Beyond Unloaders: Delaying Knee OA Progression, Part I

Unloader knee brace technology has been in development and use for several decades. The concept of knee braces to provide support and alleviate pain has been around since at least the mid-20th century, but the specific design of unloader braces, which aim to reduce load on one compartment of the knee (typically the medial compartment), became more refined and widely adopted starting in the 1980s and 1990s.

The unloader brace technology saw significant advancements during these decades, with improvements in materials, design, and the understanding of biomechanics. Modern unloader knee braces are designed to be more comfortable, effective, and adjustable, catering to the specific needs of individuals with knee osteoarthritis (OA).

While improvements have been made in unloader knee brace materials, brace comfort, and reduced brace migration, the conceptual approach to unloader bracing has not changed significantly. Unloaders reduce the load on the affected knee compartment, providing significant improvements in knee pain and function while in the brace. However, unloader knee braces do have some clinically relevant limitations. These can include:

• Dependency risk: Prolonged use of an unloader brace often leads to muscle atrophy due to reduced muscle engagement while wearing the brace. Clinical research suggests that over time, the OA patient may lose muscle strength even while using the knee unloader.
• Little to no carryover benefit: The unloader knee brace’s primary role is to alleviate pain and improve function while braced. When the brace is removed there is no meaningful rehabilitative carryover benefit to unloader brace use.
• Increased risk of bicompartmental knee OA: Traditional unloaders shift forces away from the affected compartment, toward the unaffected knee compartment. Shifting forces over time can increase the risk of bicompartmental knee OA.
• Altered gait biomechanics: Use of an OA unloader over time can result in additional loss of terminal extension in gait both braced and unbraced. Loss of terminal extension results in decreased quadriceps firing and further loss of muscle strength in the affected leg.

Unloader Knee Bracing Versus Rehabilitative Knee Bracing

A functional unloader brace is designed to support and protect a weakened or surgically repaired knee joint. Functional knee braces in general do not provide rehabilitative carryover benefits after routine use of the brace. While activity levels tend to increase with functional unloader knee brace use, clinical research suggests that there are not statistically significant improvements in unbraced gait biomechanics, leg strength, or unbraced pain levels with routine brace use. The patient is tied to the unloader for pain management and improved function. The eventual fix is a total knee replacement.

A New Class of Unloader

Traditional unloaders work by offloading the forces on the knee joint from the affected compartment to the unaffected side. Traditional unloaders generally do not provide sufficient unloading for patellofemoral or multicompartmental knee OA. A relatively new product, the Levitation Knee Brace, uses dynamic extension assist of up to 200 inch-pounds to supplement the OA weakened quadriceps muscles by offloading approximately 40 pounds of load from the leg. This makes sit to stand, descending stairs, and other activities while in-brace far easier for the OA patient. This multicompartment unloading technology assists the quadriceps by decompressing the knee joint during flexion, redistributing mechanical forces away from the affected joint during activities of daily living (ADLs). Compared to a traditional unloader, the dynamic assist patellofemoral unloader reduces the risk of early-stage OA patients developing bicompartmental knee OA, as the brace does not simply shift the load from the affected to the unaffected knee compartment.

The Levitation brace would be categorized as a patellofemoral unloader that has the potential to provide multicompartmental unloading. While ADLs are less challenging with the use of the dynamic extension assist device, there is currently no clinical evidence that there is any carryover rehabilitative benefits to this technology other than reducing the risk of developing bicompartmental knee OA.

A rehabilitative knee brace is designed to provide a rehabilitative carryover benefit that can include unbraced normalized gait biomechanics, a reduction in unbraced biomechanical forces on the knee joint, increased leg strength to better support the joint, and significant improvements in unbraced knee pain as a result of device use. Rehabilitative bracing options can significantly improve patient outcomes from brace use, which includes the ability to delay or eliminate the need for a total knee replacement. The significant reductions in the need for pain medications, injections, and ancillary care from a rehabilitative approach to knee bracing offers significant cost savings to health plans.

Clinical Research Insight

Knee OA is associated with significant leg strength loss, particularly in the quadriceps muscle group, with reductions ranging from 20 to 50 percent depending on OA severity and duration.¹ This loss is influenced by pain, disease duration, and activity levels, highlighting the importance of comprehensive management strategies to maintain muscle strength and function. As OA progresses, quadriceps strength loss becomes more significant. The greater the loss of leg strength, the greater the unwanted forces on the knee joint due to related biomechanical alterations in gait.

OA progression is primarily due to a compensatory gait pattern universal to OA patients. The altered gait biomechanics are intended to reduce weight bearing torque on the affected compartment (i.e., varus patients load on the lateral side of the foot to shift the weight bearing load from the medial compartment to the lateral compartment). While effective in reducing weight bearing impulse forces and pain at weight bearing, this abnormal gait pattern significantly reduces muscle firing, weakening the muscles necessary for maintaining a balanced knee joint. The greater the alteration in gait biomechanics, the greater the muscle strength loss and wear and tear on the knee joint.

Knee OA is a degenerative knee condition directly tied to gait biomechanics. Normalizing gait biomechanics has been clinically proven to reduce knee wear and tear and significantly delay knee OA progression. Traditional unloaders have not been found to provide improved unbraced gait biomechanics with continued use and can lead to additional loss of terminal extension and muscle activity over time.

What is needed are bracing solutions that either unload the knee joint and normalize gait biomechanics over time or regenerate the knee joint. These changes must be evident while unbraced after several weeks of brace use. Normalizing gait biomechanics reactivates unbraced quadriceps firing, strengthens the weakened leg, and reduces unwanted biomechanical forces on the knee joint. Normalizing gait biomechanics delays the progression of knee OA by significantly reducing unwanted biomechanical forces on the knee joint (lower knee adduction moment, lower knee impulse torque at weight bearing, and reduced or eliminated reverse screw home mechanism).

Knee OA Includes Neurological Impairments

With knee OA or after injury or surgery, pain and swelling can lead to a phenomenon called arthrogenic muscle inhibition (AMI). AMI is a reflex inhibition of the muscle caused by the joint itself, often mediated by altered afferent signals from the joint. It leads to a cocontraction of the flexors and extensors during the swing phase of gait and a loss of terminal extension, which is necessary for full quadriceps activation.

Full quadriceps activation in gait requires knee terminal extension be restored to maintain improved leg muscle strength. 

Loss of Terminal Extension Implications

Terminal knee extension, or the ability to fully extend the knee at the end of the stance phase of gait, is crucial for several reasons:

• Gait biomechanics: Full knee extension ensures proper alignment and stabilization of the knee joint during walking. This alignment is necessary for efficient load transfer through the leg and helps maintain proper gait mechanics.
• Quadriceps activation: The quadriceps muscle group is heavily involved in extending the knee. Achieving full extension requires significant quadriceps engagement. When terminal extension is not achieved, the demand on the quadriceps decreases, leading to reduced muscle activation. Over time, this can result in significant weakening of the quadriceps due to disuse.
• Joint stability and load distribution: Proper knee extension helps maintain stability of the knee joint and ensures even distribution of forces across the joint. Without full extension, compensatory mechanisms may alter gait mechanics, leading to uneven load distribution and potentially increasing the risk of joint degeneration and pain.
• Functional implications: Incomplete knee extension can affect overall gait efficiency, making walking less energy efficient, and more fatiguing. This can further discourage the use of the quadriceps, contributing to muscle weakening and altered gait patterns.

To summarize, a loss of terminal extension in gait can reduce quadriceps firing due to decreased biomechanical demand and altered gait mechanics. This can lead to a cycle of muscle weakening and compensatory movement patterns, which may exacerbate the underlying issue and lead to further functional impairments.

Knee unloader braces are not designed to provide more than joint unloading and decreased pain while wearing the device to improve function. In essence, the unloader provides a band-aid approach to OA-related pain management until the patient requires a total knee replacement to correct the problem. Because it often leads to additional loss of terminal extension unbraced over time, the OA unloader has limited ability to rehabilitate the OA leg.

Reversing OA-related Quadriceps Central Activation Deficits

Prolonged periods of disuse or altered movement patterns can lead to changes in the motor cortex, affecting the ability to recruit the quadriceps effectively. This is a significant neurological impairment that must be addressed to delay the progression of knee OA.

Over time, most knee OA patients develop quadriceps central activation deficits (CAD). This is the primary causal factor for knee OA–related muscle weakening. Clinical research has determined that two-thirds of the muscle weakness in a Grade III/IV knee OA patient is CAD related (neurological impairment). The remaining one-third of muscle weakening is due to diminished use of the affected muscle (use-related muscle atrophy).¹ While quad-strengthening exercise and physical therapy can be effective in reversing the disuse muscle atrophy, it does not address the neurological impairment. While use of modalities has been identified as helpful for restoring lost OA-related muscle strength, without continued therapy the muscles will eventually lose the incremental gains because the patient is not activating these muscles during gait. Terminal extension in gait must be restored unbraced to provide significant improvements to significantly delay knee OA progression.

Gait biomechanics is dependent on a precise sequence of muscle firing that creates the desired gait pattern (gait muscle memory). With knee OA, patients have altered gait biomechanics (altered firing sequence). Thousands of biomechanically improved steps over time in the brace can normalize unbraced gait biomechanics and reverse quadriceps CAD. Restoring normal gait biomechanics using dynamic extension assist orthotics is a very effective neurological approach to gait relearning. In as little as 90 days with three hours of brace use per day, a patient takes over 250,000 biomechanically improved steps, normalizing unbraced gait biomechanics over time.

More Effective Approaches to Conservative Management Are Needed

Several factors contribute to the emergence of treatment advances in conservative management of knee OA, including the following:

• Increasing geriatric population: As the elderly population grows, the prevalence of knee OA, which is highly associated with aging, is expected to rise. This demographic shift significantly contributes to the demand for OA treatments.² Advanced rehabilitative knee OA bracing is necessary to for better conservative treatment of knee OA.
• Rising awareness and better treatment options: Enhanced awareness about knee OA and the availability of improved treatment options like platelet-rich plasma (PRP) injections and stem cell therapies are encouraging more people to seek treatment, thereby driving market growth.³ Both PRP and stem cell therapies have been proven to significantly reduce joint inflammation, reduce knee pain, and improve function. Stem cell treatments have been found to have the potential for cartilage regeneration.
• Technological advancements and research: Continued research and development activities are leading to the introduction of new and more effective treatments. For instance, recent drug approvals and the development of novel therapies are expected to further boost the market.³
• Healthcare infrastructure investments: Increased healthcare spending and improvements in healthcare infrastructure are facilitating better access to treatments, contributing to market expansion.⁴
• Sedentary lifestyle and obesity: The rise in sedentary lifestyles and obesity rates, which are risk factors for knee OA, are also contributing to the increased incidence and diagnosis of the condition, thereby driving the demand for treatments.⁴

Overall, the knee OA treatment market in the US is poised for robust growth, supported by demographic trends, increased healthcare awareness, and advancements in medical technology. To capitalize on improved market conditions for the conservative treatment of knee OA, knee bracing technology needs to advance to effectively compete with the positive patient outcomes provided by other alternative treatments.

Look for a discussion of several knee OA bracing technologies in part two of “Beyond Unloaders: Delaying Knee OA Progression” in the next issue.  

John Kenney, PhD, BOCO, is the inventor of DynaPro antispasticity orthoses and holds five patents on antispasticity brace design. He is the vice president of clinical development, Ongoing Care Solutions/Guardian Brace. 

Images: Ira Dvilyuk/stock.adobe.com

References

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