Aims

The aim of this study was to determine the risk of tibial eminence avulsion intraoperatively for bi-unicondylar knee arthroplasty (Bi-UKA), with consideration of the effect of implant positioning, overstuffing, and sex, compared to the risk for isolated medial unicondylar knee arthroplasty (UKA-M) and bicruciate-retaining total knee arthroplasty (BCR-TKA).

Aims

Higher osteoblastic bone activity is expected in aseptic loosening and painful unicompartmental knee arthroplasty (UKA). However, insights into normal bone activity patterns after medial UKAs are lacking. The aim of this study was to identify the evolution in bone activity pattern in well-functioning medial mobile-bearing UKAs.

Abstract. Objectives. There is renewed interest in bi-unicondylar arthroplasty (Bi-UKA) for patients with medial and lateral tibiofemoral osteoarthritis, but a spared patellofemoral compartment and functional cruciate ligaments. The bone island between the two tibial components may be at risk of tibial eminence avulsion fracture, compromising function. This finite element analysis compared intraoperative tibial strains for Bi-UKA to isolated medial unicompartmental arthroplasty (UKA-M) to assess the risk of avulsion. Methods. A validated model of a large, high bone-quality tibia was prepared for both UKA-M and Bi-UKA. Load totalling 450N was distributed between the two ACL bundles, implant components and collateral ligaments based on experimental and intraoperative measurements with the knee extended and appropriately sized bearings used. 95th percentile maximum principal elastic strain was predicted in the proximal tibia. The effect of overcuts/positioning for the medial implant were studied; the magnitude of these variations was double the standard deviation associated with conventional technique. Results. For all simulations, strains were an order of magnitude lower than that associated with bone fracture. Highest strain occurred in the spine, under the anteromedial ACL attachment, adjacent to transverse overcut of the medial component. Consequently, Bi-UKA had little effect on strain: <10% increases were predicted when compared to UKA-M with equivalent medial cuts/positioning. However, surgical overcutting/positional variation that resulted in loss of anteromedial bone in the spine increased strain. The biggest increase was for lateral translation of the medial component: 44% and 42% for UKA-M and Bi-UKA, respectively. Conclusions. For a large tibia with high bone quality, Bi-UKA with a well-positioned lateral implant had no tangible effect on the risk of tibial eminence avulsion fracture compared to UKA-M. Malpositioning of the medial component that removes bone from the anterior spine could prove problematic for smaller tibiae. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Aims

Recent total knee arthroplasty (TKA) designs have featured more anatomical morphologies and shorter tibial keels. However, several reports have raised concerns about the impact of these modifications on implant longevity. The aim of this study was to report the early performance of a modern, cemented TKA design.

Aims

The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation.

Aims

The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position.

Aims

Metaphyseal tritanium cones can be used to manage the tibial bone loss commonly encountered at revision total knee arthroplasty (rTKA). Tibial stems provide additional fixation and are generally used in combination with cones. The aim of this study was to examine the role of the stems in the overall stability of tibial implants when metaphyseal cones are used for rTKA.

Objectives. Elevated proximal tibial bone strain may cause unexplained pain, an important cause of unicompartmental knee arthroplasty (UKA) revision. This study investigates the effect of tibial component alignment in metal-backed (MB) and all-polyethylene (AP) fixed-bearing medial UKAs on bone strain, using an experimentally validated finite element model (FEM). Methods. A previously experimentally validated FEM of a composite tibia implanted with a cemented fixed-bearing UKA (MB and AP) was used. Standard alignment (medial proximal tibial angle 90°, 6° posterior slope), coronal malalignment (3°, 5°, 10° varus; 3°, 5° valgus), and sagittal malalignment (0°, 3°, 6°, 9°, 12°) were analyzed. The primary outcome measure was the volume of compressively overstrained cancellous bone (VOCB) < -3000 µε. The secondary outcome measure was maximum von Mises stress in cortical bone (MSCB) over a medial region of interest. Results. Varus malalignment decreased VOCB but increased MSCB in both implants, more so in the AP implant. Varus malalignment of 10° reduced the VOCB by 10% and 3% in AP and MB implants but increased the MSCB by 14% and 13%, respectively. Valgus malalignment of 5° increased the VOCB by 8% and 4% in AP and MB implants, with reductions in MSCB of 7% and 10%, respectively. Sagittal malalignment displayed negligible effects. Well-aligned AP implants displayed greater VOCB than malaligned MB implants. Conclusion. All-polyethylene implants are more sensitive to coronal plane malalignments than MB implants are; varus malalignment reduced cancellous bone strain but increased anteromedial cortical bone stress. Sagittal plane malalignment has a negligible effect on bone strain. Cite this article: I. Danese, P. Pankaj, C. E. H. Scott. The effect of malalignment on proximal tibial strain in fixed-bearing unicompartmental knee arthroplasty: A comparison between metal-backed and all-polyethylene components using a validated finite element model. Bone Joint Res 2019;8:55–64. DOI: 10.1302/2046-3758.82.BJR-2018-0186.R2

Objectives. Unicompartmental knee arthroplasty (UKA) is a demanding procedure, with tibial component subsidence or pain from high tibial strain being potential causes of revision. The optimal position in terms of load transfer has not been documented for lateral UKA. Our aim was to determine the effect of tibial component position on proximal tibial strain. Methods. A total of 16 composite tibias were implanted with an Oxford Domed Lateral Partial Knee implant using cutting guides to define tibial slope and resection depth. Four implant positions were assessed: standard (5° posterior slope); 10° posterior slope; 5° reverse tibial slope; and 4 mm increased tibial resection. Using an electrodynamic axial-torsional materials testing machine (Instron 5565), a compressive load of 1.5 kN was applied at 60 N/s on a meniscal bearing via a matching femoral component. Tibial strain beneath the implant was measured using a calibrated Digital Image Correlation system. Results. A 5° increase in tibial component posterior slope resulted in a 53% increase in mean major principal strain in the posterior tibial zone adjacent to the implant (p = 0.003). The highest strains for all implant positions were recorded in the anterior cortex 2 cm to 3 cm distal to the implant. Posteriorly, strain tended to decrease with increasing distance from the implant. Lateral cortical strain showed no significant relationship with implant position. Conclusion. Relatively small changes in implant position and orientation may significantly affect tibial cortical strain. Avoidance of excessive posterior tibial slope may be advisable during lateral UKA. Cite this article: A. M. Ali, S. D. S. Newman, P. A. Hooper, C. M. Davies, J. P. Cobb. The effect of implant position on bone strain following lateral unicompartmental knee arthroplasty: A Biomechanical Model Using Digital Image Correlation. Bone Joint Res 2017;6:522–529. DOI: 10.1302/2046-3758.68.BJR-2017-0067.R1

Objectives. Up to 40% of unicompartmental knee arthroplasty (UKA) revisions are performed for unexplained pain which may be caused by elevated proximal tibial bone strain. This study investigates the effect of tibial component metal backing and polyethylene thickness on bone strain in a cemented fixed-bearing medial UKA using a finite element model (FEM) validated experimentally by digital image correlation (DIC) and acoustic emission (AE). Materials and Methods. A total of ten composite tibias implanted with all-polyethylene (AP) and metal-backed (MB) tibial components were loaded to 2500 N. Cortical strain was measured using DIC and cancellous microdamage using AE. FEMs were created and validated and polyethylene thickness varied from 6 mm to 10 mm. The volume of cancellous bone exposed to < -3000 µε (pathological loading) and < -7000 µε (yield point) minimum principal (compressive) microstrain and > 3000 µε and > 7000 µε maximum principal (tensile) microstrain was computed. Results. Experimental AE data and the FEM volume of cancellous bone with compressive strain < -3000 µε correlated strongly: R = 0.947, R. 2. = 0.847, percentage error 12.5% (p < 0.001). DIC and FEM data correlated: R = 0.838, R. 2. = 0.702, percentage error 4.5% (p < 0.001). FEM strain patterns included MB lateral edge concentrations; AP concentrations at keel, peg and at the region of load application. Cancellous strains were higher in AP implants at all loads: 2.2- (10 mm) to 3.2-times (6 mm) the volume of cancellous bone compressively strained < -7000 µε. Conclusion. AP tibial components display greater volumes of pathologically overstrained cancellous bone than MB implants of the same geometry. Increasing AP thickness does not overcome these pathological forces and comes at the cost of greater bone resection. Cite this article: C. E. H. Scott, M. J. Eaton, R. W. Nutton, F. A. Wade, S. L. Evans, P. Pankaj. Metal-backed versus all-polyethylene unicompartmental knee arthroplasty: Proximal tibial strain in an experimentally validated finite element model. Bone Joint Res 2017;6:22–30. DOI:10.1302/2046-3758.61.BJR-2016-0142.R1

Introduction. Traditional applied loading of the knee joint in experimental testing of RTKR components is usually confined to replicating the tibiofemoral joint alone. The second joint in the knee, the patellofemoral joint, can experience forces of up to 9.7 times body weight during normal daily living activities (Schindler and Scott 2011). It follows that with such high forces being transferred, particularly in high flexion situations such as stair climbing, it may be important to also represent the patellofemoral joint in all knee component testing. This research aimed to assess the inclusion of the patellofemoral joint during in vitro testing of RTKR components by comparing tibial strain distribution in two experimental rigs. The first rig included the traditional tibiofemoral joint loading design. The second rig incorporated a combination of both joints to more accurately replicate physiological loading. Five implanted tibia specimens were tested on both rigs following the application of strain gauge rosettes to provide cortical strain data through the bone as an indication of the load transfer pattern. This investigation aimed to highlight the importance of the applied loading technique for pre-clinical testing and research of knee replacement components to guide future design and improve patient outcomes. Methods. Five composite tibias (4th Generation Sawbones) were prepared with strain gauge rosettes (HBM), correctly aligned and potted using guides for repeatability across specimens. The tibias were then implanted with Stryker Triathlon components according to surgical protocol. The first experimental rig was developed to replicate traditional knee loading conditions through the tibiofemoral joint in isolation. The second experimental rig produced an innovative method of replicating a combination of the tibiofemoral and patellofemoral joint loading scenarios. Both rigs were used to assess the load distribution through the tibia using the same tibia specimens and test parameters for comparison integrity (Figure 1). The cortical strains were recorded under an equivalent 500 N cyclical load applied at 10° of flexion by a hydraulic test machine. Results. The average results comparing both experimental rigs at three strain gauge locations are shown in Figure 2. Paired t-tests were performed on all results and a p value of p<0.05 was considered significant. No significant differences were found between the rigs. There was a trend towards a reduction in proximal principal strain with the inclusion of the patellofemoral joint (p=0.058). Discussion. The results of this study indicate that there is no significant difference in tibial load transfer between the traditional and novel applied loading techniques at small flexion angles. There is a trend towards a reduction in proximal strain when including the patellofemoral joint. This reduction may be linked to the patella tendon force counteracting the effect of tibiofemoral loading at this small flexion angle. At high flexion angles the patellofemoral reaction load increases significantly relative to the tibiofemoral load. This will have a significant effect on tibial strains and so it is recommended that testing at higher flexion angles should be performed in a combined loading rig

Objectives

Initial stability of tibial trays is crucial for long-term success of total knee arthroplasty (TKA) in both primary and revision settings. Rotating platform (RP) designs reduce torque transfer at the tibiofemoral interface. We asked if this reduced torque transfer in RP designs resulted in subsequently reduced micromotion at the cemented fixation interface between the prosthesis component and the adjacent bone.

The relationship between post-operative bone density and subsequent failure of total knee replacement (TKR) is not known. This retrospective study aimed to determine the relationship between bone density and failure, both overall and according to failure mechanism. All 54 aseptic failures occurring in 50 patients from 7760 consecutive primary cemented TKRs between 1983 and 2004 were matched with non-failing TKRs, and 47 failures in 44 patients involved tibial failures with the matching characteristics of age (65.1 for failed and 69.8 for non-failed), gender (70.2% female), diagnosis (93.6% OA), date of operation, bilaterality, pre-operative alignment (0.4 and 0.3 respectively), and body mass index (30.2 and 30.0 respectively). In each case, the density of bone beneath the tibial component was assessed at each follow-up interval using standardised, calibrated radiographs. Failing knees were compared with controls both overall and, as a subgroup analysis, by failure mechanism. Knees were compared with controls using univariable linear regression.

Significant and continuous elevation in tibial density was found in knees that eventually failed by medial collapse (p < 0.001) and progressive radiolucency (p < 0.001) compared with controls, particularly in the medial region of the tibia. Knees failing due to ligamentous instability demonstrated an initial decline in density (p = 0.0152) followed by a non-decreasing density over time (p = 0.034 for equivalence). Non-failing knees reported a decline in density similar to that reported previously using dual-energy x-ray absorptiometry (DEXA). Differences between failing and non-failing knees were observable as early as two months following surgery. This tool may be used to identify patients at risk of failure following TKR, but more validation work is needed.

Cite this article: Bone Joint J 2014;96-B:1503–9.

The aim of this study was to evaluate the risk factors for dislocation of the bearing after a mobile-bearing Oxford medial unicompartmental knee replacement (UKR) and to test the hypothesis that surgical factors, as measured from post-operative radiographs, are associated with its dislocation

From a total of 480 UKRs performed between 2001 and 2012, in 391 patients with a mean age of 66.5 years (45 to 82) (316 female, 75 male), we identified 17 UKRs where bearing dislocation occurred. The post-operative radiological measurements of the 17 UKRs and 51 matched controls were analysed using conditional logistic regression analysis. The post-operative radiological measurements included post-operative change in limb alignment, the position of the femoral and tibial components, the resection depth of the proximal tibia, and the femoral component-posterior condyle classification.

We concluded that a post-operative decrease in the posterior tibial slope relative to the pre-operative value was the only significant determinant of dislocation of the bearing after medial Oxford UKR (odds ratio 1.881; 95% confidence interval 1.272 to 2.779). A post-operative posterior tibial slope < 8.45° and a difference between the pre-operative and post-operative posterior tibial slope of > 2.19° may increase the risk of dislocation.

Cite this article: Bone Joint J 2014; 96-B:914–22.

Mechanical alignment has been a fundamental tenet of total knee arthroplasty (TKA) since modern knee replacement surgery was developed in the 1970s. The objective of mechanical alignment was to infer the greatest biomechanical advantage to the implant to prevent early loosening and failure. Over the last 40 years a great deal of innovation in TKA technology has been focusing on how to more accurately achieve mechanical alignment. Recently the concept of mechanical alignment has been challenged, and other alignment philosophies are being explored with the intention of trying to improve patient outcomes following TKA.

This article examines the evolution of the mechanical alignment concept and whether there are any viable alternatives.

The December 2013 Research Roundup. 360 . looks at: Inflammation implicated in FAI; Ponseti and effective teaching; Unicompartmental knee design and tibial strain; Bisphosphonates and fracture healing; Antibiosis in cement; Zoledronic acid improves primary stability in revision?; Osteoporotic fractures revisited; and electroarthrography for monitoring of cartilage degeneration

As many as 25% to 40% of unicompartmental knee replacement (UKR) revisions are performed for pain, a possible cause of which is proximal tibial strain. The aim of this study was to examine the effect of UKR implant design and material on cortical and cancellous proximal tibial strain in a synthetic bone model. Composite Sawbone tibiae were implanted with cemented UKR components of different designs, either all-polyethylene or metal-backed. The tibiae were subsequently loaded in 500 N increments to 2500 N, unloading between increments. Cortical surface strain was measured using a digital image correlation technique. Cancellous damage was measured using acoustic emission, an engineering technique that detects sonic waves (‘hits’) produced when damage occurs in material. Anteromedial cortical surface strain showed significant differences between implants at 1500 N and 2500 N in the proximal 10 mm only (p < 0.001), with relative strain shielding in metal-backed implants. Acoustic emission showed significant differences in cancellous bone damage between implants at all loads (p = 0.001). All-polyethylene implants displayed 16.6 times the total number of cumulative acoustic emission hits as controls. All-polyethylene implants also displayed more hits than controls at all loads (p < 0.001), more than metal-backed implants at loads ≥ 1500 N (p < 0.001), and greater acoustic emission activity on unloading than controls (p = 0.01), reflecting a lack of implant stiffness. All-polyethylene implants were associated with a significant increase in damage at the microscopic level compared with metal-backed implants, even at low loads. All-polyethylene implants should be used with caution in patients who are likely to impose large loads across their knee joint. . Cite this article: Bone Joint J 2013;95-B:1339–47

Joint registries report that 25–40% of UKR revisions are performed for pain. Proximal tibial strain and microdamage are possible causes of this “unexplained” pain. The aim of this study was to examine the effect of UKR implant design and material on proximal tibial cortical strain and cancellous microdamage. Composite Sawbone tibias were implanted with cemented UKR components: 5 fixed bearing all-polyethylene (FB-AP), 5 fixed bearing metal backed (FB-MB), and 5 mobile bearing metal backed implants (MB-MB). Five intact tibias were used as controls. Tibias were loaded in 500N increments to 2500N. Cortical surface strain was measured using digital image correlation (DIC). Cancellous microdamage was measured using acoustic emission (AE), a technique which detects elastic waves produced by the rapid release of energy during microdamage events. DIC showed significant differences in anteromedial cortical strain between implants at 1500N and 2500N in the proximal 10mm only (p<0.001) with strain shielding in metal backed implants. AE showed significant differences in cancellous microdamage (AE hits), between implants at all loads (p=0.001). FB-AP implants displayed significantly more hits at all loads than both controls and metal backed implants (p<0.001). FB-AP implants also differed significantly by displaying AE hits on unloading (p=0.01), reflecting a lack of implant stiffness. Compared to controls, the FB-AP implant displayed 15x the total AE hits, the FB-MB 6x and the MB-MB 2.7x. All-polyethylene medial UKR implants are associated with greater cancellous bone microdamage than metal backed implants even at low loads

Stems improve the mechanical stability of tibial components in total knee replacement (TKR), but come at a cost of stress shielding along their length. Their advantages include resistance to shear, reduced tibial lift-off and increased stability by reducing micromotion. Longer stems may have disadvantages including stress shielding along the length of the stem with associated reduction in bone density and a theoretical risk of subsidence and loosening, peri-prosthetic fracture and end-of-stem pain. These features make long stems unattractive in the primary TKR setting, but often desirable in revision surgery with bone loss and instability. In the revision scenario, stems are beneficial in order to convey structural stability to the construct and protect the reconstruction of bony defects. Cemented and uncemented long stemmed implants have different roles depending on the nature of the bone loss involved.

This review discusses the biomechanics of the design of tibial components and stems to inform the selection of the component and the technique of implantation.