Introduction

Despite well-fixed implants, persistent pain following total hip arthroplasty (THA) remains a concern. Various surgical approaches have been advocated, yet whether patient-reported pain differs amongst techniques has not been investigated. This study's purposes were to determine differences in patient-reported pain based on surgical approach (direct anterior –DA versus posterolateral-PL) or PL approach incision length. Our hypothesis was that no differences in patient-reported pain would be present.

The purpose of this randomized controlled trial is to evaluate the efficacy of using dilute betadine versus sterile saline lavage in aseptic revision total knee (TKA) and hip (THA) arthroplasty to prevent acute postoperative deep periprosthetic joint infection (PJI).

Of the 450 patients that were randomized, 5 did not have 90-day follow-up, 9 did not receive the correct treatment, and 4 were excluded for intraoperative findings consistent with PJI. 221 Patients (144 knees and 77 hips) received saline lavage only and 211 (136 knees and 75 hips) received a three-minute dilute betadine lavage (0.35%) prior to wound closure. Patients were observed for the incidence of acute postoperative deep PJI within 90 days of surgery. Statistical analysis was performed using t-tests or Fisher's exact test where appropriate. Power analysis determined that 285 patients per group are needed to detect a reduction in the rate of PJI from 5% to 1% (alpha=0.05, beta=0.20).

There were seven PJIs in the saline group and one in the betadine lavage group (3.2% vs. 0.5%, p=0.068). There were no significant differences in any baseline demographics between groups suggesting appropriate randomization.

Although we believe the observed difference between treatments is clinically relevant, it was not statistically significant with the sample size enrolled thus far and enrollment is ongoing. Nonetheless, we believe that these data suggests that dilute betadine lavage is a simple method to reduce the rate of acute postoperative PJI in patients undergoing aseptic revision procedures.

To assess clinical outcomes, metal ion levels, and periprosthetic femoral bone mineral density (BMD) in young, active patients receiving a modular dual mobility acetabulum and recently introduced titanium, proximally coated, tapered femoral stem design.

This was a prospective study of patients  65 years of age, with a BMI  35 kg/m², and UCLA activity score > 6 who received a modular cobalt chrome acetabular liner, highly cross-linked polyethylene mobile bearing, and cementless titanium femoral stem for their primary THA. Patients with a history of renal disease and metal hardware elsewhere in the body were excluded. All patients had a minimum of 2-year clinical follow-up.

Patient reported outcome measures, whole blood metal ion levels (ug/L), and periprosthetic femur BMD were measured at baseline and at 1- and 2-years postoperatively.

43 patients (30 male, 13 female; mean age 52.6 ± 6.5 years) were enrolled. Harris Hip Scores improved from 54.1 ± 20.5 to 91.2 ± 10.8 at 2 years postoperatively (p<0.001). All patients had radiographically well-fixed components, no patients have sustained an instability event, and no patients have required a return to the operating room or revision procedure.

Mean cobalt levels increased from 0.065 ± 0.03 ug/L preoperatively to 0.30 ± 0.51 at 1-year postoperatively (p=0.01), but decreased at 2 years postoperatively to 0.16 ± 0.23 (p=0.2) (Table 1). Four patients (9.3%) had a cobalt level outside the reference range (0.03 to 0.29ug/L) at 2 years postoperatively with values from 0.32 to 0.94. None were symptomatic

The mean femoral BMD ratio was maintained in Gruen zones 2 thru 7 at both 1- and 2-years postoperatively using this stem design (Table 2). At 2 years postoperatively, BMD in the medial calcar was 101.5% of the baseline value.

Use of a modular dual mobility prosthesis and cementless, tapered femoral stem has shown encouraging results in young, active patients undergoing primary THA. Elevation in mean cobalt levels and the presence of four patients outside the reference range at 2 years postoperatively demonstrates the necessity of continued surveillance in this cohort.

For any figures or tables, please contact authors directly: barrackr@wustl.edu

Achievement of adequate exposure in revision total knee arthroplasty is critical as it reduces the surgical time, enhances the ability for both component removal and reconstruction, and avoids devastating complications such as extensor mechanism disruption. However, this can be challenging as prior multiple surgeries and limited mobility contribute to a loss of tissue elasticity, thickened capsular envelope, and peri-articular soft tissue adhesions. A thorough pre-operative assessment of a patient's past surgical history, comorbidities, pre-operative radiographs (i.e. the presence of severe patella baja), and physical examination including range of motion, prior incisions, and soft tissue pliability are useful in determining the appropriate surgical techniques necessary for a successful revision.

A systematic approach to the ankylosed knee is critical. Most techniques are geared towards mobilization of the extensor mechanism to safely displace the patella for component exposure. The initial exposure should consist of a long skin incision, a subperiosteal medial release, and debridement of suprapatellar, medial, and lateral adhesions to the femoral condyles. A lateral capsular release can prove helpful in further mobilization of the extensor mechanism. When performing a medial parapatellar arthrotomy it's important to keep in mind further extensile exposure techniques that may be required. For example, the arthrotomy should not extend proximally into the vastus intermedius or rectus femoris in the event that a quadriceps snip technique is to be used as this can compromise the ability to repair this exposure.

Despite a large exposure and release of adhesions, sometimes the extensor mechanism remains at risk of rupture and adequate visualization cannot be obtained. In this event, extensile exposures such as a quadriceps snip, quadriceps turndown or tibial tubercle osteotomy are considered. The location of the patella often dictates the best exposure option as severe patella baja may not be overcome with a proximally based release. The quadriceps snip is most commonly used and provides improved exposure without the necessity of modifying the patient's post-operative rehabilitation. In addition, it can be extended to a quadriceps turndown which vastly improves visualization, but at the expense of needing to immobilise the knee post-operatively. A tibial tubercle osteotomy can also be used and provides excellent exposure especially in the case of severe patella baja or when removal of a cemented tibial stem is required. It preserves the extensor muscles, but risks include increased post-operative wound drainage due to limited soft tissue coverage, failure of fixation, or fracture of the tibial tubercle fragment or tibial shaft.

Exposure in revision total knee arthroplasty is critical. Fortunately, this can be reliably achieved with a systematic approach to the knee and through the use of several extensile exposures at the surgeon's discretion.

Prior implant designs have relied on a four-bar link theory and featured J-curve femoral components intended to recreate femoral rollback of the native knee, but this design could lead to anterior femoral sliding or paradoxical motion. Recent kinematic analyses of the native human knee have shown the medial compartment to be more stable to anteroposterior translation than the lateral, resulting in a “medial pivot” motion as the knee flexes. “Medial pivot” designs in total knee arthroplasty were introduced in the 1990s to attempt to re-create this motion. They consist of an asymmetric tibial insert with a highly congruent medial compartment and less conforming lateral compartment. The femoral component has a single radius of curvature and a high degree of conformity.

In vivo fluoroscopic studies have shown medial pivot designs to be successful in achieving its intended motion, while other cruciate-retaining designs had a higher incidence of paradoxical anterior translation and lateral condylar lift-off. Furthermore, numerous investigations have shown medial pivot designs to have excellent outcomes and survivorship at up to 10 years post-operatively. However, the contention in this debate that medial pivot designs avoid the need for ligament balancing is incorrect. Appropriate ligament balancing remains a crucial aspect of any successful total knee arthroplasty and is no less important based on the implant design utilised.

In the Methods section of all prior reports using a medial pivot design, the authors have noted that appropriate ligament balancing was obtained both in flexion and extension consistent with the recommended technique with other primary TKA implant designs. From a kinematic standpoint, this makes absolute sense. If a patient has a valgus imbalance with loose medial structures, then as the knee is brought into flexion the femur will not maintain congruency and contact with the conforming tibial surface – thus the medial pivot motion will be lost. Thus, balancing remains critical.

Lastly, although not the focal point of this debate, whether re-creation of a medial pivot motion in total knee arthroplasty actually improves patient outcomes remains an area of debate. A recent investigation by Warth and Meneghini, et al. demonstrated that re-creation of a medial-pivot pattern intra-operatively did not correlate with patient-reported outcomes at 1-year post-operatively. Thus, although the concept of a medial pivot design has merit, whether this will consistently improve outcomes and patient satisfaction remains to be seen.

Venous thromboembolic (VTE) events including deep vein thrombosis (DVT) and pulmonary embolism (PE) remain a significant concern following total joint arthroplasty. The American Academy of Orthopaedic Surgeons (AAOS) guidelines for VTE prophylaxis have focused on the safety of prophylactic regimens, with the primary endpoint being prevention of symptomatic events while avoiding the risks of hematoma, infection, and re-operation associated with aggressive anticoagulation. In 2007, the AAOS clinical practice guideline recommended “risk stratification” of patients for VTE events and bleeding. Unfortunately, there remains limited evidence as to specific factors that should be used during pre-operative risk stratification.

A prior investigation has demonstrated the effectiveness of using a history of VTE events, active cancer, and hypercoagulable state (i.e. Factor V Leiden) as criteria for high-risk patients undergoing total joint arthroplasty. In addition, large national database systems have been used to identify risk factors for VTE events. Unfortunately, these investigations emphasise different risk factors and their importance in increasing the risk of VTE events. Thus, criteria to be used for risk stratification of patients undergoing total joint arthroplasty remain unclear. What remains clear is that even in healthy patients who are aggressively anticoagulated, a VTE event can still occur.

There has been a renewed interest in the importance of achievement of a neutral, mechanical alignment in total knee arthroplasty (TKA). The purpose of this presentation is to argue the merits behind questioning a neutral, mechanical alignment following TKA, and why the concepts of “constitutional varus” and “kinematic alignment” deserve further investigation.

The impact of alignment on outcomes following TKA has been questioned for a number of reasons. First, recent investigations have highlighted that approximately 20% of patients are not satisfied with their outcome following TKA. Second, recent studies have shown that achievement of a mechanical axis within 3 degrees of neutral does not necessarily improve survivorship or clinical outcomes. Third, as patients requiring TKA have a wide array of morphologies and alignment, targeting the exact same alignment for each patient has been questioned. Lastly, despite the advent of new implant designs with proposed benefits of improved kinematics, few studies have shown a clinical improvement with their use.

The concept of “constitutional varus” has suggested that restoration of a neutral, mechanical alignment may not be desirable and unnatural as 32% of men and 17% of women have a natural mechanical alignment of greater than 3 degrees at skeletal maturity. The “kinematic alignment” technique focuses on restoration of the joint line of the distal femur, posterior femur, and tibia to those of the non-arthritic, native knee. The kinematic alignment technique has shown promising results. However, while these concepts have merit, questions still remain regarding the optimal alignment target for each, individual patient.

Background: Metal sensitivity following total joint arthroplasty (TJA) has been of increased concern, but the impact of a patient-reported metal allergy on clinical outcomes has not been investigated. The purpose of this study was to report the incidence and impact of patient-reported metal allergy following total knee (TKA) and total hip arthroplasty (THA).

Methods: This was a retrospective, IRB-approved investigation of patients undergoing a primary, elective TJA between 2009 and 2011. All patients completed a pre-operative questionnaire asking about drug and environmental allergies. In January of 2010, a specific question was added regarding the presence of a metal allergy. UCLA Activity, SF-12, Modified Harris Hip (MHHS), and Knee Society (KSS) scores were collected pre-operatively and at most recent follow-up. Overall cohorts of metal allergy and non-metal allergy patients were compared and a 1:2 matching analysis was also performed.

Results: 906 primary THAs and 589 primary TKAs were included. The incidence of patient-reported metal allergy was 1.7% before January 2010 and 4.0% after (overall 2.3% of THAs and 4.1% of TKAs). 97.8% of metal allergy patients were female. Following TKA, post-operative KSS function, symptoms, satisfaction, and expectation scores were all decreased in the metal allergy cohort (p<0.001 to 0.002). Following THA, metal allergy patients had a decreased post-operative SF-12 MCS score and less incremental improvement in their SF-12 MCS score versus the non-metal allergy cohort (p<0.0001 and p<0.001).

Conclusion: Patient-reported metal allergy is associated with decreased functional outcomes following TKA and decreased mental health scores following THA.

Aims

The purpose of our study is to summarise the current scientific findings regarding the impact of obesity on total hip arthroplasty (THA); specifically the influence of obesity on the timing of THA, incidence of complications, and effect on clinical and functional outcomes.

Aims

The purpose of this article was to review the current literature pertaining to the use of mobile compression devices (MCDs) for venous thromboembolism (VTE) following total joint arthroplasty (TJA), and to discuss the results of data from our institution.

A recent proposed modification in surgical technique in total knee arthroplasty (TKA) has been the introduction of patient specific instrumentation or custom cutting guides (CCGs). With CCGs, preoperative three-dimensional imaging is used to manufacture cutting blocks specific to a patient's native anatomy, with proposed benefits including their ease of use; a decrease in operative times and instrument trays and improved cost-efficiency; the ability to preoperative plan component size, alignment, and position; and an improvement in postoperative alignment versus the use of standard instrumentation. However, to date the majority of reports have not confirmed these proposed benefits.

Prior studies focusing on cost-efficiency have shown limited benefits in terms of operating and room turnover times, which fail to offset the additional cost of preoperative imaging and fabrication of the CCGs. Furthermore, a number of reports have noted the frequent need for surgeon-directed changes and alterations in alignment intraoperatively, along with errors in the predetermined implant size. The use of CCGs has also failed to improve overall mechanical and component alignment versus standard instrumentation in the majority of investigations. Perhaps most importantly, no investigation has demonstrated CCGs to improve clinical outcomes postoperatively. Therefore, in the absence of proven clinical or radiographic improvements, the continued implementation of CCGs must be questioned.

Venous thromboembolic events (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE), remain one of the most common complications following total joint arthroplasty. Reported rates of symptomatic VTE following THA and TKA range from 0.83% to 15% and 2% to 10%, respectively. Thus, VTE prophylaxis should be routinely administered following total joint arthroplasty. However, while orthopaedic surgeons have considerable flexibility regarding their VTE prophylaxis regimen, it remains unclear which is optimal.

Patients at low risk of VTE may receive excessive anticoagulation and unnecessarily risk further perioperative morbidity (wound complications, bleeding) following total joint arthroplasty. With an evolving health care landscape, emphasis on complications and readmissions, and shorter inpatient hospitalizations, it is imperative that a VTE prophylaxis regimen is simple, effective, easy to monitor, and has high patient compliance. Mobile pneumatic compression devices (MCDs) have been used with greater frequency following total joint arthroplasty, with multiple reports demonstrating their effectiveness in VTE prevention with or without the addition of aspirin for chemical prophylaxis. The use of MCDs allows the avoidance of more aggressive anticoagulation in the majority of patients undergoing total joint arthroplasty, decreases the incidence of wound complications, and achieves a low overall incidence of symptomatic VTE. Future investigations are necessary to determine the necessity and impact of the addition of aspirin to the use of MCDs for VTE prophylaxis.

The optimal overall lower extremity and component alignment in total knee arthroplasty (TKA) has recently been questioned, yet the majority of studies demonstrate TKA positioning to effect the rate of implant loosening, polyethylene stresses, knee kinematics, and gait. Most commonly, extramedullary tibial and intramedullary femoral alignment guides are used to set coronal alignment in TKA, but these “conventional” methods have a limited degree of accuracy. The goal of obtaining more precise and accurate component positioning has led to the development of computer-assisted surgical (CAS) techniques. Although numerous comparative studies have shown significant improvements with the use of CAS techniques, concerns over increased operative times, large capital costs, and the learning curve associated with their use have limited their widespread acceptance.

Recently, handheld navigation devices have been introduced with the goal of providing the accuracy of large-console CAS systems in an easy-to-use manner. These devices rely on accelerometer-based navigation to set cutting guide alignment relative to the mechanical axes of the femur and tibia. Unlike most CAS systems, handheld navigation systems avoid the use of additional pin sites and reference arrays in the femur and tibia, do not require a large computer with an infrared camera, and thus eliminate intraoperative line of site issues between the camera and tracking arrays. Several investigations have demonstrated handheld navigation devices to provide the same degree of alignment accuracy as large-console CAS systems, thus improving the ability of a surgeon to achieve their intraoperative targets for coronal alignment during TKA.

Predictable fracture healing fails to occur in 5–10% of cases. This is particularly concerning among individuals with osteoporosis. With an increasing aging population, one in three women and one in five men above the age of 50 experience fragility fractures. As such, there is a critical need for an effective treatment option that could enhance fracture healing in osteoporotic bone. Lithium, the standard treatment for bipolar disorder, has been previously shown to improve fracture healing through modulation of the Wnt/beta-catenin pathway. We optimised the precise oral lithium administration parameters to improve mechanical strength and enhance healing of femoral fractures in healthy rats. A low dose of Lithium (20 mg/kg) administered seven days post fracture for a two week duration improved torsional strength by 46% at four weeks post fracture compared to non-treated animals. Application of lithium to enhance fracture healing in osteoporotic bone would have a significant healthcare impact and requires further study. Aim: To evaluate the efficacy of optimal lithium administration post fracture on quality of fracture healing in a rat osteoporotic model. Hypothesis: Lithium treatment in osteoporotic rats will improve the structural and mechanical properties of the healing bone despite the impaired nature of bone tissue.

Sprague Dawley female rats (∼350 g, age ∼3 months) were bilaterally ovariectomised and maintained for 3 months to establish the osteoporotic phenotype. A unilateral, closed mid-shaft femoral fracture was created using a weight-drop apparatus. At seven days post fracture, the treatment group received 20 mg/kg-wt lithium chloride via oral gavage daily for 14 days. The control group received an equivalent dose of saline. All animals were sacrificed at day 28 and the femurs harvested bilaterally. Treatment efficacy was evaluated based on torsional loading and stereologic analysis.

Lithium treatment positively impacted the healing femurs, with an average yield torque ∼1.25-fold higher than in the saline group (200±36 vs. 163±31 N-mm, p=0.15). Radiographically, the lithium-treated rats had a high level of restored periosteal continuity, larger bridging and intercortical callus at the fracture site. These hallmarks of healing were generally absent in the saline group. The Lithium group had significantly higher total volume (624±32 vs. 568±95 mm3), lower bone volume fraction (41±4 vs. 50±5%) and higher theoretical torsional rigidity (477±50 vs. 357±93 kN-mm2) compared to the saline group. Torsional strength and stereology values were similar for the contralateral femurs of the two groups.

Lithium was found to enhance fracture healing in osteoporotic bone under the dosing regimen optimised in healthy femora. This is promising data as treatment represents an easily translatable pharmacological intervention for fracture healing that may ultimately reduce the healthcare burden of osteoporotic fractures.

The T-lymphocyte secreted pro-inflammatory cytokine, interleukin-17F (IL-17F), was found to be a key mediator in the cellular response of the immune system in the early phase of fracture repair but its intracellular signaling processes are currently not known in osteoblasts. The objective of this study was to identify the signaling proteins and crucial gene targets involved in osteoblast activation via IL-17F. It was hypothesised that IL-17F stimulated osteoblast maturation through a novel GSK3beta / beta-catenin independent pathway.

Mouse pre-osteoblast cell line (MC3T3-E1) was used for IL-17F or Wnt3a treatment. Desired proteins were detected using western blot analysis (antibodies: Phospho-GSK-3beta (Tyr 216), Phospho-GSK-3beta (Ser9), Runx2/cbfa1, TRAF6, Act1, p-ERK2, p-JNK and p-MAPK, C/EBP-beta and & delta). Gene-specific siRNAs of mouse IL-17Ra, IL-17Rc and a non-targeting siRNA (control) were utilised. MC3T3-E1 were transfected with IL-17Ra, IL-17Rc or Negative Control and treated with IL-17F. Chromatin Immunoprecipitation (ChIP-qPCR) was used to evaluate the mouse Runx2 P1 promoter region.

IL-17F increased expression of Col1, BSP, Runx2/cbfa1 and osteocalcin in MC3T3-E1 cells. Western blot analysis confirmed expression of known Wnt signaling proteins TRAF6, Act1, p-ERK2, p-JNK and p-MAPK in both IL-17F and Wnt3a treated cultures, including up-regulation of Runx2/cbfa1, a key transcription factor associated with osteoblast differentiation. IL-17F up-regulation of Runx2/cbfa1 appears independent of the Wnt/beta-catenin pathway as phosphorylated GSK-3beta at the Ser9 site was not detected with IL-17F treatment. Despite this, IL-17F treatment still increased expression of Runx2/cbfa1 downstream, lending evidence for a GSK3beta/beta-catenin independent manner of IL-17F stimulated osteogenesis. While IL-17F and Wnt3a both induced expression of C/EBP-delta, only IL-17F treatment induced expression of C/EBP-beta, an upstream transcription factor of Runx2/cbfa1. Further, siRNA knock down of the IL-17 receptors directly decreased Act1, C/EBP-beta and Runx2/cfba1 expression. By ChIP analysis, IL-17F was shown to upregulate C/EBP-beta expression and stimulated its binding to the P1 Promoter of the Runx2/cbfa1 gene.

The C/EBP-beta transcription factor was shown to be a key regulator of early osteogenesis. C/EBP-beta up-regulates Runx2/cbfa1 expression by directly binding to the Runx2/cbfa1 P1 promoter in osteoblasts. C/EBP-beta was activated in the osteoblast by IL-17F but not by Wnt3a adding further support to a novel GSK3beta/beta-catenin independent pathway. Our data shows that IL-17F, a cytokine secreted by T-lymphocytes, stimulates osteoblast maturation through a novel GSK3beta/beta-catenin independent pathway and reveals a crucial interaction between C/EBP-beta and the Runx2/cbfa1 P1 promoter not previously been shown in osteogenesis signaling further.

Aims

This study investigated whether the use of tranexamic acid (TXA) decreased blood loss and transfusion related cost following surface replacement arthroplasty (SRA).

A national, multi-centre study was designed in which a questionnaire quantifying the degree of patient satisfaction and residual symptoms in patients following total knee replacement (TKR) was administered by an independent, blinded third party survey centre. A total of 90% of patients reported satisfaction with the overall functioning of their knee, but 66% felt their knee to be ‘normal’, with the reported incidence of residual symptoms and functional problems ranging from 33% to 54%. Female patients and patients from low-income households had increased odds of reporting dissatisfaction. Neither the use of contemporary implant designs (gender-specific, high-flex, rotating platform) or custom cutting guides (CCG) with a neutral mechanical axis target improved patient-perceived outcomes. However, use of a CCG to perform a so-called kinematically aligned TKR showed a trend towards more patients reporting their knee to feel ‘normal’ when compared with a so called mechanically aligned TKR

This data shows a degree of dissatisfaction and residual symptoms following TKR, and that several recent modifications in implant design and surgical technique have not improved the current situation.

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):96–100.

Obesity is a risk factor for acetabular malposition when total hip arthroplasty (THA) is performed with manual orientation techniques. However, conflicting evidence exists regarding the usefulness of computer-assisted surgery for performing THA in obese patients. The purpose of this study was to compare the precision and accuracy of imageless navigation for acetabular component placement in obese versus non-obese patients.

After institutional review board approval, 459 THA performed for primary hip osteoarthritis were reviewed retrospectively. The same imageless navigation system was used for acetabular component placement in all THA. During surgery the supine anterior pelvic plane was referenced superficially. THA was performed via posterolateral approach in the lateral position. A hemispherical acetabular component was used, with target inclination of 40° and target anteversion of 25°. Computer software was used to determine acetabular orientation on postoperative anteroposterior pelvic radiographs. Obese patients (BMI ≥ 30 kg/m2) were compared to non-obese patients. A 5° difference in mean orientation angles was considered clinically significant. Orientation error (accuracy) was defined as the absolute difference between the target orientation and the measured orientation. Student's t test was used to compare means. Hartley's test compared variances of the mean differences (precision). Fisher exact tests examined the relationship between obesity and component placement in the target zone (target ± 10°) for inclination and version. All statistical tests were two-sided with a significance level of 0.05.

Differences in mean inclination and anteversion between obese and non-obese groups were 1.1° (p=0.02 and p=0.08, respectively), and not clinically significant. Inclination accuracy trended toward improvement for non-obese patients (p=0.06). Inclination precision was better for non-obese patients (p=0.006). Accuracy and precision for anteversion were equal between the two groups (p=0.19 and p=0.95, respectively). There was no relationship between obesity and placement of the acetabulum outside of the target ranges for inclination (p=0.13), anteversion (p=0.39) or both (p=0.99), with a trend toward more inclination outliers in obese patients versus non-obese patients (7.3% versus 3.9%).

The observed differences in mean acetabular orientation angles were not clinically significant (< 5°), although inclination orientation was less accurate and precise for obese patients. In contrast to existing literature, we found no difference in the accuracy and precision with regard to anteversion in obese and non-obese patients. We propose that accurate superficial registration of landmarks in obese patients is achievable, and the use of imageless navigation likely improves acetabular positioning in obese and non-obese patients.

Surgeons often target the Lewinnek zone (40°±10° of inclination; 15°±10° of anteversion) for acetabular orientation during total hip arthroplasty (THA). However, matching native anteversion (20°-25°) may achieve optimal stability. The purpose of this study was to (1) determine incidence of early dislocation with increased target acetabular anteversion, and (2) report the accuracy of imageless navigation for achieving target acetabular position in a large, single-surgeon cohort.

A posterolateral approach with soft tissue repair was performed in the 553 THA meeting the inclusion criteria. The same imageless navigation system was used for acetabular component placement in all THA. Target acetabular orientation was 40° ± 10° of inclination and 25° ± 10° of anteversion. Computer software was used to measure acetabular positioning on 6-week postoperative anteroposterior pelvic radiographs. Incidence of dislocation within 6 months of surgery was determined. Repeated measures multiple regression using the Generalised Estimating Equations approach was used to identify baseline patient characteristics (age, gender, BMI, primary diagnosis, and laterality) associated with component positioning outside of the targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or the targeted zone. All tests were two-sided with a significance level of 0.05.

Mean inclination was 42.2° ± 4.9°, and mean anteversion was 23.9° ± 6.5°. 82.3% of cups were placed within the target zone. Variation in anteversion accounted for 67.3% of outliers. Only body mass index was associated with inclination outside the target range (p = 0.017), and only female gender was associated with anteversion outside the target range (p = 0.030). Six THA (1.1%) experienced early dislocation, and 3 THA (0.54%) were revised for multiple dislocations. There was no relationship between dislocation and component placement in either the Lewinnek zone (p = 0.224) or the target zone (p = 0.287).

This study demonstrates that increasing target acetabular anteversion using the posterolateral approach does not increase the incidence of early THA dislocation. However, the long-term effects on bearing surface wear and stability must be elucidated. The occurrence of instability even in patients within our target zone emphasises the importance of developing patient-specific targets for THA component alignment.

Introduction:

Concerns remain regarding both the toughness of alumina, and stability of zirconia ceramics in total hip arthroplasty (THA). A zirconia-toughened alumina (ZTA) bearing has been introduced, in which yttria-stabilized, zirconia polycrystals are uniformly distributed in an alumina matrix. The goal is to combine the wear resistance of alumina with the toughness of zirconia. Zirconia's toughness is attributed to a tetragonal to monoclinic (t-m) phase transformation that occurs in response to a crack, hindering its propagation; however, it might decrease material stability. The purposes of this study were to investigate the degree and position of metal transfer, and the occurrence of t-m phase transformation using Raman spectroscopy, in a series of retrieved, ZTA femoral heads.