The etiological factors concerned in paralytic scoliosis are complex. Four main types of paralytic scoliosis can be recognised.

1. The general C-curve due to the body's anatomical attempt to shift its centre of gravity towards the weaker side. Vertebral rotation is not usually marked. This type usually occurs when patients with relatively slight paralysis have been allowed up too early ; it does not usually progress to severe deformity but may occasionally do so, gradually changing into Type 2. This type usually responds well to a period of rest and muscle redevelopment in recumbency. It also responds favourably to correction and fusion because correction is easy and there is little tendency to deterioration. Many of the "successes" of correction and fusion are in this class—almost equal success would often have been gained without "correction." The spine is slightly, but not very, unstable and a relatively localised fusion will give the little extra support that is needed.

2. The "general collapse" type of curve due to extensive spinal weakness. This is the type in which simple head suspension produces marked correction. Rotation is moderate. Provided the patient's general condition is satisfactory extensive spinal fusion is usually the best treatment and produces gratifying improvement.

3. The primary lumbar curve due to a combination of pelvic obliquity, extraspinal imbalance and imbalance of the deep rotator muscles. Rotation is usually marked. Treatment must include the correction of all these factors. In mild cases correction of the pelvic obliquity is enough, but in marked cases the spine must also be corrected. The disability from a lumbar paralytic scoliosis is much greater than that from a lumbar idiopathic scoliosis of the same degree; so correction is necessary in this type. Correction in a Risser-type jacket is often inadequate and recourse to operative correction is usually required.

4. The primary thoracic curve—often associated with weakness of the scapular muscles. The indications for and methods of treatment are practically the same as in primary idiopathic thoracic curves. These curves tend to be progressive and uncompensated. Although the most popular treatment is correction and fusion, wedge osteotomy of the spine gives better correction in intractable cases.

The main need is for further investigation into the etiology of paralytic scoliosis so that adequate preventive measures may be undertaken at an early stage. It is essential that every child who contracts poliomyelitis should have his back muscles examined before he gets up. If there is any suggestion of scoliosis further investigations including radiography and electromyography are essential.

"Wedge excision" of the apex of the curve is the rational way of correcting a scoliosis. It is a straightforward procedure which is successful in practice.

Internal fixation with a trifin nail after displacement osteotomy of the femur permits reduction of external splintage to a degree that any patient can tolerate with ease; it also eliminates the problem of the stiff knee.

The method has been used successfully for recent and old fractures of the femoral neck, for post-irradiation fractures, for failed nailing operations or arthroplastics, for osteoarthritis, for rheumatoid arthritis, for old congenital dislocations and subluxations, and to stabilise the hip after excision of the head and neck to create a pseudarthrosis.