Biomechanical Guidance System for Periacetabular Osteotomy.

This chapter presents a biomechanical guidance navigation system for performing periacetabular osteotomy (PAO) to treat developmental dysplasia of the hip. The main motivation of the biomechanical guidance system (BGS) is to plan and track the osteotomized fragment in real time during PAO while simplifying this challenging procedure. The BGS computes the three-dimensional position of the osteotomized fragment in terms of conventional anatomical angles and simulates biomechanical states of the joint. This chapter describes the BGS structure and its application using two different navigation approaches including optical tracking of the fragment and x-ray-based navigation. Both cadaver studies and preliminary clinical studies showed that the biomechanical planning is consistent with traditional PAO planning techniques and that the additional information provided by accurate 3D positioning of the fragment does not adversely impact the surgery.

Reliability of computer-assisted periacetabular osteotomy using a minimally invasive approach.

BACKGROUND: Periacetabular osteotomy (PAO) is the treatment of choice for younger patients with developmental hip dysplasia. The procedure aims to normalize the joint configuration, reduce the peak-pressure, and delay the development of osteoarthritis. The procedure is technically demanding and no previous study has validated the use of computer navigation with a minimally invasive transsartorial approach. METHODS: Computer-assisted PAO was performed on ten patients. Patients underwent pre- and postoperative computed tomography (CT) scanning with a standardized protocol. Preoperative preparation consisted of outlining the lunate surface and segmenting the pelvis and femur from CT data. The Biomechanical Guidance System was used intra-operatively to automatically calculate diagnostic angles and peak-pressure measurements. Manual diagnostic angle measurements were performed based on pre- and postoperative CT. Differences in angle measurements were investigated with summary statistics, intraclass correlation coefficient, and Bland-Altman plots. The percentage postoperative change in peak-pressure was calculated. RESULTS: Intra-operative reported angle measurements show a good agreement with manual angle measurements with intraclass correlation coefficient between 0.94 and 0.98. Computer navigation reported angle measurements were significantly higher for the posterior sector angle ([Formula: see text], [Formula: see text]) and the acetabular anteversion angle ([Formula: see text], [Formula: see text]). No significant difference was found for the center-edge ([Formula: see text]), acetabular index ([Formula: see text]), and anterior sector angle ([Formula: see text]). Peak-pressure after PAO decreased by a mean of 13% and was significantly different ([Formula: see text]). CONCLUSIONS: We found that computer navigation can reliably be used with a minimally invasive transsartorial approach PAO. Angle measurements generally agree with manual measurements and peak-pressure was shown to decrease postoperatively. With further development, the system will become a valuable tool in the operating room for both experienced and less experienced surgeons performing PAO. Further studies with a larger cohort and follow-up will allow us to investigate the association with peak-pressure and postoperative outcome and pave the way to clinical introduction.

Clinical evaluation of a biomechanical guidance system for periacetabular osteotomy.

BACKGROUND: Populations suffering from developmental dysplasia of the hip typically have reduced femoral coverage and experience joint pain while walking. Periacetabular osteotomy (PAO) is one surgical solution that realigns the acetabular fragment. This challenging surgery has a steep learning curve. Existing navigation systems for computer-assisted PAO neither track the released fragment nor offer the means to assess fragment location. An intraoperative workstation--the biomechanical guidance system (BGS)--developed for PAO incorporates intraoperative fragment tracking and acetabular characterization through radiographic angles and joint biomechanics. In this paper, we investigate the accuracy and effectiveness of the BGS for bone fragment tracking and acetabular characterization in clinical settings as compared to conventional techniques and postoperative assessments. We also report the issues encountered and our remedies when using the BGS in the clinical setting. METHODS: Eleven consecutive patients (aged 22-48, mean 34, years) underwent 12 PAO surgeries (one bilateral surgery) where the BGS collected information on acetabular positioning. These measurements were compared with postoperative CT data and manual measurements made intraoperatively. RESULTS: No complications were reported during surgery, with surgical time-95-210 (mean 175) minutes-comparable to reported data for the conventional approach. The BGS-measured acetabular positioning showed strong agreement with postoperative CT measurements (-0.3-9.2, mean 3.7, degrees), whereas larger differences occurred between the surgeon's intraoperative manual measurements and postoperative CT measurements (-2.8-21.3, mean 10.5, degrees). CONCLUSIONS: The BGS successfully tracked the acetabular fragment in a clinical environment without introducing complications to the surgical workflow. Accurate 3D positioning of the acetabulum may provide more information intraoperatively (e.g., anatomical angles and biomechanics) without adversely impacting the surgery to better understand potential patient outcomes.

Development of a biomechanical guidance system for periacetabular osteotomy.

PURPOSE: This paper presents and validates a computer-navigated system for performing periacetabular osteotomy (PAO) to treat developmental dysplasia of the hip. The main motivation of the biomechanical guidance system (BGS) is to plan and track the osteotomy fragment in real time during PAO while simplifying the procedure for less-experienced surgeons. The BGS aims at developing a platform for comparing biomechanical states of the joint with the current gold standard geometric assessment of anatomical angles. The purpose of this study was to (1) determine the accuracy with which the BGS tracks the hip joint through repositioning and (2) identify improvements to the workflow. METHODS: Nineteen cadaveric validation studies quantified system accuracy, verified system application, and helped to refine surgical protocol. In two surgeries, navigation and registration accuracy were computed by affixing fiducials to two cadavers prior to surgery. All scenarios compared anatomical angle measurements and joint positioning as measured intraoperatively to postoperatively. RESULTS: In the two cases with fiducials, computed fragment transformations deviated from measured fiducial transformations by 1.4 and 1.8 mm in translation and 1.0° and 2.2° in rotation, respectively. The additional seventeen surgeries showed strong agreement between intraoperative and postoperative anatomical angles, helped to refine the surgical protocol, and demonstrated system robustness. CONCLUSION: Estimated accuracy with BGS appeared acceptable for future surgical applications. Several major system requirements were identified and addressed, improving the BGS and making it feasible for clinical studies.

Biomechanical factors in planning of periacetabular osteotomy.

OBJECTIVE: This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO). BACKGROUND: The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon's in determining the most beneficial new alignment of a patient's acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes. METHODS: Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments. RESULTS: There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties. CONCLUSION: While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.

The changes in health-related quality of life and related factors during the process of total hip arthroplasty.

This study was carried out to measure changes in health-related quality of life (HRQOL) in patients (n=100) undergoing total hip arthoplasty. The Sickness Impact Profile was used to measure patients' dysfunctions in 12 different categories post surgery. Improvement was observed in each category and dimension already at 3 months and at 6 months. Preoperative pain showed a statistically significant although declining correlation both with total, and with Physical and the Psychosocial dimensions of HRQOL. The greatest improvements were found in the categories Body Care and Movement, Ambulation, Alertness Behaviour, Social Interaction, Recreation and Pastimes and in Sleep and Rest. Patients' pain decreased, and 72% reported no pain at 6 months post the surgery. Patients' perceptions of their pain should be gathered carefully when deciding the need and timing for the surgery in order to minimize impairments into HRQOL.

Three-dimensional mechanical evaluation of joint contact pressure in 12 periacetabular osteotomy patients with 10-year follow-up.

BACKGROUND AND PURPOSE: Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment. PATIENTS AND METHODS: We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years. RESULTS: The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis. INTERPRETATION: The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.

Economic outcomes from patients' perspective and health-related quality of life after total hip arthroplasty.

The aim of this study was to determine the economic outcomes (service use, health care and nonhealth care out-of-pocket costs) related to total hip arthroplasty from the perspective of patients. Also, examined was the relationship between economic outcomes and health-related quality of life (HRQOL). One hundred patients, 54 female and 46 male, mean age 63.9 (SD 11.6) years, with osteoarthritis in the hip and undergoing primary or revision arthroplasty, participated in this follow-up study. The drop-out race was 13%. Patients' service use, and out-of-pocket costs were recorded, and HRQOL was measured up to 6 months. The Friedman and Wilcoxon nonparametric tests showed that use of home nursing and transportation was most frequent at 1 month, whereas physiotherapy was used most often after 1 month. The Spearman coefficient of correlation, Fisher's, Mann-Whitney U and Kruskal-Wallis tests were used to compare background factors with economic outcomes and HRQOL. Age, pain, gender, civil status, type of surgery and discharge destination showed associations with service use. Healthcare costs composed over 90% of total out-of-pocket costs, and nonhealthcare costs <10%. Age and discharge destination were related to total out-of-pocket costs. Patients' HRQOL improved after surgery. The worse it was before, or after surgery, the more services were used, but no significant correlations between costs and HRQOL were observed. When deciding the timing of surgery, patients' characteristics, especially level of pain and HRQOL should carefully evaluated, as they may predict patients' service use and ability to manage at home after surgery.

A systematic review of empirical studies between 1966 and 2005 of patient outcomes of total hip arthroplasty and related factors.

AIM: To determine patient outcomes of total hip arthroplasty and the research methods used to produce knowledge of use to clinical nursing and for purposes of health education. The review consists of three parts. Firstly, it describes the patient outcomes of total hip arthroplasty. Secondly, it addresses the factors related to the patient outcomes and thirdly the research methods used are explored. BACKGROUND: Previous research has identified that total hip arthroplasty is a very common procedure to reduce pain and improve physical function in patients with osteoarthritis. The greatest improvements have been found in reduction in pain. METHODS: Two databases, Medline and CINAHL were searched from 1966-2005. Studies were eligible for review and included if they met the following criteria: (1) publication in English, (2) empirical research and (3) the indication for total hip arthroplasty was osteoarthritis; 17 studies met the criteria. RESULTS: Total hip arthroplasty resulted in pain relief, improved physical function and enhanced health-related quality of life regardless of patients' characteristics, type of operation or type of prosthesis. The only factor affecting patient outcomes was patients' poor pre-operative function. These patients were more likely to have postoperative pain and low postoperative physical function. Long-waiting time for surgery may reduce quality-adjusted life years. Different kinds of questionnaires were used in the studies reviewed leaving out patients' perceptions concerning the outcomes of total hip arthroplasty. CONCLUSIONS: Patients' perceptions should be assessed more closely in further research to gain subjective knowledge about the outcomes of total hip arthroplasty. This could be achieved by using qualitative methods also. RELEVANCE TO CLINICAL PRACTICE: The findings can be seen as a challenge for nurses to plan patients' education. It is also important that the outcomes of total hip arthroplasty correspond to patients' expectations. Patients' preoperative function should be taken into consideration when planning the timing of surgery so that the best possible outcomes were attainable.

Periacetabular osteotomy in adult hip dysplasia - developing a computer aided real-time biomechanical guiding system (BGS).

Osteotomies around hip acetabulum have become a routine surgical intervention in cases with constant pain without joint degeneration in adult dysplasia. However, it remains a challenge to plan and realign optimally the joint after osteotomy to reach best function and longevity in the clinical outcome. Tool tracking navigation systems have been available for many years but they have not become popular among surgeons because they extend operation time, require preoperative CT scan and, on the other hand, produce only marginal advantage in hands of an experienced surgeon. Real-time biomechanical assessment, based on computer analysis using preoperative CT-scanning, has become an interesting means to adjust the acetabular reorientation during surgery according to the patient's individual structure and loading conditions. Further, real-time feedback allows the surgeon to foresee radiographic angles while performing fixation of the osteotomized fragment. Assessment of peak pressure and potential weight bearing area in real-time allows prospective and retrospective systematic biomechanical studies of patient outcomes. To conclude, a major development in navigation software is under way and we have so far seen a spectrum of new features like loading condition assessment in real time for osteotomies. This is, however, merely the start of a revolutionary change in operative planning in orthopaedics with the help of computer aided guiding and bioengineering.

Anxiety and health-related quality of life of patients undergoing total hip arthroplasty for osteoarthritis.

OBJECTIVE: Osteoarthritis in a hip not only causes pain and decreases physical function, which are the most common reasons for total hip arthroplasty, but also causes anxiety and reduces patients' health-related quality of life (HRQoL). The objective of this study was to evaluate patients' anxiety and its possible relationship with HRQoL before and after surgery. METHODS: In this longitudinal follow-up study, the State Trait Anxiety Inventory was used to measure patients' (n = 100) level of anxiety before surgery and at 1 month, 3 months and 6 months post-operatively. The Sickness Impact Profile was used to measure patients' total HRQoL before surgery and post-operatively at 3 and 6 months. RESULTS: Before surgery, patients' trait and state anxiety were moderate. Patients' pre-operative trait anxiety impaired HRQoL both before and after surgery. After surgery, state anxiety remained at a moderate level, although a few minor peaks were observed, but no relationship between state anxiety and HRQoL was found. DISCUSSION: Patients' needs and characteristics should be carefully assessed when planning post-operative care and support. Nurses should be aware of factors that may relate to anxiety and also consider different methods of supporting patients' recovery.

Evaluation of a computerized measurement technique for joint alignment before and during periacetabular osteotomy.

Periacetabular osteotomy (PAO) is intended to treat a painful dysplastic hip. Manual radiological angle measurements are used to diagnose dysplasia and to define regions of insufficient femoral head coverage for planning PAO. No method has yet been described that recalculates radiological angles as the acetabular bone fragment is reoriented. In this study, we propose a technique for computationally measuring the radiological angles from a joint contact surface model segmented from CT-scan data. Using oblique image slices, we selected the lateral and medial edge of the acetabulum lunate to form a closed, continuous, 3D curve. The joint surface is generated by interpolating the curve, and the radiological angles are measured directly using the 3D surface. This technique was evaluated using CT data for both normal and dysplastic hips. Manual measurements made by three independent observers showed minor discrepancies between the manual observations and the computerized technique. Inter-observer error (mean difference +/- standard deviation) was 0.04 +/- 3.53 degrees for Observer 1; -0.46 +/- 3.13 degrees for Observer 2; and 0.42 +/- 2.73 degrees for Observer 3. The measurement error for the proposed computer method was -1.30 +/- 3.30 degrees . The computerized technique demonstrates sufficient accuracy compared to manual techniques, making it suitable for planning and intraoperative evaluation of radiological metrics for periacetabular osteotomy.

Computed tomography measurement of acetabular dimensions: normal values for correction of dysplasia.

BACKGROUND: A successful periacetabular osteotomy includes reliable planning based on radiographs and CT scanning. However, we lack normative CT values in planning realignment of the osteotomized acetabulum. PATIENTS AND METHODS: We retrospectively studied 70 hips that had been CT-scanned. Patients who showed no signs of developmental disturbances in either of the hip joints were eligible for the study. Sex differences were also studied. RESULTS: The AA-angle, CE-angle, ACE-angle and AcetAV-angle, depicting frontal, sagittal and horizontal alignment, averaged 3 degrees (SD 4 degrees ), 41 degrees (7 degrees ), 31 degrees (5 degrees ) and 21 degrees (7 degrees ), respectively. The upper normal value (+ 2SD) for the AA-angle was 12 degrees , normal range (+/- 2SD) for CE-angle was 27 degrees -55 degrees , lower normal value (- 2SD) for the ACE-angle was 22 degrees , and normal range (+/- 2SD) for the AcetAV-angle was 6 degrees -35 degrees . However, comparison of mean angles in women with those in men showed a statistically significant difference for the AA-angle and AcetAV-angle, but we found no significant differences between the mean figures for right and left hips. INTERPRETATION: Knowledge of the normal dimensions of the acetabulum is essential in the diagnosis of the type and severity of DDH, as well as in preoperative planning. Accurate estimation of the normal contact surface orientation permits correct realignment of the osteotomized acetabulum.

Developing a pressure ulcer risk assessment scale for patients in long-term care.

Previous pressure ulcer risk assessment scales appear to have relied on opinions about risk factors and are based on care setting rather than research evidence. Utilizing 21 existing risk assessment scales and relevant risk factor literature, an instrument was developed by Finnish researchers that takes into account individual patient risk factors, devices and methods applied in nursing care, and organizational characteristics. The instrument underwent two pilot tests to assess the relevance and clarity of the instrument: the first involved 43 nurses and six patients; the second involved 50 nurses with expertise in wound care. Changes to questionnaire items deemed necessary as a result of descriptive analysis and agreement percentages were completed. After pilot testing, the final instrument addressed the following issues: 1) patient risks: activity, mobility in bed, mental status, nutrition, urinary incontinence, fecal incontinence, sensory perception, and skin condition; 2) devices and methods used in patient care: technical devices, bed type, mattress, overlay, seat cushions, and care methods; and 3) staff number and structure, maximum number of beds, and beds in use (the last group of questions were included to ensure participants understood the items; results were not analyzed). The phases of the study provided an expeditious means of data collection and a suitable opportunity to assess how the instrument would function in practice. Instrument reliability and validity were improved as a result of the pilot testing and can be enhanced further with continued use and assessment.

Outcome of periacetabular osteotomy: joint contact pressure calculation using standing AP radiographs, 12 patients followed for average 2 years.

BACKGROUND: Due to wide variations in acetabular structure of individuals with hip dysplasia, the measurement of the acetabular orientation may not be sufficient to predict the joint loading and pressure distribution across the joint. Addition of mechanical analysis to preoperative planning, therefore, has the potential to improve the clinical outcome. We analyzed the effect of periacetabular osteotomy on hip dysplasia using computer-aided simulation of joint contact pressure on regular AP radiographs. The results were compared with the results of surgery based on realignment of acetabular angles to the normal hip. PATIENTS AND METHODS: We studied 12 consecutive periacetabular osteotomies with no femoral head deformity. The median age of patients, all females, was 35 (20-50) years. The median follow-up was 2 years (1.3-2.2). Patient outcome was measured with the total score of a self-administered questionnaire (q-score) and with the Harris hip score. The pre- and postoperative orientation of the acetabulum was defined using reconstructed 3D CT-slices to measure angles in the three anatomical planes. Peak contact pressure, weight-bearing area, and the centroid of the contact pressure distribution (CP-ratio) were calculated. RESULTS: While 9 of 12 cases showed decreased peak pressure after surgery, the mean changes in weight-bearing area and peak contact pressure were not statistically significant. However, CP-ratio changed (p < 0.001, paired t-test) with surgery. For the optimal range of CP-ratio (within its mid-range 40-60%), the mechanical outcome improved significantly. INTERPRETATION: Verifying the correlation between the optimal CP-ratio and the outcome of the surgery requires additional studies on more patients. Moreover, the anatomically measured angles were not correlated with the ranges of CP-ratio, suggesting that they do not always associate with objective mechanical goals of realignment osteotomy. Mechanical analysis, therefore, can be a valuable tool in assessing two-dimensional radiographs in hip dysplasia.