Aims

Despite numerous studies on periprosthetic joint infections (PJI), there are no robust data on the risk factors and timing of metachronous infections. This study was performed to answer the following questions: 1) Is there any difference of manifestation time of metachronous PJIs between different localizations of multiple artificial joints? 2) Can we identify any specific risk factor for metachronous PJIs for different localizations of multiple artificial joints?

Aim

The prevalence of unexpected positive cultures (UPC) in aseptic revision surgery of the joint with a prior septic revision procedure in the same joint remain unknown. The purpose of this study was to determine the prevalence of UPC in aseptic revisions performed in patients with a previous septic revision in the same joint. As secondary outcome measure, we explore possible risk factors associated with UPC and the re-revision rates.

Aim

Alpha-defensin was recently introduced as a new biomarker having a very high accuracy to rule out periprosthetic joint infection (PJI). A new rapid lateral flow version of the Alpha-defensin test was developed and introduced to detect high levels of Alpha-defensin in synovial fluid quickly and with ease. We conducted a single-centre prospective clinical study to compare the results of the Alpha-defensin rapid test* against the conventional diagnostics according to MSIS criteria.

Introduction

High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee by shifting the center of force towards the lateral compartment. The amount of alignment correction to be performed is usually calculated prior to surgery and it's based on the patient's lower limb alignment using long-leg radiographs. While the procedure is generally effective at relieving symptoms, an accurate estimation of change in intraarticular contact pressures and contact surface area has not been developed. Using electromyography (EMG), Meyer et al. attempted to predict intraarticular contact pressures during gait patterns in a patient who had received a cruciate retaining force-measuring tibial prosthesis. Lundberg et al. used data from the Third Grand Challenge Competition to improve contact force predictions in total knee replacement. Mina et al. performed high tibial osteotomy on eight human cadaveric knees with osteochondral defects in the medial compartment. They determined that complete unloading of the medial compartment occurred at between 6° and 10° of valgus, and that contact pressure was similarly distributed between the medial and lateral compartments at alignments of 0° to 4° of valgus. In the current study, we hypothesised that it would be possible to predict the change in intra-articular pressures based on extra-articular data acquisition.

Injuries to the posterior cruciate ligament (PCL) and the posterolateral corner (PLC) of the knee remain a challenging orthopaedic problem. Studies evaluating PCL and PLC reconstruction have failed to demonstrate a strong correlation between the degree of knee laxity as measured by uniplanar testing and subjective outcome or patient satisfaction. The effect that changing the magnitude of posterior tibial slope has on multiplanar, rotational stability of the PCL-deficient knee has yet to be determined. We aimed to evaluate the effect that changes in posterior tibial slope would have on static and dynamic stability of the PCL-PLC deficient knee.

Ten knees were used for this study. Navigated posterior drawer and standardised reverse mechanised pivot shift maneuvers were performed in the intact knee and after sectioning the PCL, the lateral collateral ligament (LCL), the popliteofibular ligament (PFL) and the popliteus muscle tendon (POP). Navigated high tibial osteotomy (HTO) was performed to obtain the desired change in tibial plateau slope (+5® or −5® from native slope). We then repeated the posterior drawer and the reverse mechanised pivot shift test for each of the two altered slope conditions.

Mean posterior tibial translation during the posterior drawer in the intact knee was 1.4 mm (SD = 0.48 mm). In the PCL-PLC deficient knee, posterior tibial translation increased to 18 mm (SD = 5.7 mm) (P < 0.001). Increasing the amount of posterior tibial slope by 5® reduced posterior tibial translation to 12 mm (SD = 4.7 mm) (P < 0.01). Decreasing the amount of posterior slope by 5® compared to the native knee, increased posterior tibial translation to 21 mm (SD = 6.8 mm) (P < 0.01). There was a significant negative correlation between the magnitude of tibial plateau slope and the magnitude of the reverse pivot shift (R2 = 0.71; P < 0.0001).

Mean posterior tibial translation during the reverse mechanised pivot shift test in the intact knee was 7.8 mm (SD = 2.8 mm). In the PCL-PLC deficient knee, posterior tibial translation increased to 26 mm (SD = 5.6 mm) (P < 0.001). Increasing the amount of posterior tibial slope by 5® reduced posterior tibial translation to 21 mm (SD = 6.7 mm) (P < 0.01). Decreasing the amount of posterior slope by 5® compared to the native knee, increased posterior tibial translation to 34 mm (SD = 8.2 mm) (P < 0.01). There was a significant negative correlation between the magnitude of tibial plateau slope and the magnitude of the reverse pivot shift (R2 = 0.72; P < 0.0001).

Decreasing the magnitude of posterior slope of the tibial plateau resulted in an increase in the magnitude of posterior tibial translation during the posterior drawer and the reverse mechanised pivot shift test in the PCL-PLC deficient knee. Conversely, increasing the slope of the tibial plateau reduced the amount of posterior tibial translation during the posterior drawer and the reverse mechanised pivot shift test. However, the effect of the increase in slope was not sufficient to reduce posterior tibial translation to levels similar to those of the intact knee.

Accurate and reliable registration of the ankle center is a necessary requirement in computer-assisted TKR. There is debate among surgeons over which registration procedure more accurately reflects the true center of the ankle joint. The aim of this study was to compare two different ankle registration landmarks on radiographs and determine how much they differed from the anatomic center of the talus in the frontal plane. Specifically, we asked what the average deviation in tibial mechanical axis registration would be when registering the ankle center using: A) the extreme medial and lateral points; and B) the most distal points, of the respective malleoli. A second question was whether or not BMI had any significant effect on mechanical axis registration error.

We reviewed the preoperative hip-to-ankle radiographs of 40 patients who underwent navigated TKR at our institution. The patient cohort was composed of 32 females and 7 males, with a mean age of 69 years (range, 45–84 years) and a mean BMI of 29.9 (range, 14.7–43.3). All radiographs were stored in and reviewed using PACS.

No clinically significant divergence from the anatomic center of the ankle was seen when using the Extremes Midpoint technique (mean divergence = 0.2® lateral; SD = 0.5®; 95% CI = −0.3®, −0.1®) or the Distal Midpoint technique (mean divergence = 0.2® lateral; SD = 0.6®; 95% CI = −0.39®, 0®). The mean difference between both techniques was 0.02® (SD = 0.3®; 95% CI = −0.1®, 0.1®; P = 0.68). BMI had no significant effect on the divergence from the true ankle center for either the Extremes Midpoint (R² = 0.002; P = 0.78) or the Distal Midpoint techniques (R² = 0.004; P = 0.90).(Figure 2)

The center of the ankle, as determined by using the Extremes Midpoint technique, lied 1.1 mm (SD = 2.6 mm; 95% CI = −1.9 mm to −0.3 mm) from the anatomic axis of the tibia. When determined using the Distal Midpoint technique, the center of the ankle lied 1.7 mm (SD = 2.3 mm; 95% CI = −2.5 mm to −0.98 mm) from the anatomic axis. Although statistically significant (P = 0.028), this difference was not clinically relevant (<3 mm). BMI had no significant effect on these differences (R² = 0.07; P = 0.11; R² = 0.02, P = 0.38).(Figure 3)

There is no significant difference between ankle registration using the Extremes Midpoint or the Distal Midpoint techniques and the anatomic center of the ankle. Patients' BMI does not seem to affect the registration of the ankle center with either technique.