Biomechanics of the Knee

Investigations have shown that as the knee transitions to weight bearing at low knee flexion angles (15-30º), there is anterior (forward) translation of the tibia (shin bone) to the femur (thigh bone), which is normally restrained by the ACL (Schultz et al 2011 Med Sc Sp Ex, 43, 2, 287-295). These knee flexion angles are a common angle for aspects of soccer such as kicking, dribbling and fast sideways 'cutting' actions. Moreover, during side step cutting action, females have been shown to exhibit 20% higher knee adductor moments and nearly twice the knee valgus when compared with males (Sigward et al 2012, Med Sc Sp Ex, 44, 8, 1497-1503). Additional problems may include patellofemoral (anterior knee) pain in which the ability to produce knee extensor torques are reduced and the knee muscle EMG activity is eratic (Rathleff et al 2013, Med Sc Sp Ex, 45, 9, 1730-1739)

Mechanism of injury

These injuries usually occur as a result of a fast movement with a degree of rotation and pivoting involved. The foot and lower leg turn outward, relative to the upper leg turning inward, creating a gapping force on the inside of the knee. This is commonly referred to as a valgus force. People with poor hip control are thought to be more vulnerable to an uncontrolled valgus force. The combination of knee valgus strain (51Nm) and hip internal rotation strain (25.9Nm) has been demonstrated to increase the strain on the ACL by 0.115, high enough to cause it to rupture (Shin et al 2011, Med Sc Sp Ex, 43, 8, 1484-1491), as the rupture strain lies between 0.09 -> 0.  Additionally, in females with abnormal hip kinematics, femoral (thigh - hip) internal rotation has been demonstrated to increase patellofemoral (knee cap) hydrostatic pressure and octahedral shear stress (Liao et al 2016, Med Sc Ex Sp, 47, 9, 1775-1780)

Contrasting hip strength and control during landing in women.

It has been shown that individuals with reduced hip strength have greater pelvic angular displacement, peak velocity, total angular excursion and higher muscle activation of the trunk and gluteal muscles than stronger individuals (Popovich & Kulig 2012 Med Sc Sp Ex, 44, 1,146-153). Lack of control of the inward movement of the knee has been demonstrated to improve with functional hip abductor and external rotator training (Baldon et al 2012 Med Sc Sp Ex, 44, 1, 135-145). They also employed core stabilising exercises for the abdominal region. However, static core stabilising exercises have not been shown to improve knee loading (Jamison et al 2012, Med Sc Sp Ex, 44, 10, 1924-1934). Therefore, dynamic trunk exercises using pertubations of movement need to be incorporated into a rehabilitation program. Plevic floor exericses are also recommended by us as the obturator internis muscle is a hip lateral rotator whose myofascial membrane is continuous with the pelvic floor.

Dry Needling 

Dry Needling has been shown to result in significant improvements of muscular endurance of knee extensors and hip flexion that persisted 4 wk posttreatment as well as a short-term improvement of muscular endurance of knee flexors in the intragroup analysis of soccer players. Compared with placebo, DN showed a significant effect on hip flexion that persisted 4 wk posttreatment. Compared with a nontreatment control, DN also significantly improved maximum force of knee extensors also 4 wk posttreatment. Compared with a nontreatment control, placebo laser combined with water pressure massage resulted in a small but statistically significant improvement of hip flexion range of motion at treatment end and 4 wk posttreatment (Haser et al 2017 Medicine & Science in Sports & Exercise . 49(2):378-383)... further information...

Foot pronation and knee valgus

The arch of the foot comprises several bones. One of the main joints in the arch is the talo-navicular joint which is a 'ball & socket' joint, meaning that it is designed to allow a lot of rotational movement. The talus sits under the tibia (shin bone) and hence influences it's movement. 

Tibial rotation is accompanied ankle inversion/eversion and mid foot inversion/eversion

Combinations of shoes and orthotics can greatly influence the tibial rotation.

Anterior cruciate ligament (ACL) and the menstrual cycle

The ACL is designed to prevent forward shearing of the shin bone (tibia) on the thigh bone (femur).  Anterior knee laxity (AKL) and hyperextension of the knees were shown to be significant predictors of anterior tibial translation (ATT) in both males and females. Interestingly the restraining structures to knee hyperextension are the posterior cruciate ligament (PCL) and popliteus muscle, suggesting that the knee in non weight bearing is in a relative posterior position and hence allows for greater total anterior excursion of the tibia. Notably, if a females AKL changes as much as 3mm across her menstrual cycle the ATT changes by 2mm which represented a change of approx 30% in mean magnitude of the ATT (Schultz et al 2011 Med Sc Sp Ex, 43, 2, 287-295). Furthermore, in another investigation, the same authors demonstrated increased absolute and relative magnitudes of multiplanar knee laxity changes. These were seen as increased valgus coupled with relatively greater external rotation of the tibia, making the knee more susceptible to injury on ground contact and early in the landing phase (Schultz et al 2012 Med Sc Sp Ex, 44, 5, 900-909)

Muscle activation around the knee after injury affects cortical representation of muscles in the brain

Cortical representation in Patellofemoral Pain (PFP). Note the loss of topography. Te et al (2017) Pain Medicine, 0, 1-11

Transcortical muscle stimulation imaging (Abrahao Fontes Baptista 2014)

Muscle activation around the patella and the menstrual cycle

The initial firing rate is lower in the VMO (vastus medialis oblique) compared with VM (vastus medialis) in women not men. The firing rate is affected by the menstrual cycle, showing increases in initial firing during the early follicular phase through tp the late luteal phase. The initial firing was lower in VMO compared to VM during ovulatory and midluteal phases (Tenan et al 2013, Ex Sc Sp Ex, 45, 11, 2151-2157). This could play a bearing on anterior knee pain due to an increased lateral gliding of the patella over the femur, leading to patellofemoral syndrome.

Fatigue, gait and neuromuscular asymmetries after acute ACL rupture

Patients have been shown to have reduced peak knee moments for both flexion and extension in the injured knee. However, the size of the reduction in extensor moment was greater than reductions in flexor moment, when compared between limbs (Gardinier et al 2012, Med Sc Sp Ex, 44, 8, 1490-1496).

A series of squats, bilateral height jumping, and single limb landing exerices were used to induce fatigue in a population of post surgical ACL repaired males. Interestingly, altered joint biomechanics was seen, even at moderate levels of fatigue (<50%). Interestingly, little inter-limb variation was see, except for a reduction in hip extensor moment, which may represent a compensatory strategy to reduce the demand on the knee when jumping from a height. Both knees landed in more abduction (outward positioning) as fatigue set in (Webster et al 2011, Med Sc Sp Ex, 44, 5, 910-916).

Neuromuscular function during a forward lunge in meniscectomized patients

Researchers have demonstrated increased muscle coactivation, reduced range of motion, and increased rate of loading in the operated limb when compared to the other side (Thorlund et al 2012, Med Sc Sp Ex, 44, 7, 1358-1365). This coactivation was mainly the result of increased hamstring muscle activity. Another, investigation by the same researchers, during stair descending demonstrated reduced medial versus lateral muscular activity in the operated leg (Thorlund et al 2011, Med Sc Sp Ex, 43, 7, 1272 - 1279).  In a 2 year longitudinal study, post medial meniscectomy, it was shown that those subjects who underwent surgery had greater eccentric muscle strength deficit (8% and 9% hamstrings quadriceps resp) and increased external knee adduction moment. The reduction in these mitigating factors are considered significant in that they may be a contributing factors to the early onset of osteoarthritis (Hall et al 2013, Med Sc Sp Ex, 45, 11, 2036-2043).

Stages of injury

• Denial

Athletes begin an internal dialogue trying to convince themselves that it's not that bad. They try to get up and run or jump or convince themselves that it will be better in a couple of days. In extreme cases, athletes pretend there is no injury.

• Anger

 "Why me?" or "Why now?"

• Bargaining 

Athletes accept the injury and endure the pain, but they try to ignore it or overcome it by adapting their training to avoid the injured area. Generally performance drops and compensatory strategies create imbalance and over loading of other structures or body parts.

• Depression

If your training and goals were well planned out, your injury can have a greater impact, because it's more obvious what's missing. Hormonal considerations such as the lack of endorphines from training also play a critical role.

• Acceptance

For rehabilitation to be effective, this is the stage you need to get to. The preceding stages are completely natural and understandable. Recognize them for what they are. You can start working on your rehab right away, even while you are going through the other stages.

Treatment and exercises for knee rehabilitation

Whilst working in Switzerland, with professional soccer players, from the Italian Series A and German Bundesliga, I noted that soccer players have relatively tight hamstrings, adductors and hip flexors, and well developed calfs, quadriceps, hamstrings and gluteal muscles. Investigations have demonstrated that localised application of vibration can improve passive knee extension in women (Bakhtiary et al 2011, AJP, 57, 165-171). Studies have shown that women's hip muscles can atrophy after an injury as simple as an ankle sprain, due primarily to injury-caused limping or using crutches. Any hip or core muscle weakness, when combined with a woman's biomechanics, can be detremental to a female athlete returning to the soccer field. Proper rehabilitation is critical to coming back from an injury stronger and healthier. From the previous discussion, it would appear that neuromuscular balance and control are exceedingly important factors in the rehabilitation of the knee. Moreover, hip-back-pelvic-foot dynamic control are critical for a return to function and sport.

Evasive side stepping

It has been demonstrated that evasive side stepping during sport, against an opponent, activates different postures and knee moments (Lee et al 2013, Med Sc Sp Ex,45, 9, 1740-1748). Hence, stimuli realism needs to be incorporated into ACL rehabilitation programs in order to activate visual-perceptual-motor skill complexity that is required during side stepping.

Medial - Lateral Stability

Engagement of the hamstrings to extend the knee

Core Stability

Hip Stabilisation

On field rehabilitation should include

• forward - backward running
• sideways running - foot to foot, foot over foot
• running in ever smaller circles
• figure of 8 running
• running with ball and doing tricks with ball
• soccer drills

20 February 2017