Coccydynia

Coccydynia is pain in and around the coccyx, typically provoked by sitting and by rising from a seat. It is a clinical diagnosis, and an under-recognised one: the complaint is easily dismissed as trivial, yet the sitting pain can be debilitating and significantly impair quality of life and work capacity. Most cases resolve with conservative measures. The refractory minority need accurate radiographic classification and a targeted intervention, and the whole subject carries one serious trap, which is the sacrococcygeal chordoma or the infection mistaken for benign coccygeal pain.

Who. Women outnumber men 5:1, and the peak incidence is at 40-60 years. Obesity, a BMI greater than 27, is an independent risk factor, because a heavier patient puts more pressure on the coccyx when seated. Vaginal delivery is a significant risk factor, especially instrumental delivery.

Why women. The broader female pelvis positions the coccyx more posteriorly, where it is exposed to direct trauma, and women tend to sit with a more posterior pelvic tilt, which loads the coccyx directly. Childbirth stretches the sacrococcygeal and anococcygeal ligaments, and the coccyx may fracture under delivery pressure. Ligamentous laxity from hormonal influences may predispose to hypermobility.

Aetiology. Approximately 70% of cases are post-traumatic, approximately 20% idiopathic, with no identified precipitant and commonest in women, and approximately 10% other causes. Childbirth and falls are the two dominant aetiologies: a fall onto the buttocks or a direct blow to the coccyx, or a vaginal delivery that strains or fractures it. The degenerative group, meaning coccygeal disc degeneration, osteophytes or spicules and adventitious bursitis, and the neoplastic causes that must be excluded are set out under Classification.

What it costs the patient. Sedentary workers are disproportionately affected. Chronic pain leads to anxiety and depression, and somatisation must be screened for. The reduction in quality of life is comparable to chronic low back pain.

What else sits at the bottom of the spine. Coccydynia is a diagnosis of exclusion at a crowded site: sacroiliac joint dysfunction and piriformis pain refer into overlapping territory, an insidious onset in an older or osteoporotic patient should raise sacral insufficiency fracture, a traumatic onset raises sacral fracture, and the systematic work-up belongs to low back pain assessment.

The bone. The coccyx is 3-5 fused vertebral segments, most commonly four, attached to the sacrum at the sacrococcygeal joint between S5 and Co1. That joint is a fibrocartilaginous symphysis with a disc in most adults, though it may be fused, and it allows limited flexion and extension. The coccyx gives attachment to the pelvic floor muscles and supports the anus.

What attaches to it. Four structures matter clinically:

• Gluteus maximus posteriorly, through a raphe. It extends and laterally rotates the hip, and spasm or strain of it exacerbates coccygeal pain
• Coccygeus (ischiococcygeus, part of the levator ani complex) laterally, from the ischial spine to the lateral coccyx. It supports the pelvic floor, and pelvic floor dysfunction perpetuates the pain
• The anococcygeal ligament anteriorly
• The ganglion impar, the terminal ganglion of the sympathetic chain, just anterior to the sacrococcygeal junction. It is the target for blocks of sympathetically mediated pain

How it hurts. Trauma produces a direct contusion, a ligamentous strain or a fracture of the coccyx, with post-traumatic inflammation of the sacrococcygeal disc. In the hypermobile coccyx, excessive flexion on sitting stretches the sacrococcygeal ligaments. In anterior subluxation the coccyx subluxates forward under load and compresses the soft tissues; this is most common in Type IV morphology. Degeneration adds coccygeal disc degeneration, osteophytes and adventitious bursitis over the coccygeal tip.

Two systems describe the coccyx. Postacchini and Massobrio classify its static morphology on a lateral film, and the aetiological classification sorts the cause. Maigne's dynamic classification is read from the sitting-versus-standing films and is set out under Investigations, beside the films it depends on.

PostacchiniAetiological

Postacchini and Massobrio Classification (Radiographic Morphology)

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Type I

Morphology

Slightly curved, apex pointing inferiorly

Prevalence

Most common variant (approximately 40 percent)

Association with Coccydynia

Least associated with coccydynia

Treatment Implication

Conservative management usually sufficient

Type II

Morphology

Intermediate curvature, apex curved forward

Prevalence

Approximately 30 percent of population

Association with Coccydynia

Moderate association with coccydynia

Treatment Implication

Conservative, injection if refractory

Type III

Morphology

Sharply angled anteriorly (acute flexion)

Prevalence

Approximately 15 percent

Association with Coccydynia

Strongly associated with coccydynia

Treatment Implication

Injection; coccygectomy has good results

Type IV

Morphology

Anterior subluxation or hypermobile coccyx

Prevalence

Approximately 15 percent

Association with Coccydynia

Highest association with coccydynia

Treatment Implication

Coccygectomy has best outcomes in this group

Type	Morphology	Prevalence	Association with Coccydynia	Treatment Implication
Type I	Slightly curved, apex pointing inferiorly	Most common variant (approximately 40 percent)	Least associated with coccydynia	Conservative management usually sufficient
Type II	Intermediate curvature, apex curved forward	Approximately 30 percent of population	Moderate association with coccydynia	Conservative, injection if refractory
Type III	Sharply angled anteriorly (acute flexion)	Approximately 15 percent	Strongly associated with coccydynia	Injection; coccygectomy has good results
Type IV	Anterior subluxation or hypermobile coccyx	Approximately 15 percent	Highest association with coccydynia	Coccygectomy has best outcomes in this group

Read the prevalence column carefully. It is the conventionally quoted distribution. Postacchini and Massobrio's own normative series says something different: among 120 asymptomatic subjects, 68% had a Type I coccyx, the sacrococcygeal joint was already fused in 37% and the second intercoccygeal joint in 43%, so fusion and morphological variation are common findings in people with no pain at all.

And the last column. Whether morphology predicts the result of coccygectomy has since been contested by a much larger series, and that argument is taken up under Coccygectomy.

Aetiological Classification

Post-traumatic (acute)

Mechanism

Fall onto coccyx, direct blow

Clinical Features

Acute onset, focal tenderness, ecchymosis

Key Investigation

Dynamic lateral radiographs, MRI if fracture suspected

Post-childbirth

Mechanism

Vaginal delivery with coccygeal strain or fracture

Clinical Features

Post-partum coccygeal pain, worse sitting

Key Investigation

Dynamic radiographs; MRI if persistent beyond 3 months

Idiopathic

Mechanism

No clear precipitant

Clinical Features

Insidious onset, chronic course

Key Investigation

MRI mandatory to exclude tumour or infection

Degenerative

Mechanism

Coccygeal disc degeneration, osteophytes

Clinical Features

Gradual onset, older patients

Key Investigation

Dynamic radiographs show spicules or sclerosis

Neoplastic (chordoma)

Mechanism

Sacrococcygeal chordoma, plasmacytoma

Clinical Features

Night pain, mass, constitutional symptoms

Key Investigation

MRI entire sacrum; biopsy if lesion identified

Category	Mechanism	Clinical Features	Key Investigation
Post-traumatic (acute)	Fall onto coccyx, direct blow	Acute onset, focal tenderness, ecchymosis	Dynamic lateral radiographs, MRI if fracture suspected
Post-childbirth	Vaginal delivery with coccygeal strain or fracture	Post-partum coccygeal pain, worse sitting	Dynamic radiographs; MRI if persistent beyond 3 months
Idiopathic	No clear precipitant	Insidious onset, chronic course	MRI mandatory to exclude tumour or infection
Degenerative	Coccygeal disc degeneration, osteophytes	Gradual onset, older patients	Dynamic radiographs show spicules or sclerosis
Neoplastic (chordoma)	Sacrococcygeal chordoma, plasmacytoma	Night pain, mass, constitutional symptoms	MRI entire sacrum; biopsy if lesion identified

A case is labelled idiopathic only after the neoplastic causes in the last row have been excluded; the red flags that prompt that search are set out under Clinical Assessment.

History. The pain is focal to the coccyx, worse on sitting, worse on hard surfaces, and relieved by standing or by lying on the side. A sharp pain on the transition from sitting to standing is characteristic. Ask about the precipitant, which is a direct fall, childbirth, prolonged sitting or an insidious onset; about pain on defaecation, since the coccyx moves with sphincter activity; and about what has already been tried, whether NSAIDs, cushions, injections or physiotherapy.

Examination. Inspect the skin over the coccyx for a sinus, swelling or erythema. Palpate for focal coccygeal tenderness, percutaneously and then bimanually per rectum, and use the rectal examination to judge coccygeal mobility, hypermobile against ankylosed. Exclude a radiculopathy, check anal tone and perianal sensation, and feel the pelvic floor for levator spasm and trigger points.

The bimanual rectal examination. With the patient in the left lateral position, the index finger is passed into the rectum and the coccyx is held between it and the external thumb. The examiner is after three things: focal tenderness, coccygeal mobility, and reproduction of the patient's typical pain. What the findings mean:

• Focal tenderness at the sacrococcygeal joint or the coccygeal tip confirms the coccyx as the pain source
• Hypermobility, excessive flexion with gentle pressure, suggests Type IV morphology
• A fixed, ankylosed coccyx that is tender suggests a degenerative or inflammatory cause
• Always correlate with the dynamic radiographs

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Dynamic lateral radiographs. The first-line test and the single most important investigation. Standard static films may appear normal; the sitting film shows the coccyx under load and reveals the hypermobility or subluxation that is invisible on the standing film. Take a lateral standing and a lateral sitting on a hard surface, the patient having sat for approximately 2 minutes so that the coccyx settles into position, and compare the angle of coccygeal flexion between the two. Hypermobility is more than 25 degrees of additional flexion on sitting; anterior subluxation is measured as the anterior translation of the coccygeal segments. Add an AP pelvis for fracture, spicules or lytic lesions.

Maigne's dynamic classification. Where Postacchini describes static morphology, Maigne describes the lesion seen on the sitting-versus-standing films, and it is what most directly explains the mechanism:

• Normal mobility - coccygeal flexion of roughly 5-25° on sitting
• Hypermobility - flexion over 25° on sitting
• Anterior subluxation - forward luxation of a coccygeal segment on sitting, often 25% or more
• Posterior subluxation - backward displacement on sitting
• Immobile or rigid coccyx - minimal movement, often with a bony spicule at the tip, itself a recognised pain source

Body habitus. Maigne's classic correlation is that obese patients tend to develop posterior subluxation, because the coccyx cannot retrovert and so levers backward, whereas thin patients tend to develop anterior subluxation or hypermobility. It is a neat examinable link between BMI, mechanism and the dynamic-film finding.

MRI of the sacrum and coccyx. Second line, for atypical pain, night pain, constitutional symptoms, or pain persisting beyond 3 months despite treatment. It shows bone marrow oedema at the sacrococcygeal junction, indicating inflammation or a stress fracture, a presacral soft-tissue mass, disc degeneration within the coccyx and inflammation of the adjacent soft tissues. It is the study that excludes sacral insufficiency fracture, chordoma and infection.

CT of the coccyx. For a suspected coccygeal fracture not seen on the radiographs, and for pre-operative planning before coccygectomy. It shows fracture lines, cortical disruption, the degree of coccygeal curvature and bony spicules.

Management is stepwise: conservative care first, injection for the intermediate case, coccygectomy for the refractory few. Acute post-traumatic pain gets NSAIDs, a cushion and physiotherapy for 6-8 weeks; pain persisting beyond 3 months earns an MRI, repeat dynamic films and a fluoroscopic injection. Approximately 90% of patients improve with conservative management within the first 6 months, and the interventions that do the work are the coccygeal cushion, NSAIDs, pelvic floor physiotherapy and activity modification.

The wound is the risk. The proximity of the coccygectomy wound to the anus makes infection and dehiscence the most common and clinically significant complications. The two rates in the table below rest on different footings, so quote the range and say which is which: the authors of the largest modern series attribute their lower rate to an off-centre closure, and a surgeon using a midline closure should not assume 9%. Meticulous technique, antibiotic prophylaxis, careful closure and a drain reduce the risk without eliminating it, and patients must be told that wound healing problems can prolong recovery by months.

Conservative care. Acute cases improve over 2-6 weeks, chronic ones over up to 6 months, and the long-term result is excellent, with most patients maintaining the improvement.

Injection. Coccygeal steroid injection works within days to weeks, peaking at 2-4 weeks; relapse is common at 3-6 months, which is why it may be repeated. Ganglion impar block gives good relief in 50-60%, within days for the block and weeks for neurolysis, and neurolysis lasts months to years.

Coccygectomy. In selected patients the operation gives good or excellent results in the majority, with 60-70% reporting complete relief, and the full benefit takes 3-6 months to arrive. Relief is durable in responders.

Prognosis. The classical favourable profile is post-traumatic coccydynia with a confirmed hypermobile or subluxated (Type IV) coccyx, a positive diagnostic injection, a motivated patient and a short duration of symptoms; the classical poor profile is idiopathic coccydynia with normal radiographs, symptoms for longer than 2 years, pending litigation, untreated psychological comorbidity and prior failed spinal surgery. The largest modern series complicates the favourable half of that, since there a traumatic aetiology predicted a worse result and morphology predicted nothing, as set out under Coccygectomy.