Hip arthroplasty started in the beginning of the twentieth century with the procedure of contouring and interpositional-layer insertion between the articulating bony surfaces at the hip (Interpositional arthroplasty) (Fig. 1.1). Corrective osteotomy of the proximal femur was simultaneously done for fixed deformities, e.g. ankylosis of the hip joint. Osteotomy alone was the only procedure available before this to treat such conditions. Sir Robert Jones (1912) used gold foil as an interpositional layer. Murphy (1915) combined osteotomy with interposition of soft tissue at the hip. Other materials used for the purpose at that time include fascia lata, chromicised pig bladder, skin, etc. However, all had uniformly unsuccessful results.
Smith-Petersen in 1923 introduced the concept of mould arthroplasty (Fig. 1.2) as an alternative to interpositional membrane. This was based on his chance discovery of synovial tissue formation around an impregnated glass-piece in the thigh of a patient. The idea was to put in a mould of an inert material between the freshened surfaces of the femoral head and acetabulum, which would guide nature's repair to form smooth articulating surfaces. The implant could be removed once such surfaces were formed. Glass moulds were too fragile. Alternative materials like Bakelite Viscalloid and Pyrex were attempted, which were not very durable either. Besides, these materials induced severe foreign body reaction and bone destruction. Because of high failure the procedure had to be abandoned.
Fig. 1.1: Interpositional arthroplasty: Interpositional arthroplasty was used with or without osteotomy to correct ankylosis and painful hip conditions. Interposition of different materials was done to prevent recurrence of bone growth and maintain motion. Tissues of various types were tried by various surgeons: Ollier (1885)- soft tissue; Murphy (1902)- fascia lata; Loewe (1913)-skin; Baer (1918)- Pig's bladder
Fig. 1.2: Mould arthroplasty: Smith-Petersen and others tried putting a mould of inert material between the articular surfaces of the hip joint viz. Glass (1923), Pyrex (1933), Bakelite (1937) and Vitalium (1938). It proved that the acetabulum will tolerate a foreign body
In 1938 Smith-Petersen used Vitallium an alloy of cobalt, chromium and molybdenum used by dentists to line the raw bony surfaces (cup arthroplasty) (Fig. 1.3). This was found to be a suitable material. It was a kind of hemi-surface arthroplasty of the hip. Cup arthroplasty and later Aufranc's modification of the same was the standard for hip reconstruction at that time. However only about one half of the cup arthroplasties relieved pain successfully. It was not possible to replace bony deficiencies or correct bony abnormalities or shortening with this procedure. Though it was not a stable fixation and the outcomes were unpredictable some survived for many years.
Phillip Wiles (1938, London), was the first to attempt metal-on-metal (Figs 1.4 and 1.6) articulation. He used a stainless steel cup with spikes for the acetabulum. The femoral head was resurfaced with a stainless steel shell, which was fixed with an inter-trochanteric device to the side-plate on the shaft of femur. AT Moore credited Bohlman for use of a cobalt- chrome ball fitted to a Smith-Petersen nail in 1939. In early 1940's Moore and Bohlman replaced the upper end of femur in a patient with a 12-inch steel prosthesis. In 1946, the Judet brothers, used an endoprosthesis with a femoral head of acrylic attached through an acrylic stem. Because of severe wear the acrylic was changed to a metal (cobalt-chrome) alloy.
In 1950's Moore and Thompson individually developed stemmed metal prosthesis. This was the beginning of hemiarthroplasty (Fig. 1.5). Both Thompson's and Moore's metallic implants were unipolar prostheses with long stems (endoprosthesis) that allowed transmission of weight-bearing forces along the axis of the femoral shaft, unlike the previous designs (which generated high shear forces on the short stem placed within the femoral neck). The Moore prosthesis was fenestrated to permit bone growth. Thompson's prosthesis was without any fenestration and was also cemented once bone cement became available. These prostheses have worked very well; they are still in use with little modification.
Figs 1.3A and B: Cup arthroplasty: (A) A hemi-surface replacement, (B) Smith-Petersen double cup-a metal surface replacement femoral component and a polymer acetabular component
Fig. 1.4: Metal-on-metal hip prosthesis: X-ray of metal-on-metal cementless hip, note the large bearing size
Fig. 1.5: Unipolar femoral components: 1950–Thompson Prosthesis: Large head and collared curved intramedullary stem. 1952– Moore Prosthesis: Large head and collared long straight cementless stem with fenestrations for bone in growth
Fig. 1.6: McKee-Farrar prosthesis: McKee Farrar metal on metal hip prosthesis had a high initial failure due to poor neck, stem design and improper orientation of the implants. Also the concept of peri-operative asepsis was not established leading to high infection rate
These have press-fit fixation however may produce varying degrees of femoral bone loss. There may also be delayed erosion of bone on the pelvic side; that highlighted the need to resurface the acetabulum.
Kenneth McKee modified metal-on-metal (MOM) arthroplasty in 1950's. He introduced cobalt-chrome alloy articulations. Thompson-type stem of femoral implant was designed. Watson-Farrar modified the neck to reduce impingement. McKee modified the acetabulum, for cement fixation. The first series of McKee–Farrar total hip replacement (Fig. 1.6) (1956 to 1960) had a high incidence of failure. The bearing combination of MOM was suspected to be unfavorable and the cause of failure, which, we now know is not true. The failure was due to poor designing and implant placement besides non-availability of antibiotic prophylaxis and poor aseptic techniques. Some of these prostheses have functioned over 20 years. KM Sivash (Moscow, 1950's), Peter Ring (England,1964) and others designed their versions of all-metal prosthesis (Fig. 1.7).
Sir John Charnley is credited as the ‘father of total hip arthroplasty’ for his pioneering work in all aspects of total hip arthroplasty, including the concept of ‘low frictional torque arthroplasty’, lubrication, materials, design, trochanteric osteotomy, asepsis and operating room hygiene. His other major contribution was the use of polymethylmethacrylate (PMMA), a cold-curing acrylic cement for fixation of the prosthetic components.
Charnley attributed the squeak heard in patients with a Judet prosthesis to marked friction between the acrylic head and the acetabulum. This led to enough torque on the implants to loosen up the fixation on the respective bones. He confirmed the low coefficient of friction of a normal joint in the presence of joint fluid.
Fig. 1.7: Peter Ring prosthesis: Ring's prosthesis matched with Moore's stem was a metal-on-metal articulation. A high incidence of failure was reported due to breakage of the threaded stem on the acetabular component at its base
He realised that in joint replacement the articulating surfaces are subjected to boundary lubrication. He also determined that the coefficient of friction of a steel ball against polytetrafluoroethylene (PTFE/Teflon) was close to that of a normal joint. Between 1958 and 1963 he had developed and tried various types of prosthetic hips. He inserted large head Thompson stem and lined the acetabulum with PTFE shell. Charnley fixed the stem of the femoral prosthesis securely with PMMA bone cement. This permitted more uniform transfer of stress to a larger bone surface. In 1961 he realized that “the best engineering practice would be to use the smallest diameter ball which could cope with the expected load”. By trial and error the right size determined was 22.225 mm (7/8 inch). This decreased the resistance to movement by reducing the moment (lever arm) of the frictional force. He realized that with a larger head the pressure per unit of surface was less and that this would tend to reduce wear. However, he still considered it more important to reduce frictional torque and to have a cup with a thick wall. He continued using press-fit PTFE shell for a long time. PTFE shells wore off faster and were replaced with high-density polyethylene (HDPE) and later by ultrahigh molecular weight polyethylene (UHMWPE). Though the initial cementing of these cups was suspect it was eventually realized to be holding very well and from 1966 onwards UHMWPE cemented cups were the standard implants. The procedure of cementing, use of 22.225 mm diameter head metal on polyethylene articulation and trochanteric osteotomy together form the concept of ‘low frictional torque arthroplasty (LFA) (Fig. 1.8).’ Charnley had earlier attempted resurfacing the femoral head but abandoned this procedure because of high incidence of what he proposed was avascular necrosis of the head.
In an attempt to decrease the acetabular wear with the traditional endoprosthesis for hemiarthroplasty McKeever and Collision developed bipolar endoprosthesis in the 1950's. The idea was to achieve more movement between the prosthetic components than between the metal and the acetabulum. Gilberty and Bateman individually developed the current generation of bipolar hips. Despite the initial expectations the benefit of bipolar prosthesis over unipolar implant has been debated, (Fig. 1.9).
Fig. 1.9: Bipolar hip prosthesis: Components of modular bipolar hip with a cementless stem. The parts are assembled on the patient's body. The length of inner-head can be adjusted to the requirement. The outer head corresponds to the patient's natural femoral head size
Charnley first used methylmethacrylate to cement the femoral component in 1958. The basic concept of bone cement fixation still holds true. The commercial cast sheets of polymethylmethacrylate (Plexiglas), in the early 1930's, led to its development as a denture material. The original material was molded under heat and pressure. In 1936 it was discovered that a mixture of methylmethacrylate monomer and ground polymer produced moldable dough in the presence of benzoyl peroxide. In subsequent years polymer beads were added to improve mouldability. In the year 1943 it was discovered that the dough could be polymerized at room temperature if dimethyl-p-toludine was added with benzoyl peroxide. This was routinely used in 1940's for dentures and cranioplasty prosthesis. Though Judet brothers and others had used PMMA, nobody had used it as a means to stabilize the prosthetic implant. In 1958 Charnley operated on the first case at Manchester where bone cement was used to completely fill the medullary canal to adapt to the bony interface thereby facilitating stress transfer, in turn stabilizing and anchoring the prosthesis. Cementing technique has long evolved since then. This includes use of injectable low-viscosity bone cement, occlusion of medullary stem, reduction of porosity by centrifuging, pressurization of cement and centralization of the stem.
Sir John Charnley's concept of metal on polyethylene articulation and use of small diameter head has overshadowed the field of hip replacement for a long time. However, the major drawback with it is the excessive polyethylene wear and the consequent osteolysis, aseptic loosening and implant failure. This is even more pronounced with prostheses having larger diameter heads which were designed in an attempt to improve hip stability. All this led to research for alternative bearing surfaces.
Metal-on-metal (MOM) ceramic-on-polyethylene (COP), ceramic on ceramic (COC) and ceramic-on-metal (COM) articulations are few such options.
MOM surface replacement is a direct descendant of cup arthroplasty. Muller (1967) introduced the first generation metal-on-metal surface arthroplasty. This was a press fit design and had excellent preliminary result. He also designed stemmed MOM prostheses at the same time (Fig. 1.10). Though the initial results were satisfactory, he moved on to metal-on-polyethylene articulations. The results of hip resurfacing in the 1970s and 1980s were disappointing and the procedure was almost abandoned.
The credit of revival of metal-on metal articulations goes to Bernard G. Weber in collaboration with the erstwhile ‘Sulzer Orthopedics’ (Switzerland), 1988. This was due to the availability of the low-wear, high-carbon metal bearings of Co-Cr-Mo alloy (Metasul). The second generation metal-on-metal total hip arthroplasty was launched using 28 mm heads. The low wear and added stability and good range of motion were encouraging. It was noted that every one-millimeter increase in head size yielded approximately one-degree increase in range of motion. The introduction of hard cobalt-chromium alloy led to the designing of thinner acetabular implants which could accommodate correspondingly larger femoral heads. The second generation metal-on-metal surface arthroplasty evolved with the use of the arthroplasty system developed by Heinz Wagner (Germany) and Derek McMinn (England) individually in 1991. Amstutz (1996) developed the Conserve Hip Resurfacing (USA). Two designs, Cormet resurfacing hip system and the Birmingham hip resurfacing evolved from the McMinn system in 1997. These third generation MOM surface replacements were better in terms of designing and metallurgy. Durom Hip (Zimmer, Switzerland, 2001), Articular Surface Replacement (ASRTM; DePuy, UK, 2003) (Figs 1.11A and B) and others are reportedly the fourth generation metal-on-metal articular surface replacements.
Figs 1.11A and B: Surface replacement arthroplasty: (A) ASRTM Hip (J&J, DePuy), (B) Surface replacement is a bone conserving surgery for the hip permitting large range of motion. However careful patient selection is mandatory for favorable long term result
These are bone conserving surgeries, use Co-Cr-Mo alloy bearing with high carbon content, have cementless fixation of the acetabular component and the femoral component is cemented.
COC and ceramic on polyethylene (COP) modular hips are gaining attention again. Zirconia is a newer ceramic which is less prone to fractures. The ceramics exist in oxidized state and unlike metal articulations are not prone to oxidative damage in the body. Some studies have documented less wear of plastic cups with ceramic heads as compared to metal ones. Ceramic on metal hip is the latest addition. Ceramics are expensive implants.
Fig. 1.12: Cementless hip prosthesis: CorailTM stem (J&J, DePuy) is a titanium stem with HA coating. The prosthesis has shown remarkable long term survivorship
As loosening and osteolysis on the bone-cement interface is a frequent complication with cemented implants the cementless fixation has come into vogue again. The current designs may be press-fit, porous-coated and hydroxyapatite-coated (HA-coated) surfaces (Fig. 1.12). These use the principles of bone in-growth and on-growth as a means of achieving long-lasting skeletal fixation. Though the prospects look good not all designs have similar success reports. These may be due to inadequate initial fixation (a mandatory prerequisite) and excessive particle induced osteolysis. With time certain design parameters have been realized to be important for cementless fixation. Good quality, ‘super alloys’ have been discovered which have resulted in negligible breakage of the stem (Figs 1.13A and B).
Fig. 1.13A: Various hip prosthesis: Femoral components (i) Cemented femoral designs, (ii) Cementless femoral designs
Modular hip systems have evolved reducing the inventory of stock. These allow better balance of limb length and stability. They also add to the versatility of articulation and stem choice on the operating table. Smaller hip designs (mini-hip) are becoming popular in younger patients which allow easier revisions.