Poor soft tissue balance in total knee arthroplasty (TKA) is one of the most primary causes of dissatisfaction and reduced joint longevity, which are associated with postoperative instability and early implant failure. 1. Therefore, surgical techniques, including mechanical instruments and 3-D guided navigation systems, in TKA aim to achieve optimum soft tissue balancing in the knee to improve postoperative outcome. 2. Patella-in-Place balancing (PIPB) is a novel technique which aims to restore native collateral ligament behaviour by preserving the original state without any release. Moreover, reduction of the joint laxity compensates for the loss of the visco-elastic properties of the cartilage and meniscus. Following its clinical success, we aimed to evaluate the impact of the PIPB technique on collateral ligament strain and laxity behaviour, with the hypothesis that PIPB would restore strains in the collateral ligaments. 3. . Eight fresh-frozen cadaveric legs were obtained (KU Leuven, Belgium, H019 2015-11-04) and CT images were acquired while rigid marker frames were affixed into the femur, and tibia for testing. After carefully removing the soft tissues around the knee joint, while preserving the joint capsule, ligaments, and tendons, digital extensometers (MTS, Minnesota, USA) were attached along the length of the superficial medial collateral ligament (MCL) and lateral collateral ligament (LCL). A handheld digital dynamometer (Mark-10, Copiague, USA) was used to apply an abduction or adduction moment of 10 Nm at fixed knee flexion angles of 0°, 30°, 60° and 90°. A motion capture system (Vicon Motion Systems, UK) was used to record the trajectories of the rigid marker frames while synchronized strain data was collected for MCL/LCL. All motion protocols were applied following TKA was performed using PIPB with a cruciate retaining implant (Stryker Triathlon, MI, USA). Furthermore, tibiofemoral kinematics were calculated. 4. and combined with the strain data. Postoperative tibial varus/valgus stresses and collateral ligament strains were compared to the native condition using the Wilcoxon Signed-Rank Test (p<0.05). Postoperative tibial valgus laxity was lower than the native condition for all flexion angles. Moreover, tibial valgus of TKA was significantly different than the native condition, except for 0° (p=0.32). Although, tibial varus laxity of TKA was lower than the native at all angles, significant difference was only found at 0° (p=0.03) and 90° (p=0.02). No significant differences were observed in postoperative collateral ligament strains, as compared to the native condition, for all flexion angles, except for MCL strain at 30° (p=0.02) and 60° (p=0.01). Results from this experimental study supported our hypotheses, barring MCL strain in mid-flexion, which might be associated with the implant design. Restored collateral ligament strains with reduced joint laxity, demonstrated by the PIPB technique in TKA in vitro, could potentially restore natural joint kinematics, thereby improving patient outcomes. In conclusion, to further prove the success of PIPB, further biomechanical studies are required to evaluate the success rate of PIPB technique in different implant designs

The number of total knee arthroplasties continues to increase annually with over 90,000 total knee replacements performed in the United Kingdom in 2018. Multiple national bodies including the British Association for Surgery of the Knee (BASK) and the British Orthopaedic Association collaborated in July 2019 to produce best practice guidance for knee arthroplasty surgery. This study aims to review practice in a regional healthcare trust against these guidelines. Fifty total knee replacement operation notes were reviewed between January and February 2020 from 11 different consultant orthopaedic surgeons. Documents were assessed against 17 criteria recommended by the BASK guidance. Personnel names and grades were generally well documented. Tourniquet time and pressure were documented in over 98% of operation notes however, protection from spirit burns was not documented at all. Trialling and soft tissue balancing was well recorded in 100% and 96% of operation notes respectively. Areas lacking in documentation included methods utilised to optimise cementation technique and removal of cement debris. Protection of key knee structures was documented in only 56% of operation notes clearly. Prior to closure, final assessment of mechanism integrity, collateral ligament was not documented at all and final ROM after implantation of components was recorded 34% of the time. Subsequently authors have created a universal operation note template, uploaded onto the patient electronic notes, which prompts surgeons to complete documentation of the relevant criteria advocated by BASK. In conclusion, detailed and systematic documentation is vital to prevent adverse events and reduce the risk of litigation. By producing detailed operative templates this risk can be mitigated

Physiological kinematics is very difficult to restore after total knee arthroplasty (TKA). A new model of medial stabilized (MS) TKA prosthesis has a high spherical congruence of the internal compartment, which guarantees anteroposterior (AP) stability associated with a flat surface of the insert in the lateral compartment, that allows a greater AP translation of the external condyle during knee flexion. The aim of our study is to evaluate, by dynamic radiostereometric analysis (RSA), the knee in vivo kinematics after the implantation of a MS prosthesis during sit to stand and lunge movements. To describe the in vivo kinematics of the knee after MS Fixed Bearing TKA (GMK Sphere (TM) Medacta International AG, Castel San Pietro, Switzerland) using Model Based dynamic RSA. A cohort of 18 patients (72.1 ± 7.4 years old) was evaluated by dynamic RSA 9 months after TKA. The kinematic evaluation was carried out using the dynamic RSA tool (BI-STAND DRX 2), developed at our Institute, during the execution of sit to stand and lunge movements. The kinematic data were processed using the Grood and Suntay decomposition and the Low Point method. The patients performed two motor tasks: a sit-to-stand and a lunge. Data were related to the flexion angle versus internal-external, varus-valgus rotations and antero-posterior translations of the femur with respect to the tibia. During the sit to stand, the kinematic analysis showed the presence of a medial pivot, with a significantly greater (p=0.0216) anterior translation of the lateral condyle (3.9 ± 0.8 mm) than the medial one (1.6 ± 0.8 mm) associated with a femoral internal rotation (4.5 ± 0.9 deg). During the lunge, in the flexion phase, the lateral condyle showed a larger posterior translation than the medial one (6.2 ± 0.8 mm vs 5.3 ± 0.8 mm) associated with a femoral external rotation (3.1 ± 0.9 deg). In the extension phase, there is a larger anterior translation of the lateral condyle than the medial one (5.8 ± 0.8 mm vs 4.6 ± 0.8 mm) associated with femoral internal rotation (6.2 ± 0.9 deg). Analysing individual kinematics, we also found a negative correlation between clinical scores and VV laxity during sit to stand (R= −0.61) and that the higher femoral extra-rotation, the poorer clinical scores (R= 0.65). The finding of outliers in the VV and IE rotations analysis highlights the importance of a correct soft tissue balancing in order to allow the prosthetic design to manifest its innovative features

Restoration of anatomy is paramount in total hip arthroplasty (THA) to optimise function and stability. Leg-length discrepancy of ≥10mm is poorly tolerated and can be the subject of litigation. We routinely use a multimodal protocol to optimise soft tissue balancing which involves pre-operative templating, leg-length measurement supine and in the lateral position after positioning, and the use of an intra-operative leg-length measurement device to ensure optimisation of leg-length. We have analysed the results of our protocol in restoring leg-length in primary THA. Radiological leg-length was measured in a consecutive series of 50 patients who had THA for unilateral arthritis by an independent observer pre- and post-operatively using validated methods utilising radiological software. The measurements pre- and post-operative were compared. Patients with bilateral hip arthritis and poor imaging were excluded. Leg-length was successfully restored to within 5.0mm of the target leg-length in 84.0% of patients (mean +0.7mm (95% CI +0.2 to +1.1)). The other 14.0% of patients were restored to within 5.1–8.0mm (mean +2.2mm (95% CI −2.7 to +7.1)) and 2.0% of patients were restored to within 8.1–10.0mm. Leg length was accurately restored across the subset of patients within a narrow range of either side of the mean target leg length. Intra-operative measurement of leg length can be difficult but is vital in ensuring appropriate restoration of leg-length. We recommend a similar multimodal protocol to ensure restoration of leg-length within narrow limits to maximise function and patient satisfaction

During TKA surgery, the usual goal is to achieve equal balancing between the lateral and medial side, which can be achieved by ligament releases or “pie crusting”. However little is known regarding a relationship between the balancing forces on the medial and lateral plateaus during TKA surgery, and the varus and valgus and rotational laxities when the TKA components are inserted. It seems preferable that the laxity after TKA is the same as for the normal intact knee. Hence the first aim of this study was to compare the laxity envelope of a native knee, with the same knee after TKA surgery. The second aim was to examine the relationship between the Varus-Valgus (VV) laxity and the contact forces on the tibial plateau. A special rig that reproduced surgical conditions and fit onto an operating table was designed (Verstraete et al. 2015). The rig allows application of a constant varus/valgus moment, and an internal-external (IE) torque. A series of heel push tests under these loading conditions were performed on 12 non-arthritic half semibodies hip-to-toe cadaveric specimens. Five were used for method development. To measure laxities, the flexion angle, the VV and the IE angle were measured using a navigation system. After testing the native knee, a TKA was performed using the Journey II BCS implant, the navigation assuring correct alignments. Soft tissue balancing was achieved by measuring compressive forces on the lateral and medial condyles with an instrumented tibial trial (Orthosensor, Dania Beach, Florida). At completion of the procedure, the laxity tests were repeated for VV and IE rotation and the contact forces on the tibial plateau were recorded, for the full range of flexion. The average of the varus-valgus and the IE laxity envelope is plotted for the native (yellow), the TKA (pink) and the overlap between the two (orange). The average for six specimens of the contact force ratio (medial/medial+lateral force) during the varus and valgus test is plotted as a function of the laxity for each flexion angle. The Journey II implant replicated the VV laxity of the native knee except for up to 3 degrees more valgus in high flexion. For the IE, the TKA was equal in internal rotation, but up to 5 degrees more constrained in varus in mid range. Plotting contact force ratio against VV laxity, as expected during the varus test the forces were clustered in a 0.85–0.95 ratio, implying predominant medial force with likely lateral lift-off. For the valgus test, the force ratio is more spread out, with all the values below 0.6. This could be due to the different stiffness of the MCL and LCL ligaments which are stressed during the VV test. During both tests the laxity increases progressively with flexion angle. Evidently the geometry knee reproduces more lateral laxity at higher flexion as in the anatomic situation

Soft tissue balancing is critical to successful knee arthroplasty. Pre-operative planning ensures that the surgeon is prepared for any eventuality. We report a large femoral exostosis resulting in gross instability, requiring revision to a constrained implant. An 81 year old female presented with osteoarthritis of the left knee. Xray showed a medial bony mass. CT noted a large bony exostosis arising from the posteromedial femoral condyle. Review showed the exostosis was not related to the medial collateral ligament (MCL). At surgery, the exostosis was noted to be tenting the MCL – excision resulted in complete flaccidity. A trial of the Biomet AGC prosthesis revealed gross medial instability. The decision was taken to convert to a DePuy Sigma TC3 system. Whilst removing TC3 trial components, a lateral condyle fracture occurred. This was fixed with a 1/3 tubular plate and interfragmentary screw. The TC3 system and an AGC patellar button were found to be congruent. A small lateral release was performed, the deep MCL was replaced with tagging sutures through the MCL and the pes anserinus. At 9 weeks post operatively, the patient was pain free and mobilising independently. The knee was stable, with range of movement from 0 to 110 degrees. To our knowledge, this is the first report of such a complication in the literature. It highlights that despite optimal preoperative planning, the surgeon must be prepared to adapt to the situation at hand. It also highlights the importance of having ‘bail out’ options available on shelf when performing routine surgery

In total knee replacement (TKR), neutral mechanical alignment (NMA) is targeted in prosthetic component implantation. A novel implantation approach, referred to as kinematic alignment (KA), has been recently proposed (Eckhoff et al. 2005). This is based on the pre-arthritic lower limb alignment which is reconstructed using suitable image-based techniques, and is claimed to allow better soft-tissue balance (Eckhoff et al. 2005) and restoration of physiological joint function. Patient-specific instrumentation (PSI) introduced in TKR to execute personalized prosthesis component implantation are used for KA. The aim of this study was to report knee kinematics and electromyography (EMG) for a number lower limb muscles from two TKR patient groups, i.e. operated according to NMA via conventional instrumentation, or according to KA via PSI. 20 patients affected by primary gonarthrosis were implanted with a cruciate-retaining fixed-bearing prosthesis with patella resurfacing (Triathlon® by Stryker®, Kalamazoo, MI-USA). 17 of these patients, i.e. 11 operated targeting NMA (group A) via convention instrumentation and 6 targeting KA (group B) via PSI (ShapeMatch® by Stryker®, Kalamazoo, MI-USA), were assessed clinically using the International Knee Society Scoring (IKSS) System and biomechanically at 6-month follow-up. Knee kinematics during stair-climbing, chair-rising and extension-against-gravity was analysed by means of 3D video-fluoroscopy (CAT® Medical System, Monterotondo, Italy) synchronized with 4-channel EMG analysis (EMG Mate, Cometa®, Milan, Italy) of the main knee ad/abductor and flexor/extensor muscles. Knee joint motion was calculated in terms of flex/extension (FE), ad/abduction (AA), and internal/external rotation (IE), together with axial rotation of condyle contact point line (CLR). Postoperative knee and functional IKSS scores in group A were 78±20 and 80±23, worse than in group B, respectively 91±12 and 90±15. Knee motion patterns were much more consistent over patients in group B than A. In both groups, normal ranges were found for FE, IE and AA, the latter being generally smaller than 3°. Average IE ranges in the three motor tasks were respectively 8.2°±3.2°, 10.1°±3.9° and 7.9°±4.0° in group A, and 6.6°±4.0°, 10.5°±2.5° and 11.0°±3.9° in group B. Relevant CLRs were 8.2°±3.2°, 10.2°±3.7° and 8.8°±5.3° in group A, and 7.3°±3.5°, 12.6°±2.6° and 12.5°±4.2° in group B. EMG analysis revealed prolonged activation of the medial/lateral vasti muscles in group A. Such muscle co-contraction was not generally observed in all patients in group B, this perhaps proving more stability in the knee replaced following the KA approach. These results reveal that KA results in better function than NMA in TKR. Though small differences were observed between groups, the higher data consistency and the less prolonged muscle activations detected using KA support indirectly the claim of a more natural knee soft tissue balance. References

The assessment of knee laxity by application of varus and valgus stress is a subjective clinical manoeuvre often used for soft tissue balancing in arthroplasty or for diagnosis of collateral ligament injuries. Quantitative adjuncts such as stress radiographs have enabled a more objective measurement of angular deviation but may be limited by variations in examination technique. The aim of this study was to quantify clinical knee laxity assessment by measurement of applied forces and resultant angulations. A novel system for measuring the manually-applied forces and moments was developed. Both hardware and software components underwent laboratory validation prior to volunteer testing. Two clinicians performed multiple blinded examinations on two volunteers and the corresponding angular deviations were measured using a validated non-invasive system with a repeatability of ±1° for coronal alignment. The distance between the kinematically-determined knee and ankle centres was used as the moment arm. Comparison of single measurements of laxity showed a wide intra- and inter-observer variation (up to 3°). However, when the median value of repeated measurements was used there was good repeatability for both a single surgeon on different days and between the two clinicians with angular measurements agreeing within 1°. In spite of this agreement, the magnitudes of the tangential forces and moments applied varied between clinicians and did not correlate with the corresponding angular deviations. It was not possible to standardise clinical examination using the current system. Orientation of the applied force with respect to the leg was not quantified and during force measurement it became apparent that the assumed tangential direction of application was not true. This may explain the lack of correlation between the force and angulation data. However, for quantitative measurement of coronal knee laxity using non-invasive laxity measurements, the use of a repeated measures protocol may be accurate enough for clinical application