- The Current State of Hip Joint Revisions
Data from the American Joint Replacement Registry (AJRR) reveals that from 2012 to 2017, hip joint revision surgeries accounted for 12.4% (54,959 cases) of total hip replacements.
During the same period (2012-2017), out of 47,378 cases of hip joint revisions, 25,607 were confirmed diagnoses. Among these, 12% (5,696 cases) were due to aseptic loosening, 10.9% (5,158 cases) resulted from other mechanical issues, 8.2% (3,895 cases) were caused by infections, 4.1% (1,947 cases) were attributed to joint surface wear, 3.7% (1,758 cases) were due to periprosthetic fractures, and 2.2% (1,036 cases) were linked to bone resorption.
As the number of hip joint revision surgeries continues to rise, cases of acetabular defects are also on the increase. Today, we'll delve into how we categorize and approach hip joint defects to provide targeted treatment.
Main Classification Methods for Acetabular Defects:
1. Paprosky Classification
2. AAOS Classification
3. Saleh Classification
4. Gustilo and Pasternak Classification
5. Gross Classification
6. Parry Classification
7. Engh Classification
Among these, Paprosky and AAOS classifications are currently recognized as the mainstream approaches.
Paprosky Classification
- Building upon other classification systems, Paprosky classification assesses osseous structural defects based on anatomical features.
- It involves preoperative X-ray assessment of prosthetic migration and the condition of acetabular support structures (anterior column, posterior column, superior weight-bearing area, and medial wall).
Degree Description:
1. Degree of upward displacement of the hip joint center: Not obvious vs. obvious (refers to an upward displacement of 3 cm or more above the acetabular teardrop line).
2. Degree of acetabular bone erosion (distance below the acetabular teardrop line): Mild (0-7 mm), moderate (8-14 mm), severe (15 mm or further below the line).
3. Degree of hip joint medialization (Kohler's line): Grade I (outside Kohler's line), Grade II (at Kohler's line), Grade II+ (inside Kohler's line), Grade III (into the pelvic cavity), Grade III+ (significantly into the pelvic cavity).
4. Degree of teardrop bone erosion: Mild (refers to a small amount of bone loss at the outer edge), moderate (refers to complete loss at the outer edge), severe (refers to bone loss at both the outer and inner edges).
Paprosky Type I
Upward Center Displacement: None
Iliac Bone Erosion: None
Teardrop Bone Erosion: None
Kohler's Line: Intact
Features: Minimal bone defect within the Acetabular Cup.
Paprosky Type II A
Upward Center Displacement: <3 cm
Iliac Bone Erosion: None
Teardrop Bone Erosion: Mild
Kohler's Line: Intact
Features: Mild upward displacement with accommodating bone defect.
Paprosky Type II B
Upward Center Displacement: <3 cm
Iliac Bone Erosion: Mild
Teardrop Bone Erosion: Mild
Kohler's Line: Intact
Features: Moderate upward displacement.
Paprosky Type II C
Upward Center Displacement: <3 cm
Iliac Bone Erosion: Mild
Teardrop Bone Erosion: Moderate
Kohler's Line: Grade III
Features: Severe medialization, mild upward displacement.
Paprosky Type III A
Upward Center Displacement: >3 cm
Iliac Bone Erosion: Moderate
Teardrop Bone Erosion: Moderate
Kohler's Line: Intact
Features: Severe upward and medial displacement, bone defects at 10 o'clock and 2 o'clock positions.
Paprosky Type III B
Upward Center Displacement: >3 cm
Iliac Bone Erosion: Severe
Teardrop Bone Erosion: Severe
Kohler's Line: Grade III to Grade III+
Features: Severe upward and medial displacement, bone defects at 9 o'clock and 5 o'clock positions.
- Main Approaches for Treating Acetabular Deficiencies
The purpose of acetabular repair is to:
1. Restore the integrity of the acetabular bone structure.
2. Reestablish the hip joint's center of motion to its anatomical position, thus restoring normal hip joint function.
3. Ensure maximal contact between the prosthesis and the host bone to achieve strong initial fixation of the prosthesis.
4. Securely fix transplanted allograft or autograft bone and provide proper support for the new prosthesis.
The currently most mainstream method for acetabular repair is:
1. Jumbo Cup
- Larger than the initial acetabular cup by more than 10mm.
- Generally reported in foreign literature to be between 60-70mm.
- Slightly lower in domestic standards (due to the physique of the population).
Features:
- Provides a larger contact area with the host bone.
- Maintains a center of rotation close to normal.
- Good tension in soft tissues.
- Minimal bone impingement, capable of accommodating larger femoral heads.
- Simpler and effective in operation compared to the use of oblong, IBG, and reinforcement rings.
2. Cage/GAP
Features:
- Fixed onto the host bone.
- Maximizes contact with the host bone, especially in the upper region.
- In cases of posterior superior defects, hooks are used below, near the teardrop or inserted into the ischium, and screws are used at the ilium to secure the placement of the acetabular prosthesis without affecting the Cage.
3. IBG (Impacted Bone Grafting) / Structural Bone Grafting
Features:
- An effective way to increase bone volume.
- IBG requires a titanium mesh at the bottom, which needs to be tightly packed, making it technically demanding for the surgeon.
- Postoperative stability cannot be achieved immediately; weight-bearing is only possible after bone integration between the graft and host bone has occurred.
- Currently, it is only used in cases involving minimal bone defects.
4. Double Socket Technique
Features:
- Essentially involves using a Jumbo Cup to replace structural bone grafting at the bottom.
- Offers high mechanical strength and immediate stability.
- Shows favorable mid-term follow-up data.
- In some cases, prosthetic components protruding into the pelvic cavity may lead to tissue adhesion.
- Relies on the bone ingrowth into the cup and surrounding bone for stability.
- Limited effectiveness for acetabular defects larger than the cup size.
- Lack of long-term follow-up data.
5. Metal Spacer
Features:
- Three-dimensional permeability.
- High porosity.
- Large pore size.
- High friction coefficient.
- Monolithic construction.
JUST HIP
JUST Medical 3D JCT Medical Engineering Interaction Center
Provides a variety of 3D customized solutions for acetabular defects.
