Shin SplintsAnatomy, foot posture and orthoticsBy Nelson Rodriguez De Leon, PTMaster Of Manipulative Physiotherapy by CourseworkID 125479

Introduction

In the medical literature pain presenting along the middle to distal medial border of the tibia, that starts at the beginning of walking or running (jogging), resolves during the activity and presents again after it has been named shin splints, medial periostitis and medial tibial stress syndrome and no agreement has been reached to put an end to this long list of names. Different aetiologies have been proposed, among them the presence of a pronated foot and an abnormal and excessive eccentric contraction of the tibialis posterior muscle. However, none of them have provided a definite answer to the problem and the answer remains elusive.

The aim of this essay will be:

To describe the anatomy and biomechanics of the subtalar joint and posterior compartment of the leg and its implication on the development of shin splints.

To determine if foot posture has an influence in the gait and running patterns and the development of shin splints.

To determine if foot posture can be modified through the use of orthotics devices and how these devices alter the firing of some of the muscles that control the subtalar joint during running (jogging).

Anatomy and Biomechanics of the Subtalar Joint

First of all we will start defining the movements of inversion eversion and supination and pronation regarding the subtalar joint and the ankle. Eversion/inversion are the movements taking place in the frontal plane on an AP axis and moves the calcaneus laterally and medially. Supination is the combination of adduction, inversion and plantarflexion and pronation is the combination of abduction, dorsiflexion and eversion (Norkin and Levangie 2000) (Fig.1).

Fig 1. The movements of pronation and supination. From www.orthogate.com

The subtalar joint complex presents two distinct articulations which are oblique to each other, posteriorly the calcaneus joint surface is convex and the talus concave and anteriorly this disposition is reversed (Perry 1983). Perry (1983), Czernecki (1988) and Sarrafian (1993) give different degrees of tilt and inclination for the subtalar joint quoting the work of Inman and Manter (Table 1) (Fig. 2). The subtalar joint functions as a mittered hinge converting the torque of the foot into external and internal rotation of the tibia when the foot is fixed and viceversa.

Fig 2. The angulation and tilt of the subtalar joint. From www.orthogate.com

Generally speaking, in normal gait the entire lower limb rotates medially during the swing phase and laterally during the stance phase. Prior to heel strike the tibia is internally rotated and transmits the medial rotation to the talus. At heel strike the calcaneus contacts the ground laterally “creating a pronatory movement on the subtalar joint” (Rodgers 1988). As the talus is rotated medially the calcaneus is forced into pronation.

Author Upward Tilt Medial Angulation

Inman(1976)

42 9 degrees 23 11 degrees

Manter(1941)

42 degrees(range 29-47 degrees)

16 degrees(range 8-24 degrees)

Table 1. Degrees of tilt and angulation of the subtalar joint

Generally speaking, in normal gait the entire lower limb rotates medially during the swing phase and laterally during the stance phase. Prior to heel strike the tibia is internally rotated and transmits the medial rotation to the talus. At heel strike the calcaneus contacts the ground laterally “creating a pronatory movement on the subtalar joint” (Rodgers 1988). As the talus is rotated medially the calcaneus is forced into pronation.

Eversion of the calcaneus is initiated at foot strike. At this stage the calcaneus contacts the ground with its lateral aspect thus lateral to the axis of the subtalar joint and because body weight is transmitted to the talus at heelstrike a valgus force is created on the subtalar joint (Perry 1983). The net resultant of this action is eversion of the calcaneus. This eversion is determined by an inferolateral movement of the

anterior facet which, in turn, is going to cause internal rotation of the talus and subsequently of the tibia by the mittered hinge effect (Czernecky 1988, Perry 1983).

The main difference in gait and running (jogging and sprinting) patterns is that during running there is a phase where both feet are off the ground (airborne phase) (Brown and Yavorsky 1987). This has two main implications one being an increase in the ground reaction forces from 70-80% of bodyweight to 275-300% and the second being a shortening of the stance phase from 0.6 sec to 0.2 (Brown and Yavorsky 1987).

Some authors (Donatelli, 1994) implicate tightness of the Achilles tendon as a possible mechanism that can cause abnormal pronation of the foot. They hypothesise that in an overpronated foot a tight gastronecmius has an increased muscle pull that positions the calcaneus into more eversion due to its insertion point being changed from medial to lateral thus changing the line of pull. They also add that limited dorsiflexion impedes the tibia to translate anteriorly to the talus during the stance phase of gait and this is compensated by subtalar joint pronation.

Influence of Foot Posture on Shin Splints

In a study to investigate the correlation between foot posture and the medial tibial stress syndrome (Sommer and Vallentyne, 1995) 25 subjects were recruited, 10 had been diagnosed with MTSS and 15 hadn’t. Of the 10 subjects of the affected group 4 had bilateral MTSS leaving the group with 14 limbs to study against 36 of the control group because the unaffected leg of the control group was included in the control group. Methods to evaluate foot posture were qualitative in nature including forefoot and rearfoot valgus and varus measures and quantitative (standing foot angle). The measurements were studied on its interrater reliability and it found to be good. There was a tendency toward forefoot and rearfoot varus in the cases without MTSS and a combined varus tendency toward hindfoot and forefoot varus was more common in the MTSS group. The SFA was found to be statistically significant showing a tendency toward a lower SFA in the MTSS group. Part of the control subjects used for this study was the non-affected limbs. This could have biased the study due to the fact that they are assuming that the pes planus can be the cause of shin splints and clinically we more often than not we see that the individuals have the same arch characteristics in both feet. It would have been much better to use a control group composed of normal non-injured subjects or non-injured runners. Also even though the interrater reliability was studied and found to be good the intrarater reliability was not and this has been found to be poor for physiotherapist measuring subtalar joint mobility (Elveru, Rothstein and Lamb, 1988).

To determine the relation between selected biomechanical and anthropometric variables and shin splints (Messier and Piatalla 1988) a group of 17 runners diagnosed as having shin splints and a control group consisting of 19 non-injured runners were evaluated. Anthropometric variables included dorsiflexion range of motion and biomechanical variables included total rearfoot movement, maximum pronation and maximum pronation velocity measured in a gait analysis laboratory. They found a trend that was not statistically significant towards a decrease in range of motion in the shin splints group and a significant correlation between maximum pronation and maximum pronation velocity in the shin splint group. No evidence of reliability or

validity is given for the anthropometric measures used in the study. The biomechanical assessment was performed using video analysis. However, no details are given regarding to the position of the camera or the placement of the markers. The type of shoes used by the subjects was not standardised. Shoes have been shown to alter foot and ankle biomechanics and this can have an influence biasing the results of the movement analysis (Nigg and Segesser, 1992).

Three groups of athletes were studied in terms of their foot and ankle and lower leg posture and dynamic and static kinematics (Vitassallo and Kvist 1983). Subjects were allocated into three groups a control group (n=13) consisting of subjects without history or present symptoms of shin splints and two experimental groups: a “bad” shin splints group (n=13) which had frequent and long lasting pain in the shin and a “slight” shin splint group (n=22) which had occasional shin pain lasting between 2 and 4 weeks. They measured the subtalar passive joint mobility and the position of the subtalar joint. They found that both groups of athletes with shin splints had an increased range of motion, which was statistically significant. The standing foot posture values were greater in the shin splint group although not statistically significant. The shin splint group also showed increased pronation during treadmill running just before touch down and during full contact than the control group, which was statistically significant. The subtalar joint mobility was assessed using a method that is not reliable (Elveru et al., 1988). The position of the subtalar joint in normal standing also was measured from angles obtained by photographs but no further detail is given on the use of this method. It’s is not stated if the video analysis used was 2D or 3-D which can have significant differences in the results (Engsberg and Andrews, 1987). The groups were not homogeneus particularly regarding the sample size.

To correlate foot structure and kinematics of the rearfoot (Nawoczenski, Saltzman and Cook 1998) 20 recreational runners that had sought consultation for a diversity of musculoskeletal injuries in the lower limb were studied. They divided the subjects into two groups classified as high and low rearfoot following radiographic criteria consisting in the measurement of standard lateral and AP radiographs which has been proven to have high reliability to classify foot by its structure according to the authors. Motion analysis was carried out while the subjects ran in a treadmill for a period of two minutes after a 5 minute warm-up period and consisted in the measurement of calcaneal inversion and eversion and the tibial medial and lateral rotation during the stance phase of running. They found that the high rearfoot group had greater magnitudes of tibial lateral and medial rotation and the low rearfoot group had greater magnitude of calcaneal inversion and eversion. However, in the period from heel contact to maximum pronation both groups showed similar calcaneal inversion and eversion magnitudes questioning the clinical notion that subjects with high arches have hipomobile feet and and subjects with low arches have hipermobile feet. They concluded that an imbalance between tibial rotation and calcaneal movement maybe the culprit for the diverse pathologies seen in runners. It must be noted that all the subjects in the study wore sandals, which make the heel to be free of any restrictions. Results could have been biased by the use of this method. This method was justified to make the placement of skin markers easier. However a method similar to that of Genova and Gross (Genova and Gross, 2000) could have been used.

Even though all the studies reviewed above have several threats to internal and external validity and the methods vary in a significant way there seem to be a consensus in that the presence of pronated foot and lack of dorsal flexion are consistent factors in the development of shin splints (Table 2). A possible explanation could be that in the presence of a pronated foot the tibialis posterior has to contract more eccentrically to decelerate the foot to avoid collapse of the medial structures. This deceleration maybe accompanied by an increased pulling of the tibialis posterior tendon on the medial border of the tibia creating a constant microtrauma on the point of insertion that ends developing an overuse injury. Another possible explanation is that a shortening of the soleus muscle increases the valgus vector over an everted calcaneum maintaining the abnormal position of the foot on the gait cycle and diminishing the shock absorption capabilities of the lower limb. None of the studies reviewed took in consideration the tibial rotations and its coupling mechanics with the calcaneum. However, further research is needed to implicate this mechanism in the development of shin splints.

Author Pathology Measurement Method ResultsSommer andVallentine (1995)

MTSS Rear and Forefoot Varus and Valgus (Goniometry)Standing Foot Angle (SFA)(Radiographic)

SFA was greater in MTSS

MTSS had a tendency toward rear and forefootVarus (not statistically significant)

Vitassallo andKvist (1983)

Shin Splints Subtalar Passive ROM(Goniometric)Video Analysis(Not Specified 2D or 3D)

Shin splints subjects had increase subtalar ROM

Shin splints subjects had increase pronation in early stance

Nawocszenski,Saltzman andCook (1998)

Lower limbMusculoskeletal Injuries (Non-Specific)

Lateral and AP ViewsFor planus and cavus foot (Radiographic)3-D Video Analysis

Increase calcaneal inversion and eversion in low rearfoot group (pes planus)

Messier and Piatalla(1988)

Shin splints Anthropometric measuresVideo Analysis

Subjects with shin splintsHad decrease dorsiflexionAnd lower pronation velocities

Table 2. Summary of postural findings and Shin Splints

Anatomy of the posterior compartment of the leg

In a dissection study of ten cadaveric legs using an incision running just posterior to the medial border of the tibia the distance were the tibialis posterior muscle crosses the flexor digitorum longus muscle starting from the medial malleolus was measured (Saxena, O’Brien and Bunce, 1990). A second measurement was then done to note the most distal attachment of the tibialis posterior. They found that the mean distance of insertion of the most distal point of the tibialis posterior muscle was 7.77 cm. and the distance were it crossed the flexor digitorum muscle was 8.16 cm. They concluded that the insertion point of the tibialis posterior muscle runs more distally than what previous studies stated, thus possibly implicating the tibialis posterior muscle

insertion as a possible cause of shin splints. They didn’t find any attachments of the soleus muscle on the lower third of the leg (Fig. 3).

Fig 3 Proximal insertion of the TP, FDL and FHL. From www.vesalius.com

In a study to determine the origin site of the soleus, flexor digitorum longus, tibialis posterior muscles and deep crural fascia (Beck and Osternig 1994) the legs of 50 cadaveric specimens were dissected (Beck and Osternig, 1994). To quantify the site of attachments they divided the tibia bone on six equal parts along the longitudinal axis of the tibia. They found that the soleus and the flexor digitorum longus were the only muscles that possessed attachments to the medial border of the tibia specifically at 35 and 48% from the medial malleolus, respectively. The crural fascia had attachments along the medial border of the tibia in all specimens. No insertion of the tibialis posterior muscle was found in the medial border of the tibia. Regarding the study by Saxena et al. (see above) the authors state: “There is a disparity between the findings of the present study and those of Saxena et al. who concluded that the tibialis posterior consistently arises from the distal third of the tibia. An explanation for this disparity may be that the measurement of the inferiormost attaching fibers of the tibialis posterior can be complicated by the configuration of the muscle itself. Sometimes a proportion of the inferior fibers of the tibialis posterior arise from a very lateral position on the tibia… In other words, the inferior fibers of the tibialis posterior muscle often attach in the distal half of the leg; however the attachment site of the fibbers is normally the interosseus membrane not the tibia” (Fig 2).

Fig. 4 Proximal and distal insertions of the soleus. From www.vesalius.com

There is a tendency in the literature to implicate foot posture, particularly pronation, in the development of shin splints. Clinically, it can be assumed that in the pronated

foot the invertor muscles of the ankle specially the tibialis posterior have to excessively eccentrically contract to decelerate pronation to avoid a collapse of the structures of the foot. This causes an increased pull on the superior insertion of the tibialis posterior on the tibia that can lead to periosteal inflammation. Perry (1983) states that the soleus muscle has twice the torque of the tibialis posterior for inversion. However extrapolating this fact to Donatelli’s hypothesis of the change in the line of pull of the Achilles tendon in the pronated foot it can be assumed that the tibialis posterior must contract in excess to decelerate the eversion movement created for the subtalar joint. However, the study by Beck and Osternig denies this fact stating that the tibialis muscle does not insert along the medial border of the tibia.

The study by Beck and and Osternig however, can partially support the hypothesis proposed by Donatelli mentioned above. The gastronecmius and soleus muscles attatch to the calcaneus by a common tendon. If the gastronecmius causes an increased pull to take the subtalar joint into eversion one can expect that by having the same line of pull the soleus would also be responsible for this over pronation.

Foot posture, orthotics and running biomechanics

Different studies have proved that foot orthotics have an effect on calcaneal eversion during the different phases of gait and running. However, very little has been done on how the muscle recruitment changes because of the use of orthotics (Eng and Pierynowski 1994; Genova and Gross 2000; Nawocszenski et al 1995).

Twelve recreational runners were study to determine the effects of foot orthoses in the electromyographic activity of selected muscle groups on the stance phase of running in a treadmill (Nawoczenski and Ludewig, 1999). All subjects had a history of lower limb injuries. The results indicate an increase in EMG activity for the tibialis anterior

Fig. 5 An everted calcaneus. Note the lateral position of the subtalar joint with respect to the ankle joint and how the insertion of the Achilles tendon goes from medial to lateral. From www.vesalius.com

muscle (37.5%) and a decrease of EMG activity for the biceps femoris muscle (-11.1%) that were statistically significant. A decrease in the medial gastronecmius was also noted although it was not statistically significant. The authors hypothesised that an increase in tibialis anterior EMG could be due to the orthotics placing this muscle in a mechanical advantage to resupinate the foot. The decrease in EMG activity of the biceps femoris may be due to the diminished need for this muscle to control the internal rotation of the tibia while wearing orthotics. This study supports the hypothesis that in the pronated foot the gastronecmius muscle can be overactive

thus inducing more pronation (Fig. 5). When an orthotic is placed and the subtalar joint position is “normalised” the outcome is a reduced activity in the gastronecmius muscle. However, further study is needed in this area to generalise the results.

Conclusions

There is no definite agreement on the exact anatomical insertion sites of the muscles of the posterior compartment of the leg. The studies reviewed contradict each other adding little to the clear understanding of the anatomical facts regarding the pathology. Further research is needed to clarify this question. There is tendency towards implicating pronated or planovalgus feet type and lack of dorsiflexion range of motion as aetiological factors in the development of shin splints and running pathomechanics. However, all the studies reviewed present several threats to internal and external validity, which can bias the results obtained. Specially, there is a lack of reliability in the measurement of the subtalar joint motion, which can be an important clinical tool for the design of foot orthotics. Furthermore there is a need for more research involving 3-D analysis in running regarding subtalar joint motion. Recent studies using this technique have shown results that contradict the common clinical notion of subtalar joint pronation and its correlation with foot characteristics adding new insight in the movement coupling between the tibia and the subtalar joint. Orthotics devices seem to be an effective way of altering subtalar joint mechanics in the pronated foot by reducing calcaneal eversion during the stance phase and tibial internal rotation. However there is no agreement on how to construct such devices or which postural parameters must be meet by the patient due to the lack of a gold standard in the measurement of the subtalar joint position.

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