Kaj Knutson

Patient satisfaction after knee arthroplasty: A report on 27,372 knees operated on between 1981 and 1995 in Sweden

During a validation process of the Swedish Knee Arthroplasty Register (SKAR), living registered patients were sent a questionnaire to ask if they had been reoperated on. This gave an opportunity to pose a simple four-point question with respect to patient satisfaction which 95% of patients answered. We analyzed the answers of patients operated on between 1981 and 1995 and found that only 8% of the patients were dissatisfied regarding their knee arthroplasty 2-17 years postoperatively. The satisfaction rate was constant, regardless of when the operation had been performed during the 15-year period. The proportion of satisfied patients was affected by the preoperative diagnosis, patients operated on for a long-standing disease more often being satisfied than those with a short disease-duration. There was no difference in proportions of satisfied patients, whether they had primarily been operated on with a total knee arthroplasty (TKA) or a medial unicompartmental arthroplasty (UKA). For TKAs performed with primary patellar resurfacing, there was a higher ratio of satisfied patients than for TKAs not resurfaced, but this increased ratio diminished with time passed since the primary operation. Unrevised knees had a higher proportion of satisfied patients than knees that had been subject to revision, and among patients revised for medial UKA, the proportion of satisfied patients was higher than among patients revised for TKA. We conclude that satisfaction after knee arthroplasty is stable and long-lasting in unrevised cases and that even after revision most patients are satisfied.

The Swedish Knee Arthroplasty Register 1975-1997: an update with special emphasis on 41,223 knees operated on in 1988-1997

From 1975, when the Swedish Knee Arthroplasty Register (SKAR) started, until the end of 1997, 57,533 primary arthroplasties and revisions have been registered. Recently, the register underwent a comprehensive validation and update regarding revisions. We now report on general demographic and epidemiological data for the whole period and on the survivorship of arthroplasties performed in Sweden during 1988-1997. During this 10-year period, 41,223 primary knee arthroplasties were performed on 34,877 patients. We found, as in our earlier reports, that survivorship was affected by patient-, time-, implant- and method-related factors but, apart from an overall higher cumulative revision rate, general conclusions reported from the register in recent years appeared to be unaffected.

The infected knee arthroplasty. A 6-year follow-up of 357 cases.

The incidence of deep infection after 12,118 primary knee arthroplasties performed in Sweden from October 1, 1975 through 1985 with a median follow-up of 6 years was 1.7 percent for arthrosis and 4.4 percent for rheumatoid arthritis. Risk factors for infection were large prostheses, postoperative wound-healing complications, rheumatoid arthritis, a prior deep infection, and skin infections. We have analyzed the treatment of 357 knee arthroplasties with a deep infection. Systemic antibiotics alone were primarily used in 225 knees, with healing of the infection in 44 knees, 20 of which had a functioning prosthesis at the final follow-up; the treatment did not compromise later revision surgery. Soft-tissue surgery was used in 154 knees--37 healed, 15 of which had a functioning prosthesis. Resection arthroplasty resulted in healing of the infection in 11 of 22 knees. Revision arthroplasty was performed in 107 knees, with eventual healing of the infection in 81 knees, 36 of which had a functioning prosthesis; there were no differences in the outcome of one-stage and two-stage procedures. Arthrodesis was attempted in 135 knees, with eventual healing of the infection in 120 knees and fusion in 105. Twenty-two patients were amputated. Thus, the infection healed in 315 knees (88 percent), but only 71 (20 percent) recovered with a functioning prosthesis, and 8 patients died of the infection. Attention should therefore focus on prophylactic measures directed towards the soft-tissue problems--by avoiding conflicting skin incisions, by gentle handling of the periarticular soft tissues, by avoiding the use of constrained prostheses and oversized compartmental prostheses, by letting wound healing take priority over motion in knees with compromised soft tissues, and by using prophylactic antibiotic treatment for skin ulcers until these have healed.

The routine of surgical management reduces failure after unicompartmental knee arthroplasty

A total of 10,474 unicompartmental knee arthroplasties was performed for medial osteoarthritis in Sweden between 1986 and 1995. We sought to establish whether the number of operations performed in an orthopaedic unit affected the incidence of revision. Three different implants were analysed: one with a high revision rate, known to have unfavourable mechanical and design properties; a prosthesis which is technically demanding with a known increased rate of revision; and the most commonly used unicompartmental device. Most of the units performed relatively few unicompartmental knee arthroplasties per year and there was an association between the mean number carried out and the risk of later revision. The effect of the mean number of operations per year on the risk of revision varied. The technically demanding implant was most affected, that most commonly used less so, and the outcome of the unfavourable design was not influenced by the number of operations performed. For unicompartmental arthroplasty, the long-term results are related to the number performed by the unit, probably expressing the standards of management in selecting the patients and performing the operation.

Revision of unicompartmental knee arthroplasty: outcome in 1,135 cases from the Swedish Knee Arthroplasty study

From 1975 through 1995, 45,025 knee arthroplasties were recorded in the prospective Swedish Knee Arthroplasty study. By the end of 1995, 1,135 of 14,772 primary unicompartmental knee arthroplasties (UKA) for localized, mainly medial arthrosis had been revised. The Marmor/Richards and St. Georg sledge/Endo-Link prostheses were used in 65%. Mean age at revision was 72 (71) years. 232 revisions were performed as an exchange UKA (partial in 97) and 750 as a total knee arthroplasty (TKA). 153 were revised by other modes. In medial UKA, the indication for revision was component loosening in 45% and joint degeneration in 25% and in lateral UKA, the corresponding figures were 31% and 35%, respectively. In 94 cases, unicompartmental components were added to the initially untreated compartment, in 14 with partial exchange of a component. The CRRR was estimated using survival statistics. After only 5 years, the risk of having a second revision was more than three times higher for failed UKAs revised to a new UKA (cumulative rerevision rate (CRRR 26%) than for those revised to a TKA (CRRR 7%). This difference remained, even if those revised before 1985, when modern operating technique was introduced, were excluded (CRRR 31% and 5%, respectively). UKA is a safe primary procedure, when performed with well-designed components and modern surgical technique. It gives documented good patient satisfaction, range of motion, pain relief and relatively few serious complications. However, once failed, the knee should be revised to a TKA. This applies to most modes of failure. Not even joint degeneration of the unoperated compartment can be safely treated by adding contralateral components; CRRR after this procedure was 17%, while it was 7% when converted to a TKA.

Survival of knee arthroplasties. A nation-wide multicentre investigation of 8000 cases

A prospective nation-wide study of knee arthroplasty has been under way in Sweden since October 1975. By the end of 1983, 4505 arthroplasties for osteoarthritis and 3495 for rheumatoid arthritis had been recorded and reviewed one, three and six years after the operation. Using actuarial methods, the probability of the prosthesis remaining in situ after six years was calculated. In osteoarthritis this probability ranged from 65% for hinged prostheses to 90% for medial compartment prostheses. Two-and three-compartment prostheses produced intermediate results with 87% survival. In rheumatoid arthritis the probability varied from 72% for medial compartment prostheses to 90% for two- and three-compartment prostheses. The main reason for failure was loosening of the components, the second most common was infection. The probability of revision for infection by six years was 2% in osteoarthritis and 3% in rheumatoid arthritis. Most revisions were to a three-compartment prosthesis. Knee fusion at primary revision was required in 2% of the cases at six years.

Oxford meniscal bearing knee versus the Marmor knee in unicompartmental arthroplasty for arthrosis. A Swedish multicenter survival study

In the Swedish Knee Arthroplasty Study, all 699 Oxford meniscal bearing cemented unicompartmental prostheses (Biomet, Bridgend, UK) were identified and analyzed regarding failure pattern and compared with all Marmor prostheses (Smith & Nephew Richards, Orthez, France) and with a time-, age-, and sex-matched subset of Marmor prostheses using survival statistics expressed as cumulative revision rates. After 1 year there was already a higher rate, and after 6 years the rate of the Oxford group was more than twice that of the Marmor group. There were 50 revisions in the Oxford group: dislocating meniscus in 16, loosening of the femoral component in 6, tibial component in 4, both components in 4, contralateral arthrosis in 10, infection in 4, and technical failure with instability, pain, and/or impingement of the meniscal bearing anterior in the femoral condyle in 6. It is still unclear if the design with the sliding menisci will, in the long turn, reduce wear and loosening, thereby compensating for the initially inferior results. It is recommended that until this question is clarified, the Oxford knee should be used on a limited scale for long-term comparative studies only.

Use of unicompartmental instead of tricompartmental prostheses for unicompartmental arthrosis in the knee is a cost-effective alternative. 15,437 primary tricompartmental prostheses were compared with 10,624 primary medial or lateral unicompartmental prostheses.

Unicompartmental knee arthroplasty (UKA) is known to have a higher risk of revision than tricompartmental arthroplasty (TKA), while UKA implants are generally less expensive than TKA implants. We estimated the costs of implants and hospital stay of both procedures and related the cost difference at primary operation to the difference in number of revisions to be expected. We compared 15,437 primary TKAs and 10,624 primary medial or lateral UKAs. The operations were all done on patients with arthrosis during 1985-1995. By matching patients in the Swedish Patient Administration System with the Swedish National Knee Arthroplasty Register, the groups could be compared regarding the length of the hospital stay. The cumulative revision rate (CRR) and the relative risk of revision were calculated with survival statistics, as well as the risk of a second revision and the risk of infection. The weighted mean cost of the commonest implants in each group was used as an estimate of the implant cost. We found that the TKA patients were, on average, 2 years older at operation and had a lower CRR than the UKA patients-i.e., 10-year CRR of 12% and 16%, respectively. After adjusting for age, gender and year of operation, UKA patients were found to have a 2-day shorter hospital stay and fewer serious complications than TKA patients. The mean estimated cost of a unicompartmental implant was 57% of that of a tricompartmental implant. We conclude, that by using UKA instead of TKA in appropriate patients, money can be saved, even after taking into account the increased number of revisions to be expected.

Past incidence and future demand for knee arthroplasty in Sweden: a report from the Swedish Knee Arthroplasty Register regarding the effect of past and future population changes on the number of arthroplasties performed

By combining data from the Swedish Knee Arthroplasty Register and Swedish census registers we have calculated the past age-specific incidence of primary knee arthroplasties and predicted the demand. During the last 20 years, osteoarthrosis has accounted for the largest increase in number of knee arthroplasties while operations for rheumatoid arthritis remained constant. The mean yearly number of operations between the periods 1976-1980 and 1996-1997 increased more than five-fold, while only 6% of that increase could be explained by changes in the age-profile of the population. Most operations were performed on persons of 65 years and older who also had the largest increase in incidence. By using the incidences for 1996 and 1997 and taking into account the expected future changes in the age profile of the Swedish population, we estimate that, in the absence of an effective preventive treatment, the number of knee arthroplasties will increase by at least one third until 2030.

Microbiology of the infected knee arthroplasty: Report from the Swedish Knee Arthroplasty Register on 426 surgically revised cases.

Surgically revised deep infected primary knee arthroplasties reported to the Swedish knee arthroplasty register during the years 1986–2000 were studied with respect to microbiology, antimicrobial susceptibility pattern and changes over time. In early, delayed and late infections, coagulase-negative staphylococci (CoNS) were most prevalent (105/299, 35.1%), and twice as common as Staphylococcus aureus (55/299, 18.4%). In haematogenous infections, S. aureus was the dominating pathogen (67/99, 67.7%), followed by streptococci and Gram-negative bacteria. Methicillin resistance was found in 1/84 tested isolates of S. aureus and 62/100 tested isolates of CoNS. During the study period, methicillin resistance among CoNS increased (p=0.002). Gentamicin resistance was found in 1/28 tested isolates of S. aureus and 19/29 tested CoNS isolates. A relative decrease in infections caused by S. aureus was observed, while enterococci increased. In empiric treatment of infected knee arthroplasty the type of infection should direct the choice of antibiotics. Awareness of the fact that most early infections are caused by CoNS can increase the chances of successful treatment with retained implant. Due to the high rate of gentamicin resistance among CoNS in infected knee arthroplasty, other antibiotics should be used in bone cement at revision.