A P Monk

The patho-anatomy of patellofemoral subluxation

Patella subluxation assessed on dynamic MRI has previously been shown to be associated with anterior knee pain. In this MRI study of 60 patients we investigated the relationship between subluxation and multiple bony, cartilaginous and soft-tissue factors that might predispose to subluxation using discriminant function analysis. Patella engagement (% of patella cartilage overlapping with trochlea cartilage) had the strongest relationship with subluxation. Patellae with > 30% engagement tended not to sublux; those with < 30% tended to sublux. Other factors that were associated with subluxation included the tibial tubercle-trochlea notch distance, vastus medialis obliquus distance from patella, patella alta, and the bony and cartilaginous sulcus angles in the superior part of the trochlea. No relationship was found between subluxation and sulcus angles for cartilage and bone in the middle and lower part of the trochlea, cartilage thicknesses and Wiberg classification of the patella. This study indicates that patella engagement is a key factor associated with patellar subluxation. This suggests that in patients with anterior knee pain with subluxation, resistant to conservative management, surgery directed towards improving patella engagement should be considered. A clinical trial is necessary to test this hypothesis.

Loosening of the femoral component after unicompartmental knee replacement

We describe a technique for the diagnosis of loosening of the femoral component of the Oxford Unicompartmental Knee Replacement using accurately aligned lateral radiographs in extension and flexion. If gaps are present between the component and cement on one radiograph and not on the other, the component is loose.

Automatic bone segmentation in ultrasound images using local phase features and dynamic programming

We present a novel method for bone structure segmentation in two-dimensional (2D) ultrasound (US) images as a precursor to 3D bone surface reconstruction and registration. The main contributions of this paper are to develop a dynamic programming segmentation solution that: (a) eliminates the soft tissues above a bone structure by taking into consideration acoustic characteristics of the intensity profile along each US scan line, including the integrated backscattering (IBS) and acoustic shadows; and (b) combines the local energy, the local phase and local phase feature symmetry to highlight areas of the image that have a high probability of being bone structures. The automatic segmentation results were compared to manual segmentation ground truth carried out by clinical experts. The average Euclidean distance (ED) error between the two methods was less than 2 pixels (approximately 0.2mm). Our method significantly decreases the number of erroneous detections of the soft tissue compared to existing methods [1].

Evidence in managing traumatic anterior shoulder instability: a scoping review

Background Traumatic anterior shoulder instability (TASI) accounts for 95% of glenohumeral dislocations and is associated with soft tissue and bony pathoanatomies. Non-operative treatments include slings, bracing and physiotherapy. Operative treatment is common, including bony and soft-tissue reconstructions performed through open or arthroscopic approaches. There is management variation in patient pathways for TASI including when to refer and when to operate. Methods A scoping review of systematic reviews, randomised controlled trials, comparing operative with non-operative treatments and different operative treatments were the methods followed. Search was conducted for online bibliographic databases and reference lists of relevant articles from 2002 to 2012. Systematic reviews were appraised using AMSTAR (assessment of multiple systematic reviews) criteria. Controlled trials were appraised using the CONSORT (consolidation of standards of reporting trials) tool. Results Analysis of the reviews did not offer strong evidence for a best treatment option for TASI. No studies directly compare open, arthroscopic and structured rehabilitation programmes. Evaluation of arthroscopic studies and comparison to open procedures was difficult, as many of the arthroscopic techniques included are no longer used. Recurrence rate was generally considered the best measure of operative success, but was poorly documented throughout all studies. There was conflicting evidence on the optimal timing of intervention and no consensus on any scoring system or outcome measure. Conclusions There is no agreement about which validated outcome tool should be used for assessing shoulder instability in patients. There is limited evidence regarding the comparative effectiveness of surgical and non-surgical treatment of TASI, including a lack of evidence regarding the optimal timing of such treatments. There is a need for a well-structured randomised control trial to assess the efficacy of surgical and non-surgical interventions for this common type of shoulder instability.

Surgeons' Accuracy in Achieving Their Desired Acetabular Component Orientation.

BACKGROUND Wide variability in cup orientation has been reported. The aims of this study were to determine how accurate surgeons are at orientating the acetabular component and whether factors such as visual cues and the side of operating table improved accuracy. METHODS A pelvic model was positioned in neutral alignment on an operating table and was prepared as in a posterior approach. Twenty-one surgeons (9 trainers and 12 trainees) were tasked with positioning an acetabular component in a series of target orientations. The orientation of the component was measured using stereophotogrammetry, and the difference between the achieved orientation and the target orientation was calculated. Tasks included stating the surgeons preferred orientation and thereafter placing the cup in that orientation, reproducing visual cues (transverse acetabular ligament and alignment guide), altering orientation by 10°, and estimating orientation while on the assistants side. RESULTS The preferred inclination was 42° and the preferred anteversion was 21°. On average, surgeons decreased the inclination by 4° and increased the anteversion by 11° when tasked with replicating their desired orientation. The variability (defined as 2 standard deviations) in achieving a target orientation was 14°. The use of visual cues, such as the transverse acetabular ligament or the alignment guide, significantly improved accuracy to 1° for anteversion (p < 0.001) and -3° for inclination (p = 0.003). In addition, the use of an alignment guide reduced the variability by one-third. Trainees and trainers had similar accuracy and variability. There was greater variability in assessing cup inclination when standing on the assistants side compared with the surgeons side of the table, which has implications for training. CONCLUSIONS Surgeons overestimate operative inclination and underestimate anteversion, which is of benefit, as this, on average, helps to achieve the desired radiographic cup orientation. Although the use of visual cues helps, conventional techniques result in a large variability in acetabular component orientation. New and better guides and methods for training need to be developed.

Greater trochanter tracking in ultrasound imaging during gait

We are developing a new system called Computer-Aided Tracking and Motion Analysis with Ultrasound System (CAT & MAUS) to dynamically describe joint kinematics for pathology research on musculoskeletal conditions. It is essential to have computer-aided bony structure tracking in ultrasound (US) sequences in such a system for practical use. However, unlike CT or MRI imaging, the appearance of bony landmarks in US imagery can be distorted by the image formation process. In this paper, a target patch tracking approach is presented for tracking ultrasound landmarks. The tracker is based on compressed intensity features which are stored in k-dimensional (K-D) trees for fast and discriminatory image patch searches. Dynamic programming is used to find the optimal track through the ultrasound video. We find that our method is more accurate than the mean-shift and the KLT trackers for bony structures, especially with large movements.

Measurement of in-vivo patella kinematics using motion analysis and ultrasound (MAUS)

This paper describes a motion analysis ultrasound system (MAUS) designed for the in-vivo study of the kinematics of patellofemoral joints (PFJ) in both normal and replaced knees. This system utilises non-iodising radiation to effectively acquire kinematic data during weight-bearing activities. Validation studies on a phantom established that the measurement accuracy of the system was 1.43 mm. A clinical validation trial is included.

The failing medial compartment in the varus knee and its association with CAM deformity of the hip.

BACKGROUND Since 2011, the knee service at the Nuffield Orthopaedic Centre has been offering a neutralising medial opening wedge high tibial osteotomy (HTO) to a specific group of patients with genu varum and early knee osteoarthritis. An observation was made concerning this group of patients and the presence of CAM deformity at the hip. The aim of this study is to establish whether or not any association exists between the OA phenotype shared by our HTO group and the incidence of CAM deformity at the hip. METHODS A cross-sectional study was designed to estimate the prevalence of CAM-type lesions across different groups of individuals. Our HTO group (n=30) was compared to a pre-arthroplasty group (n=20) and control group (n=20). A total of 70 subjects were identified across the different groups all of whom had long-leg radiographs (LLRs) available for analysis. LLRs were analysed using an in house developed Matlab®-based (Matlab R2009b; MathWorks) software package for hip measurements and MediCAD® (Hectec GmbH, Germany) for lower limb alignment measurements. RESULTS The HTO group had a significantly higher prevalence of CAM lesions (57%) than both the pre-arthroplasty (40%) and control (30%) groups. This difference was maintained when results were adjusted for potential confounding factors (age, gender and laterality). Across the groups, individuals with tibia vara were more likely to have CAM-deformity of the hip (p=0.021). CONCLUSION Patients with symptomatic early knee OA and varus deformity of the knee have a high prevalence of CAM deformity in the hip.

A preliminary modeling investigation into the safe correction zone for high tibial osteotomy.

BACKGROUND High tibial osteotomy (HTO) re-aligns the weight-bearing axis (WBA) of the lower limb. The surgery reduces medial load (reducing pain and slowing progression of cartilage damage) while avoiding overloading the lateral compartment. The optimal correction has not been established. This study investigated how different WBA re-alignments affected load distribution in the knee, to consider the optimal post-surgery re-alignment. METHODS We collected motion analysis and seven Tesla MRI data from three healthy subjects, and combined this data to create sets of subject-specific finite element models (total=45 models). Each set of models simulated a range of potential post-HTO knee re-alignments. We shifted the WBA from its native alignment to between 40% and 80% medial-lateral tibial width (corresponding to 2.8°-3.1° varus and 8.5°-9.3° valgus), in three percent increments. We then compared stress/pressure distributions in the models. RESULTS Correcting the WBA to 50% tibial width (0° varus-valgus) approximately halved medial compartment stresses, with minimal changes to lateral stress levels, but provided little margin for error in undercorrection. Correcting the WBA to a more commonly-used 62%-65% tibial width (3.4°-4.6° valgus) further reduced medial stresses but introduced the danger of damaging lateral compartment tissues. To balance optimal loading environment with that of the historical risk of under-correction, we propose a new target: WBA correction to 55% tibial width (1.7°-1.9° valgus), which anatomically represented the apex of the lateral tibial spine. CONCLUSIONS Finite element models can successfully simulate a variety of HTO re-alignments. Correcting the WBA to 55% tibial width (1.7°-1.9° valgus) optimally distributes medial and lateral stresses/pressures.

Medial meniscal extrusion: a validation study comparing different methods of assessment

PurposeLongitudinal cohort studies of knee OA aetiology use MRI to assess meniscal extrusion within the same knee at sequential time points. A validated method of assessment is required to ensure that extrusion is measured at the same location within the knee at each time point. Absolute perpendicular extrusion from the tibial edge can be assessed using the reference standard of segmentation of the tibia and medial meniscus. This is labour intensive and unsuitable for large cohorts. Two methods are commonly used as proxy measurements. Firstly, the apex of the medial tibial spine is used to identify a reproducible MRI coronal slice, from which extrusion is measured. Secondly, the coronal MRI slice of the knee demonstrating the greatest extrusion is used. The purpose of this study was to validate these two methods against the reference standard and to determine the most appropriate method to use in longitudinal cohort studies. We hypothesised that there is no difference in absolute meniscal extrusion measurements between methods.MethodsTwenty high-resolution knee MRI scans were obtained in asymptomatic subjects. The tibia and medial meniscus were manually segmented. A custom MATLAB program was used to determine the difference in medial meniscal extrusion of the knee using the reference standard compared to the two other methods.ResultsAssessing extrusion using the single coronal MRI slice demonstrating the greatest extrusion overestimates the true extrusion of the medial meniscus. It incorrectly places the greatest meniscal extrusion at the anterior part of the tibia. Assessing extrusion using a consistent anatomical landmark, such as the medial tibial spine, most reliably corresponds to the reference of segmentation and measurement of true perpendicular extrusion from the tibial edge. Clinicians and researchers should consider this when assessing meniscal extrusion in the knee, and how it changes over time.ConclusionThis study suggests measuring meniscal extrusion on the coronal MRI slice corresponding to the apex of the medial tibial spine as this correlates most closely with the true perpendicular extrusion measurements obtained from manually segmented models.Level of evidenceDiagnostic, Level I.