The hip joint is a major ball and socket joint optimally designed to provide low-friction motion over a wide range with inherent stability. Mechanical hip dysfunction comprises hip problems attributable to morphological variations of the femur and acetabulum that affect hip function.
Requirements for Normal Hip Function
- 1 Healthy articular cartilage
- 2 Stable femoral head in the acetabulum
- 3 Adequate impingement-free range of motion
- 4 Neuromuscular control
Primary cartilage and synovial disorders that degrade the cartilage, neuromuscular conditions that affect hip function, and primary bone conditions such as infections, tumours, and metabolic bone disease are non-mechanical causes of hip dysfunction requiring disease-specific treatment. Morphological sequelae of these diseases can cause mechanical hip dysfunction.
Interaction of Morphological Features
Minor variations are common and do not usually cause problems. Some major variations may also not produce problems when compensated by countering morphological factors:
| Variation | Compensated By |
|---|---|
| Lateral dysplasia | Coxa vara or flattening of the sourcil angle |
| Coxa profunda | Coxa valga and increased head-neck offset |
| Cam morphology / mild SCFE | Increased anteversion or a shallow acetabulum |
| Anterior dysplasia | Femoral retroversion |
| Posterior dysplasia | Femoral anteversion |
Morphology, Biology, and Activity Level
Each morphological variation has a specific effect on the hip, and the effects can be additive — causing disease early — or compensatory, allowing good function. As mechanical hip disease is activity-related, more active people are more likely to become symptomatic early. Beyond morphology, biology dictates who becomes more symptomatic from the same activity level, making the prognosis of each variation unknown for any given individual.
The most effective way to correct morphological variations is with surgery. As surgery carries cost, risk of complications, and no guaranteed outcome, surgical treatment is offered only to symptomatic and active patients who understand all the risks and benefits. The exception is a painless condition with poor prognosis without treatment — such as dysplasia in a growing child that worsens without causing pain.