Which primary total knee replacement? A review of currently available TKR in the United Kingdom.

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.

Sins of omission: what the brochures don't tell you.

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.

Increased awareness of glove perforation in major joint replacement. A prospective, randomised study of Regent Biogel Reveal gloves.

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.

Intramedullary goniometer can improve alignment in knee arthroplasty 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.

Development of a six station knee wear simulator and preliminary wear results.

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.

Comparison of results of different types of knee arthroplasties.

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.

Stress fracture of the femoral component in total knee replacement: a report of 3 cases.

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.

Current techniques in total knee replacement: results of a national survey.

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.

Safety and efficacy of ethylene oxide sterilized polyethylene in total knee arthroplasty.

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).

Effects of sterilization on wear in total knee arthroplasty.

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.

Transesophageal echocardiographic monitored events during total knee arthroplasty.

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.

Functional analysis of cemented medial unicompartmental knee arthroplasty.

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.

[Sliding axis endoprosthesis in severe unstable gonarthrosis and as revision prosthesis]. / Gleitachsenendoprothese bei schweren instabilen Gonarthrosen und als Revisionsprothese.

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.

The prosthesis-bone interface adjacent to tibial components inserted without cement. Clinical and radiographic follow-up at nine to twelve years.

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.

Fracture of the metal tibial tray after Kinematic total knee replacement. A common cause of early aseptic failure.

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.