Why is hamstring lengthening preferred over gastrocnemius (calf muscle) lengthening for managing muscle contractures in patients with cerebral palsy or other neurological conditions?

Why Hamstring Lengthening Over Gastrocnemius Lengthening?

The question fundamentally misframes the surgical decision-making in cerebral palsy—hamstring lengthening and gastrocnemius lengthening address completely different anatomical deformities and are not interchangeable alternatives. Hamstring lengthening corrects knee flexion contractures and crouch gait, while gastrocnemius/Achilles lengthening addresses equinus deformity at the ankle 1, 2.

Anatomical Targets and Indications

Hamstring Lengthening

• Indicated specifically for knee flexion contractures causing crouch gait in cerebral palsy, where the hamstrings are demonstrably short and/or lengthening slowly during gait 3, 4
• Targets the semimembranosus, semitendinosus, and biceps femoris muscles crossing the knee joint 3, 5
• Primary hamstring lengthening improves stance knee extension by ≥10 degrees in 71% of patients 4

Gastrocnemius/Achilles Lengthening

• Indicated for equinus deformity (foot drop) and forefoot plantar pressure elevation in cerebral palsy 1, 2
• The IWGDF guidelines demonstrate that Achilles tendon lengthening combined with total contact casting increases ulcer healing (RR 1.10) and sustained healing (RR 3.41) while reducing forefoot plantar pressure by 218 kPa 1
• Ankle-foot orthosis should be prescribed immediately for foot drop in hemiplegic cerebral palsy to improve gait mechanics 2

Critical Clinical Decision Points

The choice between these procedures depends entirely on which joint deformity is present:

When Hamstring Lengthening Is Appropriate

• Popliteal angle contracture documented on physical examination 4, 6
• Excessive knee flexion at initial contact (>10-15 degrees beyond normal) 4, 7
• Increased minimum knee flexion in stance phase on gait analysis 3, 4
• Dynamic semimembranosus muscle-tendon length more than 2 standard deviations shorter than controls 3

When Gastrocnemius Lengthening Is Appropriate

• Limited ankle dorsiflexion with knee extended 6
• Equinus deformity causing forefoot loading 1
• Elevated forefoot plantar pressures on gait analysis 1
• Foot drop in hemiplegic cerebral palsy 2

Surgical Technique Considerations

For hamstring lengthening, the "slow surgical lengthening" (SSL) technique is superior to traditional acute complete correction:

• SSL maintains muscle strength postoperatively, with mean peak isokinetic knee flexion torque actually increasing by 0.076 Nm/kg at 1 year 7
• Traditional acute lengthening with forced manipulation invariably causes muscle weakness 7
• SSL allows tendinous tissue to separate spontaneously without forcing further acute lengthening, minimizing muscle damage 7
• Mean popliteal angle improves by 16.2 degrees with SSL while preserving strength 7

Important Caveats and Pitfalls

Repeat Hamstring Lengthening Has Poor Outcomes

• Only 28% of repeat hamstring lengthening patients improve stance knee extension by ≥10 degrees, compared to 71% with primary surgery 4
• Repeat hamstring lengthening does not result in long-term correction of crouch gait 4
• When crouch recurs after initial hamstring lengthening, the problem is usually NOT short hamstrings—26/28 limbs in primary surgery and 13/14 limbs in repeat surgery had short/slow hamstrings preoperatively 3
• Recurrent crouch after hamstring lengthening indicates other pathology: quadriceps insufficiency, rotational malalignment, fixed knee flexion contractures, patella alta, weak calf muscles, or loose heelcords 3, 4

Gastrocnemius Lengthening Complications

• Large increases in new rearfoot ulcers (RR 9.56) 1
• Increased falls (RR 5.31) and infections (RR 3.19) 1
• These risks must be weighed against benefits when non-surgical offloading has failed 1

Timing and Integration with Comprehensive Management

Both procedures should be considered within comprehensive single-event multilevel surgery when indicated, not as isolated interventions:

• Early intervention is critical—delaying treatment causes progressively irreversible modifications to muscle and bone growth 2, 8
• Implement task-specific motor training (CIMT for hemiplegia, GAME for all CP subtypes) immediately upon diagnosis 2, 8
• Regular surveillance with anteroposterior pelvic radiographs every 6-12 months starting at age 12 months prevents hip displacement 2, 8
• Both hamstring and gastrocnemius lengthening reduce spasticity by at least one Ashworth grade in 89% and 78% of patients respectively 6