Improving cup positioning using a mechanical navigation instrument

A Novel Device for Intraoperative Measurement of Stem Anteversion Angle in Total Hip Arthroplasty

Background

Stem anteversion plays a crucial role in mitigating postoperative complications in total hip arthroplasty (THA). The application of the combined-anteversion theory in THA necessitates the intraoperative measurement of the stem anteversion angle (SAA). However, estimating SAA intraoperatively poses challenges for surgeons lacking a computer-assisted navigation system. In this study, we assessed the precision of intraoperative SAA measurements using a recently developed device, comparing them with 3-dimensional measurements obtained from postoperative computed tomography.

Methods

We examined 127 hips in 127 patients who underwent unilateral THA at our institution. Employing our newly constructed device, attachable to rasping broach handles, we measured the SAA intraoperatively. This process involved incorporating the correction angle derived from the preoperative epicondylar view. We then compared the postoperative SAA with the intraoperative measurements, both with and without the correction angle, to ascertain the device's utility.

Results

The device yielded an intraoperative SAA measurement of 17.93 ± 7.53°. In contrast, the true SAA measured on postoperative computed tomography was 26.40 ± 9.73°. The discrepancy between intraoperative and true SAA was 8.94 ± 5.44° (without the correction angle) and 4.93 ± 3.85° (with the correction angle). Accuracy within a discrepancy of <5° was achieved in 77 cases (60.6%), and <10° was achieved in 113 cases (89.0%). The accuracy remained consistent regardless of the stem-placement angle (varus/valgus, or flexion/extension) or the presence of ipsilateral knee osteoarthritis.

Conclusions

The SAA-measuring device, attachable to various rasping handles, proves useful for straightforward, cost-effective, and noninvasive intraoperative SAA measurement during THA.

Accuracy of Acetabular Cup Placement During Total Hip Arthroplasty in Supine Position Using a Pelvic Rotation Correction Device

Background

Accurate cup placement during total hip arthroplasty (THA) is difficult because the intraoperative pelvic position changes even in supine patient position. We developed a device known as HipPointer; it corrects pelvic rotation and creates a functional pelvic plane as a reference. The aim of this study was to determine the device placement accuracy and investigate causes of error.

Material and methods

HipPointer was used for cup placement in 353 hips of 308 patients who underwent direct-anterior-approach THA in supine position. The mean age at surgery and body mass index were 63.9 (17-90) years and 24.9 (16.6-42.0) kg/m², respectively. The mean observation period was 40.5 (12-73) months. To investigate the accuracy of HipPointer, preoperative planning and postoperative cup placement angles relative to the functional pelvic plane were evaluated using a three-dimensional analysis software, and absolute errors were determined.

Results

The means ± standard deviations of radiographic inclination (RI) and radiographic anteversion (RA) were 40.2 ± 3.0° and 15.8 ± 3.6°, respectively. The absolute errors of RI and RA were 2.2 ± 2.0° and 2.7 ± 2.3°, respectively. The ratio of the cup placement angle for which both RI and RA are ≤10° in the target zone was 99% (350/353 hips), and the ratio of the absolute errors for which both RI and RA are ≤5° was 80.4% (284/353 hips).

Conclusions

HipPointer is simple in structure, easy to use, and useful for direct-anterior-approach THA in supine position. It provides good cup placement accuracy.

Mechanical and Anatomical Alignment Guide Techniques Are Superior to Freehand in Achieving Target Orientation of an Acetabular Component

Background

Achieving accurate and consistent acetabular component orientation remains a major challenge in total hip arthroplasty.

Methods

We used a pelvic model to compare freehand techniques vs mechanical and anatomical alignment guides in achieving a target operative inclination (OI) and operative anteversion (OA). Thirty subjects comprising consultant orthopedic surgeons, orthopedic trainees, and nonsurgical staff positioned an acetabular component in a pelvic model using 3 different methods for guiding inclination and another 3 for guiding version.

Results

Using either a standard mechanical alignment guide (MAG) or a spirit level MAG technique eliminated outliers from target OI, while the freehand method resulted in 46.7% of measurements outside the OI target range. The spirit level MAG technique significantly outperformed the standard MAG technique in median unsigned deviation from target OI (0.8° vs 2.1°, P < .001). Either method of referencing the transverse acetabular ligament for version yielded lower deviations from target OA than the freehand method and fewer outliers from the ±5° target range. Surgical experience was not a significant factor for accurately achieving target OI and OA.

Conclusions

Even in an idealized in vitro model, a wide range of OI and OA is seen with the freehand technique of cup placement by subjects of all levels of surgical experience. Using either a standard MAG or a spirit level MAG reduces deviations in target OI, with the spirit level MAG method yielding the best accuracy. Using the transverse acetabular ligament to guide cup anteversion yields more accurate OA.

Early postoperative clinical recovery of robotic arm-assisted vs. image-based navigated Total hip Arthroplasty

BACKGROUND

This study compared the early clinical recovery of total hip arthroplasty (THA) using computer navigation systems (nTHA) and robotic arm-assisted THA (rTHA).

METHODS

Thirty prospective subjects who underwent rTHA were clinically compared to 30 subjects who underwent nTHA. Clinical data (surgical time, intraoperative blood loss, pain severity, number of days to independent walking, and Harris Hip Score (HHS) at discharge), and radiographic parameters (inclination and anteversion angles) were statistically compared between the two groups.

RESULTS

Follow-up times were 24.3 ± 6.0 and 27.0 ± 7.0 days in the rTHA and nTHA groups, respectively. The surgical time (135.1 ± 13.9 min vs. 146.2 ± 12.8 min, p = 0.002), number of days to independent walking (7.2 ± 2.0 vs. 11.5 ± 3.0 days, p < 0.001), and postoperative pain using a numeric rating scale on postoperative days 7, 10,, and 14 (1.4 ± 0.9 vs. 2.2 ± 1.2, p = 0.005; 1.0 ± 0.8 vs. 1.8 ± 1.1, p = 0.002; 0.3 ± 0.5 vs. 1.1 ± 0.9, p < 0.001; respectively) were significantly reduced in the rTHA group compared to the nTHA group. The rTHA group showed a significantly higher postoperative HHS compared to the nTHA group (85.3 ± .3.2 vs. 81.0 ± 8.5, p = 0.014). No statistically significant difference was observed in radiographic parameters between the groups; however, the incidence of intraoperative target angle changes was significantly lower in the rTHA group than in the nTHA group (0/30 subjects [0%] vs. 11/30 subjects [36.7%], p < 0.001).

CONCLUSION

The surgical time, postoperative pain, and number of days to independent walking were significantly shorter, and the HHS at discharge was significantly higher in the rTHA group than in the nTHA group. Thus, compared to the nTHA group, the rTHA group showed improved early clinical recovery.

3D Printed Guides and Preoperative Planning for Uncemented Stem Anteversion Reconstruction during Hip Arthroplasty: A Pilot Study

Objective

To investigate if 3D printed guides and preoperative planning can accurately control femoral stem anteversion.

Methods

A prospective comparative study was carried out from 2018 to 2020, including 53 patients who underwent hip arthroplasty for femoral neck fracture. The target rotation center of the femoral head is determined by three-dimensional planning. In group A, planning was made by 2D templates. In group B, preoperative 3D planning and 3D printed osteotomy/positioning guides were performed. After the operation, 3D model registration was performed to calculate the accuracy of anteversion restoration.

Results

We screened 60 patients and randomized a total of 53 to 2 parallel study arms: 30 patients to the group A (traditional operation) and 23 patients to the group B (3D preoperative planning and 3D printed guide). There were no significant differences in demographic or perioperative data between study groups. The restoration accuracy of group A was 5.42° ± 3.65° and of group B was 2.32° ± 1.89°. The number and rate of abnormal cases was 15 (50%) and 2 (8.7%), respectively. Significant statistical differences were found in angle change, restoration accuracy, and number of abnormal cases.

Conclusion

Three-dimensional preoperative planning and 3D printed guides can improve the accuracy of the restoration of femoral anteversion during hip arthroplasty.

Improving MiniHip femoral prosthesis positioning using a cross-laser projection system in total hip arthroplasty by an anterolateral supine approach

Background

The authors developed a cross‐laser projection system (CLP) to place a femoral neck‐sparing short stem using the minimally invasive anterolateral supine approach in total hip arthroplasty. This study aimed to verify the utility of CLP.

Methods

Thirty joints were assessed with the MiniHip (Corin). The authors compared femoral component implantation with a patient‐specific femoral osteotomy guide (PSG) for the femoral neck‐cut (PSG group), with the CLP attached to the rasp handle to irradiate the cross‐laser to the target of PSG (CLP group), and without PSG or CLP (control group).

Results

In the CLP group, the positional deviation of anteversion, anterior/posterior tilt and varus/valgus placement of the stem postoperatively were 1.8° ± 0.2°, 2.0° ± 2.0° and 2.0° ± 0.1°, respectively. The positional deviation of anteversion (p < 0.001) and anterior/posterior tilt (p = 0.036) were significantly smaller than those in the other groups.

Conclusions

CLP improves the accuracy of MiniHip femoral prosthesis placement.

The Impingement-free, Prosthesis-specific, and Anatomy-adjusted Combined Target Zone for Component Positioning in THA Depends on Design and Implantation Parameters of both Components

BACKGROUND

Lewinnek's recommendation for orienting the cup in THA is criticized because it involves a static assessment of the safe zone and because it does not consider stem geometry. A revised concept of the safe zone should consider those factors, but to our knowledge, this has not been assessed.

QUESTIONS/PURPOSES

(1) To determine the shape, size, and location of target zones for combined cup and stem orientation for a straight stem/hemispheric cup THA to maximize the impingement-free ROM and (2) To determine whether and how these implant positions change as stem anteversion, neck-shaft angle, prosthetic head size and target range of movements are varied.

METHODS

A three-dimensional computer-assisted design model, in which design geometry was expressed in terms of parameters, of a straight stem/hemispheric cup hip prosthesis was designed, its design parameters modified systematically, and each prosthesis model was implanted virtually at predefined component orientations. Functional component orientation referencing to body planes was used: cups were abducted from 20° to 70°, and anteverted from -10° to 40°. Stems were rotated from -10° to 40° anteversion, neck-shaft angles varied from 115° to 143°, and head sizes varied from 28 to 40 mm. Hip movements up to the point of prosthetic impingement were tested, including simple flexion/extension, internal/external rotation, ab/adduction, combinations of these, and activities of daily living that were known to trigger dislocation. For each combination of parameters, the impingement-free combined target zone was determined. Maximizing the size of the combined target zone was the optimization criterion.

RESULTS

The combined target zones for impingement-free cup orientation had polygonal boundaries. Their size and position in the diagram changed with stem anteversion, neck-shaft angle, head size, and target ROM. The largest target zones were at neck-shaft angles from 125° to 127°, at stem anteversions from 10° to 20°, and at radiographic cup anteversions between 17° and 25°. Cup anteversion and stem anteversion were inverse-linearly correlated supporting the combined-anteversion concept. The range of impingement-free cup inclinations depended on head size, stem anteversion, and neck-shaft angle. For a 127°-neck-shaft angle, the lowest cup inclinations that fell within the target zone were 42° for the 28-mm and 35° for the 40-mm head. Cup anteversion and combined version depended on neck-shaft angle. For head size 32-mm cup, anteversion was 6° for a 115° neck-shaft angle and 25° for a 135°-neck-shaft angle, and combined version was 15° and 34° respectively.

CONCLUSIONS

The shape, size, and location of the combined target zones were dependent on design and implantation parameters of both components. Changing the prosthesis design or changing implantation parameters also changed the combined target zone. A maximized combined target zone was found. It is mandatory to consider both components to determine the accurate impingement-free prosthetic ROM in THA.

CLINICAL RELEVANCE

This study accurately defines the hypothetical impingement-free, design-specific component orientation in THA. Transforming it into clinical precision may be the case for navigation and/or robotics, but this is speculative, and as of now, unproven.

A review of computer-assisted orthopaedic surgery systems

BACKGROUND

Computer-assisted orthopaedic surgery systems have great potential, but no review has focused on computer-assisted surgery systems for the spine, hip, and knee.

METHODS

A systematic search was performed in Web of Science and PubMed. We searched the literature on computer-assisted orthopaedic surgery systems from 2008 to the present and focused on three aspects of systems: training, planning, and intraoperative navigation.

RESULTS AND DISCUSSION

In this review study, we reviewed 34 surgical training systems, 31 surgical planning systems, and 41 surgical navigation systems. The functions and characteristics of the surgical systems were compared and analysed, and the current concerns about and the impact of the surgical systems on doctors and surgery were clarified.

CONCLUSION

Computer-assisted orthopaedic surgery systems are still in the development stage. Future surgical training systems should include synthetic models with patient anatomy. Surgical planning systems with automatic planning should be developed, and surgical navigation systems with multimodal fusion, robotic assistance and imaging should be developed.

Patient-Specific Surgical Guide for Total Hip Arthroplasty

Three-dimensional printing technique has been adapted for orthopedic surgery, and a patient-specific surgical guide (PSG) has been introduced as a convenient surgical instrument and implicated in the ideal positioning of the components, including acetabular and femoral components in total hip arthroplasty (THA). PSG is designed and manufactured based on preoperative imaging data, mainly computed tomography (CT) data. PSGs for implantation in THA are classified into three types: PSG for guidewire insertion, PSG for bone cutting, and PSG for bone reaming and implant fixation. PSG positioning accuracy depends on the PSG design and surgical preparation in contact area on the bone surface. PSGs for the acetabular component, for the conventional femoral component, and for the resurfacing femoral component have been clinically used. To achieve precise implantation, precise PSG setting needs and careful surgical preparation of soft tissues are important.

Robot-assisted total hip arthroplasty: Clinical outcomes and complication rate

BACKGROUND

The purpose of this study was to report minimum 2-year outcomes and complications for robotic-arm-assisted total hip arthroplasty (THA).

METHODS

Data were prospectively collected and retrospectively reviewed between June 2011 and April 2014. Inclusion criteria were primary robotic-arm-assisted THAs treating idiopathic osteoarthritis with ≥ 2-year follow-up. Demographics, operating time, complications, 2-year outcome scores and satisfaction, and subsequent surgeries were recorded.

RESULTS

There were 181 cases eligible for inclusion, of which 162 (89.5%) had minimum 2-year follow-up. At the latest follow-up, the mean visual analogue scale was 0.7, satisfaction was 9.3, Harris hip score was 91.1 and forgotten joint score was 83.1. Six (3.7%) intraoperative complications and six (3.7%) postoperative complications were reported. No leg length discrepancies (LLDs) or dislocations were reported.

CONCLUSIONS

Robotic-arm-assisted THA demonstrates favourable short-term outcomes and does not result in a higher complication rate compared to non-robotic THA as reported by the literature.

A new approach for safe planning transfer using semi-automatically adjustable instrument guides

Accurate planning transfer is a prerequisite for successful operative care. For different applications, diverse computer-assisted systems have been developed and clinically evaluated. This paper presents the implementation and evaluation of a new modular concept. The approach is based on passive application specific kinematics that are semi-automatically adjusted using a universal hand-held computer controlled Smart Screw Driver. The system was realized for pedicle screw instrumentation and evaluated according to IEC 60601-1-6 (usability engineering). The accuracies of the drill holes achieved were comparable with robotic approaches, while operation time and radiation were reduced compared with conventional operation techniques. The adjustment procedure has proven high learnability and user satisfaction. The next step will be optimization of the kinematic structure and fixation to the patient in order to increase accuracies of planning transfer as well as evaluation of the overall system by medical staff in preclinical and clinical studies.

The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA

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.

Efficacy of a Pelvic Lateral Positioner With a Mechanical Cup Navigator Based on the Anatomical Pelvic Plane in Total Hip Arthroplasty

BACKGROUND

The acetabular component orientation in total hip arthroplasty (THA) is of critical importance to the good clinical results. However, traditional widely used cup alignment guides for cup placement are reported to be relatively unreliable. The present study aims at comparing a novel cup alignment guide, which can be attached to our anatomical pelvic plane (APP) pelvic lateral positioner for reducing discrepancies in sagittal pelvic tilt and indicate a targeted cup angle based on the APP, with a conventional cup alignment guide.

METHODS

The subjects were 136 hips of 136 patients who underwent unilateral THA using the APP positioner. The procedure was performed with the conventional cup alignment guide (conventional group; 60 hips) and with the novel cup navigator (mechanical navigator group; 76 hips). Postoperative cup angles and discrepancies of postoperative cup angles (inclination and anteversion angles) from the targeted angles were compared between the 2 groups to evaluate the usefulness of these navigators.

RESULTS

The mean cup angles in the conventional group were 39.0° ± 5.3° for the inclination angle and 21.7° ± 6.4° for the anteversion angle, whereas those in the mechanical navigator group were 40.6° ± 3.2° and 18.3° ± 4.6°, respectively (P = .018, P < .0001). The discrepancies from the targeted angles were 3.5° ± 3.1° for the inclination angle and 4.6° ± 3.4° for the anteversion angle in the conventional group and 2.3° ± 2.3° and 3.2° ± 2.7°, respectively, in the mechanical navigator group (P = .020, P = .012).

CONCLUSION

The mechanical cup navigator easily attachable to the APP positioner is a tool that can improve the accuracy of cup placement in a simple, economical, and noninvasive manner in THA via the lateral position.

Quantification of Imaging Error in the Measurement of Cup Position: A Cadaveric Comparison of Radiographic and Computed Tomography Imaging

Postoperative radiographs remain the standard for assessment of component placement following total hip arthroplasty (THA), despite the known limitations of radiographs. Computed tomography (CT) scanning offers improved accuracy, but its costs and radiation exposure are prohibitive. The authors performed a cadaver study to compare the error associated with radiographs with that of CT scans following THA. The authors also compared imaging with a novel mini-navigation system. Three board-certified orthopedic surgeons each performed 4 THA procedures (6 cadavers, 12 hips) via the posterior approach using a mini-navigation tool to assist with component placement. Cup position from imaging was compared with corrected CT values for anteversion and inclination, created by correcting the initial scan to align the anterior pelvic plane coplanar with the CT table, thus representing cup position not distorted by imaging or positioning. Anteversion from standard CT scans was within 2.5° (standard deviation [SD], 1.5°) of reference values (P=.25); radiographs showed an average error of 7.8° (SD, 4.3°) vs reference values (all values absolute means) (P<.01). The mini-navigation system provided anteversion values within an average of 4.0° (SD, 4.0°) of reference anteversion (P<.01). Standard CT values for inclination were within 2.4° (SD, 2.0°) of reference values (P=.53), whereas radiographic inclination values were within 2.5° (SD, 2.3°) (P=.12). Mini-navigation values for inclination were within 3.9° (SD, 3.2°) of reference inclination (P=.26). This study demonstrated that cup position as measured by radiographs is significantly less accurate than CT scans and that the mini-navigation system provided anteversion measurements that were of comparable accuracy to CT scans. [Orthopedics. 2017; 40(6):e952-e958.].

Technology in Arthroplasty: Are We Improving Value?

PURPOSE OF REVIEW

Total joint arthroplasty is regarded as a highly successful procedure. Patient outcomes and implant longevity, however, are related to proper alignment and position of the prostehses. In an attempt to reduce outliers and improve accuracy and precision of component position, navigation and robotics have been introduced. These technologies, however, come at a price. The goals of this review are to evaluate these technologies in total joint arthroplasty and determine if they add value.

RECENT FINDINGS

Recent studies have demonstrated that navigation and robotics in total joint arthroplasty can decrease outliers while improving accuracy in component positioning. While some studies have demonstrated improved patient reported outcomes, not all studies have shown this to be true. Most studies cite increased cost of equipment and longer operating room times as the major downsides of the technologies at present. Long-term studies are just becoming available and are promising, as some studies have shown decreased revision rates when navigation is used. Finally, there are relatively few studies evaluating the direct cost and value of these technologies. Navigation and robotics have been shown to improve component position in total joint arthroplasty, which can improve patient outcomes and implant longevity. These technologies offer a promising future for total joint arthroplasty.

The Evolution of Computer-Assisted Total Hip Arthroplasty and Relevant Applications

In total hip arthroplasty (THA), the accurate positioning of implants is the key to achieve a good clinical outcome. Computer-assisted orthopaedic surgery (CAOS) has been developed for more accurate positioning of implants during the THA. There are passive, semi-active, and active systems in CAOS for THA. Navigation is a passive system that only provides information and guidance to the surgeon. There are 3 types of navigation: imageless navigation, computed tomography (CT)-based navigation, and fluoroscopy-based navigation. In imageless navigation system, a new method of registration without the need to register the anterior pelvic plane was introduced. CT-based navigation can be efficiently used for pelvic plane reference, the functional pelvic plane in supine which adjusts anterior pelvic plane sagittal tilt for targeting the cup orientation. Robot-assisted system can be either active or semi-active. The active robotic system performs the preparation for implant positioning as programmed preoperatively. It has been used for only femoral implant cavity preparation. Recently, program for cup positioning was additionally developed. Alternatively, for ease of surgeon acceptance, semi-active robot systems are developed. It was initially applied only for cup positioning. However, with the development of enhanced femoral workflows, this system can now be used to position both cup and stem. Though there have been substantial advancements in computer-assisted THA, its use can still be controversial at present due to the steep learning curve, intraoperative technical issues, high cost and etc. However, in the future, CAOS will certainly enable the surgeon to operate more accurately and lead to improved outcomes in THA as the technology continues to evolve rapidly.

A Patient-Specific Instrument for Femoral Stem Placement During Total Hip Arthroplasty

To ensure that the femoral stem is placed in the proper position during total hip arthroplasty, the authors developed a patient-specific instrument. A total of 10 total hip arthroplasties were performed with the assistance of the patient-specific instrument during this study. The mean accuracy of stem tilt, varus/valgus, and anteversion was 2.1°±4.1°, 1.0°±0.7°, and 4.7°±1.2°, respectively. No complications were observed and no reoperations were required for any of the patients who underwent surgery included in this study. The results support the feasibility of this patient-specific instrument for use during stem placement in total hip arthroplasty. [Orthopedics. 2017; 40(2):e374-e377.].

Cup implantation accuracy using the HipCOMPASS mechanical intraoperative support device

Background

While navigation systems have been developed to increase implantation accuracy in total hip arthroplasty (THA), they are not yet sufficiently versatile or commonly used. Therefore, to elevate the appeal of such systems, we have developed HipCOMPASS, a simple and effective mechanical angle indicator for use in supine THA.

Questions/purposes

How accurate is the mean cup orientation [in terms of errors in radiographic anteversion (RA) and inclination (RI)] in cases where HipCOMPASS is used for intraoperative support? Does HipCOMPASS increase this cup orientation accuracy compared to THA cases without it? Does HipCOMPASS increase mean operation time?

Methods

We measured cup orientation in 97 THA cases with HipCOMPASS and in 80 cases without it. Then we compared the angles determined in preoperative planning with the angles revealed by postoperative computed tomography (CT) for both groups. The discrepancy between them was defined as an error. Errors greater than 10° were considered outliers. Additionally, mean operative time with and without the Hip COMPASS were compared.

Results

With the use of HipCOMPASS, the mean absolute error values in radiographic anteversion and inclination were 2.9° ± 2.3° (range 0°–12.8°) and 2.9° ± 2.1° (0.1°–7.7°), respectively. In contrast, without the use of HipCOMPASS, radiographic anteversion and inclination error values were 8.8° ± 5.8° (0.1°–25.4°) and 6.1° ± 4.5° (0.2°–21.0°), respectively. Outlier occurrence rates were 1.0 % with HipCOMPASS and 48.8 % without it. Mean operative times with and without HipCOMPASS use were 109.2 ± 23.8 min (74–199 min) and 137.6 ± 40.6 min (71–298 min), respectively.

Conclusions

The study has found that HipCOMPASS dramatically increases implantation accuracy and it is also a simple and highly versatile tool that can be implemented quickly. Given its low cost in addition to its favourable accuracy, simple implementation, and short operative time, HipCOMPASS can be regarded as a very useful and effective THA support device.

Level of evidence

Retrospective comparative study, Level 3.

Accuracy of Component Placement in Robotic-Assisted Total Hip Arthroplasty

Robotic-assisted total hip arthroplasty (THA) is a recent platform introduced to decrease the risk of malpositioned components. The goals of this study were to determine whether intraoperative data on robotic-assisted THA acetabular component position accurately predict postoperative radiographic acetabular component position and to determine whether intraoperative data on robotic-assisted THA leg length and offset accurately predict postoperative radiographic leg length and offset data. In 146 patients, pre- and postoperative radiographs and intraoperative component measurements were reported for acetabular inclination, anteversion, leg length change, and offset change. Component position obtained by the robotic system and radiographic data were compared with subgroup analysis for the posterior and direct anterior approaches. The average difference between groups was 3.3°±3.1° for inclination, 2.9°±2.3° for anteversion, 3.0±2.3 mm for leg length change, and 4.0±3.1 mm for change in global offset. Correlation between the robotic system and postoperative radiographs was within 10° for 95.9% of cases for inclination and 99.3% for anteversion. Posterior approach correlation was within 10° for 97.1% of cases for inclination and 100% for anteversion. Anterior approach correlation was within 10° for 92.7% of cases for inclination and 97.6% for anteversion. Intraoperative data on component position obtained from the robotic system compared well with radiographic data on component position. Surgeons must remain vigilant to ensure outliers related to robotic system malfunction do not occur. [Orthopedics. 2016; 39(3):193-199.].

Independent Evaluation of a Mechanical Hip Socket Navigation System in Total Hip Arthroplasty

BACKGROUND

Acetabular cup malpositioning during total hip arthroplasty may lead to impingement, instability, wear-induced osteolysis, and increased rates of revision surgery. The purpose of this study was to independently evaluate the accuracy of acetabular cup orientation using a novel mechanical navigation device.

METHODS

An adjustable, reusable mechanical navigation device was used in a consecutive series of patients. Angles (inclination and anteversion) were measured by 2 independent reviewers with a validated 2-dimensional/3-dimensional matching application using a preoperative computed tomographic scan and a postoperative plain film.

RESULTS

There were no outliers for inclination or anteversion for errors within 10° of the preoperative plan. There were 6 (12.8%) outliers for inclination and 11 (23.4%) for anteversion for errors within 5° of the preoperative plan. All patients simultaneously met both targets when an outlier was considered 10°, whereas 30 (63.8%) simultaneously met both targets when the criteria was tightened to 5°. The absolute errors for both inclination and anteversion were significantly less than both 5° and 10° (P<.001).

CONCLUSION

This device reliably navigates acetabular cup inclination and anteversion individualized for each patient to within 10° of a preoperative plan. Outliers increased when this criteria is tightened to 5° but still appears to be more accurate than conventional acetabular cup component placement. Further research is warranted to assess the clinical impact of reducing outliers using this device.

Accuracy of Component Positioning in 1980 Total Hip Arthroplasties: A Comparative Analysis by Surgical Technique and Mode of Guidance

The purpose of this multi-surgeon study was to assess and compare the accuracy of acetabular component placement, leg length discrepancy (LLD), and global offset difference (GOD) between six different surgical techniques and modes of guidance in total hip arthroplasty (THA). A total of 1980 THAs met inclusion criteria. Robotic- and navigation-guided techniques were more consistent than other techniques in placing the acetabular cup into Lewinnek's safe zone (P<0.005 and P<0.05, respectively). Robotic-guided surgery was more consistent than other techniques in placing the acetabular component within Callanan's safe zone (P<0.005). No statistically significant differences were found between groups in the frequency of patients with excessive LLD. Clinically significant differences between groups were not found in the frequency of patients with excessive GOD. Level of Evidence: IV.

Does Robotic-Assisted Computer Navigation Affect Acetabular Cup Positioning in Total Hip Arthroplasty in the Obese Patient? A Comparison Study

Obese populations present challenges for acetabular cup placement during total hip arthroplasty (THA). This study examines the accuracy of acetabular cup inclination and version in the obese patient with robotic-assisted computer navigation. A total of 105 patients underwent robotic-assisted computer navigation THA with a posterior approach. Groups were divided on body mass index (BMI, kg/m(2)) of <30, 30-35, and >35. There was no statistical difference between the BMI <30 (n=59), BMI 30-35 (n=34) and BMI >35 (n=12) groups for acetabular inclination (P=0.43) or version (P=0.95). Robotic-assisted computer navigation provided accurate and reproducible placement of the acetabular cup within safe zones for inclination and version in the obese patient.

Does Intraoperative Fluoroscopy Optimize Limb Length and the Precision of Acetabular Positioning in Primary THA?

Reduced limb length discrepancy and more accurate cup positioning are purported benefits of using fluoroscopy for total hip arthroplasty (THA). The authors compared limb length discrepancy and cup position in 200 patients (group I, posterior approach without fluoroscopy; group II, anterior supine approach with fluoroscopy) who underwent primary THA. Mean limb length discrepancy was 2.7 mm (SD, 5.2 mm; range, -9.8 to 20.9 mm) and 0.7 mm (SD, 3.7 mm; range, -11.8 to 10.5 mm) for groups I and II, respectively (P=.002). In group I, 7% of hips had limb length discrepancy greater than 1 cm compared with 3% in group II. Mean cup inclination measured 40.8° (SD, 5.0°; range, 26.1°-53.7°) in group I and 43.4° (SD, 5.6°; range, 31.3°-55.9°) in group II (P=.008). In group I, 96% of cups had inclination within 10° of the mean compared with 92% in group II (P=.24). Mean anteversion measured 35.3° (SD, 7.1°; range, 17.8°-60.7°) in group I and 25.9° (SD, 8.2°; range, 1.5°-44.8°) in group II (P=.0001). In group I, 87% of hips exhibited anteversion within 10° of the mean compared with 76% in group II (P=.045). Although the anterior approach with intraoperative fluoroscopy reduced mean limb length discrepancy, the clinical significance of this reduction is unclear. Fluoroscopy reduced the incidence of limb length discrepancy greater than 1 cm. However, the use of fluoroscopy did not help to improve the precision of cup positioning.

Accuracy of an adjustable patient-specific guide for acetabular alignment in hip replacement surgery (Optihip)

Implant malalignment in hip arthroplasty increases the risk of revision surgery due to problems such as hip instability, wear, and impingement. Traditional instrumentation lacks accuracy and does not individualize the goal. Computer-assisted surgery (CAS) and patient-specific solutions improve accuracy but add considerably to the cost, amongst other drawbacks. We developed an adjustable mechanical device, called Optihip, which is set to a patient-specific goal preoperatively and is independent of pelvis position intraoperatively. The purpose of the present study was to evaluate Optihip's accuracy ex vivo. Acetabular components were implanted into six cadaveric specimens, 12 hips, by two surgeons, with the device individually adjusted according to preoperative templating on computed tomography (CT) images relative to defined acetabular rim landmarks; options also exist for templating on single or biplanar X-rays. Intraoperatively, the device was positioned on the corresponding anatomical landmarks allowing the insertion of a guide pin, which then defined the desired orientation of the acetabular cup during impaction. Mean absolute difference between the preoperatively planned cup alignment and final acetabular cup orientation, measured from postoperative CT images, was 2.5±1.2° for inclination and 2.5±2.2° for version with maximum values of 4.7° and 6.8°, respectively. Compared with previous in vivo reports, Optihip guided the acetabular cup orientation more accurately than conventional hip arthroplasty, and comparably to CAS or patient-specific systems, while fitting into the normal surgical workflow. Although clinical testing is required to confirm these experimental results, the positive ex vivo accuracy suggests good potential for improving revision rates and patient functional outcome.

Numerical optimization of alignment reproducibility for customizable surgical guides

Purpose

Computer-assisted orthopedic surgery aims at minimizing invasiveness, postoperative pain, and morbidity with computer-assisted preoperative planning and intra-operative guidance techniques, of which camera-based navigation and patient-specific templates (PST) are the most common. PSTs are one-time templates that guide the surgeon initially in cutting slits or drilling holes. This method can be extended to reusable and customizable surgical guides (CSG), which can be adapted to the patients’ bone. Determining the right set of CSG input parameters by hand is a challenging task, given the vast amount of input parameter combinations and the complex physical interaction between the PST/CSG and the bone.

Methods

This paper introduces a novel algorithm to solve the problem of choosing the right set of input parameters. Our approach predicts how well a CSG instance is able to reproduce the planned alignment based on a physical simulation and uses a genetic optimization algorithm to determine optimal configurations. We validate our technique with a prototype of a pin-based CSG and nine rapid prototyped distal femora.

Results

The proposed optimization technique has been compared to manual optimization by experts, as well as participants with domain experience. Using the optimization technique, the alignment errors remained within practical boundaries of 1.2 mm translation and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$0.9^\circ $$\end{document}0.9∘ rotation error. In all cases, the proposed method outperformed manual optimization.

Conclusions

Manually optimizing CSG parameters turns out to be a counterintuitive task. Even after training, subjects with and without anatomical background fail in choosing appropriate CSG configurations. Our optimization algorithm ensures that the CSG is configured correctly, and we could demonstrate that the intended alignment of the CSG is accurately reproduced on all tested bone geometries.

The learning curve associated with robotic-assisted total hip arthroplasty

There are no reports examining the learning curve during the adoption of robotic assisted THA. The purpose of this study was to examine the learning curve of robotic assisted THA as measured by component position, operative time, and complications. The first 105 robotic-assisted THAs performed by a single surgeon were divided into three groups based on the order of surgery. Component position, operative time, intra-operative technical problems, and intra-operative complications were recorded. There was a decreased risk of acetabular component malpositioning with experience (P<0.05). Operative time appeared to decrease with increasing surgical experience (P<0.05). A learning curve was observed, as a decreased incidence of acetabular component outliers and decreased operative time were noted with increased experience.

A novel non-invasive mechanical technique of cup and stem placement and leg length adjustment in total hip arthroplasty for dysplastic hips

PURPOSE

This study assessed the accuracy of cup and stem positioning and limb length adjustment for developmental dysplasia of the hip (DDH) using our new mechanical technique compared with imageless navigation or a computed tomography (CT)-based navigation system.

METHODS

One hundred thirteen primary total hip arthroplasties (THAs) for DDH were evaluated. At pre-operative positioning, patients were placed in a precise lateral decubitus position by tilting the surgical table using simple ready-made devices (two shot pipe, metal chain, level gauge and goniometer). During surgery, cups were intentionally placed at 45° inclination and 15° anteversion on radiograph by using a level gauge and goniometer.

RESULTS

Cup inclination was 44.2° ± 3.4° (range, 32.0-51.2°), cup anteversion was 19.6° ± 6.1° (range, 3.0-33.1°), stem alignment was 0.04° ± 0.8° valgus (range, 2.1° varus to 1.9° valgus), and leg length discrepancy was -0.37 ± 3.7 mm (range, -12.8 to 8.8 mm) in postoperative radiographs. Outliers (outside ±10° from intentional position) occurred in 15 cases (13.3 %) in inclination or anteversion. Postoperative dislocation did not occur in any cases.

CONCLUSIONS

Cup and stem positioning in THAs with our new mechanical technique yielded satisfactory results compared with previously reported imageless navigation or CT-based navigation. Our results were superior with regard to being non-invasive and low cost and involving minimum radiation exposure.

Validation of patient specific surgical guides in total hip arthroplasty

BACKGROUND

The validation of patient-specific surgical guides (PSGs) by their design and the comparison of planned and actual PSG setting in total hip arthroplasty (THA) have not previously been reported.

METHODS

The errors between preoperative planning and computed tomography (CT)-based PSG setting (E1), and between preoperative planning and implantation (E2) were evaluated using CT in 16 fresh cadaveric hips.

RESULTS

E2 was significantly smaller with the wide-base-contact resurfacing-THA PSG than with the narrow-base-contact type (P<0.05). E1/E2 of the wide-base-contact neck-cut PSG was 1.6±0.7°/2.4±1.1° for the coronal plane and 1.2±0.8 mm/0.7±0.5mm for the medial neck-cut height. E1/E2 of the wide-base-contact cup-impaction PSG was 1.0±0.9°/3.4±1.9° for inclination and 1.7±1.1°/6.6±4.4° for anteversion.

CONCLUSIONS

The wide-base-contact PSG in resurfacing-THA and the PSG for neck-cut in THA could be applied clinically. Although cup-impaction PSG setting was acceptable, errors were made due to the impaction process during cup implantation.

Navigated Acetabular Cup Fixation for Acetabular Deformity or Revision Total Hip Arthroplasty

Purpose

To evaluate the usefulness of navigated acetabular cup fixation for total hip arthroplasty in patients with acetabular deformity or revision total hip arthroplasty.

Materials and Methods

This study enrolled 28 patients with at least 12 months' follow-up. The safe zone of the acetabular cup was defined as 40°±10°in inclination and 15°±10°in anteversion. The authors used the navigation and radiographic data to determine whether the acetabular cup was located within the safe zone or not. To evaluate the clinical outcomes, preoperative and last follow-up Harris hip scores were checked, and the occurrence of complications was evaluated.

Results

According to the navigation data, the mean inclination and anteversion were 38.5°±4.7°(range, 32°-50°) and 16.6°±4.0°(range, 8°-23°), respectively. According to the radiographic data the mean inclination and anteversion were 40.5°±4.6°(range, 32°-50°) and 19.4°±4.2°(range, 8°-25°), respectively. In both cases, all values were within the safe zone. Harris hip score was improved in all patients from preoperative 52.3±14.4 points (range, 29-87 points) to 88.0±9.0 points (range, 65-99 points) at the last follow-up. There was no dislocation or loosening of both cases.

Conclusion

Navigated acetabular cup fixation is a useful technique for total hip arthroplasty in patients with acetabular deformity or revision total hip arthroplasty because it prevents the malposition and related complications.

Computed tomography for preoperative planning in total hip arthroplasty: what radiologists need to know

The number of total hip arthroplasties is continuously rising. Although less invasive surgical techniques, sophisticated component design, and intraoperative navigation techniques have been introduced, the rate of peri- and postoperative complications, including dislocations, fractures, nerve palsies, and infections, is still a major clinical problem. Better patient outcome, faster recovery and rehabilitation, and shorter operation times therefore remain to be accomplished. A promising strategy is to use minimally invasive techniques in conjunction with modular implants, aimed at independently reconstructing femoral offset and leg length on the basis of highly accurate preoperative planning. Plain radiographs have clear limitations for the correct estimation of hip joint geometry and bone quality. Three-dimensional assessment based on computed tomography (CT) allows optimizing the choice and positions of implants and anticipating difficulties to be encountered during surgery. Postoperative CT is used to monitor operative translation and plays a role in arthroplastic quality management. Radiologists should be familiar with the needs of orthopedic surgeons in terms of CT acquisition, post-processing, and data transfer. The CT protocol should be optimized to enhance image quality and reduce radiation exposure. When dedicated orthopedic CT protocols and state-of-the-art scanner hardware are used, radiation exposure can be decreased to a level just marginally higher than that of conventional preoperative radiography. Surgeons and radiologists should use similar terminology to avoid misunderstanding and inaccuracies in the transfer of preoperative planning.

Learning curve of acetabular cup positioning in total hip arthroplasty using a cumulative summation test for learning curve (LC-CUSUM)

Despite advances in surgical techniques and instrumentation, optimal cup positioning in total hip arthroplasty (THA) is challenging with a limited accuracy. We evaluated whether a learning curve exists for the optimal cup positioning, using the LC-CUSUM test (Learning curve cumulative summation test). We evaluated the first 100 consecutive THA performed by two surgeons, who had a year of fellowship training in the same teaching hospital. A learning curve of cup positioning was plotted in each series using the LC-CUSUM score. There was no significant difference of numbers of outlier between two surgeons (P = 0.079). Both surgeons completed the learning curve of optimal cup positioning before 50 procedures, and maintained competence. A substantial learning period is necessary in the optimal positioning of an acetabular cup.

A novel method for accurate and reproducible functional cup positioning in total hip arthroplasty

Cup positioning is an important variable for short and long term function, stability, and durability of total hip arthroplasty (THA). This novel method utilizes internal and external bony landmarks, and the transverse acetabular ligament for positioning the acetabular component. The cup is placed parallel and superior to the transverse ligament and inside the anterior wall notch of the true acetabulum, then adjusted for femoral version and pelvic tilt and obliquity based on weight bearing radiographs. In 78 consecutive THAs, the mean functional anteversion and abduction angles were 17.9° ± 4.7° and 41.7° ± 3.8°, respectively. 96% of the functional anteversion measurements and 100% of the functional abduction angles were within the safe zone. This technique is an easy, reproducible, and accurate method for functional cup placement.

A novel device to measure acetabular inclination with patients in lateral decubitus

The ability to measure acetabular cup orientation accurately during total hip arthroplasty represents a significant challenge. The aim of this research was to develop and evaluate a novel low cost mechanical device for measuring operative acetabular inclination. Cup implantation was simulated in two trials using the novel device: firstly involving surgeons and engineers orientating acetabular cups with sawbone pelves at a range of inclination angles (20°-55° in 5° increments); secondly in a simulated intra-operative scenario with surgeons. Target angles were compared with achieved angles and deviations from desired angles were recorded. In addition, all participants orientated cups under the same conditions using two other techniques: freehand and with a propriatory Mechanical Alignment Guide. In the first trial, the mean errors (deviations) using freehand technique, the mechanical alignment guide and the new device were 5.2° +/- 4.3° (range 0.1-22.0), 3.6° +/- 3.9° (range 0.1°-33.6°) and 0.5° +/- 0.4° (range 0.0-1.9) respectively. In the second trial, the mean error for freehand technique, mechanical alignment guide and the new device were 6.2° +/- 4.2° (range 0.2-18.2), 3.8° +/- 3.3° (range 0.0-19.1) and 0.6° +/- 0.5° (range 0.0-1.8) respectively. The new device has the potential to allow the surgeon to choose and record operative inclination accurately during total hip arthroplasty in the lateral decubitus position.

Computer-assisted orthopaedic surgery and robotic surgery in total hip arthroplasty

Various systems of computer-assisted orthopaedic surgery (CAOS) in total hip arthroplasty (THA) were reviewed. The first clinically applied system was an active robotic system (ROBODOC), which performed femoral implant cavity preparation as programmed preoperatively. Several reports on cementless THA with ROBODOC showed better stem alignment and less variance in limb-length inequality on radiographic evaluation, less incidence of pulmonary embolic events on transesophageal cardioechogram, and less stress shielding on the dual energy X-ray absorptiometry analysis than conventional manual methods. On the other hand, some studies raise issues with active systems, including a steep learning curve, muscle and nerve damage, and technical complications, such as a procedure stop due to a bone motion during cutting, requiring re-registration and registration failure. Semi-active robotic systems, such as Acrobot and Rio, were developed for ease of surgeon acceptance. The drill bit at the tip of the robotic arm is moved by a surgeon's hand, but it does not move outside of a milling path boundary, which is defined according to three-dimensional (3D) image-based preoperative planning. However, there are still few reports on THA with these semi-active systems. Thanks to the advancements in 3D sensor technology, navigation systems were developed. Navigation is a passive system, which does not perform any actions on patients. It only provides information and guidance to the surgeon who still uses conventional tools to perform the surgery. There are three types of navigation: computed tomography (CT)-based navigation, imageless navigation, and fluoro-navigation. CT-based navigation is the most accurate, but the preoperative planning on CT images takes time that increases cost and radiation exposure. Imageless navigation does not use CT images, but its accuracy depends on the technique of landmark pointing, and it does not take into account the individual uniqueness of the anatomy. Fluoroscopic navigation is good for trauma and spine surgeries, but its benefits are limited in the hip and knee reconstruction surgeries. Several studies have shown that the cup alignment with navigation is more precise than that of the conventional mechanical instruments, and that it is useful for optimizing limb length, range of motion, and stability. Recently, patient specific templates, based on CT images, have attracted attention and some early reports on cup placement, and resurfacing showed improved accuracy of the procedures. These various CAOS systems have pros and cons. Nonetheless, CAOS is a useful tool to help surgeons perform accurately what surgeons want to do in order to better achieve their clinical objectives. Thus, it is important that the surgeon fully understands what he or she should be trying to achieve in THA for each patient.

Pelvic tilt is minimally changed by total hip arthroplasty

BACKGROUND

While surgical navigation offers the opportunity to accurately place an acetabular component, questions remain as to the best goal for acetabular component positioning in individual patients. Overall functional orientation of the pelvis after surgery is one of the most important variables for the surgeon to consider when determining the proper goal for acetabular component orientation.

QUESTIONS/PURPOSES

We measured the variation in pelvic tilt in 30 patients before THA and the effect of THA on pelvic tilt in the same patients more than a year after THA.

METHODS

Each patient had a CT study for CT-based surgical navigation and standing and supine radiographs before and after surgery. Pelvic tilt was calculated for each of the radiographs using a novel and validated two-dimensional/three-dimensional matching technique.

RESULTS

Mean supine pelvic tilt changed less than 2°, from 4.4° ± 6.4° (range, -7.7° to 20.8°) before THA to 6.3° ± 6.6° (range, -5.7° to 19.6°) after THA. Mean standing pelvic tilt changed less than 1°, from 1.5° ± 7.2° (range, -13.1° to 12.8°) before THA to 2.0° ± 8.3° (range, -12.3° to 16.8°) after THA. Preoperative pelvic tilt correlated with postoperative tilt in both the supine (r(2) = 0.75) and standing (r(2) = 0.87) positions.

CONCLUSIONS

In this population, pelvic tilt had a small and predictable change after surgery. However, intersubject variability of pelvic tilt was high, suggesting preoperative pelvic tilt should be considered when determining desired acetabular component positioning on a patient-specific basis.

Does degree of the pelvic deformity affect the accuracy of computed tomography-based hip navigation?

Although some navigation systems have been used for improvement of component positioning, there have been few reports regarding cases of severe pelvic deformity. We performed a retrospective review of 25 cases of total hip arthroplasty with a computed tomography-based navigation system in patients with severe pelvic deformities and estimated acetabular component position and angle between severe deformity group and mild dysplastic group as a control. There were no significant differences in accuracy of navigation system between 2 groups in terms of 3-dimensional component position or angle. Accuracy of computed tomography-based hip navigation does not depend on the degree of pelvic deformity, and this system is also useful to identify acetabular orientation and for precise component implantation in cases of pelvic deformity.

Understanding acetabular cup orientation: the importance of convention and defining the safe zone

Understanding acetabular cup orientation is important in all aspects of total hip arthroplasty including preoperative planning, intraoperative positioning, and postoperative analysis. New concepts in ideal cup orientation such as 'combined anteversion' have emerged. Using computer navigation and three-dimensional imaging, the potential for accuracy and precision of implantation have improved. Nevertheless, the varying manner in which the terms "anteversion" and "abduction" are often used in the literature is indicative of a nebulous understanding of the complex spatial anatomy of acetabular cup orientation.

Implementation of an accelerated mobilization protocol following primary total hip arthroplasty: impact on length of stay and disposition

With improvements in surgical techniques, implant design, and patient caremaps, surgeons have sought to accelerate early rehabilitation after total hip arthroplasty. Many authors have reported results of fundamentally similar protocols to achieve this end. These protocols focus on multi-modal pain management, early therapy, tissue-preserving surgical technique, and careful blood management. We present the implementation and results of such a protocol involving a different surgical approach, and highlight the published literature on this topic.

Compensation of sound speed deviations in 3-D B-mode ultrasound for intraoperative determination of the anterior pelvic plane

An accurate determination of the pelvic orientation is inevitable for the correct cup prosthesis placement of navigated total hip arthroplasties. Conventionally, this step is accomplished by percutaneous palpation of anatomic landmarks. Sterility issues and an increased landmark localization error for obese patients lead to the application of B-mode ultrasound imaging in the field of computer-assisted orthopedic surgery. Many approaches have been proposed in the literature to replace the percutaneous digitization by 3-D B-mode ultrasound imaging. However, the correct depth localization of the pelvic landmarks could be significantly affected by the acoustic properties of the penetrated tissues. Imprecise depth estimation could lead to a miscalculation of the pelvic orientation and subsequently to a misalignment of the acetabular cup implant. But so far, no solution has been presented, which compensates for acoustic property differences for correct depth estimation. In this paper, we present a novel approach to determine pelvic orientation from ultrasound images by applying a hierarchical registration scheme based on patch statistical shape models to compensate for differences in speed of sound. The method was validated based on plastic bones and a cadaveric specimen.

The future of hip resurfacing

With experience in metal-metal resurfacing, several opportunities to improve resurfacing technology have been identified. There is a need for better education on hip resurfacing in residency training programs. The majority of short-term complications associated with resurfacing are related to surgical technique or component position. Innovations to improve acetabular component position and femoral-acetabular mating are needed. Although the majority of high wear and adverse local tissue reactions (ALTR) can be prevented by proper component positioning, the variable exposure to metal particles and ions associated with metal-metal resurfacing components continues to be a concern and bearing surface technology will evolve.