CHAPTER SYNOPSIS
Hip resurfacing has now shown good mid-term results in Great Britain and is gaining popularity in the United States. Understanding the proper indications and surgical pitfalls to prevent femoral neck notching and postoperative fracture are paramount to give the patient the optimal chance at a good long-term outcome.
IMPORTANT POINTS
Indications for this procedure include the following:
- 1
Young, active patients with osteoarthritis and good bone stock, normal femoral anatomy, a long femoral neck length, no leg-length discrepancy, and normal bone density.
- 2
Patients with deformities of the upper femur from either fracture or previous osteotomy or other causes often can be more easily treated with resurfacing because placement of a stem in the upper deformed femur is not necessary.
Absolute contraindications for this procedure include the following:
- 1
Loss of femoral head (severe bone loss)
- 2
Large femoral neck cysts found at surgery
- 3
Small or bone-deficient acetabulum
Relative contraindications for this procedure include the following:
- 1
Poor bone stock (assessed by dual-energy x-ray absorptiometry scan)
- 2
Chronological age older than 65 years
- 3
Body mass index greater than 35
CLINICAL/SURGICAL PEARLS
- 1
The key to the operation is achieving an exposure that allows accurate placement of the components regardless of the approach.
- 2
Once the femoral head is dislocated, the head-neck template is used to indicate the minimal head that could be achieved; this, in turn, indicates the smallest acetabular component possible.
- 3
Care must be taken to maximize the head/neck ratio, and a slight anterior translocation of the component may improve the range of flexion.
- 4
Low-viscosity antibiotic-loaded cement is mixed and poured into the appropriate femoral component.
INTRODUCTION
Hip resurfacing has conceptually been an attractive way to treat arthritic hips for many years.
In 1938 Phillip Wiles at the Middlesex Hospital, London, replaced an entire hip joint with stainless steel components that were ground to fit together accurately. Surface replacement is a direct descendant of the cup arthroplasty originally conceived by Smith-Peterson. However, Sir John Charnley is credited by most authors as having performed the first hip resurfacing operation with thin cups of Teflon (DuPont, Wilmington, Del.) in the early 1950s. The initial results were encouraging, but Charnley found that with early deterioration in function came corresponding radiologic changes—indicating that the femoral head was necrotic. In the mid-1960s Muller and Boltzy used a metal-on-metal (cobalt-chromium-molybdenum) resurfacing system that was press fit. Despite satisfactory early results, this system was abandoned because of loosening of the components.
In the 1970s Furuya, in Japan, developed an arthroplasty that at first was made of a stainless steel acetabular cup and a high-density polyethylene femoral component. This series had failures, and he postulated that the bony atrophy was caused by either the biologic effect of wear particles of the polyethylene or cement or circulatory disturbance.
In London, Freeman was using the Imperial College-London Hospital (ICLH) prosthesis, consisting of a metal femoral head and polyethylene acetabular component. Both were cemented in place with polymethylmethacrylate. Freeman published an analysis of the first 10 years of using ICLH in 1983. Twenty-one percent of the 204 arthroplasties reviewed with a minimum of 2 years of follow-up had failed. Seventeen percent of these were caused by aseptic loosening, 1.5% by infection, and 1% by fracture of the femoral neck.
In 1974 Wagner, in Germany, developed a resurfacing prosthesis with a polyethylene acetabular component and a femoral component made of either ceramic or metal; both were cemented in place. Wagner sought to make the prosthesis as thin as possible and considered the anterior approach to be essential for optimal exposure and to preserve the posterior retinacular vessels. In 1978 Wagner published a large series of 426 consecutive hip resurfacing procedures performed in the previous 4 years with a minimum of 6 months of follow-up. At this early stage his results were encouraging, with excellent pain relief and mobility. He reported at that stage only six cases requiring revision for loosening.
Amstutz, working from Los Angeles in the early 1970s, designed the THARIES (total hip articular replacement by internal eccentric shell). This was cemented and consisted of a cobalt-chromium-molybdenum femoral component and polyethylene acetabular component. Clinically the results were good; however, at 2 years of follow-up progressive radiolucencies were noted in 67% of the cases. Of the 322 THARIES implanted by Amstutz between 1975 and 1984, 189 revisions were necessary. Average follow-up had been 117 months. Interestingly, one or both components were responsible for 97% of all failures.
The attractive concept of resurfacing as a bone-conserving procedure was again disgraced. By 1982 reports of high failure rates resulted in the procedure being abandoned by many surgeons.
However, between 1966 and 1987 surgeons in Birmingham, Great Britain, found that at the revision of metal-on-metal McKee, Stanmore, and ring hip replacements, the absence of osteolysis was notable, and the concept of hip resurfacing with metal-on-metal bearing surfaces was in favor again.
In 1989 Derek McMinn, in collaboration with Corin Medical Ltd. (Cirencester, UK), started to develop the McMinn prosthesis. A pilot study was undertaken, with the first surface replacement being performed in February 1991. This was an uncemented, uncoated, press-fit type of acetabular and femoral component. This was implanted in 70 hips between February 1991 and 1992. Average follow-up was 50.2 months, with nine complications.
The second design of resurfacing had hydroxyapatite coating to the shells and was implanted from February 1992 to March 1992 in six hips. Average follow-up of 40.2 months showed excellent outcomes.
The third design was a cemented design on both the acetabular and femoral sides; this was conducted in 43 hips from March 1992 to December 1993. An average follow-up of 33.2 months showed four complications.
The fourth design included an acetabulum designed for cementless fixation with hydroxyapatite coating, a central peg for axial stability, and two peripheral splines for rotational stability. The femoral component remained unchanged, and four sizes were available. A total of 116 hips between March 1994 and October 1995 were treated with this hybrid system. Average follow-up of 8.3 months showed excellent results. McMinn chose this system of an uncemented cup with a cemented femoral component as his first choice. However, as a result of various manufacturing inconsistencies, McMinn changed manufacturers and the Birmingham hip replacement was produced. This differed from the McMinn prosthesis in that it had a cast rough, beaded surface on the back of the hemispherical acetabular component that also was coated in hydroxyapatite.
A total of 235 hips in patients with a mean age of 48.7 years were operated on in this pilot study, with no femoral neck fractures, dislocations, avascular necrosis, or deaths. Three patients had nonfatal pulmonary embolisms and one had sciatic nerve palsy that partially recovered. All patients had satisfactory alignment in the anterior-posterior radiograph. A total of 95% of the femoral components had neutral and 5% had valgus alignment. No patient had varus positioning.
The Birmingham resurfacing technique has continued unchanged except for the recent introduction of the femoral component in 2-mm rather than 4-mm increments. All the major manufacturers now offer a version of hip resurfacing and in many cases believe they have made improvements to the metallurgy, tolerances, or shape of the components ( Fig. 14-1 ).
METALLURGY
High carbide content confers wear resistance, and any diminution is considered unacceptable. This resulted in closer scrutiny of casting methods with hot isostatic pressing and solution heat treatment commonly used in the manufacturing industry to eliminate microporosity and improved strength. It was found to deplete carbide levels; thus the search for an alternative manufacturing process led to the development of the Porocast method (Centaur Precision Castings, Sheffield, UK; and Midland Medical Technologies Ltd., Birmingham, UK). This method obviated the need for hot isostatic pressing and solution heat treatment as a post-cast treatment.
INDICATIONS AND CONTRAINDICATIONS
Indications
The classic choice for hip resurfacing is the young, active patient with good bone stock who has been shown in the past to experience a higher failure rate with conventional joint replacement. The hope in this group of patients is that the functional outcome will be better, the design of the head will prevent proximal femoral stress shielding, and the metal-on-metal bearing surface will improve longevity. If failure does occur, revision to conventional joint replacement is straightforward. The perfect subgroup of this classic indication includes normal femoral anatomy, a long femoral neck length, and no leg-length discrepancy.
The indication can be extended to include the older active male patient. Ankylosing spondylitis, rheumatoid arthritis, and other inflammatory joint disease can be treated if the bone quality remains good.
Patients with deformities of the upper femur from either fracture or previous osteotomy or other causes often can be more easily treated with resurfacing because placement of a stem in the upper deformed femur is not necessary. Patients with a high susceptibility for infection, either those with previous history of hip infection or because of disease or drugs therapy, also may be beneficially treated with resurfacing. If infection does occur, it can be more easily be revised.
The reduced dislocation rate attributable to the large-diameter head also can be of benefit to patients with neuromuscular conditions and some connective tissue disorders.
Developmental dysplasia of the hip can in some cases be treated with standard resurfacing, although a dysplasia socket may be needed.
Beginning surgeons should start with patients with normal femoral morphology, a high head/neck ratio (1.3 or greater), and good bone quality.
Contraindications
Absolute contraindications to this procedure include the following:
- •
Loss of femoral head (severe bone loss)
- •
Large femoral neck cysts found at surgery
- •
Small or bone-deficient acetabulum
Relative contraindications include the following:
- •
Poor bone stock (assessed by dual-energy x-ray absorptiometry scan)
- •
Chronological age older than 65 years
- •
Body mass index greater than 35
Caution is required in the following patients:
- •
Patients with rheumatoid arthritis
- •
Tall and thin patients
- •
Female patients
- •
Patients with femoral head cyst greater than 1 cm, as demonstrated in a preoperative radiograph
- •
Patients with osteonecrosis of the femoral head
SURGICAL TECHNIQUES
Resurfacing is acknowledged to be technically more demanding than standard total hip replacement, and reported incision lengths for resurfacing range from 25.4 to 50.8 cm. However, focus on the minimally invasive techniques is a recent topic.
Hip resurfacing, as described by its originator McMinn, was classically performed by way of a posterior approach (Kocher-Langenbeck), and the available mid-term results have been achieved with this approach. The criticism of this approach has always been of devascularization of the femoral head (Lavigne et al and Nork et al both emphasized the presentation of the blood supply to the femoral head by way of the medial femoral circumflex artery), and many other approaches have recently been used. Wagner described the anterior approach, but Nork et al noted that visualization of the acetabulum is quite difficult with this approach. Mont et al championed the procedure with an anterior approach, and others have used the trochanteric osteotomy described by Ganz to try to achieve resurfacing with the least damage to the upper femoral blood supply. This consists of an anterior dislocation through a posterior approach with a “trochanteric flip” osteotomy. The external rotator muscles are not divided, and the medial femoral circumflex artery is protected by the intact obturator externus.
Minimally invasive surgical approaches have been described with the anterolateral approach, and McMinn performed the procedure by way of the posterior approach with a 9- to 12-cm incision.
Operative Technique
The key to the operation is achieving an exposure that allows accurate placement of the components regardless of the approach.
Acetabular Preparation
- •
Once the femoral head is dislocated, the head-neck template is used to indicate the minimal head that could be achieved; this, in turn, indicates the smallest acetabular component possible.
- •
The acetabulum is exposed by circumferential retraction.
- •
The transverse acetabular ligament is identified and used to orientate the acetabulum and, if necessary, excised to give a clearer view of the acetabulum.
- •
Reaming is then carried out as for any hemispherical socket and usually will be 1 to 2 mm smaller than the acetabular component, but this will depend on the system used.
- •
A trial cup insertion is performed and, with this in situ, rim osteophytes are removed.
- •
The acetabular component is then mounted on the introducer and impacted into position with 40- to 45-degree inclination and 15- to 20-degree anteversion. This angle is important because variations are associated with edge loading of the bearing and high wear and metal ion levels.
Femoral Preparation
A problem with resurfacing is the smaller head/neck ratio it produces compared with total hip arthroplasty. Care must be taken to maximize this ratio, and a slight anterior translocation of the component may improve the range of flexion. In addition, the femoral component must be implanted in valgus to reduce the incidence of femoral neck fracture, and care must be taken to avoid notching.
In McMinn’s classic technique the alignment pin is inserted into the mid-lateral cortex (position measured from the tip of the greater trochanter during templating), as follows:
- •
The McMinn alignment guide is hooked onto the pin and the leg internally rotated to deliver the head into the wound. The guide is set to the diameter of the femoral neck and is adjusted so that a valgus position of the femoral component can be achieved without femoral neck notching. Once the proximal stylus can be freely moved around the femoral neck at an equal distance, the guide is locked into position.
- •
The guide wire is inserted through the cannulated central rod and the rest of the guide removed.
- •
The stylus is reinserted and its free passage around the head rechecked. In this position a supporting rim of the femoral head should be left. This is important for support of the implant and cement pressurization.
- •
The guide wire is overdrilled to allow a rigid rod to be inserted as a guide for the subsequent cutting tools.
- •
At this stage a drill hole is placed by way of the lesser trochanter and a suction portal is inserted.
- •
A drill is used to make shallow holes into the head to improve the rotational control of the cement, and any cysts are curetted.
- •
Lavage is applied and the head dried.
- •
The head neck junction is marked with the appropriate head-neck template to ensure the femoral component is fully seated.
- •
Low-viscosity antibiotic-loaded cement is mixed and poured into the appropriate femoral component. This is inserted onto the femoral head and impacted to the head-neck mark previously made.
- •
After further lavage the femoral component is reduced into the socket and the range of movement checked.
- •
The posterior capsule, the insertion of gluteus maximus, and quadratus femoris are repaired and the rest of the wound closed with suction drainage as necessary ( Fig. 14-2 ).
