MRI Web Clinic — August 2004

Lesser Tuberosity Avulsion Fracture
Pamela H. Burdett, M.D.

Clinical History: A 14 year old water polo player presents with chronic anterior shoulder pain. Axial proton density (1a) and oblique sagittal (1b) T1-weighted images are submitted for review. What are the findings? What is your diagnosis?

1a
1b
Figure 1:

Axial proton density (1a) and oblique sagittal (1b) T1-weighted images

Findings

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2b
Figure 2:

(2a) Axial proton density and (2b) Sagittal T1-weighted images demonstrate corticated ossifications (arrows) medial to the lesser tuberosity of the humerus, abutting the undersurface of the subscapularis tendon (arrowhead).

Diagnosis

Isolated avulsion fracture of the lesser tuberosity.

Discussion

Isolated fractures of the lesser tuberosity of the humerus are uncommon, with only a few pediatric cases reported.1-9 It is thought that in such cases the recently fused lesser tuberosity of the adolescent is the point of weakness, rather than the subscapularis tendon insertion.10 The injury most commonly occurs with forced external rotation during abduction, and can be seen in contact sports such as football or wrestling. However, it may also present, as in this case, as a chronic overuse injury in throwing athletes. In these patients, the stress upon the lesser tuberosity from contraction of the subscapularis tendon is maximal as the thrower transitions from the fully abducted cocking phase to the internal rotation of the acceleration phase.11

Affected patients most often present with a history of chronic shoulder pain. Physical exam may reveal tenderness over the anterior aspect of the shoulder, weakness in internal rotation, increased passive external rotation, or a positive lift-off test.

Delayed union of the lesser tuberosity fracture is common at presentaton, and the fracture is often not visible on AP x-rays. It can be visulized on axillary x-rays, but is best seen on MRI, which also assesses the integrity of the subscapularis tendon.

Images below are from an MRI on another patient who presented three months after being tackled while throwing a football.

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Figure 3:

(3a) An axial gradient echo image demonstrates a medially displaced lesser tuberosity fragment (arrow) with a slip of tendon still attached to it (arrowhead).

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Figure 4:

(4a) The higher axial image shows a partial thickness tear of the subscapularis tendon (arrowhead) and again demonstrates the lesser tuberosity fragment (arrow).

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Figure 5:

(5a) Marrow edema is visible at the fracture site (arrow) on the coronal fat suppressed T2 weighted image.

 

Because the majority of cases of lesser tuberosity avulsion present with malunion or delayed union, continued pain and weakness with internal rotation frequently results. A trial of conservative treatment may be undertaken, but displaced fracture fragments and surrounding fibrosis may have to be excised to restore full strength and pain free throwing ability in the adolescent athlete.

Conclusion

Avulsion fractures of the lesser tuberosity are unusual injuries that should be suspected in an adolescent athlete who presents with chronic pain and focal anterior tenderness. The fracture is often not visible on AP x-rays. MRI not only reveals the size and location of the avulsed lesser tuberosity fragment, but can also provide important assessment of the integrity of the subscapularis tendon.

References

1 Klasson SC, Vander Schilden JL, Park JP: Late effect of isolated avulsion fractures of the lesser tubercle of the humerus in children: Report of two cases. J Bone Joint Surg Am 75: 1691-1694, 1993

2 Kunkel SS, Monesmith EA: Isolated avulsion fracture of the lesser tuberosity of the humerus: A case report. J Shoulder Elbow Surg 2: 43-46, 1993

3 Le Huec JC, Schaeverbeke T, Moinard M, et al: Isolated avulsion fracture of the lesser tubercle of the humerus in children. Acta Orthop Belg 60: 427-429, 1994

4 Paschal SO, Hutton KS, Weatherall PT: Isolated avulsion fracture of the lesser tuberosity of the humerus in adolescents: A report of two cases. J Bone Joint Surg Am 77: 1427-1430, 1995

5 Ross GJ, Love MB: Isolated avulsion fracture of the lesser tuberosity of the humerus: Report of two cases. Radiology 172: 833-834, 1989

6 Shibuya S, Ogawa K: Isolated avulsion fracture of the lesser tuberosity of the humerus: A case report. Clin Orthop 211: 215-218, 1986

7 Sugalski MT, Hyman JE, Ahman CS, et al: Avulsion Fracture of the Lesser Tuberosity in an Adolescent Baseball Pitcher: A Case Report, Am J of Sports Med vol 32, no 3, 004

8 Sikka RS, Neualt M, Guanche CA: An avulsion of the subscapularis in a skeletally immature patient: Case Report

9 Earwaker J: Isolated avulsion fracture of the lesser tuberosity of the humerus. Skeletal Radiol 19: 121-125, 1990

10 White GM, Riley LH Jr: Isolated avulsion of the subscapularis insertion in a child. J Bone Joint Surg (Am) 67A: 635-636, 1990

11 Werner SL, Gill TJ, Murray TA, et al: Relationships between throwing mechanics and shoulder distraction in professional baseball pitchers. Am J Sports Med 29: 354-358, 2001

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