This article was originally published in July 2013. In response to the unfortunate injury news that has forced six (6) time Female World Surfing Champion, Stephanie Gilmore to withdraw from the upcoming Oi Rio Pro in Brazil, we have decided to republish as this feature considers some of the likely issues involved. Gilmore withdrew from the Drug Aware Margaret River Pro because an initial X-ray showed a “hairline fracture” of the fibula. She sought medical attention back home on the Gold Coast and a subsequent MRI revealed: ” … multiple hairline fractures through the fibula and tibia around the fibula head and tibia plateaux, with some minor bone bruising around the knee cap and associated tendinitis …” (Source: World Surf League). This article does not address the management of fractures. It focuses on ligamentous and soft-tissue structure trauma, specifically Medial Collateral Ligament (MCL) injury. We hope you find this feature informative. We wish Stephanie a full and speedy recovery, and look forward to seeing her back in the water soon!

Authors:

Gonçalo Saldanha (Physiotherapist – Private practice),

Nuno Lança (MD, Orthopaedic and Trauma Surgery Specialty Registrar, Hospital de Nossa Senhora do Rosário – Centro Hospitalar Barreiro-Montijo),

Nuno Oliveira (MD, Orthopaedic and Trauma Surgery Specialty Registrar – Hospital de São Francisco Xavier – Centro Hospitalar de Lisboa Ocidental).

Editor:

Arvid Schigt (MD, EASD board member).

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Getting barreled. Tube time. The Green Room. Isn’t that something every surfer dreams about? Tiago Pires has been living this dream for quite some time  now, but he recently woke up from a nightmare when he injured his left knee only a couple of weeks before the third stop in the 2013 ASP Tour.

As stated by Nathanson in 2002: “Tube riding appeared to lead to a disproportionate number of injuries. Tubular waves are only rarely encountered because they require an optimal combination of swell, wind, and underwater topography. Although many surfers aspire to ride tubular waves, even the most accomplished surfers spend far less than 1% of their time “getting tubed.” Yet this maneuver accounted for 10% of all acute surfing injuries.”

Following our previous article about John John Florence’s ankle injury, we now invited two Portuguese orthopedic registrars, and a Portuguese physiotherapist to analyze Tiago’s injury by means of trauma mechanism specifically related to surfing barrels, the injury of the medial collateral ligament (MCL) itself, and the rehabilitation process to recovery.

Enjoy!

 

The surfer’s position in the barrel

Tube riding is one of the most challenging performances in surfing because of the many external and surfer-related factors involved. Although technically demanding but highly rewarding, the barrel might also be an unsafe secret spot.

The aim of this article is to reveal the technical aspects related to the surfer’s position and its influence on the anatomic structures involved in the body stabilization when performing a barrel ride. As demonstrated by the recent example of the Portuguese Tiger, Tiago Pires, who has injured his knee during a fall in a barrel, any surfer may get seriously harmed when attempting this maneuver. The focus of this article is to comment on the ligamentous structures of the knee, which are the main static stabilizers of the lower limb during barrel riding.

Tube riding requires the perfect match of static and dynamic positioning of the body to achieve a continuous adaptation to the wave during the ride. Many factors are involved, such as body balance on the board and wave, muscular dynamic control, articular proprioception and ligamentous stability. Barreling applies different stresses on the knees, depending on the surfer’s stance (goofy/regular), the type of wave (frontside/backside) and timing of the barrel. The bottom-turn into the pocket, the break on the wall to enter the tube, the still positioning during the barrel and the pumping inside the wave are specific situations that are highly demanding on the knees and are critical moments that can either make up a harmonic move or trigger a dangerous fall. We consider these the main 4 stages of the tube riding.

Regardless of the position on the board, tube riding requires perfect distribution of weight on the board and minimum volume to fit in the tube. Generally, the surfer advances the back foot onto the middle of the board and lowers their center of gravity, bending the knees and flexing the hips to perfectly match the tube. During the still phase on a frontside wave, weight is shifted to the front leg, and thereby stabilized by static muscular contraction and ligamentous tightness. The rather unstable back knee acts like a rudder, positioned in flexion and bending inwards, with less muscular tone (dynamic stability) and more ligamentous stress (static stability), especially on the medial side, rendering it more prone to injury.

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Conversely in the backhand, the body weight is transferred slightly backwards with both front knee and ankle bent outwards. This is a more stable position, allowing the surfer to apply more power to the rail on the wave wall. This is perfectly elucidated but the amazing tube riding of Kelly Slater.

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The threatening and more challenging situations are those related to bigger waves, shallower reefs and heavier lips, which in combination, can be dramatically dangerous during a wipeout. Under these circumstances, various mechanisms of injury are involved, such as direct impact or slipping on the board, rolling in the tube and being projected on the reef and compressed over by the water column.

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Injury to the medial ligamentous structures of the knee is most often caused by a valgus force. The lesion mechanism is aggravated if an external rotation movement of the leg is added to the valgus moment [1]. Muscular ruptures, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL) or both ligaments’ injuries, meniscal tears and osteochondral fractures, can be associated with MCL injuries.

General anatomy of the knee – ligamentous

The main stabilizer of the medial knee is the MCL complex. Three main anatomic structures constitute the MCL complex:

  • Superficial component – the largest structure of the medial aspect of the knee (extending from the femoral condyle to its double tibial insertion, approximately 12.2 mm and 61.2 mm distal to the joint line [2]);
  • Deep component – comprising the thickened medial aspect of the joint capsule that is deep to the superficial MCL;
  • Posterior oblique ligament (POL) – arising from the distal semimembranous tendon and inserting on the posteromedial portion of the joint capsule.

knee

From Morelli V, Bright C, Fields A. Ligamentous Injuries of the Knee. Prim Care Clin Office Pract 2013 (Article in Press).

The main function of the MCL is to stabilize the knee against valgus and some rotational forces [4]. The MCL is composed of dense and regular collagen tissue, with fibers arranged in a parallel fashion and surrounded by scanty areolar tissue, thereby allowing for gliding. No vascular supply enters through the bony attachments. Elastic fibers are absent from the ligament itself but are found in the loose areolar covering [5].

Another important structure accounting for the medial stability of the knee is the pes anserinus, composed by the combined insertion of the sartorius, gracilis and semitendinous muscles on the medial aspect of the proximal tibia. Inserting on the posteromedial aspect of the tibial methaphysis, the semimembranous muscle also supports the medial stability of the knee. A good tone of this group of muscles can ultimately support the dynamic medial stability.

Epidemiology of MCL injury

The reported incidence of MCL tear is 24 per 100,000 athletes per year in the US [6]. The true incidence is likely to be higher because many mild strains remain  unreported [7]. Most MCL tears are isolated injuries, occurring mainly in young athletes and involving males twice as frequently as females [4].

In surfing, an acute injury is preceded by tube riding in about 10% of cases [8]. Two thirds of all sprains in acute traumatic surfing injuries are localized in the knee [Nathanson 2002], especially due to performing cutback and tail slides, which are considered forceful, weight bearing, and knee-flexed motions [Sunshine 2003]. There remains no literature on the incidence of knee injuries caused by barrel riding.

Type and classification of ligamentous lesions of the knee

In a study of experimental rupture of the MCL in cats, it was concluded that healing occurs with regeneration of regular collagen to form a new ligament with good tensile strength, provided the ends of the torn ligament are in reasonable apposition, and provided the blood supply is adequate. The tear pattern is also an influencing factor to healing, with transverse ruptures creating a wider gap and hence a major burden to repair [5].

Normal healing process of ligament ruptures typically has 4 phases [9]:

  1. Bleeding into the lesion gap;
  2. Inflammation and cell proliferation, converting the clot to granulation tissue;
  3. Repair with neovascularization and an intense cellular reaction;
  4. Remodelling.

At day 4 or 5, formation of new collagen fibrils begins and quickly adopts the normal architecture. After 2 weeks, granulation tissue is replaced by well-developed parallel immature type collagen fibers. At the third week, a sufficient tensile strength has been generated and cells and vessels gradually start to diminish. Within 7 to 8 weeks, the ligament appears virtually normal to the naked eye except for minor local thickening and, in some cases, surface adhesions [5].

MCL injuries, according to the American Medical Association Standard Nomenclature of Athletic Injuries, are classified in 3 grades [10]:

  • Grade I – tear partially affects the substance of the ligament and there is no laxity;
  • Grade II – more fibers involved, but still opposed ends, presenting with localized tenderness and there may or may not be pathologic laxity;
  • Grade III – complete disruption, presenting with laxity on valgus stress.

Grades 1+, 2+ and 3+ correspond to subjective gapping of the medial joint line of 3-5mm, 6-10mm and >10 mm, respectively, when compared with the uninjured, contralateral side [11].

knee2

From Wijdicks CA, Griffith CJ, Johansen S, Engebretsen L, LaPrade RF. Injuries to the Medial Collateral Ligament and Associated Medial Structures of the Knee. J Bone Joint Surg Am. 2010;92:1266-80

Assessment of Medial Collateral ligamentous injuries and imaging examination

Patients often describe a mechanism of injury involving a contact or non-contact valgus force to the knee. Sometimes there is an audible “pop” at the time of rupture.  Pain and swelling along the medial aspect of the knee may be reported too.

Physical examination of the knee remains the most suitable tool for obtaining a diagnosis of injury to its medial structures. Beginning with visual inspection, clinicians may observe localized swelling or ecchymosis over the femoral or tibial attachment of the superficial component of the MCL. It is important to understand the anatomy of the medial side of the knee to appropriately palpate and assess the structures involved [2].

A valgus load applied at 20º to 30º of knee flexion is used to detect medial joint opening. Applying the valgus stress at both 0º and 30º of knee flexion can further assist in the diagnosis of the injury pattern because when a knee has increased medial joint space opening at 30º of flexion but not at 0º the POL is most likely still intact.

An additional assessment performed at this time of valgus moment application is evaluation of the integrity of the so-called end point. If the medial knee structures are completely ruptured, there will be no definitive end point and the anterior cruciate ligament may be providing a secondary restraint to the valgus stress [12]. It is therefore important to verify this observation with the Lachman [13], anterior drawer, and pivot shift tests and assess the integrity of the anterior cruciate ligament in association with a medial knee injury.

Anteromedial rotary instability is apparent, with stress testing, when the medial plateau of the tibia rotates anteriorly and externally as the joint opens on the medial side. This implies disruption of the medial capsular ligament, the MCL (with the POL component) and the ante­rior cruciate ligament.

Valgus stress radiographs can also be useful for quantitative grading of medial knee injuries and to verify the location of medial compartment gapping. In one study, a load applied by a clinician to a knee with a simulated isolated grade-III superficial MCL injury increased medial joint gapping, compared with the intact knee, by 1.7 and 3.2 mm at 0º and 20º of flexion, respectively.

Magnetic resonance imaging is commonly used to assess the involved structures in patients with injuries to the MCL [14].

Treatment options in MCL knee injuries

Despite the fact that the medial structures are the most frequently injured knee ligaments, controversy remains concerning their treatment. Historically, treatment of acute MCL injuries has focused on nonoperative therapies with early controlled motion and protected weight bearing, and fairly good patient outcomes have been reported [15]. Several rehabilitation protocols are available, and each has had successful results [16].

Treatment of Grade I tears is entirely symptomatic, and the patient usually can return to normal function and activities within a few days. Rest, ice, and a compression bandage are usually all that is required.

Grade II tears require protection. In these injuries, the strength of the ligament has been significantly impaired. Patients should be advised not to participate in sports activities in order to prevent complete disruption of the ligament. These patients are best treated with a controlled motion brace, allowing full, protected motion for 4 to 6 weeks. Recovery usually can be expected with no residual laxity once the rehabilitation program has been completed.

Isolated grade III tears of the medial collateral ligament can be treated successfully by nonoperative means. MRI or stress testing with the patient under general anesthesia and an arthroscopic examination are usually required to rule out any associated articular cartilage, menisci, or cruciate ligaments injuries. Nonoperative treatment of grade III tears of the MCL is more predictable and successful if the tear is at the proximal attachment and there is no evidence of other ligamentous damage. Approximately 65% of MCL sprains occur at the proximal insertion site on the femur [17].

A high frequency of combined superficial MCL and POL injuries has been reported in knees with severe acute or chronic valgus instability, signifying the important role of the POL in providing static stabilization to the medial side of the knee [18]. Operative techniques for these combined injuries include direct repair of the superficial MCL and POL, primary repair with augmentation, advancement of the tibial insertion site of the superficial MCL, pes anserinus transfer, advancement of the superficial MCL with pes anserinus transfer, and reconstruction techniques that have not been validated biomechanically [4].

The best possible repair restores the anatomical integrity and tension of a torn ligament and should be done without unnecessary delay. Optimal surgical dissection and repair become increasingly difficult beyond 7 to 10 days after injury.

The treatment of combined lesions of the MCL and the Anterior Cruciate Ligament have a proper rationale that is beyond the scope of this article.

Prevention and Rehab of MCL knee injuries

With respect to surfing and tube riding, the most important preventive measures to  barrel injuries for surfers is to know his limits, and to understand and study all the external elements (reefs, tides, swell, wind, crowd) of a particular surf point. This will help the surfer to choose the appropriate moment and conditions for challenging his skills. Also specific training directed to barrels will improve muscular conditioning and proprioception. Lastly, surfing on appropriate boards and fins for these specific types of waves, together with proper waxing of the board (especially on the front, middle, and rails) diminishes the risk on injuries from barrel riding.

Research on prophylactic knee bracing has shown tendency of decreasing MCL injuries in soccer players in 2 epidemiological studies [29, 30]. However, more recent studies have shown no clear benefit [31]. Furthermore, bracing leads to a decrease in athletic performance by restricting motion and affecting speed and agility [19]. Studies are necessary to evaluate effectiveness and athlete’s performance with braces in surfing.

The current approach of acute isolated MCL injuries is conservative and includes limited immobilization, early mobilization, range-of-motion (ROM) stretching and strengthening and graduated return to sport activity [4,19]. All isolated MCL injuries, regardless of grade, are usually treated with a brief period of immobilization and symptomatic management [4].

Athletes with grade I injuries are ready to return to sports activities within a recovery period of 10 days, but for grade II lesions this period can last 20 to 30 days [32,33]. One study showed that 74% of patients with grade I and grade II lesions returned to their baseline performance within three months [34]. Athletes with grade III lesions can be expected to regain 80% of the strength within 13 weeks and return to full physical activity within 1 year [4].

Early mobilization and rehabilitation has proven to be successful at both histological and clinical level [23, 24, 25, 26]. Adjunctive ultrasound therapy has also shown to be of benefit in animal studies [27, 28].

Treatment of a grade I lesion includes increasing ROM and muscular strengthening, especially the quadriceps. In case of a grade II or even III injury, it is beneficial to perform physiotherapy in combination with an “active rest” program, making weight transfer to the affected limb gradually. The use of crutches is recommended for the first week [20]. Despite controversy regarding the proper treatment of grade III injuries, several studies have shown that conservative treatment is equally effective compared with surgical repair [21,22]. The control of pain and swelling is the first step. It is desirable to use a hinged knee brace that protects valgus stress and the knee is mobilized as soon as possible on the normal ROM. It should be accompanied by a progressive increase of strength in the lower limbs.

The rehabilitation following an isolated MCL sprain can be planned in 3 phases:

At stage 1 the goals are to minimize pain and swelling and to obtain full weight bearing and normal gait with or without a brace or immobilizer. The rehab program involves ROM reassurance, early healing promotion and stress protection of the affected MCL. Restoring ROM is progressed in a non painful range preventing the detrimental effects of joint/limb immobilization. Collagen synthesis can be accelerated by functional motion. The patient is encouraged to bear weight as tolerated with or without protective devices, to provide nourishment of articular cartilage and subchondral bone. Cryotherapy and elevation is used as much as possible throughout the day to control pain and swelling. Immobilization is dependent on the patient’s ligamentous instability and pain. Bracing is used as needed, for patients with grade I injury; bracing and immobilization used for grade II lesions; and  immobilizer for grade III. Rehab progression will depend on the location of the tear, degree of instability, concomitant injuries, age and activity demands [19].

At stage 2, rehabilitation emphasizes restoring non-painful full ROM and beginning a strengthening program for the entire involved lower extremity. Patients exhibit nearly full ROM, although terminal knee flexion and extension may still be limited because of pain. Patients should demonstrate a normal gait cycle pattern. Closed kinetic chain strengthening exercises are initiated to restore and enhance proprioception and neuromuscular control. Non impact aerobic training, such as stationary bicycle, elliptical stepper and stair stepper are started. In addition, pool exercises may be initiated to improve total body conditioning. On completion of the second stage, the patient should possess full ROM and mild or no swelling [19].

The final stage, phase 3, of rehabilitation focuses on return to functional activities. All exercises are progressed, particularly closed kinetic chain strengthening, endurance exercises, proprioception activities, and functional/agility drills. The goals include pain-free activities of daily living without a brace, weight room strengthening and return to sport or work. A running program is initiated starting with jogging and progressing to sprinting. A functional knee brace may be used. The patient will need to continue an exercise program to continually increase strength and function, not merely to maintain strength [19].

The nonsurgical rehabilitation protocol should be performed only when there isn´t any major associated lesion [35], such as ACL ruptures or meniscal tears. In MCL injuries, it is important to note that although clinical healing is complete after some weeks, microscopic remodeling and continued ligament strengthening continues for up to 1 year. This microscopic healing process has been shown to be enhanced by the early mobilization [36].

Examples of rehabilitation protocols:

table

From Phisitkul P, James SL, Wolf BR, Amendola A. MCL Injuries of the knee: current concepts review. Iowa Orthop J. 2006;26:77-90.

Table 2 – A rehab protocol

Table 2 – A rehab protocol

Note: This program is based on a grade II injury, but can be accelerated to grade I lesions or injuries slowed to grade III. Adapted from: Kisner C, Colby L. Exercicios Terapêuticos – Fundamentos e Técnicas. (5th ed.). 2007, Philadelphia.

Conclusion

Surfing is increasingly developing into a more athletic sport. Speed and power are some of the attributes of the modern surfer. In their pursuit to ride bigger and hollower waves, surfers are taking risks.

Knee sprains, usually associated with contact sports such as football or rugby are affecting a higher number of surfers. Injury to the medial structures of the knee is precipitated by a valgus stress that can be aggravated by the external rotation of the leg. The diagnosis of MCL lesions is essentially clinic, but stress X-Rays and MRI can have a role in grading the injury.

Treatment is mostly conservative with early controlled motion and protected weight bearing, with surgical repair reserved for more complex injuries with associated lesions or cases of chronic instability.

References

[1] Hughston JC, Barrett GR. Acute anteromedial rotatory instability. Long-term results of surgical repair. J Bone and Joint Surg Am 1983; 65:145-53.

[2] LaPrade RF, Engebretsen AH, Ly TV, Johansen S, Wentorf FA, Engebretsen L. The anatomy of the medial part of the knee. J Bone Joint Surg Am. 2007;89:2000-10.

[3] Beall DP, Googe JD, Moss JT, Ly JQ, Greer BJ, Stapp AM, Martin HD. Magnetic Resonance Imaging of the Collateral Ligaments and the Anatomic Quadrants of the Knee. Radiologic Clinics of North America. 2007; 45:983-1002.

[4] Morelli V, Bright C, Fields A. Ligamentous Injuries of the Knee. Prim Care Clin Office Pract 2013 (Article in Press).

[5] Ewen, J. Experimental Rupture of the Medial Collateral Ligament of The Knee. The Journal of Bone and Joint Surgery 1950; 32B(3): 396-402.

[6] Quarles JD, Hosey RG. Medial and lateral collateral injuries: prognosis and treatment. Prim Care 2004; 31 (4): 957-75.

[7] Miyamoto RG, Bosco JA, Sherman OH. Treatment of medial collateral ligament injuries. J Am Acad Orthop Surg 2009; 17(3): 152-61.

[8] Nathanson et al, Am J Emergency Med, 2002

[9] DeLee J, Drez D, Miller MJ. DeLee and Drez’s orthopaedic sports medicine: principles and practice. Philadelphia: Saunders; 2003:39-49.

[10] American Medical Association. Committee on the Medical Aspects of Sports. Standard nomenclature of athletic injuries. Chicago: American Medical Association; 1966. p 99-100

[11] Phisitkul P, James SL, Wolf BR, Amendola A. MCL Injuries of the knee: current concepts review. Iowa Orthop J. 2006;26:77-90.

[12]. Griffith CJ, LaPrade RF, Johansen S, Armitage B, Wijdicks C, Engebretsen L. Medial knee injury: part 1, static function of the individual components of the main medial knee structures. Am J Sports Med. 2009;37:1762-70.

[13]. Torg JS, Conrad W, Kalen V. Clinical diagnosis of anterior cruciate ligament instability in the athlete. Am J Sports Med. 1976;4:84-93

[14]. Wijdicks CA, Griffith CJ, Johansen S, Engebretsen L, LaPrade RF. Injuries to the Medial Collateral Ligament and Associated Medial Structures of the Knee. J Bone Joint Surg Am. 2010;92:1266-80

[15]. Narvani A, Mahmud T, Lavelle J, Williams A. Injury to the proximal deep medial collateral ligament: a problematical subgroup of injuries. Bone Joint J. 2010;92B(7):949-53.

[16]. Noyes FR, Barber-Westin SD. The Treatment of Acute Combined Ruptures of the Anterior Cruciate and Medial Ligaments of the Knee. Am J Sports Med.1995;23:380-9.

[17] Carlo M, McDivitt. Rehabilitation of the knee. In: Voigh M, Hoogenboom B, Prentice W, editors. Musculoskeletal interventions: techniques for therapeutic exercise. New York: McGraw Hill; 2007. p. 607-50

[18]. Hughston JC. The importance of the posterior oblique ligament in repairs of acute tears of the medial ligaments in knees with and without an associated rupture of the anterior cruciate ligament. Results of long-term follow-up. J Bone Joint Surg Am.1994;76(9):1328-44.

[19] Carlo M, Armstrong B. Rehabilitation of the Knee Following Sports Injury. 2010;29:81-106

[20] Crowther C. Cuidados Primérios em Ortopedia (2nd edition). Loures – 2005: Lusociência.

[21] Indelicato PA. Non-operative treatment of complete tears of the medial collateral ligament of the knee. J Bone Joint Surg Am. 1983;65:323-9

[22] Reider B, Sathy MR, Talkington J, et al. Treatment of isolated medial collateral ligament injuries in athletes with early functional rehabilitation: a five-year follow-up study. Am J Sports Med. 1993;22:470-7

[23] Padgett LR, Dahners LE. Rigid immobilization alters matrix organization in the injured rat medial collateral ligament. J Orthop Res 1992;10:895-900

[24] Woo SL, Gomez MA, Seguchi Y, et al. Measurement of mechanical properties of ligament substance from a bone-ligament-bone preparation. J Orthop Res 1983;1:22-9

[25] Steadman JR. Rehabilitation of first- and second-degree sprains of the medial collateral ligament. Am J Sports Med 1979;7:300-2

[26] Gianotti BF, Rudy T, Graziano J. The non-surgical management of isolated medial collateral ligament injuries of the knee. Sports Med Arthrosc 2006;14(2):74-7

[27] Sparrow KJ, Finucane SD, Owen JR, et al. The effects of low-intensity ultrasound on medial collateral ligament healing in the rabbit model. Am J Sports Med 2005;33:1048-56

[28] Warden SJ, Avin KG, Beck EM, et al. Low intensity pulsed ultrasound accelerates and a nonsteroidal anti-inflammatory drug delays knee ligament healing. Am J Sports Med 2006;34:1094-102

[29] Albright JP, Powell JW, Smith W, et al. Medial collateral ligament knee sprains in college football. Brace wear preferences and injury risk. Am J Sports Med. 1994;22(1):2-11

[30] Albright JP, Powell JW, Smith W, et al. Medial collateral ligament knee sprains in college football. Effectiveness of preventive braces. Am J Sports Med. 1994;22(1):2-11

[31] Najibi S, Albright JP. The use of knee braces, part 1: prophylatic knee braces in contact sports. Am J Sports Med. 2005;33(4):602-11

[32] Derscheid GL, Garrick JG. Medial collateral ligament injuries in football: nonoperative management of grade I and grade II sprains. Am J Sports Med. 1981;9:365-8

[33] Holden DL, Eggert AW, Butler JE. The nonoperative treatment of grade I and II medial collateral ligament injuries to the knee. Am J Sports Med 1983;11:340-4

[34] Lundberg M, Messner K. Long-term prognosis of isolated partial medial collateral ligament ruptures: a ten-year clinical and radiographic evaluation of a prospectively observed group of patients. Am J Sports Med 1996;24:160-3

[35] Sandberg R, Balkfors B, Nilsson B, Westlin N. Operative versus non-operative treatment of recent injuries to the lligaments of the knee. A prospective randomized study. J Bone joint Surg Am. 1987;69:1120-6

[36] Thornton GM, Johnson JC, Maser RV, et al. Strenght of medial structures of the knee joint are decreased by the isolated injury to the medial collateral ligament and subsequent joint immobilization. J Orthop Res. 2005; 23:1191-8

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