Christopher L. Peters

Treatment of femoro-acetabular impingement with surgical dislocation and débridement in young adults.

BACKGROUND Femoro-acetabular impingement has been associated with acetabular labral and/or articular cartilage damage that may ultimately result in osteoarthritis of the hip. Surgical treatment of femoro-acetabular impingement is directed at restoring a more normal femoral head-neck offset to alleviate femoral abutment against the acetabular rim and treating associated labral and articular cartilage damage. METHODS Thirty hips with femoro-acetabular impingement (in twenty-nine patients) underwent débridement through a greater trochanteric flip osteotomy and anterior dislocation of the femoral head. There were sixteen male patients and thirteen female patients with a mean age of thirty-one years. Cam (femoral based) impingement was noted in fourteen hips; pincer (acetabular based) impingement, in one hip; and combined cam and pincer impingement, in fifteen hips. The mean duration of clinical and radiographic follow-up was thirty-two months. All patients were followed according to a prospective protocol, with Harris hip scores and plain radiographs obtained preoperatively and at six months, one year, and annually for a minimum of two years. RESULTS The mean Harris hip score improved from 70 points preoperatively to 87 points at the time of final follow-up (p < 0.0001). Osteonecrosis did not develop in any hip, and there were no trochanteric nonunions. In eighteen hips, severe damage of the acetabular articular cartilage that had not been appreciated on preoperative plain radiographs or magnetic resonance arthrography was noted on arthrotomy. Eight of these eighteen hips subsequently had radiographic evidence of progression of the osteoarthritis, and four of the eight hips required or were expected to soon require conversion to a total hip arthroplasty to treat progressive pain. CONCLUSIONS At the time of early follow-up, we found that surgical dislocation and débridement of the hip for the treatment of femoro-acetabular impingement in hips without substantial damage to the articular cartilage can reduce pain and improve function. This procedure has a low rate of complications. Radiographic signs of progression of osteoarthritis and clinical failure requiring conversion to a total hip arthroplasty were seen only in patients with severe damage to the acetabular articular cartilage, a finding that emphasizes the need for better imaging methods to assess the extent of damage to the acetabular articular cartilage in patients with this disorder.

Subject-Specific Finite Element Model of the Pelvis: Development, Validation and Sensitivity Studies

A better understanding of the three-dimensional mechanics of the pelvis, at the patient-specific level, may lead to improved treatment modalities. Although finite element (FE) models of the pelvis have been developed, validation by direct comparison with subject-specific strains has not been performed, and previous models used simplifying assumptions regarding geometry and material properties. The objectives of this study were to develop and validate a realistic FE model of the pelvis using subject-specific estimates of bone geometry, location-dependent cortical thickness and trabecular bone elastic modulus, and to assess the sensitivity of FE strain predictions to assumptions regarding cortical bone thickness as well as bone and cartilage material properties. A FE model of a cadaveric pelvis was created using subject-specific computed tomography image data. Acetabular loading was applied to the same pelvis using a prosthetic femoral stem in a fashion that could be easily duplicated in the computational model. Cortical bone strains were monitored with rosette strain gauges in ten locations on the left hemipelvis. FE strain predictions were compared directly with experimental results for validation. Overall, baseline FE predictions were strongly correlated with experimental results (r2=0.824), with a best-fit line that was not statistically different than the line y=x (experimental strains = FE predicted strains). Changes to cortical bone thickness and elastic modulus had the largest effect on cortical bone strains. The FE model was less sensitive to changes in all other parameters. The methods developed and validated in this study will be useful for creating and analyzing patient-specific FE models to better understand the biomechanics of the pelvis.

Acetabular Cartilage Delamination in Femoroacetabular Impingement: Risk Factors and Magnetic Resonance Imaging Diagnosis

BACKGROUND Delamination of acetabular articular cartilage is a common abnormality in hips with femoroacetabular impingement. The purpose of the present study was to identify clinical and radiographic factors predisposing to delamination and to assess the diagnostic accuracy of magnetic resonance arthrography for the detection of these lesions. METHODS Following a retrospective review of records, we determined that acetabular cartilage delamination had been present in twenty-eight of sixty-four hips that had undergone a surgical dislocation procedure for the treatment of femoroacetabular impingement. Multivariable logistic regression was performed to assess the correlation of radiographic findings (i.e., magnetic resonance imaging and computerized tomography findings) with the status of delamination. The preoperative interpretations of the magnetic resonance arthrograms for twenty-seven hips that underwent surgical dislocation were reviewed to assess the accuracy of detecting delamination. At the time of surgery, nine of these twenty-seven hips were found to have delamination. Magnetic resonance arthrography interpretations that did not correlate with operative findings were subjected to conspicuity assessment and error analysis. RESULTS The rate of delamination of the acetabular cartilage as noted at the time of surgical dislocation was 44% (twenty-eight of sixty-four). Delamination was strongly associated with male sex and femoral sided signs of impingement; however, it was not associated with acetabular overcoverage (center-edge angle, >40 degrees) (odds ratio = 0.16; p < 0.05). While there was no significant difference in the prevalence of labral lesions between groups, whenever labral and delamination lesions were found in the same hip, they were directly adjacent to one another. Preoperative magnetic resonance arthrography had a low sensitivity for delamination (22%) but had a high specificity (100%). Two-thirds of the delamination lesions were visible on retrospective review of these images when the reader was unblinded to the surgical findings. Delamination could most often be identified on the sagittal T1-weighted image and on the proton-density sequences with fat saturation. DISCUSSION There should be a high level of suspicion for articular cartilage delamination in men and in patients with primarily cam-type femoroacetabular impingement. Acetabular overcoverage may be protective against delamination. Preoperative high-quality magnetic resonance arthrograms should be carefully analyzed for evidence of delamination in this patient population.

Validation of finite element predictions of cartilage contact pressure in the human hip joint.

Methods to predict contact stresses in the hip can provide an improved understanding of load distribution in the normal and pathologic joint. The objectives of this study were to develop and validate a three-dimensional finite element (FE) model for predicting cartilage contact stresses in the human hip using subject-specific geometry from computed tomography image data, and to assess the sensitivity of model predictions to boundary conditions, cartilage geometry, and cartilage material properties. Loads based on in vivo data were applied to a cadaveric hip joint to simulate walking, descending stairs, and stair-climbing. Contact pressures and areas were measured using pressure sensitive film. CT image data were segmented and discretized into FE meshes of bone and cartilage. FE boundary and loading conditions mimicked the experimental testing. Fair to good qualitative correspondence was obtained between FE predictions and experimental measurements for simulated walking and descending stairs, while excellent agreement was obtained for stair-climbing. Experimental peak pressures, average pressures, and contact areas were 10.0 MPa (limit of film detection), 4.4-5.0 MPa, and 321.9-425.1 mm(2), respectively, while FE-predicted peak pressures, average pressures, and contact areas were 10.8-12.7 MPa, 5.1-6.2 MPa, and 304.2-366.1 mm(2), respectively. Misalignment errors, determined as the difference in root mean squared error before and after alignment of FE results, were less than 10%. Magnitude errors, determined as the residual error following alignment, were approximately 30% but decreased to 10-15% when the regions of highest pressure were compared. Alterations to the cartilage shear modulus, bulk modulus, or thickness resulted in +/-25% change in peak pressures, while changes in average pressures and contact areas were minor (+/-10%). When the pelvis and proximal femur were represented as rigid, there were large changes, but the effect depended on the particular loading scenario. Overall, the subject-specific FE predictions compared favorably with pressure film measurements and were in good agreement with published experimental data. The validated modeling framework provides a foundation for development of patient-specific FE models to investigate the mechanics of normal and pathological hips.

Arthroscopy for Labral Tears in Patients with Developmental Dysplasia of the Hip: A Cautionary Note

Patients with developmental dysplasia of the hip may present with acetabular rim overloading, labral hypertrophy, and tear. Our hypothesis was that isolated arthroscopic treatment of labral tear is likely to fail in most patients. We investigated 34 patients who underwent at least one arthroscopy of the hip for labral tear. Developmental hip dysplasia or other morphologic abnormalities of the hip were confirmed in all patients. Arthroscopy failed to relieve pain in 24 patients. We observed accelerated arthritis in 14 patients and migration of the femoral head in 13 patients. Sixteen patients underwent further surgery (further surgeries included periacetabular osteotomy [6 patients], femoroacetabular osteoplasty [7 patients], and total hip arthroplasty [3 patients]). At the latest follow-up, all patients but one were pain-free. Patients with evidence of abnormal hip morphologies may not benefit from hip arthroscopy and isolated treatment of the labrum; in fact, the latter may accelerate the process of arthritis in some patients.

Early Results of the Bernese Periacetabular Osteotomy: The Learning Curve at an Academic Medical Center

BACKGROUND Most reports on the results of the Bernese periacetabular osteotomy for the treatment of developmental dysplasia of the hip have been by the originators of the procedure. In 1997, we began to use this osteotomy without direct training from the originators of the procedure. METHODS Seventy-three patients (eighty-three hips) underwent a Bernese periacetabular osteotomy between 1997 and 2003 and were followed prospectively with use of the Harris hip score to assess clinical results and with use of anteroposterior pelvic and false-profile lateral plain radiographs to assess radiographic results. The three-dimensional position of the acetabulum was recorded preoperatively and postoperatively. The mean duration of follow-up was forty-six months. RESULTS The average Harris hip score improved from 54 to 87 points (p < 0.001). Three hips (three patients) had a conversion to total hip arthroplasty at two, three, and four years after the periacetabular osteotomy. Preoperatively, fifty-four of the eighty-three acetabula were anteverted, and twenty-nine were either retroverted or had neutral wall relationships. Postoperatively, sixty-five hips (78%) were anteverted. Radiographically, in preoperatively anteverted hips, the average center-edge angle improved from 3 degrees to 29 degrees (p < 0.0001), the average anterior center-edge angle improved from 5 degrees to 31 degrees (p < 0.0001), and the acetabular index improved from 25 degrees to 5 degrees (p < 0.0001). In preoperatively retroverted or neutral hips, the average center-edge angle improved from 13 degrees to 33 degrees (p < 0.0001), the average anterior center-edge angle improved from 15 degrees to 36 degrees (p < 0.0001), and the acetabular index improved from 19 degrees to 2 degrees (p < 0.0001). Complications included four hematomas, three transient femoral nerve palsies, two deep wound infections, and one transient sciatic nerve palsy. Nine of the ten major complications and all four of the failed osteotomies occurred in the first thirty hips in which the index procedure was performed. CONCLUSIONS In our experience, the early results of the Bernese periacetabular osteotomy have been encouraging, with a 92% survival rate at thirty-six months. The occurrence of complications demonstrates a substantial learning curve. Recognition of the true preoperative acetabular version and reorientation of the acetabulum into an appropriately anteverted position have become important factors in surgical decision-making. LEVEL OF EVIDENCE Therapeutic Level IV.

Radiographic prevalence of femoroacetabular impingement in collegiate football players: AAOS Exhibit Selection.

BACKGROUND The prevalence of femoroacetabular impingement may be greater in athletes than in the general population because of increased loading of the hip during sports. This study evaluated the radiographs of collegiate football players in order to quantify the prevalence of femoroacetabular impingement in asymptomatic athletes. METHODS Sixty-seven male collegiate football players (age, 21 ± 1.9 years) participated in this prospective study. Both hips (n = 134) were evaluated independently by two orthopaedic surgeons for radiographic signs of femoroacetabular impingement. The alpha angle and femoral head-neck offset were measured on frog-leg lateral radiographs. The lateral center-edge angle, acetabular index, crossover sign, and alpha angle were measured on anteroposterior radiographs. Data for continuous variables were averaged between observers prior to assessing prevalence. Cam femoroacetabular impingement was considered to be present if the femoral head-neck offset was <8 mm and/or the alpha angle was >50° on either radiograph. Pincer femoroacetabular impingement was considered to be present if the lateral center-edge angle was >40°, the acetabular index was <0°, and/or a positive crossover sign was detected by both observers. RESULTS Ninety-five percent of the 134 hips had at least one sign of cam or pincer impingement, and 77% had more than one sign. Twenty-one percent had only one sign of cam femoroacetabular impingement and 57% had both signs. Fifty-two percent had only one sign of pincer femoroacetabular impingement, 10% had two, and 4% had all three signs. Specifically, 72% had an abnormal alpha angle, 64% had a decreased femoral head-neck offset, 61% had a positive crossover sign, 16% had a decreased acetabular index, and 7% had an increased lateral center-edge angle. Fifty percent of all hips had at least one sign of pincer femoroacetabular impingement and at least one sign of cam impingement. Interobserver and intraobserver repeatability was moderate or better for each measure (range, 0.59 to 0.85). CONCLUSIONS Morphologic abnormalities associated with cam and pincer femoroacetabular impingement were common in these collegiate football players. The prevalence of cam and pincer femoroacetabular impingement was substantially higher than the previously reported prevalence in the general population.

Total Knee Arthroplasty: Muscle Impairments, Functional Limitations, and Recommended Rehabilitation Approaches

UNLABELLED The number of total knee arthroplasty (TKA) surgeries performed each year is predicted to steadily increase. Following TKA surgery, self-reported pain and function improve, though individuals are often plagued with quadriceps muscle impairments and functional limitations. Postoperative rehabilitation approaches either are not incorporated or incompletely address the muscular and functional deficits that persist following surgery. While the reason for quadriceps weakness is not well understood in this patient population, it has been suggested that a combination of muscle atrophy and neuromuscular activation deficits contribute to residual strength impairments. Failure to adequately address the chronic muscle impairments has the potential to limit the long-term functional gains that may be possible following TKA. Postoperative rehabilitation addressing quadriceps strength should mitigate these impairments and ultimately result in improved functional outcomes. The purpose of this paper is to describe these quadriceps muscle impairments and discuss how these impairments can contribute to the related functional limitations following TKA. We will also describe the current concepts in TKA rehabilitation and provide recommendations and clinical guidelines based on the current available evidence. LEVEL OF EVIDENCE Therapy, level 5.

Acetabular revision with the Burch-Schnieder antiprotrusio cage and cancellous allograft bone

A retrospective review of 25 patients who underwent 28 acetabular revisions with the Burch-Schnieder antiprotrusio cage (Protek, Berne, Switzerland) and cancellous allograft bone was performed. Follow-up periods averaged 33 months. Patients had averaged 2.1 prior operations per hip. Twenty-two hips had American Academy of Orthopaedic Surgeons type III (combined segmental and cavitary bone loss) acetabular deficiency. Five hips had type II (cavitary bone loss) and one hip had type I (segmental bone loss) acetabular deficiency. After surgery, 80% of the patients had mild or no pain and 80% functioned as at least a community ambulator. Radiographic analysis included a detailed study of implant migration and the degree to which the hip center and bone stock were restored. Significant component migration was documented in 14% of the acetabular reconstructions. The hip center was improved from a preoperative side-to-side difference of 12.5 mm to 4.9 mm at final evaluation (P = .01). Average medial wall bone stock was improved from 1.9 mm before surgery to 10.1 mm postrevision (P < .01). No patients required revision of the antiprotrusio cage for problems related to the acetabular reconstruction. For failed acetabular components associated with moderate to massive bone loss, the antiprotrusio cage reliably reconstituted the hip joint center and acetabular bone stock. The short-term incidence of mechanical loosening parallels that of previously reported acetabular reconstruction techniques.

The Bone-Implant Interface of Femoral Stems with Non-Circumferential Porous Coating. A Study of Specimens Retrieved at Autopsy*

A histological study was performed of the bone-implant interface of fifteen titanium-alloy femoral stems with porous coating limited to three proximal areas that did not cover the full circumference of the device. The specimens were obtained at autopsy from ten cadavera at a mean of forty-six months (range, one to eighty-nine months) after the implant had been inserted without acrylic cement. The volume fraction of bone within the porous spaces (the percentage of the porous space that was filled with bone) and the extent of bone ingrowth (the percentage of the porous-coated surface covered with ingrown bone that was more than one-half fiber-diameter deep, as measured from the outer surface of the porous coating), were determined with histomorphometric methods. Eleven of the fifteen stems had bone within the porous coating that was in continuity with the surrounding medullary bone. The mean volume fraction of bone ingrowth in these specimens was 26.9 per cent (range, 12.2 to 61.0 per cent), and the mean extent of bone ingrowth was 64.3 per cent (range, 28.6 to 95.2 per cent). Both of these parameters increased with time. In the other four stems, the bone lacked continuity with the surrounding trabecular bed. Two of these stems had a limited amount of bone within the porous coating, and two stems (from one patient) had no bone ingrowth. Periprosthetic membranes surrounded by a shell of trabecular bone covered the uncoated surfaces of the stems. The membranes of implants that had been in situ for eight months or more demonstrated polyethylene wear debris, and other particles generated at the level of the joint, within histiocytes throughout the length of the femoral stem. CLINICAL RELEVANCE: The findings in this study are relevant to the utilization and mechanisms of failure of femoral stems inserted without cement. Bone ingrowth and the resulting stability of the implant can be achieved with porous-coated stems. However, the extent of the surface that is porous-coated must be sufficient to prevent trabecular fracture as a secondary mechanism of loosening. Interruptions in the circumferential extent of the porous surface are associated with the formation of periprosthetic membranes, which provide a pathway for migration of particulate wear and corrosion products to the distal part of the stem. A circumferential coating may retard the access of particles and thus decrease the possibility of diaphyseal osteolysis.