Dissection of the Subtalar Joint
Understanding anatomy and function of the sublar joint and its ligaments will allow PTs to better assess lower quarter and spinal dysfunctions
By Jeffrey Carson, PT
The subtalar joint (STJ) has a complex osseous and ligamentous structure. The ligaments of the STJ function to maintain articular congruency and check excessive triplanar motion. When these ligaments are injured or become lax, excessive motion may develop, which may have an adverse effect on the STJ and distant joints. An understanding of the mechanics of the subtalar joint is essential for physical therapists to realize the origin of many lower quarter and even spinal dysfunctions. Similarly, many lower quarter dysfunctions can affect the capsuloligamentous integrity of the STJ with resultant STJ dysfunction.
Therapists have a bag of tricks that can help normalize STJ function (orthoses, taping, mobilization and strength training); however, the STJ cannot be assessed or optimally treated without understanding its triplanar motion, which is dictated by extrinsic forces, articular shape and its capsuloligamentous structure. The ligaments of STJ, specifically of the sinus tarsi, have a key role in guiding and checking STJ motion, and they will be the focus of this discussion.
Dissection of the rear and midfoot unveils a complex architectural masterpiece. The foot accepts five times body weight when it is asked to run, yet it often functions well throughout life without contemplating a total arthroplasty.
The foot is a system of intercalated bones. Some joints have to deal with shear forces placed on them by two joint muscles; flexor hallucis longus and peroneus longus are seven-joint muscles! The foot is the only area in the body that has to withstand second class lever forces. These two factors introduce tremendous shear forces across the intercalated segments. It is no wonder that the foot has a very complex ligamentous structure.
Lateral or inversion ankle sprains are the most common athletic injury.1 Injuries of the lateral ligaments have been correlated with abnormalities of the sinus tarsi ligaments.2-4 Breitensheher found that 39 percent of patients with chronic lateral ankle ligament tears have abnormal MRI findings in the sinus tarsi.4 Kjaersgaard-Anderson has correlated lateral ligamentous sprains with abnormalities of the contents of the sinus tarsi.5 The roles of the subtalar ligaments are difficult to predict in part due to the complexity of triplanar motion.
Within the canal, there are five ligaments with definite orientation and function. They are all clearly extracapsular and triplanar. Manter described the triplanar motions of the ankle.6 Logically, ligaments that check and guide movement about a triplanar axis must be triplanar themselves. Beltram demonstrates this with MRI studies.3
Ligament Function Beltram
The cervical ligament (external talocalcaneal) runs at 45 degrees to the vertical and from anterior and superomedial to inferolateral and posterior, but its orientation does change with subtalar joint position2, 7-9 (Figs. 1 and 2). Shear stated that the cervical ligament helps to prevent rearfoot valgus.10 On the other hand, Smith and Cahill are in agreement that the cervical ligament limits supination,8, 9 as is this author based on my own dissections.
Sectioning of the cervical ligament in the cadaveric subtalar joint resulted in improvements in passive inversion but not eversion range of motion. Furthermore, 3D renderings of the calcaneus (Fig. 2) suggest that the cervical ligament should become taught with supination. It is difficult to envisage simultaneous motion in three planes, but it must be remembered that supination is much different from inversion.
The cervical ligament is so far away from the STJ axis that it clearly will be under more strain as the STJ supinates. All three plane motions contribute to increasing tension in the ligament with supination. In Figure 2, it can be seen as the calcaneus spins on its axis, it adducts, plantar flexes and inverts. Since motion is relative between any two joint surfaces, one might be considered stationary.
Figures 1 and 2 consider that the talus is held stationary above. This is quite different from what actually happens in vivo. In vivo, talar rotation is driven by tibial rotation, while calcaneal rotation is driven mainly by muscle and ground reaction forces. Nevertheless, relative motion between the two surfaces remains on the same axis. At heel strike, in the coronal plane, the calcaneus is forced to land slightly inverted due to the medial plantar calcaneal tubercle being much larger than the lateral tubercle. It is known that pronation follows heel strike, but the motion is relative. It is the talus that internally rotates (supinates on the STJ axis) on the calcaneus while the calcaneus is actually moving in the opposite direction with the foot (pronation).
This would be similar, though not equivalent, to saying that with left rotation at L4-5, L5 rotates to the right on L4. The difference in the two systems is that L5 is simultaneously rotating to the left on S1, while the calcaneus has no inferior member. This "counter rotation" is necessary for normal subtalar and midfoot arthrokinematics and it could be partially abolished with rigid orthoses with a deep heel seat or a cuboid block. This may limit calcaneal eversion and STJ pronation, which may not always be the desired result. A possible adverse effect on the patient would be decreased shock absorption, which could lead to patellofemoral, hip and lumbopelvic dysfunction.
The Interosseous Ligament
The interosseous ligament also runs its course from superomedial to inferolateral but it runs parallel to the canal it lies within (Fig. 3). Again, it needs to be remembered since both bones are moving independently, the orientation of the interosseous ligaments will change when the ankle is moved into varus or valgus (Figs. 1 and 2). Shear stated that the interosseous ligament becomes taut with supination and lax with pronation, without explanation or reference.10
There is still some controversy in the literature as to the exact role of the interosseous and cervical ligaments. Cahill stated that the interosseous ligament has a stabilizing role and does not limit either motion.9 Smith and Donatelli stated that it limits pronation.8, 12 Dissec-tion findings also agreed with Cahill that the interosseous ligament serves to maintain articular congruency. However, Cahill possibly makes a faulty supposition. He stated that the subtalar axis may go through the interosseous ligament and in this case the ligament would not particularly resist end range pronation or supination. This logic holds up in two dimensions, but important rotatory ligaments like the cruciates at the knee and the interosseous and cervical ligament at the STJ have a three-dimensional relationship with their 3D axis (Figs. 1 and 2).
Ligaments that control and create (coupled with external forces) rotatory motion have the least mechanical disadvantage when they are near the axis of the joint. They are less susceptible to over-strain when they are close to the axis. Muscles (like peroneus tertius), have more mechanical advantage when they are further away from the axis that they act on. Figure 1 depicts the STJ axis almost running through the interosseous (axial12) ligament. However, it is clear that the ligament is not parallel to the axis. Possibly it gets pierced in the frontal plane (this would simply mean it would not develop strain with inversion or eversion), but pronation also involves calcaneal dorsiflexion and abduction (Fig. 1).
STJ pronation leads to a taut, more vertical interosseous ligament. One might envisage this by observing that the height of the sinus increases with pronation and decreases with supination. Therefore, Smith's 1958 conclusion that the interosseous ligament limits pronation would seem most accurate.8 In order for a 3D ligament like the interosseous not to develop strain or slacken with movement about the STJ axis, it would have to be pierced through its long axis. Fig. 1 (right) depicts the tension that develops in the interosseous as the STJ pronates.
The key ligaments of the subtalar joint are the cervical and the interosseous ligaments. They are perhaps analogous to the cruciate ligaments of the knee. They function to maintain congruency of both facets. With closed chain lower extremity extension, tension in the cervical ligament locks the calcaneus and talus into one rigid mass. The talonavicular and the calcaneocuboid joints (the midtarsal joint) become locked as their axis become antiparallel. Now the hind and midfoot are locked into a rigid mass ready for push off. Gravity takes care of unwinding into pronation. Pronation is checked by the interosseous ligament. Many local and distant dysfunctions may result when this screwing and unscrewing is not normal. The therapist will gain insight into evaluation and treatment of lower quarter dysfunction by understanding these two functions. The accompanying case studies help to illustrate this point.
1. Mann, R. (1993). Surgery of the foot and ankle, Sixth edition, volume 2. St. Louis: Mosby, pp. 1121-1123.
2. Klein, A.S. (1993, January). MR imaging of the tarsal sinus and canal. Radiology, 186: 230-234.
3. Beltram, J. (1990). Ligaments of the lateral aspect of the ankle and sinus tarsi. Radiology, 177: 455-458.
4. Breitenseher, M.J. (1997, March). MRI of the sinus tarsi in acute ankle sprain injuries. Journal of Computerized Assistive Tomography, 21(2): 274-279.
5. Kjaersgaard-Anderson, P. The stabilizing effect of the lateral ligamentous structures in the sinus and canalis tarsi on movement in the hindfoot: An experimental study. American Journal of Sports Medicine, 16: 512-516.
6. Manter, JT. (1941). Movements of the subtalar and transverse tarsal joints. Anat. Rec, 80: 397.
7. Sarafian, SK. (1993). Anatomy of the foot and ankle, descriptive, topographic, functional., second edition. Philadel-phia: J.B. Lipincott Co. pp. 185-199.
8. Smith, J.W. (1958). The ligamentous structure in the canalis and sinus tarsi. Journal of Anatomy, Vol. 92, Part 4.
9. Cahill, D.R. (1965). The anatomical record, Vol. 153. Philadelphia: Winston Institute of Anatomy and Biology, pp. 1-18.
10. Shear, S.M. (1993, July). Sinus tarsi syndrome: The importance of biomechanically based evolution and treatment. Archives of Physical Medicine and Rehabilitation, 74: 777-781.
11. Giorgini, R.J. (1990, April). Sinus tarsi syndrome in a patient with talipes equinovarus. Journal of the American Podiatric Association, 80(4): 212-222.
12. Donetelli, R.A. (1996). The biomechanics of the foot and ankle. Philadelphia: F.A. Davis Co., p. 19.
Jeff Carson is a certified manual therapist and clinical coordinator of STAR (Sports Treatment and Rehabilitation), Palm Coast of Memorial Health Systems, Ormond Beach, FL.
F.P. was a 36-year-old Caucasian female who sustained a C4 cervical fracture and a comminuted right calcaneal fracture with subsequent open reduction and internal fixation in a high speed head-on collision. She was stabilized with halo fixation. Initially, she had 0 degrees to 36 degrees of talocrural plantarflexion with no measurable subtalar inversion or eversion. She had 3-/5 dorsiflexor and plantar flexor strength. She had a severely hypomobile talonavicular joint and moderately hypomobile calcaneocuboid joint. There was minimal inflammation and edema at the medial first metatarsal phalangeal (MTP) joint.
X-ray film revealed a good joint space at the subtalar joint (STJ). She was able to walk without an assistive device, although gait was antalgic with extra external rotation of the lower extremity throughout stance phase. She was unable descend stairs with alternating steps. She had 45 degrees of MTP extension with a muscle end feel. She complained of 8/10 pain in the right ankle, heel and great toe. As her walking tolerance began to improve, she experienced increasing right MTP joint pain, anterior talocrural joint pain, inferior heel pain and right-sided low back pain.
Mobilization of the STJ was not possible. It had an immediate hard end feel in all directions. The tight intrinsics were stretched with Muscle Energy techniques (contract relax) and the hallux was mobilized. Mobilizations cosisted of grade-4 posterior talar glides, anterior mortice glides (weight bearing), anterior glides of the first proximal phalanx and positional distraction of the lumbar spine. She was asked to wear sneakers with a thick midsole, and to perform strength and conditioning ex-ercises. She was discharged at nine weeks of therapy.
F.P. she had regained enough MTP extension (71 degrees to 85 degrees is recommended for normal running) to run a few feet. She regained 15 degrees of passive dorsiflexion. She was still unable to descend stairs with alternating steps. Minimal external rotation of the foot persisted during gait. She did not complain of low back pain. She was able to return to light duty work as a nurse.
X-ray film prior to discharge confirmed suspicions of talocalcaneal coalition. It can be learned from this case that a hypomobile subtalar joint will put more stress on the neighboring and distant structures.
The increased heel pain was likely due to extra friction on the fat pad due to the shear from the calcaneus (normally much of this internal rotation shear is absorbed by the STJ during stance). Without full supination and a hypomobile midtarsal joint, the foot intrinsics were passively insufficient creating the MTP hypomobility. The anterior talocrural joint pain is almost always a given with mobilization after prolonged relative immobilization of the ankle. The tightened mortice was unable to accommodate the wider anterior talar dome. Insufficient length of the STJ ligaments may have a similar effect as the fusion on the STJ and surrounding articulations. With the STJ not absorbing the normal amount of shock, knee, hip and low back problems often develop (Gray, G. (July 1996). The relationship of low back pain to the foot. Biomechanics.)
P.T. was a 29-year-old Caucasian female aerobics instructor and casual runner who experienced midfoot pain during a year's time. She had also experienced intermittent bouts of knee and back pain throughout the past year. She had to discontinue running and began to experience pain with walking. She experienced relief only when off of her feet.
Standing, P.T. had apparent internal femoral torsion, mild genu valgum, grade 3 hyperpronation and a "too many toes sign" bilaterally. She had a positive navicular drop test bilaterally; 9 degrees and 10 degrees of eversion on the left and right respectively; 3 degrees of hindfoot varus with the STJ placed in neutral. During gait, she would push off a pronated foot bilaterally.
Her nonweight-bearing exam revealed good external rotation mobility at the hips, negative Craig's tests, excessive subtalar inversion (46 degrees and 49 degrees, left and right respectively) and eversion (17 degrees and 18 degrees, left and right respectively), apparent forefoot varus (10 degrees bilaterally) in prone with excessive midtarsal joint mobility. She had 10 degree hallux abductovalgus deformities bilaterally.
No X-ray studies were ordered.
The plan of treatment was strengthening of her ankle inverters and the intrinsic musculature of the foot and a trial of orthotic devices. It was felt that there was good potential for controlling her symptoms if some of the STJ hypermobility could be stabilized.
STJ neutral casts were taken to fabricate semirigid orthoses. Six degree varus posts to the forefoot and 5-degree posts were added to the hindfoot bilaterally. She was given strengthening exercises for her ankle inverters and foot intrinsics. The orthoses were added to her running shoes.
P.T. immediately experienced no further pain while resuming her normal running and aerobics schedule. Standing exam revealed significant correction of her apparent structural problems observed at the hip and knee above. Follow-up two months later revealed continued relief but only with orthotics use.
Immediate improvement of the pa-tient's symptoms are not uncommon with dysfunctions of hypermobility. Especially when the symptoms are only produced with running or jumping, where forces upwards of five times body weight may result at the medial longitudinal arch. The orthoses serve to prevent the lax STJ and midtarsal joint from collapsing too far away from STJ neutral.
This case demonstrates how simply pathological motion can sometimes be controlled (in this case with orthotics). It also illustrates how STJ hypermobility (commonly capsuloligamentous laxity) can have an adverse effect on the alignment of the entire lower quarter.