- Crowe Classification: (also see Paprosky classification and total hip replacement menu)
          - type of classification for severity of adult DDH;
          - grade 1: hips have less than 50% subluxation;
          - grade 2: hips have between 50% to 75% subluxation;
                  - usually do not have leg length inequality or loss of bone stock; 
                  - w/ low dislocation, femoral head articulates w/ false acetabulum which partially covers the true acetabulum;
                  - on x-ray there may be 2 overlapping acetabula:
                          - inferior part of the false acetabulum is an osteophyte which is located the level of the superior rim of the true acetabulum;
                          - visible part of the true acetabulum can therefore be missed;
                   - reference:
                          - The effect of superior placement of the acetabular component on the rate of loosening after total hip arthroplasty.
          - grade 3: hips have between 75% to 100% subluxation;
                  - complete loss of superior acetabular roof;
                  - may have thin medial wall;
                  - anterior and posterior columns are intact; 
                  - consider medial protrusion technique
                  - references:
                          - Results of total hip arthroplasty for Crowe Type III developmental hip dysplasia. 
                          - [Reconstruction of the Acetabulum with Structured Bone Graft in Press-Fit Technique.]  
                          - Acetabular Cup Revision With the Use of the Medial Protrusio Technique at an Average Follow-up of 6.6 Years.
                          - Durable Fixation Achieved With Medialized, High Hip Center Cementless THAs for Crowe II and III Dysplasia
          - grade 4: hips have more than 100% subluxation;
                  - true acetabulum is deficient but remains recongnizable; 
                  - if cup is placed at level of true acetabular then a subtrochanteric shortening osteotomy is often required;
                  - Total hip arthroplasty for Crowe type IV developmental hip dysplasia: a long-term follow-up study.
                  - Cementless Total Hip Arthroplasty and Limb-Length Equalization in Patients with Unilateral Crowe Type-IV Hip Dislocation. 
                  - Total Hip Arthroplasty with Shortening Subtrochanteric Osteotomy in Crowe Type-IV Developmental Dysplasia
                  - Total Hip Arthroplasty with Shortening Subtrochanteric Osteotomy in Crowe Type-IV Developmental Dysplasia: Surgical Technique 
                  - Treatment of Crowe IV high hip dysplasia with total hip replacement using the Exeter stem and shortening derotational subtrochanteric osteotomy.
                  - Greater Trochanter Osteotomy With Cementless THA for Crowe Type IV DDH
                  - Subtrochanteric shortening osteotomy combined with cemented total hip arthroplasty for Crowe group IV hips
                  - Wake-up Test in Total Hip Arthroplasty With High-riding Developmental Dysplasia
                  - Total hip arthroplasty followed by traction and delayed reduction for Crowe IV developmental dysplasia of the hip.
                  - Lesser trochanteric osteotomy in total hip arthroplasty for treating CROWE type IV developmental dysplasia of hip.
          - references:
                  -Total hip replacement in congenital dislocation and dysplasia of the hip.
                  - Influence of the Crowe rating on the outcome of total hip arthroplasty in congenital hip dysplasia.
                  - Total hip arthroplasty with cement and without acetabular bone graft for severe hip dysplasia. A concise follow-up, at a minimum of twenty years, of a previous report..