Porous Tantalum Femoral Metaphyseal Cones for Large Femoral Bone Defects in Revision Total Knee Arthroplasty.

INTRODUCTION: The use of porous tantalum metaphyseal cones provides reliable metaphyseal support and fixation to help restore the joint line in difficult revision total knee arthroplasties (TKAs) in patients with large femoral bone defects. STEP 1 PREOPERATIVE PLANNING: Adequate preoperative radiographs are important to determine the approximate size of the femoral bone defect prior to surgery. STEP 2 INCISION AND EXPOSURE: Adequate exposure during revision knee surgery is key for the safe removal of implants and to minimize bone loss. STEP 3 COMPONENT REMOVAL: It is essential to disrupt the prosthesis-cement interface before attempting to extract well-fixed components. STEP 4 ESTABLISHING A TIBIAL PLATFORM: The first step in revision knee reconstruction is to establish a stable tibial platform. STEP 5 RECONSTRUCTION OF THE FEMUR: Restoring the joint line and posterior condylar offset are the goals of femoral reconstruction. STEP 6 INTRAOPERATIVE ASSESSMENT OF FEMORAL BONE LOSS: Thoroughly assess the quality, quantity, and location of the remaining cancellous and cortical bone to determine the proper technique for reconstruction. STEP 7 SELECTING THE APPROPRIATE METAPHYSEAL CONE AND SHAPING THE FEMORAL METADIAPHYSIS FOR THE FEMORAL CONE: There are different sizes and shapes of metaphyseal cones that can be used when addressing large femoral bone defects. STEP 8 IMPLANTING THE ACTUAL POROUS METAPHYSEAL CONE: During the final impaction of the femoral metaphyseal cone, take care to not cause a fracture. STEP 9 FINAL TRIAL AND CEMENTING OF THE FINAL STEMMED FEMORAL COMPONENT: Place the final stemmed femoral component through the metaphyseal cone and cement it into place. STEP 10 POSTOPERATIVE PROTOCOL: If a stable construct was achieved, the patient may bear weight as tolerated with no specific restrictions on range of motion. RESULTS: We recently performed a retrospective review of the midterm outcomes at mean of 5 years (range, 2 to 10 years) after 159 consecutive revision TKAs with a porous metal femoral metaphyseal cone in 157 patients with large bone defects 4.

Factors Associated With 20-Year Cumulative Risk of Infection After Aseptic Index Revision Total Knee Arthroplasty.

BACKGROUND: The purpose of this study was to calculate the cumulative risk of periprosthetic joint infection (PJI) after aseptic index knee revisions and to identify the surgical, perioperative, and medical comorbidity risk factors associated with deep infection. METHODS: We retrospectively reviewed 1802 aseptic index revision total knee arthroplasties performed at our institution from 1970 to 2000. From this cohort, there were 60 reoperations performed for deep infection. RESULTS: The cumulative risk of infection at 1, 5, 10, and 20 years after index revision was 1%, 2.4%, 3.3%, and 5.6%, respectively. CONCLUSIONS: Male gender, use of constrained implants, increased operative times, increased Charlson Comorbidity Index, and a history of liver disease were all significantly associated with PJI. The development of cardiovascular disease, endocrine disorders, and renal disease were also associated with PJI.

Lateral patellar facet impingement after primary total knee arthroplasty: it does exist.

The existence of the diagnosis "lateral patellar facet impingement" (LPFI) is controversial and the outcomes for surgical revision for symptomatic LPFI uncertain. We found that of the 3361 index knee revisions performed at our institution from 1995 to 2008, eleven were done for symptomatic LPFI. Their clinical histories and radiographic imaging were reviewed before and after revision TKA and were also compared to a group of control patients. We found no statistically significant differences between the groups in preoperative KS pain and function scores or radiographic features. However, the combined findings of pain in the subpatellar/lateral aspect of the knee post TKA and radiographic lateral facet contact were significantly associated with revision due to LPFI. Surgical revision results were variable, but~2/3 of the patients were satisfied with the operation and had a significant improvement in KS function scores.

Using checklists in a gross anatomy laboratory improves learning outcomes and dissection quality.

Checklists have been widely used in the aviation industry ever since aircraft operations became more complex than any single pilot could reasonably remember. More recently, checklists have found their way into medicine, where cognitive function can be compromised by stress and fatigue. The use of checklists in medical education has rarely been reported, especially in the basic sciences. We explored whether the use of a checklist in the gross anatomy laboratory would improve learning outcomes, dissection quality, and students' satisfaction in the first-year Human Structure didactic block at Mayo Medical School. During the second half of a seven-week anatomy course, dissection teams were each day given a hardcopy checklist of the structures to be identified during that day's dissection. The first half of the course was considered the control, as students did not receive any checklists to utilize during dissection. The measured outcomes were scored on four practice practical examinations and four dissection quality assessments, two each from the first half (control) and second half of the course. A student satisfaction survey was distributed at the end of the course. Examination and dissection scores were analyzed for correlations between practice practical examination score and checklist use. Our data suggest that a daily hardcopy list of anatomical structures for active use in the gross anatomy laboratory increases practice practical examination scores and dissection quality. Students recommend the use of these checklists in future anatomy courses.

Chromosomal position mediates spinal cord expression of a dbx1a enhancer.

Dbx homeodomain proteins are important for the production of multiple spinal cord cell types. To examine the regulation of Dbx genes in more detail, we have generated transgenic zebrafish in which fluorescent protein expression is driven by predicted dbx1a enhancers. We identified three areas of sequence conservation upstream of the dbx1a coding sequence and generated fluorescent reporter constructs driven by these predicted enhancer elements and the endogenous dbx1a promoter. In multiple stable insertions of a 3.5-kb enhancer fragment, we observed that there was additional reporter expression in the dorsal spinal cord not normally observed by dbx1a in situ hybridization. In addition, these lines exhibited only transient reporter expression, unlike the endogenous gene. Surprisingly, a single insertion line expressed the reporter in the endogenous pattern, indicating that other local regulatory elements modulate gene expression through the 3.5-kb enhancer.

Proliferation and patterning are mediated independently in the dorsal spinal cord downstream of canonical Wnt signaling.

Canonical Wnt signaling can regulate proliferation and patterning in the developing spinal cord, but the relationship between these functions has remained elusive. It has been difficult to separate the distinct activities of Wnts because localized changes in proliferation could conceivably alter patterning, and gain and loss of function experiments have resulted in both types of defects. To resolve this issue we have investigated canonical Wnt signaling in the zebrafish spinal cord using multiple approaches. We demonstrate that Wnt signaling is required initially for proliferation throughout the entire spinal cord, and later for patterning dorsal progenitor domains. Furthermore, we find that spinal cord patterning is normal in embryos after cell division has been pharmacologically blocked. Finally, we determine the transcriptional mediators of Wnt signaling that are responsible for patterning and proliferation. We show that tcf7 gene knockdown results in dorsal patterning defects without decreasing the mitotic index in dorsal domains. In contrast, tcf3 gene knockdown results in a reduced mitotic index without affecting dorsal patterning. Together, our work demonstrates that proliferation and patterning in the developing spinal cord are separable events that are regulated independently by Wnt signaling.

Regulation and function of Dbx genes in the zebrafish spinal cord.

Dbx homeodomain proteins are important for spinal cord dorsal/ventral patterning and the production of multiple spinal cord cell types. We have examined the regulation and function of Dbx genes in the zebrafish. We report that Hedgehog signaling is not required for the induction or maintenance of these genes; in the absence of Hedgehog signaling, dbx1a/1b/2 are expanded ventrally with concomitant increases in postmitotic neurons that differentiate from this domain. Also, we find that retinoic acid signaling is not required for the induction of Dbx expression. Furthermore, we are the first to report that knockdown of Dbx1 function causes a dorsal expansion of nkx6.2, which is thought to be the cross-repressive partner of Dbx1 in mouse. Our data confirm that the dbx1a/1b/2 domain in zebrafish spinal cord development behaves similarly to amniotes, while extending knowledge of Dbx1 function in spinal cord patterning.