PennHIP
University of Pennsylvania Hip Improvement Program — a radiographic method measuring passive hip joint laxity in dogs. More sensitive than OFA for detecting early hip laxity; can be performed from 16 weeks.
PennHIP (University of Pennsylvania Hip Improvement Program) is a radiographic evaluation method that quantifies hip joint laxity — the degree of looseness between the femoral head and acetabulum — using a standardized distraction technique.
Distraction Index (DI)
PennHIP measures passive hip laxity through a distraction view, where a specially designed device applies outward force to the femoral heads during radiography. The resulting Distraction Index (DI) measures how far the femoral head moves from the center of the acetabulum:
- DI of 0.0 = no laxity (femoral head perfectly seated)
- DI of 1.0 = complete luxation (femoral head fully dislocated)
- Practical range: 0.2–0.7 in most dogs
Higher DI values correlate with increased lifetime risk of osteoarthritis from hip dysplasia.
Interpreting PennHIP Scores
PennHIP reports DI relative to the breed database — dogs are compared against their breed, not a universal standard. A dog in the tightest 25th percentile for the breed has relatively low laxity risk compared to breed average.
General interpretation:
| DI | Risk Level |
|---|---|
| < 0.30 | Low laxity, low OA risk |
| 0.30–0.50 | Moderate laxity; monitor |
| > 0.50 | Higher laxity; elevated OA risk |
These are population generalizations — breed-specific thresholds vary.
Advantages Over OFA
PennHIP offers several advantages over the OFA extended-hip method:
- Age: valid from 16 weeks (OFA certification requires 24 months)
- Sensitivity: the distraction technique is more sensitive for detecting passive laxity that predicts future OA
- Quantitative: the DI is a continuous metric vs. OFA’s ordinal grades
- Predictive: longitudinal studies show DI measured at 4 months predicts OA presence at 24 months with reasonable accuracy
Training Requirement
PennHIP evaluation must be performed by a PennHIP-certified veterinarian. General practitioners must complete the PennHIP certification course and submit initial cases for quality review before becoming certified.