Improved mediolateral load distribution without adverse laxity pattern in robot-assisted knee arthroplasty compared to a standard manual measured resection technique.

PURPOSE: Robot-assisted total knee arthroplasty (rTKA) remains in its infancy, is expensive but offers the promise of improved kinematic performance through precise bone cuts, with minimal soft tissue disruption, based on pre-resection soft tissue behaviour. This cadaveric study examined load transfer, soft tissue performance and radiographic indices for conventional (sTKA) versus rTKA. The null hypothesis was there would be no difference between the two modes of implantation. METHODS: Whole (ten) cadaveric limbs were randomised to receive either robotic (rTKA, N = 5) or conventional measured resection (sTKA, N = 5) knee arthroplasty. Laxity patterns were established using validated fixed sensors (Verasense) with manual maximum displacement for six degrees of freedom. Tibiofemoral load and contact points were determined dynamically using remote sensor technology for medial and lateral compartments through a functional arc of motion (0-110 degrees of motion). Final component position was assessed using pre- and post-implantation CT. RESULTS: No significant intergroup differences for laxity were found (n.s.). The rTKA group exhibited consistently balanced mediolateral load throughout the full arc with significantly reduced overall total load across the joint (for distinct points of measurement, p < 0.05). Despite using flexion-extension and mediolateral gap balancing with measured resection, the sTKA group failed to achieve balance in at least three points of the flexion arc. Post-operative CT confirmed satisfactory component alignment with no significant differences for positioning between the two groups. CONCLUSION: This work found improved load sharing for rTKA when compared to conventional surgery for same donor knees. Laxity and CT determined final component positioning was not significantly different. The work supports the contention that robot-assisted TKA delivers improved tibiofemoral load sharing in time zero studies under defined conditions but such offers the promise of improved clinical performance and reduced implant wear.

A load-measuring device can achieve fine-tuning of mediolateral load at knee arthroplasty but may lead to a more lax knee state.

PURPOSE: A balanced knee arthroplasty should optimise survivorship and performance. Equilibration of medial and lateral femorotibial load requires guided judicious pericapsular ligament release. The null hypothesis was that there would be no difference between use of a tensiometer device and a remote load sensor final load transfer across the joint through functional arc of motion. METHODS: A cadaveric study, using eight knees, was performed to define the impact of an established gap distraction device against load sensor-aimed soft tissue release in a TKA setting. Using validated measures of laxity in six degrees of freedom and true real-time load sensing four states were examined: native knee, TKA using spacer blocks (TKA), TKA with soft tissue release aided by a monogram tensiometer (TKA-T) and finally where load across the tibiofemoral articulation remains unbalanced final soft tissue release using a sensor device (TKA-OS). RESULTS: The laxity pattern was equivalent for TKA-T and TKA-OS. However, in only four of these seven knees despite the tensiometer confirming equivalence of rectangular flexion-extension gap dimensions and centralisation of collateral ligament distraction, there remained a > 15lb medial to lateral load difference for at least one point of the flexion arc. This was corrected by further final soft tissue release guided by the OS sensor device in the final three knees. CONCLUSION: Tensiometer-guided soft tissue release at two points of flexion failed to achieve balance for three out of seven knee arthroplasty procedures. Sensor technology guided final soft tissue balancing to equilibrate load across the joint through full arc of motion. This work argues for the role of continuous sensor readings to guide the soft tissue balancing during total knee arthroplasty.

Internal femoral component rotation adversely influences load transfer in total knee arthroplasty: a cadaveric navigated study using the Verasense device.

PURPOSE AND HYPOTHESIS: Correct femoral component rotation at knee arthroplasty influences patellar tracking and may determine function at extremes of movement. Additionally, such malrotation may deleteriously influence flexion/extension gap geometry and soft tissue balancing kinematics. Little is known about the effect of subtle rotational change upon load transfer across the tibiofemoral articulation. Our null hypothesis was that femoral component rotation would not influence load across this joint in predictable manner. METHODS: A cadaveric study was performed to examine load transfer using the orthosensor device, respecting laxity patterns in 6° of motion, to examine load across the medial and lateral compartments across a full arc of motion. Mixed-effect modelling allowed for quantification of the effect upon load with internal and external femoral component rotation in relation to a datum in a modern single-radius cruciate-retaining primary knee design. RESULTS: No significant change in maximal laxity was found between different femoral rotational states. Internal rotation of the femoral component resulted in significant increase in medial compartment load transfer for knee flexion including and beyond 60°. External rotation of the femoral component within the limits studied did not influence tibiofemoral load transfer. CONCLUSIONS: Internal rotation of the femoral component will adversely influence medial compartment load transfer and could lead to premature polyethylene wear on the medial side.

Investigation of Taper Failure in a Contemporary Metal-on-Metal Hip Arthroplasty System Through Examination of Unused and Explanted Prostheses.

BACKGROUND: Large-diameter (≥36-mm) metal-on-metal (MoM) total hip replacements have been shown to fail at an unacceptably high rate. Globally, the DePuy Pinnacle prosthesis was the most widely used device of this type. There is evidence to suggest that one of the main reasons for the poor clinical performance of large-diameter MoM prostheses is the metal debris released from the head-stem taper junction-i.e., taper junction failure. The aim of this study was to investigate variation in the as-manufactured finish of the female taper surface and to determine its influence on material loss. We hypothesized that rougher surfaces with higher relative material peaks would be significantly associated with greater taper wear rates. METHODS: We analyzed 93 Articul/eze femoral head tapers with a 36-mm bearing diameter that had been used in combination with a Corail titanium uncemented stem. The influence of the surface topography of the as-manufactured female taper surface on taper wear was examined by means of a multiple regression model, taking into account other known variables. RESULTS: We identified great variation in the as-manufactured surface finish of the female taper surface, with a range of measured Ra values from 0.14 to 4.20 µm. The roughness of the female taper surface appeared to be the most important variable associated with taper wear (p < 0.001). The best-fitting regression model, including duration in vivo, head offset, reduced peak height (Rpk) value, stem shaft angle, and bearing surface wear rate, explained approximately 44% of the variation in taper wear rates. CONCLUSIONS: We concluded that the roughness of the female taper surface appears to be a significant factor in metal debris release from head-stem taper junctions. CLINICAL RELEVANCE: This study shows evidence that previously unappreciated variations in manufacturing processes may have a major impact on the clinical outcomes of patients.

Tibiofemoral forces for the native and post-arthroplasty knee: relationship to maximal laxity through a functional arc of motion.

PURPOSE: Accurate soft tissue balance must be achieved to improve functional outcome after total knee arthroplasty (TKA). Sensor-integrated tibial trials have been introduced that allow real-time measurement of tibiofemoral kinematics during TKA. This study examined the interplay between tibiofemoral force and laxity, under defined intraoperative conditions, so as to quantify the kinematic behaviour of the CR femoral single-radius knee. METHODS: TKA was undertaken in eight loaded cadaveric specimens. Computer navigation in combination with sensor data defined laxity and tibiofemoral contact force, respectively, during manual laxity testing. Fixed-effect linear modelling allowed quantification of the effect for flexion angle, direction of movement and TKA implantation upon the knee. RESULTS: An inverse relationship between laxity and contact force was demonstrated. With flexion, laxity increased as contact force decreased under manual stress. Change in laxity was significant beyond 30° for coronal plane laxity and beyond 60° for rotatory laxity (p < 0.01). Rotational stress in mid-flexion demonstrated the greatest mismatch in inter-compartmental forces. Contact point position over the tibial sensor demonstrated paradoxical roll-forward with knee flexion. CONCLUSION: Traditional balancing techniques may not reliably equate to uniform laxity or contact forces across the tibiofemoral joint through a range of flexion and argue for the role of per-operative sensor use to aid final balancing of the knee.

Lack of evidence to support present medial release methods in total knee arthroplasty.

PURPOSE: The aim of this review was to identify a reliable sequential medial release protocol for restoration of soft tissue balance in total knee arthroplasty of the varus osteoarthritic knee and to allow for improved intraoperative decision-making. METHOD: Current medial release sequences and applicability based upon pre-operative deformity have been reviewed. Furthermore, risks associated with over release, and the necessity of medial release, are discussed. RESULTS: The different medial release sequences are discussed in relation to pre-operative deformity, along with potential complications associated with medial release. It was found that release sequences may include the deep and superficial components of the medial collateral ligament, the posteromedial capsule, the posterior oblique ligament, the pes anserinus (pes A), and tendons of the semimembranosus and medial gastrocnemius muscle. The sequences described were found to vary substantially between studies, and very few studies had systematically quantified the effect of each release on balance. CONCLUSION: While medial release is the standard intraoperative mode of balancing, there is a lack of evidence to support current methods. The correct method for defining intraoperatively the sequence, extent and magnitude of releases required remains ill-defined. It could be argued that the classic extensive medial release may be unnecessary and may be associated with iatrogenic injury to the pes A and saphenous nerve, instability and abnormal knee kinematics. Minimal medial release may allow for improved soft tissue balancing leading ultimately to improved functional outcome. LEVEL OF EVIDENCE: V (expert opinion).

How does laxity after single radius total knee arthroplasty compare with the native knee?

Patients with total knee arthroplasties (TKAs) continue to report dissatisfaction in functional outcome. Stability is a major factor contributing to functionality of TKAs. Implants with single-radius (SR) femoral components are proposed to increase stability throughout the arc of flexion. Using computer navigation and loaded cadaveric legs, we characterized the "envelope of laxity" (EoL) offered by a SR cruciate retaining (CR)-TKA compared with that of the native knee through the arc of flexion in terms of anterior drawer, varus/valgus stress, and internal/external rotation. In both the native knee and the TKA laxity increased with increasing knee flexion. Laxities measured in the three planes of motion were generally comparable between the native knee and TKA from 0° to 110° of flexion. Our results indicate that the SR CR-TKA offers appropriate stability in the absence of soft tissue deficiency.

Stiffness after total knee arthroplasty: does component alignment differ in knees requiring manipulation? A retrospective cohort study of 281 patients.

This study aims to evaluate component alignment in a large cohort of total knee arthroplasties (TKAs) and ascertain whether alignment in TKAs undergoing postoperative manipulation under anesthetic is significantly different from those achieving good function. A retrospective review of 281 consecutive primary TKAs was performed. All TKAs underwent computed tomographic scanning (Perth computed tomography knee protocol). Of 281 TKAs, 21 (7.4%) underwent manipulation, performed at a mean of 8.1 weeks (range, 3-14 weeks) after surgery. No statistically significant difference was seen between groups for any of 12 parameters of alignment. Postoperative stiffness with the need for manipulation under anesthetic is multifactorial in origin. This study found insufficient evidence to support the theory that component alignment contributes significantly to the etiology of this difficult problem.

Acetabular reconstruction using morcellised bone with ring support--medium-term results at three to nine years.

Marked acetabular bone loss in revision hip arthroplasty is challenging. Reconstruction or reinforcement rings may be used in moderate or severe cases with morcellised bone graft to restore bone stock. We report a single surgeon series of 45 hips over a 5-year period. There were 6 complex primary and 39 revision hip arthroplasties with a mean follow-up of 85 months (range: 42-106). Mean age at surgery was 75.6 years (range: 31-95). Contour (Smith & Nephew) titanium acetabular rings were used in all cases. At time of assessment 12 patients had died; of the 30 alive patients (33 hips), 23 patients (26 hips) were available for clinical evaluation. Forty of 45 grafts healed uneventfully with good graft incorporation, 2 were radiologically loose and both were infected. No loosening occurred in the absence of infection. Based on this experience, we recommend this as a safe and effective technique with low complication rates.

Good alignment after total knee arthroplasty leads to faster rehabilitation and better function.

The aim of this study was to identify what aspects of implant alignment and rotation affect functional outcome after total knee arthroplasty (TKA). One hundred and fifty-nine total knee arthroplasties were performed at the authors' institution between May 2003 and July 2004. All patients underwent an objective and independent clinical and radiological assessment before and after surgery. A computed tomography scan was performed at 6 months. The alignment parameters that were measured included sagittal femoral, coronal femoral, rotational femoral, sagittal tibial, coronal tibial, and femorotibial mismatch. The cumulative error score, which represents the sum of the individual errors, was calculated. Functional outcome was measured using the Knee Society Score. Good coronal femoral alignment was associated with better function at 1 year (P = .013). Trends were identified for better function with good sagittal and rotational femoral alignment and good sagittal and coronal tibial alignment. Patients with a low cumulative error score had a better functional outcome (P = .015). These patients rehabilitated more quickly and their length of stay in hospital was 2 days shorter.