Structured Oral Hip Examination Question 3
Structured Oral Hip Examination Question 3
EXAMINER: This is an anteroposterior (AP) radiograph of a 78-year-old man presenting with increasing right hip pain. He had a THA performed 17 years ago.
CANDIDATE: The AP radiograph demonstrates severe osteolysis of both femoral and acetabular components. There are radiolucent lines at the bone–cement interface located circumferentially around all seven DeLee and Charnley zones in the acetabulum. The femoral component has separated from the femoral cement with lucencies in all seven Gruen zones.
The femoral implant is a Stanmore prosthesis and no cement plug has been used in the femur, so-called first generation cementing techniques.
EXAMINER: What do you mean by first-generation cementing techniques?
CANDIDATE: First-generation cementing techniques involved hand mixing of cement and finger packing of bone cement in the doughy phase into an unplugged, unwashed femoral canal. Clinical results with first-generation cementing have been variable and in general have produced some disappointing results due to the inability to produce a consistent cement mantle.
Second-generation techniques involved plugging the medullary canal, cleaning the canal with pulsed lavage and inserting cement in a retrograde manner using a cement gun. This reduced the incidence of gross voids and filling defects in the mantle.
Third-generation techniques involved porosity reduction via vacuum mixing or centrifugation and cement pressurization.
Fourth-generation cementing techniques include stem centralization both proximally and distally to ensure an adequate and symmetrical cement mantle. This is important as uneven and excessively thin cement mantles are associated with early failure and revision.
EXAMINER: How is cementing technique graded?
CANDIDATE: The quality of the cement mantle has been described by Harris and Barrack using a scale of A to D.1
Complete filling of the medullary cavity by cement, a socalled ‘white-out’ at the cement–bone interface is graded ‘A’. Slight radiolucency of the cement–bone interface is defined as ‘B’. Radiolucency involving 50% to 99% of the cement–bone interface or a defective or incomplete cement mantle is graded ‘C’. Grade ‘C2’ is given to a defect where the tip of the stem abuts the cortex with no intervening cement. Radiolucency at the cement–bone interface of 100% in any projection, or a failure to fill the canal with cement such that the tip of the stem is not covered, is classified ‘D’.
EXAMINER: What are you going to do?
CANDIDATE: I would want to take a full history from the patient.
I would enquire about pain.
I would also want to exclude the possibility of infection (septic loosening) and would ask about problems with the hip postoperatively such as a wound infection requiring washout or a prolonged course of antibiotics. A history of fever, chills or a sinus tract suggests infection. Night pain, rest pain or constant pain would also suggest infection.
With aseptic loosening typically the pain is aggravated by weightbearing. Pain is significant with the first few steps of walking (start-up pain) which improves slightly with further walking only to worsen again with more walking. The pain is always improved with rest and rarely constant.
With aseptic loosening of a THA examination may reveal a shortening of the affected limb, antalgic gait and positive Trendelenberg sign. Pain at the extremes of movement suggests loosening.
It is important to exclude other causes of intrinsic hip pain such as trochanteric bursitis, tendinitis or impingement. Extrinsic sources of hip pain should also be excluded, particularly the lumbar spine especially if the pain has neurogenic features such as radiation below the knee, numbness, paraesthesia or dysaesthesias. Pulses and skin temperature should be checked to rule out a vascular cause for pain.
EXAMINER: Assume there is no infection in the hip and referred causes of pain have been ruled out. What are you going to do?
CANDIDATE: I would assess the patient. Find out how bad the pain is and whether the hip should be revised or whether symptoms are manageable and the patient can be reviewed regularly at the orthopaedic follow-up clinic.
EXAMINER: The patient can only walk about 200 yards before severe pain.
CANDIDATE: I would offer him revision hip surgery provided comorbidity issues have been optimized and the risks of surgery had been discussed and understood. Both components would need to be revised.
EXAMINER: What are the complications that you would need to mention to the patient when consenting for surgery?
CANDIDATE: I would mention
Infection.
Dislocation. Usually component malpositioning or laxity of soft tissues around the hip.
Fracture/perforation of femoral shaft.
Nerve palsy (peroneal, sciatic, femoral) 2–7%.
Vascular injury (femoral, iliac, obturator).
Leg-length discrepancy.
Heterotopic ossification.
Death (cardiac/pulmonary).
DVT/PE.
In addition the patient is going to require an extended trochanteric osteotomy (ETO) to remove the cement distally and this will increase operating time and blood loss. There is always the concern that the osteotomy site will go on to either malunion or non-union. Osteotomy migration or fracture can also occur.
EXAMINER: What about the bone loss? How do you plan for this?
CANDIDATE: Bone loss can be classified on the femoral side by using either the AAOS (Table 2.1) or the Paprosky classification system (Table 2.2).
The Paprosky classification evaluates the femoral diaphysis for its ability to support an uncemented, fully porous coated prosthesis. It is less detailed than the AAOS classification but is more useful in decision making if an uncemented revision is to be performed.
Table 2.1 AAOS classification system for femoral defects.
|
I Segmental defect Proximal (partial or complete) Intercalary Greater trochanter |
|
II Cavitary defect Cancellous Cortical Ectasia (dilatation) |
|
III Combined segmental and cavity defect |
|
IV Malalignment Rotational Angular |
|
V Femoral stenosis |
|
VI Femoral discontinuity |
Table 2.2 Paprosky classification system for femoral defects.
|
I Minimal metaphyseal cancellous bone loss/normal intact diaphysis |
|
Type I defects are seen after removal of uncemented component without biological ingrowth on surface. Usually seen with Austin Moore type prosthesis or resurfacing procedures. The diaphysis and metaphysis are intact and there is partial loss of the calcar and anteroposterior (AP) bone stock |
|
II Extensive metaphyseal cancellous bone loss/ normal intact diaphysis |
|
Often seen after removal of cemented prosthesis. Calcar deficiency and major AP bone loss |
|
IIIA Metaphysis severely damaged/ > 4 cm diaphyseal bone for distal fixation |
|
Grossly loose femoral component First-generation cementing techniques |
|
IIIB Metaphysis severely damaged/ < 4 cm diaphyseal bone for distal fixation |
|
Type IIIB defects extend slightly further than type IIIA, however reliable fixation can be achieved just past the isthmus of the femur Cemented with cement restrictor Uncemented with substantial distal osteolysis |
|
IV Extensive metaphyseal and diaphyseal bone loss/isthmus non-supportive |
|
Extensive defect with severe metaphyseal and diaphyseal bone loss and a widened canal that cannot provide adequate fixation for a long stem |
Table 2.3 AAOS classification system for acetabular defects.
|
Type I Segmental defects |
|
Peripheral – superior/anterior/posterior |
|
Central – medial wall absent |
|
Type II Cavitary defects |
|
Peripheral – superior/anterior/posterior |
|
Central – medial wall intact |
|
Type III Combined segmental and cavitary bone loss |
|
Type IV Pelvic discontinuity |
|
Separation of anterior and posterior columns |
|
Type V Arthrodesis |
Table 2.4 Gross and associates classification system for acetabular bone defects.
|
Type |
Description |
|
I |
No substantial loss of bone stock |
|
II |
Contained loss of bone stock (columns and/or rim intact) |
|
III |
Uncontained loss of bone stock (< 50% acetabulum) |
|
IV |
Uncontained loss of bone stock (> 50% acetabulum) |
|
V |
Contained loss of bone stock with pelvic discontinuity |
Acetabular bone loss
Acetabular defect classification systems are used to predict the extent of intraoperative bone loss and guide reconstructive options.
Several classification systems exist; the three most commonly used are the American Academy of Orthopaedic Surgeons (AAOS) system (Table 2.3), the Gross and associates system (Table 2.4) and the Paprosky classification system (Table 2.5).
Gross and associates classification system (Table 2.4)
This classification is based on the nature of the bone graft needed for reconstruction on standard preoperative AP and lateral radiographs. A bone defect is considered uncontained if morselized bone graft cannot be used to fill the defect.
|
Table 2.5 Paprosky classification of acetabular bone defects.
|
Paprosky acetabular bone loss classification
This classification is based on information that can be obtained from AP radiographs. Four radiographic criteria are assessed:
1. Superior migration of the hip centre
Indicates damage to anterior and posteriorcolumns.
Superomedial indicates greater damage toanterior column.
Superolateral indicates greater damage toposterior column.
2. Ischial osteolysis
Bone loss inferior posterior column andposterior column.
3. Teardrop osteolysis Inferior anterior column and medial wall.
4. Position of the implant relative to Kohler’s line Deficiency of anterior column and/or medial wall deficiency.
A trial component with full inherent stability does not change position when the surgeon pushes its rim or performs a trial reduction. A trial component with partial inherent stability does not change position with removal of the inserter, but does not withstand the force of pushing on the rim or performance of a trial reduction. A trial component with no inherent stability changes position with the simple act of removing the inserter.
The Paprosky classification (Table 2.5) is often used clinically in preference to the AAOS classification as it not only predicts bone loss encountered intraoperatively but also assists in determining reconstructive options.
EXAMINER: How would you plan for surgery?
CANDIDATE:I would get an anaesthetic review to make sure the patient was fit enough for surgery and risks acceptable and also so they could order any special tests such as echocardiogram or pulmonary function tests etc.
I would cross match for four units and make sure the cell
saver was available.
I would order one femoral head frozen allograft and have freeze dried allograft available if required.
Implant removal kit which would include curved and straight osteotomes for the cemented cup and femur, ultrasonic tools, high speed burrs.
Accurately template the revision implants required taking into account the level of the ETO.
I would use uncemented components as generally they are preferred if previously cement was used. Cement would be relatively contraindicated if using an ETO as it may get into the osteotomy site and prevent healing.
A long stem femoral implant, multihole revision (tantulum) acetabular shell and a metal-on-polyethylene bearing surface. I would attempt to use at least 32 mm head but preferably a 36 mm head as this significantly reduces the risk of postoperative dislocation.
I would need Dall–Miles cables grip system to rewire the ETO back into place.
I would need a flexible light source for visualizing the medullary canal of the femur.
I would generally prefer a posterior approach with ETO unless the risk of dislocation was deemed high in which case I would use an anterolateral approach with ETO.
EXAMINER: How do you remove the cemented femoral component?
CANDIDATE: It is important to clear the shoulder of the prosthesis removing any cement or bone overhanging the proximal aspect of the greater trochanter as either stem removal will be obstructed or a greater trochanter fracture will occur with stem removal.
Flexible osteotomes and a small burr can then be used to further disrupt the cement/implant interface.
The ETO will greatly simplify implant and cement removal. I would use cement splitters to remove cement along with ultrasonic tools. Cement is split radially and then removed.
EXAMINER: What about the acetabular component?
CANDIDATE: The safest way is to disrupt the PE cup from the cement using curved gouges. This prevents inadvertent damage to the bone of the acetabulum bed. After removal of the cup the cement is removed piecemeal. Sometimes a threaded extractor through a drill hole in the PE can be used. High-speed burrs are sometimes needed to debulk cement within acetabular anchoring holes.
Endnote
1. Barrack RL, Mulroy RD Jr, Harris WH. Improved cementing techniques and femoral component loosening in young patients with hip arthroplasty: a 12 year radiographic review. J Bone Joint Surg Br 1992;74:385–389.
This is a classic hip paper. You should know the key message, relevance and why it is important.