R. J. van Heerwaarden

Axial and torsional stability of supracondylar femur osteotomies: biomechanical comparison of the stability of five different plate and osteotomy configurations

PurposeLittle is known regarding the biomechanical stability and stiffness of implants and techniques used in supracondylar femur osteotomies (SCO). Therefore, fixation stability and stiffness of implants to bone was investigated under simulated physiological loading conditions using a composite femur model and a 3D motion-analysis system.MethodsFive osteotomy configurations were investigated: (1) oblique medial closing-wedge fixated with an angle-stable implant; (2) oblique and (3) perpendicular medial closing-wedge, both fixated with an angled blade plate; and lateral opening-wedge fixated with (4) a spacer plate and (5) an angle-stable lateral implant. The motion measured at the osteotomy was used to calculate the stiffness and stability of the constructs.ResultsThe least amount of motion and highest stiffness was measured in the medial oblique closing-wedge osteotomy fixated with the angled blade plate. The lateral opening-wedge techniques were less stable and had a lower stiffness compared with the medial; the oblique saw cuts were more stable and had a higher stiffness than the perpendicular.ConclusionThis experimental study presents baseline data on the differences in the primary stability of bone–implant constructs used in SCO. The data in this study can be used as reference for future testing of SCO techniques. Furthermore, it is recommended that based on the differences found, the early postoperative rehabilitation protocol is tailored to the stability and stiffness of the fixation method used.

Axial and torsional stability of an improved single-plane and a new bi-plane osteotomy technique for supracondylar femur osteotomies

PurposeAn important disadvantage of the standard medial closing-wedge distal femur osteotomy for lateral compartment osteoarthritis of the knee is the immediate effects on the extensor mechanism function. Therefore, a novel bi-plane osteotomy technique was developed. The stability and stiffness of this newly developed technique and a modification of the proximal screw configuration were tested in a composite femur model and compared to the standard single-plane technique. Research question was if the new bi-plane technique and/or modified screw configuration would improve the stability and stiffness of the construct.MethodsIn 12 femurs, motion at the osteotomy under axial and torsion loading was measured using a 3D motion analysis system. All were subsequently tested to failure. The data recorded were used to calculate stability and stiffness of the constructs.ResultsThe stability and stiffness were highest in the bi-plane technique under axial loads, but were lower under torsional loading, compared to the single-plane technique. The screw configuration modification improved axial stability and stiffness, but had no influence on torsional stability.ConclusionIn replicate femurs, the new bi-plane technique improved axial stability, but in contrast to what was theorized, decreased torsional stability, compared to the single-plane technique. The addition of a bi-cortical screw proximally improved stability under axial loading, but not torsion. Further clinical testing will have to prove if early full weight bearing using the new bi-plane technique is possible.

Effect of pretension in reconstructions of the anterior cruciate ligament with a Dacron prosthesis: a retrospective study

To study the effect of the pretension level in reconstructions of the anterior cruciate ligament (ACL) we examined 26 patients with isolated ACL insufficiency and intact Dacron ligament prosthesis at 4-year follow-up. The patients were divided into two groups of 13 each, based on pretension level applied at the reconstruction: in group I the ligament was pretensioned to 60 N and in group II to 40 N. The patients were evaluated by the Tegner and Lysholm scores, KT-1000 arthrometer measurements, and isokinetic muscle performance testing and were assessed by the Knee Ligament Standard Evaluation Form of the International Knee Documentation Committee. At followup there were no differences between the two groups in any of the evaluated parameters except for squatting ability. The two groups differed significantly (P<0.01) with regard to the squatting score: 11 patients in group I had decreased squatting ability, and 6 of these were not able to squat beyond 90° of flexion. In contrast, only 4 patients in group II had slightly impaired squatting ability. It is likely that this difference between the two group is related to the magnitude of the pretension applied to the ligament prosthesis, and that the pretension exerts its influence through a change in the knee kinematics introduced at the time of the reconstruction.

THU0442 Knee Joint Distraction Compared with Total Knee Prosthesis: A Randomized Controlled Trial (Preliminary Results)

Background Placement of a total knee prosthesis (TKP) in case of end-stage knee OA in young patients is less successful than in the elderly, with high revision rates of up to 44% later in life. [1,2] However, in severe end-stage knee OA, effective joint saving treatments are scarce. Recently, knee joint distraction (KJD) showed results of clinical improvement and cartilaginous tissue repair in patients with knee OA. [3] However, no comparative data on efficacy is available. A RCT was set out and determined whether there was a clinical relevant difference between KJD and TKP in clinical outcome 1-year after treatment. Methods 60 patients with severe knee osteoarthritis were included and randomized to KJD (20 patients) or TKP (40 patients). As clinical outcome parameter a WOMAC questionnaire (100 being the best) and a VAS Pain (0 mm being the best) were assessed at baseline (BL) and 12 months. Off all values mean ± SEM is given. Results 26 patients, who received a TKP, had at least one-year of follow-up and of the patients who received KJD 16 at least one-year of follow-up available at the cut-off date (December 31st 2014). The 26 patients in the TKP group had a mean age at surgery of 54.8±1.2, a mean BMI of 29.6±0.7 kg/m2 and a mean Kellgren & Lawrence grade of 2.7±0.1. The 16 patients in the KJD group had a mean age at surgery of 57.1±1.8, a mean BMI of 26.8±1.0 and a mean Kellgren & Lawrence grade of 3.6±0.2. Total WOMAC scores demonstrated significant clinical improvement in both groups (see also figure 1). The KJD group increased from 50±3 points at BL to 80±4 points at 1-year (p<0.001). Similarly, the TKP group had a score of 47±3 points at BL, which increased to 82±3 points (p<0.001). Parallel results were seen for the three subscales of the WOMAC (stiffness, pain and function) and for the VAS. None of the parameters showed a statistical significant difference between the two groups at 1-year (p=0.730 for WOMAC total and p=0.116 for the VAS). Conclusions KJD does not lead to a clinical relevant difference in outcome compared with TKP after 1-year. Importantly KJD preserves the knee-joint and therefore represents a promising therapeutic option for young patients with severe knee OA. References Julin J, Jamsen E, Puolakka T, Konttinen YT, Moilanen T. Younger age increases the risk of early prosthesis failure following primary total knee replacement for osteoarthritis. A follow-up study of 32,019 total knee replacements in the Finnish Arthroplasty Register. Acta orthopaedica. 2010;81(4):413-9. Kurtz SM, Lau E, Ong K, Zhao K, Kelly M, Bozic KJ. Future young patient demand for primary and revision joint replacement: national projections from 2010 to 2030. Clinical orthopaedics and related research. 2009;467(10):2606-12. Wiegant K, van Roermund PM, Intema F, Cotofana S, Eckstein F, Mastbergen SC, et al. Sustained clinical and structural benefit after joint distraction in the treatment of severe knee osteoarthritis. Osteoarthritis and cartilage/OARS, Osteoarthritis Research Society. 2013;21(11):1660-7. Acknowledgements ZonMw (The Netherlands Organisation for Health Research and Development) and the Dutch Arthritis Association support this study. Disclosure of Interest None declared

SAT0536 Axial alignment of the knee – importance in cartilage repair? high tibial osteotomy vs. distraction

Background Opening-wedge high tibial osteotomy (HTO) is primarily indicated in treating varus gonarthrosis. The rationale behind HTO treatment of knee osteoarthritis (OA) is to unload the affected compartment, this is accomplished by correcting the angular deformity towards the unaffected compartment, i.e. shifting the hip-knee-ankle angle (HKA; mechanical axis) towards varus for a medial lesion. Knee joint distraction (KJD) is an alternative joint-sparing treatment for knee OA and has been demonstrated to decrease pain, improve function, and increase joint space width (JSW)1. Objectives To investigate the importance of axial alignment (and correction) in these two effective (joint-sparing) treatments of medial knee OA. Methods Patients with medial knee OA, a HKA less than 12° varus, normal knee stability, younger than 65 years, and a BMI less than 35 kg/m2 were randomized to HTO (n=46) or KJD (n=23). WOMAC and VAS pain were collected at baseline and after twelve months. To assess structural outcome, JSW was measured on knee radiographs, before and after both treatments. HTO patients had full leg standing anteroposterior radiographs taken before and after surgery, KJD patients only had these taken before surgery. Therefore, the femur-tibia angle (FTA; anatomical axis), acquired using Knee Image Data Analysis (KIDA), was investigated as an alternative for assessing axial alignment. Agreement between axial alignment as defined by HKA and by FTA appeared to be fair (ICC=-0.414). WOMAC and VAS Pain were then related to (changes in) axial alignment, Kellgren & Lawrence (K&L) grade, BMI, gender, pre-operative range of motion (ROM), and age as independent variables in linear regression models. Results Patient baseline characteristics were not statistically significantly different between patients treated with KJD or HTO (see table 1). WOMAC increased statistically significantly one year after either treatment (KJD:Δ21.05±19.93; HTO:Δ27.80±15.32; both p<0.001). Likewise, VAS pain decreased (KJD:Δ-23.89±29.67,p=0.001; HTO:Δ-35.42±24.06,p<0.001). KJD led to a statistically significant increase in mean JSW (Δ0.50±0.88mm,p=0.014), and both treatments led to a statistically significant increase in medial (KJD:Δ0.81±1.16mm,p=0.004; HTO:Δ0.47±0.69mm,p<0.000) as well as minimal JSW (KJD:Δ0.85±0.96mm,p<0.000; HTO:Δ0.35±0.51mm,p<0.000) after one year. The FTA changed significantly in the HTO group after one year (Δ0.73o,p=0.005), while the KJD group showed a trend (Δ0.77o,p=0.105). In the KJD group, changes in clinical outcomes were not associated with pre-operative HKA, changes in FTA, K&L grade, BMI, gender, pre-operative ROM, or age. In contrast, in the HTO group a significant association was demonstrated for a change in WOMAC with a change in FTA (std.β=-0.341) and for a change in VAS Pain with baseline age (std.β=-0.323), as seen in table 2. Conclusions Both KJD and HTO lead to a statistically significant clinical and structural benefit after one year. Nevertheless, the change in FTA was associated with WOMAC change after one year in the HTO group, but not in the KJD group. This indicates that axial alignment correction may not per se be necessary for clinical benefit. References van der Woude et al. Five-Year Follow-up of Knee Joint Distraction. 2016 Cartilage. Disclosure of Interest None declared

AB0098 The Beneficial Role of PAI-1 in Bone-Cartilage Interaction

Background In osteoarthritis (OA) subchondral bone changes are seen in addition to cartilage changes. In treatments targeted at bone, such as treatment with strontium ranelate [1], or treatments with bone involvement such as osteotomy [2] or joint distraction [3], cartilage repair has been demonstrated. These studies support the hypothesis that changes in bone metabolism can lead to cartilage repair. However, the exact biochemical interactions and how they contribute to repair and degradation processes is less well known. Plasminogen activator inhibitor (PAI)-1 inhibits plasmin which causes higher levels of MMPs in OA. It is expressed in subchondral bone and cartilage. Objectives The present study evaluates the role of PAI-1 in bone-cartilage interaction and its direct effects on osteoarthritic cartilage. Methods Both healthy and OA cartilage was cultured with supernatant from healthy (n=14) and OA (n=16) donors and proteoglycan (PG) synthesis was studied. Expression levels of mediators were assessed in the osteoblast culture supernatants by Luminex analysis. Subsequently, OA cartilage (n=11 donors) was cultured in absence/presence of PAI-1 and PG synthesis changes were studied. Results PG synthesis of OA cartilage was increased (+34%, p=0.036) upon addition of healthy osteoblast supernatant. Importantly, a decrease was seen when OA osteoblast supernatant was added to healthy cartilage (-31% PG synthesis, p=0.001). PAI-1 was expressed at significant higher levels in healthy osteoblasts compared to OA osteoblasts (184ng/ml vs 91ng/ml, resp.p=0.015). Moreover, osteoblast PAI-1 levels were positively correlated with PG synthesis (r=0.595, p=0.042) influenced by the osteoblasts. Culturing OA cartilage in direct presence of PAI-1 (2000ng/ml) revealed 33% (p=0.026) increase of PG synthesis confirming the beneficial role of PAI-1 in the osteoblast cultures. Conclusions Healthy osteoblast derived mediators lead to PG synthesis increase in OA cartilage, while it has no effect on healthy cartilage. Moreover, OA osteoblast derived mediators lead to a decrease in PG synthesis in healthy cartilage, but not in OA cartilage. Higher PAI-1 levels in these osteoblasts cultures are clearly correlated with higher PG synthesis in cartilage, which hints at a role for PAI-1 in cartilage repair. Its direct effects on OA cartilage, increasing PG synthesis, further confirmed the relevance of PAI-1. This supports that targeting bone directly or involvement of bone might be feasible as treatment for OA. References Reginster JY, Beaudart C, Neuprez A, Bruyère O (2013) Ther Adv Musculoskelet Dis. 5(5): 268-76. Jung WH, Takeuchi R, Chun CW, Lee JS, Ha JH, Kim JH, Jeong JH (2014) Arthroscopy 30(1):72-9. Intema F, Van Roermund PM, Marijnissen AC, Cotofana S, Eckstein F, Castelein RM, Bijlsma JW, Mastbergen SC, Lafeber FP (2011) Ann Rheum Dis.:70(8):1441-6. Acknowledgements This study was funded by the Dutch Arthritis Association. Disclosure of Interest None declared