1 Principles topenlarge
Arthroplasty for femoral neck fractures
Displaced intracapsular femoral neck fractures in the elderly have a high risk of failed fixation, non-union, and avascular necrosis. For appropriately selected patients, arthroplasty with either a hemi-arthroplasty or total hip replacement may be more successful. Arthroplasty reduces the need for reoperation. It should also allow early weight bearing. It is, however, a bigger operation with possible serious complications.
For split fractures of the head with displaced neck fracture, arthroplasty might be the most successful treatment, particularly for older patients or unreconstructable head fractures.
For split and depression fractures of the femoral head, arthroplasty or total hip replacement is very rarely the primary choice, but may be necessary for salvage.
Hemiarthroplasty vs total hip replacement
The surgeon is faced with several choices for arthroplasty for a femoral neck fracture. The first is whether to fix the fracture or to perform an arthroplasty. If arthroplasty is chosen, the next issue is what kind of arthroplasty. The two major types are hemiarthroplasty (replacement of the femoral head and neck) or total hip replacement, in which both the proximal femur and the acetabular surface are replaced. Hemiarthroplasty is a less complicated operation, and provides generally satisfactory results for less active patients. Reported results of total hip replacement for femoral neck fractures are improving, so that total hip replacement is increasingly favored for displaced femoral neck fractures, particularly for more active patients.
Type of hemiprosthesis
The original proximal femoral hemiarthroplasty prostheses were made of a single casting with a femoral stem attached to the femoral neck and head. The Austin-Moore prosthesis is a common example.
More modern hemiarthroplasties are modular, allowing different combinations of stem, neck length, and head. These provide a better-fitting prosthesis for most patients, so that leg length and femoral offset may be equalized, and hip muscle tension can be adjusted for better function and reduced risk of dislocation.
So-called bicentric or bipolar prostheses have a smaller inner ball that articulates within a larger head component that fits the acetabulum. However, their reported results so far are no better than non-articulated (unipolar) prostheses. Thus their extra cost and complexity are not justifiable.
Total hip prosthesis
Based on current publications, total hip arthroplasty is becoming an attractive option for healthy, active older patients with displaced femoral neck fractures. In particular, patients with pre-existing hip arthritis have a poorer outcome with other alternatives. Thus, total hip arthroplasty is optimal treatment for such patients. To date, available high-quality studies do not demonstrate a convincing difference between hemiarthroplasty and total hip arthroplasty. Larger trials are necessary to demonstrate what if any differences exist between these procedures regarding results, indications, and variations.
Primary indication for total hip replacement (example)
A patient with preexistent osteoarthritis of the hip joint and a femoral neck fracture. The x-ray on the right was made nine years after total hip prosthesis.
Conversion of a modular hemiprosthesis to total hip prosthesis
Dislocation of hip arthroplasty for femoral neck fractures is a significant and occasional complication.
These x-rays show (left) a dislocated hemiarthroplasty and (right) its salvage by conversion to a hip replacement. In this case the original femoral stem was retained, with a replacement of its head and neck for total hip arthroplasty. The acetabular component (with supporting bone graft) was inserted before the new head and neck were attached.
Cemented or uncemented prosthesis
The proximal femoral prosthesis is inserted into the femur after cutting the femoral neck to fit, and preparing the medullary canal.
The canal can be shaped so that the prosthetic stem fits snugly, but without great stability (press-fit). Stability can be increased by using a smaller stem than the canal and anchoring it with methyl-methacrylate cement. Proper cement insertion improves stability. It typically includes use of a femoral plug and pressurized injection of a more fluid cement. These measures also reduce the risk of cement failure.
Another alternative for stable fixation is to use a stem that fits the bone snugly and has a surface that promotes bony ingrowth. This alternative requires a more expensive prosthesis and protection from early weight bearing, thus it is less appropriate for the elderly.
2 Preoperative planning and approaches for hip arthroplasty topenlarge
Whatever arthroplasty is chosen, the procedure should be carefully planned with sufficient detail. Select the prosthesis with the aid of radiographic templates (or electronic planning software with digital x-rays) and appropriate x-rays of the normal and injured hip.
In addition to the selected prosthesis, possible alternatives should be available in the operating room.
Many surgeons prefer an anterior or anterolateral approach for arthroplasty, with the patient positioned laterally or supine. An anterior arthrotomy with preservation of the posterior capsule may reduce the risk of prosthetic dislocation, particularly for hemiarthroplasties. Hip arthroplasty can be performed through several different incisions. There is no convincing evidence that one is better. Thus, the choice is up to the surgeon.
A posterior approach, with the patient on her side, is also commonly used. Dislocation may be more frequent with a posterior approach, according to many, but not all, reports. Other factors are also important. Proper positioning of the prosthesis, and perhaps repair of the posterior capsule may improve stability.
3 Removal of the femoral head topenlarge
The operation begins with adequate exposure of the fracture site through a sufficient capsular incision. For hemiarthroplasty, the acetabular labrum should be preserved, as it improves stability.
Next, remove the femoral head. Use a “corkscrew” (threaded handle), as illustrated, retracting the distal femur, and dividing the ligamentum teres as necessary.
An additional osteotomy of the femoral neck is usually required to obtain correct neck length and to fit the flange of the prosthesis (if there is one).
Inspect the acetabulum and remove small bone fragments. If arthrosis of the acetabulum is observed, a total hip prosthesis might be preferable to a hemiprosthesis.
4 Hemiarthroplasty vs total hip replacement topenlarge
If hemiarthroplasty is planned, the femur is prepared, an appropriate femoral head and neck size is chosen and confirmed with trial components, and then the definitive prosthesis is inserted.
For a detailed description of hemiarthroplasty, continue with step 5.
If total hip replacement is chosen, the acetabular preparation and component insertion are done prior to definitive insertion of the femoral component.
For details on total hip replacement, continue with step 8.
5 Hemiarthroplasty - Determine size of femoral head component topenlarge
To determine the diameter of the femoral head component, measure the removed femoral head. The chosen size should be confirmed by manually testing the fit of a trial femoral head prosthesis within the acetabulum.
6 Hemiarthroplasty - Prepare stem insertion topenlarge
Osteotomy of the femoral neck
Choose the correct level for the definitive osteotomy, which determines the height of the prosthesis. The remaining femoral neck should be long enough to maintain equal leg lengths, as well as proper soft-tissue tension.
The orientation of the osteotomy depends on the chosen prosthesis. It usually begins in the fossa below the greater trochanter. If the prosthesis has a flange, the osteotomy must match this. The osteotomy should also be perpendicular to the axis of the femoral neck, so the prosthetic anteversion is correct.
Pitfall - Short femoral neck
Too short a femoral neck can result in insufficient muscle tension, which may increase the risk of a postoperative dislocation of the prosthesis, or hip abductor weakness. Usually, at least a centimeter or two of neck should remain proximal to the lesser trochanter. Plan carefully according to the prosthetic design.
Ensure correct rotation of the prosthesis
The prosthesis must be correctly aligned in the femoral transverse plane. The neck of the femoral component should usually be co-axial with the femoral neck, as in the illustration. "β" indicates the angle of anteversion of the femoral neck, and of the prosthesis. Avoid excessive anterior rotation (anteversion), and especially posterior rotation (retroversion), as the latter predisposes to dislocation of the prosthetic hip.
Correct rotational alignment is achieved by cutting the femoral neck perpendicularly to its axis (to accept a flange on the prosthesis), and maintaining the desired anteversion while preparing the femoral medullary canal with rasps and broaches.
Correct rotation of the prosthesis with the patient supine (anterior approach)
To ensure correct rotation of the prosthesis, the leg is in full external rotation and the knee flexed to 90° (“figure 4” position). External rotation of the prosthesis, (away from the plane of the tibia) increases anteversion. The correct position is approximately 15° externally rotated relative to the axis of knee flexion.
Correct rotation of the prosthesis, using an anterolateral approach, with the patient in the lateral decubitus position
Exposure of the proximal femur is accomplished by careful placement of the involved limb in an externally rotated and flexed position with the lower leg hanging over the edge of the operating table. To maintain sterility, the lower leg is inserted into an envelope or pocket made from a sterile sheet. The assistant holds the patient’s leg perpendicular to the table surface, which is thus the plane of the knee axis. Proper anteversion is achieved by externally rotating the femoral prosthesis, so its neck is aimed approximately 15° anteriorly to the knee axis (or table surface).
Posterolateral or posterior approach with patient in lateral decubitus position
With this approach, the hip is accessed through a posterior capsulotomy, through which the femoral head is removed. Internal rotation of the lower extremity delivers the femoral neck for osteotomy and femoral canal preparation. Correct rotational orientation of the prosthesis requires reference to the femoral coronal plane, shown by flexing the knee to 90°. An assistant holds the leg internally rotated, so that the tibia is perpendicular to the table surface. The anteversion angle of the femoral neck and prosthesis (β = approximately 15°) is then estimated as illustrated.
The femoral awl is inserted, initially laterally, in the femoral neck, and rotated to match the femoral neck anteversion (approximately 15°). The lateral starting point helps avoid varus malposition.
Intramedullary cancellous bone is progressively removed, usually with a series of rasps, until the prosthesis fits appropriately within the medullary canal.
Although the size of the femoral stem was estimated with preoperative planning, it should be confirmed definitively by the fit of the rasp within the medullary canal.
Choice of the right stem size
If an uncemented implant is used, the stem of the prosthesis should snugly fill the prepared medullary cavity.
If cement is used, the stem size should be somewhat smaller than the prepared medullary cavity to allow for an appropriate layer of cement.
7 Hemiarthroplasty - Insertion and assembly of the prosthesis topenlarge
Introduction and correct position of the prosthesis in the frontal plane
The prosthesis is introduced into the prepared femoral medullary canal. Because both the femur and the prosthesis are eccentrically loaded, bending forces are acting on the prosthetic head, forcing the prosthetic stem in varus. The prosthesis – cemented or uncemented - should be inserted in valgus orientation, with the proximal stem laterally, and its distal tip close to the medial femoral cortex.
This illustration shows a cemented femoral stem with correct valgus alignment on the left and excessive varus on the right.
Since new cementing techniques have been introduced, the long-term results of the cemented prosthesis have been considerably improved.
A cement restrictor, placed a centimeter or so below the prosthesis, allows the cement to be pressurized so that it flows into the cancellous bone rather than into the distal femur.
Before inserting cement, clean the canal with irrigation and an appropriate brush. Place a temporary dry sponge in the canal, to be removed just before the cement is inserted.
By mixing the cement liquid and powder in a low-pressure container, air bubbles are avoided, and the cement is stronger.
Cementing of the medullary canal
The prepared medullary cavity is filled from bottom to top with a cement gun, as illustrated. Withdraw the cement gun as the medullary canal fills. Avoid mixing blood or air with the cement.
Compressing the cement before and by prosthesis insertion pushes it into the surrounding bone, thus improving its anchorage.
Before the cement hardens, the prosthesis is inserted with correct rotation (anteversion) and valgus alignment. It must be placed to the appropriate, predetermined depth. Once the stem is seated, allow the cement to set undisturbed. Trim off any excessive cement, and carefully remove all cement fragments from the hip joint and surrounding wound.
Assembly of the prosthesis
For a hemiarthroplasty, use a trial femoral head prosthesis on the cemented stem to confirm both diameter and neck length. The latter affects both leg length soft-tissue tension, and hip stability.
For total hip arthroplasty a similar trial prosthesis is used to check length and offset. Head size, however, is determined by the preoperatively selected acetabular component. Total hip prostheses with larger heads tend to be more stable.
With the hip reduced, confirm range of motion and stability. Adjust the neck and head if necessary.
Once satisfactory, attach the definitive femoral head to the stem, and reduce the hip. Confirm complete reduction, stability, and range of motion.
8 Total hip replacement topenlarge
With total hip replacement, the acetabulum is replaced in addition to the femoral head and neck. The acetabular component is chosen based upon the patient’s anatomy, with the aid of preoperative x-rays and intraoperative trials.
While the external diameter of the acetabular component is definitively selected intraoperatively, its internal diameter, the same as that of the matching femoral head component, is a feature of the chosen prosthetic system.
The acetabular prosthesis must be fixed to the pelvis. This can be either uncemented (with bony ingrowth) or cemented. Early weight bearing may be safer with cement. This is usually preferable in the elderly and will be illustrated.
First, the acetabular cartilage has to be removed with a reamer. Orient this anatomically, perpendicular to the plane of the bony acetabulum. Ream until cancellous bone is exposed and the desired fit is achieved, but without removing the inner table of the innominate bone.
Note: In osteoarthritis, the acetabular bone is often sclerotic, and the reaming may require some effort. Hip fractures occur in patients with osteoporosis, and if there was no pre-existing arthritis, the bone is often very soft and reaming should be performed gently and carefully.
For better anchorage of the cement and cup, several holes with a diameter of about 6 mm are drilled in multiple locations as illustrated.
Impaction of bone
With a corresponding punch the cancellous bone in the drilled holes may be impacted.
Choosing the right size for the acetabular prosthesis
The cup should fill as much of the available space in the acetabulum as possible, extending only a little beyond the bone. Choose an acetabular prosthesis that needs as little surrounding cement as possible.
Confirm the correct size with a trial prosthesis, as shown in the photograph.
Placement of prosthesis
It is important that the acetabular prosthesis is oriented correctly, usually in the same way as the patient's own acetabulum. It should not be directed posteriorly (retroverted) nor too anteriorly (excessive anteversion).
For optimal hip joint stability and prosthetic wear, approximately 45° abduction and 15° anteversion are commonly advised.
The cement is applied in a putty-like solid state by hand and pushed into the drill-holes.
Under firm pressure the acetabular prosthesis is inserted in an anatomical position and the cement is allowed to harden.
Orientation of acetabular component
The normal acetabulum faces anteriorly, approximately 15°. It is also oriented obliquely (abducted, from a horizontal position) so that the superior part of the femoral head has adequate coverage by the acetabulum.
The illustrations demonstrate the anterior rotation (acetabular anteversion = α) ...
... and also abduction (= A, approximately 45°). Both anteversion and abduction must be set correctly during placement of the acetabular prosthesis.
The steps for stem insertion are the same as for a hemiarthroplasty. Please refer to step 6 for further details.
Attachment of femoral head component
Use a trial head and neck component to confirm range of motion and stability. Then attach the definitive head head-neck component(s) and reconfirm that the prosthetic joint performs satisfactorily.
Reduction of the artificial hip
Once the prosthetic components are in place and stable, the hip is gently reduced.
Make sure that cement debris are removed first and that soft tissues are retracted.
Place the leg in normal extension. With gentle traction and internal rotation, the hip joint can usually be reduced.
Reduction of the artificial hip
It may help to guide the femoral head into the acetabulum.
Pitfall – decreased joint stability
Ensure correct rotational alignment (normal anteversion) of both acetabular and femoral components. Retroversion of either acetabular or femoral component increases the risk of dislocation.
After reduction, check stability and soft-tissue tension. A more appropriate neck length may improve stability.
Equalizing leg length is a valid goal, but avoiding dislocation is probably more important. Occasionally, special prosthetic designs may be required.