FRANCESCOBENAZZO, MARIOMOSCONI, GIACOMOZANON
Introduction
Overuse injuries develop when repetitive stresses to bone and musculo-tendi- nous structures are applied and cause changes that damage tissue at a greater rate than that at which the body can repair itself. A combination of extrinsic factors, such as training errors and environmental factors; and intrinsic or anatomical factors, such as bony alignment of the extremities, flexibility deficits, and ligamentous laxity, predisposes athletes to overuse injuries [1].
Lower-extremity stress fractures are common injuries most often associated with participation in sports involving running, jumping, or repetitive stress, such as in soccer [2].
Stress fracture is the consequence of bone structure failure after repeated micro-traumas. The effect of repeated injuries is stronger than bone remod- elling potential. Different populations can be affected, and different patterns of insufficiency fracture can be seen related. Also among athletes, differences in terms of sport specialty, morphotype of the athlete, age, and race, must be considered [3, 4]. Many different factors are involved in generating a stress fracture [5]:
- Running is the most important factor in stress fracture of the inferior limb; 84% of inferior-limb stress fracture in athletes is related to running.
Furthermore, a sport-specificity of injury must be considered. Specific actions involved in a particular sport determine site and type of fracture.
As described, the specific way of running in soccer influence the typical stress fracture related to this sport (of the metatarsal bone).
- Frequency, speed, and amount of load, as well as recovery time between load phases, are important. In athletes, risk of stress fracture increases proportionally to load increase. This risk is related to muscular fatigue:
when the buffer action of muscle fails, the impact of injuring force on bone increases. The buffer action of muscles is related to load application on bone, including control of piezo-electric activity and distribution of electrical changes. A concentration of positive changing has been consid-
ered a trigger factor due to stimulation of osteoclastic activity. However, muscular strength can be a risk factor, as well. For instance, in case of trac- tion force at the muscle insertion site, the stronger the muscle, the higher the risk of stress injuries (olecranon in throwers, fifth metatarsal base in soccer players).
- Vectors of load application related to bone structure are also involved.
Individual anatomic features (limb length, load axis) can condition bio- mechanics and kinematics of sport. Abnormalities in alignment can also be important in stress-fracture pathogenesis (flat foot, valgus knee, hyper- pronation).
- Quality of bone related to age and gender (hormonal influence) [6]. Stress fractures are overall more frequent in women, basically related to nutri- tional habits and menstrual abnormalities. Furthermore, adolescent age is a risk factor for the following reasons: articular cartilage in growing sub- jects (especially in elbow, knee and ankle) is particularly vulnerable; over- load injuries at this level are quite frequent. Long bones and tendon-mus- cle unit growing speeds are not the same. This fact can lead to muscular imbalance and consequently to joint stiffness and high-traction tension at apophysis [4].
- Ground conditions are extremely important in soccer, especially in lower series where terrain can be uneven and re-covered with uniform grass.
Terrain is also subjected to changes due to weather conditions (harder surfaces in winter time) [7].
- Other controversial issues concern materials and shoes and particularly their shock-absorbing power, which could protect the skeleton from injur- ing stresses.
- Malalignment of the lower extremity, including excess femoral antever- sion, increased Q angle, lateral tibial torsion, tibia vara, genu varum or val- gum, subtalar varus, and excessive pronation, are frequently cited as pre- disposing to lower-limb overuse injuries [8].
Diagnosis
Diagnosis of a stress fracture may be easy if the clinical suspicion is high in case of bony pain secondary to high physical performance. The only symp- toms may be pain and functional impairment, both having different clinical aspects.
Pain
Pain can be progressive and insidious, increasing with sport activity, espe- cially if the athlete has an increase in:
- Length of sport activity;
- Intensity;
- Frequency in training;
- Equipment;
- Training playground.
Pain is generally localised and increases during sport activity, decreasing with rest, and progressively presenting over 2–3 weeks. In the complete phase of evolution of the fracture, pain may be so intense as to prevent every kind of sport participation where terrain can be uneven and uncovered with uni- form grass or on harder winter surfaces.
Imaging
Conventional x-rays can help in diagnosing the stress fracture if the follow- ing radiological patterns are seen:
- Parosteal bony formation;
- Sclerotic area;
- Bone callus;
- Fracture line;
- Cancellous bone sclerosis.
The standard radiological aspect is quite typical: sclerosis and parosteal bony callus and the dreaded black line – a cortical radiolucency line at the side of the bone submitted to tension. The fracture line cannot be considered the “must be present” sign. Although pathognomonic, these radiological pat- terns are not frequent; they can appear either late after the clinical suspicion or not at all [9].
Bone Scan
In case of high clinical suspicion, when stress fracture is not visible on x-rays, a bone scan with 99m Tc-MDP or EDP is useful because of its sensitivity in spotting high bone remodelling areas (Fig. 1). Some factors affect the radionuclide concentration, such as blood flow, extra-cellular compartment, local enzymatic activity, and quality of osteoid matrix. Nowadays, the tripha- sic method is used. The first phase of vascularisation shows the blood supply, the second shows the soft tissue and extra-vascular bone tissue activities, and the third – the metabolic phase – detects the bony formation activity.
Comparison of the three allows a dynamic evaluation of stress injuries that would otherwise be impossible in a static mode. The main limitation of this method is non-specificity: a concentration of radionuclide can be seen in painless areas. These are areas of “stress reaction”, a positive compensatory reaction to overload [10].
Computed Tomography (CT)
Once the area is identified in which the metabolic increase is present, the lack of specificity left by the bone scan can be fulfilled by computed tomography (CT). Some pathognomonic radiological alterations that can be detected by CT are:
- Sclerosis;
- Periosteal and endosteal reaction;
- Trabecular reaction;
- Fracture line (if present).
Thus, CT must be performed in the positive bone-scan hyper-captation areas only if painful. Otherwise, in stress reaction painless areas, it would mean needless x-ray exposure. CT is diagnostic especially in navicular tarsal bone, talus, and vertebral lamina fractures [11].
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging (MRI) can now be considered the gold standard in stress-fracture diagnosis. MRI can spot bone marrow abnormalities, soft tissue oedema, as well as any blooding phenomenon and for these reasons is useful in diagnosis of even very small stress reactions [12]. Stress fractures are spotted early by decreased bone marrow intensity in T1- weighted images.
Fig. 1.In bone scan, the radionuclide accumulation is the expression of the sensitivity of this examination in bone remodelling areas
Intensity is increased in T2-weighted images after gadolinium injection and in short tau inversion recovery (STIR) sequences. Periosteal oedema can be also detected, as well as the fracture line. The latter appears as a low-density intramedullary line that prolongs in cortex bone. When the bone repair phase begins, a decrease of intensity is visible in T2-weighted sequences, as well as the bony callus phase [13].
Tibia and “Shin Splints”
In the tibia, pain may present in an acute or subacute manner accompanied by swelling, oedema, and clear dolorability that may be extended to a very large area, with peak pain intensity in the actual fracture sight. The differen- tial diagnosis between shin splint, tibial medial syndrome, and compartmen- tal syndrome may be difficult. The tibia has 3 different areas that are most commonly involved:
- Anterior and anteromedial cortical bone;
- Posteromedial cortical bone at the superior third;
- Medial malleolus.
In soccer, the most commonly involved area is the medial shaft, even though the proximal metaphysis or the medial malleolus may be rarely involved [3]. The pathogenesis is directly connected to the shape of the tibia, the distribution of muscular forces, and the kind of functional weight-bear- ing of the athlete. Muscular groups occupy the anterolateral and the posteri- or district of the tibia while the anteromedial cortical has no muscles.
Furthermore, the tibia has an anteroexternal curvature, evident as more varus is present. In addition to the arch principle (the tibia) stretched by its chord (the muscles), loading forces and muscular contraction generate compression vectors in the concave side (posteromedial cortical) and distraction forces in the convex side (anterior cortical). This situation is increased in those ath- letes with great flexor strength with triceps suralis hypertrophy.
On the anterior cortical, “tensile” fractures are produced, with transversal rim fracture, cortical hypertrophy, and difficult healing. “Compressive” frac- tures in the posterior cortex (especially proximally) are produced, with hypertrophy cortico-spongeous, difficult visualisation of the fracture rim, and easier healing.
The stress fracture of the medial malleolus (Fig. 2) is connected to the bearing: pes cavus without pronation stresses this area of the tibia with astra- galus impingement [14].
There is another situation connected to overuse injury of the tibia with similar pathogenesis and clinical aspects. The “shin splint” is a situation char- acterised by pain and oedema at the distal two third of the tibia in differen- tial diagnosis with stress fractures, insertional tendinopathies, and compart-
mental syndrome. The American Medical Association (AMA) defines shin splints as “leg pain derived either from running on hard ground, or from excessive dorsiflexion of the foot”. The AMA recommends that this definition be reserved to muscle-tendinous problems as opposed to fractures or ischemic pathologies. In the shin splint definition, we may find anterior over- use pathologies such as anterior tibialis tendinopathies, but many authors suggest that this definition should be indicated for posterior tibialis tendinopathy, the soleus, and finger flexors: they prefer to define this situa- tion as “medial tibial syndrome”, which includes:
- Periostitis and insertional tendinopathies;
- Compartmental syndrome;
- Stress fractures.
Actual general agreement is to consider periostitis and posteromedial insertional tendinopathies as the only cause of tibial medial syndrome, just for the differences in prognosis and therapy management.
Metatarsal
In the metatarsal bone, pain may start in a sub-acute way or may be acute after a functional overload (up-hill running): in any case, the fracture is sec- ondary to previous alteration of the bone and may be either in one side on the cortical or circumferentially.
Fig. 2.Stress fracture of medial malleolus occurs mainly in pes cavus without pronation
Second, Third, and Fourth Metatarsals
Stress fractures of the metatarsal bones occur in all sports that have running as the fundamental athletic activity. Functional overload caused by various activities required by soccer players (running, change of direction, kicking) favours the onset of these fractures, which are frequently localised in the neck and distal metaphysis of the second and third metatarsal. The second is the longest metatarsal bone, through which the entire propulsion force is gener- ated, particularly if its difference in length with the first metatarsal is remark- able. (The metatarsus brevis, the metatarsus adductus; it should be noted that these anatomical situations are also correlated with the fractures of the nav- icular bone).
As a consequence of the repetitive application of forces generated and unloaded through it, the second metatarsal can positively respond with a reactive cortical hypertrophy from remodelling or sustain a duration lesion of the distal metaepiphysis, with a callus that appears after 2–3 weeks from the beginning of symptoms.
A pronated foot, associated with calcaneous valgus, is responsible for pro- longed support of the metatarsal heads, with increased quantity of strength of load that they must absorb. Similarly, a foot cable constitutes the anatomical sub-stratum for an ineffective amortisation and adaptation of the foot to the ground, with increase of mechanical solicitations on the metatarsal.
Fifth Metatarsal
The pathogenesis of a fracture of the fifth metatarsal base as well as clinical features are different from fracture of the metatarsal bones (Fig. 3). This type of fracture has been described by Jones [13], and as such, it is now defined. In soccer players, this type of fracture is particularly frequent because of jump- ing, repetitive tackles, and changing of directions. It is important to note that the Jones fracture, which occurs in the proximal metaphysis, must not be con- fused with more proximal partial separations: in the past, this has generated confusion around their natural history and the best method of treatment.
Besides, this fracture may be presented in acute form, which happens when the foot is bent in plantar-flexion and inversion and in a chronic form when traction of a smaller entity working on the brief peroneus with inversion of the foot provokes a rim of fracture in an area affected by pain from previous functional overload. An acute fracture does not have radiological signs of previous injury, as intramedullary sclerosis and cortical hypertrophy, with narrowing of the channel or even obliteration of the same, situation leading to pseudoarthrosis.
Torg et al. classified these lesions into 3 categories: acute (type I), late of consolidation (type II), and pseudoarthrosis (type III) [16]. Type I lesions are
considered stress fractures in the precocious phase; type II, in phase of delay, a widening of the fracture rim is underlined with medullar sclerosis; type III have the characteristics of pseudoarthrosis. This classification was formulat- ed in accordance with treatment, as we shall see later.
Treatment
Stress-fracture treatment may be either conservative or surgical, depending on the involved bone, the sight of the fracture, length of injury time, or the athlete’s activity level. In a tibia stress fracture, in case of limited dimensions, therapy is generally conservative. A cast may be useful in resting, controlling pain, and favouring the bone remodelling processes. Bone electrostimulation treatments (capacitive fields) stimulate neo-angiogenesis processes, especial- ly in the early phases [15]. Sport activity suspension is generally 6–12 weeks.
Conservative treatment may be different, as we said before, and depends on the fracture sight. In the posterior proximal cortex, rest and muscular reconditioning is important, with exercises of triceps stretching, anterior reinforcement, and proprioceptive exercises. If the proximal anterior cortex is Fig. 3.Base of fifth metatarsal frac- ture may be acute when the foot is bent in plantar-flexion and inversion or chronic when traction of a smaller entity works on the brief peroneus with inversion of the foot
involved, an orthesis must be added, which may correct the dynamic contact with the ground that may be altered and be the cause of the fracture. In soc- cer players, it is generally the medium shaft of the tibia that may more easily sustain a stress fracture. In this case, conservative treatment, as suggested before, may be ineffective, and the fracture may not heal. Surgical treatment has different options:
- Bone perforation (Fig. 4); removal of fracture rim with bone transplanta- tion; cast for 4 weeks
- Endomedullary blocked nailing.
When sclerosis and cortical hypertrophy are present, it may be necessary to use both surgical procedures in order to obtain the biological effect (endosteal healing, angiogenesis) and the mechanical effect (stiffness of the system without using a cast).
In case of a metatarsal fracture, localisation is typically at the medium shaft, with callus hypertrophy and easy and speedy healing. Treatment is gen- erally conservative (cast). It may, however, be different in case of fracture of the base of the fifth metatarsal (Jones fracture). According to Torg et al.’s clas- sification [16], we suggest that therapy may be:
- Conservative: type I fracture - Surgical: types II and III fractures.
Fig. 4a, b.Surgical treatment of tibia stress fracture with bone perforation
a b
A cast and bearing extension is recommended until healing is obtained – approximately 6 weeks. Considering this and the athlete’s activity level, we prefer a surgical approach with endomedullary screw or compression plate because of the possibility of praecox full weight bearing and easier return to sport activities – generally in 6–8 weeks [16].
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