Biomechanical Study of Patellar Component Fixation with Varying Degrees of Bone Loss.

BACKGROUND: The decision as to whether or not to resurface the patella in revision total knee arthroplasty (TKA) is affected by the amount of patellar bone stock remaining; however, the impact of the cancellous bone status on patellar component fixation has not been studied. Therefore, we conducted a biomechanical study of patellar component fixation with varying degrees of cancellous bone loss. METHODS: Sixty pairs of cadaveric patellae were randomly assigned between 3 groups and prepared in similar manner to a TKA with the standard 3-hole configuration. A control patella and an experimental patella were designated in each pair. To simulate bone loss in the experimental patellae, 1, 2, and 3 of the standard drill holes were uniformly enlarged to 12 mm in group 1, group 2, and group 3, respectively. Afterward, an all-polyethylene patellar component was cemented to each patella, as done intraoperatively. Patellar components were then sheared off using a materials testing system. The resulting mean offset yield force was analyzed within each group using paired t-tests. RESULTS: The mean offset yield force for the control patellae was greater than the experimental patellae in group 1. In groups 2 and 3, the experimental patellae produced a greater mean offset yield force than the control patellae. Comparison within each group did not demonstrate a statistically significant difference. CONCLUSION: Bone loss with enlargement of the patellar fixation holes, as is frequently seen in revision TKA, with holes up to 12 mm, does not significantly decrease patellar component fixation shear strength in this biomechanical cadaveric study.

Muscular architecture of the popliteus muscle and the basic science implications.

BACKGROUND: The function of the popliteus muscle is largely treated as a static stabilizer and has a lack of basic muscular architectural data to enable study of its dynamic function. A large volume of literature supports its static function and the essential need for reconstruction in the posterolateral knee when injured to restore knee stability. HYPOTHESIS/PURPOSE: We hypothesize that the popliteus muscle is more significant as a dynamic presence in the knee. METHODS: A collection of popliteus architectural data was collected from 28 cadaver specimens (mean (SD) 76 years (11)). Physiological cross-sectional area of the popliteus and semimembranosus muscles were calculated from muscle volume and fiber length to power future muscle force prediction models. Posterior knee muscle trajectories were measured with respect to the longitudinal axis of the tibia. A 2-tailed T test was performed. RESULTS: Significant differences between males and females were found for both the popliteus (p = 1.1E-05) and semimembranosus (p = 2.0E-05) muscle volumes. Significant differences between males and females were also found in PCSA for the popliteus (p = 0.005) and semimembranosus (p = 4.1E-05) muscles. There were no significant differences in fiber length, overall muscle length (with tendon removed), age, and orientation. CONCLUSION: Further consideration should be given to include the popliteus muscle as a dynamic entity in the knee given its mechanical properties, trajectory, and prior biomechanical evidence showing when and how it is activated. The present study provides data that may shape future directions of research and treatment with regard to posterolateral corner injuries and ligamentous balancing of the knee.

Single stage bilateral flexible intramedullary fixation of periprosthetic distal femur fractures.

We present a patient with bilateral Rorabeck II/Su III periprosthetic distal femur fractures treated successfully with bilateral single stage flexible intramedullary fixation. Flexible intramedullary fixation of Rorabeck II/Su III periprosthetic distal femur fractures provides the benefits of shorter operative time, lower blood loss, and preservation of bone stock compared to plate fixation and distal femur replacement. We suggest that for patients with similar injuries flexible intramedullary fixation can be a viable treatment option.

The Radiographic Prepatellar Fat Thickness Ratio Correlates With Infection Risk After Total Knee Arthroplasty.

BACKGROUND: Obesity has been associated with complications after a total knee arthroplasty (TKA). Surgical site infection (SSI) after TKA is one of the feared complications as it increases revision rates, costs, and stress to the patient. There is conflicting evidence in the literature regarding body mass index (BMI) and risk of infection after TKA, and some studies have suggested that site-specific fat distribution may be a better metric for determining risk of postoperative infections. Here, we investigate the correlation of soft tissue distribution about the knee to SSI after TKA. METHODS: We retrospectively review 572 patients who underwent primary TKA at a single institution from 2006 to 2010. We introduce the prepatellar fat thickness ratio (PFTR) as a radiographic means to quantitatively assess fat distribution about the knee and evaluate this measurement's ability to assess the risk of developing an SSI after TKA. RESULTS: The PFTR was shown to be a better predictor of SSI than BMI in both the univariate (P = .05) and multivariate (P = .01) analyses. CONCLUSION: Although BMI cannot fully account for variations in adipose distribution, the PFTR may account for this variability and may be a helpful tool for assessing a patient's preoperative risk of SSI after TKA.

Protecting the PCL During Total Knee Arthroplasty Using a Bone Island Technique.

BACKGROUND: Prior studies have shown that the posterior cruciate ligament (PCL) may be partially resected during cruciate retaining (CR) total knee arthroplasty (TKA) using highly experienced hands and standard surgical technique; therefore, proper surgical technique is aimed at preservation and balance of the PCL during CR TKA. The central objective of this study is to evaluate the effectiveness of a simple surgical technique to prevent PCL damage during performance of a CR TKA. METHODS: Sixty embalmed cadaver specimens were randomized into 2 groups, experimental and control. The control group consisted of standard tibial resection without the use of an osteotome. The experimental group utilized an osteotome in addition to standard technique to preserve a bone island anterior to the tibial attachment of the PCL. RESULTS: In the control group, PCL damage was noted in 73% (22/30) of specimens. In the experimental group, where an osteotome was used, PCL damage was found in 23% (7/30) of specimens. The use of an osteotome was found to have an absolute risk reduction of 50% when compared to the control group which did not use an osteotome to protect the PCL. CONCLUSION: In the setting of minimal surgical experience, the use of an osteotome to preserve the PCL during CR TKA by forming a bone island was found to be an effective means of protecting the PCL over standard technique. In addition, standard technique with the use of a Y-shaped PCL retractor was found to provide questionable protection to the PCL.

Effect of Posterior Tibial Slope on Flexion and Anterior-Posterior Tibial Translation in Posterior Cruciate-Retaining Total Knee Arthroplasty.

Reduced posterior tibial slope (PTS) and posterior tibiofemoral translation (PTFT) in posterior cruciate-retaining (PCR) total knee arthroplasty (TKA) may result in suboptimal flexion. We evaluated the relationship between PTS, PTFT, and total knee flexion after PCR TKA in a cadaveric model. We performed a balanced PCR TKA using 9 transfemoral cadaver specimens and changed postoperative PTS in 1° increments. We measured maximal flexion and relative PTFT at maximal flexion. We determined significant changes in flexion and PTFT as a function of PTS. Findings showed an average increase in flexion of 2.3° and average PTFT increase of 1mm per degree of PTS increase when increasing PTS from 1° to 4° (P<.05). Small initial increases in PTS appear to significantly increase knee flexion and PTFT.

Periprosthetic Femoral Stress Fracture After Bisphosphonate Treatment Resulting in Nonunion Successfully Treated with Teriparatide: A Case Report.

CASE: We present the case of a postmenopausal osteoporotic woman, treated with bisphosphonates, who developed a stress fracture at the tip of a revision femoral component, resulting in nonunion after several operative treatment attempts. The nonunion healed after 7 months of subcutaneous injections of 20 µg/day of teriparatide. CONCLUSION: Teriparatide treatment should be considered for use in recalcitrant stress fractures after total hip arthroplasty.

Shortening femoral osteotomy with stemmed resurfacing total knee arthroplasty for severe flexion contracture in Juvenile Rheumatoid Arthritis.

Juvenile Rheumatoid Arthritis (JRA) is a progressive disease characterized by pain, swelling, and loss of motion in the joints of adolescents. Total knee arthroplasty (TKA) can be indicated, during the adolescent years, in patients with advanced JRA to alleviate pain and improve function. Because of the relative infrequency of TKA in patients with JRA, evaluation of the type of TKA performed and the results merit review. This case report present two distinct operations performed to obtain full extension. 1. Distal femoral resection with conversion to hinged arthroplasty. 2. Femoral shortening osteotomy with resurfacing TKA.

Efficacy of skin preparation in eradicating organisms before total knee arthroplasty.

The solution of 2% chlorhexidine gluconate and 70% isopropyl alcohol (Chloraprep) is commonly used for antiseptic skin preparation before surgery. We conducted a study to evaluate the efficacy of this solution in eradicating organisms during skin preparation for total knee arthroplasty (TKA), to isolate the organism type, and to evaluate possible contributing factors leading to infection. Ninety-nine patients who were undergoing TKA were swabbed for cultures in the popliteal fossa before and after solution application. Swabs were collected, cultured, and read. Culture isolates grew in 20 (20%) of the 99 patients before solution application and in 5 (5%) of the 99 after application. Mean presolution body mass index (BMI) was 38 for patients with bacterial isolates and 34 for patients without isolates (P<.03). Mean postsolution BMI was 40 for patients with bacterial isolates and 35 for patients without isolates. BMI was a statistically significant factor in predicting presence of isolates after solution application. In addition, presence of bacteria in presolution cultures was predictive of isolation in postsolution cultures. Diabetic patients were 3.6 times more likely than nondiabetic patients to have a bacterial isolate. Other factors did not predict organism isolation. No patient developed a postoperative infection.

Displaced ischial stress fracture following revision total hip arthroplasty.

Stress fractures of the ischium are uncommon and are most likely caused by excessive stretching or contracture of the hamstring muscles. In addition, revision total hip arthroplasty (THA) may weaken the ilium, and metabolic bone disease may also contribute to a fracture. Treatment is usually conservative and prognosis is favorable. We present a rare case of spontaneous displaced fracture of the entire ischium following revision THA that healed without requiring operative intervention.

Quadriceps and patellar tendon pie-crusting as a treatment for limited flexion in total knee arthroplasty.

The pie-crusting method of ligament and tendon lengthening has been used successfully in various tissues but is not reported in the literature as an option for patellar or quadriceps tendons to address flexion limitation. Our case report discusses a patient with longstanding flexion limitation who underwent primary total knee arthroplasty. The report reviews the literature on intraoperative treatments, which primarily pertains to the condition of patella baja, and demonstrates that the pie-crusting technique should be included as a treatment option for a tight extensor mechanism while having some advantages over tibial tubercle osteotomy or Z-plasty.

Total knee arthroplasty with concurrent femoral and tibial osteotomies in osteogenesis imperfecta.

Three total knee arthroplasties (TKA) with concurrent femoral and/or tibial osteotomies in 2 patients with osteogenesis imperfecta were performed from 2004 to 2009. The 2 patients were followed for a mean of 6 years. One patient with concurrent TKA, and femoral and tibial osteotomies developed a nonunion of the tibial site that responded to open reduction and internal fixation with iliac crest bone graft. The second patient underwent right TKA with bi-level tibial osteotomies, which healed uneventfully, allowing pain free, unassisted ambulation. The same patient then elected to undergo left TKA with bi-level tibial osteotomies. Intraoperatively he sustained a minor tibial plateau fracture requiring the use of a stemmed component and postoperatively, he developed a nonunion at the proximal site and valgus malunion of the distal site. Revision of fixation was performed at both osteotomy sites, and both healed within 3 months. Both patients are now pain free and ambulate without assistance.

Evaluating factors affecting patellar component fixation strength in total knee arthroplasty.

Complications related to the patellofemoral joint after total knee arthroplasty (TKA) represent up to 50% of TKA reoperations. Shear forces across the knee produce wear and occasionally result in failure of fixation of all-polyethylene patellar components. We conducted a study to evaluate the effect of 2 factors on the shear strength of patellar component fixation: time between cement mixing and application of the patellar component, and amount of pressure applied during implantation. Fifty-four patellae were harvested from 27 cadavers and were prepared as for a TKA, allowing 3 different amounts of time for the cement to set or cure before application, and using 3 different pressures. The patellae were mounted and tested for fixation strength with a materials testing machine. Fixation was significantly stronger (P = .006) at 42 pounds of pressure after curing the cement for 8 minutes (compared with 2 minutes) and was significantly stronger (P = .005) after 2 minutes of curing at 42 pounds of pressure (compared with 62 pounds of pressure). We concluded that allowing the cement to cure while cementing the femoral and tibial components does not jeopardize fixation of the patellar component and that excessive compression of a patellar clamp may weaken fixation.

Simultaneous proximal femoral rotational and distal femoral varus osteotomies for femoral retroversion and genu valgum.

Whereas excess femoral anteversion and its related symptoms have been described many times, excess femoral retroversion is less well documented. We report the case of a 30-year-old woman who had a history of chronic bilateral hip and knee pain and evidence of excess femoral retroversion, genu valgum, early-onset lateral and patellofemoral compartment osteoarthritis of both knees, and hip arthritis. She experienced symptomatic relief after undergoing staged bilateral simultaneous proximal femoral rotational and distal femoral lateral opening wedge osteotomies. Although this combination of alignment problems is not an infrequent clinical occurrence, we have found no literature on this condition or treatment. The patient provided written informed consent for print and electronic publication of this case report.

Risk factors in total joint arthroplasty: comparison of infection rates in patients with different socioeconomic backgrounds.

Infection after total joint arthroplasty is a serious complication. Several risk factors have been shown to increase the risk of total joint infections. The purpose of this study was to evaluate whether socioeconomic background was a risk factor for infection in primary total joint arthroplasty. A retrospective chart review was conducted over a 4-year period on a single surgeon's split practice between private patients with mostly private insurance and Medicare and county based patients with predominately indigent county health coverage and Medicaid. An infection rate was calculated for each population in both primary total knee and hip arthroplasty. The two populations were statistically analyzed for differences in age, preoperative diagnoses, and socioeconomic background. To our knowledge, this is the first study showing an increased risk of infection in total joint arthroplasty based on socioeconomic background.

Failed closed reduction of hip arthroplasty secondary to prosthetic incarceration in the pelvis.

This report describes a patient with dislocation of a unipolar hemiarthroplasty that could not be reduced by closed reduction methods because of perforation of the prosthesis through the ileum.