Uncommon injuries: external iliac artery endofibrosis

In the series on unusual sporting injuries and conditions, Chris Mallac explores a condition known as external iliac artery endofibrosis, including its pathogenesis in athletes, the typical symptoms, its diagnosis, and the management options available to the clinician.

Many athletes experience a certain degree of muscle pain, cramp, and fatigue during high-intensity efforts. Most of these sensations are caused by the usual metabolic fatigue associated with intense efforts during exercise. However, leg pain and weakness may be caused by an unusual source – the arteries. Damage to the arteries occurs when stretched or ‘kinked’ during exercise, which may restrict or obstruct blood flow. This may produce pain, burning, and weakness during exercise. The most common site is the external iliac artery.\

External iliac artery endofibrosis (EIAE) – also known as ‘cyclist’s iliac syndrome’ - is a relatively new clinical entity and is a poorly understood condition by medical practitioners. It as was originally described in the 1980s as a cause of lower-leg pain in professional cyclists^(1,2). Although amateur and professional cyclists under the age of 40 appear to be the primary demographic affected by this condition, it may also be a problem in runners, triathletes, soccer players, rugby players, rowers, tennis players and speed skaters⁽³⁾. This condition is often undiagnosed or misdiagnosed, as vascular disease is unexpected in these athletes. Instead, lower limb (and sometimes buttock pain) is usually attributed to musculoskeletal or neurologic causes.

Etiology

In professional cycling, there seems to be a correlation between EIAE and the distance and intensity of cycling training⁽⁴⁾. That is, the more professional a cyclist, the greater the chance EIAE of occurring in these athletes. Vascular injuries have been reported to account for up to 20% of all overuse lower limb injuries in cyclists⁽⁵⁾. Other features relating to the incidence of EIAE include:

1. The majority of sufferers (85%) seem to be male. However, this may be biased as the number of men who cycle is greater than the number of women⁽⁶⁾.
2. Seems to only affect one side - only a small percentage (15%) of cases are bilateral⁽⁷⁾.
3. Seems to affect the left side more often than the right side⁽⁸⁾.

Pathogenesis

Endofibrosis is a pathologic process whereby the lumen of the artery becomes progressively occluded due to a thickening of the arteries intima, and this can lead to claudication symptoms at maximal effort. These endofibrotic lesions have an accumulation of sub-endothelial loose connective tissues, which contain collagen, elastin and smooth muscle. This process does not involve the arterial endothelium. The most common site of injury (90% of cases) is the external iliac artery (see figure 1), but can infrequently involve the common iliac, profundal femoris and common femoral arteries^(9-11).

Figure 1: Anatomy of the External Iliac Artery

---

A tough fibrous tissue build-up may exist on the inside layer of the damaged artery. This tissue may then narrow the artery and prevent it from dilating during high-intensity exercise. Some of the intrinsic variables that influence the development of EIAE include:

• The flexed posture of the athlete (such as cycling), which may cause repetitive stretching and deformation of the iliac arteries⁽¹²⁾(see figure 2).
• Unusually long iliac vessels may increase the chance of ‘kinking’ during hip flexion⁽⁶⁾.
• The external iliac artery being fixed by surrounding soft tissue or branches of the iliopsoas muscle⁽¹³⁾.
• A hypertrophied psoas muscle increases the stretching of the external iliac artery during hip flexion and increases mechanical stress, which may lead to endofibrosis. In addition to creating endofibrosis, hypertrophy of the psoas exacerbates kinking of the external iliac artery⁽¹²⁾.

These factors may together result in a continuous, repetitive flexing of the artery while under pressure. This stress, over hundreds of hours of high-intensity training, may cause damage to the various layers of the artery wall, or may cause the artery to be stretched, or kinked.

Figure 2: How cycling ‘kinks’ the external iliac artery

---

Signs and symptoms

Subjective

The key subjective findings that may be elucidated during the history taking are as follows:

1. Patients are usually asymptomatic whilst at rest or during submaximal exercise⁽¹⁴⁾.
2. Symptoms usually appear at maximal or near maximal exertion, and cease during rest.
3. Symptoms include muscle cramping, weakness, paraesthesia and numbness, and swelling of the thigh^{(7, 15-18)}.
4. A sensation that the muscle is ‘suffocating’.
5. Pain usually felt in the thigh; however, it may also be felt in the calf and buttock.

Objective

EIAE usually presents without any definitive physical signs. Peripheral pulses are usually intact, and capillary refill is not elongated. An audible bruit over the femoral artery may be found in 44% of cases, which might be better detected after exercise or with the hip flexed^(7,16). It was found that in 79% of positive cases, a combination of clinical history with a specific vascular questionnaire, and the finding of an audible femoral bruit plus normal back mobility facilitated identification of a vascular cause⁽⁵⁾.

More direct measures, such as a drop in the ankle brachial pressure index (ABPI) during exercise allows identification of up to 85% of patients with flow limitations^(18,19). An ABPI test before and after exercise is the least invasive test to get an initial diagnosis. This test measures blood pressure at the ankles and in the arm at rest and then after exercise. A normal resting ankle-brachial index is 1 or 1.1 and anything below that is abnormal. Athletes with arteriopathy generally have normal readings at rest, but after exercise (treadmill running or cycling) the ankle pressure in the affected leg drops dramatically, indicating reduced blood flow. A drop of at least 0.4 of difference is considered to be significant⁽²⁰⁾and ABI measurements that are less than 0.5 in the supine position completed 1 minute after exercise can identify 80% of cases with 100% specificity for the condition⁽²¹⁾.

Imaging

Doppler ultrasound is the first imaging modality used. Doppler is a non-invasive, cost-effective way to assess for endofibrotic lesions. However, it is highly operator dependent, and high sensitivity has been found in patients presenting with severe disease. It allows the measurement of peak systolic velocity, which is sensitive for endofibrotic stenosis.

This should be performed in hip flexion, isometric contraction of the hip flexors, or after exercise. In this manner, the test will detect flow limitations in up to 85% of cases^(22-24); combined with clinical history, physical examination, and ABPI, this imaging mode will reach an accuracy of more than 90%⁽²⁵⁾.

Additional imaging tests that may be recommended are CT angiography or static magnetic resonance angiography (MRA). CT angiography allows for 3-dimensional reconstructions while MRA allows for assessment of vessel length, stenosis, and kinking. The test should be performed with the hips flexed since the majority of cases do not kink unless in hip flexion. Despite all the advantages of MRA, it should be performed in addition to Doppler imaging because movement artifact might lower the MRA sensitivity.

Management

Conservative treatment includes positional changing (avoiding extreme hip flexion) and, in the recreational athlete, avoiding maximal exertions. Competitive cyclists should be advised to raise the handlebar and bring the saddle forward. In doing so, they are reducing hip flexion; however, changing cycling position might not be feasible for professional cyclists as it renders them less aerodynamic.

In the short term, to quickly resolve the symptoms temporarily and quickly, a balloon angioplasty may be attempted⁽²⁶⁾. This may get an athlete through an important competition without the complications of post-operative trauma. When a clear arterial pathology accounts for the symptoms, or in the case of failed conservative management, surgical intervention is warranted. Open vascular surgery is currently the preferred surgical option. Several reports have shown endovascular techniques to be unsuitable for this pathology^(20,26,27).

The most common method of repair is endofibrosectomy with patch angioplasty⁽²⁾. This involves opening or removing the narrowed section of the artery and placing a synthetic patch or natural tissue graft over the artery. In more complex cases, reconstruction with either autologous or prosthetic interposition graft has been documented to have excellent results, with 90% primary patency and a 99% return-to-sport rate, including a return to high-level competition⁽²⁸⁾.

Other possible surgical interventions include bypassing the damaged artery or simply releasing the inguinal ligament or psoas muscle attachments to the artery, which have also been implicated in compressing or kinking the external iliac artery. The best treatment option seems to depend upon the exact location and cause of the damage, as well as the athlete's long-term goals. Depending upon the type of surgical procedure performed, the athlete may be walking within two weeks, cycling easily on a trainer by week three and on the road in four to six weeks.

Conclusion

EIAE is a rare but potentially disabling condition suffered by athletes, particularly cyclists. The hip-flexed nature of certain sports with high blood flow conditions such as high-intensity exercise may predispose the athlete to potentially compression, stretch and ‘kinking’ of the external iliac artery. This presents as a cramping, weakness and loss of power in the legs. The medical professional may refer the athlete for specific vascular studies such as the ankle brachial pressure index (ABPI), Doppler ultrasound and CT angiograms. In the non-professional cyclist, it is managed conservatively with activity and position modifications. In the elite athlete, and in the event of failed conservative treatment, surgery is recommended.

References

1. Helv Chir Acta. 1985;51:793-795
2. Ann Vasc Surg. 1986;1:297303
3. Lancet 2002;359(9305):466-73
4. Acta Chir Belg. 2004;104:635-640
5. Int J Sports Med. 2002;23:313-321
6. Med Sci Sports Exerc. 2002;34:385-393
7. Eur J Vasc Endovasc Surg. 2003;26:629-634
8. Sports Med. 2004;34:419-425
9. Hum Pathol. 1990;21:524-529
10. J Vasc Surg. 2003;38:180-182
11. JBR-BTR. 2009;92:184-185
12. Sports Med. 2004;34:427-442
13. Surg Radiol Anat. 1989;11:33-36
14. Eur J Vasc Endovasc Surg. 2009;38:180186
15. J Mal Vasc. 1996;21:95-97
16. J Vasc Surg. 2002;36:565-570
17. Br J Sports Med. 1997;31:155-156
18. Med Sci Sports Exerc. 2001;33:1862-1867
19. J Vasc Surg. 2001;33:935-942
20. G Chir. 2015. Vol. 36 - n. 6 - pp. 267-271
21. Eur J Vasc Endovasc Surg 2012;43(2):208-17
22. Am J Sports Med. 1993;21:861-863
23. Eur J Vasc Endovasc Surg. 2004;28:513-519
24. Eur J Ultrasound. 2001;14:129-140
25. Int J Sports Med. 1999;20:421-428
26. Br J Sports Med 2001;35:70–71
27. Cardiovasc Intervent Radiol. 2006;29:866-869
28. J Vasc Surg. 2010;52(1):219-21