Joern B. Seeger

Correlation of positioning and clinical results in Oxford UKA

In a prospective clinical study, 59 patients with anteromedial osteoarthritis of the knee (61 knee joints) underwent minimally invasive medial Oxford unicompartmental arthroplasty phase 3. Clinical and radiographic examinations of 56 knees were carried out at five (4–7) years. American Knee Society (AKS) scores improved from mean 45.5 (20–80) points (knee score) and 55 (15–100) points (function score) before surgery to 90 (30–100) points in both scores after surgery. The position of each implant was determined on screened radiographs using an image intensifier. The implant position was analysed according to the Oxford X-ray rating system. We evaluated nine measures, and there was no detectable correlation between implant position and clinical result. However, long-term studies are needed before it is possible to elaborate an evidence-based guideline on positioning.

Periprosthetic tibial fractures in unicompartmental knee arthroplasty as a function of extended sagittal saw cuts: An experimental study

Periprosthetic tibial plateau fractures (TPF) are rare but represent a serious complication of unicompartmental knee arthroplasty (UKA). As TPFs usually occur perioperatively, these can be associated with extended sagittal saw cuts during surgery. The aim of the study was to evaluate TPF as a function of extended sagittal saw cuts. The hypothesis was that extended sagittal saw cuts reduce the loading capacity of the tibial plateau and increase the risk of periprosthetic TPF. In a randomised study, standardised cemented Oxford UKA tibial component implantation was performed in six matched, paired fresh-frozen tibiae. In group A, a regular preparation of the tibial plateau was performed, whereas in group B a standardised extended sagittal saw cut was made at the dorsal cortex of the tibia. All tibiae were fractured under standardised conditions and fracture patterns and fracture loads were analysed. In group A, tibiae fractured with a mean load of F(max)=3.9 (2.3-8.5) kN, whereas in group B fractures occurred at a mean load of F(max)=2.6 (1.1-5.0) kN. The difference was statistically significant (p<0.05). Extended sagittal saw cuts in UKA weaken the tibial bone structure. Our results show that descendent extended sagittal saw cuts of 10 degrees reduce fracture loads by about 30%. Surgeons should be aware of the potential pitfalls of an extended sagittal saw cut, as this can lead to reduced loading capacity of the tibial plateau and increase the risk of periprosthetic TPF.

Fracture Load for Periprosthetic Femoral Fractures in Cemented Versus Uncemented Hip Stems: An Experimental In Vitro Study

This cadaveric study examined fracture loads in cemented and uncemented hip stems. Additionally, individual data and bone quality were analyzed and correlated to fracture patterns and fracture load. Cemented or uncemented hip stems were implanted in a randomized fashion in 10 matched paired fresh-frozen femora (donor median age, 78 years, and donor median weight, 74.2 kg). Bone density was measured before the femurs were fractured under load (maximum load of 10,000 N), and fracture patterns were analyzed according to the Vancouver and Johansson classification systems. In the uncemented group, all of the femurs fractured with a median load of 2625 N (range, 1725-7647 N). In the cemented group, 5 femurs fractured with a median maximum load of 9127 N (range, 2845-10,000 N) and 5 femurs did not fracture with a maximum load of 10,000 N. Fracture load corresponded to 4 times and 8.8 times body weight in the uncemented and cemented groups, respectively. Fracture patterns corresponded to Vancouver type A fractures in uncemented stems and Vancouver type C fractures in cemented hip stems. Analysis showed a significant correlation between fracture load and bone density in the uncemented group, whereas there was no correlation in the cemented group. Patients with poor bone quality treated with an uncemented hip stem are at higher risk for periprosthetic fractures; therefore, we recommend cemented stems in this group of patients. Cementation appears to protect against periprosthetic fractures, probably from internal stiffening of the femoral cavity.

Femoral fixation pattern in cemented Oxford unicompartmental knee arthroplasty — An experimental cadaver study

Femoral component loosening is a rare but serious complication in cemented Oxford unicompartmental knee arthroplasty (OUKA). In a cadaver study, OUKA was performed in 24 knees to evaluate the femoral fixation pattern. Due to the geometry of bone and implant, three different zones were identified. Complete cement mantles and good interdigitation were found in the spherical part of the implant (zone 1) and around the peg (zone 3), which implies that these are most important for implant fixation. The posterior plane facet (zone 2) is the weak point of the interface due to incompleteness of the cement mantle and a lack of interdigitation. This study suggests that the cancellous bone in zone 2 and the drill holes in sclerotic bone areas should be filled with cement and pressurised prior to component seating.

The UniSpacer™: correcting varus malalignment in medial gonarthrosis

While options for operative treatment of leg axis varus malalignment in patients with medial gonarthrosis include several established procedures, such as unicompartmental knee arthroplasty (UKA), total knee arthroplasty (TKA) or high tibial osteotomy (HTO), there has been little focus on a less invasive option introduced more recently: the UniSpacer™ implant, a self-centering, metallic interpositional device for the knee. This study evaluates clinical and radiological results of the UniSpacer™, whether alignment correction can be achieved by UniSpacer™ arthroplasty and alignment change in the first five postoperative years. Anteroposterior long leg stance radiographs of 20 legs were digitally analysed to assess alignment change: two relevant angles and the deviation of the mechanical axis of the leg were analysed before and after surgery. Additionally, the change of the postoperative alignment was determined one and five years postoperatively. Analysing the mechanical tibiofemoral angle, a significant leg axis correction was achieved, with a mean valgus change of 4.7 ± 1.9°; a varus change occurred in the first postoperative year, while there was no significant further change of alignment seen five years after surgery. The UniSpacer™ corrects malalignment in patients with medial gonarthrosis; however, a likely postoperative change in alignment due to implant adaptation to the joint must be considered before implantation. Our results show that good clinical and functional results can be achieved after UniSpacer™ arthroplasty. However, four of 19 knees had to be revised to a TKA or UKA due to persistent pain, which is an unacceptably high revision rate when looking at the alternative treatment options of medial osteoarthritis of the knee.

Saw cuts in unicompartmental knee arthroplasty: An analysis of sawbone preparations

Unicompartmental knee arthroplasty (UKA) has become a frequently used treatment option for anteromedial osteoarthritis (OA) of the knee due to good clinical and functional results. However, serious complications like tibial plateau fractures have been reported. These can be associated with saw cuts during surgery. The purpose of this study was to analyse saw cuts during Sawbone preparations at instructional unicompartmental knee courses and to identify potential sources of surgical error. One hundred Sawbone preparations were performed by knee surgeons inexperienced with UKA. Sawing errors during preparation were analysed and quantified. Tibial and femoral errors can occur during preparation. At the proximal tibia three errors can be found: extended vertical cuts (A), extended horizontal cuts (B) and perforation of the posterior cortex. An ascending cut at the posterior femoral condyle (C) is possible during femoral preparation. Errors type A were found at a mean length of 2.4 mm+/-2.3 mm with a maximum value of 10.1 mm. In 18% errors of more than 4.0 mm were found. Type B errors showed an average value of 2.0 mm+/-1.7 mm with maximum values of 7.4 mm. Type C errors were found at a mean of 1.3 mm+/-1.0 mm (maximum value 5.1 mm). Our data showed that in 18% of the cases, vertical cutting errors of more than 4.0 mm occurred in inexperienced surgeons.

Tibial Cementing in UKA: A Three-Dimensional Analysis of the Bone Cement Implant Interface and the Effect of Bone Lavage

Loosening is a common cause for revision in cemented UKA. In a cadaver study, we analyzed the three-dimensional cement distribution under the tibial implant and the effect of bone lavage (pulsed lavage, syringe lavage) on maximum cement penetration and penetration volume. Analyses were determined by performing bone cuts in medio-lateral direction and converting this data into a 3D model. Pulsed lavage led to an increased mean maximum cement penetration 5.79 ± 2.63 mm and penetration volume 6471.34 ± 1156.43 mm(3) compared to syringe lavage 4.62 ± 2.61 mm, 5069.81 ± 1177.09 mm(3) (P<0.001; P<0.001). Our results show a complete cement mantle for both investigated lavage techniques. Cleansing the cancellous tibial bone bed using pulsed lavage is more effective than conventional syringe lavage and leads to a deeper cement penetration and lager cement penetration volume under the tibial component.

Toxicity of Polyhexanide and Hydrogen Peroxide on Human Chondrocytes In Vitro

The treatment of acute joint infections has an important impact on long-term outcome and remains an unsolved problem. The most frequent bacteria are staphylococci, streptococci, and gram-negative bacteria. In septic surgery, polyhexanide and hydrogen peroxide are the most frequently used local antiseptics. The aim of this study was to examine the hypothesis that antiseptics induce cell death of human chondrocytes after a short incubation time.Human chondrocytes were treated with different concentrations of polyhexanide and hydrogen peroxide. Toxicity analysis was determined by visualization of cell structure using light microscopy, lactate dehydrogenase release, and determination of living and total cell numbers after addition of polyhexanide and hydrogen peroxide. Light microscopic data revealed a defect cell structure after addition of both antiseptics. Lactate dehydrogenase activity showed a significant increase of enzyme expression after a short incubation with polyhexanide. The determination of vital chondrocytes showed a significant decrease of vital and total cell numbers after addition with polyhexanide and hydrogen peroxide.Both antiseptic solutions induce significant cell death of human chondrocytes after a short incubation time. Polyhexanide possibly has more toxic potential than hydrogen peroxide against human chondrocytes after an application >15 minutes. Therefore, both substances should only be applied for a short time (<15 minutes) and the joint irrigated to wash out the antiseptic substance prior to wound closure.

Mechanical properties of a cemented porous implant interface

Background — Revision arthroplasty often requires anchoring of prostheses to poor-quality or deficient bone stock. Recently, newer porous materials have been introduced onto the market as additional, and perhaps better, treatment options for revision arthroplasty. To date, there is no information on how these porous metals interface with bone cement. This is of clinical importance, since these components may require cementing to other prosthesis components and occasionally to bone. Methods — We created porous metal and bone cylinders of the same size and geometry and cemented them in a well-established standardized setting. These were then placed under tensile loading and torsional loading until failure was achieved. This permitted comparison of the porous metal/cement interface (group A) with the well-studied bone/cement interface (group B). Results — The group A interface was statistically significantly stronger than the group B interface, despite having significantly reduced depth of cement penetration: it showed a larger maximum tensile force (effect size 2.7), superior maximum tensile strength (effect size 2.6), greater maximum torsional force (effect size 2.2), and higher rotational stiffness (effect size 1.5). Interpretation — The newer porous implants showed good interface properties when cemented using medium-viscosity bone cement. The axial and rotational mechanical strength of a porous metal/cement interface appeared to be greater than the strength of the standard bone/cement interface. These results indicate that cementing of porous implants can provide great stability in situations where it is needed.