A controlled study of 46 long leg casts found that cutting the cast on either the lateral (outer) or medial (inner) side produces equivalent reductions in skin surface pressure, giving clinicians flexibility in choosing univalve location based on practical considerations rather than pressure management concerns.
Long leg fiberglass casts are a standard treatment for certain lower extremity fractures in children, but they create a problem: the rigid cylindrical design can't accommodate the swelling that naturally occurs after injury. This puts patients at risk of compartment syndrome, a serious condition where pressure builds within muscle compartments and can compromise circulation and tissue viability. To manage this risk, orthopedic surgeons often "univalve" the cast, cutting it along one side to relieve pressure and allow room for edema.
The practical question has been whether the location of that cut matters. Should clinicians cut along the lateral (outside) or medial (inside) surface of the leg? The theory proposed was that a lateral univalve might preferentially reduce pressure in the anterior compartment of the leg, while leaving posterior pressures unchanged. To test this, researchers placed pressure transducers under both anterior and posterior leg compartments in a series of long leg casts. They systematically measured how skin surface pressures changed when casts were univalved on either side, then progressively separated with spacers, and finally converted to bivalves (cuts on both sides).
The results were straightforward: univalve location made no meaningful difference. Whether clinicians chose to cut the lateral or medial side, both anterior and posterior compartment pressures dropped by similar amounts. The study measured pressures through four stages: univalved only, univalved with a 3-millimeter spacer, univalved with a 6-millimeter spacer, and bivalved. Across all four stages and both compartments, lateral and medial univalves performed equivalently. The researchers found no statistically notable differences between the two approaches in any measurement.
What did matter significantly was the progression from univalve to bivalve. Comparing the initial univalved state to the final bivalved state, skin surface pressures dropped substantially in both anterior and posterior compartments across all groups (P < 0.001). This confirms that opening the cast helps relieve pressure, but the side on which you open it doesn't influence the magnitude of that relief. The authors conclude with a "dealer's choice" recommendation: practitioners can select either medial or lateral univalve based on practical factors like ease of access, patient comfort during the procedure, or other clinical considerations, without worrying that one location provides superior pressure management.
If you or a family member is receiving a long leg cast for a lower extremity fracture, this research suggests your orthopedic team has genuine flexibility in how they approach univalving without compromising the goal of pressure relief. Clinical decisions about cast management can be based on what works best logistically for your specific injury pattern or anatomy rather than pressure considerations. This is particularly relevant for pediatric patients, where accommodating swelling safely while maintaining fracture stability is a central concern during the first weeks of treatment.
The broader implication is that compartment syndrome prevention through univalving is a robust strategy that doesn't depend on technical precision in choosing a specific side. What matters more is that univalving occurs when needed and is done appropriately.
| Parameter | Details |
|---|---|
| Study type | Controlled experimental (testing 46 casts total) |
| Sample | 20 anterior compartment casts and 26 posterior compartment casts on volunteers |
| Intervention | Lateral vs. medial univalve in long leg fiberglass casts, with progressive spacer separation |
| Outcome measured | Skin surface pressure change across four stages |
| Primary finding | No notable pressure difference between lateral and medial univalve in either compartment |
| Statistical confidence | P < 0.001 for univalve vs. bivalve comparison across groups |
| Limitations | Single-volunteer model; doesn't address clinical outcomes like complication rates or patient tolerance; ex vivo testing rather than in-patient follow-up |
Harrop JS, et al. "Dealer's Choice": Univalve Location Effect on Skin Surface Pressures in Long Leg Casts. *J Am Acad Orthop Surg Glob Res Rev*. 2024. PubMed ID: 42175675. Link to PubMed
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