More proof for the Cross Over Gait for the non-believers and debaters.

For those of you who have been with us for a few years, you are no stranger to our articles and videos on the web for piecing together many aspects of the CROSS OVER GAIT in a manner more comprehensive and more clear.  If you are not familiar with our work on this, please click here.

Today we add a little more “proof to our pudding”.

“Changing step width alters lower extremity biomechanics during running.” Brindle et al.
http://www.gaitposture.com/article/S0966-6362(13)00291-9/abstract

• Step width influences frontal plane biomechanics of all body parts
• Changes in step width affects arm swing symmetry and often creates arm abduction
• Hip and knee biomechanics change from their normal predicted path and mechanics
• Hip adduction, rearfoot eversion and internal tibial spin decrease as step width increases
• Knee adduction/valgus stress decreases as step width increased.
• Increased step width improves cephalad stacking of all lower extremity joints
• The swing limb is a hinging pendulum. Striving for a level pelvis and normal step width promotes a normal sagittal pendulum path and improves the likelihood of a recurring sagittal pendulum swing for the opposite leg. 

As Brinkle et al. say in their paper, “step width is a spatiotemporal parameter that may influence lower extremity biomechanics at the hip and knee joint.”  We would argue that it is even more far reaching than the hip and knee. You have likely learned here at the Gait Guys that arm swing is heavily predicated on the dynamics of contralateral leg function and positioning.

The above video shows a classic cross over gait. The limbs can be seen crossing over the midline thus guaranteeing that the pendulum is moving through an arc and not along a straighter progression. This adduction of the limb virtually guarantees that the foot is striking greater on the lateral heel and forefoot than it should, that the rear foot is going to move through eversion with greater speed and force and internal tibial spin and arch control will need to be controlled better.  And if they are not controlled better, pathology may eventually occur.  Do you want any of this to occur at an accelerated rate as occurs in running ? One doesn’t need to just heel strike to suffer these problems, midfoot strike will still see them if the cross over occurs.

Shawn and Ivo, the Cross Over Guys.

Hip Biomechanics Part 2

Figure 1 shows the condensed version of the parameters (forces and moment arms) affecting movement and stability of the femur-acetabulum complex in the frontal plane during the closed kinetic chain.  (A moment arm such as D1 and D2 is defined as the length of a line that extends from the axis of rotation to a point of right angle intersection with a respective force, in this case HAM or BW.)

In Figure 1 above we see several parameters.  HAM represents the Hip Abductor Muscles, D1 represents the internal moment arm, D2 represents the external moment arm and BW represents the Body Weight of the individual.  These factors all come into play when considering the frontal plane equilibrium of the hip joint.  The equation representing the interaction of all of these parameters is HAM x D1 = D2 x BW.  Both sides of this equation must be equal and balanced in order for the pelvis to remain stable and without movement when in the closed chain stance phase of gait. In this diagram, if the left side of the equation is greater than the right the net effect will be a counterclockwise hip moment and the patient will move their torso over the hip creating a hiking or lifting of the contralateral hip.  This net movement will create abduction at the hip joint.  If the right side of the equation is greater than the left the net effect will be a clockwise hip moment and the patient will move their torso away from the hip creating a dropping of the contralateral hip.  This net movement will create adduction at the hip joint seen here and thus the classic Trendelenberg gait.  We need to keep in mind that this is not a perfect model presented here since we are ignoring acceleration of the body in the forward sagittal plane and rotational planes.  Investigating the equation further should bring the reader to further realization that if the body weight (BW) were to increase, mathematically the D2 external moment arm could decrease to keep the equation balanced.  However, since the length of this D2 moment arm is rather fixed (unless the pelvis were to go through a counterclockwise  rotation which would draw the body weight center closer to the hip joint center effectually abducting the stance hip, thus reducing the D2 moment arm) this is not a more likely scenario. Rather, the response would be to attempt to increase the left side of the mathematical equation thus increasing the HAM forces to attempt to keep the pelvis level and the equation from changing.  In other words, when body weight increases we must increase the gain or contraction in the HAM group during each step to keep the pelvis level and balanced.  Unfortunately the HAM strength has its limits of maximal contraction, sometimes far below any major increases in body weight.  One must keep in mind that with increased HAM contraction there is a corresponding increase in joint compression across the hip articular surfaces which at reasonable levels is well embraced but at unreasonable levels can damage articular cartilage.  One should thus conclude that maintaining a reasonable body weight for one’s bone structure keeps the right and left sides of the mathematical equation at tolerable levels, both for movement, stability and cartilage longevity.  Fortunately the equation has a built in safety mechanism for these counterclockwise hip moments, one that is beneficial.  In such scenarios, as the body is brought over the hip thus decreasing the D2 moment arm, the D1-internal moment arm increases in length and since the equation must be balanced the HAM force can decrease.  Thus, the magnitude of the HAM force is inversely proportional to the length of the D1-internal moment arm.  The whole equation can better be visualized and conceptualized by a teeter totter diagram with a sliding pivot point.

Shawn and Ivo,  The Gait (and biomechanics) Guys

Yesterday’s Video Case: The Gaits of Hell

We have received many emails on this case already. Overwhelmingly people are saying……. “Hey, this isn’t easy….. It’s easy when you guys tell us right away because we can see it."  
Yes, when we are all alone to solve these gait problems our heads can start to swim with all the variables. Gait analysis is not easy.  Even the video assessment computer programs do not give you the answers and diagnosis, they just give you variables and data.  The thinking still has to be  done at the end of the day.

I remember how much I struggled with this case back during my orthopedics residency. I remember even pulling out my undergrad notes from Univ. of Waterloo as a student of the famous Dr Stewart McGill and mapping out FBD’s (Force-Body Diagrams) on this case. Oh, the horror !!!  I still have occasional FBD nightmares, being asked to solve an equation in front of the whole class. Pure anxiety ! Holy night terrors ! But, it is amazing what a few decades of study will do for you, we can now look at this case and see things for what they are, see them quickly and know what is going on almost immediately.  It takes some time, so if you are new to this stuff, be patient…… it will come.

CASE REVIEW:

in this video we see the following:

1. large step length off of the left foot abruptly onto the right, this step is sudden and he crashes down on to the right foot sooner than he normally would to catch his forward moving body mass. ( this will make more sense after reading #5).
2. there is a delayed left heel rise and delayed left calf recruitment , actually, it’s not delayed, it’s absent. )
3. the left foot remains supinated through the entire gait cycle. 
4. the left foot shows extraordinary long toe flexor recruitment (seen on the end of the video during the foot close up)…….this point is important
5. pelvic unleveling is apparent but a mirage for the most part. We really do not see a true Trendelenberg style gait (although it sort of looks like the left hip drops) rather, what you see is the result of the manufactured delayed left limb departure and subsequent impact at right limb load … but this is not a Trendelenberg gait, he had no Gluteus medius weakness.  Explained another way, he is having troubles departing off of the left foot (this diagnosis is the reason, he has compensated from a neurologic lesion affecting the strength of the calf) and so he extends ( behind him) the left leg longer and further than normal because he cannot push off, plus he hyperextends the left knee because of these factors. Normally, the calf fires after passive heel lift occurs. But with a lesion affecting the calf it has arrested the push off. So, in his case, the heel stays on the ground until it is dragged off from enough  forward body carriage. So, when you see this from a sagittal view the left hip will look like it is dipping as it does here, but it is not truly, he is just taking a long lurching step off of the left and onto the right, the longer left hip extension behind him sets up the illusion of a left hip drop.  Try this at home to feel this gait, walk down your hallway and try to delay the left heel rise for as long as you can.  You will find that you get into your left gluteals more, take a longer step on the left, and take a sudden lurching load onto the right limb to catch your forward progressing body mass. This is exactly what this chap is doing.  But why ? The left calf lesion. 
6. continuing on #5, there is abrupt right frontal plane loading (because of the sudden transition from left foot to right the frontal plane is engaged longer than normal) and thus the pelvis is carried further to the right in the frontal plane.  He makes a  noble attempt to protect this range by turning out the right foot into the frontal plane (aka. increased right foot progression angle) to allow the quadricep muscles to assist the gluteus medius, abdominal obliques and lateral limb stabiliers in decelerating this frontal plane challenge.

Diagnosis:This doctor came to see me while I was completing my orthopedics residency and mid way through my course work in the neurology post doctoral program. He had been treated for mechanical low back pain with failed results ( well, to be accurate. his low back pain had resolved but pain had peripheralized into the left leg. To review, peripheralizing pain is rarely a good neurologic sign.)  After an examination showing an absent left S1 Achilles reflex it was highly suspicious we were dealing with a radiculopathy. An MRI confirmed a substantial left foraminal disc herniation obliterating the left S1 nerve root foraminally. The S1 nerve root expands into branches feeding input into the lower limb muscles.  In this case, the unfortunate group affected was the gastrocnemius almost exclusively. So in this case this makes sense to what is presented clinically and on gait evaluation. He is overutilizing his long toe flexors (fortunately untouched) as seen in the video because they are basically all that is available to him to plantarflex the foot ( create heel rise and push off).  They are certainly not well suited for this task but subconsciously the brain will use what is available to it, worthy or not. In this case they are a feeble attempt at best. There is no way the long toe flexors can lift his body mass into heel rise and propulse it forward, they are synergists of this task and not agonists / prime movers.
Sequencing Summary:So, this is a case of an aberrant or pathological gait pattern that will be permanent because the nerve damage was fixed by the time i had seen him.  Muscular wasting of the gastroc complex had already occurred.  The culprit was the space occupying lesion (disc in this case) in the left spinal vertebral foramina effacing and deforming the nerve root sufficient enough to create dennervation.  A surgical consult and EMG/NCV (as best as i can recall) confirmed this case was non-surgical at that time (no one wanted to touch the case).  The nerve damage disabled the calf so that push off was impaired.  He thus delays his ability to create adequate heel rise and propulsion so the long toe flexors are called to attempt the feat.  The foot supinates to maintain its rigidity ( it is also hard to pronate through the foot when the toe flexors are in an all out contraction). And because the heel does not rise on its own from muscular strategies, the foot waits to be lifted off of the ground by simple forward progression of the body.  This creates an increased left hip extension range and gives the appearance of a left hip drop which is a false appearance pseudo-Trendelenberg sign.  Due to the fact that he is on the left limb longer, he will be on the right limb for a shorter period.  This right stance phase is initiated abruptly as he falls from the delayed left stance phase. The abruptness of the load on the right challenges the right frontal plane as evidenced by the right foot turn out and right pelvis sway (subtle).  He then departs off the right to  begin the cycle once again.
PS: It is coming a little late, but thank you Dr McGill. Your teachings to a young undergrad set my biomechanical thinking on the right path very early in my studies of human kinetics. Thank you, Sincerely. 
Dr Shawn Allen…… The other half of The Gait Guys