CHAPTER 120 Coccydynia
INTRODUCTION
Although coccygeal pain was first described in relation to a fracture by sixteenth-century French surgeon Ambroise Paré, the term coccydynia was not introduced until 1859 by Simpson.1 The awareness of this condition led to numerous studies, but it has remained poorly understood until recently. The use of dynamic films, described by the author in 1992, has led to a better understanding of the various possible causes of coccydynia and their associated specific symptoms and therefore to a better management.
FUNCTIONAL ANATOMY OF THE COCCYX
Very little information is available in the literature regarding coccyx anatomy. According to Gray, the sacrococcygeal joints are very thin intervertebral discs of fibrocartilage and the intercoccygeal joints can be either synovial joints or discs.2
By examining nine aged coccyges from fresh cadavers, the author found that the sacrococcygeal joint was a disc in one case, a synovial joint in four cases and, in the four remaining cases, an intermediate structure composed of a disc containing a fairly extensive cleft, parallel to the endplates, and bordered by annular fibers or synovial cells.3 This intermediate pattern was not found in the intercoccygeal joints. It is unknown if the same distribution is found in young individuals, which raises the question as to whether the cleft extends throughout life as a result of mechanical constraints, with the disc gradually changing to a synovial joint in the same individual. Synovial joints allow more mobility than discs. A fourth type found consisted of complete ossification of the sacrococcygeal joint. A study of two different populations found the frequency of this type to be 22% and 68% of the cases, respectively.4 In some instances, the entire coccyx was ossified.
The physiological movements of the coccyx are restricted to flexion and extension. Active flexion (movement in a forward direction) is performed by the levator ani and the external sphincter muscles. Extension (movement in a backward direction) is caused by a relaxation of these muscles and increased intra-abdominal pressure, which occurs during defecation and parturition.5 It is always a passive movement. To the best of the author’s knowledge, the movements of the coccyx in the sitting position have never been reported in the literature. They consist either of flexion (moving forward) or extension (moving backward) or a lack of mobility (rigid coccyx).
The angle of incidence determines the direction of sagittal movement of the coccyx. The author has described the coccygeal incidence as the angle at which the coccyx strikes the seat when the subject sits down.6 If the incidence is low, the coccyx will be more or less parallel to the seat surface. The pressure exerted by the seat will push the coccyx forward and upward in flexion. If the angle of incidence is high, the coccyx will be somewhat perpendicular to the seat surface. The coccyx will then be pushed backward in extension by increased intrapelvic pressure. The incidence is influenced by the shape of the coccyx and the sagittal pelvic rotation.7 Coccyges with more than two vertebrae are often curved and long, and have a low incidence. Conversely, straight, short coccyges have a higher incidence. Four types of coccyx have been described according to the Postacchini and Massobrio8 classification ranging from the straightest (type I) to the most sharply angled coccyx (hooked coccyx, type IV). The coccygeal shape can also be determined by measuring the intercoccygeal9 or sacrococcygeal angle (Maigne), this latter formed by the intersection of the coccygeal and the 4th sacral vertebra axis. A sacrococcygeal angle close to 180° corresponds to a straight coccyx while a curved coccyx will have an angle close to 90°. The incidence is related to another angle; the degree of sagittal pelvic rotation. This angle measures the sagittal rotation of the pelvis when the subject moves from the standing to the sitting position. This rotation is accompanied with reduction of lumbar lordosis. When the sagittal pelvic rotation is high (up to 60°), the incidence is low. This is usually observed in subjects with a normal or low body mass index (BMI). Conversely, when the pelvic rotation is low (less than 30°), the incidence is high. This is the case in subjects with high BMI (>27). It is believed that the pelvic volume in obese subjects restricts the natural movements of pelvic rotation. Other factors can restrict pelvic rotation, including loss of mobility of the lumbosacral junction as a result of degenerative disc changes, sequelae of discectomy and arthrodesis, or, more simply, a high seat. Hyperlaxity of the ligaments and a low seat can also increase rotation. Such factors can affect the occurrence of coccygeal pain.
HISTORICAL ASSESSMENT
Interviewing the patient with coccydynia should include the following four steps:
Confirm the diagnosis: where do you feel the pain?
It is therefore essential to ask the patient to turn his or her back toward the examiner and point to the painful area. The identified region must correspond to the coccyx. Diffuse pain or pain present in both the standing and sitting positions does not indicate common coccydynia. Frequent differential diagnoses include pain associated with depression, low back pain radiating to the coccyx, pudendal neuralgia, anal pathology, or certain sacroiliac pains.
Identify a cause
Trauma is a classical cause of coccydynia. Sometimes, patients blame a traumatic event sustained several years earlier, although the role of this past event is questionable. Based on the fact that luxation (see below) is the most commonly observed condition after a trauma, it was demonstrated that the interval between the trauma and the onset of coccydynia is a determining factor.7 A very short or nonexistent interval (such as in postpartum coccydynia) is almost certainly indicative of trauma-related pain. Traumatic coccydynia is very likely if the pain occurs within a month of an injury. After 3 months, it is unlikely that trauma is the cause. It is important to know whether the traumatic event is an occupational injury or not, as the treatment results may be less effective when the trauma is work related.
In some cases, coccydynia may develop after moderate trauma, as a result of a long car journey, or riding a bicycle or a horse. In obese patients, excess weight in conjunction with the particular way of changing from standing to sitting (see below), and even sitting itself can be considered as repeated microtraumas. Generally, post-traumatic coccydynia is more frequent in straight coccyges that move into extension when the subject sits down than in curved coccyges that move into flexion.7,9 Curved coccyges are actually relatively well protected during the impact of sitting. Thus, contrary to a common opinion, hooked coccyges are less at risk than straight ones regarding post-traumatic coccygodynia.
Apart from a possible trauma, it has been shown that other factors such as BMI and the presence of pain when standing up from sitting could have diagnostic value.6 Determining body mass index is essential, as this factor greatly affects coccygeal biomechanics and, therefore, the culprit lesion. Luxation is more frequently observed in the obese population. The obese subject has a low angle of sagittal pelvic rotation when sitting down. As a result, the coccyx is more or less perpendicular to the seat surface, which increases the risk of luxation. In a normal-weight or lean person, the angle of sagittal pelvic rotation is greater, and the coccyx is parallel to the seat and prone to flexion and hypermobility. In lean patients, a spicule may cause significant irritation due to the absence of perineal fat (see below).
PAIN ON STANDING UP FROM SITTING The presence of sharp pain on passing from the sitting to the standing position is a sign that suggests a lesion that can be identified with radiologic imaging. These radiographic abnormalities are usually luxation or osseous spicules.7 As with any information gleaned during history taking, this element is of greater value if the patient mentions it spontaneously.
PHYSICAL EXAMINATION
The rest of the consultation should be focused upon the radiologic procedure and the therapeutic management. An etiologic diagnosis is sometimes possible at this stage. Failing this, it may be possible to identify elements suggesting the presence of a radiologic lesion (Table 120.1).
Table 120.1 Clinical Elements Suggesting the Presence of a Radiologic Lesion on Dynamic Films Versus no Lesion
| Items Suggesting a Radiologic Lesion | Items Suggesting Normal Radiographs |
|---|---|
| Local coccygeal pain | Pain radiating to the buttocks and thighs |
| Pain only in the sitting position | Significant pain also present in the standing position |
| Pain on standing up from sitting (especially if mentioned spontaneously) | Absence of pain on standing up from sitting |
| Pain occurring immediately after sitting down | Pain occurring after 30–60 minutes of sitting |
| Painful sitting position from the beginning of the day | Painful sitting position especially at the end of the day |
| Pain relieved for at least a month by a steroid injection | Pain unresponsive to a steroid injection |
INITIAL MANAGEMENT
Standard radiographs
Fractures
Coccygeal fractures are very rare (two in a thousand according to the author’s findings, where the fracture only involved the first coccygeal vertebra). This is easily understood as the weak point of the coccyx is the sacrococcygeal or intercoccygeal joint and not the coccyx itself. Luxation is the most common trauma-related injury. However, fractures of the distal portion of the sacrum are slightly more common (1% in the author’s cases). The real figure may be higher, as most of the author’s patients are referred with chronic coccydynia. Fractures are only responsible for acute coccydynia, since they resolve spontaneously, typically within 3 weeks. Pseudoarthrosis seems to be exceedingly rare as this entity has never been observed in the author’s patients.
