Gerard A. Engh

Osteolysis after total knee arthroplasty without cement.

The prevalence and characteristics of osteolysis were studied after 174 consecutive total knee arthroplasties, performed without cement; 16 per cent (twenty-seven) of the implants (in twenty-six patients) were identified as being associated with osteolysis. The diagnosis was made an average of thirty-five months after the operation. Fifteen (56 per cent) of the twenty-seven prostheses were revised after an average of forty-five months in situ. The remaining twelve implants were still in situ five years or more postoperatively. In the patients who were managed with revision, six implants were judged to be stable radiographically and intraoperatively. The remaining nine implants were loose. The average age of the patients who had osteolysis was sixty-three years, and the average weight was seventy-six kilograms (168 pounds). Eighteen of the twenty-six patients who had osteolysis were women. The medial aspect of the tibial metaphysis was the most common site for resorption of bone (twenty-four knees). Sequential radiographs demonstrated progressive extension of the osteolytic process around the tibial base-plate of the prosthesis and distally into the tibial metaphysis along the screw-bone interface in all patients. Histological evaluation of tissue obtained at the revision procedures revealed sheets of histiocytes and occasional giant cells. Intracellular particulate polyethylene and metal were found; most particles were less than one micrometer in size, although particles as large as three micrometers were identified. Mechanical failure of the thin, modular, polyethylene tibial insert; excessive abrasion of the prominent polyethylene tibial eminence, with secondary wear and impingement of the pin on the femoral component; and failure of the metal-backed patellar component all contributed to the extensive amount of polyethylene and the variable amount of metal debris that were generated. Corrosion between the angulated titanium screws and the cobalt-chromium base-plate also contributed particulate metal to the osteolytic process locally. This study demonstrated that osteolysis occurs in association with cementless total knee replacement.

Polyethylene wear of metal-backed tibial components in total and unicompartmental knee prostheses

We examined 86 polyethylene inserts, retrieved from total and unicompartmental knee prostheses after an average of 39.5 months in situ, grading them from 0 to 3 for seven modes of polyethylene degradation. Severe wear, with delamination or deformation, was observed in 51% of the implants, and was associated with time in situ, lack of congruency, thin polyethylene, third-body wear debris, and heat-pressed polyethylene. Significant under-surface cold flow was identified in some areas of unsupported polyethylene, and was associated with delamination in the load-bearing areas of thin inserts above screw holes in the underlying metal tray. We recommend the use of thicker polyethylene inserts, particularly in young, active patients and in designs with screw holes in the tibial baseplate. Thin polyethylene inserts which are at risk for accelerated wear and premature failure should be monitored radiographically at annual intervals.

Radiographic assessment of knee alignment after total knee arthroplasty

Standard anteroposterior standing radiographs (14 X 17-inch cassettes) and full-limb radiographs (51-inch) from a randomized group of 50 patients undergoing total knee arthroplasty between January 1985 and June 1986 were analyzed. The mean tibiofemoral angle on short films was 5.8 degrees valgus, compared with 7.2 degrees valgus on full-limb films. This 1.4 degrees discrepancy had a standard deviation of 2.2 degrees, emphasizing the measurement variability in any individual case. The distance from the knee center to the mechanical axis related linearly to the tibiofemoral angle. Twenty-six percent (13 of 50) of knee arthroplasties failed to achieve satisfactory postoperative alignment of 4-10 degrees valgus in this study.

Tibial insert undersurface as a contributing source of polyethylene wear debris.

Sixty-seven ultrahigh molecular weight polyethylene tibial inserts from cementless total knee arthroplasties were retrieved at autopsy and revision surgery and analyzed for evidence of articular and nonarticular surface wear after a mean implantation time of 62.8 months (range, 4-131 months). Polyethylene cold flow and abrasive wear on the nonarticular insert surface (undersurface) were assigned a wear severity score (Grade 0-4). The severity of articular wear was assessed quantitatively and graded. Corresponding prerevision radiographs were evaluated for evidence of tibial metaphyseal osteolysis and osteolysis around tibial fixation screws. Exact nonparametric conditional inference methods were used to establish correlations between different variables and the occurrence of tibial metaphyseal osteolysis. Severe Grade 4 wear of the tibial insert undersurface was associated with tibial metaphyseal osteolysis or osteolysis around fixation screws. Time in situ statistically was related to Grade 4 undersurface wear and tibial metaphyseal osteolysis. The occurrence of tibial osteolysis was not related statistically to articular wear severity, insert thickness, or implant type. The main articulation between the femoral implant and ultrahigh molecular weight polyethylene insert has been assumed to be the primary source of polyethylene debris contributing to osteolysis and total knee arthroplasty implant failure. The undersurface of the insert is an additional source of polyethylene debris contributing to tibial metaphyseal osteolysis. To lessen polyethylene debris produced at this modular interface, the tibial implant locking mechanism should fix the insert firmly to the metal backing to decrease relative micromotion. Because motion between the insert and metal backing may be inevitable, the wear characteristics of the inner tray surface should be optimized to minimize wear debris production at this other articulation.

Comparison of Proprioception in Arthritic and Age-Matched Normal Knees*

Background: Proprioception - ones ability to sense joint position and joint motion - is affected by factors such as age, muscle fatigue, and osteoarthritis. Most proprioception studies have focused on young active subjects or on recipients of total knee replacements. Few have involved a population with arthritic knees prior to total knee replacement or persons similar in age to patients with advanced knee arthritis who are to have total knee arthroplasty. The purpose of the present study was to determine (1) if proprioception in arthritic knees differs from proprioception in nonarthritic, age-matched, normal knees; (2) if, when proprioception in one knee is reduced by the presence of advanced gonarthrosis, it also is reduced in the contralateral knee irrespective of the presence of arthritis; and (3) if a persons grade of arthritis is associated with his or her level of proprioception.Methods: This study compared the proprioception levels of a group of 117 patients who were scheduled for total knee arthroplasty because of severe arthritis (mean age, 67.9 years) with those of a control group of forty patients who were recruited from a hospital-based cardiac rehabilitation program and did not have knee arthritis (mean age, 68.3 years). We used a customized Biodex System 2 Multi-Joint Testing and Rehabilitation System to compare proprioception (the threshold to detection of passive motion) between the two groups.Results: Middle-aged and elderly persons with advanced knee arthritis were significantly less able to detect passive motion of the knee than were middle-aged and elderly persons without knee arthritis. Patients who had arthritis in only one knee had a reduced ability to detect passive motion of both knees. There was no significant association between the radiographic severity of arthritis and the threshold to detection of passive motion in patients with advanced knee arthritis.Conclusions: Knee proprioception in middle-aged and elderly persons with advanced knee arthritis is reduced in comparison with that in middle-aged and elderly persons without arthritis. Such loss of proprioception is independent of the severity of knee arthritis and may foretell the development of arthritis. When a patient has reduced proprioception with regard to one knee affected by arthritis, he or she also has reduced proprioception with regard to the contralateral knee, independent of the presence or severity of degenerative arthritis. When an investigator is evaluating changes in proprioception after knee arthroplasty, it is best to compare the knee with the patients untreated knee rather than with age-matched controls.

Revision of failed unicompartmental knee arthroplasty.

Little information has been published on the salvage of failed unicompartmental knee arthroplasty. The current authors examined the failure mechanisms, complexity of surgery, and complications in such revisions. Of 39 consecutive unicompartmental knee revisions, two patients died within 2 years of surgery, four had inadequate followup, and one was excluded because of infection before revision. Therefore, 30 patients (32 knees) were followed up a mean 53 months. The patients were a mean age of 59 years at the time of unicompartmental knee arthroplasty and were predominantly male (60%). Revisions were done 9 to 204 months after the unicompartmental knee arthroplasty. The predominant failure mechanism was polyethylene wear; however, nine failed because of loosening. The mean polyethylene thickness of the failed arthroplasties was 7.3 mm. Revision procedures were straightforward. Ten patients required local autograft but no allografts were used. Primary femoral components were used in all patients; 25 were cruciate-retaining. Fourteen patients had stemmed tibial components; eight had wedge augments. The mean range of motion after revision was 111°. Six patients had complications not requiring intervention. Three patients had rerevision surgery for polyethylene wear at 76, 77, and 102 months, respectively, two of whom required polyethylene insert and patellar component revision. The third patient also required tibial component revision for osteolysis. Although this is a small series, the simplicity of the procedure and the complications encountered compare favorably with those of total knee revision.

Wear and Osteolysis Around Total Knee Arthroplasty

Osteolysis induced by wear debris of ultra-high-molecular-weight polyethylene has emerged as a significant problem after total knee arthroplasty. The generation of polyethylene wear and the development of osteolysis around total knee arthroplasty are caused by a combination of patient, implant, and surgical factors. Activity level over time may be the most important patient factor affecting the loads placed on a total knee replacement, but it is the most difficult to manage. Multiple factors related to the manufacturing of the polyethylene implant influence the extent of wear, and surgeons should be cautious in considering enhanced polyethylenes pending results of further investigations. The optimal design of the articular bearing surface remains controversial but needs to be considered with respect to the stresses imparted on component-bone and modular tibial backside interfaces. Surgical factors, including restoration of alignment and ligament balance, are important for long-term durability of the implant. Methods of measuring the wear of total knee implants are still evolving. Thus, when confronted with a worn total knee implant and developing osteolysis, the surgeon should consider each of these factors in selecting the best management option to eliminate the source of debris and minimize the potential for wear and osteolysis following revision.

The effect of alignment of the knee on the outcome of unicompartmental knee replacement

Many authors have recommended undercorrection of the deformity when carrying out unicompartmental knee arthroplasty (UKA). The isolated effect of alignment of the knee on the outcome of UKA has, however, received little attention. We reviewed 185 UKAs at a minimum of five years after surgery. They had been carried out by a single surgeon using metal-backed tibial components in the management of arthritis of the medial compartment. We measured the tibiofemoral angle (TFA) before and at four months after operation and at the most recent assessment. The amount of correction of the TFA and any subsequent loss were recorded. While adjusting for the effects of age, weight and gender of the patients and the type and thickness of the implants, the mean correction was significantly less for those with a Marmor rating of failure (6.8 degrees) than for those rated excellent (9.2 degrees). The mean correction was also significantly less for patients with a Marmor rating of failure (6.8 degrees) than for those rated poor (11.1 degrees). The mean correction for the UKAs which were revised (6.6 degrees) was significantly less than for those not revised (9.1 degrees). Additionally, revised UKAs had a significantly higher percentage (63%) of thinner tibial implants (<8 mm) than the surviving UKAs (27%). These findings suggest that undercorrection of the TFA in UKA of the medial compartment should be avoided, particularly if a thin tibial polyethylene insert is used.

Factors associated with the loss of thickness of polyethylene tibial bearings after knee arthroplasty.

BACKGROUND Wear of the polyethylene tibial bearing is a leading cause of failure of knee replacements done prior to the current decade. The objective of this study was to determine how patient-related factors, implant-related factors, and limb or tibial component alignment influenced the amount of thickness loss in polyethylene tibial bearings that were retrieved at the time of revision surgery or after the death of the patient. METHODS We retrieved polyethylene tibial bearings from eighty-one unicondylar and eighty-nine total knee replacements that had been performed because of osteoarthritis with varus deformity from 1984 to 1998. All of the polyethylene bearings had been sterilized with gamma radiation in air. Polyethylene loss was quantified as the change in the minimum bearing thickness per years in vivo (the mean time in vivo [and standard deviation] was 8 +/- 4 years). Multiple linear regression was used to assess whether polyethylene loss was associated with age, weight, gender, varus angle of the tibial component, postoperative hip-knee-ankle angle, initial thickness of the polyethylene, shelf age of the polyethylene, and either the type of polyethylene (for total knee replacements, which were of one posterior cruciate ligament-retaining design) or the manufacturer (for unicondylar knee replacements), and to determine the magnitude by which polyethylene loss would change if any of the significant risk factors were changed. RESULTS The mean loss (and standard deviation) of polyethylene thickness in the medial compartment of total knee replacements (0.33 +/- 0.28 mm/yr) and that in medial unicompartmental knee replacements (0.49 +/- 0.40 mm/yr) were significantly (p < 0.05) associated with the same three variables: patient age, postoperative hip-knee-ankle angle, and shelf age of the polyethylene. A total knee bearing with a one-year increase in shelf age, a unicondylar knee bearing with a six-month increase in shelf age, a patient who was ten years younger at the time of operation, or a limb that was aligned in 5 degrees more varus (less valgus) had similar effects on the loss of polyethylene thickness in the medial compartment; the coefficients of the linear regression equations indicated that any one of these changes would increase polyethylene loss by 0.11 to 0.14 mm/yr. CONCLUSIONS The wear-related loss of thickness in gamma-irradiated-in-air polyethylene bearings from unicondylar and total knee replacements implanted in osteoarthritic knees with varus deformity is influenced mainly by the shelf age of the polyethylene, the age of the patient, and the postoperative angulation of the knee in the coronal plane. CLINICAL RELEVANCE Although polyethylene bearings have not been sterilized with gamma radiation in air since the end of the last decade, many arthroplasty patients have polyethylene bearings that were sterilized with use of this method. An understanding of the findings of this study may be of value as these patients return for follow-up care. Whether the study findings have relevance to bearings sterilized with other methods is unclear and will remain so for many years. LEVEL OF EVIDENCE Prognostic Level II.

A midvastus muscle-splitting approach for total knee arthroplasty.

This study presents a modification of the medial parapatellar surgical approach for total knee arthroplasty. This approach separates the vastus medialis muscle in the direction of its fibers beginning at the superior pole of the patella. One hundred eighteen consecutive total knee arthroplasty cases, performed by a single surgeon, were randomized prospectively to receive a medial parapatellar or midvastus muscle-splitting surgical approach. The frequency of lateral retinacular releases was recorded, patellar tilt and translation were measured, and quadriceps strength was tested. The midvastus muscle-splitting approach provided excellent exposure to all knees. Patellar stability and quadriceps strength were equivalent for the two approaches. It is concluded that the midvastus muscle-splitting approach is an efficacious alternative to the medial parapatellar approach for primary total knee arthroplasties.