Modular tumor prostheses: are current stem designs suitable for distal femoral reconstruction? A biomechanical implant stability analysis in Sawbones.

INTRODUCTION: High loosening rates after distal femoral replacement may be due to implant design not adapted to specific anatomic and biomechanical conditions. MATERIALS AND METHODS: A modular tumor system (MUTARS®, Implantcast GmbH) was implanted with either a curved hexagonal or a straight tapered stems in eight Sawbones® in two consecutively generated bone defect (10 cm and 20 cm proximal to knee joint level). Implant-bone-interface micromotions were measured to analyze main fixation areas and to characterize the fixation pattern. RESULTS: Although areas of highest relative micromotions were measured distally in all groups, areas and lengths of main fixation differed with respect to stem design and bone defect size. Regardless of these changes, overall micromotions could only be reduced with extending bone defects in case of tapered stems. CONCLUSIONS: The tapered design may be favorable in larger defects whereas the hexagonal may be advantageous in defects located more distally.

Periprosthetic infection is the major indication for TKA revision - experiences from a university referral arthroplasty center.

BACKGROUND: We hypothesized, that periprosthetic joint infection (PJI) accounts for the major proportion of first (primary) and repeated (secondary) Total Knee Arthroplasty revisions at our university referral arthroplasty center. METHODS: One thousand one hundred forty-three revisions, performed between 2008 and 2016 were grouped into primary (55%) and secondary (45%) revisions. The rate of revision indications was calculated and indications were categorized by time after index operation. The odds ratios of the indications for primary versus secondary revision were calculated. RESULTS: In the primary revision group PJI accounted for 22.3%, instability for 20.0%, aseptic loosening for 14.9% and retropatellar arthrosis for 14.2%. PJI (25.6%) was the most common indication up to 1 year after implantation, retropatellar arthrosis (26.8%) 1-3 years and aseptic loosening (25.6%) more than 3 years after implantation. In the secondary revision group PJI accounted for 39.7%, aseptic loosening for 16.2% and instability for 13.2%. PJI was the most common indication at any time of revision with 43.8% up to one, 35.4% 1-3 years and 39.4% more the 3 years after index operation. The odds ratios in repeated revision were 2.32 times higher (p = 0.000) for PJI. For instability and retropatellar arthrosis the odds ratios were 0.60 times (p = 0.006) and 0.22 times (p = 0.000) lower. CONCLUSIONS: PJI is the most common indication for secondary TKA revision and within one year after primary TKA. Aseptical failures such as instability, retropatellar arthrosis and aseptical loosening are the predominant reasons for revision more than one year after primary TKA.

Bicompartmental individualized knee replacement : Use of patient-specific implants and instruments (iDuo™).

OBJECTIVE: Bicompartmental knee replacement in patients with combined osteoarthritis (OA) of the medial or lateral and patellofemoral compartment. Patient-specific instruments and implants (ConforMIS iDuo™) with a planning protocol for optimal implant fit. INDICATIONS: Bicompartmental OA of the knee (Kellgren & Lawrence stage IV) affecting both the medial or lateral and patellofemoral compartment after unsuccessful conservative or joint-preserving surgery. CONTRAINDICATIONS: Tricompartmental OA, knee ligament instabilities, knee deformities >15° (varus, valgus, extension deficit). Relative contraindication: body mass index >40; prior unicompartmental knee replacement or osteotomies. SURGICAL TECHNIQUE: Midline or parapatellar medial skin incision, medial arthrotomy; identify mechanical contact zone of the intact femoral condyle (linea terminalis); remove remaining cartilage and all osteophytes that may interfere with the correct placement of the individually designed instruments. Balance knee in extension with patient-specific balancing chips. Resection of proximal tibia with an individual cutting block; confirm axial alignment using an extramedullary alignment guide, balance flexion gap using spacer blocks in 90° flexion. Final femur preparation with resection of the anterior trochlea. After balancing and identification of insert heights, final tibial preparation is performed. Implant is cemented in 45° of knee flexion. Remove excess cement and final irrigation, followed by closure. POSTOPERATIVE MANAGEMENT: Sterile wound dressing; compressive bandage. No limitation of active/passive range of motion (ROM). Partial weight bearing the first 2 weeks, then transition to full weight bearing. Follow-up directly after surgery, at 12 and 52 weeks, then every 1-2 years. RESULTS: In all, 44 patients with bicompartmental OA of the medial and patellofemoral compartment were treated. Mean age 59 years. Minimum follow-up 12 months. Implant converted to TKA due to tibial loosening (1 patient); patella resurfacing (3 patients). No further revisions or complications. Radiographic analyses demonstrated ideal fit of the implant with less than 2 mm subsidence or overhang. KSS pain scores improved from preoperatively 5.7 to 1.7 postoperatively with level walking, and from 7.3 preoperatively to 2.8 postoperatively with climbing stairs or inclines. The WOMAC score improved from preoperatively 43 to 79 postoperatively.

[Individualized unicondylar knee replacement : Use of patient-specific implants and instruments]. / Individualisierte unikondyläre Kniegelenkendoprothetik : Einsatz patientenspezifischer Implantate und Instrumente.

OBJECTIVE: Unicompartmental knee replacement in patients with osteoarthritis (OA) of the medial compartment. Individualized instruments and implants with a planning protocol for optimal fit. The individualized instruments and implants (ConforMIS Inc.; Burlington, MA, USA) are manufactured based on a computed tomography scan of the affected lower extremity and are provided together with a planning protocol (iView®) of the surgery. INDICATIONS: Unicompartmental OA of the knee (Kellgren & Lawrence stage IV) or Morbus Ahlbäck after unsuccessful conservative or joint preserving surgery. CONTRAINDICATIONS: Bi- or tricompartmental OA, knee ligament instabilities, knee deformities >15° (varus, valgus, extension deficit). Relative contraindication: body mass index >40. SURGICAL TECHNIQUE: Limited medial arthrotomy, identification of mechanical contact zone of the femoral condyle (linea terminalis); removal of remaining cartilage and all osteophytes that may interfere with the correct placement of the individually designed instruments. Balancing of knee in extension using patient-specific balancing chips of incremental heights. Resection of tibia with a fitted individualized tibial cutting block; confirmation of axial alignment with an extramedullary alignment tower; balancing flexion gap using spacer blocks in 90° flexion. Final femur preparation with the individual cutting instruments. Final tibial preparation with an individual drill jig for the placement of cavities fitting the cement pegs of the prosthesis. Lavage, cementing of implants in 45° of knee flexion, removal of excess cement, and wound closure. POSTOPERATIVE MANAGEMENT: Sterile wound dressing, compressive bandage. Unlimited active/passive range of motion. Functional rehabilitation with partial weight bearing first 2 weeks, then transition to full weight bearing. Clinical/radiographic follow-up directly after surgery, at 12 and 52 weeks, then every 1-2 years. RESULTS: In all, 31 patients with medial OA (27 medial knee osteoarthritis, 4 osteonecrosis) were treated. Mean age 60 years. Minimum follow-up 17 months. One aseptic loosening needed exchange; one acute late-onset infection with consecutive implant removal. No further revisions/reoperations or complications. X-rays showed an ideal fit of the implant with less than 2 mm subsidence or overhang in all cases. Clinically the VAS changed from 6.51 preoperatively to 1.11 postoperatively. The mean KSS (Knee Society Score) improved from 111.23 preoperatively to 180.61 postoperatively; the functional part of KSS improved from mean 60.39 to 94.51.

Acetabular defect classification in times of 3D imaging and patient-specific treatment protocols.

Parallel to the rising number of revision hip procedures, an increasing number of complex periprosthetic osseous defects can be expected. Stable long-term fixation of the revision implant remains the ultimate goal of the surgical protocol. Within this context, an elaborate preoperative planning process including anticipation of the periacetabular defect form and size and analysis of the remaining supporting osseous elements are essential. However, detection and evaluation of periacetabular bone defects using an unsystematic analysis of plain anteroposterior radiographs of the pelvis is in many cases difficult. Therefore, periacetabular bone defect classification schemes such as the Paprosky system have been introduced that use standardized radiographic criteria to better anticipate the intraoperative reality. Recent studies were able to demonstrate that larger defects are often underestimated when using the Paprosky classification and that the intra- and interobserver reliability of the system is low. This makes it hard to compare results in terms of defects being studied. Novel software tools that are based on the analysis of CT data may provide an opportunity to overcome the limitations of native radiographic defect analysis. In the following article we discuss potential benefits of these novel instruments against the background of the obvious limitations of the currently used native radiographic defect analysis.

[Individualized total knee arthroplasty]. / Individualendoprothetik am Kniegelenk.

This article describes the rationale and the surgical technique of patient-specific uni-, bi-, or three-compartmental knee arthroplasty using the second generation (G2) of ConforMIS™ technology. The patient-individual implants and instruments are designed and fabricated based on data from a preoperative computed tomography of the lower limb. The disposable patient-specific drill guides and cutting-jigs are manufactured under consideration of the anatomical and biomechanical axes of the knee joint and mediate efficient pre-navigation of the saw-cuts on the femoral and tibial bone without the need for an additional navigation or balancing device. The surgical technique for all types of knee resurfacement comprises the steps of cartilage removal, knee balancing in extension and flexion, sparing bony cuts, final preparation of femur and tibia, trialling, cementing of components and final choice of tibial insert. The use of individualized three-dimensional image-derived resurfacing implants, as well as personalized single-use instrumentation, facilitates the surgeon to perform an almost anatomical knee resurfacement that has the potential to restore almost normal knee kinematics. The limited data on this novel technology is promising, however long-term clinical data is needed for final evaluation of this technology.

[Reconstruction of osteochondral defects with a collagen I hydrogel. Results of a prospective multicenter study]. / Rekonstruktion von Gelenkknorpeldefekten mit einem Kollagen-I-Hydrogel. Ergebnisse einer prospektiven Multicenterstudie.

STUDY GOALS: The aim of the study was to evaluate the therapeutic benefit of CaReS®, a type I collagen hydrogel-based autologous chondrocyte implantation technique, for the treatment of osteochondral defects of the knee (Outerbridge grades III and IV) within a prospective multicenter study. MATERIAL AND METHODS: A total of 116 patients in 9 clinical centers were treated with CaReS between 2003 and 2008. The Cartilage Injury Evaluation Package 2000 of the International Cartilage Repair Society (ICRS) was employed for data acquisition and included the subjective International Knee Documentation Committee score (IKDC score), the pain level (visual analog scale, VAS), the physical and mental SF-36 score, the overall treatment satisfaction and the functional IKDC status of the indexed knee. Follow-up evaluation was performed 3, 6 and 12 months after surgery and annually thereafter. RESULTS: The mean defect size treated was 5.4 ± 2.7 cm(2) with 30% of the cartilage defects being ≤4 cm(2) and 70% ≥4 cm(2). The mean follow-up period was 30.2 ± 17.4 months (minimum 12 months and maximum 60 months). The mean IKDC score significantly improved from 42.4 ± 13.8 preoperatively to 70.5 ± 18.7 (p < 0.01) in the mean follow-up period. Global pain level significantly decreased (p < 0.001) from 6.7 ± 2.2 preoperatively to 3.2 ± 3.1 at the latest follow-up. Both the physical and mental components of the SF-36 score significantly increased. At the latest follow-up 80% of the patients rated the overall treatment satisfaction as either good or very good. The functional IKDC knee status clearly improved from preoperative to the latest follow-up when 23.4% of the patients reported having no restriction of knee function (I), 56.3% had mild restriction (II), 17,2% had moderate restriction (III) and 3.1% revealed severe restriction (IV). CONCLUSIONS: The CaReS technique is a clinically effective and safe method for the reconstruction of isolated osteochondral defects of the knee joint and reveals promising clinical outcome up to 5 years after surgery. A longer follow-up period and larger patient cohorts are needed to evaluate the sustainability of CaReS treatment.