Stress fractures of the tarsal navicular are an uncommon injury in the general population. However, people who engage in ballistic sporting events or recreational activities are at an increased risk of such an injury. The recognition of this injury seemed to parallel an increased fitness craze in the population over the last 30 years. Since Towne, et al., originally described tarsal navicular stress fractures in 1970, they have increased in prevalence secondary to our increased awareness of the injury and the emergence of faster and more powerful athletes.1
The formation of a stress injury to the navicular involves an interplay between a genetic predisposition and environmental stimuli. The genetic component is the foot structure and mechanics that one inherits while the repetitive athletic activity is the environmental stimuli.
A delay in diagnosing this injury can lead to frustration on behalf of the athlete, chronic pain, decreased performance, increased morbidity and possible loss of sporting activity. Accordingly, let us take a closer look at clinical recognition of this injury, diagnostic imaging, degrees of injury severity and key treatment considerations. It is imperative for the clinician to recognize these injuries occur along a continuum of severity.
A Guide To The Physical Exam And Biomechanical Considerations
Patients who present for consideration of navicular stress fractures are usually under the age of 40, are in good health and are invariably involved in some type of ballistic sports training and/or participation. Their involvement in ballistic sports may be sporadic or more along the lines of a highly trained athlete.
Most patients will present with a prodrome of midfoot pain that has become progressively worse over time. There is usually no acute injury. Most athletes will present when the pain has started to hamper participation and performance.
A high index of suspicion is paramount if one is to diagnose this injury in a timely fashion. It is the probing history of the presenting problem that will mandate a specific evaluation for a stress-related injury to the navicular. Bear in mind that the physical exam may not be impressive during the early stages of the injury. This is often the case as the athlete may have rested for a few days prior to the exam.
The pain can be difficult to localize and one may confuse this with regional tendonitis. It is not uncommon to note tenderness of the dorsomedial tendons of the affected foot during the clinical exam. Often the maximum area of tenderness is along the dorsal navicular between the anterior tibial tendon and the extensor hallucis longus tendon. This is commonly referred to as the “N” spot.2 Physicians should screen female athletes for the female triad, which consists of an irregular menstrual cycle, repetitive stress fractures and eating disorders.3
The research has described multiple biomechanical explanations for stress injuries to date. Commonly, the clinician will appreciate a cavus foot, a relative or absolute long second ray and possible forefoot adductus. However, no statistical proof to date has supported these anecdotal findings.4 It is commonly accepted that there is an increase in longitudinal shear to the central portion of the navicular.5 This area of the navicular has a well defined area of hypovascularity that will predispose it to a decreased ability to respond to repetitive stress.6
I believe the central portion of the navicular (unlike the medial and lateral poles) has a decreased amount of cancellous bone that will also decrease the navicular bone’s ability to handle compression. Do not overlook the torsional shear to the central portion as the strong posterior tibial tendon, spring ligament and tibio-navicular ligament pull medially while the bifurcate ligament pulls laterally. It is the combination of these genetically induced shear and longitudinal forces superimposed upon a hypovascular region that sets the stage for a stress injury. However, it is training errors that allow for this injury to occur. This acute increase in both types of stress overwhelms the body’s ability to respond successfully and subsequently leads to bone failure.
What You Should Know About Diagnostic Imaging
The common initial evaluation of medial foot and ankle pain routinely involves the use of conventional radiographs. These images are routinely negative or overlooked when it comes to early stress reaction and subacute injuries of the navicular, with the exception of traumatic events.7
However, one should use radiographs to rule out other causes of medial foot and ankle pain such as an accessory navicular, acute fracture, midfoot joint arthritis, coalition and bony impingement of the ankle and malalignment of the foot. If radiographs are negative and one still has a high index of suspicion for a navicular injury, there are advanced imaging options physicians may consider.
When weighing the use of advanced imaging, one must consider the pros and cons of each modality in not only diagnosing the injury but in characterizing and staging the navicular injury as these findings will guide treatment and possibly predict morbidity.
Saxena, et al., recommend evaluating all questionable injuries of the tarsal navicular for the presence of a stress injury, the extent of the fracture line if present and its orientation.8 In addition to characteristic changes associated with the fracture such as avascular necrosis, one should note whether there is sclerosis of the fracture lines and cystic changes. These latter changes are commonly present with advanced injuries.
Assessing The Use Of Three-Phase Bone Scans
Physicians commonly use traditional three-phase bone scans with these injuries. While this modality provides a high level of sensitivity, it provides a low level of specificity and can be positive in many other clinical scenarios that are less problematic.9 It is also common for bone scans to show increased uptake in bones in clinically asymptomatic areas of the lower extremity in athletes.
Bone scans are only valuable to confirm the absence of a stress injury/reaction. Secondly, bone scans yield no qualitative information about the fracture and when physicians use this as the only imaging modality, scans may lead the physician to under-appreciate the injury. This modality also has no value in assessing healing as it may stay positive for up to 16 months after the injury shows all signs of clinical healing.
Accordingly, I no longer consider the bone scan useful by itself in the diagnosis of navicular stress fractures. In the case of navicular stress fractures, physicians should only use the bone scan as a screening tool. If it is positive, physicians should pursue further advanced imaging.
Does MRI Have An Impact In Diagnosing Navicular Stress Injuries?
The use of magnetic resonance imaging (MRI) for navicular stress injuries has increased in acceptance and understanding over the past decade. This imaging modality provides a high level of sensitivity and specificity for navicular stress injuries. This modality is simple to perform, provides minimal discomfort to the patient and does not expose the patient to radiation.
Magnetic resonance imaging also allows the clinician to fully image this area in multiple planes. Magnetic resonance imaging has the added advantage of enabling physicians to evaluate all soft tissues in this area including the tibialis posterior tendon, the distal anterior tendon, spring ligament and possible fibrous coalition. The MRI is also valuable in helping to determine the possible presence of avascular necrosis and the extent of talonavicular arthritis.
The common use of MRI has been hampered by its cost and a lack of understanding of its benefits. I would argue that the benefit of MRI for the patient is greater than its cost. The only deficiency in MRI to date for tarsal navicular fractures is its inability to fully define and characterize the fracture.
I initially use MRI with suspected stress injuries of the navicular. If the MRI is positive for stress injury with or without a fracture line, one should order a computed tomography (CT) scan as these two tests are complementary.
When Should You Consider CT Imaging?
Physicians should only consider CT imaging of the tarsal navicular after making the primary diagnosis of a stress injury either by bone scan or MRI. If CT scanning is the only imaging tool physicians use with this injury, then one will not appreciate early stress reactions without fracture. Failure to identify early stress reactions could lead to a misdiagnosis and eventual fractures.
The CT scan allows for complete evaluation of the fracture line(s).10 Bear in mind that these fractures are commonly in two parts and vary from just a dorsal break of the cortex to propagation into the body of the bone as well as traversing both cortices. The fracture line itself will most commonly be in the sagittal plane. However, it is common to see involvement of both the sagittal and frontal plane.
Appreciating the orientation of the fracture is imperative for proper screw placement. The CT scan will allow the appreciation of chronic qualitative changes such as the presence of sclerosis of the fracture margins, cyst formation, bone collapse and malalignment. A CT scan can also play a vital role to confirm healing of the fracture even with the presence of screw fixation over both MRI and bone scan.
Magnetic resonance imaging and CT scans serve vital roles in the diagnosis, evaluation and classification of navicular stress fractures, and in treatment planning. Their importance should not be overshadowed by monetary considerations. Failure to fully appreciate this injury can lead to poor outcomes for the physician and patient.
How To Address Stress Reactions Of The Tarsal Navicular
The specific treatment for tarsal navicular stress reactions will depend upon advanced imaging findings. General guidelines for specific injury patterns are starting to be well accepted but continue to evolve.11
Stress reaction of the tarsal navicular. These injuries will show a positive bone scan and MRI but will be negative for a definitive break of either cortex via MRI and/or CT scanning. Physicians often diagnose these injuries early and direct their attention toward stopping the propagation of the injury. In regard to treatment, one should also attempt to thwart the longitudinal and shear stress across the navicular.
I recommend four to six weeks of non-weightbearing with immobilization in a removable boot walker or below knee cast. Physicians should perform serial examination and appreciate the resolution of tendon and bone pain. If the navicular is still painful after six to eight weeks, obtain a repeat CT as the initial injury may have progressed to a fracture. This may be the the result of the full extent of the stress injury having not reached a crescendo and not being apparent on initial imaging.
If the symptoms have resolved, attempt a trial of partial protective weightbearing and progress the treatment accordingly. In regard to this injury, I have seen patients take an average of three to four months before they could return to ballistic sports activity or normal activities of daily life, etc.
Pertinent Insights On Partial Stress Fractures
Partial stress fracture of the navicular. This is more of a subacute to chronic presentation or diagnosis that will be positive on the bone scan. Also bear in mind that the MRI and the CT will show a break of the dorsal cortex only. The fracture margins usually will be negative for sclerosis, bone collapse, malalignment and/or cystic changes.
One can treat acute incomplete fractures with no sclerosis or cystic changes conservatively by closely following the above protocol. Conservative management would entail strict protective non-weightbearing for a period of time. One should reexamine the patient to look for a resolution of clinical symptoms and then the patient can progress as tolerated.
The use of screw fixation is up to physician preference depending on the extent of the fracture propagation into the body of the navicular. One should consider screw fixation when the fracture line involves greater than 50 percent of the bone. Those with advanced changes will need debridement of the fracture, autogenous bone grafting and possible screw fixation.
Postoperatively, I have patients maintain immobilization for eight weeks. This is followed by four to six weeks of open kinetic chain range of motion. Begin protective weightbearing at 12 weeks postoperatively and progress the patient’s treatment as tolerated. In order to ensure that progressive healing has occurred, one should consider a repeat CT prior to the patient returning to sporting activity.
When A Patient Has A Complete Fracture
Complete fractures of the tarsal navicular. Physicians normally see this injury pattern with an acute traumatic event or in cases of a chronic stress reaction of the navicular. This injury will be positive on bone scan and MRI, and the CT scan will show a fracture that violates the dorsal and plantar cortex. One must evaluate the fracture for sclerosis, bone cysts and/or malalignment. In addition to these changes, one may also see the collapse, most commonly, of the lateral pole of the navicular or dorsal extrusion of fragments. Physicians will also readily appreciate avascular necrosis of the bone on MRI as well as articular changes.
In regard to complete fractures without sclerosis and good alignment, surgeons can employ percutaneous screw fixation as opposed to open reduction. This approach reduces local morbidity and maintains the blood supply to the bone. Fractures with chronic changes and/or displacement will need debridement, possible bone grafting and anatomical reduction with screw fixation. When screw fixation is necessary, I recommend a titanium screw as opposed to a stainless steel screw. The titanium screw will lend itself to advanced imaging, if necessary in the future, and its modulus of elasticity is closer to bone than steel.
The fractures with advanced avascular necrosis, bone collapse, chronic changes and multiple parts are a great challenge for even the most experienced surgeon. These patterns usually require excision of the fragments and, at times, the entire navicular with a large autogenous bone graft and primary fusion of the talonavicular joint. This is a salvage procedure that is meant to restore a plantigrade stable foot without return to athletic activity.
Stress injuries of the tarsal navicular will progress and present along a continuum of severity. Chronic changes can result from a delay in diagnosis or presentation. Chronic injury to this bone will lead to more complex surgical intervention, protracted recovery and increased morbidity. A timely diagnosis is in the best interest of the patient and physician. I recommend the complementary use of MRI and CT scanning to accurately characterize the full extent and orientation of the fracture as well as any qualitative bone changes.
After completely evaluating the injury, one can carry out a systematic and evidence-based treatment plan. Most patients are able to return to sporting activity within six months except for those who will undergo fusion. One should warn all patients of the inherent possible morbidity despite appropriate intervention. Possible complications may include delayed and non-union, recurring fracture, continued pain and failure to return to the previous level of activity.11
Dr. Allen is a partner in Sports Medicine Associates of San Antonio. He is a Fellow of the American Academy of Podiatric Sports Medicine and the American College of Foot and Ankle Surgeons. He is an Assistant Clinical Professor at the University of Texas Health Science Center in the Department of Orthopedics/Podiatry Division in San Antonio. He is a team podiatrist for the San Antonio Spurs and various other sports teams.