Cartilage thickness in the hip measured by MRI and stereology before and after periacetabular osteotomy

Accuracy of conventional motion capture in measuring hip joint center location and hip rotations during gait, squat, and step-up activities

Accurate measurements of hip joint kinematics are essential for improving our understanding of the effects of injury, disease, and surgical intervention on long-term hip joint health. This study assessed the accuracy of conventional motion capture (MoCap) for measuring hip joint center (HJC) location and hip joint angles during gait, squat, and step-up activities while using dynamic biplane radiography (DBR) as the reference standard. Twenty-four young adults performed six trials of treadmill walking, six body-weight squats, and six step-ups within a biplane radiography system. Synchronized biplane radiographs were collected at 50 images per second and MoCap was collected simultaneously at 100 images per second. Bone motion during each activity was determined by matching digitally reconstructed radiographs, created from subject-specific CT-based bone models, to the biplane radiographs using a validated registration process. Errors in estimating HJC location and hip angles using MoCap were quantified by the root mean squared error (RMSE) across all frames of available data. The MoCap error in estimating HJC location was larger during step-up (up to 89.3 mm) than during gait (up to 16.6 mm) or squat (up to 31.4 mm) in all three anatomic directions (all p < 0.001). RMSE in hip joint flexion (7.2°) and abduction (4.3°) during gait was less than during squat (23.8° and 8.9°) and step-up (20.1° and 10.6°) (all p < 0.01). Clinical analysis and computational models that rely on skin-mounted markers to estimate hip kinematics should be interpreted with caution, especially during activities that involve deeper hip flexion.

The Effects of Residual Femoral Deformity on Computed Contact Mechanics in Patients Treated With In Situ Fixation for Slipped Capital Femoral Epiphysis

OBJECTIVE

In situ fixation for treatment of slipped capital femoral epiphysis (SCFE) can stabilize the epiphysis and prevent further joint deformation but often leaves residual deformity that may adversely affect intra-articular contact mechanics. The purpose of this study was to investigate the relationship between residual deformity and contact mechanics in the post-SCFE hip.

METHODS

Patient-specific hip models were created for 19 patients with SCFE treated with in situ fixation. For each model, discrete element analysis was used to compute cumulative acetabular and femoral contact stress exposure during a walking gait cycle. Slip severity was evaluated for each patient using the two-dimensional Southwick angle and a novel three-dimensional (3D) assessment of multiplanar femoral deformity (3D slip angle).

RESULTS

Of the SCFE cases, 2/7 mild (Southwick angle ≤30 degrees) had peak cumulative femoral exposures equivalent to that of severe (Southwick angle ≥60 degrees) cases. Severe SCFE cases had higher peak ( P = 0.015) and mean ( P = 0.028) femoral contact stress exposure and lower cumulative femoral contact area ( P = 0.003) than mild (Southwick angle ≤30 degrees) SCFE cases. Mean femoral contact stress exposure was also higher in severe SCFE cases than in moderate SCFE cases ( P = 0.027). Acetabular and femoral contact mechanics metrics typically demonstrated stronger correlations with 3D slip angle than two-dimensional Southwick angle.

CONCLUSIONS

Increased slip severity adversely impacts intra-articular femoral contact mechanics. Contact mechanics metrics demonstrate higher correlations with 3D slip angle, indicating that this novel measurement may better describe global deformity and its relationship to intra-articular mechanics; however, the modest strength of these correlations may also imply that global impingement-generating deformity is not the primary factor driving contact mechanics in the post-SCFE hip.

CLINICAL RELEVANCE

Greater slip severity adversely impacts contact mechanics in the post-SCFE hip. However, focal regions of high contact stress were seen even in mild SCFE deformities, suggesting some type of deformity correction should be considered even for mild slips to alleviate secondary impingement, address focal incongruities, and reduce osteoarthritis development/progression.

Chronically elevated contact stress exposure correlates with intra-articular cartilage degeneration in patients with concurrent acetabular dysplasia and femoroacetabular impingement

Hip dysplasia is known to lead to premature osteoarthritis. Computational models of joint mechanics have documented elevated contact stresses in dysplastic hips, but elevated stress has not been directly associated with regional cartilage degeneration. The purpose of this study was to determine if a relationship exists between elevated contact stress and intra-articular cartilage damage in patients with symptomatic dysplasia and femoroacetabular impingement. Discrete element analysis was used to compute hip contact stresses during the stance phase of walking gait for 15 patients diagnosed with acetabular dysplasia and femoral head-neck offset deformity. Contact stresses were summed over the duration of the walking gait cycle and then scaled by patient age to obtain a measure of chronic cartilage contact stress exposure. Linear regression analysis was used to evaluate the relationship between contact stress exposure and cartilage damage in each of six acetabular subregions that had been evaluated arthroscopically for cartilage damage at the time of surgical intervention. A significant correlation (R2  = 0.423, p < 0.001) was identified between chondromalacia grade and chronic stress-time exposure above both a 1 MPa damage threshold and a 2 MPa-years accumulated damage threshold. Furthermore, an over-exposure threshold of 15% regional contact area exceeding the 1 and 2 MPa-years threshold values resulted in correct identification of cartilage damage in 83.3% (55/66) of the acetabular subregions loaded during gait. These results suggest corrective surgery to alleviate impingement and reduce chronic contact stress exposures below these damage-inducing thresholds could mitigate further cartilage damage in patients with hip dysplasia.

Periacetabular osteotomy to treat hip dysplasia: a systematic review of harms and benefits

INTRODUCTION

Periacetabular osteotomy (PAO) is often performed in patients with hip dysplasia. The aim of this systematic review and meta-analysis was to evaluate the harms and benefits of PAO in patients with hip dysplasia in studies reporting both adverse events and patient-reported hip pain and function.

MATERIALS AND METHODS

A systematic search combing PAO and patient-reported outcomes was performed in the databases MEDLINE, CINAHL, EMBASE, Sports Discuss and PsychINFO. Studies including both harms and benefits defined as adverse events and patient-reported hip pain and function were included. Risk of bias was assessed using The Cochrane Risk of Bias In Non-Randomized Studies - of Interventions.

RESULTS

Twenty-nine cohort studies were included, of which six studies included a comparison group. The majority of studies had serious risk of bias and the certainty of evidence was very low. The proportion of adverse events was 4.3 (95% CI 3.7; 4.9) for major adverse events and 14.0 (95% CI 13.0; 15.1) for minor adverse events. Peroneal nerve dysfunction was the most frequent adverse event among the major adverse events, followed by acetabular necrosis and delayed union or non-union. All patient-reported hip pain and function scores improved and exceeded the minimal clinically important differences after PAO. After 5 years, scores were still higher than the preoperative scores.

CONCLUSION

PAO surgery has a 4% risk of major, and 14% risk of minor adverse events and a positive effect on patient-reported hip pain and function among patients with hip dysplasia.

Hip survivorship following the Bernese periacetabular osteotomy for the treatment of acetabular dysplasia: A systematic review and meta-analysis

INTRODUCTION

The Bernese periacetabular osteotomy (PAO) is a popular joint-preservation technique aimed at addressing the structural and biomechanical abnormalities associated with acetabular dysplasia. However, the prognostic factors and long-term survivorship of the native hip, with failure defined as conversion to total hip arthroplasty (THA), is poorly understood. Our study aims to address the following: (1) What is the estimated duration of survival of the native hip post-PAO, (2) What are some prognostic factors of functional outcome and (3) What is the complication rate and complications associated with PAO.

HYPOTHESIS

The Bernese PAO is able to result in favourable mid- to long-term outcomes conditional on a stringent patient selection criteria.

MATERIALS AND METHODS

A systematic review was performed using the PRISMA guidelines. All studies that reported on the outcomes of isolated Bernese PAO for the treatment of acetabular dysplasia were included.

RESULTS

A total of 24 studies (3471 patients, 3655 hips) were included at a mean follow-up duration of 54.2months (range: 1-336months). In total, 208 hips (6.03%; 95% CI: 5.25-6.94%) converted to THA at a mean duration of 4.71years (range: 1-240months). Univariate analysis identified advanced age beyond a follow-up duration of 6years (p=0.001) and preoperative Tönnis grade 2 and above (p<0.001) to be the most significant negative prognostic factors. Beyond a follow-up duration of 2years, intraoperative fluoroscopy proved to be a significant positive prognostic factor (p<0.001). Indications for PAO, obesity and gender were not found to be significant predictors of failure. Our study found the complication rate to be 23.5% (95% CI: 21.6-25.6%). The most common complications detailed are transient lateral femoral cutaneous nerve dysesthesia (8.24%; 95% CI: 7.02-9.65%), stress fracture (5.28%; 95% CI: 4.31-6.89%) and the delayed union, non-union or pseudoarthrosis of the ramus not necessitating surgical correction (3.73%, 95% CI: 2.93-4.75%).

DISCUSSION

PAO alters the natural history of the dysplastic hip with a 10- and 20-year survivorship of approximately 75.9% and 36.5% of patients respectively. The ideal patient should be below 40years old, with a preoperative Tönnis grade of 0 or 1. Intraoperative fluoroscopy is able to guide a better precision when re-orientating the acetabulum.

LEVEL OF EVIDENCE

IV; systematic review and meta-analysis.

Preoperative Rather Than Postoperative Intra-Articular Cartilage Degeneration Affects Long-Term Survivorship of Periacetabular Osteotomy

PURPOSE

To determine whether intra-articular lesions changed in short-term follow-up after periacetabular osteotomy (PAO) and whether the intra-articular lesion changes impacted the long-term survivorship of PAO.

METHODS

We reviewed patients with hip dysplasia who underwent PAO with arthroscopic observation between 1990 and 2001. Patients who underwent second-look arthroscopy were included. The correlations between the intra-articular lesion changes and the long-term outcome of PAO were analyzed for patients with >10 years of follow-up. The possible risk factors included demographic factors (age, sex, and body mass index), radiographic factors (Tönnis grade, lateral center-edge angle, Tönnis angle, acetabular head index, crossover sign, posterior wall sign, and joint congruity), and arthroscopic findings (full-thickness lesions at the time of PAO and lesions changes at the time of second-look arthroscopy).

RESULTS

A total of 64 patients (72 hips) were studied. Second-look arthroscopy was performed at a median of 1.4 years after PAO. Intra-articular lesions were observed in 93% in the acetabulum, 81% in the femoral head, and 97% in the labrum, respectively. These lesions unchanged in 74% in the acetabulum, 76% in the femoral head, and 79% in the labrum, respectively. Cartilage repair was observed in the acetabulum and the femoral head in 24% and 17% of hips, respectively. Labral repair occurred in 10%. Intra-articular lesion changes were not a predictor of failure. Multivariate analysis identified International Cartilage Repair Society grade 4 lesion in the femoral head as an independent risk factor for failure.

CONCLUSIONS

Our results suggest that PAO prevents further deterioration in mild cartilage lesions and results in cartilage repair in some cases with advanced cartilage degenerations in the short term. However, these postoperative changes were not associated with long-term survivorship. Thus, appropriate surgical indications based on the preoperative intra-articular cartilage degeneration is paramount to achieving long-term success in PAO.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Relationship between hip joint proximity area and sagittal balance parameters: an upright computed tomography study

PURPOSE

A close relationship between sagittal spinal alignment and hip osteoarthritis (OA) has been documented. This study aimed to examine the relationship between hip joint proximity area and sagittal balance parameters in healthy subjects.

METHODS

This prospective study enrolled 47 healthy volunteers who underwent 320-detector row upright computed tomography. Acquired data were reconstructed in a virtual three-dimensional space. The proximity area was determined by < 1 mm of the Hausdorff distance between the acetabulum and the femoral head. Volunteers were divided into the anterior and posterior proximity groups depending on the position of the closest area. Sagittal balance parameters [sagittal vertical axis (SVA), T1 spinopelvic inclination (T1-SPi), T1-pelvic angle, pelvic tilt, sacral slope, pelvic incidence, lumbar lordosis, thoracic kyphosis), offset distance between the centre of the acoustic meati (CAM) and C7 plumb line (CAM-C7-offset), and offset distance between the CAM and hip axis (HA) (CAM-HA-offset)] were compared between the two groups using independent sample t test.

RESULTS

The anterior proximity group (n = 24) had higher SVA (p = 0.016) and T1-Spi (p = 0.015) than the posterior proximity group (n = 23). CAM-HA-offset was higher in the posterior than in the anterior proximity group (p < 0.000). There was no difference in other parameters (p > 0.05).

CONCLUSION

The anterior proximity group had a positive anterior spinal balance; the posterior proximity group may have a more posterior gravity line than the hip joint centre. The anterior spinal balance may contribute to the anterior loading of the hip joint, with known relation with the initiation and onset of hip OA.

Arthroscopy and arthrotomy to address intra-articular pathology during PAO for hip dysplasia demonstrates similar short-term outcomes

Periacetabular osteotomy (PAO) remains the gold standard procedure for joint preservation in symptomatic developmental dysplasia of the hip (DDH). Hip arthroscopy (HA) and open arthrotomy have been used to correct intra-articular pathology at the time of PAO, but there is limited data regarding differences in outcomes between these techniques when performed at the time of PAO. The aim of this study was to determine if short-term clinical outcomes differed between patients managed with HA versus arthrotomy to evaluate and treat intra-articular pathology at the time of PAO to discern if one technique is associated with better pain and functional results. Data were retrospectively reviewed from two surgeons at one institution managing DDH patients from September 2013 to December 2015. One surgeon treated patients with PAO and arthrotomy (N = 32), while the other performed PAO and HA (N = 39). There were 87% women, median age was 28 years and mean BMI was 25. Seventy-five percent of all patients received an intra-articular intervention. Patients completed 13 PROs at the pre-operative and 1-year post-operative clinical visits. Pre-operatively, there were no differences in any of the 13 PROs between patients treated with HA versus arthrotomy (P ≥ 0.076). Patients treated with PAO and arthrotomy experienced greater mean improvement in two out of the 13 PROs; the other 11 showed no differences. No treatment effect was observed for any of the 13 PROs using multivariable modelling that accounted for severity of dysplasia and degree of arthritis. Few differences were shown in short-term clinical outcomes between HA and arthrotomy at the time of PAO. This work highlights the need for a high quality randomized clinical trial to provide definitive guidance on whether hip preservation surgeons should address intra-articular pathology at the time of PAO for DDH and which technique best serves this purpose.

Longitudinal morphological change of acetabular subchondral bone cyst after total hip arthroplasty in developmental dysplasia of the hip

PURPOSE

The purpose of this study is to clarify morphological changes of acetabular subchondral bone cyst after total hip arthroplasty for osteoarthritis secondary to developmental dysplasia of the hip.

METHODS

Two hundred and sixty-one primary cementless total hip arthroplasties of 208 patients, 18 males, 190 females, were retrospectively reviewed. Morphological changes of subchondral bone cyst were evaluated by computed tomography (CT). The mean cross-sectional area of the cyst from CT scans at 3 months postoperatively and after 7-10 years (average 8.4 years) were compared.

RESULTS

Acetabular subchondral bone cysts were found in 49.0% of all cases in preoperative CT scans. There was no cyst which was newly recognized in CT scan performed after postoperative 7-10 years. All the cross-sectional areas of the cysts evaluated in this study were reduced postoperatively.

CONCLUSIONS

This study revealed that acetabular subchondral bone cysts do not increase or expand after total hip arthroplasty and indicated that the longitudinal morphological change of acetabular bone cysts in patients of developmental dysplasia of the hip do not influence long-term implant fixation in total hip arthroplasty.

Risk factors for the need of hip arthroscopy following periacetabular osteotomy

Despite the frequency of labral tears in symptomatic developmental dysplasia of the hip, no consensus exists regarding the treatment of coexisting dysplasia of the hip and tearing of the acetabular labrum. The purpose of this prospective, MR arthrography (MRA) based 2-year follow-up study was to identify risk factors predicting the need for a hip arthroscopy (HA) after periacetabular osteotomy (PAO). Ninety-nine patients (104 hips) scheduled for PAO were evaluated preoperatively and at 2-year follow-up. MRA was performed in all patients prior to PAO. At follow-up, patients were divided into a non-arthroscopy and arthroscopy group. The two groups were compared clinical and radiological, and risk factors for HA after PAO were calculated. Patient reported outcome measures (WOMAC, Oxford Hip and SF36) were filled out before PAO and at follow-up. Ninety-five hips (91.3%) were evaluated. Twenty-six hips (27%) required an arthroscopy within 2 years of the PAO. Risk factors were preoperative borderline dysplasia, acetabular retroversion and complete labral detachment. Labral tearing, degeneration or hypertrophy did not negatively affect the outcome of PAO. Patients not requiring an arthroscopy had a statistically significant better outcome measured by patients reported outcome measures. After PAO, 27% of the hips needed intra-articular assessment. Conventional radiographs and MRA analysis can be used to identify predictors for patients requiring HA after PAO. At 2-year follow-up, the clinical outcome improved in all patients. However, those patients who had no need of a HA after their PAO had superior results.

Cartilage Thickness and Cyst Volume Are Unchanged 10 Years After Periacetabular Osteotomy in Patients Without Hip Symptoms

BACKGROUND

Periacetabular osteotomy (PAO) may affect cartilage thickness and cyst volume in patients with hip dysplasia. However, as no studies randomizing patients to either PAO or conservative treatment have been performed, to our knowledge, it is unknown if PAO directly affects the development or progression of osteoarthritis in patients with hip dysplasia.

QUESTIONS/PURPOSES

We investigated (1) changes of cartilage thickness in the hip after PAO; (2) how many patients had subchondral bone cysts in the acetabulum or femoral head; (3) changes in cyst volume; and (4) patients' hip function and pain after PAO.

PATIENTS AND METHODS

In this prospective study, 26 patients (22 women and four men) with hip dysplasia were enrolled with the goal of having MRI of the hip before undergoing PAO and again at 1, 2½, and 10 years after PAO. Of the 26 patients, 17 (65%) underwent complete followup 10 years after PAO, whereas nine could not be included. Of those nine, three had undergone THA, three had substantial hip symptoms, and three were lost to followup. Thickness of acetabular and femoral cartilage and volume of subchondral bone cysts were estimated in the remaining 17 patients. Ten years postoperatively, the patients' Hip disability and Osteoarthritis Outcome Scores (HOOS) were collected.

RESULTS

Preoperatively, the mean thickness of the acetabular cartilage was 1.38±0.14 mm compared with 1.43±0.07 mm 10 years postoperatively (p=0.73). The mean thickness of the femoral cartilage preoperatively was 1.37±0.20 mm compared with 1.30±0.07 mm 10 years postoperatively (p=0.24). Seven patients had an increase in cyst volume, six had a decrease, and four had no cysts to start with and remained without cysts. Preoperatively, the median total cyst volume per patient was 6.0 cm3 (range, 1.6-188.3 cm3) compared with 2.9 cm3 (range, 0.7-8.2 cm3) (p=0.18) at 10 years followup. At 10 years, the mean subscores for the HOOS were: pain, 79±16; symptoms, 73±17; activities of daily living, 85±14; sport/recreation, 68±22; and quality of life, 61±19.

CONCLUSIONS

Ten years after PAO, approximately 25% of the patients who have the procedure will have substantial hip pain and/or undergo hip arthroplasty. Of the patients who do not have substantial hip pain or an arthroplasty, cartilage thickness appears to be preserved. Future studies are needed to help us decide which patients are most likely to succeed with PAO at long-term followup.

LEVEL OF EVIDENCE

Level II, therapeutic study.

A Stereological Method for the Quantitative Evaluation of Cartilage Repair Tissue

OBJECTIVE

To implement stereological principles to develop an easy applicable algorithm for unbiased and quantitative evaluation of cartilage repair.

DESIGN

Design-unbiased sampling was performed by systematically sectioning the defect perpendicular to the joint surface in parallel planes providing 7 to 10 hematoxylin-eosin stained histological sections. Counting windows were systematically selected and converted into image files (40-50 per defect). The quantification was performed by two-step point counting: (1) calculation of defect volume and (2) quantitative analysis of tissue composition. Step 2 was performed by assigning each point to one of the following categories based on validated and easy distinguishable morphological characteristics: (1) hyaline cartilage (rounded cells in lacunae in hyaline matrix), (2) fibrocartilage (rounded cells in lacunae in fibrous matrix), (3) fibrous tissue (elongated cells in fibrous tissue), (4) bone, (5) scaffold material, and (6) others. The ability to discriminate between the tissue types was determined using conventional or polarized light microscopy, and the interobserver variability was evaluated.

RESULTS

We describe the application of the stereological method. In the example, we assessed the defect repair tissue volume to be 4.4 mm(3) (CE = 0.01). The tissue fractions were subsequently evaluated. Polarized light illumination of the slides improved discrimination between hyaline cartilage and fibrocartilage and increased the interobserver agreement compared with conventional transmitted light.

CONCLUSION

We have applied a design-unbiased method for quantitative evaluation of cartilage repair, and we propose this algorithm as a natural supplement to existing descriptive semiquantitative scoring systems. We also propose that polarized light is effective for discrimination between hyaline cartilage and fibrocartilage.

No correlations between radiological angles and self-assessed quality of life in patients with hip dysplasia at 2-13 years of follow-up after periacetabular osteotomy

BACKGROUND

Only few studies have described patients' health-related quality of life (QoL) after periacetabular osteotomy (PAO). Thus, there is a lack of data on the self-assessed outcome of patients operated with PAO, and none of the existing studies correlate the results from Medical Outcomes Short Form-36 questionnaire (SF-36) with the radiological parameters.

PURPOSE

To investigate the health-related QoL for patients with hip dysplasia operated with PAO and to investigate whether QoL is associated with the acetabular angles or hypermobility.

MATERIAL AND METHODS

Out of 388 patients, 228 patients (mean age, 40.5 years; mean follow-up, 7.1 years) returned the SF-36 and Beighton questionnaires. The patient's QoL was compared to reference data from a Danish population. Center-edge (CE) and acetabular index (AI) angles were measured before and after PAO and the association with the patients' QoL was tested with logistic regression.

RESULTS

For both men and women the postoperative SF-36 score was significantly lower than for the reference data for a Danish population, especially for those dimensions concerning physical health. No association was found between the patients' CE or AI angles before or after PAO and their subsequent QoL. Significant associations were found between both Physical Component Score (PCS) and physical function (PF) and follow-up time after the operation. The adjusted OR for a PCS ≥ 50 was 0.87 (95% CI 0.76-0.99) and for a PF ≥ 85 0.81 (95% CI 0.71-0.91). No association between hyper mobility and PCS, PF, or bodily pain (BP) was found.

CONCLUSION

The physical components of QoL in patients undergoing PAO are significantly lower than the Danish population used as reference. Furthermore, the results suggest that physical function after PAO decreases with longer follow-up time. Neither the acetabular angles nor hypermobility is associated with the physical components of QoL.

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.

Imaging evaluation of developmental hip dysplasia in the young adult

OBJECTIVE

The purpose of this article is to review the clinical and imaging features as well as the potential complications of hip dysplasia in the young adult. Hip dysplasia is an important cause of secondary osteoarthrosis, which accounts for a significant proportion of patients requiring total hip arthroplasty. The radiographic diagnosis of mild hip dysplasia in the young adult may be subtle and is primarily based on the detection of deficient coverage of the femoral head by the acetabulum.

CONCLUSION

Cross-sectional imaging, including CT and MRI, afford improved detection and characterization by providing morphologic information about acetabular deficiency. MRI also allows evaluation of potential associated injuries to the articular cartilage, the labrum, and the ligamentum teres. Familiarity with the radiographic and cross-sectional imaging findings of mild hip dysplasia in the young adult may allow a timely diagnosis and implementation of treatment strategies, which may prevent or delay the development of early osteoarthritis.

Impact of triple pelvic osteotomy on contact stress pressure distribution in the hip joint

PURPOSE

We studied changes of contact stress distribution in the hip joint after Tonnis triple pelvic osteotomy applied in the treatment of dysplasia and hip joint incongruence in adolescents.

METHODS

In a group of 75 patients, 54 (72 %) female, who underwent surgery by triple pelvic osteotomy in adolescence for developmental disorder of the hip and avascular necrosis of the femoral head, a three-dimensional hip joint model was used based on the radiography of the pelvis with hips. The following biomechanical parameters were calculated: resultant hip force normalised to body weight (R/Wb), inclination of the resultant hip force (θ-R), the position of the stress pole (θ), peak contact hip stress (Pmax), and peak contact hip stress normalised to body weight (Pmax/Wb). Gait quality was also assessed.

RESULTS

After surgery the Wiberg CE angle was increased by 17.85° (114 %), resultant hip force normalised to body weight (R/Wb) was decreased by 0.107 (3.3 %), the position of the stress pole was shifted medially by 27.59° (63.5 %), and peak contact hip stress normalised to body weight (Pmax/Wb) was decreased by 2249.74 (55.9 %). Waddling gait was reduced from 17 (23.9 %) to four cases (5.6 %). All changes were statistically highly significant (p<0.01).

CONCLUSIONS

The effect of Tonnis triple pelvic osteotomy lies in the improvement of stress distribution across the acetabular cartilage of the hip joint, thus slowing down the degenerative damage of the hip joint.

Periacetabular osteotomy for hip preservation

The Bernese PAO has now been performed for nearly 30 years. In that time, it has proved itself a technically complex procedure with the potential to considerably improve the natural history of the dysplastic hip. Significant refinements in the surgical technique combined with the recognition of FAI, improvements in the understanding of hip biomechanics and acetabular orientation, and more discerning patient selection have improved the outcomes related to this procedure. Although the recovery can be demanding and the potential for complications exists, the results are reproducible and the technique has become the gold standard for acetabular reorientation.

MR imaging of early hip joint degeneration

MR imaging is one of the most commonly used imaging techniques to evaluate patients with hip pain. Intra-articular abnormalities of the hip joint are better assessed with recent advances in MR imaging technology, such as high-field strength scanners, improved coils, and more signal-to-noise ratio-efficient sequences. This article discusses the causes of early hip joint degeneration and the current use of morphologic and physiologic MR imaging techniques for evaluating the articular cartilage of the hip joint. The article also discusses the role of MR arthrography in clinical cartilage imaging.