Sacral stress fracture in a young-adult, long-distance runner: an underestimated cause of low back pain

Abstract

Sacral stress fractures (SSFs) in physically active young patients are frequently misdiagnosed due to the lack of specificity of signs and symptoms. Over the last years, these injuries have been described as rare, although some studies report that the incidence of an SSF in athletes may be as high as 20%.

We describe a case of a male long-distance runner in his late 20s with a 1-month undiagnosed SSF. The patient complaints included insidious right low back and buttock pain without trauma that started after running a marathon. MRI revealed an extensive area of bone marrow oedema in the right sacral ala consistent with an SSF.

This case highlights the importance of investigating SSF in young-athlete patients who were otherwise healthy, using appropriate imaging modalities to assess the presence and morphology of a fracture.

Background

Sacral stress fractures (SSFs) in athletes have been occasionally reported in the literature in physically active young-adult patients.^1–3 These are considered fatigue fractures resulting from abnormal stress over a healthy bone, particularly in modalities that promote overuse.

Although some studies report that the incidence of an SSF in athletes may be as high as 20%, this injury is rarely diagnosed due to the lack of specificity of their signs and symptoms.⁴

We report a massive SSF in a healthy male in his late 20s, long-distance runner with mechanic insidious low back pain and non-specific pain in the right gluteal area.

Case presentation

We report a case of a male long-distance runner in his late 20s who came to an outpatient clinic with a 1-month history of insidious right low back and buttock pain. He denied any history of trauma or constitutional symptoms. Complaints began after finishing a marathon.

The patient reported he was initially observed and advised to reduce physical exercise for 15 days, with significant pain relief.

The patient gradually increased workout intensity and a similar pain began. Initially, the pain was referred to his lower back and right gluteal muscles, worse with running, but later walking became a challenge. Ibuprofen provided minimal relief.

Clinical evaluation showed lumbosacral and right buttock tenderness, andcontracture of sacrospinalis muscles, without appreciable restriction on lumbar mobility. Muscle strength and lower extremity myotatic reflexes were symmetrical. Laségue test was negative bilaterally. Milgram test was also negative. No radicular symptoms were detected. Hip mobility was normal, with mild discomfort on right medial rotation. Flexion, abduction, external rotation (FABER) test was positive on the right side.

The patients’ personal reports did not mention metabolic diseases, hormonal disorders or regular use of medication. He took a variety of supplements, which do not interfere with bone metabolism, including magnesium, branched-chain amino acid and vitamin B complex supplements.

Investigations

Because radiographs of his lumbar spine and sacrum done 1 week after the onset of pain did not document significant abnormalities, MRI was performed at week 4 after symptomatic onset. Coronal and axial MRI imaging revealed an area with increased signal on T2-weighted images extending over the right sacral ala representing right bone marrow oedema consistent with SSF (figures 1–3).

Figure 1.

Coronal MRI one month after initial complaints revealing an extensive area with increased signal on T2-weighted images extending over the right sacral ala representing right bone marrow oedema consistent with SSF.

Figure 2.

Coronal MRI one month after initial complaints revealing an extensive area with increased signal on T2-weighted images extending over the right sacral ala representing right bone marrow oedema consistent with SSF.

Figure 3.

Axial MRI one month after initial complaints revealing an extensive area with increased signal on T2-weighted images extending over the right sacral ala representing right bone marrow oedema consistent with SSF.

A CT scan was requested in the sixth week after the initial complaints showing a fracture line involving the right sacral wing without damaging the sacral foramina (figures 4–6).

Figure 4.

Coronal image on CT six weeks after the initial complaints showing a fracture line involving the right sacral wing without damaging the sacral foramina.

Figure 5.

Coronal image on CT six weeks after the initial complaints showing a fracture line involving the right sacral wing without damaging the sacral foramina.

Figure 6.

Sagital image on CT six weeks after the initial complaints showing a fracture line involving the first sacral vertebra.

Comprehensive blood testing (blood count, sedimentation rate, C reactive protein) and bone mineral density (dual-energy X-ray absorptiometry) were unremarkable.

Treatment

After SSF diagnosis, the patient was instructed to stop high intensity training for 12 weeks, which included running and demanding activities. Crutches were prescribed for 4–6 weeks, with maintenance of axial load. Progressive low-intensity and low-impact exercises were suggested, namely walking and water based to maintain aerobic condition. After week 6, he started a core and lower limbs muscle strengthening programme, as well as proprioceptive closed kinetic chain work, not exceeding the pain threshold. This programme was maintained until the 14th week.

Outcome and follow-up

At week 12, the patient reported minimal soreness in the morning. He had a normal gait pattern and no tenderness over the sacrum or sacroiliac joints. FABER test was negative.

Kinetics modalities, including joint motion, muscle strengthening and proprioceptive training, do not cause pain or functional limitation.

At week 16, the patient began slow, aerobic and low-impact running, for short periods (15–30 min) every other day.

It was suggested to normalise running training between the 20th and 24th week, considering that there were no symptoms.

A follow-up MRI at 6 months showed no bone oedema or acute signs of fracture on short inversion time inversion recovery at his right sacrum (figure 7).

Figure 7.

Follow-up MRI at six months with no bone oedema or acute signs of fracture on short inversion time inversion recovery at his right sacrum.

During the clinical evolution, no signs or symptoms related to the involvement of the sacred roots were identified.

No further complications or sequelae were noted, being discharged from the consultation at the 24th week.

Discussion

SSF can be classified as fatigue fractures or insufficiency fractures. Fatigue fractures result from repetitive forces, often from overuse, over a normal and healthy bone resulting in progressive weakness and eventually fracture. Insufficiency fractures are often secondary to a pre-existing condition and occur due to minor pressure in a bone that is weakened, usually in the elderly related to osteoporosis, or patients undergoing radiation therapy or treated with high-dose corticotherapy.^{5 6}

The SSF was first reported in 1982 in three elderly patients and since then other cases have been described in younger patients, especially athletes whose activities include running, soccer, rugby, basketball, badminton and volleyball, and military personnel.1 3 7 8 Some studies indicate that high intensity training with rapid changes in duration and frequency could represent risk factors to SSFs in athletes.^{9 10}

Biomechanics regarding SSF in athletes is still to be unveiled. Riedl et al studied nine distance runners and triathletes with an SSF and noted that all patients had a certain degree of spinal hyperlordosis. In lumbar hyperlordosis, the axial loading is decreased and shear spinal forces over the sacrum are increased. The authors also suggest that because of the altered pelvic tilt in this spinal deformity, the interactions between bones, muscles, tendons and connective tissue in the pelvis and hip joints may result in muscular fatigue leading to higher and/or lower forces and bone stress over the sacrum.¹¹

Historically, SSFs have been reported as rare. In the first decade of the 21st century, some studies documented that only 0.5%–2% of high-performance athletes would sustain a stress fracture, in less than 1.5% of the cases in the sacrum.^{12 13} Nevertheless, over the last few years, a number of SSFs reported have been steadily increasing, which means that they are not as rare as initially thought and probably are missed in a considerable number of patients.1 3 8–12 14 15 It is possible to hypothesise that these injuries are frequently missed because of the lack of specificity of clinical manifestations, because of small knowledge in physicians, trainers and athletes, or because of failures related to the imaging diagnosis.3 4 13 16 Many of these injuries are treated for several weeks as mechanical condition of the lumbar spine, a fact probably justified by the topography and symptomatic non-specificity.

The diagnosis of SSFs can be challenging and requires a combination of clinical presentation findings, imaging studies and blood tests. Athletes with a history of recent high intensity training and excessive repetitive activity presenting lumbar, sacral and/or buttock pain, with no history of significant trauma should undergo evaluation for SSF. The onset of the pain is usually insidious and starts after sports activity, limiting their practice; but with time the pain becomes present even during daily life activities.¹⁷

Neurological examination is usually intact, although sometimes the pain can irradiate to the ipsilateral leg due to irritation of the sacral nerve roots.¹⁸ Blood examinations are typically normal but conditions associated with an altered bone metabolism, such as exercise-induced hypogonadal male condition or female athlete’s triad, rickets, thyroid dysfunction or hyperparathyroidism should be excluded.^{11 19}

The SSFs are difficult to diagnose on radiographs and may not detect the injury until fracture healing is well underway. Gold standard is the MRI having better sensitivity in an acute but also subacute setting, typically showing increased signal on T2 corresponding to bone oedema. CT scan should be performed in specific cases to characterise the fracture pattern and to exclude possible involvement of the sacral foramina.^{14 15}

Our patient presented with a 1.5-month history of lower back and buttock pain after running a marathon, which aggravated with sports activity and later limiting simple daily life activities. MRI was essential for the diagnosis in order to guide the treatment and rehabilitation programme of the athlete.

Differential diagnosis of fatigue SSF should include sacroiliac joint dysfunction, spondylolisthesis, radiculopathy, lumbar discopathy, juvenile disk disease, facet arthropathy and lumbar or pelvic muscle strains.²⁰ In several cases, CT scan might be helpful to rule out other conditions.^{4 16}

Bearing in mind that SSFs are frequently misdiagnosed in young-adult healthy athletes with non-specific symptoms, physicians should be aware of this condition and suspect in patients with known risk factors. Frequent orthopaedic check-ups should be performed in these athletes to assess normal biomechanical function of the pelvis when symptoms.

Such assessments should include checks for leg imbalances, pelvic tilt, SIJ mobility, muscle tone and shortenings, core stability.

Because sacral stress reactions commonly remain undiscovered until they have exacerbated to manifest stress fractures, a systematic sports orthopaedic check-up of the musculoskeletal status and for normal biomechanical function of the pelvis is recommended whenever first signs of moderate, but recurring buttock and/or lower back pain show up in an endurance athlete.

Future studies should focus on understanding the biological and biomechanical factors that predisposes to SSFs in young athletes.

Patient’s perspective.

My complains started as a mild low back pain that worsened with exercise and simple daily life activities, including my job. I work in industrial machine maintenance and for that period I was not able to work so I was put on sick leave and saw my monthly salary reduced.

I came to see this doctor 1 month after my complains began and until that day I was instructed to just take some painkillers and stop physical activity. No diagnosis was done until then. I am a professional long-distance-runner used to high intensity daily training habits so was really hard to stop. I got anxious and apprehensive regarding my sports return. Once the diagnosis was made the doctor told me I could make some physical exercise and started a rehabilitation programme, which for me represented a light at the end of the tunnel. We started with low impact and low intensity exercises, training essentially upper body either in the sole but also water, in order to maintain aerobic conditioning and for personal satisfaction.

Learning points.

• Sacral stress fracture should be suspected in healthy-athlete patients who perform high intensity training and/or activity that involves rapid or prolonged repetition.

• Clinical signs include lumbar, sacral and/or buttock pain, with no history of significant trauma.

• The onset of the pain is usually insidious and starts after sports activity.

• MRI is the gold standard to diagnose sacral stress fracture and to rule out other differential diagnosis.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).