The effect of tibial slope on the biomechanics of cruciate-retaining total knee arthroplasty:A musculoskeletal simulation study

Introduction/Aim: More posterior tibial slope (PTS) can prevent flexion gap tightness in cruciate-retaining Total Knee Arthroplasty (TKA) and help achieving better knee function. However, the influence of PTS on knee function during activities of daily living (ADLs) is scarcely documented. The aim of this study was to investigate the effect of PTS and surgical referencing technique on tibiofemoral joint (TFJ) kinematics, quadriceps force, and patellofemoral joint (PFJ) force during ADLs. Materials and Methods: We used a previously validated musculoskeletal model of cruciate-retaining TKA [1] to simulate a squat activity. A baseline case with the original post-operative PTS (0°) was simulated, plus four PTS cases (-3°, +3°, +6°, +9°) obtained using anterior tibial cortex-referencing (ACR, Fig. 1a) technique and four using centre of tibial plateau-referencing (CPR, Fig. 1b) technique. Results: More PTS with ACR technique caused a larger and more anterior excursion of the TFJ contact point on the lateral side, and more posterior, on the medial side, in extension (Fig. 2). More PTS with the CPR technique caused the contact point in extension to shift gradually more posterior on both medial and lateral sides, and in flexion to shift gradually more posterior mainly on the lateral side. The peak quadriceps force decreased on average by 1.7 and 1.2 % BW for every degree of more PTS, with the ACR and CPR techniques, respectively. The peak PFJ contact force decreased more importantly with more PTS with the CPR technique rather than with the ACR technique (-3.9 vs. -1.5 % BW/degree more PTS, Fig. 3). Discussion: The ACR technique loosens the TFJ, thus leading to more unstable TFJ kinematics and anterior shift on the lateral side. More PTS also reduces the quadriceps force to squat. More PTS with the CPR technique resulted in stable and more posterior TFJ kinematics, and a greater reduction of the PFJ contact force, due to preservation of patellar height. Conclusions: TFJ stability should be maximally preserved to improve knee function. More PTS with the ACR technique has severe consequences on knee kinematics and function, whilst CPR technique results in more effective reduction of quadriceps and PFJ forces, while preserving TFJ stability. References: [1] Marra MA, Vanheule V, Fluit R, et al. A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty. ASME. J Biomech Eng. 2015;137(2):020904-020904-1

The effect of flexion of the femoral component in TKA:A musculoskeletal simulation study

Introduction/Aim: More flexion of the femoral component (FFC) is a surgical option to better restore the femur anatomy in the sagittal plane in Total Knee Arthroplasty (TKA), and to prevent notching of the anterior femoral cortex. However, its true effects on the patellofemoral joint (PFJ) during activities of daily living (ADLs) remain unknown. We studied the effect of FFC on quadriceps and PFJ forces during ADLs. We hypothesised that more FFC has advantages for the knee extensor mechanism. Materials and Methods: A previous validated musculoskeletal model of cruciate-retaining TKA was used (Fig. 1) to simulate a rising-from-a-chair activity [1]. We simulated a baseline case with the original post-operative FFC (0°). We then increased the FFC by 3°, 6°, 9°, by referencing the posterior femoral condyles (Fig. 2) and repeated the simulation. Quadriceps forces, PFJ ligament forces and PFJ contact forces were calculated. Results: Peak quadriceps force decreased by 48 N (6.5 %BW), on average, for every 3° of FFC at 90° flexion (Fig. 3a). The peak PFJ contact force decreased by 64 N (8.7 %BW), on average, for every 3° of FFC at 90° flexion. Conversely, peak medial and lateral PFJ ligament forces increased by 23 N and 25 N, respectively, on average, for every 3° more FFC (Fig. 3c-d). Discussion: FFC moderately affects the PFJ mechanics. Reduced PFJ contact force with more FFC is explained by reduced quadriceps force. More FFC, thus, benefits the knee extensor mechanism, due to increased quadriceps moment arm. More FFC over-tightens both medial and lateral PFJ ligaments, due to a wider PFJ gap, although the effect on ligament forces is not dramatic. Conclusions: More FFC reduces the quadriceps and PFJ force to rise from and sit on a chair. This surgical option can potentially help preventing anterior femoral notching, while at the same time provide a better knee function. References: [1] Marra MA, Vanheule V, Fluit R, et al. A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty. ASME. J Biomech Eng. 2015;137(2):020904-020904-1

The effect of posterior tibial slope on simulated laxity tests in cruciate-retaining total knee arthroplasty

Introduction/Aim: More posterior tibial slope (PTS) can potentially prevent flexion gap tightness in Total Knee Arthroplasty (TKA). However, the effects of more PTS on knee laxity remain unclear. The aim of this study was to investigate the effect of PTS on the anterior-posterior (AP) and varus-valgus (VV) laxity in TKA. We hypothesised that the effects also depend on whether an anterior tibial cortex-referencing (ACR) technique or a centre of tibial plateau-referencing (CPR) technique is used. Materials and Methods: A previous validated musculoskeletal model of cruciate-retaining TKA was configured to simulate AP and VV laxity tests [1]. First the model was simulated without any external loads applied, with the knee spanning a 0-90° flexion range of motion (ROM). Subsequently, anterior and posterior loads of 70 N were applied alternately to the proximal tibia, and the resulting AP tibial displacement recorded throughout the knee ROM. Similarly, varus and valgus loads of 15 Nm were applied alternately to the tibia, and the resulting knee VV rotation recorded. The simulations were repeated with -3°, +3°, +6°, +9° of PTS both with the ACR and CPR techniques (Fig. 1). Laxity were calculated as the unloaded case curves minus the loaded case curves. Results: More PTS with the ACR technique increased dramatically the anterior, varus and valgus laxities, throughout the knee flexion ROM. The anterior laxity was maximal (23 mm) at 60° of knee flexion in the +9° ACR case. Conversely, variations of PTS with the CPR technique hardly affected the AP and VV laxities. Discussion: More PTS with the ACR technique compromises the overall knee stability, throughout the knee flexion-extension ROM and, most interestingly, also in extension. This is due to an increase of the flexion gap. In contrast, the CPR technique preserves the translational and rotational laxities of the knee, throughout the ROM. CPR could be achieved by pre-planning the PTS and by accurately executing the tibial cut or by using inserts with built-in PTS. Conclusions: More PTS with the ACR technique has large effects on knee stability and laxity, therefore surgeons should avoid increasing PTS using the ACR technique and, instead, reference the tibial cut height and slope from the posterior one third of the tibia. References: [1] Marra MA, Vanheule V, Fluit R, et al. A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty. ASME. J Biomech Eng. 2015;137(2):020904-020904-1

Clinical study of the novel FlexitSystem implant for high tibial open wedge osteotomy

Background: The FlexitSystem implant is a novel implant used in open wedge high tibial osteotomy.Methods: A clinical safety study was performed. Retrospective 50 patients were analyzed who were treated with an open wedge high tibial osteotomy and the new FlexitSystem implant, with a minimal follow-up of one year. Complication rate, radiographic outcomes and implant removal were investigated.Results: One patient underwent a revision surgery because of loss of correction and non-union. The complication rate was 10.0%. No other radiographic complications (screw breakage, implant failure) were found. In 24 patients (48%) the FlexitSystem implant was removed at a mean follow-up of 12.6 months (range 2.6 till 24.0 months). The mean reason was irritation of the implant.Conclusions: The FlexitSystem implant is a clinical safe and stable implant for an open wedge high tibial osteotomy, with a low complication rate. Unfortunately, the rate of implant irritation requiring removal remained high.  Trial registration number: ID-number BC/1603-15

Trochleoplasty procedures show complication rates similar to other patellar-stabilizing procedures

Purpose: Trochleoplasty aims to restore patellar stability. Various techniques have been described and almost all authors report successful results. However, the procedure has a significant risk of complications. Purpose of this study was to perform a systematic review and meta-analysis of the available literature to assess the rate of complications after the various techniques used for trochleoplasty procedures. Materials and methods: MEDLINE, EMBASE, Web of Science and Cochrane Library databases were searched. Studies on patients with recurrent patellar instability treated with a trochleoplasty with or without additional procedure, and reported complications were included. The primary outcome was the rate of complications per technique. A meta-analysis was performed whenever three or more studies per surgical technique could be included. Results: The selection process resulted in 20 studies included for analysis. A lateral facet elevating trochlear osteotomy was reported by two studies, ten studies reported on a Bereiter trochleoplasty, five on a Dejour trochleoplasty, one on an arthroscopic technique, one on a ‘modified’ technique and one on a recession wedge trochleoplasty. Meta-analysis showed that proportion of recurrent dislocation was 0.04 (95% CI 0.02–0.07) for Bereiter trochleoplasty and 0.02 (95% CI 0–0.08) for Dejour trochleoplasty. These proportions were 0.06 (95% CI 0.02–0.13) and 0.09 (95% CI 0.03–0.27) for recurrent instability, 0.07 (95% CI 0.02–0.19) and 0.12 (95% CI 0.00–0.91) for patellofemoral osteoarthritis and 0.08 (95% CI 0.04–0.14) and 0.20 (95% CI 0.11–0.32) for further surgery respectively. Conclusion: This study demonstrates that the complications after a Bereiter and Dejour trochleoplasty including additional procedures are in the range of those of other patellar stabilizing procedures. For four other techniques, no meta-analysis could be performed. The clinical relevance of this study is that it provides clinicians with the best currently available evidence on the rate of complications after trochleoplasty procedures. This can be helpful in the process of deciding whether or not to perform such a procedure, and can be used to better inform patients about the advantages and disadvantages of different trochleoplasty procedures. Level of evidence: Level IV

Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty

Purpose: When downsizing the femoral component to prevent mediolateral overhang, notching of the anterior femoral cortex may occur, which could be solved by flexing the femoral component. In this study, we investigated the effect of flexion of the femoral component on patellar tendon moment arm, patellofemoral forces and kinematics in posterior-referencing CR-TKA. Our hypothesis was that flexion of the femoral component increases the patellar tendon moment arm, reduces the patellofemoral forces and provides stable kinematics. Methods: A validated musculoskeletal model of CR-TKA was used. The flexion of the femoral component was increased in four steps (0°, 3°, 6°, 9°) using posterior referencing, and different alignments were analysed in combination with three implant sizes (3, 4, 5). A chair-rising trial was analysed using the model, while simultaneously estimating quadriceps muscle force, patellofemoral contact force, tibiofemoral and patellofemoral kinematics. Results: Compared to the reference case (size 4 and 0° flexion), for every 3° of increase in flexion of the femoral component the patellar tendon moment arm increased by 1% at knee extension. The peak quadriceps muscle force and patellofemoral contact force decreased by 2%, the patella shifted 0.8 mm more anteriorly and the remaining kinematics remained stable, with knee flexion. With the smaller size, the patellar tendon moment arm decreased by 6%, the quadriceps muscle force and patellofemoral contact force increased by 8 and 12%, and the patellar shifted 5 mm more posteriorly. Opposite trends were found with the bigger size. Conclusion: Flexing the femoral component with posterior referencing reduced the patellofemoral contact forces during a simulated chair-rising trial with a patient-specific musculoskeletal model of CR-TKA. There seems to be little risk when flexing and downsizing the femoral component, compared to when using a bigger size and neutral alignment. These findings provide relevant information to surgeons who wish to prevent anterior notching when downsizing the femoral component

Anterior referencing of tibial slope in total knee arthroplasty considerably influences knee kinematics: a musculoskeletal simulation study

Purpose: In total knee arthroplasty (TKA), the posterior tibial slope is not always reconstructed correctly, and the knee ligaments may become too tight in flexion. To release a tight flexion gap, surgeons can increase the posterior tibial slope using two surgical resection techniques: the anterior tibial cortex (ACR) or the centre of tibial plateau (CPR) referencing. It is not known how this choice affects the knee laxity and function during activities of daily living. The aim of this study was to investigate the effect of tibial slope on knee laxity, kinematics and forces during a squatting activity using computer simulation techniques. We hypothesised that the effects depend on the referencing technique utilised. Methods: A validated musculoskeletal model of TKA was used. Knee laxity tests were simulated in flexion and extension. Then, a squat motion was simulated to calculate: movement of the tibiofemoral joint (TFJ) contact points and patello-femoral joint (PFJ) contact force. All analyses were repeated with more anterior (−3°), neutral (0°), and more posterior tibial slope (+3°, +6°, +9°), and with two referencing techniques (ACR, CPR). Results: Knee laxities increased dramatically with more posterior slope with the ACR technique (up to 400%), both in flexion and in extension. The CPR technique, instead, had much smaller effects (up to 42% variations). During squatting, more slope with the ACR technique resulted in larger movements of the TFJ contact point. The PFJ contact force decreased considerably with more slope with the CPR technique (12% body weight reduction every 3° more posterior slope), thanks to the preservation of the patellar height and quadriceps–femur load sharing. Conclusion: ACR technique alters considerably the knee laxity, both in flexion and extensions, and surgeons should be cautious about its use. More slope with CPR technique induces more favourable TFJ kinematics and loading of the knee extensor apparatus and does not substantially alter knee laxity. Preferably, the tibial slope resection should be pre-planned thoroughly and performed using CPR technique as accurately as possible. Surgeons can directly translate the results of this study into the clinical practice