Tibial Stress Fracture and “Shin Splint” Syndrome in the Same Patient Diagnosed on ^99mTC-Methylene Diphosphonate Bone Scintigraphy and Single-Photon Emission/Computed Tomography

Abstract

We present a case of an 18-year-old male athlete who presented with complaints of right lower leg pain for 10 days following intense exercise. The most likely diagnosis was a possible tibial stress fracture or a "shin splint" syndrome. The radiograph did not reveal any significant abnormality in the form of any fracture or a cortical break. We performed planar bone scintigraphy including single-photon emission computed tomography (CT)/CT that revealed the presence of the two concomitant pathologies in the form of a hot spot which corresponded with a bone lesion in the tibial stress fracture and subtle remodeling activity without evidence of significant cortical lesion in the shin splints in bilateral lower limbs (R>L).

Case Summary

An 18-year-old athlete male presented with a history of sudden onset, progressive pain in the bilateral lower limb, which used to aggravate on intense exercise. The pain was more in the right limb in the lower one-third. The patient's radiograph did not reveal any significant abnormality. ^99mTc-methylene diphosphonate bone scintigraphy acquired subsequently including single-photon emission computed tomography (CT)/CT demonstrated a fusiform cortical tracer uptake in the distal one-third of the right tibia along with linear intense tracer uptake in the bilateral tibia [Figures 1-3].

Figure 1: ^99mTc-MDP blood flow (a and b) and serial blood pool images (c and d) reveal subtle increased blood flow and fusiform area of tracer pooling in the distal one-third of the right tibia, respectively. Delayed 3 h whole body (g and h) and spot images (e and f) showing a pathological fusiform area of increased tracer uptake in the medial cortex of the distal one-third of the right tibia indicating a focal bone lesion. Furthermore, the scan shows heterogeneous linearly increased cortical tracer uptake in the external and internal cortices of both tibia (R>L) suggestive of “shin splint.” MDP: Methylene diphosphonate

Figure 2: SPECT (a-c) of the bilateral tibia revealed an intense hot spot in the posterior medial aspect of the tibia, corresponding with a linear cortical disruption at the posterior portion of the right distal one-third of the tibia on the CT images (a). SPECT: Single-photon emission computed tomography/computed tomography

Figure 3: Similar slices of the other transverse uptakes in the tibial cortical bone reveal mild cortical thickening on CT images (a-c), while the vascular and pool phases are usually negative with no significant radiological bone findings. “Shin splints” is usually due to disruption of Sharpey's fibers of the soleus insertions secondary to muscle hyperactivity, resulting in pain in the posterior region of the tibia. In athletes, repeated microtears with subsequent healing reactions can result in increased tracer uptake at the site of tendon or ligament attachment. CT: Computed tomography

Discussion

Stress injuries or fractures are a common occurrence in athletes and military recruits which accounts for approximately 10% of all sports-related injuries.[^1,2] The most common involved bone is of the lower extremity with the most common being, the tibia followed by the tarsal and metatarsals of the lower limb.[^1,2,3] The fractures are the result of abnormal but repetitive loading on normal bone, leading to prolonged overuse and local cortical resorption and fracture without adequate time for adaptation and the physiologic process of bone healing.[^3,4]

The microfractures due to repetitive trauma which exceeds the remodeling capacity of bone lead to either unhealed or partially healed bone which is weak and prone to stress fractures.[³]

Shin splints are also termed medial tibial stress syndrome or soleus enthesopathy usually caused due to exercise-induced pain to the posteromedial aspect of the distal two-thirds of the tibia. It is usually characterized by diffuse nonlocalized tenderness along the posteromedial, mid to distal part of the tibia with no edema. Periosteal reaction at the site of stress shows intense transverse uptake in the distal posteromedial tibia in the delayed phase, with no significant alterations in blood flow and blood pool.[^3,5]

Both shin splints and stress fractures are the most common causes of leg pain in athletes that can coexist. Often, the clinical symptoms and findings on physical examination are inconclusive to confirm the diagnosis of a stress injury. Early diagnosis of stress fractures by imaging reduces morbidity while avoiding unnecessary time out from training or sports participation and an aggravated and prolonged process of healing. Although radiographs are readily available with high specificity, they lack sufficient sensitivity, especially in the early stages. In contrast, BS has the ability to depict areas of even subtle osseous turnover and bone remodeling within hours of injury providing sensitivities between 74% and 100% for the detection of stress injuries.[^4,6] Although the management of these two entities is different, and are clinically difficult to distinguish. The stress fracture responds only to rest, whereas “shin splint” pain responds to anti-inflammatory drugs and the patient can continue with physical activity.[^7,8]

Planar bone scintigraphy could identify both entities but not in all cases. It could clearly distinguish the two entities by combining the functional information of uptake pattern and anatomical information of bone injury due to stress on the CT scan. Osteoid osteoma is also three phase positive, which can involve any bone commonly femur and tibia which usually presents with a history of night pain. The central nidus of high bone turnover with a zone of radiolucency around it differentiates it from a stress fracture, which reveals a cortical break on CT. Osteomyelitis will have a larger area of tracer activity with any shape on a planar bone scan unlike stress fracture with the fusiform area of uptake. CT image demonstrating osseous changes such as cortical destruction, periosteal reactions, and sequestrum is seen in acute osteomyelitis. Furthermore, clinical history should be taken into account, which can further narrow down the diagnosis.[^9,10,11]

Bone scintigraphy can be used to predict the time to return to full exercise and also the response to the management by means of follow-up scintigraphy. The three-phase bone scan shows a greater diagnostic accuracy than conventional radiology.[^2,7,12]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed

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Conflicts of interest

There are no conflicts of interest.