Single Axis of Motion
The axis of the subtalar joint was studied by Manter,50
Isman and Inman,51
It is oblique,
oriented upward, anteriorly and medially. It penetrates the posterolateral corner of the os calcis, passes perpendicular to the canalis tarsi, and pierces the superomedial aspect of the talar neck. Manter reported the angulation of the axis to have a 42 degrees average inclination (range, 29 to 47 degrees) in the sagittal plane relative to the horizontal line and a 16 degrees average medial deviation (range, 8 to 24 degrees) in the transverse plane relative to the long axis of the foot passing through the first interdigital space.50
Inman provided measurements that are very similar: 42 degrees ± 9 degrees of inclination in the sagittal plane and 23 degrees ± 11 degrees of medial deviation in the horizontal plane relative to the axis of the foot passing through the second interdigital space (Fig. 10.53
Figure 10.52 Stability of the ankle in varus and valgus stress with and without vertical load of 670 N. Percentage of restraint to the varus or valgus stress by each component of the collateral ligaments and the articular surfaces is presented in neutral, dorsiflexion, and plantar flexion of the ankle. The calcaneofibular ligament is a major restraining structure in varus stress, whereas the deltoid ligament is a major restraining structure in valgus stress of the ankle. Under vertical load the stability is provided by only the articular surfaces. (Data from Stormont DM, Morrey BF, Kai-nan AN, et al. Stability of the loaded ankle. Relation between articular restraint and primary and secondary static restraints. Am J Sports Med. 1985;13:295.)
The motion components at the subtalar joint can be determined from a simple vectorial analysis of the subtalar joint axis components, which are three: longitudinal, vertical, transverse. The greater longitudinal component generates supination-pronation, the vertical component generates abductionadduction, and the lesser transverse component generates flexion-extension. Any instantaneous motion is a combination of the three simultaneously occurring motions. The axis of the talocalcaneal joint invariably generates two combination patterns of motion: pronation-abduction-extension and supination-adduction-flexion (Figs. 10.54
, and 10.56
). This basic motion of the calcaneus was clearly demonstrated in our specimens (Fig. 10.57
) and was demonstrated by Farabeuf in anatomic models (Fig. 10.58
Figure 10.53 Variations in inclination of axis of subtalar joint as projected upon sagittal plane. The single observation of an angle of almost 70 degrees was present in a markedly cavus foot. (Inman TV. The Joints of the Ankle. Baltimore: Williams & Wilkins; 1976:37.)
The turning in of the heel was termed endorotation of the calcaneus by Lewis and the reverse was termed exorotation.53
For the clinician, exorotation of the calcaneus corresponds also to valgus of the heel and endorotation to varus.
Manter, in his study of the motion around the subtalar axis, recognized and measured a longitudinal displacement along the axis and described the motion at the subtalar joint as that of a screw.50
He compared the posterior calcaneal surface to the helical surface of a screw. Serial sections of this calcaneal surface made perpendicular to the subtalar joint axis revealed spiral rather than circular arcs. He considered this surface as being an “oblique helicoid, or screw-shaped surface.” He measured the helix angle of the posterior calcaneal surface by dropping a perpendicular line from a point on the axis to the articular surface (Fig. 10.59
). The average helix angle was found to be 12 degrees. In pronation, the calcaneus, being held fixed, the talus advances along the subtalar axis approximately 1.5 mm for each 10 degrees of rotation at the joint. Van Langelaan measured also the helical motion at the subtalar joint.3
The axial translation of the talus was 1.7 mm (range, 1 to 2.6 mm) in a posterolateral direction during the exorotation of the leg of 30 degrees. Manter described the subtalar joint behavior “like a right-handed screw in the right foot and like a left-handed one in the left foot” (Fig. 10.60
The calcaneus advances along the subtalar axis during supination-adduction-flexion or varus of the heel and retreats along the same axis during pronation-abduction-extension or valgus of the heel.
The subtalar range of motion is variable, as indicated in Table 10.5
. For the clinician, 25 to 30 degrees of inversion and 5 to 10 degrees of eversion is a practical average range of motion. During the stance phase of the gait on even ground, the heel strikes with minimal inversion at the subtalar joint, followed by eversion ranging from 5 to 10 degrees at 10% of the walking cycle. From there on, inversion occurs at the subtalar joint, reaching a maximum of 5 degrees at 62% of the walking cycle.
Motion and Stability
The motion at the subtalar joint is guided by the contour of the articular surfaces, their orientation, and the intrinsic and extrinsic ligaments.
The posterior calcaneal surface has been considered as a segment of a cone with the axis of the revolution of the surface directed anteromedially, intersecting the sustentaculum tali at nearly a right angle in the adult.9
Manter considered the posterior calcaneal surface as an oblique helicoid or screw-shaped surface.50
Inman demonstrated a screwlike behavior of the surface in 58% of 42 specimens and concluded that “the remarkable variation is the important factor.”10
Huson stressed the strong curvature of this surface medially forming a “bottleneck,” whereas the lateral segment of the surface has a lesser curvature.8
The posterior talar articular surface is quadrilateral, usually rectangular medially and more or less oval laterally. The surface is strongly concave in the long axis and usually flat or minimally concave transversely. From a functional point of view, the posterior calcaneal articular surface may be considered as a male ovoid surface and the posterior talar articular
surface as a female ovoid surface. The combined anterior and middle calcaneal surfaces form a female ovoid surface and the inferior articular surface of the talar head forms a male more or less flattened ovoid surface. MacConaill and Basmajian analyzed the motion components generated by the moving ovoid surfaces relative to each other.30
A male ovoid surface moving on a female ovoid surface slides, rolls, and spins. The rolling is in a direction opposite to the sliding (Fig. 10.62
). A female ovoid surface moving on a male ovoid surface slides, rolls or rocks, and spins. The rolling is in the direction of sliding (Fig. 10.63
). The roll is a tilt that maintains the surface contact and the spin maximizes the congruency. Huson analyzed the spin at the posterior talocalcaneal joint.8
Because of the differential of the curvatures of the articular surface—more curved medially and less curved laterally—a pure sliding creates more incongruency of the corresponding surfaces, whereas an associated spin minimizes the incongruency (Fig. 10.64
). This interpretation is inclusive in the broader and more comprehensive analysis of the movement of ovoid surfaces presented by MacConaill and Basmajian.30
If the ovoid surfaces are obliquely oriented with regard to the long axis of the foot, the generated motion will have two components. The associated spin creates the third motion component.
Figure 10.54 The axis of the talocalcaneonavicular joint AA′ as indicated passing through the os calcis in neutral position. The axis AA′ has three components: XX, which generates flexion-extension (FLEX-EXTE); Y, which generates abduction-adduction (ABD-ADD); Z, which generates supinationpronation (SUP-PRO). In valgus position the anterior aspect of the os calcis is simultaneously extended, abducted, and pronated. In varus position the anterior aspect of the os calcis is simultaneously flexed, adducted, and supinated.
Figure 10.55 Axis of the talocalcaneonavicular joint AA′ seen in lateral view with the secondary axes X, Y, Z. The middle figure indicates the os calcis in varus and demonstrates the flexion (FLE) and supination (SUP) components. The bottom figure indicates the os calcis in valgus and demonstrates the components of extension (EXT) and pronation (PRO). (ABD, abduction; ADD, adduction.)
Figure 10.56 Frontal view of the os calcis. In varus of the heel the anterior aspect of the os calcis is flexed (FLE), adducted (ADD), and supinated (SUP). In valgus of the heel the anterior aspect of the os calcis is extended (EXT), abducted (ABD), and pronated (PRO). (TCN, talocalcaneonavicular axis; XX, transverse axis of flexion-extension; Y, vertical axis of abduction-adduction; Z, longitudinal axis of supination-pronation; O, O1, O2, cruciform reference line.)
Figure 10.57 Anatomic model of the hindfoot. (A) Valgus position of the os calcis involving (1) abduction, (2) extension, (3) pronation. (B) Varus position of the os calcis involving (4) flexion, (5) adduction, (6) supination.
Figure 10.58 (A) Relationship of the talus and the calcaneus in the standing position as indicated by the vertical pin inserted in the calcaneus. The posterior calcaneal surface is covered by the external apophysis of the talus. The “condylar” surface of the talus is medial relative to the “trochlear” surface of the calcaneus. The long axis of the talar condylar surface is parallel to the long axis of the trochlear surface of the cuboid. Both axes are directed inferiorly, medially, and posteriorly, and this allows an “oblique flexion inwards.”
Figure 10.58 (Continued) (B) The talus has remained unchanged. The calcaneus is turned inward, as evidenced by the obliquity of the calcaneal pin. The long axes of the talar condylar and calcaneal trochlear surfaces are convergent. This corresponds to the “physiologic varus of flexion + adduction + supination,” which results from the combined movements of the navicular on the talus, the cuboid on the calcaneus, and the calcaneus on the talus. (From Farabeuf LH. Precis de Manuel Opératoire. Paris: Maisson; 1889:827.)
Figure 10.59 Comparison of the posterior calcaneal facet of the right subtalar joint with a right-hand screw. Arrow represents the path of a body following the screw. hh′ is the horizontal plane in which motion is occurring. tt′ is a plane perpendicular to the axis of the screw. s is the helix angle of the screw, equal to the angle s′, which is obtained by dropping a perpendicular pp′ from the axis. (Manter JT. Movements of the subtalar and transverse tarsal joints. Anat Rec. 1941;80:402.)
Figure 10.60 Right-hand and left-hand screws.
TABLE 10.5 REPORTED RANGES OF SUBTALAR MOTION
Range of Motion
10 to 15 degrees
Close and colleagues (1967)
9.9 to 28 degrees
10 to 65 degrees (average, 40 degrees 6 7 degrees)
30 degrees (25 degrees inversion, 5 degrees eversion)
American Medical Association (1988)
50 degrees (30 degrees inversion, 20 degrees eversion)
Figure 10.61 Relative talocalcaneal helical axes with 10 degrees of talocalcaneal exorotation projected on sagittal plane. (Van Langelaan EJ. A kinematical analysis of the tarsal joints. An X-ray photogrammetric study. Acta Orthop Scand. 1983;54[Suppl 204]:147.)
More specifically, the posterior calcaneal articular surface is oriented obliquely from posteromedial to anterolateral. Furthermore, the posterior segment is more dorsal and the anterior segment of the surface is more plantar. A female ovoid surface moving along this surface will naturally flex or extend and at the same time will supinate-pronate. Theoretically, a convex male surface oriented transversely will generate only the motion of flexion-extension, whereas such a surface oriented longitudinally will generate only the motion of supination-pronation. The oblique orientation of the posterior calcaneal surface will generate a combination of both flexion-extension and supination-pronation (Fig. 10.65
). The inescapable spin creates the third motion component present at this joint: adduction-abduction. In “reading” into the contour and orientation of the posterior talocalcaneal joint, we can now clearly see that the generated motion is that of flexion-supination-adduction or extension-pronation-abduction. The talus and the calcaneus move in opposite directions to reach the end-position. In the clinician’s “valgus” of the heel, the calcaneus moves in extension-pronation-abduction or the talus moves in flexion-supination-adduction. In “varus,” the calcaneus is in flexion-supination-adduction and the talus moves in extension-pronation-abduction (Fig. 10.66
Figure 10.62 A male ovoid surface (posterior calcaneal articular surface) moving on a female ovoid surface (posterior talar articular surface) slides, rolls, and spins. The rolling is in a direction opposite to the sliding. The sliding advances the moving surface but creates a gap that is closed by the reverse rolling, and the maximum surface contact is achieved by the spinning of the moving surface. (Concept of MacConaill and Basmajian.)
Figure 10.63 A female ovoid surface moving on a male ovoid surface slides, rolls, and spins. The rolling is in the direction of the sliding.
Figure 10.64 Diagrammatic representation of the posterior calcaneotalar articular surfaces. The posterior calcaneal surface has “convex profiles lying in a medial, backward and upward direction. The curvatures grow stronger in the same direction and in addition the profiles of the medial and anterior part of the facet, bordering on the canalis tarsi, are more curved than the lateral ones. Such surfaces in gliding over each other will show great discongruencies when they follow their strongest or weakest curvatures,” as seen on the lower diagrams (B). “If this shift is simultaneously combined with a turn the discongruencies are limited to a circumscribed part (indicated by the asterisk) of the articular surfaces,” as seen on the upper diagrams (A). (Huson A. Anatomical and Functional Study of the Tarsal Joints. Leiden: Drukkerij, “Luctor et Emergo”; 1961:137.)
The degree of orientation of the articular surfaces affects the amplitude of the motion components. The posterior calcaneal surface has an inclination angle with an average of 65 degrees, a minimum of 55 degrees, and a maximum of 75 degrees relative to a line drawn along the superior surface of the calcaneal body. A larger inclination angle provides more flexion component to the motion (Fig. 10.67
). The posterior talar articulating surface has a declination angle with an average of 37 degrees, a minimum of 26 degrees, and a maximum of 50 degrees relative to the anterior trochlear line. A greater declination angle orients the surface in a longitudinal direction that will increase the flexion-extension component, whereas a smaller declination angle orients the surface more transversely and increases the supination-pronation component (Fig. 10.68
MacConaill and Basmajian consider the subtalar joint as a bicondylar joint between the talus and the calcaneus, and the “rotation of one or the other of the mating bones can take place around an axis between the condyles.”30
This axis of motion is indeed located and passes through the canalis tarsi and the medial segment of the talocalcaneal interosseous ligament. Farabeuf stressed the rotational motion of the talus in a “tourniquet” fashion over the os calcis, or vice versa, taking place around a center located in the innermost part of the canalis tarsi through a twisting of the fibers of the interosseous ligament.52
He clearly demonstrated this rotation on his diagram (Fig. 10.69
Figure 10.65 (A) A convex male surface oriented transversely generates the motion of flexion (F) and extension (E). (B) A convex male surface oriented longitudinally generates the motion of pronation (P) and supination (S). (C) A convex male surface oriented obliquely—as indicated—generates a combination of pronation-extension (PE) and supination-flexion (SF).
The fibers of the talocalcaneal interosseous ligament are oriented upward, medially, and anteroposteriorly. The lateral fibers are longer and have more excursion laterally, whereas the shorter fibers on the inner side have less excursion. The cervical ligament originates on the calcaneal surface of the sinus tarsi and is oriented upward, anteriorly, and medially to insert on the talar neck. This arrangement of the ligaments promotes—as qualified by Huson—a “swinging motion” with a center of movement located along the short medial fibers of the ligament of the canalis tarsi.8
The cervical ligament remains tight in both exorotation (valgus) and endorotation (varus) of the heel. The
talocalcaneal interosseous ligament of the canalis tarsi and the cervical ligament may be considered as cruciate ligaments of the subtalar joint, as determined by their opposite orientation. The cervical ligaments and the calcaneofibular ligament have an approximate similar orientation.
Figure 10.66 (A) Valgus of the heel: The calcaneus being held fixed, the talus moves in flexion-supination-adduction. The lateral process of the talus is low and strikes Gissane’s angle of the calcaneus. If the talus is held in neutral, then the calcaneus is in extension-pronation-abduction. (B) Varus of the heel: The calcaneus being held fixed, the talus moves in extension-pronation-abduction. The lateral process of the talus is high in position in the sinus tarsi. If the talus is held in neutral, then the calcaneus is in flexion-supination-adduction.
The bony stability of the subtalar joint or close-pack position is achieved with exorotation or valgus of the calcaneus. In this position there is maximum contact and near congruous fit at the posterior talocalcaneal joint. The talar lateral process descends and advances on the posterior calcaneal surface and the solid talar wedge or male V fits into the female V of the calcaneal surface. With endorotation or varus of the calcaneus, the sustentaculum talus moves toward the posteromedial tubercle of the talus and considerably narrows the medial opening of the canalis tarsi.
The talar lateral process is now dorsal on the corresponding calcaneal surface. This anatomic relationship laterally allows the clinician to recognize the valgus or varus position of the hindfoot roentgenographically. The cervical ligament and the inferior extensor retinaculum limit the endorotation of the calcaneus.54
The talocalcaneal interosseous ligament of the canalis tarsi remains tight during the endo- and exorctation of the calcaneus.8
Smith, however, considers the talocalcaneal ligament of the canalis tarsi as limiting the exorotation or eversion of the calcaneus.
Tochigi et al.55
analyzed five fresh frozen cadaver lower extremities (ages 25 to 85 years) for the three-dimensional movement of the talus and calcaneus relative to the tibia under axial loading from 89.8 to 686 N. The induced talar and subtalar motions were triaxial. When the axial load was increased from 9.8 to 686 N, the maximum total ankle rotation averaged 3.5 degrees ± 1.2 degrees with plantar flexion 2.6 degrees ±1.1 degrees, adduction 2.1 degrees ±1.0 degrees, and negligible inversion 0.1 degrees ± 0.7 degrees. In the intact subtalar joint, under axial loading the induced motion was also triaxial. The total subtalar motion averaged 3.2 degrees ± 1.3 degrees, mostly eversion, with dorsiflexion 0.8 degrees ±0.9 degrees and abduction 0.8 degrees ±1.0 degrees.
The ankle rotation did not significantly change after isolated sectioning of the anterior talofibular ligament. After the combined sectioning of the interosseous talocalcalcaneal and anterior talofibular ligaments the maximum ankle joint rotation averaged 5.2 degrees ± 1 degrees, whereas plantar flexion averaged 4.0 degrees ± 0.9 degrees, and adduction 3.3 degrees ±0.8 degrees.
Tochigi et al.56
investigated the load-displacement characteristics of the subtalar joint in six cadaver specimens, using an axial distraction test and a transverse multidirectional drawer test. Cyclical loading (± 60 N) was applied and loaddisplacement responses were collected before and after cutting the interosseous talocalcaneal ligament. The results confirmed the role of the interosseous talocalcaneal ligament in maintaining apposition at the subtalar joint suggesting that interosseous talocalcaneal ligament failure causes inversion instability of the subtalar joint. They also suggested the role of the interosseous talocalcaneal ligament in stabilizing the subtalar joint against drawer forces applied to the calcaneus from lateral to medial. The authors suggested examining a patient with possible subtalar instability with a drawer force applied “along the preferential axis roughly from the posterior aspect of the fibula to the central region of the medial malleolus.”56
Fujii et al.57
assessed the mechanical characteristics of the ankle-hindfoot complex in 13 cadaver specimens mounted in a testing apparatus. A constant rotational force in the form of inversion-eversion, internal-external rotation was applied throughout the entire range of the ankle sagittal plane and the resulting calcaneo-tibial motion was measured.
With inversion force applied, the calcaneotibial inversion was greatest in maximal plantar flexion (mean 22.1 degrees ± 6 degrees) and gradually decreased with dorsiflexion. With eversion force applied, the calcaneotibial eversion gradually increased with increasing dorsiflexion to 12.7 degrees ± 7.4
degrees. With internal rotation force applied, calcaneotibial rotation increased from plantar flexion to neutral ankle position. With external rotation force applied, calcaneotibial external rotation from neutral to maximal dorsiflexion increased. Their conclusion was that “the ankle is less stable in plantarflexion when inversion and internal rotation forces are applied” and “the ankle was less stable in dorsiflexion when eversion and external rotational forces were applied.”
Figure 10.67 (A) Inclination angle of the posterior calcaneal surface. (B) Boehler’s angle.
Kjaersgaard-Andersen and colleagues determined experimentally the stabilizing effect of the ligamentous structures in the sinus and canalis tarsi at the subtalar joint.58
In 20 cadaveric specimens, the total range of motion was measured at the subtalar joint and the subtalar-ankle joint complex.
A continuous movement was obtained by applying a constant torque and moment of 1.5 N · m. This resulted in a force transmission to the subtalar joint of 10 N (or 1.02 kg). The movement was recorded and computer analyzed in three planes. The study was conducted first in the intact specimens. In 10 specimens the motion was assessed after transection of the cervical ligament. In another 10 specimens the motion was assessed after transection of the talocalcaneal interosseous ligament of the canalis tarsi.
In the first 10 specimens, the median movement at the talocalcaneal joint was 15.5 degrees in neutral. This small range of motion may be explained by the fact that the applied force was minimal (1 kg) and the specimens may have been obtained from an older age group. Lang and Wachsmuth have demonstrated indeed that with aging the field of motion of the foot contracts in the transverse segment.9
After transection of the cervical ligament, the increase of motion was as follows:
In the horizontal plane (internal-external rotation): 10% In the frontal plane (pronation-supination): 14%. This motion
is termed adduction-abduction by the authors. In the sagittal plane (dorsiflexion-plantar flexion): 20%.
In the second group of 10 specimens, the median movement at the talocalcaneal joint with an intact ligament was 11.9 degrees in neutral.
After transection of the talocalcaneal ligament of the canalis tarsi, the increase in the range of motion was as follows:
In the horizontal plane (internal-external rotation): 21% In the frontal plane (pronation-supination): 16% In the sagittal plane (dorsiflexion-plantar flexion): 57%, with 43% of the increase in dorsiflexion and 14% in plantar flexion.
Figure 10.68 Declination angle of the posterior talar articular surface.
Figure 10.69 The rotational motion of the talus over the calcaneus. The arrows indicate the direction of rotation in a “tourniquet” fashion around the axis of rotation X located in the canalis tarsi. (A, talus; C, calcaneus; a, posterior calcaneal articular surface, cone shaped; b, sustentacular surface; c, anterior calcaneal surface.) (Farabeuf LH. Precis de Manuel Opératoire. Paris: Maisson; 1889:818.)
This study is suggestive of the more important stabilizing role of the talocalcaneal ligament of the canalis tarsi limiting the exorotation or valgus of the calcaneus.
The stabilizing role of the ankle ligaments in subtalar motion was also investigated by Kjaersgaard-Andersen and colleagues in two different studies.59
The role of the tibiocalcaneal fascicle of the deltoid ligament was analyzed in ten cadaveric ankle-feet.59
A torque or moment of 1.5 N · m was applied with an effective force of 10 N (1 kg) acting on the joint. Data were obtained from continuous movement curves and subjected to computer and statistical analysis. The motion was registered in three planes. After immobilization of the ankle joint with an external fixator, the talocalcaneal motion was assessed before and after transection of ligaments. The external fixator was removed and the total range of motion was assessed again.
The median percentage of increase of motion at the subtalar joint after transection of the tibiocalcaneal fascicle of the deltoid ligament was as follows:
In the horizontal plane (internal-external rotation): 12%, with 10% in external rotation and 2% in internal rotation
In the frontal plane (pronation-supination): 31%, with 30% in pronation and 1% in supination. This motion is termed abduction-adduction by the authors.
In the sagittal plane (dorsiflexion-plantar flexion): 40%, with 30% plantar flexion and 10% dorsiflexion.
It is apparent that the transection of this ligament results in an increase in plantar flexion, pronation, and external rotation at the talocalcaneal joint.
The motion increased also at the combined tibiotalocalcaneal joint complex, mainly in pronation, external rotation, and plantar flexion, indicating the supportive role of the ligament at the ankle joint also.
Using the same methodology, Kjaersgaard-Andersen and colleagues analyzed the role of the calcaneofibular ligament with regard to the motion at the subtalar joint.60
Ten cadaveric ankle-foot preparations were used. A torque or moment of 1.5 N · m was applied and the mobility of the talocalcaneal and tibiotalocalcaneal joint was assessed on the intact specimens and after sectioning the calcaneofibular ligament.
The motion in the frontal plane or supination (termed adduction by the authors) was assessed at different degrees of dorsiflexion-plantar flexion. After sectioning of the calcaneofibular ligament, the mean increment of supination at the combined tibiotalocalcaneal joint complex was 3 to 7 degrees, increasing from the plantar-flexed position to maximum dorsiflexion (Fig. 10.70
). The mean increment of supination at the subtalar joint was 3.1 to 4.6 degrees, increasing from 5 degrees of plantar flexion to 5 degrees of dorsiflexion (Fig. 10.71
). This study demonstrated the importance of the calcaneofibular ligament in determining the lateral stability of the subtalar joint.
This finding is contrary to that of Cass and coworkers, who detected no influence of the calcaneofibular ligament on subtalar supination (author’s adduction), which remained constant in plantar flexion or dorsiflexion.42
The variability of the orientation of the calcaneofibular ligament, as analyzed by Ruth, may contribute to the explanation
of these functional discrepancies.32
Furthermore, the functional implication of the variable anatomic relationship between the calcaneofibular ligament and the lateral talocalcaneal ligament was investigated by Trouilloud and colleagues in 26 ankles.61
They divided their specimens into three types: A, B, and C. In type A (35%), a lateral talocalcaneal ligament blends with or reinforces intimately the calcaneofibular ligament and diverges from the latter at the talar or at the calcaneal insertion. In type B (23%), a distinct lateral talocalcaneal ligament is present just anterior to the calcaneofibular ligament. In type C (42%), the lateral talocalcaneal ligament is absent.
Figure 10.70 Mean increments of adduction (or supination) at the tibiotalocalcaneal joint complex after section of the calcaneofibular ligament in ten specimens. (Kjaersgaard-Andersen P, Wethelung J-O, Nielsen S. Lateral talocalcaneal instability following section of the calcaneo-fibular ligament: A kinesiologic study. Foot Ankle. 1987;7:358.)
Figure 10.71 Mean increments of adduction (or supination) at the talocalcaneal joint after section of the calcaneofibular ligament in ten specimens. (Kjaersgaard-Andersen P, Wethelung J-O, Nielsen S. Lateral talocalcaneal instability following section of the calcaneo-fibular ligament: A kinesiologic study. Foot Ankle. 1987;7:359.)
The transection of the calcaneofibular ligament in type B did not affect the subtalar or the talocalcaneonavicular motions, whereas in types A and C it affected the subtalar motion, resulting in the author’s interpretation of a talonavicular subluxation.
Martin et al.62
investigated the elongation behavior of calcaneofibular and cervical ligaments during inversion loads in nine cadaver specimens (ages range 63-81 years). Two methods
of inversion assessment were used: manual and roentgenographic. Under inversion load with the calcaneofibular ligament intact the mean elongation of the cervical ligament was 0.58 mm ±0.33 mm by manual measurement and 0.46 mm ± 0.23 mm by x-ray measurement. With the calcaneofibular ligament transected, under inversion load, the elongation of the cervical ligament was 0.88 mm ±0.37 mm by manual measurement and 0.78 mm ±0.37 mm by x-ray measurement. With the transection of the calcaneofibular ligament, the inversion range of motion increased 7.5 degrees ± 2.75 degrees manually and 7.7
degrees ±2.95 degrees by x-ray measurement.