Quantifying the contribution of pincer deformity to femoro-acetabular impingement using 3D computerised tomography.

OBJECTIVE: To provide a simple, reliable method for the three-dimensional quantification of pincer-type hip deformity. MATERIALS AND METHODS: Computerised tomography scans of 16 normal female hips and 15 female hips with clinical femoro-acetabular impingement (FAI) and radiographic signs of pincer secondary to acetabular protrusio were analysed. After orientating the pelvis in the anterior pelvic plane, the acetabular centre was determined, and the ratios of its coordinates to the corresponding pelvic dimensions were calculated. Acetabular coverage of the femoral head and centre-edge angles were also measured for the two groups. RESULTS: In hips with a pincer, the hip was medialised by 37 % (p = 0.03), more proximal by 5 % (p = 0.05) and more posterior by 9 % (p = 0.03) compared with the normal hips. Coverage of the femoral head in protrusio hips was significantly greater than normal (average 71 % vs 82 %, p = 0.0001). Both the lateral centre-edge angle and the combined anterior-posterior centre-edge angle were greater in protrusio hips than in the normal ones (48° vs 37 °, p < 0.001; and 216° vs 176°, p < 0.0001 respectively). CONCLUSION: Displacement in acetabular protrusio occurs in all planes. This CT-based method allows for the accurate and standardised quantification of the extent of displacement, as well as 3D measurement of femoral head coverage. In the adult female population, a combined centre-edge angle of over 190° suggests an acetabulum that is too deep and a potential cause of symptoms of femoro-acetabular impingement. Conversely, an acetabulum that has a combined centre-edge angle of less than 190° may be considered to be of normal depth, and therefore not contributing a pincer to FAI should it occur.

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

OBJECTIVE: To compare two-dimensional (2D) axial with three-dimensional (3D) computerized tomography (CT) measurements of acetabular version in native hips. MATERIALS AND METHODS: CT 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. RESULTS: The 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. CONCLUSIONS: The 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.

The geometry of the trochlear groove.

BACKGROUND: In 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/PURPOSE: The 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. METHODS: Forty 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. RESULTS: The 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. CONCLUSIONS: Our study shows the importance of reliable femoral orientation when reporting the shape of the trochlear groove.

Can the acetabular position be derived from a pelvic frame of reference?

Acetabular center positioning has an effect on hip function. However, reported clinical and plain radiographic methods are inaccurate and unreliable for ascertaining acetabular implant location. In an exploratory study we asked whether the normal acetabular position can be derived from simple radiographically measurable pelvic dimensions. We analyzed computed tomographic scans of 37 normal hips using a pelvic frame of reference centered on the ipsilateral anterior-superior iliac spine. We defined the x-, y-, and z-coordinates of the hip center (C(x),C(y),C(z)) as a percentage of the corresponding pelvic dimensions (D(x),D(y),D(z)). C(x)/D(x) averaged 9%, C(y)/D(y) 34%, and C(z)/D(z) 37%. These ratios had narrow distributions with small confidence intervals. Interobserver agreement tests showed a mean intraclass correlation coefficient of 0.95. We observed gender differences in the ratios of as much as 4%, which correspond to differences of as much as 9 mm in the hip center position. The ratios provide a simple and reliable way of deriving the normal position of the hip center from the pelvic dimensions alone. This gives the surgeon a simple way of planning where the hip center should be and may be particularly helpful in revision hip arthroplasty or in cases involving extensive osteophytes, dysplasia, or protrusio.

Hip arthroscopy: Indications, outcomes and complications.

Hip arthroscopy has recently occupied an important place in the armamentarium of General Orthopedic and especially hip surgeons. It is an effective and innovative procedure with rapidly expanding indications. Advancements in surgical tools and refinement in techniques has revolutionalized modern Hip arthroscopy. Surgeons are now able to address pathology in and around the hip joint that was either misdiagnosed or poorly understood. The procedure allows detailed visualization of acetabular labrum, femoral and acetabular chondral surfaces, fovea, ligamentum teres, synovium and the extra-articular peri-trochanteric space. Minimally invasive surgery is now performed for diagnoses as well as treatment of a variety of Hip disorders. The acceptance and rates of hip arthroscopy are increasing across the board and the associated literature is expanding every day. Increasing surgical experience and improving technology is contributing for more advanced procedures to become popularized, however long-term outcome data about hip arthroscopy is still relatively sparse. We aim to review hip arthroscopy in the light of recent literature and will discuss the current indications, outcomes and complications of the procedure.

Does a Dedicated Unit for the Treatment of Hip Fractures Improve Acute Outcomes?

The aim of this study is to establish whether management of patients in a unit dedicated to the treatment of hip fractures improves acute outcomes. We prospectively studied 300 patients with hip fractures in two separate groups. Patients in Group 1 were operated on in a mixed trauma unit and recovered in a traditional trauma ward. Patients in Group 2 were operated on in dedicated theatres and recovered in a unit which catered exclusively for hip fractures. The ages, ASA grades, and type of procedure performed in the two groups were comparable. The 30-day mortality rate in Group 2 was 9% as opposed to 12% in Group 1 (P = 0.34). The inpatient length of stay was significantly lower in Group 2 (18 days versus 25 days; P = 0.0002) and so was the time taken to operate (28 hours versus 34 hours; P = 0.04). A greater percentage of patients in Group 2 were discharged home as opposed to a nursing home (75% versus 67%). This difference approached significance (P = 0.18). We conclude that prioritisation and prompt management of patients with hip fractures in a dedicated unit significantly improve time to surgery and significantly decrease length of stay.

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.

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.

Large ball metal on metal hips obscure cup angle measurement on plain radiographs.

CT when compared to plain radiograph is known to be a more valid measure of acetabular component orientation. The validity of plain radiographs may be further compromised by large diameter metal femoral heads because of obscuration of the acetabular rim. We quantified this effect by measuring acetabular cup angles (inclination and version) of 49 metal on metal (MOM) hip resurfacings using plain radiographs and 3D CT based measurement. Bland-Altman plots revealed poor agreement between plain radiographic and CT based measurement with 2 standard deviation limits of agreements of: +7 to -15 degrees for cup inclination angle; and +16 to -31 degrees for cup version angle. The large differences between plain radiographic and CT measurement of cup positions are probably due to the large diameter metal femoral head that can obscure the cup margin. We have used a metal artefact reduction CT protocol with a 3D imaging software package to overcome this problem and measure cup position relative to the Anterior Pelvic Plane.

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.