Wael Dandachli

The anatomical tibial axis RELIABLE ROTATIONAL ORIENTATION IN KNEE REPLACEMENT

The rotational alignment of the tibia is an unresolved issue in knee replacement. A poor functional outcome may be due to malrotation of the tibial component. Our aim was to find a reliable method for positioning the tibial component in knee replacement. CT scans of 19 knees were reconstructed in three dimensions and orientated vertically. An axial plane was identified 20 mm below the tibial spines. The centre of each tibial condyle was calculated from ten points taken round the condylar cortex. The tibial tubercle centre was also generated as the centre of the circle which best fitted eight points on the outside of the tubercle in an axial plane at the level of its most prominent point. The derived points were identified by three observers with errors of 0.6 mm to 1 mm. The medial and lateral tibial centres were constant features (radius 24 mm (SD 3), and 22 mm (SD 3), respectively). An anatomical axis was created perpendicular to the line joining these two points. The tubercle centre was found to be 20 mm (SD 7) lateral to the centre of the medial tibial condyle. Compared with this axis, an axis perpendicular to the posterior condylar axis was internally rotated by 6 degrees (SD 3). An axis based on the tibial tubercle and the tibial spines was also internally rotated by 5 degrees (sd 10). Alignment of the knee when based on this anatomical axis was more reliable than either the posterior surfaces or any axis involving the tubercle which was the least reliable landmark in the region.

Three-dimensional CT analysis to determine acetabular retroversion and the implications for the management of femoro-acetabular impingement

This study examined the relationship between the cross-over sign and the true three-dimensional anatomical version of the acetabulum. We also investigated whether in true retroversion there is excessive femoral head cover anteriorly. Radiographs of 64 hips in patients being investigated for symptoms of femoro-acetabular impingement were analysed and the presence of a cross-over sign was documented. CT scans of the same hips were analysed to determine anatomical version and femoral head cover in relation to the anterior pelvic plane after correcting for pelvic tilt. The sensitivity and specificity of the cross-over sign were 92% and 55%, respectively for identifying true acetabular retroversion. There was no significant difference in total cover between normal and retroverted cases. Anterior and posterior cover were, however, significantly different (p < 0.001 and 0.002). The cross-over sign was found to be sensitive but not specific. The results for femoral head cover suggest that retroversion is characterised by posterior deficiency but increased cover anteriorly.

Analysis of cover of the femoral head in normal and dysplastic hips: NEW CT-BASED TECHNIQUE

We present a new CT-based method which measures cover of the femoral head in both normal and dysplastic hips and allows assessment of acetabular inclination and anteversion. A clear topographical image of the head with its covered area is generated. We studied 36 normal and 39 dysplastic hips. In the normal hips the mean cover was 73% (66% to 81%), whereas in the dysplastic group it was 51% (38% to 64%). The significant advantage of this technique is that it allows the measurements to be standardised with reference to a specific anatomical plane. When this is applied to assessing cover in surgery for dysplasia of the hip it gives a clearer understanding of where the corrected hip stands in relation to normal and allows accurate assessment of inclination and anteversion.

The geometry of the trochlear groove.

BackgroundIn the natural and prosthetic knees the position, shape, and orientation of the trochlea groove are three of the key determinants of function and dysfunction, yet the rules governing these three features remain elusive.Questions/PurposeThe aim was to define the three-dimensional geometry of the femoral trochlea and its relation to the tibiofemoral joint in terms of angles and distances.MethodsForty CT scans of femurs of healthy patients were analyzed using custom-designed imaging software. After aligning the femur using various axes, the locations and orientations of the groove and the trochlear axis were examined in relation to the conventional axes of the femur.ResultsThe trochlear groove was circular and positioned laterally in relation to the mechanical, anatomic, and transcondylar axes of the femur; it was not aligned with any of these axes. We have defined the trochlear axis as a line joining the centers of two spheres fitted to the trochlear surfaces lateral and medial to the trochlear groove. When viewed after aligning the femur to this new axis, the trochlear groove appeared more linear than when other methods of orientation were used.ConclusionsOur study shows the importance of reliable femoral orientation when reporting the shape of the trochlear groove.

Analysis of acetabular version in the native hip: comparison between 2D axial CT and 3D CT measurements

ObjectiveTo compare two-dimensional (2D) axial with three-dimensional (3D) computerized tomography (CT) measurements of acetabular version in native hips.Materials and methodsCT scans of 34 hips in 17 consecutive patients being investigated for femoroacetabular impingement were analyzed. Acetabular version was measured using 2D CT at two different axial levels, one cranial (slice 2) and the other at the equator (slice 3). The measurements were repeated after correction for pelvic tilt. The results were compared to the measurements of anatomical version obtained using a 3D CT method that automatically corrects for pelvic tilt.ResultsThe mean acetabular version using the 3D CT method was 15.7° (SD 6.9°). The mean version using slice 2 was 9.3° (SD 6.5°) before correction for pelvic tilt and 15.7° (SD 8.0°) after the correction. The mean version using slice 3 was 16.4° (SD 4.2°) before tilt correction and 19.0° (SD 5.0°) after the correction. In relation to the 3D method, the intraclass correlation coefficient (ICC) was 0.58 for the uncorrected and 0.93 for the corrected slice 2 method. For the uncorrected and corrected slice 3 methods, the ICC was 0.64 and 0.89, respectively.ConclusionsThe 2D axial methods produced variable results. The results that correlated best with the 3D method were those of the cranial slice (slice 2) after correction for pelvic tilt. Interpretation of 2D axial CT measurements of acetabular version should be done with caution. The level at which the measurement is done and the presence of pelvic tilt appear to be significant factors.

Learning How to Resurface Cam-Type Femoral Heads with Acceptable Accuracy and Precision: The Role of Computed Tomography-Based Navigation

BACKGROUND Resurfacing arthroplasty for cam-type deformities, which are a common cause of early osteoarthritis, is a technically demanding operation. Like any other arthroplasty, it requires both accuracy and precision. On the basis of the results of series reported by expert surgeons, we considered it desirable that this operation should be performed within +/-10 degrees of the desired angular orientation and +/-6 mm of entry-point translation in 95% of hips. Technological aids are now available to help surgeons achieve that level of accuracy. Three models of cam-type hips of increasing severity were used to assess the efficacy of three systems of instrumentation at delivering the required level of accuracy and precision. METHODS Thirty-two students of surgical technology were instructed in hip resurfacing and shown detailed plans of the desired operative outcome for the three hips with cam-type deformity. They then used conventional instruments, imageless navigation, and computed tomography-based navigation to perform the operation as accurately as possible. RESULTS Conventional instrumentation produced an unacceptably wide range of entry-point errors. Imageless navigation was able to deliver adequate accuracy and precision in varus-valgus angulation and superoinferior translation, but was less satisfactory in version and anteroposterior translation. Computed tomography-based navigation enabled novice surgeons to navigate hips that had difficult cam-type deformity with acceptable precision in all four degrees of freedom measured. CONCLUSIONS Only computed tomography-based navigation appears to be appropriate for delivering both the accuracy and the precision needed by surgeons on the steep part of their learning curve. Neither conventional neck-based instrumentation nor imageless navigation provided enough help for novice surgeons learning to perform this technically challenging operation.

The influence of pelvic tilt on acetabular orientation and cover: a three-dimensional computerised tomography analysis.

The orientation of the pelvis influences that of the acetabulum. In particular, pelvic tilt in the sagittal plane may lead to inaccurate interpretation of plain pelvic radiographs. We therefore quantified the relationship between this pelvic tilt and acetabular orientation in native hips, and determined whether pelvic tilt affects femoral head cover. We analysed computed tomography scans of 93 hips (36 normal, 31 dysplastic, 26 with acetabular retroversion) and measured acetabular anteversion, inclination, and femoral head cover at pelvic tilt angles ranging from −20° to 20° in relation to the anterior pelvic plane using 5° increments. Pelvic tilt changed acetabular version with a decrease in anteversion ranging from 2.5° to 5° for every 5° of forward tilt. The effect on inclination was less marked and varied. In normal and dysplastic hips pelvic tilt increased apparent femoral head cover. A greater understanding of the influence of pelvic tilt may allow improvements in the radiological diagnosis and surgical treatment of acetabular abnormalities, particularly in relation to acetabular reorientation procedures and femoroacetabular impingement.

A pain in the backside: a case report of coxa saltans occurring at the proximal hamstring origin

Coxa saltans occurring at the proximal hamstring origin has been rarely reported in the literature. It is better known as occurring at the iliotibial band or the iliopsoas tendon. We report a case of coxa saltans due to subluxation of the origin of the long head of biceps femoris tendon at the ischial tuberosity. This was successfully treated using a mini-open surgical technique. Six weeks postoperatively, the snapping and the associated pain were abolished and the patient was able to resume their participation in athletic activities.