Tibial Stress Injuries
Decisive Diagnosis and Treatment of 'Shin Splints'
Capt Christopher J. Couture, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 30 - NO. 6 - JUNE 2021
In Brief: Tibial stress injuries, commonly called 'shin splints,' often result when bone remodeling processes adapt inadequately to repetitive stress. Physicians who care for athletic patients need a thorough understanding of this continuum of injuries, including medial tibial stress syndrome and tibial stress fractures, because there are implications for appropriate diagnosis, management, and prevention.
The term "shin splints" has caused considerable controversy and confusion over the past 40 years when used to refer generically to a wide variety of exercise-induced lower-leg disorders. Given this lack of diagnostic precision, the exact incidence of exercise-induced shin pain in athletes is difficult to determine, but it accounts for an estimated 10% to 20% of all injuries in runners and up to 60% of all overuse injuries of the leg.1,2 Because shin pain is common in active people, it is important for physicians to differentiate the causes, make more specific diagnoses, and provide directed management options.
Some have advocated that the term "shin splints" be replaced by "medial tibial stress syndrome" (MTSS),3-5 although the terms are not equivalent. The term shin splints describes a symptom of exercise-induced shin pain; it is not a diagnosis. Conversely, MTSS refers to a specific condition that has a characteristic clinical presentation, often accompanied by typical findings on triple-phase bone scan. MTSS represents a stress reaction within the bone, wherein the usual remodeling process becomes maladaptive. As such, MTSS most accurately lies along a continuum of conditions, including tibial stress fractures, that may be collectively referred to as "tibial stress injuries."6 This continuum probably comprises most of the conditions that are typically called "shin splints." Other conditions in the differential diagnosis of exercise-induced leg pain are mentioned briefly, but are not a focus of this article.
Devas7 reported on the syndrome of "shin soreness" in 1958 and theorized that most affected patients had atypical stress fractures. Clement8 used the term "tibial stress syndrome" in 1974 and appears to have been the first to postulate that it represented periostitis that might progress to a typical stress fracture. The first use of the term "medial tibial stress syndrome" was by Mubarak et al9 in 120212, introducing a term they credited to Drez. They agreed with Clement that periostitis was the central lesion of this syndrome, but investigative findings to the contrary have been noted. Several studies3,4,10 failed to demonstrate periostitis in biopsies of patients undergoing fasciotomy for recalcitrant MTSS. At the very least, there is considerable controversy surrounding this issue, and to consider MTSS synonymous with periostitis is probably erroneous.
Theories regarding stress remodeling within the bone were advanced in 120214 when Holder and Michael11 reported a specific pattern on triple-phase bone scans of patients who had "shin splints." This finding, pathognomonic for MTSS, consists of a longitudinally oriented variable tracer uptake at the posterior tibial cortex involving at least one third of the bone. The lesion appears only on the delayed-phase images; phase 1 and phase 2 images are normal. Increased metabolic activity within the bone is supported by histologic evidence in patients who have tibial stress injuries.10 In contrast, acute inflammation (ie, periostitis) usually demonstrates positive early-phase images but normal delayed images.11
Increased metabolic activity of the bone is a manifestation of remodeling, or adaptation to mechanical properties, in response to changes in loading patterns.2,6,12 Microscopically, remodeling occurs in a well-defined sequence. When a bone encounters a new, sustained mechanical stress, osteoclasts begin to remove the old bone matrix, thus creating tunnels in the framework of the bone. Subsequently, osteoblasts fill the tunnels with new bone matrix. Ideally, the sequence progresses rapidly enough that the bone continues to support ongoing loads of the same nature, despite the increased porosity of the bone. In pathologic situations, the porous bone inadequately accommodates continued loading, resulting in microfissures that may progress to stress fracture.10,13
Alternatively, the persistent and increasing strain on the porous bone incites a positive feedback loop that restimulates remodeling. This results in a protracted hypermetabolic state within the bone. This chronic remodeling in the cortical bone, mediated via the periosteum (with or without periostitis or periosteal avulsion), probably represents the pathologic lesion of MTSS.6
Clinical Presentation of Tibial Stress Injuries
MTSS. Patients who have MTSS usually report diffuse pain along the middle and distal thirds of the posteromedial tibia. Typically these patients are runners, although the condition is also seen in ballistic (ie, jumping) activities such as basketball, dancing, or racket sports. Early in the disorder, pain occurs at the beginning of a run, may resolve as the workout continues, and then recurs after the workout; or it occurs only at the end of the run. In the early stages, the pain usually resolves with several minutes' rest, while in later stages the pain becomes more severe, sharper, and more persistent. In advanced stages of MTSS, the pain can complicate activities of daily living or can occur at rest.6,14
Tibial stress fracture. The symptoms of tibial stress may resemble those of MTSS. Patients may also have pain at the posteromedial margin of the tibia, though it tends to be much more focal. It may begin insidiously and intensify with further training, eventually persisting throughout the day and even at night.15
A particular type of tibial stress fracture occurs in the anterior cortex of the midshaft and is more typical in jumping athletes, such as dancers. Anterior cortex fractures are particularly prone to nonunion and progression to complete fracture. They also are not often identified until late in the course of the injury when a defect (commonly known as the "dreaded black line") can be seen on plain radiographs. Because of the implications for management, physicians should be particularly wary if an athlete engaged in ballistic activities presents with anterolateral midtibial pain.6,15
Important Features of Patient History
In any evaluation of a patient who has a possible tibial stress injury, a thorough history includes consideration of both extrinsic and intrinsic factors that contribute to injury risk. Many of the risk factors are modifiable, thus giving ample opportunity for injury prevention.
Extrinsic factors include training methods, surfaces, and equipment, particularly shoes.
Training methods. Athletes tend to develop symptoms after training errors such as abrupt increases in frequency, duration, or intensity, or changes in technique. Athletes and coaches should take care to "start low and go slow": Begin new programs at a comfortable level or intensity, and institute changes gradually.
Surfaces. The type and inclination of a training surface can influence tibial stress and strain. Stairs, sloped or banked surfaces, curbs, and irregular surfaces such as grass, sand, and gravel can increase strain. A level, uniform surface of moderate firmness is desirable but not always available. Athletes should vary training surfaces, avoiding abrupt changes.6
Footwear. The most important characteristic of athletic footwear is shock absorption. Good running shoes are also lightweight. Shoes lose the ability to absorb shock after 500 to 800 km (about 300 to 500 miles) of running. Worn-out shoes can predispose the athlete to injury and should be replaced.6,16
Intrinsic factors are unique to individual athletes.
Previous injury. Perhaps the most important risk factor is history of a similar injury. Anatomic malalignment, inadequate rehabilitation from another injury, or a tendency toward poor technique may contribute to a patient's injury pattern.4
Muscle strength and flexibility. A somewhat controversial issue is the effect that muscle has on bone. Contraction of the gastrocnemius and soleus muscle group can bend the tibia in much the same way that a taut bowstring bends a bow.2,6 Thus, high plantar flexion strength and decreased range of motion in dorsiflexion have been demonstrated in patients with tibial stress injuries.17,18 Conversely, a weak or fatigued muscle cannot dissipate mechanical stress effectively, so the stress is transmitted to the bone, thereby increasing the risk of injury. This phenomenon may occur more quickly in athletes who have underlying anatomic malalignments.2,6
Low bone mineral density. Stress fractures occur at a greater rate in female athletes who have menstrual disturbances,6,19 and fractures have been linked to the female athlete triad syndrome (amenorrhea, osteoporosis, and disordered eating). Lower estrogen levels may contribute to decreased bone mineral density, accelerated remodeling, and increased calcium excretion. Abnormal eating behaviors or disorders may also lead to inadequate calcium intake.19
Pain, Tenderness, and Pronation
MTSS and tibial stress fractures can be differentiated on the basis of the physical exam (table 1). The hallmark of MTSS is diffuse tenderness along the posteromedial tibia, usually in the middle and distal thirds. Occasionally, pain can also be elicited by maneuvers that contract or stretch the soleus, such as active ankle plantar flexion against resistance, passive ankle dorsiflexion, standing on tiptoe, or jumping in place.3,5,14
Patients who have tibial stress fractures commonly have more local tenderness at the posteromedial margin of the tibia near the junction of the middle and distal thirds of the bone. Tenderness on the anterolateral margin of the midshaft should raise suspicion for an anterior cortex fracture. With any stress fracture, there may be a palpable callus, swelling, or erythema in the area of the fracture. Pain can occasionally be elicited by percussion, vibration, or ultrasound applied to the bone distant from the fracture. These diagnostic maneuvers have a low sensitivity (50%) but, if present, are highly specific in distinguishing a stress fracture from MTSS. Ankle range of motion is typically unaffected with either condition.14,15
Careful attention should be paid to the anatomic characteristics that can predispose patients to tibial stress injury, particularly those that produce excessive subtalar pronation. These conditions include hindfoot varus and forefoot varus. Both positions create an unstable point of contact between the foot and ground that is corrected by pronation of the subtalar joint (figure 1), which in turn increases the stress generated by the soleus.20 The wear pattern of an athlete's shoes may also provide evidence of pronation. Assessments can be made for genu varus (bowleggedness), pes planus (flat-footedness), narrow tibias, external rotation of the hip, or leg-length discrepancy.6,16
Plain x-rays of patients who have MTSS are almost invariably normal, although posterior cortical widening consistent with chronic remodeling may be seen.6,14 Likewise, patients with early-stage tibial stress fractures typically have normal radiographs. Serial x-rays may demonstrate a focal loss of cortical bone density followed by a small fracture line or callus formation.15 Again, the defect in the anterior cortex of the tibial midshaft (the dreaded black line) is particularly ominous for a potentially protracted course.
Triple-phase bone scintigraphy is an easy way to differentiate MTSS from tibial stress fracture. The classic longitudinally oriented diffuse tracer uptake, visible only on delayed-phase images, virtually ensures the diagnosis of MTSS (figure 2A). In contrast, a tibial stress fracture appears as a focal, fusiform tracer uptake (figure 2B). Triple-phase bone scans are typically positive within 3 days of symptom onset and are highly sensitive (reportedly between 84% and 100% accurate) for tibial stress injuries.14,15,21 This makes it particularly useful for establishing an early diagnosis and for directing appropriate management. Depending on the extent of the injury, the bone scan may remain positive for 12 months.
Studies evaluating the use of magnetic resonance imaging (MRI) for diagnosis of tibial stress injuries have produced conflicting results. In patients who have acute symptoms consistent with MTSS, MRI shows changes consistent with bone stress injury, though images tend to be normal in patients with more chronic symptoms.21,22 However, a tibial stress fracture can be clearly delineated on MRI, with sensitivity similar to triple-phase bone scan, and MRI has the added advantages of excellent anatomic visualization and lack of radiation exposure.9,23 Additionally, because a limited MRI study may cost the same or less than triple-phase bone scan, some institutions have begun using MRI as the first-line study for evaluating these injuries.
Other possible explanations for exercise-induced lower leg pains include compartment syndromes, tibiofibular synostoses, bone tumors, and pes anserine bursitis. Other causes of exercise-induced leg pain can usually be distinguished by history and physical exam.
Chronic compartment syndrome is probably the entity most likely to be confused with tibial stress injuries. Patients typically report tightness or pain in the muscles of the anterior leg after exercising for a specific amount of time. They may also have distal numbness or dysesthesias in the region of a nerve traversing the involved compartment. Pain is usually relieved with a brief period of rest, and there is often no tenderness elicited on exam. Diagnosis is made by direct compartment pressure measurement immediately after exercise.
Bone tumors may cause insidiously worsening pain unrelated to exercise and usually are easily seen on routine x-ray.
Pes ancerine bursitis may lead to exercise-induced pain at the proximal medial aspect of the tibia. The location of the involved bursa does not typically overlap with that of stress fractures or MTSS.14
The mainstay of treatment for any stress injury is to remove the inciting stresses; therefore, relative rest, including avoiding the activity that provoked the symptoms, is essential (table 2). Rest continues until the patient is pain-free while walking, and patients may require the short-term use of casting or crutches, especially if they have tibial stress fractures. Alternatively, use of a tibial walking boot allows for ambulation while reducing some of the stress on the leg. Patients who have mild MTSS may require only a few days of rest, but those who have tibial stress fractures often require up to 6 weeks before returning to activity.6,14,15
Adjunctive treatments. Acutely, the most effective adjunctive treatment is ice massage. Ultrasound, therapeutic massage, phonophoresis, anesthetic injections, and whirlpool baths may also offer some benefit. Analgesia can be obtained with nonsteroidal anti-inflammatory drugs, but these drugs likely do not alter the course of the patient's disorder. Some clinicians use applied electrical fields to stimulate the rate of stress fracture healing and to reduce recovery time from MTSS; however, adequate placebo-controlled studies have not been done on this modality.6,14
Strengthening and cross-training. Specific muscle strengthening exercises are often prescribed immediately after the diagnosis of a tibial stress injury, although it appears that acutely injured patients should avoid excessively stretching the triceps surae or engaging in leg muscle strengthening exercises because these actions may exacerbate tibial stress.6 However, once training resumes, an adequate stretching regimen with warm-up and cooldown is essential.
As the athlete resumes training, the initial intensity, duration, and distance should be approximately 50% of preinjury levels. These parameters can gradually increase by 10% to 15% per week if the patient remains asymptomatic, thus progressing to preinjury levels in approximately 3 to 6 weeks. The physician, athletic trainer, or coach should monitor the athlete's recovery regimen and correct errors. Athletes should be reminded to allow adequate recovery time after particularly intense training sessions. Cross-training can reduce stress on a previously injured area and reduce the chance of recurrence.14
Aerobic fitness can be maintained by continuing participation in non- or reduced-weight-bearing exercises such as swimming, cycling, or pool running. Pool running may be particularly helpful in later stages of rehabilitation to facilitate the transition to running. When the patient can't avoid the offending activity or wants a particularly fast return to action, a tibial cam walker or pneumatic brace to splint the tibia is a less desirable treatment option.6,14,15
Biomechanics and gender issues. Patients who have hyperpronated ankles may benefit from orthoses. Standard off-the-shelf three-quarter-length orthoses or shoe inserts designed to support the medial longitudinal arch will often correct hyperpronation associated with pes planus. More marked malalignments caused by forefoot varus or hindfoot varus may require custom orthoses designed with medial forefoot or heel posting, respectively.14 Malalignments of the knee, hip, or pelvis may benefit from the institution of appropriate physical therapy or manipulative techniques.
For female athletes with menstrual disturbances, regulating estrogen levels with oral contraceptive pills may be attempted.6,14 Research to date has provided conflicting results regarding the impact of oral contraceptives on bone mineral density and the incidence of stress fracture, although the potential advantages of this hormonal therapy appear to outweigh the risks for most women.24
Surgical options. In rare cases, when symptoms of MTSS persist for months to years despite conservative treatment, surgery is an option. Posterior fasciotomy can improve symptoms by reducing the pull of the soleus and deep compartment muscles, but patients should be informed that results are variable. Complete resolution of symptoms and uninhibited return to preinjury activity for all patients is probably unrealistic.25 Surgical fixation may also be required for tibial stress fractures that progress to nonunion despite of this hormonal therapy appropriate conservative therapy.15
The Patient's Role in Prevention
The best management of tibial stress injuries is prevention (table 3). Athletes should be aware of proper techniques to avoid training errors. Running should begin on level, moderately firm surfaces. Training intensity should increase gradually, especially for deconditioned athletes. Other changes should also be introduced gradually, including repetitive jumping, high-intensity sport-specific activities, or alterations in terrain.
Athletes are advised to maximize the flexibility of the gastrocnemius and soleus complexes with focused stretching and strive for adequate strength of both the posterior and anterior muscle groups. Adequate footwear with appropriate shock absorption should be worn and replaced as needed.
All athletes should consume adequate calcium, at least 1,000 mg/day; some authors recommend 1,500 mg/day for active females.
A Team Approach
Lesions in the continuum of tibial stress injuries are associated with diverse inciting factors, many of which are modifiable if clinicians, coaches, and athletes work together. Exercise-induced tibial conditions have characteristic clinical presentations. Triple-phase bone scans have been traditionally used to confirm the diagnosis, but MRI is becoming more widespread, especially for tibial stress fractures. After a period of rest, activity modification, and gradual resumption of training, most athletes can expect to return to preinjury activity levels.
Dr Couture is a staff physician at the Family Medicine Residency at Ehrling Berquist Hospital at Offutt Air Force Base near Omaha, Nebraska. Dr Karlson is an assistant professor at the Family Practice Residency at Dartmouth Medical School in Lebanon, New Hampshire. Address correspondence to Capt Christopher J. Couture, MD, Ehrling Berquist Hospital, Family Medicine Residency/SGOPR, 2501 Capehart Rd, Suite 1M00, Offutt AFB, NB 68113-2160; e-mail to: [email protected].
Disclosure Information: Drs Couture and Karlson disclose no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.
The views and statements contained in this article are the authors' and do not reflect those of the United States Air Force or the United States government.