High Hamstring Tendinopathy: MRI and Ultrasound Imaging and Therapeutic Efficacy of Percutaneous Corticosteroid Injection

Transcription

1 Musculoskeletal Imaging Clinical Perspective Zissen et al. Imaging of High Hamstring Tendinopathy Musculoskeletal Imaging Clinical Perspective Maurice H. Zissen 1 Grant Wallace 1 Kathryn J. Stevens 1 Michael Fredericson 2 Christopher F. Beaulieu 1 Zissen MH, Wallace G, Stevens KJ, Fredericson M, Beaulieu CF Keywords: corticosteroid, hamstring, MRI, percutaneous injection, tendinopathy, ultrasound DOI: /AJR Received September 23, 2009; accepted after revision March 17, Department of Radiology, Stanford University School of Medicine, 300 Pasteur Dr., Stanford, CA Address correspondence to C. F. Beaulieu (beaulieu@stanford.edu). 2 Department of Orthopedic Surgery, Stanford University School of Medicine, Sports Medicine Center, Redwood City, CA. AJR 2010; 195: X/10/ American Roentgen Ray Society High Hamstring Tendinopathy: MRI and Ultrasound Imaging and Therapeutic Efficacy of Percutaneous Corticosteroid Injection OBJECTIVE. The goals of this study were to review the MRI and sonographic findings in patients diagnosed clinically with high hamstring tendinopathy and to evaluate the efficacy of ultrasound-guided corticosteroid injections in providing symptomatic relief. CONCLUSION. MRI is more sensitive than ultrasound in detecting peritendinous edema and tendinopathy at the proximal hamstring origin. Fifty percent of patients had symptomatic improvement lasting longer than 1 month after percutaneous corticosteroid injection, and 24% of patients had symptom relief for more than 6 months. A cute strains of the mid and distal hamstring myotendinous complex are common athletic injuries [1 5]. Proximal hamstring tendon pathologic abnormalities, including tendon degeneration, partial tearing, and peritendinous inflammatory reaction, are less common [6]. These abnormalities are grouped clinically as high hamstring tendinopathy, and patients usually present with subacute onset of deep buttock or thigh pain that is exacerbated by repetitive activity, such as long-distance running, and often is aggravated by sitting. In many of these patients, conservative management is ineffective, and MRI is performed to confirm the diagnosis, to grade the extent of injury, or to search for alternative explanations. In cases where MRI establishes an abnormality at the hamstring origin, or where MRI findings are normal but clinical suspicion is high, we have performed ultrasound-guided injections of corticosteroids and local anesthetic at the hamstring origin. The goals of this article are to review our institution s experience with MRI and ultrasound imaging of the proximal hamstring tendons and to establish the efficacy of ultrasound-guided corticosteroid injection as an integral part of overall patient management. Materials and Methods Patient Selection Criteria This retrospective study was performed in compliance with HIPAA regulations and with approval from our institutional review board. We performed a computerized search of medical records and imaging reports at our institution, searching for the terms hamstring, MRI, ultrasound, and corticosteroid injection. Patients undergoing imaging and injection of hamstring disorders in the mid or distal thigh or about the knee were excluded. This search identified 65 patients who received ultrasound-guided proximal hamstring injections between January 2002 and December There were 28 men (43.1%) and 37 women (56.9%) with a mean age of 37.4 years (range, years). For 35 patients, MRI was performed at our facility and images were available to review. All patients had ultrasound images available for review. Image Review Two authors reviewed the MRI and ultrasound studies for all patients. MR studies included small field-of-view (~24 28 cm) T1- and T2-weighted fat-suppressed images in three planes using a phased-array coil at 1.5 T. MR images were reviewed for findings of peritendinous fluid or edema (peritendinitis), tendinopathy, partial tear, and bone marrow edema in the ischial tuberosity. Ultrasound images were reviewed for peritendinous fluid or edema, hypoechoic areas or thickening of the tendons consistent with tendinopathy, and echogenic foci consistent with calcifications. The mean (± SD) time between the MR and ultrasound studies was 90 ± 16 days (range, days). Ultrasound-Guided Peritendinous Injection All injections were performed by an experienced musculoskeletal radiologist after obtaining written informed consent. Patients were asked to identify, if possible, the site of maximum pain, either by AJR:195, October

2 Zissen et al. palpation or by performing resistance maneuvers. With the patient in the prone position, a 6- to 10- MHz linear transducer was used to localize the ischial tuberosity and proximal hamstring tendons in both transverse and sagittal planes. Color Doppler was used to identify and avoid visible vascular structures. Scanning laterally to the hamstring origin in the sagittal plane, the sciatic nerve was similarly identified, and injections were performed medially to this structure. A freehand technique was used in the sagittal plane to guide the injection, first using 1% lidocaine with a 1.5-inch-long 21-gauge needle. If this needle was sufficiently long to reach the hamstring tendons, the therapeutic mixture was injected through the same needle. In larger patients, a 3-inch-long 20-gauge spinal needle was inserted after removal of the 1.5-inch needle. Two therapeutic mixtures were used in this study. The first consisted of 1 ml of triamcinolone acetonide 40 (40 mg/ml) plus 5 ml of bupivacaine. The second consisted of 1 ml of triamcinolone acetonide 40 (40 mg/ml) with 0.5 ml of dexamethasone sodium phosphate (4 mg/ml) and 5 ml of bupivacaine. The therapeutic mixture was administered using a 21- or 20-gauge needle under sterile conditions as described in the previous paragraph. After needle placement, the therapeutic mixture was injected immediately superficial to the hamstring tendons, and real-time sonography was used to monitor tracking of the fluid along the peritendinous tissues in both the sagittal and transverse directions. Repositioning was performed if fluid was not tracking over a length of tendon at least 5 cm long, to spread the medication. After injection and needle removal, the peritendinous soft tissues were massaged gently for 1 2 minutes to further spread the medication in the tissue planes. With direct ultrasound visualization of the needle, we avoided intratendinous injection. Note also that, to avoid intratendinous injection, we did not attempt to inject deeper at the tendon bone interface. On completion of the procedure, patients were asked to assess pain relief in the immediate postinjection period. Telephone Questionnaire Review of clinical records showed that only a small number of patients returned to the referring physician for a follow-up visit; thus, no useful data were available regarding efficacy of the injections from this resource. We constructed a questionnaire and attempted to contact by telephone all 65 patients who received the ultrasound-guided peritendinous injection. A total of 38 patients were reached and agreed to participate in the study. The mean time to follow-up was 4 years (range, 6 months to 8 years). Verbal informed consent was obtained before asking the patients a series of TABLE 1: Imaging Findings of Patients Receiving Ultrasound-Guided Corticosteroid Anesthetic Injection Characteristic Ultrasound findings (n = 65 patients) subjective pain assessment questions that included the degree of pain relief as well as duration of symptom resolution. The patients were also asked questions related to the mechanism of injury, prior activity level, prior treatment techniques (including medical management and physical therapy), and any complications experienced as a result of the procedure. Statistical Analysis We defined patients with significant improvement of symptoms as those who reported duration of symptomatic improvement longer than 1 month and patients with insignificant improvement as those who reported having less than 1 month of symptomatic resolution. We then used a Fisher s exact test to determine whether length of symptoms before injection, presence of tendinopathy on MRI or ultrasound, presence of peritendinitis on MRI or ultrasound or absence of imaging No. (%) of Patients Peritendinitis (fluid or edema) 13 (20) Tendinopathy 11 (16.9) Calcifications 3 (4.6) Normal 40 (61.5) MRI findings (n = 35 patients) Peritendinitis (fluid or edema) 22 (62.9) Tendinopathy 9 (25.7) Bone marrow edema 7 (20) Partial tear 7 (20) Normal 8 (22.9) findings on either MRI or ultrasound were statistically associated with improved outcomes. Results Imaging Results The imaging findings observed on retrospective review of 65 ultrasound studies and 35 MRI studies are shown in Table 1. For ultrasound, 40 (61.5%) of 65 patients showed normal tendon thickness and echogenicity without surrounding fluid or tendon calcifications. MRI findings were normal for eight (22.9%) of 35 patients. On both ultrasound (20%) and MRI (62.9%), peritendinitis, manifesting as fluid or edema adjacent to the proximal hamstring origin, was the most common abnormal imaging finding. This is illustrated in Figure 1. Findings consistent with tendinopathy were shown by ultrasound in 16.9% and by MRI in 25.7% of patients, as Fig year-old woman with proximal hamstring peritendinitis. A, Axial T2-weighted fat-suppressed image shows increased T2 signal intensity surrounding hamstring tendons at their origin (arrowhead), suggestive of peritendinitis. B, Corresponding sagittal ultrasound image shows peritendinous fluid collection (arrows) superficial to hamstring tendon (t) at its origin at ischial tuberosity (it). 994 AJR:195, October 2010

3 Imaging of High Hamstring Tendinopathy Fig year-old woman with proximal hamstring tendinopathy. A, Axial T2-weighted fat-suppressed image reveals increased T2 signal within tendon origin (arrowhead), consistent with tendinopathy. B, Corresponding ultrasound image shows hypoechogenicity and heterogeneity (arrows) of hamstring tendon (t) at its origin at ischial tuberosity (it). shown in Figure 2. Ultrasound is incapable of detecting bone marrow edema, and no discrete partial tears were evident on ultrasound on retrospective image review. MRI showed bone marrow edema and small (< 5 mm) foci of near fluid signal, suggesting partial tearing at the proximal hamstring tendon origin in 20% of the studies (Fig. 3). As indicated above, patients with MR findings consistent with discrete partial tears involving the majority of the cross-section of one of the hamstring components or greater were not believed appropriate for percutaneous steroid injection. As shown in Figure 4, ultrasound was capable of depicting echogenic intratendinous foci consistent with calcifications in 4.6% of patients. The technique of percutaneous injection is described in Materials and Methods. Figure 5 shows a frame from the real-time ultrasound images during a typical injection. Clinical Outcomes A total of 65 injections were performed, with a mean time to follow-up of 4 years (range, 6 months to 8 years). A total of 38 of the original 65 patients responded to our survey (Table 2). In terms of the degree of pain relief after injection, 11 patients who responded had complete resolution of symptoms, eight had moderate resolution, and 10 had mild resolution. Nine patients experienced no pain relief either immediately or later after the injection. The duration of symptom resolution was longer than 6 months for nine (23.7%) of the 38 patients, 1 6 months for 10 patients (26.3%), 1 week to 1 month for 9 patients (23.7%), and less than 1 week for one patient (2.6%). The same nine patients who did not experience any pain relief immediately after the injection also felt no later benefit of the injection. In addition to assessment of symptomatic relief from corticosteroid injection, we surveyed study patients regarding other treatment techniques. We found that that 26 (68.4%) of 38 patients had taken oral nonsteroidal antiinflammatory medications before the ultrasound-guided peritendinous injection. The remaining 12 patients (31.6%) took no prior medication, whereas one had a previous steroid injection without ultrasound guidance. The majority of patients (30/38 [79%]) had undergone physical therapy before the injection. In terms of the ultimate outcome, 27 (71.0%) of 38 patients reported returning to their presymptom level of activity after the injection, and three of these individuals actually described a higher level of activity. At the time of follow-up questioning, seven of the patients (18.4%) had not been able to Fig year-old man with proximal hamstring injury and bone marrow edema. Axial T2-weighted fat-suppressed image shows bone marrow edema (arrows) within ischial tuberosity adjacent to hamstring tendon origin. There is also partial undersurface irregularity of adjacent hamstring tendons. Fig year-old man with hamstring injury. Sagittal ultrasound image shows small focus of hyperechogenicity consistent with calcification (arrow). it = ischial tuberosity. Fig year-old man with proximal hamstring tendinopathy. Sagittal ultrasound image shows 22-gauge needle in place (arrowheads) for sonography-guided injection. Tip is immediately adjacent to superficial surface of hamstring tendon (t). it = ischial tuberosity. AJR:195, October

4 Zissen et al. TABLE 2: Clinical Outcomes for 38 of 65 Patients Receiving Ultrasound- Guided Corticosteroid Anesthetic Injection TABLE 3: Duration of Symptoms and Imaging Characteristics Associated With Significant Symptomatic Improvement Characteristic Duration of symptoms < 1 y 0.5 Normal MRI finding 0.39 Normal ultrasound finding 0.02 Presence of tendinopathy on MRI or ultrasound 0.55 Presence of peritendinitis on MRI or ultrasound 0.14 a Fisher s exact test. Characteristic Duration of symptoms before injection return to the level of activity they enjoyed before the onset of symptoms. None of the contacted patients experienced significant complications due to the injection. To assess for imaging features that might be predictive of a positive response to steroid injections, we tested for associations between each of the imaging features in Table 2 and the clinical outcome we defined as significant improvement. The duration of symptoms before injection, the absence of MRI findings, and the presence of tendinopathy or peritendinitis on either technique were not statistically predictive of response to therapy (Table 3). There was, however, a statistically significant association between the absence of findings on ultrasound and a significant clinical response to therapy with a p value of No. (%) of Patients < 6 m 8 (21) 6 m to 1 y 15 (39.5) > 1 y 15 (39.5) Degree of symptom resolution No resolution 9 (23.7) Mild resolution 10 (26.3) Moderate resolution 8 (21) Complete resolution 11 (28.9) Duration of symptom resolution No resolution 9 (23.7) < 1 wk 1 (2.6) 1 wk to 1 m 9 (23.7) 1 6 m 10 (26.3) > 6 m 9 (23.7) p a Discussion Proximal hamstring tendinopathy is increasingly being recognized as an important cause for chronic pain in the active population [7, 8]. This injury is distinct from the more common type of acute muscle strain that is typically limited to the myotendinous junction of the biceps femoris muscle and is routinely managed clinically with the protocol of rest, ice, compression, and elevation as the preferred first-line approach [1, 4]. For proximal hamstring tendinopathy, treatments such as antiinflammatory medications for pain control as well as rehabilitation programs involving soft-tissue mobilization, frequent stretching, and progressive strengthening can help the hamstring muscles regain flexibility and are frequently used in attempts to prevent further injury or reinjury [2, 5]. For the majority of conservatively managed patients, the time to full recovery is typically 2 6 months. However, in up to 20% of patients, symptoms can persist for more than 6 months and become recalcitrant to conservative treatment [9, 10]. With more frequent use of ultrasound and MRI in these patients, we are increasingly able to diagnose the source of the pain and focus our treatments specifically to the injured muscle. Adler et al. [11, 12] have described an effective method of ultrasound-guided anesthetic corticosteroid injections into the adjacent bursa of the iliopsoas tendon that is useful in diagnosing and treating exerciserelated iliopsoas pathology. Although peritendinous hamstring injections have been reported by other groups in limited numbers, the efficacy of this technique has not been evaluated. This work represents our institution s substantial experience with imaging of the hamstring origin and sonographically guided percutaneous treatments in the setting of a clinical diagnosis of high hamstring tendinopathy. Areas of proximal hamstring tendinopathy were identified by locating the thickened and hypoechoic areas of tendon on sonography, allowing us to target our therapy to this location under direct visualization. Ultrasound is a low-cost nonionizing readily available technique for the evaluation of tendons, muscles, cysts, and other fluid collections. Ultrasound guidance for soft-tissue injections has been found to be an excellent tool for needle localization because of the real-time imaging and excellent resolution of desired structures [13 16]. In the setting of tendinopathy, it is hypothesized that the use of corticosteroids is beneficial by limiting the chronic inflammation that may lead to tendon scarring and adhesion formation [17 19]. Although there is concern that the introduction of corticosteroids to a site of injury could limit healing and subsequently weaken the underlying tendon, leading to future degeneration and rupture, there is no reliable documentation of the deleterious effects of peritendinous injections [7, 20]. It has also been suggested by multiple groups that the major benefit of performing these injections with ultrasound guidance is the accurate placement of the injection into the tendon sheath, avoiding the tendon itself and thereby minimizing adverse events [11, 16]. The immediate improvement of symptoms resulting from the injected anesthetic also serves as a clinical indicator that the medication was delivered accurately and that the hamstring tendon was indeed the cause of the patient s discomfort. The goals of imaging in the setting of hamstring pain are threefold to confirm injury, to provide a comprehensive assessment of the extent of the injury, and to identify which patients may benefit from intervention. In our study, both MRI and ultrasound were found 996 AJR:195, October 2010

5 Imaging of High Hamstring Tendinopathy to be helpful in determining the extent of the injury and detecting imaging findings suggestive of tendinopathy in patients with clinical symptoms suggestive of high hamstring tendinopathy. However, MRI was more sensitive overall in detecting both chronic and acuteon-chronic hamstring pathologic abnormalities, particularly peritendinitis. Peritendinous fluid or edema was seen in 62.9% of patients on MRI, compared with only 20% on ultrasound. As would be expected, MRI was the only technique capable of detecting associated bone marrow edema within the ischial tuberosity. At the same time, ultrasound was able to detect calcifications in the hamstring tendons in a subset of patients, findings that were not apparent on MRI. The main advantage of ultrasound is the real-time imaging capability and excellent spatial resolution, which allows targeted therapy. The ultrasound findings were compatible with the MRI findings in 13 of the 35 patients, revealing peritendinitis in three patients and tendinopathy in four patients. In six patients, the hamstring tendons appeared unremarkable on both the ultrasound and MRI studies. The imaging studies were discordant in 22 patients, with 20 studies showing abnormal findings on MRI that were not apparent on ultrasound (16 peritendinitis and four tendinopathy). In two patients, there were positive findings of peritendinous fluid on ultrasound that were not apparent on the MRI. However, these differences may be due, in part, to the time interval between the original MRI scan and subsequent ultrasound. Although MRI is quite sensitive for detecting peritendinous edema, it is possible in some cases that ultrasound might be able to detect small amounts of fluid that are not obvious on MRI. Similarly, the absence of findings on ultrasound may be due to resolution of edema during the time interval between the MRI and ultrasound. To provide rigorous comparison on the sensitivity of MRI and ultrasound, a much shorter time interval between studies would be needed. Our findings suggest that MRI is more sensitive overall than ultrasound in the diagnosis of proximal hamstring pathologic abnormalities. However, ultrasound imaging is more readily available and may be considered a reasonable alternative for initial diagnosis and treatment, reserving MRI for evaluating cases where the first attempt at therapeutic intervention is not effective. This is consistent with the study conducted by Unverferth and Olix [19], who reported that ultrasound approximates MRI in depicting acute hamstring injuries where peritendinous fluid may be the predominant imaging finding, whereas MRI is more sensitive for follow-up of chronic hamstring injuries where tendinopathy may be the predominant imaging finding. It is notable that neither MRI nor ultrasound was highly sensitive in defining an abnormality of the hamstring tendons as the responsible pain generator. Nearly 23% of MR studies and 62% of ultrasound studies were considered normal; however, a substantial number of patients with normal studies benefited from corticosteroid injection. These results underscore the importance of having a skilled clinician for patient assessment, referral to diagnostic imaging, and referral for imaging-guided injection. In general, ultrasound-guided interventions are increasingly being used as adjuvant treatment in chronic musculoskeletal pain [11, 13 17, 21]. Our study confirms that ultrasoundguided corticosteroid injections are a safe and effective treatment in patients who are recalcitrant to conservative management. All but nine of the patients in our study reported immediate symptomatic improvement after injection of the local anesthetic, confirming that the hamstring tendon was indeed the cause of their discomfort. No significant side effects or complications were reported by any of the patients undergoing injection. Furthermore, there was an excellent clinical response to corticosteroid injection, with 50% of patients reporting moderate-to-complete resolution of their symptoms for at least 1 month after the injection and 28.9% reporting complete and sustained resolution of symptoms postinjection. Even though some patients did experience complete pain resolution after the injection, an adequate treatment plan should also include physical therapy and activity modification to allow healing. In the population reported here, inciting activities such as long-distance running or sprinting were curtailed but patients were engaged in crosstraining sports or deep water pool running to maintain overall fitness. The only imaging characteristic that was associated with a statistically significant improvement in outcomes was the absence of findings on ultrasound. We hypothesize that those patients with normal ultrasound findings likely had more mild injuries that perhaps would have resolved on their own over time. In these patients, MRI would not be useful to further characterize their condition. Conversely, in patients with abnormal ultrasound examinations, further trials would be necessary to evaluate whether MRI could be useful in further characterizing their injury and possibly predict which patients would benefit from intervention. In our discussions with study participants, we also observed a trend that those patients who had longer periods of rest and physical therapy before resuming their prior activity level experienced longer lasting relief of symptoms. Subsequent studies are necessary to further evaluate the relationship of rest to overall symptom resolution. A more in-depth understanding of the pathophysiologic features of hamstring tendinopathy and associated imaging findings may help predict which patients would benefit most from intervention. A prospective study correlating imaging findings with symptoms, response to treatment, and clinical outcomes would further elucidate the mechanism of chronic tendon degeneration and repair. This knowledge may, in turn, benefit future studies looking at the potential of biologic therapies for treatment of tendon pathologic abnormalities, such as platelet-rich plasma injection [22, 23], a technique for which there are no published data on hamstring tendinopathy at this time, to our knowledge. This study has several limitations. We were unable to identify a matched control cohort of patients who did not receive corticosteroid injection. However, 79% of our patients had symptoms lasting longer than 6 months before the injection, thereby in principle serving as their own controls. The study was retrospective and relied on patient recall of symptoms dating back to 2002 in some cases. There was a variable time to follow-up for each patient, and the time difference between MRI and ultrasound studies was relatively long, owing to periods of conservative therapy undertaken between MRI diagnosis and ultrasoundguided injection. Furthermore, the subjective nature of the pain questionnaire used made it difficult to standardize the effectiveness of the procedure across the patients. Although the results were favorable, too few patients replied to the survey to allow rigorous statistical confirmation of our findings. As a result, our findings do not help refine selection criteria for patients to undergo proximal hamstring injection. Therefore, a prospective, randomized study evaluating the MRI and ultrasound imaging findings and efficacy of corticosteroid injections would be beneficial to evaluate the true potential of this procedure. In conclusion, the use of ultrasound-guided injections of corticosteroid and local anesthetic is a safe and effective technique that AJR:195, October

6 Zissen et al. can provide both immediate and long-term symptomatic relief of proximal hamstring pain in appropriately referred patients. Advances in ultrasound-guided interventional techniques allow accurate needle localization to optimize the diagnostic and therapeutic effectiveness with minimal morbidity. This procedure should be performed in conjunction with physical therapy and a progressivestrengthening program to achieve optimal results, and avoid recurrent injury leading to a more prolonged period of convalescence. This technique serves as an excellent adjuvant in the treatment of chronic hamstring injuries recalcitrant to conservative management. Acknowledgment We thank the Stanford Transactional Research Integrated Database Environment for performing the computerized search of our imaging databases. References 1. Clanton TO, Coupe KJ. Hamstring strains in athletes: diagnosis and treatment. J Am Acad Orthop Surg 1998; 6: Croisier JL. Factors associated with recurrent hamstring injuries. Sports Med 2004; 34: De Smet AA, Best TM. MR imaging of the distribution and location of acute hamstring injuries in athletes. AJR 2000; 174: Kujala UM, Orava S, Jarvinen M. Hamstring injuries: current trends in treatment and prevention. Sports Med 1997; 23: Malliaropoulos N, Papalexandris S, Papalada A, Papacostas E. The role of stretching in rehabilitation of hamstring injuries: 80 athletes follow-up. Med Sci Sports Exerc 2004; 36: Fredricson M, Moore W, Guillet M, Beaulieu C. High hamstring injuries: etiology, diagnosis, and treatment. Phys Sports Med 2005; 33: Lempainen L, Sarimo J, Mattila K, et al. Proximal hamstring tendinopathy: results of surgical management and histopathologic findings. Am J Sports Med 2009; 37: Puranen J, Orava S. The hamstring syndrome: a new diagnosis of gluteal sciatic pain. Am J Sports Med 1988; 16: Khan K, Cook J. The painful nonruptured tendon: clinical aspects. Clin Sports Med 2003; 22: Wilson JJ, Best TM. Common overuse tendon problems: a review and recommendations for treatment. Am Fam Physician 2005; 72: Adler RS, Buly R, Ambrose R, Sculco T. Diagnostic and therapeutic use of sonography-guided iliopsoas peritendinous injections. AJR 2005; 185: Adler RS, Sofka CM. Percutaneous ultrasoundguided injections in the musculoskeletal system. Ultrasound Q 2003; 19: Bentley S. The treatment of sports injuries by local injection. Br J Sports Med 1981; 15: Cardinal E, Chhem RK, Beauregard CG. Ultrasound-guided interventional procedures in the musculoskeletal system. Radiol Clin North Am 1998; 36: Kannus P, Jarvinen M, Niittymaki S. Long- or short-acting anesthetic with corticosteroid in local injections of overuse injuries? A prospective, randomized, double-blind study. Int J Sports Med 1990; 11: Sofka CM, Collins AJ, Adler RS. Use of ultrasonographic guidance in interventional musculoskeletal procedures: a review from a single institution. J Ultrasound Med 2001; 20: Fredberg U. Local corticosteroid injection in sport: review of literature and guidelines for treatment. Scand J Med Sci Sports 1997; 7: Levine WN, Bergfeld JA, Tessendorf W, Moorman CT 3rd. Intramuscular corticosteroid injection for hamstring injuries: a 13-year experience in the National Football League. Am J Sports Med 2000; 28: Unverferth LJ, Olix ML. The effect of local steroid injections on tendon. J Sports Med 1973; 1: Lin J, Jacobson JA, Fessell DP, Weadock WJ, Hayes CW. An illustrated tutorial of musculoskeletal sonography. Part 4. Musculoskeletal masses, sonographically guided interventions, and miscellaneous topics. AJR 2000; 175: Scott WA. Injection techniques and use in the treatment of sports injuries. Sports Med 1996; 22: Mishra A, Collado H, Fredericson M. Plateletrich plasma compared with corticosteroid injection for chronic lateral elbow tendinosis. PM & R, 2009; 4: Mishra A, Woodall J Jr, Vieira A. Treatment of tendon and muscle using platelet-rich plasma. Clin Sports Med 2009; 28: AJR:195, October 2010