Varus alignment in total knee replacement (TKR) results in a larger portion of the joint load carried by the medial compartment.[1] Increased burden on the medial compartment could negatively impact the implant fixation, especially for cementless TKR that requires bone ingrowth. Our aim was to quantify the effect varus alignment on the bone-implant interaction of cementless tibial baseplates. To this end, we evaluated the bone-implant micromotion and the amount of bone at risk of failure.[2,3] Finite element models (Fig.1) were developed from pre-operative CT scans of the tibiae of 11 female patients with osteoarthritis (age: 58–77 years). We sought to compare two loading conditions from Smith et al.;[1] these corresponded to a mechanically aligned knee and a knee with 4° of varus. Consequently, we virtually implanted each model with a two-peg cementless baseplate following two tibial alignment strategies: mechanical alignment (i.e., perpendicular to the tibial mechanical axis) and 2° tibial varus alignment (the femoral resection accounts for additional 2° varus). The baseplate was modeled as solid titanium (E=114.3 GPa; v=0.33). The pegs and a 1.2 mm layer on the bone-contact surface were modeled as 3D-printed porous titanium (E=1.1 GPa; v=0.3). Bone material properties were non-homogeneous, determined from the CT scans using relationships specific to the proximal tibia.[2,4] The bone-implant interface was modelled as frictional with friction coefficients for solid and porous titanium of 0.6 and 1.1, respectively. The tibia was fixed 77 mm distal to the resection. For mechanical alignment, instrumented TKR loads previously measured Introduction
Methods
Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture to restore range of motion and knee function. However, the effect of joint line elevation on the resulting TKA kinematics including frontal plane laxity is unclear. Thus, our goal was to quantify the effect of additional distal femoral resection on passive extension and mid-flexion laxity. Six computational knee models with capsular and collateral ligament properties specific to TKA were developed and implanted with a contemporary posterior-stabilized TKA. A 10° flexion contracture was modeled by imposing capsular contracture as determined by simulating a common clinical exam of knee extension and accounting for the length and weight of each limb segment from which the models were derived (Figure 1). Distal femoral resections of 2 mm and 4 mm were simulated for each model. The knees were then extended by applying the measured knee moments to quantify the amount of knee extension. The output data were compared with a previous cadaveric study using a two-sample two-tailed t-test (p<0.05) [1]. Subsequently, varus and valgus torques of ±10 Nm were applied as the knee was flexed from 0° to 90° at the baseline, and after distal resections of 2 mm, and 4 mm. Coronal laxity, defined as the sum of varus and valgus angulation in response to the applied varus and valgus torques, was measured at 30° and 45°of flexion, and the flexion angle was identified where the increase in laxity was the greatest with respect to baseline.Introduction
Methods
Great strides have been made in perioperative pain management after total knee arthroplasty (TKA) leading to reduced length of hospital stay, cost reduction, improved patient satisfaction, and more rapid recovery without affecting the rates of readmission after surgery. To assure a happy patient, early recognition of patients at risk for persistent postoperative pain prior to surgery is key. Patients on chronic pain medication should be evaluated by pain management specialists with the intention of reducing overall narcotic requirement prior to TKA. Patients with high anxiety levels, pain catastrophizing, and Kinesphobia are at increased risk for increased pain and poor outcomes and should be referred for cognitive behavioral therapy and coping strategies. Finally, patients with hypersensitivity syndromes localised in the soft tissue around the knee should undergo desensitization protocols prior to TKA. Patient education on the risk of increased postoperative pain is crucial to manage expectations and optimise modifiable risk factors prior to TKA. To assure a happy patient indicated for TKA, a comprehensive pain management strategy divided into pre-, intra-, and post-operative periods should be employed.
The rate of periprosthetic joint infections (PJI) after primary total hip arthroplasty (THA) is approximately 1%. As the number of THAs performed each year continue to increase (550,000 by 2030), a corresponding increase in the number of hip PJI cases is likely to occur. A chronic deep infection may be treated by either chronic suppression, irrigation and debridement, single-stage exchange, or two-stage exchange. In the United States, the gold standard for chronic PJI continues to be a two-stage exchange. The benefit of an antibiotic impregnated cement is that they produce higher local concentrations of antibiotics than systemic intravenous administration. Hip spacers may be either static or articulating. Static spacers are reserved for cases of massive acetabular bone loss in which an articulating spacer is not feasible. A static spacer consists of a block of antibiotic cement in the native acetabulum and antibiotic coated rod in the femoral canal. Limb shortening, loss of soft tissue planes, and disuse osteopenia and muscle atrophy are all limitations of static spacers. In contrast, articulating spacers fulfill the goals of the interim construct during two-stage exchange which is to enhance eradication of the infecting organism through drug elution, to maintain limb length, to facilitate exposure during revision surgery, and to improve functional mobilization. Articulating spacers may be divided into three general categories based on method of spacer creation: Handmade custom spacers, prefabricated spacers, custom molded spacers (hemiarthroplasty molds and molded stem with cemented all-polyethylene cup). Handmade custom spacers are usually created with K-wire or rush rods coated with antibiotic cement. Handmade spacers are relatively simple to make, they are economical, and the amount and type of antibiotics incorporated can be customised for the infecting organism. Commercially available hemiarthroplasty spacers can be either prefabricated (Spacer G, Exactech, Gainesville. FL) or made intraoperatively (Stage One, Zimmer Biomet, Warsaw, IN) are available in several head and stem sizes. The advantage of prefabricated spacers is that they do not require additional time to mold in the operating room. The downside of prefabricated spacers is that the antibiotic concentration and type is predetermined. A custom molded stem with cemented all-polyethylene cup can be made with off the shelf implants or used as part of a commercially available spacer (PROSTALAC, DePuy Synthes, Warsaw, IN). A common antibiotic/cement combination includes Tobramycin (3.6 g/40 g of cement) and vancomycin (1.5 g/40 g of cement). In all of these spacer constructs, the principles of using a high-elution cement mixed without a vacuum and with high doses of heat stable antibiotics are consistent. Tobramycin works synergistically to improve Vancomycin elution properties and is usually added in higher doses. Overall infection eradication is similar between all categories of spacers and range between 90–97%. Complications after placement of an articulating spacer are often specific to the type of spacer used. Handmade spaces that have K-wires for support are at risk for spacer cement fracture. Spacer dislocation is also a common complication in up to 15% of cases with all types of spacers. In addition, periprosthetic fractures can occur postoperatively in up to 10% of patients. Overall, despite this complication profile, articulating antibiotic spacers have excellent rates of infection eradication and offer improved mobilization in the interim two stage period and reduce operative time, complexity, and morbidity during reimplantation.
Restoring the overall mechanical alignment to neutral has been the gold standard since the 1970s and remains the current standard of knee arthroplasty today. Recently, there has been renewed interest in alternative alignment goals that place implants in a more “physiologic” position with the hope of improving clinical outcomes. Anywhere from 10 – 20% of patients are dissatisfied after knee replacement surgery and while the cause is multifactorial, some believe that it is related to changing native alignment and an oblique joint line (the concept of constitutional varus) to a single target of mechanical neutral alignment. In addition, recent studies have challenged the long held belief that total knee placed outside the classic “safe zone” of +/− 3 degrees increases the risk of mechanical failure which theoretically supports investigating alternative, more patient specific, alignment targets. From a biomechanical, implant retrieval, and clinical outcomes perspective, mechanical alignment should remain the gold standard for TKA. Varus tibias regardless of overall alignment pattern show increased polyethylene wear and varus loading increases the risk of posteromedial collapse. While recently questioned, the evidence states that alignment does matter. When you combine contemporary knee designs placed in varus with an overweight population (which is the majority of TKA patients) the failure rate increases exponentially when compared to neutral alignment. A recent meta-analysis on mechanical alignment and survivorship clearly demonstrated reduced survivorship for varus-aligned total knees. The only way to justify the biomechanical risks associated with placing components in an alternative alignment target is a significant clinical outcome benefit but the evidence is lacking. A randomised control trial comparing mechanical alignment (MA) and kinematic alignment (KA) found a significant improvement in clinical outcomes and knee function in KA patients at 2 year follow-up. In contrast, Young et al. recently published a randomised control trial comparing PSI KA and computer assisted mechanical TKA and found no difference in any clinical outcome measure. Why were the clinical outcomes scores in the MA patients so different: One potential explanation is that different surgical techniques were used. In the Dosset study, the femur was cut at 5 degrees valgus in all patients and femoral component rotation was always set at 3 degrees externally rotated to the posterior condylar axis. We know from several studies that this method leads to inaccuracies in both coronal plane and axial plane in some patients. Young et al. used computer assisted navigation to align his distal femur cut with the mechanical axis and adjusted femoral component rotation to the transepicondylar axis. The results suggest that a well performed mechanical aligned total knee replacement has excellent clinical performance equal to that of kinematic alignment without any of the long term risks of implant failure. Most contemporary TKA implants are designed to be loaded perpendicular to the polyethylene surface and placing them in shear without extensive biomechanical testing to support this alignment target may put patients at long term risk for an unproven benefit. Have we not learned our lesson?
Stiffness after total knee arthroplasty (TKA) is a common problem occurring between 5% and 30% of patients. Stiffness is defined as limited range of motion (ROM) that affects activities of daily living. A recent International Consensus on definition of stiffness of the knee graded stiffness as mild, moderate or severe (90–100, 70–89, <70, respectively) or an extension deficit (5–10, 11–20, >20). Stiffness can be secondary to an osseous, soft tissue, or prosthetic block to motion. Heterotopic bone or retained posterior osteophytes, abundant fibrotic tissue, oversized components with tight flexion or extension gaps or component malrotation can all limit knee motion. Infection should always be considered in the knee that gradually loses motion. Alternative causes include complex regional pain syndrome and Kinesiophobia that can limit motion without an underlying mechanical cause. The evaluation of knee stiffness radiographs of the knee and cross-section imaging should be performed if component malrotation is considered. A metal suppression MRI assists in quantifying the extent of fibrosis and its location in the anterior or posterior compartment of the knee. Inflammatory markers and joint aspiration as indicated to rule out infection. Arthrofibrosis, or post-surgical fibrosis, is related to abnormal scar formation after surgery that leads to loss of motion. The cause of arthrofibrosis is multifactorial and likely related to genetic host factors. Current research is focusing on molecular signatures that may better identify patients at risk. In addition, therapeutic interventions are being studied that best prevent fibrosis and its recurrence and include the use of anti-inflammatories, corticosteroids, Colchicine, biologic medications (IL-1 inhibitors) and low-dose radiation. Early treatment of the stiff TKA includes physical therapy and manipulation under anesthesia (MUA). MUA performed within 3 months may have the greatest increase in ROM but notable improvement can occur up to 6 months after TKA. After six months, arthroscopic or open surgery is recommended for persistent stiffness. Arthroscopic lysis of adhesions can improve ROM greater than 1 year after index TKA. Average improvement of ROM for both MUA and arthroscopic lysis of adhesions (usually in conjunction with MUA) is approximately 30 degrees. The outcome after open lysis of adhesions are reportedly poor but current adjuvant therapies may improve these clinical outcomes as this addresses the biologic, in addition to the mechanical, basis of fibrosis. Component revision performed for component malposition and stiffness has variable outcomes but a recent study reports a mean increase in ROM of 20 degrees and a modest improvement in overall knee function. The cause of post-operative stiffness after TKA is a complex interplay of the patient, surgeon, and post-operative factors. Correct diagnosis of the underlying cause of the stiff total knee is essential to optimizing treatment outcomes. More research in needed in how to best prevent and treat the biologic risk factors and pathways that contribute to post-surgical fibrosis.
Successful cementless acetabular designs require sufficient initial stability between implant and bone (with interfacial motions <150 μm) and close opposition between the porous coating and the reamed bony surface of the acetabulum to obtaining bone ingrowth and secondary stability. While prior generations of cementless components showed good clinical results for long term fixation, modern designs continue to trend toward increased porosity and improved frictional characteristics to further enhance cup stability. We intend to experimentally assess the differences in initial stability between a hemispherical acetabular component with a highly porous trabecular tantalum fixation surface (Continuum® Acetabular System, Zimmer Inc, Warsaw, IN)(Fig 1) and a hemispherical component with the new highly porous Trabecular Titanium® surface (Delta TT, Lima Corporate, Italy)(Fig 2) manufactured by electron beam melting.Introduction
Objectives
The optimal management of severe tibial and/or femoral bone loss in a revision total knee arthroplasty (TKA) has not been established. Reconstructive methods include structural or bulk allografts, impaction bone-grafting with or without mesh augmentation, custum prosthetic components, modular metal augmentations of prosthesis and tumor prosthesis. Recently metaphyseal fixation using porous tantalum cones (Zimmer, Warsaw, IN) has been proposed as alternative strategy for severe bone loss. The purposes of this study were to determine the clinical and radiographic outcomes in patients who underwent revision knee arthroplasty with tantalum cones with a minimum of 5-year follow-up.Introduction
Objectives
The vascular anatomy of the femoral head and neck has been previously reported, with the primary blood supply attributed to the deep branch of the Medial Femoral Circumflex Artery (MFCA). This understanding has led to development of improved techniques for surgical hip dislocation for multiple intra-capsular hip procedures including Hip Resurfacing Arthroplasty (HRA). However, there is a lack of information in the literature on quantitative analysis of the contributions of the Lateral Femoral Circumflex Artery (LFCA) to femoral head and neck. Additionally, there is a lack of detailed descriptions in the literature of the anatomic course of the LFCA from its origin to its terminal branches. Twelve fresh-frozen human pelvic cadaveric specimens were studied (mean age 54.3 years, range 28–69). One hip per specimen was randomly assigned as the experimental hip, with the contralateral used as a control. Bilateral vascular dissection was performed to cannulate the MFCA and LFCA. Specimens were assigned as either LFCA-experimental or MFCA-experimental. All specimens underwent a validated quantitative-MRI protocol: 2mm slice thickness with pre- and post- MRI contrast sequences (Gd-DTPA diluted with saline at 3:1). In the LFCA-experimental group 15ml of MRI contrast solution was injected into the LFCA cannula. In the MFCA-experimental group 15ml of contrast solution was injected into the MFCA cannula. On the control hip contrast solution was injected into both MFCA and LFCA cannulas, 15ml each (30ml total for the control hip). Following MRI, the MFCA and LFCA were injected with polyurethane compound mixed with barium sulfate (barium sulfate only present in either MFCA or LFCA on each hip). Once polymerization had occurred, hips underwent thin-slice CT scan to document the extra- and intra-capsular course of the LFCA and MFCA. Gross dissection was performed to visually assess all intra-capsular branches of both the MFCA and LFCA and assess for extravasation. Quantitative-MRI analysis was performed based on Region of Interest (ROI) assessment. Femoral heads were osteotomized at the level of the largest diameter proximal to the articular margin and perpendicular to the femoral neck, for placement of a 360° scale. Measurements using the 360° scale were recorded. For data processing, we used right-side equivalents and integrated our 360° data into the more commonly used imaginary clock face.Introduction
Materials & Methods
A surgical hip dislocation provides circumferential access to the femoral head and is essential in the treatment pediatric and adult hip disease. Iatrogenic injury to the femoral head blood supply during a surgical may result in the osteonecrosis of the femoral head. In order to reduce vessel injury and incidence of AVN, the Greater Trochanteric Osteotomy (GTO) was developed and popularized by Ganz. The downside of this approach is the increased morbidity associated with the GTO including non-union in 8% and painful hardware requiring removal in 20% of patients. (reference) Recent studies performed at our institution have mapped the extra-osseous course of the medial femoral circumflex artery and provide surgical guidelines for a vessel preserving posterolateral approach. In this cadaveric model using Gadolinium enhanced MRI, we investigate whether standardized alterations in the postero-lateral surgical approach may reliably preserve femoral head vascularity during a posterior surgical hip dislocation In 8 cadaveric specimens the senior author (ES) performed a surgical hip dislocation through the posterolateral approach with surgical modifications designed to protect the superior and inferior retinacular arteries. In every specimen the same surgical alterations were made using a ruler: the Quadratus Femoris myotomy occurred 2.5 cm off its trochanteric insertion, the piriformis tenotomy occurred at its insertion and extended obliquely leaving a 2 cm cuff of conjoin tendon (inferior gemellus), and the Obturator Externus (OE) was myotomized 2 cm off its trochanteric insertion. (Figure 1) For the capsulotomy, the incision started on the posterior femoral neck directly beneath the cut obturator externus tendon and extending posteriorly to the acetabulum. Superior and inferior extensions of the capsulotomy ran parallel to the acetabular rim creating a T-shaped capsulotomy. After the surgical dislocation was complete, the medial femoral circumflex artery (MFCA) was cannulated and Gadolinium-enhanced MRI performed in order to assess intra-osseous femoral head perfusion and compared to the gadolinium femoral head perfusion of the contra-lateral hip as a non-operative control. Gross-dissection after polyurethane latex injection in the cannulated MFCA was performed to validate MRI findings and to assess for vessel integrity after the surgical dislocation.Introduction:
Methods:
Successful total joint arthroplasty requires accruate and reproducible acetabular component position. Acetabular component malposition has been associated with complications inlcuding dislocation, implant loosening, and increased wear. Recent literature had demonstrated that high-volume fellowship trained arthroplasty surgeons are in the “safe zone” for cup inclination and anteversion only 47% of the time. (1) Computer navigation has improved accuracy and reproducibility but remains expensive and cumbersome to many hospital and physicians. Patient specific instrumentation (PSI) has been shown to be effective and efficient in total knee replacements. The purpose of this study was to determine in a cadaveric model the anteversion and inclination accuracy of acetabular guides compared to a pre-operitive plan. 8 fresh-frozen cadaveric pelvis specimens underwent Computer Tomography (CT) in order to create a 3D reconstruction of the acetabulum. Based on these 3D reconstruction, a pre-operative plan was made positioning the patient specific acetabulum guides at 40 degrees of inclination and 20 degrees of anteversion in the pelvis.(Figure 1) The guides were created based on the specific bony morphology of the acetabular notch and rim. The guides were created using a 3D printer which allowed for precise recreation of the virtual model. 7 cadaveric specimens underwent creation and implantation of a acetabular guide specific to each specimens bony morphology. Ligamentum, pulvinar, and labum were removed for each cadaver prior to implantation to prevent soft tissue obstruction. The guides were inserted into the acetabular notch with the final position based on the fit of the guide in the notch. (Figure 2) Post-implantation CT was then performed and inclination and anteversion of the implanted guide measured and compared to the preoperative plan.Introduction:
Methods:
