Benjamin M. Stronach

Patient-specific Total Knee Arthroplasty Required Frequent Surgeon-directed Changes

BackgroundPatient-specific instrumentation potentially improves surgical precision and decreases operative time in total knee arthroplasty (TKA) but there is little supporting data to confirm this presumption.Questions/purposesWe asked whether patient-specific instrumentation would require infrequent intraoperative changes to replicate a single surgeon’s preferences during TKA and whether patient-specific instrumentation guides would fit securely.MethodsWe prospectively evaluated the plan and surgery in 60 patients treated with 66 TKAs performed with patient-specific instrumentation and recorded any changes. A subset of six postoperative radiographic changes to the femoral and tibial components (implant size, coronal and sagittal alignment) was analyzed to determine if surgeon intervention was beneficial. Each guide was evaluated to determine fit. We compared patient demographics and implant sizing in the patient-specific instrumentation group with a control group in which traditional instrumentation was used.ResultsWe recorded 161 intraoperative changes in 66 knee arthroplasties (2.4 changes/knee) performed with patient-specific instrumentation. The predetermined implant size was changed intraoperatively in 77% of femurs and 53% of tibias. We identified a subset of 95 intraoperative changes that could be radiographically evaluated to determine if our changes were an improvement or detriment to reaching goal alignment. Eighty-two of the 95 changes (86%) made by the surgeon were an improvement to the recommended alignment or size of patient-specific instrumentation. The guide did not fit securely on eight femurs (12%) and three tibias (5%). Tourniquet time and blood loss were not improved with patient-specific instrumentation.ConclusionsWe caution surgeons against blind acceptance of patient-specific instrumentation technology without supportive data.Level of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Lipid metabolism related gene-expression profiling in liver, skeletal muscle and adipose tissue in crossbred Duroc and Pietrain Pigs.

Body-weight differences in animals may be ascribed to genetic and environmental factors. Here we utilized two divergent porcine genotypes, the highly muscled, leaner PietrianxYorkshire pigs and less muscled, fatter DurocxYorkshire growing pigs (75-110 kg), to examine the role of genetic background on expression of genes associated with anabolic (Fatty acid synthase, FAS; glucose transporter 4, GLUT-4; stearoyl CoA desaturase, SCD; Sterol regulatory binding protein-1, SREBP-1; leptin) and catabolic lipid metabolism (Carnitine palmitoyltransferase-1B, CPT-1B; acyl-CoA dehydrogenase, ACDH) in adipose tissue (AT), liver (L) and skeletal muscle (SKM). Pietrain pigs had lower mRNA abundance for FAS, SREBP-1, SCD and leptin in AT and L, but higher mRNA abundance for L ACDH and SKM ACDH and CPT-1B than Durocs. Duroc pigs exhibited higher expression of FAS, SREBP-1, SCD, leptin in AT and FAS in L and lower expression of ACDH and CPT-1B in L SKM. GLUT-4 expression did not differ in SKM between the two genotypes. Feeding of a beta adrenergic agonist (Paylean) for 52 days lowered expression of lipid anabolic and enhanced lipid catabolic genes expressions similarly in both genotypes. Overall, the lipid metabolism genes differential expression patterns documented here showed that in Pietrain pigs mRNA abundances of synthesis genes were lower and of catabolic genes were higher than in Duroc pigs.

Patient-Specific Instrumentation in Total Knee Arthroplasty Provides No Improvement in Component Alignment

Improved component alignment in TKA remains a commonly cited benefit of MRI based patient-specific instrumentation (PSI). We hypothesized that PSI would lead to improved alignment versus traditional instrumentation (TI) during primary TKA. Fifty-eight knees (54 patients) that underwent TKA with PSI were compared to 62 knees that had previously undergone TKA with TI. Radiographs were evaluated for mechanical axis and alignment of the femoral and tibial components. Alignment was similar between the groups. However, the PSI group showed fewer knees in the target range for posterior tibial slope (PSI 38% vs. TI 61%, P=0.01) in addition to a trend for fewer knees in target range for femoral flexion (PSI 40% vs. TI 56%, P=0.07). This study demonstrated no improvement in overall alignment and perhaps a worsening of the tibial slope.

Hybrid total knee arthroplasty revisited: midterm followup of hybrid versus cemented fixation in total knee arthroplasty.

The optimal method of fixation in total knee arthroplasty is still debated. Hybrid total knee arthroplasty (TKA), with cemented tibial and cementless femoral components, is a proposed method of fixation to improve outcomes. Although several studies have shown favorable outcomes, there is still lack of consensus in the literature. We hypothesized that hybrid TKA yields similar clinical, radiographic, and survivorship results compared to fully cemented TKA. The clinical and radiographic outcomes of 304 cruciate retaining TKAs with minimum two-year followup, including 193 hybrid (mean followup of 4.1 years) and fully cemented TKAs (mean followup of 3.2 years) were evaluated. Knee society scores were similar between the two groups. The total number of femoral radiolucencies was also similar between the two groups, while a greater number of femoral Zone 4 radiolucencies were seen in the cemented group (9% versus 1.6%, P = 0.005). The hybrid group demonstrated a 99.2% survival rate of the femoral component out to seven years for aseptic loosening. No significant difference in survivorship was seen between the groups for all cause or aseptic failure at seven years. We conclude that hybrid fixation leads to similar intermediate-term outcomes as fully cemented components and remains a viable option in total knee arthroplasty.

Failure of Emperion modular femoral stem with implant analysis

Modularity in total hip arthroplasty provides multiple benefits to the surgeon in restoring the appropriate alignment and position to a previously damaged hip joint. The vast majority of modern implants incorporate modularity into their design with some implants having multiple modular interfaces. There is the potential for failure at modular junctions because of fretting and crevice corrosion in combination with mechanical loading. This case report details the failure of an Emperion (Smith and Nephew, Memphis, TN) femoral stem in a 67-year-old male patient 6 years after total hip replacement. Analysis of the implant revealed mechanically assisted crevice corrosion that likely accelerated fatigue crack initiation in the hip stem. The benefits of modularity come with the potential drawback of a combination of fretting and crevice corrosion at the modular junction, which may accelerate fatigue, crack initiation and ultimately reduce the hip longevity.

Direct anterior total hip arthroplasty

The direct anterior approach to hip arthroplasty has become a popular technique. This technique, which was described almost 70 years ago, allows the surgeon to approach the hip through an internervous and intermuscular plane. Preliminary studies show that direct anterior hip arthroplasty may allow patients to recover faster with a lower dislocation rate. It is helpful to understand the history, scientific basis, and surgical technique of direct anterior hip arthroplasty.Introduction In theory, the direct anterior approach offers the only path to performing minimally invasive total hip arthroplasty in an intermuscular, internervous plane. Step 1 Position and Drape Patient Careful positioning is necessary to complete this procedure on a standard operating room table. Step 2 Superficial Exposure Incise the fascia overlying the tensor fasciae latae and lift up the anterior edge, avoiding the perforating vessels. Step 3 Deep Exposure The hip is flexed 30° during the deep dissection. Step 4 Prepare Acetabulum and Implant Acetabular Component Ream the acetabulum in 10° to 15° of anteversion with an abduction angle of 40° to 45°. Step 5 Prepare Femur and Implant Femoral Component Use offset broaches to access the femur and prevent perforation through the greater trochanter. Step 6 Trial and Close Specifically check for impingement of bone on the implant with the hip flexed 90°. Results This approach has been used successfully for total hip arthroplasty for decades. What to Watch For IndicationsContraindicationsPitfalls & Challenges.