Arthrokinetic Reflex: Definition, Mechanism, and Clinical Relevance
The arthrokinetic reflex is an important orthopedic and neuromuscular concept that explains the relationship between joint mechanics and muscle activity. In the context of temporomandibular joint (TMJ) disorders, this reflex helps explain why internal derangement of the joint can lead to muscle spasm, pain, and dysfunction—and why these symptoms often improve when joint mechanics are restored.
Understanding the arthrokinetic reflex is essential in the evaluation and management of TMJ internal derangement, disc displacement, myofascial pain, and occlusal dysfunction.
What Is the Arthrokinetic Reflex?
The arthrokinetic reflex describes a phenomenon in which abnormal joint motion or internal derangement triggers reflexive muscle hyperactivity in the muscles that support or move that joint. This increased muscle activity often manifests as muscle spasm, fatigue, or pain.
When the underlying joint abnormality is corrected or temporarily normalized, the reflexive muscle spasm decreases or resolves, confirming that the muscle symptoms are secondary to joint pathology rather than a primary muscular disorder.
Arthrokinetic Reflex in TMJ Internal Derangement
In the temporomandibular joint, the arthrokinetic reflex is most commonly observed in patients with disc displacement with reduction.
During mandibular closure in these patients, the condyle slides over the posterior band of the displaced disc, creating an abnormal mechanical stimulus within the joint. This abnormal motion activates joint mechanoreceptors, which in turn trigger increased electromyographic (EMG) activity in the muscles of mastication—most notably the temporalis and masseter muscles.
This reflexive increase in muscle activity is often perceived by the patient as:
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Muscle tightness or spasm
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Jaw fatigue
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Facial pain or headache
Resolution of Muscle Spasm with Disc Reduction
A key feature of the arthrokinetic reflex is its reversibility.
When the mouth opens and the disc reduces to a normal position, joint mechanics temporarily normalize. As a result:
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Abnormal joint stimulation decreases
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EMG activity in the temporalis and masseter muscles diminishes
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Muscle spasm and discomfort improve
This explains why many patients report relief of muscle pain with jaw opening or during maneuvers that restore disc position.
Clinical Significance
The arthrokinetic reflex highlights several important clinical principles:
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Muscle pain may be secondary to joint pathology, not a primary muscle disorder
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Treating the internal derangement can reduce associated myofascial symptoms
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Persistent muscle spasm despite joint correction suggests additional pathology
This concept supports treatment strategies aimed at normalizing joint mechanics, such as splint therapy, disc repositioning techniques, arthrocentesis, arthroscopy, or open joint procedures—depending on the stage of internal derangement.
Relevance to TMJ Diagnosis and Treatment
Recognition of the arthrokinetic reflex helps clinicians:
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Differentiate joint-driven muscle pain from primary myofascial pain
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Interpret EMG findings in TMJ patients
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Understand why some muscle symptoms resolve with conservative joint therapy
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Counsel patients on expected symptom improvement when joint mechanics are addressed
It also reinforces why late-stage internal derangement with fixed disc displacement and degenerative changes may show less muscle symptom reversibility, as joint mechanics can no longer be normalized.
Board Exam and Clinical Pearl
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Internal derangement → abnormal joint motion → reflex muscle spasm
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Disc displacement with reduction shows increased EMG activity during closure
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Muscle activity decreases when disc position is normalized
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Muscle symptoms may resolve when the joint pathology is treated
Conclusion
The arthrokinetic reflex provides a unifying explanation for the close relationship between TMJ internal derangement and masticatory muscle pain. By understanding this reflex, clinicians can better diagnose TMJ disorders, select appropriate treatments, and explain symptom patterns to patients. Addressing joint mechanics is often the key to resolving secondary muscle dysfunction.
