Kang-Il Kim and Ameet Pispati
DEFINITION
Surface replacement is a significant development in the evolution of hip arthroplasty.
Hip resurfacing is based on the premise that femoral bone can be preserved.
The femoral head is “resurfaced” by insertion of a cemented component. The cup is press-fit.12
Resurfacing Systems
Several hip resurfacing devices of various designs are available, but the most critical factor in resurfacing is the surgeon's level of expertise.
These various devices differ in terms of material, surface treatments, cup design, manufacturing process, carbide content, component thickness, clearance, possibility of including a cement mantle under the femoral component, fixation methods, and size ranges offered (Table 1).
SURGICAL MANAGEMENT
Indications
Hip resurfacing is used optimally in younger, active patients with good bone quality.
This procedure is indicated for a degenerative hip joint with pain and decreased range of motion.
When joint-preserving procedures such as femoral osteotomy, acetabular osteotomy, or vascularized bone grafting are not ideal for an early stage of unambiguous coxarthrosis, hip resurfacing can be considered.
Resurfacing usually is reserved for patients with good bone stock, high activity level, and a need for a high degree of motion.
Hemiresurfacing, in which only the femoral head is resurfaced, has largely been abandoned because it provided suboptimal results.
Resurfacing recently was approved by the U.S. Food and Drug Administration.
General indications for hip resurfacing are as follows:
Primary osteoarthritis
Secondary osteoarthritis as sequela of childhood disease, including hip dysplasia or infection
Osteonecrosis of the femoral head
Post-traumatic arthritis
Ankylosing spondylitis
Rheumatoid arthritis
Contraindications
Abnormal anatomy of femoral head or neck
Severe limb-length discrepancy that may require some correction during arthroplasty
Severe bone deficiency
Large and cystic lesions of the femoral head
Severe dysplasia, because screw fixation for the acetabulum cannot be performed with resurfacing
Special Considerations
Osteonecrosis of the Femoral Head
Osteonecrosis of the femoral head presents a special problem for hip resurfacing.
The presence of a necrotic lesion of the femoral head can compromise fixation of the component.
In general, survival of hip resurfacing is lower for avascular necrosis than for osteoarthritis in the counterpart hip.3
Use of a Computer-Assisted Navigation System
A computer-assisted navigation system is an intraoperative image-guided localization system used to enable proper cutting of bone and exact location of the implants in total knee or total hip arthroplasty (THA) and in minimally invasive surgery.
Although hip resurfacing arthroplasty has been used for a long time with acceptable results without any navigation system, one of the main concerns following resurfacing arthroplasty is femoral neck fracture.
In general, slight valgus positioning of the implant is recommended to reduce the tension and shear stresses across the head–neck junction, but intraoperative neck notching during femoral cutting often is a consequence of extreme valgus position.
Many mechanical femoral alignment guides have been developed to help surgeons achieve optimal positioning of the femoral implant.
As for THA, early loosening or dislocation resulting from impingement due to the malposition of both components should be prevented.12
In hip resurfacing arthroplasty, avoidance of femoral notching by the femoral component and the position of the stem of the femoral component are critical. This may be technically difficult, even for an experienced surgeon, and it adds time to the procedure.
Computer-assisted navigation systems have been developed to surmount the intrinsic limitations of manual techniques.
Intraoperative navigation can demonstrate real-time positioning of instrumentation by imaging, thereby improving the accuracy of component positioning in hip resurfacing arthroplasty.
Specific surface landmarks may be difficult to make out, however, and registration procedures often are the most timeconsuming and accuracy-related segment of the procedure.
Irregular soft tissue distribution around the femoral neck also can affect navigation precision.
Surgical navigation may be especially helpful during femoral procedures.
To reduce the potential risk of femoral neck fracture, we perform total hip resurfacing arthroplasty using computer-assisted navigation.
We have used the hip resurfacing systems with Vectorvision (BrainLAB, Munich, Germany) since 2005 (FIG 1).10
FIG 1 • Image-free hip navigation system for hip resurfacing.
When using an image-free hip navigation system, the surgeon must digitize the pelvic and femoral planes of the patient to determine the individual pelvic and femoral coordinate system for prosthesis positioning.
Preoperative Planning
Templates are used to determine approximate component sizes. Standard-sized conventional radiographs must be used rather than digital films, and the magnification factor must be taken into account.
The femoral component must be sized such that there is no over-reaming of the femur or risk of notching of the neck. Oversizing also should be avoided to preserve acetabular bone stock.
Femoral component alignment is the most important preoperative consideration. Varus positioning must be avoided— neutral or slight valgus alignment is preferred (FIG 2).
When optimum femoral template positioning has been achieved, the distance from the tip of the greater trochanter to the pin insertion point on the lateral femoral cortex is measured with the ruler printed on the template.
The relation between the exit-point of the guidewire on the template relative to the lesser trochanter should be noted and reproduced during surgery.
An acetabular component should be selected of the size that fills the acetabular fossa and accommodates the selected femoral component.
Approach
All of the standard exposures of the hip have been successfully used to perform surface replacement.
Hip resurfacing is technically demanding, and the surgical approach used should allow adequate exposure of the acetabulum and proximal femur without compromising postoperative muscle function.
The posterior approach is the most popular approach for total hip resurfacing.
The anterior approach, the exposure advocated by Wagner,15 is not popular.
The anterolateral approach was described by Hardinge6 and modified by Learmonth.
Exposure of the femoral head is achieved by flexion, adduction, and external rotation of the lower extremity. Exposure of the acetabulum is accomplished by depressing the femoral head into a posterior and inferior position.
FIG 2 • Templating. A slight valgus position without notching the femoral neck should be the goal. The distance (60 mm) between the tip of the greater trochanter and the lateral pin that is inserted to the lateral cortex of the proximal femur should be measured for conventional resurfacing procedures. The level of lateral pin insertion usually is similar to the level of the lesser trochanter.
This approach has the advantage of preserving the posterior retinacular vessels, which reduces the possibility that an iatrogenic avascular state will develop postoperatively in the remaining femoral head.8
Critics of this approach believe that the exposure offered is inadequate, leading to a greater risk of complications and improper component positioning of both implants in total hip resurfacing. There may be a higher incidence of heterotopic new bone formation, and decreasing abductor muscle function often is compromised following this approach.13
The trans-trochanteric approach for hip resurfacing was popularized by Amstutz.2
This approach provides excellent exposure, but it rarely is used for this operation, primarily because of problems associated with trochanteric osteotomy and a higher incidence of heterotopic ossification.
The posterior or posterolateral approach is the standard approach used for total hip resurfacing.
FIG 3 • Unlike conventional THA, the joint capsule and synovial membrane around the femoral neck should be preserved as much as possible to reduce vascular damage to the femoral head in hip resurfacing.
In this approach, the tendon of insertion of the gluteus maximus is released to allow easy anterior displacement of the femur.
The capsule and synovium around the femoral neck are preserved as much as possible to prevent further vascular damage to the femoral neck and head. The femoral head then is dislocated (FIG 3).
The femoral neck is sized using neck gauges. Sizing also gives an idea about the minimum acetabular size required.
Usually, the acetabular preparation is done first, unless the femoral head is especially large, which results in inadequate acetabular preparation. In such cases case the femoral head is prepared to one or two sizes larger than the targeted femoral component size.
TECHNIQUES
POSTEROLATERAL APPROACH
Exposure
The patient is placed in the lateral position.
The hip is flexed to 45 degrees, and a straight incision is made centered on the posterior edge of the greater trochanter.
Alternatively, the hip is extended and a conventional incision, curved posteriorly, is made (TECH FIG 1A).
The fascia lata is incised, the fibers of the gluteus maximus are split, and a Charnley retractor is inserted (TECH FIG 1B).
The tendon of insertion of the gluteus maximus usually is released to allow subsequent easy anterior displacement of the femur; the underlying perforator vessels may require coagulation (TECH FIG 1C).
The trochanteric bursa is divided and swept posteriorly, after which the sciatic nerve may be easily seen or palpated.
The posterior edge of the gluteus medius is retracted anteriorly to reveal the piriformis tendon.
The fibers of the gluteus minimus are separated from the superior border of the piriformis tendon.
The interval between the gluteus minimus and the superior acetabulum and superior hip capsule is developed with electrocautery.
The hip is held in internal rotation, and the piriformis tendon is divided as close as possible to its insertion, along with the hip capsule.
The other external rotators and the hip capsule are divided with electrocautery, leaving a cuff of quadratus femoris for later suturing.
The joint capsule is incised along the line formed by the superior margin of the piriformis muscle. The posterior capsule is detached cautiously, along with the base of the femur neck, to save intracapsular blood vessels around the femoral neck.
The femoral head is dislocated, the hip is fully extended (by bringing the knee to the midline), and maximum internal rotation of the leg is performed (TECH FIG 1D).
TECH FIG 1 • A. Posterolateral approach. The patient is in the lateral position with the affected hip flexed 45 degrees. A straight incision is made at the posterior border of the greater trochanter. B. The gluteus maximus fibers are split proximally and the iliotibial band is incised distally. C. A diathermy is used to release the insertion of the gluteus maximus tendon, leaving behind a small fringe for later suturing. Perforator vessels in this area may cause furious bleeding, requiring ligation or cauterization. D. Circumferential capsulotomy. With the hip fully extended and in maximal internal rotation, the anteroinferior capsule is divided inferiorly. The hip is then flexed to 45 degrees in maximum internal rotation and the anterosuperior hip capsule is divided superiorly. The capsulotomy is extended down to meet the previous inferior cut, giving a full circumferential capsulotomy. E,F. Diagram illustrating sizing of the femoral neck. The neck is sized in its maximum diameter.
The anteroinferior hip capsule is divided, beginning inferiorly, just in front of the psoas tendon, using Muller capsular scissors or electrocautery.
The femoral neck is sized using neck gauges or templates (TECH FIG 1E,F); this also gives an idea about the minimum acetabular size required.
An anterolateral soft tissue pocket is created using a curved periosteal elevator or a Cobb elevator.
A Hohmann retractor is placed over the anterosuperior acetabulum and impacted into the anteroinferior iliac spine, and the leg is externally rotated to allow the femoral head to prolapse under the abductors into the pocket.
Acetabular Preparation
A pin retractor (Judd pin) is inserted into the ischium, retracting the posterior capsule and external rotators.
Two Hohmann retractors are placed from inferior to the teardrop, directed antero- and posteroinferiorly (TECH FIG 2A).
The labrum, transverse acetabular ligament, and other soft tissue in the cotyloid fossa are excised, giving a complete view of the bony acetabulum.
Sequential reaming is performed (TECH FIG 2B), with under-reaming by 1 to 2 mm.
An acetabular component that provides the best possible fit without reaming excess acetabular bone is preferred; this choice then determines the size of the femoral component.
A trial cup is inserted and tested for stability (TECH FIG 2C).
The true acetabular component is then inserted in “native” version, usually 20 degrees, and at a 45-degree angle (TECH FIG 2D).
Any protruding acetabular osteophytes should be removed.
The Hohmann retractors and pin retractor are removed.
Inserting the Guide Pin
The limb is then hyperrotated to expose the femoral head.
Lines are drawn on the center of the femoral head and neck in both anteroposterior (135–140 degrees of neck–shaft angle) and lateral planes (normal anteversion) and are extended up into the femoral head, where they intersect (TECH FIG 3A,B).
The intersection point should be the entry point for the guide pin.
A guide pin is drilled into the femoral head and neck using a guide instrument (TECH FIG 3C).
A stylus is placed over the guide pin. This should pass around the femoral neck without impingement (TECH FIG 3D) to avoid notching of the femoral neck.
The guide pin normally is inserted from the superior part of the femoral head about 1 to 2 cm above the fovea.
In the coronal plane, 5 to 10 degrees of valgus is desirable; a 135- to 140-degree angle must be maintained with the long axis of the femoral neck (TECH FIG 3E).
Because a deformed femoral head or osteophytes around the femoral head and neck may make it difficult to recognize the actual state and relation of the femoral head and neck junction, excessive osteophytes should be removed carefully before femoral pinning.
Femoral Head Resurfacing
In most systems, femoral head preparation is done using cannulated reamers that pass over the previously inserted femoral guide pin (TECH FIG 4A).
Consecutive reaming or milling using specialized instrumentation forms the femoral head into a chamfer-cut cylindrical shape (TECH FIG 4B–D).
Non-impinging osteophytes present on the femoral neck are best left untouched.
Any necrotic bone should be removed.
The femoral head is then pulse lavaged, and a suction vent is placed into the lesser trochanter to keep the femoral head dry and to prevent embolism (TECH FIG 4E).
A number of cement keyholes are drilled into the femoral head (TECH FIG 4F).
A final check is made to confirm that there has been no notching from the trial component (TECH FIG 4G).
TECH FIG 2 • A. An anterosuperolateral acetabular pocket is created and the femoral head delivered into it with the hip in external rotation. B. The acetabulum is reamed in 2-mm increments, with 1-mm increments used in dense bone. The reamer handle is kept at 45 degrees inclination and native anteversion. C. Trial cup insertion after complete acetabular reaming. The trial's stability and the relation between the peripheral margin of the acetabulum and the trial after it is fully seated must be checked. D. Acetabular resurfacing with cup impaction in the desired position. The transverse ligament is a useful landmark for determining cup inclination.
TECH FIG 3 • A,B. Planning the guidewire entry point in the AP plane. A line is drawn in the mid-lateral plane of the femoral neck. A second line is drawn in the center of the femoral neck such that it is parallel to the calcar femorale. This gives the guide pin a valgus orientation of about 5 to 10 degrees. The point where the two lines intersect, usually 1 to 1.5 cm superior to the fovea, should be the entry point for the guidewire. C. Planning the guidewire entry point in the superoinferior plane using guide instruments from various companies. D. Planning for slightly valgus placement for the femoral guide pin and checking for notching in the femoral neck. The stylus on the guide pin should move freely around the femoral neck at the head–neck junction without impingement. Moreover, the surgeon can confirm the head size through this procedure. E. The angle in the coronal plane is checked intraoperatively using a goniometer.
TECH FIG 4 • A. The guide rod is inserted after drilling over the guide pin, and the head cutter is advanced through the guide rod. During this procedure the surgeon should check for and avoid femoral notching at the head–neck junction. A head cutter one size larger may be used initially. B. After safe cutting has been accomplished, all instruments are removed, and the top of the head guide is placed through the prepared femoral head. The inferior margin of the guide is placed next to the superior margin of the head–neck junction. The locking lever is securely fixed, and the top area is resected using a saw. C. The chamfer cutter for the femoral head then is used on the reinserted guide rod. D. The final shape of the chamfer-cut femoral head. E. The prepared femoral head is irrigated using a motorized pulsatile lavage instrument. F. Multiple cement keyholes are made, being sure to keep the femoral head dry. G. A head trial is used to recheck the possibility of femoral notching and to determine the point between inferior margin of the trial and femoral head–neck junction.
TECH FIG 5 • A. Low- or intermediate-viscosity cement is injected into the femoral component using a cement syringe. High-viscosity cement may alter full positioning of the component to the femoral head. B. The femoral component is advanced to the femoral head. C. In cases with femoral head defects, such as osteonecrosis, cement can be applied to the defect area of the femoral head and then the head component can be inserted. D. Femoral implant in place.
Cementing
Bone cement is placed into the femoral component, which is then impacted onto the resurfaced femoral head (TECH FIG 5A,B).
Alternatively, in case of femoral head defect after curettage of necrotic bone, cement is applied to give a uniform 2-mm cement mantle around the femoral head (TECH FIG 5C), and the femoral component is placed over the head and lightly tapped into place (TECH FIG 5D).
Excess cement is removed and pulse lavage is used.
The joint is then reduced and tested for stability and range of motion.
Wound Closure
Good closure of the capsule and the external rotators is important.
The tendinous insertion of the gluteus maximus also is repaired, and the fascia lata, subcutaneous fat, and skin are closed.
SPECIAL TECHNIQUE FOR OSTEONECROSIS OF THE FEMORAL HEAD
Because the surgical approach and acetabular preparation are almost the same, only the technique for the femoral side is described.
Femoral Preparation
Accurate placement of the guide pin can be accomplished using pin alignment guides or a navigation system (TECH FIG 6A,B).
In most systems, femoral head reaming is performed by cannulated reamers that pass over the central guide pin.
A series of reaming or milling devices form the femoral neck into a cylindrical shape (TECH FIG 6C).
To reduce the stress resulting from femoral notching, reaming should be stopped before the peripheral rim of the distal part of femoral head is cut.
The remaining distal rim of the femoral head is carefully removed using a rongeur (TECH FIG 6D).
After chamfer cutting, the remaining necrotic area of the femoral head can be seen clearly (TECH FIG 6E).
Using a small curette and rongeur, the remaining necrotic area is removed and irrigated with aseptic saline to remove tiny fragments of bone debris (TECH FIG 6F).
TECH FIG 6 • The centering jig is located over the guide pin (A), and the pin is then drilled through the centering jig (B). (continued)
TECH FIG 6 • (continued) C. Femoral head reaming is performed by cannulated reamer through the central guide rod. The reaming should be stopped before the peripheral rim of the distal part of the femoral head is cut to reduce stress resulting from femoral notching. D. The final shape of femoral head reaming with distal peripheral cut using a rongeur. E. After chamfer cutting, the remaining necrotic area of the femoral head can be clearly recognized. Necrotic bone usually is yellowish, because it does not bleed, so the margin between necrotic bone and living bone is well recognized. F. The necrotic part of the femoral head should be completely removed, and the remaining femoral head well bled. G. The percentage of volume loss of the inner femoral head after removal of necrotic bone can be measured using a size-matched femoral head trial. It has been our experience that resurfacing procedures can be continued if the volume loss is less than 50%. H,I. If the necrosis extends to the distal peripheral margin of the femoral head such that any circumference of the femoral head and neck junction is not covered by the lower margin of the head trial, we recommend a metal-on-metal, modular THA with large-diameter femoral head or the surgeon's preferred conventional THA if the acetabular side is not yet finished for hip resurfacing. J. Postoperative radiograph shows both hip resurfacing and large-head, metal-on-metal THA.
The trial femoral head is inserted, and the percentage of volume loss after removal of necrotic bone in the trial is measured (TECH FIG 6G).
In our experience, if the volume loss is less than 50% and the necrosis does not extend to the lower margin of the trial in any circumference of the femoral head and neck junction, resurfacing can be accomplished.
Otherwise, we recommend either metal-on-metal THA with a modular large-diameter femoral head in cases where acetabular preparation has already been completed, or conventional THA if preparation has not yet begun on the acetabular side (TECH FIG 6H–J).
Cementing
Using pulsatile lavage, thorough saline irrigation is repeated, taking care to keep the femoral head dry. A special suction system is used during the preparation of bone cement (TECH FIG 7A).
The bone defect is filled with bone cement and pressurized.
TECH FIG 7 • A. After thorough pulsatile saline irrigation, the femoral head is kept dry for implantation with cement. B. During cement filling of the defect area of the femoral head, a continuous suction drain is inserted to the central lumen for guide rod. C. The cement is applied onto the defect area of the femoral head with a bone cement syringe and finger pressure. D. The cement is filled inside the femoral component as a volume half using a cement syringe. E,F. The femoral component is applied to the femoral head with an impactor. G,H. Any extruding cement should be removed with a curette, continuing until the bone cement becomes solid.
The femoral component is placed on the femoral head and impacted gently, with the cement inside the femoral component removed as a volume half using a cement syringe (TECH FIG 7B–D).
The femoral component is applied to the femoral head with an impactor, and extruding cement is removed with a curette, continuing until the bone cement hardens (TECH FIG 7E–H).
HIP RESURFACING USING A NAVIGATION SYSTEM
Patient Positioning
At our institution, we use a posterolateral approach for hip resurfacing arthroplasty. When we use the hip resurfacing systems with image-free navigation for an acetabular procedure, certain initial maneuvers must be done with the patient in the supine position before moving the patient to the lateral position and undertaking the posterolateral approach, because pelvis registration cannot be performed conveniently in the lateral position.
Once the pelvis registration has been completed, the patient can be moved to the lateral position.
If the surgeon uses the navigation system only on the femoral side, the supine position for acetabular registration is not needed, and femoral registration is performed during surgery with the patient in the lateral position.
Precise location of the registration points is a key factor in ensuring proper matching at every step.
Pelvis Registration
A small-step incision is made on the iliac crest of the operative side, and the fixation pin is inserted for the reference array using an automatic drill at low speed (TECH FIG 8A,B).
The second pin is inserted in the same manner using a drill template (TECH FIG 8C).
Once two pins have been inserted, the bone fixator and the pelvis reference array are attached (TECH FIG 8D).
The bone fixator should remain attached until the end of the entire navigation procedure.
The plane of the pelvis is defined by entering points on the pelvis according to the navigation software (TECH FIG 8E,F).
Bony landmarks of interest are the left and right anterior superior iliac spine and the most anterior parts of both pubic bones, which, in most patients, are the pelvic tubercles (TECH FIG 8G,H).
Once registration has been completed, the pelvis reference array is removed without dislodging the fixation pins and bone fixator (TECH FIG 18I).
The reference array is stored in a sterile location until it is reattached.
TECH FIG 8 • A. The anterior pelvic plane is defined using four points: the operated and contralateral sides of the anterior superior iliac spine and the most prominent pubic points on both the operated and the contralateral sides. B. After local sterilization, a small stab incision is made on the operated iliac crest, and the fixation pin is inserted with a low-speed automated drill. The fixation pins should not be inserted near the anterosuperior iliac spine point, because this point is required for pelvic registration. C. The second pin is inserted in the same manner using a drill template. D. Once the second fixation pin has been inserted correctly, the bone fixator is attached and the pelvic reference array is corrected to it. The reference array should be detected by the cameras both in the supine and ateral positions during the operation. E. The pelvic plane is defined by entering points on the pelvis as prompted by the software. F. The pointer is put in the left anterosuperior iliac spine. G,H. The pointer is placed on the right pubic point according to the navigation system. I. Once registration has been completed, the pelvis reference array is removed without dislodging the fixation pins and bone fixator.
TECH FIG 9 • A. When the pelvis registration procedure is finished, the patient is moved into the lateral decubitus position. During this change in the patient's position and draping, the surgical team should pay attention to the acetabular fixator and pins to protect them from contamination or loosening. B. With the patient repositioned and secured, the surgical area is sterilized and the patient is draped.
Repositioning the Patient
When the pelvis registration procedure is finished, the patient is moved into the lateral decubitus position, and the surgical area is sterilized and draped thoroughly (TECH FIG 9).
During draping, the surgical team should pay attention to the acetabular fixator and pins to protect against contamination or loosening.
Acquiring Acetabular Landmarks
The skin is incised in a routine manner, and the acetabulum is exposed. A
TECH FIG 10 • A,B. Multiple point acquisition on the cotyloid fossa, the deeper part of the acetabulum, is used to register bony areas. Points acquired in this way are used to calculate the three-dimensional model. The number of points to be acquired is shown in the center of an acquisition clock. C,D. Acquiring points on the acetabular wall. E,F. Once the bone model has been calculated, pelvis registration is verified.
Multiple landmark acquisition is used to register the cotyloid fossa and acetabular surface, including margins (TECH FIG 10A–D).
To begin multiple landmark acquisition, the tip of the pointer is touched to the required structure and pivoted slightly.
Points are acquired by sliding the pointer tip along the defined structure.
Once the bone model has been calculated in the navigation monitor, pelvis registration should be verified immediately (TECH FIG 10E,F).
Inserting the Acetabular Cup
To insert the cup at the desired angle, the bone must be reamed at the same angle as the planned cup (TECH FIG 11A).
The acetabulum initially is reamed with an 8-mm diameter reamer, which is smaller than the planned cup size (TECH FIG 11B,C).
Subsequent reaming can then continue in increments of 2 mm.
The planned inclination and version values for the implant are shown during reaming, and the values are updated dynamically (TECH FIG 11D).
Once the reamer has been navigated to the planned position and reaming has been completed, a trial cup generally is used to confirm that the selected cup size is correct (TECH FIG 11E).
The cup is calibrated with the trial cup or cup inserted (TECH FIG 11F,G).
The cup inserter is navigated to the planned position, and the cup is inserted according to the manufacturer's recommendations until correct cup placement has been achieved (TECH FIG 11H).
TECH FIG 11 • A. The size of the acetabular cup is calculated automatically, with the position of the cup planned per the surgeon's request. B,C. During acetabular reaming, these angles are updated dynamically, indicating how far they are inclined, anteverted, or retroverted. Ideally, the cup reamer should be directed according to the planned angles. D. Subsequent reaming can then continue in increments of 2 mm, with under-reaming by 2 mm less than the acetabular component to be inserted. Finally, the planned inclination and version values for the implant are shown. E. Before the actual acetabular cup is inserted, a trial cup generally is used to verify that the selected cup size and angle are correct. F. Calibrating the trial cup inserter with adapter. G. The angle of the acetabular cup is shown dynamically during insertion of the component. H. The cup inserter is used to place the acetabular cup in alignment with the bone. (continued)
TECH FIG 11 • (continued) I. Cup placement is verified by acquiring five points along the peripheral margin of the acetabular cup. J. The tab page shows both inclination and version of the acetabular cup and compares the difference between real and planned angles.
The cup should be positioned using the anatomy as a reference and aligned with the bone.
To verify cup position, the pointer is used to acquire four or five points along the margin of the cup (TECH FIG 11I).
The navigation screen shows various values for the position of the cup implant (TECH FIG 11J).
Once cup verification has been finished, the pelvic reference array, bone fixator, and two pins are removed, and femoral preparation proceeds.
Acquiring Femoral Landmarks
For femoral pin insertion, two pins are inserted to the lesser trochanteric area (TECH FIG 12A).
The location of the pins varies. They can be inserted into the proximal diaphyseal area, but the lesser trochanteric area is more comfortable and requires a smaller incision.
Once two pins have been inserted, the bone fixator and femoral reference array are attached (TECH FIG 12B).
Before starting registration, as many osteophytes are removed as possible, because the presence of osteophytes will affect the femoral notching calculation.
The first step in femur registration is marking of the medial and lateral epicondyles using a sterile pointer (TECH FIG 12C,D). The pointer then is held to the piriformis fossa and head-neck junction (TECH FIG 12E,F).
To acquire femoral head points, the pointer is slid across the surface of the bone following the navigator's direction (TECH FIG 12G,H).
TECH FIG 12 • A. The fixation pin is inserted to the lesser trochanter using an automated drill at low speed. The second pin is inserted in the same manner using a drill template. The fixation pins should be placed bicortically for stability. B. Once the second fixation pin has been inserted correctly, the bone fixator is attached and the femoral reference array connected to it. Sufficient space should be available to facilitate drilling, reaming, and implant positioning without moving the reference array. C,D. Medial and lateral condyle points are acquired using single landmark acquisition. Each point is acquired by holding the tip of the pointer to the surface of the skin at the required location. E,F. Acquiring a point on the piriformis fossa. This point is essential for navigation to define the proximal endpoint of the shaft axis. If this point is not defined correctly, the calculated neck axis and implant position may not be accurate. (continued)
Once the femoral head points have been acquired, points are acquired on the anterior, superior, posterior, and inferior neck in sequence (TECH FIG 12I,J).
Finally, it is necessary to ensure that there are sufficient points in the most critical area of the bone, where notching is more likely to occur (TECH FIG 12K,L).
Once registration has been accomplished, a threedimensional bone model is made on the navigation monitor based on the points acquired (TECH FIG 12M).
Once the bone model has been made, registration of the femur is verified (TECH FIG 12N,O).
The current neck–shaft angle (ie, varus or valgus, anteversion or retroversion) and calculated inner diameter of the head implant (head size) are shown automatically with images on the navigation screen (TECH FIG 12P).
TECH FIG 12 • (continued) G,H. Acquiring points on the femoral head. To acquire points, the pointer is simply slid across the surface of the bone. This step is important for precise morphologic estimation and for determining the center of rotation and the required implant size. I,J. Acquiring points on the anterior, superior, posterior, and inferior neck. These points are used for estimating the neck axis and required implant size and for generating the femoral bony model. K,L. Acquiring points in the superior notching zone. This step is used to ensure that sufficient points have been acquired in the most critical area of the femur, where notching is most likely to occur. M,N,O. Once the bone model has been calculated, the femoral registration is verified. P. After verification of the femoral model, the current neck–shaft angle is shown automatically, and the surgeon can adjust the angle if necessary. Q. The size of the femoral component is calculated automatically, and the position of the component is planned per the surgeon's request.
TECH FIG 13 • A,B. As the drill guide is moved, the angle values are updated dynamically, indicating how far varus or valgus, anteverted or retroverted the implant is compared to the planned values. C,D.A stylus is used through the guide pin to estimate anterior, posterior, superior, and inferior femoral cutting lines and the possibility of femoral notching. E,F. The drill guide is placed over the pin and slid onto the surface of the femoral head to verify the position of the guide pin. The navigation system calculates the position of the implant according to the position of the drill guide. This is the last step in navigation for hip resurfacing. Once the verification process has been finished, the surgeon proceeds to the next step without navigation.
The software selects the implant size and angle to determine the smallest possible implant that will not cause femoral notching (TECH FIG 12Q).
If necessary, the surgeon adjusts the implant size manually according to the preoperative planning and matches the size with the acetabular component.
Femoral Preparation Using Navigation
Once navigation planning for head implantation has been finished, the drill guide pin is inserted into the femoral head using navigation.
The guide pin is moved along the varus–valgus axis and along the antegrade–retrograde axis. The drill guide pin then is relocated to the entry point selected following the navigation system so that it will not result in femoral notching (TECH FIG 13A,B).
Once the final adjustment has been made, drilling begins via the centering guide pin, and femoral notching is rechecked using a stylus (TECH FIG 13C,D).
Once the hole is successfully drilled and the implant positioned, femoral verification is undertaken (TECH FIG 13E,F).
The remaining procedures for femoral component are done in the same manner as those for conventional resurfacing procedures described earlier.
POSTOPERATIVE CARE
The patient receives a second-generation cephalosporin before anesthesia induction and for 48 hours postsurgery.
An antithromboembolic stocking is applied immediately after the operation to prevent deep vein thrombosis and permit mobilization on the first day after the operation.
Coumadin can be administered for several weeks for medical prevention of deep vein thrombosis.
Various protocols for rehabilitation may be followed.
We continue partial weight bearing with crutches for 4 to 6 weeks to allow initial bony ingrowth on the acetabular side and to allow the patient to regain normal gait and balance.
To allow femoral remodeling around the neck area, we usually recommend that the patient use a cane until the end of the second month after the operation, after which full weight bearing is permitted. Light sports activity may begin no sooner than 3 months after the operation, after which the patient may even squat on the floor.
Patients are allowed to ride in a car as a passenger, drive a car, sleep on their side, or engage in any activities if able and so desired.
Regular sports activities are allowed after 6 months.
OUTCOMES
Daniel and McMinn4 reported on the results of metalon-metal resurfacing in patients younger than 55 years with hip osteoarthritis.
446 resurfacings were performed in 384 patients, with a maximum follow-up of 8.2 years (mean 3.3 years).
Of the remaining 440 hips, there was only one failure (0.02%), giving a survival of 99.8%.
31% of the men with unilateral resurfacings and 28% with bilateral resurfacings could do heavy or moderately heavy jobs; 92% of men with unilateral resurfacings and 87% of the whole group could participate in leisure-time sports activity.
DeSmet5 reported on a Belgian experience of hip resurfacing.
Of 1114 resurfacings performed between 1998 and 2004, the author presented a consecutive series of 252 patients with a follow-up of 2 to 5 years (mean 2.8 years).
Three failures required revision or reoperation: one femoral neck fracture (at 3 weeks); one progressive avascular necrosis of the femoral head that failed at 2 years; and one low-grade infection leading to failure at 2 years.
Two traumatic dislocations were incurred by an inebriated patient; these were reduced without anesthesia.
Sixty-one percent of patients could perform regular strenuous activities.
Nineteen percent of the patients experienced a clicking, locking, or clunking noise or feeling in the first 6 months after surgery, but it was painless and disappeared gradually.
Lilikakis and Villar11 reported the results of uncemented resurfacings with a hydroxyapatite-coated femoral implant with a minimum of 2 years of follow-up.
Seventy resurfacings were done in 66 patients.
At a mean of 28.5 months of follow-up, the overall survival rate of the prosthesis was 97.1%; the survival rate of the femoral component alone was 98.6%.
Itayem et al9 used radiostereophotogrammetric analysis to study the stability of 20 resurfacing arthroplasties over a follow-up period of 20 months.
This analysis found no evidence of excessive early migration or loosening of the components.
Yoo et al16 prospectively investigated the effect of resurfacing arthroplasty on the bone mineral density (BMD) of the femur by comparing 50 patients with hip resurfacing to 50 patients with uncemented THA.
The resurfacing patients demonstrated BMD loss of 2.6% in Gruen zone 1 and 0.6% in zone 7, whereas the THA patients had BMD loss of 7.8% in Gruen zone 1 and 7.7% in zone 7 at 1 year after surgery.
On the acetabular side, the resurfacing patients demonstrated BMD loss of 8% in Delee and Charnley zone 1 and 17.5% in zone 2, whereas the THA patients had BMD loss of 9.8% in zone 1 and 22.3% in zone 2. These results suggest that the hip resurfacing system transfers load to the proximal femur in a more physiologic manner than conventional long-stem devices, that it may prevent stress shielding, and that it preserves the bone stock of the proximal femur.
Shimmin and Back14 carried out a national review of fractures associated with Birmingham Hip Resurfacing systems implanted between 1999 and 2003 in Australia.
3497 Birmingham hips were inserted by 89 surgeons.
Fracture of the neck of the femur occurred in 50 patients, an incidence of 1.46%.
The relative risk of fracture was higher for women than for men.
The mean time to fracture was 15.4 weeks, and it often was preceded by a prodromal phase of pain and limping.
Significant varus placement of the femoral component, intraoperative notching of the femoral component, and technical problems were the common factors in 85% of cases.
Amstutz et al1 presented their experience with femoral neck fractures that occurred after metal-on-metal hybrid surface arthroplasty.
In a series of 600 resurfacings, five femoral neck fractures occurred (incidence 0.83%).
Four of the fractures occurred in the first 5 months after surgery.
All five fractures were associated with structural or technical risk factors, which may have weakened the femoral neck.
We suggest avoiding or minimizing notching of the femoral neck by performing the cylindrical reaming at the recommended angle of 140 degrees and by stopping reaming before the reamer touches the lateral cortex.
COMPLICATIONS
Femoral neck fracture
Neck notching (impingement)
Neck narrowing
Femoral loosening
Femoral head collapse
Acetabular loosening
Stem tip condensation
Metal hypersensitivity
Metal ion release into the bloodstream
Infection
Femoral/sciatic nerve palsy
Deep vein thrombosis
Dislocation
Heterotopic ossification
Spur formation
REFERENCES
1. Amstutz HC, Campbell PA, Le Duff MJ. Fracture of the neck of the femur after surface arthroplasty of the hip. J Bone Joint Surg Am 2004;86A:1874–1877.
2. Amstutz HC, Graff-Radford A, Gruen T, et al. Tharies surface replacements: A review of the first 100 cases. Clin Orthop Relat Res 1978;134:87–101.
3. Amstutz HC, Grigoris P, Safran MR, et al. Precision fit surface hemiarthroplasty for femoral head osteonecrosis: long term results. J Bone Joint Surg Br 1994;76B:423–427.
4. Daniel J, Pysent PB, McMinn DJW. Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br 2004;86B:177–184.
5. DeSmet KA. Belgium experience with metal-on-metal surface arthroplasty. Orthop Clin North Am 2005;36:203–213.
6. Hardinge K. The direct lateral approach to the hip. J Bone Joint Surg Br 1982;64B:17–18.
7. Howie DW, Cornish BC, Vernon-Roberts B. Resurfacing hip arthroplasty. Classification of loosening and the role of prosthetic wear particles. Clin Orthop Relat Res 1990;255:144–159.
8. Howie DW, Cornish BC, Vernon-Roberts B. The viability of the femoral head after resurfacing hip arthroplasty in humans. Clin Orthop Relat Res 1993;291:171–184.
9. Itayem R, Arndt A, Nistor L, et al. Stability of the Birmingham hip resurfacing arthroplasty at two years. A radiostereophotogrammetric analysis study. J Bone Joint Surg Br 2005;87B:158–162.
10. Kim KI, Yoo MC, Cho YJ, et al. Comparison of results of resurfacing arthroplasty performed using a navigation system and conventional technique. Abstract book of the 21st Annual Congress of the International Society for Technology in Arthroplasty (ISTA). Seoul, Korea, 2008.
11. Lilikakis AK, Vowler SL, Villar RN. Hydroxyapatite-coated femoral implant on metal-on-metal resurfacing hip arthroplasty: minimum of two years follow-up. Orthop Clin N Am 2005;36:215–222.
12. McMinn D, Treacy R, Lin K, et al. Metal on metal surface replacement of the hip: Experience of the McMinn prosthesis. Clin Orthop Relat Res 1996;329(Suppl):S89–S98.
13. Ramesh M, O'Byrne JM, McCarthy N, et al. Damage to the superior gluteal nerve after the Hardinge approach to the hip. J Bone Joint Surg Br 1996;78B:903–906.
14. Shimmin AJ, Back D. Femoral neck fractures following Birmingham hip resurfacing. A national review of 50 cases. J Bone Joint Surg Br 2005;87B:463–464.
15. Wagner H. Surface replacement arthroplasty of the hip. Clin Orthop Relat Res 1978;134:102–130.
16. Yoo MC, Cho YJ, Kim KI, et al. Changes in BMD in the proximal femur after cementless total hip arthroplasty and resurfacing arthroplasty. Prospective, longitudinal, comparative study. J Korean Orthop Assoc 2006;41:212–219.
17. Yoo MC, Cho YJ, Kim KI, et al. Resurfacing arthroplasty in osteonecrosis of the femoral head [abstract]. Abstract book of the 23rd World Congress of the SICOT/SIROT. Istanbul, Turkey, 2005.