Knee Flashcards
What is considered in the calculation of PCSA?
PCSA = sum of cross sections of all the muscle fibers within a muscle and thus represents the force producing capabilities of a muscle.
PCSA takes into consideration the mass of the muscle (higher mass, more fibers), the pennation angle (how much force is transmitted to the tendon), the fiber length, and the density (constant for human skeletal muscle)
PCSA is directly proportional to maximal muscle froce. Compare that of a parallel muscle to a pennate muscle. Describe the pros and cons of pennation angle in a pennated mm.
Parallel muscle: CSA (perendicular cut through mm belly) = how many mm fibers are parallel to one another. If each fiber can produce a certain amount of force, the more side-by-side fibers = more force production.
Pennate muscle: CSA does not represnt # of fibers in that section (b/c must be perpendicular cut to fibers) ex. Soleus. Even though a pennation angle reduces the amount of force transmitted to a tendon, there is an increase in the number of fibers you can pack into a muscle.
PCSA takes into account the additional fibers in a pennate muscle without overestimating their contribution to force production. (Gives us a true understanding of the cross sections of all muscle fibers in the muscle)
Muscle fiber length is directly proportional to muscle excursion and velocity. Why?
Longer mm fiber = more sarcomeres in series as compared to a shorter mm fiber
Longer mm fibers can have greater excursion and maximal shortening velocity.
Ex. 5 sarcomeres shortening in 1 second = 5 mm/second
vs.
10 sarcomeres shortening in 1 second = 10 mm/second
Draw and describe the length-tension relationship.
There is an optimal length of the sarcomeres that allows for maximal force production (due to optimal cross bridging). As sarcomeres shorten and lengthen from this point, force production decreases.
Length-tension relationship can also describe mm length and joint angle. While there is an optimal muscle length and joint angle for each muscle/joint, this varies throughout the body and is dependent upon mm architecture and joint structure.
Draw the length-tension relationship for a muscle with a large PCSA. Why does the curve look this way?
Muscle with a large PCSA has greater force producing capabilities.
Assuming fiber length remains constant, it has the same range of mm length it operates through with an increase in max force capabilities.
Draw the length-tension relationship of a muscle with a long fiber length. Why does the curve look this way?
Longer muscle has more sacromeres in series. It can produce the same amount of force (no increase in PCSA); however, due to longer length it can work through a greater range and peak force occurs at a longer length.
Draw and describe the force-velocity curve.
As velocity of contraction increases, concentric mm force decreases. Peak force production (in isometric/concentric point of curve), occurs during an isometric contraction.
Draw and describe the force-velocity curve of a muscle with a large PCSA. Why does the curve look this way?
Maximal force increases because PCSA increases; maximal velocity is the same though because there is no change in fiber length.
Draw the force-velocity curve of a muscle with a long fiber length. Why does the curve look this way?
Sarcomeres added in series allow for a great contraction velocity of the muscle. With no PCSA increase, maximal tension (max force production) does not change.
Due to the increased number of sarcomeres in eries, for each given velocity, the mm can produce more force as the sarcomeres shorten at a slower rate than a short muscle. This is a more favlorable force-velocity relationship.
Draw the length-tension relationship for the Sartorius (orange) and Vastus Lateralis (blue). Describe.
Sartorius (orange): long fiber length and low PCSA = less maximal force, but produces force through a larger range than the Vastus Lateralis (blue; higher PCSA, shorter fiber length).
Draw the force-velocity curve for the Sartorius (orange) and Vastus Lateralis (blue). Describe.
Sartorius (orange): Longer fiber length allows force production at higher velocities and thus has a greater maximal contraction velocity. Lower PCSA of sartorius limits its max force production capabilities.
Vastus Lateralis (blue): larger PCSA allows for greater isometric force production, but short fiber length limits the ability of the muscle to produce force at high contraction velocities.
What is the “big picture” of muscle architecture/Why is it important to understand?
Muscle architecture highly relates to muscle function. A muscle like the Vastus Lateralis can produce a lot of force, but the Sartorius allows for more excursion.
Important for muscles to work together at a joint. Muscles can work together to optimize movement; we don’t limit our joint capabilities in a movement (can have force and velocity). Ex. Hip Flexion
Observe and distinguish the differences between MCL and LCL.
Collateral ligaments: stabilizers for side-to-side stability of the joint. Limit excessive knee motion in the frontal plane.
MCL: Broader ligament made of 2 ligament structures (deep and superficial).
LCL: Distinct cord-like structure.
Relatively taut in full extension (posterior to the medial-lateral axis of rotation)
How would you test the integrity of the MCL and LCL?
MCL: Valgus stress test at full extension and 30˚ (open-packed position).
LCL: Varus stres at full extension and 30˚ (open-packed position).
*More provocative at open-packed position (isolates ligaments, knee not stabilized by PCL and bony articulations)
What translation does the ACL control? What special test tests ACL integrity? Does the rotation of the tibia have an effect on ACL laxity?
ACL controls anterior translation of the tibia on the femur.
Lachman’s test will demonstrate excessive anterior tibial translation compared to normal side.
Describe how tibial IR and tibial ER affects the ACL.
Tibial IR: As tibia translates forward, ACL becomes taut. ACL also becomes taut with IR of tibia on femur due to orientation of ACL (anterior intercondylar area of tibial plateau to medial side of lateral femoral condyle). ACL twists around PCL to be further stretched during tibial IR.
Tibial ER: Clips ACL against sharp edge of the lateral femoral condyle.
ACL may be injured with forceful or excessive tibial IR or ER, valgus stress or hyperextension at knee.
Describe ACL orientation and structure.
Where does its blood supply come from?
What is the primary function?
ACL runs from the medial wall of the lateral femoral condyle in the intercondylar notch to the tibial plateau where it attaches in front of the intercondylar eminence and blends with the anterior horn of the medial meniscus.
Two bundles: (1) anteromedial = taut in flexion; (2) posterolateral (more important) = taut in extension
Blood supply comes from the geniculate artery.
*Likely plays a role in providing proprioceptive information.
Primary function is to control anterior translation of the tibia. Secondary restraint to tibial rotation and valgus/varus stresses.
ACL Clinical Presentation. What is the most common mechanism? Describe non-contact versus contact mechanisms. What is the unhappy triad?
Most common mechanism: Noncontact during athletic activity
Non-contact Mechanism: Running or jumping athlete who suddenly decelerates and changes directions or pivots in a way that involves rotation or lateral bending of the knee
Contact Mechanism: Usually occur from a direct blow causing hyperextension or valgus stress. (*NFL players when players foot is planted and an opponent strikes him on the lateral spect of the planted leg.
Unhappy Triad: Medial meniscus, MCL, ACL
Describe the screw home mechanism. What factors contribute to this mechanism?
Screw home mechanism: external rotation of the tibia relative to the femur (OKC) or internal rotation of the femur relative to the tibia (CKC) when the joint is approaching full extension (final 30˚).
Screw mechanism driven by three factors: shape of the medial femoral condyle, passive tension in the ACL, and the lateral pull of the quads.
What is pennation angle? What is the benefit of having a pennation angle?
Pennation angle is defined as the acute angle between the direction of the mm fibers and the central tendon line of pull.
Benefit of having a pennation angle: allows for packing more mm contractile proteins in parallel - leading to greater force generating ability.
Compared to parallel muscle, with the same mass and density, a pennate muscle has a larger PCSA. Can therefore generate more force compared to a parallel muscle.
What is the effect of the vertical component of the VL and VMO on the knee joint?
The vertical component of the VL and VMO contribute to knee extension as well as patellar superior translation and compression.
What is the effect of the horizontal component of the VL and VMO on the knee joint?
Horizontal component of VL : patella lateral translation
Horizontal component of VMO: patella medial translation
Describe where the infrapatellar tendon runs, where it is palpable, and the common site of pathology and lesion.
The infrapatellar tendon runs from the inferior border of the patella.
It is palpable along its length at the insertion at the tibial tubercle.
Common site of pathology is at the inferior pole of the patella.
Lesion is often located posteriorly.
Skill: Tibial Nerve Bowstring
Tibial nerve is palpated as it courses through the popliteal fossa by perfroming a bowstring maneuver.
Hip and knee flexed to 90. Distal LE can be placed on examiner’s shoulder. Therapist palpates (with thumbs in horizontal fashion) medial aspect of popliteal fossa for popliteal artery pulse and tibial nerve.
Bowstring maneuver completed as therapist extends the knee and feels resistance from tibial nerve as it comes into therapist’s thumb.
Positive test: if radicular symptoms are reproduced.
Intervention: Iliopsoas stretch (prone)
Patient prone. Uninvolved LE off table with foot supported. May need to use wedge under patient heel for comfort. Patient’s hip positioned so that table “crack” matches up with hip to be stretched.
Pre-position trunk in contralateral SB to increase stretch. Use a mobility belt to stabilize patient’s pelvis and prevent them from coming out of SB.
Place involved hip into IR (from knee or femur, patient comfort)
PT cranial forearm: ensure hip is maintained against table and keeps femur in IR.
PT caudal arm: initiating contract-relax technique for further extension. Conclude contract-relax by having pt. contract glute max.
