Moritz Tannast

Debridement of the Adult Hip for Femoroacetabular Impingement: Indications and Preliminary Clinical Results

Untreated femoro-acetabular impingement is a common cause of osteoarthrosis of the hip. Surgical debridement of the adult hip with femoro-acetabular impingement recently has been advocated with the aim of relieving symptoms and slowing or halting progression of the arthrosis. At surgery, femoral sources of impingement are relieved by debriding the aspheric peripheral portion of the femoral head and the adjacent femoral neck. Acetabular sources of impingement can be relieved by debridement of the anterior rim. The most fundamental questions concerning these procedures relate to the preoperative and postoperative function, postoperative survivorship of these hips and the incidence of osteonecrosis. The current study assesses a group of 23 hips in 23 patients treated by surgical debridement for impingement. Twenty-two patients were treated by full surgical dislocation and one patient was treated by relief of impingement without dislocation. Followup ranged from a minimum of 2 years to 12 years. At most recent evaluation, seven patients had been converted to total hip arthroplasty, one had arthroscopic debridement of a recurrent labral tear, and 15 patients have had no further surgery. No hips developed osteonecrosis. Of the seven patients who had to have their procedure converted to total hip arthroplasty, three of these hips failed early and four patients’ hips recovered and functioned well and subsequently deteriorated with total hip arthroplasty done between 6.4 and 9.5 years after debridement. Hips at greatest risk of failure have advanced arthrosis or a combination of impingement and instability preoperatively. The procedure effectively treats hips with impingement and without considerable secondary arthrosis or instability.

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.

Tilt and Rotation Correction of Acetabular Version on Pelvic Radiographs

Anteroposterior pelvic radiographs are the gold standard of imaging for mechanical hip problems. However, correct interpretation is difficult because the projected morphologic features of the acetabulum and nearly all routinely used hip parameters depend on individual pelvic position, which can vary considerably during acquisition. We developed software that recreates the projected acetabular rim and the measured hip parameters as if obtained in a standardized orientation. The vertical and horizontal distances between two easy identifiable points were used as indicators of tilt and rotation. These points were the middle of the sacrococcygeal joint and the middle of the upper border of the symphyseal gap. Calibration of the indicators was achieved by means of serial pelvic radiographs of 20 cadaver pelves. Validation of tilt indicator in 100 patients and a theoretical error analysis revealed that for accurate tilt prediction an additional one-time lateral radiograph of the pelvis is mandatory. The computer-assisted method allows standardized evaluation of anatomic morphologic differences of femoral coverage (dysplasia, retroversion), making their clinical relevance for development of early osteoarthritis more valuable.

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.

The accuracy of free-hand cup positioning - a CT based measurement of cup placement in 105 total hip arthroplasties

We studied 105 patients who received a total hip arthroplasty between June 1985 and August 2001 using freehand positioning of the acetabular cup. Using pelvic CT scan and the hip-plan module of SurgiGATE-System (Medivision, Oberdorf, Switzerland), we measured the angles of inclination and anteversion of the cup. Mean inclination angle was 45.8°±10.1° (range: 23.0–71.5°) and mean anteversion angle was 27.3°±15.0° (range: −23.5° to 59.0°). We compared the results to the “safe” position as defined by Lewinnek et al. and found that only 27/105 cups were implanted within the limits of the safe position. We conclude that a safe position as defined by Lewinnek et al. [13] was only achieved in a minority of the cups that were implanted freehand.RésuméNous avons étudié 105 malades qui ont eu une Arthroplastie Totale de la Hanche entre juin 1985 et août 2001 avec positionnement manuel de la cupule acétabulaire. Utilisant une tomodensitométrie pelvienne et le module de hanche de SurgiGATE© - System (Medivision, Oberdorf, Suisse) nous avons mesuré les angles d’inclination et d’antéversion de la cupule. L’angle moyen d’inclination était 45.8°±10.1° (gamme: 23.0° à 71.5°) et l’angle moyen d’antéversion était 27.3°±15.0° (gamme: -23.5° à 59.0°). Nous avons comparé les résultats à l’orientation de sécurité définie par Lewinnek et al. et nous avons trouvé que seulement 27/105 cupules ont été implantées dans les limites de l’orientation correctes. Nous concluons qu’une orientation de sécurité, comme défini par Lewinnek et al. [13] n’a été obtenue que dans une minorité des cupules implantées manuellement.

Anatomic referencing of cup orientation in total hip arthroplasty.

Pelvic tilt and rotation can drastically affect the apparent cup orientation on conventional anteroposterior pelvic radiographs. It was hypothesized that nonstandardized radiographic cup version and abduction can differ significantly from the corresponding anatomic angles if not measured to the anterior pelvic plane, defined by the pubic tubercles and the anterior superior iliac spine. Differences in preoperative and postoperative pelvic orientation and their influence on radiographic measurements of the two angles were analyzed. Conventional radiographs and preoperative and postoperative computed tomography scans of 37 total hip arthroplasties were compared. Calculations were made with the preoperative planning station of a computer navigation system. Significantly smaller values of cup version were seen on nonstandardized radiographs, whereas abduction could be measured reliably when referenced to horizontal pelvic landmarks seen on radiographs. The underlying cause for this difference was the variation of pelvic tilt that ranged 27° (range, −7°-20°). Influence of pelvic tilt on the apparent cup orientation can be seen with simple nomograms. The orientation of the anterior pelvic plane before and after surgery did not differ. We think that version measurement on nonstandardized radiographs without anatomic referencing is highly inaccurate. Level of Evidence: Diagnostic study, Level II-1 (development of diagnostic criteria on basis of consecutive patients-with universally applied reference “gold” standard). See Guidelines for Authors for a complete description of levels of evidence.

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.

Two to Twenty-Year Survivorship of the Hip in 810 Patients with Operatively Treated Acetabular Fractures

BACKGROUND The aims of the study were (1) to determine the cumulative two to twenty-year survivorship of the hip after open reduction and internal fixation of displaced acetabular fractures, (2) to identify factors predicting conversion to total hip arthroplasty or hip arthrodesis, and (3) to create a predictive model that calculates an individuals probability of early need for total hip arthroplasty or hip arthrodesis. METHODS Eight hundred and sixteen acetabular fractures treated with open reduction and internal fixation by one surgeon over a twenty-six-year period were analyzed. Cumulative two to twenty-year Kaplan-Meier survivorship analyses of the hip, including best and worst-case scenarios, were performed with total hip arthroplasty or hip arthrodesis as the end point. Univariate and multivariate Cox regression analyses were performed to identify negative predictors, which were then used to construct a nomogram for predicting an individuals probability of needing an early total hip arthroplasty. RESULTS The cumulative twenty-year survivorship of the 816 hips available for follow-up was 79% at twenty years. The best and worst-case scenarios corresponded to cumulative twenty-year survivorship of 86% and 52%, respectively. Significant independent negative predictors were nonanatomical fracture reduction, an age of more than forty years, anterior hip dislocation, postoperative incongruence of the acetabular roof, involvement of the posterior acetabular wall, acetabular impaction, a femoral head cartilage lesion, initial displacement of the articular surface of ≥ 20 mm, and utilization of the extended iliofemoral approach. CONCLUSIONS Open reduction and internal fixation of displaced acetabular fractures was able to successfully prevent the need for subsequent total hip arthroplasty within twenty years in 79% of the patients. The results represent benchmark comparative data for any future and past studies on the outcome of surgical fixation of acetabular fractures.

Impingement Adversely Affects 10-year Survivorship After Periacetabular Osteotomy for DDH

BackgroundAlthough periacetabular osteotomy (PAO) for developmental dysplasia of the hip (DDH) provides conceptual advantages compared with other osteotomies and reportedly is associated with joint survivorship of 60% at 20 years, the beneficial effect of proper acetabular reorientation with concomitant arthrotomy and creation of femoral head-neck offset on 10-year hip survivorship remains unclear.Questions/purposesWe asked the following questions: (1) Does the 10-year survivorship of the hip after PAO improve with proper acetabular reorientation and a spherical femoral head; (2) does the Merle d’Aubigné-Postel score improve; (3) can the progression of osteoarthritis (OA) be slowed; and (4) what factors predict conversion to THA, progression of OA, or a Merle d’Aubigné-Postel score less than 15 points?MethodsWe retrospectively reviewed 147 patients who underwent 165 PAOs for DDH with two matched groups: Group I (proper reorientation and spherical femoral head) and Group II (improper reorientation and aspherical femoral head). We compared the Kaplan-Meier survivorship, Merle d’Aubigné-Postel scores, and progression of OA in both groups. A Cox regression analysis (end points: THA, OA progression, or Merle d’Aubigné-Postel score less than 15) was performed to detect factors predicting failure. The minimum followup was 10 years (median, 11 years; range, 10–14 years).ResultsAn increased survivorship was found in Group I. The Merle d’Aubigné-Postel score did not differ. Progression of OA in Group I was slower than in Group II. Factors predicting failure included greater age, lower preoperative Merle d’Aubigné-Postel score, and the presence of a Trendelenburg sign, aspherical head, OA, subluxation, postoperative acetabular retroversion, excessive acetabular anteversion, and undercoverage.ConclusionsProper acetabular reorientation and the creation of a spherical femoral head improve long-term survivorship and decelerate OA progression in patients with DDH.Level of EvidenceLevel III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Radiographic analysis of femoroacetabular impingement with Hip2Norm-reliable and validated.

The purpose of this study was to validate the accuracy, consistency, and reproducibility/reliability of a new method for correction of pelvic tilt and rotation of radiographic hip parameters for pincer type of femoroacetabular impingement on an anteroposterior pelvic radiograph. Thirty cadaver hips and 100 randomized, blinded AP pelvic radiographs were used for investigation. To detect the software accuracy, the calculated femoral head coverage and classic hip parameters determined with our software were compared to reference measurements based on CT scans or conventional radiographs in a neutral orientation as gold standard. To investigate software consistency, differences among the different parameters for each cadaver pelvis were calculated when reckoned back from a random to the neutral orientation. Intra‐ and interobserver comparisons were used to analyze the reliability and reproducibility of all parameters. All but two parameters showed a good‐to‐very good accuracy with the reference measurements. No relevant systematic errors were detected in the Bland–Altman analysis. Software consistency was good‐to‐very good for all parameters. A good‐to‐very good reliability and reproducibility was found for a substantial number of the evaluated radiographic acetabular parameters. The software appears to be an accurate, consistent, reliable, and reproducible method for analysis of acetabular pathomorphologies.