by Edward S Glaser1, David C Fleming2*, and Norma Reece2
The Foot and Ankle Online Journal 9 (1): 8
Purpose: To better understand the anatomical variation in angles that each of the three facets of the subtalar joint has with relation to the transverse, frontal and sagittal planes along the facet’s long axis.
Design: An investigation of Calcaneo-Talo interaction.
Samples: Calcaneal samples were obtained from the Smithsonian Institute from the Terry, Argentina, Aleutian Islands, Peru, Virginia, Seminole Indian, and Egyptian skeletal collections.
Methods: Photographs were obtained of each calcaneus held at a 27 degree calcaneal inclination angle, angles were determined by a bisection of the facet measured against the transverse plane via a round ground protractor level. Sagittal and Frontal plane deviations were determined via ImageJ angle tool from the transverse plane photographs.
Main Outcome Measures: We measured the angle of the bisection of each of the three facets with respect to the transverse plane, sagittal plane, and frontal plane for 162 calcanei.
Results: The mean angulation of deviation from the transverse plane were: anterior facet 27.4°, middle facet 14.7°, and posterior facet 9.0°. Standard deviations were 7.3°, 6.1°, and 5.0° respectively. The mean angulation of deviation from the sagittal plane were: anterior facet 31.42°, middle facet 34.44°, and posterior facet 44.16°. Standard deviations were 11.88°, 7.95°, and 10.36° respectively. The mean angulation of deviation from the frontal plane were: anterior facet 58.58°, middle facet 55.56°, and posterior facet 45.84°. Standard deviations were 11.88°, 7.95°, and 10.36° respectively.
Conclusions: The axis of the posterior cone shaped facet is directed toward the middle facet. The anterior facet sits 27°±7° from the transverse.
ISSN 1941-6806
doi: 10.3827/faoj.2016.0901.0008
1 – Founder and CEO of Sole Supports, Inc.
2 – Sole Supports, Inc.
* – Correspondence: dfleming@solesupports.com
Forces being applied to the sub talar joint are influenced, as to their effect on the bones, by the angulation of the facets in all three planes by measuring two planes we can extrapolate the third. No literature was found as to calcaneal facet angles and certainly none with a large sample size. This was an investigation into foot biomechanics. In this study, we described a method for measuring calcaneal facets, using the skeletal collections at the Smithsonian museum. We further describe possible reasons for our findings.
Methods
Study Design and Samples
This Interval study included a total of 162 calcanei from the Smithsonian Institute from the following collections: Aleutian Islands of Wislow and Kagamil, Argentina from San Zavier and San Blas, Chicama Peru, Egyptian XII Dynasty, Lewis Creek Virginia Indians, and the Terry Collection which spans 1920 to 1945. Inclusion criteria consisted of intact Sustentaculum Tali. Intact anterior, middle, and posterior facets. Intact portion of the calcaneus between the calcaneal tuberosity and the calcaneal tubercle. Exclusion criteria consisted of large heel spur (>4mm). Overall, 36 calcanei were excluded from this study.
Measurement of Facet Angles
Figure 1 Photograph showing the Calcaneal holding instrument and position on Calcaneal samples.
Each calcaneus was held in a position of rectus with a 27⁰ calcaneal inclination angle by a modified Hewlett Packard printer paper tray. The tray was selected for applying equal pressure to both sides of the calcaneus simultaneously. The paper tray was fitted with L-shaped brackets lined with 1 inch of 35 durometer EVA foam (Figure 1). The bisection of the anterior and middle facets was determined from the most proximal articular surface point to the most distal articular surface point. Then an imaginary line was drawn, a real line was not drawn on the bones as to preserve the Smithsonian’s samples. The posterior facet bisection was determined from the most superior point equidistant from the lateral and medial edges of the articular surface of the cone-shaped facet to the apex of the articular portion of the facet. The line was then measured with respect to the transverse plane using an Empire Level 36 magnetic polycast protractor. The sagittal plane deviations were obtained via the photographs of each calcaneus (Figure 1) utilizing ImageJ’s angle tool. Excel was then used to determine the deviation from the frontal plane using the following formula: (90-(Sagittal deviation)=Frontal deviation). The cone shaped posterior facet protrudes from the dorsal surface of the calcaneus its axis runs posterolateral to anteromedial angulated off of the frontal plane. The curved medial and lateral articular surfaces can be bisected by the connection of those bisection points. This bisection, if continued medially, intersected the middle facet. (Figure 2)
Figure 2 Photograph showing bone markings and bisection lines of the anterior, middle, and posterior facets on calcaneal sample.
Statistical Analysis
Statistical analyses were performed using Excel 2013 for Windows (Microsoft, Redmond, VA). Mean, standard deviation, and range for each region as well as across all 162 samples was derived for all three facets.
Results
One hundred sixty-two (n=162) calcanei were included in this study. The mean deviation angle, standard deviation, and range were taken of each facet with respect to the three spatial planes. (Table 1)
Transverse Plane Deviation
The mean angle ± standard deviation (range) was 27.43±6.95 (9-50) for the anterior facet, 14.35±6.09 (0-30) for the middle facet, and 8.94±4.81 (0-24) for the posterior facet. Each facet was quantified by collection. Seventeen (n=17) calcanei from Argentina measured 24.18±5.71 (11-33) for the anterior facet, 12.71±5.13 (3-20) for the middle facet, and 8.12±3.95 (1-15) for the posterior facet. Fifteen (n=15) calcanei from the Aleutian Islands measured 26.40±4.97 (14-33) for the anterior facet, 12.27±7.60 (0-29) for the middle facet, and 8.00±4.46 (2-16) for the posterior facet. Twenty five (n=25) calcanei from Peru measured 30.76±5.25 (21-40) for the anterior facet, 11.12±4.46 (5-20) for the middle facet, and 8.48±4.02 (1-16) for the posterior facet. Eleven (n=11) calcanei from Virginia measured 21.64±5.57 (13-32) for the anterior facet, 16.73±6.48 (7-28) for the middle facet, and 9.27±4.90 (0-16) for the posterior facet. Fifty eight (n=58) calcanei from the Terry Collection measured 27.59±7.13 (9-45) for the anterior facet, 16.12±6.29 (2-30) for the middle facet, and 8.72±5.44 (0-24) for the posterior facet. Thirty six (n=36) calcanei from Egypt measured 28.19±7.90 (14-50) for the anterior facet, 14.64±5.29 (3-27) for the middle facet, and 10.28±4.74 (1-21) for the posterior facet.
Sagittal Plane Deviation
The mean angle ± standard deviation (range) was 31.42±11.88 (1.9-66.35) for the anterior facet, 34.44±7.95 (4.75-58.93) for the middle facet, and 44.16±10.36 (18.01-74.06) for the posterior facet. Each facet was quantified by collection. Seventeen (n=17) calcanei from Argentina measured 29.83±16.31 (1.9-62.25) for the anterior facet, 38.15±6.29 (25.82-52.5) for the middle facet, and 34.42±8.81 (18.01-51.18) for the posterior facet. Fifteen (n=15) calcanei from the Aleutian Islands measured 34.77±6.22 (20.33-43.53) for the anterior facet, 35.03±6.79 (19.89-43.6) for the middle facet, and 45.71±9.00 (33.78-64.9) for the posterior facet. Twenty five (n=25) calcanei from Peru measured 26.73±9.31 (10.18-47.73) for the anterior facet, 34.70±9.93 (4.75-53.02) for the middle facet, and 47.20±7.30 (34.41-60) for the posterior facet. Eleven (n=11) calcanei from Virginia measured 29.85±10.06 (16.62-55.44) for the anterior facet, 29.32±8.33 (14.08-42.99) for the middle facet, and 37.56±7.08 (26.5-46.07) for the posterior facet. Fifty eight (n=58) calcanei from the Terry Collection measured 31.82±11.95 (2.7-58.39) for the anterior facet, 33.54±6.53 (12.8-45.97) for the middle facet, and 48.68±8.72 (26.3-74.06) for the posterior facet. Thirty six (n=36) calcanei from Egypt measured 33.59±12.25 (5.79-66.35) for the anterior facet, 34.51±7.86 (16.76-58.93) for the middle facet, and 43.31±11.35 (22.18-70.2) for the posterior facet.
Frontal Plane Deviation
The mean angle ± standard deviation (range) was 58.58±11.88 (23.65-88.10) for the anterior facet, 55.56±7.95 (31.07-85.25) for the middle facet, and 45.84±10.36 (15.94-71.99) for the posterior facet. Each facet was quantified by collection. Seventeen (n=17) calcanei from Argentina measured 60.17±16.31 (27.75-88.1) for the anterior facet, 51.85±6.29 (37.5-64.18) for the middle facet, and 55.58±8.81 (38.82-71.99) for the posterior facet. Fifteen (n=15) calcanei from the Aleutian Islands measured 55.23±6.22 (46.47-69.67) for the anterior facet, 54.97±6.79 (46.4-40.11) for the middle facet, and 44.29±9.00 (25.1-56.22) for the posterior facet. Twenty five (n=25) calcanei from Peru measured 63.27±9.31 (42.27-79.82) for the anterior facet, 55.30±9.93 (36.98-85.25) for the middle facet, and 42.80±7.30 (30-55.59) for the posterior facet. Eleven (n=11) calcanei from Virginia measured 60.15±10.06 (34.56-73.38) for the anterior facet, 60.68±8.33 (47.01-75.92) for the middle facet, and 52.44±7.08 (43.93-63.5) for the posterior facet. Fifty eight (n=58) calcanei from the Terry Collection measured 58.18±11.95 (31.61-87.3) for the anterior facet, 56.46±6.53 (44.03-77.2) for the middle facet, and 41.32±8.72 (15.94-63.7) for the posterior facet. Thirty six (n=36) calcanei from Egypt measured 56.41±12.25 (23.65-84.21) for the anterior facet, 55.49±7.86 (31.07-73.24) for the middle facet, and 46.69±11.35 (19.8-67.82) for the posterior facet.
It was noticed in the vast majority of cases the bisection of the posterior facet, when extended medially, passes through the middle facet. Therefore, as the talus slides medially along the axis of the cone shaped posterior facet, the middle facet which sits on a lever of bone protruding from the medial side of the calcaneus, is loaded encouraging calcaneal eversion.
Discussion
In our study, we described a method for quantifying the angle long axis of each calcaneal facet makes with respect to the three spatial planes. Samples are divided for different historical and geographical populations.
We showed when the calcaneus is at a twenty-seven degree of inclination, the anterior facet is 27 degrees from being parallel to the transverse plane. When the anterior facet of the calcaneus is parallel to the transverse plane the calcaneus is inverted, and the talar head can easily rotate about the STJ axis. This occurs, ideally, at heel strike; a condition that neither favors pronation nor supination as the force moving down the extremity runs into a perpendicular anterior articular facet. This supinated posture provides an efficient platform for propulsion as the talus cannot rotate in the sagittal plane with relation to the calcaneus. The head of the talus is resting on the anterior facet of the subtalar joint physically blocking sagittal plane rotation between the calcaneus and talus. Contraction of the gastroc-soleus muscle isolates ankle rotation. More research is necessary to see to what extent talar head transverse plane motion plays in the locking and unlocking of the foot during the stance phase of gait.
One deficit in this study is the lack of data regarding the rotational angle of each facet around the axis formed by the longitudinal bisection. There is always some subjective decision making in determining these angles since borders of facets are not standard geometric figures. This variable was minimized by using a relatively large sample size.
