Klaus A. Siebenrock

Anterior Femoroacetabular Impingement Part I. Techniques of Joint Preserving Surgery

The exact pathomechanism responsible for osteoarthritis (OA) of the nondysplastic hip has remained unknown for many years. There is, however, emerging clinical evidence implicating femoroacetabular impingement as an etiologic factor for having early OA of the hip develop. Femoroacetabular impingement is an abutment conflict occurring between the proximal femur and the acetabular rim arising from morphologic abnormalities affecting the acetabulum or the proximal femur, or both. The repetitive mechanical conflict occurring during motion, particularly flexion and internal rotation, can lead to lesions of acetabular labrum and, even more serious, the adjacent acetabular cartilage. Surgical treatment of femoroacetabular impingement focuses on improving the clearance for hip motion and alleviation of femoral abutment against the acetabular rim. We will describe the rationale for the treatment of this condition, and discuss the technique of joint-preserving surgery.

Effect of pelvic tilt on acetabular retroversion: a study of pelves from cadavers.

Pelvic inclination is difficult to control on a standard radiograph of the pelvis and has a direct influence on the appearance of acetabular version. By defining the normal range of the distance between the symphysis and the sacrococcygeal joint on 86 standard anteroposterior radiographs of pelves a technique was developed to evaluate pelvic inclination. A statistically significant correlation between this distance and pelvic inclination was shown in four cadaver pelves. Acetabular retroversion signs (cross-over, posterior wall signs) were evaluated on normal pelves from cadavers (two females, two males) after mounting on a holding device and wire marking of the acetabular rims. Radiographs were taken 3° stepwise through the range of 9° inclination to 12° reclination. At the neutral position, two acetabula appeared with both positive retroversion signs compared with none at 6° reclination. At 9° pelvic inclination all acetabula had both signs. Retroversion signs were significantly more pronounced and found at lower pelvic tilt angles in the pelves from males than from females. Evaluation of pelvic inclination will help to decrease measurement errors in assessment of acetabular orientation and femoral head coverage. This will be valuable in preoperative planning of reorientation procedures.

Abnormal extension of the femoral head epiphysis as a cause of cam impingement.

The etiology of an insufficient femoral head-neck offset has not been identified yet. It was investigated whether a decreased head-neck offset might be correlated with an unusual orientation of the physeal capital scar. Therefore, the femoral head-neck offset and the extension of the physeal scar onto the femoral neck were measured with specific magnetic resonance imaging arthrography. The measurements were done in 15 patients with anterior femoroacetabular impingement attributable to a nonspherical head and were compared with 15 age- and gender-matched control subjects. Eight serial magnetic resonance imaging sections perpendicular to the femoral neck axis were used in each hip to measure the head-neck offset and the epiphyseal extension toward the femoral neck at 16 measurement points. In both groups there was an inverse correlation between the amount of head-neck offset and the relative extension of the capital physeal scar in the cranial hemisphere of the head. Within the anterosuperior head quadrant, there was statistically significant different decrease of the head-neck offset and increase of the lateral epiphyseal extension in the patients compared with the control subjects. These findings suggest a growth abnormality of the capital physis as one probable underlying cause for a nonspherical head.

The reproducibility of classification of fractures of the proximal end of the humerus.

The radiographs of ninety-five fractures of the proximal end of the humerus were classified with the Neer and the AO/ASIF systems by five orthopaedic surgeons who had a special interest in problems of the shoulder. Without access to their initial interpretations, the same five orthopaedic surgeons reevaluated the same radiographs eight weeks later. Intraobserver and intraobserver reliability were found to be fair or poor for both classification systems. Kappa values for the interobserver reliability were 0.40 for the Neer system and 0.53 for the AO/ASIF system. When the fractures were subclassified, according to the recommendations of the AO/ASIF, into groups and subgroups, reproducibility became progressively worse. Intraobserver reliability showed kappa values of 0.60 and 0.58, respectively. A so-called extended radiographic trauma series, consisting of three perpendicular radiographs, was available for thirty-five fractures; the third perpendicular projection did not significantly improve the reproducibility values for either classification compared with those obtained with only two perpendicular projections. We concluded that neither the Neer nor the AO/ASIF classification of fractures of the proximal end of the humerus is sufficiently reproducible to allow meaningful comparison of similarly classified fractures in different studies.

Early osteoarthritic changes of human femoral head cartilage subsequent to femoro-acetabular impingement☆

OBJECTIVE To use the surgical samples of patients with femoro-acetabular impingement due to a nonspherical head to analyze tissue morphology and early cartilage changes in a mechanical model of hip osteoarthritis (OA). DESIGN An aberrant nonspherical shape of the femoral head has been assumed to cause an abutment conflict (impingement mechanism) of the hip with subsequent cartilage lesions of the acetabular rim and surface alterations of the nonspherical portion of the head. In this study, 22 samples of the nonspherical portions of the head have been obtained during hip surgery from young adults (mean 30.4 years, range 19-45 years) with an impingement conflict. The samples were first compared with tissue from the same area obtained from six age-matched deceased persons (control group) with normal hip morphology and second with cartilage from 14 older patients with advanced OA. All samples were characterized histologically and hyaline cartilage was graded according to the Mankin criteria. They were further subjected to examination on a molecular basis by immunohistology for cartilage oligomeric matrix protein (COMP), tenascin-C and a collagenase cleavage product (COL2-3/4C(long)) and by in situ hybridization for collagen type I and collagen type II. RESULTS All samples from the patient group revealed hyaline cartilage with degenerative signs. According to the Mankin criteria, the cartilage alterations were significantly different when compared with the control group (p=0.007) but were less distinct when compared with cartilage from patients with advanced OA (p=0.014). Positive staining and distribution pattern for COMP, tenascin-C and COL2-3/4C(long) showed similarities between the samples from the impingement group and osteoarthritic cartilage but they were distinctly different when compared with healthy cartilage. Levels of collagen I and II transcripts were upregulated in 6 and 10, respectively, of the 14 samples with OA and in 9 and 12, respectively, of the 22 samples from the impingement group. None of the samples from the control group showed upregulation of Collagen I and II mRNA. CONCLUSIONS The aberrant nonspherical portion of the femoral head in young patients with an impingement conflict consists of hyaline cartilage which shows clear degenerative signs similar to the findings in osteoarthritic cartilage. The tissue alterations are distinctly different when compared with a control group, which substantiates an impingement conflict as an early mechanism for degeneration at the hip joint periphery.

Hip Damage Occurs at the Zone of Femoroacetabular Impingement

Although current concepts of anterior femoroacetabular impingement predict damage in the labrum and the cartilage, the actual joint damage has not been verified by computer simulation. We retrospectively compared the intraoperative locations of labral and cartilage damage of 40 hips during surgical dislocation for cam or pincer type femoroacetabular impingement (Group I) with the locations of femoroacetabular impingement in 15 additional hips using computer simulation (Group II). We found no difference between the mean locations of the chondrolabral damage of Group I and the computed impingement zone of Group II. The standard deviation was larger for measures of articular damage from Group I in comparison to the computed values of Group II. The most severe hip damage occurred at the zone of highest probability of femoroacetabular impact, typically in the anterosuperior quadrant of the acetabulum for both cam and pincer type femoroacetabular impingements. However, the extent of joint damage along the acetabular rim was larger intraoperatively than that observed on the images of the 3-D joint simulations. We concluded femoroacetabular impingement mechanism contributes to early osteoarthritis including labral lesions.Level of Evidence: Level II, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Range of motion in anterior femoroacetabular impingement.

The range of motion of normal hips and hips with femoroacetabular impingement relative to some specific anatomic reference landmarks is unknown. We therefore described: (1) the range of motion pattern relative to landmarks; (2) the location of the impingement zones in normal and impinging hips; and (3) the influence of surgical débridement on the range of motion. We used a previously developed and validated noninvasive 3-D CT-based method for kinematic hip analysis to compare the range of motion pattern, the location of impingement, and the effect of virtual surgical reconstruction in 28 hips with anterior femoroacetabular impingement and a control group of 33 normal hips. Hips with femoroacetabular impingement had decreased flexion, internal rotation, and abduction. Internal rotation decreased with increasing flexion and adduction. The calculated impingement zones were localized in the anterosuperior quadrant of the acetabulum and were similar in the two groups and in impingement subgroups. The average improvement of internal rotation was 5.4° for pincer hips, 8.5° for cam hips, and 15.7° for mixed impingement. This method helps the surgeon quantify the severity of impingement and choose the appropriate treatment option; it provides a basis for future image-guided surgical reconstruction in femoroacetabular impingement with less invasive techniques.

Rationale of Periacetabular Osteotomy and Background Work

The Bernese periacetabular osteotomy is a joint-preserving procedure used after growth plate closure to correct acetabular coverage and stabilize the femoral head. The polygonal, juxta-articular osteotomy respects the vascular blood supply to the acetabular fragment and facilitates an extensive acetabular reorientation. It achieves improvement of the insufficient coverage of the femoral head, reduction of mediolateral displacement, and correction of the version of the fragment. All osteotomies are performed through the modified Smith-Petersen approach, which also allows for an anterior capsulotomy. Joint inspection not only provides information on lesions of the rim but also facilitates the control of an impingement-free range of motion after the correction. The posterior column remains partially intact, allowing minimal internal fixation of the acetabular fragment and early mobilization similar to that after an intertrochanteric osteotomy. Because the majority of this patient population consists of young women, it is important to note that the dimensions of the true pelvis and thus the potential for future vaginal delivery are preserved.

Perfusion of the femoral head during surgical dislocation of the hip: MONITORING BY LASER DOPPLER FLOWMETRY

We used laser Doppler flowmetry (LDF) with a high energy (20 mW) laser to measure perfusion of the femoral head intraoperatively in 32 hips. The surgical procedure was joint debridement requiring dislocation or subluxation of the hip. The laser probe was placed within the anterosuperior quadrant of the femoral head. Blood flow was monitored in specific positions of the hip before and after dislocation or subluxation. With the femoral head reduced, external rotation, both in extension and flexion, caused a reduction of blood flow. During subluxation or dislocation, it was impaired when the posterosuperior femoral neck was allowed to rest on the posterior acetabular rim. A pulsatile signal returned when the hip was reduced, or was taken out of extreme positions when dislocated. After the final reduction, the signal amplitudes were first slightly lower (12%) compared with the initial value but tended to be restored to the initial levels within 30 minutes. Most of the changes in the signal can be explained by compromise of the extraosseous branches of the medial femoral circumflex artery and are reversible. Our study shows that LDF provides proof for the clinical observation that perfusion of the femoral head is maintained after dislocation if specific surgical precautions are followed.

Estimation of pelvic tilt on anteroposterior X-rays—a comparison of six parameters

ObjectiveTo compare six different parameters described in literature for estimation of pelvic tilt on an anteroposterior pelvic radiograph and to create a simple nomogram for tilt correction of prosthetic cup version in total hip arthroplasty.DesignSimultaneous anteroposterior and lateral pelvic radiographs are taken routinely in our institution and were analyzed prospectively. The different parameters (including three distances and three ratios) were measured and compared to the actual pelvic tilt on the lateral radiograph using simple linear regression analysis.PatientsOne hundred and four consecutive patients (41 men, 63 women with a mean age of 31.7 years, SD 9.2 years, range 15.7–59.1 years) were studied.ResultsThe strongest correlation between pelvic tilt and one of the six parameters for both men and women was the distance between the upper border of the symphysis and the sacrococcygeal joint. The correlation coefficient was 0.68 for men (P<0.001) and 0.61 for women (P<0.001). Based on this linear correlation, a nomogram was created that enables fast, tilt-corrected cup version measurements in clinical routine use.ConclusionThis simple method for correcting variations in pelvic tilt on plain radiographs can potentially improve the radiologist’s ability to diagnose and interpret malformations of the acetabulum (particularly acetabular retroversion and excessive acetabular overcoverage) and post-operative orientation of the prosthetic acetabulum.