Classifications Used in Total Hip Arthroplasty Classifications Used in Total Hip Arthroplasty

Total hip arthroplasty is one of the most successful operation to be done and is definitely a rewarding procedure for both the surgeon and the patient. Ever since 3 days of low friction arthroplasty by Sir John Charnley, there has been considerable interest in improve- ment in the knowledge of surgical techniques and hip biomechanics. Over the past two decades there has been an exponential increase in total hip replacements. Therefore strat- egies to simplify the procedure and classifications to encounter difficulties in treatment plans were devised. It is imperative for consultants and trainees to be aware of these classifications systems which are helpful in pre op, intra op and postop planning. 4: Impaction bone grafting with tapered cemented stem if intact cortex. Composite prosthesis allograft if no proximal cortex.

1. Paprosky classification of acetabular deficiencies for revision hip arthroplasty 1

Classification
Type I: Defect with undistorted rim.
Type II: Defect with distorted rim but adequate to support a hemispherical cup.
• IIB: Superior with less than one-third superior rim deficient.
Type III: Defect with non-supportive rim.
• III A: Superior and lateral with 40 to 60% of the host bone intact and partial inherent mechanical stability.
• III B: Superior and medial with host bone less than 40% and possibility of occult discontinuity.

Clinical applications
Bone grafting techniques depends on the type of acetabular bone defect. Superior dome defect will need structural distal femoral allografts or trabecular metal wedges. Medial wall and ischial defect will need particulate bone grafts. Pelvic discontinuity needs ORIF versus triflanged custom cage. Unsupportive bone stock will need cup and cage construct.

Reliability
Gozzard et al. had performed a study to assess the reliability and validity of classification systems used for defects in acetabulum during revision arthroplasty [2]. It was found that there was poor to good intra observer agreement with the consultants (0.24) and moderate to good intra observer agreement with the registrars (0.36). Interobserver agreement was noted to   (Figure 2).

Classification
Type I No significant bone loss.
Type II Contained loss of bone stock where there is cavitary enlargement of the acetabular cavity but no wall deficiency.
Type III Uncontained loss of bone stock where there is <50% segmental loss of the acetabulum involving anterior or posterior column.
Type IV Uncontained loss of bone stock where there is >50% segmental loss of the acetabulum affecting both anterior or posterior columns (if there is >50% loss of the acetabulum, involving mostly the medial wall but the columns are intact, then this type of defect is considered type II because of the availability of the columns for reconstruction).
Type V Acetabular defect with uncontained loss of bone stock in association with pelvic discontinuity.

Reliability
Gozzard et al. had observed an Inter-observer reliability testing revealed kappa values of 0.89 for the acetabulum. Average validation value was kappa = 0.86 for the acetabulum [2]. To put things into perspective: clinical epidemiologists consider correlation values of 0.6-0.8 to be "substantial" and between 0.8 and 1.0 to be "perfect association".
3. Hodgkinson classification of radiographic demarcation of the socket following total hip arthroplasty

Introduction
This classification was proposed by Hodgkinson et al. from Wrightington, UK in 1988. He reviewed 200 patients undergoing revision arthroplasty and found out strong correlation between the extent of radiographic demarcation at bone-cement interface and intraoperative loosening of cemented acetabular components [4].
Type 1: Demarcation of outer one-third.
Type 2: Demarcation of outer and middle thirds.

Clinical significance
This classification helps surgeon help decide between partial or complete revision preoperatively.

Introduction
This classification was described by Wayne Paprosky et al. from Illinois, USA. He emphasized that his classification will help the surgeon determine the most appropriate option for reconstruction and thereby assists with ensuring that the appropriate implants and instruments are available at the time of surgery [5]. Gozzard et al. found moderate agreement between the preoperative and intraoperative validity; but the reliability of the classification was found to be fair ( Figure 3).

Classification
Type 1: Minimal metaphyseal and diaphyseal bone loss.
Type 2A: Absent calcar extend just below the inter-trochanteric region.
Type 3A: 2A plus diaphyseal bone loss but at least 4 cm of diaphyseal support possible.
Type 3B: 2B plus diaphyseal bone loss with less than 4 cm of diaphyseal support available.

Clinical applications
Type 1: Cemented or proximally porous coated cementless implant can be used.
Type 2A, 2B, 2C: Extensively porous coated cementless stem is preferred. Cemented stem should be avoided because of loss of metaphyseal endosteal bone.
Type 3A: Extensively porous coated stems or modular distal fitting tapered stems can be used.
Type 3B: Modular tapered cementless stems are used if adequate bone stock.
Impaction bone grafting is also an option.

Classification
Type I: Segmental deficiencies.
1a: Proximal either partial or complete.
Type III: Combined.
Type IV: Rotational or angular malalignment.

Clinical applications
This classification is very useful in describing the bone defect accurately but has less role in guiding the surgeon determine the reconstructive option.

Reliability
Gozzard et al. in their study observed the inter observer agreement among consultants and registrars. They noted a fair agreement (k value of 0.28) among consultants and a poor agreement (k value of À1.0) among the registrars.

Reliability
In the study by Saleh et al., they noted an inter observer reliability of k value 0.88 and average validity, k value of 0.88; indicating perfect association. The classification also provides probable treatment options for each type.

Dossick and Dorr classification of proximal femoral geometry 7.1. Introduction
Based on the calcar-to-canal ratio which is defined as the diameter of the femur at the midportion of the lesser trochanter divided by the diameter at a point 10 cm distal [7].
No thinning of cortices on AP or lateral radiographs.
Thinning of the posterior cortex on the lateral view.

Clinical significance
Type A suitable for cementless femoral stem, type C requires use of cemented stem and type B is intermediate.  C3: Displaced or unstable fracture [8].

Clinical applications
Type A1: Bone graft alone.
Type A2: Circelage wire if using proximally porous coated stem and can be ignored if using fully porous coated stem and there is no distal extension into diaphysis.
Type B3: Long stem with cortical allograft fixation.
Type C1: Morselized bone graft AE bypass stem and cortical allograft.
Type C2: Circelage wire AE bypass stem and cortical allograft.

Clinical application
This classification guides the surgeon with treatment decision.
AG and AL: Usually stable and can be treated non-operatively.
B2: Revision to long stem.
C: ORIF.   Since then it has been in widespread use and has stood the test of time [12].

Classification
Class I: Isolated islands of bone.
Class II: Gap between bones at least 1 cm.
Class III: Gap between bones less than 1 cm.

Clinical application
This classification is useful in the follow up of the high-risk patients and in patients with post HO resection.

Reliability
Vasileiadis et al. from mayo clinic in their study noted a moderate to substantial agreement (k value 0.49-0.71) in the inter observer reliability. Grade IV had best inter observer reliability [13,14] ( Figure 8).

Classification
Grade A: White-out with complete filling.
Grade B: Slight defects at the cement-bone interface.
Grade C: Defective cement mantle or radiolucency involving 50 to 99% of the cement-bone interface.
Grade D: 100% lucency or failure to cover the tip of the stem.

Clinical applications
This classification helps in predicting the survivability of the implant based on the grade of cementing.