What is the procedure for administering a motor point block in the hip adductor muscles to manage spasticity?

Motor Point Block Technique for Hip Adductor Spasticity

Motor point blocks for hip adductor spasticity should be performed using anatomically-defined injection sites with neuromuscular blocking agents (typically botulinum toxin or local anesthetics like 1% etidocaine), guided by surface landmarks and ideally with electrostimulation to confirm motor point localization.

Anatomical Localization of Motor Points

The motor points for hip adductor muscles are located along a reference line drawn from the pubic tubercle to the medial epicondyle of the femur (or medial joint line at the distal extent of the medial femoral condyle), expressed as percentage distances 1, 2:

• Adductor longus: 26-31% distal to pubic tubercle 1, 2
• Adductor brevis: 21-22% distal to pubic tubercle 1, 2
• Adductor magnus: 30-38% distal to pubic tubercle 1, 2
• Gracilis: 32-44% distal to pubic tubercle 1, 2

For mediolateral positioning, measure along a horizontal line from the pubic tubercle to the greater trochanter 2:

• Adductor longus: 24.9% lateral to pubic tubercle 2
• Adductor brevis: 24.9% lateral to pubic tubercle 2
• Adductor magnus: 33.6% lateral to pubic tubercle 2

Procedural Technique

Equipment and Setup

• Specific needle designed for motor point blocks 3
• Neurostimulator for precise motor point localization 3
• Aspiration capability to avoid intravascular injection 4

Agent Selection

For diagnostic/assessment blocks (to determine contribution of spasticity vs. contracture):

• 1% non-adrenalized etidocaine is the preferred local anesthetic due to its optimal onset and duration of action 3
• This allows immediate assessment of functional improvement and helps predict outcomes of more permanent interventions 3

For therapeutic blocks (longer-term spasticity reduction):

• Botulinum toxin type A (Dysport or Botox) is the standard therapeutic agent 4
• Optimal dose: 1000 units Dysport (approximately 250-300 units Botox equivalent) divided between adductor magnus, longus, and brevis muscles bilaterally 4
• Maximum safe doses: 1500 units Dysport (400 units Botox) per treatment session; 250 units Dysport (50 units Botox) per injection site 4
• Botulinum toxin type B (10,000-22,000 IU total dose bilaterally) may be more cost-effective when type A has failed 5

Injection Technique

1. Position the patient supine with hip in slight abduction 3

2. Mark surface landmarks: Identify pubic tubercle, medial epicondyle of femur, and greater trochanter 1, 2

3. Calculate injection sites using percentage distances along reference lines 1, 2

4. Insert needle at calculated motor point location 3

5. Use neurostimulator to confirm motor point by observing muscle contraction at low current (typically 1-2 mA) 3

6. Aspirate before injection to ensure needle is not intravascular 4

7. Inject agent slowly at confirmed motor point 3

8. Repeat for each target muscle (typically adductor longus, brevis, and magnus bilaterally) 4

Assessment and Outcome Measures

Evaluate at baseline, 4 weeks, and 12 weeks post-injection 4:

• Modified Ashworth Scale (expect 2-3 point reduction) 3
• Tardieu Scale (more sensitive than Ashworth for detecting changes) 3
• Distance between medial femoral condyles with thighs extended (measured in cm) 4
• Active and passive range of motion using goniometry 4
• Visual Analog Scale for pain assessment 4
• Functional measures: 10-meter walking time, perineal hygiene score (0-5), sitting position comfort 4

Critical Technical Considerations

Multiple motor branches occur in approximately 26% of adductor muscles (21 of 80 muscles in anatomical studies), though rarely in more than one muscle per limb 1. This means:

• Single injection per muscle is usually sufficient 1
• If initial response is suboptimal, consider that multiple motor points may exist 1

Patient cooperation is essential for accurate assessment of functional outcomes 3. The procedure requires:

• Ability to follow commands for active movement testing 3
• Tolerance of positioning for injection 3

Adjunctive Therapy

Following motor point block, combine with physiotherapy and passive stretching to maximize hip abduction gains 4. Consider:

• Serial casting or orthotic devices to maintain increased passive hip abduction 4
• Active strengthening of hip abductors (antagonist muscles) once spasticity is reduced 3

Expected Outcomes and Duration

• Onset: Local anesthetic blocks provide immediate effect; botulinum toxin shows effect within 2 weeks 5, 3
• Duration: Botulinum toxin effects typically last 3-4 months 5, 4
• Functional improvements: Reduced muscle tone, decreased painful spasms, improved gait, easier nursing care and perineal hygiene 5, 4

Safety Profile

Side effects are local and transient at therapeutic doses 4:

• Local muscle weakness (expected therapeutic effect) 4
• Pain at injection site 4
• Hematoma (minimized by aspiration technique) 4
• Systemic effects are exceptional when proper dosing and technique are used 3