Stress fractures of the foot - current evidence on management

Abstract

Stress fractures are a consequence of repeated submaximal loads with inadequate time for recovery and biologic repair or remodelling. The foot and ankle complex (FAC) represents a common site for development of stress fractures. Whilst the overall incidence of stress fractures is low, they are prevalent in athletes and military personnel causing significant time away from sports or work. Within these populations, certain stress fractures directly correlate to specific activities.

Factors that commonly influence these fractures include an acute increase in new repetitive physical activity combined with muscle fatigue, training errors or improper athletic techniques, which challenge the regenerative and remodelling capacity of bone. Depending on the site that is subject to repetitive loading, various biomechanical factors can result in abnormal concentration of forces to specific areas of the FAC resulting in stress fracture. Decreased bone marrow density (BMD) is a major biologic cause for developing stress fractures. The female athlete triad comprising eating disorder, amenorrhea and osteoporosis in competitive athletes also predisposes to stress fractures. Vitamin D deficiency is also postulated to be the cause of these fractures and may contribute to poor healing.

Clinical presentation is usually with vague pain of insidious onset which worsens with activity and improves with rest. Diffuse tenderness over the affected bone is common with only a minority having any visible swelling. Plain radiographs are the first line of investigation but rarely reveal an obvious fracture. MRI scans aid in diagnosis and CT scans help in treatment and characterisation of the fracture and monitor healing.

Management relates to the site of injury, which stratifies them into high or low-risk. Stress fractures of the calcaneus, cuboid and cuneiforms are classed as low-risk fractures as they usually heal with simple activity modification or short duration of non-weight bearing. Stress fractures of the navicular, talus and hallucal sesamoids are classed as high-risk fractures due to higher rates of non-union and prolonged recovery time. Metatarsal fractures can be considered high or low-risk depending on location. These warrant aggressive management, often requiring surgical intervention. Adjuncts such as vitamin D supplements, external shockwave therapy, low-intensity pulsed ultrasound therapy have been used with varying success but there remains little supportive evidence of superiority in the available literature.

1. Introduction

Stress fractures of the foot and ankle complex (FAC), whilst relatively rare in the general population, are frequently seen in athletes. They occur when bone fails to adapt to an acute increase in strenuous repetitive high-impact loading.¹ They are typically characterised by activity-related pain, localised tenderness and swelling.¹ Evaluation can be difficult as onset of symptoms is often hard to pinpoint, and initial baseline radiographs may be normal. A high index of suspicion must be maintained when reviewing patients presenting with persistent foot pain, particularly those with high levels of physical activity or decreased bone mineral density (BMD).

2. Basic science and aetiology

Stress fractures are the result of repeated submaximal loads without adequate recovery time or inadequate biologic repair.² In the FAC, cortical bone contributes a majority of the biomechanical support for long bones, whereas the metaphyseal ends of the tarsal bones are composed mainly of trabecular bone.³ Cortical bone has a high modulus of elasticity, and is therefore able to withstand compressive forces with relative intolerance to bending and shearing; conversely, trabecular bone tolerates more compression.³ Both cortical and trabecular bone respond to muscle activity and repetitive loads by remodelling, therefore increasing BMD and strength.¹ During targeted remodelling of trabecular bone, supporting struts can change their orientation to better tolerate applied stresses, thus strengthening the bone along the axis of applied stress.³ Over time however, the dynamic reaction of skeletal remodelling in response to progressive overload is unable to keep up with repeated external force.³ As stresses increase, the elastic range of bone is exceeded and plastic deformation occurs, resulting in trabecular microfractures. Accumulation of these micro-injuries can result in macro-structural failure and fracture.⁴

Intrinsic and extrinsic factors are implicated in the development of stress fractures in the FAC. Intrinsic factors directly relate to the patient's metabolic status such as hormonal imbalances, cardiovascular fitness, bone quality, and anatomic characteristics such as cavus feet, limb-length discrepancies, tarsal coalitions, prominent posterior calcaneal process and tight heel cords.⁵ Extrinsic factors include the type of activity, new or excessive training regimens, technique, training surface, footwear and equipment.^5,6

Studies in military,⁷ athletic⁸ and civilian⁹ populations have demonstrated that women have increased rates of lower limb stress fractures. Postulated causes for this include reduced muscle bulk in females, and compensatorily increased Q-angle and foot protonation due to anatomic variations in the female pelvis.⁵ Relative energy deficiency (RED) syndrome or the ‘female athlete triad’, comprising deficient calorie intake, reduced BMD and menstrual dysfunction, is considered central to stress fractures among adolescent and active adult women.¹ Low energy availability leads to unpredictable release of Gonadotrophin-releasing hormone, resulting in impaired production of oestrogen which plays a key role in bone mineral density regulation.¹ Menstrual dysfunction, prior bone stress injuries and cross-country running have been found to be independent risk factors.¹ Low vitamin-D levels as well as low body mass index¹⁰ correlate with lower extremity stress injuries.

Stress fractures in the FAC behave differently based on their location, due to the unique anatomic characteristics of the bones and the forces acting upon them. Low-risk fractures are those which have a favourable natural history, usually located at the compressive side of the bone and less likely to recur or become a non-union.¹¹ Locations which endure more tensile forces are considered high-risk and have a comparatively greater tendency to progress to non-union or complete fracture. These include the talus, navicular, proximal fifth metatarsal and the sesamoids of the hallux.^11,12 Note that the distinction is vital as it affects management; low-risk fractures may generally be managed conservatively, but high-risk stress fractures are likely to warrant more aggressive intervention.^5,6

3. Epidemiology

Stress fractures in athletes and military personnel account for 98.5% of all stress fractures¹³ with those involving the FAC responsible for up to 20% of clinic visits¹⁴ in the athletic population. Incidence and site-specific distribution are largely dependent on the activities performed by the group under consideration. The most frequently encountered stress fractures in military personnel include those of the tibia, metatarsals and calcaneum.^15,16 Runners or those involved in explosive sprinting activities are prone to fractures of the navicular^5,6; dancers more commonly suffer stress fractures of the metatarsals, including the bases.^5,6,17 Jumping activities and intense exercise involving repetitive gastrocnemius muscle activity can result in stress fractures of the calcaneus.^2,6 Gymnasts are at risk of cuboid and medial malleolus fractures.^18,19

4. Evaluation

A typical presentation is with insidious onset of activity related pain in a focal area. The exact relationship with exercise should be ascertained. Initially, pain may settle on activity cessation, however with continued exercise over time, pain may persist after exercise is terminated. Note should be taken of any recent changes to activities, such as increased quantity or intensity of training, or any change in training surface, footwear, equipment or technique. A full dietary history and in females, menstrual history must be obtained.

Point tenderness, oedema, warmth and in some cases palpable callus may be present on examination. It is crucial to examine not only the foot and the ankle but the entire lower limb to look for any anatomic features of malalignment in all planes. For example, cavovarus deformity will cause the individual to weight bear on the lateral border during propulsive ambulation placing an abnormal concentration of ground reaction forces (GRF) in this region and lateral ray stress fracture is not an uncommon presenting feature in these patients.

Radiographic findings early on may include subtle trabecular sclerosis due to formation of microcallus in cancellous bone, or in injured cortical bone, subtle cortical lucency and periosteal reaction.³ However, initial radiographs may be normal as clinical symptoms of stress fracture typically predate the radiographic findings by 2–3 weeks.³

If clinical concern persists, then further imaging options include repeat radiographs after a two-to-three-week interval, or magnetic resonance imaging (MRI). Radionuclide bone scanning is a sensitive but poorly specific, largely historic examination.³ MRI, has comparable sensitivity and superior specificity for accurate diagnosis of lower extremity stress fractures, is non-invasive, avoids ionising radiation exposure and can delineate alternative aetiologies.²⁰

MRI features vary based on the chronicity of the injury, the bone involved and the location within the bone.^1,3 Early findings include oedema of the periosteum and bone marrow. In more established fractures, intracortical signal changes or intramedullary low-signal intensity fracture lines may be visualised.³

5. Low-risk stress fractures

5.1. Calcaneus

Calcaneal fractures are the second most commonly encountered stress fracture of the FAC⁶ and the most common tarsal stress fracture in military recruits, representing around a quarter of stress injuries in this population. Repetitive force during heel-strike as well as the opposing tension through the Achilles tendon are thought to contribute to the pathophysiology of this injury.^1,6

Clinical presentation is with a prodromal period followed by plantar heel pain. Heel squeeze test may be positive. Leabhart²¹ described two key clinical examination findings: oedema of the pre-calcaneal bursa and tenderness over the posterosuperior calcaneus, with no exacerbation of pain on stretching of the heel-cord with foot dorsiflexion. There may be associated plantar fascia rupture. As fractures occur perpendicular to the trabeculae, plain radiographs may demonstrate sclerosis or endosteal callus formation perpendicular to the long axis of the calcaneus.^6,22 MRI is usually diagnostic.

Treatment is largely guided by symptoms with an initial period of rest and modification of activity/intensity. Low impact rehabilitation initially is useful, especially in athletes to maintain activity in the rest of the body whilst placing physiological loads on the fractured area. Activity may cautiously be increased in line with decreasing symptoms. Surgical intervention is rarely warranted.^22,23

5.2. Cuboid and cuneiforms

Cuneiform and cuboid stress fractures are rare with only a few case reports and small case series in the literature. Stress fractures in these bones are generally seen with predisposing malalignment or structural abnormalities such as plantar fascia rupture or plantar fasciotomy.⁶

MRI is the preferred imaging modality.⁶ Cuneiform and cuboid stress fractures (Fig. 1) are generally considered low-risk and typically managed conservatively.³ An initial period of partial weight-bearing with or without immobilisation is recommended until pain has subsided during weight-bearing activities.⁵

Fig. 1.

coronal, sagittal and axial T2 weighted MRI scans showing stress fractures of the cuboid and lateral and intermediate cuneiforms in a marathon runner. Treated conservatively and a successful return to previous sport.

6. High-risk stress fractures

6.1. Hallucal sesamoids

The sesamoids of the hallux reside in and increase the mechanical advantage of the flexor hallucis brevis; these subject them to excessive forces when the phalanx is dorsiflexed and planted. Cavus feet with the plantarflexed first metatarsal in particular are susceptible to sesamoid injury due to increased load on the first metatarsal head.²⁴

Typical presentation is with pain just proximal to the plantar aspect of the first metatarsophalangeal (MTP) joint, or pain on toe-off. Palpation directly over the sesamoid produces pain. Range of motion of the first MTP joint may be reduced. One must be careful to exclude sesamoiditis, avascular necrosis (AVN) and bipartite sesamoid. MRI is useful for evaluation when plain radiographs are equivocal.^22,24

Initial treatment is non-operative, with offloading in a boot or heel-bearing shoe, and activity/training modification. Orthoses such as a Morton extension or footwear adjuncts like a metatarsal pad may be used to alleviate pressure on the sesamoid after the acute phase. Surgical management may be indicated in recalcitrant cases. Depending on fracture configuration, sesamoidectomy (total or partial) or open reduction internal fixation (ORIF) may be offered. Complications include digital nerve injury, flexor weakness and rarely hallux deformity.^1,24 Robertson et al. in their systematic review²⁵ looking at returning to sport following sesamoid stress fractures suggest that sesamoidectomy offers the quickest return to sport and ORIF offers the best possibility of returning to the previous level of sport, which may be useful to discuss with the patient during pre-operative counselling.

6.2. Talus

Stress fractures of the talus are rare, with a reported incidence of 4.4/10,000 person-years in military recruits.²⁶ Patients present with activity-related pain at the lateral ankle or sinus tarsi. Excessive subtalar protonation and plantar flexion are thought to predispose to injury due to impingement of the lateral process of the calcaneus on the posterolateral corner of the talus.²⁷ The head is affected most commonly, followed by the body, and least commonly the posterior talus.²⁶

Talar stress fractures may be occult on radiographs, with MRI demonstrating bone marrow oedema with or without a visible fracture line.⁶ Due to paucity of information in extant literature, no established treatment protocol exists, however, they are generally considered high-risk. General treatment principles advocated are a period of initial non-weightbearing and rest followed by supervised rehabilitation.²⁸ Orthoses for excessive protonation may be of benefit to reduce lateral loading.⁵ Rarely they may require internal fixation.

6.3. Navicular

Navicular stress fractures are rare in the non-athletic population but constitute up to 35% of all stress fractures in athletes.²⁹ These high-risk fractures are particularly common in male athletes performing jumping and running activities²⁹; recent studies suggest an increasing trend amongst female athletes.³⁰

Relative avascularity in the middle third of the bone has historically been thought to be a significant contributory factor, but a recent cadaveric study notes dense blood supply throughout the bone suggesting other possible causes.³¹ The navicular is subject to considerable stresses due to its location between the talar head and cuneiforms.³² During foot-strike, its medial aspect transmits forces from the first and second ray to the talus, but the lateral aspect does not share these forces, resulting in shear.³² The navicular is also influenced by the powerful attachment of the tibialis posterior tendon causing a significant adduction and rotational force on the navicular, particularly during heel-raise: this rigidises the midfoot, which causes the medial navicular to be compressed in its keystone position in both the longitudinal and transverse arches. This combination of compressive, shear and rotational forces on the navicular in an athletic individual could play a significant role in the evolution of stress fracture in these individuals. Other recognised predisposing factors include metatarsus adductus, pes cavus, short first metatarsal, and restricted movement of the ankle and subtalar joints.³³

Typical presentation is with an insidious course of vague pain over medial mid foot, exacerbated with activity. Examination may often elicit a point of maximal tenderness over dorsal prominence of the navicular described as the ‘N-spot’.³⁴ Isolating talonavicular movement can usually locate the site of pain to the navicular. Range of motion at the ankle is usually normal or minimally reduced, with pain elicited on subtalar movements.³⁵

Classic radiographic features are a fracture line oriented sagittally in the central third of the bone often commencing at the dorsal aspect, but these are visible in only 18% of cases.³⁶ MRI is highly sensitive at identifying stress reactions.⁶ CT may be more useful for characterising fractures and assessing healing.³²

Literature largely supports non-operative management using non-weightbearing casts for six weeks for stress reactions and undisplaced fractures, with a success rate of 86–96% and return to full activity in 5.6 months.³⁶ For displaced fractures or complete fractures with sclerosis, surgical management using one or two partially threaded cancellous screws have been shown to result in quicker return to sports.³⁷ Some authors advocate surgical fixation in all athletes with the aim of a quicker return to sports,³² but Torg et al. in their meta-analysis concluded that there was no advantage of surgical intervention in comparison to non-operative management with complete non-weightbearing.³⁸

Nunley et al.³⁹ recently reported the results of their treatment algorithm wherein acute fractures were treated with ORIF, chronic (>3 months) fractures were treated with ORIF and iliac crest bone graft, and chronic fractures with evidence of sclerosis, avascular necrosis or previous surgical failure were managed with ORIF with new hardware, iliac crest graft and/or vascularised bone graft. Their results demonstrated no significant difference in radiographic healing or return to sport between the three groups, with ORIF alone achieving 80% union rates, ORIF with bone graft had 75% union and 100% union rates following ORIF with vascularised bone grafting.

6.4. Metatarsals (excluding the fifth)

Metatarsal fractures are the most common stress fractures of the foot¹⁴ accounting for 38% of all stress fractures in athletes.⁸ Risk stratification is site-specific. Runners and military recruits most commonly sustain second through fourth metatarsal diaphyseal fractures.¹⁶ Stress fractures of the base of the second metatarsal, commonly seen in dancers,⁴⁰ are considered high-risk owing to the high rates of non-union. Conversely, diaphyseal metatarsal fractures are considered low-risk.¹⁴

The second to fourth metatarsals are subject to significant forces on weightbearing. Owing to their small cross-sectional area, they are prone to stress fractures (Fig. 2).⁴¹ A long second metatarsal relative to the first (Morton's toe) may contribute to second metatarsal stress fractures¹; Achilles contracture may contribute to metaphyseal fractures of the second metatarsal. The unique posture adopted by dancers wherein the ankle and foot are placed in extreme plantar flexion whilst weightbearing, results in locking of the metatarsocuneiform joints leading to increased stress at second and third metatarsal bases.⁴⁰ Pes planus and plantar fascia rupture have been implicated in second and third metatarsal fracture due to an increase in metatarsal strain.¹ Variation in sagittal declination of the metatarsals may also contribute to the evolution of stress fractures as increased plantar declination increases the GRF through the metatarsal.

Fig. 2.

Right foot radiographs taken on day 1 of injury, 6 weeks post injury and 5 months post conservative management of a second metatarsal diaphyseal fracture. Note the complete absence of any bony abnormality on the day of injury: hence the need for a high index of suspicion and a review of such patients with these fractures in the athletic population.

These present amongst highly active individuals with vague midfoot pain² which worsens on activity and tenderness over the affected metatarsals. Plain radiographs may rarely reveal a cortical lucency or fracture with MRI scans most often showing a stress reaction.

The primary treatment of metatarsal stress fractures is activity restriction. Immobilisation in a boot for a period of two to six weeks is advocated with gradual return to previous activities once symptoms resolve and radiographs demonstrate healing.⁵ Fractures of the base of second metatarsal in dancers might require 4–6 weeks of non-weight bearing immobilisation for adequate healing.¹⁷ Good clinical outcomes with use of extracorporeal shockwave therapy (ECSWT) has been reported.⁴⁰ If the fracture is noted to be dorsiflexed, early operative intervention should be considered to minimise the risk of dorsiflexion malunion and subsequent transfer lesion¹; a plantar-flexion metatarsal osteotomy can be performed to rebalance the metatarsals.¹ Operative intervention may also be indicated for symptomatic nonunions; this involves taking down of the nonunion and rigid ORIF with or without the use of bone graft.¹

6.5. Fifth metatarsal

Fifth metatarsal stress fractures commonly present in athletes participating in activities involving running, cutting or pivoting such as basketball or football,⁴² with an incidence of up to 4.4% in elite football players.⁸

Fifth metatarsal base fractures often carry the eponym ‘Jones’ fracture’ after Sir Robert Jones who first described these injuries based on his own experience. Whilst many classifications exist, the most widely used is that popularised by Lawrence et al.,⁴³ which describes three distinct anatomic zones: Zone 1 refers to the highly vascular tuberosity. Stress fractures here are rare and operative treatment is seldom indicated.¹ A transverse fracture in Zone 2, as defined by the proximal and distal margins of the fourth-fifth intermetatarsal articulation, is a true ‘Jones’ fracture’. Distal to this for 1.5 cm into the diaphysis accounts for Zone 3.

Hindfoot varus, metatarsus adductus, cavus foot, and genu varum are all thought to be risk factors for proximal fifth metatarsal fractures.⁴² Several structures inserting in the vicinity of the base of the fifth metatarsal place stress at this area; these include the pull of peroneus brevis and tertius, the tarsometatarsal ligaments and the lateral band of the plantar aponeurosis, resulting in significant tension across the metadiaphyseal region of the bone.⁴²

Stress fractures of Zones 2 and 3 are at high-risk for non-union,¹ likely due to poor vascularity. The retrograde blood flow to the proximal half of the fifth metatarsal is derived from a single nutrient artery which travels in a retrograde fashion, creating a watershed area at the proximal metaphysis.⁴⁴

Most present with insidious onset of lateral foot pain along with pain on palpation over the proximal fifth metatarsal. Plain radiographs often appear normal, but a fracture line may appear as a radiolucent line arising from the lateral cortex. When radiographs are inconclusive MRI often demonstrates oedema suggestive of stress reaction.

Non-operative management using a non-weightbearing boot has been advocated for stress reactions and undisplaced fractures in non-athletes.² However, this approach has a higher rate of non-union and a prolonged recovery period.¹⁴ In comparison, quicker recovery and union time has been observed with operative management⁴⁵ which has led some authors to recommend surgical treatment for athletes as standard practice.⁴² With surgical fixation union rates of 100% have been reported.⁴⁶ Surgical options include intramedullary screw fixation (Fig. 3) or ORIF using a plate and screw construct with or without bone grafting, however, none have demonstrated superiority.⁴⁷

Fig. 3.

Nonunion of a zone 3 stress fracture - intraoperative radiographs demonstrating injection of bone marrow, curettage of nonunion site, drilling of sclerotic part of stress fracture and screw fixation with subsequent radiograph at 6 weeks postoperatively. Surgery was performed minimally invasively with a stab incision for curettage and a further stab incision to insert the screw.

7. Adjuncts

Potential pharmacologic strategies include calcium and vitamin D supplementation. Gaffney-Stomberg et al. in their randomised placebo-controlled trial⁴⁸ demonstrated increased circulating markers of calcium and bone metabolism and improved measures of bone density and strength in orally supplemented military trainees. Various guidelines for dosage of oral calcium and vitamin D exist in the literature.^1,2 Improvements in union rate and recovery time have not been demonstrated with the use of bisphosphonates in young, athletic populations.¹

Bone stimulation with ECSWT has shown promise in improving fracture healing¹ but its efficacy in the treatment of stress fractures remains uncertain. A recent study⁴⁹ reported their use of moderate-to-high intensity electromagnetic ECSWT to treat bone stress injuries in runners, demonstrating a 98% pain-free return to running in their participants. However, this study of 40 patients is one of the larger cohorts reported, highlighting the need for large scale studies.

Another emerging trend is the use of low intensity pulsed ultrasound (LIPUS) therapy. A recent systematic review⁵⁰ evaluating the use of LIPUS in stress fractures was performed; of five included studies only three demonstrated statistically significant improvement in time to return to activity.

Lack of evidence means that the use of both ECSWT and LIPUS remains controversial. Some authors advocate liberal use of bone stimulators and biweekly shockwave therapy in the athletic population²; others remain guarded and suggest that the use of LIPUS is reasonable to consider in delayed fracture union¹. It is however safe to use these measures as no ill effects have been reported and no bridges burnt by trying these methods.

8. Conclusion

Stress fractures of the foot can occur in patients with vague activity-related foot pain, even in the absence of initial radiological abnormality. Particular attention must be paid to the patient's metabolic status and anatomic variations, as well as the nature and intensity of precipitating activity. Imaging such as MRI is warranted if clinical concern persists. Specific treatment is based on the location of injury, but principles involve immobilisation and temporary cessation of activities. High-risk stress fractures may merit early operative treatment, particularly in the athlete. The importance of extrinsic causes of stress fractures cannot be overemphasised. Footwear, running surface and load has to be adjusted to prevent recurrence. The outcomes of treatment especially in young athletes is difficult to determine, as most will return to high intensity sports and symptoms may recur. Discussion is often frustrating due to the uncertainty of the ‘return to sport’ status, and the patient must be warned that these fractures may end one's athletic career.

CRediT authorship contribution statement

Thumri Paavana: Project administration, Visualization, Writing – original draft, Writing – review & editing. R. Rammohan: Writing – original draft. Kartik Hariharan: Conceptualization, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.