MCQs – Neuromuscular

Modern Study Review (AI-Generated)

High-Yield Summary

Paralytic hip dislocation in cerebral palsy (CP), Duchenne muscular dystrophy (DMD), spina bifida, and polio represent core topics frequently tested in orthopaedic board exams. This topic is a staple of the Royal College exam, focusing heavily on surgical decision thresholds and neuromuscular pathology. The single most important clinical trade-off is timing and choice of surgical intervention based on muscle imbalance versus bony deformity progression (e.g., Salter vs. Dega osteotomy in CP hips). While classic exam answers emphasize static surgical procedures, modern practice increasingly integrates early orthotic management and minimally invasive techniques (e.g., Botox for dynamic equinus). Understanding neuromuscular disease inheritance, functional prognosis, and deformity patterns is essential for exam success and clinical excellence.

High-Yield Decision Matrix

Active Recall Q&A

Cerebral Palsy Hip Dislocation

Q: Why does a Salter osteotomy fail to address paralytic hip dislocation in CP patients?
A: Because it does not correct muscle imbalance and the acetabulum is not initially deformed.
Related Pearl: Early acetabular remodeling is minimal in CP; addressing muscle imbalance is critical before bony procedures.

Q: What osteotomy is preferred later in CP patients for posterior acetabular coverage?
A: Dega osteotomy.
Related Pearl: Dega osteotomy provides enhanced posterior coverage, important as deformity progresses.

Duchenne Muscular Dystrophy (DMD)

Q: How is IQ affected in Duchenne Muscular Dystrophy?
A: The average IQ is lower than normal.
Related Pearl: Cognitive involvement in DMD is mild but consistent, reflecting dystrophin’s role in the brain.

Q: Is myotonia a feature of Duchenne Muscular Dystrophy?
A: No, myotonia is not part of DMD.
Related Pearl: Myotonia is characteristic of myotonic dystrophy, not DMD.

Q: Which muscles are affected first in DMD?
A: Proximal muscles.
Related Pearl: Proximal weakness leads to characteristic Gower’s sign and early functional decline.

Q: What is the inheritance pattern of DMD?
A: X-linked recessive; sons inherit the affected gene from their mother.
Related Pearl: Female carriers are usually asymptomatic but can have mild symptoms due to lyonization.

Q: When is the best time to biopsy muscle in DMD?
A: When muscle strength is grade 3 (some preserved strength).
Related Pearl: Early biopsy shows dystrophic changes; late biopsy shows fibrosis and fatty replacement, limiting diagnostic yield.

Q: Are contractures common in DMD?
A: Yes, contractures are common.
Related Pearl: Contractures contribute to loss of function and are a target for early intervention.

Q: What urinary abnormality is seen in DMD patients?
A: Excess creatinine excretion.
Related Pearl: Reflects increased muscle breakdown and turnover.

Q: How can walking ability be prolonged in DMD?
A: Heel-cord lengthening combined with braces.
Related Pearl: Maintaining ankle dorsiflexion range delays loss of ambulation.

Cerebral Palsy Hand Surgery

Q: What are the ideal characteristics of a CP patient for hand surgery?
A: Motivated, intelligent, good sensibility, and voluntary use of the extremity.
Related Pearl: Sensory testing includes stereognosis, graphesthesia, two-point discrimination, and proprioception.

Q: How is sensibility assessed in CP hand surgery candidates?
A: Using stereognosis, graphesthesia, two-point discrimination, and proprioception.
Related Pearl: Better sensibility correlates with improved functional outcomes post-surgery.

Q: Why would an FCU to EDC transfer fail in a CP patient?
A: If the patient lacks voluntary ability to release grasp (finger extension).
Related Pearl: Voluntary motor control is critical for functional tendon transfers.

Q: What is the best indicator of prognosis for hand surgery in CP?
A: Voluntary use of the limb is most important, more than sensation or spasticity.
Related Pearl: Spasticity may limit voluntary use, reducing functional gains.

Spina Bifida Hip Dislocation and Foot Deformities

Q: Which spina bifida level has the highest incidence of hip dislocation?
A: L3 level with 36% incidence.
Related Pearl: Higher lumbar levels correlate with increased hip instability.

Q: What is the incidence of hip dislocation in thoracic spina bifida?
A: 28%.
Related Pearl: Thoracic level involvement still carries significant risk for hip dislocation.

Q: What is the incidence of hip dislocation in L1/2 spina bifida?
A: 30%.
Related Pearl: High lumbar levels have a high risk of hip instability.

Q: What is the incidence of hip dislocation in L4 spina bifida?
A: 22%.
Related Pearl: Lower lumbar levels have reduced but still significant risk.

Q: What is the incidence of hip dislocation in L5 spina bifida?
A: 7%.
Related Pearl: L5 involvement has a relatively low risk of hip dislocation.

Q: What is the incidence of hip dislocation in sacral spina bifida?
A: 1%.
Related Pearl: Sacral level lesions rarely cause hip instability.

Q: What foot deformity is associated with intact L4 in spina bifida?
A: Cavovarus deformity.
Related Pearl: L4 preservation allows some muscle function, leading to cavus foot patterns.

Q: What foot deformity is typical at L5 spina bifida?
A: Calcaneal valgus deformity.
Related Pearl: Loss of intrinsic foot muscles with preserved extrinsics causes valgus alignment.

Q: What percentage of spina bifida newborns have normal feet?
A: 20%.
Related Pearl: Most spina bifida patients present with foot deformities at birth.

Q: What foot deformity is seen in a newborn with L4 spina bifida?
A: Cavus/varus feet.
Related Pearl: Early recognition guides orthotic and surgical planning.

Q: Which spina bifida level is associated with cavus feet?
A: L4 level.
Related Pearl: Muscle imbalance at this level leads to high-arched foot deformities.

Q: What causes claw toes in myelomeningocele patients?
A: Loss of intrinsic muscles with functioning extrinsic muscles.
Related Pearl: Unopposed extrinsics cause toe hyperextension and clawing.

Cerebral Palsy Equinovarus and Hip Adduction

Q: How is a passively correctable equinovarus deformity treated in hemiplegic CP?
A: AFO with a lateral T strap to correct supination.
Related Pearl: Orthotic management can delay or prevent fixed deformities.

Q: What surgical treatment is indicated for a CP patient with 20° hip adduction and 25% femoral head uncovering?
A: Adductor tenotomy ± obturator neurectomy plus femoral derotation varus osteotomy.
Related Pearl: Early intervention prevents hip subluxation progression.

Q: What is the initial treatment for dynamic equinus deformities in CP?
A: Bracing (AFO) or BOTOX injections.
Related Pearl: Early nonoperative management can delay surgical intervention.

Polio

Q: In a child with polio who walks with hand on thigh, which muscles are weak?
A: Hamstrings, gluteus maximus, and rectus femoris are weak; gluteus medius is probably spared.
Related Pearl: Preservation of gluteus medius helps maintain pelvic stability despite weakness elsewhere.

Q: What muscle transfer is considered for a polio patient with drop foot but good plantar flexion?
A: Tibialis posterior transfer to dorsum of foot through interosseous membrane.
Related Pearl: Transfers restore dorsiflexion while preserving plantar flexion.

Q: What are the acute symptoms of polio?
A: Listlessness, sore throat, vomiting, hyperesthesia, paresthesia, fever, severe headache, asymmetric paralysis.
Related Pearl: Early recognition is critical to prevent respiratory failure.

Q: What is the reflex status in muscles paralyzed by polio?
A: Reflexes are absent.
Related Pearl: Lower motor neuron lesion pattern due to anterior horn cell involvement.

Q: Are sensory signs present in polio paralysis?
A: No objective sensory signs are noted.
Related Pearl: Polio affects motor neurons, sparing sensory pathways.

Q: What lab test is most helpful for diagnosing polio?
A: Spinal fluid cell count and protein level (usually unremarkable).
Related Pearl: Diagnosis relies on clinical and epidemiological data; CSF findings are nonspecific.

Classic Clinical Notes

• For the paralytic hip dislocation in the CP patient – a Salter osteotomy fails to address the problem of muscle imbalance, and initially the acetabulum is not really deformed anyways and does not need to be re-directed. Eventually, it may need some re-direction in which case a Dega is good to give them more posterior coverage.

• In Duchenne MD, the average IQ is lower. Myotonia is not part of this disease. Contractures are common, and the proximal muscles are affected first (typical of muscular dystrophies). It is inherited sex-linked recessive – the son evidently gets it from his mother (because he gets the Y from the father).

• The best time to biopsy a DMD muscle is when it still has some strength – grade 3. Waiting too long and it will only show fibrosis and fatty replacement.

• Contractures are common with DMD.

• A child with polio who puts his hand on his thigh to walk has weak hamstrings, gluteus maximus, rectus femoris. The gluteus medius is probably not affected.

• In DMD, the son that is affected evidently gets it from his mother. Mom has 2 X chromosomes – one with the affected gene. Therefore, half of the daughters will be carriers.

• The key protein deficiency in DMD is dystrophin.

• The ideal CP hand surgical patient is motivated, intelligent, with good sensibility, and most importantly, demonstrates voluntary use of the extremity. Sensibility is assessed with stereognosis, graphesthesia, two point discrimination, and proprioception. The better the sensibility, the more useful the extremity. If you did an FCU to EDC transfer to achieve finger extension, I think a good result would be precluded if the patient did not have the voluntary ability to release grasp (ie. extend his fingers).

• An L3 level of spina bifida has the highest incidence of hip dislocation. Thoracics – 28%, L1/2 (high lumbar) – 30%, L3 – 36%, L4 – 22%, L5 – 7%, and sacral – 1%.

• If the L4 is intact, the spina bifida patient may develop a cavovarus deformity.

• DMD patients excrete excess creatinine in the urine.

• Heel-cord lengthening and braces can prolong the ability of DMD patients to walk.

• For a hemiplegic CP who has a passively correctable equinovarus deformity – can try an AFO (for the equinus) with a lateral T strap to pull the foot out of supination.

• In a CP patient who has a 20 degree adduction deformity and 25% uncovering of the femoral head – ie. it’s on its way out – do an adductor tenotomy +/- obturator neurectomy, plus femoral derotation varus osteotomy.

• There is a recurrent question about best indicator of prognosis for surgery of the hand in CP patient. The suggestion in a number of these answers is that sensation in the form of stereognosis and proprioception is the most important, but in reality, it seems as if voluntary use is the most important thing. Spasticity may limit voluntary use of the limb, and would seem to be a more important factor.

• Treatment of dynamic equinus deformities should start with bracing (AFO) or BOTOX.

• The lowest level in spina bifida with cavus feet – L4 probably. L5’s get calcaneal valgus deformity.

• Clawtoes in the myelomeningocele patient come from a loss of intrinsics but functioning extrinsics.

• A newborn L4 spina bifida will have cavus/varus feet; only 20% of spina bifida kids have normal feet at birth.

• In a polio patient with a drop foot but good plantar flexion – consider tib post transfer to dorsum of foot through interosseous membrane.

• Beware the acute presentation of polio: listlessness, sore throat, vomiting, hyperesthesia, paresthesia, fever, severe headache, and an asymmetric paralysis or neurologic findings. Reflexes are absent in the muscle groups that are paralyzed. No objective sensory signs are noted (this is anterior horn disease). The most helpful lab procedure to diagnose polio would be spinal fluid cell count and protein level (unremarkable). In patients with upper extremity involvement, watch out for intercostals and diaphragmatic weakness, which may lead to severe respiratory embarrassment.

Last Updated on January 25, 2026 by Christian Veillette