The Cohen Index is a quick way to assess your athlete’s lower extremity and to evaluate the likelihood of developing an overuse injury. The Cohen Index can also assess whether the athlete’s biomechanics are preventing them from achieving their maximum athletic performance.
The Cohen Index is based on 10 factors. Each of these factors is given a point for an abnormal finding. There are 10 possible points. The more points your athlete scores the more likely he/she is at risk for an injury.
The factors include:
- Limb length discrepancy (LLD)
- Thigh position and flexibility.
- Frontal plane knee position.
- Sagital plane knee position.
- Ankle position and range of motion.
- Subtalar joint range of motion.
- Heel position in stance
- Forefoot to rear foot position.
- First metatarsal phalangeal joint range of motion.
- Normal or abnormal gait analysis.
Factor 1 – Limb Length Discrepancy (LLD)
Limb length discrepancy is divided into functional and structural categories and is a common cause of injury. Limb length discrepancy can pre dispose an athlete to a range of injuries from plantar fascitiis to the development of sciatica
LLD is a difficult assessment to make simply because LLD can be a structural or functional or both. Therefore, this evaluation is simply to assess whether LLD possibly exists.
Evaluating an LLD involves a visual inspection and palpation of the Anterior Superior Iliac Spine (ASIS). It is a weight bearing assessment involving the placement of your thumbs on the most prominent areas of the ASIS right and left then visually evaluate whether your thumbs are level or not.
Another way to evaluate the ASIS levels is to place the athlete in the supine position, check the height of the medial malleolus by placing your thumbs on the highest prominent point of the medial malleolus and the higher or lower of the medial malleolus. You may also feel comfortable using a tape measure evaluation weight bearing and non-weight bearing.
You may also decide to use the Allis Test to help you in your evaluation.
Shoulder unleveling as well as hip unleveling and scoliosis present can tip you off to the possibility of LLD.
A unilateral flat foot deformity can also signal the possibility of LLD. The long side usually appears to be more pronated than the shorter side.
For further evaluation and a more in depth study the most accurate assessment is a scanogram. This is a weight bearing radiological study which can determine the actual bone length without the imposition of soft tissue.
In the case of suspected limb length discrepancy LLD one point is assigned. If there is no suspicion of a LLD, no points are assigned.
Factor 2 – Thigh Examination, Hamstring, Range of Motion
Possible factors related to limited range of motion of the hamstrings include 1. Back pain which can lead to tension of the hamstring and gluteal muscles. 2. Poor posture with limited movements within the knee, chest and shoulders can restrict the mobility of the spine and increase further tension to the hip flexors (the cilis muscle). 3. Lack of stretching, improper or not enough stretching during physical activity and after physical activity will allow muscles to contract and restrict normal ranges of motion. 4. Other inhibiting conditions may be an old injury that was not completely rehabed or arthritic conditions which may be present.
Although historically the range of motion was considered to by 90 degrees of straight leg extension, recent studies have shown that that range has decreased dramatically. It is now believed that normal range of motion of the hamstring is closer to 45 degrees or greater.
This assessment is made by having the athlete lie supine on examination table, raising each leg individually making sure that the opposite knee is in the extended position.
The measurement is made at the highest angle that the athlete can raise the leg without discomfort.
Another way to assess the hamstring range of motion is to visually examine the athlete from the side both right and left to see whether the athlete’s stands with a bent knee. If they do this is a good indicator of tight hamstring.
If your assessment reveals tight hamstrings (less than 45 degrees or bent knees while standing) one point is assigned.
Factor 3 – Frontal Plane Assessment of the Knee
The frontal plane assessment of the knee is made primarily through the measurement of the “Q” angle. The “Q” angle represents the relationship and alignment between the pelvis, leg and foot.
A normal “Q” angle is between 18-22 degrees with males being at the lower end of the scale. An increased “Q” angle can lead to patellar tracking disorders, low back disorders, leg and foot problems. It also is responsible for preloading condition of the ACL or the Anterior Crucient Ligament. Therefore, it is a pre disposition for ACL rupture.
This angle measurement is very important when dealing with cleated athletes.
Elevated “Q” angles receive 1 point on the Cohen Index. Normal “Q” angles receive no points.
Factor 4 – Knee Position Sagital Plane
Genu recurvatum is a common problem that may have negative consequences to knee structures.
Defined as knee extension greater than 5 degrees, individuals who exhibit genu recurvatum may experience knee pain, display an extension gait pattern and have poor control of terminal knee extension.
Genu recurvatum can be responsible for anterior knee pain, patellar subluxation and add to the complication of normal patellar tracking.
It is also associated with ankle equinus, tight gastrocnemius as well as ligamentous laxity.
We visualize genu recurvatum from the side view both right and left to see if the athlete stands with a back knee configuration.
If your athlete presents with genu recurvatum assign one point on the Cohen Index.
Factor 5 – Ankle Range of Motion
The ankle joint must dorsiflex with the knee extended and the foot in neutral position a minimum of 10 degrees (with the knee in extended position) to be considered within the normal range of motion. This is determined through non-weight bearing examination.
Some studies show that non-weight bearing exam may not be as accurate as the weight bearing exam. Other studies show that 25 degrees of dorsiflexion is needed for normal running rather than the 10 degree value generally considered.
In our office we continue to use the 10 degree minimum as we feel that almost every athlete can benefit with the use of additional calf and posterior muscle group stretching.
This 10 degree motion is just prior to heel lift as the leg moves forward over the foot.
A myriad of foot, ankle and leg morphology from stress syndromes of the metatarsals to posterior ankle impingement syndrome to leg, knee, hip and low back posture symptoms can be caused by lack of normal ankle dorsiflexion.
Therefore, if ankle dorsiflexion is not a minimum of 10 degrees with the knee extended assign one point on the Cohen Index. If you find that you have normal ranges of motion no points are assigned.
Factor 6 – The Subtalar Joint
The subtalar joint is a tri-plane motion joint. It has almost equal frontal plane motion (calcaneus inversion and eversion) as it does transverse plane motion (abduction and adduction) with only limited dorsiflexion and plantarflexion (sagital plane motion).
The subtalar joint is responsible for converting transverse plane motion into frontal plane heel motions. Properly functional subtalar joints (STJ) need a minimum of 4 degrees pronation for the individual to remain injury free. This 4 degrees of pronation is measured from the subtalar joint neutral position. The normal supination range of motion from the neutral position is 12 degrees.
Some studies show this ratio to be lower than this 3:1 and show it more to be a 2:1 ratio. This 2:1 means twice as much inversion and eversion instead of three times as much inversion and eversion.
Subtalar joint pronation is the body primary shock absorbing mechanism. Without normal pronation the shock absorption factor is high and can cause injury all along the kinetic chain.
We examined the subtalar joint by grasping the heel with one hand and using the other hand to invert the foot and evert the foot with the patient in the proned position.
We would like to see the ratio of inversion to eversion at approximately 2:1 in the favor of inversion. We also want to see a symmetrical range of motion right to left. Than by viewing the posterior aspect of the calcaneus with the athlete standing, we want to see whether the heel position is inverted, everted or neutral. If your athlete is in normal range of motion and a normal heel perpendicular position you can usually see that this position is normal position and will not cause the athlete any major difficulties.
If the range of motion is limited in the either direction, either inversion or eversion and you see the heel position is either overly inverted or everted in weight bearing than you would assign one point for the Cohen Index on your examination.
Factor 7 – Heel Position in Stance
This is one of the most important factors of the Cohen Index. It is also one of the easiest to view.
With your athlete standing, with their body to you in shorts and shoes and socks off, visualize the posterior aspect of their heels.
An inverted or everted heel is typically demonstrative of an abnormal foot type.
Inverted heels can be seen in uncompensated or partially compensated rearfoot varus, rigid forefoot valgus, or as compensation if it is unilateral for a short limb. It may be normal for a rigid cavus foot or rigid plantarflexed first ray, however it is still an abnormal foot type prone to injury.
An everted calcaneus can be seen in the following clinical situations. In a partially or fully compensated forefoot varus, forefoot supinatus, a compensated congenital gastrocnemius equinus, a compensated transverse plane pronation conductor, ankle valgus, peroneal spastic flatfoot, rigid vertical talus or as a compensation for a LLD on the long limb side (unilateral everted heel).
A vertical calcaneus is considered a normal position for the calcaneus in static stance. There may be some abnormal foot type or a vertical calcaneus such as compensated rearfoot varus, uncompensated forefoot varus or a flexible forefoot valgus.
Although they show up with a normal appearing calcaneal position, they will be penalized in other parts of the index exam.
One point is assigned to any inverted or everted position of the heel.
Factor 8 – Forefoot Position
One of the most important criteria in the description of normal foot is that the forefoot be parallel to the rear foot. This allows for normal forward progression of the body with the least amount of muscle energy expended.
Abnormal forefoot to rear foot positions not only cause overuse muscle, but actually causes muscles to work out of phase which then causes other muscles to overwork.
This leads to instability in gait and abnormal muscle use.
As a result we see a higher preponderance of shin splints, tendonitis, plantar fascitiis in these foot types.
The forefoot to rear foot measurement is taken with the individual prone, one leg crossed over the other with the foot maintained in its neutral position. With one arm of a tractograph placed parallel to the plantar forefoot while the other arm of a tractograph is resting perpendicular to the calcaneal bi-section. Any angle measured either inverted or everted is abnormal.
It is not uncommon to see a plantarflexion deformity of the first ray while doing these measurements. This may be flexible or it may be a rigid deformity. Either of these positions is abnormal.
Assign one point to any measurement either inverted or everted that appears on the forefoot or if you note the plantarflexion deformity of a first ray.
Factor 9 – First Metatarsal Phalangeal Joint Range of Motion
As you know the first metatarsal phalangeal joint (MPJ) must have a normal range of motion for normal progression of the body’s weight forward. You also know that 60% of the weight goes thru the first metatarsal phalangeal joint in normal propulsion. Therefore, the first metatarsal phalangeal joint range of motion is usually considered 65 degrees dorsiflexion with 35 degrees plantarflexion.
Although 65 degrees of dorsiflexion is necessary for idea propulsion, as little as 40 degrees hallux dorsiflexion will still allow the foot to move through the early stages of propulsion without injury. If there is limited range of motion, the individual may terminate the propulsion by prematurely flexing the hip or knee, or by shifting their weight off of the first metatarsal phalangeal joint laterally to second and third metatarsal phalangeal joints causing injury by overuse to these areas. It is not uncommon to have first metatarsal phalangeal joint pain, second metatarsal or third metatarsal phalangeal joint pain with stress reaction or stress fracture of the metatarsals. You may develop nerve pain or interdigital neuritis or neuroma in these areas as well.
Retro grade forces due to lack of motion in this joint may radiate proximally into the extremity and cause pain anywhere up the kinetic chain.
Assign one point to any measurement of the first metatarsal phalangeal joint range of motion less than 40 degrees of dorsiflexion. There are no points assigned to limitation of plantarflexion as in most running activities the plantarflexion range of motion is not used.
Factor 10 – Basic Gait Analysis
Observe your athlete in a 15′ walk back and forth approximately 10-15 times. Observe basic excess pronation or excess supination.
Observation of a medial heel whip, early heel lift or any of these abnormalities assign the athlete one point for gait analysis. Any abnormality either in a scissor type gait, antalgic gait or limp the athlete demonstrates is also assigned one point.
Biomechanical Normalcy of the Foot and Ankle
1. The mid foot must be stabilized in sagital plane as heel lift so you can have stable active propulsion.
2. The forefoot must make full contact on the ground at mid stance.
3. The forefoot must be stable and does not have any insolence of inversion or eversion on the rear foot which affects the forefoot landing parallel to the ground.
4. 60% of the forefoot load is on the first metatarsal and heel lift because the first metatarsal is thicker and designed to handle this.
5. The first metatarsal phalangeal joint is not limited in dorsiflexion so we can go directly off the first metatarsal phalangeal joint straight ahead in a propulsive gait.
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For that reason, if you wear a wide variety of shoes, you may need to purchase multiple pairs of insoles. A dress shoe insole can not function as a sports insole and a work shoe insole may also not be appropriate for your other activities.
We will discuss what is best for you during your follow-up visits. Once again congratulations and now let’s get started.
/1 1. LLD Functional Structural Both
/1 2. Hamstring Flexibility Abnormal
R L Normal
/1 3.Genu Valgum Genu Varum Genu Varum
/1 4. Genu Recuvatum Yes
R L No
/1 5. Ankle Dorsiflexion Abnormal
R L Normal
/1 6. STJ Rom 2: 1 Equal
INV EV Symmetrical
INV EV R L
/1 7. Rearfoot Position Neutral Inv. Ever.
/1 8. Forefoot Position F.F Valgus
F.F Varus F.F Supinatus
P.F 1st Ray Other
/1 9. 1st MPJ ROM Limited
R L Normal
10. Gait Abnormal Normal
Dr. Lee S. Cohen and Associates