Magnetic resonance imaging of the elbow. Part I: Normal anatomy,imaging technique,and osseous abnormalities

Part I of this comprehensive review on magnetic resonance imaging of the elbow discusses normal elbow anatomy and the technical factors involved in obtaining high-quality magnetic resonance images of the elbow. Part I also discusses the role of magnetic resonance imaging in evaluating patients with osseous abnormalities of the elbow. With proper patient positioning and imaging technique, magnetic resonance imaging can yield high-quality multiplanar images which are useful in evaluating the osseous structures of the elbow. Magnetic resonance imaging can detect early osteochondritis dissecans of the capitellum and can be used to evaluate the size, location, stability, and viability of the osteochondritis dissecans fragment. Magnetic resonance imaging can detect early stress injury to the proximal ulna in athletes. Magnetic resonance imaging can detect radiographically occult fractures of the elbow in both children and adults. Magnetic resonance imaging is also useful in children to further evaluate elbow fractures which are detected on plain-film radiographs.Part II of this review can be found at:     

Magnetic resonance imaging in the evaluation of treatment response of lateral epicondylitis of the elbow

The purpose of this study was to investigate the treatment response in lateral epicondylitis (tennis elbow) by MRI. Magnetic resonance imaging was obtained in 30 patients with clinical symptoms of lateral epicondylitis of the elbow using T1-, T2- and T2-weighted fat-saturated (FS) sequences. The patients were randomised to either i.m. corticosteroid injection (n=16) or immobilisation in a wrist splint (n=14). Magnetic resonance imaging of the elbow was performed on a 1.5-T MR system at baseline and after 6 weeks. The extensor carpi radialis (ECRB) tendon, the radial collateral ligament, lateral humerus epicondyle at tendon insertion site, joint fluid and signal intensity changes within brachio-radialis and anconeus muscles were evaluated on the MR units workstation before and after 6 weeks of treatment. The MRI was performed once in 22 healthy controls for comparison and all images evaluated by an investigator blinded to the clinical status of the subjects. The MR images showed thickening with separation of the ECRB tendon from the radial collateral ligament and abnormal signal change in 25 of the 30 patients on the T1-weighted sequences at inclusion. The signal intensity of the ECRB tendon was increased in 24 of the 30 patients with lateral epicondylitis of the elbow on the T2-weighted FS sequences. In the patients there were no associations between pathologically signal intensity within the ECRB tendon on T1- and T2-weighted sequences and the degree of self-reported pain (Dumbells test) at inclusion. In general, the MRI changes persisted in the patients at follow-up after 6 weeks despite clinical remission. The increased signal intensity within the extensor tendon is indicative of lateral epicondylitis humeri. The changes in signal intensity and morphology of ECRB tendon seem to be chronic and may persist despite clinical improvement.     

MR imaging findings of lateral ulnar collateral ligament abnormalities in patients with lateral epicondylitis.

OBJECTIVE: The purpose of this paper was to use MR imaging to determine whether a relationship exists between lateral epicondylitis and abnormalities of the lateral ulnar collateral ligament. SUBJECTS AND METHODS: The study group comprised 35 consecutive patients who were referred for MR imaging to rule out lateral epicondylitis. On MR imaging, "lateral epicondylitis" was defined as increased signal intensity of the extensor tendons close to their insertion on the lateral epicondyle. The severity of the lateral epicondylitis was graded as mild, moderate, or severe. The origin of the lateral collateral ligamentous complex was characterized, and the lateral ulnar collateral ligament was graded as normal, thickened, partially torn, or torn. Eleven patients underwent elbow surgery after the initial MR examination. RESULTS: In 15 patients, MR imaging revealed characteristics of mild lateral epicondylitis. In 13 of these patients, the lateral ulnar collateral ligament was normal; one patient showed a thickened ligament; and one patient had a thinned ligament. In 11 patients, MR imaging showed features of moderate lateral epicondylitis. In eight of these patients, the lateral ulnar collateral ligament was thickened, and in the remaining three patients the ligament was normal. All nine patients with severe lateral epicondylitis showed abnormalities of the lateral ulnar collateral ligament on MR imaging. In one of these patients the lateral ulnar collateral ligament was thickened, in three patients we saw a partial tear, and in the remaining five patients we saw a complete tear of the ligament. CONCLUSION: In our study, MR imaging features of lateral epicondylitis were often associated with thickening and tears of the lateral ulnar collateral ligament.     

Sonographic examination of lateral epicondylitis

OBJECTIVE: The purpose of this study was to describe the sonographic appearance of the common extensor origin in cadavers and asymptomatic volunteers, and to relate this appearance to the findings in patients with lateral epicondylitis. SUBJECTS AND METHODS: Seventy-two elbows in 71 patients with lateral epicondylitis were examined on sonography. Most of the patients (60/71) gave a history of repetitive microtrauma. The injuries were evaluated with respect to location and severity. Focal areas of degeneration, discrete cleavage tears, and involvement of the lateral collateral ligament were identified. Calcification and bony changes were noted. The appearance of the normal common extensor tendon was described, and cadaveric specimens were dissected. Twenty-one patients subsequently underwent surgery. RESULTS: The normal common extensor origin is composed of longitudinal fibrils bound closely with the extensor carpi radialis brevis constituting most of the deep fibers, with the extensor digitorum making up the superficial part. The lateral collateral ligament can be identified as a discrete and separate band. The most common appearance of lateral epicondylitis is a focal hypoechoic area in the deep part of the tendon (46/72). These focal areas were identified at surgery and corresponded histologically to collagen degeneration with fibroblastic proliferation. Often discrete cleavage planes traversing the tendon were manifest as partial (18/72) and complete (2/72) tears. The lateral collateral ligament was involved in eight of 72 elbows. CONCLUSION: Sonography of the common extensor origin can be used to confirm lateral epicondylitis in patients with lateral elbow pain and provide information about the severity of the disease.     

The effectiveness of diagnostic imaging methods for the assessment of soft tissue and articular disorders of the shoulder and elbow

There are no clear guidelines for diagnostic imaging of articular and soft tissue pathologies of the shoulder and elbow. Several methods are used, including magnetic resonance imaging (MRI), magnetic resonance arthrography (MRA) and ultrasound (US). Their cost-effectiveness is still unclear. We performed a meta-analysis of the relevant literature and discussed the role of MR imaging of the shoulder and elbow compared with other diagnostic imaging modalities. For the shoulder impingement syndrome and rotator cuff tears, MRI and US have a comparable accuracy for detection of full-thickness rotator cuff tears. MRA and US might be more accurate for the detection of partial-thickness tears than MRI. Given the large difference in cost of MR and US, ultrasound may be the most cost-effective diagnostic method for identification of full-thickness tears in a specialist hospital setting (Evidence level 3). Both MRA and CT arthrography (CTA) are effective methods for the detection of labrum tears. More recently, multidetector CTA has offered the advantages of thinner slices than with MRA in a shorter examination time. Still, MRA has the advantage towards CTA to directly visualize the affected structures with a better evaluation of extent and location and to detect associated capsuloligamentous injuries. For the elbow pathologies, plain MRI or MRA have the advantage towards CTA to detect occult bone injuries. CTA is better for the assessment of the thin cartilage of the elbow. Both US and MRI are reliable methods to detect chronic epicondylitis; US is more available and far more cost-effective (Evidence level 2). MRA can differentiate complete from partial tears of the medial collateral ligament. US or MRI can detect partial and complete biceps tendon tears and/or bursitis. MRI can provide important diagnostic information in lesions of the ulnar, radial, or median nerve.     

Sonographic probe induced tenderness for lateral epicondylitis: an accurate technique to confirm the location of the lesion

The purpose of this study is to evaluate the hypothesis that ultrasonographic probe-induced tenderness is a useful adjunct to the simple sonography in confirming the location of the pathology within the extensor carpi radialis brevis tendon in patients with lateral epicondylitis of the elbow. We conducted a case controlled study by evaluating 27 consecutive patients in the age group of 37–59 years (median 44) who had typical symptoms of lateral epicondylitis and a visual analogue score of more than 4 and evaluating a same number of asymptomatic healthy volunteers in the age group of 37–59 years (median 43) by means of ultrasound examination of the lateral elbow in a period of 5 months from 2007 to 2008. When we identified sonographic anechoic or hypoechoic lesions within the common extensor tendon we compressed it with the ultrasound probe to elicit tenderness so as to confirm the site of lesion within the affected tendon. We observed that the abnormal lesion detected by ultrasonography corresponded to the point of maximal tenderness when compressed by the probe in all the symptomatic patients. We therefore conclude that as it is essential to accurately detect the lesion within the extensor carpi radialis brevis for the purpose of diagnosis and treatment of lateral epicondylitis of elbow the technique of inducing tenderness at site of abnormal shadow on ultrasound within the extensor carpi radialis brevis tendon improves the accuracy of identifying the site of lesion, prevents the misinterpretation of anisotropy as pathological lesion and also can be useful to maximize the efficacy of interventions aimed in treating the lateral epicondylitis.     

Magnetic resonance diagnosis of meniscal tears in patients with acute anterior cruciate ligament tears

OBJECTIVE: To evaluate the accuracy of magnetic resonance imaging in the diagnosis of meniscal tear in patients with acute anterior cruciate ligament tears. METHODS: Magnetic resonance images obtained from 41 patients imaged within 6 weeks of injury who had acute anterior cruciate ligament tears identified at arthroscopy were retrospectively reviewed for meniscal tear. RESULTS: With MR imaging the sensitivity, specificity and accuracy for diagnosing meniscal tears in the presence of acute anterior cruciate ligament tears were 71%, 93%, and 88%; for the lateral meniscal tears were 57%, 100% and 85%; and for the medial meniscal tears were 100%, 88%, 90%. All false negative cases (n = 6) involved the posterior horn of the lateral meniscus. CONCLUSION: In the presence of acute anterior cruciate ligament tears, MRI imaging has relatively low sensitivity for detecting meniscal tears due to missed tears in the lateral meniscus.     

Magnetic resonance imaging of the posterior cruciate ligament. Clinical use to improve diagnostic accuracy.

This study was undertaken to determine the accuracy of magnetic resonance image scanning in detecting posterior cruciate ligament injury, and to determine those clinical situations where it can add the most useful information. A retrospective study was conducted on 201 patients who underwent surgery after magnetic resonance scanning of their knees. Two additional patients who did not have surgery but had clinical findings grossly positive for posterior cruciate ligament injury were included in the analysis of magnetic resonance imaging accuracy. In all, there were 190 intact and 13 torn posterior cruciate ligaments. In a review of the clinical findings in the 11 patients with surgically documented tears, we found that all 11 had positive magnetic resonance scans. In 4 of the 11, magnetic resonance imaging provided especially useful information regarding the status of the ligament. For the 190 normal ligaments, there were no false-positive scans; for the 13 torn ligaments, there were no false-negative scans. Therefore, specificity and sensitivity estimates for this group were both 100%. Magnetic resonance imaging proved to be an accurate modality for evaluating the integrity of the posterior cruciate ligament. If used in the proper setting, it can provide useful information for diagnosing posterior cruciate ligament injuries.     

Ultrasonography of the elbow

Ultrasonography (US) of the elbow is an increasingly utilized modality for a variety of diagnoses. US is advantageous in many cases because of the ability to perform a dynamic examination while obtaining patient feedback. Furthermore, US is cost effective, widely available, and beautifully demonstrates superficial soft tissue structures. Finally, US is an excellent option for patients whose studies are degraded by motion artifact or those with claustrophobia concerns. The most common pathologies about the elbow are discussed in this article, including partial- and full-thickness tears of the biceps and triceps tendons, common extensor and flexor tendinosis, medial and lateral epicondylitis, radial and ulnar collateral ligament tears, ulnar nerve entrapment, cubital or olecranon bursitis, joint effusions, and intra-articular bodies. Relevant anatomy is detailed as it pertains to sonographic evaluation and appearance. In addition, specific imaging techniques and positions are described for optimum visualization of the various structures around the elbow because US is highly operator dependent.     

Knee dislocations: a magnetic resonance imaging study correlated with clinical and operative findings

OBJECTIVES: Our objectives were to determine retrospectively the prevalence, patients' demographics, mechanism of injury, combination of torn ligaments, associated intra-articular and extra-articular injuries, fractures, bone bruises, femoral-tibial alignment and neurovascular complications of knee dislocations as evaluated by magnetic resonance (MR) imaging. MATERIALS AND METHODS: From 17,698 consecutive knee examinations by magnetic resonance imaging (MRI) over a 6-year period, 20 patients with knee dislocations were identified. The medical records of these patients were subsequently reviewed for relevant clinical history, management and operative findings. RESULTS: The prevalence of knee dislocations was 0.11% [95% confidence interval (95% CI) 0.06-0.16)]. There were 16 male patients and four female patients, with ages ranging from 15 years to 76 years (mean 31 years). Fifteen patients had low-velocity injuries (75%), of which 11 were amateur sports related and four were from falls. Four patients (20%) had suffered high-velocity trauma (motor vehicle accidents). One patient had no history available. Anatomic alignment was present at imaging in 16 patients (80%). Eighteen patients had three-ligament tears, two had four-ligament tears. The four-ligament tears occurred with low-velocity injuries. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were torn in every patient; the lateral collateral ligament (LCL) was torn in 50%, and the medial collateral ligament (MCL) in 60%. Intra-articular injuries included meniscal tears (five in four patients), fractures (eight in seven patients), bone bruises (15 patients), and patellar retinaculum tears (eight partial, two complete). The most common extra-articular injury was a complete biceps femoris tendon tear (five, 25%). There were two popliteal tendon tears and one iliotibial band tear. One patient had received a vascular injury following a motor vehicle accident (MVA) and had been treated prior to undergoing MRI. Bone bruises (unrelated to fractures), four-ligament tears, biceps femoris tears, and popliteus tendon tears were encountered only in the low-velocity knee dislocations. Twelve were treated surgically, five conservatively, and three had been lost to follow-up. The biceps femoris tendon was repaired in every patient who was treated surgically. CONCLUSIONS: Knee dislocations occurred more commonly in low-velocity injuries than in high-velocity injuries, predominantly affecting amateur athletes. Biceps femoris tendon tears were the most common extra-articular injury requiring surgery. Neurovascular injury (5%) was uncommon. At imaging, femoral-tibial alignment was anatomic in the majority of patients.     

Characteristics of displaceable and nondisplaceable meniscal tears at kinematic MR imaging of the knee

PURPOSE: To prospectively determine if kinematic magnetic resonance (MR) imaging of the knee may demonstrate displacement of menisci with tears and, if so, to characterize displaceable and nondisplaceable meniscal tears. MATERIALS AND METHODS: The study was approved by the hospital's review board, and informed consent was obtained. Forty-two patients (30 men, 12 women; mean age, 36.9 years) with 43 arthroscopically documented meniscal tears visible at 1.5-T MR imaging underwent kinematic MR imaging with an open-configuration 0.5-T MR imager with their knees in supine neutral, supine with 90 degrees flexion and external or internal rotation, and upright weight-bearing positions. Analysis of meniscal movement was performed in different knee positions in the coronal MR imaging plane. Meniscal displacement--that is, meniscal movement of 3 mm or more (in the medial direction for the medial meniscus, in the lateral direction for the lateral meniscus)--was compared with the patient's pain level as assessed with a visual analog scale by using analysis of variance. RESULTS: Between the different knee positions, meniscal displacement of 3 mm or more (displaceable meniscal tears) was noted in 18 (42%) of 43 menisci with tears. Simultaneous occurrence of grade II or III ipsilateral collateral ligament lesions was present in all 18 displaceable meniscal tears, whereas a normal-appearing collateral ligament or collateral ligament lesion (grade I) was present in 22 of 25 nondisplaceable tears (P < .05). Displaced menisci most commonly had complex, radial, or longitudinal tear configurations (16 of 18, 89%). Patients with displaceable meniscal tears had significantly more pain than did patients with nondisplaceable meniscal tears (P < .001), independent of the concomitant knee abnormalities. CONCLUSION: Displaceable meniscal tears usually have longitudinal, radial, or complex configurations; such tears are associated with substantial ipsilateral collateral ligament lesions and pain.     

Magnetic resonance imaging of the wrist: diagnostic performance statistics

AIM: To review the published diagnostic performance statistics for magnetic resonance imaging (MRI) of the wrist for tears of the triangular fibrocartilage complex, the intrinsic carpal ligaments, and for osteonecrosis of the carpal bones. MATERIALS AND METHODS: We used Medline and Embase to search the English language literature. Studies evaluating the diagnostic performance of MRI of the wrist in living patients with surgical confirmation of MR findings were identified. RESULTS: We identified 11 studies reporting the diagnostic performance of MRI for tears of the triangular fibrocartilage complex for a total of 410 patients, six studies for the scapho-lunate ligament (159 patients), six studies for the luno-triquetral ligament (142 patients) and four studies (56 patients) for osteonecrosis of the carpal bones. CONCLUSIONS: Magnetic resonance imaging is an accurate means of diagnosing tears of the triangular fibrocartilage and carpal osteonecrosis. Although MRI is highly specific for tears of the intrinsic carpal ligaments, its sensitivity is low. The diagnostic performance of MRI in the wrist is improved by using high-resolution T2* weighted 3D gradient echo sequences. Using current imaging techniques without intra-articular contrast medium, magnetic resonance imaging cannot reliably exclude tears of the intrinsic carpal ligaments. Hobby, J. L. (2001). Clinical Radiology, 56, 50-57.     

Evaluation of the quadriceps tendon, patellar tendon, and collateral ligaments after total knee arthroplasty: appearances in the early postoperative period.

OBJECTIVE: To evaluate and compare the normal appearance on ultrasound and magnetic resonance imaging (MRI) of the quadriceps tendon, patellar tendon, and collateral ligaments in the early postoperative period following total knee arthroplasty. METHODS: Within a 6-month period, 10 patients with a total knee arthroplasty were referred for imaging. All patients had surgery within 12 weeks, and both MRI and ultrasound were performed on the same day. Two experienced musculoskeletal radiologists, blind to the results of the opposing modality, assessed the integrity of the quadriceps tendon, patellar tendon, and collateral ligaments. RESULTS: Using ultrasound, we identified a focal defect within the medial aspect of the quadriceps tendon in 8 (80%) patients; a similar defect was detected in 5 (50%) patients on MRI. The patellar tendon was thickened in 10 (100%) patients in both modalities. The medial collateral ligament was visualized in 10 (100%) patients with ultrasound and was demonstrated in only 2 (20%) patients with MRI. The lateral collateral ligament was visualized in 7 (70%) and 4 (40%) patients with ultrasound and MRI, respectively. One moderately sized superficial hematoma was demonstrated on ultrasound but was missed on MRI. All abnormalities identified on MRI were also seen with ultrasound. CONCLUSION: A medial defect in the quadriceps tendon and thickened patellar tendon and medial collateral ligament can be considered normal findings. Knowledge of these findings will assist in preventing incorrect diagnosis of a tear. In our cases, ultrasound detected more findings than did MRI.     

Heterotopic calcification and tears of the ulnar collateral ligament: radiographic and MR imaging findings

OBJECTIVE. The purpose of this paper is to describe the radiographic and MR imaging appearance of heterotopic calcification in the ulnar collateral ligament. MATERIALS AND METHODS. Retrospective radiographic review of 710 patients examined for elbow pain yielded 42 individuals (age range, 16-38 years) with heterotopic calcification in the ulnar collateral ligament. Radiographic and MR imaging findings were compared with surgical findings. RESULTS. Fifty-one heterotopic calcifications were identified in 42 patients; nine patients had two sites of heterotopic calcification. Average initial calcification size in the craniocaudal dimension was 4 mm (range, 1-12 mm) and in the transverse dimension was 1 mm (range, 1-4 mm). Five of 42 patients had enlargement of the calcification on follow-up radiography. The largest heterotopic calcification that was not visualized on MR imaging measured 5 x 4 mm in craniocaudal and transverse dimensions. Of 34 patients with heterotopic calcification who underwent surgery, 26 patients (76%) had either partial or complete tears of the ulnar collateral ligament. CONCLUSION. Heterotopic calcification in the ulnar collateral ligament may be associated with partial or complete tears. The MR imaging detection of heterotopic calcification is less sensitive than that of radiography of the elbow.     

MR imaging of the elbow.

Of 27 patients who underwent magnetic resonance (MR) imaging of the elbow, 11 underwent elbow arthroscopy and/or an open surgical procedure. Surgical findings were compared with those from MR imaging. Five healthy volunteers also underwent MR imaging to demonstrate anatomic relationships. Transchondral fracture (osteochondritis dissecans) was identified in three of the 11 patients and was proved at surgery. Loose bodies were suspected at MR imaging in the three patients but were found in only two. One complete avulsion of the ulnar collateral ligament (UCL) and four cases of intact, thickened UCLs were identified at MR imaging and surgery. Loose bodies from the olecranon tip were found in three patients at surgery but were seen on MR images in only two. MR imaging depicted olecranal osteophytes in three cases, which were confirmed at surgery. Two complete avulsions of the biceps tendon and one partial triceps tendon tear were identified with MR imaging and proved at surgery. A postoperative soft-tissue infection and a synovial cyst were also seen at MR imaging and surgery. These results suggest that MR imaging is useful in the evaluation of the elbow.     

Posteromedial tibial plateau injury including avulsion fracture of the semimembranous tendon insertion site: ancillary sign of anterior cruciate ligament tear at MR imaging.

PURPOSE: To evaluate posteromedial tibial plateau injuries of or about the semimembranous tendon insertion site and their association with anterior cruciate ligament (ACL) tears on magnetic resonance (MR) images. MATERIALS AND METHODS: A retrospective study of MR images and conventional radiographs was performed in 10 patients with posteromedial tibial plateau injuries, including avulsion fractures of the semimembranous tendon insertion site. Associated abnormalities were analyzed, including ACL tears, medial meniscal tears, and other lateral femorotibial compartment injuries. Findings from the clinical history and physical examination were correlated with radiographic and MR imaging findings. Nine patients had arthroscopically or surgically documented ACL tears. RESULTS: All 10 patients had ACL tears at MR imaging. Five patients had posteromedial tibial plateau fractures: Four had avulsion fractures of the tendon insertion site, and one had a fracture lateral to the site. Five patients had posteromedial tibial plateau bruises: Two had bruises at the tendon insertion site. Five patients had tears of the posterior horn of the medial meniscus. Two patients had posterior meniscocapsular separations. Three patients showed evidence of the O'Donoghue triad. Six patients had bruises of the lateral tibial plateau and of the lateral femoral condyle. CONCLUSION: There appears to be an association between posteromedial tibial plateau injuries and ACL tears. Posteromedial tibial plateau injuries may be predictive of ACL status.     

Medial collateral ligament reconstruction of the elbow using the docking technique

BACKGROUND: Medial collateral ligament insufficiency of the elbow with resultant valgus instability in throwing athletes is typically treated with free tendon graft reconstruction as described by Jobe. HYPOTHESIS: Improved results could be obtained with the use of the docking technique. STUDY DESIGN: Uncontrolled retrospective review. METHODS: The study group consisted of 36 athletes who had symptomatic insufficiency of the medial collateral ligament confirmed by magnetic resonance imaging and by surgical findings. Average follow-up was 3.3 years. Key elements of the docking technique included a muscle-splitting approach without routine transposition of the ulnar nerve, routine arthroscopic assessment, treatment of associated lesions, and docking the two ends of the tendon graft into a single humeral tunnel. RESULTS: Thirty-three of 36 patients (92%) returned to or exceeded their previous level of competition for at least 1 year, meeting the Conway-Jobe classification criteria of "excellent." All 22 professional or collegiate athletes returned to or exceeded their previous competition level. CONCLUSIONS: The docking technique allowed simplified graft tensioning and improved graft fixation.     

Sports-related injuries of the elbow: an approach to MRI interpretation

MRI is a valuable tool for evaluating the athlete with elbow pain, particularly in those with nonlocalizable pain. MRI also is helpful in sorting out the cause of pain in athletes who may have acute trauma superimposed on tendinopathy or other chronic injuries from repetitive microtrauma. Even in athletes in whom the cause of pain confidently can be diagnosed clinically, MRI can document the injury severity, which can be helpful for estimating recovery time or in preoperative planning. By contributing to an accurate early diagnosis, MRI also can help minimize the time that athletes are away from their sports. The authors describe their approach to the MRI interpretation of elbow injuries in athletes, including osteochondral lesions, epicondylitis, and tears of the medial collateral ligament.     

Avulsion fracture of the ulnar sublime tubercle in overhead throwing athletes

BACKGROUND: Injuries to the ulnar collateral ligament are relatively common in throwing athletes and result from either acute traumatic or repeated valgus stress to the elbow. Avulsion fracture of the sublime tubercle of the ulna is a rarely reported site of ulnar collateral ligament injury. PURPOSE: We retrospectively reviewed our cases of ulnar collateral ligament injuries to study avulsion fractures of the sublime tubercle of the ulna. STUDY DESIGN: Case series. METHODS: Data, including radiographs and magnetic resonance imaging scans, were obtained by review of hospital and office records and by follow-up examination. Of 33 consecutive patients treated for ulnar collateral ligament injuries, 8 had avulsion fractures of the sublime tubercle of the ulna. All eight were male baseball players with dominant arm involvement, an average age of 16.9 years, and an average follow-up of 23.6 months. RESULTS: Six of eight patients had failure of nonoperative treatment and required surgical repair. Two of the six underwent ulnar collateral ligament reconstruction and four had direct repair of the sublime tubercle avulsion with bioabsorbable suture anchors. At last follow-up, all eight had returned to their preinjury level of activity. No patient had residual medial elbow pain or laxity. CONCLUSIONS: Diagnosis of sublime tubercle avulsion fracture is made with history, physical examination, and radiographic studies. Magnetic resonance imaging can help identify an avulsion fracture not visible radiographically and can help determine whether direct repair or reconstruction is needed.