Patient Presentation | Hyperextension

To select the most effective brace for a patient, many variables must be considered. To help in this process at Cascade we have defined seven patient groupings, based on the foot, ankle and knee presentations most often seen in our patients. Within each group, we defined the range of severity that is likely within that group, then matched each of these presentations to an appropriate brace design. Directly associating a brace design or bracing strategy with a defined patient presentation has worked well, both in theory and in practice.

We have used our grouping system, with the understanding that, while not perfect, it is a reasonable (and clinician friendly) way of presenting the brace selection process. In this issue we will look at hyperextension. You can visit our website to see detailed information about all seven identified patient groupings. We have also produced a poster, which can be folded and carried to appointments. It demonstrates this approach and has easy to use reference information for helping make a brace selection. You can request a free poster from our website www.cascadedafo.com, or by calling 1-800-848-7332.

Hyperextension

Chronic hyperextension of the knee is usually the result of one of two causes. Patients with weakness in the muscles that control the knee (quadriceps femoris) may hyperextend their knees to improve stability in stance and gait. For patients with chronic high tone contractures of the calf muscles (similar to those that result in toe walking in some patients), the excess ankle plantarflexion that is generated can drive the knee back into hyperextension, or into a combination of toe walking and hyperextension.

An assessment of the patient’s muscle tone, level of voluntary control, and range of movement of the entire kinetic chain is required to determine the factors leading to hyperextension. Knowing all the underlying causes, which are important in developing a bracing strategy, may take considerable time to fully ascertain. The severity of the hyperextension can be gauged based on several factors:

• Mild Hyperextension: can be voluntarily corrected; is inconsistent or irregular; and/or little or no force is imparted to the knee joint.
• Moderate Hyperextension: is difficult to voluntarily correct; might be inconsistent but occurs frequently and/or moderate force is imparted to the knee joint.
• Severe Hyperextension: cannot be voluntarily corrected; is consistent and/or imparts considerable force to the knee.

Some simple testing will help quickly determine the patient’s level of voluntary control, how much postural improvement is possible, and whether DAFO / AFO bracing will be effective. Here are two common assessment techniques:

• Method 1: With the patient standing and holding on to something secure (or being held securely by someone else), attempt to correct the hyperextended posture by gently pushing on the back side of the patient’s knees. Repeat until you have a good sense of how much correction is possible for each limb and how much resistance there is to the correction.

• Method 2: With the patient standing, ask them to bend their knees and stay in a crouched position for as long as they are able. This will help determine if sufficient voluntary control and/or strength is present to move out of the hyperextended position and into a controlled crouched posture without collapsing.

Hyperextension Due to Weakness

The very mildest form of hyperextension, also discussed in the “Inconsistent Ankle Modulation” section of the Cascade patient groups on www.cascadedafo.com, may only require a proprioceptive reminder of ankle position. The DAFO 4 with a posterior strap works well for this task.

If the patient’s hyperextension is a result of muscle weakness, an assessment of the patient’s level of strength is required to determine the positional correction that will be possible. In mild cases, the patient will have adequate strength and voluntary control to maintain a slightly flexed knee position without assistance for some period of time. The stability of the hyperextended knee has probably become habitual. With a suitable level of brace control, resisting or preventing ankle plantarflexion will encourage the knee to remain slightly flexed and will force the patient to develop the additional strength and control required to maintain stability without hyperextension.

Limiting hyperextension by resisting ankle plantarflexion can be achieved with the DAFO 3.5 (DF Resist; PF Resist). The DAFO 3 provides full PF block with free dorsiflexion in a simple one-piece design. The DAFO 2 also provides full PF block and free dorsiflexion in a hinged design that offers additional medial-lateral support.

As the severity of muscle weakness increases, the patient’s ability to maintain a flexed knee position without assistance decreases. If the patient does not have adequate strength or control, moving the knee out of the stable hyperextended position will result in the patient dropping into excess dorsiflexion (crouching). In these cases, the patient’s dorsiflexion will also need to be controlled in order to maintain a functional posture. The DAFO FA (fixed ankle) provides plantarflexion block to control hyperextension and sufficient dorsiflexion block to support a smaller patient. For the larger patient, the DAFO Turbo brace provides plantarflexion block to control hyperextension and sufficient dorsiflexion block to support a larger / heavier patient.

Hyperextension Due to Spastic Contractures

Chronic contractures of the calf muscles (gastrocnemius and soleus) will result in excess ankle plantarflexion. In patients with relatively good knee control, the excess plantarflexion will usually result in toe walking. For patients with poor knee control, the excess plantarflexion will drive the knee back into hyper-extension. With a suitable brace to resist or block the ankle plantarflexion, the knee is prevented from moving to the hyperextended position.

Control of mild to moderate high tone hyperextension requires some force be applied to the ankle to resist plantarflexion, hence, resisting knee hyperextension. The DAFO 3.5 has a flexible proximal strut that resists plantarflexion and can be made with a range of flexibility, depending on the strength of the high tone contractures, the degree of hyperextension and/or the size of the patient. The DAFO 3 and DAFO 2 both provide full PF block with free dorsiflexion. The DAFO 3 is a simple one-piece design while the DAFO 2 is a hinged design that offers additional medial-lateral support.

As the severity of the high tone contractures increase, the brace must apply more force to counteract the plantarflexion. The DAFO Turbo brace provides the strongest plantarflexion block available. If the excess plantarflexion cannot be adequately corrected, whether due to limited range or high tone, and the best corrected position is unsuitable for standing, additional range needs to be gained before optimal results with bracing can be achieved. To gain ankle range, serial casting with Botox® treatments, an active stretching program with night positioning bracing, or heel cord surgery are required. If these options are not available, a wedge of support material under the heel of a brace (heel wedge) will lift the heel and bring the knee forward. This extra material, however, can make the brace difficult to wear with a shoe.

Visit www.cascadedafo.com to learn more about Cascade Dafo’s seven patient groupings approach.