Monday, October 22, 2018

How Does Human Movement Occur - Kinetic Chain in Action - Part III

Last week we ended our discussion looking at how poor posturing loads various portions of the body.  We will continue to see how this posturing impacts thoracic spine on down to the foot.

Thoracic scoliosisKeener JD, Brophy RH. Superior labral tears of the shoulder: pathogenesis, evaluation, and treatment. J Am Acad Orthop Surg. Oct 2009;17(10):627-37.

·       Causative factors – because baseball and especially pitching is an asymmetrical sport, pitchers tend to over develop on one side and under develop on the other side as noted earlier.  In the thoracic spine, this results in increased muscle tension on one side of the spine and decreased muscle tension on the contralateral side.  Since the spine is a mobile structure, this can result in the bending toward the stronger side or the side with increased tension.  This will present as scoliosis.  It should also be mentioned that baseball, especially professional baseball, tends to attract demographics and recruit internationally from regions which tend to have higher incidences of scoliosis.  So, although scoliosis in the example may be associated with the factors mentioned above, this can also be associated with genetic factors as well.

·       Potential injuries – with thoracic scoliosis, because of the abnormal position of the spine there is also abnormal loading of the spine.  The human spine is meant to be loaded in an 80/20 relationship where 80% of the weight is absorbed through the bone disc bone interface and 20% of the weight is absorbed through the facet joints.  Abnormal spine positioning of the spine alters this loading relationship.  This can add to accelerated breakdown of tissues and pain in the joints, ligaments or muscles of the thoracic spine.  Curvature in the frontal plane also adds to distraction of the costalvetebral joints on the concave side and compression on the convex side.  This can add to costalvetebral pain as well as increase the potential for costalvetebral subluxations.

·       Performance issues – with a change in position of the spine, there is also a significant change in the length tension relationships of the musculature that attaches at various portions of the spine.  With curvature in the frontal plane, muscles are lengthened and shortened on the convex and concave side.  These altered length tension relationships add to imbalances in strength along the spine and the lower extremities.  This not only impacts transfer of kinetic energy but also then power output.  In instances where there is pain, this results in even further weakness of the spinal extensors, which if not addressed can lead to loss of up to 25% of the cross sectional area of the muscle (Hides et al, Spine, 1996).[i]   In the pitcher example, this can cause increased fatigue in the thoracic spine earlier in the game which puts increased demands on the shoulder and scapula stabilizers.  If they are also weakened, this accentuates the impact on overall performance, pitching velocity and pitching tolerance or endurance.

Pelvic asymmetry

·       Causative factors – in a closed kinetic chain situation, positioning of one end of the chain impacts positioning on the other end.  In the spine and pelvis, this is especially true since the two are connected via the sacroiliac joint (SI).  Therefore, one cause of pelvic asymmetry can be scoliosis.  However, if there is a pelvic asymmetry, this will also cause curvature of the lumbar and thoracic spine in the frontal plane.  So, does pelvic asymmetry cause curvature of the spine in the frontal plane or does curvature in the frontal plane cause the pelvic asymmetry?  This is an important question to answer during a differential diagnosis.  Another factor that can lead to a pelvic asymmetry is a leg length discrepancy.  Although a “true” leg length discrepancy is rare and usually the result of genetic factors (hemihypertrophy), tumors (hemangioma - blood vessel tumor or Wilm’s tumor – tumor of kidney causing hypertrophy of the limb) or epiphyseal issues (injuries or infections in the growth plate), these are typically not diagnosed during a visual examination alone and require further testing to uncover.  An “apparent” leg length discrepancy, though, can be assessed during visual and musculoskeletal evaluation.  There can be a plethora of causative factors, including lumbar spine and core weakness or tightness, pelvic weakness or excessive flexibility (common in women who carry a child on a single hip predominantly) or excessive foot pronation.

·       Potential injuries – with pelvic asymmetry, many tissues and structures are abnormally loaded.  In reviewing just the most proximal and distal structures, one could expect to see abnormal loading of the lumbar spine, the sacroiliac (SI) joint, the hip joint, trochanteric bursa and the iliotibial band.  The lumbar spine is placed in a more side bending position with pelvic asymmetry, and therefore there is increased potential for low back pain.  There is increased shear stress in the SI joint which can contribute to pain.  At the hip, there is increased compression of the femoral head in the acetabulum which may contribute to hip labral tears, wearing of articular cartilage and pain.  On the side of the hip, where the ilium appears to be elevated, there is increased tension on the iliotibial band.  This can add to increased incidence of trochanteric bursitis and IT band friction syndrome.    

·       Performance issues – besides the indirect impact the asymmetry would have on performance as a result of potential pain issues, pelvic asymmetry also can have a more direct impact on performance as well.  As a result of the frontal plane motion that occurs during gait and sport related activities, when there is pelvic asymmetry there can be marked decrease in endurance of the hip, core and lower extremity.  Endurance and overall power output are also affected because of the change in the length tension relationships of the musculature of the lower extremity, hip and core.  In the example of the pitcher, pelvic asymmetry can result in increased fatigue in the lumbar spine, hips and lower extremity which places increased demands on the upper body to maintain velocity or power output.  The impact on overall performance, pitching velocity and pitching tolerance or endurance is compounded if there are weaknesses and poor postural alignments higher up the kinetic chain.

Foot Asymmetry

·       Causative factors – because the foot is the first portion of the kinetic chain to impact or be in
contact with the ground, misalignment of the foot will have a dramatic impact on the alignment and loading of all of the proximal joints, including the ankle, knee, hip and lumbar spine.  Two common alignment issues that we see in a postural assessment are supination (in relation to position of the calcaneous) resulting in pes cavus (in relation to the position of the medial arch) of the foot and pronation resulting in pes plantus of the foot.   The position we most often observe in athletics however is calcaneal pronation resulting in pes plantus.  This may present bilaterally but in many cases will present with an asymmetrical pattern, meaning that it will be much more pronounced on one side versus the other or be present on one side and not present at all on the other.  In cases that present asymmetrically, we often see much greater dysfunction during sports performance and/or increased injury potential on the side with the most pronounced pronation.  This can result in the athlete being plagued with injuries along the kinetic chain on the side with the greatest magnitude of pronation.  When the calcaneous falls into excessive pronation in a closed kinetic chain the result is genu valgum at the knee, adduction at the hip and pelvic asymmetry.  Although many believe this is the “main cause” of pathokinematics, research has shown us that proximal weakness in the hip and core can also result in pronation and pes plantus at the foot and ankle.  In fact, pronation and pes plantus can be caused by a multitude of factors including weakness of the posterior tibialis, intrinsics of the foot on the plantar aspect, hypermobility of the plantar fascia or calcaneous, or proximal weakness in the hips and core.   

·       Potential injuries – with calcaneal pronation, many structures are loaded in an abnormal fashion.  In reviewing proximal and distal structures, one could expect to see abnormal loading of the medial arch of the foot, the retrocalcaneal bursa and Achilles tendon, the anterior tibialis, tibia (shins) and knee.  With the decreased arch, the foot becomes flat footed in full weight bearing (pes plantus) which increases potential for pain in the arch of the foot as well as the heel, and posterior heel.  With the loss of shock absorption with the fallen arch, this can place more work and strain on the anterior tibialis and the shins adding to anterior shin pain.  At the knee, there is a resultant genu valgum which increases the potential for strain on the cruciate ligaments and meniscal injuries.  Along with this positioning of the knee, there is alteration of the “normal” articulating pattern of the patella in the femoral groove which can lead to patellar tendonitis or patellofemoral syndrome. 

·       Performance issues -- besides the indirect impact the asymmetry would have on performance as a result of potential pain issues, pronation can also have a more direct impact on performance as well.  As a result of the large degree of motion that occurs during gait and sport related activities, when there is excessive calcaneal pronation there can be a marked decrease in endurance of the foot, ankle, lower leg, knee and hip.  Endurance and overall power output are also affected as a result of the abnormal positioning and alignment of the joints in the closed kinetic chain.  In an example of a basket ball player, vertical height may be compromised when attempting to achieve a jump shot.  With excessive pronation of the foot and accompanying genu valgum, the force the athlete is able to generate through the quads and hamstrings is affected and the transfer of that energy to the foot/ankle and ground is also compromised.  Therefore there is not only a decrease in the force that is generated but also a decrease in the energy transfer as it is crossing a less efficient system.    

So, we can tell a lot about an athlete’s potential for certain types of injury as well as potential performance issues and limitations he or she might face by looking at posture as seen in these examples.  Addressing deviations like these can reduce the potential for injury, improve efficiency of the entire system and lead to higher athletic performance.

As basic as it sounds, to truly change movement, we must change the way that we think.  And although it is not 100% data driven, it is 150% science driven.  And that is, assess it better.  Move better, feel better, perform better and last longer.  That simple!   

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Dr. Nessler is a practicing physical therapist with over 20 years sports medicine clinical experience and a nationally recognized expert in the area of athletic movement assessment and ACL injury prevention.  He is the founder | developer of the ViPerform AMI, the ACL Play It Safe Program, Run Safe Program and author of a college textbook on this subject.  Trent has performed >5000 athletic movement assessments in the US and abroad.  He serves as the National Director of Sports Medicine Innovation for Select Medical, is Vice Chairman of Medical Services for USA Obstacle Racing and movement consultant for numerous colleges and professional teams.  Trent is also a competitive athlete in Brazilian Jiu Jitsu. 

[i] Hides, Julie A. PhD; Richardson, Carolyn A. PhD; Jull, Gwendolen A. MPhty. Multifidus Muscle Recovery Is Not Automatic After Resolution of Acute, First-Episode Low Back Pain. Spine. 21(23):2763-2769,1996

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