Summary Statement

Cross-talk between cells from immune and bone system might play a role in molecular regulation of subchondral bone sclerosis in osteoarthritis. Macrophages, B-lymphocytes and tartrate-resistant acid phosphatase activity are specifically increased in sclerotic subchondral bone of patients with knee osteoarthritis.

Background

Currently existing optical navigation systems have ergonomic disadvantages such as size, the “line of sight” problem and extended registration procedures. The operation room becomes crowded by additional installations and competitive supporting devices around the patient. These points reduce and limit the acceptance of navigation systems for further applications. But especially for surgical quality management, navigation systems have a high potential as objective measurement systems.

A robust frame of reference is required to accurately characterize pathoanatomy in the proximal femur and quantify the femoral head-neck relationship. A three dimensional (3D) femoral neck axis (FNA) could serve such a purpose, but has not yet been established in the current literature.

The primary aim of this study was to develop and evaluate a reliable method of determining the 3D femoral neck axis. Secondly, we wanted to quantify the translational relationship between the femoral head and neck in normal and cam type hips.

Pelvic computed tomographic scans (CT) and radiographs were retrieved from our database of patients who had undergone navigated hip surgery or CT colonography. All patients had given informed consent for their medical files and imaging to be used for research purposes, as approved by the institutional review board.

Pre-operative scans were performed using the Siemens Sensation 64 slice scanner (Siemens Medical Solutions, Erlangen, Germany). The Imperial Protocol developed at the authors’ orthopaedic unit was applied, allowing acquisition of Digital Imaging and Communications in Medicine (DICOM) files of 0.75mm thickness.

Normal and cam type hips (n=30) were identified for analysis. ‘Normal’ hips (n=15) were defined in asymptomatic patients with no previous history of hip disease, and, no obvious abnormality on radiographs or CT. The ‘cam’ hip type (n=15) was defined by the presence of an anterior osseous bump at the head-neck junction, and an alpha angle greater than 50° on hip radiographs.

DICOMs were converted to 3D stereolith (STL) images using validated commercial image processing and analysis software (3-Matics, Materialise Group, Leuven, Belgium).

In order to determine the 3D-FNA, a best fit sphere was applied to the femoral head with a root mean square error of less than 0.5mm. The border between sphere and femoral neck defined the head -neck junction. The bone surface was marked here (including the anterior bump in cam hips) and at the neck base, providing two anatomical rings that defined the superior and inferior limits of the femoral neck. The centre point of each ring was calculated. A line connecting these points defined the femoral neck axis, and was verified on a DICOM viewer in sagittal, axial and coronal planes. The offset between the femoral head centre and neck axis was measured.

The 3D image and axis were further analysed to examine the femoral head-neck relationship, using customized software developed at our institution and previously validated in previous research projects.

To standardize rotational alignment, the femoral neck was aligned vertically in two planes by creating an axis between the tip of the greater trochanter and the center of the lesser trochanter. The aligned proximal femur was viewed end on, and the version of the head relative to the neck determined by calculating the angle between the head centre and a vertical marker placed at the 12 o’clock position. Angles below 180° demonstrated anteversion, while those above 180° demonstrated retroversion.

A profound understanding of the pathoanatomy of the patellofemoral joint is considered to be fundamental for navigated knee arthroplasty. Previous studies used less sophisticated imaging modalities such as photography and plain radiographs or direct measurement tools like probes and micrometers to define the morphology of the trochlear groove, with differing results. This may be due to the complexity of the biomechanics and the geometry of this joint. Our primary goal was to compare normal, osteoarthritic and dysplastic PFJs in terms of angles and distances. To do this we first had to establish a reliable frame of reference.

Computed tomography scans of 40 normal knees (> 55 years old), 9 knees with patellofemoral osteoarthritis (group A) and 12 knees with trochlear dysplasia (group B) were analyzed using 3D software. The femurs were orientated using a robust frame of reference. A circle was fitted to the trochlear groove. The novel trochlear axis was defined as a line joining the centres of two spheres fitted to the trochlear surfaces, lateral and medial to the trochlear groove. The relationship between the femoral trochlea and the tibiofemoral joint was measured in term of angles and distances (offsets). T-test for paired samples was used (p< 0.05). The study was approved by the institutional review conforming to the state laws and regulations.

The normal trochlear groove closely matched a circle (RMS 0.3mm). It was positioned laterally in relation to the mechanical, anatomical, and trans-condylar axes of the femur. It was not co-planar with any of the three axes. After aligning to the new trochlear axis, the trochlear groove appeared more linear than when other axes were used. In comparison to the normal knees; the medial trochlear was smaller in group A (p=0.0003)- see figure 2. The lateral trochlear was smaller in group B (p=0.04). The trochlear groove was smaller in groups B (p=0.0003). Both trochlear centers in groups A+B were more centralized (p=0.00002–0.03). The medial trochlear center was more distal in group A (p=0.03) and the lateral trochlear center was more distal in group B (p=0.00009). The trochlear groove started more distal in group B (p=0.0007).

A better understanding of the 3-dimensional geometry can help better treat or even prevent the progression of disease to the stage of patellofemoral osteoarthritis. In osteoarthritic and dysplastic patellofemoral joints, the trochlea is both smaller and more distally located along the femur. These two factors may contribute to excessive loads that lead to early joint wear. These differences could have biomechanical implications and give us an insight into why joints fail. The data collected may also help in improving current designs and current navigational and surgical techniques used for the treatment of patellofemoral osteoarthritis.

When navigating patellofemoral/unicompartmental knee surgery, the surgeon makes assumptions based upon algorithms developed for total knee arthroplasty. In this study we set out to show how variable the normal knee is. Minor anatomical variations in the shape of our knee may make a big difference in terms of orientation and joint wear patterns. Tibial patho-morphology has been described as a factor that predisposes to medial compartment osteoarthritis of the knee (anteromedial-OA), yet this is limited to 2D analysis. We aimed to describe the 3D morphology of both the tibial and femoral components of the medial compartment of the knee. We hypothesized that morphological differences do exist between normal knees and those predisposed to osteoarthritis.

A total of 20 normal (group A) and 20 pre-OA knees (group B) were included. Group A consisted of contra lateral knees of young patients (< 55 years) awaiting hip surgery and group B of asymptomatic contra lateral knees of patients awaiting unicompartmental knee arthroplasty (UKA). Using 3D reconstructions from CT scans, we analyzed the tibiofemoral joint, which consists of the femoral condyles and the tibial plateau. The femur was aligned to the transcondylar and anatomical axes. The medial femoral extension facet (MFEF) was modeled as a segment of a sphere. The offsets between the MFEF centre and the medial femoral flexion facet centre were measured. The MFEF radius and the MFEF 2D arc angle in the sagittal plane were also measured. The tibias were aligned for flexion-extension and varus-valgus to a flat portion of the flexion facet (flexion facet plane), which lie’s roughly perpendicular to the tibial mechanical axis. To control for axial rotation, the anatomical tibial axis was used. A model of analysis was developed by rotating several increments towards and away from the midline to obtain several sagittal section images. For each sagittal section the medial tibial extension facet (MTEF) slope angle, its length, and the medial tibial submeniscal plane (MTSP) angle and length were analyzed. The relative length proportions of the MTEF, medial tibial flexion facet and MTSP were also measured.

The MFEF was larger and more offset in pre-OA knees. Pre-OA knees also had a significantly larger MFEF arc angle than normals (p< 0.05). The MTEF appeared similar between normal and pre-OA knees. The submeniscal plane was highly variable between subjects but on average horizontally inclined (median 0o, range −15–14o) and formed a crescent shape anteriorly. There was no significant difference in tibial measured parameters between normal and pre-OA tibias (p> 0.05). The method showed good reproducibility using intraclass correlation coefficient (ICC value> 0.9) and Bland-Altman plot analysis.

This study gives the CAOS surgeon some interesting insights into the anatomical variation of the normal knee. We have found evidence of a predisposing patho-morphology to medial-OA in the femoral condyle, but not the tibia. There is evidence of an enlarged flatter extension facet on the medial femoral condyle in the pre-OA knees, with no significant difference in the geometry of the medial tibial plateau, which is now reliably defined based upon a flexion plateau frame of reference.

Differing descriptions of patellar motion relative to the femur have resulted from many in-vitro and in-vivo studies. The aim of this study was to examine the tracking behaviour of the patella. We hypothesized that patellar kinematics would correlate to the trochlear geometry and that differing previous descriptions could be reconciled by accounting for differing alignments of measurement axes.

Seven normal fresh-frozen knees were CT scanned and their kinematics with quadriceps loading was measured by an optical tracker system and calculated in relation to the previously-established femoral axes. CT scans were used to reliably define frames of reference for the femur, tibia and the patella. A novel trochlear axis was defined, between the centres of best-fit medial and lateral trochlear articular surfaces spheres.

The path of the centre of the patella was circular and uniplanar (RMS error 0.3mm) above 16°±3° knee flexion. The distal end of the median ridge of the patella entered the groove at 6° knee flexion, and the midpoint at 22°. This circle was aligned 6.4° ± 1.6° (mean± SD) from the femoral anatomical axis, 91.2°±3.4° from the epicondylar axis, and 88.3°±3° from the trochlear axis, in the coronal plane. In the transverse plane it was 91.2°±3.4° and 88.3°±3° from the epicondylar and trochlear axes. Manipulation of the data to different axis alignments showed that differing previously-published data could be reconciled. When the anatomic axis of the femur was used to align the coordinates, there was an initial medial and then a lateral translation. Comparing this with the uniplanar and circular path of the center of the patella, it shows that the orientation of the femoral coordinate system affects the description of the patellar medial-lateral translation.

This study has shown the effect of using different coordinate systems on reporting the patellar translation. Choosing a femoral reference that is more in line with the plane of the circular path of motion and the trochlear groove in the coronal plane diminishes the reported subsequent lateral translation of the patella. Once the frame of reference had been aligned to the trochlear axis, there was minimum medial-lateral translation of the patella.

Background: Traumatic dislocations of the knee are uncommon (< 1% of all dislocations), but they account to the most serious ligament and soft tissue injuries of the knee. Diagnosis and treatment of the dislocated knee present a major challenge to the orthopaedic surgeon. The purpose of our retrospective study was to critically analyze the clinical outcome of all traumatic knee dislocations treated operatively between 1996 and 2006 in our institution.

Methods: Retrospective clinical case series study of all patients treated for traumatic knee dislocation (m: w=12:4; mean age 31 yrs, range 17–63 yrs) from 1998–2006.

The mechanism of injury was a traffic accident (n=7), a sport trauma (n=8) and slip and fall (n=1). The charts of all patients were analyzed.

The clinical outcome was assessed by personal telephone interview by a modified SSK questionnaire by Insall. Surgery was performed by one team of surgeons 2–89 days after trauma.

Mean and range were reported for continuous variables and relative and absolute frequencies vor categorial variables. Data were analyzed using Stata version 8. The level of significance was defined as p< 0.05.

Results: The injury pattern is reported below:

15 anterior cruciate ligament (ACL) lesions (11x ACL reconstruction), 15 posterior cruciate ligament (PCL) lesions (9x refixation, 3x reconstruction), 13 medial collateral ligament (MCL) lesions (8x reconstruction), 6 medial posterior collateral ligament (MPCL) lesions (4x reconstruction), 4 lateral collateral ligament (LCL) lesions (1x reconstruction), 3 popliteal muscle injuries (2x reconstruction), 5 medial meniscal lesions, 10 lateral meniscal lesions (9x suture, 1x partial meniscectomy), 3 femoral fractures, 1 proximal tibial fracture.

Conclusions: Even though in a orthopaedic clinic specialized in the treatment of knee injuries traumatic knee dislocations remain a demanding therapeutic challenge. A highly specialized, customized and sophisticated treatment strategy of a experienced team of surgeons, nurses and physiotherapists is mandatory for acheivement of optimal functional and subjective outcome.