Is it CRPS? Unraveling Complex Regional Pain Syndrome's Mysteries

Introduction and Epidemiology

During the American Civil War, Silas Weir Mitchell described a syndrome that occurred in patients who had suffered gunshot injuries to major nerves. Noting that a leading feature was burning pain, he called the condition causalgia. At the beginning of the 20th century, Paul Südeck, a clinician in Hamburg, Germany, used the newly invented technique of roentgenology to investigate patients with severe pain after injury. He described a posttraumatic pain syndrome with edema, trophic changes, and osteoporosis. In 1979, the AO group advocated open reduction and rigid internal fixation to prevent fracture disease, which was defined as a combination of circulatory disturbance, inflammation, and pain as a result of dysfunction of joints and muscles. In an intriguing vignette, Channon and Lloyd noted that finger stiffness after Colles fracture could be either simple or associated with swelling and changes in hand temperature. In the latter case, it did not respond well to physiotherapy.

The modern term for the syndrome described in different circumstances by these researchers is complex regional pain syndrome, usually abbreviated as CRPS. CRPS consists of abnormal pain, swelling, vasomotor and sudomotor dysfunction, contracture, and osteoporosis. It used to be considered a rare, devastating complication of injury, caused by abnormalities in the sympathetic nervous system and seen mainly in psychologically abnormal patients. Modern research is altering this view radically. This review examines CRPS within the context of orthopaedic trauma surgery, distinguishing between CRPS Type I (occurring without a definable major nerve lesion, formerly reflex sympathetic dystrophy) and CRPS Type II (occurring after a distinct major nerve injury, formerly causalgia).

A cardinal feature of CRPS involves abnormalities of pain perception, which are often foreign to orthopaedic surgeons. They have been codified by Merskey and Bogduk and represent the foundation of clinical diagnosis.

Allodynia literally translates to other pain and represents a painful perception of a stimulus that should not usually be painful. Thus, a patient will find gentle stroking of the affected part painful. Allodynia differs from referred pain, but allodynic pain can occur in areas other than the one stimulated. There are several forms of allodynia. Mechanical or tactile allodynia implies pain in response to touch. It may be further subdivided into static mechanical allodynia, implying pain in response to light touch or pressure, and dynamic mechanical allodynia, where the pain occurs as a result of brushing. In thermal hot or cold allodynia, the pain is caused by mild changes in skin temperature in the affected area.

Hyperalgesia is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves. Thus, the patient finds gentle touching with a pin unbearably painful. Hyperalgesia is usually experienced in focal, discrete areas, typically associated with injury. Focal hyperalgesia may be divided into two subtypes. Primary hyperalgesia describes pain sensitivity that occurs directly in the damaged tissues. Secondary hyperalgesia describes pain sensitivity that occurs in surrounding undamaged tissues. Rarely, hyperalgesia is seen in a more diffuse, bodywide form.

Hyperpathia is a temporal and spatial summation of an allodynic or hyperalgesic response. Thus, the patient finds gentle touching painful, but repetitive touching either on the same spot or on another part of the affected limb becomes increasingly unbearable and the pain continues for a period of up to thirty minutes after the stimulus has been removed.

Epidemiologically, CRPS most frequently manifests following fractures, crush injuries, and sprains. Distal radius fractures represent the most common inciting orthopaedic injury, with historical literature suggesting an incidence as high as thirty percent, though modern diagnostic criteria place the true incidence closer to five percent. There is a distinct female predominance, with a female-to-male ratio approximating four to one, and a peak age of onset between forty and sixty years.

Surgical Anatomy and Biomechanics

Neuroanatomy of the Sympathetic Nervous System

Understanding CRPS requires a thorough grasp of the peripheral and autonomic nervous systems. The sympathetic nervous system plays a central role in the vasomotor and sudomotor abnormalities characteristic of CRPS. The sympathetic efferent fibers originate in the intermediolateral horn of the spinal cord. For the upper extremity, preganglionic fibers exit the spinal cord from T1 to T6, ascend the sympathetic chain, and synapse in the cervical ganglia. The stellate ganglion, formed by the fusion of the inferior cervical and first thoracic ganglia, lies anterior to the transverse process of C7 and the neck of the first rib. It provides the primary sympathetic innervation to the upper limb.

For the lower extremity, sympathetic innervation originates from T10 to L2. These fibers descend to synapse in the lumbar sympathetic ganglia located anterolateral to the lumbar vertebral bodies. Postganglionic fibers then join the lumbosacral plexus to innervate the lower extremity. In CRPS, an abnormal coupling occurs between the sympathetic efferent fibers and the sensory afferent fibers, leading to sympathetically maintained pain.

Pathophysiology and Central Sensitization

The biomechanical and physiological underpinnings of CRPS are multifactorial, involving neurogenic inflammation, peripheral sensitization, and central sensitization. Following tissue trauma, nociceptive C-fibers release neuropeptides such as substance P and calcitonin gene-related peptide. These neuropeptides cause profound vasodilation and protein extravasation, leading to the classic edematous and erythematous presentation of early CRPS.

Peripheral sensitization occurs when inflammatory mediators lower the activation threshold of peripheral nociceptors. This manifests clinically as primary hyperalgesia. Prolonged nociceptive input subsequently leads to central sensitization, characterized by the wind-up phenomenon in the dorsal horn of the spinal cord. N-methyl-D-aspartate receptor activation plays a critical role in this process, amplifying pain signals and expanding the receptive fields of central neurons, which manifests as secondary hyperalgesia and allodynia.

Bone Metabolism and Trophic Changes

The hallmark radiographic finding in CRPS is periarticular patchy osteopenia. This results from localized osteoclastic overactivity driven by neurogenic inflammation and disuse. The biomechanical consequence is a significant weakening of the trabecular architecture, increasing the risk of secondary fractures and complicating orthopaedic hardware fixation. Trophic changes in the skin, hair, and nails result from chronic microvascular dysfunction and altered sympathetic tone, leading to tissue hypoxia and fibrosis.

Indications and Contraindications

The management of CRPS is primarily medical and rehabilitative. However, orthopaedic surgeons and pain specialists must recognize specific indications for interventional and surgical management. Surgery in the setting of active CRPS is generally contraindicated unless absolutely necessary, as surgical trauma can precipitate a severe flare of the disease.

Interventional and Surgical Indications

Surgical and interventional management is reserved for patients who have failed exhaustive conservative measures, including physical therapy, pharmacotherapy, and psychological support. Interventions range from minimally invasive sympathetic blocks to advanced neuromodulation and, in end-stage cases, salvage amputations.

Contraindications to Intervention

Absolute contraindications to elective orthopaedic surgery in a patient with CRPS include an active disease flare characterized by severe edema, erythema, and uncontrolled allodynia. Operating during this phase reliably exacerbates the condition. Relative contraindications for neuromodulation include untreated major psychiatric disorders, active systemic infection, and coagulopathy.

Pre Operative Planning and Patient Positioning

Perioperative Risk Mitigation

When orthopaedic surgery is unavoidable in a patient with a history of CRPS, meticulous preoperative planning is mandatory to prevent disease reactivation. The surgical team must employ a multidisciplinary approach involving anesthesiology, pain management, and physical therapy.

Pharmacologic prophylaxis is a cornerstone of preoperative planning. The administration of Vitamin C has been historically debated, but evidence suggests that five hundred milligrams daily for fifty days post-injury may reduce the incidence of CRPS following distal radius fractures. For patients with established CRPS undergoing surgery, perioperative N-methyl-D-aspartate receptor antagonists, specifically subanesthetic ketamine infusions, are highly recommended. Ketamine blocks central sensitization and mitigates the wind-up phenomenon in the dorsal horn. Gabapentinoids and membrane-stabilizing agents should be optimized prior to the surgical date.

Anesthetic Considerations

Regional anesthesia is strongly preferred over general anesthesia alone. Continuous peripheral nerve blocks or epidural anesthesia provide profound sympathectomy and preemptive analgesia, blunting the surgical stress response. If general anesthesia is required, it should be combined with a regional technique. The regional block should ideally be maintained for several days postoperatively to facilitate early, pain-free mobilization.

Tourniquet Management and Positioning

Tourniquet use must be carefully considered. Ischemia-reperfusion injury and mechanical nerve compression from the tourniquet are known triggers for CRPS. If a tourniquet is necessary, the surgeon should utilize the lowest effective pressure and minimize inflation time. Wide, contoured cuffs are preferred to distribute pressure evenly.

Patient positioning must avoid excessive traction or pressure on peripheral nerves. In patients with severe allodynia, even the pressure of resting on a standard operating table can induce a pain flare. Generous padding with gel mats and careful handling of the affected extremity during prepping and draping are critical.

Detailed Surgical Approach and Technique

While CRPS itself is not "cured" by a single surgical procedure, orthopaedic surgeons frequently perform operations to prevent fracture disease, manage complications, or facilitate neuromodulation. The surgical technique must prioritize atraumatic tissue handling.

Atraumatic Fracture Management

The AO principle of rigid internal fixation was partly developed to prevent fracture disease, a precursor concept to CRPS. When treating fractures in patients at high risk for CRPS, the surgical approach must be precise. Internervous planes must be respected to avoid iatrogenic nerve injury. Retraction must be gentle; forceful retraction leads to neuropraxia and subsequent neurogenic inflammation.

For distal radius fractures, a standard volar Henry approach is utilized. The flexor carpi radialis sheath is incised, and the tendon is retracted ulnarly. The floor of the sheath is incised to expose the pronator quadratus. Careful elevation of the pronator quadratus preserves the volar blood supply to the radius. Rigid volar plate fixation allows for immediate postoperative mobilization, which is the most effective deterrent against CRPS. The median nerve must be protected throughout the procedure, and any symptoms of acute carpal tunnel syndrome should prompt immediate release to prevent CRPS Type II.

Neuromodulation Techniques

For refractory CRPS, spinal cord stimulation is a validated surgical intervention. The procedure is typically performed in two stages. The patient is positioned prone on a radiolucent table. Under fluoroscopic guidance, an epidural needle is advanced into the posterior epidural space using a loss-of-resistance technique. For upper extremity CRPS, the leads are typically steered to the lower cervical or upper thoracic spine. For lower extremity CRPS, the leads are positioned in the lower thoracic spine.

Intraoperative testing is performed with the patient awake to ensure paresthesia coverage over the painful region. If the trial is successful, a permanent implantable pulse generator is placed in a subcutaneous pocket, usually in the gluteal region or abdominal wall, and connected to the epidural leads. Dorsal root ganglion stimulation is a newer technique that targets the specific sensory ganglion, providing highly localized therapy without the positional variations seen in traditional spinal cord stimulation.

Salvage Amputation and Targeted Muscle Reinnervation

In end-stage CRPS characterized by a useless, contracted limb, chronic infection, or intractable pain, amputation may be considered. This is a procedure of last resort. The surgical technique must address the high risk of recurrent CRPS and neuroma formation in the residual limb.

Targeted muscle reinnervation should be performed concurrently with the amputation. This involves identifying the major peripheral nerves (e.g., tibial and common peroneal nerves in a below-knee amputation) and transferring them to redundant motor branches of adjacent intact muscles. By providing the transected nerves with a physiological target to reinnervate, targeted muscle reinnervation significantly reduces the incidence of symptomatic neuromas and phantom limb pain, which are critical considerations in a nervous system already primed for central sensitization.

Complications and Management

The complications associated with CRPS are severe and often permanent if not addressed early. Furthermore, surgical interventions aimed at treating CRPS or orthopaedic conditions in CRPS patients carry their own unique risk profiles.

Disease Related Complications

Chronic CRPS leads to profound musculoskeletal and dermatological complications. Joint contractures develop due to chronic immobility, edema, and fibrosis of the periarticular structures. In the hand, this often manifests as severe stiffness of the metacarpophalangeal and proximal interphalangeal joints. Osteoporosis can become so severe that spontaneous insufficiency fractures occur. Dermatological complications include chronic skin ulceration, recurrent cellulitis, and loss of appendages.

Intervention Related Complications

Surgical interventions, particularly neuromodulation, carry risks of hardware failure, lead migration, and infection. Epidural hematoma is a rare but catastrophic complication of spinal cord stimulator placement.

Post Operative Rehabilitation Protocols

Rehabilitation is the absolute foundation of CRPS management. Following any orthopaedic procedure or intervention, the rehabilitation protocol must be initiated immediately. The primary goal is the restoration of function, which secondarily reduces sympathetically maintained pain.

Graded Motor Imagery

Traditional physical therapy can be intolerable for patients with severe allodynia. Graded motor imagery is a sequential rehabilitation protocol designed to retrain the brain and reverse the cortical reorganization associated with central sensitization. The protocol consists of three phases. The first phase is laterality training, where the patient views images of left and right limbs and must identify them, restoring the brain's working body schema. The second phase involves imagined movements, where the patient visualizes moving the affected limb without actually contracting the muscles. The final phase utilizes mirror visual feedback. The patient places the affected limb behind a mirror and moves the unaffected limb while watching its reflection. This creates a visual illusion that the affected limb is moving painlessly, helping to extinguish the fear-avoidance pain response.

Desensitization and Stress Loading

As tolerance improves, tactile desensitization is introduced. This involves stimulating the allodynic skin with progressively rougher textures, starting with silk and progressing to cotton, velcro, and eventually mild pressure. Contrast baths, alternating between warm and cool water, help retrain the autonomic nervous system and improve vasomotor tone.

Stress loading protocols, initially described by Carlson and Watson, involve active exercises that require compressive force through the extremity with minimal joint motion. For the upper extremity, this involves scrubbing (using a brush on a table with increasing weight) and carrying (carrying a weighted bag with the arm extended). These activities stimulate large-diameter mechanoreceptors, which theoretically close the pain gate in the dorsal horn while avoiding the pain associated with active range of motion.

Summary of Key Literature and Guidelines

The diagnosis and management of CRPS are guided by rigorous clinical criteria and evolving literature. Orthopaedic surgeons must be familiar with the consensus guidelines to ensure accurate diagnosis and evidence-based treatment.

The Budapest Criteria

The International Association for the Study of Pain adopted the Budapest Criteria as the gold standard for clinical diagnosis. To meet the criteria, the patient must have continuing pain that is disproportionate to any inciting event. Additionally, the patient must report at least one symptom in three of the four following categories, and display at least one sign at the time of evaluation in two of the four following categories. The categories include sensory (hyperalgesia or allodynia), vasomotor (temperature asymmetry or skin color changes), sudomotor and edema (edema, sweating changes, or sweating asymmetry), and motor and trophic (decreased range of motion, motor dysfunction, or trophic changes in hair, nail, or skin). The criteria also mandate that no other diagnosis can better explain the signs and symptoms.

Landmark Literature

The role of Vitamin C in preventing CRPS remains a highly discussed topic in orthopaedic literature. Zollinger and colleagues published landmark randomized controlled trials demonstrating a significant reduction in CRPS incidence following distal radius fractures when patients were supplemented with five hundred milligrams of Vitamin C daily for fifty days. While subsequent meta-analyses have questioned the robustness of these findings, the extremely low risk profile of Vitamin C makes it a common prophylactic recommendation in trauma surgery.

O'Connell and colleagues published comprehensive Cochrane reviews on interventions for CRPS, highlighting the efficacy of physical therapy, graded motor imagery, and bisphosphonates for acute osteoporotic changes. The literature strongly supports the use of ketamine infusions for refractory pain, demonstrating significant reductions in central sensitization markers.

Current guidelines emphasize a multidisciplinary approach. The orthopaedic surgeon's role centers on atraumatic surgical technique, stable internal fixation to permit early motion, vigilance in recognizing the early signs of disproportionate pain, and prompt referral to a multidisciplinary pain management team before irreversible trophic changes and cortical reorganization occur.