Planning acetabular redirection osteotomies based on joint contact pressures

Slotted acetabular augmentation for the treatment of residual hip dysplasia in adults: early results of 12 patients

INTRODUCTION

Different pelvic osteotomies and various shelf procedures are used for the operative treatment of hip dysplasia. Slotted acetabular augmentation (SAA) is a well-established technique for the treatment of children and adolescents with hip dysplasia. It has not been widely accepted for treating hip dysplasia in adults although good outcomes have been reported with other augmentation techniques in adults.

MATERIALS AND METHODS

Since 1997, SAA has been used for the prevention of hip arthrosis in 14 dysplastic hips in 12 female patients. The median age at operation was 38.5 (17-42) years; the median follow-up period was 4 (1-8) years. The patients were evaluated on the basis of radiographic, biomechanical and clinical data prior to surgery and at follow-up.

RESULTS

The median centre-edge angle of Wiberg increased from 9 degrees (1-26) before the operation to 43 degrees (31-55) at the latest follow-up (P < 0.001). The median peak stress on the weight-bearing area of the hip, calculated mathematically, was reduced from 14.9 (6.3-28-1) MPa prior to the operation to 4.1 (3-6.1) MPa at the latest follow-up (P < 0.001); the median Harris Hip Score increased from 60 (45-98) points preoperatively to 93 (49-100) points at the follow-up (P < 0.001). There was no difference between the preoperative and follow-up hip joint-space width (P = 0.2).

CONCLUSION

There were no postoperative complications. In our series, the procedure has proved reliable and safe. Its advantages include symptomatic pain relief, adequate acetabular roof coverage and reduced peak stress on the weight bearing area of the hip. It can be used to postpone the development of hip arthrosis in adults with acetabular dysplasia.

Hip2Norm: an object-oriented cross-platform program for 3D analysis of hip joint morphology using 2D pelvic radiographs

We developed an object-oriented cross-platform program to perform three-dimensional (3D) analysis of hip joint morphology using two-dimensional (2D) anteroposterior (AP) pelvic radiographs. Landmarks extracted from 2D AP pelvic radiographs and optionally an additional lateral pelvic X-ray were combined with a cone beam projection model to reconstruct 3D hip joints. Since individual pelvic orientation can vary considerably, a method for standardizing pelvic orientation was implemented to determine the absolute tilt/rotation. The evaluation of anatomically morphologic differences was achieved by reconstructing the projected acetabular rim and the measured hip parameters as if obtained in a standardized neutral orientation. The program had been successfully used to interactively objectify acetabular version in hips with femoro-acetabular impingement or developmental dysplasia. Hip(2)Norm is written in object-oriented programming language C++ using cross-platform software Qt (TrollTech, Oslo, Norway) for graphical user interface (GUI) and is transportable to any platform.

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.

Physical validation of a patient-specific contact finite element model of the ankle

A validation study was conducted to determine the extent to which computational ankle contact finite element (FE) results agreed with experimentally measured tibio-talar contact stress. Two cadaver ankles were loaded in separate test sessions, during which ankle contact stresses were measured with a high-resolution (Tekscan) pressure sensor. Corresponding contact FE analyses were subsequently performed for comparison. The agreement was good between FE-computed and experimentally measured mean (3.2% discrepancy for one ankle, 19.3% for the other) and maximum (1.5% and 6.2%) contact stress, as well as for contact area (1.7% and 14.9%). There was also excellent agreement between histograms of fractional areas of cartilage experiencing specific ranges of contact stress. Finally, point-by-point comparisons between the computed and measured contact stress distributions over the articular surface showed substantial agreement, with correlation coefficients of 90% for one ankle and 86% for the other. In the past, general qualitative, but little direct quantitative agreement has been demonstrated with articular joint contact FE models. The methods used for this validation enable formal comparison of computational and experimental results, and open the way for objective statistical measures of regional correlation between FE-computed contact stress distributions from comparison articular joint surfaces (e.g., those from an intact versus those with residual intra-articular fracture incongruity).

Lateral acetabular rotation improves anterior hip subluxation

Surgical reorientation of the acetabulum is used to improve stability of subluxated or dysplastic hips, but the specific mechanical consequences of reorientation have not been quantified. I used a rigid body spring model of the human hip to study the effects of different acetabular positions on hip stability during single-limb stance. The model predicted subluxation direction and magnitude, and the effective joint contact area, as functions of acetabular position. Frontal plane acetabular orientation varied from 20 degrees medial rotation to 50 degrees lateral rotation, corresponding to center-edge angles from 0 degrees to 70 degrees. Sagittal acetabular orientation varied from 45 degrees anterior rotation to 15 degrees posterior rotation. Center-edge angles less than 20 degrees produced progressive anterolateral subluxation, with dislocation occurring when center-edge angles were less than 0 degrees. Lateral subluxation disappeared when cen-ter-edge angles were 30 degrees or greater. Anteroposterior subluxation was controlled by anterior or posterior rotation of the acetabulum in the presence of low center-edge angles, but there was no specific position of stability that effectively stabilized the femoral head. Anterior subluxation also was controlled by lateral rotation of the acetabulum. Joint contact area increased 1% for every 3 degrees lateral acetabular rotation. The anterolateral subluxation associated with hip dysplasia can be controlled by acetabular reorientation. Joint contact area will increase, thereby reducing peak joint pressure. Anterior and lateral subluxation can be improved by lateral rotation alone, which may reduce the severity of anterior femoroacetabular impingement after periacetabular osteotomy.

Acetabular cysts heal after successful periacetabular osteotomy

The presence of subchondral bone cysts reflects degeneration or defects of the articular cartilage and elevated local stresses in the subchondral bone. We asked whether the presence of acetabular cysts deleteriously influenced the clinical and radiographic results of periacetabular osteotomy for treatment of dysplastic hips. We retrospectively reviewed 46 hips in 43 patients with cartilage narrowing who had periacetabular osteotomies. Of the 46 hips, 21 had acetabular cysts (cyst group) and 25 did not (control group). The average followups were 5.8 and 5.4 years in the cyst and control groups, respectively. We compared the Harris hip score and coverage of the femoral head between the two groups. The clinical results were similar between the two groups. There were no differences in radiographic evaluations between the two groups at the latest followup. In the cyst group, complete or partial healing of the cysts was observed in 17 of the 21 hips. A postoperative increase in the center-edge angle of 20 degrees or greater was found in 14 of the 17 hips. The preoperative presence of acetabular cysts did not influence the results of periacetabular osteotomy. Adequate rotation of the acetabular fragment induced cyst remodeling.

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.

The Bernese periacetabular osteotomy: clinical, radiographic and mechanical 7-15-year follow-up of 26 hips

BACKGROUND

The Bernese periacetabular osteotomy is used in dysplastic hips to increase the load-bearing area of the hip and to prevent osteoarthritis. The aim of our work was to determine the contact hip stress before and after the osteotomy and to compare the relief of stress with the long-term radiographic and clinical outcome.

PATIENTS AND METHODS

We followed 26 dysplastic hips (26 patients) for 7-15 years after the index operation. Clinical evaluation was based on the WOMAC score, osteoarthrosis was evaluated with the Tönnis classification, the angles of lateral (CE) and anterior (VCA) femoral coverage were measured, and biomechanical parameters were studied.

RESULTS

Periacetabular osteotomy increased the mean CE from 15 degrees to 37 degrees , and the mean VCA from 22 degrees to 38 degrees . The mean normalized peak contact stress was reduced from 5.2 to 3.0 kPa/N. Four hips required total hip arthroplasty after an average of 4.5 years, 8 hips showed considerable arthrosis progression, and 14 hips had no or mild arthrosis at follow-up. Preoperative WOMAC score, preoperative Tönnis grade and postoperative normalized peak contact stress were the most important predictors of outcome.

INTERPRETATION

The Bernese periacetabular osteotomy improves the mechanical status of the hip. Long-term success depends on the grade of arthrosis preoperatively and on the magnitude of operative correction of the contact hip stress.

Long-term results of the dial osteotomy in the treatment of high-grade acetabular dysplasia

The dial osteotomy, an acetabular reorientation procedure based on radiographs, was developed by R. H. Eppright for treatment of hip dysplasia; however, long-term results are not recorded. The aim of this study was to evaluate retrospectively the results of the dial osteotomy as done in 37 patients (44 hips) at an average followup of 12.6 years. Articular pressures with the application of a time and pressure algorithm were calculated from radiographs to correlate calculated intraarticular pressures with progression of degenerative disease. Clinical results at followup were 32 (73%) satisfactory and 12 (27%) unsatisfactory hips. Six (13%) hips failed between 10-20 years (average 14.7 years). A satisfactory result correlated with the preoperative functional score. Radiographically, the anterior center-edge angle increased from an average of 6.7 degrees to 37.9 degrees. At followup, radiographic indices of degeneration indicated that eight (18%) hips had improved, 18 (41%) had stabilized, and 18 (41%) had deteriorated. Severin indices improved in 21 (48%) hips. Joint space width at followup provided the only correlation between radiographic parameters and clinical result. Contact pressures were reduced from 4.45 MPa to 1.12 MPa. The cumulative exposure to articular pressures averaged 61.6 MPa-years, and did not correlate with radiographic parameters or clinical success.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series--no, or historical control group). See the Guidelines for Authors for a complete description of levels of evidence.

Three-dimensional distribution of acetabular cartilage thickness in patients with hip dysplasia: a fully automated computational analysis of MR imaging

OBJECTIVE

The aim of this study was to evaluate three-dimensional (3D) distribution of acetabular articular cartilage thickness in patients with hip dysplasia using in vivo magnetic resonance (MR) imaging, and to compare cartilage thickness distribution between normal and dysplastic hips.

DESIGN

Forty-five dysplastic hips without joint space narrowing on radiographs and 13 normal hips underwent MR imaging with fat-suppressed 3D fast spoiled gradient echo (SPGR) sequence. Acetabular cartilage thickness was measured with a fully automated segmentation technique, and cartilage thickness distribution was compared between the dysplastic and normal hips on the celestial spherical coordinate system.

RESULTS

Average cartilage thickness was significantly greater for the dysplastic hips than the normal hips (1.77 mm vs 1.34 mm). There was a general trend of gradient increase of cartilage thickness at the superolateral area in normal and dysplastic hips. The gradient increase of cartilage thickness was significantly greater in the dysplastic hips than the normal hips.

CONCLUSIONS

Dysplastic hips have general thick cartilage distribution as well as more prominent gradient increase of thickness at the superolateral portion. The knowledge of fundamental morphological feature of dysplastic hips at a preradiologic stage may aid early detection of cartilage thinning in association with osteoarthritic progression, accurate computational biomechanical analysis in the hip joint, and planning periacetabular osteotomy with satisfactory cartilaginous congruency.

Gradient of contact stress in normal and dysplastic human hips

The stress gradient index (G(p)) is introduced for the assessment of dysplasia in human hip joint. The absolute value of G(p) is equal to the magnitude of the gradient of the contact stress at the lateral acetabular rim. The parameter G(p) normalized with respect to the body weight (W(B)) is determined from the standard anteroposterior radiographs of adult human hips and pelvises using the mathematical model. The average value of G(p)/W(B) was determined for the group of dysplastic hips and for the group of normal hips. In the group of normal hips the average value of G(p)/W(B) is smaller (-0.445x10(5) m(-3)) than in the group of dysplastic hips (+1.481x10(5) m(-3)). The difference is statistically significant P<0.001. The average value of G(p)/W(B) changes its sign at the value of the centre-edge angle theta(CE) approximately 20( composite function ) which is usually considered as the boundary value of theta(CE) (lower limit) for the normal hips. Accordingly we suggest a new definition for the hip dysplasia with respect to the size and sign of the normalized stress gradient index G(p)/W(B). The hips with positive G(p)/W(B) are considered to be dysplastic while the hips with negative G(p)/W(B) are considered to be normal. The statistically significant correlation between the value of the Harris hip score, used in the clinical assessment of the hip dysplasia, and the normalized stress gradient index was found.

Polygonal triple (Kotz) osteotomy in the treatment of acetabular dysplasia: 17 patients (19 hips) with 4-9 years of follow-up

We reviewed 19 hips in 17 patients between 17 and 33 years of age, who underwent a Kotz polygonal triple osteotomy. Their average follow-up was 7 (4.5-9) years. Although 13 patients had less pain after surgery, 3 continued to limp. The average corrections were 36 degrees for the center-edge angle, 31 degrees for the vertical center-edge angle and 19 degrees for Sharp's angle. 3 patients developed transient palsy of the sciatic nerve, and 3 asymptomatic nonunion of the ischium or pubic bone. The degree of arthrosis decreased in 10 hips.

Kotz and Ganz osteotomies in the treatment of adult acetabular dysplasia

In hips with acetabular dysplasia, we performed Kotz osteotomy (group 1) in 22 hips (20 patients; mean age 24.3 years) and Ganz osteotomy (group 2) in 23 hips (22 patients; mean age 23.1 years). Group 1 was followed 83.3 (56-112) months and group 2 40.9 (24-66) months. In group 1, Harris hip score improved from average 74.9 to 86.9, mean center edge (CE) angle from -4.5 degrees to 30.3 degrees, and mean vertical center edge (VCE) angle from 5.3 degrees to 36.2 degrees. In group 2, Harris hip score improved from average 76.6 to 91.1, mean CE angle from -5.9 degrees to 32.0 degrees, and mean VCE angle from 5.0 degrees to 41.3 degrees. Using Pauwels criteria, regression was observed in 12 hips in group 1 and one progressed. In group 2, 15 hips showed regression and three progressed. In patients treated with Ganz osteotomy, the complication rate was higher and the complications more serious than in patients treated with Kotz osteotomy. Most complications were, however, seen among the first ten patients treated with Ganz osteotomy. Although we detected no significant difference between the two groups in terms of clinical and radiological findings, we believe the outcome to be slightly better after a properly performed Ganz osteotomy.

Acetabular dysplasia: a paradigm of arthroscopic examination of chondral injuries

The current authors show the value of arthroscopy in diagnosing labral and acetabular cartilage injury and examining the relationship between those injuries and acetabular dysplasia. Between 1989 and 2000, 170 hips in 163 patients with mild acetabular dysplasia or moderate dysplasia with joint preservation had arthroscopic evaluation. Surgical findings were classified by location and by severity of the chondral lesions of the femoral head, acetabulum, and labrum. Of the 170 hips with dysplasia, 122 had labral tears (72%) at the free-margin articular surface and 113 had anterior tears (66%). One hundred hips (59%) had anterior acetabular chondral lesions. Among the 113 patients who had anterior labral tears, 78 hips (69%) had anterior acetabular chondral defects, and 44 hips (39%) had anterior femoral head chondral lesions. Mild uncovering of the anterior femoral head subjects the labrum to increased load and potential susceptibility to tearing most frequently anteriorly. Labral tears may contribute to or can occur in association with articular cartilage lesions of the contiguous femoral head or acetabulum. The mechanism of injury is most likely hyperextension or torque of the hip or both. The findings in the current study support the concept that labral disruption frequently is a predecessor in the continuum of degenerative joint disease.

Subchondral cysts arise in the anterior acetabulum in dysplastic osteoarthritic hips

The distribution of subchondral cysts in 57 dysplastic osteoarthritic hips of 38 patients was assessed by computed tomography and by a new computerized technique. The cyst count in osteoarthritic hips was inversely correlated with the width of the joint space. A greater accumulation of cysts was found in the acetabulum than in the femoral head, and more cysts were found in the anterior part of the hip than in the posterior part. Osteoarthritic change was more predominant in the acetabulum than in the femoral head, and was more predominant in the anterior part of the hip than in the posterior part.

Mathematical estimation of stress distribution in normal and dysplastic human hips

By using a mathematical model of the adult human hip in the static one-legged stance position of the body, the forces acting on the hip, peak stress in the hip joint and other relevant radiographic and biomechanical parameters were assessed. The aims were to examine if the peak stress in dysplastic hips is higher than in normal hips and to find out which biomechanical parameters contribute significantly to higher peak stress. The average normalized peak stress in dysplastic hips (7.1 kPa/N) was markedly higher (to approximately 100%) than the average normalized peak stress in normal hips (3.5 kPa/N). The characteristic parameters that contributed to higher peak stress in dysplastic hips included the smaller lateral coverage of the femoral head, the larger interhip distance, the wider pelvis, and the medial position of the greater trochanter. These results are consistent with the hypothesis that stress distribution over weight-bearing surface of the hip joint is the relevant parameter for assessment of the risk for developing coxarthrosis.

Hip stress reduction after Chiari osteotomy

A mathematical model was developed to study the effect of the Chiari osteotomy on the distribution of contact hip stress over the weight-bearing area. It was shown that Chiari osteotomy can increase the weight-bearing area directly (on the lateral side), owing to the additional area formed by the ala ossis ilii segment, and indirectly (on the medial side), owing to the shift of the stress pole in the medial direction. As a consequence, the contact hip stress is reduced after Chiari osteotomy. The indirect effect is important and often larger than the direct one. Using the proposed mathematical model and standard anteroposterior roentgenographs from archives, the average peak stress on the weight-bearing area, normalised with respect to the body weight (pmax/ W(B)), was determined before and after Chiari osteotomy (8,310m(-2) and 4,480 m(-2), respectively) on a population of 29 dysplastic hips. The difference was statistically significant (p < 0.005). Based on the results presented, it can be concluded that the hip joint contact stress in dysplastic hips considerably decreases after Chiari osteotomy, indicating a favourable biomechanical effect of this operation.

Middle-term results of Salter innominate osteotomy

This study evaluated middle-term clinical and radiographic results of Salter innominate osteotomy for treatment of dysplastic, subluxated, or congenitally dislocated hips. Thirty-five hips in 33 patients with a mean age at index surgery of 4 years 7 months were followed up for an average of 16.5 years. Radiographic center-edge angle of Wiberg, acetabular index, and regularity of the femoral head were evaluated. Fifteen (43%) hips were in Group I, 11 (31%) hips were in Group II, six (17%) hips were in Group III, and three (9%) hips were in Group IV according to the Severin classification. Significant differences were found in the preoperative and recent center-edge angle (average, 1.1 degrees and 28.8 degrees in the excellent and good groups versus -5.3 degrees and 15.0 degrees in the fair and poor groups) and regularity of the femoral head (very irregular versus others). The current results indicate that after middle-term followup, Salter innominate osteotomy is an effective treatment. The authors conclude this procedure is indicated in patients who meet the criteria proposed by Salter.

Determination of contact hip stress from nomograms based on mathematical model

Nomograms are presented that enable determination of maximal stress on the hip joint weight bearing area if certain geometrical parameters of the hip and pelvis and the body weight are known. The nomograms are calculated by using previously developed mathematical models. It is demonstrated how the maximal stress on the hip joint weight bearing area is determined from the presented nomograms for a hip for which the geometrical parameters were obtained from a standard anteroposterior rentgenograph. This simple and noninvasive method may give insight into the biomechanical status of the hip which should be considered in routine surgical planning and as a part of the routine examination of the patient without the use of any additional tools.

Articular cartilage abnormalities in dysplastic hips without joint space narrowing

Three-dimensional magnetic resonance imaging in the coronal and sagittal planes was performed in 25 normal hips of 16 volunteers and 70 dysplastic hips of 50 patients with clinical symptoms but without radiologic joint space narrowing. A high prevalence of cartilage abnormalities was detected, mostly located at the anterosuperior area in the hip: 31 hips (44%) in the acetabular cartilage and five hips (7%) in the femoral cartilage showed a mild to moderate defect of cartilage thickness. The presence of cartilage abnormalities had a statistically significant correlation with age of the patients and severity of hip pain. Of 31 hips with cartilage abnormalities, sagittal magnetic resonance images showed abnormalities in 30 (97%), whereas coronal magnetic resonance images revealed abnormalities only in 11 (35%). A high incidence of cartilage abnormalities in the preradiologic stage suggests the need for more sensitive modalities for early diagnosis. Magnetic resonance imaging in the sagittal plane allows detailed assessment of early cartilage abnormalities.

Contact Stresses in the Human Hip: Implications for Disease and Treatment

Contact stresses in the hip articular surfaces relate in some way to normal maintenance as well as destruction of joints. In vivo determinations of cartilage-on-cartilage contact pressure histories have never been reported, and current technology does not allow such measurements without the potential for artifact: all experimental methods require introducing some material between the surfaces, and all numerical methods have yet to be fully validated. Nonetheless, a variety of distinct experimental and numerical approaches lead to estimates of contact stresses and surprisingly, despite the choice of technique, values for peak contact stresses lie within a range of one order of magnitude (i.e. 0.5–5.0 MPa) and usually closer. Pathological conditions increase this to the range of over 5.0 MPa, while surgical procedures designed to reduce peak pressures theoretically can achieve reductions. Two critical unresolved issues are 1.) What aspect of the contact stress history (e.g. contact stress gradients over time) in fact cause the biological responses? 2.) What level of contact stress history is tolerated by the cartilage? Future research will need to address these critical issues.