Femoroacetabular impingement (FAI) results from a morphological deformity of the hip and is associated with osteoarthritis (OA). Increased bone mineral density (BMD) is observed in the antero-superior acetabulum rim where impingement occurs. It is hypothesized that the repeated abnormal contact leads to damage of the cartilage layer, but could also cause a bone remodelling response according to Wolff's Law. Thus the goal of this study was to assess the relationship between bone metabolic activity measured by PET and BMD measured in CT scans. Five participants with asymptomatic cam deformity, three patients with uni-lateral symptomatic cam FAI and three healthy controls were scanned in a 3T PET-MRI scanner following injection with [18F]NaF. Bone remodelling activity was quantified with Standard Uptake Values (SUVs). SUVmax was analyzed in the antero-superior acetabular rim, femoral head and head-neck junction. In these same regions, BMD was calculated from CT scans using the calibration phantom included in the scan. The relationship between SUVmax and BMD from corresponding regions was assessed using the coefficient of determination (R. 2. ) from linear regression. High bone activity was seen in the cam deformity and acetabular rim. SUVmax was negatively correlated with BMD in the antero-superior region of the acetabulum (R. 2. =0.30, p=0.08). SUVmax was positively correlated with BMD in the antero-superior head-neck junction of the femur (R. 2. =0.359, p=0.067). Correlations were weak in other regions. Elevated bone turnover was seen in patients with a cam deformity but the relationship to BMD was moderate. This study demonstrates a pathomechanism of hip degeneration associated with FAI deformities, consistent with Wolff's law and the proposed mechanical cause of hip degeneration in FAI. [18F]-NaF PET SUV may be a biomarker of degeneration, especially in early stages of degeneration, when joint preservation surgery is likely to be the most successful

Introduction. Hip resurfacing arthroplasty (HRA) with metal-on-metal bearing is currently emerging as a major evolution of hip arthroplasty. It could be an alternative to total hip arthroplasty. HRA also may allow young patients to perform high sports activities. It preserves proximal femoral bone stock and keeps the medullary canal intact. A large diameter of the femoral head provides wider range of the hip motion. Incidence of dislocation is very low. Most of HRA have been reported for young patients with stage of osteoarthritis. But, reports of HRA for osteonecrosis of the femoral head (ONFH) are rare and the outcomes are uncertain. Methods. This study was performed to introduce our indication and technique of HRA for the patients with ONFH and to assess the outcomes after a minimum 5-year follow up. After the biomechanical study, we set our own indications for HRA as follows: when the size of a lesion was less than 50% of the entire head and the rim at the head-neck junction was intact at least to a 5 mm above from the head-neck junction. From December 1998 to July 2004; 157 hips (139 patients) underwent HRA under the diagnosis of ONFH. Their mean age was 37 years. One hundred and fourteen hips were in men and 25 hips were in women. The average follow-up period was 88 months (range, 60 to 128 months). Clinical outcomes were evaluated with Harris Hip Scores, hip or thigh pain, limb length discrepancy, and range of motion. As a radiological evaluation, the preoperative size and staging of the lesion, patterns of bone remodeling, and complications such as femoral neck fracture, neck narrowing, loosening, and osteolysis were analyzed. Results. Sixty-two percent of the hips were staged as Steinberg IV or more. The size of the necrotic lesion in magnetic resonance imaging ranged from 23 to 50%. The Harris Hip Score increased from 77 points pre-operatively to 98 points at the final visit. All range of motions significantly improved after the operation. No patient complained of limb length discrepancy. Twenty-eight hips showed painless radiographic changes including impingement (22 hips), focal radiolucency (4 hips), and neck narrowing (2 hips). All patients showed no clinical symptoms. There was no detectable wear, dislocation, femoral neck fracture, or other complications. No revision or additional surgery was required in all patients. Conclusion. Even for the patients with ONFH, the overall minimum 5-year outcomes of HRA are promising and superior to other reports of conventional THA. Patient satisfaction is extremely high. A strict application of indications and meticulous surgical technique are critical for these successful results

Biomechanical analysis is important to evaluate the effect of orthopaedic surgeries. CT-image based finite element method (CT-FEM) is one of the most important techniques in the computational biomechanics field. We have been applied CT-FEM to evaluate resorptive bone remodeling, secondary to stress shielding, after total hip arthroplasty (THA). We compared the equivalent stress and strain energy density to postoperative BMD (bone mineral density) change in the femur after THA, and a significant correlation was observed between the rate of changes in BMD after THA and equivalent stress. For periacetabular osteotomy cases, we investigated mechanical stress in the hip joint before and after surgery. Mechanical stress in the hip joint decreased significantly after osteotomy and correlated with the degree of the acetabular coverage. For arthroscopic osteochondroplasty cases, we examined mechanical strength of the proximal femur after cam resection using CT-FEM. The results suggested that both the depth and area of the resection at the distal part of femoral head-neck junction correlated strongly with fracture risk after osteochondroplasty. This talk consists of our results of clinical application studies using CT-FEM, and importance of application of CT-FEM to biomechanical studies to assess the effect of orthopaedic surgeries

Modular femoral stems for total hip arthroplasty (THA) were introduced to allow additional options for surgeons in controlling leg lengths, offset, and implant stability. This option is widely used in Region Emilia Romagna, Italy, where the study was conducted, having a modular neck stem nearly 35% of primary THA in 2013. Great majority of modular neck is made of Titanium alloy. The study was designed as a retrospective descriptive case series of 67 hips in patients who underwent revision of a THA. All had a Titanium modular neck. In 44 cases revision was due to breakage of the neck, in the remaining 23 it was due to different reasons unrelated to modular neck such as bone fracture, breakage of a ceramic component, cup loosening. Mean follow up was 3.5 yrs. For all patients excised capsule and surrounding tissue were graded for presence of necrosis, inflammatory exudate, lymphocytes, and wear particles using light microscopy of routine paraffin sections stained with hematoxylin and eosin. The retrieved modular neck-body and head-neck junctions were examined for evidence of fretting and corrosion. For some patient dosage of circulating Titanium was obtained. Approval was obtained from institutional review board. It resulted that a variable amount of wear was observed in the first group of patients, with no evidence of lymphocytic reaction, but with variable notes of necrosis. Broken necks showed different patterns of damage, with different degree of corrosion, beside the fatigue fracture. In the second group wear was less evident or absent and negativity of lymphocyte reaction was substantially confirmed. Circulating Titanium ions were one order of magnitude higher in first group (mean 35 micrograms /litre). It can be concluded that fracture of Titanium modular necks occurs progressively, wear does not induce lymphocytic reaction and circulating ions increase. Level of Evidence. III retrospective, comparative study. Acknowledgments. The research was funded by Ministry of Health, grant ‘Early diagnosis of pending failure…’RF 20091472961

Osteoarthritis is associated with changes to the matrix composition of subchondral bone. Raman spectroscopy has the potential to detect in vivo the molecular changes in osteoarthritic subchondral bone. The objectives were to determine the levels of mineralisation, carbonate accumulation and bone remodelling in osteoarthritic subchondral bone, which we defined as within 3mm of articular cartilage. This was compared to the proximal-compartment (10mm distal to articular cartilage) and the head-neck junction. Five osteoarthritic (average age: 76 years) and five normal cadaveric femoral heads (average age: 72 years) were scanned using peripheral quantitative computed tomography and then sectioned coronally. Raman spectroscopy was then used to scan the femoral heads. All scans were done in the plane of the longitudinal axis of the diaphysis. Cores were subsequently extracted and sodium dodecyl sulphate polyacrylamide gel electrophoresis performed to determine the levels of homotrimeric collagen. The phosphate-to-amide I ratio, from the Raman spectra, in osteoarthritic subchondral bone was significantly greater than controls (p=0.023). Within osteoarthritic specimens, the phosphate-to-amide I ratio increased proximally. The density in osteoarthritic subchondral bone was 89mg/cm3 higher than controls (p=0.022), and 494mg/cm3 higher than the osteoarthritic proximal-compartment (p<0.001). Moreover, carbonate substitution into the apatite crystals decreased in osteoarthritic specimens. The carbonate-to-amide I ratio was highest in osteoarthritic subchondral bone. Furthermore, the median α1-to-α2-chain ratio in osteoarthritic specimens was 2:1. The changes found in subchondral bone are important in the pathogenesis of osteoarthritis. This study shows that Raman spectroscopy can detect differences between osteoarthritic specimens and controls, further supporting its potential use in diagnosing bone disorders

Femoral neck fractures remain the leading cause of early failure after metal-on-metal hip resurfacing. Although its' exact pathomechanism has yet to be fully elucidated, current retrieval analysis has shown that either an osteonecrotic event and/or significant surgical trauma to the femoral head neck junction are the leading causes. It is most likely that no single factor like patient selection and/or femoral component orientation can fully avoid their occurrence. As in osteonecrosis of the native hip joint, a certain cell injury threshold may have to be reached in order for femoral neck fracture to occur. These insults are not limited to the surgical approach, but also include femoral head preparation, neck notching, and cement penetration. Although some have argued that the posterior approach does not represent an increased risk fracture for ON after hip resurfacing because of the so-called intraosseous blood supply to the femoral head, to date, the current body of literature on femoral head blood flow in the presence of arthritis has confirmed the critical role of the extraosseous blood supply from the ascending branch of the medial circumflex, as well as the lack of any substantial intraosseous blood supply. Conversely, anterior hip dislocation of both the native hip joint as well as the arthritic hip preserves femoral head vascularity. The blood supply can be compromised by either sacrificing the main branch of the ascending medial femoral circumflex artery or damaging the retinacular vessels at the femoral head-neck junction. Thus an approach which preserves head vascularity, while minimizing soft tissue disruption would certainly be favorable for hip resurfacing. This presentation will review the current state of knowledge on vascularity of the femoral head as well as surgical techniques enhancing its preservation

Femoroacetabular impingement (FAI) is the result of abnormal contact/impingement of the femoral head-neck junction and acetabulum during motion. This can be corrected by surgical dislocation (using Ganz's trochanteric osteotomy) and femoral osteochondroplasty +/− acetabular rim resection. Our study aimed to assess the improvement in hip scores following open osteochondroplasty to predict outcomes based on patient characteristics. This was a retrospective case note analysis of a single surgeon case series over a 4 year period. Inclusion criteria were open osteochondroplasty, complete pre- and post-op hip scores available), Tonnis osteoarthritis grade 0 or 1, with 1 year followup. Data was extracted from electronic and paper case notes for pre- and post-op Modified Harris Hip Scores (MHHS), Non-arthritis Hip Scores (NAHS) and SF-12 general satisfaction scores, as well as baseline patient demographics. Two independent observers used the PACS radiology system to examine x-rays and MRI. SPSS version 19 was used for statistical analysis. 42 patients met the inclusion criteria. There was an overall improvement in hip scores after the procedure. Mean pre-op scores were MHHS 52.5, NAHS 44.0, SF-12 32.1. Mean post-op scores were MHHS 66.1, NAHS 58.7, SF-12 36.4. Therefore mean improvements were seen in MHHS (13.6), NAHS (14.7) and SF-12 (4.3), all significant at p<0.005 when paired t-test was used for analysis. Pearson correlation for subgroup analysis showed no significant correlation of scores with age, centre-edge angle or alpha angles. Furthermore, no significant difference was seen between males and females (independent t test). Open osteochondroplasty improves symptoms and function based on patient reported outcome measures. Although the mean scores improved, some patients’ scores deteriorated. We have not identified any statistically significant predictors of outcome, and therefore patient selection remains unclear

Summary. The cartilage layer from cam-type femoroacetabular impingement deformities had lower stiffness and increased permeability compared to normal cartilage. This is consistent with osteoarthritis and supports the hypothesis of abnormal contact stresses. Introduction. Femoroacetabular impingement (FAI) has recently been associated with osteoarthritic (OA) degeneration of the hip and may be responsible for up to 90% of adult idiopathic OA cases. FAI results from deformities in the hip joint which may lead to abnormal contact stresses and degeneration. The more common cam-type deformity consists of a convex anterior femoral head-neck junction which impinges the anterosuperior acetabular rim during flexion and internal rotation of the hip. Increased subchondral bone density has been reported in this region which may be a bone remodelling response to increased contact stress. The abnormal contact is expected to cause degeneration of the cartilage layer. The goal of this study was to assess the mechanical properties of cartilage retrieved from the cam deformity and to compare this with normal articular cartilage from the femoral head. It is hypothesised that the cartilage will have a lower elastic modulus and higher permeability than normal cartilage. Patients & Methods. Osteochondral biopsies were retrieved from nine patients undergoing surgical correction of a symptomatic cam deformity as well as 10 fresh cadaveric specimens (10 hips, 6 donors). An indentation stress relaxation test was performed on each specimen to 10% of the estimated cartilage thickness. A needle penetration test was performed to accurately measure the thickness. The equilibrium modulus was calculated per Hayes et al. A specimen-specific axisymmetric finite element model was used in a non-linear optimization to obtain the fibril-reinforced poroelastic properties of the cartilage that best fit the experimental data. The material properties were non-fibrillar modulus (E. s. ), Poisson's ratio (ν. s. ) and permeability (k) and strain-independent and –dependent moduli (E. 0. , E. ε. )[4]. Results. The equilibrium modulus was 0.14 MPa and 0.63 from surgical and cadaver specimens, respectively (p=0.002). Compared to cadaver specimens, E. s. in surgical specimens was 73% lower (p=0.01), ν. s. was 43% lower (p=0.01) and k was an order of magnitude higher (p=0.02). Fibril moduli were not significantly different (p>0.35). Discussion/Conclusions. This study showed decreased elastic modulus and increased permeability in cartilage from cam deformities compared to cadaver controls. These differences are consistent with changes expected in osteoarthritic cartilage degeneration. Fibril moduli were 14% to 57% lower in surgical specimens consistent with fibrillation, however results were not significant due to high variability. Altered cellular activity and proteoglycan depletion has been reported in cartilage of cam deformities, which are similar to changes expected in osteoarthritis. The altered mechanical and biochemical properties of this cartilage therefore support the hypothesis that osteoarthritis is secondary to cam FAI deformities and is a result of abnormal contact stresses between the deformity and acetabular rim

Objectives

Taper junctions between modular hip arthroplasty femoral heads and stems fail by wear or corrosion which can be caused by relative motion at their interface. Increasing the assembly force can reduce relative motion and corrosion but may also damage surrounding tissues. The purpose of this study was to determine the effects of increasing the impaction energy and the stiffness of the impactor tool on the stability of the taper junction and on the forces transmitted through the patient’s surrounding tissues.

Objectives

The aim of this study was to systematically review the literature on measurement of muscle strength in patients with femoroacetabular impingement (FAI) and other pathologies and to suggest guidelines to standardise protocols for future research in the field.

In spite of extensive accounts describing the blood supply to the femoral head, the prediction of avascular necrosis is elusive. Current opinion emphasises the contributions of the superior retinacular artery but may not explain the clinical outcome in many situations, including intramedullary nailing of the femur and resurfacing of the hip. We considered that significant additional contribution to the vascularity of the femoral head may exist. A total of 14 fresh-frozen hips were dissected and the medial circumflex femoral artery was cannulated in the femoral triangle. On the test side, this vessel was ligated, with the femoral head receiving its blood supply from the inferior vincular artery alone. Gadolinium contrast-enhanced MRI was then performed simultaneously on both control and test specimens. Polyurethane was injected, and gross dissection of the specimens was performed to confirm the extraosseous anatomy and the injection of contrast. The inferior vincular artery was found in every specimen and had a significant contribution to the vascularity of the femoral head. The head was divided into four quadrants: medial (0), superior (1), lateral (2) and inferior (3). In our study specimens the inferior vincular artery contributed a mean of 56% (25% to 90%) of blood flow in quadrant 0, 34% (14% to 80%) of quadrant 1, 37% (18% to 48%) of quadrant 2 and 68% (20% to 98%) in quadrant 3. Extensive intra-osseous anastomoses existed between the superior retinacular arteries, the inferior vincular artery and the subfoveal plexus.

The medial periosteal hinge plays a key role in fractures of the head of the humerus, offering mechanical support during and after reduction and maintaining perfusion of the head by the vessels in the posteromedial periosteum. We have investigated the biomechanical properties of the medial periosteum in fractures of the proximal humerus using a standard model in 20 fresh-frozen cadaver specimens comparable in age, gender and bone mineral density. After creating the fracture, we displaced the humeral head medial or lateral to the shaft with controlled force until complete disruption of the posteromedial periosteum was recorded. As the quality of periosteum might be affected by age and bone quality, the results were correlated with the age and the local bone mineral density of the specimens measured with quantitative CT.

Periosteal rupture started at a mean displacement of 2.96 mm (sd 2.92) with a mean load of 100.9 N (sd 47.1). The mean maximum load of 111.4 N (sd 42.5) was reached at a mean displacement of 4.9 mm (sd 4.2). The periosteum was completely ruptured at a mean displacement of 34.4 mm (sd 11.1). There was no significant difference in the mean distance to complete rupture for medial (mean 35.8 mm (sd 13.8)) or lateral (mean 33.0 mm (sd 8.2)) displacement (p = 0.589).

The mean bone mineral density was 0.111 g/cm³ (sd 0.035). A statistically significant but low correlation between bone mineral density and the maximum load uptake (r = 0.475, p = 0.034) was observed.

This study showed that the posteromedial hinge is a mechanical structure capable of providing support for percutaneous reduction and stabilisation of a fracture by ligamentotaxis. Periosteal rupture started at a mean of about 3 mm and was completed by a mean displacement of just under 35 mm. The microvascular situation of the rupturing periosteum cannot be investigated with the current model.

A cadaver study using six pairs of lower limbs was conducted to investigate the accuracy of computer navigation and standard instrumentation for the placement of the Birmingham Hip Resurfacing femoral component. The aim was to place all the femoral components with a stem-shaft angle of 135°.

The mean stem-shaft angle obtained in the standard instrumentation group was 127.7° (120° to 132°), compared with 133.3° (131° to 139°) in the computer navigation group (p = 0.03). The scatter obtained with computer-assisted navigation was approximately half that found using the conventional jig.

Computer navigation was more accurate and more consistent in its placement of the femoral component than standard instrumentation. We suggest that image-free computer-assisted navigation may have an application in aligning the femoral component during hip resurfacing.

Recently, femoroacetabular impingement has been recognised as a cause of early osteoarthritis. There are two mechanisms of impingement: 1) cam impingement caused by a non-spherical head and 2) pincer impingement caused by excessive acetabular cover. We hypothesised that both mechanisms result in different patterns of articular damage. Of 302 analysed hips only 26 had an isolated cam and 16 an isolated pincer impingement. Cam impingement caused damage to the anterosuperior acetabular cartilage with separation between the labrum and cartilage. During flexion, the cartilage was sheared off the bone by the non-spherical femoral head while the labrum remained untouched. In pincer impingement, the cartilage damage was located circumferentially and included only a narrow strip. During movement the labrum is crushed between the acetabular rim and the femoral neck causing degeneration and ossification.

Both cam and pincer impingement lead to osteoarthritis of the hip. Labral damage indicates ongoing impingement and rarely occurs alone.