DJD advice title

Big Toe Pain – Diagnosing 1st MTP Joint DJD

Big toe joint pain is a common complaint seen in the clinic. Most pain arises from the 1st metatarsophalangeal (MTP) joint structures directly, although other sources of pain within this area, should also be considered. These include pain originating from the sesamoids, hallux flexor tendons, or the interphalangeal joint.

 

Symptoms and motion

Symptoms arising from the 1st MTP joint can develop from inflammatory diseases (although they less commonly affect the 1st MTP joint) as well as biochemical causes, such as gout. However, symptoms at this joint usually have origins within abnormal stresses inside the MTP joint that cause damage within the cartilage and subchondral bone beneath. Excessive or poorly directed stresses result in degenerative joint disease (DJD) as a result of the destructive wear that damages the integrity of the 1st MTP joint. This process is usually called osteoarthritis (OA). However, it is more appropriately called osteoarthrosis, as inflammation only has a secondary role compared to the mechanical wear and tear processes. The 1st MTP joint is the joint most commonly affected by OA reported in the foot (Roddy and Menz, 2018).

While the healthy anticipated range of hallux motion can vary from person to person, a hallux extension range of motion around the 1st metatarsal head of approximately 75º (but 65º from the ground) has been historically suggested as the necessary range used during heel lift and terminal stance (Root et al, 1977 pp.57-58). Further research has made this questionable. Passive non-weight bearing ranges have been reported to be around 75º dorsiflexion (Frimenko, et al., 2012). However, a range of 40-65º has been reported to be adequate for effective ambulation (Frimenko et al., 2012; Halstead et al., 2005; Nawoczenski, 1999; Nawoczenski & Ludewig, 2004).

 

MTP joint articular degeneration

The pathomechanics of DJD lie within the biomechanical dysfunction of articular cartilage. Once the mechanical properties of cartilage are compromised, persistent cycles of cartilage damage start as a consequence of either insufficient or excessive joint extension (Chan and Sakellariou, 2020; Horwood and Chockalingam, 2023a pp.800-805). These processes cause degenerative joint stiffening, which further increases the internal joint stresses as the heel lifts during acceleration. This is a result of compromising the mechanics of ankle plantarflexion power from the Achilles elastic recoil, as a consequence of removing the normal pivot (fulcrum) point of the foot to permit heel lift (Horwood and Chockalingam, 2023a pp.398-401; pp.801-803).

The ability to rotate the rearfoot off the ground through digital extension at the MTP joints allows elastic recoil power stored within the Achilles to be released just before opposite heel contact. This adds some extra acceleration power directed towards the next step when the swing foot’s heel is around 1cm above the ground, allowing it to fall and make ground contact. The power from the Achilles tendon provides effort (E) that raises the resistance weight of the lower leg (R) from the ground, driving the ankle and knee into flexion about a fulcrum point (F-star) that permits digital extension. The 1st MTP joint normally provides a significant part of this fulcrum point and without it, acceleration power and ideal limb positioning can be compromised (see figure 1).

 

Figure 1. The effort power (E) applied on the posterior heel from the Achilles lifts the heel by pivoting the foot around the medial MTP joints acting as the fulcrum (F). This lifts the resistance (R-spot) of the centre of mass of the leg: By so doing, acceleration power is applied to the centre of mass (CoM) of the head, arms, and trunk (HAT) segments of the body, dropping the swing limb to the floor by around 1 cm. (copyright www.healthystep.co.uk)

 

Nomenclature

1st MTP joint pathology has suffered from inconsistent nomenclature when describing varying clinical presentations, often depending on the reported pain from the patient and the clinically observed range of motion available. The term hallux rigidus is often used and implies the joint is rigid and exhibits no or very little movement. The term hallux limitus is also commonly used and can be considered through a spectrum of a range of motion spreading from sub-optimal motion to the point when the joint becomes rigid. Both these terms have in common the progressive degeneration of the joint. Where rigidus begins and where limitus starts and stops has not been defined (Horwood and Chockalingam, 2023a p.804)..

Horwood and Chockalingam (2023 pp.801-804) identify and discuss issues in terminology, highlighting that early stages of OA change in the 1st MTP joint have been referred to as hallux limitus. However, hallux limitus was originally the term used for hallux flexus. Hallux flexus is the term now adopted to describe a deformity of excess 1st MTP joint plantarflexion with concurrent extension reduction (Camasta, 1996). 

Additionally, hallux limitus should not be confused with the term ‘functional hallux limitus’ which is referred to as a functional loss of extension during gait, rather than an actual loss of motion available (Dananberg, 1986; Horwood and Chockalingam, 2023a p.803). Therefore, it is recommended in describing degenerative clinical presentations, to refer to OA or  DJD of the 1st MTP joint to avoid confusion, thus giving a more precise diagnosis. 

Advanced degenerative changes that relate to a severe loss or absence of hallux extension, and sometimes also plantarflexion, are commonly known as hallux rigidus.

 

Classification

Due to the progressive nature of the pathology, to describe the severity of degeneration, DJD of the 1st MTP has been broken into stages within the literature. A grading system of 1st MTP joint DJD (OA) has been classified by Coughlin and Shurnas (2003) where the term hallux rigidus is used for all stages (Chan and Sakellariou, 2020). However, hallux limitus can be classified to best fit the grades between 0 and 1 (Horwood and Chockalingam, 2023a p.804).

 

 

Table adapted from Coughlin, M. J., & Shurnas, P. S. (2003). Hallux rigidus. Grading and long-term results of operative treatment. The Journal of bone and joint surgery. American volume, 85(11), 2072–2088.

 

 

 

Slidin’, Glidin’ & Rollin’ – 1st MTP joint function

There are many potential causes of pain around the big toe (hallux). This is because the 1st MTP joint has complex anatomy, constructed as it is from several tendons, many ligaments, complex fascial reinforcements, and four bones. Each structure can cause symptoms for many different reasons. However, 1st MTP joint DJD can result from a failure in any of the supportive anatomy, leading to altered biomechanical properties of the articular (hyaline) cartilage.
How 1st MTP joint should work

Big toes (halluces) help stabilise the forefoot on the ground during the stance phase, particularly as the heel lifts off the ground during terminal stance. In this task, the hallux works with all the other smaller digits. However, the two most important joints for acceleration are the 1st and 2nd MTP joints. There are several reasons for this. These include the fact that these joints usually align to the direction of travel of the body over the foot, making them ideal to rotate forward upon (Horwood and Chockalingam, 2023a pp.69-71; 777-780). The 2nd metatarsal is also the most passively stable and maintains the highest functional metatarsal declination angle at heel lift to accelerate from. The 1st metatarsal is highly adaptable in the level of stability it offers. This variable stiffening ability of the 1st metatarsal provides flexibility to adjust its functional declination angle and proximal joint mobility to manage acceleration forces coherently with the 2nd metatarsal. Disruption of these stability/mobility relationships affects the acceleration power derived from the Achilles tendon, as well as the kinematics of MTP joint motion itself (Horwood and Chockalingam, 2023a pp:590-591; 776-789).

Efficient 1st MTP joint function relies upon adaptable stability from proximal joints and muscles along the medial foot to help maintain a declined position for the metatarsal head compared to its base (a declination angle). Metatarsal declination is critical at the heel lift boundary as its angulation greatly influences the ease of digital extension as the foot rotates into plantarflexion at the ankle and midfoot (Horwood and Chockalingam, 2023a pp.593-601). This requires the talonavicular, 1st tarsometatarsal, and cuneonavicular joints to provide plantarflexion motion that couples with 1st MTP joint extension, which is achieved as long as the 1st metatarsal declination angle can reach 20 degrees very early during terminal stance (Phillips et al, 1996).

The 1st MTP joint requires strong plantar muscles and ligaments to stabilise it to resist excessive dorsal, medial (adduction towards the body midline), and eversion motion at its tarsometatarsal joint (Horwood and Chockalingam, 2023a pp. 590-592). Excessive motion risks metatarsal instability under the high peak forces generated during acceleration. Forefoot forces build to a peak at heel lift, an event which causes a rapid rise in ground reaction forces under the three most medial metatarsal heads. Usually, the highest pressure developes under the more stable 2nd and 3rd metatarsal heads (Horwood and Chockalingam, 2023a pp.61-63; 75-77). Ideal MTP joint biomechanics at this time provide stable medial metatarsal heads, with digits held firmly against the ground. As long as the metatarsal head remains stable through interacting forces of body weight and the digital flexor muscles, the MTP joint axis of rotation should move superiorly within each metatarsal head during increasing extension angles. The change in the joint axis location helps to maintain a smooth arc of MTP joint rotation without any joint impingement (Horwood and Chockalingam, 2023 p.604-606). See figure 2, which shows force directions (vectors) demonstrated for a lesser digit MTP joint, but these are also applicable to the 1st MTP..

Figure 2. Copyright www.healthystep.co.uk

As the foot is most prone (flattest) just before heel lift (Hunt et al, 2001), the declination angle of the metatarsal starts to rise from its lowest functional position just as acceleration begins (see figure 3, part A). This explains why controlling the medial metatarsals’ declination angle during late midstance is important (think ‘arch support’), particularly the angle of the potentially more mobile 1st metatarsal. As the functional declination angle increases after heel lift, the digital flexors’ proximal force becomes directed increasingly into the metatarsal head to stabilise it (see figure 3, part B).

Figure 3. Copyright www.healthystep.co.uk

The midfoot and ankle are both plantarflexing in proportion to the digital extension angle in a coupled manner. In this respect, forefoot motion should be considered much like an athlete completing a pole vault (see figure 4). By increasing ankle and midfoot plantarflexion moments and angles, the force from the remaining body weight loaded on the foot becomes more vertically directed downwards, compressing the medial foot bones together toward the metatarsal head. These changing foot segmental angles also start to tighten the plantar fascia to initiate the ‘Windlass effect’, adding extra stability across the foot a little after heel lift (Horwood and Chockalingam, 2023b pp.600-604).

Figure 4. Copyright www.healthystep.co.uk

At the heel lift boundary, power from tibialis posterior and the peroneal muscles continues to stiffen the foot and shifts the peak loads to the medial side of the forefoot by generating midfoot adduction and eversion power (Horwood and Chockalingam, 2023a’s pp.546-548). Thus, tibialis posterior’s and peroneus longus’ activity together are essential for 1st MTP joint stability. In figure 5, the tibialis posterior is represented by the darker-blue arrows of force from its tendon slips and peroneus longus’ tendon as the light-blue force arrows, with the Achilles tendon force in red. During late midstance (A), these muscles work together to create stability through compression across the midfoot and over the important tarsometatarsal joints. At heel lift (B), their power is used to maintain midfoot stability but also to adduct and evert the midfoot, moving peak forefoot forces towards the 1st and 2nd MTP joints.

 

Figure 5. Copyright www,healthystep.co.uk

These mechanisms of stability all work together so that digital extension and foot vault recoil during acceleration improve foot and ankle stability and lower limb kinematics. The correct (yet slightly variable) level of freedom of motion at the MTP joint during each step, helps to guide the proximal phalanx extension end-range towards the extensor groove. The extensor groove is a small indentation or sulcus, found dorsally behind the metatarsal head, (see figure 3 again). Its presence helps avoid the proximal phalanx bumping into the metatarsal neck. Thus, ankle and midfoot plantarflexion improve 1st MTP joint stability under extension. This occurs as the metatarsal head rotates over the sesamoids, providing digital extension while maintaining variable midfoot stability and allowing the foot vault to recoil back into shape (Horwood and Chockalingam, 2023 pp.593-613). This arch recoil helps the mechanical efficiency of gait by helping the lower leg (tibia) to angle correctly for lift off of the foot for the start of swing phase (Welte et al, 2023).

 

 

Jammin’ – 1st MTP joint dysfunction

MTP joint stability is provided by the surrounding soft tissues of the medial foot that increase the functional declination angle of the 1st metatarsal at the appropriate time (Horwood and Chockalingam, 2023a pp.790-796). The MTP joints themselves, offer a significant point of flexibility across the forefoot that can be used to manage the power used to create heel lifts. Failure to provide the correct level of compliance/stiffness across the MTP joints significantly affects the power and energy used/dissipated during acceleration (Cen et al, 2020; Kawakami et al, 2023). Indeed, having points of flexibility too far from or too near to the ankle joint, will potentially create problems for the efficient (safe?) use of acceleration power from the Achilles (Horwood and Chockaingam, 2023a pp.786-789). The positioning of each MTP joint to the line of progression of the foot is therefore important for gait efficiency, while 1st metatarsal mobility/adaptability offers different levels of energy dissipation between steps that the stiffer 2nd and 3rd metatarsals (usually) cannot offer. Figure 6 indicates the relative amounts of mobility offered at each tarsometatarsal joint (variable between individuals), with the central-medial metatarsals offering important forefoot stability. The 1st metatarsal offers highly variable flexibility or stability, depending on surrounding muscular activity and connective tissue stiffness.

Figure 6. Copyright www.healthystep.co.uk

The potential for increased mobility within the 1st ray (1st metatarsal and cuneiform), gives it an ability to control acceleration power and the amount of negative or positive work generated across it and at the 1st MTP joint. This adaptability is achieved by either increasing or decreasing muscle power, which should concurrently alter the functional declination angle of the 1st metatarsal around the heel lift boundary. Creating a higher angle makes digital extension easier, while stiffening the articular soft tissues makes extension harder, requiring greater force to create rotation. Decreasing the functional metatarsal angle makes large extension angles difficult to create, while relaxing and thus de-tensioning the soft tissues across the MTP joint, makes extension easier. Therefore, changing these relationships can set the mobility levels to suit the acceleration power application and digital extension freedoms required.

 

Why Is The 1st MTP joint the most prone to develop DJD?

Other than acute traumatic events that directly damage ligaments, bone, and/or cartilage of a joint, DJD develops within articulations of the lower limb as a result of recurrent poorly directed stresses during gait. Having 1st ray flexibility potential, provides important joint protecting flexibility to manage forces but it also creates some vulnerability if stability is inappropriate or inadequate for any particular step (Horwood and Chockalingam, 2023a pp.800-804). A high metatarsal declination angle is often a significant feature of high cavoid feet, but higher heels on shoes can also induce higher functional declination angles. Steep metatarsal declination angles keep MTP joints at higher extension angles during midstance, in turn positioning the axis of rotation of MTP joints in a more superior location. Unless digital flexor muscles are kept strong, digits such as the hallux, can then extend too far too easily and into their end range of motion during late terminal stance. As a result of this hyperextension, the 1st MTP joint cartilage is prone to becoming split and damaged by being repeatedly impinged between its articular surfaces. See figure 7.

 

Figure 7. Copyright www.healthystep.co.uk

End range extension can also cause injury during acute events, such as a ‘tuft toe’ injury that usually results from a sudden high-force induced 1st MTP joint hyperextension (Chan and Sakellariu, 2020). Because cartilage works mechanically better when moving than when held statically because of its poroviscoelastic properties, long periods of holding the big toe at its end range of extension can also be a source of 1st MTP joint damage. This is often seen in sustained crouched-down postures associated with carpet fitters, plumbers, or other such trades. See figure 8 for acute and sustained hyperextension injuries.

 

Figure 8. Copyright www.healthystep.co.uk

Not only is hyperextension a risk of causing impingement cartilage damage, but so too is hypoextension.

This risk results from the arc of rotation of the hallux being blocked through consistently positioning the axis of MTP joint rotation too inferiorly during terminal stance. If controlled stability of the 1st ray is not maintained from the talonavicular to the medial tarsometatarsal joints, the 1st metatarsal can excessively (hyper) dorsiflex in late midstance and at heel lift under rising medial forefoot ground reaction forces (GRFs). These high GRFs will displace any unstable metatarsals dorsally and increase midfoot dorsiflexion that will together, essentially relatively elevate the affected metatarsals. In functional reality, it is the rearfoot and midfoot that will collapse downwards as a result of this forefoot dorsiflexion. This causes functional metatarsal angles to be lower than they should be at heel lift, with mobile metatarsal like the 1st metatarsal disproportionately affected. With bodyweight tending to move towards the medial forefoot in most peoples’ gait, the 1st metatarsal is highly vulnerable. This is particularly a risk in lower profiled foot vaults (pes planus feet) because they offer lower metatarsal declination angles naturally.

Thus, a foot with a low starting declination angle takes longer for the 1st MTP joint to reach 20° extension during terminal stance, which in turn delays1st cuneonavicular plantarflexion stabilisation (Philips, 1996). In most feet (compared to high vaulted feet) this medial forefoot instability is a risk if the muscles that stabilise the forefoot and create plantarflexion moments upon the midfoot and forefoot, are weak. A low functional metatarsal angle prevents the axis of rotation of the MTP joint gliding freely in a superior direction during terminal stance. This is a mechanical shift in the point of rotation that prevents the arc of hallux rotation from causing the proximal phalanx to go crashing into the dorsal aspect of the metatarsal head. If the point of rotation fails to shift superiorly frequently, there is a risk of dorsal joint impingement damage at both the 1st MTP joint and also the proximal joints of the 1st ray, during terminal stance. See figure 9.

 

 

Figure 9. Copyright www.healthystep.co.uk.

Reduction in the functional declination angle can be prevented by possessing strong tibialis posterior, peroneus longus, and hallux flexor muscles, and effective abductor hallucis activity. This is because any plantarflexion power generated at the 1st tarsometatarsal or cuneonavicular joints increases the rate of rising of the functional 1st metatarsal declination angles during terminal stance. All these important muscles provide moments of plantarflexion force on the medial column of the foot that increase the power of the digital flexor proximal stabilisation force (vector). Thus, the loss of declination angle-raising power from muscles results in failure to stabilise the MTP joint for digital extension control.

Foot vault stability and elastic recoil during terminal stance can also be assisted by the plantar aponeurosis (fascia) if metatarsal declinations become sufficient. At heel lift, the windlass stiffening mechanism is not active because the plantar aponeurosis is still lengthening and the digits are not yet significantly increasing their extension angles on lower metatarsal declination angles. It is only at higher digital extension and metatarsal declination angles, that the foot starts to shorten and the foot vault raises significantly. As this happens, the plantar aponeurosis starts winding around the metatarsal heads. Thus, if digital extension angles remain low due to reduced metatarsal declination angles, the windlass mechanism does not activate effectively, making it harder for the vault to self-stabilise during latter terminal stance. This loss of stability can further compound the impingement of the 1st MTP joint. See figure 9 again.

Often patients with 1st MTP joint DJD develop interphalangeal (IP) joint hyperextension ‘deformities’. Creating hallux IP joint hyperextension after DJD has developed, may offer some relief for those with from ‘blocked’ 1st MTP articular extension forces. Indeed, the extension motion offered by a hyperextended distal phalanx is likely a mechanism of mechanical redundancy (an alternative mechanism) that prevents some MTP joints from developing impingement in the first place. In both situations, it achieves benefits by offering extension motion at the more distal joint, thus reducing the amount of 1st MTP joint extension required during gait (Horwood and Chockalingam, 2023a pp. 597-601).

 

 

Sortin’ – 1st MTP joint Treatment options

The 1st MTP joint may fail in its biomechanical role to supply adaptable stability and appropriate freedom of motion. Failure to provide sufficient and appropriate flexibility can result in degenerative changes within the cartilage and subchondral bone due to recurrent joint impingement. This can be due to either insufficiently restrained hallux dorsiflexion (1st MTP joint hyperextension) or restricted freedom (hypoextension) of the proximal phalanx of the hallux to travel its full arc of rotation without impingement (Horwood and Chockalingam, 2023a pp.800-805). Both hyperextension and hypoextension issues are linked to incorrect setting of the metatarsal declination angle under inappropriate local soft tissue tensions. Be the cause repetitive, poorly directed stresses or acute high stresses on the joint in either hyper- or hypoextension positions, once the 1st MTP joint is afflicted with degenerative joint disease (DJD) its lubrication and compression resistance is lost. This is because cartilage’s whole structure must be intact for its poroelastic properties to work (Horwood and Chockalingam, 2023b pp.282-294).

How to prevent 1st MTP joint DJD

Those with excessively high metatarsal declination angles are at risk of hyperextension impingement. The key to avoiding 1st MTP DJD in such cases is to keep the hallux flexor muscles strong to restrain the freedom to extend the hallux. Healthy Step’s website demonstrates some excellent exercises to strengthen the digital flexor muscles, including our famous foot ball exercise. Using shoes that are stiffer across the MTP joint area is also beneficial in preventing too much digital extension. Some sole flexibility is usually better than none at all but very flexible shoes should be avoided

In those who do not develop sufficient declination angles in their metatarsals during terminal stance, total vault (arch) supporting insoles are a very quick solution. Foot orthoses by rising up under the foot vault, limit the extent to which the metatarsal bases can move downwards. Not only do longitudinal vault supports (‘arch’ being a poor pedal term) of orthoses help, but those with both metatarsal ‘domes’ and transverse plane vault supports built-in, are better. These features are something Healthy Step’s entire range of foot orthoses have built-in as standard, giving the vault specific 3-dimensional contouring.

For feet that lower their vault excessively by the end of midstance, exercises to strengthen plantar intrinsic and extrinsic muscles will be highly beneficial. See our exercise videos linked within the Advice Hub for more details. For feet that struggle to improve their strength over time, the best long-term protection is by using a vectorthotic or alleviate select device, because they possess more spring-like properties and have a profile that encourages MTP joint extension moments to be directed across the MTP joints as metatarsal declination angles increase.

However, once degenerative joint disease (DJD) processes start, other treatments should be used to help the patient who may be experiencing increased pain locally, or as compensation for loss of acceleration power application through the medial forefoot.

What can I do about big toe pain?

Although conservative treatments should always be considered first, surgery to the 1st metatarsophalangeal (MTP) joint is an option, but consensus on which procedures has not been reached (Coster et al, 2021). To improve motion, surgery can consist of removing the sclerotic bone around the joint edges (cheilectomy), altering the bone shape (osteotomy), and also trying to encourage the formation of fibrocartilage by drilling holes into the degenerated joint surface (fenistration). This type of surgery can help for a while but only fusions of the joint (arthrodesis), removing the joint (arthroplasty) or a replacement joint can be offered as a long-term solution for hallux rigidus. However Joint replacements have variable success, for they are not as good as hip or knee replacements. Fusion (fixing the joint stiff) tends to sort out the joint pain, but the loss of this important joint motion can affect the ability to walk or run comfortably (Chan and Sakellariou, 2020).

Conservative treatments may offer better outcomes, especially in the early stages of DJD (0-2, hallux limitus?), whereas grade 3 and 4 osteoarthritic changes (hallux rigidus?) are more likely to require surgery.

By starting conservative treatment for osteoarthritis (OA) early, less degeneration of the joint structures will have occurred, representing a better mechanical environment to work upon. There may even be a chance that the damage can be repaired. In these cases, approach the problem as you would prevention, (see ‘How to prevent 1st MTP joint DJD’)

Once the special mechanical properties of the cartilage as a functional unit are lost, the best that can be achieved is to prevent or slow further damage. This is because the ability of cartilage to maintain its mechanical properties of lowering friction and allowing free motion (via its fluid and solid phases) relies on all the internal structural elements being wholly intact (Horwood and Chockalingam, 2023b pp.282-294). Once any structural integrity is lost, cartilage’s biomechanical properties (poroviscoelasticity) fail, utterly. These mechanical properties rely on the rate of fluid flow (the fluid phase) within the solid phase of connective tissue via tiny interconnected pores. The tiny pores restrain the flow of fluid under compression so that when loaded, cartilage ‘pumps-up’ to create a highly lubricated incompressible joint where surfaces do not contact. In DJD, the tiny pores break up into large voids where fluid can easily flow away from loads, allowing surfaces to contact and then wear down.

It is therefore important to grade 1st MTP joint DJD to decide on the best course of action and then discuss the pros and cons of the most appropriate options, with the patient. The table presented here by Coughlin and Shurnas (2003), is a helpful guide. Grades 0-2 presentations offer the most positive outcomes for conservative therapies.

 

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