Objectives

Periprosthetic femoral fractures (PFFs) have a higher incidence with cementless stems. The highest incidence among various cementless stem types was observed with double-wedged stems. Short stems have been introduced as a bone-preserving alternative with a higher incidence of PFF in some studies. The purpose of this study was a direct load-to-failure comparison of a double-wedged cementless stem and a short cementless stem in a cadaveric fracture model.

Despite high success rates following total knee arthroplasty (TKA), knee kinematics are altered following TKA. Additionally, many patients report that their reconstructed knee does not feel ‘normal’ [1], potentially due to the absence of the anterior cruciate ligament (ACL), an important knee stabilizer and proprioceptive mechanism. ACL-retaining implants have been introduced with the aim of replicating native knee kinematics, however, there has yet to be a detailed comparison between knee kinematics in the native knee and one reconstructed with an ACL-retaining implant.

Six fresh-frozen right legs (77±10 yr, 5 male) were mounted in a kinematic rig and subjected to squatting (40°-105°) motions. The vertical positon of the hip was manipulated with a linear actuator to induce knee flexion while the quadriceps were loaded with an actuator to maintain a vertical load of 90 N at the ankle [2]. Medial/lateral hamstring forces were applied with 50 N load springs. During testing, an infrared camera system recorded the trajectories of spherical markers rigidly attached to the femur and tibia. Two trials were performed per specimen. Following testing on the native knee, specimens were implanted with an ACL-retaining TKA (Vanguard XP, Zimmer Biomet) and all trials were repeated. Three inlay thicknesses were tested to simulate optimal balancing as well as over- (1 mm thicker) and understuffing (1 mm thinner) relative to the optimal thickness.

Pre-operative computed tomography scans allowed identification of bony landmarks and marker orientation, which were used define anatomically relevant coordinate systems. The recorded marker trajectories were transformed to anatomical translations/rotations and resampled at increments of 1° of knee flexion. Translations of the medial and lateral femoral condyle centers were scaled to maximum anterior-posterior (AP) width of the medial and lateral tibial plateau, respectively. For all kinematics, statistical analysis between knee conditions was conducted using repeated measures ANOVA in increments of 10° knee flexion.

Internal rotation of the tibia was significantly lower (p<0.05) for the three reconstructed conditions relative to the native knee at flexion angles of 60° and below. No significant differences in tibial rotation were observed between the balanced, overstuffed, or understuffed conditions. The varus orientation was not significantly influenced by implantation, regardless of inlay thickness, for all flexion angles. At 40° flexion, the AP position of the femoral medial condyle was significantly more anterior for the native knee relative to the balanced and understuffed conditions. This finding was not significant for the other flexion angles. No significant differences were found for the lateral condyle center AP position at any flexion angle.

Preservation of the cruciate ligaments during total knee arthroplasty may allow better physiologic representation of knee kinematics. The implants tested in this study were able to replicate kinematics of the native knee, except for tibial rotation and AP position of the medial femoral condyle in early knee flexion. Interestingly, the impact of inlay thickness was generally small, suggesting some tolerance in the choice of inlay thickness.

The use of neck modular adapter is a relative new solution for hip revision arthroplasty. This device assure a lot of advantages for the orthopaedic surgeon because Bioball can be use in different situations in order to solve different complications: hip prosthesis dislocation, correction of length (up to +21mm), save an old stem not mobilized, reduction of operation length.

The hip prosthesis dislocation, in spite of the continuous progress of implants’ materials and design, is still an actual event in the orthopaedic clinical practice, both after total hip replacement or a endoprosthesis. Furthermore, dislocation has an important social-economic impact because of a protracted hospitalization and rehabilitation and elevated costs of an eventual revision. Although using heads with a diameter larger than 28 mm we obtain virtually a greater range of motion, with a contemporary increase of degree necessary to cause the head-neck impingement, the risck of dislocation hasn’t a significant increase using head with a diameter of 22 mm.

Neck modular adapters (Bioball) allow to correct easily the biomechanics parameters of the dislocated prosthesic joint, avoiding the revision of the stem. Other indications for the use of the neck modular adapter are total hip replacement and intraoperatory correction of the limb length. Vantages are the possibilty to obtain a great range of motion through a small thickness of the 12/14 adapter, the possibility to extend the limb length up to 21 mm and to use ceramic heads during revisions, because the combination head/neck has a tribological unweared surface. In fact, in normal conditions, if the stem is not mobilizated, the use of ceramic head is rash; the Bioball adapter, instead, can be used with a old stem, so we can set a ceramic head. Every stem with a Biolox cone can be combined with a metal or ceramic head up to the 5XL size (+21 mm) through a Bioball adapter; in this way the cup is not removed.

We have two kinds of neck modular adapters: 12/14 allow both to extend the neck and to correct the offset, and 14/16 that allow to extend only the neck, because of the largest diameter of the prosthesic neck and the small thickness of the adapter. For these neck modular adapters exist different sizes, from M to 5XL (+21mm). Recently to these two types of Bioball were introduced also solutions for special stems (like for Exeter, ABG I, ABGII, PCA and others) We have also proving heads and necks. The proving and definitive heads have to be of the Bioball system because these are inserted on a modular neck with a no-standard diameter.

In the common practice the use of these adaptors has not to be considered as a routinary procedure, but have to be taken in consideration as a valid aid for orthopaedic surgeon to quickly and less invasively, solve technically demanding procedures with a real benefit for high-surgical risk patients.

Femoral off-set is the perpendicular distance between femur longitudinal axle and the femoral head’s rotation’s centre. Femoral off-set influences following yardsticks: stability of the joint, range of movement (ROM), muscular forcibleness, solicitations on the femoral component and acetabular component’s usury. From numerous radiographies studies, is shown as off-set is not an indefeasible measure, but an average with a range of variability. Offset is one of the most important yardsticks to consider during the pre-operating planning since, as is broadly documented, it has a positive effect on the functionality of the prosthesis; difficulty remains to individualize the optimal offset value in patient with bilateral coxofemural pathology or carriers of opposite side total hip prosthesis. Modular necks act indipendently in three spatial variables allowing to reach 27 points in the space, disposing of heads with three lenghts the real disponibility become of 81 points.

Usually we estimate the sizes and the orientation of the components manually and through a radiographic intra-operative control in order to choose the best match head-neck.

If we make a minimum mistake in cup position, the use of modular necks allow to correct this failure to obtain the most correct anatomic position producing negligible debris and the reduction of the mechanic stress.

Basing on our experience we think that the possibility to change length and version independently and sequentially is the unique technique avaible to correct the implant’s orientation, even if in our series we have choose neutral neck in most cases. To obtain better functional outcome we are studing a device based on gait analysis and superficial electromyography to calculate pre and post operative off-set. The data that we have achieved are still too few to be able to produce results; if there is possible, presenting them in future editions.