Fig. 1.1
Posteroanterior (a) and lateral (b) full-length X-rays of a 36-year-old woman with known history of adolescent idiopathic scoliosis with superimposed degenerative changes who presented with low back pain and left leg radicular pain
Adult Degenerative Scoliosis
Degenerative scoliosis is the most commonly encountered form of adult lumbar scoliosis in clinical practice. It is synonymous with de novo scoliosis or primary degenerative scoliosis ( Fig. 1.2 ).
Fig. 1.2
Posteroanterior (a) and lateral (b) full-length X-rays of a 69-year-old man with adult degenerative lumbar scoliosis and sagittal imbalance
The true incidence of adult scoliosis is not known. The reported prevalence of adult scoliosis ranges from 8.3 to 68% [ 4 – 9 ], with the majority of patients at least 60 years of age [ 3 , 8 ]. The prevalence is gradually increasing due to a combination of increasing life expectancy and increased clinical awareness [ 10 ]. The mean age at presentation has been reported to be approximately 70 years [ 9 ], with most literature suggesting a higher proportion of women [ 5 , 11 , 12 ]. Among degenerative deformities, lumbar scoliosis curves are more common than thoracic or thoracolumbar curves [ 8 ].
The pathogenesis is likely multifactorial in origin. It is thought to be a result of age-related asymmetric disc degeneration in combination with facet arthropathy and ligament laxity that results in regional malalignment [ 1 , 9 , 13 , 14 ]. This can be exacerbated by osteoporosis-related vertebral compression fractures and concurrent sagittal and rotational components [ 3 , 15 ]. Other less common but increasingly prevalent causes include previous lumbar fusion resulting in iatrogenic flat back deformity or a history of trauma.
Adult degenerative lumbar curves typically have an apex at L3 and are associated with a distal fractional curve and may include a nonstructural compensatory curve [ 9 ]. There is typically a rotational component and often lateral listhesis, involving the apical region of the curve [ 1 , 9 ]. Curve magnitude is inversely proportional toprevalence, with only 24 % of the curves greater than 20° in magnitude [ 16 ]. Curve progression is more commonly seen in curves with Cobb angle greater than 30°, apical vertebral rotation greater than a grade II (Nash-Moe classification), lateral listless greater than 6 mm, and/or cases in which the intercrest line passes through L5 [ 17 ].
Progression of degenerative scoliosis typically occurs slowly. Current literature reports the natural rate of progression for adult degenerative scoliosis is 1–6° per year, with an average of 3°. One caveat to this are compression fractures due to poor bone density which can result in accelerated progression [ 17 ].
Adult Idiopathic Scoliosis
Adult idiopathic scoliosis is the continuation of adolescent idiopathic scoliosis into adulthood after skeletal maturity ( Fig. 1.3 ). Thus the typical age of presentation is younger than those patients with adult degenerative scoliosis. The prevalence of adolescent idiopathic scoliosis (AIS) ranges from 0.4–3.9 % in North America [ 18 ]. These patients usually have major thoracic/thoracolumbar and/or lumbar curves with compensatory curves that have become structural. The major curves tend to have greater Cobb angles compared to adult degenerative scoliosis. Curve progression is seen most commonly with Cobb angles greater than 50 degrees [ 19 , 20 ].
Fig. 1.3
Posteroanterior (a) and lateral (b) full length X-rays of 18YF with adolescent idiopathic scoliosis
Unlike adolescent scoliosis, curve progression in skeletally mature patients typically occurs slowly. Years or even decades may pass without significant radiographic progression. Most reported progression rates in the literature for lumbar curves greater than 30° in skeletally mature patients are similar [ 20 – 23 ]. Weinstein et al. reported an average progression of 16.2° over 29 years in their small cohort [ 20 ], and Ascani et al. in their 29 patients reported a progression rate of 16° over the same time frame [ 23 ]. Thus, the typical rate of progression is roughly 0.5° per annum.
Adult idiopathic curves typically have a multilevel rotational component and a multilevel lateral listhesis component. In isolated lumbar curves, lateral listhesis is most commonly seen at L3–4 [ 20 ]. Concurrent sagittal malalignment may be seen in AIS patients who underwent fusion with distraction rods and among older patients with superimposed degenerative scoliosis.
The main differences between adult degenerative scoliosis and adult idiopathic scoliosis are summarized in Table 1.1 .
Table 1.1
Primary differences between adult idiopathic scoliosis and adult degenerative scoliosis
Adult idiopathic scoliosis | Adult degenerative scoliosis | |
|---|---|---|
Age at presentation | Younger | Older |
Presenting complaints | Deformity, cosmetic concerns, psychosocial issues, back pain | Back pain, leg pain, disability |
Spinal stenosis | Less common | Common |
Compensatory curves | Common, usually structural | Less common, usually nonstructural |
Sagittal malalignment | Not common unless previously fused | Common |
Coronal Cobb | Large Cobb angles | Small-to-moderate Cobb angles |
Rotatory component | Involves large segment of the curve | Generally at the apex |
Lateral listhesis | Involves multiple segments | Generally at the apex |
Clinical Presentation
Adult scoliosis patients typically present with pain and disability. This is in contrast to adolescent scoliosis patients who typically present with deformity progression resulting in cosmetic concerns and pain.
Back Pain
Back pain is the most common symptom of adult degenerative scoliosis [ 1 , 2 , 14 , 24 – 27 ]. The prevalence of low back pain in adult degenerative scoliosis patients ranges from 60 to 93 % [ 14 , 16 , 26 ]. There is usually a combination of axial back pain and radicular leg pain [ 14 , 24 ].
The etiology of back pain is not always clear, and in all likelihood is multifactorial. Potential causes include muscle fatigue due to spinal imbalance, from facet joint arthropathy, or disc degeneration and micro-instability resulting in central or foraminal stenosis [ 1 , 14 , 21 ]. Age-related asymmetric disc degeneration and facet joint arthropathy causes segmental instability and results in lateral listhesis, antero-/posterolisthesis, rotatory subluxation, or a combination thereof. This abnormal motion results in more pain and progression of degenerative changes. Ligamentous hypertrophy, disc herniation, and osteophyte formation with resultant spinal canal and foraminal stenosis can cause radiculopathy. In severe coronal curves, the rib cage on the concave side may impinge on the pelvis and produce severe pain. Low back pain from chronic muscle fatigue is most commonly seen in patients with sagittal imbalance [ 28 ].
Back pain is a less common chief complaint in patients with adult idiopathic scoliosis. Pain in this group of patients is associated with more significant thoracolumbar/lumbar curves and with curve progression [ 19 , 22 ]. In a 50-year study of AIS patients, Weinstein et al. reported a higher prevalence of back pain in scoliosis patients compared with age-matched controls [ 11 ]. Patients with AIS in early life are not immune to developing degenerative disease in the spine as they age. As these age-related degenerative changes progress throughout their lives, AIS patients can thus present with axial back pain and radiculopathy similar to the non-scoliosis population. It can occasionally be challenging to properly diagnose a 60-year-old who presents with back pain and newly discovered scoliosis and age-appropriate spinal degeneration.
Radicular Symptoms
Ligamentous hypertrophy, osteophyte formation, and disc degeneration can result in central canal and foraminal stenosis [ 12 ]. Disc herniation, lateral end plate osteophyte formation, and facet joint hypertrophy along with abovementioned degenerative changes can cause direct lateral recess or foraminal stenosis and resultant radiculopathy. Disc height loss can cause foraminal stenosis indirectly. Radicular symptoms tend to occur on the concave side of the curve. However, stretching of a nerve on the convex side may also produce radiculopathy. In their retrospective study, Smith et al. reported the prevalence of severe radicular leg pain among adult degenerative scoliosis patients seeking operative treatment to be 64 % [ 24 ].
Neurogenic Claudication and Weakness
Neurogenic claudication is an important symptom at presentation in adult degenerative scoliosis [ 1 ]. It is mainly due to central canal stenosis, although severe lateral recess and foraminal stenosis can result in similar symptoms. Spinal stenosis is seen more frequently with adult degenerative scoliosis (90 %) when compared to adult idiopathic scoliosis (31 %) [ 16 ]. Again, age-related changes and symptoms will be seen more frequently in an older population. With neurogenic claudication, patients typically describe bilateral leg weakness and pain with walking or standing, which improve with sitting or bending forward [ 29 ]. The classic description is that patients are in less pain and can walk further while leaning on a grocery cart. In severe cases of stenosis, neurogenic bladder [ 30 ] or cauda equina symptoms can develop.
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