Poliomyelitis

Background

Poliomyelitis is first known to have occurred nearly 6000 years ago, as evidenced by the withered and deformed limbs of certain Egyptian mummies. Polio was epidemic in the United States and the world in the 20th century, especially in the 1940s and 1950s. It was not until the 1950s that a vaccine became available.

Since May 1988, when the World Health Assembly resolved to eradicate poliomyelitis, the estimated global incidence of polio has decreased by more than 99%, and three World Health Organization (WHO) regions (the Americas, the Western Pacific, and Europe) have been certified as polio-free. Since 1994, when the countries of the WHO South-East Asia Region (SEAR) began accelerating polio-eradication activities, substantial progress toward that goal has been made.

Problems remain due to the difficulties involved in extending immunization coverage to some regions (especially Africa), integrating new vaccines into routine immunization schedules, and securing sufficient funding for programs. Injection safety is also a major problem that should be resolved by utilization and proper disposal of single-use autodisabling syringes. The forthcoming availability of new vaccines and the action of the Global Alliance for Vaccines and Immunization hold reasonable hope for the future. Other problems remain, such as new conditions resembling polio paralysis caused by viral infection other than by poliovirus 2 and postpolio syndrome (PPS).

In developed countries, on the other hand, residual poliomyelitis is still occasionally seen in the elderly and immigrants.^{[1, 2, 3, 4, 5, 6, 7, 8]}

Transmission of wild poliovirus (WPV) continues in only three countries: Afghanistran, Pakistan, and Nigeria. WPV type 1 (WPV1) is the only circulating serotype. Starting in 2015, injectable trivalent inactivated poliovirus vaccine (IPV) has been introduced as a part of routine immunization program in place of oral polio vaccine (OPV).^[9]

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Pathophysiology

Poliovirus is spread by the fecal-oral route and by aerosol droplets. The poliovirus is shed in oral secretions for several weeks and in the feces for several months. The poliovirus destroys the anterior horn cells in the spinal cord.

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Etiology

Acute poliomyelitis is caused by small RNA viruses of the Enterovirus genus of the Picornaviridae family. The single-stranded RNA core is surrounded by a protein capsid without a lipid envelope, which makes poliovirus resistant to lipid solvents and makes it stable at a low pH. Three antigenically distinct strains are known, with type 1 accounting for 85% of cases of paralytic illnesses. Infection with one type does not protect from the other types; however, immunity to each of the three strains is lifelong.

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History and Physical Examination

Stages of presentation

Acute stage

Poliovirus is primarily spread by fecal-hand-oral transmission from one host to another. The virus is shed in oral secretions for several weeks and in the feces for several months. It destroys the anterior horn cells in the spinal cord. Poliovirus infections can be divided into minor and major forms.^[10]

The minor associated illnesses occur 1-3 days before the onset of paralysis, with gastrointestinal complaints such as nausea and vomiting, abdominal cramps and pain, and diarrhea. There are also systemic manifestations, such as sore throat, fever, malaise, and headache. This stage usually lasts for 2-3 weeks but may extend for up to 2 months; the presence of any tenderness in the muscles is evidence that the acute stage is not over.

The major associated illnesses include all forms of central nervous system (CNS) disease caused by poliovirus, including aseptic meningitis (or nonparalytic polio), polio encephalitis, bulbar polio, and paralytic poliomyelitis, alone or in combination.

The clinical findings associated with an attack of polio are as follows:

• Fever, neck stiffness (nuchal rigidity), and a pleocytosis in the cerebrospinal fluid (CSF)
• Profound asymmetrical muscle weakness
• The initial phase is typically followed by some recovery of muscle strength, but permanent weakness results from necrosis of anterior horn cells
• Rarely, a transverse myelitis with paraparesis, urinary retention, sensory symptoms and signs, autonomic dysfunction (including hyperhidrosis or hypohidrosis), and decreased limb temperature may occur

Recovery stage

In the recovery stage, also known as the convalescent stage, the acute symptoms and muscle tenderness disappear, and the paralyzed muscles begin to recover. This stage lasts for up to 2 years after the onset of the disease. During this entire period, there is gradual recovery of the muscles; the recovery is rapid in the first 6 months but is slower during the subsequent months.

Residual-paralysis stage

The period beyond 2 years after the onset of the disease is called the residual-paralysis stage. No recovery of muscle power occurs in this stage. Deformities are liable to occur as a consequence of imbalance of muscle power and poor posture. There is also disuse atrophy of muscles and shortening of the leg from interference with growth. In neglected cases, gross fixed deformities of the hip, knee, and foot occur with severe wasting of muscles. Children with extensive paralysis and gross deformities have to crawl on all fours to move from place to place. (See the image below.)

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Typical contractures of postpolio residual paralysis.

Pattern of muscle weakness and deformities

Upper-limb involvement

Late functional deterioration is common in long-term poliomyelitis patients. Whereas upper-limb pain in individual functional regions is common, its overall prevalence and pattern in long-term poliomyelitis are poorly documented.^[11]  There are data in support of overuse due to greater mobility and independence as a cause of increasing upper-limb pain in long-term poliomyelitis, especially among severely paralyzed polio patients.

Lower-limb involvement

Typical osseous or soft-tissue abnormalities around the knees associated with poliomyelitis include the following:

• External rotation of the tibia
• Excessive valgus alignment
• Ligamentous laxity
• Genu recurvatum (see the image below)

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Genu recurvatum deformity of right knee.

With localized wasting, the quadriceps can help compensate for a weak calf. With hamstring weakness, the ability to decelerate the tibia is lost, and therefore, flexion of the knee will persist throughout the stance phase. In order to prevent this, the patient may attempt to compensate with increased quadriceps activity for a longer portion of the stance phase of gait.

In the case of a weak quadriceps and hamstrings, the occurrence of an equinus contracture or a hinged ankle-foot orthosis (AFO) with a dorsiflexion block will prevent excessive ankle dorsiflexion, as well as knee flexion during the stance phase. Lengthening of the Achilles tendon should be avoided in these patients. They may require an ischial weightbearing double upright locked knee orthosis, which helps prevent the knee from buckling during gait.

Common foot and ankle deformities seen include the following:

• Pes cavovarus (hindfoot cavus) due to evertor paralysis (peroneus brevis and longus)
• Pronated everted foot due to invertor paralysis (tibialis anterior and posterior)

Foot intrinsics are typically spared in poliomyelitis. Claw toes result from relative overactivity of the long toe flexors and extensors (to compensate for weakness of the triceps).

Spine involvement

Scoliosis is seen in young children with paralysis of trunk muscles and typically involves the thoracic spine. In older children, scoliosis develops gradually and typically involves the lumbar region. The curve may affect walking and sitting ability.^[12]

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Postpolio Syndrome

Postpolio syndrome (PPS) is the term used for the newly occurring late manifestations of poliomyelitis that develop in patients 30-40 years after the occurrence of the acute illness. It has been estimated that 25-60% of patients who had acute polio may experience these late effects of the disease.^{[13, 14, 15]}

The specific cause of PPS is unknown; the etiology has been attributed to pathophysiologic and functional causes. Pathophysiologic causes include the following:

• Chronic poliovirus infection
• Death of the remaining motor neurons with aging
• Premature aging
• Damage to the remaining motor neurons caused by increased demands or secondary insults
• Immune-mediated syndromes

Functional causes include the following:

• Greater energy expenditure as a result of weight gain
• Muscle weakness caused by overuse or disuse

PPS has been recognized for over 100 years, but it is more common at present because of the large epidemics of poliomyelitis that occurred in the 1940s and 1950s.

PPS is characterized by neurologic, musculoskeletal, and general manifestations. Musculoskeletal manifestations include muscle pain, joint pain, spinal changes such as spondylosis and scoliosis, and secondary root and peripheral nerve compression. General manifestations include generalized fatigue and cold intolerance. The slowly progressive muscle weakness occurs in those muscle groups already involved, such as the quadriceps and calf muscles.

Diagnostic criteria for this syndrome include the following:

• A prior episode of paralytic poliomyelitis with residual motor neuron loss (which can be confirmed through a typical patient history, a neurologic examination, and, if needed, an electrodiagnostic examination^[16]
• A period of neurologic recovery followed by an interval (usually ≥15 years) of neurologic and functional stability
• A gradual or abrupt onset of new weakness or abnormal muscle fatigue (decreased endurance), muscle atrophy, or generalized fatigue
• Exclusion of medical, orthopedic, and neurologic conditions that may be causing the symptoms mentioned in the preceding criterion

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Approach Considerations

Treatment options for poliomyelitis include the following^{[12, 17]} :

• Release of joint contractures
• Reestablishment of muscle balance around the joint to prevent deformities
• Muscle transplantation to replace a paralyzed muscle
• Stabilization of a relaxed or flail joint by means of (a) tenodesis, (b) fixation of ligaments, or (c) construction of artificial check ligaments
• Arthrodesis
• Osteotomies
• Limb lengthening,^[18]  Ilizarov techniques^[19]
• Joint replacement surgery

The surgeon managing the residual weakness of poliomyelitis and postpolio syndrome (PPS) must possess an understanding of the pathologic process in poliomyelitis, as well as the variations in the pattern of the disease in different parts of the body. Poliomyelitis causes a lower-motor-neuron disease unlike other types of neuromuscular paralysis. The neurologic problems and the pattern of paralysis following poliomyelitis are different from upper-motor-neuron paralysis or, indeed, lower-motor-neuron paralysis caused by other diseases.

Provocative poliomyelitis is paralysis following the administration of an intramuscular (IM) injection in children with acute viremia and indicates that (probably) muscle paralysis has been provoked by IM injections. Unnecessary injection must be avoided in children during acute viremic states, and use of the oral polio vaccine should be encouraged.^[20]

The surgeon must have a solid knowledge of the pathoanatomy before embarking on operative treatment. The mainstay of management remains physiotherapy and orthotic appliances.

The priorities of management, as described by Watts, are as follows^[21] :

• To get the patient walking
• In children, to correct factors that will create deformity with growth
• To correct factors that will obviate or reduce the need for an orthosis
• To correct upper-extremity problems
• To treat scoliosis 

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Nonoperative Therapy

Acute stage

In the acute stage of poliomyelitis, treatment is mainly medical, involving the pediatric physicians. General supportive treatment for the pyrexia and irritation, prevention of secondary respiratory infection, and treatment of any respiratory paralysis are the main aspects of therapy.

The paralyzed legs are supported by plaster splints or pillows and sandbags to keep the hip joints in 5° of flexion and in neutral rotation. The knee joint is held at 5° of flexion, and the foot is supported in a 90° position. Splinting relieves pain and spasm and prevents the development of deformities.

Recovery stage

Treatment in the recovery stage is mainly by the orthopedics department, involving physiotherapy and splinting.

The aims of treatment are as follows:

• To assist in the recovery of paralyzed muscles by remedial exercises
• To prevent deformities by the use of orthotic devices

An assessment is first made of the extent of muscle paralysis by charting the power of various groups of muscles and grading them according to the international nomenclature (Medical Research Council grading) as follows:

• 0 - Complete paralysis
• 1 - Slight flicker of contraction present
• 2 - Muscle can move a joint only when gravity is eliminated.
• 3 - Muscle can move a joint against gravity
• 4 - Muscle can move a joint against gravity and resistance
• 5 - Full normal power

Total functional assessment of the limbs is made before planning treatment. This will include the following:

• Charting the muscle power grades
• Extent of contractures and deformities
• Method of ambulation
• Shortening of the limb

Efficient physiotherapy is the mainstay of the management of this stage of poliomyelitis; exercise therapy, hydrotherapy, and electrical stimulation of muscles are essential in the management of paralytic polio. (See the images below.)

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Manipulation of deformities of hip.

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Manipulation of ankle and foot deformities.

Orthotic management

Appropriate orthotic appliances are prescribed to prevent deformities due to muscle imbalance (see the image below).

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Orthotic treatment for deformities around knee in poliomyelitis. (Click image to enlarge.)

The current international nomenclature for orthotic appliances describes the joints that are stabilized by the appliance (eg, what was once commonly referred to as a below-knee appliance is now referred to as an ankle-foot orthosis [AFO]).^{[22, 23, 24, 25]}

When the muscles controlling the hip and knee have normal power and the weakness is only in the dorsiflexors or plantarflexors of the ankle or the invertors or evertors of the foot, the patient is prescribed an AFO (below-knee orthosis or caliper). When quadriceps power is 2 or below, the knee must be stabilized, and hence, a knee-ankle-foot orthosis (KAFO; full or above-knee caliper) is prescribed. If hip abduction power is poor (ie, <2), the appliance will include a KAFO with a cane in hand to compensate for weak hip abductors.

In the recovery stage, a child who starts with a full appliance with a pelvic band may be able to manage gradually with a shorter appliance and ultimately may be able to discard it when the muscles fully recover as a result of intensive physiotherapy.

Residual-paralysis stage

The final aim should be for patients to return home and be accepted and integrated into their communities. Because overuse weakness is frequently present in these patients, the role of slowly progressive, nonfatiguing exercise in their rehabilitation is emphasized. New muscle weakness of a mild-to-moderate degree responds well to a nonfatiguing exercise program and pacing of activity, with rest periods to avoid muscle overuse. Generalized fatigue may be treated with energy conservation, weight-loss programs, and lower-extremity orthoses.

An orthosis is a device that externally supports an existing body part, with the objective of supporting, correcting, or compensating for skeletal deformity or weakness. There are currently many various types of orthoses, and the range of devices available to the prescriber continues to increase with the advent of new materials such as carbon fiber, as well as advances in manufacturing techniques.^{[22, 23]}

Orthoses are available for all parts of the body and aid in conservative and definitive treatment for many deformities. The thermoplastic leaf spring AFO, or drop foot splint, is a good example of an orthosis commonly used. It assists dorsiflexion and uses three-point pressure to stabilize the ankle joint.

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Surgical Therapy

Hip and knee contractures greater than 30°

In general, hip and knee contractures exceeding 30° will all require surgical treatment, unless one or both arms are weak in addition to bilateral lower-limb paralysis, making the use of crutches difficult or impossible. In a young child with fairly recent contractures, the most important single factor responsible for the deformity is tightness of the tensor fasciae latae and iliotibial band. In the older child or adult, however, other ligamentous and tendinous structures play an important part and must be divided as well.

The iliotibial band contracture produces flexion deformities of the hip and knee on the same side. The Soutter release involves the soft-tissue release on the anterolateral aspect of the hip joint, whereby the tensor fasciae latae and gluteus maximus are released from their origins, as they contribute to the formation of the iliotibial band. The Yount release involves excision of the thickened anterolateral fascia lata so that the knee contracture is better corrected. (See the image below.)

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Surgical correction of fixed flexion deformity of knee and hip due to iliotibial band contracture by Soutter and Yount release.

The percutaneous method of division is highly satisfactory for less severe contractures, provided that it is done correctly and as extensively as necessary. Care must be taken to avoid damaging the femoral and popliteal arteries, as well as the common peroneal nerve. The biceps, however, should always be divided under direct vision because of the risk of damaging the adjacent lateral popliteal nerve.

Tendon transfer to reestablish muscle power

In the selection of a tendon to transfer, the muscle should be sufficiently strong to supplement the power of a paralyzed muscle. The nerve and blood supply of the transferred muscle should be preserved in order to avoid iatrogenic weakness.

For efficiency, the transferred tendon should be securely attached (with tension) close to the insertion of a paralyzed tendon and should be routed in a direct line between its origin and the new insertion. The transferred tendon loses its power by one grade.

The transferred tendon should also be retained in its own sheath, avoiding tunnels in fascia or bone or an interosseous membrane so as to minimize adhesions.

The joint across which the muscle acts must be in a satisfactory position; all contracted structures must be released before the tendon transfer.

When possible, an agonist muscle, with the same range of excursion of its tendon, should be chosen.

Muscle transplantation to replace paralyzed muscle

In muscle transplant procedures, unlike tendon transfer procedures, both the origin and the insertion of a muscle are detached along with its neurovascular pedicle. This procedure is not as popular as tendon transfer, because of the difficulty in finding a normal muscle to transplant, donor-side morbidity, the technical difficulty of the procedure, and the shortage of microvascular surgeons in developing nations, where residual polio is still seen.

Stabilization of relaxed or flail joint

Tenodesis, fixation of ligaments, and construction of artificial check ligaments are used to restrict the range of movement or to eliminate abnormal motion of a joint. With few exceptions, these procedures have been discarded; deformity in the opposite direction may occur, and the tendon or artificial check ligaments may stretch with time. This technique can still be helpful in skeletally immature patients.

Arthrodesis

Arthrodesis is used to correct a deformity, relieve pain in arthritic joints, and reduce the number of joints across which a weak muscle is acting. Arthrodesis is more popular than tenodesis. In skeletally immature patients, extra-articular arthrodeses can be performed, allowing continued growth of the skeleton.^[26] (See the image below.)

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Surgical correction of rigid foot deformities by osteotomies and fusion.

Osteotomies

The osteotomy most commonly performed in this setting is a supracondylar distal femoral flexion osteotomy to correct recurvatum deformity at the knee.^[21]

Limb lengthening

Often, poliomyelitis is unilateral, causing limb-length inequality, which occasionally requires limb lengthening. In leg lengthening for patients with poliomyelitis, callus maturation is slow, and patients tend to develop contractures despite physiotherapy, bracing, or joint fixation. Concomitant and secondary surgery are frequently required to treat associated problems or residual deformities. Lengthening along an intramedullary locked nail can significantly shorten the treatment time with relatively few complications.^{[18, 27]}

Joint replacement surgery

In patients with postpolio residual deformities, joint replacement can be indicated. In one study, pain and knee scores improved following total knee arthroplasty (TKA) in patients with a history of poliomyelitis and antigravity quadriceps strength, but there was less pain relief in patients with less than antigravity quadriceps strength.^{[28, 29]}

Recurrence of instability and progressive functional deterioration are possible in all knees affected by poliomyelitis that have undergone total knee replacement, but they appear to occur more commonly in more severely affected knees.

Rahman et al found TKA using a rotating hinge prosthesis to be effective in pain relief; the hinge provided stability to correct instability.^[30] DeDeugd et al found no problems with hip instability or loosening after total hip arthroplasty (THA) at 10-year follow-up.^[31] Sonekatsu et al found no loosening or osteolysis or dislocations after THA at 8-year follow-up.^[32] Sobrón et al found THA to yield significant clinical improvement in patients with paretic limbs after postpolio residual paralysis.^[33] In a long-term study of clinical and radiologic outcomes of unconstrained THA (minimum follow-up, 84 months), Buttaro et al found that all patients improved in function and had pain relief.^[34]

Shoulder arthroplasty has been used successfully in patients with poliomyelitis with shoulder arthritis. In a study of seven polio patients who were treated with shoulder arthroplasty (one reverse arthroplasty, two hemiarthroplasties, and four total arthroplasties), Werthel et al found it to yield pain relief and improved movement; however, radiographic instability was noted, which remained asymptomatic.^[35]  

Ilizarov techniques

There are many drawbacks to using conventional approaches for the treatment of complex foot deformities, such as the increased risk of neurovascular injury, soft-tissue injury, and shortening of the foot. An alternative approach that can eliminate these problems is the Ilizarov method. Pin-tract problems, contractures, residual deformity, and recurrence of deformity can complicate the Ilizarov method.^[19]

In a study involving 25 patients with knee extension and ankle dorsiflexion dysfunction who were treated with ankle arthrodesis and tibial lengthening with an external fixator followed by plating and bone grafting, Wu et al found that gait improved significantly in all patients.^{[36, 37]} Complete bone healing was noted in all patients, with an average healing time of 4 months after plating. In a study by Kirienko et al, foot and ankle deformities in 27 patients were treated with the Ilizarov method with concomitant treatment of limb-length discrepancy; simultaneous deformity correction and limb-length equalization were achieved.^[38]

Management of fractures in poliomyelitis patients

Survivors of polio are still present in several parts of the world. Fractures that occur in these patients can be difficult to treat because of poor bone quality and deformities. Locking plates, nails, an external fixator, or various combinations thereof can be used to treat these fractures.^[39]  Wang et al used locking plates to treat distal femoral fractures in 19 postpolio patients and found that bony union and good function could be achieved but that delayed union and minimal callus could occur.^[40]

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Management of Postpolio Syndrome

Many patients with PPS require revision of orthotic devices such as braces, canes, and crutches or may use new, lighter orthotic devices to treat new symptoms. Common issues include genu recurvatum, knee pain, back pain, degenerative arthritis, or arthralgia. Surgery for scoliosis or fractures may also be necessary to treat new conditions.^{[15, 41]}

Nonsurgical treatments for PPS were examined in a 2015 Cochrane review by Koopman et al.^[42] The reviewers concluded that intravenous (IV) immunoglobulin (IVIg), Iamotrigine, muscle-strengthening exercises and static magnetic fields may be beneficial but that at present, it is impossible to draw definite conclusions about their effectiveness.

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Complications

Mortality due to postpolio syndrome

With the exception of poliomyelitis patients with respiratory failure, long-term mortality following poliomyelitis appears to increase 20 years after recovery from the acute illness.^[43]  Contracting severe paralytic poliomyelitis at a young age seems to increase long-term mortality.

Spinal deformity

Polio and PPS can result in paralytic spinal deformity. Godzik et al found that surgery had a high complication rate but also noted significant improvement in outcome scores.^[44]

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