J Orthop Sci (2004) 9:256–263 DOI 10.1007/s00776-004-0770-y
Femoroacetabular impingement caused by a femoral osseous head– neck bump deformity: clinical, radiological, and experimental results Marcus Jäger, Alexander Wild, Bettina Westhoff, and Rüdiger Krauspe Department of Orthopedics, Heinrich-Heine University Hospital Duesseldorf, Moorenstrasse 5, D-40225 Duesseldorf, Germany
Abstract Femoroacetabular impingement is often associated with reduced femoral anteversion or an osseous bump deformity on the femoral head–neck junction. We report prospectively on 17 patients showing an osseous bump at the anterolateral head–neck junction on radiography (22 hips) and typical signs of femoroacetabular impingement on clinical examination. Following three plans of treatment, nine patients (10 hips) underwent nonoperative treatment, and eight patients (12 hips) had surgery. In eight hips with labral defects but minor cartilage damage, the bump was surgically removed via trochanter flip osteotomy. Two hips were treated surgically through an anterior surgical approach without hip dislocation. Four hips with severe signs of osteoarthritis and significantly reduced range of motion underwent total replacement. To elucidate a local osteogenic differential potential, tissue specimens of the perilesional capsule were investigated immunohistochemically. Various antigens and protein synthesis products served to identify osteoblastic and progenitor cells. There was a significant improvement in internal rotation and pain relief in patients who underwent surgical resection of the osseous bump. No avascular osteonecrosis or other significant severe side effects were observed during follow-up. In contrast, no nonoperatively treated patients improved. Furthermore, immunohistochemical studies showed perilesional recruitment of osteoprogenitor cells. Key words Hip · Femoroacetabular impingement · Bump · Osteoblast differentiation
Introduction Groin pain associated with osteoarthritis of the hip is a common, typical clinical finding, but in active young people groin pain may be reproduced only on clinical
Offprint requests to: M. Jäger Received: September 8, 2003 / Accepted: January 17, 2004
examination by internally rotating the hip at 90° flexion with additional axial load.14 Femoroacetabular impingement may result from reduced antetorsion or an osseous bump at the anterolateral femoral head–neck junction (or both). Although the etiology of this deformity is unclear, it has been shown that several disorders are associated with an abnormal anatomical relation between the femoral head and the neck resulting in bump formation. Chronic slipped capital femoral epiphysis (SCFE) with posterior displacement of the femoral head,5,13 reduced antetorsion of the femoral neck,15 and protrusio acetabuli are typical pathoanatomical findings that may cause impingement symptoms. In addition an elliptical femoral head, decreased anterior femoral offset,3 posttraumatic rotational deformities of the femoral head,1 or secondary impingement after periacetabular osteotomy7 may lead to “bump-related” impingement symptoms, groin pain, and progressive reduction of internal rotation and flexion of a hip joint. These mechanisms seem to be involved in secondary lesions of the acetabular labrum and the articular cartilage of the acetabulum, with subsequent development of osteoarthritis. Several studies suggest that even mild bump deformities can significantly lead to secondary osteoarthritis of the hip.6,10 The diagnosis of an osseous bump deformity is based on standard radiographs of the proximal femur in two planes, whereas magnetic resonance imaging (MRI) scans, including MRI arthrography studies, are commonly used to evaluate labral lesions. The advantage of surgical remodeling of the femoral neck (bumpectomy) in patients with femoroacetabular impingement caused by an osseous bump at the femoral head–neck junction is controversial. Other treatment modalities, such as physiotherapy, osteopathy, or antiinflammatory drug therapy, may be alternatives to prevent early osteoarthritis and may at least delay total hip replacement in these patients. We report compara-
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tive clinical and radiological results of 17 patients (22 hips) with bump-associated femoroacetabular impingement who underwent various operative or nonoperative treatments. Furthermore, immunohistochemical investigations of the local perilesional capsule tissue were performed to elucidate the pathophysiological aspects of this deformity.
Materials and methods Typical radiographic findings of osseous bump deformities on the anterolateral head–neck junction were found in 22 hips of 17 patients (13 men, 4 women). All of the patients showed typical symptoms of femoroacetabular impingement. The patients’ average age was 33.6 years (14–60 years, SD 14.4 years); the average body height was 176.7 cm (159–198 cm, SD 9.8 cm); and the mean body weight was 82.4 kg (50–122 kg, SD 30.2 kg). In two patients a chronic CSFE had been diagnosed during adolescence, and in the other cases the etiology and pathophysiology of the bump deformity was unknown. According to clinical and radiographic findings and MRI scans, the patients underwent three types of therapy. Nine patients (10 hips; average age 34.5 years) with moderate clinical symptoms (up to 5 points on the visual analogue pain scale, which ranges from 0 “no pain” to 10 “severe pain”) but morphological signs of degenerative destruction of hip joints underwent nonoperative treatment with physiotherapy and antiinflammatory cyclooxygenase-2 (COX-2) inhibitor drugs. In cases of progression of symptoms over more than 6 months, total hip replacement was indicated (group A). In six patients (eight hips; average age 27.3 years) with labral defects but only minor cartilage destruction on MRI, the bump was removed surgically: in five hips via trochanter flip osteotomy and surgical dislocation and in two hips via an anterior surgical approach without hip dislocation (group B). Two patients (four hips, average age 49.5 years) with severe signs of osteoarthritis on standard radiographs underwent bilateral total hip replacement (group C). Postoperative standardized clinical examinations and radiographic investigations in two standard planes served to evaluate the results of the treatment. Clinical parameters of interest were (1) the interval from the occurrence of symptoms to the diagnosis of a “bump”; (2) the range of motion (ROM) of a hip joint; (3) preand postoperative pain; and (4) postoperative activities of daily life. All patients were asked to evaluate the efficiency and outcome of the treatment regimen at the end of follow-up. Possible answers were “excellent,” “good,” “satisfactory,” and “poor.”
a,b Fig. 1. a Acetabular angle of Ullmann and Sharp (Y) for evaluation of dysplasia of the hip. Normal Y values depend on age: 1–11 years, ⱕ49°; 11–13 years, ⱕ47°; 13–14 years, ⱕ45°; ⬎14 years, ⱕ43°. b Femoral head–neck index of Heyman and Herndon (I) for evaluation of femoral neck deformities. I ⫽ a/b ⫻ 100; normal 190–150
Radiological parameters were the center-edge (CE) angle, the collum-caput diaphyseal (CCD) angle, the acetabulum angle of Ullman and Sharp (Fig. 1a), the length and width of the bump on the anteroposterior (AP) radiographic plane, and the femoral head–neck index of Heymann and Herndon (normal 150–190) (Fig. 1b). Digitalized radiographs in two planes were evaluated using a computer imaging system (Magic View; Fa. Siemens, Munich Germany). The average follow-up periods were 16.2 months (SD 2.5 months) for the conservatively treated patients (group A), 21.7 months (SD 7.7 months) for patients treated by surgical bump removal (group B), and 26.5 months (SD 12.5 months) in patients who underwent total hip arthroplasty (group C). To elucidate the local osteogenic differential potential, specimens of the perilesional capsule tissue of a hip joint in three patients who underwent surgery were obtained for an immunohistochemical investigation. For differentiation of osteoblasts from undifferentiated mesenchymal progenitor cells, surface antigens and protein synthesis products described by Pittenger et al.11 served for the histological evaluations. Alkaline phosphatase (ALP), osteocalcin (OC)⫹, osteopontin (OP)⫹, osteonectin (ON)⫹, and collagen type I (Col I)⫹ were used as osteoblast-specific markers; and for mesenchymal stem cell detection CD13⫹, CD31⫹, CD34⫺, CD45⫹, and CD105⫹ antigen expression was detected. Specimens were fixed with 5% paraformaldehyde at 4°C for 30 min, rinsed in phosphate-buffered saline (PBS), and dehydrated in graded alcohols. Endogenous peroxidases of the specimens were blocked by 3% perhydrol-isopropanol solution. After rinsing in Tris buffer, thin sections were incubated with primary antibodies against CD antigens and then at 4°C for 12 h. The second antibody system with avidin-biotin complex and
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Fig. 2. Femoral head specimen from a 39year-old patient (group C) with severe osteoarthritis. It was removed during total hip replacement surgery. The anterolateral bump is covered with cartilage that communicates directly with the femoral head cartilage (arrows)
3,3-diaminobenzidine was used for optical visualization. ALP activity was measured by direct substrate incubation (SK-5.200; Vector, Burlingame, CA, USA) for 30 min at room temperature (RT). Light and immunofluorescence microscopy served for histological evaluation of the tissue specimens.
Results The average interval between the onset of symptoms and the diagnosis of a bump deformity was 5.4 years (range 0–30 years). All patients showed subcortical osteopenia corresponding to reduced roentgenological density in standard radiographic planes of the proximal femur at the site of the bump. In one case there was a subcortical cyst. All patients who underwent surgical hip clearance graded the result of the operative treatment as “excellent” or “good” and showed no clinical signs of femoroacetabular impingement postoperatively (they were pain-free). Except for one patient with a persisting hematoma, which was surgically removed, there were no perioperative complications and no recurrence of the osseous bump. The two patients who underwent total hip replacement were free from pain as well and showed uneventful function. Other than one patient with diabetes mellitus, there were no other diseases in their medical histories. All bumps that were surgically exposed showed a cartilage surface communicating directly with the joint cartilage of the femoral head, even in cases of severe osteoarthritis (Fig. 2). To prove the impingement and squeeze effects of the bump a dynamic investigation of
a,b Fig. 3. Radiographic findings before (a) and after (b) corrective osteotomy and bump resection. Femoroacetabular impingement under dynamic stress in 70° flexion and 10° internal rotation. The deformity after chronic slipped capital femoral epiphysis was treated with corrective intertrochanteric osteotomy and internal fixation using a blade plate. a The osseous bump squeezes the femoral head out of the acetabulum (arrow). b There is no biomechanical impingement after “bumpectomy” via a modified Smith-Peterson approach. The internal rotation increased from 0° to 40° postoperatively. The impingment symptoms disappeard after surgery
hip movement was carried out under clinical and imaging intensifier control (Fig. 3). In contrast to patients who underwent the above treatments, all nonoperatively treated patients were still complaining of pain and hip dysfunction. A 34-year-old patient changed his profession because of disabilities in daily life activities, and two other patients were not able to play sports any longer. Figure 4 shows MRI scans and radiographs of a 35-year-old patient with a moderate bump but severe secondary cartilage damage (Fig. 4). Measurements on the bilateral AP radiographs of hips showed an average CCD angle of 131.1° (range
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Fig. 4. Radiographic and magnetic resonance imaging (MRI) scans of the right hip joint of a 35-year-old patient with a significant bump deformity. Although the roentgenograms showed no severe osteoarthritic changes of the joint space, MRI clarified severe cartilage destruction of the acetabulum
Fig. 5. Comparative range of motion in patients before and after surgical removal of an osseous bump (“bumpectomy”). The data show significant postoperative improvement in internal rotation
126.0°–140.0°, SD 3.4°), a mean CE angle of 44.6° (34.0°–52.0°, SD 6.0°), and an acetablum angle according to Ullmann and Sharp of 41.6° (34.0°–49.0°, SD 4.1°) for all patients. The average length of the bump was 15.5 mm (5.0–29.0 mm, SD 6.5 mm) and the average width 3.8 mm (2.0–8.0 mm, SD 1.6 mm).
All patients showed reduced internal rotation before treatment. After surgical hip clearance the internal rotation was significantly improved compared to the preoperative findings, without signs of impingement (Fig. 5). This was due to normalization of the preoperatively increased femoral head–neck index (Fig. 6). In
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Fig. 6. Femoral head–neck index is normalized by surgical removement of the bump deformity (“bumpectomy”). There was no recurrence during the follow-up period
contrast, none of the conservatively treated patients showed improvement in the range of internal hip rotation or alleviation of the pain. The immunohistochemical investigation of perilesional capsule tissue showed activation of osteoblastic cell differentiation. Osteoblasts (OP⫹, OC⫹, ON⫹, ALP⫹, col 1-positive cells) were localized in the capsule near calcification centers and thus close to the osseous bump. Some of these cells showed direct contact with these bony structures. In contrast, mesenchymal progenitor cells (CD105⫹, CD45⫹, CD31⫹, CD13⫹, CD34⫺, OC⫺, OP⫺ cells) were detected only in the absence of bone or calcification centers in the side of the capsule opposite that of the bump. Some of the mesenchymal progenitor cells were close to osteoblasts but never showed direct cellular contact with them (Fig. 7). These phenomena were not found in control groups (capsule specimens obtained from patients with primary osteoarthritis during total hip replacement surgery without the bump deformity).
Discussion The femoral head–neck bump deformity is well known as a risk factor for developing osteoarthritis of the hip. In 1975 Stuhlberg et al. described this deformity as a “pistol-grip deformity” and reported its presence in 40% of all patients who developed osteoarthritis of the hip.3 Although the deformity has been described in the literature many times, the average interval of 5.4 years
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from occurrence of symptoms to diagnosis means that there may still be a delay in diagnosis and no generally accepted therapeutic management. The early clinical and radiological results of this investigation supported the concept of resecting the bump deformity. It was shown that biomechanically based surgical treatment for a bump associated with femoroacetabular impingement provided improved internal rotation and pain relief. However, it is not yet clear whether pain relief and prevention of osteoarthritis continue for the long term. Nöztli et al.9 showed that surgical hip dislocation may lead to significantly reduced blood flow, which may result in avascular osteonecrosis of the femoral head. To minimize this risk the surgical technique was modified by Ganz et al.2 with the medial femoral circumflex artery protected by the intact obturator externus muscle. In their study none of the 213 treated hips developed avascular osteonecrosis during a 7-year follow-up.2 Even though the bump deformity may be one of the most common causes of femoroacetabular impingement symptoms, rare origins must be considered too. Siebenrock and Ganz13 reported four patients with osteochondromas of the femoral neck that caused femoroacetabular impingement. Tschauner and Urban16–18 described tension and shear stress of a dysplastic acetabulum on the superolateral capsular–labrum complex caused by a poorly covered femoral head (“guide rail phenomen”), which also can lead to femoro-acetabular impingement. Furthermore, trauma to a hip joint can be associated with impingement symptoms.4 The immunohistochemical and histological studies of capsule tissue in patients with a bump showed active cellular differentiation and bone remodeling mechanisms involved in pathogenesis. Wagner et al. compared tissue specimens of nonspherical portions of femoral heads obtained during hip surgery from young adults with hip impingement to specimens from the same area of older patients with advanced osteoarthritis.19 They concluded that the aberrant nonspherical portion of the femoral head in young patients with an impingement problem consists of hyaline cartilage that shows clear degenerative signs similar to the findings in osteoarthritic cartilage. Some other investigators found microtrauma and local strain, which may occur in impingement zones to promote and initiate osteoblastic differentiation.8,12,20 The β-integrin subunits may play a crucial role in biomechanically caused osteoblast differentiation and tissue calcification.12 We hypothesize that local recruitment of osteoprogenitor cells, stimulated by biomechanical forces, is responsible for secondary tissue calcification in impingement zones and thus may pro-
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Fig. 7. Immunohistological staining of capsular tissue for mesenchymal stem cell (a) and osteoblast (b) detection. Cells with typical osteoblast markers were localized in calcification areas in capsule tissue (arrow) close to the osseous bump, whereas mesenchymal progenitor cells were detected only in the absence of ossification centers. All specimens of three analyzed patients showed similar morphology and immunostaining characteristics
a
mote a growing osseous bump deformity. Furthermore, the osteopenia, which was localized underneath the bump cortex, supports the hypothesis of an active bone remodeling process as well. In summary, we advocate surgical hip clearance (“bumpectomy”) in patients with persisting inguinal pain and hip impingement symptoms under conservative treatment over 6 months or longer, combined with a radiographically diagnosed osseous bump deformity at the femoral head–neck junction, signs of labral lesions seen by MRI arthrography, and the absence of signs of severe articular cartilage damage on MRI scans. Patients with bump deformities and severe cartilage damage of the hip joint corresponding to osteoarthritis, with symptoms persisting more than 6 months under conservative treatment, should be
treated by hip replacement (total hip arthroplasty or hip resurfacing). Although the results in conservatively treated patients were poor, we recommend in all other cases to continue with symptomatic treatment, considering the (peri)operative risks and the lack of data regarding clinical outcomes for large patient cohorts treated by surgical hip clearance. Other hip impingementassociated deformities, such as reduced femoral antetorsion or acetabular anteversion, should be excluded or may be treated by corrective osteotomies to prevent secondary osteoarthritis. In borderline cases, an individual decision must be made based on the patient’s age, intensity of symptoms, daily activities and demands, degree of restrictions, preexisting co-morbidity, operative risks, and social factors.
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Fig. 7. Continued
b
Conclusions For patients with a bump associated with a femoroacetabular impingement syndrome but intact joint cartilage, hip clearance seems to be a therapeutic alternative to reduce pain and increase the range of motion. The immunohistological findings of this study suggest active bone remodeling of perilesional capsule tissue. These effects may be caused by biomechanically promoted recruitment of local osteoprogenitor cells.
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