This is a preview of an article appearing on Dynamic Fitness Coach [next Monday]. Let me know what you think!
Walk a Mile, Buddy-A Look at Knee Pain
By Jordan Feigenbaum MS*, CSCS, HFS
You might know the feeling yourself and you most likely have someone close to you that is familiar with it- knee pain- in all its glory and annoyance. Recently I’ve compiled a journal club presentation on the anatomical and functional characteristics of the anterior leg compartment in humans, or the quadriceps in short. Journal club is a meeting of academic minds to discuss current scientific literature relative to the department hosting the event and I happened to be up to bat this time. I wanted to find a paper that was both relevant (to the anatomy department) and interesting (clinical implications), so I dug up the following article:
Prevalance and Morphology of the Vastus Medialis Oblique Muscle
in Human Cadavers
The Anatomical Record 1997 249:135-142
John K. Hubbard, * H. Wayne Sampson, and Jerry R. Elledge
Department of Human Anatomy and Neurobiology, School of Medicine,
Texas A&M University, College Station, Texas
In putting together a presentation to educate the faculty and students on the peccadilloes of the vastus medialis oblique I ended up doing a fairly intensive literature review on patellofemoral pain syndrome (PFPS), or knee pain in general. This inspired me to pen this article because I was simply astounded by what is actually known and accepted in the medical field for causative agents of knee pain and furthermore, what the recommended treatments are. If you have ever had knee pain or are worried that you might be developing some knee issues (ie- runners) then this article is for you.
In this article I will (briefly) cover the anatomy of the lower limb, currently accepted causes of PFPS, currently accepted treatments of PFPS, and then circle the wagon back around to offer a (perhaps) more practical recommendation to avoid or ameliorate knee pain. To begin, let’s talk about the anatomy of the lower extremity.
Anatomy of the Leg
In anatomy there are a few basic conventions that need to be understood before we go down this rabbit hole. Muscles (skeletal) connect a bone across a joint or joints to another bone. By contracting, the muscle brings its sites of attachment closer to each other. Similarly, when a muscle relaxes its sites of attachment move further away from each other. The sites of attachment for a muscle are known as its origin and insertion. Classically, the origin is relatively stationary and immobile, whereas the insertion moves towards the origin upon contraction of the muscle. The insertion tends to be less extensive than the origin; that is the origin has a more substantial connection the bone it connects to than the insertion. Tendons connect muscles to bone (and ligaments connect bone to bone) and thus there are tendinous connections of each muscle to its origin and insertion. To be considered a separate and unique entity, each muscle must meet the following requirements:
1) have a distinct origin and insertion
2) have a distinct innervation (nerve supply)
a) this allows it to be stimulated and contracted independently of another muscle
3) have a fascial tissue sheath (epimysium covering the muscle) that separates it from other muscles and allows free movement of the individual muscle
4) has a distinct function/action- i.e. its agonist movement that is opposed by an antagonistic movement
a)ex. the biceps brachii flexes the shoulder, elbow, and supinates the forearm (its agonist movements) and is opposed by the triceps brachii with respect to the shoulder and elbow joints as its functions are to extend the elbow and shoulder. So in elbow flexion the biceps is the agonist and the triceps is the antagonist.
*Definition taken from Grant’s Method of Anatomy (Basmajian, 1980)
The currently accepted treatment for PFPS and many other forms of knee pain mainly focuses around strengthening the quadriceps muscle group. As such we will describe that muscle group here and expound upon their specific actions.
In the anterior compartment there are four major muscles comprising a single muscular group, the quadriceps. The quadriceps is made up of the (from lateral to medial) vastus lateralis, rectus femoris, vastus intermedius (lies underneath the rectus femoris), and vastus medialis. In general, these muscle’s tendons insert into the quadriceps tendon, which the patella resides in, and continues on to the patellar ligament, which connects the quadriceps tendon and patella to the tibial tuberosity on the tibia-below the knee joint. The three vasti muscles (lateralis, intermedius, and medialis) all have an origin from the femur near the hip. When these muscle contract (shorten) they exert a force on the quadriceps tendon, which acts on the patella, and finally acts on the patellar ligament (connecting the patella to the tibia- which is bone to bone- and thus dubbed a “ligament”) which causes the knee joint to be extended (straightening of the leg at the knee joint). The rectus femoris is the only muscle in this group that also crosses the hip joint, as its origin is from the hip-bone (anterior inferior iliac spine). In addition to extending the knee joint via the quadriceps tendon, it also flexes the hip, which may become important later on. In short- the quadriceps muscles are split into four separate muscles and they chiefly extend the knee.
The above actions of the quadriceps on the knee can be considered gross actions, in that they are large scale. Some of these muscles also exert more subtle actions on the patella itself. A landmark study published in The Journal of Bone and Joint Surgery in 1968 describes the following characteristics of the individual muscles of the quadriceps:
1) The vastus intermedius acting alone was the most efficient extensor [of the knee]. A 12% greater mean force was required by each of the other single long heads [of the quadriceps] to complete the same motion.
2) When various combinations of tendons [of the quadriceps muscles] were tested, the total force requirement for each combination [to extend the knee] was very close to that for the vastus intermedius alone.
3) No extension of the knee could be accomplished by applying weight only to the vastus medialis oblique tendon. In fact the femur was fractured in each case before any extension was accomplished.
*bold, italics, and [comments] are mine
So what we’ve learned initially about the quadriceps is that the vastus intermedius is likely the most powerful extensor of the knee, whereas the other muscles likely play a role in patellar positioning. This paper goes on to say:
1) During the earlier tests, marked lateral patellar subluxation was noted when the vastus lateralis was loaded singly, particularly in the range from 90 degrees to 60 degrees. Subluxation was minimal when loads where applied to either the long or the oblique portions of the vastus medialis.
2) Maitenance of patellar alignment as a function of the vastus medialis oblique thus seemed most significant in relation to the efficiency of the vastus lateralis.
3) The findings in this study suggest that early atrophy of the vastus-medialis prominence and loss of terminal knee extension are indicative of general quadriceps weakness rather than of a deficiency localized to the medialis.
This paper has been cited over 350 times (a lot for a research paper in anatomy) and has led clinicians and other health professionals to the conclusion that the vastus medialis/vastus medialis oblique prevents subluxation (lateral displacement/dislocation) of the patella as caused by the vastus lateralis. Other research has implicated the illiotibial (IT) band as a misaligning lateral force that is countered by the force of the vastus medialis. As you’ll see in the next section the current recommendations for PFPS involve strengthening the quadriceps, specifically the vastus medialis oblique (VMO) even though this paper concluded it wasn’t the medialis by itself, but rather a general quadriceps weakness. I’ll put out another proposal here, what if it’s just general weakness and deconditioning of which the quadriceps are surely implicated (if it’s general it’s everything). I’ll save my interpretation until the end, however.