Lee M. Longstaff

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

PurposeThe 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.MethodCurrent 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.ResultsThe 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.ConclusionWhile 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 evidenceV (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.

Isolated popliteus tendon injury does not lead to abnormal laxity in posterior-stabilised total knee arthroplasty.

AbstractPurpose The popliteus tendon is crucial to postero-lateral stability and prone to iatrogenic injury intra-operatively. Its role in the stability of the replaced knee remains contentious. The aim of this study was to use computer navigation to quantify the effect of popliteus sectioning on the ‘envelope of laxity’ (EoL) offered by a posterior-stabilised (PS) total knee arthroplasty (TKA) and compare with that of the native knee.MethodsLoaded cadaveric legs were mounted on a purpose built rig. EoL was measured in 3 degrees of freedom using computer navigation. Knees were subjectively stressed in varus/valgus, internal/external rotation and anterior draw. This was performed preoperatively, during TKA and after sectioning of the popliteus tendon. Real-time data were recorded at 0°, 30°, 60° and 90° of flexion as the operating surgeon stressed the knee in 3 degrees of freedom to its subjective endpoint. Mixed-effect modelling was used to quantify the effects of intervention on degree of laxity.ResultsIn all conditions, there was an increase in laxity with knee flexion. Insertion of a PS TKA resulted in increased constraint, particularly in rotation. Sectioning of the popliteus did not result in a significant increase in knee laxity to 90º of knee flexion. However, at deeper flexion angles, tendon sectioning overcame the constraints of the implant resulting in a significant increase in rotatory and varus/valgus laxity towards the native condition.ConclusionThese findings support the view that certain current designs of PS knee replacement can constrain the knee in flexion in the absence of postero-lateral deficiency. For this implant, isolated sectioning of the popliteus tendon did not substantially generate abnormal knee laxity.

No statistically significant kinematic difference found between a cruciate-retaining and posterior-stabilised Triathlon knee arthroplasty: a laboratory study involving eight cadavers examining soft-tissue laxity

The aim of this study was to compare the maximum laxity conferred by the cruciate-retaining (CR) and posterior-stabilised (PS) Triathlon single-radius total knee arthroplasty (TKA) for anterior drawer, varus-valgus opening and rotation in eight cadaver knees through a defined arc of flexion (0º to 110º). The null hypothesis was that the limits of laxity of CR- and PS-TKAs are not significantly different. The investigation was undertaken in eight loaded cadaver knees undergoing subjective stress testing using a measurement rig. Firstly the native knee was tested prior to preparation for CR-TKA and subsequently for PS-TKA implantation. Surgical navigation was used to track maximal displacements/rotations at 0º, 30º, 60º, 90º and 110° of flexion. Mixed-effects modelling was used to define the behaviour of the TKAs. The laxity measured for the CR- and PS-TKAs revealed no statistically significant differences over the studied flexion arc for the two versions of TKA. Compared with the native knee both TKAs exhibited slightly increased anterior drawer and decreased varus-valgus and internal-external roational laxities. We believe further study is required to define the clinical states for which the additional constraint offered by a PS-TKA implant may be beneficial.

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 &mgr;m. 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.

Influence of increasing construct constraint in the presence of posterolateral deficiency at knee replacement: A biomechanical study.

When faced with posterolateral corner (PLC) deficiency, surgeons must choose a total knee replacement (TKR) construct that provides the appropriate level of constraint. This should match the internal constraint of the device to the soft tissue host laxity pattern. Little guidance is available peroperatively, with factors influencing final component choice remaining ill defined. This study aimed to quantify the effect of PLC insufficiency on the “envelope of laxity” (EoL) after TKR and the effect of increasingly component constraint upon knee behavior through a functional arc of flexion. Using computer navigation, mixed effect modeling and loaded cadaveric legs—laxity was quantified under separate states: the native knee, after implantation of a posterior stabilized (PS)‐TKR, after sectioning the lateral (fibular) collateral ligament and popliteus tendon (PS‐TKR‐PLC), and after re‐implantation with a semi‐constrained “total stabilized” knee replacement (TS‐TKR). Laxity was quantified from 0 to 110° of flexion for anterior draw, varus–valgus, and internal–external rotation. Implantation of the PS‐TKR was consistently associated with increased constraint when compared to the native knee. PLC sectioning led to significantly increased laxity during varus stress from mid to deep flexion. Revision to a TS‐TKR construct restored constraint mimicking that of the primary state but only for the arc of motion 0–90°. In a posterolateral deficient state, a fixed bearing semi‐constrained TS‐TKR restored the knee to near normal kinematics but this was only achieved from an arc of motion 0–90° of flexion. At higher flexion angles, there remained an unfavorable laxity pattern with varus stress opening.

Sagittal flexion arc evaluation for a modern generation single-radius femoral component design

Single-radius femoral total knee design aims to deliver improved kinematic behaviour when compared to the standard two-radii geometry. This study has evaluated the behaviour, through a functional range of motion in the sagittal plane, of a single-radius femoral component compared to a dual-radius standard knee construct. Particular focus was placed on how the flexion axes of the native and replaced knee approximated to the transepicondylar axis through a loaded navigated knee design. Significant differences in flexion arcs were noted between the native and total knee arthroplasty state. These arcs were not uniform in all knees and did not display single-radius behaviour. There were no significant differences in the location of flexion axes in the native and total knee arthroplasty knee. Both exhibited similar posterior and inferior transverse axes of motion with respect to the anatomical epicondylar axis. This work has cast doubt on the reliability under loaded conditions of the single-radius concept, but the close proximity of the flexion axes of each replaced knee in relation to the functional flexion axis of the native knee may be the true basis of this purported improved kinematic performance.

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

PurposeA 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.MethodsA 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).ResultsThe 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.ConclusionTensiometer-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.