southwest Netherlands), 22 , 54 was settled in 1286. 55 It was often flooded being in a delta near the North Sea. Rebuilding always occurred after the floods until the 1570 All Saint's Flood, after which the villagers did not return. In 1953, a North Sea flood unearthed the church foundations and cemetery. 22 The skeletal remains were exposed and heavily disturbed and were excavated in 1959 to prevent further damage. The Klaaskinderkerke skeletal collection is that of a poor, rural population.
The excavation at Middenbeemster focused on the older foundations of the Keyserkerk (Keyser Church) and associated cemetery (1615‐1866). The skeletal assemblage from Middenbeemster is that of an agricultural rural population from the postmedieval period containing individuals of all socioeconomic status.
When using 3 α angles to define a cam lesion (≥50°, ≥55°, and ≥60°), the prevalence of cam deformity was 25%, 16%, and 10% respectively. The prevalence for the 3 different sites (51% for Klaaskinderkerke, 28% for Middenbeemster, and 21% for Alkmaar Paardenmarkt) supports the physical activity hypothesis as the etiology of a cam lesion when reviewing the daily activities of these 3 different groups. The highest prevalence (51%) was in the medieval Klaaskinderkerke collection. The Klaaskinderkerke people were heavily agricultural with an emphasis on crop cultivation and also engaged peat and salt extraction from the land and later the herring fishery, which were strenuous tasks. 56 , 57 Historical data suggest a labor division between the sexes. The men performed the more strenuous jobs related to farming, 58 which included long periods of standing, excessive bending and kneeling, and the lifting and carrying of heavy objects, all for extended periods of time and across uneven ground. 59 Women were committed to food production, household tasks, and fabric production. 58 This possibly explains the difference in cam deformity prevalence between males (35%) and females (9%) in these Dutch people, which has also been noted in present‐day cam deformity populations. 47 , 60 , 61
The other medieval collection is that of Alkmaar Paardenmarkt. These 35 femora came from either the mass grave containing soldiers or the cemetery connected to the monastery and who were likely not soldiers. From the mass grave there were 13 femora from 7 male soldiers; from the cemetery proper there were 22 femora from 14 individuals. In the 13 mass grave femora, a cam lesion was present in 8 (62%) femora and in 5 of 7 individuals (71%). The male soldiers from the mass grave had pathologies, indicating a highly active, high‐risk lifestyle of being a soldier in an ongoing war: recent and healed fractures, Schmorl's nodes, blunt object trauma, and 2 cases of cranial projectile trauma. It is unknown how long they were employed as soldiers and at what age they joined the military. When the soldiers died during the Siege of Alkmaar in 1573, the conflict had been going on for roughly 7 years. They may have already developed the cam lesion prior to the war. The 22 nonsoldier femora from the cemetery connected to the monastery comprised 12 female and 9 male femora with 1 of unknown sex; 6 were middle‐aged adults and 16 young adults. A cam lesion (α angle ≥ 50°) was present in 2 of the 22 femora (9%) or 0 of 22 (55° α angle cutoff). The levels of physical activity in these Franciscan monastery individuals were likely much lower than those of the soldiers. The fact that there were both sexes interred in the Franciscan monastery cemetery likely indicates that both monks/priests as well as nuns and other members of the community were buried there. 62 The average α angle for the soldier group was 52° ± 8° and for the nonsoldiers 42° ± 5° (P = .005).
The cam deformity prevalence in the Middenbeemster postmedieval collection was 13%. The sociological changes that occurred between the medieval and the postmedieval periods were increased population growth, urbanism, and the emergence of the market economy, with a concomitant decrease in self‐sufficiency 62 , 63 This decrease in self‐sufficiency likely resulted in lower levels of physical exertion, explaining the 13% prevalence in the postmedieval Middenbeemster population compared with the 51% prevalence in the medieval Klaaskinderkerke population. It appears that it was only the men affected by these changes (Figure 6), as they were likely the ones that were performing the strenuous jobs, and as such were affected by these changes, whereas the tasks/occupations of the women likely remained static from the medieval to postmedieval times.
Socioeconomic factors are a proxy for physical activity levels in both modern and historical populations. Present‐day individuals with a lower socioeconomic status are usually more physically active than individuals of higher status. This depends on a range of factors, such as occupation, household, transport methods, and available leisure time. 64 , 65 , 66 Similar studies have been conducted on past populations. Havelkova et al. 67 showed a correlation between a person's occupation/profession (which is linked to socioeconomic status) and entheseal changes (changes in muscle and ligament attachments sites on bone). Individuals with a higher socioeconomic status had fewer entheseal changes compared with individuals with highly active occupations, indicating they were less physically active than individuals of lower socioeconomic status. The cemetery of Middenbeemster contained a mix of socioeconomic statuses, whereas the others contain people of low (Klaaskinderkerke) and middle to low (Alkmaar) status. In Middenbeemster, the lower prevalence is likely due to the inclusion of higher‐socioeconomic‐status individuals.
The findings from this study raise several questions for further investigation. Cam impingement has been recently described in soldiers. Royston et al. 68 published 1 case in a 21‐year‐old soldier, but activity‐level details before entering the military are not given. Gwathmey and Kadrmas 69 discuss cam impingement in soldiers but no prevalence data are given. Further exploration of physically active military personnel regarding the prevalence of cam impingement should be pursued. Similarly, the prevalence of cam impingement in 19th‐century farmers, before automation when much of the work was manual, with/without draft horses (lack of tractors, combines, etc.) should also be investigated if such populations exist. Finally, cam lesions can be used as a proxy for physical activity levels in ancient populations and could be used as an aid in determining levels of physical activity and socioeconomic status in such groups.
Limitations
This study is not without limitations. Certain skeletons from Klaaskinderkerke had postmortem damage so age at death as well as sex could not be determined. Additionally, the population's biological sex was unequal with more males. 62 There is also the possibility that the remains of individuals from nearby towns or even the remains of individuals who died during battle are also included. 55 The site of Alkmaar Paardenmarkt has 2 mass graves whose poor preservation and completeness led to 9 of the mass‐grave individuals being excluded. Interobserver reliability of the angular measurements is not known as only 1 individual (N.B.) made the measurements. Although we can understand a little about the socioeconomic class of the specimens due to their burial circumstances, the exact occupation of each person is not known.
CONCLUSIONS
Cam deformities that correlate with physical activity levels were found in historical Dutch skeletal specimens.
DISCLOSURES
The author (S.S.) declares that financial support was provided by Embodied Inequality Talent program, Dutch Research Council. The other authors (N.B., D.C., R.T.L.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
FUNDING
This publication is part of the project Embodied Inequality (project number NWO #VI.Vidi.201.153) of the Talent program, funded by the Dutch Research Council.
ACKNOWLEDGMENTS
The authors extend their thanks to the Middenbeemster Historical Society (Historisch Genootschap Beemster), Gemeente Alkmaar, and Stichting Cultureel Erfgoed Zeeland for facilitating this research. The authors also thank Ms. Marijke Irving‐Langevoort for photographic assistance.
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