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OR8.1,OR9.1 | Neuromuscular Orthopaedics — PBL Case

CLINICAL SETTING

The orthopaedic outpatient clinic is seeing two patients referred by the paediatric and general medicine teams on the same morning. The registrar asks the final-year students to take initial histories and perform focused examinations before presenting to the consultant. Patient 1 — Arjun, 23 years old, male. A government schoolteacher. His mother mentions he had a fever with limb weakness at age 18 months. He recovered partially but has always had 'a bad right leg.' He now presents because he cannot lift the right foot properly when walking, frequently trips, and has developed a valgus deformity at the right knee over the past two years. He has no pain, no bladder or bowel problems, and no sensory symptoms. Patient 2 — Rohan, 7 years old, male. Born at 34 weeks gestation with a birth weight of 1.8 kg. The neonatal records show severe jaundice on day 3 requiring a double exchange transfusion. His mother says he 'walked late' (first steps at 22 months) and has always walked on his toes. Recently, a teacher noticed he scissor-walks and trips frequently. He has no learning difficulties and attends mainstream school.

Trigger 1: Examination Findings

The students examine both patients and report findings to the registrar: Arjun (23 y/o): Right lower limb — marked wasting of the quadriceps and anterior compartment; power: quadriceps 3/5, tibialis anterior 1/5, tibialis posterior 4/5, hamstrings 4/5, gluteus medius 3/5. Knee jerk absent on the right; plantar reflex flexor bilaterally. No sensory deficit. Fixed valgus deformity at right knee. Right foot: equinovarus at rest with inability to actively dorsiflex. Rohan (7 y/o): Both lower limbs — bilateral equinus on standing; passive dorsiflexion possible to 5° above neutral bilaterally with knees extended; brisk knee jerks (3+); 2+ clonus at both ankles; plantar reflexes extensor bilaterally. Scissoring on walking. No focal sensory deficit. Power appears functionally limited but cannot be formally assessed due to age and cooperation.

DISCUSSION POINTS

  • What is the significance of absent knee jerk vs brisk knee jerk in these two patients? Map each finding to its anatomical site of pathology.
  • Arjun has foot drop but no sensory loss. Which specific neurological lesion explains this combination? Why is common peroneal nerve palsy a less likely explanation here?
  • Rohan's equinus foot passively dorsiflexes to 5° above neutral. What is the clinical term for this type of deformity and what are its management implications compared to a foot that cannot be passively corrected?
  • Identify the neurological classification (UMN or LMN) for each patient and list three clinical signs from the examination that support your classification.
Click to reveal Trigger 2: Investigation Results and Surgical Planning (discuss previous trigger first!)

Trigger 2: Investigation Results and Surgical Planning

After further assessment, the following information is available: Arjun: X-rays confirm valgus knee deformity with no osteoarthritis. MRI of the lumbar spine is normal. Nerve conduction studies show reduced compound muscle action potentials in right tibialis anterior and quadriceps with no sensory nerve abnormality — consistent with old anterior horn cell disease. The consultant confirms post-polio residual paralysis. Rohan: Neuroimaging (MRI brain) shows periventricular leukomalacia consistent with perinatal white matter injury. The physiotherapist has performed the GMFCS assessment and records that Rohan walks independently on flat surfaces but cannot run and needs a railing for stairs. The consultant asks the students: For Arjun, we are considering a tendon transfer for his foot drop. For Rohan, we need to decide on immediate management before considering any surgery. Present your reasoning for each.

DISCUSSION POINTS

  • What is the minimum MRC power grade required in the tibialis posterior before transferring it to restore dorsiflexion in Arjun? What happens to the expected power after transfer?
  • Describe the surgical route of the tibialis posterior tendon transfer for foot drop in PPRP. Why is the route through the interosseous membrane preferred over the medial route around the medial malleolus?
  • Assign Rohan a GMFCS level and justify your answer using the functional milestones described.
  • For Rohan's dynamic equinus, the team discusses botulinum toxin A injection. Explain the mechanism of action of BtA at the neuromuscular junction. Which muscle group would you target? How long does the effect last?
Click to reveal Trigger 3: Outcomes, Complications, and Long-term Planning (discuss previous trigger first!)

Trigger 3: Outcomes, Complications, and Long-term Planning

Arjun undergoes tibialis posterior transfer (anterior route through the interosseous membrane to the dorsum of the foot). Six weeks post-operatively, his foot drop is corrected but he has developed slight planovalgus. The surgical team notes the entire tibialis posterior was transferred without leaving any invertor balance. Rohan receives bilateral gastrocnemius-soleus botulinum toxin A injections combined with intensive physiotherapy and bilateral AFOs. At 4-month follow-up, his equinus has reduced and gait has improved. However, his mother asks: 'Will he need surgery eventually? What are the risks?' The consultant uses both cases to teach the students: 'The most feared complication of equinus correction surgery in CP is not infection or bleeding — it is getting the correction wrong in the other direction.'

DISCUSSION POINTS

  • Why has Arjun developed planovalgus after a complete tibialis posterior transfer? What modification to the surgical technique would have reduced this risk?
  • The consultant refers to a deformity that is 'worse than the original equinus' as the feared complication of tendo Achilles lengthening. Name this deformity, explain its mechanism, and describe how the surgeon prevents it.
  • If Rohan's equinus deformity becomes fixed and unresponsive to conservative treatment by age 10, what surgical options would then be appropriate? What timing principle applies to triple arthrodesis in a child with CP?
  • Reflect on the key principle that distinguishes surgical planning in PPRP (LMN) from CP (UMN): Why do tendon transfers work differently in a flaccid paralysed muscle vs a spastic over-active muscle? What does this mean for preoperative assessment?

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [OR8.1] What are the aetiopathogenesis, clinical features, grading systems, and principles of orthopaedic management of post-polio residual paralysis, including tendon transfer prerequisites and triple arthrodesis indications?
  2. [OR9.1] What are the aetiopathogenesis, classification (GMFCS, CP type by motor pattern and distribution), clinical features, and evidence-based management principles for cerebral palsy, including the distinction between dynamic and fixed deformity and the role of botulinum toxin A versus surgery?