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1.  Subcapital Correction Osteotomy for Malunited Slipped Capital Femoral Epiphysis 
Journal of pediatric orthopedics  2013;33(4):345-352.
Background
Slipped capital femoral epiphysis (SCFE), causing posterior and inferior displacement and retroversion of the femoral head, is a well-recognized etiology for femoroacetabular impingement (FAI) and can lead to premature arthritis in the young adult. The treatment of malunited SCFE remains controversial. Surgical dislocation and subcapital correction osteotomy (SCO) has been described as a powerful method to correct the proximal femoral deformity.
Methods
Between January 2003 and January 2010, 11 patients (12 hips) with closed femoral physes and symptomatic FAI from malunited SCFE were treated with surgical dislocation and SCO. We performed a retrospective review of patient histories, physical exams, operative findings, and pre and postoperative anteroposterior (AP) and groin lateral (GLat) radiographs. Mean follow-up was 61 months.
Results
There were 4 female and 7 male patients with an average age of 15 years at the time of SCO. On the AP radiograph the mean inferior femoral head displacement (AP epiphyseal-neck angle) was significantly improved (-26° to -6°, p<0.001). On the groin lateral radiograph the mean posterior femoral head displacement (Lateral epiphyseal-neck angle) was significantly improved (-45° to -3°, p<0.001). The mean alpha angle was also significantly improved on both views (AP: 85° to 56°, P<0.001; GLat: 85° to 46°, p<0.001). Operative findings included one femoral osteochondral defect, 8 Outerbridge grade 3-4 acetabular cartilage lesions, and 10 labral lesions. Significant improvement of the mean Harris hip score (HHS) was seen at latest follow-up (54 to 77, p=0.016). Complications occurred in 4 of the 12 cases with AVN in two patients, a worse postoperative HHS in one patient, and failure of fixation treated successfully with revision open reduction internal fixation in one patient.
Conclusions
Subcapital correction osteotomy as an adjunct to surgical dislocation and osteochondroplasty can be used to correct the deformity of the proximal femur associated with malunited SCFE. Normalization of proximal femoral anatomy may postpone progression to severe osteoarthritis and thus delay the need for arthroplasty in this young patient population. However, surgeons and patients should be aware that the risks of this procedure in this population are significant.
doi:10.1097/BPO.0b013e31827d7e06
PMCID: PMC3648794  PMID: 23653020
2.  Three-dimensional quantification of femoral head shape in controls and patients with cam-type femoroacetabular impingement 
Annals of biomedical engineering  2013;41(6):1162-1171.
An objective measurement technique to quantify 3D femoral head shape was developed and applied to normal subjects and patients with cam-type femoroacetabular impingement (FAI). 3D reconstructions were made from high-resolution CT images of 15 cam and 15 control femurs. Femoral heads were fit to ideal geometries consisting of rotational conchoids and spheres. Geometric similarity between native femoral heads and ideal shapes was quantified. The maximum distance native femoral heads protruded above ideal shapes and the protrusion area were measured. Conchoids provided a significantly better fit to native femoral head geometry than spheres for both groups. Cam-type FAI femurs had significantly greater maximum deviations (4.99±0.39 mm and 4.08±0.37 mm) than controls (2.41±0.31 mm and 1.75±0.30 mm) when fit to spheres or conchoids, respectively. The area of native femoral heads protruding above ideal shapes was significantly larger in controls when a lower threshold of 0.1 mm (for spheres) and 0.01 mm (for conchoids) was used to define a protrusion. The 3D measurement technique described herein could supplement measurements of radiographs in the diagnosis of cam-type FAI. Deviations up to 2.5 mm from ideal shapes can be expected in normal femurs while deviations of 4 to 5 mm are characteristic of cam-type FAI.
doi:10.1007/s10439-013-0762-1
PMCID: PMC3640621  PMID: 23413103
cam FAI; femur morphology; asphericity
4.  A New Discrete Element Analysis Method for Predicting Hip Joint Contact Stresses 
Journal of biomechanics  2013;46(6):1121-1127.
Quantifying cartilage contact stress is paramount to understanding hip osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses. Previous applications of DEA have underestimated cartilage stresses and yielded unrealistic contact patterns because they assumed constant cartilage thickness and/or concentric joint geometry. The study objectives were to: 1) develop a DEA model of the hip joint with subject-specific bone and cartilage geometry, 2) validate the DEA model by comparing DEA predictions to those of a validated finite element analysis (FEA) model, and 3) verify both the DEA and FEA models with a linear-elastic boundary value problem. Springs representing cartilage in the DEA model were given lengths equivalent to the sum of acetabular and femoral cartilage thickness and joint space in the FEA model. Material properties and boundary/loading conditions were equivalent. Walking, descending, and ascending stairs were simulated. Solution times for DEA and FEA models were ~7 seconds and ~65 minutes, respectively. Irregular, complex contact patterns predicted by DEA were in excellent agreement with FEA. DEA contact areas were 7.5%, 9.7% and 3.7% less than FEA for walking, descending stairs, and ascending stairs, respectively. DEA models predicted higher peak contact stresses (9.8–13.6 MPa) and average contact stresses (3.0–3.7 MPa) than FEA (6.2–9.8 and 2.0–2.5 MPa, respectively). DEA overestimated stresses due to the absence of the Poisson’s effect and a direct contact interface between cartilage layers. Nevertheless, DEA predicted realistic contact patterns when subject-specific bone geometry and cartilage thickness were used. This DEA method may have application as an alternative to FEA for pre-operative planning of joint-preserving surgery such as acetabular reorientation during peri-acetabular osteotomy.
doi:10.1016/j.jbiomech.2013.01.012
PMCID: PMC3623562  PMID: 23453394
Hip; cartilage; cartilage mechanics; contact stress; discrete element analysis; finite element analysis; computational modeling
5.  Prevalence and Treatment of Intraarticular Pathology Recognized at the Time of Periacetabular Osteotomy for the Dysplastic Hip 
Background
The indication for hip arthrotomy accompanied by intraarticular work during periacetabular osteotomy (PAO) has not been precisely defined. To validate a role for routine hip arthrotomy accompanied by intraarticular work, frequent intraarticular pathology must exist, and the adjunct procedures must not be associated with inferior relief of pain, reduced function, radiographic osteoarthritis progression, or conversion to THA.
Questions/purposes
(1) What is the prevalence of intraarticular pathology at the time of PAO? (2) Does concomitant hip arthrotomy with associated intraarticular work negatively affect PAO as reflected by differences in Harris hip scores (HHS), Tönnis grade, and failure rates?
Methods
We retrospectively reviewed the intraarticular findings in all 151 patients who underwent PAO accompanied by routine hip arthrotomy and intraarticular work from 2002 to 2009. Using multivariate regression models, we compared the HHS and Tönnis grades of patients receiving arthrotomy with a cohort of 39 patients who received PAO alone.
Results
The overall prevalence of intraarticular pathology identified during PAO was 89%. Eight (5.3%) failures were identified within the arthrotomy cohort with mean postoperative HHS, postoperative Tönnis grade, postoperative change in HHS, and postoperative change in Tönnis grade of 87.5, 0.7, 29.8, and 0.3, respectively. By contrast, seven (17.9%) failures were identified in the nonarthrotomy cohort. The mean postoperative HHS, postoperative Tönnis grade, postoperative change in HHS, and postoperative change in Tönnis grade for the nonarthrotomy cohort were 83.1, 1.3, 19.0, and 0.3, respectively.
Conclusions
We believe the high prevalence of intraarticular pathology is sufficient to warrant routine joint inspection at the time of PAO. Hip arthrotomy accompanied by intraarticular work at the time of PAO is safe and does not impose additional patient morbidity.
Level of Evidence
Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-012-2602-2
PMCID: PMC3549169  PMID: 23054510
6.  Patient-specific Total Knee Arthroplasty Required Frequent Surgeon-directed Changes 
Background
Patient-specific instrumentation potentially improves surgical precision and decreases operative time in total knee arthroplasty (TKA) but there is little supporting data to confirm this presumption.
Questions/purposes
We asked whether patient-specific instrumentation would require infrequent intraoperative changes to replicate a single surgeon’s preferences during TKA and whether patient-specific instrumentation guides would fit securely.
Methods
We prospectively evaluated the plan and surgery in 60 patients treated with 66 TKAs performed with patient-specific instrumentation and recorded any changes. A subset of six postoperative radiographic changes to the femoral and tibial components (implant size, coronal and sagittal alignment) was analyzed to determine if surgeon intervention was beneficial. Each guide was evaluated to determine fit. We compared patient demographics and implant sizing in the patient-specific instrumentation group with a control group in which traditional instrumentation was used.
Results
We recorded 161 intraoperative changes in 66 knee arthroplasties (2.4 changes/knee) performed with patient-specific instrumentation. The predetermined implant size was changed intraoperatively in 77% of femurs and 53% of tibias. We identified a subset of 95 intraoperative changes that could be radiographically evaluated to determine if our changes were an improvement or detriment to reaching goal alignment. Eighty-two of the 95 changes (86%) made by the surgeon were an improvement to the recommended alignment or size of patient-specific instrumentation. The guide did not fit securely on eight femurs (12%) and three tibias (5%). Tourniquet time and blood loss were not improved with patient-specific instrumentation.
Conclusions
We caution surgeons against blind acceptance of patient-specific instrumentation technology without supportive data.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-012-2573-3
PMCID: PMC3528928  PMID: 22956239
8.  Early Experience With a Comprehensive Hip Preservation Service Intended to Improve Clinical Care, Education, and Academic Productivity 
Background
The field of hip preservation surgery has grown substantially over the past decade. Although open hip procedures reportedly relieve pain and restore function, arthroscopic treatment has increasingly become a reasonable alternative. In 2008, we formed a comprehensive hip preservation service (HPS) to address clinical, educational, and research needs.
Questions/Purposes
We compared (1) volume, type, and corresponding improvement in pain and function of open and arthroscopic treatments; (2) orthopaedic resident test performance; and (3) academic productivity before and after creation of the HPS.
Methods
We retrospectively reviewed 212 patients undergoing 220 open procedures from 1996 to 2007 (Group 1) and 260 patients undergoing 298 procedures (153 open, 145 arthroscopic) from 2008 to May 2010 (Group 2). At each clinic visit, we recorded Harris hip score (HHS) and conversion to THA. Minimum followup was 1 year for Group 1 (mean, 4 years; range, 1–13 years) and Group 2 (mean, 1.5 years; range, 1–3 years). We compared orthopaedic resident performance on two standardized tests and the number of academic works (publications, book chapters, electronic media) and peer-reviewed grants funded before and after creation of the HPS.
Results
Mean HHS improved from 63 to 90 in Group 1 and from 76 to 91 in Group 2. Rate of conversion to THA was similar between groups despite expansion of surgical volume. Standardized orthopaedic resident test performance improved. Academic productivity as measured by publications and grant funding was facilitated by the HPS.
Conclusions
Early experience with a multidisciplinary HPS was positive; it facilitated clinical volume expansion while maintaining improvement in pain and function in young adults. Additional benefits included educational and academic productivity gains.
Level of Evidence
Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-012-2549-3
PMCID: PMC3492621  PMID: 22926493
9.  Coxa Profunda: Is the Deep Acetabulum Overcovered? 
Background
Coxa profunda, or a deep acetabular socket, is often used to diagnose pincer femoroacetabular impingement (FAI). Radiographically, coxa profunda is the finding of an acetabular fossa medial to the ilioischial line. However, the relative position of the acetabular fossa to the pelvis may not be indicative of acetabular coverage.
Questions/purposes
We therefore determined the incidence of coxa profunda and evaluated associations between coxa profunda and other radiographic parameters of acetabular coverage commonly used to diagnose pincer FAI and acetabular dysplasia.
Methods
We evaluated the radiographs of three cohorts for coxa profunda, lateral center edge (LCE) angle, acetabular index, posterior wall sign, and crossover sign. Data from 67 collegiate football players were collected prospectively (Cohort 1). We identified two patient cohorts through retrospective review of all 179 hips undergoing hip preservation surgery from 2002 to 2008 (83 periacetabular osteotomies [Cohort 2] and 96 surgical dislocation and osteochondroplasties [Cohort 3]).
Results
In all three cohorts, we detected no difference in the LCE angle or acetabular index between hips with and without coxa profunda. Coxa profunda existed in hips representing the spectrum of acetabular coverage measured by LCE angle (−18° to 60°) and acetabular orientation determined by the crossover sign.
Conclusions
Coxa profunda was a common radiographic finding in both symptomatic patients and asymptomatic football players. Coxa profunda existed in hips representing the spectrum of acetabular coverage and was not associated with an overcovered acetabulum. We conclude coxa profunda is unrelated to overcoverage and suggest its use in diagnosis of pincer FAI be abandoned in favor of other determinants of focal or general overcoverage.
Level of Evidence
Level III, diagnostic study. See Instructions for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-012-2509-y
PMCID: PMC3492622  PMID: 22898988
11.  Hybrid Total Knee Arthroplasty Revisited: Midterm Followup of Hybrid versus Cemented Fixation in Total Knee Arthroplasty 
BioMed Research International  2013;2013:854871.
The optimal method of fixation in total knee arthroplasty is still debated. Hybrid total knee arthroplasty (TKA), with cemented tibial and cementless femoral components, is a proposed method of fixation to improve outcomes. Although several studies have shown favorable outcomes, there is still lack of consensus in the literature. We hypothesized that hybrid TKA yields similar clinical, radiographic, and survivorship results compared to fully cemented TKA. The clinical and radiographic outcomes of 304 cruciate retaining TKAs with minimum two-year followup, including 193 hybrid (mean followup of 4.1 years) and fully cemented TKAs (mean followup of 3.2 years) were evaluated. Knee society scores were similar between the two groups. The total number of femoral radiolucencies was also similar between the two groups, while a greater number of femoral Zone 4 radiolucencies were seen in the cemented group (9% versus 1.6%, P = 0.005). The hybrid group demonstrated a 99.2% survival rate of the femoral component out to seven years for aseptic loosening. No significant difference in survivorship was seen between the groups for all cause or aseptic failure at seven years. We conclude that hybrid fixation leads to similar intermediate-term outcomes as fully cemented components and remains a viable option in total knee arthroplasty.
doi:10.1155/2013/854871
PMCID: PMC3800574  PMID: 24224179
12.  An Algorithmic Approach to Surgical Decision-making in Acetabular Retroversion 
Orthopedics  2011;34(1):10.
We prospectively collected clinical data during the period 2001–2006 on 60 hips with symptomatic femoroacetabular impingement that had radiographic evidence of acetabular retroversion defined as a crossover sign on an adequate anteroposterior radiograph or retroversion on magnetic resonance imaging or computed tomography. Our treatment algorithm for acetabular retroversion used measurements of acetabular coverage (lateral center edge angle and the posterior wall sign) and condition of acetabular cartilage to direct treatment of acetabular retroversion. The algorithm directed the surgeon to perform a periacetabular-osteotomy (PAO) in 30 hips and in 30 hips a surgical-dislocation and osteochondroplasty (SDO) of the femoral head-neck junction and acetabular rim. HHS and Tönnis radiographic grading were collected preoperatively and at latest followup. The HHS improved from 52 to 90 in the hips treated with SDO and 72 to 91 in the hips treated with PAO, with an overall survivorship of 96% at four years. Patient follow-up averaged 46 months (range 24–75). Elimination of the crossover sign and correction of the posterior wall sign occurred in over 90% of all patients when present. The results indicate that hips with acetabular retroversion, deficient posterior and/or lateral acetabular coverage and intact hyaline cartilage can be effectively treated with acetabular reorientation while retroverted hips with anterior over-coverage but sufficient posterior coverage are effectively treated with osteochondroplasty of the acetabulum and proximal femur.
doi:10.3928/01477447-20101123-07
PMCID: PMC3399593  PMID: 21210626
13.  Finite Element Prediction of Cartilage Contact Stresses in Normal Human Hips 
Journal of Orthopaedic Research  2011;30(7):1133-1139.
Our objectives were to determine cartilage contact stress during walking, stair climbing and descending stairs in a well-defined group of normal volunteers and to assess variations in contact stress and area among subjects and across loading scenarios. Ten volunteers without history of hip pain or disease with normal lateral center-edge angle and acetabular index were selected. Computed tomography imaging with contrast was performed on one hip. Bone and cartilage surfaces were segmented from volumetric image data, and subject-specific finite element models were constructed and analyzed using a validated protocol. Acetabular contact stress and area were determined for seven activities. Peak stress ranged from 7.52±2.11 MPa for heel-strike during walking (233% BW) to 8.66±3.01 MPa for heel-strike during descending stairs (261% BW). Average contact area across all activities was 34% of the surface area of the acetabular cartilage. The distribution of contact stress was highly non-uniform, and more variability occurred among subjects for a given activity than among activities for a single subject. The magnitude and area of contact stress were consistent between activities, although inter-activity shifts in contact pattern were found as the direction of loading changed. Relatively small incongruencies between the femoral and acetabular cartilage had a large effect on the contact stresses. These effects tended to persist across all simulated activities. These results demonstrate the diversity and trends in cartilage contact stress in healthy hips during activities of daily living and provide a basis for future comparisons between normal and pathologic hips.
doi:10.1002/jor.22040
PMCID: PMC3348968  PMID: 22213112
Hip; Finite Element; Biomechanics; Cartilage Contact Stresses; Cartilage Pressure
14.  Mean 5-Year Clinical and Radiographic Outcomes of Cementless Total Hip Arthroplasty in Patients under the Age of 30 
BioMed Research International  2013;2013:649506.
We performed a retrospective review of 40 consecutive modern cementless THAs with 65-month mean followup in 34 patients under the age of 30 primarily for diagnoses other than inflammatory arthritis. We found acceptable functional improvement and radiographic outcomes at mean 5-year followup. We found a high transfusion rate, dislocation rate (10%), and midterm overall aseptic revision rate (17%). Twenty-eight (67.5%) of hips in this series were metal on metal, with a large percentage of aseptic revisions related to metallosis (57%). When revisions due to metallosis were excluded, the aseptic revision rate was 7.5%. The high prevalence of prior pediatric hip surgery in these patients (50%) may predispose to increased technical difficulty resulting in increased complications and higher revision rates. Although our revision rate was high in these young patients, it is favorable compared to older techniques and consistent with the limited data available with modern cementless techniques in patients of similar age. Cementless THA with modern designs remains a viable option for the treatment of arthritis in the young patient.
doi:10.1155/2013/649506
PMCID: PMC3707213  PMID: 23865060
15.  Sequelae of Perthes Disease 
Journal of pediatric orthopedics  2010;30(8):758-766.
Background
Sequelae of Perthes disease commonly manifests as complex hip pathomorphology including coxa magna, coxa brevis, and acetabular dysplasia. These abnormalities contribute to femoroacetabular impingement and early osteoarthritis. This report describes our experience with correction of the proximal femoral deformity associated with Perthes disease via surgical dislocation, osteochondroplasty (SDO), trochanteric advancement, and treatment of intra-articular chondrolabral injury.
Methods
Between January 2003 and January 2009, 14 patients with Perthes disease (4 female and 10 male patients) with an average age of 19.6 years (range 14 – 28) were treated with SDO and trochanteric advancement. One patient had a subsequent staged periacetabular osteotomy to improve acetabular coverage. Patient histories, physical exams, operative findings, and pre and postoperative radiographs were evaluated.
Results
Operative findings demonstrated 6 acetabular cartilage lesions, 6 labral lesions, and 4 femoral osteochondritis dissecans (OCD) lesions treated with autografts. Mean center trochanteric distance improved from −20 mm to −1 mm. 4/14 hips deteriorated 1 Tönnis grade and 1/14 hips 2 grades. The Harris hip scores improved from an average of 62 preoperatively (range 51–72) to 95 postoperatively (range 93–97) versus 71 (range 65–76) to 88.6 (range 63–100) in the hips without OCD lesions. There was no statistically significant difference in the age, pre or postoperative HHS between the OCD and non-OCD groups. Mean follow up was 45 months. There were no major perioperative complications and all patients in both groups have their native hip to date.
Conclusions
The typical adult sequelae of Perthes disease predispose the hip to the development of chondrolabral injury and poor clinical function. Treatment with SDO and trochanteric advancement reduces impingement, improves hip biomechanics and allows treatment of intra-articular pathology. The described approach is associated with clinical improvement without major perioperative complication. Additionally, we have found a high rate of OCD lesions of the femoral head in Perthes hips undergoing surgical dislocation. Osteochondral autograft transfer from the resected femoral head-neck junction been found in the 4 patients treated thus far to be safe and effective with comparable clinical and radiographic outcomes to those hips without OCD lesions.
doi:10.1097/BPO.0b013e3181fcbaaf
PMCID: PMC3031125  PMID: 21102198
16.  Perioperative Closure-related Complication Rates and Cost Analysis of Barbed Suture for Closure in TKA 
Background
The use of barbed suture for surgical closure has been associated with lower operative times, equivalent wound complication rate, and comparable cosmesis scores in the plastic surgery literature. Similar studies would help determine whether this technology is associated with low complication rates and reduced operating times for orthopaedic closures.
Questions/purposes
We compared a running barbed suture with an interrupted standard suture technique for layered closure in primary TKA to determine if the barbed suture would be associated with (1) shorter estimated closure times; (2) lower cost; and (3) similar closure-related perioperative complication rates.
Methods
We retrospectively compared two-layered closure techniques in primary TKA with either barbed or knotted sutures. The barbed group consisted of 104 primary TKAs closed with running barbed suture. The standard group consisted of 87 primary TKAs closed with interrupted suture. Cost analysis was based on cost of suture and operating room time. Clinical records were assessed for closure-related complications within the 6-week perioperative period.
Results
Average estimated closure time was 2.3 minutes shorter with the use of barbed suture. The total closure cost was similar between the groups. The closure-related perioperative complication rates were similar between the groups.
Conclusions
Barbed suture is associated with a slightly shorter estimated closure time, although this small difference is of questionable clinical importance. With similar overall cost and no difference in perioperative complications in primary TKA, this closure methodology has led to more widespread use at our institution.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-011-2104-7
PMCID: PMC3237999  PMID: 21952745
17.  Role of the Acetabular Labrum in Load Support Across the Hip Joint 
Journal of biomechanics  2011;44(12):2201-2206.
The relatively high incidence of labral tears among patients presenting with hip pain suggests that the acetabular labrum is often subjected to injurious loading in vivo. However, it is unclear whether the labrum participates in load transfer across the joint during activities of daily living. This study examined the role of the acetabular labrum in load transfer for hips with normal acetabular geometry and acetabular dysplasia using subject-specific finite element analysis. Models were generated from volumetric CT data and analyzed with and without the labrum during activities of daily living. The labrum in the dysplastic model supported 4-11% of the total load transferred across the joint, while the labrum in the normal model supported only 1-2% of the total load. Despite the increased load transferred to the acetabular cartilage in simulations without the labrum, there were minimal differences in cartilage contact stresses. This was because the load supported by the cartilage correlated to the cartilage contact area. A higher percentage of load was transferred to the labrum in the dysplastic model because the femoral head achieved equilibrium near the lateral edge of the acetabulum. The results of this study suggest that the labrum plays a larger role in load transfer and joint stability in hips with acetabular dysplasia than in hips with normal acetabular geometry.
doi:10.1016/j.jbiomech.2011.06.011
PMCID: PMC3225073  PMID: 21757198
acetabular labrum; hip; cartilage mechanics; finite element; dysplasia
18.  Correlation between radiographic measures of acetabular morphology with 3D femoral head coverage in patients with acetabular retroversion 
Acta Orthopaedica  2012;83(3):233-239.
Background and purpose
Acetabular retroversion may result in anterior acetabular over-coverage and posterior deficiency. It is unclear how standard radiographic measures of retroversion relate to measurements from 3D models, generated from volumetric CT data. We sought to: (1) compare 2D radiographic measurements between patients with acetabular retroversion and normal control subjects, (2) compare 3D measurements of total and regional femoral head coverage between patients and controls, and (3) quantify relationships between radiographic measurements of acetabular retroversion to total and regional coverage of the femoral head.
Patients and methods
For 16 patients and 18 controls we measured the extrusion index, crossover ratio, acetabular angle, acetabular index, lateral center edge angle, and a new measurement termed the “posterior wall distance”. 3D femoral coverage was determined from volumetric CT data using objectively defined acetabular rim projections, head-neck junctions, and 4 anatomic regions. For radiographic measurements, intra-observer and inter-observer reliabilities were evaluated and associations between 2D radiographic and 3D model-based measures were determined.
Results
Compared to control subjects, patients with acetabular retroversion had a negative posterior wall distance, increased extrusion index, and smaller lateral center edge angle. Differences in the acetabular index between groups approached statistical significance. The acetabular angle was similar between groups. Acetabular retroversion was associated with a slight but statistically significant increase in anterior acetabular coverage, especially in the anterolateral region. Retroverted hips had substantially less posterior coverage, especially in the posterolateral region.
Interpretation
We found that a number of 2D radiographic measures of acetabular morphology were correlated with 3D model-based measures of total and regional femoral head coverage. These correlations may be used to assist in the diagnosis of retroversion and for preoperative planning.
doi:10.3109/17453674.2012.684138
PMCID: PMC3369147  PMID: 22553905
19.  Open Treatment of Femoroacetabular Impingement is Associated with Clinical Improvement and Low Complication Rate at Short-term Followup 
Background
Since the modern description of femoroacetabular impingement (FAI) a decade ago, surgical treatment has become increasingly common. Although the ability of open treatment of FAI to relieve pain and improve function has been demonstrated in a number of retrospective studies, questions remain regarding predictability of clinical outcome, the factors associated with clinical failure, and the complications associated with treatment.
Questions/purposes
We therefore described the change in clinical pain and function after open treatment, determined whether failure of treatment and progression of osteoarthritis was associated with Outerbridge Grade IV hyaline cartilage injury, and described the associated complications.
Methods
We retrospectively reviewed all 94 patients (96 hips) (55 males and 39 females; mean age, 28 years) who underwent surgical dislocation for femoroacetabular impingement between 2000 and 2008. Seventy-two of the 96 hips had acetabular articular cartilage lesions treated with a variety of methods, most commonly resection of damaged hyaline cartilage and labral advancement. Patients were followed for a minimum of 18 months (mean, 26 months; range, 18–96 months).
Results
Mean Harris hip scores improved from 67 to 91 at final followup. Six of the 96 hips (6%) were converted to arthroplasty or had worse Harris hip score after surgical recovery. Four of these six had Outerbridge Grade IV acetabular cartilage lesions and two had Legg-Calvé-Perthes disease or slipped capital epiphysis deformities. Two hips (2%) had refixation of the greater trochanter.
Conclusions
At short-term followup, open treatment for femoroacetabular impingement in hips without substantial acetabular hyaline cartilage damage reduced pain and improved function with a low complication rate. Treatment of Outerbridge Grade IV acetabular cartilage delamination remains the major challenge.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-009-1152-8
PMCID: PMC2806994  PMID: 19885709
20.  Factors Influencing Cartilage Thickness Measurements with Multi-Detector CT: A Phantom Study 
Radiology  2008;246(1):133-141.
PURPOSE
To prospectively assess in a phantom the reconstruction errors and detection limits of cartilage thickness measurements from MDCT arthrography as a function of contrast agent concentration, imaging plane, spatial resolution, joint space and tube current, using known measurements as the reference standard.
MATERIALS AND METHODS
A phantom with nine chambers was manufactured. Each chamber had a nylon cylinder encased by sleeves of aluminum and polycarbonate to simulate trabecular bone, cortical bone, and cartilage. Variations in simulated cartilage thickness and joint space were assessed. The phantom was scanned with and without contrast agent on three separate days, with chamber axes both perpendicular and parallel to the scanner axis. Images were reconstructed at intervals of both 1.0 and 0.5 mm. Contrast agent concentration and tube current were varied. Simulated cartilage thickness was determined from image segmentation. Root mean squared and mean residual errors were used to characterize the measurements. CT scanner and image segmentation reproducibility were determined.
RESULTS
Simulated cartilage was reconstructed with < 10% error for thicknesses >1.0 mm when no contrast agent or a low concentration of contrast agent (25%) was used. Errors grew as concentration of contrast agent increased. Decreasing the simulated joint space to 0.5 mm caused slight increases in error; below 0.5 mm errors grew substantially. Measurements from anisotropic image data had errors greater than those for isotropic data. Altering tube current did not affect reconstruction errors.
CONCLUSION
Our study establishes lower bounds and repeatability of simulated cartilage thickness measurement using MDCT arthrography, and provides data pertinent to choosing contrast agent concentration, joint spacing, scanning plane, and spatial resolution to reduce reconstruction errors.
doi:10.1148/radiol.2461062192
PMCID: PMC2881220  PMID: 18096534
CT arthrography; phantom; reconstruction error; cartilage; thickness
21.  Validation of Finite Element Predictions of Cartilage Contact Pressure in the Human Hip Joint 
Methods to predict contact stresses in the hip can provide an improved understanding of load distribution in the normal and pathologic joint. The objectives of this study were to develop and validate a three-dimensional finite element (FE) model for predicting cartilage contact stresses in the human hip using subject-specific geometry from computed tomography image data, and to assess the sensitivity of model predictions to boundary conditions, cartilage geometry, and cartilage material properties. Loads based on in vivo data were applied to a cadaveric hip joint to simulate walking, descending stairs and stair-climbing. Contact pressures and areas were measured using pressure sensitive film. CT image data were segmented and discretized into FE meshes of bone and cartilage. FE boundary and loading conditions mimicked the experimental testing. Fair to good qualitative correspondence was obtained between FE predictions and experimental measurements for simulated walking and descending stairs, while excellent agreement was obtained for stair-climbing. Experimental peak pressures, average pressures, and contact areas were 10.0 MPa (limit of film detection), 4.4-5.0 MPa and 321.9-425.1 mm2, respectively, while FE predicted peak pressures, average pressures and contact areas were 10.8-12.7 MPa, 5.1-6.2 MPa and 304.2-366.1 mm2, respectively. Misalignment errors, determined as the difference in root mean squared error before and after alignment of FE results, were less than 10%. Magnitude errors, determined as the residual error following alignment, were approximately 30% but decreased to 10-15% when the regions of highest pressure were compared. Alterations to the cartilage shear modulus, bulk modulus, or thickness resulted in ±25% change in peak pressures, while changes in average pressures and contact areas were minor (±10%). When the pelvis and proximal femur were represented as rigid, there were large changes, but the effect depended on the particular loading scenario. Overall, the subject-specific FE predictions compared favorably with pressure film measurements and were in good agreement with published experimental data. The validated modeling framework provides a foundation for development of patient-specific FE models to investigate the mechanics of normal and pathological hips.
doi:10.1115/1.2953472
PMCID: PMC2840996  PMID: 19045515
Hip; Finite Element; Biomechanics; Pressure Film

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