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Comparative information on total knee replacements (TKRs) is not readily available. With the help of implant manufacturers and distributors, we have compiled a list of TKRs on the market in the UK and summarised the information about these implants in a table. There are 37 different TKRs, marketed by 14 companies; 54% have been introduced since 1990. The number of different implants is increasing. At least eight designs have undergone major modifications, while many have had minor alterations. Of the TKRs on the market, 60% are modular. Some 54% of TKRs have no published results in peer-reviewed journals; only one of the four most widely used prostheses has published survival figures. New and modified implants are introduced without clinical evidence of their superiority over other available designs. Published results in peer-reviewed journals are currently the best evidence available on the reliability of an implant. When selecting an implant, surgeons should be aware if the prosthesis has any such results, the length of the follow-up, and the survival rates that are achieved. More detailed interpretation is difficult because of the different combinations used in modular implants and because of the frequent modification of existing designs. Properly conducted long-term clinical trials should be encouraged as they are the only means of evaluating new designs.

I have had an opportunity to share with you a few items about surgical technique and instrumentation that are not in most brochures. There are two other instruments that we have not discussed yet that are probably the most important ones to bring into your operating room: your eyes and your brain. Use them wisely and you will have success.

An intact barrier between the hands of the surgeon and the patient remains the single most important factor in protection against infection for both. Increasing the awareness of possible glove perforation without skin penetration will decrease the risk of contamination. We performed a prospective, randomised trial comparing the incidence of glove perforation using a new type of glove (Regent Biogel Reveal) and standard double-gloves in total hip and knee replacement. One or more perforations was detected in 14.6% of all gloves. The new gloves increased significantly the awareness of perforation. Multiple perforations at the base of the ring finger were found in surgeons who wore wedding rings during the operation and we recommend that rings be removed before undertaking surgery.

Fifty total knee arthroplasties were performed using an intraoperative intramedullary goniometer to measure the angle of the distal femoral cut. When deviations of 1 degree or more were found, angled cutting blocks ranging from 1 degree to 5 degrees were used to recut the distal femur. Revised femoral cuts were made it 25 knees (50%). Postoperative evaluation from weight-bearing long-standing anteroposterior radiographs revealed an average distal femoral angle deviation from preoperative planning of 0.64 degree (range, 0 degree-3 degrees). This was statistically significantly different from the value for a comparison group of 50 knees on which arthroplasties were performed without the intraoperative goniometer with an average femoral angle deviation of 1.44 degrees (range, 0 degree-4 degrees) (P < .05). In the control group, there were 7 knees (14%) that deviated by 3 degrees or more versus only 2 knees in the study group. The authors conclude that an intramedullary goniometer is fast, is simple to use, and leads to more accurate preparation of the distal femur in total knee arthroplasty.

In order to assess the wear performance of different designs of total knee replacements (TKR), a six station multi-axis knee simulator has been designed, built and commissioned. The most important features of a knee simulator are representative angles of flexion-extension synchronized with a dynamically applied load, and a combination of rolling and sliding motion. The simulator typically applies flexion-extension of 0-65, anterior-posterior translation of up to 15 mm, a dynamic load of up to 5.0 kN, and operates at 1.0 Hz. The loads and motions are applied using computer controlled servohydraulic actuators and hence their profiles are easily modified. A preliminary wear test has been conducted using a Kinemax (Howmedica, United Kingdom) TKR. The test was conducted in 30 per cent bovine serum which was changed every 150,000 cycles, at which time the bearing surfaces were examined and the UHMWPE tibial component was weighed. Over eight million cycles, a tibial wear rate of 2.62 mg/10(6) cycles was measured. The mild wear observed was characterized by burnishing and slight scratching in the anterior posterior direction. These observations are broadly in line with both in vitro and ex vivo studies reported in the literature for this type of prosthesis. Delamination wear sometimes observed in vivo was not seen.

We summarise our experience gained with knee arthroplasties over 18 years. Between 1976 and 1994 1103 knee arthroplasties (1044 primary cases, 59 revisions) were performed at the Orthopaedic Department of the National Institute of Rheumatology and Physiotherapy in Budapest, Hungary. The diagnoses were osteoarthritis (OA) in 50.9%, rheumatoid arthritis (RA) in 40.7% and other causes in 8.4%. The average age of the patients at the time of the operation was 57.6 years (range 14-81 years). The types of primary implant were as follows: 60 constrained (hinge) prostheses, 876 unconstrained (sledge) prostheses, 108 semiconstrained (total condylar) prostheses. The mean follow-up period was 11.4 years for the hinge-type prostheses, 10.3 years for the unconstrained prostheses and 1.6 years for the semiconstrained prostheses. Reviewing the 59 revision cases, we conclude that complications with the constrained prostheses reached 17.8% and, most presented within the 1st year. Because of this high complication rate, the use of hinge prostheses has been reduced in this department to only selected cases. After sledge prosthesis implantation most of the complications (overall 5.3%) appeared after 1 year in aseptic circumstances. Given the short follow-up period of the semi-constrained total condylar knee replacement, apart from one infection in a patient with rheumatoid arthritis no other complication has been recorded. Summarising these data, it can be concluded that on average the knee function, using a standardised scoring system, improved from 38% to over 80% by introducing the semiconstrained total condylar knee prosthesis.

We report 3 cases of stress fracture of the femoral component (small size Whiteside Ortholoc II) in total knee replacements which occurred at 32, 52, and 73 months after operation. The site was at the junction between the medial posterior bevelled surface and the posterior flange. The most likely cause of failure is due to the thinness of the metal at this point.

A postal questionnaire was sent to all Fellows of the British Orthopaedic Association to obtain a census of total knee replacement (TKR) preferences in the United Kingdom; 1162 questionnaires were sent and 721 replies received. There were 92 Fellows who had retired or filled in the forms incorrectly, and 32 no longer perform TKR. Thus, 597 responded correctly, giving a 62% response rate. This gives an extrapolated total of 34,677 TKRs being implanted per year in the UK, with an average of 34.3 being performed by each surgeon per year. Only 9% perform more than 90 per year. There were 41 different prostheses in current use among the respondents to our questionnaire, of which five prostheses constituted 61% of the total. Cemented prostheses were used by 95.2%. Resurfacing of the patella was always carried out by 32%, while 19% never resurface it; the most common reason for doing so being patellofemoral arthropathy at operation. Intramedullary alignment was used for the femoral component in 86%, 76% preferred extramedullary alignment for the tibial component. Regarding cementing technique, 43% use pulsatile lavage, 9% used a cement gun, 88% dry the bone and 56% seal the hole made by the femoral alignment device in the femur before cementing. All components were cemented simultaneously by 65% and one at a time by 31%. Metal-backed tibial prostheses are now used by 98% of surgeons, modular tibial components being preferred by 80%. Metal-backed patellar components were used by 13%. An onlay type of patella was preferred by 51%. This survey highlights the great diversity of surgical practice in the UK, which may reflect uncertainty regarding best practice in total knee replacement.

Twenty-nine Ortholoc II ultrahigh molecular weight polyethylene tibial components were retrieved from 27 patients at revision surgery from the same hospital. The polyethylene material grade, method of sterilization, and sterilization dosage for 26 of the tibial components were determined by tracing the material lot number for each component. Each tibial surface was scored for wear using a qualitative scoring system that evaluated delamination, pitting, scratching, cold flow, abrasion, and burnishing. After the wear score analysis, 14 of the 26 components were analyzed to determine the physical and mechanical properties of the polyethylene including toughness and elongation. Seven of these 14 components were sterilized using ethylene oxide and 7 were sterilized using gamma radiation. Tibial components sterilized with gamma radiation had significantly higher wear rates than those sterilized with ethylene oxide. Thirteen of the 18 components sterilized with gamma radiation had delamination of the articular surface compared with 2 of 8 components sterilized with ethylene oxide. Mechanical properties were significantly affected by the sterilization method. Components sterilized with ethylene oxide had significantly higher toughness and percent elongation than those sterilized with gamma radiation. These findings suggest that ethylene oxide sterilization caused less microstructural damage to the polyethylene and resulted in significantly less wear than was found in those components sterilized with gamma radiation.

Eleven unassembled metal backed patellar interfaces were inoculated with 0.1 ml of Sportol (Bacillus subtilis variety niger spore) and then assembled. Ten of the 11 implants were exposed to 1/2 of a standard ethylene oxide sterilization cycle. The remaining implant was left unsterilized as a control. All the implants were separately incubated in soybean casein digest broth for 7 days at 30 degrees to 35 degrees C and tested for positive growth of Bacillus subtilis. To measure residual ethylene oxide content, 4 ultrahigh molecular weight polyethylene tibial inserts were exposed to a full ethylene oxide sterilization cycle. The implants were removed from the sterilization chamber and tested for residual ethylene oxide at 3, 5, 8, and 9 days after sterilization using an exhaustive extraction headspace technique. Residual ethylene oxide was measured in 3 additional implants 26 days after sterilization. No growth of Bacillus subtilis occurred on any of the 10 inoculated and ethylene oxide sterilized metal backed patellar components, whereas positive growth occurred on the inoculated, unsterilized control implant. Residual ethylene oxide measured in the tibial inserts at 3, 5, 8, and 9 days after sterilization was 23, 15, 12, and 9 ppm, respectively. Twenty-six days after sterilization, residual ethylene oxide was below the minimum detectable level of the measurement technique (5 ppm).

Although the risk of pulmonary embolism or other embolic events associated with total joint arthroplasty have been recorded for some time, to date no direct means of monitoring these events in human arthroplasty have been reported. The authors used transesophageal echocardiography to monitor directly the release of embolic particles into the circulatory system during the course of total knee arthroplasty. The transesophageal echocardiography, in conjunction with intramedullary instrumentation, revealed that showers of embolic particles entered the heart in repeated and unpredictable patterns during the course of conventional intramedullary instrumented total knee procedures. In response to the presence of these embolic showers in the heart, an extramedullary pneumatically positioned system of instrumentation permitting automatic and accurate alignment of the knee with the mechanical axis of the femur has been developed. This new instrumentation establishes proper knee kinematics by semiautomatically determining and maintaining accurate positioning of the femoral component along the mechanical axis of the knee. Qualitative and quantitative monitoring of embolic events using transesophageal echocardiography in conjunction with conventional intramedullary and the new instrumentation suggests that the embolic risk is substantially reduced using the new procedure. Furthermore, the new extramedullary instrumentation was able to align the femoral knee component to within 1 degree of the mechanical axis in an initial series of 25 procedures. Excellent component alignment in conjunction with a substantially reduced quantity of embolic particles in the right heart as seen using transesophageal echocardiography was achieved using the newly developed extramedullary positioning and alignment arm.

Gait analysis was used to study patients who underwent cemented medial unicompartmental knee arthroplasty (UKA) for medial compartment degenerative knee disease. All had excellent clinical function of the operated knee, with minimal involvement of other joints. Ten patients met the inclusion criteria for this study. Gait findings from this study group, as well as those from a similar cohort of patients who had undergone total knee arthroplasty (TKA), were compared with those for a group of normal patients. A greater percentage of patients (7 of 10) following UKA maintained the normal biphasic flexion/extension moment pattern about the knee or demonstrated a quadriceps overuse pattern, when compared with similar groups following TKA. In addition, the adduction moment in patients following UKA was significantly larger than in patients following TKA. The postoperative limb alignment correlated with the peak adduction moment recorded during the patient's gait analysis. The postoperative alignment may explain the differences in the adduction moment between the UKA and TKA patients, as there tended to be residual varus in the UKA population. The results of this study imply that preservation of the anterior cruciate ligament during UKA allows patients to maintain normal quadriceps mechanics, and that residual varus alignment subjects a medial UKA to higher loads.

42 patients with 45 implanted total knee endoprostheses (sliding axis endoprosthesis Lübeck, Rp. SG implant) were investigated clinically according to the score of the Knee Joint Society in mean 27.9 months postoperatively. Mean total knee score increased from 34.9 +/- 14.7 to 72.5 +/- 3.1 and mean total functional score could be ameliorated from 40.2 +/- 25.7 to 55.7 +/- 4.5 (maximum points: 100). Evaluation of X-rays (anterior-posterior and lateral views) exhibited a satisfactory position of the prosthesis. Comparison between cemented and cementless implants as well as between primary implants and revision did not reveal any statistically significant differences. Patients with a longer follow-up period (59.8 months) showed results comparable to the mean of the total group. Frequently observed malposition of the axis of more than 3 degrees requires modifications of the orientation instruments. For revision surgeries a modular system for elongation of the stem would be desirable.

We reviewed 1567 elective knee replacements performed between 1980 and 1990, using either the Total Condylar prosthesis with an all-plastic tibial component, or the Kinematic prosthesis which has a metal tibial tray. The ten-year probability of survival was 92.1% for the Total Condylar design and 87.9% for the Kinematic. The difference was mainly due to 16 revisions required in the Kinematic series for fracture of the metal base-plate. This was the most common cause of aseptic failure in this group. These fractures were strongly associated with a preoperative varus deformity (hazard ratio (HR) 8.8) and there was a slightly increased risk in males (HR 1.9) and in osteoarthritic knees (HR 1.8). In the nine fractures which occurred within four years of primary implantation (group 1), failure to correct adequately a preoperative varus deformity and the use of a bone graft to correct such a deformity were both strongly associated with fracture (HR 13.9 and 15.8, respectively). In eight fractures which occurred more than five years after primary replacement (group 2) we could detect no significant risk factors. Early complications occurred in two patients after the 16 revision procedures for tray fracture. One had a deep infection and the other refracture of the tray.

We evaluated the radiographic and functional status of a one-piece composite tibial component, designed to be inserted without cement, that was developed and used only at our institution. Thirty-six patients (thirty-seven knees) were managed with the component between November 1981 and September 1983, and none were lost to follow-up. When they were last seen, thirty-four (92 per cent) of the thirty-seven knees had a well-fixed tibial component, both clinically and radiographically. Eight patients (eight knees; 22 per cent) died. Eleven patients (eleven knees; 30 per cent) had a revision at an average of sixty-five months (range, four to ninety-five months) postoperatively. The reason for the revision was failure of a metal-backed patellar component in three knees, excessive wear of the polyethylene of the tibial component in one, a hematogenous infection in four, aseptic loosening of the tibial component in two, and chronic synovitis in one. The remaining seventeen patients (eighteen knees; 49 per cent) were seen for clinical and radiographic follow-up at an average of eleven years (range, nine to twelve years) after the operation. With removal of the implant as the end point, the cumulative rate of survival was 83 per cent at fifty-six months and 67 per cent at 108 months. Some of the failures were secondary to features of the prosthetic design that currently are considered to be inadequate, including a metal-backed patellar component and carbon-fiber-reinforced polyethylene. In the twenty-six knees in which the prosthesis had been retained, the implant was stable and the prosthesis-bone interface was unchanged as seen radiographically at the time of the most recent follow-up examination. This finding demonstrates that a porous ingrowth surface is capable of providing a secure interface for biological fixation over the long term.

Total knee replacement has been carried out in the 4 knees of 2 patients for spontaneous bony ankylosis. Minimally constrained prostheses were used because the ligaments were usually intact and the patellofemoral and tibiofemoral joint lines could be re-established. The approach and repair was by a V-Y quadricepsplasty. Satisfactory results were obtained.

In the period from 1988 to 1992, 23 patients (16 females and 7 males, average age at operation 57.3 years) with metastatic disease of the proximal femur were treated by resection of the lesion and insertion of a modular prosthesis (PGR). At latest review (at an average 3.2 years following the operation, range 1 to 5 years) twelve patients were still alive. Local recurrence of the neoplasia occurred at, respectively 6, 8, and 12 months after prosthesis insertion in the three patients in whom surgery was performed because of a pathological fracture. Pain relief was obtained in all cases after surgery and no patient developed any complication during or after surgery. Functional results (Enneking Function Evaluation system) were excellent in 2 patients, good in 13 and fair in 8. PGR modular prostheses appear to be a safe form of palliative treatment in a patient with proximal femoral metastases.

Flat-on-flat, posterior cruciate ligament-sparing total knee prostheses recently have shown problems of wear, loosening, and multiple design changes. Two thousand one Anatomical Graduated Components total knee arthroplasties with compression molded, nonmodular polyethylene tibial components were done between 1983 and 1991 at 3 institutions. All knees were evaluated clinically and radiographically every 2 to 3 years; 71 knees were seen in followup > 10 years. There were 8 failures secondary to revision (5 tibial failures; 2 secondary to metalosis from patellar polyethylene dissociation; and 3 femoral failures) resulting in a 98% survival rate at 10 years. The tibial design was flat-on-flat with a compression molded polyethylene that the authors believe is the primary reason for its success.

This report constitutes a followup of a previous study of 28 knees in 25 patients with metal wedge augmentation for tibial bone deficiency. Those patients were reviewed 2.3 years after surgery; 79% had excellent results, and 21% had good results. Twenty-four knees in 21 patients with a metal wedge augmentation for tibial bone deficiency were reviewed 5.6 years clinically and 4.8 years radiographically after surgery. Clinical results were excellent in 67%, good in 29%, and poor in 4%. The only poor result was in 1 knee that required 2 revision procedures: the first for failure of a metal-backed patellar component and the second for aseptic loosening of the femoral component. Radiolucent lines at the cement bone interface beneath the metal wedge were present in 13 knees. Eleven of those radiolucencies were < 1 mm in width, and 2 were 1 to 3 mm in width. None of those lucent lines were progressive. Metal wedge augmentation for tibial bone deficiency is a useful option. No deterioration of the wedge-prosthesis or wedge-cement-bone interface was seen at midterm followup.

Twenty-six patients with late infected total knee arthroplasties were treated by debridement and removal of components and all cement, preserving collateral ligaments. At time of debridement, an articulating spacer was fashioned to allow partial weightbearing and knee range of motion (ROM) during rehabilitation. This spacer was implanted using antibiotic-impregnated bone cement. For this purpose, 4.8 g of powdered tobramycin was mixed with each 40-g batch of Simplex cement. Cement was applied early to the components, but applied late to the femur, tibia, and patella to allow molding to the defects and bone without adherence to bone. Patients received tailored intravenous antibiotic therapy for 6 weeks in addition to this antibiotic-impregnated cement for treatment of a variety of gram positive and gram negative organisms. All patients had cemented revision total knee arthroplasty using antibiotic-impregnated cement with standard cementing techniques used. All patients but 1 had reimplantation; this patient died of unrelated causes before revision. Range of motion before revision was 10 degrees to 95 degrees. Followup averaged 30 months (range, 13-70 months). The average Modified Hospital for Special Surgery Knee Score after revision was 87 points (range, 53-100 points), with 92% good to excellent results. Range of motion after reimplantation was 5 degrees to 106 degrees. There have been no recurrences of infection. Use of an articulating spacer to treat infected total knee arthroplasty improves ultimate ROM and soft tissue health and significantly decreases the risk of reinfection.

A comparative radiographic review of 217 cementless total knee replacements was done 4 years after surgery to look for radiographic change at the screw-bone interface. There were 102 Miller Galante I knee prostheses, 59 Miller Galante II prostheses, and 56 Anatomic Modular Knee prostheses studied. If the appearance of the screw-bone interface had changed, this was classified according to the width of the lucency. Two hundred sixty-five of the 851 screws that were studied showed some evidence of change, with 185 (21.7%) of the screws showing a cavitary appearance change. The AMK prosthesis showed the higher incidence of cystic and cavitary changes. Polyethylene debris is thought to be responsible for generation of osteolysis and the radiographic appearance change. Design of the components and particularly the polyethylene attachment mechanisms may be responsible for the differences in the frequencies of osteolysis.

The cases of ten total knee arthroplasty after a proximal tibial osteotomy were compared with those of 50 primary total knee arthroplasty for osteoarthritis. The groups were matched according to age of patients, length of follow-up and type of prosthesis used. On the basis of HSS, an excellent or good result was obtained in 90% of patients who had had arthroplasty after osteotomy and in 94% of patients after a primary arthroplasty. Though some intraoperative difficulty may be encountered in a secondary prosthesis, osteotomy does not compromise a subsequent arthroplasty.

Distal femoral fracture or nonunion in elderly patients with osteopenic bone and coexisting gonarthrosis poses a difficult treatment challenge. Open reduction and internal fixation with or without the use of bone cement may not provide sufficient stabilization, requires a prolonged period of weightbearing restrictions, and does not address preexisting knee arthrosis. We report five patients, three with distal femoral nonunion, two with acute distal femoral fracture, and all with concomitant gonarthrosis treated with total knee replacement including a modular distal femoral component [distal femoral replacement (DFR)]. In this group of patients, modular DFR provided immediate pain relief and allowed early weightbearing and aggressive rehabilitation. We recommend this treatment modality in selected osteopenic elderly patients with difficult distal femoral reconstructive problems and coexisting gonarthrosis.

Between 1979 and 1986, 37 patients with sarcoma of the distal femur underwent limb salvage using a custom prosthetic knee replacement. Thirteen (35%) had early complications. Fourteen (38%) had late complications, which consisted of 6 aseptic femoral loosenings, 1 aseptic tibial loosening, 2 tibial fractures, 2 contractures, 1 femoral fracture, 1 prosthetic fracture, and 1 septic loosening. By 1988, nine patients died. Thirteen prostheses failed in 12 patients, resulting in 9 revisions, 2 above-knee amputations, and 2 Van Nes rotationplasties. The 2- and 5-year prosthetic survival rates were 82% and 57%, respectively. Twenty-two of the 26 survivors (85%) had successful limb salvage. Preventable factors were implicated in the loosening of six femoral components and in one femoral fracture. The mean Hospital for Special Surgery Knee Score was 69 (range: 62 to 86).

Sudden cardiac arrest, a rare and often fatal complication of total joint replacement, usually occurs during the insertion of polymethyl methacrylate cement and a prosthesis. We describe a cardiac arrest during insertion of a customized long-stem prosthesis (without the use of a tourniquet) for revision of an earlier total knee replacement. We attribute this complication to the "fat embolism syndrome" (FES)--hypoxemia from an acute pulmonary embolism composed of fat and marrow elements extruded into the venous circulation--coupled with systemic hypotension from absorption of the cement monomer. The syndrome appears to be more common when long-stem prostheses are used. Hypoxemia also correlates with the release of tissue-thromboplastic products as well as the bone marrow elements. Phase 1 of the syndrome consists of particulate obstruction of the pulmonary circulation that causes cor pulmonale and bradycardia or other dysrhythmia. Phase 2 is characterized by respiratory and neurologic manifestations associated with the classic conception of the syndrome. Intraoperative increases in pulmonary artery and pulmonary artery occlusion pressures and pulmonary vascular resistance during unexplained hypoxemia should alert the clinician to the possibility of FES. Proper diagnosis relies on recognizing the three most common clinical manifestations: hypoxemia, neurologic derangements, and fever. Other manifestations of FES are petechiae, thrombocytopenia, anemia, lipuria, changes on ECG, tachycardia, and dyspnea.

The authors discuss the results of 81 total knee arthroplasties in 65 patients performed between April 1987 and April 1989 using a Tricon hybrid system, consisting of the Tricon M bio-ingrowth femoral prosthesis and the Tricon C cemented tibial component. The Tricon metal-backed patella was used until February 29, 1988, when the all-plastic Tricon C patella was introduced. With an average follow up of 24 months (range: 12 to 48), 38 arthroplasties using this hybrid system were rated as excellent (47%) and 38 were rated as good (47%). The Hospital for Special Surgery scores, which averaged 53 preoperatively, averaged 80 at the most recent follow-up assessment. At the most recent follow-up assessment, 79% of osteoarthritis patients and 56% of rheumatoid arthritis patients have no pain at rest, while 19% of osteoarthritis patients and 44% of rheumatoid arthritis patients have mild pain at rest. Sixty-four percent of osteoarthritis patients and 33% of rheumatoid arthritis patients have no pain while walking, whereas 26% of osteoarthritis patients and 56% of rheumatoid arthritis patients have mild pain while walking. Postoperative complications included fragmentation of the patella in five patients, all occurring with the metal-backed patella. Five patients also experienced petellar subluxation (two metal-backed and three all-polyethylene). One patient had deep venous thrombosis which was treated successfully by re-hospitalization and heparin therapy; one patient with chronic heart disease expired 4 days postoperatively. Use of the Tricon hybrid system has resulted in 94% of all patients having a good or excellent result an average of 24 months postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)

The position of the patellar component and patellofemoral symptoms were assessed in a series of 72 cemented polyethylene patellar components in total condylar arthroplasties. A small (25 mm) component was used. The minimum follow up was 2 years and maximum 3 years. A lateral retinacular release was carried out in 22 knees. Clinical results were assessed by questionnaire and 86% had no patellofemoral symptoms. The mean postoperative patellar height was not changed compared to the preoperative height. Lateral placement of the patellar component was associated with both increased medial tilt and lateral subluxation. The component should be inserted so that its centre is slightly medial to the centre of the bone.

We have analyzed the operation of knee arthroplasty using the Whiteside Mark II prosthesis, and found that it could be broken down into 42 steps, some of which are more important than others and can be considered as critical. We have identified 4 criteria to evaluate a critical step: 1) it must be necessary to complete the procedure, 2) it must take a significantly longer time to perform than other steps, 3) it must be revised significantly more frequently than other steps and 4) it must take significantly longer to revise than other steps. Two steps have been found to which all 4 criteria applied, namely placement of the femoral cutting jig and the first femoral saw cuts.

A total of 22 cases of Kinemax prostheses implanted consecutively from January to June 1990 for the treatment of primary gonarthrosis were evaluated; in these cases remodeling of the patella was performed, and the corresponding component of the prosthesis was not used. The mean age of the patients was 64 years, mean follow-up was obtained after 48 months. According to the HSS form results were: excellent: 9 (40.9%); good: 12 (54.5%); fair: 1 (4.6%). The postoperative femorotibial axis measured a mean of 173.8 degrees. There were no complications in the patella, only in 1 case did we observe mild anterior pain. Knee arthroplasty without substitution of the patella seems to guarantee good results in patients with primary gonarthrosis, as long as patellar reconstruction is performed and correct femoropatellar alignment is guaranteed, as well as recovery of the femorotibial axis with accurate positioning of the prosthetic components.

Five cases of septic loosening of total knee arthroplasty were treated by two-stage revision using a cement mixed with antibiotic. The spacer block was responsible for greater mechanical stability of the joint in the interval between the two stages of the operation, and the association of the antibiotic favored resolution of septic complications, allowing at the same time for systemic antibiotic treatment at doses lower than usual. In all of the cases treated reimplantation was performed in conditions of apparent sterility. The minimum amount of time between the first operation and reimplantation was 3 months, maximum was 5 months. Four to 18 months after reimplantation there was no recurrence of infection. Despite the short follow-up, the technique used appears to constitute a valid solution for septic complications in total knee arthroplasty.

The purpose of the present study was to assess the effects of pegs and screws on bone ingrowth into the tibial component in cementless total knee replacement. Left total knee replacements were performed in 21 mature male dogs with 3 cementless porous-coated tibial tray configurations (7 animals per group): (1) 4-peg design implanted with cortical screws passing through the pegs; (2) 4-peg design implanted without screws; and (3) pegless design secured by 4 cortical screws. The animals were allowed unrestricted activity and were euthanized 6 months postoperatively. The pegless components (Group 3) had the highest extent of bone ingrowth into the tray (90.3% +/- 9.4%), followed by the components with 4 pegs only (Group 2, 82.8% +/- 9.2%), and the components with 4 pegs and 4 screws (Group 1, 75.9% +/- 11.8%). The difference between Groups 1 and 3 was statistically significant (p < 0.05). The volume fraction of bone ingrowth in the tray did not differ among the 3 groups, with an overall mean of 22.5% (+/- 4.6%). At the posterolateral quadrant, Group 1 had significantly less bone ingrowth than Group 3 within the tray whether measured as the extent (63.6% +/- 20.5% versus 91.0% +/- 10.6%, p < 0.05) or volume fraction (19.1% +/- 8.8% versus 32.9% +/- 10.5%, p < 0.05). There were no between-group differences at the other quadrants. This study indicated that pegs provided no added benefit in a circumstance where sufficient initial fixation was obtained with screws.

A knee simulator that mimics the plowing/rolling wear mechanisms of the knee was used to compare wear properties of cobalt chromium and oxidized zirconium femoral components. The simulator flexes and extends the knee so that the femoral components travels from 0 degrees to 30 degrees while applying axial loads from 130 to 1300 lb. Three oxidized zirconium and 3 cobalt chromium femoral components were tested with 10-mm tibial polyethylene components. The oxidized zirconium femoral components caused significantly less ultra high molecular weight polyethylene wear than cobalt chromium femoral components. Tibial inserts that were articulated against the cobalt chromium components had evidence of scratching, burnishing, and delamination, but none of the surfaces that were articulated against oxidized zirconium components had evidence of delamination. Cobalt chromium surface roughness significantly increased during the 2,000,000 cycle test, but oxidized zirconium surface roughness was not affected. Polyethylene wear was correlated to a significant degree with the surface roughness of the femoral components. The improved wear characteristics of the ceramic articular surfaces can be explained by the wettability of the ceramic surface, which minimized adhesive wear, and the resistance of the hard, ceramic surface to roughening.

Tibial migration in 33 cementless total knee replacements, which were performed with a cooled saw blade vs. a conventional blade, was studied in a randomized prospective study using roentgen stereophotogrammetric analysis (radiostereometry). All cases were clinically successful after 2 years and inducible displacement was smaller in the group operated with the cooled saw blade. This group also had a tendency towards less continuous migration.

Severe coronal deformity of the knee is frequently associated with erosion of one tibial condyle. This can cause problems with fixation and alignment during total knee arthroplasty. If the tibia is cut to the level of the more worn side, valuable bone is sacrificed; if the less worn side is chosen, the deficiency must be filled with bone--graft, cement, or a prosthesis. Tibial components with an integral polyethylene wedge on the undersurface were introduced in 1980 for use in patients with a bony deficit on one tibial condyle. The authors believe that the Denham prosthesis (Biomet, Wales, U.K.) was the first knee arthroplasty to offer such spacers. Twenty-six patients with preoperative varus deformity in whom a wedged component was used were compared with 29 historic control subjects. None of the wedged components loosened after a median follow-up period of 8 years compared with loosening in five of the control subjects (P = .01). In three of the control subjects a fractured triangle of cement was present on the radiographs. Use of the wedges was not accompanied by an improvement in postoperative alignment. The authors conclude that the wedges resulted in improved fixation that was independent of postoperative alignment.

Objective: To provide estimates of patient outcomes following tricompartmental knee replacement and to examine variation in outcomes due to patient and prosthesis characteristics., Data Sources: English-language articles identified through a computerized literature search and bibliography review., Study Selection: Studies were included if they enrolled 10 or more patients at the time of initial knee replacement and measured patient outcomes using a global knee-rating scale., Data Extraction: Each study was subjected to a blinded qualitative assessment and unblinded abstraction of patient characteristics, surgical techniques, and outcomes., Data Synthesis: A total of 130 studies reporting patient outcomes on 154 cohorts satisfied inclusion criteria. The total number of enrolled patients was 9879 with a mean enrollment of 64.1 patients. The mean follow-up was 4.1 years. The mean patient age was 65.0 years, 71.7% of patients were women, 62.6% had osteoarthritis, and 26.6% underwent bilateral knee replacement. Global rating scale scores improved by 100% for the typical enrolled patient, and 89.3% of patients reported good or excellent outcomes. Anatomic classification of the prosthesis, percentage of enrolled patients with osteoarthritis, publication year, and number of enrolled patients explained 27% of the variation in reported mean postoperative global rating scale scores. The weighted mean complication rate was 18.1%, and the mean mortality rate per year of follow-up was 1.5%. The overall rate of revision during 4.1 years was 3.8%., Conclusions: Tricompartmental knee replacement was a safe and effective procedure for the patients reported in these studies. The knee pathology and the type of prosthesis were significant predictors of outcomes. Limitations in the reporting style of these articles severely constrain the ability to explore variation in outcomes due to study, patient, or prosthesis characteristics and restrict their generalizability.

Various design criteria were examined in combination to find the ideal geometry for a condylar knee replacement. The criteria were the contact stresses on the plastic, femoral-tibial size interchangeability, patella lever arm, laxity and stability and the amount of bone resection required. The variables were the radii of curvature of the femoral and tibial bearing surfaces in the sagittal and frontal planes. Metal toroidal indentors were loaded onto dished surfaces of UHMWPE covering a range of radii and the contact areas measured. Using elasticity equations, the apparent elastic modulus of UHMWPE ranged from 400 to 600 MPa for less conforming to closely conforming surfaces. Using a value of 600 MPa, contact stresses were predicted for a complete spectrum of radii of curvature. Finite element analysis was used to determine the stresses beneath the contact patches when different femoral-tibial sizes were interchanged. A computergraphics program was written to analyse the effects of flexion, rotation and femoral roll-back on the contact point locations. An influential variable was the sagittal curvature of the femoral component, notably the point of transition between the posterior curve of small radius and the distal curve of larger radius. This affected the patella lever arm, the stability, and the bone resection. Interchangeability was primarily dependent upon the relative frontal radii. Contact stresses and contact locations depended upon the combination of sagittal and frontal radii. The most suitable geometrical combinations overall were discussed.

Screw fixation of the tibial component offers advantages in fixation in cementless total knee arthroplasty (TKA). In a group of 447 cementless TKA tibial components fixed without screws, 24% had partial undersurface radiolucent lines and 3% had complete radiolucent lines. Both of these parameters were significantly decreased (p < 0.01) when screws were used. In a group of 1442 cementless tibial trays fixed with screws, 4% had partial and 0.1% had complete radiolucent lines. Cyst formation around smooth pegs was also more common in trays fixed without screws. Two of the 5758 screws inserted in 1442 trays developed nonprogressive radiolucent lines, but no case of major osteolysis has been seen. Although screw fixation of cementless tibial components appears to improve the metal-bone interface, the potential for long-term complications still exists. The use of screws should be reserved for difficult fixation problems.

This study evaluated the effects of intramedullary instrumentation when used on the femur and tibia. Twenty-six patients (52 knees) undergoing bilateral index cemented total knee arthroplasty were analyzed. Bilateral knee arthroplasties were chosen because the increased surgery would theoretically maximize any perioperative hemodynamic or hematologic changes. Patients were randomized into one of two groups depending on the exact form of surgical instrumentation used. Group I (intramedullary) knees were implanted with standard intramedullary fluted instruments. No special measures to vent the entrance holes were made. Group II (extramedullary) knees were implanted with an extramedullary tibial guide, in conjunction with an intramedullary femoral guide placed through a vented femoral hole. All patients manifested significant changes in their hematologic and hemodynamic values after arthroplasty. Leukocytes increased 85% on average, whereas fibrinogen (106%) and erythrocyte sedimentation rates (145%) also showed significant increases. Conversely, patients exhibited a relative thrombocytopenia (63%) nadiring on the second postoperative day. However, there was no significant differences seen between the two instrumentation groups. Hemodynamically, all patients exhibited rises in cardiac index (52%) and pulmonary artery pressures (64%). Analysis of the hemodynamic results in this study does demonstrate subtle evidence of increased pulmonary vascular resistance in the intramedullary group. Specifically, the intramedullary group had lower cardiac indexes, in association with higher pulmonary pressures. This increase in pulmonary vascular resistance with the use of intramedullary instrumentation may represent subtle evidence of increased lung injury in this group. Results point to the continued use of fluted intramedullary rods and vented entrance holes as a reasonable surgical technique in patients undergoing knee arthroplasty.

Cutting errors that occur during preparation of the femoral component can deter fixation in cementless total knee arthroplasty. This study evaluated the causes of femoral cutting errors and identified methods to minimize these errors. The cutting error caused by toggle of the saw blade in the guide-slot was measured with wood blocks, a cutting guide with 1.5 mm guide slots, and four kinds of saw blades (narrow and wide blades with thicknesses of standard 1.2 mm and thicker 1.4 mm). Another cause of cutting errors, relative motions between the cutting guide and distal femur due to vibration of the saw blade during bone cuts, was measured with preserved cadaver femurs. Various combined fixation methods with intramedullary rod, pins, and clamps were compared. The maximum cutting error caused by toggle of the saw blade in the slot was significantly reduced by using the thicker 1.4 mm saw blade, but the differences between wide and narrow blades in each thickness were not significant. Mean maximum cutting error at the cutting depth of 5 cm with 1.2 mm thick saw blades was 802 microns, and with 1.4 mm thick saw blades it was 488 microns. In the measurement of relative motion, fixation with only pins or clamps did not provide tight fixation and had deflections from 200 microns to more than 1 mm. The best fixation was obtained by combining fixation methods of intramedullary rod and pins or clamps. This resulted in total movement of less than 100 microns. The results of this study indicate that both toggle of the saw blade in the slot and motion of the cutting guide can cause major cutting errors. Cutting error can be minimized by using thicker saw blades and by fixing the cutting guide to the distal femur with combined fixation methods of a central rod and peripheral pins or clamps.

Thirty consecutive cases requiring total knee replacement (TKR) were treated using the Richards Tricon Total Knee System with ASAP (All Six, All Precise) instrumentation (Richards Medical Company, Memphis, TN, USA). Preoperative and postoperative overall coronal alignment were measured using long-leg anteroposterior X-rays. The femoral and tibial bone cuts in this plane were assessed using intraoperative films. The aim was to achieve a postoperative coronal tibio-femoral alignment of 7 degrees valgus. The mean preoperative alignment was 1 degree valgus (SD = +/- 13.5 degrees). A mean postoperative alignment of 8 degrees valgus was obtained (SD = +/- 5.6 degrees). The results obtained in this series suggest that the ASAP system with careful use simplifies the technique of total knee replacement while maintaining accuracy.

A survey of all 261 National Health Service hospitals in the 14 regions of England performing joint replacement surgery was carried out to determine inter-regional variations in the surgeon's choice of hip and knee replacements. There are over 30 types of cemented, 35 types of uncemented hip replacements, and more than 35 types of knee prostheses for the surgeon to choose from. The Charnley low friction arthroplasty is the market leader in hip surgery and is used in 193 hospitals (74%). There is a marked North-South divide in the use of this prosthesis. The Kinematic and Insall Burstein prostheses are the most popular knee replacements. At present, there is a huge choice of joint replacement on the market and many implants have yet to prove that they offer any real advantages over established and often cheaper alternatives. It is suggested that special centres for joint replacement surgery within each region should run clinical trials to determine which prostheses have the best long-term results. The resulting standardization of implants within each hospital would enable Regional Health Authorities to reduce costs in the short-term by cutting stock levels, and should reduce costs in the long-term by reducing the revision rate of failed joint replacements.

Among 52 patients with porous-coated anatomic total knee arthroplasties, three (6%) underwent revision surgery because of failure of the tibial polyethylene at two years and three months, four years and three months, and four years and nine months after surgery. Thinning of the tibial polyethylene may have contributed to the failure in one patient. Heat pressing fabrication and the articular geometry possibly played a role in the development of failure in all three patients. Surgical latitude of the prosthetic design was considered to be too narrow to be applied to knee joints with severe deformity, for which knee prostheses with more intrinsic stability might be appropriate.