Arthritis

Hip osteoarthritis (OA) is a progressive condition that affects the hip joint as a whole. Although cartilage loss is its defining feature, OA also affects the underlying bone, joint lining, and labrum 1. Normal articular cartilage provides a smooth, low-friction surface and distributes load across the femoral head and acetabulum. Because mature articular cartilage is avascular and has limited intrinsic reparative capacity, progressive cartilage loss can become effectively irreversible once degeneration starts.

Hip OA may develop through several pathways, but in the hip preservation population, abnormal joint mechanics are particularly important. Many cases previously considered “primary” or idiopathic OA are now understood to occur in hips with underlying structural abnormalities that chronically alter joint contact and load distribution 2.

Important mechanical contributors include:

• Femoroacetabular impingement, particularly cam morphology, which produces repetitive chondrolabral shear during hip motion.
• Acetabular dysplasia, in which reduced femoral head coverage decreases the effective weight-bearing surface and concentrates load at the acetabular rim.
• Abnormal acetabular or femoral version, which may alter joint contact or stability.
• Instability or capsular insufficiency, producing abnormal femoral head translation and repetitive cartilage loading.
• Previous trauma, osteonecrosis, inflammatory arthropathy, infection, or other secondary joint disorders.

Femoroacetabular impingement provides a well-described model of mechanically mediated degeneration. Cam morphology produces abnormal engagement of the nonspherical femoral head-neck junction with the acetabular rim, generating shear at the chondrolabral junction and characteristic anterosuperior acetabular cartilage damage. Pincer morphology produces repetitive contact between the femoral neck and acetabular rim, with predominant labral injury and a narrower zone of adjacent cartilage damage 2,3. Repeated injury can ultimately progress from focal structural damage to generalized joint degeneration.

The major pathological distinction for hip preservation is between focal, potentially containable chondral injury and established diffuse arthritis. A focal acetabular cartilage lesion associated with cam impingement may occur in an otherwise well-preserved joint. In contrast, established OA reflects broader failure of the articular system, frequently including substantial cartilage loss on both sides of the joint, subchondral remodeling, osteophyte formation, and progressive loss of normal joint architecture.

This distinction matters because correction of the original mechanical abnormality cannot reverse advanced structural degeneration. Removing an impingement mechanism, stabilizing the capsule, or restoring labral function may reduce ongoing abnormal loading, but these interventions do not restore extensively lost hyaline cartilage or normalize an already degenerative osteochondral environment.

Across systematic reviews, increasing pre-existing arthritic severity and greater chondral damage are consistently associated with less durable outcomes and a greater likelihood of subsequent conversion to total hip arthroplasty 4-6. In patients with radiographic osteoarthritis, particularly those with joint-space narrowing, diffuse cartilage loss, or advanced chondral damage, reported outcomes are substantially less favorable than in patients with preserved joint surfaces. A systematic review of hip arthroscopy performed in the setting of OA found that approximately 25% of patients underwent conversion to total hip arthroplasty at a mean follow-up of about 2 years, although rates varied considerably according to disease severity, patient age, and study population 4. In another systematic review, patients with more advanced radiographic arthritis, including Tönnis grade 2 or greater, demonstrated inconsistent clinical improvement and a higher risk of early arthroplasty conversion; some studies reported conversion rates approaching 40%-50% within short- to intermediate-term follow-up 5,6. Radiographic joint-space narrowing is particularly important: patients with joint space of 2 mm or less have been reported to have markedly increased odds of requiring total hip arthroplasty after arthroscopy, with some cohorts demonstrating approximately 10-fold greater risk compared with patients with wider preserved joint spaces. Advanced chondral lesions, especially full-thickness acetabular or femoral head defects and bipolar cartilage loss, are similarly associated with inferior patient-reported outcomes and reduced survivorship of the native hip. These findings do not imply that every patient with mild radiographic degeneration will fail arthroscopy. Rather, they demonstrate that the probability of durable joint preservation decreases as cartilage loss becomes more extensive, more diffuse, and more closely associated with subchondral bone changes. The arthroscopic decision should therefore account for the distribution and depth of cartilage damage, joint-space preservation, radiographic arthritis grade, patient age, symptom duration, and the presence of correctable mechanical pathology, rather than relying on a single imaging feature.