Does cup position differ between trabecular metal and titanium cups? A radiographic propensity score matched study of 300 hips.

Background and purpose - The use of trabecular metal cups in primary total hip arthroplasty (THA) is increasing, despite the survival of Continuum cups being slightly inferior compared with other uncemented cups in registries. This difference is mainly explained by a higher rate of dislocation revisions. Cup malpositioning is a risk factor for dislocation and, being made of a highly porous material, Continuum cups might be more difficult to position. We evaluated whether Continuum cups had worse cup positioning compared with other uncemented cups. Patients and methods - Based on power calculation, 150 Continuum cups from 1 center were propensity score matched with 150 other uncemented cups from 4 centers. All patients had an uncemented stem, femoral head size of 32 mm or 36 mm, and BMI between 19 and 35. All operations were done for primary osteoarthrosis through a posterior approach. Patients were matched using age, sex, and BMI. Cup positioning was measured from anteroposterior pelvic radiograph using the Martell Hip Analysis Suite software. Results - There was no clinically relevant difference in mean inclination angle between the study group and the control group (43° [95% CI 41-44] and 43° [CI 42-45], respectively). The study group had a larger mean anteversion angle compared with the control group, 19° (CI 18-20) and 17° (CI 15-18) respectively. Interpretation - Continuum cups had a greater anteversion compared with the other uncemented cups. However, the median anteversion was acceptable in both groups and this difference does not explain the larger dislocation rate in the Continuum cups observed in earlier studies.

Pelvic positioning in the supine position leads to more consistent orientation of the acetabular component after total hip arthroplasty.

AIMS: This study aims to: determine the difference in pelvic position that occurs between surgery and radiographic, supine, postoperative assessment; examine how the difference in pelvic position influences subsequent component orientation; and establish whether differences in pelvic position, and thereafter component orientation, exist between total hip arthroplasties (THAs) performed in the supine versus the lateral decubitus positions. PATIENTS AND METHODS: The intra- and postoperative anteroposterior pelvic radiographs of 321 THAs were included; 167 were performed with the patient supine using the anterior approach and 154 were performed with the patient in the lateral decubitus using the posterior approach. The inclination and anteversion of the acetabular component was measured and the difference (Δ) between the intra- and postoperative radiographs was determined. The target zone was inclination/anteversion of 40°/20° (± 10°). Changes in the tilt, rotation, and obliquity of the pelvis on the intra- and postoperative radiographs were calculated from Δinclination/anteversion using the Levenberg-Marquardt algorithm. RESULTS: The mean postoperative inclination/anteversion was 40° (± 8°)/23° (± 9°) with Δinclination and/or Δanteversion > ± 10° in 74 (21%). Intraoperatively, the pelvis was anteriorly tilted by a mean of 4° (± 10°), internally rotated by a mean of 1° (± 10°) and adducted by a mean of 1° (± 5°). Having Δinclination and/or Δanteversion > ± 10° was associated with a 3.5 odds ratio of having the acetabular component outside the target zone. A greater proportion of THAs that were undertaken with the patient in the lateral decubitus position had Δinclination and/or Δanteversion > ± 10° (35.3%, 54/153) compared with those in the supine position (4.8%, 8/167; p < 0.001). A greater number of acetabular components were within the target zone in THAs undertaken with the patient in the supine position (72%, 120/167), compared with those in the lateral decubitus position (44%, 67/153; p < 0.001). Intraoperatively, the pelvis was more anteriorly tilted (p < 0.001) and more internally rotated (p = 0.04) when the patient was in the lateral decubitus position. CONCLUSION: The pelvic position is more reliable when the patient is in the supine position, leading to more consistent orientation of the acetabular component. Significant differences in pelvic tilt and rotation are seen with the patient in the lateral decubitus position. Cite this article: Bone Joint J 2018;100-B:1280-8.

Is the cup orientation different in bilateral total hip arthroplasty with right-handed surgeons using posterolateral approach?

BACKGROUND: The impact of surgeon handedness on acetabular cup orientation in total hip arthroplasty (THA) is not well studied. The aim of our study is to investigate the difference of cup orientation in bilateral THA performed by right-handed surgeons using posterolateral approach and which cup could be fitter to Lewinneck's safe zone. METHODS: The study consisted of 498 patients that underwent bilateral THA by three right-handed surgeons in our hospital. Postoperative acetabular cup anteversion and abduction on an anteroposterior pelvic radiograph were measured by Orthoview software (Orthoview LLC, Jacksonville, Florida). Furthermore, the percentage of cup placement within the safe zone was compared. RESULTS: The mean anteversion was 25.28 (25.28° ± 7.16°) in left THA and 22.01 (22.01° ± 6.35°) in right THA (p < 0.001). The mean abduction was 37.50 (37.50° ± 6.76°) in left THA and 38.59 (38.59° ± 6.84°) in right THA (p = 0.011). In the left side, the cup was positioned in Lewinnek's safe zone in 52% for anteversion, 87% for abduction, and 46% for both anteversion and abduction. But the cup placement within Lewinnek's safe zone was 71, 88, and 62% in the right side, respectively. There were significant differences in the percentage of acetabular cup placement within the safe zone for anteversion (p < 0.001) and for both anteversion and inclination (p < 0.001). Dislocation occurred in 7.0% (35/498) of cases in left THA and 3.2% (16/498) in right THA. The percentages of patients experiencing dislocation were significantly different between the two sides (p = 0.006). CONCLUSIONS: This current study demonstrated that surgeon handedness is likely to be a contributing factor that affects cup inclination and anteversion in bilateral THA and that the placement of cup performed by dominant hands of surgeons is more accurate than that performed by non-dominant sides.

Digital Radiography in Total Hip Arthroplasty: Technique and Radiographic Results.

BACKGROUND: Obtaining the ideal acetabular cup position in total hip arthroplasty remains a challenge. Advancements in digital radiography and image analysis software allow the assessment of the cup position during the surgical procedure. This study describes a validated technique for evaluating cup position during total hip arthroplasty using digital radiography. METHODS: Three hundred and sixty-nine consecutive patients undergoing total hip arthroplasty were prospectively enrolled. Preoperative supine anteroposterior pelvic radiographs were made. Intraoperative anteroposterior pelvic radiographs were made with the patient in the lateral decubitus position. Radiographic beam angle adjustments and operative table adjustments were made to approximate rotation and tilt of the preoperative radiograph. The target for cup position was 30° to 50° abduction and 15° to 35° anteversion. Intraoperative radiographic measurements were calculated and final cup position was determined after strict impingement and range-of-motion testing. Postoperative anteroposterior pelvic radiographs were made. Two independent observers remeasured all abduction and anteversion angles. RESULTS: Of the cups, 97.8% were placed within 30° to 50° of abduction, with a mean angle (and standard deviation) of 39.5° ± 4.6°. The 2.2% of cups placed outside the target zone were placed so purposefully on the basis of intraoperative range-of-motion testing and patient factors, and 97.6% of cups were placed between 15° and 35° of anteversion, with a mean angle of 26.6° ± 4.7°. Twenty-eight percent of cups were repositioned on the basis of intraoperative measurements. Subluxation during range-of-motion testing occurred in 3% of hips despite acceptable measurements, necessitating cup repositioning. There was 1 early anterior dislocation. CONCLUSIONS: Placing the acetabular component within a target range is a critical component to minimizing dislocation and polyethylene wear in total hip arthroplasty. Using digital radiography, we positioned the acetabular component in our desired target zone in 97.8% of cases and outside the target zone, purposefully, in 2.2% of cases. When used in conjunction with strict impingement testing, digital radiography allows for predictable cup placement in total hip arthroplasty.

Intra-operative digital imaging: assuring the alignment of components when undertaking total hip arthroplasty.

AIMS: The aims of this study were to examine the rate at which the positioning of the acetabular component, leg length discrepancy and femoral offset are outside an acceptable range in total hip arthroplasties (THAs) which either do or do not involve the use of intra-operative digital imaging. PATIENTS AND METHODS: A retrospective case-control study was undertaken with 50 patients before and 50 patients after the integration of an intra-operative digital imaging system in THA. The demographics of the two groups were comparable for body mass index, age, laterality and the indication for surgery. The digital imaging group had more men than the group without. Surgical data and radiographic parameters, including the inclination and anteversion of the acetabular component, leg length discrepancy, and the difference in femoral offset compared with the contralateral hip were collected and compared, as well as the incidence of altering the position of a component based on the intra-operative image. RESULTS: Digital imaging took a mean of five minutes (2.3 to 14.6) to perform. Intra-operative changes with the use of digital imaging were made for 43 patients (86%), most commonly to adjust leg length and femoral offset. There was a decrease in the incidence of outliers when using intra-operative imaging compared with not using it in regard to leg length discrepancy (20% versus 52%, p = 0.001) and femoral offset inequality (18% versus 44%, p = 0.004). There was also a difference in the incidence of outliers in acetabular inclination (0% versus 7%, p = 0.023) and version (0% versus 4%, p = 0.114) compared with historical results of a high-volume surgeon at the same centre. CONCLUSION: The use of intra-operative digital imaging in THA improves the accuracy of the positioning of the components at THA without adding a substantial amount of time to the operation. Cite this article: Bone Joint J 2018;100B(1 Supple A):36-43.

Inestabilidad de la artroplastia total de cadera: estudio clínico y computacional de sus factores de riesgo / Instability of total hip replacement: a clinical study and determination of its risk factors

Objetivos. Determinar los factores de riesgo asociados a la luxación protésica y simular un modelo mediante elementos finitos que determine los arcos de movimiento seguros en cada angulación y anteversión del cotilo. Material y métodos. Casos-control retrospectivo con 46 pacientes luxados desde 1994 hasta 2011. Grupo control: 83 pacientes elegidos de forma aleatoria. Se recogieron los factores de riesgo de luxación descritos en la literatura. Se simuló un modelo protésico mediante elementos finitos con cabezas de 28, 32, 36 mm y cotilo de 52 mm. Posición acetabular de 25°, 40° y 60° de inclinación y 0°, 15° y 25° de anteversión. Para cada combinación se estudió la flexión de 90° y la extensión de 0° aplicando rotación interna y externa midiendo el rango de movimiento y el momento resistente hasta el choque-luxación y la distribución de tensiones en la superficie del cotilo. Resultados. Mayor edad en luxados (p = 0,002). Mayor luxación en fracturas respecto artrosis (p < 0,001). Menor anteversión en luxados (p = 0,043). Mayor longitud de cuello femoral en luxados (p = 0,002). Simulación de finitos: menor luxación cuanto mayor inclinación, anteversión y diámetro de cabeza femoral. Discusión-conclusiones. La edad avanzada y la fractura son los principales factores favorecedores de la luxación. El área de seguridad libre de luxación comprende 40°-60° de inclinación y 15°-25° de anteversión. Tanto el defecto como el exceso de tensión de las partes blandas predisponen a la luxación. Las cabezas de mayor tamaño son más estables (AU)

Objectives. To determine the risk factors associated with prosthetic dislocation and simulate a finite element model to determine the safe range of movement of various inclination and anteversion cup positions. Material and methods. Retrospective Case Control study with 46 dislocated patients from 1994 to 2011. Control Group: 83 randomly selected patients. Dislocation risk factors described in the literature were collected. A prosthetic model was simulated using finite elements with 28, 32, 36 mm heads, and a 52 mm cup. Acetabular position was 25°, 40°, and 60° tilt and with 0°, 15° and 25° anteversion. In extension of 0° and flexion of 90°, internal and external rotation was applied to analyze the range of movement, maximum resisting moment, and stress distribution in the acetabulum to impingement and dislocation. Results. There was greater dislocation in older patients (p = 0 .002). Higher dislocation in fractures than in osteoarthritis (p = 0 .001). Less anteversion in dislocated patients (p = 0 .043). Longer femoral neck in dislocated patients (p = 0 .002). Finite element model: lower dislocation when there is more anteversion, tilt and bigger femoral heads. Discussion-conclusions. Advanced age and fractures are the major risk factors for dislocation. “Safe zone” of movement for dislocation avoidance is 40°-60° tilt and 15°-25° anteversion. Both the defect and excess of soft tissue tension predispose to dislocation. Bigger femoral heads are more stable (AU)

Intra-operative assessment of femoral antetorsion using ISO-C 3D: a cadaver study.

AIM: The aim of this study was to check the feasibility and accuracy of measuring antetorsion during surgery using a mobile image intensifier (IF) with computed tomography (CT) function (ISO-C 3D; Siemens, Erlangen, Germany) in comparison to a conventional multi-slice CT scanner (LightSpeed QX/I CT; GE Healthcare, VA, USA). MATERIALS AND METHODS: A total of 10 intact femora with intact soft tissue of five fresh frozen cadavers were used. After fixation on a surgical table, IF CT scans of the hip and knee were performed at both 190° and 120° of scanning rotation. Afterwards, a conventional CT scan was performed. Antetorsion was calculated according to the method of Jend et al. Analysis of variance (ANOVA) and Lin's concordance correlation coefficient (LCC) were used to test the agreement between the three measurement techniques. RESULTS: There was no significant difference in femoral antetorsion angle measurements between the different techniques (P>0.05). The mean time required to perform a scan using the ISO-C 3D was 9±3 min. The mean time required to measure antetorsion was 8±2 min. We found a high positive correlation between CT-based measurements and measurements performed using both the ISO-C 3D at 190° (LCC=0.99; mean difference=0.02°±1.8°) and the ISO-C 3D at 120° (LCC=0.99; mean difference=0.6°±1.5°), and a high positive correlation was also seen between both ISO-C 3D methods (LCC=0.99; mean difference=0.6°±1.7°). CONCLUSIONS: Measuring femoral antetorsion using an intra-operative IF with CT function is a feasible and accurate method. This technique could be used when there is doubt about the antetorsion angle in the operated femur and it could help decrease the need for a separate revision surgery.

The role of the transverse acetabular ligament in total hip arthroplasty.

We performed a systematic literature review to evaluate the role of the transverse acetabular ligament as a reference aid when determining acetabular component anteversion in total hip arthroplasty. We conducted a literature search in the MEDLINE, EMBASE and Pubmed databases using the key words 'transverse acetabular ligament' and 'arthroplasty'. Four studies published between 2006 and 2011, reporting on 1,217 procedures met our inclusion and exclusion criteria and were eligible for final evaluation. Outcome measures were the ability to identify the transverse acetabular ligament, anteversion of the acetabular component and dislocation rate. The methodological quality of the studies was variable and they were not homogenous enough for metaanalysis. We found that there was good evidence for the use of the transverse acetabular ligament in terms of accuracy of acetabular component anteversion. However, the ligament could not be routinely identified intra-operatively and other methods of determining the correct anteversion are recommended in this situation. The dislocation rate using this technique was low but it must be stressed that the cause of postoperative dislocation in total hip arthroplasty is multi-factorial and cannot solely be attributed to acetabular component orientation.

The importance of acetabular component position in total hip arthroplasty.

Correct acetabular cup position is critical to successful total hip replacement. Unfortunately, malposition of acetabular cups is common and leads to increased rates of dislocation, wear, and ion toxicity. Despite the popularity of Lewinnek's safe zone, the exact target of acetabular abduction and version remains elusive. Differences in functional pelvic position, surgical approach, and femoral anteversion affect the optimal cup position for individual patients. Surgeons need to be aware of pelvic position changes from the supine to lateral decubitus position.

Progress towards intra-operative measurement of femoral antetorsion.

Rotational malalignment following intramedullary nailing is a well-recognised problem. The threshold for clinically relevant malrotation has been established to be in the region of 15° whereas the incidence of significant malrotation following femoral nailing ranges from 22 to 43 percent. Many studies have been performed to address this issue with the major challenge acknowledged to be intraoperative control of femoral anteversion. In the current study, the investigators developed and analysed a novel method to estimate the femoral antetorsion based on computed tomography (CT) data. They hypothesized that this method would be intra-operatively feasible and repeatable without further radiation. CT scans (n=166) of femoral neck fractures performed between 2005 and 2010 were evaluated. Twenty patients had a femoral neck fracture and thus were excluded. Every femoral neck was measured according the method described by Jend et al. and the current authors. In contrast to the Jend method, the current authors described femoral antetorsion as the angle between the ventral cortex of the femoral neck and the posterior condylar line. To determine this angle, the axial cuts from computed tomography data were studied. In order to maximise measurement consistencty among cases, the axial cut which displayed the intertrochanteric crest was selected. Mean femoral antetorsion is 12.15°±10.04° according to Jend et al. In comparison, a mean angle of 12.61°±11.16° was demonstrated in the current study. The absolute difference in measuring the femoral neck angle when these different methods are compared was 4.44°. Statistically, there is no significant difference between the mean results for femoral antetorsion. The advantage of the method proposed in the current study, is the opportunity to enter the ventral femoral cortex during the surgical procedure without disturbing the process of femoral nailing. Thus, the surgeon can avail of continuous control of femoral rotation intra-operatively.

Navigated femoral shaft fracture treatment: current status.

Femoral malrotation is a common complication after internal fixation of a femoral shaft fracture. The only valid, objective monitoring method is computer tomography-assisted torsion measurement between the proximal and distal femur; unfortunately, this can only be carried out postoperatively. A difference of 15° compared to the contralateral femur is seen as an indication for revision. With the development of computer-assisted surgery, new possibilities for performing torsion control and correction intraoperatively has been introduced. These methods also allow for navigation-assisted definition of the optimal incision site, intramedullary access, femoral nail and interlocking. The main problem lies in the extra time of surgery, which is due to performing all the steps of the surgery navigated. The solution for this problem is "hybrid navigation", in which the surgeon can select the steps he needs from the navigation system, depending on his experience or surgical technique.

Improving acetabular cup orientation in total hip arthroplasty by using smartphone technology.

Acetabular cup placement in total hip arthroplasty is often difficult to assess, especially in the lateral position and using the posterior approach. Conventional techniques and computer-assisted surgery are the 2 most popular methods for proper placement of the acetabular cup in Lewinnek's safe zone of orientation (anteversion 15° ± 10° and lateral inclination 40° ± 10°). We developed a system that uses the accelerometer and camera function of the iPhone. A level indicator application and protractor application were downloaded to the iPhone and used to improve acetabular cup placement. This system has proven to be accurate and quick. Our series of 50 prospective cases showed good results with all our acetabular cups being placed within a narrow range in the safe zone and with less than 5% difference between the preoperative, intraoperative, and postoperative acetabular inclinations.

Accuracy of acetabular cup positioning using imageless navigation.

BACKGROUND: Correct placement of the acetabular cup is a crucial step in total hip replacement to achieve a satisfactory result and remains a challenge with free-hand techniques. Imageless navigation may provide a viable alternative to free-hand technique and improve placement significantly. The purpose of this project was to assess and validate intra-operative placement values for both inclination and anteversion as displayed by an imageless navigation system to post-operative measurement of cup position using high resolution CT scans. METHODS: Thirty-two subjects who underwent primary hip joint arthroplasty using imageless navigation were included. The average age was 66.5 years (range 32-87). 23 non-cemented and 9 cemented acetabular cups were implanted. The desired position for the cup was 45 degrees of inversion and 15 degrees of anteversion. A pelvic CT scan using a multi-slice CT was used to assess the position of the cup radiographically. RESULTS: Two subjects were excluded because of dislodgement of the tracking pin. Pearson correlation revealed a strong and significant correlation (r = 0.68; p < 0.006) for cup inclination and a moderate non-significant correlation (r = 0.53; p = 0.45) between intra-operative readings and cup placement for anteversion. CONCLUSIONS: These findings can be explained with the possible introduction of systematic error. Even though the acquisition of anatomic landmarks is simple, they must be acquired with great precision. An error of 1 cm can result in a mean anteversion error of 6 degrees and inclination error of 2.5 degrees. Whilst computer assisted surgery results in highly accurate cup placements for inclination, anteversion of the cup cannot be determined accurately.