Acetabular Side Research Articles

Acetabular retroversion in post slipped capital femoral epiphysis deformity

While the femoral deformity in post slipped capital femoral epiphysis (SCFE) hips has been implicated in the development of femoral acetabular impingement, little has been studied about the acetabular side. The purpose of our study was to determine the frequency of morphologic changes suggestive of acetabular retroversion in patients who have sustained a SCFE. IRB approval was obtained and the records of patients from 1975 to 2010 were searched for ICD-9 codes for SCFE. A total of 188 patients were identified for the study. Two observers evaluated AP radiographs for evidence of acetabular retroversion as characterized by the presence of either an ischial spine sign or a crossover sign. Demographic data, date of onset, and treatment were recorded. For analysis, the right hip was used in patients with bilateral involvement. Of the 188 patients identified, 5 patients had an incorrect diagnosis and 41 patients had missing or inadequate films, leaving 142 patients (284 hips) for review. 57 patients (114 hips) had bilateral SCFE and 85 patients had unilateral SCFE. 79% (n=45) of the right hips with bilateral SCFE and 82% (n=70) of the unilateral involved hips had at least one sign of retroversion. Uninvolved hips had at least one sign of retroversion 76% (n=65) of the time. When compared to previously published values for normal patients, patients with SCFE appear to have an increased incidence of acetabular retroversion.

Orthopedic perspectives on femoroacetabular impingement

Femoroacetabular impingement (FAI) is a cause of hip pain in which there is abnormal and repetitive contact between the proximal femur and the acetabulum. FAI can occur as a primary condition in children with distinct anatomical abnormalities or can occur as a secondary process in cases of developmental hip conditions or trauma. There are two main categories of FAI, cam and pincer, which are distinguished based on whether the anatomical abnormality is on the femoral side or the acetabular side of the hip joint, respectively. Good outcomes have been achieved with early surgical intervention, but once advanced degenerative changes have occurred the chances for a successful surgical outcome are severely diminished. The orthopedic surgeon's ability to appropriately treat FAI depends on an accurate understanding of the etiology and features of each child. The ability to make an early, accurate diagnosis is enhanced with the use of imaging modalities such as radiographs, MRI and CT. This review will focus on orthopedic perspectives in the use of these imaging modalities in defining the anatomical features of and guiding treatment for FAI.

Charnley-Kerboull total hip arthroplasty combining zirconia on polyethylene. A minimum eight-year follow-up prospective study

Zirconia was introduced in the 1980s for total hip arthroplasty (THA) with the expectation of lower polyethylene wear. The purpose of this prospective study was to evaluate the results of a continuous series of total hip arthroplasties combining a zirconia head with polyethylene socket at a minimum eight-year follow-up. We performed an open prospective clinical trial in 1997. Our study involved 51 consecutive patients (55 hips) with a mean age of 52.5 ± 12 years (range, 25-76 years). All patients had a Charnley-Kerboull all-cemented hip replacement. A 22-mm stabilised yttrium tetragonal polycrystalline zirconia head (Y-TZP) was used in association with moderately cross-linked and annealed polyethylene. Clinical and radiological outcomes were assessed yearly. A survival analysis was performed using revision for any reason as the end-point. At a minimum eight-year follow-up, 12 patients (13 hips) were lost to follow-up (mean 26.8 months), two patients (two hips) had died, and six patients (six hips) were revised. The remaining 31 patients (34 hips) were alive and had not been revised on either the femoral or acetabular side at a mean follow-up of 117.1 months (range, 96-150 months). Mean functional score at last follow-up was 17.7. Mean linear head penetration was 0.23 mm/year. More than 90% of the remaining hips had signs of periprosthetic osteolysis. Five stems were loosened. The survival at eight years was 87.3% (95% IC: 76.7-97.8). This study confirms earlier short-terms results, and demonstrates that zirconia should no longer be used in THA.

Leg-Length Discrepancy After Revision Hip Arthroplasty: Are Modular Stems Superior?

We retrospectively reviewed data for 79 consecutive patients who underwent revision hip arthroplasty using cementless femoral stems at our center between September 2008 and November 2010. Two cohorts were included, one using MP (modular) femoral stems and the other using Wagner (monoblock) femoral stems. We assessed leg-length discrepancy (LLD) before and after revision and compared the occurrence of leg-length inequality between the 2 cohorts. We found that the incidence of LLD was high in revision hip arthroplasty and that leg shortening was more common than lengthening. Both acetabular and femoral sides contributed to postoperative LLD. Appropriate placement of the femoral components was most critical in adjusting LLD. We also found that compared with monoblock stems, modular stems made adjustment of postoperative leg length easier.

Revision total hip replacement using the cement-in-cement technique for the acetabular component

The technique of femoral cement-in-cement revision is well established, but there are no previous series reporting its use on the acetabular side at the time of revision total hip replacement. We describe the technique and report the outcome of 60 consecutive acetabular cement-in-cement revisions in 59 patients at a mean follow-up of 8.5 years (5 to 12). All had a radiologically and clinically well-fixed acetabular cement mantle at the time of revision. During the follow-up 29 patients died, but no hips were lost to follow-up. The two most common indications for acetabular revision were recurrent dislocation (46, 77%) and to complement femoral revision (12, 20%). Of the 60 hips, there were two cases of aseptic loosening of the acetabular component (3.3%) requiring re-revision. No other hip was clinically or radiologically loose (96.7%) at the latest follow-up. One hip was re-revised for infection, four for recurrent dislocation and one for disarticulation of a constrained component. At five years the Kaplan-Meier survival rate was 100% for aseptic loosening and 92.2% (95% CI 84.8 to 99.6), with revision for any cause as the endpoint. These results support the use of cement-in-cement revision on the acetabular side in appropriate cases. Theoretical advantages include preservation of bone stock, reduced operating time, reduced risk of complications and durable fixation.

In vivo implant fixation of carbon fiber‐reinforced PEEK hip prostheses in an ovine model

Carbon fiber-reinforced polyetheretherketone (CFR/PEEK) is theoretically suitable as a material for use in hip prostheses, offering excellent biocompatibility, mechanical properties, and the absence of metal ions. To evaluate in vivo fixation methods of CFR/PEEK hip prostheses in bone, we examined radiographic and histological results for cementless or cemented CFR/PEEK hip prostheses in an ovine model with implantation up to 52 weeks. CFR/PEEK cups and stems with rough-textured surfaces plus hydroxyapatite (HA) coatings for cementless fixation and CFR/PEEK cups and stems without HA coating for cement fixation were manufactured based on ovine computed tomography (CT) data. Unilateral total hip arthroplasty was performed using cementless or cemented CFR/PEEK hip prostheses. Five cementless cups and stems and six cemented cups and stems were evaluated. On the femoral side, all cementless stems demonstrated bony ongrowth fixation and all cemented stems demonstrated stable fixation without any gaps at both the bone-cement and cement-stem interfaces. All cementless cases and four of the six cemented cases showed minimal stress shielding. On the acetabular side, two of the five cementless cups demonstrated bony ongrowth fixation. Our results suggest that both cementless and cemented CFR/PEEK stems work well for fixation. Cup fixation may be difficult for both cementless and cemented types in this ovine model, but bone ongrowth fixation on the cup was first seen in two cementless cases. Cementless fixation can be achieved using HA-coated CFR/PEEK implants, even under load-bearing conditions.

Papers Presented at the Annual Meetings of The Hip Society 2012: Editorial Comment

This symposium is composed of selected papers delivered at the Fall 2011 Closed Meeting of The Hip Society in New Albany, OH, USA, and the Open Scientific Meeting of The Hip Society on Specialty Day at the 2012 Annual Meeting of the American Academy of Orthopaedic Surgeons in San Francisco, CA, USA. These meetings focused on current basic and clinical research related to novel biomaterials and alternative bearing surfaces, outcome studies on different surgical techniques and prosthesis designs for primary and revision hip arthroplasty, patient characteristics that may influence clinical outcome, and hip-preserving procedures. Metal-on-metal (MOM) hip articulations continue to undergo close scrutiny. Indeed, a recent FDA panel meeting was held to discuss pertinent scientific and clinical aspects related to this articulation. The present Hip Society symposium highlights several important studies that address topics such as the interpretation of metal ion levels after MOM hip arthroplasty and outcome studies on MOM total and resurfacing hip arthroplasty. Whereas some MOM bearings appear to be functioning quite well, others have been withdrawn from the market. Ongoing clinical surveillance, including periodic analysis of metal ion levels and imaging studies using advanced metal suppression techniques, will shed more light on the future of this bearing couple. Acetabular components containing crosslinked polyethylene (XLPE) continue to perform well in the intermediate term. Coupled with a metal or ceramic femoral head, XLPE now is the material of choice for the acetabular side. Larger femoral heads are being used with XLPE to obtain a more stable articulation, decreasing the dislocation rate substantially. Furthermore, patient activity appears to decrease with age, thus giving the possibility of increased longevity of currently implanted XLPE liners. However, overly thin polyethylene liners and suboptimal cup position are still discouraged because of the possibility of fracture of the plastic. Which patient characteristics increase the complication rate after THA? Recent evidence implicates smoking and excessive alcohol use as potential risk factors for early failure. Dislocation is also increased in patients with neurologic disorders and in complex revision cases. So-called minimally invasive surgical approaches have also garnered much recent attention. However, it appears no one surgical approach leads to a better outcome in experienced hands. Revision surgery on the femoral side often presents great challenges due to deficient bone stock and soft tissue compromise. Recent intermediate-term studies have shown modular tapered stems can have a satisfactory outcome in these difficult situations. Longer-term studies are needed to compare clinical outcomes with monoblock revision stems. This symposium highlights some of the important basic and clinical research reported by members of The Hip Society and serves an educational purpose for surgeons undertaking surgical procedures of the hip. The studies reported in this symposium have all undergone rigorous peer review. The Hip Society is pleased to present this information to help improve patient outcomes and stimulate ongoing research in this area. Fig. 1 Stuart B. Goodman MD, PhD is shown.

Do Revised Hip Resurfacing Arthroplasties Lead to Outcomes Comparable to Those of Primary and Revised Total Hip Arthroplasties?

A theoretical clinical advantage of hip resurfacing (HR) is the preservation of femoral bone. HR femoral component revision reportedly yields postoperative function comparable to that of primary THA. However, few studies have looked at the outcome of both HR femoral and acetabular side revisions. We determined whether (1) patients undergoing HR revision to THA have perioperative measures and outcome scores comparable to those of patients undergoing primary THA or revision of primary THA and (2) patients undergoing HR revision of both components have perioperative measures and outcome scores comparable to those of patients undergoing HR revision of the femoral component only. We retrospectively reviewed and compared 22 patients undergoing revision HR to a THA to a matched (age, sex, BMI) group of 23 patients undergoing primary THA and 12 patients undergoing primary THA revision. Patients completed the WOMAC and SF-12 questionnaires before surgery and at latest followup (range, 24-84 months for HR revision, 28-48 months for primary THA, and 24-48 months for revision THA). Blood loss, days in hospital, complications, and outcome scores were compared among groups. We observed no differences in SF-12 scores but observed lower WOMAC stiffness, function, and total scores in the HR revision group than in the primary THA group. Patients undergoing HR revision of both components had comparable SF-12 and WOMAC stiffness, function, and total scores but overall lower WOMAC pain scores compared to patients undergoing HR revision of the femoral side only. The HR revision group had greater intraoperative blood loss compared to the primary THA group but not the revision THA group. The perioperative measures and outcome scores of HR revision are comparable to those of revision THA but not primary THA. Longer followup is required to determine whether these differences persist. Patients undergoing HR revision of one or both components can expect comparable stiffness and function. Level IV, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Changes in bone mineral density of the acetabulum, femoral neck and femoral shaft, after hip resurfacing and total hip replacement

It is accepted that resurfacing hip replacement preserves the bone mineral density (BMD) of the femur better than total hip replacement (THR). However, no studies have investigated any possible difference on the acetabular side. Between April 2007 and March 2009, 39 patients were randomised into two groups to receive either a resurfacing or a THR and were followed for two years. One patient's resurfacing subsequently failed, leaving 19 patients in each group. Resurfaced replacements maintained proximal femoral BMD and, compared with THR, had an increased bone mineral density in Gruen zones 2, 3, 6, and particularly zone 7, with a gain of 7.5% (95% confidence interval (CI) 2.6 to 12.5) compared with a loss of 14.6% (95% CI 7.6 to 21.6). Resurfacing replacements maintained the BMD of the medial femoral neck and increased that in the lateral zones between 12.8% (95% CI 4.3 to 21.4) and 25.9% (95% CI 7.1 to 44.6). On the acetabular side, BMD was similar in every zone at each point in time. The mean BMD of all acetabular regions in the resurfaced group was reduced to 96.2% (95% CI 93.7 to 98.6) and for the total hip replacement group to 97.6% (95% CI 93.7 to 101.5) (p = 0.4863). A mean total loss of 3.7% (95% CI 1.0 to 6.5) and 4.9% (95% CI 0.8 to 9.0) of BMD was found above the acetabular component in W1 and 10.2% (95% CI 0.9 to 19.4) and 9.1% (95% CI 3.8 to 14.4) medial to the implant in W2 for resurfaced replacements and THRs respectively. Resurfacing resulted in a mean loss of BMD of 6.7% (95% CI 0.7 to 12.7) in W3 but the BMD inferior to the acetabular component was maintained in both groups. These results suggest that the ability of a resurfacing hip replacement to preserve BMD only applies to the femoral side.

Evaluation of bipolar hemiarthroplasty for the treatment of steroid-induced osteonecrosis of the femoral head

Bipolar hemiarthroplasty (BHA) for idiopathic osteonecrosis of the femoral head (ONFH) is performed at our institution. The purpose of this study was to evaluate the clinical and radiographic findings after BHA for the treatment of steroid -induced ONFH. Thirty-seven hips in 27 patients were assessed (seven men, 11 hips; 20 women, 26 hips), average patient age at the time of surgery of 42.6 (range 20-83) years, with steroid-induced ONFH treated with BHA between 1995 and 2005. The mean follow-up duration was approximately ten (range five to 15) years. Patients were evaluated according to the Japan Orthopaedic Association (JOA) hip score. Kaplan-Meier survivorship was calculated to examine revision arthroplasty failure rate. Radiographic analysis of loosening included radiolucent lines and osteolysis of the acetabulum or femur. Causes of loosening were analysed using multiple logistic regression. JOA hip score increased from 53 points (preoperative) to 87 points (final follow-up). Survival rates were 96.8 % and 78.6 % at ten and 15 years, respectively. Prosthesis loosening occurred on the acetabular side in five hips (13.5 %). No femoral-component loosening was observed. BHA had poor results in patients with Association Research Circulation Osseous (ARCO) stage IV ONFH and in patients under 40 years of age. BHA, with strict surgical indications, may be a good option for treating ONFH. Based on these results, total hip arthroplasty is recommended for patients with ARCO stage IV ONFH or for patients under 40 years of age.

Finite element analysis of the ovine hip: Development, results and comparison with the human hip

The ovine hip is often used as an experimental research model to simulate the human hip. However, little is known about the contact pressures on the femoral and acetabular cartilage in the ovine hip, and if those are representative for the human hip. A model of the ovine hip, including the pelvis, femur, acetabular cartilage, femoral cartilage and ligamentum transversum, was built using computed tomography and micro-computed tomography. Using the finite element method, the peak forces were analysed during simulated walking. The evaluation revealed that the contact pressure distribution on the femoral cartilage is horseshoe-shaped and reaches a maximum value of approximately 6 MPa. The maximum contact pressure is located on the dorsal acetabular side and is predominantly aligned in the cranial-to-caudal direction. The surface stresses acting on the pelvic bone reach an average value of approximately 2 MPa. The contact pressure distribution, magnitude, and the mean surface stress in the ovine hip are similar to those described in the current literature for the human hip. This suggests that in terms of load distribution, the ovine hip is well suited for the preclinical testing of medical devices designed for the human hip.

High 10-Year Survival Rate with an Anatomic Cementless Stem (SPS)

BackgroundProximal cementless fixation using anatomic stems reportedly increases femoral fit and avoids stress-shielding. However, thigh pain was reported with the early stem designs. Therefore, a new anatomic cementless stem design was based on an average three-dimensional metaphyseal femoral shape. However, it is unclear whether this stem reduces the incidence of thigh pain.Questions/purposesWe asked whether this stem design was associated with a low incidence of thigh pain and provided durable fixation and high function.MethodsOne hundred seventy-one patients (176 THAs) who had the anatomic proximal hydroxyapatite-coated stem implanted were reviewed. Eleven (6%) patients were lost to followup and 34 (20%) died without revision surgery. We used the Harris hip score (HHS) to assess pain and function. We evaluated femoral stem fixation and stability with the score of Engh et al. and also calculated a 10-year survival analysis. We assessed 126 patients (131 hips) at a mean followup of 10 years (range, 8–11 years)ResultsAt last followup, two patients described slight thigh pain that did not limit their physical activities. All stems appeared radiographically stable and one stem was graded nonintegrated but stable. Five patients had revision surgery: one on the femoral side (for posttraumatic fracture) and four on the acetabular side. Considering stem revision for aseptic loosening as the end point, survivorship was 100% (range, 95.4%–99.9%) at 10 years.ConclusionThis anatomic cementless design using only metaphyseal fixation with a wide mediolateral flare, a sagittal curvature, and torsion, allowed durable proximal stem stability and fixation.Level of EvidenceLevel IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Outcomes of Charnley total hip arthroplasty using improved cementing with so-called second- and third-generation techniques

BackgroundTechniques of cemented total hip arthroplasty have developed over time. We present the outcomes of Charnley total hip arthroplasty performed using improved second- and third-generation cementing techniques. MethodsWe reviewed the radiologic results of 91 Charnley total hip arthroplasties performed using second- and third-generation cementing techniques. Second-generation techniques involved making multiple anchor holes, a double-cementing method on the acetabular side and an intramedullary plug, and retrograde filling with a cement gun on the femoral side in 57 hips. Third-generation techniques involved additional vacuum mixing and cement pressurization in 34 hips. ResultsJoint survival rates at 20years when using second-generation techniques were 89% for the socket and 94% for the stem with aseptic loosening as the end point; the survival rates at 10years when using third-generation techniques were 97 and 100%, respectively. According to our radiographic evaluation system for the clear zone at 5years, there was less clear zone in the acetabular side with the third-generation techniques than with second-generation techniques. In the femoral side, there was very little development of the clear zone, but the difference between generations was not significant. ConclusionsSecond- and third-generation cementing techniques showed excellent survivorship. The clear zone scores at 5years indicated that third-generation techniques were effective, especially in the acetabular side, and may produce better long-term results than second-generation techniques.

Ceramic Hip Replacement History

t L i Sir John Charnley, in the early 1960s, began the orthopedic revolution of joint replacement surgery with his lowriction arthroplasty.1 Years earlier, he had been unsuccessful with a similar design, but with an inferior material, Teflon. Although the use of medical-grade polyethylene seemed to provide good midterm results, there were a number of individuals who had some doubt about the durability of this metalon-plastic combination developed by Charnley. McKee was concerned with polyethylene and developed a metal–metal hip replacement in the mid 1960s. Other substitute materials for the polyethylene were sought, and in 1970, the Parisian, Boutin, performed the first ceramic–ceramic total hip replacement.2 The feeling then was the same as the one today; alumina is an excellent bearing material because of its hardness and scratch resistance. This first ceramic hip was performed cementless on the acetabular side, whereas the ceramic ball was cemented to the femoral stem. Although the tribological properties of alumina ceramics for joint replacement were appreciated as early as 1970, there were other practical issues. The material was quite brittle, and fractures could occur, and they did, but infrequently, as the cementing of the ceramic ball to the trunnion of the stem was an adequate way to prevent high levels of stress caused by an imprecise fit of the components. However, the lack of fixation on the acetabular side often led to loosening and pain, although rarely was there significant bone loss due to the lack of inflammatory particles. This early loosening of the socket was addressed in 2 ways: the French camp decided to cement the alumina socket, whereas Mittlemeier, from Germany, created a new system that now used a threaded ceramic cup that was “screwed” into the acetabulum.3 This new system also used a ress-fit femoral component and more precise manufacturng of the ceramic ball and the metal trunnion of the femoral omponent. This manufacturing improvement led to the limination of cement as a fixation material required for the ating of the ball to the stem. Although both camps enjoyed

Trochanteric Slide for Revision Total Hip Arthroplasty: Opening the Barn Door

A trochanteric osteotomy offers extensile exposure of the hip on both the acetabular and femoral sides. The classical trochanteric osteotomy, which is transverse and involved a release of the vastus lateralis muscles, is complicated by a significant incidence of trochanteric nonunion, and more importantly, trochanteric migration. The trochanteric slide was designed to avoid trochanteric migration by keeping the trochanteric fragment in continuity with the abductors and the vastus lateralis. This exposure provides an extensile exposure of the pelvis and femur. If femoral component removal is anticipated to be difficult, then we use exactly the same approach but we extend the trochanteric fragment down as in an extended trochanteric osteotomy. The purpose of this study was to evaluate our clinical and radiographic results of the modified trochanteric slide osteotomy exposure.

Femoral Neck Fracture After Arthroscopic Management of Femoroacetabular Impingement

Ganz and colleagues recently identified femoroacetabular impingement as the predominant cause of labral tears in nondysplastic hips1. Structural abnormalities of the hip can limit motion and result in repetitive impact of the proximal part of the femoral neck against the acetabular labrum and adjacent cartilage. Osseous impingement as a result of a decrease in femoral head-neck offset or an aspherical femoral head is termed cam impingement. On the acetabular side, pincer impingement results from various degrees of overgrowth of the osseous acetabulum and excessive acetabular retroversion2. Pincer impingement can be subdivided into coxa profunda or protrusio, anterosuperior overcoverage, and true acetabular retroversion. Regardless of whether arthroscopic or open techniques are employed, the goal of surgical treatment of femoroacetabular impingement is a complete decompression of the impingement from the pathologic osseous anatomy. Recent work with a cadaveric model by Mardones et al. suggested that up to 30% of the diameter of the femoral neck can be resected to restore neck offset without increasing the risk of postoperative fracture3. We present a case of a nondisplaced, iatrogenic femoral neck fracture sustained after arthroscopic osteoplasty for the treatment of femoroacetabular impingement. This case provides a sentinel reminder to hip surgeons that femoral neck fracture can occur after a modest osteoplasty done for the treatment of cam impingement and warrants consideration of a period of protected weight-bearing postoperatively. The patient was informed that data concerning the case would be submitted for publication, and he consented. A fifty-one-year-old man presented with a three-year history of insidious-onset, increasingly intense anterior right groin pain, exacerbated by standing from a seated position or by playing golf. The patient had completed a trial of nonsteroidal anti-inflammatory medications and physical therapy without relief of symptoms. An intra-articular injection of corticosteroids provided excellent but transient …

Femoroacetabular impingement: a review of diagnosis and management.

Hip pain in adults has traditionally been associated with osteoarthritis in the joint. However, many young patients with hip pain do get referred to orthopaedic surgeons without arthritis. Subtle bony and soft tissues abnormalities can present with hip pain in the active young adult. These abnormalities can lead to premature arthritis. With the improvements in clinical examination for hip impingement, radiological imaging using magnetic resonance arthrography (MRA) and or computed tomograms (CT) Scans, these lesions are being detected early. Though the cause of primary osteoarthritis is unknown, it is suggested that femoro-acetabular impingement (FAI) may be responsible for the progression of the disease in these patients. FAI is a pathological condition leading to abutment between the proximal femur and the acetabular rim. Two different mechanisms are described, although a combination of both is seen in clinical practice. Cam impingement is a result of reduced anterior femoral head neck offset. Pincer lesion is caused by abnormalities on the acetabular side. FAI due to either mechanism can lead to chondral lesions and labral pathology. Patients present with groin pain and investigated with radiographs, CT and MRA. Surgery is the treatment of choice. Open or arthroscopic exploration of the hip is undertaken with bony resection to improve the femoral head neck junction with resection or repair of the damaged labrum. This may involve femoral osteochondroplasty for the cam lesion and acetabular rim resection for pincer lesion. There is no difference in outcome between open and arthroscopic surgery for FAI.

Reply to Letter to the Editor: Cams and Pincer Impingement Are Distinct, Not Mixed: The Acetabular Pathomorphology of Femoroacetabular Impingement

Dr. Beck rightly points out that Figure 1 [3] suggests that a cam-type hip can be diagnosed from an AP radiograph. In the original version of the figure, the CT image in three orthogonal views was included beneath the radiograph, to show that the diagnosis was a three-dimensional one. This original figure is appended (Fig. 1) by way of reassurance that an AP radiograph is not relied on for this diagnosis. Dr. Beck therefore can be assured that cam hips were not misdiagnosed. Fig. 1 Plain radiographs of normal, cam, and pincer-type hips are shown, with CT images of 3d, axial, sagittal and coronal reconstructions below. The green normal hip has alpha and centre-edge angles in the normal range. The red cam hip has a large alpha angle ... If the 3-D method of Beaule et al. [1] is used to describe a cam on the femoral side, I have yet to find a case with an acetabulum that is deeper than normal, thus being able to act as a pincer as described by Ganz et al. [4] in a seminal and widely cited article. Therefore I agree with the conclusion that Dr. Beck draws from the data presented [3]: the acetabulum in pincer hips does appear to be distinctly different from the acetabulum in cam hips. Dr. Beck describes exactly what was observed: there are two separate methods of impingement. However, in a later paper that also is cited widely, Beck et al. stated that the majority of cases are of ‘mixed’ type [2]. Although I agree that most cases have evidence of impingement on the femoral and acetabular sides, I do not agree that the mechanism is ever mixed, and wonder if this important point might have been ‘lost in translation’. I continue to look for the first reported case of coxa profunda with a cam on the femur, or of a cam hip with an acetabulum that is even of average depth. This issue is clinically relevant: the acetabulum of the cam hip is shallow - not deep, therefore “rim trimming” of the acetabular iliac eminence in these hips runs the risk of causing iatrogenic acetabular insufficiency, leading to rapidly progressive hip damage.

A novel technique for impaction bone grafting in acetabular reconstruction of revision total hip arthroplasty using an ex vivo compaction device

BackgroundImpaction bone grafting allows restoration of the acetabular bone stock in revision hip arthroplasty. The success of this technique depends largely on achieving adequate initial stability of the component. To obtain well-compacted, well-graded allograft aggregates, we developed an ex vivo compaction device to apply it in revision total hip arthroplasty on the acetabular side, and characterized mechanical properties and putative osteoconductivity of allograft aggregates. MethodsMorselized allograft bone chips were compacted ex vivo using the creep technique and subsequent impaction technique to form the bone aggregates. Impaction allograft reconstruction of the acetabulum using an ex vivo compaction device was performed on eight hips. The mechanical properties and three-dimensional micro-CT-based structural characteristics of the bone aggregates were investigated. ResultsIn clinical practice, this technique offered good reproducibility in reconstructing the cavity and the segmental defects of the acetabulum, with no migration and no loosening of the component. In vitro analysis showed that the aggregates generated from 25g fresh-frozen bone chips gained compression stiffness of 13.5–15.4MPa under uniaxial consolidation strain. The recoil of the aggregates after compaction was 2.6–3.9%. The compression stiffness and the recoil did not differ significantly from those measured using a variety of proportions of large- and small-sized bone chips. Micro-CT-based structural analysis revealed average pore sizes of 268–299 μm and average throat diameter of pores in the bone aggregates of more than 100 μm. These sizes are desirable for osteoconduction, although large interconnected pores of more than 500 μm were detectable in association with the proportion of large-sized bone chips. Cement penetration into the aggregates was related to the proportion of large-sized bone chips. ConclusionThis study introduces the value of an ex vivo compaction device in bone graft compaction in clinical applications. In vitro analysis provided evidence that compaction of sequential layers of well-compacted, well-graded bone aggregates, i.e., the aggregates comprising smaller sized chips at the host bone side and larger sized chips at the component side, may have the advantages of initial stability of the acetabular component and biological response of the grafted aggregates.

Benefits of thin‐shelled acetabular components for metal‐on‐metal hip resurfacing arthroplasty

The theoretical advantage of using thinner acetabular components in hip resurfacing has not yet been clinically verified. Our purpose was to test the hypothesis of bone conservation and assess the effects of using a thinner acetabular component on hip biomechanics and clinical outcome. We compared the bone conservation, biomechanical results, and functional outcomes between hips in 35 patients who received bilateral metal-on-metal resurfacing arthroplasties with acetabular components of 5 mm thickness on one side and 3.5 mm thickness on the other. Acetabular abduction angle and acetabular anteversion were measured using Ein-Bild-Röentgen-Analysis software. Medial acetabular wall thickness and position of the hip center of rotation were measured using Image J software. The change in position of the hip center of rotation was minimal and did not reach significance. Thin-shelled components showed greater bone conservation on the acetabular side measured by an increase in the medial acetabular wall thickness. Bone conservation on the femoral side was achieved as well with thin shells. Range of motion, pain scores, and complication rates were comparable. No appreciable difference was found in bone-cup radiographic appearance between the two types of components. These data suggest that patients can experience good clinical outcomes for resurfacing with either thin or thick-shelled acetabular components. However, thin-shelled components preserve acetabular bone stock and allow the use of a larger femoral component. The use of thinner acetabular components is an improvement in bone conservation for a hip resurfacing design.