Aims

The survival of humeral hemiarthroplasties in patients with relatively intact glenoid cartilage could theoretically be extended by minimizing the associated postoperative glenoid erosion. Ceramic has gained attention as an alternative to metal as a material for hemiarthroplasties because of its superior tribological properties. The aim of this study was to assess the in vitro wear performance of ceramic and metal humeral hemiarthroplasties on natural glenoids.

Aims

In recent conflicts, most injuries to the limbs are due to blasts resulting in a large number of lower limb amputations. These lead to heterotopic ossification (HO), phantom limb pain (PLP), and functional deficit. The mechanism of blast loading produces a combined fracture and amputation. Therefore, to study these conditions, in vivo models that replicate this combined effect are required. The aim of this study is to develop a preclinical model of blast-induced lower limb amputation.

Aims

Patients with recurrent anterior dislocation of the shoulder commonly have an anterior osseous defect of the glenoid. Once the defect reaches a critical size, stability may be restored by bone grafting. The critical size of this defect under non-physiological loading conditions has previously been identified as 20% of the length of the glenoid. As the stability of the shoulder is load-dependent, with higher joint forces leading to a loss of stability, the aim of this study was to determine the critical size of an osseous defect that leads to further anterior instability of the shoulder under physiological loading despite a Bankart repair.

Introduction: Classical studies have defined axes from prominent scapular landmarks that have been used to synthesise many applications. The morphology of the scapula is however known to be highly variable between individuals1,2,3. This introduces significant variability on the use of these classical axes for various clinical applications. Also, some of the literatureapplied landmarks were highly dependant on the presence of pathology, thus introducing more variability in the products they parented. This limits accuracy in inter-subject comparisons from such applications. Therefore there is a need to identify and define pathology-insensitive anatomical landmarks that are less variable between individuals than the variability of the overall scapular shape. The aim of this study was to define more scapular axes from clearly identifiable landmarks, analysing these and other classical definitions for the best axis that minimizes variability and is closely related to the scapular clinical frame of reference.

Materials and Method: Fourteen different axes of new and classical definitions from clearly identifiable landmarks were quantified by applying medical images of 21 scapulae. The orientations of the quantified axes were calculated. The plane of the blade of the scapula was defined, bounded by the angulus inferior4, the spine/medial border intersection5 and the most inferolateral point of the infra-glenoid tubercle. This was applied to grade the alienation of the quantified axes from the scapular blade. The angular relationships between individual axes of a spcapula were quantified, averaged over the 21 specimens and their standard deviations (SD) applied to grade the sensitivity of each axis to interscapular variations in the others. The volume of data required to define an axis (VDA) was noted for its dependency on pathology. These three criteria were weighted according to relative importance such that

axes bearing 10° or more from the blade deviated significantly and were eliminated;

Results: A least square line through the centre of the spine root was the most optimal medio-lateral axis. The normal to the plane formed by the spine root line and a least square line through the centre of the lateral border ridge was the most optimal antero-posterior axis.

Conclusion: These body-fixed axes are closely aligned to the cardinal planes6 in the anatomical position and thus are clinically applicable, specimen invariant axes that can be used in generalised and patient-specific kinematics modelling.

Objective patellar instability has been correlated with dysplasia of the femoral trochlea. This in vitro study tested the hypothesis that trochleoplasty would increase patellar stability and normalise the kinematics of a knee with a dysplastic trochlea. Six fresh-frozen knees were loaded via the heads of the quadriceps. The patella was displaced 10 mm laterally and the displacing force was measured from 0° to 90° of flexion. Patellar tracking was measured from 0° to 130° of knee flexion using magnetic sensors. These tests were repeated after raising the central anterior trochlea to simulate dysplasia, and repeated again after performing a trochleoplasty on each specimen. The simulated dysplasia significantly reduced stability from that of the normal knee (p < 0.001). Trochleoplasty significantly increased the stability (p < 0.001), so that it did not then differ significantly from the normal knee (p = 0.244). There were small but statistically significant changes in patellar tracking (p< 0.001).

This study has provided objective biomechanical data to support the use of trochleoplasty in the treatment of patellar instability associated with femoral trochlear dysplasia.

Many different clinical examinations are used to assess instability of the glenohumeral joint. Validation of these includes clinical data, follow-up, imaging, and arthroscopy. In spite of these many works, there currently exists no clear unique method for identifying and validation novel clinical examinations. The aim of this study was to use a computational tool to quantify the specificity of clinical examinations in assessing glenohumeral ligament (GHL) pathology. Five GHLs were modelled according to the literature [1]. Physiological kinematics data [2] were applied to simulate 23 clinical examination manoeuvres for the glenohumeral joint. Individual ligament forces were computed as a percentage of the total ligamentous restraint. The 0° abduction anterior-laxity test was most specific for the superior GHL (82.3%). The anterior apprehension in the coronal plane and 90° anterior-laxity tests were specific for the anterior band of the inferior GHL (abIGHL – 100%). Pure scapular plane abduction and the 90° abduction inferior-laxity tests were specific for the axillary pouch of the IGHL (apIGHL – 100%, 89.6%). Specific tests for posterior band of the IGHL were posterior apprehension (95.1%), 0° and 20° abduction posterior-laxity, and 30° to 45° flexion Norwood and Terry test (100% each). The middle GHL did not exhibit any exclusive loading pattern for any of the tests. A secondary insertional morphology was simulated with the abIGHL positioned at the 4 o’clock position as opposed to the 3 o’clock position [1,2,3]. Significant loading differences were computed for the same ligaments during the same tests. This study demonstrates the sensitivity of specific tests for individual GHLs, but provides the significant caveat that ligament loading is significantly influenced by normal anatomical variations.

Introduction: By characterising ACL strain behaviour in intact and posteromedial deficient knees under a variety of external loading conditions the aim of this work was to demonstrate whether posteromedial corner insufficiency could increase strain in an ACL reconstruction graft.

Materials and Methods: 15 fresh cadaveric knees were mounted on a materials testing machine. A miniature extensometer was implanted onto the anteromedial bundle (AMB) of the ACL. The knees were loaded in: Anterior draw (150N), varus/valgus rotation (5Nm) and internal/external rotation (5Nm) at 0°, 15°, 30°, 60° & 90° flexion. The posteromedial corner structures – posteromedial capsule, superficial MCL and deep MCL – were cut sequentially and the effect AMB strain measured.

Results: Strain data for analysis was available for 11 intact knees: Tibial internal rotation produced increased strain in the AMB at all angles of knee flexion (p< 0.05). Tibial external rotation reduced ACL strain at 0° to 30° (p< 0.05) and 60° to 90° knee flexion (p> 0.05).

Anterior loading of the tibia increased AMB strain. With the tibia free to rotate, strain was highest at 90 degrees knee flexion (5.3%) and lowest at 0 degrees (1.6%). Fixed internal and external tibial rotation reduced AMB strain produced by a 150 N anterior drawer force at all knee flexion angles.

Strain data for analysis was available for 6 Posteromedial Corner deficient knees:

With the tibia free to rotate or when locked in internal rotation, cutting the posteromedial structures had no effect on AMB strain with a 150 N anterior drawer force applied to the tibia. However, with the tibia locked in external rotation, cutting the posteromedial structures increased AMB strain at 60 and 90 degrees flexion. This difference however did not reach statistical significance.

Conclusions: The findings that division of the posteromedial structures may cause increased AMB strain and that there is significant load sharing by the peripheral ligamentous structures, suggests that valgus and rotational stresses to the knee in a patient with posteromedial corner insufficiency could lead to increased strain in the ACL graft, that would otherwise have been restrained by the posteromedial corner complex. It would also therefore seem to be appropriate to recommend the use of a collateral ligament brace in the post-operative period when combining a repair of the posteromedial structures and the ACL, to again prevent excessive graft strains.

Introduction: Models of shoulder motion differ with intended application and shoulder models often simplify the complex movement. Therefore, the design often negates clinical usage, in which, for example, multidirectional instabilities are present. To aid the work of clinicians in treating articulations without simplifying physiological constraint, a full open-chain 6 Degrees Of Freedom per articulation has been suggested (Inui et al., 2002).

Aim: Develop a spatial linkage model in order to facilitate communication between surgeon and engineer, and to apply this model to image datasets.

Model Design: Modification of Grood and Suntay’s (1983) 3-cylinder open chain model of the Tibiofemoral articulation to faithfully determine spatial parameters throughout a large range of motion, about clinically relevant axes.

Method: A computer program was scripted (Matlab, Mathworks Inc.) to embed orthogonal coordinate frames in both Humerus and Scapula. These were specified in respect of the planes of clinical rotation and well defined anatomical landmarks. A floating axis was defined within the script as the bipolar common perpendicular to both fixed frames. The magnitude of relative rotations, α, β and γ – flexion, abduction and axial rotation respectively – between Scapula and Humeral frames are measured directly, whilst translations occur along the axis about which rotation is measured. Gimbal lock limitations were minimised.

Validation: A physical linkage was made to validate the computations resulting in further model modification to create continuous rotational data throughout the following range: α from −90° – 270°, β from −90° – 270° and γ from −180° – 180°. This model provided an iterative development and examination tool for enhancing the capabilities of the modelling program.

Application: The model was applied to functional images acquired from both Electron Beam Computed Tomography and MRI. Anatomical landmark coordinates were digitised and input into the customised software. The real-time output displays rotations and translations of the humerus relative to the scapula.

Conclusion: The model circumvents a rotational sequence dependent outcome by determining the joint displacements within the modelled system as independent of the order in which segmental translations and rotations occur: 2 axes are fixed within articulating segments, whist a third mutually perpendicular floating axis moves in relation to both. The method facilitates multi-disciplinary communication: the parameters have a rigorous mathematical description and they correspond to clinical measures of position and orientation. Finally, this method accounts for Codman’s paradox with geometric principles.

Purpose: The glenoid labrum is a significant passive stabiliser of the shoulder joint. However, its microstructural form remains largely unappreciated, particularly in the context of function. An understanding of the labral structure leads to mechanical hypotheses, and therefore functional role in stability and load distribution, will aid an educated approach to surgical timing and repair.

Method: Fresh frozen cadaveric shoulders were grossly harvested via an extended Deltopectoral incision. The Glenohumeral joint was arthroscoped using a modification of Snyders (1989) routine in order to determine the specific anatomy of the capsulolabral complex. The glenoid fossa was then osteotomised before using micro-surgical loupes to section the labrum. Specimens were analysed using Scanning and Transmission Electron Microscopy and Confocal microscopy. Standard processing procedures were used to examine TEM specimens and the data was quantified by computational analysis. Specimens for SEM were cryofractured and Extracellular Matrix removed using a cell maceration technique to expose collagen fibre networks. Images were evaluated qualitatively. Sliced specimens for confocal were serially analysed along their z-axis, and post-processed to form 3-D reconstructions of collagen fibres.

Results: Two distinct homogenous areas were identified: (1) a superficial tight meshwork of fibrils and (2) a deep layer with a densely packed fibrous braid which were circumferential in orientation. A third area showed varying distribution of loosely arranged collagen fibres ranging from small fibres apposing area 1 to larger interleaved groupings near area 2. In radial transverse section, both normal and abnormal (stellate and spiral) fibrils were identified.

Conclusion: Contrary to published evidence, our results suggest the glenoid labrum is subjected a number of mechanical environments. Possibly distinct regions of the labrum contribute to load sharing; a well vascularised hydrated compressive zone and a tensile component distributing circumferential hoop stress, whilst both braiding and region interfaces suggest shear conditions.

We have reviewed the literature on the anatomy of the posteromedial peripheral ligamentous structures of the knee and found differing descriptions. Our aim was to clarify the differing descriptions with a simplified interpretation of the anatomy and its contribution to the stability of the knee.

We dissected 20 fresh-frozen cadaver knees and the anatomy was recorded using video and still digital photography. The anatomy was described by dividing the medial collateral ligament (MCL) complex into thirds, from anterior to posterior and into superficial and deep layers. The main passive restraining structures of the posteromedial aspect of the knee were found to be superficial MCL (parallel, longitudinal fibres), the deep MCL and the posteromedial capsule (PMC). In the posterior third, the superficial and deep layers blend. Although there are oblique fibres (capsular condensations) running posterodistally from femur to tibia, no discrete ligament was seen. In extension, the PMC appears to be an important functional unit in restraining tibial internal rotation and valgus.

Our aim was to clarify and possibly simplify the anatomy of the posteromedial structures. The information would serve as the basis for future biomechanical studies to investigate the contribution of the posteromedial structures to joint stability.

We have tested the hypothesis that the meniscofemoral ligaments make a significant contribution to resisting anteroposterior and rotatory laxity of the posterior-cruciate-ligament-deficient knee. Eight cadaver human knees were tested for anteroposterior and rotatory laxity in a materials-testing machine. The posterior cruciate ligament (PCL) was then divided, followed by division of the meniscofemoral ligaments (MFLs). Laxity results were obtained for intact, PCL-deficient, and PCL-MFL-deficient knees.

Division of the MFLs in the PCL-deficient knee increased posterior laxity between 15° and 90° of flexion. Force-displacement measurements showed that the MFLs contributed 28% to the total force resisting posterior drawer at 90° of flexion in the intact knee, and 70.1% in the PCL-deficient knee. There was no effect on rotatory laxity.

This is the first study which shows a function for the MFLs as secondary restraints to posterior tibial translation. The integrity of these structures should be assessed during both imaging and arthroscopic studies of PCL-injured knees since this may affect the diagnosis and management of such injuries.

The aim of this study was to determine the function of the meniscofemoral ligament in the cranio-caudal and rotatory laxity of the ovine stifle.

Twenty fresh cadaveric ovine stifles were harvested from fully mature sheep, average weight 25kg. The joint was denuded of its muscular attachments leaving the capsule, including the patella and patellar tendon undisturbed. The femur and tibia were divided 10 cm from the joint line, positioned in cylindrical pots, and secured in polymethylmethacrylate bone cement. The stifles were tested in a four-degree-of-freedom rig positioned in an Instron materials testing machine. This allowed unconstrained coupled tibial rotations and translations during application of cranial (anterior) and caudal (posterior) draw forces. Forces up to a maximum of 100Nm were applied in the anterior and posterior directions, and the resultant translations were measured. These parameters were assessed at 30, 60, 90, and 110 degrees of flexion in ten intact stifles. Similar measurements were carried out after division of the caudal (posterior) cruciate ligament, followed by division of the meniscofemoral ligament. The sequence of division was reversed for a further ten stifles.

Division of the meniscofemoral ligament resulted in an 18–38% increase in posterior translation at all angles of flexion, both in the intact and in the caudal cruciate ligament-deficient stifle (p< 0.05). There was no significant increase in anterior translation. This effect was largest with the joint relatively extended (at 30°). Division of the meniscofemoral ligament also resulted in a 5–32% increase in internal rotation of the tibia after application of a 6Nm torque in the caudal cruciate-deficient knee. This was significant at 30° and 110° flexion (p< 0.05).

The meniscofemoral ligament is a significant secondary restraint in resisting the posterior draw and internal tibial rotation in the sheep stifle joint. This is the first study demonstrating a functional role for this structure in any animal. Its counterpart in the human is the posterior meniscofemoral ligament of Wrisberg. Several studies have demonstrated similarities between the sheep stifle and the human knee. Confirmation of a similar role for the ligament of Wrisberg in the human knee would have a significant bearing on the prognosis and management of the posterior cruciate ligament injured knee.

Aim: To accurately assess cross-sectional areas of the MFLs and distinguish between the mechanical properties of the anterior and posterior meniscofemoral ligaments.

Methods: Twenty-eight fresh frozen cadaveric knees were dissected to isolate the lateral meniscus and MFLs, which remained attached to the femur. The cross-sectional areas of MFLs were determined using the Race-Amis¹ casting method for measurement. The ligaments were then tensile tested in an Instron materials testing machine. The stress and strain in each sample was calculated from measurements of cross sectional area, load applied, and increase in length,.

Results: The mean cross sectional area for the anterior MFL (aMFL) was 14.7 mm² (±14.8mm²) whilst that of the posterior MFL (pMFL) was 20.9mm² (±11.6mm²). The mean loads to failure were 300.5N (±155.0N) for the aMFL and 302.5N (±157.9N) for the pMFL, with elastic moduli of 281MPa (±239MPa) and 227MPa (±128MPa) respectively. There were no significant differences in structural or material properties between the two MFLs. When compared with the posterior cruciate ligament (PCL), the mean ultimate loads of the MFLs were similar to those of the posterior bundle of the PCL (pPC), and their elastic moduli were analogous to the anterior bundle (aPC).

Discussion: This is the first study to distinguish between the properties of the aMFL and pMFL, and indicates that both ligaments must be given equal consideration when formulating hypotheses on function. The aMFL and pMFL may also serve mutually distinct functions in the human knee. Previous authors² have commented that the reciprocal tightening and slackening of the aPC (taut in flexion) and pPC (taut in extension) indicates a difference in function of these two components of the PCL. Others³ have similarly commented on the reciprocal tightening and slackening of the two MFLs. This may also indicate differing functions for these ligaments. It is proposed that the aMFL supplements the function of the aPC, whilst the pMFL supplements the function of the pPC. This hypothesis stimulates debate on preservation of these structures during PCL reconstruction.

Race A., Amis A.A., 1996. Cross-sectional area measurement of soft tissue. A new casting method. Journal of Biomechanics 29(9), 1207–1212.

Aim: To accurately identify the meniscofemoral ligaments in cadaveric human specimens, and to determine anatomical variations in the posterior cruciate ligament that may lead to mis-identification of these structures.

Methods: A total of 79 fresh frozen knees were examined from 45 cadavers Combined anterior and posterior approaches were used to inspect the vicinity of the posterior cruciate ligament (PCL) for the presence of the anterior and posterior meniscofemoral ligaments. The anterior approach utilised a medial parapatellar incision followed by division of the anterior cruciate ligament, whilst a midline posterior arthrotomy was used for the posterior approach. Further dissection facilitated inspection of the meniscal and femoral attachments of the MFLs, and measurement of their lengths. Videos of MFL and PCL motion during passive flexion of the cadaveric were also performed.

Results: In total, 74 (94%) of the 79 specimens contained at least one meniscofemoral ligament. The posterior meniscofemoral ligament (pMFL) was present in 56 (71%) specimens, whilst the anterior meniscofemoral ligament (aMFL) was present in 58 specimens (73%). Both ligaments coexisted in 40 (51%) of knees. In 15 specimens the PCL was seen to have oblique fibres, which attached proximal to the tibial attachment of the main part of the PCL. We termed this “the false pMFL”, as it could be easily mis-identified as the posterior meniscofemoral ligament. Several other anatomical variations were also identified. The mean length of the aMFL was 20.7±3.9mm, whilst that of the pMFL was 23±4.2mm. Although the lengths of the MFLs were relatively constant, there was a wide variation in thickness.

Discussion: This study confirms the high incidence of at least one MFL in humans, which suggests a functional role for these structures. The oblique fibres of the PCL can be readily mis-identfied as the pMFL. These caveats should be borne in mind, during both arthroscopic examination and in the interpretation of magnetic resonance imaging (MRI) scans of the knee. Although some variations of the MFLs have been reported on MRI imaging2, there has been no note of the oblique fibres of the PCL reported in the present study. As this variation was present in almost one in five of our specimens, its appearance on MRI scanning requires investigation.

The function of the meniscofemoral ligaments is undetermined, although many hypotheses comment on a role in guiding the motion of the lateral meniscus during knee flexion. Other possibilities include a function as a secondary restraint supplementing the posterior cruciate ligament.

Objective: To provide a functional, anatomical description of the posteromedial structures, allowing future biomechanical studies to evaluate how they act to restrain tibio-femoral joint motion and contribute to joint stability.

Methods: Twenty fresh cadaveric knee joints were dissected. The appearance of the medial ligament complex was recorded using still and video digital photography as the specimens were flexed, extended, internally and externally rotated.

Results: We divided the medial structures into thirds, from anterior to posterior, and into three layers from superficial to deep: Layer 1: Fascia. Layer 2: Superficial MCL. Layer 3: Deep MCL and capsule. In the Posteromedial Corner (posterior third) it is not possible to separate Layers 2 and 3. The posteromedial corner (PMC) envelops the posterior medial femoral condyle. A discrete posterior oblique ligament (POL) is not identifiable. The PMC appears to be a functional unit with a role in passively restraining tibio-femoral valgus and internal rotation with the knee extended. The semimembranosus, through its tendon sheath attachments, may act as a dynamic stabiliser.

Conclusion: The MCL appears to have three functional units:Superficial MCL, Deep MCL and PMC. We believe that this description allows a logical approach to understanding the biomechanics and surgical reconstruction of the posteromedial structures. We plan to use this anatomical study as the basis for further work to evaluate the how these functional units act.

Our objectives were to establish the envelope of passive movement and to demonstrate the kinematic behaviour of the knee during standard clinical tests before and after reconstruction of the anterior cruciate ligament (ACL). An electromagnetic device was used to measure movement of the joint during surgery.

Reconstruction of the ACL significantly reduced the overall envelope of tibial rotation (10° to 90° flexion), moved this envelope into external rotation from 0° to 20° flexion, and reduced the anterior position of the tibial plateau (5° to 30° flexion) (p < 0.05 for all). During the pivot-shift test in early flexion there was progressive anterior tibial subluxation with internal rotation. These subluxations reversed suddenly around a mean position of 36 ± 9° of flexion of the knee and consisted of an external tibial rotation of 13 ± 8° combined with a posterior tibial translation of 12 ± 8 mm. This abnormal movement was abolished after reconstruction of the ACL.

The meniscofemoral ligaments were studied in 84 fresh-frozen knees from 49 cadavers. Combined anterior and posterior approaches were used to identify the ligaments. In total, 78 specimens (93%) contained at least one meniscofemoral ligament. The anterior meniscofemoral ligament (aMFL) was present in 62 specimens (74%), and the posterior meniscofemoral ligament (pMFL) in 58 (69%). The 42 specimens (50%) in which both ligaments were present were from a significantly younger population than that with one MFL or none (p < 0.05). Several anatomical variations were identified, including oblique fibres of the posterior cruciate ligament (PCL), which were seen in 16 specimens (19%). These were termed the ‘false pMFL’.

The high incidence of MFLs and their anatomical variations should be borne in mind during arthroscopic and radiological examination of the PCL. It is important to recognise the oblique fibres of the PCL on MRI in order to avoid wrongly identifying them as either a pMFL or a tear of the lateral meniscus. The increased incidence of MFLs in younger donors suggests that they degenerate with age.