Physiological kinematics is very difficult to restore after total knee arthroplasty (TKA). A new model of medial stabilized (MS) TKA prosthesis has a high spherical congruence of the internal compartment, which guarantees anteroposterior (AP) stability associated with a flat surface of the insert in the lateral compartment, that allows a greater AP translation of the external condyle during knee flexion. The aim of our study is to evaluate, by dynamic radiostereometric analysis (RSA), the knee in vivo kinematics after the implantation of a MS prosthesis during sit to stand and lunge movements. To describe the in vivo kinematics of the knee after MS Fixed Bearing TKA (GMK Sphere (TM) Medacta International AG, Castel San Pietro, Switzerland) using Model Based dynamic RSA.

A cohort of 18 patients (72.1 ± 7.4 years old) was evaluated by dynamic RSA 9 months after TKA. The kinematic evaluation was carried out using the dynamic RSA tool (BI-STAND DRX 2), developed at our Institute, during the execution of sit to stand and lunge movements. The kinematic data were processed using the Grood and Suntay decomposition and the Low Point method. The patients performed two motor tasks: a sit-to-stand and a lunge. Data were related to the flexion angle versus internal-external, varus-valgus rotations and antero-posterior translations of the femur with respect to the tibia.

During the sit to stand, the kinematic analysis showed the presence of a medial pivot, with a significantly greater (p=0.0216) anterior translation of the lateral condyle (3.9 ± 0.8 mm) than the medial one (1.6 ± 0.8 mm) associated with a femoral internal rotation (4.5 ± 0.9 deg). During the lunge, in the flexion phase, the lateral condyle showed a larger posterior translation than the medial one (6.2 ± 0.8 mm vs 5.3 ± 0.8 mm) associated with a femoral external rotation (3.1 ± 0.9 deg). In the extension phase, there is a larger anterior translation of the lateral condyle than the medial one (5.8 ± 0.8 mm vs 4.6 ± 0.8 mm) associated with femoral internal rotation (6.2 ± 0.9 deg). Analysing individual kinematics, we also found a negative correlation between clinical scores and VV laxity during sit to stand (R= −0.61) and that the higher femoral extra-rotation, the poorer clinical scores (R= 0.65).

The finding of outliers in the VV and IE rotations analysis highlights the importance of a correct soft tissue balancing in order to allow the prosthetic design to manifest its innovative features.

Anterior cruciate ligament (acl) reconstruction is one of the most commonly performed procedures in orthopedics for acl injury. While literature suggest short-term good-to-excellent functional results, a significant number of long-term studies report unexplained early oa development, regardless type of reconstruction. The present study reports the feasibility analysis and development of a clinical protocol, integrating different methodologies, able to determine which acl reconstruction technique could have the best chance to prevent oa. It gives also clinicians an effective tool to minimize the incidence of early oa.

A prospective clinical trial was defined to evaluate clinical outcome, biochemical changes in cartilage, biomechanical parameters and possible development of oa. The most common reconstruction techniques were selected for this study, including hamstring single-bundle, single-bundle with extraarticular tenodesis and anatomical double-bundle. Power analysis was performed in terms of changes at cartilage level measurable by mri with t2 mapping. A sample size of 42 patients with isolated traumatic acl injury were therefore identified, considering a possible 10% to follow-up. Subjects presenting skeletal immaturity, degenerative tear of acl, other potential risk factors of oa and previous knee surgery were excluded. Included patients were randomized and underwent one of the 3 specified reconstruction techniques. The patients were evaluated pre-operatively, intra-operatively and post-operatively at 4 and 18 months of follow-up. Clinical evaluation were performed at each time using subjective scores (koos) and generic health status (sf-12). The activity level were documented (marx) as well as objective function (ikdc).

Preliminary results allow to verify kinematic patterns during active tasks, including level walking, stair descending and squatting using dynamic roentgen sterephotogrammetric analysis (rsa) methodology before and after the injured ligament reconstruction. Intra-operative kinematics was also available by using a dedicated navigation system, thus to verify knee laxity at the time of surgery. Additionally, non-invasive assessment was possible both before the reconstruction and during the whole follow-up period by using inertial sensors. Integrating 3d models with kinematic data, estimation of contact areas of stress patterns on cartilage was also possible.

The presented integrate protocol allowed to acquired different types of information concerning clinical assessment, biochemical changes in cartilage and biomechanical parameters to identify which acl reconstruction could present the most chondroprotective behavior. Preliminary data showed all the potential of the proposed workflow. The study is on-going and final results will be shortly provided.

The main purpose of the present study was to determine long-term implant fixation of 15 unicompartmental knee arthroplasty (UKAs) with an all-poly tibial component using Roentgen stereophotogrammetric analysis (RSA) at a mean 10-year follow-up. The secondary purpose was to investigate whether the progressive loss of implant's fixation correlates with a reduction in Knee society score (KSS). Fifteen non-consecutive patients with primary knee osteoarthritis received a UKA with an all-poly tibial component were assessed using KSS scores pre-operatively and post-operatively and RSA on day 2 after surgery, then at 3, 6, and 12 months and yearly thereafter. The mean last follow-up was 10 years. An increase in maximum total point motion (MTPM) values from 6 months to 1 year post-operatively was found respect to post-operative reference. Implants’ displacement values were always 2 mm during the first 6 months, and then, two different trends were noticed in revised and non-revised implants. MTPM increase between 1 and 2 years of follow-up in non-revised UKAs was always 0.2 mm, whereas it was [0.2 mm in revised UKAs. A linear and negative correlation with statistical significance was found between MTPM and both clinical and functional KSS scores (p 0.001). Also in a long-term follow-up evaluation, RSA is an effective tool to predict functional results after an all-poly UKA providing also a relevant predictive value at 1 year follow-up, and this can be very useful for both patients and surgeons.

Background

Roentgen Stereophotogrammetric Analysis (RSA) represents nowadays an excellent solution for high-accuracy fixation measurement of UKAs. To date, to the best of our knowledge, no previous study has investigated long-term micromotions of a UKA using RSA. For this reason, the main purpose of the present study is to determine long-term implant fixation of 15 UKAs with all-poly tibial component using RSA at a mean 10-years follow-up. The secondary purpose was to investigate whether the progressive loss of implant's fixation correlates with a reduction of KSS scores.

Introdution:

Over the last years research has focused on attempts to achieve better fixation in knee prosthesis by improving cementing techniques and prosthetic designs; thus prosthetic fixation is critical while loosening at the bone-cement interface is still an important matter for the orthopaedic surgeon.

The Rizzoli Orthopaedic Institute has been involved in RSA since 1998. During last 25 years, several investigations have been carried on to evaluate both implant fixation and poliethylene deformation in unicompartmental and total knee replacements. Nevertheless, RSA has also been used to investigate the relative micromotions and the kinematic modifications in cadaveric models of ankles with ligamentous injuries. RSA evaluation has demonstrated that in a particular TKR implant, with mobile half-bearings, the threshold for loosening was 1.3° for rotation about the longitudinal axis and 0.5 mm for medio-lateral translation. Moreover, RSA has revealed cold flow to be concentrated in the posterior region of the medial half-bearing. This has lead to further improvement in polyethilene and implant design. RSA has also demonstrated that in all-poly tibial UKR, poliwear does not impair tibial component fixation and that deformation of the all-poly tibial component is strictly correlated to implant loosening. Moreover, RSA has been used to investigate stress-inducible displacement of the tibial component in all-poly UKRs. It has been demonstrated that rotations around the transverse axis of the knee joint are the most common form of stress-inducible displacement, while stress-induced translations are negligible. Moreover, stress-inducible translational displacement has reached significantly higher values for those patients with unexplained painful UKR, despite no sign of loosening on conventional radiographic and standard supine RSA evaluations.

Further application of RSA has focused on the kinematic evaluation of poliethilene motion pattern modifications throughout a 3 years follow-up period after a mobile-bearing TKR. Patients have been investigated in weight-bearing conditions and results demonstrated that longitudinal rotations and medio-lateral translations tended to increase at last follow-up, while sagittal translations dod not show any significant modification over time.

At present, a new device has been installed at the Istituto Ortopedico Rizzoli. It was specifically designed and made for RSA, static and fluoroscopic. This device can work both in mono- and bi-planar configuration as required by the RSA protocols. Moreover it is able to acquire image stacks in order to study the in-vivo and real time kinematics of a joint. he theoretical biomechanical resolution of a static RSA followup tests is 0.2 mm for translation and 0.3° for rotation. In fluoroscopic configuration the theoretical resolution is 1 mm for translation and 1° for rotations, depending on the used frame rate and on the joint movement speed. A kinematic comparison of different prosthetic designs is currently ongoing, to evaluate different motion patterns under dynamic weight-bearing conditions and to compare them with passive kinematics acquired intra-operatively using a navigation system.