In the last years custom-fit cutting guides using magnetic resonance imaging (MRI) were introduced by orthopedic surgeons for total knee arthroplasty (TKA). One of the advantages of these shape-fitting jigs is the possibility to transfer the preoperative planning of the TKA directly to the individual patient's bone. However, one has to be aware, that the jigs are designed for single-use and have to be custom made by an external manufacturer. This increases the cost of implantation and unlinks the surgeon from this process. In addition a potentially necessary adjustment of the preoperatively planned implant size and position in a surgical situation is not possible.

The purpose of our development was to combine the advantages of custom-fit cutting guides as a 3-D-computer-assisted planning tool with the option to adjust and improve the preoperative planning and the jig in the actual surgical situation. In addition no outside jig manufacturing would occur in this concept. This leaves the surgeon in control of the entire process.

The purpose of this study was to examine the reliability of this screw-based shape – fitting system. In order to do this we assessed the inter- and intra-observer reliability of the recurrent placement of the plate on a set of bone samples with preset screws.

We developed a plate with the dimension of 66 × 76 × 10 mm, containing 443 threaded holes. A connector for further instrumentation is mounted on the proximal part of the plate,. As the plate and the screws are made of aluminum and steel, sterilization is possible.

After computer tomography (CT) scans were taken from three human femoral bones, eight to nine variably positioned screws (50.45 mm length, 2.75 mm diameter), reversibly fixed by locknuts, formed an imprint of a bone's surface. For calculating precise screw positions, a computer-based planning software was developed resulting in a three-dimensional reconstruction of the bony surfaces. The plate was integrated in the 3-D reconstruction software. With a defined distance to the distal part of the femurs, allowed the proper length and position of the screws to be calculated. These calculations were transferred to the screws on the real plate.

In the next step the plate was positioned on the bony surface and after reaching the planned position the plate's connector was rigidly fixed to the bone. The plate was removed to give place to link saw jigs to the connector.

Planning and setting of the plate and the screws were conducted on three femoral bones.

Examinations were performed by five investigators with ten repetitions on each bone with three distinct plates. Intra- and inter-observer variability was assessed by measuring the variation in plate position between the trials.

The jigs were placed in a mean frontal tilting (medial to lateral) of 0.83°. The mean axial tilting (proximal to distal) was 1.66° and the mean shift on the axis from proximal to distal 8.48 mm. The shift and the tilting were significantly bone dependent but not user dependent. Compared with previous studies the deviation from the mechanical axis were comparable with conventional TKA (2.6° and 0.4°), computer assisted TKA (1.4° and 1.9°) and Custom-fit TKA (1.2°).

We developed a preoperative planning system for TKA that allows a transfer of the planning and the calculated imprint of the bones surface on a grid-plate during surgery by the surgeons themselves. Neither external manufacturers to create a fixed device nor a navigation system is necessary. Results showed the functioning of the screw – based shape fitting technique within the accuracy mentioned above. These findings are encouraging to do further research to examine the ideal number of screws to offer a perfect fitting.

INTRODUCTION

While standard instrumentation tries to reproduce mechanical axes based on mechanical alignment guides, a new “shape matching” system derives its plan from kinematic measurements using pre-operative MRIs. The current study aimed to compare the resultant alignment in a matched pair cadaveric study between the Shape Match and a standard mechanical system.

In minimally invasive direct anterior total hip arthroplasty double offset broach handles are used, in order to facilitate the preparation of the femoral canal. The maximum value of the main force peak and the impulse of two types of double offset broach handles (A European version, B American version) were compared to a single offset broach handle (S). Results have demonstrated that the highest values of the main force peak and force impulse were found in the single offset broach handle. Broach handle A had higher impulse values and lower maximum force values compared to broach handle B. In double offset broach handles less energy is transmitted to the tip. Broach handle A has a lower force peak than B and therefore a reduced risk of bone fracture.

Background

Computer-assisted navigation systems for total knee arthroplasty (TKA) were introduced to improve implantation accuracy and to optimize ligament balancing. Several comparative studies in the literature confirmed an effect on the component position and other studies could not confirm these results. For ligament balancing most studies found no significant influence on the clinical outcome using a navigation system for TKA. In the literature there were no reports of mid-term results after navigated TKA. With our study we wanted to show if the use of a navigation system for TKA will have an influence on the component's position and on the clinical results at 5-year follow up.

In Total Hip Arthroplasty (THA) bone loss is recovered by using compacted porous bone chips. The technique requires the morsellised allograft to be adequately compacted to provide initial stability for the prosthesis in order to prevent early massive subsidence and to induce bone remodeling. Therefore the bone grafts provide initial stability and an environment in which revascularization and incorporation of the graft into the host skeleton may occur. Acetabular reconstruction with impacted morsellised cancellous grafts and cement leads to satisfactory long-term results. In the acetabular impact-grafting procedure, a hammer and an impaction stick is used for manual compaction. Another technique uses a hammer driven by compressed air, which could lead to higher density and improved stability of bone chips in the acetabulum. The aim of this study was to compare two different compaction modes for bone impaction grafting for the acetabulum. The hypothesis was that a pneumatic impaction method would produce less variable results than the manual impaction mode and lead to better compaction results of the bone chips in less time.

Bone mass characteristics were measured by force and distance variation of a penetrating punch, which was lowered into a plastic cup filled with bone chips. For each compaction method and for each time interval (0, 3, 6, 9, 12, 15 and 30 [s] of compaction time) 30 measurements of force and distance variations were taken. From the measurements of force and distance variations bulk density, contact stiffness, impaction hardness and penetration resistance were calculated before and after the established time intervals of compaction. Since not all data was normally distributed the non-parametric U-Test was used for comparison of the two impaction methods. Particle size distribution was determined using sieve analysis according to Din 18123 standard after the compaction experiments.

Results have shown that the pneumatic method leads to higher values in impaction hardness, contact stiffness and bulk density and is more suitable to increase the primary stability of the implant. The differences in bulk density, impaction hardness and contact stiffness where statistically significant (p<0.01). No significant differences were found between the two different methods concerning the penetration resistance. The coefficient of uniformity C_u, calculated from the particle size distribution determined by the sieve analysis, has a value of 3.8.

The particle size distribution is comparable to the results published in literature. Pneumatic impaction achieves higher density values in less time with less force applied and results in more reproducible outcomes when used. It reduces therefore the risk of bone fracture, as smaller peak forces are used for less time. However for optimal osteointegration it is not recommended to achieve maximum density. Further clinical studies should determine a reference value for optimal growth-in of osteocytes. Manual impaction shows more variable results and depends much on the experience of the surgeon. The pneumatic hammer is therefore a suitable tool to standardize the impaction process for acetabular bone defects.

Background and purpose: Implantation of the femoral component at 10 to 15 degrees of anteversion is recommended in total hip arthroplasty. Surgical guidelines suggest that the lower leg be positioned horizontally or vertically with the knee flexed to 90° (figure of four). By constructing a perpendicular axis (a “figure-of-four” axis) to the lower leg, anteversion of the stem is approximated. This study was performed to validate the figure-of-four axis as a reliable intraoperative tool to approximate the retrocondylar line as reference for stem version.

Method: In 21 cadavers placed supine on an operating table, the lower legs were aligned to the horizontal plane. Using a box column drill, Steinmann nails were inserted perpendicular to the lower leg into the medial epicondyles. The Steinmann nails were replaced by cannulated titanium screws, representing the figure-of-four axis. The femoral neck axes, retrocondylar lines and the figure-of-four axes were determined using CT images of the specimen.

Results: The median version of the femoral neck axis was anteversion of 9.8° (IQR 4.5°–15.1°). The median figure-of-four axis showed a deviation of 0.5° (IQR −2.1°−2°) in relation to the retrocondylar line, whereas the median difference of the axis in relation to the femoral neck axis was 9.5° (IQR −13.6° – −2.1°).

Interpretation: The figure-of-four axis, being nearly parallel to the retrocondylar line, is a valid indirect method to determine stem version intraoperatively in patients without varus/valgus deviations of the knee.

Introduction: Minimally invasive total hip arthroplasty has evoked substantial controversy with regard to whether it provides superior outcomes compared with conventional total hip arthroplasty. The objective of this study was to compare the results of a minimal invasive direct anterior approach (MIDA) with those of a conventional lateral transgluteal approach (CLT).

Methods: 120 patients (120 hips) admitted for unilateral total hip arthroplasty were randomized to undergo surgery via minimal invasive direct anterior or conventional lateral transgluteal approach. Patients with a body mass index of more than 35, previous hip surgery, preoperative neurological deficits and with an age of more than 80 years were excluded. Two surgeons performed all procedures. To estimate muscle damage serum creatinkinase was assessed. Blood loss was calculated according to Rosencher by comparing preoperative to postoperative hematocrit. Postoperative pain and the ability to perform the activities of daily living were recorded in a dairy via modified WOMAC first on a daily basis, then on each second day and finally once a week for a total of 12 weeks. WOMAC questionnaire and SF-36 were administered at 6 weeks and 3 months follow-up.

Results: The groups were similar demographically. Patients in MIDA group had significantly less total blood loss (p = 0.006), postoperative blood levels of creatinine kinase were significantly lower (p = 0.001). Operative time was similar in both groups, we found no difference in component placement. Physical component summary of SF-36 at 12 weeks follow-up showed a significant benefit for the MIDA group. Averaged modified WOMAC scores and their pain and function subscores demonstrated a clear advantage on every recorded day during the first 12 weeks for MIDA. Median WOMAC sum score and respective pain as well as function subscores were better in the MIDA group at 6 and 12 weeks follow up.

Conclusions: A minimally invasive direct anterior approach is superior to a conventional lateral transgluteal approach with regard to blood loss and muscle trauma, resulting in better health related quality of life in the first three months after operation.

Objective: To compare the cup and stem position in matched pairs of cadaveric hips performing a minimally invaisve total hip arthroplasty (MIS-THA) either by using manual guidance tools or by the STRYKER Hip-track Navigation System.

Background: Minimally invasive techniques are currently introduced to THA. Our workgroup has developed a direct anterior single incission approach. Special instruments have been designed for retraction and implantation. Instruments are navigable with the STRYKER hiptracksystem. Perfect positioning of the acetabular and femoral component are among the most important factors in THA. Malpositioning may result in significant clinical problems such as dislocation, impingement, limited range of motion or extensive wear.

Design/Methods: In twelve fixated human cadavers hemispherical pressfit cups (TRIDENT, Stryker, Alledale, NJ) and straight femoral components (ACCOLADE, Stryker, Allendale, NJ) were implanted. All implantation were done throught the minimally invasive direct anterior approach. On one side the surgery was performed with spezial MIS instruments. On the oposite side the navigation system was used for placement of the implants. The aim was to achieve an alignment for the cups with 45° of inclination and 15° of anteversion in reference to the frontal pelvic plane. For the stem the goal was to position the stem in 0° of varus/valgus relative to the proximal shaft axes. This plane and the resulting cup positions were measured on CT-scans with a 3D imaging software (Stryker-Leibinger, Freiburg, Germany).

Results: The Innsbruck MIS approach to the hip could be performed in all cases. For both groups cup and stem position where within the range of variation reported in the literature. Yet, variance of the deviation from the goal was higher in the conventional group for both inclination and anteversion with the medians for the navigated group for inclination, anteversion and stem position being closer to the goal then in the conventional group.

Conclusion: The described minimally invasive approach to the hip is feasible and renders results compareable to those reported for conventionally operated THA. By the use of the navigation system tested it is possible to increase placement precission

Aims: For planning of Total Hip Arthroplasties (THA) plain X-rays of the pelvis in anterior posterior orientation are used. New methods such as CT scans and intraoperative digitization with navigation devices introduce the third dimension into orthopaedic planning. In order to compare measurements derived from three-dimensional data-acquisition with standard pelvic measurements it is important to estimate the underlying variances of those standards. Methods: 120 patients were investigated and subdivided in 4 groups depending of their age or the condition of their hip joints. The patients were positioned in a supine position on a table and in a standing position. Three landmarks at the patientñs pelvis (left and right anterior superior iliac spine (ASIS) and the pubic tubercle (PT)) were percutaneously digitized with a digitizing arm (Micro-Scribe-3DX, Vizion, Glendale, CA). The pelvic positions in space were calculated in relation to the horizontal and the vertical plane. Results: Despite the anatomical deþnition (0¡), we found an inclination of 4-6¡. There is no signiþcant difference between supine and standing position and no signiþcant difference between the groups and no diffenrence between genders. All patients lyed ßat in supine position without special positioning effort Conclusions: The pelvis orientation ist very stable in standing as well in supine position no matter if the patient is old or young, has coxarthrosis ore none or a THA. Therefore it can be concluded that our knowledge derived from measurements of planar a.-p.x-rays is not inßuenced by a massive variance in pelvic positions