Elimination of Preoperative Flexion Contracture as a Contraindication for Unicompartmental Knee Arthroplasty.

INTRODUCTION: Unicompartmental knee arthroplasty (UKA) is an effective alternative to total knee arthroplasty (TKA) for the management of unicondylar osteoarthritis. Historical contraindications limit patients' eligibility for UKA. However, recent reports have suggested that some contraindications may not be absolute. This study evaluates preoperative flexion contracture with regard to UKA. METHODS: This study was a retrospective review of 53 patients with preoperative flexion contracture between 11° and 20° who underwent fixed-bearing UKA and a matched cohort of 53 patients who underwent cruciate-retaining TKA. RESULTS: Preoperatively, the average flexion contracture was 13.8° in the UKA group and 14.1° in the TKA group (P = 0.42). Mean preoperative motion was greater in the patients treated with UKA (106°) than in those treated with TKA (97°; P < 0.001). Postoperatively, patients who underwent UKA had greater motion than patients who underwent TKA had (121° versus 113°; P < 0.01). Residual flexion contracture was greater in the UKA group (4.1°) than in the TKA group (2.1°; P = 0.02). The two groups demonstrated similar improvements in Knee Society clinical scores (P = 0.32). However, patients treated with UKA demonstrated higher Knee Society functional scores, compared with patients treated with TKA (86 versus 75; P = 0.03). DISCUSSION: Although residual flexion contracture was worse after UKA, this group had similar clinical improvement, greater postoperative motion, and greater function scores, compared with the matched TKA group. Preoperative flexion contracture >5° may not be an absolute contraindication to UKA. CONCLUSION: The contraindications to UKA regarding flexion contracture may not be as absolute as previously thought. Larger, prospective studies are needed to generalize these findings to a wider population.

Patellar Cut and Composite Thickness: The Influence on Postoperative Motion and Complications in Total Knee Arthroplasty.

BACKGROUND: Little data exist on the influence of patellar thickness on postoperative motion or complications after total knee arthroplasty (TKA). This study addresses the following questions: Is postoperative motion influenced by change in composite patellar thickness? Is change in patellar thickness associated with more complications? And do more complications occur in the knees with a patellar bone remnant (<12 mm) and a native patellar thickness <18 mm? METHODS: In total, 3655 TKAs were performed by 3 surgeons over a 28-year interval. All knees had caliper measurement of patellar thickness before the patellar cut, after implantation of the component and postoperative motion recorded in the database 1 or 2 years after TKA. RESULTS: Patellar composite thickness was the same (1034 knees), thicker (1617 knees), and thinner (1004 knees). A significant but weak relationship was identified between the change in patellar thickness and motion (P < .01, ρ = -0.046); an increase in "composite patellar thickness" of 10 mm would result in a 3° loss of knee motion. Significant differences were identified between change in thickness and manipulations (P < .05), ruptures (P = .01), and patellar clunk/crepitus (P < .01). Examining knees with bone remnant thicknesses (<12 mm/≥12 mm), there was no difference in fractures (P = .26). No extensor ruptures occurred in knees with remnant thickness <12 mm. Comparing knees with native bone thickness (≤18 mm/>18 mm), significant differences were found in fractures (P < .01) and patellar radiolucencies (P = .01). CONCLUSION: As this data does not demonstrate a strong tendency toward losing motion when the patellar thickness is increased, the authors recommend avoiding compromise of the patellar bone stock and tendon insertion. When native patellar bone is thin (<18 mm), we recommend maintaining 12 mm of patellar bone stock and accept the increase in composite thickness.

Can We Quantify Functional Improvement Following Total Knee Arthroplasty in the Clinical Setting?

The purpose of this study was to determine if improvements in knee function after arthroplasty could be practicably measured in the clinical setting using available, validated technology. The tools we assessed included a timed test of common activities, a platform posturography analysis, and a portable gait laboratory device to quantify body segment motion. We measured the function of 25 total knee arthroplasty patients before surgery and at 1, 4, 12, and 24 months after surgery. Assessment of sit-to-stand, walking, stair climbing, lunging, Knee Society Scores, and Oxford Survey Scores were collected at each interval. Patients showed significant improvement in step length, gait speed, symmetry of weight distribution, symmetry of lunging, and speed of stair climbing. Changes in function with long-term follow-up can be precisely measured, making this technology promising for clinical or research applications.

Mechanical thromboembolic prophylaxis with risk stratification in total knee arthroplasty.

The purpose of this study was to determine the rate of thromboembolic and bleeding complications when using mechanical prophylaxis with preoperative risk stratification following total knee arthroplasty (TKA). Between 1994 and 2007, 4037 TKAs were performed on 3144 patients at our institution. Mechanical VTE prophylaxis was used for standard risk patients, which included AV impulse foot pumps, thigh high stockings, and early mobilization. Chemoprophylaxis was only given to patients who were at increased thromboembolic risk. The incidence of DVT identified by ultrasound following TKA was 2.1%. A retrospective review showed 1 patient had a fatal pulmonary embolism, and 5 patients had bleeding complications in the knee. We conclude that mechanical thromboembolic prophylaxis using risk stratification is safe and effective following TKA.

A prospective randomized study of bicompartmental vs. total knee arthroplasty with functional testing and short term outcome.

The purpose of this study was to compare 50 bicompartmental knee arthroplasty (BKA) and total knee arthroplasty (TKA) cases, particularly in restoring knee function. Patients were between 30 and 65 years old, with a BMI under 35, and had osteoarthritis in the medial and patellofemoral compartments. Knee Society scores, Oxford questionnaires, radiographs, and functional tests were performed preoperatively, and at 1, 4, 12, and 24 months postoperatively. Functional testing included gait analysis, stair climbing, lunging, and sit-to-stand analysis. Both groups achieved equivalent Knee Society scores (2 year mean 93.6 vs. 92.6, P=0.43) and Oxford scores (2-year mean 43 vs. 41, P=0.35). Functional testing showed significant improvement. Two years postoperatively the BKA and TKA groups achieved equivalent results in clinical scores and functional testing.

The functional assessment test: a method of evaluating improvement in function after knee arthroplasty.

Questionnaires are marginally useful for objectively measuring function after knee arthroplasty. The Functional Assessment (FA) test is an easily administered, timed test of a person's ability to stand, walk and ascend/descend stairs that would be useful for quantifying a patient's function after knee arthroplasty. Four hundred forty-five individuals were included in the study: 313 without lower extremity arthritis or neurologic disease and 132 with advanced degenerative arthritis prior to knee arthroplasty. As expected, the test times were longer for individuals afflicted with knee arthritis. Arthroplasty patients were tested pre- and postoperatively to determine if their FA test time improved. The FA test takes less than a minute and is practical for use in the clinical setting as a simple means of quantifying function before and after knee arthroplasty.

Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.

BACKGROUND: Historically, a functional ACL has been a prerequisite for patients undergoing unicondylar knee arthroplasty (UKA). However, this premise has not been rigorously tested. QUESTIONS/PURPOSES: We compared (1) the survivorship free from revision and (2) the failure mechanisms of UKAs in ACL-deficient knees and UKAs in ACL-intact knees performed over the same time interval. METHODS: Between November 2000 and July 2008, a fixed bearing UKA was performed in 72 patients (81 knees) with intraoperatively confirmed ACL deficiency. Five patients (five knees) with preoperative instability underwent ACL reconstruction and were excluded from analysis. Of the remaining 67 patients (76 knees) without preoperative instability, implant status was known for 68 UKAs in 60 patients. Survivorship and failure mechanisms for these knees were compared to those of 706 UKAs in ACL-intact knees performed during the same time interval by the same surgeon using the same implant system. Minimum followup for the ACL-deficient group was 2.9 years (mean, 6 years; range, 2.9-10 years). RESULTS: Revision rates between UKAs with and without intact ACLs were similar in the absence of clinical instability (p = 0.58). Six-year UKA survivorship was 94% (95% CI: 88%-100%) in ACL-deficient knees and 93% (95% CI: 91%-96%) in ACL-intact knees (p = 0.89). Five knees (7%) in the ACL-deficient group were revised: disease progression (two), loose tibia (one), persistent pain (one), and revised elsewhere/reason unknown (one). Thirty-six knees in the ACL-intact group underwent revision (5%): aseptic loosening (13), revised elsewhere/reason unknown (11), disease progression (three), tibial subsidence/fracture (four), infection (three), pain (one), and lateral compartment overload (one). CONCLUSIONS: At 6 years, deficiency of the ACL in patients without clinical knee instability did not impact the survivorship of UKAs compared to UKAs performed in knees with intact ACLs.

Radiographically measured total knee wear is constant and predicts failure.

Knee wear is commonly measured with the most recent radiograph based on the assumption that wear progresses at a constant rate. Changing patient activity or in vivo polyethylene deterioration are examples of factors that could cause wear rates to change over time. Using six or more radiographs on each of 251 knees over a mean 10-year follow-up, we determined the pattern of polyethylene wear. 92% of knees had linear wear with a mean wear rate of 0.09 ± 0.12 mm/yr. Ten knees (4%) had late accelerated wear. Knees with accelerated wear and those with a wear rate of 0.15 mm/yr or greater had lower survivorship rates. We conclude that wear is linear with rare exceptions and that higher wear is correlated with failure.

Can microcomputed tomography measure retrieved polyethylene wear? Comparing fixed-bearing and rotating-platform knees.

BACKGROUND: Wear of total knee polyethylene has been quantified gravimetrically with thickness measurements and evaluation of surface wear modes. However, these techniques do not localize volumetric wear. QUESTIONS/PURPOSES: We used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear. METHODS: We retrieved 12 fixed and 12 rotating-platform bearings after a mean 52 months of use. Inserts were weighed and thickness was measured. Micro-CT scans of retrieved and matched new liners were superimposed to compare the location and magnitude of wear. RESULTS: The average total wear was 254 ± 248 mm(3). The average wear rate was 58 ± 41 mm(3)/year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43 ± 25 mm(3)/year and the fixed-bearing rate was 74 ± 49 mm(3)/year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate. CONCLUSIONS: Micro-CT can determine the volume and location of wear of retrieved tibial liners. Because the magnitude of the manufacturing tolerances was approximately half the magnitude of the total wear on average, accounting for the potential influence of tolerances is important to accurately measure volumetric wear if the unworn (preimplantation) geometry of the insert is unknown. Without accounting for tolerances, this technique may not be applicable for retrievals with a short followup that have low wear. However, application of micro-CT could be of value in determining the exact location of wear in knee simulator studies in which the same insert is measured repeatedly and manufacturing tolerances are not a concern.

Current controversies in partial knee arthroplasty.

Partial knee arthroplasty has enjoyed renewed interest during the past decade. It is helpful to be familiar with the classic and current indications, contraindications, and technical aspects of partial knee arthroplasty, including patellofemoral, medial unicompartmental, and lateral unicompartmental knee arthroplasty. Various implant choices for partial knee arthroplasty can be compared and evaluated based on patient characteristics, design qualities, and reported outcomes. It is also helpful to review the indications and techniques for performing medial or lateral unicompartmental knee arthroplasty in combination with arthroscopically assisted reconstruction of the anterior cruciate ligament.

Polyethylene quality affects revision knee liner exchange survivorship.

BACKGROUND: Options to treat patients with wear or osteolysis include full revision, partial (tibial or femoral) revision, and isolated polyethylene exchange. It is unclear whether one choice is superior to the other. Polyethylene quality reportedly influences the survivorship of primary TKA, but similar reports are not described for revision TKA. QUESTIONS/PURPOSES: We compared the failure rate for the three procedures and the influence of polyethylene quality on failure. PATIENTS AND METHODS: We retrospectively evaluated 123 patients with 135 TKAs in which wear or osteolysis was thought to have contributed to the need for surgery. Twenty-five percent had an isolated polyethylene exchange, 39% a single-component revision, and 36% a full revision. We determined survivorship of the revisions. The mean follow-up for the 123 patients was 6.2 years. Fifteen patients (16 knees, or 12%) were lost before 5-year evaluations leaving 108 patients (119 knees, or 88%) for comparison of rerevision rates. RESULTS: Five-year survivorship was similar for all three procedures: 82% ± 14% for polyethylene exchange, 89% ± 8% for partial revision, and 88% ± 10% for a full revision. Polyethylene sterilization had the strongest influence on rerevision. Survivorship was 73% ± 16% for knees revised with gamma-in-air polyethylene compared to 92% ± 6% for nongamma or gamma-in-barrier sterilization methods. CONCLUSIONS: The survival rates of isolated polyethylene exchange for wear or osteolysis are similar to those of a single-component or full revision when the components are well aligned and well fixed. Polyethylene sterilization influenced revision TKA survivorship in this study and should be reported in future studies.

Learning curve with minimally invasive unicompartmental knee arthroplasty.

This study examined 445 consecutive minimally invasive unicompartmental knee arthroplasties (UKAs) from one institution to determine whether revision and reoperation rates would decrease as the number of cases performed increased, indicating the presence of a learning curve with this procedure. At a mean of 3.25 years, 26 knees required revision yielding an overall revision rate of 5.8%; survivorship at 2 years with revision as an end point was 96% +/- 1.7%. Both revisions and reoperations decreased over time but not significantly. For the first half of UKA cases performed vs the second half, revision rates fell from 5.0% to 2.5%, and reoperation rates fell from 8.1% to 5.4%. These data demonstrate that despite modifications made to improve surgical technique across time, a substantial complication rate with this procedure persists.

Mechanical stability of well-functioning tibial baseplates from postmortem-retrieved total knee arthroplasties.

In joint replacement, cyclic motion at the bone-prosthesis interface is considered a precursor to component loosening. This study characterized the mechanical stability of 13 total knee arthroplasties harvested postmortem after an average time in situ of 10.3 years. With loads applied to the medial and then the lateral tibial plateau, motion between the tibial component and underlying bone was measured with extensometers. The amount of motion between the tibial component and underlying bone under medial and lateral loads of 500 N and then twice body weight was typically less than 20 microm. Tray depression under load application and the liftoff on the contralateral side indicated that the tibial stems limited implant rotation and that implant fixation did not deteriorate with time in situ.

Analysis of wear in retrieved mobile and fixed bearing knee inserts.

One purported advantage for mobile bearing (MB) knee implants is reduced polyethylene wear. Twenty-three retrieved Low Contact Stress (LCS) MB and 31 Anatomic Modular Knee (AMK) fixed bearing tibial polyethylene inserts, both Enduron (Depuy, Warsaw, IN) and sterilized by gas plasma, were graded for top and backside wear using the Hood grading system. For articular surface wear, there was no statistical difference between pitting and scratching, but burnishing was twice as much for MB inserts (P = .003). For backside scores, there was a minimal amount of pitting for both, but the scratching score was twice (P = .000) and the burnishing score was 3 times greater for MB inserts (P = .000). At more than 5 years in situ, the linear wear measurements were similar for the 2 groups (mean penetration was 0.329 mm for MB and 0.320 mm for fixed bearing).

Radiographic assessment of the thickness lost from polyethylene tibial inserts that had been sterilized differently.

BACKGROUND: Archived serial radiographs of knee replacements provide indirect evidence of the clinical performance of ultra-high molecular weight polyethylene tibial bearings. Our purpose was to determine the loss of thickness in polyethylene tibial inserts that were of the same design but had been sterilized differently. METHODS: Four hundred and sixteen knees with an Anatomic Modular Knee primary total knee replacement had five to eighteen years of follow-up and a posterior cruciate ligament-retaining polyethylene tibial insert that had been sterilized with either gamma radiation in air (from 1987 to 1993) or gamma radiation in an inert gas (from 1993 to 1995), or by means of a nonirradiation gas-plasma method (from 1995 to 2001). Readings were taken from 1975 weight-bearing anteroposterior radiographs of the knee on which the top surface of the metal tibial tray had nearly projected as a line. In each tibiofemoral compartment, loss of polyethylene thickness was calculated as the standard thickness of the insert minus the measured magnification-corrected thickness. For each sterilization method, thickness loss was plotted versus the corresponding follow-up time, and a mixed linear regression model was used to quantify the change in thickness over time. Multiple linear regression analysis was used to determine whether loss of thickness was associated with implant factors, patient variables, and early postoperative limb alignment. RESULTS: According to the mixed model regression coefficients, loss of medial compartment thickness was greatest for inserts that had been sterilized with gamma radiation in air (0.15 mm/yr), least for those sterilized with gamma radiation in an inert gas (0.02 mm/yr), and of an intermediate magnitude for those sterilized with a nonirradiation method (0.06 mm/year); loss of lateral compartment thickness ranged from 0.03 to 0.06 mm/yr. Notably, no insert irradiated in an inert gas showed a loss of thickness of >1 mm, and no nonirradiated insert showed a loss of >2 mm. Loss of medial compartment thickness in inserts sterilized with radiation in air increased significantly with a greater polyethylene shelf age, lesser patient age, and more varus alignment of the limb in the early postoperative period (p < 0.01). CONCLUSIONS: In this total knee design, tibial polyethylene performance improved markedly after discontinuation of the gamma radiation in air sterilization technique. Future concerns are that bearings sterilized with radiation in an inert gas may oxidize in vivo and develop fatigue wear because of free radicals generated during sterilization with radiation and that nonirradiated bearings may undergo greater losses in thickness from routine burnishing since they lack the cross-linking that accompanies sterilization with radiation.

Use of structural allograft in revision total knee arthroplasty in knees with severe tibial bone loss.

BACKGROUND: Tibial bone loss is frequently encountered at the time of revision total knee arthroplasty, and the outcome of the revision often depends on the management of this bone deficiency. We examined the clinical and radiographic outcomes of a series of revision total knee arthroplasties in which a structural allograft had been used to reconstruct a tibial bone defect encountered at the time of the revision procedure. METHODS: From January 1985 through September 1999, one surgeon performed revision arthroplasty in forty-nine knees (forty-seven patients) with a severe tibial bone defect. The reasons for the revisions included polyethylene wear and osteolysis in twenty-four knees, aseptic loosening in seventeen knees, infection in five knees, and failure for another reason for three knees. Structural allograft was used alone in thirty-five knees and in conjunction with a tibial augment in fourteen knees. The mean age of the patients at the time of the revision arthroplasty with the allograft was sixty-seven years. The patients were assessed clinically with use of the Knee Society score and radiographically. RESULTS: The status of the implant was known for forty-six of the forty-nine knees in this study. It was unknown for one patient (one knee) who was lost to follow-up and for two patients (two knees) who died less than five years postoperatively. Four revision procedures in four patients failed and required a reoperation. Two of the failures were due to infection. At a mean of ninety-seven months postoperatively, the mean Knee Society clinical score was 84 points for the knees that had not had a reoperation due to failure. The mean arc of motion improved from 87 degrees preoperatively to 103 degrees at the most recent follow-up evaluation. Histological evaluation of specimens retrieved at two autopsies demonstrated graft union to host bone. CONCLUSIONS: A structural allograft provides a stable and durable reconstruction of a tibial bone deficiency. At a mean of ninety-five months postoperatively, we found no instance of graft collapse or aseptic loosening associated with the structural allograft. We recommend the use of a structural allograft for the management of severe tibial bone deficiency at the time of revision total knee arthroplasty.

Advances in knee arthroplasty for younger patients: traditional knee arthroplasty is prologue, the future for knee arthroplasty is prescient.

Total knee arthroplasty (TKA) was a remarkable development in orthopedic surgery. Joint arthroplasty and arthroscopy were perhaps the greatest innovations in orthopedics in the 20th century and occurred without the advantages of today's technology. Initially, TKA was performed only on elderly patients and those with advanced rheumatoid arthritis because of concerns with long-term wear of polyethylene. Surgeons strongly discouraged this surgery for patients younger than age 60 years because both patients and many orthopedic surgeons believed that knee implants would last only for approximately 10 years, particularly in younger and more active patients. Reports in the late 1980s and early 1990s about accelerated polyethylene wear and osteolysis substantiated the conviction that TKA was contraindicated in younger patients. This led to complacency toward TKA, thus inhibiting technological advances in the procedure to develop implants for younger and more active patients.

Lateral tibiofemoral compartment narrowing after medial unicondylar arthroplasty.

UNLABELLED: Many surgeons have sought to avoid valgus postoperative limb alignment when performing medial unicondylar arthroplasty under concern that such posture accelerates lateral tibiofemoral compartment joint space narrowing. To test whether postoperative limb alignment was associated with lateral compartment narrowing, we measured the lateral compartment joint space width from the most recent single-leg erect anteroposterior radiograph and similarly-obtained early postoperative radiographs of 113 medial unicompartmental arthroplasties (eight designs, 91 patients) that had a minimum of 10 years (range 10-19 years) clinical followup. The mean (+/- standard deviation) narrowing was 0.03 +/- 0.13 mm per year (< 0.10 mm per year, 89 knees) or 7% +/- 30% (< 25%, 90 knees). Narrowing increased with more valgus (less varus) of the early postoperative hip-knee-ankle angle. However, the effect of alignment was small (narrowing increased by 0.01 mm per year per each 1 degree) and it was not linked with an outcome of 25% or greater, 50% or greater, or 75% or greater narrowing. In summary, narrowing increased slightly with more valgus (less varus) early postoperative limb alignment, but limb alignment was a poor predictor of which knees would develop more complete joint space thinning. LEVEL OF EVIDENCE: Level IV, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.