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Supplemental material, sj-pdf-1-ajs-10.1177_03635465221092118 for Medial Collateral Ligament Reconstruction for Anteromedial Instability of the Knee: A Biomechanical Study In Vitro by Nobuaki Miyaji, Sander R. Holthof, Simon V. Ball, Andy Williams and Andrew A. Amis in The American Journal of Sports Medicine

© 2017 The Author(s). Meniscal allograft transplantation (MAT) has become relatively commonplace in specialized sport medicine practice for the treatment of patients with a symptomatic knee after the loss of a functional meniscus. The technique has evolved since the 1980s, and long-term results continue to improve. However, there still remains significant variation in how MAT is performed, and as such, there remains opportunity for outcome and graft survivorship to be optimized. The purpose of this article was to develop a consensus statement on the practice of MAT from key opinion leaders who are members of the International Meniscus Reconstruction Experts Forum so that a more standardized approach to the indications, surgical technique, and postoperative care could be outlined with the goal of ultimately improving patient outcomes.

© 2018, European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA). The structure and function of the anterolateral complex (ALC) of the knee has created much controversy since the ‘re-discovery’ of the anterolateral ligament (ALL) and its proposed role in aiding control of anterolateral rotatory laxity in the anterior cruciate ligament (ACL) injured knee. A group of surgeons and researchers prominent in the field gathered to produce consensus as to the anatomy and biomechanical properties of the ALC. The evidence for and against utilisation of ALC reconstruction was also discussed, generating a number of consensus statements by following a modified Delphi process. Key points include that the ALC consists of the superficial and deep aspects of the iliotibial tract with its Kaplan fibre attachments on the distal femur, along with the ALL, a capsular structure within the anterolateral capsule. A number of structures attach to the area of the Segond fracture including the capsule-osseous layer of the iliotibial band, the ALL and the anterior arm of the short head of biceps, and hence it is not clear which is responsible for this lesion. The ALC functions to provide anterolateral rotatory stability as a secondary stabiliser to the ACL. Whilst biomechanical studies have shown that these structures play an important role in controlling stability at the time of ACL reconstruction, the optimal surgical procedure has not yet been defined clinically. Concern remains that these procedures may cause constraint of motion, yet no clinical studies have demonstrated an increased risk of osteoarthritis development. Furthermore, clinical evidence is currently lacking to support clear indications for lateral extra-articular procedures as an augmentation to ACL reconstruction. The resulting statements and scientific rationale aim to inform readers on the most current thinking and identify areas of needed basic science and clinical research to help improve patient outcomes following ACL injury and subsequent reconstruction. Level of evidence V.

Highlights • A finite element model was developed to calculate micromotion of ankle implants. • Both optimally-positioned and malpositioned cases were considered. • Fixation nearer to the joint line relying on plural pegs improved implant stability. • Gaps between the implant and bone greatly increased micromotion and bone strains., Implant loosening – commonly linked with elevated initial micromotion – is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning – previously linked with higher failure rates – remain unexplored. The aim of this study was to estimate implant-bone micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX®, Mobility® and Salto®) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone micromotion and bone strains, thereby increasing the risk for TAR failure.

Supplemental material, DS_10.1177_0363546519841304 for Properties and Function of the Medial Patellofemoral Ligament: A Systematic Review by Christian Huber, Qiang Zhang, William R. Taylor, Andrew A. Amis, Colin Smith and Seyyed Hamed Hosseini Nasab in The American Journal of Sports Medicine

Background - Revision total knee arthroplasty (RTKA) has poorer results than primary total knee arthroplasty (TKA), and the prostheses are invasive and cause strain-shielding of the bones near the knee. This paper describes an RTKA system with extracortical fixation. It was hypothesised that this would reduce strain-shielding compared with intramedullary fixation.Methods - Twelve replica tibiae were prepared for full-field optical surface strain analysis. They were either left intact, implanted with RTKA components with cemented intramedullary fixation stems, or implanted with a novel design with a tibial tray subframe supported by two extracortical fixation plates and screw fixation. They were loaded to simulate peak walking and stair climbing loads and the surface strains were measured using digital image correlation. The measurements were validated with strain gauge rosettes.Results - Compared to the intact bone model, extracortical fixation reduced surface strain shielding by half versus intramedullary fixation. For all load cases and bone regions examined, the extracortical implant shielded 8 to 27% of bone strain, whereas the intramedullary component shielded 37 to 56%.Conclusions - The new fixation design, which offers less bone destruction than conventional RTKA, also reduced strain-shielding. Clinically, this design may allow greater rebuilding of bone loss, and should increase long-term fixation.

Definite glenoid implant loosening is identifiable on radiographs, however, identifying early loosening still eludes clinicians. Methods to monitor glenoid loosening in vitro have not been validated to clinical imaging. This study investigates the correlation between in vitro measures and CT images. Ten cadaveric scapulae were implanted with a pegged glenoid implant and fatigue tested to failure. Each scapulae were cyclically loaded superiorly and CT scanned every 20,000 cycles until failure to monitor progressive radiolucent lines. The superior and inferior rim displacements were also measured. A finite element (FE) model of one scapula was used to analyse the interfacial stresses at the implant/cement and cement/bone. All ten implants failed inferiorly at the implant-cement interface, two also failed at the cement-bone interface inferiorly, and three showed superior failure. Failure occurred at of 80,966 ± 53,729 (mean ± SD) cycles. CT scans confirmed failure of the fixation, and in most cases, was observed either before or with visual failure, indicating its capacity to detect loosening earlier for earlier intervention if needed. Significant correlations were found between both increasing inferior rim displacement (ASTM standard F2028-14), increasing vertical head displacement and failure of the glenoid implant. The FE model showed peak tensile stresses inferiorly and high compressive stresses superiorly, corroborating experimental findings. Similar failure modes have been cited in clinical and in vitro studies. In vitro monitoring methods correlated to failure progression in clinical CT images. Clinical Significance: The study highlights failure at the implant-cement interface and early signs of failure are identifiable in CT images.

© 2016, European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA). In the original article, one of the co-authors’ name has been published incorrectly. The correct name should be Jeremy M. Burnham. The original article has been updated accordingly.

Supplemental material, FAI762442_ICMJE for Strength of Interference Screw Fixation to Cuboid vs Pulvertaft Weave to Peroneus Brevis for Tibialis Posterior Tendon Transfer for Foot Drop by Daniel Marsland, Joanna M. Stephen, Toby Calder, Andrew A. Amis and James D. F. Calder in Foot & Ankle International

Purpose The aim of the study was to investigate varus and normal knee morphologies to identify differences that may affect knee replacement alignment or design for varus knees. Methods Computed tomography scans of varus and normal knees were analyzed, and geometric shapes, points and axes were fit to the femur and tibia independently. These points were then projected in the three anatomical planes to measure the variations between the two groups. Results In the femur, varus knees had less femoral anteversion (p

Fixation failure of glenoid components is the main cause of unsuccessful total shoulder arthroplasties. The characteristics of these failures are still not well understood, hence, attempts at improving the implant fixation are somewhat blind and the failure rate remains high. This lack of understanding is largely due to the fundamental problem that direct observations of failure are impossible as the fixation is inherently embedded within the bone. Twenty custom made implants, reflecting various common fixation designs, and a specimen set-up was prepared to enable direct observation of failure when the specimens were exposed to cyclic superior loads during laboratory experiments. Finite element analyses of the laboratory tests were also carried out to explain the observed failure scenarios. All implants, irrespective of the particular fixation design, failed at the implant-cement interface and failure initiated at the inferior part of the component fixation. Finite element analyses indicated that this failure scenario was caused by a weak and brittle implant-cement interface and tensile stresses in the inferior region possibly worsened by a stress raiser effect at the inferior rim. The results of this study indicate that glenoid failure can be delayed or prevented by improving the implant/cement interface strength. Also any design features that reduce the geometrical stress raiser and the inferior tensile stresses in general should delay implant loosening.

Fixation failure of glenoid components is the main cause of unsuccessful total shoulder arthroplasties. The characteristics of these failures are still not well understood, hence, attempts at improving the implant fixation are somewhat blind and the failure rate remains high. This lack of understanding is largely due to the fundamental problem that direct observations of failure are impossible as the fixation is inherently embedded within the bone.Twenty custom made implants, reflecting various common fixation designs, and a specimen set-up was prepared to enable direct observation of failure when the specimens were exposed to cyclic superior loads during laboratory experiments. Finite element analyses of the laboratory tests were also carried out to explain the observed failure scenarios.All implants, irrespective of the particular fixation design, failed at the implant–cement interface and failure initiated at the inferior part of the component fixation. Finite element analyses indicated that this failure scenario was caused by a weak and brittle implant–cement interface and tensile stresses in the inferior region possibly worsened by a stress raiser effect at the inferior rim.The results of this study indicate that glenoid failure can be delayed or prevented by improving the implant/cement interface strength. Also any design features that reduce the geometrical stress raiser and the inferior tensile stresses in general should delay implant loosening.

© 2017, European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA). Persistent rotatory knee laxity is increasingly recognized as a common finding after anterior cruciate ligament (ACL) reconstruction. While the reasons behind rotator knee laxity are multifactorial, the impact of the anterolateral knee structures is significant. As such, substantial focus has been directed toward better understanding these structures, including their anatomy, biomechanics, in vivo function, injury patterns, and the ideal procedures with which to address any rotatory knee laxity that results from damage to these structures. However, the complexity of lateral knee anatomy, varying dissection techniques, differing specimen preparation methods, inconsistent sectioning techniques in biomechanical studies, and confusing terminology have led to discrepancies in published studies on the topic. Furthermore, anatomical and functional descriptions have varied widely. As such, we have assembled a panel of expert surgeons and scientists to discuss the roles of the anterolateral structures in rotatory knee laxity, the healing potential of these structures, the most appropriate procedures to address rotatory knee laxity, and the indications for these procedures. In this round table discussion, KSSTA Editor-in-Chief Professor Jón Karlsson poses a variety of relevant and timely questions, and experts from around the world provide answers based on their personal experiences, scientific study, and interpretations of the literature. Level of evidence V.

There are several different factors, why an anterior cruciate ligament (ACL) graft may fail. One reason is missed peripheral injuries, especially on the anterolateral side of the knee, which may be responsible for different grades of instability after ACL rupture. Thus, the aim of this thesis was to investigate the role of the anterolateral structures in restraining knee instability and provide a surgical rationale for extra-articular lateral reconstruction. A cutting study was performed using a six degree of freedom robotic setup. The anterolateral structures were subsequently transected in ACL-intact and ACL deficient knees and the drop in force was analysed. The iliotibial tract was the primary restraint to internal tibial rotation in 30°, 60°, and 90° knee flexion. The ACL presented the main contribution in full extension. In high-grade anterolateral rotatory instability (ALRI), an ACL reconstruction and an additional extra-articular lateral reconstruction may control this instability better than an isolated ACL reconstruction. Furthermore, it will share the load with the intra-articular graft and therefore prevent re-rupture. Cadaveric knees were tested in a muscle loading rig and the length changes of the native anterolateral structures and several extra-articular reconstructions were measured using a suture and a linear variable displacement transducer (LVDT). The Lemaire and the MacIntosh reconstruction, which were guided deep to the lateral collateral ligament (LCL) had preferable length change pattern, being tight in extension and slacken in flexion. The iliotibial tract was the primary restraint to internal tibial rotation and an injury should be expected in high-grade ALRI. Regarding length change pattern of lateral extra-articular reconstructions a Lemaire or MacIntosh reconstruction, guided deep to the LCL should be used. Open Access

No abstract available

Anterior cruciate ligament (ACL) rupture is a common injury associated with a failure to return to sport and early osteoarthritis. The optimal technique for ACL reconstruction (ACLR) is yet to be determined. The aim of this PhD was to investigate novel concepts in ACL anatomy and reconstruction, and thus provide quantifiable data to help clinicians choose the correct graft type, configuration, preparation and augmentation technique. A robotic testing system was utilised to perform cadaveric experiments. The load bearing characteristics of the fibres of the native ACL tibial attachment were quantified and compared to a blinded anatomical assessment. It was found that the most important fibres in resisting tibial displacements attach to the ‘C’-shaped anterior-medial area of the native ACL tibial attachment. The femoral attachment site has the most effect on ACL graft isometry, so a simplified 3-socket (3S) construct utilising two femoral sockets is attractive. The ability of 3S, single- and double-bundle surgery to restore native knee kinematics was assessed. No significant benefit was observed over single-bundle surgery. Smaller tunnels for compressed grafts reduce bone loss. Instron materials testing machines were used to test non-irradiated allograft tendons following graft compression. Graft compression did not cause adverse mechanical effects. The grafts significantly increased in size during joint simulation with no effect on graft stability. Lateral extra-articular tenodesis (LEAT) is a popular adjunct to ACLR. It was not known whether closing the ilio-tibial band (ITB) defect overconstrains tibial rotation. Robotic testing found this was not the case. Therefore, it is advised that surgeons use a ribbon-like single-bundle reconstruction aligned with the anteromedial border of the tibial attachment. Graft compression downsizing should be used if bone loss is to be minimised. When considering an LEAT, the ITB defect can be left open or closed depending on patient or surgeon specific factors. Open Access

Current standard techniques used for anterior cruciate ligament reconstruction are unable to restore normal knee biomechanics. One explanation for this is that ongoing anterolateral rotatory instability is due to damage to anterolateral knee structures that current surgical techniques fail to address. Focus had previously moved away from the periphery of the knee towards intra-articular reconstruction, however in the past rotational instability was addressed with a lateral extra- articular tenodesis, and these were widely used techniques in the 1970s and 80s before falling out of favour. A detailed review of this surgery, including the Lemaire, Macintosh and Ellison procedures has been performed in this thesis, as well as a review of the pre existing anatomical knowledge of the anterolateral knee structures. Due to gaps in knowledge identified, an attempt to further define anterolateral knee anatomy has been made. 40 fresh frozen cadaveric knees have been dissected. A consistent structure termed the anterolateral ligament (ALL) was identified in 33 (83%) of the specimens. The ALL passed antero- distally from a femoral attachment point posterior and proximal to the lateral femoral epicondyle. It passed superficial to the lateral collateral ligament, to an attachment point midway between Gerdy’s tubercle and the fibula head. We sought to further determine the biomechanical role of the structure using length change experiments. The ALL was isometric from 0° to 60° degrees of flexion, and then slackened when the knee was flexed to 90°. Two independent musculoskeletal radiologists reviewed MRI appearances of the ALL and findings were consistent with our anatomical observations. The ALL may be involved in resisting the pivot shift and inserts at the site of the Segond fracture. Since the experiment numerous anatomical, biomechanical and radiological investigations have been published on the ALL and these are reviewed in detail. Open Access

The material selection plays a major role in the design of a patellofemoral joint (PFJ) replacement due to the reported damage of the femoral condyles in deep knee flexion using ultra-high molecular weight polyethylene for the patellar components. The use of softer materials such as PCU and PVA/PVP may induce fluid film lubrication and thus reduce the risk of cartilage damage. This research aims to investigate in-vitro tribological performance of the articulation of cartilage-on-PCU (Bionate® I 80A and Bionate® II 80A) and cartilage-on-PVA/PVP (different concentrations and PVA to PVP fractions) using a custom-designed multi-directional pin-on-plate rig. PVA/PVP showed low COF values (between 0.12±0.01 and 0.14±0.02) which were closer to the cartilage-on-cartilage articulation (0.03±0.01) compared to PCUs (0.41±0.02 for Bionate® II 80A and 0.50±0.02 for Bionate® I 80A). However, these PVA/PVP hydrogels were worn massively after 15 h articulation against the condyles. On the other hand, the counter-face condyles of PCUs were severely damaged, similar to the damage observed in the cartilage-on-stainless steel articulation. Among the PCUs, Bionate® II 80A showed superior tribological performance without depending on the lubricant and surface roughness parameters. When a migrating cartilage contact was achieved by articulating PCU pins on cartilage plates, PCUs revealed similar COF values (0.04±0.01) to the cartilage-on-cartilage articulation. This work has shown that PVA/PVP hydrogels require further development to enhance their wear resistance if they are to be used as part of a joint replacement. However, they have low COF against articular cartilage and so are attractive possibilities for the future. The tested PCU grades have shown PCUs (especially Bionate® II 80A) can work with acceptably low COF under the right articulating conditions and that they have low wear in those tests. Therefore, the work in this thesis supports the further development of patellofemoral joint prostheses which include PCU components. Open Access

Total knee arthroplasty (TKA) is a common surgical procedure to combat the onset of osteoarthritis; however failure of TKA may occur due to instability of the knee joint as a result of soft-tissue deficiency or imbalance, or incorrect implant choice. The aim of this PhD was to investigate how soft-tissues help stabilise knees implanted with different TKA designs and thus provide more quantifiable data to help clinicians choose the correct implant and soft-tissue release for patients. Cadaveric experiments utilising a robotic testing system investigated soft-tissue contributions in three different implants, and found that the collateral ligaments are the primary restraints in the implanted knee. On the lateral aspect of the knee, the lateral collateral ligament (LCL) provided restraint to varus and internal-external rotations in a primary TKA implant. On the medial side of the knee, the superficial medial collateral ligament (sMCL) is the main valgus, internal-external and anterior stabiliser in primary TKA: this was also the case in a more constrained implant which may have been expected to provide inherent stability to reduce the reliance on the sMCL. After resecting the medial structures in the constrained TKA knee, a soft-tissue reconstruction of the structures using a hamstring tendon was tested, and this was found to restore internal-external and varus-valgus rotational stability to pre-sectioned values. Therefore it is advised that surgeons should preserve the sMCL/ LCL when attempting to correct a varus/ valgus deformity, as it may result in a combined laxity pattern that cannot be compensated by the other soft-tissues. In the event of collateral deficiency, either a more constrained implant such as a hinged implant would be required to provide enough stability, or performing a soft-tissue reconstruction in conjunction with a less constrained implant may restore stability to the knee. Open Access

Total knee replacement (TKR) is a common and successful treatment for severe osteoarthritis of the knee. However, a large minority of people remain dissatisfied after the operation, despite adequate pain relief. Over 50 designs of TKR are used in the UK each year, but differentiating between these devices in terms of patient function and making the right choice for each patient remains challenging. The aim of this research was to characterise designs of TKR in the laboratory, using pre-clinical testing methods, in order to better understand TKR function, and make suggestions for improved implant design and testing. Conventional, medial-pivot, guided-motion and bicruciate retaining (BCR) TKRs were tested. Standard ASTM test methods used for CE-marking purposes were demonstrated to differentiate between devices, but did not produce enough information to adequately understand how a new device will behave clinically, or what the potential benefits of a new device would be to patients. Guided-motion devices are meant to replicate normal knee motion, but there has been concern that they might cause too much rotation of the knee, leading to anterolateral knee pain. Results from cadaveric testing suggest that they do not adequately mimic normal knee motion and small design changes may have little impact on performance. A BCR TKR, designed to improve stability in the replaced knee joint, was also tested. Knee kinematics were measured for three design phases and surgical feasibility was also assessed for this more complicated procedure. BCR TKR was shown to lead to more normal levels of anteroposterior tibiofemoral laxity, compared to a conventional, anterior-cruciate-ligament-sacrificing TKR. Inherent variability between people’s anatomy and osteoarthritis pathology suggests there will never be a single, perfect, TKR, but more comprehensive pre-clinical testing could improve the regulatory approval process and inform better device selection, leading to improved patient outcomes. Open Access

The use of total ankle replacement (TAR) for treatment of arthritis is rapidly increasing, but survival rates are of major concern. The primary indication for TAR revision is implant loosening, which is linked with inadequate primary stability manifested in higher levels of initial implant-bone micromotion. Finite-element (FE) modelling has been utilised to assess micromotion of arthroplasty implants, but not TAR. Additionally, the biomechanical consequences of TAR malpositioning during surgery – previously linked with higher failure rates – remain unexplored. The aim of this thesis was therefore to apply FE modelling to estimate implant-bone micromotion and peri-implant bone strains of current TAR designs under optimally-positioned and malpositioned cases, and thereby identify fixation features and malpositioning scenarios that place the reconstructed ankle at risk of early loosening. Computational models simulating commonly-used TAR designs (BOX®, Mobility® and Salto®) implanted into the tibia and talus were developed; the loads applied were the contact forces acting in the ankle during gait, as calculated using a previously-validated musculoskeletal model, while implementing muscle-architecture data obtained through dissections of cadaveric legs. Micromotion and strain outcomes were larger for the tibial compared with the talar components, in agreement with previous clinical observations. The tibial Mobility® and talar Salto® components demonstrated the largest micromotion. A gap between the tibia/talus and implant component resulted in a considerable increase in implant-bone micromotion and peri-implant bone strains; the Salto® design was relatively ‘forgiving’ for such malpositioning. It was concluded that better primary stability can be achieved through fixation nearer to the joint line, while relying on more than a single fixation peg, and preserving more of the cortical sidewalls of the bone; incomplete seating of the implant on the bone increases the risk for TAR failure. The models presented in this thesis may assist implant designers and surgeons in improving TAR designs and surgical techniques. Open Access

Low dual energy X-ray absorptiometry (DXA) measured bone mineral density (BMD) is used as an indicator of reduced bone strength and increased risk of fracture. BMD is widely used to identify patients for fracture prevention treatment. However, many fracture patients are not osteoporotic and would not have been identified by BMD screening. Also, BMD screening vastly overpredicts the number of patients who will progress to fracture. In summary, there is a need to improve explanation and prediction of femoral fracture. The overall aim of this thesis was to develop a finite element (FE) methodology that can explain (better than BMD) femoral fractures. An additional aim was to develop a novel experimental methodology, computed tomography (CT)-based digital volume correlation (CT-DVC). This method measures internal strain and fracture and served as validation for the FE methodology. The study included three groups of femur specimens; Group 1: 15 cadavers served as non-fracture controls, Group 2: 14 patients who had suffered a femoral fracture and Group 3: 13 patients scheduled for arthroplasty due to osteoarthritis served as a second non-fracture control group. The correlation of FE-predicted fracture load with in-vitro testing of cadaveric femurs was superior to that of BMD predictions (R2 = 0.77 and R2 = 0.59). Also, the match between CT-based FE models and the experimental observations was reasonably good (73% match) whereas BMD is unable to explain the fracture type. FE-predicted fracture types matched 13 of 14 patient-specific clinical fractures. Including bone quality and load (fall) direction, FE explained many of the clinical fractures that BMD was unable to explain and critical fall directions were identified. FE predicted lower strength of the fracture group which was associated with smaller sizes of anatomical parameters. Also the CT- DVC method demonstrated consistent results and was deemed to have great potential for a wide range of orthopaedic applications. Open Access

Background: Gait analysis is used to measure objectively the ability to walk before and after hip and knee joint replacement. Most gait literature to date has measured patients walking at slow speeds, which may have unintentionally characterized successful lower limb operations as the same regardless of its operation type. The aim of this thesis was to use an instrumented treadmill to (1) test the upper limits of gait performance of patients awaiting and after lower limb arthroplasty and (2) describe and compare different joint procedures to healthy controls. Method: Gait analysis was carried out using an instrumented treadmill. Study participants walked at their preferred walking and top walking speed on the treadmill. Their vertical ground reaction force and spatiotemporal data was captured for both limbs by tandem force plates beneath the treadmill’s belt. Results: The results suggest that at preferred walking speed on the flat, all subjects’ gait characteristics were similar irrespective of joint state. The differences between patient groups became more apparent at top walking speed. Weight acceptance, step length and stride length were the most useful variables assessing these differences. Unicompartmental knee replacement and hip resurfacing had closer to normal gait patterns when compared to total knee replacement and conventional total hip replacement respectively. Predictably patients with knee osteoarthritis had asymmetrical gait patterns, impulse was found to be the best variable distinguishing patients with knee osteoarthritis from healthy controls. The downhill walking assessment established that patients with unicompartmental knee replacements had a more normal gait pattern than total knee replacement patients. Conclusion: The gait results suggest that an instrumented treadmill is a useful metric to describe patient gait patterns. Testing performance at higher walking speeds allowed differences to be detected, which were undetectable at slower speeds. Anatomically conserving procedures such as unicompartmental knee replacement and hip resurfacing appear to have convincing functional advantages compared to less conserving joint replacement procedures. Open Access

At the limits of the range of hip motion, impingement, subluxation and edge loading can cause osteoarthritis in natural hips or early failure hip replacements. The aim of this PhD was to investigate the role of hip joint soft tissues throughout the range of hip motion to better understand their role in preventing (or perhaps even causing) these problematic load cases. A musculoskeletal model was used to investigate the muscular contribution to edge loading and found that in the mid-range of hip motion, the lines of action of hip muscles pointed inward from the acetabular rim and thus would stabilise the hip. However, in deep hip flexion with adduction, nearly half the muscles had unfavourable lines of action which could encourage edge loading. Conversely, in-vitro tests on nine cadaveric hips found that the hip capsular ligaments were slack in the mid-range of hip motion but tightened to restrain excessive hip rotation in positions close to the limits of hip motion. This passive restraint prevented the hip from moving into positions where the muscle lines of action were found to be unfavourable and thus could help protect the hip from edge loading. The ligaments were also found to protect the hip against impingement and dislocation. Out of the labrum, the ligamentum teres and the three capsular ligaments, it was found that the iliofemoral and ischiofemoral ligaments were primary restraints to hip rotation. These two capsular ligaments should be prioritised for protection/repair during hip surgery to maintain normal hip passive restraint. Whilst this can be technically demanding, failing to preserve/restore their function may increase the risk of osteoarthritic degeneration or hip replacement failure. Open Access

Osteoarthritis of the knee is one of the most prevalent diseases. The primary treatment for young patients is regenerative cartilage repair. The best treatment for the middle aged group is cartilage substitution material. Although in the worst case scenario, knee replacement becomes an option, giving proper treatment in advance, most patients can postpone or even avoid the irreversible replacement procedure. Since the surface varies in size and shape among patients, the conventional standard sized instruments are not appropriate for these novel treatments. The existing preparation technique used by surgeons is freehand debridement, which relies on highly skilful and experienced surgeons to yield good results. Although there are some patient-specific instrumentations on the market, the majority of them are designed to assist the conventional knee replacement implants, and are not applicable on curved surfaces. The aim of this study was to develop effective, simple and standardized patient-specific instrumentations for large joint surface preparation. The study started from verifying the accuracy of experimental equipment and proposed patient-specific techniques and instruments. Then, an experiment on plastic bone samples was performed. The outcomes showed that the errors of repairing surface, depth, and position were less than ±0.5 mm, ±0.5 mm and ±1.0 mm respectively. This is regarded as sufficiently accurate to prepare the knee surface. Then, some improvements were made on the surgical jigs and procedures for the later cadaveric experiment. Eight cadaveric samples were tested. The outcomes showed that the 5% and 95% percentiles of errors in repairing surface, position errors and depth errors were -0.22 mm to 0.56 mm, -1.40 mm to 1.04 mm, and -0.58 mm to 0.20 mm respectively. Furthermore, patient-specific instrumentations were designed for arthroscopic procedures, which is the only patient-specific guide that can be used arthroscopically for orthopaedic surgeries. A tibial preparation guide was also designed, but further tests are needed for this device. Open Access

Injury of the Medial Patellofemoral Ligament (MPFL) occurs during patellofemoral joint (PFJ) dislocation. Reconstruction of this ligament is a common treatment for this patient population. This thesis is composed of a series of cadaveric experiments examining the MPFL. The MPFL was found to originate from the midpoint between the medial epicondyle and adductor tubercle. Its length change pattern was close to isometric through knee flexion range. Transection of the MPFL resulted in significant increases in lateral patellar translation, tilt and increased lateral PFJ contact pressures in early knee flexion (all: P0.05). Femoral tunnels positioned too proximal resulted in increased medial contact pressures and patellar motion in deeper knee flexion, whilst distal tunnels caused increased medial contact pressures near extension (P0.05). The radiographic femoral MPFL attachment point, assuming the anterior-posterior medial femoral condyle diameter to be 100%, was; 40% from the posterior, 50% from the distal and 60% from the anterior femoral border. Reduction in medial quadriceps muscle tension was similar to the effect of MPFL transection causing a significant increase of lateral patellar tracking and lateral PFJ contact pressures (all: P0.05). With tibial tuberosity-trochlear groove (TT-TG) distances of up to 15mm PFJ mechanics were satisfactorily restored with anatomical MPFL reconstruction (P>0.05). However in cases with TT-TG distances greater than 15mm, MPFL reconstruction alone was not sufficient to restore PFJ contact mechanics and patellar kinematics (P

There is increasing use of Unicondylar or Unicompartmental Knee Replacements (UKR), especially following publication of good survival data and a trend towards ‘minimally invasive surgery’. The UKR preserves one of the femoral condyles and its meniscus, plus both of the cruciate ligaments. Therefore, the knee functions more normally following UKR than after Total Knee Replacement (TKR). However, the odds for failure of the UKR are higher than the TKR, and a principal reason is loosening of the tibial and femoral components. There is a need for the development of more reliable UKR fixation designs. The overall aim of this research was to understand fixation of UKR and make recommendations for improvement to designers and surgeons. Since the Oxford mobile-bearing UKR is most widely used in the UK, it was used as the benchmark in this study. To assess initial fixation, in-vitro bone-constructs were prepared from ten cadavers implanted with the Oxford mobile-bearing UKR and tested for bone strain and bone-implant interface motion with the implants fixed using first cementless and then cemented methods. Cementless fixation produced higher proximal tibia strain and bone-implant displacement than cemented fixation. Peak bone strain increased with reduced bone density, such that the lowest density specimen fractured when implanted with the cementless UKR. To assess long-term fixation, an in-vivo prospective follow-up study of 11 Oxford UKR patients was developed and conducted for one-year, taking measurements of bone density using Dual X-Ray Absorptiometry (DXA) scanning. The average bone resorption under the tibial implant was found to be low; while it was higher under the femoral component and very high under the tibial intercondylar eminence. The fixation of the Oxford UKR implant was considered to be adequate at 1-year. Finite Element (FE) simulation techniques were reviewed and developed to simulate the UKR knee for investigation of bone strain, bone-implant interface micromotion and bone remodelling to assess initial and long-term fixation performance. Computer simulations of the tibiae and femora of 2 patients and 4 cadaveric specimens (obtained from the in-vivo and in-vitro studies) were developed and validated for bone strain, bone-implant interface micromotion and bone remodelling. Comparative multi-specimen computational studies were conducted to understand how particular design features affected fixation. Good fixation was indicated for cementless UKRs when implanted in dense bone, but bone strains were very high in low density tibia. Cementation of the implants spread the loads more evenly and reduced bone strains. The cementless tibial implant caused less bone resorption (compared to the cemented equivalent) but the difference in the femur was small. Bone resorption was highest at the anterior tibia and posterior to the femoral peg. Bone density was an important factor in the fixation performance of implant design features. Less bulky fixation features reduced bone resorption, provided that the underlying bone was sufficiently dense to maintain bone strains below the failure limit of bone. For patients with dense bone, fixation could be improved with shorter tibial keels and less stiff femoral implants. For patients with low density bone, fixation could be improved with cementation and bone resection that avoids creating stress-raisers.

Arthroplasty of the knee has become one of the commonest orthopaedic procedures performed today. In the UK alone over 75,000 were performed in 2011. Patients requiring arthroplasty are getting younger and have higher demands on their replaced joints leading to continued evolution of prosthetic design. This biomechanical work has compared two different designs of Total Knee Arthroplasty (TKA) in relation to each other and the native un-resurfaced knee. The TKAs differed from each other in design of the femoral component. One had a single radius design and a trochlea that ran from the lateral side proximally, to the medial side distally, and the other prosthesis had a multi radius design with a symmetrical trochlea, essentially an unsided femoral prosthesis. The principal areas of study were the kinematics of the tibiofemoral articulation (TF), the patellofemoral joint (PFJ), the stability of the patella in the replaced knee joint and contact pressures of the tibiofemoral articulation. This was a cadaveric study using a knee navigation system to record the kinematic data for analysis. All the experiments involved cadaveric left legs of different genders and sizes. All the work was carried out at the same laboratory at Imperial College, London between July 2006 and October 2008. Both TKAs allowed significantly greater laxity than the intact knee with an anterior drawer force applied as the knees moved from 40 degrees of flexion to full extension. No significant difference was found between the two TKAs used in this study in the TF work. For the PFJ, the multiradius design was significantly more stable when the patella was displaced medially than the intact knee (p=0.016) at 30 degrees of flexion. It was also more stable than the single radius design from 0-30 degrees of flexion. There were no significant differences found between the single radius TKA and the intact knee during any of the PFJ work. Both TKAs appeared to behave differently when assessing patellar flexion with marked differences shown graphically but no statistically significant difference shown on post testing.In conclusion, both designs of TKA replicated the intact knee very well throughout all the experiments, apart from the differences noted above. This study was unable to show any significant advantage of using the newer single radius design when compared to the established multi-radius design. The single radius design did not appear to mimic the kinematics of the intact knee any closer than the established multiradius design.

The scope of this thesis was to verify whether anatomic reconstruction of the anterior cruciate ligament (ACL) with close replication of its two main bundles ensures better knee kinematics and improved clinical outcomes. The thesis articulates into three parts. In the first part the current anatomic knowledge is reviewed with regard to the double bundle ACL structure and an anatomic study is presented: its results will serve as a basis for the following kinematics and clinical studies. In the second part, a method to investigate cadaveric knee laxities is presented and employed to test intact and ACL deficient knees and to explore the function of the anteromedial and posterolateral ACL bundles. The ACL was found to be a primary restrain to anterior tibial translation mainly because of the action of the anteromedial bundle, with the posterolateral acting as a secondary restrain. Both bundles then were found to equally contribute to control the limit of internal rotation. Finally the reconstruction of both ACL bundles was demonstrated to be superior to traditional single bundle reconstruction in restoring intact knee anterior and rotational laxity. The third part focused on double bundle surgical technique with the development of surgical instruments that were validated on cadaver knees and found to be extremely accurate on the tibial side, less on the femur. Surgical technique was then improved and introduced into clinical practice. Two clinical studies were conducted and demonstrated the superiority of double bundle anatomic reconstruction in improving subjective and objective results as well as instrumented knee laxity measurements. In conclusion the main finding of this thesis was that, after a deep understanding of ACL anatomy and biomechanics, the replication at surgery of its native structure improves knee stability and patients’ satisfaction.

Compared to hip and knee, anatomic shoulder arthroplasty is relatively poorly understood, underdeveloped and reported loosening rates are very high, the common cause of failure being glenoid aseptic loosening. The aim of this thesis was first to establish in-vitro and in-vivo CT protocols allowing direct monitoring of glenoid fixation and aseptic loosening and secondly to identify key elements of the procedure that could improve results of prosthetic surgery. First, in-vitro, the ASTM standard method for evaluating loosening of glenoid implants was modified, so that, with the use of CT-scans at regular interval basis, it allows the direct monitoring of the failure observed in the laboratory setting. The failure was observed at the cement-implant interface and progressed from the edges of the implants, both superior and inferior, towards the keel. Secondly, an in-vivo CT protocol was established that eliminates most of the metallic artefacts caused by the humeral head and consequently enhances the visualisation of the radiolucent lines and osteolysis around the glenoid. The link between radiological lucencies and aseptic loosening was confirmed first in a study including 68 cases using this CT protocol, which confirmed the progression of the lucencies over time, and secondly, by the use of Spect-CT. The 3-dimensional spatial (mal)position of the glenoid component and the resulting consequences were analysed in three additional studies. The effect of malposition on clinical results and radiological lucencies; the relationship to the preoperative eroded glenoid and the relationship to polyethylene wear were all investigated. These studies stressed how inaccurately the glenoid components are positioned in clinical practise and that this inaccuracy has a detrimental effect on polyethylene wear; aseptic loosening and ultimately on clinical outcome. Future work should focus on establishing the optimal position of the glenoid implant, and how to achieve this optimal placement in surgical practise.

Aims To determine the effects of tibial component rotation and posterior slope on kinematics following Scorpio CR navigated TKR in cadaver specimens. Methods & Results Knee kinematics were monitored using a validated IR Navigation System. Ten normal comparable cadaver specimens were mounted in a custom rig allowing assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR. The surgery was performed as per normal operating surgical protocols by an expert knee surgeon. However an augmented tibial component was implanted allowing the researchers to precisely modify its rotation and posterior slope. A pneumatic cylinder attached to the quadriceps tendon was then used to repetitively flex and extend the knee with a variety of applied loads. Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. Combined malrotations over 10 degrees with posterior slopes over 6 degrees resulted in prosthetic subluxation under certain loading conditions. Discussion Knee kinematics are different after TKR. Increasing internal and external malrotation as well as the addition of posterior slope resulted in deviations of TKR kinematics through alteration of the neutral path of movement and or the envelope of laxity. Combined misalignments of slope and rotation resulted in the greatest deviations from normal kinematics, and in some cases, prosthetic subluxation. Incompatibilities of alignment may result in increased ligament tension and component articulation dysfunction that may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.

Long-term survivorship of a total knee replacement (TKR) relies on the strength of bone around the implant and its initial stability. Aseptic component loosening caused by mechanical factors is a recognised failure mode for knee prostheses. Bone resorption due to “stress-shielding” of the stiff stemmed implants will potentially lead to weakened bone strength, and presents a challenge for revision TKR surgery. The aim of this study was to develop analytical methodologies for the investigation of fixation performance of TKR, and to gain a better understanding of the prosthetic design requirements, addressing two major mechanical problems of bone remodelling and aseptic loosening. Patient-specific finite element (FE) modelling incorporated with a strain-adaptive bone remodelling theory was used to simulate bone remodelling responses of the postoperative tibial fixation. The choice of cementing technique was found to influence the remodelling behaviour; cemented fixationmodelled as a firm anchorage of the prosthesis onto the bone, was predicted to induce greater stress-shielding effect consequently leading to severe proximal bone resorption; for a fixation relying on biological attachment of bony ingrowthmodelled as a less firmly anchored boneprosthesis interface, lesser proximal bone resorption was predicted. The consideration of bone remodelling in FE simulations for fixation analyses is paramount as it influenced the risk prediction of aseptic loosening between prosthesis designs. The cement tensile stresses and bone-prosthesis interface micromotions predicted were different prior to and after bone adaptation. FE predictions of the MIS mini-keel and standard stemmed prosthesis fixations after simulating six months of bone adaptation correlated well with the RSA measurements at a similar period. A modified in-vitro technique of measuring bone-prosthesis relative micromotion was developed for relating initial stability of the cemented and cementless (press-fit) tibial prostheses fixations to late aseptic loosening. The developed computational and invitro methods should be applicable to other joint replacements.

INTRODUCTION: Patellofemoral dysfunction following total knee replacement (TKR) is significant. Due to the intimate relationship of the femoral component and patella, aspects of knee arthroplasty such as femoral component malrotation and patellofemoral overstuff have been sited as predisposing factors to such complications. The principal structures of the extensor retinaculum act as a checkrein for the patella as it tracks over the femur. Little biomechanical information is available on the behaviour of these structures, or the effects of TKR on them. AIM: The aim of this thesis was to measure retinacular behaviour in the normal knee and following TKR. We hypothesise that TKR will cause significant elongation of the retinacula and this would be further deranged with the addition of femoral component malrotation and patellofemoral overstuff. METHODS: Retinacular length changes were measured by threading fine sutures along the retinacula and attaching these to displacement transducers. The intact knee was flexed-extended on a custom built rig, while the quadriceps were tensed. Measurements were repeated post-TKR (Genesis II CR, Smith & Nephew Co.), following internal/external rotation of the femoral component 5° and finally altering the resurfaced patellar thickness by 2mm increments. RESULTS: The medial patellofemoral ligament (MPFL) was close to isometric, whereas the lateral retinaculum slackened significantly with knee extension. TKR did not cause statistically significant elongation of the retinacula. Internal rotation of the femoral component resulted in the MPFL slackening whereas external rotation resulted in the MPFL tightening as the knee extended. The lateral retinaculum showed no significant differences. Overstuffing the patellofemoral joint caused significant stretching of the MPFL at all angles of knee flexion, but very little change in the lateral retinaculum. CONCLUSION: This work has shown a correctly positioned TKR does not cause significant retinacular length changes sufficient to affect knee function. It has shown that small changes in femoral component rotation and patellofemoral overstuff of 4mm cause significant changes, particularly in the medial structures and not the lateral structures, contrary to current understanding. This work has described for the first time how the lateral retinaculum’s mobile attachments allow its principal fibres to move anteriorly and posteriorly with the patella, taking up any slack/tension produced by abnormal patellar shift/tilt. This work provides important insight into the contribution of the retinacula to patellofemoral biomechanics after knee replacements and may help in developing a more soft tissue friendly knee prosthesis.