POPLITEUS STRAIN WITH CONCURRENT DELTOID LIGAMENT SPRAIN IN AN ELITE SOCCER ATHLETE: A CASE REPORT

Abstract

Study Design:

Case Report (Differential diagnosis)

Background and Purpose:

Differential diagnosis of knee pathology after trauma may be difficult when diagnosing an isolated popliteus strain and concurrent medial deltoid ligament sprain. Upon a thorough search of the published literature, the authors found no reports delineating a popliteus strain in professional soccer in the United States. The joints most affected by injury in soccer players are the knee and ankle joints. The purpose of this case report is to describe the presentation of and difficulties encountered in diagnosing a popliteus strain in a Major League Soccer athlete.

Case Description:

During an in-season away game, an outside defender was slide-tackled from behind when his right shank was caught in an externally rotated position underneath himself and the opposing player. The initial point of contact was made to the proximal third of the posterior right shank with an anteromedially directed force. The medial longitudinal arch of the foot was forced into a more midfoot pronated position and the subtalar joint was forced into eversion.

Diagnosis:

The athlete was diagnosed with a moderate strain of the right popliteus muscle with a concurrent medial deltoid ligament sprain of the right ankle. This mechanism of injury, pain with passive knee flexion and internal rotation during McMurray's test, pain with Garrick's Test and magnetic resonance imaging (MRI) study confirmed the diagnosis. The athlete returned to full ninety-minute game participation after an intensive 15-day rehabilitation program.

Discussion:

This case is unique because the injury manifested itself at multiple joints and specifically involved the popliteus muscle. The mechanism of injury can be associated with many other soft tissue injuries to the knee, and thus, may not lead the clinician initially to consider the diagnosis of a popliteus strain. Diagnosis of this entity may be difficult due to the possible shared attachment of the popliteus muscle to the lateral meniscus, and the lack of available testing methods to assess damage to the popliteus muscle.

Level of Evidence:

Level 5

INTRODUCTION

Differential diagnosis of knee pathology after trauma may be difficult especially with regard to an insult of the popliteus muscle and concurrent injury to another joint. Immediate and accurate diagnosis is critical in professional soccer as coaches and managers need to make decisions in order to keep the team competitive when a key player sustains a time loss injury. The necessity of quick decision-making after a player's injury requires a thorough examination, skilled differential diagnosis, and the possible use of diagnostic imaging.

In Major League Soccer (MLS), Morgan and Oberlander reported that 77% of injuries were to the lower extremity, with the knee and ankle being the most frequently affected joints.¹ They reported strains to the hip adductors, hamstrings, and quadriceps muscles with no mention of a strain to the popliteus muscle. The only published epidemiological study performed in MLS was limited to the inaugural season in 1996. Since this study the league has added additional expansion teams and the schedule has been lengthened, both in terms of number of matches and duration of the season. With more matches and a longer training season, players are currently more likely to experience an injury than the athletes who were the subjects in the original report. Adding additional games during the week is directly correlated to increased injury rates.²

In a systematic review of lower extremity injuries in soccer, Wong and Hong found that professional soccer players have a higher injury rate in competitions than do adolescent players.³ In addition to higher injury rates in competition, the most common mechanisms of injury were tackling, running, shooting, twisting and turning, and jumping and landing.³ The authors concluded that most soccer injuries were contusions, followed by sprains and strains.

Injuries to the ankle are very common in soccer. One study recorded the mechanisms of injury to the ankle in four international soccer competitions.⁴ Tackles caused most ankle injuries with lateral or medial forces creating an inversion or eversion rotation at the ankle. In this study, of 76 ankle injuries, 52 were contusions, 20 were sprains, and 4 were fractures. Several other studies demonstrate that injury to the ankle or knee joint are the top injuries incurred by soccer players.^5,6,7,8,9 Even though injuries to the ankle occur with the most frequency, knee injuries result in more time loss from practice and games.^10,11

MLS is the highest professional soccer level in the United States. Upon a thorough search of the published literature (Pubmed & Google Scholar), there are no published reports delineating a popliteus strain injury with a concurrent deltoid ligament sprain in professional soccer in the United States. The purpose of this case report is to describe the presentation of and difficulties encountered in diagnosing a popliteus strain in a Major League Soccer athlete.

CASE DESCRIPTION

At the time of incident, the subject was a male, twenty-six year old outside defender (Caucasian/Hispanic) professional soccer athlete with a height of 1.75 meters and weight of 65.7 kilograms. The athlete had 4 years of professional soccer experience. The weather on the day of the injury was 26.7 °C and cloudy. During an in-season, away soccer match on a grass field, the athlete was slide-tackled from behind and his right shank was caught in an externally rotated position underneath himself and the opposing player. The initial point of contact was made to the proximal third of the posterior right shank with an anteromedial directed force. Moreover, the subtalar joint was forced into eversion causing injury to the athlete's right ankle. The tackle occurred in the 20^th minute of the game and resulted in a foul being called by the referee and yellow card caution issued to the opponent. The athlete attempted to play after the incident but was unable to continue due to pain in the right knee and right ankle and was removed from the contest after several minutes. Upon evaluation of the injury, the injured athlete reported localized pain to the posterior lateral complex of his right knee and medial deltoid ligament of his right ankle.

Past orthopaedic history revealed a second-degree right ankle sprain of the deltoid ligament two weeks prior to the injury described in this case report. The athlete returned to play once he achieved bilaterally equal figure eight girth measurements, open and closed chain dorsiflexion range of motion and lower leg muscle strength to the opposite side. Additionally, he was cleared to play with an appraisal of his movement during closed chain exercises such as squatting, single leg deadlifting, and on field movements such as running and cutting maneuvers. The healing of the ankle was sufficient with his functional performance in order to allow him to return to play with athletic tape applied to the ankle using a closed basket technique. The two-week therapeutic exercise program during recovery from this injury focused on flexibility of the gastrocnemius muscle, strengthening of muscles at the hip, knee and ankle, and proprioception training through single leg stance and ladder agility work. Also, over the course of the three previous professional soccer seasons, the athlete sprained the medial collateral ligament of his left knee twice, and the lateral collateral ligament of his left knee. In addition to the ligament sprains sustained to the knee over his career, he had undergone two right ankle arthroscopies where osteophytes were identified and debrided. The most recent arthroscopic procedure had been performed the previous year and the other was performed prior to his professional soccer career.

The athlete stated that the pain intensity incurred as a result of the injury that is the basis of the case report as not as severe as the previous ankle sprain sustained two weeks prior. In addition to the pain on the medial deltoid ligament, the athlete complained of diffuse pain across the retinaculum of the right ankle. Previous history showed no significant right knee or ankle injury with the exception of the aforementioned second-degree deltoid ligament sprain sustained two weeks prior to this injury and the surgically debrided osteophytes.

EXAMINATION RESULTS

The Lachman and anterior drawer test were both negative for an anterior cruciate ligament tear. The posterior drawer test was negative but slight laxity was noted in the right knee relative to the left knee with minor discomfort in the posterior lateral complex. Valgus and varus ligament stress tests to the right knee were both negative. During McMurray's test, the athlete experienced pain with full passive knee flexion and internal rotation but no locking was reported. The athlete reported concordant pain during Garrick's Test.¹² Upon examination of the right ankle, an increased eversion during the talar tilt test when compared to the contralateral side was noted. Initial exam findings by the head athletic trainer were confirmed by the orthopaedic team physician and subsequently, by magnetic resonance imaging (MRI). Imaging of the ankle was not initially required based on the Ottawa Ankle Rules.¹³

DIFFERENTIAL DIAGNOSIS

The athlete was diagnosed with a moderate strain of the right popliteus muscle with a concurrent grade II medial deltoid ligament sprain to the right ankle. The opponent slide-tackled the athlete putting an anterior-medial directed force to his right knee thereby placing the athlete into excessive knee external rotation and subtalar eversion. The extrinsic force placed on the knee exceeded the popliteus muscle's threshold to resist the force causing a strain. In addition, the medial deltoid ligament was re-injured secondary to forced eversion as a result of the tackle. The diagnosis was agreed upon due to the mechanism of injury that forced the athlete into external tibial rotation, pain that was reproduced with passive knee flexion and internal rotation, and edema present in the popliteus muscle confirmed which was demonstrated on the MRI study. The physical examination eliminated the notion of insult to the anterior cruciate ligament, lateral collateral ligament (LCL), medial collateral ligament, hamstring muscle group (biceps femoris, semitendinosus, and semimembranosus), and meniscus. During examination the athlete did not report his concordant pain, except during McMurray's test and Garrick's Test. Laxity was noted when the posterior cruciate ligament of the right knee was tested as well as the medial deltoid ligament of the right ankle relative to the contralateral side. As a result of the injury, the PCL may have been affected, but overall testing was inconclusive. In addition to McMurray's test, the menisci were assessed with palpation at the entirety of the tibiofemoral joint lines but no pain was reported.

THERAPEUTIC INTERVENTIONS

After the injury the patient was treated immediately with cold and intermittent pneumatic compression (Game Ready® Injury Treatment System, Concord, CA). This device circulates cold water and provides compression through a tube connected to a bladder, and was used 20 minutes every 2 hours on both the knee and ankle. The athlete also maintained elevation of the right leg above the level of the heart whenever possible, and kept both knee and ankle compressed with a Comperm compression sleeve (©2013 HARTMANN USA, Inc in Rock Hill, SC). The day after the game, treatment was limited to protection, rest, ice, compression and elevation due to the team traveling from the away venue to their home area. Crutches were supplied by the opposing home team, so the athlete could ambulate without weight bearing. Further treatment of the athlete's injury began two days after the incident. Axial distraction and grade II mobilizations were performed to the right ankle in order to decrease pain. To facilitate motion, and ensure the talus was located in the proper anatomical position an anterior to posterior grade III talocrural mobilization was performed. Subsequently, aquatic therapy was chosen as the primary course of restorative exercise because it allowed for early closed chain activities, reproduction of movement similar to on-field activities, reduction of axial loads, true multidirectional resistance, and support of the injured body part. Early exercises in the pool consisted of walking, jogging forward, backward and side-to-side, high knees, and heel kicks. Each pool exercise was performed once over a 25 yard distance. He then progressed to running in the water, cariocas, bounding, single leg and double leg jumps, treading of water, and swimming. Pool workouts were approximately 45-60 minutes long depending on athlete's fatigue and pain level. Contrast therapy was utilized in the acute stages of healing to decrease amount of swelling in ankle and knee. The athlete started and ended with hot water, doing a 3:2 ratio of hot to cold water for 25 minutes. Although limited evidence exists on the effectiveness of contrast therapy on decreasing edema, based on previous anecdotal success with other soccer players, the clinicians chose contrast therapy as one of several interventions to decrease edema and enhance lower extremity function. Contrary evidence suggests that change in temperature of the soft tissue would not be significant enough to cause change in the vascular system.^14,15,16 Also, the athlete performed 2 sets of 20 repetitions using elastic resistance (Theraband®, Akron, Ohio) resistance exercises of the ankle in all directions (plantar flexion, dorsiflexion, eversion and inversion) while supine starting with the red band and progressing to the blue band.

Nine days after the injury the athlete began to jog outside of the pool. Initially he reported no pain, but after 20 minutes he described a “fatigued” sensation in the ankle at which point he was switched to the spinner exercise bike for 20 minutes with low-level resistance (Level 4 on Keiser® spinner bike, Fresno, CA). Ultrasound was used on both the medial deltoid ligament and posterior lateral corner of the knee. The athlete received six treatments of ultrasound (©Dynatronics Corporation, Salt Lake City, UT) set to 3.0 MHZ at an intensity of 1.0 W/CM² for 9.0 minutes. Evidence suggests that the use of ultrasound in the acute stages of healing after injury will aid the inflammatory and healing process.^17,18,19,20 The Solaris D880 plus Infrared Cluster Probe (©Dynatronics Corporation, Salt Lake City, UT) was used throughout the 15-day rehabilitation. The laser used 32 infrared super luminous diodes emitting a wavelength of 880 nm and 4 red diodes emitting a wavelength of 660 nm, and has a maximum power output of 1000 mW. Despite limited and contradictory evidence, some studies have shown laser to be effective in reducing pain and aiding in treatment after musculoskeletal trauma.^21,22 To facilitate recovery in this professional athlete, a multi-modality approach was utilized. In addition to manual axial distraction and mobilizations, proprioceptive neuromuscular facilitation strengthening techniques were added to the rehabilitation exercises for the ankle and knee.

Ten days after the injury the athlete reported pain while actively externally rotating his ankle. He had discomfort stabilizing his ankle when kicking a soccer ball and during various multi-planar movements with his right knee. The athlete reported he was pain free during linear movements and progressed to one-on-one non-contact field activities with the assistant coach. He worked on agility ladder and running drills, progressed to technical drills with a soccer ball (cone dribbling and passing patterns around cones), and finally at 12 days post-injury he progressed to non-contact practice with the team playing as a neutral player. Playing neutral occurs during possession oriented drills where either team can pass to the neutral but not have contact with the player. This allows the injured player to assimilate to the game type movements and speeds with minimal risk of re-injury. He continued to train as a neutral for two additional days.

Fifteen days after injury the athlete participated in a full training session and only reported minimal pain with axial loads that resolved quickly (within several seconds). Throughout this 15-day rehabilitation program (refer to Table 1) the athlete completed an open kinetic chain leg-strengthening program with ankle weights that included movements such as hip flexion, extension, abduction, straight leg raises, knee flexion and extension. Open chain strengthening was chosen because of the popliteus' role in movement and stabilization of the knee during open chain movements involved in soccer, most specifically with kicking, trapping, and dribbling the ball. In addition to the leg strengthening program with the ankle weights, the athlete completed single leg and double leg squats on both compliant and non-compliant surfaces, as well as standing resisted hip abduction and adduction whilst standing on a Pilates reformer machine (Figure 1). The athlete performed 10 repetitions of each exercise and over the course of the strengthening program progressed to three sets of 10 repetitions. The criteria for return to play were based on the athlete's ability to participate in sports specific activities without apprehension of performing cutting and change of direction maneuvers. From time of injury to returning to play, the athlete reported minimal but tolerable pain and achieved full active range of motion at the knee.

Table 1.

Progression of Knee Strengthening Exercises: A Popliteus Focus

Phases 1	Exercises	Sets/Repetitions	Commentary
I	Open chain exercises with ankle weights while supine/prone Hip: flexion, extension, abduction, adduction Knee: flexion, extension Exercises were also performed seated for knee extension and hip flexion	1 set of 10 reps.	Start with low weight and low number of repetitions
II	Open chain exercises with ankle weights in supine/prone and seated Combination movements seated Hip flexion→ knee extension → knee flexion hip extension Knee extension → hip flexion → hip extension→ knee flexion	3 set of 10 reps.	Low weight (increase by 1 pound from phase I], increase number of sets to enhance the aerobic capacity of the muscles.
III	Standing open chain exercises with ankle weights or Theraband Theraband 4 way hip movement Hip flexion from externally rotated position to mimic soccer pass	3 sets of 20 reps.	Low weight (increase by 1 pound from phase II), increase intensity by standing and increasing volume of repetitions.
IV	Squats Progress to single leg Progress to non-compliant surface Deadlifts Progress to single leg Progress to non-compliant surface	1 set of 10 eps. Progress to 3 sets of 10 reps.	Move from open chain exercise to closed chain exercises. Increase level of difficultly by including kettlebells or dumbbells to the exercises.
v	Standing Pilates Reformer exercises with resistance Hip Abduction Hip Adduction Single leg skate Supine Pilates Reformer exercises with resistance Calf raises knee straight/bent Squats Single leg squats Squats with plyometric jumping (double leg and single leg) Clockwise/Counter clockwise hip circumduction using reformer or tower	Start with 1 set of 10 reps. Progress to 1 set of 30 reps. Increase number of reps and/or type of resistive springs.	Before advancing to Phase VI of this progression it is important to start plyometric exercises to prepare the athlete for sports specific exercises.
VI	Sports Specific Exercises Juggling Passing soccer ball with instep Agility ladder Cone dribbling Passing patterns around cones	Repetitions/sets and duration vary amongst these exercises.	Progress to phase VII once athlete can demonstrate proficiency with exercises, normal movement and gait patterns.
VII	Advanced Sports Specific Drills Long distance ball passing & shooting High velocity cutting drills with and without the ball 5 v. 2 possession drill Open field conditioning with various directional and force cutting Unpredictable reaction drills	Repetitions/sets and duration vary amongst these exercises. Depending on athlete's tolerance and muscular endurance.	Progress to phase VIII once athlete can perform cutting maneuvers without apprehension and with ideal biomechanics.
VIII	Return to play Play as a neutral (non-contact) in possession soccer drills Progress to full participation in practices with no contact restrictions		Athlete demonstrates prior level of function on the soccer field.

Figure 1.

DISCUSSION

This case is unique because the injury manifested itself at multiple joints and specifically involved the popliteus muscle. Few case studies have been reported on popliteus injuries, and even fewer with a concomitant injury of the ankle. The mechanism of injury, weight bearing with knee in flexion, sustaining an anteromedial external traumatic force to the right shank, is associated with many potential soft tissue injuries to the knee including the menisci, ACL, MCL, and others. Therefore, the typical differential diagnoses originally hypothesized based upon this mechanism of injury may not lead the clinician to the diagnosis of a popliteus strain. Injury to the ankle in addition to the knee could further compromise accurate diagnosis. This case report presents the unique difficulties in diagnosing a popliteus strain and can help others make an accurate diagnosis of an injury to this muscle. To diagnose this entity, clinicians must have an understanding of the anatomy of the posterolateral complex of the knee, mechanisms that can lead to this injury, diagnostic utility of special tests performed, range of motion assessment, and manual muscle testing.

Previous authors determined the various attachments of the popliteus muscle by examining cadaveric knee specimens.²³ In 15 specimens, the popliteus had a broad attachment to the lateral femoral condyle and a small filmy attachment to the lateral meniscus. In 18 specimens the popliteus muscle had an isolated attachment to the lateral femoral condyle and no attachment to the meniscus. Seven specimens displayed dual attachment to the lateral femoral condyle and the lateral meniscus. Since the popliteus muscle may share an attachment site with the meniscus, investigation of any potential injury to the meniscus in a suspected popliteus muscle injury is imperative. The athlete in this case report had no lateral tibiofemoral joint line pain and McMurray's test was negative, however the athlete felt his concordant pain during the internal rotation component of the McMurray's test. Hegedus et al performed a meta-analysis on the diagnostic utility of the McMurray's test to identify a meniscal tear, and found it had a sensitivity of 70%, specificity of 71%.²⁴ Palpation of the joint line in order to identify injury to the meniscus yielded a sensitivity of 63% and specificity of 77%.²⁴ Although the athlete felt his concordant pain during the McMurray's test, the clinical impression of the sports medicine team was that McMurray's test was negative. Since joint line palpation has higher specificity diagnostic values, tenderness to palpation would have helped confirm injury to the meniscus. Diagnostic imaging was ordered by the physician to confirm whether any soft tissue structures were damaged.

Another aspect that made this case difficult was the lack of ability to isolate the popliteus muscle during testing. Kendall describes testing the activation of the popliteus muscle with the patient sitting and actively internally rotating the tibia.²⁵ This only tests the recruitment or activation of the popliteus muscle, while adding resistance to this motion may recruit bigger muscles such as the semitendinosus, semimembranosus, posterior tibialis, or triceps surae muscle group to perform the internal rotation motion. The most notable physical findings for the patient in this case report were pain with maximal internal rotation and knee flexion during McMurray's test, tenderness to palpation at the posterior lateral corner of the knee and pain with Garrick's Test. Likely, the athlete experienced pain with full flexion and internal rotation during McMurray's test because the popliteus muscle shares a connection to the posterior horn of the lateral meniscus. Moreover, the MRI study confirmed the strain occurred near the superior attachment site in the area where the popliteus shares a connection to the lateral meniscus. In addition to pain during McMurray's test, the patient reported pain during Garrick's test, which mimics the function of the popliteus muscle in open chain activity. Authors of this case report were unable to find any studies describing the diagnostic utility of Garrick's Test.

In another cadaver study, researchers found that the LCL and popliteofibular ligament play an equal role in stabilizing a more extended knee (0°-60°) when external rotation torque is applied, but the contribution of the LCL as a stabilizer becomes less and the popliteofibular ligament greater when an external rotation torque is applied to a flexed knee between 60° to 90°.²⁶ In addition to the cadaveric studies, an electromyographic (EMG) study on the activation of the popliteus muscle during both dynamic and static exercises found that the popliteus muscle exhibited the highest EMG activity when going into knee flexion during a squat.²⁷ Upon review of the video of the injury, the athlete in this case report was slide tackled from behind while the knee was flexed to approximately 65°, and this flexion angle increased to 120° after the tackle. Thus, a high possibility exists that the popliteus muscle was the principal knee stabilizer to the external force and was subjected to dramatic forces during the slide tackle.

Nyland described the popliteus tendon as providing maximal resistance to a tibial external rotation force when the knee is bent.²⁸ The authors also noted that mechanical injury to the posterior cruciate ligament is common with an external rotation force and should definitely be included in the differential diagnosis when evaluating injury to the knee that could involve the popliteus musculotendinous complex. In this case report, the athletic trainer noted slight increased laxity in the right knee when compared to the left when the posterior drawer test was performed.

Additionally, Nyland described the three functions of the popliteus muscle as being able to provide tibial internal rotation, inhibit external rotation of tibia on a fixed femur, and causes femoral external rotation when the tibia is in a fixed position.²⁸ When the athlete in this case report was slide-tackled from behind his foot was fixed to the ground.

The literature contains two case studies reporting a diagnosis of popliteus tendon ruptures.^29,30 Both injuries were the result of a traumatic contact that forced the shank of an athlete into external rotation. In both cases, the clinicians were concerned about a potential meniscal tear and ordered MRI studies. In this particular case report, diagnostic imaging was necessary to rule out more serious ligamentous and/or meniscal pathologies of the knee. MRI is an effective tool in identifying insult to soft tissue structures in the knee.^31,32 In professional sports, knowledge of an athlete's injury imparted by the medical team assists the management to make choices with regard to the team in order to stay competitive, particularly when a key player is injured mid-season. Management of this athlete's injury would have been significantly different had the MRI confirmed a meniscal injury.

In an injury study of Union of European Football Associations (UEFA) competitions, the authors identified the intrinsic factors that lead to lower extremity muscle injury.³³ Muscle injuries were documented from 26 teams between the years 2001 and 2010, with injuries occurring of the adductors, hamstrings, quadriceps, and calf muscles. Intrinsic factors found to increase muscle injury rates in professional soccer were previous injury, older age (above 25.8 years old), and the kicking leg.³³ The athlete's dominant leg in this report was his left leg, and he sustained previous ligamentous and muscular injuries to the left leg. Moreover, this athlete would have been considered in the older age group of this study, and experienced an ankle sprain two weeks prior to the knee and ankle injury described in this case report. Despite the traumatic mechanism of injury, the athlete shared some of the intrinsic factors identified in the study for risk of muscular injury.

Dupont et al analyzed the effects of two games per week verses one game on male professional soccer player's performance and injury rates.³⁴ Researchers examined 32 professional soccer players during two seasons of the UEFA Champions League. They concluded that recovery time between two matches, of 72 to 96 hours, appears sufficient to maintain level of physical performance tested, but is not long enough to maintain a low injury rate.³⁴ The researchers graded the severity of injuries sustained by the soccer players on a time loss basis and reported the injury rate in injuries per thousand hours of matches. Injury rate was approximately six times higher when the team played two games in one week as opposed to one. Additionally, the athletes experienced more traumatic injuries (contact injuries), overuse injuries, and reinjury during the second game in a week as oppose to one. The game during which the athlete incurred the injury delineated in this case report was his third game in a single week. During the second game of the week, the athlete played a full 90 minutes in the outside defender position. A greater frequency of games in a season, congested match schedules, increased exposure to other players and fatigue may be factors predisposing an elite soccer athlete to injury.

CONCLUSION

Few case studies on popliteus muscle injuries are reported and even fewer discuss concomitant injury at multiple joints. Popliteus muscle injuries are difficult to diagnose as they can present as other knee pathologies and may be overlooked by novice clinicians during evaluation. The medical community could benefit from additional prospective research in order to elucidate the mechanism of injury that can contribute to a popliteal injury. This knowledge will increase the likelihood of proper and timely assessment during physical exam, optimal utility of radiographic and other diagnostic testing, and the development of a comprehensive treatment protocol to address the mechanical deficits associated with such an injury.