Osteoarthritis of the Foot and Peripheral Nerve Damage
Osteoarthritis of the foot does not directly cause peripheral nerve damage; rather, the relationship is reversed—pre-existing peripheral neuropathy can lead to a destructive form of osteoarthropathy (Charcot neuro-osteoarthropathy), while primary osteoarthritis may cause secondary nerve sensitization and structural nerve changes within the joint, but not true peripheral nerve damage.
Understanding the Relationship Between Foot OA and Nerve Pathology
Primary Osteoarthritis Does Not Cause Peripheral Nerve Damage
Foot osteoarthritis primarily affects joint structures including cartilage, bone, and soft tissues, with the first metatarsophalangeal joint most commonly involved, followed by the second cuneometatarsal and talonavicular joints 1.
OA causes peripheral nerve sensitization, not damage: Structural alterations in joint innervation occur during OA progression, including reorganization of joint afferents and neuroplasticity, but these represent sensitization mechanisms rather than true peripheral nerve damage 2.
Inflammatory mediators in the OA joint (nerve growth factor, chemokines, cytokines) contribute to peripheral sensitization of nociceptors within the joint, creating hyperexcitability of the nervous system 2, 3.
The Reverse Scenario: Neuropathy Leading to Osteoarthropathy
When peripheral neuropathy exists first (most commonly from diabetes), it can lead to Charcot neuro-osteoarthropathy (CNO), a destructive inflammatory process affecting bones and joints:
CNO is an inflammatory process in persons with peripheral polyneuropathy that results in injury to bones, joints, and soft tissues of the foot and ankle 4, 5.
The pathophysiology involves trauma (perceived or not) triggering an acute inflammatory response in the neuropathic foot, with disproportionate cytokine release activating osteoclastogenesis through the RANKL pathway 4.
This inflammatory process combined with mechanical forces during ambulation on a neuropathic foot leads to ligament disruption, joint dislocations, and fractures 4.
CNO affects approximately 0.3% of patients with diabetes mellitus, representing about 1.6 million people worldwide 4, 5.
Types of Nerve Involvement in Foot Conditions
In Primary Osteoarthritis (Not True Nerve Damage)
Peripheral nociceptor sensitization: Mediators in the OA joint sensitize nerve endings, creating a strong peripheral nociceptive drive that maintains pain and central sensitization 2.
Structural reorganization of joint afferents: Joint innervation undergoes structural changes including neuroplasticity, but this represents adaptation rather than peripheral nerve damage 2.
In Charcot Neuro-Osteoarthropathy (Pre-existing Neuropathy)
Peripheral polyneuropathy (typically sensory and motor) must exist before CNO develops 4, 5.
The neuropathy type is most commonly diabetic peripheral polyneuropathy, presenting with sensory deficits in a "glove and stocking" distribution 6.
Impaired pain perception from the neuropathy allows continued ambulation on damaged joints, perpetuating the destructive cycle 5.
Clinical Implications and Management
For Primary Foot Osteoarthritis
Pain management focuses on addressing peripheral sensitization rather than nerve damage, using paracetamol, topical NSAIDs, and if needed, oral NSAIDs or COX-2 inhibitors at the lowest effective dose 4.
Non-pharmacological interventions include appropriate footwear with shock-absorbing properties, foot orthoses (with evidence supporting prefabricated orthoses in midfoot OA), and physical therapy 4, 1.
Intra-articular corticosteroid injections can provide relief for moderate to severe pain 4.
For Charcot Neuro-Osteoarthropathy
Immediate immobilization with a non-removable knee-high device (preferably total contact cast) is the primary treatment once CNO is suspected 5.
Below-ankle devices should never be used as they provide inadequate immobilization 5.
After remission, customized below-knee devices are essential for patients with deformity or joint instability to prevent reactivation 5.
Critical Distinctions to Avoid Misdiagnosis
Red Flags Suggesting CNO Rather Than Primary OA
Warm, erythematous, edematous foot with intact skin in a patient with known peripheral neuropathy 5.
Rapid progression of deformity with fractures or dislocations on imaging 5.
History of diabetes mellitus with documented peripheral neuropathy 4, 5.
Common Pitfalls
Mistaking CNO for cellulitis or gout due to the warm, swollen presentation—always consider CNO in neuropathic patients 5.
Failing to recognize that OA causes nerve sensitization, not peripheral nerve damage—this distinction is crucial for appropriate treatment planning 2.
Using inadequate offloading devices in CNO, such as below-ankle devices or removable walkers, which fail to prevent progression 5.