Transfemoral Amputation: Myodesis vs Myoplasty and Adductor Magnus Preservation
In short
Securing the adductor magnus through bone drill holes preserves hip adduction strength, eliminates severe femoral abduction drift, and stabilizes prosthetic stance.
In this guide (4 sections)
Surgical Biomechanics of Transfemoral Amputation
During transfemoral amputation, transecting the distal femur disrupts the insertion of the powerful adductor magnus. Without surgical anchor, the unchecked hip abductors (gluteus medius and minimus) pull the residual femur into marked abduction, producing severe lateral trunk lean and prosthetic instability during single-leg stance.
Surgical management of the transected musculature dictates long-term prosthetic outcomes. The two primary techniques are myodesis (anchoring transected tendons directly to bone via drilled cortical perforations) and myoplasty (suturing opposing agonist and antagonist muscle bellies to each other across the bone end).
Mechanical Comparison: Myodesis vs Myoplasty
| Surgical Parameter | Myodesis Technique | Myoplasty Technique | Functional Impact on Prosthetic Gait | |
|---|---|---|---|---|
| Anatomical Anchor | Tendon sutured directly to drilled femoral cortex | Muscle sutured to opposing muscle fascia over bone | Myodesis prevents muscle retraction and preserves length-tension curve | |
| Adductor Magnus Power | Preserves up to 70% of baseline adduction moment | Preserves less than 40% of baseline adduction moment | Myodesis maintains narrow base of support and prevents wide-based gait | |
| Femoral Abduction Drift | Minimal drift (femur remains anatomically aligned) | High incidence of progressive residual femur abduction | Myoplasty leads to lateral socket gaping and ischial unseating | |
| Cushioning at Bone End | Firm, stable distal tissue envelope | Bulky, mobile distal tissue wad | Mobile myoplasty wads roll under load, creating friction blisters | |
| Indications | Trauma, oncology, young active dysvascular patients | Severe peripheral vascular disease with poor cortical hold | Myodesis is gold standard whenever cortical bone viability permits |
Physiotherapy Rehabilitation Protocol for Myodesed Transfemoral Limbs
- Early Isometric Hip Adduction: Begin gentle isometric adduction over a pillow in supine on postoperative day 3; avoid forceful resisted adduction until bony healing occurs at week 6.
- Prone Hip Extension Positioning: Position the patient prone for 30 minutes 3 times daily to prevent hip flexion and external rotation contractures.
- Pelvic-Femoral Dissociation Drills: Teach isolated hip extension without compensatory anterior pelvic tilt or lumbar hyperextension.
- Pre-Prosthetic Residual Limb Loading: Gradually introduce axial loading over firm foam once surgical incision has achieved full primary intention closure.
Frequently Asked Questions
Why does my residual limb naturally pull outward to the side after above-knee amputation?
The hip abductors insert high on the greater trochanter and remain intact, whereas the adductor magnus inserts distally. If not anchored to the bone via myodesis, the uncountered abductors pull the residual femur into outward abduction.
When can I begin aggressive hip strengthening after myodesis?
Gentle isometric contractions begin within days, but resisted concentric and eccentric strengthening against elastic resistance must wait until 6 weeks post-surgery to ensure bone-tendon union.
Can an above-knee amputee walk without an adductor myodesis?
Yes, but walking requires significantly higher energy. Without adductor control, the patient exhibits a wide base of support, lateral trunk lean, and reduced prosthetic socket comfort.
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