The Knee Society Index of Severity for failed total knee arthroplasty: development and validation.

Compared with primary knee replacement, total knee arthroplasty revision surgery is a more complex procedure and accounts for greater expenditures of healthcare resources at each clinical stage. Overall, patients having revision procedures have poorer functional outcomes and higher complication rates than patients having primary arthroplasty. Despite the expanded scope of revision problems and the rapidly emerging technology in revision surgery, the long-term success of any method remains in question. Because there is little consensus on the timing of revision surgery, optimal surgical reconstruction, and the type of prosthesis to be implanted, the Knee Society began development of an Index of Severity for Failed Total Knee Arthroplasty. Fifty-four percent of Knee Society members completed an 82-item questionnaire that determined their clinical impression about potential risk factors for the outcomes of revision surgery for failed total knee replacements. Using these results, a consensus group developed the final version of the index. The result of the nominal group process was the Knee Society Index of Severity, which was based on eight distinct domains. Each domain was divided into attributes and weights based on the questionnaire responses and consensus meeting. Actual case scenarios from five institutions were used to test interrater reliability and validity. The interrater reliability of the average score of all ratings was 0.95; the correlation of the criterion rating with the mean rating was 0.77. When three outliers were not included, the Pearson product correlation increased to 0.92. These data support the application of the Knee Society Index of Severity as a critical component of risk factor studies, effectiveness research, and cost-effectiveness analysis involving revisions of total knee replacements.

The Knee Society Index of Severity for failed total knee arthroplasty: practical application.

Previous classifications of severity for total knee arthroplasty revisions have been based largely on bone loss of the femur and tibia. These approaches failed to address the more technically difficult issues in revision surgery such as surgical exposure, contractures, extremity alignment, implant removal, soft tissue stability (in the anteroposterior and in the sagittal planes), extensor mechanism integrity, and patellar revisability. Through the Knee Society, the authors developed a severity index that incorporated these latter factors into one measure. The current authors describe the application of the Knee Society Index of Severity for failed total knee arthroplasty and its method of scoring.

Total knee arthroplasty using cruciate-retaining kinematic condylar prosthesis.

The purpose of the current study was to evaluate the long-term results of the Kinematic I condylar prosthesis with retention of the posterior cruciate ligament. One hundred sixty-eight total knee arthroplasties in 118 patients (mean age, 65.2 years; range, 21-88 years) were inserted with cement, an all-polyethylene patella, metal-backed tibia, and posterior cruciate ligament retention. Sixty-one patients (86 knees) died, one patient had an above-knee amputation, and three patients (five knees) were lost to followup; therefore, 66 knees (excluding revisions) in 50 patients were available for followup at a mean of 15.7 +/- 1.1 years (range, 14-20 years). Of the entire cohort of 168 knees, 13 have been revised: one for medial femoral condyle fracture, one for tibiofemoral instability, one for femoral and two for tibial component aseptic loosening, four for tibial polyethylene wear, and four for patellar component aseptic loosening. The 15-year survivorship free of any component revision excluding infections was 88.7% (confidence interval, 82%-95%). The 15-year survivorship free of radiographic loosening and/or revision of any component was 85.1% (confidence interval, 78%-92%). The current study shows good function and survivorship of the posterior cruciate-sparing Kinematic I condylar prosthesis at a mean of 15.7 +/- 1.1 years.

The influence of weakness in the vastus medialis oblique muscle on the patellofemoral joint: an in vitro biomechanical study.

OBJECTIVE: Investigation of the influence of weakness in the vastus medialis oblique muscle on patellar tracking. DESIGN: In vitro biomechanical study. BACKGROUND: Currently, the influence of weakness in the vastus medialis oblique muscle on patellar tracking has not been well understood. METHODS: Seven human cadaveric knees were used. The direction of loading forces in the rectus femoris/vastus intermedius, vastus medialis oblique, and the vastus lateralis muscles was decided by the muscle alignment of each cadaver knee measured at the time of dissection. The loads used were 60 N in the rectus femoris, 50 N in the vastus lateralis, and 40 N in the vastus medialis oblique, according to the ratio calculated from the cross-sectional study. The weakness of vastus medialis oblique was simulated at 30 N (75%), 20 N (50%), 10 N (25%), and 0 N (0%), and the patellar position was measured for each condition using a magnetic 3 Space Tracker System. The influence of weakness in the vastus medialis oblique muscle on patellar position was investigated with seven cadaver knees using a magnetic 3 Space Tracker System. RESULTS: At 0 degrees and 15 degrees of knee flexion, 75%, 50%, 25% and 0% of the normal vastus medialis oblique muscle led to a significant difference in lateral patellar shift compared to the normal (P<0.05). CONCLUSIONS: Weakness of the vastus medialis caused the patellar lateral shift at 0 degrees and 15 degrees of knee flexion. RELEVANCE: Weakness of the vastus medialis is thought to be an important factor causing patellar subluxation and dislocation. Understanding the relationship between the vastus medialis weakness and patellar tracking will be useful in diagnosis, treatment and prevention of patellar subluxation and dislocation.

Total knee arthroplasty for steroid-induced osteonecrosis.

There have been only a few reports that evaluate the outcome of total knee arthroplasty in patients with steroid-induced osteonecrosis of the knee. We retrospectively reviewed 31 total knee arthroplasties in 24 patients with confirmed steroid-induced osteonecrosis of the knee. The average follow-up was 64 months. Of surviving knees, 92% had significant improvement in knee scores. Five knees (16%) required a revision procedure. Reasons for revision were aseptic loosening in 3 knees and sepsis in 2 knees. Complications not requiring revision occurred in 6 of 31 knees (19%). Survivorship of total knee arthroplasty to revision in patients with steroid-induced avascular necrosis of the knee was 84% at 5 years. Although there was a slightly higher complication rate, this may, in part, be due to the severity of the patients' underlying disease processes. Total knee arthroplasty can be a successful procedure for chronically ill patients with steroid-induced osteonecrosis.

Modular augments in revision total knee arthroplasty.

Modularity in total knee arthroplasty is extremely helpful in the management of patients with complex primary and revision total knee arthroplasties. Modularity allows selective augmentation to deal with bone deficiencies on the distal and posterior femur. The ability to selectively augment the femur is very helpful in balancing the soft tissues and providing stability. Selective augmentation of the femur allows restoration of the joint line and more normal patellar and collateral ligament kinematics. Selective modular augments on the tibia allow dealing with bone deficiency without the concerns of bone graft incorporation. Modular extended intramedullary stems allow the option of either press-fit or cement fixation of the stem, entailing the stem diameter length to the given patient.

Cement versus cementless fixation in total knee arthroplasty.

A prospectively studied group of 55 uncemented Press Fit Condylar total knee arthroplasties was compared retrospectively with a matched group of 51 cemented Press Fit Condylar total knee arthroplasties at a mean of 10 years after operation. For the cemented group, the pain and function scores improved from 32 and 45 preoperatively to 95 and 77, respectively. For the uncemented group the scores improved from 33 and 50 preoperatively to 93 and 60, respectively. There were 10 revisions in the uncemented group for femoral or tibial aseptic loosening or osteolysis compared with two revisions in the cemented group. Exclusive of problems related to patellar metal backing, survival to revision for aseptic failure or radiographic loosening was 72% in the uncemented group and 94% in the cemented group at 10 years. A significantly higher revision rate was found in the uncemented compared with cemented total knee arthroplasty of the Press Fit Condylar design.

Tensile stress of the lateral patellofemoral ligament during knee motion.

Abnormal patellar retinacular tension has been considered to result in patellar lateral subluxation/dislocation. In this study, an in vitro experimental model was developed to determine the tensile stress of the lateral patellofemoral ligament, the thickest portion of the retinaculum, under loading conditions simulating two knee motion patterns: passive knee motion and unweighted active knee extension. The results indicate that the tensile stress increased significantly before 30 degrees of knee flexion, which strongly supports the clinical findings that patellar subluxation/dislocation occurs at approximately 20 degrees to 30 degrees knee flexion angles.

Influence of lateral release on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty.

The influence of lateral release of retinaculum on patellofemoral kinematics and contact characteristics after total knee arthroplasty was investigated in vitro. Lateral release altered the patellar tracking in patellar flexion, rotation, tilting, and translation. The contact force was decreased at high flexion angles. The contact area was slightly decreased and the contact region shifted laterally on the patellar button and medially on the femoral component at most of the flexion angles. The results suggest that the lateral release in total knee arthroplasty can change some patellar tracking and patellofemoral joint contact characteristics.

Differences in patellar tracking and knee kinematics among three different total knee designs.

Patellar complications are the primary reason for reoperation of the current condylar type designs. The aim of this study was to compare patellar tracking of various knee implant designs: Genesis II NexGen, and the P.F.C. Sigma Modular Knee System regarding trochlear groove center curvature. Nine unembalmed whole cadaveric lower extremities were used. The quadriceps and hamstrings were dissected into their individual muscles and loads were applied onto the muscles proximally based on the cross sectional area of the muscles. The three-dimensional kinematics of the patellofemoral and tibiofemoral joint of the intact knee were measured using a 3Space tracking system. Three implants (one from each company) were implanted onto the same cadaveric knee in random order consecutively. This was done to ensure consistency of the soft tissue constraints in influencing the amount of patellar tracking. Patellar rotation, patellar tilting, patellar lateral shift and patellar displacement in relation to groove center were measured. There was no significant difference between the intact knee and the various implants regarding patellar rotation and lateral shift. However, all three prosthetic designs showed a significant degree of lateral tilting when compared with the intact knee. At 60 degrees knee flexion, the normal patella was tilted laterally to 0.44 degree +/- 2.15 degrees as compared with the Genesis II patella at 4.75 degrees +/- 4.81 degrees, the NexGen patella at 4.85 degrees +/- 4.81 degrees, and the P.F.C. Sigma patella at 4.89 degrees +/- 3.79 degrees lateral tilt. There was no difference between the intact knee compared with the resurfaced patella in patellar displacement in relation to the groove center. This study suggests the relatively similar kinematic behavior between the implant designs as compared with the intact knees. However, additional modification of implant geometry may be required to help decrease the amount of patellar tilt.

Serial sodium Amytal interviews in the clinical setting.

The purpose of this study was to review the authors' experiences with serial sodium Amytal (amobarbital) interviews and to compare these results with those found in the literature. A chart review of 21 patients with suspected conversion disorder evaluated by Amytal interview was conducted retrospectively. Presenting symptoms included movement disorders, focal neurologic deficits, chronic pain, "spells," and pseudoseizures. The serial Amytal interviews confirmed the presence of psychopathology noted on admission and revealed underlying psychosocial stressors. In 2 of 21 patients, agents other than Amytal were used after the first interview. This series confirms that the serial Amytal interview has utility in the clinical setting as a diagnostic and therapeutic tool.

Cement viscosity affects the bone-cement interface in total hip arthroplasty.

Quantitative information regarding the interface strength and degree of cement penetration associated with cement viscosity during total hip arthroplasty is limited. The aim of the present study was to determine the effect of the viscosity of bone cement at the time of implantation on the mechanical integrity of total hip arthroplasty. Cement that was injected at an early less viscous stage produced greater failure strength in a push-out test than its more viscous counterpart.

Importance of soft tissue integrity on biomechanical studies of the patella after TKA.

This study evaluated the effects of soft tissue integrity on patellar tracking and patellofemoral joint force after total knee arthroplasty. The results indicate that partial dissection of the soft tissue integrity in the in vitro biomechanical studies of the patellofemoral joint can alter patellar tracking and joint force significantly, leading to improper conclusions.

Correlation of patient questionnaire responses and physician history in grading clinical outcome following hip and knee arthroplasty. A prospective study of 201 joint arthroplasties.

Questionnaires are commonly used in orthopaedic outcome studies. This study sought to determine if responses to a simple standardized questionnaire correlated with responses obtained during a physician interview in evaluation of clinical outcome following hip and knee arthroplasty. One hundred sixty-two patients with 201 hip and knee arthroplasties were asked to fill out a questionnaire prior to returning for routine follow-up evaluation. There was a highly significant correlation (P < .0001, r = .74) between scores calculated from patient responses on the questionnaire and those calculated from responses recorded during the subsequent physician visit. There was no significant difference between patient and physician clinical hip scores, but physicians gave significantly higher knee scores than patients for both long- ( > 4.5 years, P < .05) and short-term ( < or = 4.5 years, P < .0001) follow-up periods; however, 97% of patient responses were within one grade of physician-recorded answers to the same questions. Eight and one-half percent of scores differed in overall evaluation from good-excellent to fair-poor categories. This study both validates and defines more clearly the limitations of questionnaires for follow-up evaluation of clinical results following total hip and knee arthroplasty.

Influence of patellar thickness on patellar tracking and patellofemoral contact characteristics after total knee arthroplasty.

Although total knee arthroplasty (TKA) has become a very common procedure, patellar problems remain a major cause of disability. Patellar thickness is one of the most challenging factors. The influence of patellar thickness on patellofemoral kinematics and contact characteristics following TKA was investigated. Seven unembalmed whole-lower-extremity cadaveric specimens were used. The kinematics was measured with a magnetic tracking device (3Space Tracker System, Polhemus Navigation Sciences Division, Colchester, VT). Contact area was calculated from the kinematic data and the digitized joint surface geometrics based on a theoretical method. The patellofemoral joint contact force was measured directly using a uniaxial force transducer. Kinematically, the influence of patellar thickness on patellar flexion, rotation, and proximodistal shift was not significant. Orthopaedic surgeons are often challenged by derangement of the patellofemoral joint, especially following TKA. It is commonly assumed that restoration of overall patellar thickness is most desirable. A thin patella can reduce the contact force, but it also poses the potential risks of stress fracture and anteroposterior instability. Increasing patellar thickness might be expected to increase the effective quadriceps moment arm at low flexion angles of the knee, but potentially reduces the range of motion of the knee and predisposes to patellar subluxation. Either a thicker or a thinner patella had a smaller contact area than intact and normal-thickness patella. Therefore, the surgical technique of patellar resurfacing during TKA should attempt to reproduce the original patellar thickness.

In vitro study of patellar position during sitting, standing from squatting, and the stance phase of walking.

Muscle balance in quadricep muscles is an important factor for patellar instability. However, in vivo, the activity of the quadriceps varies during knee motion. To simulate this clinical condition, different loading conditions of the rectus femoris, vastus lateralis, and vastus medialis oblique at different knee flexion angles were studied, and patellar motion during knee extension was determined. Seven fresh-frozen adult cadaver knees were use. Patellar motion in terms of patellar shift, patellar tilt, and rotation were measured using a magnetic tracker system. The loads applied to each quadriceps muscle were calculated using clinical electromyographical data for three activities: 1) knee extension while sitting, 2) standing from squatting, and 3) stance phase of walking. The patellar tracking in these three loading patterns was compared with that under constant loading of each quadriceps muscle. Each activity demonstrated a neutral patellar shift and tilt, as did the traditional constant loading. However, the patella in walking showed internal rotation when the rectus femoris was much weaker than the other vasti.

Comparison of inset and resurfacing patellar prostheses in total knee arthroplasty.

A comparison of 135 resurfacing with 116 inset biconvex patellar components with a single total knee arthroplasty design was performed. At 2.5 +/- 0.5 years postoperatively, patellar tilt in the resurfacing group was 4 degrees +/- 6 degrees compared with 0.5 degree +/- 5 degrees in the biconvex group (p < 0.0001). Lateral patellar subluxation was 6% +/- 10% in the resurfacing group compared with 3% +/- 9% in the biconvex group (p < 0.05). Lateral release was required in 79% of the resurfacing group compared with 56% in the biconvex group (p < 0.0001). Complete patellar radiolucent lines were seen adjacent to 4 biconvex and 2 resurfacing patellar prostheses. Patellar radiolucent lines were seen more frequently in area 1 in the biconvex group compared with the resurfacing group (p < 0.01). An inset patellar implant appears to provide better radiographic alignment than a resurfacing implant, but it has a higher incidence of radiolucent lines.