Hannah D. Morgan

Constraint in primary total knee arthroplasty.

Abstract Instability is an important cause of failure following total knee arthroplasty. Increasing component constraint may reduce instability, but doing so also can cause increased forces to be transmitted to fixation and implant interfaces, which may lead to premature aseptic loosening. Constraint is defined as the effect of the elements of knee implant design that provides the stability needed to counteract forces about the knee after arthroplasty in the presence of a deficient soft‐tissue envelope. Determining the amount of constraint necessary can be challenging. Most primary total knee arthroplasties are performed for knees without substantial deformity or the need for difficult ligament balancing; in these cases, either a posterior‐stabilized or a posterior cruciate‐retaining design is appropriate. In certain situations, such as patients with prior patellectomies, rheumatoid arthritis, or substantial preoperative deformities, a posterior‐stabilized knee may be favored. With their large posts, varus‐valgus constrained implants typically are reserved for patients with substantial coronal plane instability, which is difficult to balance with a posterior‐stabilized or cruciate‐retaining implant alone. Rotatinghinge knee implants usually are recommended for patients with severe deformity or instability that cannot be managed with a varus‐valgus implant.

Critical evaluation of Mirels' rating system for impending pathologic fractures.

This project examined the hypothesis that Mirels’ rating system for impending pathologic fractures is reproducible, valid, and applicable across various experience levels and training backgrounds. Twelve true clinical histories and corresponding radiographs for patients with femoral metastatic lesions were reviewed by 53 participants from five experience levels: orthopaedic residents, musculoskeletal radiologists, orthopaedic attendings, fellowship-trained practicing orthopaedic oncologists, and radiation or medical oncologists. Each examiner provided individual and total Mirels’ scores and independent determination of impending fracture using clinical judgment. A subset of seven histories without prophylactic fixation provided a natural history group. There was highly significant agreement across experience categories for overall Kappa and for the concordance for individual and overall scores. Kappa analysis showed good agreement for site, moderate agreement for type, and fair agreement for size and pain. There was no significant difference in overall scores across experience levels. The pooled odds ratio favored Mirels rating system over clinical judgment regardless of experience level. Overall sensitivity was 91% and specificity was 35%. Mirels’ system seems to be reproducible, valid, and more sensitive than clinical judgment across experience levels. However, although the system is a valuable screening tool, more specific parameters are needed.

Survival of tumor megaprostheses replacements about the knee

Limb salvage surgery is an effective procedure with a low risk of tumor recurrence. In an attempt to define the incidence of implant failure at 2, 5, and 10 years postoperatively, we retrospectively reviewed implant survival in a group (n = 105) of pediatric (< 18 years of age) and adult patients who were treated with distal femoral and/or proximal tibial implants for extremity tumors. Issues regarding the timing of failure, reason for failure, and whether pediatric patients had higher rates of failure were posed as secondary questions. The median followup was 57 months (1-235 months). Thirty-two (32/105, 31%) patients had 42 implant failures. The mean prosthesis Kaplan-Meier survivorship of the index group was 84% at 2 years, 73% at 5 years, and 59% at 10 years. Forty-seven percent of all failures occurred within 2 years postoperatively, and 69% occurred within 5 years postoperatively. Pediatric patients had a higher failure rate than adults (42% versus 24%). Aseptic loosening was the most common reason for failure (n = 18/32; 56%). The incidence of failure in tumor megaprostheses is similar to early published literature and the incidence of these failures is highest within the first 3 years.Level of Evidence: Therapeutic study, level IV. See Guidelines for Authors for a complete description of levels of evidence.

Impaction allografting for femoral component revision: clinical update.

The technique of cancellous impaction allografting with cement aims to reconstitute a bone-deficient proximal femur while also gaining stable fixation of the femoral prosthesis. Some reports of this technique imply it is a system, requiring not just an exacting surgical method, but also a particular implant design, the polished, double-tapered stem. Other series consider it a surgical technique, and have varied the femoral component design, the method of graft delivery, and other elements of the procedure. Our review evaluates the current literature, with the goal of beginning to ascertain whether published results suggest impaction grafting must be considered a system, requiring a particular stem design, or simply another means to achieve femoral reconstruction in the revision setting. The conclusive answer will require randomized, controlled clinical trials to evaluate particular elements of the procedure, and these studies have yet to be done. However, investigators have shown similarly good short-term to intermediate-term results with various femoral stems at numerous centers. Currently, femoral impaction allografting, whether as a system using particular implant designs or as a surgical technique, is an accepted alternative for revision of a failed femoral component, particularly when bone-stock deficiency is present.

Transiently increased bone density after irradiation and the radioprotectant drug amifostine in a rat model.

At therapeutic levels in pediatric patients, radiation causes damage to the growth plate and contributes to growth deformity and fractures. The purpose of this project was to examine the effects of x-ray irradiation on regional bone mineral density (BMD) and osteoclast histology of rat bone with and without radioprotectant amifostine (AMF) pretreatment. Seventy-two weanling rats had their right knee irradiated with single fraction 17.5 Gy, whereas the left leg was used as an internal control. Twelve animals were euthanized at each of 6 time periods (0.5–6 wk) after irradiation, half having received 100 mg/kg amifostine. BMD (g/cm3) was determined for both the right and left femurs using peripheral quantitative computed tomography (CT) (pQCT). Tibial sections were stained for osteoclasts/chondroclasts with tartrate-resistant acid phosphatase. Statistically significant increases in BMD within the radiation field were seen in the treatment groups’ right irradiated legs over the control unirradiated left legs at all time points from 0.5 through 6 weeks. Anatomically, a peak in BMD occurs in the region immediately adjacent to the chondro-osseous junction at 2 weeks after irradiation and then moves proximally within the adjacent metaphysis after 3 weeks. Corresponding to these findings, histologically a 2-week nadir occurs after irradiation in osteoclasts/chondroclast numbers adjacent to the chondro-osseous junction with a 71.9% decrease compared with controls (p <0.05). At 3 weeks, the numbers of osteoclasts/chondroclasts in this region have increased to 47.4% greater than the control legs (p <0.03) The animals receiving amifostine had BMD that was consistently closer to controls only adjacent to the chondro-osseous junction at 0.5, 2, and 3 weeks and osteoclast/chondroclast numbers that were closer to controls only at 4 weeks.

Fluorodeoxyglucose positron emission tomography scanning: Basic principles and imaging of adult soft-tissue sarcomas

Positron emission tomography (PET) has become a powerful tool to evaluate various biological processes involving the musculoskeletal system. The positron-emitting radioisotopes commonly used in positron emission tomography in clinical practice (F-18, C-11, and O-15) can be incorporated into a number of physiologic tracers and substrates, with the synthesis of these radiopharmaceuticals taking place in association with a radioisotope-producing cyclotron. The ability of radiopharmaceuticals to function as indicators of specific physiologic processes provides an important measure of an aspect of a disease or repair that might not be apparent on the basis of structural changes alone. The use of positron emission tomography imaging and specific radiopharmaceuticals to measure biological activity of tissue quantitatively and to relate it to structure is unique in the diagnostic imaging process. Radioactive decay involves the emission of a positron (a positive electron) from a proton excess in a radioactive nucleus. The positron travels only a few millimeters in the tissue before colliding with a negative electron. This encounter results in the annihilation of both particles, with the creation of two gamma rays of 511 keV each, the energy equivalent of the two electron masses. These annihilation photons travel in 180° opposite directions from their source (Fig. 1). For positron emission tomography, positron detectors are lined up in a ring formation around the patient and they detect the pair of gamma rays resulting from the positron-electron annihilation. The paired detectors are located on opposite sides of the patient and register a count only if both detect a photon at precisely the same time, a coincidence event (Fig. 2). Computer-controlled image-manipulation techniques are used to reconstruct a cross-sectional image from the electronic information registered from the emission coming from the patient who received an injected radiopharmaceutical for the scan. Fig. 1 In the unstable atomic nucleus, a proton decays to …

Contained femoral defects: biomechanical analysis of pin augmentation in cement.

Although in the proximal tibia the need for pin augmentation of cemented giant cell tumor defects depends on whether the defect is contained, there is controversy regarding the role for pins in the distal femur. The current study investigated whether Steinmann pin augmentation offers biomechanical advantages in cement reconstruction of contained defects of the lateral femoral condyle. Twelve pairs of human femurs were used. They were tested either with the bone intact, with a standardized contained defect in the lateral condyle, with a defect repaired with cement alone, and with a defect repaired with pins in the cement. Intact specimens had significantly higher load to failure than specimens with a defect. In the repaired specimens there were no significant differences in stiffness, peak load to failure, and energy to failure between the specimens repaired with just cement or augmented with pins. This study did not show any significant biomechanical advantage of this configuration of Steinmann pin reinforcement in cement for contained defects of the lateral femoral condyle.