Orthopedics

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Tips & Techniques 

Treatment of Femoroacetabular Impingement: A Modified Resection Osteoplasty Technique Through an Anterior Approach

Luca Pierannunzii, MD; Marco d'Imporzano, MD

Abstract

Femoroacetabular impingement has emerged as a cause of osteoarthritis of the young hip. This article presents a modified open procedure for cases that cannot be completely managed arthroscopically.

Cover illustration © Lisa Clark

Femoroacetabular impingement is considered responsible for many young, nondysplastic, osteoarthritic hips. According to that theory, repetitive conflict between the head–neck junction and acetabular rim can determine degenerative modifications in the labrum and chondral surfaces up to advanced osteoarthritis.1,2

The hip joint clearance is wide enough to avoid conflict if femoral and acetabulum anatomy is normal. Congenital or acquired changes in head–neck offset and acetabular coverage may reduce clearance and induce femoroacetabular impingement.

Impingement has been detected mainly in the anterolateral part of the joint; thus, liable movements are flexion and internal rotation. Clinical observations confirm this hypothesis because patients often refer symptoms to this position.

Pain in flexion-internal rotation of the hip is known as impingment sign.3 Although extremely sensitive, the impingement sign is unspecific,because the anterolateral labrum frequently is involved by early osteoarthritis and primary labral lesions. Thus, the physical examination always should be followed by adequate imaging: a standing anteroposterior view of the pelvis, a lateral view, and a false profile view to detect gross femoral and acetabular abnormalities.

Dynamic fluoroscopic examination represents the gold standard in demonstrating the conflict, but the significant exposure of both the operator and the patient prohibits routine use.

A computed tomography (CT) scan or magnetic resonance imaging (MRI) should be obtained before any surgical decision, as they allow more precise evaluations of cartilage thickness, labral lesions and ossification, and exact acetabular version. We prefer CT scans in acetabular anomalous coverage, as it outlines the bony margins of the socket. Although arthro-MRI and arthro-CT scans seem to be more sensitive in detecting labral detachments, we do not consider them essential.

Figure 1: Cam type impingement determined by pistol grip deformity of the femoral head.
Figure 1: Cam type impingement determined by pistol grip deformity of the femoral head.

With regard to the pathophysiology, two mechanisms have been postulated to explain degenerative arthropathy originated by femoroacetabular impingement: cam effect and pincer effect.

Cam effect is determined by aspherical heads in which radius increases from the central zone to the peripheral one. The anomalous head shows a “pistol grip shape” in the anteroposterior view because it is abnormally extended over the anterolateral part of the neck (Figure 1). When the abnormal part of the head is forced into the socket by flexion-internal rotation, it generates shear forces against the cartilage of the anterosuperior quadrant of the acetabulum. This stress produces abrasion and then chondropathy. The labrum is just partially involved.4

Pincer effect is the linear contact between a normal neck and an overcovering rim. This occurs in hips affected by acetabular retroversion and by coxa profunda. In the former type of dysplasia the overcoverage is selective for the anterosuperior quadrant of the socket; in the latter type, it is general (Figures 2-4). According to Ruelle and Dubois,5 coxa profunda is a mildly deepened acetabulum in which the medial wall touches the ilioischial line (or is slightly medial), and protrusio is extremely deepened with the femoral head overlapping the ilioischial line.

Pincer femoroacetabular impingement is characterized by labral lesions up to its complete ossification. Chondral lesions may be present in the opposite posteroinferior quadrant because of the repetitive leverage of the head on the anterosuperior rim. In fact, while the head is partially levered out of the socket, dislocation is resisted by the shear stress between the head and the opposite side of the acetabulum. Less important cartilage involvement makes pincer femoroacetabular impingement more benign than cam femoroacetabular impingement.6

If physical examination and imaging (radiograph, CT scan,…

Femoroacetabular impingement has emerged as a cause of osteoarthritis of the young hip. This article presents a modified open procedure for cases that cannot be completely managed arthroscopically.

 

Cover illustration

 

Cover illustration © Lisa Clark

Femoroacetabular impingement is considered responsible for many young, nondysplastic, osteoarthritic hips. According to that theory, repetitive conflict between the head–neck junction and acetabular rim can determine degenerative modifications in the labrum and chondral surfaces up to advanced osteoarthritis.1,2

The hip joint clearance is wide enough to avoid conflict if femoral and acetabulum anatomy is normal. Congenital or acquired changes in head–neck offset and acetabular coverage may reduce clearance and induce femoroacetabular impingement.

Impingement has been detected mainly in the anterolateral part of the joint; thus, liable movements are flexion and internal rotation. Clinical observations confirm this hypothesis because patients often refer symptoms to this position.

Pain in flexion-internal rotation of the hip is known as impingment sign.3 Although extremely sensitive, the impingement sign is unspecific,because the anterolateral labrum frequently is involved by early osteoarthritis and primary labral lesions. Thus, the physical examination always should be followed by adequate imaging: a standing anteroposterior view of the pelvis, a lateral view, and a false profile view to detect gross femoral and acetabular abnormalities.

Dynamic fluoroscopic examination represents the gold standard in demonstrating the conflict, but the significant exposure of both the operator and the patient prohibits routine use.

A computed tomography (CT) scan or magnetic resonance imaging (MRI) should be obtained before any surgical decision, as they allow more precise evaluations of cartilage thickness, labral lesions and ossification, and exact acetabular version. We prefer CT scans in acetabular anomalous coverage, as it outlines the bony margins of the socket. Although arthro-MRI and arthro-CT scans seem to be more sensitive in detecting labral detachments, we do not consider them essential.

Figure 1: Cam type impingement determined by pistol grip deformity of the femoral head.
Figure 1: Cam type impingement determined by pistol grip deformity of the femoral head.

 

With regard to the pathophysiology, two mechanisms have been postulated to explain degenerative arthropathy originated by femoroacetabular impingement: cam effect and pincer effect.

Cam effect is determined by aspherical heads in which radius increases from the central zone to the peripheral one. The anomalous head shows a “pistol grip shape” in the anteroposterior view because it is abnormally extended over the anterolateral part of the neck (Figure 1). When the abnormal part of the head is forced into the socket by flexion-internal rotation, it generates shear forces against the cartilage of the anterosuperior quadrant of the acetabulum. This stress produces abrasion and then chondropathy. The labrum is just partially involved.4

Pincer effect is the linear contact between a normal neck and an overcovering rim. This occurs in hips affected by acetabular retroversion and by coxa profunda. In the former type of dysplasia the overcoverage is selective for the anterosuperior quadrant of the socket; in the latter type, it is general (Figures 2-4). According to Ruelle and Dubois,5 coxa profunda is a mildly deepened acetabulum in which the medial wall touches the ilioischial line (or is slightly medial), and protrusio is extremely deepened with the femoral head overlapping the ilioischial line.

Pincer femoroacetabular impingement is characterized by labral lesions up to its complete ossification. Chondral lesions may be present in the opposite posteroinferior quadrant because of the repetitive leverage of the head on the anterosuperior rim. In fact, while the head is partially levered out of the socket, dislocation is resisted by the shear stress between the head and the opposite side of the acetabulum. Less important cartilage involvement makes pincer femoroacetabular impingement more benign than cam femoroacetabular impingement.6

If physical examination and imaging (radiograph, CT scan, and MRI) demonstrate impingement, the first therapeutic step is nonsteroidal anti-inflammatory drugs to relieve pain, followed by postural rehabilitation to reduce pelvic inclination.

The reclination of the pelvic ring can be obtained by strengthening the abdominal muscles and the gluteus maximus and stretching the iliopsoas and the paravertebral muscles. This postural change can reduce the anterior coverage of the femoral head, as has been demonstrated in patients affected by decresed lumbar lordosis.7 Athletes should avoid specific actions responsible for conflict. High knee running (a common exercise for running back training in football), sprinting (it requires a hip flexion >80° with the limb almost neutrally rotated), deep squat (squat performed up to the full hip and knee flexion), and cycling on a low saddle are examples of activities that should be ceased. High impact sports generally should be discouraged.

Figure 2: In a normal hip, the anterior rim is medial, while the posterior rim is lateral

Figure 3: In a retroverted socket, the anterior rim crosses the posterior rim

Figure 4: In coxa profunda, the acetabular floor, represented by the tear drop is widely medial to the ilioischial line

Figure 2: In a normal hip, the anterior rim (dotted line) is medial, while the posterior rim (continuous line) is lateral, suggesting the overall anteversion of the socket. Figure 3: In a retroverted socket, the anterior rim (dotted line) crosses the posterior rim (continuous line), generating the crossover sign, as the upper part of the acetabulum is retroverted. Figure 4: In coxa profunda, the acetabular floor, represented by the tear drop (dotted line) is widely medial to the ilioischial line (continuous line).The Wiberg angle slightly overcomes 40 (superior limit for normal hips).

If conservative treatment is not effective, surgery must be considered. Young patients with minimal or no osteoarthitic changes should undergo a joint-preserving operation, while older patients with degenerative hip disease are better treated by total hip arthroplasty (THA).

Joint-preserving surgery is divided into reorientation osteotomy and resection osteoplasty. Reverse periacetabular osteotomy is useful in patients affected by acetabular retroversion with posterior wall deficiency and without important cartilage lesions.8 Rotational osteotomy of the femur is rarely indicated, because femoral retroversion is an uncommon cause of femoroacetabular impingement.

Resection osteoplasty is the excision of the prominent parts of the head and the rim. The head–neck junction should be reshaped and the acetabular rim reduced to increase the clearance in the anterolateral quadrant of the joint.

Resection osteoplasty through a trochanteric flip approach with hip dislocation was originally described by Ganz et al9 and Lavigne et al.10

The authors have modified this technique performing an anterior approach. The exposure of the anterolateral side of the joint makes direct assessment of impingement and complete excision of impinging structures without dislocating the hip easier.

The most suitable patients are young adults affected by femoroacetabular impingement without advanced osteoarthritis (grade 1 at most according to Tönnis’11 classification).

In this series, we observed frequent superior acetabular cysts that were associated early with the retroverted socket, even in the absence of major degenerative joint disease. If the joint space is just slightly reduced and no gross osteophytes are visible, we do not consider cysts and marginal sclerosis a contraindication to the proposed technique.

Arthroscopic debridement of the femoral neck is preferred if the surgeon is sufficiently experienced, as it has been effective and minimally invasive in pure cam impingement.12,13 However, many cases of femoroacetabular impingement are pincer type or combined, and for these hips we recommend the following procedure.

Anterior Approach

The patient is placed in the supine position on a radiolucent operating table. The skin is incised along the anterior third of the iliac crest and then from the anterior superior iliac spine the incision curves distally and laterally (Figure 5).

Figure 5: ASI=Santerior superior iliac spine

Figure 6: Dissection between tensor fasciae latae and sartorius muscle

Figure 7: ASIS=anterior superior iliac spine, G=glutei muscles, IC=iliac crest, S=sartorius muscle, and T=tensor fasciae late

Figure 8: Complete exposure of the hip

Figure 5: Skin incision. The head of the patient is on the right side. ASI=Santerior superior iliac spine. Figure 6: Distal window. Dissection between tensor fasciae latae and sartorius muscle. ASI=Santerior superior iliac spine, S=sartorius muscle, and T=tensor fasciae late. Figure 7: Two windows. The superior window is located between the iliac wing and glutei muscles and the inferior window between the tensor and the sartorius. ASIS=anterior superior iliac spine, G=glutei muscles, IC=iliac crest, S=sartorius muscle, and T=tensor fasciae late. Figure 8: Complete exposure of the hip. C=capsule and RH=reflected head of the rectus.

Subcutaneous dissection in the distal part of the incision exposes the fascia that is split on the tensor muscle along its fibers. The lateral femoral cutaneous nerve can be damaged if the fascia is cut between the tensor and the sartorius muscle, while lateral dissection is safe. After the fascial split, the surgeon can elevate the medial aponeurotic flap (that contains the nerve) and open the internervous space between the sartorius muscle and the tensor fasciae latae. Abduction and external rotation of the leg decrease muscle tension, making penetration into the interval easier (Figure 6).

The proximal part of the incision shows the iliac insertion of the gluteus medius muscle. The muscle is detached from the iliac crest, then a Cobb elevator is introduced to complete the dissection of the gluteus medius and minimus from the external iliac fossa.

Two windows have been created: the superior window between the glutei muscles and the iliac wing and the inferior window between the sartorius and tensor muscles (Figure 7). Using a cautery, the tensor is detached from the anterior superior iliac spine, joining the windows into a great intermuscular space in front of the hip.

We prefer the two-window technique rather than dissecting along the whole incision because, until the tensor is inserted onto the anterior superior iliac spine, soft-tissue tightness makes it easier to develop the correct anatomical interval.

Deep dissection is performed with a Cobb elevator between the rectus femoris and the abductor muscles. To avoid injuries to the lateral circumflex vessels, this interval should not be more distal than the superior part of the capsule. The inferior window does not need to be exposed for our purposes.

A Hohmann retractor is inserted out of the capsule above the greater trochanter to displace the glutei laterally.

The reflected head of the femoral rectus is detached from the acetabular rim, then the muscle (that originates from the anterior inferior iliac spine with its direct tendon) is displaced medially by a second Hohmann retractor placed on the internal capsule (Figure 8).

Capsulotomy and Assessment of Impingement

If the labrum does not exhibit important degenerative changes or if it is torn from the bone rim, the space between labrum and bone is developed with the scalpel from 12 o’clock (superior position) to 4 o’clock (anteromedial position). If the labrum is ossified, it may be temporarily left in situ while the capsule is detached from it. The diseased labrum will later be removed together with the bone rim (Figure 9).

This periacetabular capsulotomy is suitable to perform the rim excision.

In cases of cam type femoroacetabular impingement, when a femoral osteoplasty must be performed, the capsule should be split longitudinally for 2 cm, starting from 1- or 2-o’clock position to obtain a T-shaped capsulotomy (Figure 10). Two blunt retractors are inserted on the head under the medial and the lateral capsular flaps and the cartilage is evaluated (Figure 11).

Aspherical heads generally show an easily recognizable reddish fraying cartilage coating the femoral bump (Figure 12). The impingement test is performed to locate the prominent part that must be removed.

Figure 9: Periacetabular capsulotomy

Figure 10: T-shaped capsulotomy

Figure 11: Exposure of the femoral head

Figure 12: The femoral bump is coated with fraying reddish cartilage

Figure 9: Periacetabular capsulotomy. C=capsule, H=femoral head, and L=ossified labrum. Figure 10: T-shaped capsulotomy. C=capsule. Figure 11: Exposure of the femoral head. The surgeon indicates the chondral lesion in the impinging site. H=femoral head and L=ossified labrum. Figure 12: The femoral bump is coated with fraying reddish cartilage. B=bump.

Acetabular Resection Osteoplasty

The rim is trimmed with an osteotome from 3 o’clock (anterior resection) to 1 o’clock (lateral resection).

Hips affected by important acetabular overcoverage require massive excision of the bone rim <10-15 mm (Figure 13). The resection may be thicker in marginal acetabular osteophytes, although significant osteophytosis should be regarded as a contraindication to the joint-preserving surgery.

We usually perform a mild acetabular osteoplasty even in pure cam type impingement because it increases the clearance without compromising the stability, facilitates femoral osteoplasty and makes imperfect cephalic shape more tolerable.

Femoral Resection Osteoplasty

In cam type femoroacetabular impingement the anterolateral bump must be removed with the osteotome to restore the concave contour of the head–neck junction (Figure 14). Complete excision of the bump is possible if an assistant rotates the leg internally and externally.

Fluoroscopy may be useful to control the reshaping procedure: the anteroposterior view in neutral rotation shows the lateral outline; the anteroposterior view in external rotation shows the anterolateral outline; and the froglike axial view shows the anterior outline.

When the head appears round in all views, the osteoplasty is completed by smoothing the surface with a burr, and then bone wax is applied to prevent bleeding and neck–capsule adhesions.

In severe chondropathy, microfracture should be performed.

Figure 13: Acetabular resection osteoplasty

Figure 14: Femoral head resection osteoplasty

Figure 15: Capsular reconstruction by anchor sutures

Figure 13: Acetabular resection osteoplasty. H=femoral head, L=ossified labrum, and R=bony rim. Figure 14: Femoral head resection osteoplasty. Figure 15: Capsular reconstruction by anchor sutures. AS=anchor suture, C=capsule, and H=femoral head.

Capsule and Wound Closure

Before suturing, the impingement test must be repeated to verify the absence of residual conflict.

The longitudinal capsular split, if present, will be closed without tension and the capsule will be reapproximated to the bone rim by two anchor sutures at 1 and 3 o’clock, respectively (Figure 15). The reflected head of the rectus femoris may be reattached. Tensor fascie latae together with the glutei are repositioned anatomically onto the anterosuperior iliac spine and the iliac crest by transosseous suture. Fascia between the sartorius and tensor is closed and a drainage is positioned into the external iliac fossa.

Postoperative Care

The drainage tubes are removed after 24 hours and the patient is mobilized. Light passive range of motion (ROM) exercises are encouraged to prevent stiffness, avoiding the impingement position. The patient should ambulate with crutches, partially weight bearing for 3 weeks to allow soft tissues to heal.

Return to sports is permitted after 3 months, although high impact activities are discouraged to avoid potential progression of joint disease.

Materials and Methods

From November 2003 to January 2005, 8 patients (6 men and 2 women) underwent resection osteoplasty via the anterior approach. Mean patient age at the time of surgery was 30 years (range: 26-39 years).

All patients received a unilateral procedure, although five patients showed bilateral disease. Two of the five patients were initially operated at one side only, but will later be treated for the contralateral hip, while the remaining three have been ruled out for further surgery for advanced osteoarthritis.

The preoperative assessment included a complete set of plain radiographs and a CT scan. Among the operated hips, the diagnosis was pure cam type impingement in one patient, pure pincer type impingement in four (three retroverted acetabula and one coxa profunda), and combined impingement in three (aspherical head and anterolateral overcoverage).

According to Tönnis’11 classification, 2 hips showed no arthritic changes, 4 hips showed grade 1 coxarthrosis and 2 hips showed grade 2 coxarthrosis. Four hips showed a similar cluster of supra-acetabular cysts; interestingly all these hips were affected by pincer or combined impingement.

Clinical data were collected at 1, 3, 6, and 12 months, and then every year. In each visit the Harris hip score was measured.14 Plain radiographs were required at 6 months and 1 year after surgery, and every 2 years thereafter.

The current study is still in progress: six patients have had 1-year follow-up, 1 patient has had 6-month follow-up, and 1 patient has had 3-month follow-up.

To prevent any bias related to inadequate follow-up, we excluded the last patient from the present evaluation and we assessed the score improvement of the first 7 hips using the paired Student t test. The overall Harris hip score and partial scores (pain, function, range of motion and absence of deformity) were compared. The significance level was set at P<.05.

Results

No major complications have been reported, and no hip has shown any sign of avascular necrosis. One patient developed an upper limb superficial thrombophlebitis and was managed without consequences.

Hospital discharge occurred 4.1 days after surgery on average (range: 3-5 days).

The overall Harris hip score improved significantly from a mean preoperative value of 74.4 to a mean postoperative value of 85.3 (P=.001), while the mean pain score improved from 25.7 to 34.3 (P=.001).

The function score change is less important (from an average of 40.1 to an average of 42.4), but it reaches the significance level (P=.012). No significant modification in the motion score has been recorded: from 4.53 to 4.61 on average (P=.225).

The deformity score did not change: no patient was affected by a deformity before the procedure, and no patients developed a deformity later.

To date, no patient has undergone a THA. From a clinical perspective, six patients gained an appreciable improvement (>10 points in overall Harris hip score), while one gained no remarkable result (+2 points in overall Harris hip score) and has recently reported that he will undergo a cartilage transplant in a different hospital.

Discussion

Femoroacetabular impingement affects the anterolateral side of the hip. For this reason the best surgical approach should completely expose that side of the joint, avoiding useless and potentially dangerous dissection on the posterolateral side.

The anterior approach is a straightforward approach to the impingement site, and few know that Smith-Petersen,15 who first described this approach to the hip, used it to treat a case of femoroacetabular impingement in 1935; although at the time the importance of this pathomecanism was underestimated.

The anterolateral capsular wall generally does not contain important retinacular vessels (that are especially concentrated on the posterolateral side) and a T-shaped capsulotomy can be performed without risk of avascular necrosis.

Evaluation of head shape is made easier by fluoroscopy. This does not require hip dislocation, that would entail extensive dissection and round ligament excision. These maneuvers could theoretically compromise blood supply, although Ganz et al9 developed a special technique to reduce the risk.

A limit of our procedure is the impossibility to expose the acetabular cartilage that would be visible only femoral head removal. Computed tomography scan and MRI can easily predict chondral status, making its direct assessment unnecessary.

We cannot draw conclusions due to the limited cohort of patients and of the short follow-up. However, short-term results are satisfactory and encouraging.

We observed a clinically remarkable improvement in pain scores (average: >8.57 points), a mild improvement in function (>2.29), but no clinically nor statistically significant increase in ROM. The only insufficient result in our 7 patient series concerns a grade 2 osteoarthritis. These data are consistent with the observations of the Bernese group.16

In light of these facts, we recommend the resection osteoplasty mainly for painful hips with mild or no osteoarthritis (grade 1). Painless patients with restricted ROM or grade 2 and 3 osteoarthritis are unsuitable for the suggested procedure.

Hip arthroscopy is an attractive option, but its indication is limited to selected cases. It originally was described for surgical correction of impingement in Legg-Calvè-Perthes disease in 1993.17

Recently this technique has been formalized both in supine and in lateral decubitus, and the presented results confirm its efficacy in dealing with cam impingement.12,13 The neck bump can be removed arthroscopically, and a limited excision of the rim can be added sacrificing the labrum. But this action is allowed and desirable only if the labrum is ossified or severely damaged. Rim resection in an undamaged or slightly damaged labrum that should be retained has yet to be resolved.

In these cases, while Bare and Guanche12 suggest the necessity to perform an open procedure, Sampson13 proposes the possibility of detaching the labrum, removing the excessive rim and then repairing it. This solution, never performed to date, seems to be demanding.

In our series, the anterosuperior labrum had to be removed in three of seven patients with pincer or combined femoroacetabular impingements eligible for rim excision.

The arthroscopic option should be considered only if acetabular trimming is not required (pure cam femoroacetabular impingement) or if the labrum appears grossly ossified in the preoperative assessment. Otherwise the open approach is preferable.

In comparison with the trochanteric flip approach, resection osteoplasty of the hip by means of anterior approach is technically less invasive because it spares the ligamentum teres, most of the capsule, and the greater trochanter; and it is performed through an anatomical space. The preliminary results do not seem to be compromised, but consistent with the former technique.

The surgical dislocation of the hip should still be considered the gold standard in a general acetabular overcoverage (ie, coxa profunda), because it allows the surgeon to address the entire acetabular rim and not just the anterosuperior portion. In our series we treated one case of coxa profunda with the anterior procedure and the limited osteoplasty of the anterosuperior rim sufficed to gain a satisfactory outcome.

Surgical management of femoroacetabular impingement is a developing field. The proposed technique, although borne out only by short-term results, appears to be a reliable procedure for the painful impinging hip. Longer term follow-up will demonstrate its potential capacity to delay the onset of a degenerative joint disease.

References

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  2. Tönnis D, Heinecke A. Acetabular and femoral anteversion: relationship with osteoarthritis of the hip. J Bone Joint Surg Am. 1999; 81:1747-1770.
  3. Hofmann S, Tschauner C, Urban M, Eder T, Czerny C. [Clinical and diagnostic imaging of labrum lesions in the hip joint]. Klinische und Bildgebende Diagnostik der labrumlasion des Huftgelenks. Orthopade. 1998; 27:681-689.
  4. Ito K, Minka MA II, Leunig M, Werlen S, Ganz R. Femoroacetabular impingement and the cam-effect. A MRI-based quantitative anatomical study of the femoral head–neck offset. J Bone Joint Surg Br. 2001; 83:171-176.
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  9. Ganz R, Gill TJ, Gautier E, Ganz K, Krugel N, Berlemann U. Surgical dislocation of the adult hip. A technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br. 2001; 83:1119-1124.
  10. Lavigne M, Parvizi J, Beck M, Siebenrock KA, Ganz R, Leunig M. Anterior femoroacetabular impingement: part I. Techniques of joint preserving surgery. Clin Orthop Relat Res. 2004; 418:61-66.
  11. Tönnis D. Normal values of the hip joint for the evaluation of X-rays in children and adults. Clin Orthop Relat Res. 1976; 119:39-47.
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  15. Smith-Petersen MN. Treatment of malum coxae senilis, old slipped upper femoral epiphysis, intrapelvic protrusion of the acetabulum, and coxa plana by means of acetabuloplasty. J Bone Joint Surg. 1936 ;18:869-880.
  16. Beck M, Leunig M, Parvizi J, Boutier V, Wyss D, Ganz R. Anterior femoroacetabular impingement: part II. Midterm results of surgical treatment. Clin Orthop Relat Res. 2004; 418:67-73.
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Authors

Drs Pierannunzii and d’Imporzano are from the Third Division of Orthopedics and Trauma, Gaetano Pini Orthopedic Institute, Milan, Italy.

Correspondence should be addressed to: Luca Pierannunzii, MD, Via P. Finzi, 15 - 20126, Milan, Italy.

10.3928/01477447-20070201-17

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