Shoulder Stability (1 of 3)

The shoulder is one of the most complex joints in the human body.  It has an amazing amount of inherit mobility, which in turn requires an adequate about of dynamic and static stability to function.  Then if you consider the manner in which we use our shoulders and the lack of anatomical support, it's easy to see why stability is the most important factor to consider when treating shoulders.To improve your shoulder assessment and treatment skills it is important to fully comprehend the details of static and dynamic stability.  This will be a 3 post series that will hopefully clear up some confusion and allow you to understand stability on a deeper level.

Why We Need Stability

A couple quick facts about the shoulder...The humeral head is 3 times larger than the glenoid fossa.  The base of shoulder stability is a “floating” physiologic joint.  The only true bony attachment is through the acromion process to the sternoclavicular joint.  There are over 25 muscles that are involved with shoulder girdle movement.  There is more movement (ROM) at the shoulder than any other joint.  Which means there is a complex interaction with the muscle-length tension relationships and the sensorimotor system.Take all this into account and you’ll quickly realize that the shoulder doesn’t have a whole lot going for it.  Then add in the fact that we abuse our shoulders with respective motions, terrible postures, and athletic activities.  The result is a joint that requires a great deal of coordinated dynamic and static support just to stay healthy.

Dynamic and Static Stabilizers

Understanding the complex interplay between the dynamic and static components of the shoulder is of paramount importance and a prerequisite for proper examination and intervention.  Before one can consider how the dynamic and static components interact, it is necessary to understand the difference.

• The dynamic components include the contractile tissues (rotator cuff, deltoid, scapular muscles) and the sensorimotor system
• The static components include the connective tissue (labrum, capsule, ligaments)

This post series is intended to be a review of the anatomy and function stated in a concise form to use as a reference.  There is a wealth of articles, websites, and posts regarding these concepts.  For a more in-depth information please refer to the references listed at the end of this series.

Understanding Shoulder Movement

Osteokinematics / Arthrokinematics

Understanding the correlation between physiologic and accessory motion will allow one to better assess kinematic motion and capsular extensibility.  Evaluating either shoulder motion or capsular integrity can help guide the clinician in their examination.  For instance, a lack of range of motion in abduction may correlate with a decrease in inferior capsule extensibility.  The interpretation of the osteokinematics and arthrokinematics can also help guide the clinician in their treatment by revealing where stability is needed.It is important to keep in mind that changes in capsule or ligament integrity will alter the normal mechanics of the shoulder joint.  For example, posterior capsule tightness can create an imbalance in the normal arthrokinematics and result in an obligatory anterosuperior migration of the humeral head and loss of internal range of motion (Ticker et al 2000, Sethi PM et al 2004).

Shoulder Stability

Part 1 - Components and MotionPart 2 - Static StabilityPart 3 - Dynamic Stability --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Book Review: Anatomy Trains by Tom Myers

Today there are so many healthcare professionals/salesmen out there that are repackaging the same old wheel and selling it as the newest innovation to medicine.  It seems like all it takes to innovate in the medical industry is a good marketing plan and a thesaurus.  However, this is by no means what Tom Myers does in his book Anatomy Trains.  Myers has created an easy to read, easy to understand book that truly advances our understanding of the human body.  Anatomy Trains is a fresh new perspective on fascia and the human body and it leaves the reader with an addition “lens” of which to view the body through.In school I learned a very limited amount about the facial system.  Much of it was described as simply a “connective tissue sweater” under the skin and around muscles.  However, the truth about fascia couldn’t be further from this “sweater” concept.  As Myers points out with sound logic and research, the fascial system is a complex tensegrital system that is continuous throughout all of the human body.  Not only does Anatomy Trains clarify the fascial system, but it describes the system with 7 clinically applicable  myofascial lines (anatomy trains).

• Superficial Back Line
• Superficial Front Line
• Lateral Line
• Spiral Line
• Arm Lines
• Functional Line
• Deep Front Lines

A Few Things I Learned

Fascia is Continuous

Fascia is a fibrillar structure composed of collagen, elastin, and reticulin.  It is not only the sheath that surrounds muscles and bones, but it is also the cotton-candly like net surround each individual cell.  Simply put, fascia is what holds our cells together.  It helps to organize our structure, provides support for other tissues, adapts to our postures and movements, and affects our everyday function.

Tensegrity is Just as Important as Biomechanics

Tensegrity (tesion integrity) describes a “structural relationship principle in which structural shape is guaranteed by the finitely closed, comprehensively continuous, tensional behaviors of the system and not by the discontinuous and exclusive local compressional member behaviors”.  As Myers often describes, it's how the body is structured more like a sail boat than a brick wall.  Tensegrity can be an explanation for how the peri-spinal muscles keep us upright and why releasing hamstring tension can sometimes alieviate plantar fasciitis.

How to Better Assess Posture and Manually Treat

With the new “lens” of the fascial system one can more easily and accurately assess posture and presume what structures may be lengthened and/or shortened.  Using the anatomy trains allows for a more methodical visual examination of the patient and can help to guide the clinician in their plan of care.  Throughout the book and DVD, Myers offers many useful tips and techniques on how to best affect these myofascial lines.  My personal favorite is a manual technique for the erector spinae fascia.  Myers recommends to “pile up on the mountains, and dig out the valleys”.  Meaning, if the spinous process protrudes (“mountains”) then you should direct the myofascial tissues medially.  Conversely, if the spinous process sinks below the surround tissue (“valleys”) then you should direct your manual intervention laterally.

Summary

Reading medical books and research tend to be as interesting as reading a phone book.  Anatomy Trains is a refreshing departure from this format.  It reads with great clarity and is able to simplify complex concepts in a way that the reader can best understand.  For a society that is predominately visually based, the book has more pictures and diagrams to aid the readers understanding.  Anatomy Trains is a must read for anyone that works with the musculoskeletal system.

 References

Myers T.W. (2009).  Anatomy Trains: myofascial meridians for manual and movement therapists 2^nd Edition.  Elsevier Limited.www.anatomytrains.com --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Keys to Achilles Tendon Repair Rehab

Achilles tendon ruptures can be a very frustrating rehab for both the patient and the clinician.  The patient has to wear a boot of shame for 4-8 weeks and are very limited in the amount of activity they can perform.  Clinicians are often frustrated since these surgeries require a very particular rehab protocol and are limited as to which interventions they can use. However, one good thing about treating a achilles tendon repair is that you really only have to be worried about two things:

1. Protecting the passive tension and integrity of the repaired Achilles tendon to prevent an insufficiency of the muscle-length tension relationship (avoid stretching past neutral for 3 months)
2. Strengthening end-range plantarflexion strength

Avoid Insufficiency of the Achilles Tendon

Remember taking of the rubber bands off that new baseball glove that you have been trying to break in?  They didn't exactly recoil back to their normal shape.  In fact, you had to throw them away most of the time because they lost their function.  They were stretched out too much and the elasticity was now only mildly useful with a object much larger than your baseball glove.Achilles tendon repair rehabilitation is very similar to this rubber band.  The surgeon and the patient go through a lot of trouble to regain the passive tension and viscoelastic properties of the newly repaired tendon.  The worst thing you can do as a physical therapist is to compromise the surgery by lengthening the achilles tendon in the first 3 months when the structure is vulnerable.

Why Not to Stretch

Stretching the tendon too early will cause the collagen to heal in an insufficient length.  More specifically, pre-mature anatomical lengthening will increase tendon compliance, decrease viscoelastic properties, and a shift the muscle length-tension relationship to the right.  Thus, the muscle would be unable to produce adequate force at shorter lengths.  This increased tendon lengthening would also cause greater muscle shortening during muscle contraction, further preventing an optimal muscle-length tension relationship for force production.Given the nature of the surgery and rehabillitation, I feel it is important to opt on side of caution when considering dorsiflexion ROM.  You can always add ROM later in the course of recovery when the structure is completely healed, but you cannot put back the passive tension and elasticity in the tendon once it is over stretched.This conservative approach will help keep the surgeon and the patient satisfied in the long run.  Two keys to avoiding insufficiency and decreased function of the achilles tendon are:

• Do not stretch the achilles tendon past neutral for 3 months
• Add a heel-lift to footwear

Strengthen End-Range Plantarflexion

End-range plantarflexion strength goes hand in hand with the muscle-length tension relationship mentioned above.  You can help to further accelerate your patients outcome by strengthening the gastroc-soleus complex in the end-range, shortened position.  This is not only a safe intervention due to the absent passive tension placed on the structure, but it is a very functional ability for everyday activities (walking, stair negotiation, landing from a jump, etc.).Mullaney et al studied the strength of end-range plantarflexion in 20 patients post-operatively after an Achilles tendon repair (mean 1.8 years).  They found that there was a decrease in passive stiffness in dorsiflexion (see above) as well as a weakness in end-range plantarflexion strength.  Testing end-range plantarflexion with a decline heel raise, they found that 14 out of 20 of the patients could not perform this task.  The authors hypothisized that this was due to anatomical lengthening, increase tendon compliance, and insufficient rehab.

Interventions for End-Range Plantarflexion

To ensure that you are not apart of the "insufficient rehab" variable, strengthen your patients plantarflexors in the end-range position.  There are two ways to do this: toe walking and decline heel raises.  Toe walking may be a more advanced technique due to increased amount of weight bearing and stability required.  Therefore, I would begin with a small angle of decline heel rises and progress as tolerated.

Bottom Line

Achilles tendon repair rehabillitation can be a difficult process for both the clinician and patient.  Preventing anatomical lengthening of the Achilles tendon will lead to greater satisfaction and function for your patient in the long run.

• Do not stretch past neutral into dorsiflexion for the first 3 months
• Add a heel lift into footwear
• Increase end-range plantarflexion strength (decline heel raises, toe walking)

References

Mullaney MJ, Mchugh MP,Tyler TF, et al.  Weakness in End-Range Plantar Flexion After Achilles Tendon Repair.  Am J Sports Med. 2006 Jul;34(7):1120-5 --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Sensitivity and Specificity

Sensitivity and Specificity

Often when reading peer-reviewed articles I feel like I need an advanced degree in statistics to understand how the hell they analyzed the information and quantified the results.  There is an amazing amount of jargon when looking at the objective measurements.  This is rarely a clinical problem since understanding the statistical analysis is not applicable to the patient.  I've never been mobilizing a patients shoulder and been concerned of whether it was a pearsons analysis or t-something in the article I just read.However, the one part of statistics that is very important clinically is understanding specificity and sensitivity.  Sensitivity and Specificity are used to discriminate relevant information that allows clinicians to make meaningful decisions.  They are a statistical measurement for a classification function.  Using sensitivity and specificity can allow clinicians to improve their examination, optimize their assessment, clear up any suspicions, and most importantly, lead clinicians to the proper interventions and prevent patients from receiving unnecessary treatment.So what's the problem then?  Unfortunately, due to poor explanations, difficult concepts, and confusion among peers they often become used interchangeably.   For the quick explanation scroll down to the chart at the bottom of this post.

Statistical Example

To attain these statistical values, studies have to be performed on the accuracy of a test against the current gold standard.  Here's an example of a possible test to determine the sensitivity and a specificity of the Lachmans test (completely fictional).If 100 patients known to have an ACL tear were tested with the Lachman's test, and 90 of them tested positive, then the Lachman's test would have a 90% sensitivity.  If 100 patients known to have an intact ACL were tested with the Lachman's test, and 90 of them tested negative, then the test would have a 90% specificity.

Sensitivity

Sensitivity can be defined as the proportion of patients with a pathology who test positive.  It relates to the test's ability to identify positive results.   A test that has a sensitivity of 1.0 would be able to correctly diagnose every person who has the target pathology (predicts all people from the sick group as sick).  A highly sensitive test implies that it has the ability to identify the patient who actually has the pathology.  In other words, sensitivity determines the amount of true positive outcomes.Since a highly sensitive test would identify anyone that tested positive for the pathology, then someone who tested negative could be ruled out for the pathology.  This is because if they were positive, it would have been proven with the test.  Therefore for a negative result would confirm that the patient does NOT have the pathology.  This is where the "SnOut" rule comes in.  Because a negative response to a high sensitive test rules out the pathology.In terms of statistics and errors, you could say that if it is a true positive, then it is not going to be a false negative.  A 100% true positive would mean there is no type II error.  There is no false negative.  A negative result would be considered valid and not an error.

Clinically Application

Sensitivity tests are used to screen for pathologies.  An upper or lower quarter screen isn't used to try to rule anything in.  Instead it is used to rule out any possible pathologies.  It's why many use the term "clearing" the upper/lower quarter.  The FMS is also a sensitive screening test.  On the functional movement's you are not analyzing and testing for a certain pathology, you're simply ruling out the individuals who are not at risk.  By doing so it allows you to identify which individuals need to be evaluated more in depth.Another example of the clinical application of sensitive tests would be with shoulder pathologies.  I have found clinically that most acute shoulders test positive for just about every special test.  This may be due to the acute irritation of the joint and increased sensitivity to pain, which is often the positive sign.  Therefore, it might be better to use tests with high sensitivity in this acute stage in attempt to rule out what pathology the patient does not have.

Real Life Example

Think of tequilla.  The past couple times you've taken shots of tequilla it has ALWAYS ended up with you not feeling so well.  You are positive that no matter how many limes you chase it with, you are definitely going to be feeling bad if you drink tequilla.  And when you don't have tequilla you feel fine and don't get sick at all.  So when you're at the bar ordering something to drink what do you NOT order?  What drink do you immediately rule out?  Tequilla.  You know tequilla will definitely make you sick and not having it will leave you feeling good.  So you can "SnOut" tequilla.So in this spring break example, Tequilla would have a 100% sensitivity to you.  You are positive you'll get sick off of it if you have it.  So when the bartender does his test of asking you what you want to drink, you give him a confident negative result that you don't have tequilla.

Specificity

Specificity can be defined as the proportion of patients without the disease who test negative.  A test with 1.0 specificity would be able to correctly identify every person who does not have the target disorder (not predict anyone from the health group as sick).  A test with high specificity would be able to determine the population that does not have the pathology.  Specificity shows the true negatives.As mentioned above in sensitivity, it is a process of elimination between two options.  Because of this binary classification, the results are directly proportional.  Since a highly specific test would definitely display the absence of the pathology, then if the patient test positive, you can be certain that they actually have it.  Therefore, a positive test result rules in the target disorder ("SpIn").In terms of statistics and errors, you could say that if it is a true negative, then it is not going to be a false positive.  A 100% true negative would mean there is no type I error.  There is no false positive.  A positive result would be considered valid and not an error.

Clinical Application

Specific tests are used for rule in a pathology that a clinician may be suspicious of.  For example, if during your examination you become suspicious that your patient may have a meniscus tear.  Sure you could use a sensitive test such as joint line tenderness to rule it out, but if all signs and symptoms are leading to a meniscus tear, then you really want to use a specific test to rule it in.  The Apley's test has been shown to have a high specificity.  If this test is negative, then it would be logical to use a sensitive test to further rule it out.  For further confidence in test results, using a test with both high specificity and sensitivity (e.g. Thessaly test) would be ideal.

Real Life Example

Staying with the alcohol example of ordering a drink at a bar, think of that tasty micro brew on tap.  Everytime you have that tasty beer you have a great time and have never been sick off of it.  It never has a negative effect on you.  You are certain that it will go great with those mozarella sticks and nacho's you just ordered.  So when the bartender asks you what you want to drink what do you rule in?  What are you positive that you want to drink?  The micro brew beer, especially if it's 2 for 1.  So you can "SpIn" beer.So in this happy hour example, beer is 100% specific to you.  You are certain that beer will not make you sick.  So when the bartender tests you by asking you what do you want to drink, you give him a confident positive result that you want to order a beer.

Summary

If the application of specificity and sensitivity seems backwards, it’s because it is.  This is the fun world of statistical analysis, binary classification function, and errors associated with the null hypothesis.

• A high sensitive test would definitely catch anyone that is positive.  So if they’re not positive, you can be sure that they’re negative.
• A high specificity test would definitely catch anyone that is negative.  So if they’re not negative, you can be sure that they’re positive.

The general rule for a good test value is approximately 80%.

Chart of Sensitivity and Specificity

 

Bottom Line

Sensitivity and specificity are great values to guide you in your clinical examination.  It can give more information regarding the patient and lead to a better assessment and a more valid diagnosis.  Keep in mind that there is always the possibility of false positives and negatives.  Special tests should never be the only sign to determine a patients pathology.  It is merely a piece of the clinical examination and assessment.

References

Dutton M.   Orthopaedic Examination, Evaluation, & Intervention.  New York: McGraw-Hill; 2004.Magee DJ.  Orthopedic Physical Assessment (5th ed.).  St. Louis: Saunders; 2008.  --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Article Review: Acetabular Labral Tears (Lewis & Sahrman 2006)

Article Review: Acetabular Labral Tears

Lewis CL, Sahrman SA.  Acetabular Labral Tears.  Phys Ther. 2006;86:110-121In 2006 Lewis and Sahrmann produced a great article on acetabular labral tears.  They provided great information regarding the anatomy and function, the concepts on the eitiology, clinical characteristics, diagnosis, and treatment of labral tears.  This is an important article to read since labral tears have become more prevalent in the past few decades and surgical management of this disorder continues to progress.  It’s important to fully understand labral tears before attempting to manage a patient’s care.  This article provides the information that can help orthopedic professionals better understand this pathology.  This post will go over some of the key points from the article.  For a deeper understanding please refer the original article.

Acetabular Labrum Anatomy

• Consists of a ring of both fibrocarticlage and connective tissue that is attached to the bony rim of the acetabulum
• Thinner and wider in the anterior region
• Thought to be avascular

Acetabular Labrum Function

Stability

• Increases the stability of the hip joint, thus decreasing the stress through the joint
• Deepens the acetabulum by 21%

Contact Area & Pressure

• Increases the surface area of the acetabulum by approximately 28%
• Increased Contact Area = Distributed Pressure = Decreased Focal Contact Stress
• Provides a sealing mechanism for the joint itself.  This keeps fluid within the articular cartilage, allowing some of the load to be borne by fluid pressurization and preventing direct contact between the femoral head and acetabulum.

Clinical Presentation

Etiology of Labral Injury

Movements such as rotation or twisting, hyperabduction, hyperextension, and hyperextension with lateral rotation have all been reported to lead to labral tears.However, up to 74.1% are not associated with any known or specific causes.  This could be why labral tears often evade detection, resulting in long duration of symptoms (greater than 2 years on average).  It is often thought that repetitive microtrauma may be the cause of the labral lesions in these insidious causes.

Structural Risk Factors

Hip dysplasia is often a significant risk factor in labral tears.  Hip dysplasia can be defined as an abnormality of the femur or acetabulum that results in inadequate containment of the femoral head within the acetabulum.Other structural factors include decrease clearance between the femur and acetabulum, decreased femoral head-neck offset, and acetabular retroversion.  Structural factors can have a significant effect on hip biomechanics and could lead to hip impingement even within a normal ROM.

Common Symptoms

Greater than 90% of the patients report pain in the anterior hip or groin region.  Anterior hip or groin pain is more consistent with anterior labral tear, whereas buttock pain is more consistent with a posterior labral tear.  Mechanical symptoms include clinicking, locking, catching, or giving way.  Clicking was the most diagnostic symptom with 100% sensitivity and 85% specificity.Symptoms usually report a long duration of symptoms (average of > 2yrs).

5 Possible Reasons for Prevalence of Anterior Tears

1. Poor vascular supply compared to other regions, more susceptible to wear and degeneration without the ability for repair
2. Anterior region is subjected to higher forces or greater stresses throughout daily activities
3. Hip joint contact forces are anteriorly directed in the last 20-30% of stance phase of gait
4. Anterior labrum is mechanically weaker than the tissue in other regions of the labrum
5. The anterior orientation of both the acetabulum and femoral head leads to the least bony constraint anteriorly.  So the body relies on the labrum, joint capsule, and ligaments for anterior stability.

Radiographic Diagnosis

Standard magnetic resonance imaging produces both false-positive results and an underestimation of labral pathology and has only a 30% sensitivity and a 36% accuracy.  Whereas magnetic resonance arthrography produces better results, with reported accuracies as high as 91%.

Provocative Tests

There are a wide range of provocative tests that may be attributed to the differences in the location of the tear:

◊ Hip extension alone or combined with medial rotation

◊ Flexion with medial rotation alone or combined with adduction or axial compression

◊ Flexion with lateral rotation

◊ Resisted straight leg raise

Common symptoms elicited for a positive test are sharp pain in the anterior hip or groin (with or without a click)

Anterior Labral Tear

Full flexion, lateral rotation, and full abduction into extended with medial rotation and adduction

Posterior Labral Tear

Extension, abduction and lateral rotation into flexion with medial rotation and adduction

Best Bet

Suspect an acetabular labral tear when a patient with normal radiographs complain of a long duration of anterior hip or groin pain and clicking, pain with passive hip flexion combined with adduction and medial rotation, and pain with active straight leg raise and has minimal to no restriction in ROM.

Treatment

Intervensions should be focused on reducing anteriorly directed forces on the hip by addressing the recruitment patterns of muscles that control hip motion.  Correcting the movement patterns during exercises is very important to intervene the maladaptive compensations that may already be occuring.  For example, patients with an anterior labral tear have the tendency extend their hip with hamstring dominance over the gluteus maximus.  Therefore emphasis should be placed on activating the glut over the hamstring during exercises involving hip extension.  Instructions to avoid loaded pivoting motions should also be emphasized.The overall goal is to optimize the alignment and control of the hip joint.  Controlling the accessory motion (particularly during flexion and lateral rotation) and avoiding excessive forces into the anterior hip joint should make up the majority of the interventions.

Avoid Postures and Maladaptive Motions

• Standing with hip hyperextension (knee hyperextension and/or pelvic posterior tilt)
• Sitting with legs crossed or hips rotated
• Lack of knee flexion at heal-strike and prolonged foot flat during stance
• Walking in hip hyperextension can increase the angular hip flexion impulse, thereby increasing the demands on the anterior hip joint

During Treatment

• Avoid active straight leg (including any type of trunk curl with the hip flexion such as a sit up)
• No recumbent bike
• Any exercise requiring hip extension beyond neutral (prone hip extension)

During active hip extension in the prone position, the femur exerts an anteriorly directed force on the acetabulum once the hip is extended approximately 5 degrees.  This force is even greater on the anterior acetabulum when the hamstrings dominated the motion (as opposed to the gluteus maximus).

Sequelae of Labral Tears

Like most impairments that involve damage to a stabilizing tissue; acetebular labral lesions have been associated with chondral damage and hip osteoarthritis.

Surgery

At the time of this article the authors found that the repaired labrum had the slowest recovery and required a second procedure, whereas excision or debridement of the torn tissue by arthroscopy is the most common and has a more prompt resolution.  However, surgical methods have progressed greatly since this article.  Recently, I have been seeing good clinical results in patients with hip labral repairs with a illiopsoas tenotomy.Of course there are always modifiers of surgical outcome, such as hip dysplasia and osteoarthritis.  In these cases there have been reports of the best surgical outcomes when the torn labrum was excised and a procedure to improve the containment of the femoral head within the acetabulum was performed.

Bottom Line

This article does a great job of correlating the hip joint anatomy, biomechanics, and function with the etiology, diagnosis, and treatment.  Understanding the provocative kinesiology of the labral impairment is necessary in providing an effective treatment.

• Labrum function is for hip stability and distribution of pressure (decreased contact stress)
• Most labral injuries are not associated with any known/specific causes
• Hip dysplasia is a MAJOR risk factor
• Anterior Tears are most common
• ...because of histological and biomechanical reasons
• Examine for groin pain with passive hip flexion, adduction, and medial rotation
• Treatment should focus on optimizing the alignment, avoiding excessive anterior forces, and controlling/stabilizing the hip joint

Dig Deeper

http://thebodymechanic.ca/2011/04/13/a-critique-of-jandas-prone-hip-extension-test/http://www.mikereinold.com/2011/03/femoroacetabular-impingement-etiology-diagnosis-and-treatment-of-fai.html  --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Basic Biomechanics: Pressure

Pressure

Pressure is an important aspect of physical force systems.  It can have a profound affect on the body from both external and internal forces.  The results of pressure depends on many different variables, indluding: the body position, type of external force orientation, and medium through which the force is applied.  Manipulating these variables can help a clinician to use pressure as a therapeutic stress as opposed to a noxious stimuli.

What is Pressure?

Pressure = Force / Area

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object.  It is proportional to force and inversely proportional to area.  

Clinical Application Examples

Manual techniques and soft tissue mobilization is a great example of pressure in clinical practice.  When performing any manual technique always pay attention to the amount of contact area your hands are producing.  A broad surface is much more comfortable for the patient then a pointy finger (increased area to disperse pressure).  As Tom Myer's advises, melt tissues with your finger pads, don't push with your pointy finger tips.Another practical application is with joint surface area contact.  The less joint range of motion, the less the joint surface area contact, the more pressure localized in a focal area.  This may lead to decreased joint lubrication and nutrition, impaired accessory joint motion, and possible accelerated chondral damage.  Studies showing the increase in knee osteoarthritis after a meniscectomy are largely based off of this principle.Osteokinematics are also greatly affected by pressure, especially when a sesamoid bone is involved.  The patella is a great example of this.  The patella facets have a increased surface area in contact with femur as knee flexion increases.  This allows for the forces to disperse over greater area during movements that create high forces (stairs, squatting, etc.).  Towards 20 degrees there is little contact, therefore any force would result in greater pressure.

Bottom Line

Pressure plays a great role in clinical practice with both intrinsic and extrinsic factors.  Keeping this in mind may prevent unwanted noxious stimuli to your patient.

• Pressure = Force / Area
• Pressure can come from intrinsic (osteokinematics, joint surface area contact) and extrinsic factors (manual intervention)
• Integrate this pressure relationship to manual techniques and the details of movement assessment

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Basic Biomechanics: Gravity

Gravity

Gravity is a very important force to consider when dealing with biomechanics.  It is constantly affecting the body in both static and dynamic movement.  It can be looked at as the gravitational downward pull on an object.  Whereas the center of mass is the mean position of matter in a body or system.  Gravity, like all forces, has a point of application, a magnitude, and a direction.The point of application is the center of gravity or center of mass (COG or COM).  This changes relative to how many segments are involved.  For instance, the COG of the forearm alone will be different then the COG of the arm, forearm, and hand.  The magnitude is dependent on the the orientation of the segment in space and is proportional to the mass of the involved segment.  The direction of gravity is commonly referred the line of gravity (LOG).  This direction is always vertically downward towards the center of the earth, regardless of the orientation of the segment/object to space.

Gravity in Biomechanics

Gravity has a profound affect on biomechanics.  The gravitational force acts on the levers of the body to create torque at various body segments and joints.  Thus, it encompasses almost all basic biomechanical concepts when acting on the human body.  We use this knowledge of gravity and anatomy to manipulate muscle positions for manually grading muscle strength, movement analysis, and specific therapeutic interventions.

Center of Gravity within the Body Segments

The COG in the anatomical position is just anterior to the second sacral vertebrae.  However, it’s important to note that COG/COM is conceptual.  It is not a piece of anatomy; it is constantly changing with motion.  With every movement and change of position the COG changes the way joints react and muscles perform.  For example, the picture below shows the how the COG changes when the hip is flexed to 90°.  This brings the COG anteriorly and creates a clockwise torque at the hip joint.  To counteract this moment of torque created by the COG, the contralateral hip extensors must fire to keep the body statically erect.

Center of Gravity Outside the Body

Another consideration is that COG does not have to be a part of the body.  Many exercises and movements cause the body's COG to become displaced outside of the body.  This would create an increase in the lever arm of the resistance force.  Proper lifting mechanics are simply a means of decreasing this lever arm as much as possible.  As seen the figure below, bending forward at the hip causes the COG to actually fall outside of the human body.

Center of Gravity and Stability

Determining the COG and LOG is the beginning of understanding stability.  For an object to have stability the LOG must fall within their base of support (BOS).  This is rarely the case when it comes to human movement.  Many times the LOG falls outside of the BOS and the body must counteract the subsequent torque and moment forces created by this unstable system to achieve functional stability.  The concepts behind stability and functional stability are very detailed and very complex and will be discussed in a future post.  Nonetheless, understanding basic biomechanics and how gravity affects the body will help to understand stability and balance.

Bottom Line

Applying basic biomechanics to gravity will give a better understanding of how postures, movement, and exercises affect the body.  A simple change in position of one extremity can cause a significant change in joint forces, muscle activation patterns, and neuromuscular coordination demands.  Keep this in mind when assessing movements and implementing interventions.

• Gravity is the force that attracts a body toward the earth (downward)
• Center of Gravity/Center of Mass is the point of application of the gravitational force
• The direction of gravity is the Line of Gravity (LOG) and is always perpendicular to the ground
• COG in the anatomical position is just anterior to the second sacral vertebrae
• COG is not a piece of anatomy, it is conceptual and changes with different positions and motion
• COG is relevant to the body segments that are included in the system
• COG may be located outside of the body
• The LOG position relevant to the BOS is the basis for stability

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Basic Biomechanics: Moment Arm & Torque

Moment Arm

The first step of understanding and calculating torque is identifying the moment arm.  The moment arm (lever arm) of a force system is the perpendicular distance from an axis to the line of action of a force.  In other words, moment arm determines the quality of the torque. An important concept to remember is that the moment arm changes with the angle of application of the force (angle of insertion).

Torque

Simply stated, torque is the ability of a force to cause rotation on a lever (moment of force).  The more detailed definition of torque is that it is a force applied over a distance (lever arm) that causes rotation about a fulcrum (axis of rotation).

Torque is Dependent on 3 Variables:

1. Amount of force
2. Angle of application of force
3. Length of the moment arm

To calculate force you must first draw a detailed free-body diagram of the force system, including the all force components.  Then torque can be calculated using on of the following formulas:

• Torque =Lever Arm x Fy (or Force sin())
• Torque = Force (Fm) x Moment Arm

Torque in Biomechanics

Torque is what creates biomechanical movement.  It is what creates the movement of the lever system (bones).  This is important to understand.  Being able to maximize the amount of torque a muscle can generate will allow for optimal strengthening of that muscle.  The greater the torque a muscle can produce, the greater the movement it will produce on the body's levers.  If your goal of treatment is to increase movement, you can manipulate the torque variables to maximize the efficiency of the muscles to move the body part.  The barbell biceps curl exercise provides a great example of this.  It's much harder to move the bar when your elbows are fully extended compared to when they're at 90°.  This is because of the angle-torque relationship.  In this relationship, the greatest amount of torque is always when the force is applied at a 90 degree angle to it's lever.This concept can also be used with the opposite goal in mind.  By adjusting the angle of application and moment arm, you can change the force vector components and increase the amount of compressive force.  Increasing the compressive force is often the goal when attempting to maximize stability.  The rotator cuff demonstrates this type of force vector when the muscles synergistically contract to create a compressive force couple to stabilize the humeral head in the glenoid fossa.When attempting to manipulate torque,  it is important to realize that the joint ROM does not always correlate with the amount of torque a muscle can create.  The angle of insertion is independent of joint ROM.  There are many muscles that cross joints that have many different insertions.  To determine the force vectors (torque and compression) of a muscle, one must evaluate the line of pull in relation to the lever arms and joint axis.A common example of the effect of moment arm and angle of application have on torque is the patella's affect on quadriceps torque.  As you can see below, the patella bone increases the angle of application of the quadriceps tendon and therefore moment arm, thus increasing the amount of torque the quadriceps can create.  Without the patella most of the quadriceps force would create more of a compression/joint stability moment.

Bottom Line

Torque is the driving force for human movement.  Being able to manipulate the target muscle torque will allow for a more specific intervention.

• Moment Arm of a force system is the perpendicular distance from an axis to the line of action of a force.
• Torque is the ability of a force to cause rotation on a lever
• Torque is dependent on the amount of force, angle of application of force, and moment arm
• Joint ROM does not always correlate with the amount of torque a muscle can create
• Greatest Torque/Moment Arm) = Force applied at 90 degree angle to it's lever

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships  --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Basic Biomechanics: Levers

A lever is a rigid object that is used with an axis to either multiply the mechanical force (effort) or resistance force (load) applied to it.  The efficiency of the lever is called mechanical advantage (MA).  The greater the mechanical advantage, the less effort required.  Mechanical advantage can be calculated by dividing the effort arm by the resistance arm (MA = EA/RA).In assessing the efficiency of the lever (mechanical advantage), it is important to identify and quantify the components included in the system.  This can be achieved by calculating the distance between the axis and the where the force acts.

3 Components to a Lever

• Axis (pivot or fulcrum)
• Resistive Load (weight)
• Force (effort)

The location of these 3 components determines the mechanical advantage and the lever class.  It's important not to confuse this with moment and torque, which will be discussed in the next post.

Three Classes of Levers

1st Class Levers

The fulcrum is located between the applied force and the load.  Classic examples are a seesaw or crowbar.Mechanical Advantage = 1 

1st Class Levers in the Human Body

There are very few in the human body.A rare example is the force of the triceps at the olecranon.

2nd Class Levers

The load is situated between the fulcrum and the force.  Therefore the force lever arm would always be greater than the load lever arm.  Classic examples are a wheelbarrow, push-up exercise, or nutcracker.Mechanical Advantage = Greater than 1 

2nd Class Levers in the Human Body

This class commonly occurs in the body when gravity, an external force, and or inertia is the effort force and muscles are the resistance (load).  In this situation the muscle is contracting eccentrically against the force.  Think of an eccentric biceps curl.Another circumstance where this class occurs is when the muscle is acting on its proximal segment while the distal segment is fixed (weight bearing).  The result is movement of the proximal lever.  An example of this type of 2nd class lever is triceps surae lifting the body around the axis of the toes.

3rd Class Levers

The force is applied between the fulcrum and the load.  Therefore the load lever arm is always greater than the force lever arm.  A classic example is a pair of tweezers or a diving board.Mechanical Advantage = Less than 1 

3rd Class Levers in the Human Body

Most muscles in the human body are 3rd class levers and create rotation of the distal segment.  With this type of leverage the muscles would be acting concentrically, as long as the distal lever is free.An example of this type of lever system is the biceps brachii acting concentrically on the forearm.

Mechanical Advantage in Biomechanics

It may seem confusing that most of the muscles in the human body are 3rd class levers, since these levers are at a mechanical disadvantage in terms of effort versus load.  However, this only holds true in terms of resistance.  The opposite is true when you consider the distal lever displacement.  A small arc of motion proximally at the muscle insertion will create large angular displacement and velocity distally.  Since most human movement is aimed at maximizing angular displacement of a distal segment through space, the use of 3rd class levers for is very efficient.This creates a relationship between the lever arm distance, distal angular displacement/velocity, and torque production.  The shorter the lever arm of the effort force (decreased mechanical advantage), the greater angular displacement and angular velocity of the distal end of the lever for a given arc of displacement of the effort force.  The larger the lever arm of the effort force (increased mechanical advantage), the increased torque production.This lever arm and force/torque production relationship needs to be taken into consideration when assessing movement and prescribing interventions.  For example, applying a 5 pound weight at the distal end of a lever during a scaption/SLR exercise creates a mechanical disadvantage for the supraspinatus/illiopsoas.  This results in the muscle being overloaded in attempt to create the amount of torque necessary for the distal angular displacement.

Bottom Line

Understanding lever systems are a very important part of biomechanics.  It helps to conceptualize the amount of effort force required for movement and also can determine the efficiency of static and dynamic positions.  Once you determine the lever arm system, you can then begin to quantify moment and torque.

• A lever is an object that can multiply mechanical force (effort) or resistance force (load)
• Lever arm is the distance from the axis of rotation to the line of action of the force
• Mechanical Advantage is the efficiency of the lever system (MA=EA/RA)
• 1st Class Lever = fulcrum is located between the applied force and the load
• 2nd Class Lever = load is situated between the fulcrum and the force
• 3rd Class Lever = force is applied between the fulcrum and the load
• Lever System Assessment - Define lever system, identify lever arms (effort & load), determine lever class, calculate mechanical advantage
• Biomechanical Application - manipulate the lever arms to either increase or decrease mechanical advantage, depending on the therapeutic intention

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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