Nonsurgical Management of Ulnar Collateral Ligament Injuries : JAAOS Global Research & Reviews

Journal Logo

Review Article

Nonsurgical Management of Ulnar Collateral Ligament Injuries

Swindell, Hasani W. MD; Trofa, David P. MD; Alexander, Frank J. MS, ATC; Sonnenfeld, Julian J. MD; Saltzman, Bryan M. MD; Ahmad, Christopher S. MD

Author Information
JAAOS: Global Research and Reviews 5(4):e20.00257, April 2021. | DOI: 10.5435/JAAOSGlobal-D-20-00257


Ulnar collateral ligament (UCL) injuries of the elbow are a common source of pain and disability in the overhead athlete and more particularly, baseball pitchers.1-8 Nevertheless, UCL injuries have also been described in javelin throwers, tennis players, arm wrestlers, collegiate wrestlers, and quarterbacks.6,9-14 For high-demand overhead athletes, surgical management is often recommended for complete tears of the anterior bundle or after failed conservative therapy in throwing athletes with partial tears as a way to effectively return athletes to their preoperative level of play. As the recognition of this injury has increased, surgical management, in the form of UCL reconstruction or UCL repair among younger populations, has become more commonplace, and current research has focused on the surgical management of these injuries and their subsequent outcomes.15 Over the past 10 to 15 years, a significant increase has been noted in UCL reconstructions with an even greater incidence of injury in baseball athletes aged 15 to 19 years and a 193% increase in procedure volume, in New York State alone, over a 10-year period.16-19 Similar results have been seen at the professional level as UCL reconstructions have also increased across Major League Baseball since 1986.17

Nonsurgical treatment of UCL injuries may be helpful among not only nonthrowing athletes and lower demand patient populations but also high-demand overhead athletes suffering from partial tears and sprains on MRI.20-22 Older athletes preferring to defer prolonged postoperative recovery times with surgical intervention may also opt for an accelerated course of nonsurgical therapy and physical therapy. In addition, for younger patients with an acute injury or patients with partial tears, a trial of conservative therapy may be appropriate. Seasonal and career timing also play a role in the decision to elect nonsurgical treatment. The variety of indications for nonsurgical management only further stresses the need for a discussion of patient-specific goals and injury characteristics before determining a course of treatment. To date, the focus of conservative therapy primarily revolves around physical therapy protocols, rest, anti-inflammatory medication, and immobilization under certain conditions; however, few studies have been published detailing the nonsurgical treatment options currently in practice. This article reviews the current nonsurgical treatment strategies available for UCL injuries of the elbow.

Imaging Considerations

Imaging modalities can aid in the diagnosis and stratification of a UCL injury to determine the most appropriate treatment approach. A standard radiographic series should be obtained consisting of anterior-posterior, lateral, internal/external oblique views, and oblique axial views. Such images are especially helpful in identifying pathology suggestive of chronic ligamentous deficiency such as ossifications within the ligament and posteromedial osteophytes. Stress radiographs of the injured and uninjured elbow performed with the elbow in 110° of flexion can further provide information on the degree of injury.23 Rijke et al23 reported medial joint opening differences of >0.5 mm were consistent with notable partial or complete UCL tears, whereas <0.5 mm of widening compared with the contralateral elbow had normal or small partial tears that could benefit from conservative management. However, the efficacy of this examination is limited by the examiner-dependent nature of stress testing and the presence of joint laxity at baseline, a common finding in uninjured throwing athletes.24

CT and MRI are more detailed imaging modalities that can aid in diagnosing and characterizing UCL injuries. CT with arthrography has reported sensitivities and specificities of 86% and 91%, respectively, when extravasated contrast is visualized from the medial joint.1,25 Lower sensitivities (57%) are reported when identifying complete tears with nonenhanced MRI, but higher specificities (100%) are noted in identifying partial tears.13,25 MR arthrography is a proven modality for the evaluation of medial elbow pathology because contrast visualized around the bony detachment of the UCL produces the pathognomonic “T-sign” filling pattern.25-28 Increased sensitivities and specificities up to 92% and 100%, respectively, have been reported using this imaging modality. Despite this, there is support for using contemporary MRI without intra-articular contrast to distinguish between partial and full-thickness UCL injuries as a view with the elbow extended allows adequate visualization of the anterior bundle on stretch.25-29 In addition to identifying partial versus full-thickness tears, MRI allows localization of the tear which is notable for patient prognosis. For example, Frangiomore et al found that among throwing athletes undergoing a trial of nonsurgical management, 82% of treatment failures had distal tears compared with 19% with more proximal tears (P < 0.0001).30 On adjusting for age, location, and evidence of chronic changes on MRI, the likelihood of failing nonsurgical management was 12.40 times greater (P < 0.020) with distal tears. These findings highlight the possible influence of the degree of injury and location on potentially indicating patients for conservative management.22,30

Dynamic ultrasonography has been proposed for the rapid evaluation of the UCL, although limitations exist. Using ultrasonography, the dominant arms of asymptomatic Major League Baseball players were found to have a thicker anterior band of the UCL, ulnohumeral joint space gapping, increased calcifications, and were more likely to have either a hypoechoic appearance, when visualized between the medial humeral epicondyle and proximal ulna, or anechoic in the presence of complete disruption.31-33 The utility of ultrasonography remains unclear because it is operator-dependent, and the interpretation of obtained information may be inconclusive, given the presence of abnormal findings in asymptomatic overhead athletes.32

Injury Prevention

Although injury prevention is a critical concern with athletic activity, there is a paucity of information on preventing elbow injuries outside of the Thrower's Ten exercise programs (also known as the Jobe exercise programs) and variations thereof.34 These exercise programs have become a staple of warm-up and “off-day” routines for throwing athletes, but a recent shift toward enhancing core strength and hip mobility has been noted. The addition of such movements has provided an additional layer to these injury prevention regimens, yet limited research exists on the efficacy of such prevention programming.35

The “original” Thrower's Ten consisted of isotonic internal and external rotation exercise programs performed in abduction and at 90° of abduction, along with shoulder and periscapular strengthening exercise programs.34 In 2011, Wilk et al35 introduced the more demanding Advanced Thrower's Ten to enhance the transition from the postinjury rehabilitative phase to more specific training phases. Although the program introduced supplemental features to the original Thrower's Ten, such as progressive challenges to the postural muscles and increased muscle endurance through the application of sustained holds with alternating arm movements mixed with sustained hold sequences, these proposed enhancements are intended to decrease muscle fatigue and increase neuromuscular control subject; however, outcome data related to the program's ability to prevent UCL injuries remains unknown.

Weighted baseball throwing programs have been a growing topic of discussion because there has been some literature supporting its use as a tool to improve pitching velocity, arm strength, and arm speed.36,37 From the literature, lighter balls (∼4 oz) can be used to increased arm speed, whereas heavier balls (ranging up to 32 oz) can act as a form of resistance training to strengthening the rotator muscles, improve arm kinetics, and increased maximal shoulder external rotation.36,38 Using underweight balls may ultimately be protective against injury as multiple studies have found significantly decreased elbow varus torque and shoulder internal rotation torque when training with lightweight balls.39,40 Conversely, despite the proposed benefits of weighted ball training, there are concerns that the excess weight could increase forces imparted on already stressed shoulder and elbow joints and thus could further predispose athletes to injury.40 Furthermore, there remains notable variability in how overweight balls can be instituted within throwing programs. This variability further limits accurate assessments of the respective efficacy and outcomes seen with overweight ball use.41 Ultimately, additional investigation is needed to effectively analyze the potential injury rates associated with overweight ball use and to standardize which elements of a throwing protocol may be best suited for this training tool.

Crotin et al42 designed the “Pitchers Baseball Bat Training Program” with the intention of reducing risk and severity of medial elbow injuries. This program, intended for youth athletes aged six and older, consists of seven exercise programs performed after pitch outings and on “off-days.” In addition to their proposed prevention regimen, Crotin and Ramsey42 advocated for continual evaluation of throwing mechanics and annual elbow examinations to facilitate early detection of maladaptive changes resulting from repetitive throwing. While providing a number of flexor-pronator mass exercise programs to complement the Throwers Ten, there has been no research on the efficacy of the “Pitchers Baseball Bat Training Program” in prevention of medial elbow injuries.

More recently, Sakata et al43 developed and studied the efficacy of the Yokohama Baseball-9 (YKB-9) program. The frequency of elbow pain in youth players has been estimated at 1.5 per 1,000 athlete exposures (AEs) with the incidence of medial elbow injury at nearly at 1.4 per 1,000 AEs.44 The 20-minute program consists of 18 stretching (9) and strengthening (9) exercise programs targeting both upper and lower extremities. It is designed to improve physical function parameters previously identified as risk factors for throwing injuries.44 Stretching exercise programs are geared to improve the range of motion (ROM) of the elbow, shoulder, hip, and improve posture, whereas strengthening exercise programs focus on the rotator cuff, scapular function, and lower extremity balance.

Sakata et al43 followed over 300 participants for longer than a year that were divided into intervention (136 participants) and control subject groups (169 participants). The intervention group performed the YKB-9 during their warm-up or at home at least once a week. Overall, medial elbow injuries were identified in 12.5% of the intervention group compared with 25.4% of the control subject group. Compared with control subjects, a 49.2% (P = 0.16) reduction in the incidence of medial elbow injury was found in the intervention group. In addition, the incidence rate of shoulder injury was 0.7 per 1000 AE in the intervention group compared with 0.9 per 1000 AE in the control subject group. The authors further found improvements in the total arc of motion, nondominant internal rotation, and a decreased thoracic kyphosis angle to be the most important variables for preventing medial elbow injuries. To date, the study by Sakata et al is the only study evaluating the effectiveness of an intervention program on preventing medial elbow injuries, thus highlighting a notable void in the body of knowledge on elbow injuries in overhead athletes.

Physical Therapy

Although variations exist, most physical therapy regimens for UCL treatment can be divided into three phases. The goal of phase I is to reduce inflammation and restore elbow ROM. Modalities emphasized include rest, cryotherapy, nonsteroidal anti-inflammatory medications, and bracing treatment. In phase II, the focus shifts to progressive muscle strengthening and endurance in preparation of a return to play. Phase three is a gradual return to sport (RTS) through an interval-throwing program. Interval-throwing programs are designed to rehabilitate the UCL at increasing distances to add progressive stress to the ligament and surrounding musculature. The three phases typically exist on a continuum where players can progress as long as the goals of each phase are adequately met. However, throughout the rehabilitation process, a fine balance is needed to gradually strengthen the ligament and flexor—pronator mass while also facilitating an environment that minimizes undue stress to the healing medial elbow tissues.

Cain et al2 recommended a rehabilitation protocol consisting of “active rest” with cessation of throwing during the first 2 to 6 weeks after injury. Rettig et al45 proposed a more prolonged period of throwing cessation up to 2 to 3 months. To decrease inflammation, a nonpainful arc of 10° to 100° can be permitted with bracing treatment or orthotics, in the acute post-injury period, to restrict motion, prevent valgus loading and minimize stress on the UCL.46 During this period, basic exercise programs to maintain aerobic conditioning and stamina such as light jogging or stationary biking can be performed; yet, the senior author's preferred protocol emphasizes complete cessation of overhead throwing or sport-specific activities to limit the risk of exacerbating injury or inciting recurrent pain. For the purpose of protecting the medial elbow, nighttime wear of long arm splints, or range-of-motion braces positioned at 90°, with daytime use primarily for pain control subject can also be attempted with gradual discontinuation of the brace as pain resolves.45

Flexibility, stretching, and proprioceptive training of surrounding muscles are key components of rehabilitation. Concomitant findings such as decreased balance and glenohumeral internal rotation deficits have been documented, further stressing the need for a comprehensive rehabilitation program after UCL injury.47,48 The correction of underlying muscle deficits is essential to the rehabilitation process because these deficiencies can increase stress on the healing elbow. The elbow functions within a kinetic chain allowing both the development and transfer of force. The risk of further injury is subsequently reduced when all components of the kinetic chain function both efficiently and in concert with one another.49 Initially, isometric exercise programs of the shoulder, elbow, wrist, lower extremity, and trunk can be performed to prevent muscle atrophy, improve balance, and potentially reduce excess stress to the recovering elbow when a return to throwing is permitted.46,50 An elbow hyperextension brace providing sustained stretch to the flexor-pronator mass can be used during the early lifting and strengthening phases to decrease additional stress to elbow.45

As soreness is alleviated and ROM is restored, isotonic strengthening of the medial flexor-pronator muscle complex can begin with some degree of caution so as to avoid imparting excess stress to this muscle complex.46 The flexor-pronator mass is a common source of muscle weakness after UCL injury because it is maximally activated during the acceleration phase of the throwing.51,52 However, in athletes with valgus instability, decreased activity has been observed.51,52 Strengthening the flexor-pronator muscle complex restores the proper valgus stabilizing forces and thus increases the functional protection of the medial elbow.51,53 Of these muscles, the flexor digitorum superficialis, pronator teres, and flexor carpi ulnaris (FCU) seem to be the active stabilizers against valgus stress to the elbow.54 In a cadaveric study, Park and Ahmad demonstrated that the FCU provided the greatest stability in the UCL-insufficient elbow when compared with the loading of the other flexor-pronator muscles individually.83 Cocontraction of flexor digitorum superficialis and FCU were also found to be comparable with the dynamic stability of FCU alone, thus confirming that the FCU is optimally positioned to provide direct in-line support with the UCL.83

Throughout the rehabilitation process, modalities such as electronic stimulation, ultrasonography, cupping, soft-tissue mobilization, and scraping are used to enhance recovery. A newer modality, blood flow restriction (BFR), has garnered increased popularity among athletic trainers and physical therapists, within the senior author's practice, as a progressive rehabilitation tool. With resistance training, increase in muscle size and strength are best seen with lifting loads of at least 60% of an individual's one- repetition maximum (1RM).55 However, such training comes at the risk of imparting notable mechanical stress to healing tissues during the rehabilitation period. BFR is a technique where a nonsterile tourniquet, or other restrictive device, is placed at the proximal end of the extremity to reduce the amount of arterial blood flow and venous return from the musculature distally. Restricting blood flow is intended to create a hypoxic environment resulting in the pooling of blood and metabolic byproducts in the distal extremity and subsequent muscle activation.56

BFR is typically used with low-load, high-repetition exercise programs and has been shown to be effective in increasing skeletal muscle size, strength, and the induction of vascular and bone adaptations to the surrounding tissues.57-60 A recent systematic review on low-load exercise training with BFR in musculoskeletal injuries indicated that BFR utilization can produce greater responses in muscular strength and may act as a surrogate for heavy-load training.61 Specifically, when combined with resistance training, loads as low as 20% 1RM have been shown to produce comparable gains in muscle hypertrophy and strength as traditional high-load resistance training.60,62 To date, specific protocols on the usage of BFR after UCL or ligamentous elbow injuries are yet to be published in the literature.

The author's preferred protocol for BFR uses 50% of the maximum occlusion pressure for the upper extremity. Depending on the level of pain and phase of rehabilitation, athletes start with isometric movements with a steady and gradual transition to isotonic movements. Athletes start with two different exercise programs per session and advance, over time, to a maximum of five exercise programs per session. Exercise movements are performed 2 to 3 times per week starting with loads 15% to 30% of the athlete's 1RM. In the early stages of rehabilitation, 1RM is not usually tested; however, the rate of perceived exertion by the athlete can be used as a proxy. Athletes perform 4 sets consisting of 30/15/15/15 repetitions with a 30-second rest between sets. Exercise programs are performed over a 2 second concentric contraction, followed by an equal period of eccentric contraction of the specified muscle group. Between sets, the author prefers a period of continued inflation of the cuff; however, between exercise programs, the cuff will be deflated as athletes rest over a 1-minute period. Common exercise programs performed include wrist flexion/extension using resistance bands or dumbbells, ulnar deviation, radial deviation, supination and pronation at the wrist while grasping a steel mace or sledgehammer, shoulder internal rotation/external rotation/abduction, farmer carries or holds, resisted finger and elbow flexion, and resisted external rotation/internal rotation isometrics at neutral with a progression to performing the exercise programs while in the throwing position (Figure 1).

Figure 1:
Clinical photograph of overhead athlete performing (A) prone shoulder abduction to 90°, (B) shoulder internal rotation at side, (C) and external rotation while at 50% limb occlusion pressure to the injured upper extremity.

Functional exercise programs, plyometrics, and an interval throwing program are typically instituted after the alleviation of pain and inflammation at the medial elbow.1,63 At this stage, plyometrics are continued throughout the training period as a way to maintain functional gains as the athlete progresses toward a return to competitive play.21 Plyometric ball throwing may also be implemented because the player nears a return to throwing progression to increase the dynamic stability and endurance needed in overhead throwing over the course of a long season. Reinold et al used biomechanical data to develop a dual-phase interval throwing program consisting of flat-ground and off-mound throwing with special attention to proper throwing mechanics.64-66 Flat-ground throwing has commonly been used in the rehabilitation and conditioning of baseball pitchers; however, the timing of this intervention must be considered. Increased elbow torque occurs during maximum distance flat-ground throwing and should be avoided in the early throwing stages after UCL injuries.67 In addition, long-toss throws have been found to be biomechanically useful for rehabilitation purposes because they progressively allow athletes to generate greater force, torque, ROM, and speed when compared with actual pitching.68,69 To reduce the risk of reinjury when engaging in these throwing programs, careful supervision by physical therapists, athletic trainers, or clinicians is necessary to monitor for appropriate tissue healing and joint ROM.67 In addition, supervision by an athletic trainer and/or experienced pitching coach can help with early detection of poor throwing mechanics to prevent future injury. For most athletes, return to competition can be attempted after the pain-free completion of the rehabilitation and interval throwing program.70 Ultimately, if symptoms persist after nonsurgical rehabilitation measures, surgical intervention may be necessary.

Before initiating a return to throwing progression, it is the senior author's preference to have the athlete undergo a RTS or “Thrower's Assessment.” RTS assessments have been studied in the lower extremity, specifically after anterior cruciate ligament reconstruction surgery. Similar to other RTS assessments, the “Thrower's Assessment” contains a battery of dynamic elbow and shoulder mobility tests designed to provide objective measures to monitor an athlete's progression and ensure a safe return to competition71 (Figure 2) In the lower extremity, RTS assessments have varied regarding the content of the battery; however, the tests are designed to evaluate several domains associated with reinjury and early failure.71

Figure 2:
Clinical photograph of overhead athlete performing (A) “plyometric 90-90 throws” and (B) “90-90 wall taps” as a part of the battery of tests contained in the author's “Thrower's Assessment.”

Biologic Therapies

The use of biologic therapies in orthopaedic injuries offers the potential benefits of improving the tissue-healing environment and decreasing healing time.72,73 In contrast to their common use for multiple orthopaedic conditions, corticosteroid injections are avoided because they can lead to further attenuation and destruction of the remaining ligament.74 Platelet-rich therapy (PRP) uses autologous blood products to isolate and deliver high concentrations of alpha granules with growth factors and proteins to the site of injury.72,73 These products have been shown to stimulate angiogenesis, cell recruitment, function, and proliferation.73,75 Several studies on PRP injections have been performed on rotator cuff tears, lateral epicondylitis, medial collateral ligament injuries of the knee, Achilles tendon tears, patellar tendinopathy, and UCL pathology with successful results in certain conditions.76-83

Podesta et al performed one of the first investigations on PRP therapy in partial-thickness UCL tears in overhead athletes that had failed 6 weeks of conservative therapy. The authors used a single, ultrasound-guided, leukocyte-rich (LR) PRP injection, followed by a progressive course of physical therapy.84 By week 8 to 10, a progressive interval throwing program was instituted with sport-specific training at weeks 10 to 12.84 At an average of 70 weeks of follow-up, 88% of athletes had returned to their preinjury level of play at an average 12 weeks.84 In addition, notable improvements were seen in Kerlan-Jobe Orthopedic Clinic and Disabilities of the Arm, Shoulder, and Hand outcome scores, and a notable decrease was observed in the average valgus-stressed humeral-ulnar joint space compared with nonstressed elbows.84

Similar efficacy of PRP was found among baseball players with UCL insufficiency in an investigation performed by Dines et al.85 Using a similar study design, and following a trial of conservative therapy consisting of rest, activity modification, pain control subject, and physical therapy, PRP was injected in 44 athletes near the location of the tear. Patients then underwent postinjection therapy consisting of progressive stretching and strengthening for 4 to 6 weeks, followed by an interval throwing program. At the final follow-up, 34% had excellent outcomes, described as a return to preinjury level of competition or performance, with another 39% able to return to a lower level of competition or performance.85 Consistent with the imaging study by Frangiamore et al, all patients with distal partial tears were found to have poor outcomes, characterized by an inability to return to previous sport at any level.30,85 Average time for return to throwing was 5 weeks with a mean of 12 weeks until return to competition without any injection-related complications.85

Finally, Deal et al investigated 23 patients with primary partial tears of the UCL. The author's practice consisted of a 2-injection series of PRP spaced two weeks apart in addition to bracing treatment and physical therapy. This regimen resulted in a 96% return to play rate, and a 91% rate of full reconstitution of the ligament among the players who returned to play based on an MRI performed four weeks after initiation of treatment.

Dines, Podesta, and Deal's investigations analyzed athletes with a mean age of 17.3, 18, and 18 years, respectively, yet the case by Gordon et al reported on a 14-year-old baseball pitcher with chronic medial elbow pain provides insight on PRP use in an adolescent athlete.84-86 In the setting of a low-grade, proximal, partial UCL tear, the athlete underwent a single 5 mL, ultrasonography-guided PRP injection at the site of injury.86 After injection, the patient underwent 2 weeks of rest and a gradual, 12-week throwing rehabilitation protocol with interval healing on ultrasonography at 8 weeks after injection with reduced valgus laxity on examination. At 16 weeks after injection, complete healing was noted on ultrasonography, and he was able to return to full pitching without symptoms.86

There are important differences to highlight between the above investigations. First, although the report by Gordon et al report highlights using a single injection, Dines and Podesta described using varying frequencies of injections, whereas Deal et al performed two.84-86 Although these reports demonstrate success, the correct dosage, timing, and frequency of PRP use is remains unknown. In addition, the type of PRP used may be notable. Both Dines and Podesta used a LR PRP as opposed to a leukocyte-poor formulation.84,85 The data presented above illustrate clinical and radiographic success of LR-PRP formulation likely because of the increase inflammatory response that stimulates the body's healing response as has been previously document. However, to the authors' knowledge, there have been no studies regarding leukocyte-poor-PRP use in the setting of UCL pathology.

Most recently, Chauhan et al87 performed87 a retrospective-matched cohort study examining PRP use for UCL injuries using the MLB Health and Injury Tracking System (HITS), a centralized database for player injuries in minor LB (MiLB) and Major League Baseball. Of the 544 included players from 2011 to 2015, 24% received at least one PRP injection before starting a rehabilitation program compared with the remaining players in the no-PRP group. Older players and MLB players were statistically more likely to receive PRP injections before starting a rehabilitation program.87 The overall nonsurgical cohort had a 54% RTP rate with the PRP group experiencing a markedly lower RTP rate (46% vs 57%) and missed significantly more time. Ultimately, no difference in survival of the native of ligament was seen regardless of PRP use. Despite these findings, the major limitation of the study by Chauhan et al87 lies in the variability of PRP formulations and rehabilitation protocols used.

Currently, no dedicated studies on the efficacy of stem cell therapy for UCL injuries in humans have been published. Thus, the primary drawback preventing its use has been the inability to differentiate progenitor cells into ligamentous tissue.88 The use of adipose-derived stem cells has been attempted by examining the expression of ligament markers after growth factor treatment; however, no notable, or consistent, upregulation of cell lines has been observed.89 Coculturing of cells has had some success in rabbit models because mesenchymal stem cells (MSCs) have been cocultured on enzymatically digested ACL fibroblasts. In this study, follow-up immunohistochemical staining revealed the differentiation of viable MSCs when cocultured on a bioscaffold.90 This study showed there is potential for ligament tissue engineering; however, further investigation is needed to determine the true merit and efficacy of such an endeavor.

One of the only investigations of stem cells regarding the UCL was detailed in a case report where a construct containing dermal allograft, PRP, and MSC was used to augment an UCL reconstruction in professional baseball player.91 MSCs are thought to demonstrate dynamic reparative properties through direct differentiation and paracrine signaling.92-94 As a result, they are capable of differentiating into multiple tissue-forming cell lineages and release growth factors into the surrounding environment.92-94 Previous research into its use in augmenting rotator cuff repairs have shown successful improvements in postoperative healing as evidenced by an increase in the promotion of collagen fiber reorganization, remodeling and incorporation into native tissue, angiogenesis, and neural infiltration.95,96 Per the study by Hoffman, a postoperative MRI performed at 3 months showed an intact dermal allograft without evidence of any inflammatory response and a throwing program was initiated at 4 months postoperatively.91 However, despite the intriguing possibilities behind biologics as an option for augmentation, more research is needed on its use as a modality for nonsurgical management. To date, the primary limitation to MSC use is the consistent identification and isolation of specific cell isolates that can differentiated into cell lineages that can be used toward tendon-tendon or tendon-bone healing.97,98

Outcomes With Nonsurgical Management

Outcomes of conservative therapy are variable, but much of the decision to pursue nonsurgical management is dependent on patient characteristics and the degree of injury.20,21,30 In lower demand patients and nonthrowing athletes, nonsurgical treatment has been found to arrest the progression of instability and functional impairment.21 Throwing athletes on the other hand present a separate challenge. Barnes and Tullos99 performed one of the initial studies on the management of elbow pathology by looking at a random series of 100 professional and collegiate throwing athletes with either elbow or shoulder problems. Of the 50 patients with elbow-related problems, 26 were able to return to throwing without surgical intervention.99 Of those players requiring surgery, three cases were for UCL rupture or attenuation.99 Given the relative infancy of UCL injuries at the time of publication, the major limitation to this study was the lack of information on the exact pathology afflicting the medial collateral ligament. This weakness is likely because of the absence of advanced imaging at the time. As such, it seems that both surgical and nonsurgical management seem to be effective in permitting continued high-level athletic participation, but it is unclear what pathology these interventions apply to. Jobe proposed his own nonsurgical protocol composed of two cycles of rest from throwing and rehabilitation exercise programs after acute injury. In these patients, surgery was indicated if pain persisted when throwing at 75% of baseline intensity. Although a nonsurgical strategy was proposed, no rates on return to play or failure of nonsurgical management were reported.

Rettig et al45 performed one of the landmark studies on RTS after nonsurgical treatment in 31 throwing athletes with UCL tear or insufficiency. After diagnosis, patients underwent a dual-phase physical therapy program for which 42% were able to RTS at their preinjury level of play at an average of 24.5 weeks from the time of diagnosis.45 When stratifying the results according to the longevity of symptoms, acute or insidious injury or age at the time of return to play, no notable differences were found between those with either successful or unsuccessful therapy.45 Furushima et al100 were later able to identify the presence of a residual ossicle at the ligament-bone junction, ongoing pain, and most markedly, complete tears of UCL as the primary risk factor for failure of nonsurgical therapy in baseball players with a 33% return to play rate.100 However, 82% of players with partial injury were able to return to play at a competitive level.100

A retrospective review of UCL tears occurring within a single NFL team, and across the entire league, was performed over a 5-year study period. Analysis of injuries from a single team (n = 5) involved mostly nonoverhead athletes (1 quarterback, 1 running back, and 2 centers), with only the quarterback requiring surgery for a suspected loose body.20 Seventy-five percent of players returned to full practice the day after injury with the remaining player returning after 2 days of rest without any evidence of instability at a mean follow-up of 3.4 years.20 Expanded analyses across the entire NFL showed a 15% prevalence of UCL injuries in mostly nonoverhead athletes (1 quarterback), with blocking at the line of scrimmage as the most common mechanism of injury. All UCL injuries were treated nonsurgically with rest, anti-inflammatory medications, and immobilization. Average time lost from injury was 0.64 games and thus exhibiting relatively improved outcomes in nonoverhead athletes with UCL injuries.20 Successful return to play was also found in quarterbacks, which may highlight biomechanical differences in the stress imparted to the medial elbow across American football quarterbacks and other overhead athletes. For example, less rotational, medial, and compressive forces are applied to the elbow in throwing a football when compared with a javelin or a baseball.101,102 This may be secondary to a less dramatic cocking phase or hand and wrist positioning during the throwing motion with a football compared with a baseball.20 Further study of NFL quarterbacks with UCL injuries showed 9/10 (grades 1-3) players were treated without surgery with an average return to play of 27.4 days.103 Players with grade 3 injuries experienced a longer return to play of 67.3 days compared with lower grade 1 and 2 injuries of 7.8 and 7 days, respectively, introducing the possibility of different treatment strategies for contact-related UCL injuries.103

A comparison of UCL reconstruction and nonsurgical management in MRI-graded tears showed a 93% (26/28) rate of return to play at a similar level in those with partial tears.104 On stratification, of the 10 positional players, 90% returned to their previous level of play and among the 18 pitchers, 94% returned to play.104 Within the study by Ford et al104, three players (all pitchers) with incomplete tears failed nonsurgical management. This study only provides more support for the possible use of MRI grading to predict return to play and the need for surgery. More recently, using the MLB HITS database on MiLB and MLB players found lower rates of return to throwing and RTP with Grade III injuries (81% and 44%, respectively) and distal tears (81% and 58%, respectively).87 After multivariate regression modelling, the only risk factor predictive of inability to return to play was age older than 25 years, whereas playing status at the major league level was only a notable predictor of recurrent injury or failing nonsurgical treatment.87 Using much of the aforementioned findings in the literature, the senior author's preferred indications for nonsurgical treatment are listed in Table 1. Of note, treatment decisions are not finite, and multiple permutations exist based on a given athlete's level of play, degree of symptoms, MRI findings, seasonal and career timing, and their aspirations for competitive play in the future.

Table 1 - Indications and Treatment Options for Ulnar Collateral Ligament Injuries
Tear Location Grade Position Treatment Options
Proximal 1 Pitcher/Fielder Nonsurgicala ± PRP
2 Pitcher Reconstruction/Repairb
3 Fielder Nonsurgicala ± PRP vs reconstruction/Repairb
Pitcher/Fielder Reconstruction/Repairb
Midsubstance 1 Pitcher/Fielder Nonsurgicala ± PRP
2 Pitcher Reconstruction vs. Repairb
3 Fielder Nonsurgicala ± PRP vs reconstruction/Repairb
Pitcher/Fielder Reconstruction vs. Repairb
Distal 1 Pitcher/Fielder Nonsurgicala ± PRP
2 Pitcher Reconstruction vs. Repairb
3 Fielder Nonsurgicala ± PRP vs reconstruction/Repairb
Pitcher/Fielder Reconstruction vs. Repairb
aNonsurgical management includes rest, physical therapy (including stretching, range of motion, blood-flow restriction exercise programs. and plyometrics) with frequent clinical reassessments to evaluate for the presence of recurrent pain, decreased function, reinjury, or an inability to perform at a competitive level.
bConsiderations for UCL reconstruction versus repair are subject to discussion with the patient on seasonal/career timing of the injury, the athlete's current level of play (high school vs collegiate vs professional), and their subsequent career aspirations.
PRP = platelet-rich therapy; UCL = ulnar collateral ligament


There is a spectrum on which injuries to the UCL of the elbow can exist. Nonsurgical management remains a possibility for definitive management of UCL pathology; however, attention must be paid toward identifying appropriate athletes who may benefit. A plethora of literature tends to support the reconstruction in complete ruptures in overhead throwing athletes, but partial and, specifically, proximal tears seem to achieve similar outcomes with nonsurgical therapies. Much is still to be said toward the utility of imaging to grade UCL injuries and thus stratify patients based on pathology, and the influence of injury location and their associated outcomes. Furthermore, examination of the overhead motion and stress imparted to the medial elbow may help to further predict success of nonsurgical management in overhead athletes across other sports. When engaging in nonsurgical modalities, the importance of graded and tailored physical therapy regimens and throwing patterns cannot be understated. Finally, the role of biologic augmentation in conservative therapy remains in its infancy; however, the recent literature has presented exciting and promising outcomes supporting the use of LR- PRP for partial UCL injuries. As our scientific capabilities continue to grow, investigation into these therapies will be useful for the ongoing care of athletes with UCL injuries.


1. Azar FM, Andrews JR, Wilk KE, Groh D: Operative treatment of ulnar collateral ligament injuries of the elbow in athletes. Am J Sports Med 2000;28:16-23.
2. Cain EL, Dugas JR, Wolf RS, Andrews JR: Elbow injuries in throwing athletes: A current concepts review. Am J Sports Med 2003;31:621-635.
3. Chen FS, Rokito AS, Jobe FW: Medial elbow problems in the overhead-throwing athlete. J Am Acad Orthop Surg 2001;9:99-113.
4. Conway JE: Arthroscopic repair of partial-thickness rotator cuff tears and SLAP lesions in professional baseball players. Orthop Clin North Am 2001;32:443-456.
5. Indelicato PA, Jobe FW, Kerlan RK, Carter VS, Shields CL, Lombardo SJ: Correctable elbow lesions in professional baseball players: A review of 25 cases. Am J Sports Med 1979;7:72-75.
6. Jobe FW, Stark H, Lombardo SJ: Reconstruction of the ulnar collateral ligament in athletes. J Bone Joint Surg Am 1986;68:1158-1163.
7. Kuroda S, Sakamaki K: Ulnar collateral ligament tears of the elbow joint. Clin Orthop Relat Res 1986:266-271.
8. Safran MR: Ulnar collateral ligament injury in the overhead athlete: Diagnosis and treatment. Clin Sports Med 2004;23:643-663.
9. Tullos HS, Erwin WD, Woods GW, Wukasch DC, Cooley DA, King JW: Unusual lesions of the pitching arm. Clin Orthop Relat Res 1972;88:169-182.
10. Wright P: No title. Campbell's Oper Orthop 1992:5;3003-3054.
11. Yocum LA: The diagnosis and nonoperative treatment of elbow problems in the athlete. Clin Sports Med 1989;8:439-451.
12. Dodson CC, Thomas A, Dines JS, Nho SJ, Williams RJ, Altchek DW: Medial ulnar collateral ligament reconstruction of the elbow in throwing athletes. Am J Sports Med 2006;34:1926-1932.
13. Thompson WH, Jobe FW, Yocum LA, Pink MM: Ulnar collateral ligament reconstruction in athletes: Muscle-splitting approach without transposition of the ulnar nerve. J Shoulder Elb Surg 2001;10:152-157.
14. Waris W: Elbow injuries of javelin-throwers. Acta Chir Scand 1946;93:563-575.
15. Dugas JR, Looze CA, Capogna B, et al.: Ulnar collateral ligament repair with collagen-dipped FiberTape augmentation in overhead-throwing athletes. Am J Sports Med 2019;47:1096-1102.
16. Cain EL, Andrews JR, Dugas JR, et al.: Outcome of ulnar collateral ligament reconstruction of the elbow in 1281 athletes: Results in 743 athletes with minimum 2-year follow-up. Am J Sports Med 2010;38:2426-2434.
17. Erickson BJ, Gupta AK, Harris JD, et al.: Rate of return to pitching and performance after tommy John surgery in major league baseball pitchers. Am J Sports Med 2014;42:536-543.
18. Erickson BJ, Nwachukwu BU, Rosas S, et al.: Trends in medial ulnar collateral ligament reconstruction in the United States. Am J Sports Med 2015;43:1770-1774.
19. Hodgins JL, Vitale M, Arons RR, Ahmad CS: Epidemiology of medial ulnar collateral ligament reconstruction. Am J Sports Med 2016;44:729-734.
20. Kenter K, Behr CT, Warren RF, O'Brien SJ, Barnes R: Acute elbow injuries in the national football league. J Shoulder Elb Surg 1996;9:1-5.
21. Miller CD, Savoie FH: Valgus extension injuries of the elbow in the throwing athlete. J Am Acad Orthop Surg 1994;2:261-269.
22. Kim NR, Moon SG, Ko SM, Moon WJ, Choi JW, Park JY: MR imaging of ulnar collateral ligament injury in baseball players: Value for predicting rehabilitation outcome. Eur J Radiol 2011;80:e422-6.
23. Rijke AM, Goitz HT, McCue FC, Andrews JR, Berr SS: Stress radiography of the medial elbow ligaments. Radiology 1994;191:213-216.
24. Ellenbecker TS, Mattalino AJ, Elam EA, Caplinger RA: Medial elbow joint laxity in professional baseball pitchers: A bilateral comparison using stress radiography. Am J Sports Med 1998;26:420-424.
25. Timmerman LA, Schwartz ML, Andrews JR: Preoperative evaluation of the ulnar collateral ligament by magnetic resonance imaging and computed tomography arthrography. Am J Sports Med 1994;22:26-32.
26. Timmerman LA, Andrews JR: Histology and arthroscopic anatomy of the ulnar collateral ligament of the elbow. Am J Sports Med 1994;22:667-673.
27. Schwartz ML, al-Zahrani S, Morwessel RM, Andrews JR: Ulnar collateral ligament injury in the throwing athlete: Evaluation with saline-enhanced MR arthrography. Radiology 1995;197:297-299.
28. Timmerman LA, Andrews JR: Undersurface tear of the ulnar collateral ligament in baseball players: A newly recognized lesion. Am J Sports Med 1994;22:33-36.
29. Schreiber JJ, Potter HG, Warren RF, Hotchkiss RN, Daluiski A: Magnetic resonance imaging findings in acute elbow dislocation: Insight into mechanism. J Hand Surg Am 2014;39:199-205.
30. Frangiamore SJ, Lynch TS, Vaughn MD, et al.: Magnetic resonance imaging predictors of failure in the nonoperative management of ulnar collateral ligament injuries in professional baseball pitchers. Am J Sports Med 2017;45:1783-1789.
31. Nazarian LN, McShane JM, Ciccotti MG, O'Kane PL, Harwood MI: Dynamic US of the anterior band of the ulnar collateral ligament of the elbow in asymptomatic major league baseball pitchers. Radiology 2003;227:149-154.
32. Sasaki J, Takahara M, Ogino T, Kashiwa H, Ishigaki D, Kanauchi Y: Ultrasonographic assessment of the ulnar collateral ligament and medial elbow laxity in college baseball players. J Bone Joint Surg Am 2002;84A:525-531.
33. Ciccotti MG, Atanda A, Nazarian LN, Dodson CC, Holmes L, Cohen SB: Stress sonography of the ulnar collateral ligament of the elbow in professional baseball pitchers: A 10-year study. Am J Sports Med 2014;42:1-8.
34. Wilk KE, Andrews JR, Arrigo CA: Preventive and Rehabilitation Exercises for the Shoulder and Elbow. Birmingham, AL, American Sports Medicine Institute, 1997.
35. Wilk KE, Yenchak AJ, Arrigo CA, Andrews JR: The advanced throwers ten exercise program: A new exercise series for enhanced dynamic shoulder control in the overhead throwing athlete. Phys Sports Med 2011;39:90-97.
36. Escamilla RF, Speer KP, Fleisig GS, Barrentine SW, Andrews JR: Effects of throwing overweight and underweight baseballs on throwing velocity and accuracy. Sports Med 2000;29:259-272.
37. Yang WW, Liu YC, Lu LC, Chang HY, Chou PP, Liu C: Performance enhancement among adolescent players after 10 weeks of pitching training with appropriate baseball weights. J Strength Cond Res 2013;27:3245-3251.
38. Reinold MM, Macrina LC, Fleisig GS, Aune K, Andrews JR: Effect of a 6-week weighted baseball throwing program on pitch velocity, pitching arm biomechanics, passive range of motion, and injury rates. Sports Health 2018;10:327-333.
39. Fleisig GS, Phillips R, Shatley A, et al.: Kinematics and kinetics of youth baseball pitching with standard and lightweight balls. Sport Eng 2006;9:155-163.
40. Okoroha KR, Meldau JE, Jildeh TR, Stephens JP, Moutzouros V, Makhni EC: Impact of ball weight on medial elbow torque in youth baseball pitchers. J Shoulder Elb Surg 2019;28:1484-1489.
41. Caldwell JME, Alexander FJ, Ahmad CS: Weighted-ball velocity enhancement programs for baseball pitchers: A systematic review. Orthop J Sport Med 2019;7:2325967118825469.
42. Crotin R, Ramsey D: Injury prevention for throwing athletes. Part I: Baseball bat training to enhance medial elbow dynamic stability. Strength Cond J 2012;34:79-85.
43. Sakata J, Nakamura E, Suzuki T, et al.: Efficacy of a prevention program for medial elbow injuries in youth baseball players. Am J Sports Med 2018;46:460-469.
44. Sakata J, Nakamura E, Suzukawa M, Akaike A, Shimizu K: Physical risk factors for a medial elbow injury in Junior baseball players: A prospective cohort study of 353 players. Am J Sports Med 2017;45:135-143.
45. Rettig AC, Sherrill C, Snead DS, Mendler JC, Mieling P: Nonoperative treatment of ulnar collateral ligament injuries in throwing athletes*. Am J Sports Med 2001;29:15-17.
46. Wilk KE, Macrina LC, Cain EL, Dugas JR, Andrews JR: Rehabilitation of the overhead athlete's elbow. Sports Health 2012;4:404-414.
47. Dines JS, Frank JB, Akerman M, Yocum LA: Glenohumeral internal rotation deficits in baseball players with ulnar collateral ligament insufficiency. Am J Sports Med 2009;37:566-570.
48. Garrison JC, Arnold A, Macko MJ, Conway JE: Baseball players diagnosed with ulnar collateral ligament tears demonstrate decreased balance compared to healthy controls. J Orthop Sport Phys Ther 2013;43:752-758.
49. Ben Kibler W, Sciascia A: Kinetic chain contributions to elbow function and dysfunction in sports. Clin Sports Med 2004;23:545-552, viii.
50. Seroyer ST, Nho SJ, Bach BR, Bush-Joseph CA, Nicholson GP, Romeo AA: The kinetic chain in overhand pitching: Its potential role for performance enhancement and injury prevention. Sports Health 2010;2:135-146.
51. Hamilton CD, Glousman RE, Jobe FW, Brault J, Pink M, Perry J: Dynamic stability of the elbow: Electromyographic analysis of the flexor pronator group and the extensor group in pitchers with valgus instability. J Shoulder Elb Surg 1996;5:347-354.
52. Glousman RE, Barron J, Jobe FW, Perry J, Pink M: An electromyographic analysis of the elbow in normal and injured pitchers with medial collateral ligament insufficiency. Am J Sports Med 1992;20:311-317.
53. Davidson PA, Pink M, Perry J, Jobe FW: Functional anatomy of the flexor pronator muscle group in relation to the medial collateral ligament of the elbow. Am J Sports Med 1995;23:245-250.
54. Udall JH, Fitzpatrick MJ, McGarry MH, Leba TB, Lee TQ: Effects of flexor-pronator muscle loading on valgus stability of the elbow with an intact, stretched, and resected medial ulnar collateral ligament. J Shoulder Elb Surg 2009;18:773-778.
55. Goodman CA, Frey JW, Mabrey DM, et al.: The role of skeletal muscle mTOR in the regulation of mechanical load-induced growth. J Physiol 2011;589:5485-5501.
56. Abe T, Kearns CF, Sato Y: Muscle size and strength are increased following walk training with restricted venous blood flow from the leg muscle, Kaatsu-walk training. J Appl Physiol (1985) 2006;100:1460-1466.
57. Jessee MB, Mattocks KT, Buckner SL, et al.: Mechanisms of blood flow restriction: The new testament. Tech Orthop 2018;33:72-79.
58. Abe T, Sakamaki M, Fujita S, et al.: Effects of low-intensity walk training with restricted leg blood flow on muscle strength and aerobic capacity in older adults. J Geriatr Phys Ther 2010;33:34-40.
59. Aguayo D, Mueller SM, Boutellier U, et al.: One bout of vibration exercise with vascular occlusion activates satellite cells. Exp Physiol 2016;101:295-307.
60. Barnett BE, Dankel SJ, Counts BR, Nooe AL, Abe T, Loenneke JP: Blood flow occlusion pressure at rest and immediately after a bout of low load exercise. Clin Physiol Funct Imaging 2016;36:436-440.
61. Hughes L, Paton B, Rosenblatt B, Gissane C, Patterson SD: Blood flow restriction training in clinical musculoskeletal rehabilitation: A systematic review and meta-analysis. Br J Sports Med 2017;51:1003-1011.
62. Gorgey AS, Timmons MK, Dolbow DR, et al.: Electrical stimulation and blood flow restriction increase wrist extensor cross-sectional area and flow meditated dilatation following spinal cord injury. Eur J Appl Physiol 2016;116:1231-1244.
63. Boone DC, Azen SP: Normal range of motion of joints in male subjects. J Bone Joint Surg Am 1979;61:756-759.
64. Reinold M, Wilk KE, Reed J, Crenshaw K, Andrews JR: Interval sport programs: Guidelines for baseball, tennis and golf. J Orthop Sport Phys Ther 2002;32:293-298.
65. Fleisig GS, Escamilla RF, Barrentine SW, Zheng N, Andrews J: Kinematic and kinetic comparison of baseball pitching from a mound and throwing from flat ground. 20th Annual Meeting of the American Society of Biomechanics, Atlanta, GA, October 17, 1996.
66. Fleisig GS, Zheng N, Barrentine S, Escamilla R, Andrews J, Lemak L. Kinematic and kinetic comparison of full-effort and partial effort baseball pitching. 20th Annual Meeting of the American Society of Biomechanics, Atlanta, GA, October 17, 1996.
67. Fleisig GS, Bolt B, Fortenbaugh D, Wilk KE, Andrews JR: Biomechanical comparison of baseball pitching and long-toss: Implications for training and rehabilitation. J Orthop Sport Phys Ther 2011;41:296-303.
68. Wilk KE, Meister K, Andrews J: Current concepts in the rehbilitation of the overhead throwing athlete. Am J Sports Med 2002;30:136-151.
69. Wilk KE, Obma P, Simpson CD, Cain EL, Dugas J, Andrews JR: Shoulder injuries in the overhead athlete. J Orthop Sport Phys Ther 2009;39:38-54.
70. Wilson FD, Andrews JR, Blackburn TA, McCluskey G: Valgus extension overload in the pitching elbow. Am J Sports Med 1982;11:83-88.
71. Webster KE, Hewett TE: What is the evidence for and validity of return-to-sport testing after anterior cruciate ligament reconstruction surgery? A systematic review and meta-analysis. Sport Med 2019;49:917-929.
72. Hall MP, Band PA, Meislin RJ, Jazrawi LM, Cardone DA: Platelet-rich plasma: Current concepts and application in sports medicine. J Am Acad Orthop Surg 2009;17:602-608.
73. Lopez-Vidriero E, Goulding KA, Simon DA, Sanchez M, Johnson DH: The use of platelet-rich plasma in arthroscopy and sports medicine: Optimizing the healing environment. Arthrosc J Arthrosc Relat Surg 2010;26:269-278.
74. Walsh WR, Wiggins ME, Fadale PD, Ehrlich MG: Effects of a delayed steroid injection on ligament healing using a rabbit medial collateral ligament model. Biomaterials 1995;16:905-910.
75. Jo CH, Kim JE, Yoon KS, Shin S: Platelet-rich plasma stimulates cell proliferation and enhances matrix gene expression and synthesis in tenocytes from human rotator cuff tendons with degenerative tears. Am J Sports Med 2012;40:1035-1045.
76. Mishra A, Pavelko T: Treatment of chronic elbow tendinosis with buffered platelet-rich plasma. Am J Sports Med 2006;34:1774-1778.
77. Peerbooms JC, Sluimer J, Bruijn DJ, Gosens T: Positive effect of an autologous platelet concentrate in lateral epicondylitis in a double-blind randomized controlled trial. Am J Sports Med 2010;38:255-262.
78. Randelli P, Arrigoni P, Ragone V, Aliprandi A, Cabitza P: Platelet rich plasma in arthroscopic rotator cuff repair: A prospective RCT study, 2-year follow-up. J Shoulder Elb Surg 2011;20:518-528.
79. Jo CH, Kim JE, Yoon KS, et al.: Does platelet-rich plasma accelerate recovery after rotator cuff repair? A prospective cohort study. Am J Sports Med 2011;39:2082-2090.
80. Foster TE, Puskas BL, Mandelbaum BR, Gerhardt MB, Rodeo SA: Platelet-rich plasma. Am J Sports Med 2009;37:2259-2272.
81. Filardo G, Kon E, Della Villa S, Vincentelli F, Fornasari PM, Marcacci M: Use of platelet-rich plasma for the treatment of refractory jumper's knee. Int Orthop 2010;34:909-915.
82. Kon E, Filardo G, Delcogliano M, et al.: Platelet-rich plasma: New clinical application. Injury 2009;40:598-603.
83. Sanchez M, Anitua E, Azofra J, Andia I, Padilla S, Mujika I: Comparison of surgically repaired Achilles tendon tears using platelet-rich fibrin matrices. Am J Sports Med 2006;35:245-251.
84. Podesta L, Crow SA, Volkmer D, Bert T, Yocum LA: Treatment of partial ulnar collateral ligament tears in the elbow with platelet-rich plasma. Am J Sports Med 2013;41:1689-1694.
85. Dines JS, Williams PN, ElAttrache N, et al.: Platelet-rich plasma can Be used to successfully treat elbow ulnar collateral ligament insufficiency in high-level throwers. Am J Orthop (Belle Mead NJ) 2016;45:296-300.
86. Gordon AH, De Luigi AJ: Adolescent pitcher recovery from partial ulnar collateral ligament tear after platelet-rich plasma. Curr Sports Med Rep 2018;17:407-409.
87. Chauhan A, McQueen P, Chalmers PN, et al.: Nonoperative treatment of elbow ulnar collateral ligament injuries with and without platelet-rich plasma in professional baseball players: A comparative and matched cohort analysis. Am J Sports Med 2019;47:3107-3119.
88. Mautner K, Blazuk J: Where do injectable stem cell treatments apply in treatment of muscle, tendon, and ligament injuries? PM&R 2015;7:S33-S40.
89. Eagan MJ, Zuk PA, Zhao KW, et al.: The suitability of human adipose-derived stem cells for the engineering of ligament tissue. J Tissue Eng Regen Med 2012;6:702-709.
90. Fan H, Liu H, Toh SL, Goh JC: Enhanced differentiation of mesenchymal stem cells co-cultured with ligament fibroblasts on gelatin/silk fibroin hybrid scaffold. Biomaterials 2008;29:1017-1027.
91. Hoffman JK, Protzman NM, Malhotra AD: Biologic augmentation of the ulnar collateral ligament in the elbow of a professional baseball pitcher. Case Rep Orthop 2015;2015:1-5.
92. Zhong ZN, Zhu SF, Yuan AD, et al.: Potential of placenta-derived mesenchymal stem cells as seed cells for bone tissue engineering: Preliminary study of osteoblastic differentiation and immunogenicity. Orthopedics 2012;35:779-788.
93. Krampera M, Pizzolo G, Aprili G, Franchini M: Mesenchymal stem cells for bone, cartilage, tendon and skeletal muscle repair. Bone 2006;39:678-683.
94. Rahaman MN, Mao JJ: Stem cell-based composite tissue constructs for regenerative medicine. Biotechnol Bioeng 2005;91:261-284.
95. Protzman NM, Stopyra GA, Hoffman JK: Biologically enhanced healing of the human rotator cuff: 8-month postoperative histological evaluation. Orthopedics 2013;36:38-41.
96. Gordon NM, Maxson S, Hoffman JK: Biologically enhanced healing of the rotator cuff. Orthopedics 2012;35:498-504.
97. Wagner W, Ho AD: Mesenchymal stem cell preparations—comparing apples and oranges. Stem Cell Rev 2007;3:239-248.
98. Ju YJ, Muneta T, Yoshimura H, Koga H, Sekiya I: Synovial mesenchymal stem cells accelerate early remodeling of tendon-bone healing. Cell Tissue Res 2008;332:469-478.
99. Barnes DA, Tullos HS: An analysis of 100 symptomatic baseball players. Am J Sports Med 1978;6:62-67.
100. Furushima K, Itoh Y, Iwabu S: What are the risk factors for failure after conservative treatment of ulnar collateral ligament injuries of the elbow in baseball players? Orthop J Sport Med 2013;1:2325967113S00015.
101. Fleisig GS, Barrentine SW, Escamilla RF, Andrews JR: Biomechanics of overhand throwing with implications for injuries. Sports Med 1996;21:421-437.
102. Fleisig GS, Escamilla RF, Andrews JR, Matsuo T, Satterwhite Y, Barrentine SW: Kinematic and kinetic comparison between baseball pitching and football passing. J Appl Biomech 1996;12:207-224.
103. Dodson CC, Slenker N, Cohen SB, Ciccotti MG, DeLuca P: Ulnar collateral ligament injuries of the elbow in professional football quarterbacks. J Shoulder Elb Surg 2010;19:1276-1280.
104. Ford GM, Genuario J, Kinkartz J, Githens T, Noonan T: Return-to-Play outcomes in professional baseball players after medial ulnar collateral ligament injuries. Am J Sports Med 2016;44:723-728.
Copyright © 2021 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Orthopaedic Surgeons.