There are so many ways to measure the achilles tendon and I will only show the one method that I have used over the years. I think most methods are fine, so changing is not necessary unless you do not find the three types of presentations consistently. By this I mean, you find patients with normal flexibility, patients that are tight (equinus), and patients that are super flexible (hypermobile). Dr. Merton Root taught my Podiatry class that in his hands 1/3 of patients had normal flexibility, 1/3 of patients were tight, and 1/3 of patients had some hypermobility issues. This is my experience also, so if the next 10 patients whom I measure the achilles tendon for flexibility, I will find some that are normal, some that are tight, and some that are over flexible. You can also have patients that are tight in the gastrocnemius, but too flexible in the soleus, or tight on the right side and not on the left for example. So, you really need to be consistent in whatever method you utilize, which is typically the method that you were taught in your training. Here is the place for your numbers after measuring.
AJDF
(Right) straight knee______ bent knee________
(Left) straight knee______ bent knee_______
Image 1: Our landmarks from head of fibula to lateral side of foot
Image 2: A tractograph/goniometer is used to measure the bend of the ankle while a slight loading of the first metatarsal head ensures that the subtalar joint does not pronate. The patient will assist the dorsiflexion motion actively while you push the ankle passively.
Image 3: The bent knee position is easier to see your landmarks. Again subtalar joint neutral with slight loading of the first metatarsal head plantarly. The patient is asked to help actively dorsiflex their ankle while you are moving the joint passively.
My students at Samuel Merritt’s College of Podiatry are taught to measure consistently to be able to see changes during treatment. Therefore, if you find tightness, a stretching exercise(s) are prescribed and then followed for improvement in the visits that follow. If you find over-flexibility, stretching exercises would make matters worse, and the patient is advised only to work on their strength for that muscle. A typical force length (tension length) curve for the achilles looks like the one below. It is based on the concept that every muscle/tendon complex has an ideal length for the neuromuscular activity. That ideal length is the resting length or normal physiological length. This is where the actin and myosin can produce the best contraction. When a muscle is too tight, aka muscle bound, the power produced by the muscle is weakened the tighter it gets. The opposite is true when the muscle is too flexible, aka hypermobility, the longer the muscle, the weaker it gets. Therefore, the further away from the Resting Length, on either side of the curve, the weaker that muscle is to have a great contraction when asked by an activity. If it is functioning weaker, it fatigues easier, and strains easier. This produces pain in the muscle/tendon complex.
Yet, the problems do not stop there. A tight or weak muscle can also cause all sorts of problems due to compensations. The two easiest to explain are 1) any weak muscle can force other muscles around to work harder than normal to share more load for a movement, and 2) any weak muscle that does not do its normal activity can force compensatory motions. A tight achilles is known to force too much plantargrade force on the metatarsals, too much subtalar joint pronation, and occasionally knee hyper-extension. We know of the myriad of problems these can produce. Thus, finding and correcting a tight achilles makes for good treatment of a variety of problems. A weak achilles causes all the other ankle plantarflexors to work harder as we need to push off. Therefore, patients can present with tendonitis of the post tib, too long flexors, or the two peroneals, with the root of the problem being a weak achilles. The body can not tolerate any weakness of the achilles, when doing normal activities, without a problem developing somewhere. Therefore, the measurement of achilles tendon flexibility, with the ability to find both tendons that are tight and hypermobile, is crucial to the understanding of a patient’s lower extremity biomechanics.
So, back to the measurements. The normal range of motion of ankle joint dorsiflexion is 8-12 degrees with the knee straight, and 15-18 with the knee bent. You have to measure both as one can be normal and the other hypermobile, or one tight and the other loose, etc. Next week, before I will move on to achilles strength, I will go over principles of stretching and the desired stretches for the gastrocnemius and soleus muscles.
