New quantitative radiographic parameters for vertical and horizontal instability in acromioclavicular joint dislocations

acromioclavicular-radiograph

Open access article New quantitative radiographic parameters for vertical and horizontal instability in acromioclavicular joint dislocations, by Zumstein, Schiessl, Ambuehl, et al. KSSTA (2018) 26(1): 125–135.

Abstract:

Purpose
The aim of this study was to identify the most accurate and reliable quantitative radiographic parameters for assessing vertical and horizontal instability in different Rockwood grades of acromioclavicular joint (ACJ) separations. Furthermore, the effect of projectional variation on these parameters was investigated in obtaining lateral Alexander view radiographs.

Methods
A Sawbone model of a scapula with clavicle was mounted on a holding device, and acromioclavicular dislocations as per the Rockwood classification system were simulated with the addition of horizontal posterior displacement. Projectional variations for each injury type were performed by tilting/rotating the Sawbone construct in the coronal, sagittal or axial plane. Radiographic imaging in the form of an anterior–posterior Zanca view and a lateral Alexander view were taken for each injury type and each projectional variation. Five newly defined radiographic parameters for assessing horizontal and vertical displacement as well as commonly used coracoclavicular distance view were measured. Reliability, validity and the effect of projectional variation were investigated for these radiographic measurements.

Results
All radiographic parameters showed excellent intra- and interobserver reliability. The validity was excellent for the acromial centre line to dorsal clavicle (AC–DC) in vertical displacement and for the glenoid centre line to posterior clavicle (GC–PC) in horizontal displacement, whilst the remaining measurements showed moderate validity. For AC–DC and GC–PC, convergent validity expressed strong correlation to the effective distance and discriminant validity demonstrated its ability to differentiate between various grades of ACJ dislocations. The effect of projectional variation increased with the degree of deviation and was maximal (3 mm) for AC–DC in 20° anteverted malpositioning and for GC–PC in 20° retroverted malpositioning.

Conclusions
AC–DC and the GC–PC are two novel quantitative radiographic parameters of vertical and horizontal instability in ACJ dislocations that demonstrate excellent reliability and validity with reasonable inertness to malpositioning. The use of AC–DC for assessing vertical displacement and GC–PC for assessing horizontal displacement in a single Alexander view is recommended to guide the appropriate management of ACJ dislocations. A better appreciation of the degree of horizontal instability, especially in lower Rockwood grades (II, III) of ACJ dislocations, may improve management of these controversial injuries.

Preoperative CT planning of screw length in arthroscopic Latarjet

laterjet-ct-planning-alpha-angle

Preoperative CT planning of screw length in arthroscopic Latarjet, by Hardy, Gerometta, Granger, et al. KSSTA (2018) 26(1):24-30.

Abstract

Purpose
The Latarjet procedure has shown its efficiency for the treatment of anterior shoulder dislocation. The success of this technique depends on the correct positioning and fusion of the bone block. The length of the screws that fix the bone block can be a problem. They can increase the risk of non-union if too short or be the cause of nerve lesion or soft tissue discomfort if too long. Suprascapular nerve injuries have been reported during shoulder stabilisation surgery up to 6 % of the case. Bone block non-union depending on the series is found around 20 % of the cases. The purpose of this study was to evaluate the efficiency of this CT preoperative planning to predict optimal screws length. The clinical importance of this study lies in the observation that it is the first study to evaluate the efficiency of CT planning to predict screw length.

Methods
Inclusion criteria were patients with chronic anterior instability of the shoulder with an ISIS superior to 4. Exclusion criteria were patients with multidirectional instability or any previous surgery on this shoulder. Thirty patients were included prospectively, 11 of them went threw a CT planning, before their arthroscopic Latarjet. Optimal length of both screws was calculated, adding the size of the coracoid at 5 and 15 mm from the tip to the glenoid. Thirty-two-mm screws were used for patients without planning. On a post-operative CT scan with 3D reconstruction, the distance between the screw tip and the posterior cortex was measured. A one-sample Wilcoxon test was used to compare the distance from the tip of the screw to an acceptable positioning of ±2 mm from the posterior cortex.

Results
In the group without planning, screw 1 tended to differ from the acceptable positioning: mean 3.44 mm ± 3.13, med 2.9 mm, q1; q3 [0.6; 4.75] p = 0.1118, and screw 2 differed significantly from the acceptable position: mean 4.83 mm ± 4.11, med 3.7 mm, q1; q3 [1.7; 5.45] p = 0.0045. In the group with planning, position of screw 1 or 2 showed no significant difference from the acceptable position: mean 2.45 mm ± 2.07 med 1.8 mm, q1; q3 [1; 3.3] p = 1; mean 2.75 mm ± 2.32 med 2.3 mm, q1; q3 [1.25; 3.8] p = 0.5631.

Conclusion
Unplanned Latarjet can lead to inaccurate screw length especially in the lower screw and can increase the risk of non-union and nerve damage. The clinical relevance of this article is that CT planning of screw length before surgery showed good results on post-operative CT.

The glenocapsular ligament and the posterosuperior part of the joint capsule of the shoulder are well vascularized

The glenocapsular ligament and the posterosuperior part of the joint capsule of the shoulder are well vascularized, by Põldoja, Rahu, Kask, et al. KSSTA (2018) 26(1): 146-151.

Abstract
Purpose
A detailed structural anatomy of the posterosuperior shoulder capsule and “glenocapsular ligament” is still rather unknown. The purpose of this study was meticulously to investigate and describe the structure and blood supply of the glenocapsular ligament on the posterosuperior shoulder joint capsule.

Method
Sixteen fixed and twelve fresh cadaveric shoulder specimens with a mean age of 73.4 (±6.4) years were analysed. Dissection without arterial injection was performed on the 16 fixed specimens—using an alcohol–formalin–glycerol solution. Before dissection, the 12 fresh specimens received of arterial injection a 10% aqueous dispersion of latex solution. After the injection, these shoulders were also fixed in an alcohol–formalin–glycerol solution.

Results
The glenocapsular ligament was found in all 28 specimens. Single or double parallel-running bundles of connective tissue fibres were found to form a capsular-ligamentous structure on the posterosuperior part of the joint capsule. One part of the ligament was mediosuperior, another posterosuperior. The mediosuperior part varied in shape, and in 12 of 28 cases, it was absent. The glenocapsular ligament arose from the supraglenoid tubercle and posterior part of the collum scapulae and inserted into the semicircular humeral ligament. The posterior ascending branch of the circumflex scapular artery directly fed small branches laterally and medially to the joint capsule, supplying the glenocapsular ligament and the deep layer of the joint capsule.

Conclusion
The glenocapsular ligament is a constant anatomical structure that consists of one or two different parts. The glenocapsular ligament and the posterosuperior part of the joint capsule appear well vascularized via the posterior ascending branch of the circumflex scapular artery.

Clinical relevance
It is the hope of the authors that this anatomical study can help surgeons who perform open or arthroscopic surgery to the posterior part of the shoulder. Knowledge of the vascular anatomy presented in this study may be especially important when incisions are made to the posterior part of the shoulder, and should minimize the risk of complications.

Posterior cruciate ligament a twisted and flat structure, and the tibio-femoral ligament

Posterior cruciate ligament is twisted and flat structure: new prospective on anatomical morphology, by Kato et al. KSSTA (2018) 26(1):31–39

Abstract:

Purpose
This cadaveric study aimed to elucidate PCL morphology by observing the anatomical relationship with other structures and the fibre layers of the PCL in cross section for remnant preserving PCL reconstruction.

Methods
Seventeen fresh-frozen cadaveric knees were studied, using the clock-face method to analyse the anatomical relationship between the PCL and Humphrey’s ligament. The width and thickness of the PCL, Humphrey’s and Wrisberg’s ligaments were measured. The PCL was cut sharply perpendicular to the tibia shaft, and the fibre layers were observed in cross section.

Results
The PCL was located between 12 and 4 o’clock in the right knee (8 and 12 o’clock in the left), while Humphrey’s ligament was located between 2 and 4 o’clock in the right knee (8 and 10 o’clock in the left). Humphrey’s ligament at femoral insertion, midsubstance and lateral meniscus insertion averaged 8.7 ± 2.3, 5.9 ± 2.1 and 6.1 ± 2.0 mm, respectively, while the thickness at each level averaged 2.0 ± 1.2, 1.6 ± 0.6 and 1.9 ± 0.6 mm. The width of the PCL at midsubstance and at medial meniscus level averaged 13.3 ± 2.0 and 11.0 ± 1.6 mm, respectively, while the thickness of the PCL averaged 5.4 ± 0.8 and 5.5 ± 1.4 mm. In cross section, multiple, interconnected layers were observed which could not be divided. The main layers at each level were aligned from the posterolateral to the anteromedial aspect and formed a C-shape at the medial meniscus level.

Conclusion
The PCL at midsubstance is flat. PCL appears as a twisted ribbon composed of many small fibres without clearly separate bundles. When remnant preserving PCL reconstruction is performed, it is necessary to take account of not only PCL morphology but also the ligaments of Humphrey and Wrisberg. These findings may affect the PCL footprint and the graft shape in the future remnant preserving PCL reconstruction.

kato2017-Wrisberg-tibio-femoral-ligament
The variability of Wrisberg’s ligament. The “tibio-femoral” ligament.

Interesting excerpts:

Frequency of the ligaments of Humphrey and Wrisberg
Humphrey’s ligament alone was found in 6 out of 17 specimens (35.3%), while Wrisberg’s ligament alone was found in 3 out of 17 specimens (17.6%). Both were observed in 8 out of 17 specimens (47.1%).

The clock‑face method and the angle measurement for the ligaments of Humphrey and Wrisberg
All right PCLs were located between 12 and 4 o’clock; meanwhile, all right Humphrey’s ligaments were located between 2 and 4 o’clock. All left PCLs were located between 8 and 12 o’clock; meanwhile, all left Humphrey’s ligaments were located between 8 and 10 o’clock. The angle of the PCL averaged 86.4 ± 4.4°, whereas the angle of Humphrey’s ligament averaged 45.2 ± 8.7°. The angle of Wrisberg’s ligament averaged 34.1 ± 4.4°.

The variability of Wrisberg’s ligament
The “tibio-femoral” ligament, a posterior medial oblique ligament, covered the PCL like Wrisberg’s ligament in four specimens (Fig. 3a). This posterior ligament was superficial to the PCL and attached to the tibia more laterally than the PCL in spite of the same femoral attachment of Wrisberg’s ligament. Because the layer was obviously different from the PCL, it was recognized that this ligament did not form part of the PCL. This ligament was observed in the knees that did not have the typical Wrisberg’s ligament. It was named the “tibio-femoral” ligament, distinct from the PCL.

Morphology of the PCL and the fibre layers in cross section
The PCL is composed of many small fibres (Fig. 1). A relatively flat structure could be observed at the midsubstance (Fig. 4a), while multiple layers were observed in cross section. The layers connected with each other and could not be divided. The main layers observed in the cross section were aligned from the posterolateral to the anteromedial direction at the midsubstance, but formed a C-shape at the level of the medial meniscus (Fig. 4b). The axis of the arc was aligned in a similar direction at midsubstance.

ACL tibial footprint is elliptical or triangular shaped in healthy young adults (3-T MRI analysis)

Anterior cruciate ligament tibial insertion site is elliptical or triangular shaped in healthy young adults: high-resolution 3-T MRI analysis, Tashiro et al. KSSTA (2018) 26(2):485-490.

Abstract:

Purpose
To clarify the morphology of anterior cruciate ligament (ACL) tibial insertion site in healthy young knees using high-resolution 3-T MRI.

Methods
Subjects were 50 ACL-reconstructed patients with a mean age of 21.4 ± 6.8 years. The contralateral healthy knees were scanned using high-resolution 3-T MRI. The tibial insertion sites of the anteromedial (AM) and posterolateral (PL) bundle fibres, and the ACL attachment on the anterior horn of lateral meniscus (AHLM) were segmented from the MR images, and 3D models were reconstructed to evaluate the morphology. The shape of ACL footprint was qualitatively analysed, and the size of AM and PL attachments and AHLM overlapped area was measured digitally.

Results
Tibial AM and PL bundles were clearly identified in 42 of 50 knees (84.0%). Morphology of the whole ACL tibial insertion site was elliptical in 23 knees (54.8%) and triangular in 19 knees (45.2%), but not classified as C-shape in any knees. However, the AM bundle attachment was of C-shape in 29 knees (69.0%) and band-like in 13 knees (31.0%). Overlap of ACL on AHLM was found in 26 knees (61.9%), and the size of the overlapped area was 4.8 ± 4.7% of the whole ACL insertion site.

Conclusion
3D morphology of the intact ACL tibial insertion site analysed by high-resolution 3-T MRI was elliptical or triangular in healthy young knees. However, the AM bundle insertion site was of C-shape or band-like. A small lateral portion of the ACL was overlapped with the AHLM. As for clinical relevance, these findings should be considered in order to reproduce the native ACL insertion site sufficiently.

Level of evidence
III.

tashiro2017-ACL-footprint-bundles
If PL bundle was eliminated, AM bundle footprint looked C-shape (a) in 29 knees (69.0%) and band-like in 13 knees (31.0%) (b)

Preoperative MRI predicts eligibility for arthroscopic primary ACL repair

ACL-tear-tipe-II

Preoperative magnetic resonance imaging predicts eligibility for arthroscopic primary anterior cruciate ligament repair, by van der List and DiFelice, KSSTA (2018), 26(2):660–671

Abstract:

Purpose
To assess the role of preoperative magnetic resonance imaging (MRI) on the eligibility for arthroscopic primary anterior cruciate ligament (ACL) repair.

Methods
All patients undergoing ACL surgery between 2008 and 2017 were included. Patients underwent arthroscopic primary repair if sufficient tissue length and quality were present, or they underwent single-bundle ACL reconstruction. Preoperative MRI tear locations were graded with the modified Sherman classification: type I (>90% distal remnant length), type II (75–90%), or type III (25–75%). MRI tissue quality was graded as good, fair, or poor. Arthroscopy videos were reviewed for tissue length and quality, and final treatment.

Results
Sixty-three repair patients and 67 reconstruction patients were included. Repair patients had more often type I tears (41 vs. 4%, p < 0.001) and good tissue quality (89 vs. 12%, p < 0.001). Preoperative MRI tear location and tissue quality predicted eligibility for primary repair: 90% of all type I tears and 88% of type II tears with good tissue quality were repaired, while only 23% of type II tears with fair tissue quality, 0% of type II tears with poor tissue quality, and 14% of all type III tears could be repaired. Conclusions This study showed that tear location and tissue quality on preoperative MRI can predict eligibility for arthroscopic primary ACL repair. These findings may guide the orthopaedic surgeon on the preoperative assessment for arthroscopic primary repair of proximal ACL tears. Level of evidence Level IV.

ACL-tear-MRI-repair-flowchart
Flowchart, based on preoperative MRI tear location and tissue quality, shows the percentage of patients that were repaired per tear location and tissue quality

The importance of Blumensaat’s line morphology for accurate femoral ACL footprint evaluation using the quadrant method

The importance of Blumensaat’s line morphology for accurate femoral ACL footprint evaluation using the quadrant method, by Yahagi, Iriuchishima,, Horaguchi, et al. KSSTA (2018) 26(2):455–461.

Morphological variation of the Blumensaat’s line
Following Iriuchishima’s classification*, the morphology of the Blumensaat’s line was classified into straight, small hill, and large hill types.

Straight type
The Blumensaat’s line (intercondylar roof) appeared more or less straight, and the transition from the Blumensaat’s line to the posterior cortex was clearly defined.

Small hill type
A protrusion spanning less than half of the line was observed at the posterior (proximal) part of the Blumensaat’s line.

Large hill type
A protrusion spanning more than half of the line was observed at the proximal part of the the Blumensaat’s line.

*Iriuchishima T, Ryu K, Aizawa S, Fu FH (2016) Blumensaat’s line is not always straight: morphological variations of the lateral wall of the femoral intercondylar notch. Knee Surg Sports Traumatol Arthrosc 24:2752–2757

iriuchishima-blumensaat-line-morphology
Morphological variations of the Blumensaat’s line. In Iriuchishima’s classification, the morphology of the Blumensaat’s line has three types of variations: straight type, small hill type, and large hill type

Grid placement in the quadrant method
In the same images used for the morphological evaluation of the Blumensaat’s line, four types of quadrant grid placement were evaluated according to the morphological variations of the Blumensaat’s line and the chondral lesion

  • Grid (1) Without consideration of hill existence and not including the chondral lesion. The baseline of the quadrant grid was matched to the anterior part of the Blumensaat’s line. The lower and side line of the grid were tangential to the medial wall of the lateral femoral condyle.
  • Grid (2) Without consideration of hill existence and including the chondral lesion. The base line of the grid was determined as in Grid 1. The lower and side line were tangential to the articular surface.
  • Grid (3) With consideration of hill existence and not including the chondral lesion. The baseline of the grid was the line connecting the anterior edge of the Blumensaat’s line and the top of the hill. The lower and side line of the grid were tangential to the medial wall of the lateral femoral condyle.
  • Grid (4) With consideration of hill existence and including the chondral lesion. The baseline of the grid was determined as in Grid 3. The lower and side line were tangential to the articular surface. The measurement accuracy of the Image J software were, 0.1 mm and 0.1 mm2.
yahagi2017-quadrant-grid-placement
Quadrant grid placement according to the morphological variations of the Blumensaat’s line and the chondral lesion. According to the morphological variations of the Blumensaat’s line and the chondral lesion, quadrant grids were placed as: Grid (1) without consideration of hill existence and not including the chondral lesion. Grid (2) without consideration of hill existence and including the chondral lesion. Grid (3) with consideration of hill existence and not including the chondral lesion. Grid (4) with consideration of hill existence and including the chondral lesion

3D graft-bending angle measurement and finite-element analysis

3D-FEM-ACL-graft

Peak stresses shift from femoral tunnel aperture to tibial tunnel aperture in lateral tibial tunnel ACL reconstructions: a 3D graft-bending angle measurement and finite-element analysis, by Van Der Bracht et al. KSSTA (2018) 26(2): 508–517.

Abstract:

Purpose
To investigate the effect of tibial tunnel orientation on graft-bending angle and stress distribution in the ACL graft.

Methods
Eight cadaveric knees were scanned in extension, 45°, 90°, and full flexion. 3D reconstructions with anatomically placed anterior cruciate ligament (ACL) grafts were constructed with Mimics 14.12®. 3D graft-bending angles were measured for classic medial tibial tunnels (MTT) and lateral tibial tunnels (LTT) with different drill-guide angles (DGA) (45°, 55°, 65°, and 75°). A pivot shift was performed on 1 knee in a finite-element analysis. The peak stresses in the graft were calculated for eight different tibial tunnel orientations.

Results
In a classic anatomical ACL repair, the largest graft-bending angle and peak stresses are seen at the femoral tunnel aperture. The use of a different DGA at the tibial side does not change the graft-bending angle at the femoral side or magnitude of peak stresses significantly. When using LTT, the largest graft-bending angles and peak stresses are seen at the tibial tunnel aperture.

Conclusion
In a classic anatomical ACL repair, peak stresses in the ACL graft are found at the femoral tunnel aperture. When an LTT is used, peak stresses are similar compared to classic ACL repairs, but the location of the peak stress will shift from the femoral tunnel aperture towards the tibial tunnel aperture. Clinical relevance: the risk of graft rupture is similar for both MTTs and LTTs, but the location of graft rupture changes from the femoral tunnel aperture towards the tibial tunnel aperture, respectively.

How pelvic tilt influences intraoperative digital radiography in total hip arthroplasty

pelvis-radiograph-tha

Digital Radiography in Total Hip Arthroplasty: Technique and Radiographic Results, by Penenberg et al. JBJS (2018) 100 (3): 226

Abstract:

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.

The safe zone range for cup anteversion is narrower than for inclination in THA

THA-cup-anteversion-safe-zone

The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA by William et al. CORR (2018) 476 (2): 325–335.

Abstract:

Background Cup malposition is a common cause of impingement, limitation of ROM, acceleration of bearing wear, liner fracture, and instability in THA. Previous studies of the safe zone based on plain radiographs have limitations inherent to measuring angles from two-dimensional projections. The current study uses CT to measure component position in stable and unstable hips to assess the presence of a safe zone for cup position in THA.

Questions/purposes (1) Does acetabular component orientation, when measured on CT, differ in stable components and those revised for recurrent instability? (2) Do CT data support historic safe zone definitions for component orientation in THA?

Methods We identified 34 hips that had undergone revision of the acetabulum for recurrent instability that also had a CT scan of the pelvis between August 2003 and February 2017. We also identified 175 patients with stable hip replacements who also had a CT study for preoperative planning and intraoperative navigation of the contralateral side. For each CT study, one observer analyzed major factors including acetabular orientation, femoral anteversion, combined anteversion (the sum of femoral and anatomic anteversion), pelvic tilt, total offset difference, head diameter, age, sex, and body mass index. These measures were then compared among stable hips, hips with cup revision for anterior instability, and hips with cup revision for posterior instability. We used a clinically relevant measurement of operative anteversion and inclination as opposed to the historic use of radiographic anteversion and inclination. The percentage of unstable hips in the historic Lewinnek safe zone was calculated, and a new safe zone was proposed based on an area with no unstable hips.

Results Anteriorly unstable hips compared with stable hips had higher operative anteversion of the cup (44° ± 12° versus 31° ± 11°, respectively; mean difference, 13°; 95% confidence interval [CI], 5°-21°; p = 0.003), tilt-adjusted operative anteversion of the cup (40° ± 6° versus 26° ± 10°, respectively; mean difference, 14°; 95% CI, 10°-18°; p < 0.001), and combined tilt-adjusted anteversion of the cup (64° ± 10° versus 54° ± 19°, respectively; mean difference, 10°; 95% CI, 1°-19°; p = 0.028). Posteriorly unstable hips compared with stable hips had lower operative anteversion of the cup (19° ± 15° versus 31° ± 11°, respectively; mean difference, -12°; 95% CI, -5° to -18°; p = 0.001), tilt-adjusted operative anteversion of the cup (19° ± 13° versus 26° ± 10°, respectively; mean difference, -8°; 95% CI, -14° to -2°; p = 0.014), pelvic tilt (0° ± 6° versus 4° ± 6°, respectively; mean difference, -4°; 95% CI, -7° to -1°; p = 0.007), and anatomic cup anteversion (25° ± 18° versus 34° ± 12°, respectively; mean difference, -9°; 95% CI, -1° to -17°; p = 0.033). Thirty-two percent of the unstable hips were located in the Lewinnek safe zone (11 of 34; 10 posterior dislocations, one anterior dislocation). In addition, a safe zone with no unstable hips was identified within 43° ± 12° of operative inclination and 31° ± 8° of tilt-adjusted operative anteversion. Conclusions The current study supports the notion of a safe zone for acetabular component orientation based on CT. However, the results demonstrate that the historic Lewinnek safe zone is not a reliable predictor of future stability. Analysis of tilt-adjusted operative anteversion and operative inclination demonstrates a new safe zone where no hips were revised for recurrent instability that is narrower for tilt-adjusted operative anteversion than for operative inclination. Tilt-adjusted operative anteversion is significantly different between stable and unstable hips, and surgeons should therefore prioritize assessment of preoperative pelvic tilt and accurate placement in operative anteversion. With improvements in patient-specific cup orientation goals and acetabular component placement, further refinement of a safe zone with CT data may reduce the incidence of cup malposition and its associated complications.

Level of Evidence
: Level III, diagnostic study.