Knee
ACL injury
A cruciate ligament injury is very common—due to the high loads combined with high mobility of your knee—especially during sports and leisure activities.
Because it happens so often, this topic is widely discussed and researched in science.
In the last "Sport Switzerland" survey conducted by the Observatory of Sport and Physical Activity (Federal Office of Sport FOSPO) in 2014, aiming to draw a detailed picture of the Swiss population's current sports habits, 35.4% of respondents stated they ski [1]. Alongside hiking (44.3%), cycling (38.3%), and swimming (35.8%), skiing is one of the most popular sports in Switzerland [1].
Compared to hiking, however, your risk of injuring your knee and cruciate ligaments, especially your anterior cruciate ligament (ACL), is considerably higher when skiing. Data from the latest survey by the Swiss Council for Accident Prevention (bfu.ch) showed that an average of 22,260 people were injured per year while hiking, compared to roughly 51,700 while skiing [2]—30.9% of these injuries affect the knee joint [3], especially the anterior cruciate ligament. We see this anew every winter at BodyLab, osteopathy and Physiotherapy, Rehabilitation and Training in Zurich.
Outside the ski season, soccer is one of the most widespread amateur sports in the world, including Switzerland. In this sport, too, injuries to the lower extremity repeatedly occur—especially to your knee, as studies show [4].
Various studies estimate that up to about 17.6% of soccer-related injuries presenting to the emergency room involve the knee [5,6,7,8,9].
The majority of these injuries in soccer occur through non-contact mechanisms (85% of injuries, without the involvement of an opponent), although contact injuries during tackles or collisions are of course also possible [10,11]
ACL Anatomy and Function
The ACL is one of the most important ligament structures around and inside your knee joint. Together with your posterior cruciate ligament (PCL) and collateral ligaments, it helps stabilize your knee joint by spanning from the back of your femur (thigh bone) to the front of your tibial head (shin bone).
The dense connective tissue of your ACL consists mainly of type I collagen fibers and is divided by type III fibers into two primary bundles with different functions. The anteromedial bundle is on average 36 mm long and comes under tension from 30° of knee flexion. The main task of the anteromedial bundle is stabilization against anterior tibial translation—meaning it stops your shinbone (tibia) from sliding forward.
The posterolateral bundle is approximately 18 mm long and comes under tension at less than 30° flexion. Together with other ligament structures, this part of your ACL serves to stabilize rotational forces in your knee joint.
Your ACL is not just a passive stabilizing structure in your knee joint. Through Pacinian and Ruffini corpuscles as well as other free nerve endings in the ligament's insertion area, vibrations, tensile, and shear forces are sensed. This information serves your joint position sense (proprioception) to generate adapted muscular responses. In the case of your ACL, this means an increased activation of your hamstrings to reduce anterior tibial translation.
Injury Mechanisms
A cruciate ligament injury can be triggered by contact as well as non-contact mechanisms.
Typical mechanisms and the most common way you can suffer an anterior cruciate ligament injury involve a combination of twisting and buckling trauma to your knee joint under load (a forceful valgus collapse of your knee inward with slight knee flexion and combined rotation).
Injury Mechanisms in Soccer
Because cleated boots fix your foot firmly into the grass, huge uncontrolled forces can act on your knee. In fact, 85% of all cruciate ligament injuries in soccer result from non-contact situations [10,11]. Video analyses of professional soccer players also show an increased risk of ACL injury through non-contact situations within the first 9 minutes of a match, as well as a higher risk of injury during defending and tackling activities [12,13,14].
Injury Mechanisms in Skiing
Using video analyses of elite alpine skiers after an ACL rupture, Bere et al. identified three accident mechanisms [15]:
Slip-Catch
Dynamic snowplow
Landing after jumps
Slip Catch
In almost 50% of all cases, a so-called slip-catch mechanism was the cause. Here, the skier lost snow contact with the outer ski during a turn. Upon regaining snow contact, the ski caught abruptly, leading to increased knee flexion, internal rotation of the tibia, and a buckle of the knee inward (valgus position). This mechanism often brings with it an injury to your medial meniscus and your medial collateral ligament—the so-called Unhappy Triad.
Dynamic Snowplow
Another injury scenario (15%) was the dynamic snowplow. Here, the skier was thrown off balance while leaning back, causing the less loaded leg to drift away and forcing the skier into a split position. The ski rolled from its outer edge to its inner edge, caught in the snow, and forced the knee back into a valgus position and tibial internal rotation.
Landing After Jumps
The final mechanism (20%) occurred when landing after jumps. The skier lost balance, with body weight being driven backward. In attempting to regain balance, your ACL was subjected to excessive loads due to a combination of increased knee compression and a large anterior tibial shift (forward movement of your tibia relative to your femur).
Considering that much greater forces are at work with professional skiers due to higher speeds and specialized equipment, these mechanisms cannot be transferred entirely to amateur athletes. However, the individual movement components (strong flexion, valgus position, and tibial internal rotation) remain the exact same.
For recreational skiers, so-called forward twisting falls are the most frequent accident mechanism at 54% [16]. This involves a valgus position and tibial internal rotation after catching your ski edge while turning.
The second most frequent injury pattern is called a backward twisting fall or phantom foot [6]. This rupture mechanism accounts for 26% of all cases. Here, your center of gravity shifts backward and downward onto one leg due to the pelvis dropping (increased knee flexion)—whether turning or after a fall—and weight presses down onto the tail of your ski. In combination with stiff ski boots, your tibia is pushed forward, causing your ACL to tear.
Knee trauma frequently results in concomitant injuries (see Unhappy Triad, medial collateral ligament injuries, meniscus tears, cartilage damage, secondary osteoarthritis).
Contributing Factors / Equipment
With the emergence of carving skis, it became apparent that the increased aggressiveness of the ski's sidecut, combined with stiff ski boots, leads to more ACL injuries [15]. Tighter turns can be carved and higher speeds generated. This demands more strength from you and makes controlling your equipment harder. Due to the stiffness of ski boots, shifting your weight backward pushes your tibia anteriorly, placing additional stress on your ACL. Furthermore, video analyses showed that in 100% of all slip-catch cases, the binding failed to release or released too late [15].
Biomechanics in Your Knee After an ACL Rupture
First and foremost, you experience a combination of anterior knee instability with anterior tibial translation and rotational instability. This impacts the entire biomechanics of your knee. The center of rotation in your knee joint shifts medially (inward). This leads to increased strain on your collateral ligaments (medial and lateral collateral ligaments) and meniscus horns, which also places more stress on your cartilage surfaces. For example, your medial collateral ligament is subjected to up to 140% more load, while your posterolateral structures must withstand up to 400% more demand [17]. When walking, this shows up as prolonged flexion during the stance phase and increased anterior tibial translation toward the end of the stance phase [17].
Surgery or Conservative Treatment
After an anterior cruciate ligament injury, you generally have two options: surgical reconstruction of your ACL followed by Physiotherapy, or conservative management with physiotherapy measures—with the option of surgery later if needed.
In Switzerland, the Swiss Medical Board addressed this very question (and also published an information leaflet [19]): After an extensive literature review, the panel concluded that both surgical and conservative approaches can achieve satisfactory results—in most cases, you can return to your previous physical activities. This is demonstrated by studies assessing outcomes at one and five, and even up to 15 years after a cruciate ligament injury. No significant differences were found when comparing conservative treatment with surgery [18].
With conservative treatment, if you continue to experience knee instability during your therapy, surgery can still be performed later without losing valuable time.
Conclusion: "When choosing a treatment method, you should carefully weigh the respective advantages and disadvantages (particularly the surgical risk); if necessary, obtain a second opinion." [19]
Conservative Therapy
The goal of conservative therapy and Physiotherapy after your cruciate ligament injury is to restore physiological mobility, as well as the stability of your knee joint and leg alignment. Following injuries, your body responds through specific biological phases (inflammatory phase, proliferation phase, remodeling phase), which your physiotherapist must consider in order to facilitate your fastest possible healing and functional recovery.
In line with these healing phases, short-, medium-, and long-term goals are established for therapists and patients. During the first 1–2 weeks (inflammatory phase), reducing swelling and relieving your pain through passive measures such as lymphatic drainage and gravity-eliminated/low-gravity movements are key priorities in your treatment [20].
During the proliferation phase (weeks 3–6), the focus shifts to regaining your mobility, progressively increasing load (possibly weaning off crutches, from partial to full weight-bearing), improving stability, and strengthening muscular deficits in closed kinetic chains. You will accomplish this through passive as well as active exercises [20].
From the 7th post-traumatic week onward (remodeling phase), the primary focus is the complete restoration of your leg axis stability (pelvis-leg axis) and building muscle through resistance training with weights in the gym. The ultimate goal is for you to be pain-free in everyday life and to successfully return to your previous sports activities [20].
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References
[1] Sportaktivität und Sportinteresse der Schweizer Bevölkerung.
Lamprecht, M., Fischer, A. & Stamm, H.P.
Sport Schweiz 2014: Sportaktivität und Sportinteresse der Schweizer Bevölkerung. Magglingen: Bundesamt für Sport BASPO.
[2] Verletzte nach Sportart und Alter, Ø 2010–2014
[3] Verletzungslokalisation bei den UVG-Versicherten nach Sportart (pro 100 Verletzte), Ø 2008–2012
Woods C, Hawkins R, Hulse M, Hodson A.
Br J Sports Med. 2002;36(6):436-441. doi:10.1136/bjsm.36.6.436.
[5] The FIFA 11+ injury prevention program for soccer players: a systematic review.
Sadigursky D, Braid JA, De Lira DNL, Machado BAB, Carneiro RJF, Colavolpe PO.
BMC Sports Sci Med Rehabil. 2017;9:18. doi:10.1186/s13102-017-0083-z.
Volpi P, Bisciotti GN, Chamari K, Cena E, Carimati G, Bragazzi NL.
Muscles Ligaments Tendons J. 2016;6(4):480-485. doi:10.11138/mltj/2016.6.4.480.
[7] Soccer-related injuries treated in emergency departments: 1990-2014.
Smith NA, Chounthirath T, Xiang H.
Pediatrics. 2016;138(4). doi:10.1542/peds.2016-0346.
Leininger RE, Knox CL, Comstock RD.
Am J Sports Med. 2007;35(2):288-293. doi:10.1177/0363546506294060
[9] Childhood soccer injuries treated in U.S. emergency departments.
Adams AL, Schiff MA.
Acad Emerg Med. 2006;13(5):571-574. doi:10.1197/j.aem.2005.12.015.
Woods C, Hawkins R, Hulse M, Hodson A.
Br J Sports Med. 2002;36(6):436-441. doi:10.1136/bjsm.36.6.436
[11] Severe injuries in football players. Influencing factors.
Chomiak J, Junge A, Peterson L, Dvorak J.
Am J Sports Med. 2000;28(5 Suppl):S58-68. doi:10.1177/28.suppl_5.s-58.
[12] Anterior cruciate ligament injury in elite football: a prospective three-cohort study.
Waldén M, Hägglund M, Magnusson H, Ekstrand J.
Knee Surg Sports Traumatol Arthrosc. 2011;19(1):11-19. doi:10.1007/s00167-010-1170-9.
Waldén M, Krosshaug T, Bjørneboe J, Andersen TE, Faul O, Hägglund M.
Br J Sports Med. 2015;49(22):1452-1460. doi:10.1136/bjsports-2014-094573.
Grassi A, Smiley SP, Roberti di Sarsina T, et al.
Eur J Orthop Surg Traumatol. 2017;27(7):967-981. doi:10.1007/s00590-017-1905-0.
BereT, FlørenesTW, KrosshaugT, et al.
Am J Sports Med. 2011;39:1421–1429
Ruedl G, Webhofer M, Linortner I, et al.
Int J Sports Med. 2011; 32 (10):801-6.
[17] Riss des vorderen Kreuzbandes. Biomechanische Auswirkungen auf das Kniegelenk
PD Dr. M. Herbort, Prof. Dr. C. Fink:
in: Arthroskopie (01/2015)
[18] Review Fachbericht «Ruptur des VKB: operative oder konservative Behandlung?»
[19] Merkblatt Riss des vorderen Kreuzbandes: operative oder konservative Behandlung?
[20] VKB Ruptur-Therapie, AGA-Knie-Ligament-Komitee
Cover Image Credit
Kari Stammen, Human Knee Anatomy, designated as public domain, details on Wikimedia Commons
