Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

183. Bernese Periacetabular Osteotomy

Travis H. Matheney and Michael B. Millis

DEFINITION

images Hip dysplasia is the most common etiology of coxarthrosis, often leading to arthroplasty long before joint replacement can be considered a lifetime solution.3

images Surgical realignment of the congruous dysplastic acetabulum can improve or eliminate symptoms for years, sometimes indefinitely, in a majority of appropriately selected patients, even in those with some degree of preoperative arthrosis.1,3,4,68

images Age limits for this procedure are adolescence (closed triradiate cartilage) to an indefinite upper age limit (limited by preoperative arthrosis and other considerations that might make arthroplasty a better choice).

ANATOMY

images The acetabulum lies between the anterior and posterior columns of the pelvis.

images The most common area of acetabular deficiency in developmental dysplasia of the hip (DDH) is anterior and lateral.

images The Bernese periacetabular osteotomy (PAO) differs from the triple osteotomy primarily by maintaining the integrity of the posterior column of the pelvis.

images The Bernese PAO uses five steps to divide the acetabular fragment from the remainder of the pelvis, allowing multiplanar reorientation.

images Important bony landmarks include:

images Iliopectineal eminence (which marks the medialmost extent of the acetabulum)

images Infracotyloid groove (just distal to the acetabulum, where the obturator externus tendon lies; this is the site of the anterior ischial osteotomy)

images Anterosuperior iliac spine (ASIS)

images Apex of the greater sciatic notch

images Ischial spine

images The posterior column is triangular and thickest just posterior to the acetabulum; it becomes much thinner closer to the sciatic notch. For this reason, the optimal plane for the posterior column is angled obliquely to the medial cortex and perpendicular to the lateral cortex of the ischium–posterior column.

PATHOGENESIS

images Genetic and developmental causes exist for “developmental dysplasia.”

images Neuromuscular: Charcot-Marie-Tooth disease and spastic diplegia

images Posttraumatic: injuries to the triradiate cartilage; aggressive excision of the limbus in the infant hip

NATURAL HISTORY

images There is a clear correlation between acetabular dysplasia and osteoarthrosis of the hip.

images The more severe the acetabular dysplasia and any subluxation, the earlier the onset of symptoms from arthrosis.

images Murphy et al5 found that every patient with a lateral center–edge angle less than 16 degrees developed osteoarthritis by age 65.

PATIENT HISTORY AND PHYSICAL FINDINGS

images Key portions of the history include:

images Personal or family history or treatment of DDH

images History of other hip disorders, including Legg-CalvéPerthes

images Trauma

images Skeletal dysplasias

images History of cerebral palsy

images Birth order and weight

images Description of pain or mechanical symptoms, including location, duration, activity limitation, giving way, “clicking,” “catching,” and “popping”

images Physical examination should include gait, limb length, assistive devices, and strength.

images Specific hip tests include the following:

images Trendelenburg test: Demonstrates weakness in abductors.

images Anterior apprehension test: A positive result is a subjective noting of “apprehension” or instability by the patient.

images Anterior impingement test (pain with passive hip flexion, adduction, and internal rotation): Test of anterior labral pathology, not just a tear.

images Bicycle test for abductor fatigability.

images Range of motion (ROM): Dysplastic hips may demonstrate a relative increase in flexion due to anterior acetabular uncoverage. Decreased ROM with pain may indicate arthrosis.

IMAGING AND OTHER DIAGNOSTIC STUDIES

images Radiography includes weight-bearing anteroposterior (AP) views of bilateral hips (FIG 1A), false profile of hips (FIG 1B), and AP views of the hips in maximal abduction and internal rotation (von Rosen view; FIG 1C). These studies allow assessment of lateral and anterior coverage of the femoral head as well as congruency of the hip joint. Additionally noted will be presence of hinge abduction, which is a relative contraindication to PAO.

images Radiographic parameters include the following:

images Lateral center–edge angle of Wiberg measured from AP view of the hip (lower limits of normal about 25 degrees; see Fig 1A)

images Anterior center–edge angle of Lequesne and de Seze (lower limits of normal 20 degrees measured on the false profile view; see Fig 1B)

images Tönnis acetabular roof angle measured on the AP view of the hip (upper limits of normal 10 to 15 degrees; FIG 1D)

images

FIG 1  A. AP view of pelvis and hips. Lateral center–edge angle of Wiberg is marked on right hip. B. False profile view of right hip. Anterior center–edge angle of Lequesne and de Seze is marked. The anterior edge is marked to the edge of the sourcil. C. Von Rosen AP view of pelvis with hips in maximal abduction and internal rotation. This is used to assess congruency and mimic the appearance of the hip after reorienting acetabular osteotomy. D. AP view of pelvis and hips. The Tönnis acetabular roof angle is marked on the right hip.

images Crossover sign (anterior wall shadow crossing posterior wall shadow on AP view of the pelvis)

images Assessment of the line of Shenton for breaks indicative of femoral head subluxation

images Computed tomography (CT) scan of both hips with threedimensional reconstruction as well as with axial slices through the femoral condyles may be of assistance in preoperatively assessing the amount and direction of correction required as well as the potential need for proximal femoral osteotomy.

images Magnetic resonance imaging (MRI) of involved hips with radial sequences centered at the femoral head allows assessment of articular and labral cartilage.

images Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) is a recently developed technique that assesses the mechanical damage to the articular cartilage. It has been demonstrated to be a better preoperative predictor than plain radiographs in determining outcome after PAO.2

NONOPERATIVE MANAGEMENT

images Activity and job modification may be of benefit in delaying or mitigating arthritic symptoms.

images Physical therapy may be of some benefit in increasing ROM and strength. To date, there are no data to suggest that a specific therapy regimen can affect the onset of arthritis in the dysplastic hip.

SURGICAL MANAGEMENT

images Indication: Symptomatic, congruous acetabular dysplasia (closed triradiate cartilage) with lateral and anterior center– edge angles 18 degrees or less

images Contraindications: Tönnis osteoarthrosis grade 2 or more (subchondral cysts, significant joint space narrowing); severe limitation of motion secondary to arthrosis; active joint infection

Preoperative Planning

images Radiographs and MRI are evaluated to assess the following:

images Degree and character of dysplasia

images Amount and direction of correction required to normalize the Tönnis acetabular roof angle (0 to 10 degrees), correct subluxation, and improve mechanical stability

images Proximal femoral deformity may also require treatment at time of PAO.

images Presence of acetabular articular or labral lesions (seen on MRI) should also be taken into consideration, as treatment either arthroscopically (before the osteotomy) or intraoperatively through limited arthrotomy may be required for best long-term results.

images Isolated treatment of a labral lesion in the presence of acetabular dysplasia is contraindicated. Simultaneous acetabular realignment must be considered.

images The torn acetabular labrum is usually associated with other structural abnormality within the hip (femoral acetabular impingement or DDH), which may also require correction for best results.9

images Partial weight-bearing technique is taught preoperatively in preparation for postoperative mobilization.

Positioning

images The patient is positioned supine on a radiolucent table.

images The operative extremity is prepared and draped free up to the costal margin; the surgeon should be certain to prepare and drape posteriorly to at least the posterior third of the ilium and medially to the umbilicus.

images Analgesia: We typically use an epidural for perioperative pain management; it is removed by postoperative day 3. However, this is not mandatory.

Approach

images The standard longitudinal anterior Smith-Petersen incision and approach to the hip provides the appropriate access (FIG 2A).

images As an alternative, an ilioinguinal (bikini) incision may be used followed by a similar deep approach (FIG 2B). This incision typically provides a better cosmetic result but can limit access for the anterior ischial osteotomy. Therefore, we recommend the standard anterior incision for larger and more muscular patients.

images

FIG 2  A. Hip with traditional Smith-Petersen incision marked. B. Hip with bikini-type incision marked.

TECHNIQUES

SUPERFICIAL DISSECTION

images  The skin is incised into subcutaneous tissue.

images  The fascia over the external oblique and gluteus medius is identified and incised posterior to the ASIS and the plane between the two muscles is developed to expose the periosteum over the iliac crest.

images  The periosteum is sharply divided over the iliac crest and subperiosteal dissection carried out over the inner table of the ilium. This space is packed with sponges for hemostasis.

images  Entry into the tensor fascia lata–sartorius interval is initially accomplished via the compartment of the proximal tensor fascia lata to avoid injury to the lateral femoral cutaneous nerve. The tensor fascia lata is bluntly elevated off the intermuscular septum and the compartment floor is identified proximally until the anterior ilium is palpated.

images  Once hemostasis is attained, the ASIS is predrilled with a 2.5-mm drill and the anterior 1 × 1 × 1-cm portion is osteotomized to facilitate the medial dissection and later repair.

images Alternatively, the sartorius can be taken off with just a thin wafer of bone that will be sewn back in place at the end instead of with a screw.

images  Subperiosteal dissection is continued to the anteroinferior iliac spine (AIIS).

DEEP DISSECTION

images  Flexion and adduction of the hip facilitates the deep intrapelvic and superior ramus dissection.

images  The reflected head of the rectus femoris is divided at its junction with the direct head (TECH FIG 1A,B).

images  The direct head and underlying capsular iliacus are elevated as a unit and reflected distally and medially off the underlying joint capsule.

images  The iliacus, sartorius, and abdominal contents are reflected medially.

images  The psoas sheath is opened longitudinally, and the psoas tendon is retracted medially to allow access to the superior pubic ramus medial to the iliopectineal eminence.

images

images

TECH FIG 1  A. Deep dissection through anterior hip interval. The direct and indirect heads of the rectus femoris have been cut. B. Surgical exposure of the anterior hip capsule (arrow). The iliac crest is marked in the left half of the wound before subperiosteal dissection of the iliacus. C,D. Intraoperative fluoroscopic AP views of the right hip. Lane bone lever is used to first palpate the outer and inner aspects of the anterior ischium.

images  The interval between the medial joint capsule and the iliopsoas tendon is created and sequentially dilated using the tip of a long-handled Mayo scissor, then further by Lane bone levers, with the tips of each palpating the anterior ischium at the infracotyloid groove.

images  Proper placement of the scissor and bone levers can be confirmed with the image intensifier (TECH FIG 1C,D).

OSTEOTOMIES

Anterior Ischial Osteotomy

images  With the hip flexed 45 degrees and slightly adducted, a 30-degree forked, angled bone chisel (Synthes, USA; in 15 or 20-mm blade widths) is carefully inserted through the previously created interval between the medial capsule and psoas tendon to place its tip in contact with the superior portion of the infracotyloid groove of the anterior ischium, just superior to the obturator externus tendon (TECH FIG 2A–C).

images  Staying proximal to the obturator externus tendon helps to protect the nearby medial femoral circumflex artery. The medial and lateral aspects of the ischium should be gently palpated with the chisel. Proper chisel placement (about 1 cm below the inferior acetabular lip) is confirmed on AP and oblique projections with the image intensifier (TECH FIG 2D).

images  The osteotome is impacted in a posterior direction to a depth of 15 to 20 mm in a posterior direction and through both medial and lateral cortices of the ischium (TECH FIG 2E).

images  Care should be taken not to drive the osteotome too deeply through the lateral cortex, as the sciatic nerve is nearby.

images

images

TECH FIG 2  A. Surgical exposure and placement of osteotome for ischial cut. The osteotome is placed medial to the joint capsule and lateral to the iliopsoas. B,C. Bone models demonstrating the planned position of the osteotome for the ischial cut: Ganz angled chisel (B) and Mast curved chisel (C). D,E. Intraoperative fluoroscopic AP view of right hip with Ganz 30-degree osteotome (D) at the anterior ischium and false profile view of right hip with Mast curved chisel (E) seated into anterior ischium. The sciatic notch and ischial spine are outlined in black. Proper direction of this cut should also be confirmed on fluoroscopic false profile view.

Superior Pubic Ramus Osteotomy

images  The hip is kept flexed and adducted to relax the anterior soft tissues.

images  The psoas tendon and medial structures are gently retracted medially (TECH FIG 3A).

images  After circumferential subperiosteal dissection of the ramus, either a spiked Hohmann retractor or a largegauge Kirschner wire is impacted into the superior aspect of the ramus at least 1 cm medial to the iliopectineal eminence (TECH FIG 3B).

images  Blunt Hohmann retractors, Rang retractors, or Lane bone levers are placed anteriorly and posteriorly as well as inferior to the ramus to protect the obturator nerve and artery.

images  The osteotomy is perpendicular to the long axis of the ramus when viewed from above but oblique from distalmedial to proximal-lateral when viewed from the front and may be carried out either by passing a Gigli saw around the ramus and sawing upward away from the retractors or by impacting a straight osteotome just lateral to the spiked Hohmann or Kirschner wire. In the former method, the Gigli saw is passed with the aid of a Satinsky vascular clamp.

images The key to this osteotomy is to stay medial to the iliopectineal eminence and avoid entering the medial acetabulum (TECH FIG 3C).

images  Arthrotomy and intracapsular inspection: At a point before all osteotomies are completed, an arthrotomy may be performed to identify and treat intra-articular lesions such as a torn labrum or impingement lesions of the femoral head and neck.

images This is closed loosely with simple, interrupted absorbable suture before proceeding with the remainder of the osteotomies.

images

TECH FIG 3  A. Anterior approach. The superior pubic ramus is exposed and the iliopsoas is retracted medially. B. Bone model demonstrating the superior ramus osteotomy. The Lane bone levers are placed on either side of the ramus and a Kirschner wire is placed as a retractor. The iliopectineal eminence is marked with a circleC. Intraoperative fluoroscopic false profile view of hip. A small Hohmann retractor is placed under the abductors aiming toward the apex of the sciatic notch.

images

TECH FIG 4  Bone model demonstrating the saw cut of the ilium aiming toward a point about 1 cm above the iliopectineal line.

Supra-acetabular Iliac Osteotomy

images  A 1.5to 2-mm subperiosteal window is started beneath the anterior abductors just distal to the ASIS without disturbing the abductor origin.

images  The leg is slightly abducted and extended to allow atraumatic subperiosteal dissection using a narrow elevator posteriorly toward, but not into, the apex of the greater sciatic notch.

images  A narrow, long, spiked Hohmann retractor is placed in this window. Correct placement is confirmed with image intensifier; in the lateral projection the spike of the Hohmann should point toward the apex of the sciatic notch (TECH FIG 3C).

images  The iliacus is retracted medially with a reverse Hohmann with its tip on the quadrilateral surface.

images  Under direct vision the iliac osteotomy is performed with an oscillating saw and cooling irrigation in line with the Hohmann retractor until reaching a point about 1 cm above the iliopectineal line (well anterior to the notch). This end point of the iliac saw cut represents the posterosuperior corner of the PAO. This corner is also the starting point of the posterior column osteotomy, which will be midway between the sciatic notch and posterior acetabulum (TECH FIG 4).

images At this point, a single Schanz screw on T-handled chuck is inserted into the acetabular fragment distal and parallel to the iliac saw cut, well above the dome of the acetabulum, into a hole predrilled with a 3.2-mm drill.

Posterior Column Osteotomy

images  The leg is once again flexed and adducted to relax the medial soft tissues.

images  A reverse blunt Hohmann retractor is placed medially with the tip on the ischial spine. Dissection into the sciatic notch is neither necessary nor recommended.

images  The osteotomy is made through the medial cortex with a long, straight 1.5-cm osteotome. It extends from the posterior end of the iliac saw cut, passing over the iliopectineal line, through the medial quadrilateral plate, parallel to the anterior edge of the sciatic notch on iliac oblique fluoroscopy, and is directed toward the ischial spine (TECH FIG 5A).

images  This osteotomy must extend at least 4 cm below the iliopectineal line to avoid entry into the acetabulum when completing the final (posteroinferior) infraacetabular osteotomy. This posterior cut is made first through the medial, then second through the lateral wall of the ischium.

images The ischium is wider here than at its anterior extent. If pictured from above, it resembles a triangle with the narrower apex at the anterior edge of the sciatic notch. Therefore, the surgeon should not place the osteotome perpendicular to the medial quadrilateral plate. Instead, the free medial edge of the osteotome should be tipped 10 to 15 degrees away from the sciatic notch to create a more true coronal-plane osteotomy, perpendicular to the lateral cortex of the posterior column (TECH FIG 5B,C).

images

images

TECH FIG 5  A. Bone model demonstrating the division of the posterior column. B,C. The incorrect (B) and the correct (C) angles of the osteotome for division of the posterior column. The dotted lineindicates the relative position of the acetabulum and lateral aspect of the ischium. The proper angle of the osteotome is away from the sciatic notch about 10 to 15 degrees. D. Intraoperative fluoroscopic false profile view of the right hip. Division of the posterior column is performed here. The borders of the osteotomy (acetabulum anteriorly and sciatic notch posteriorly) should be clearly visible to avoid intra-articular or intranotch extension of the osteotomy.

images  Correct angulation and positioning are once again confirmed by the image intensifier (TECH FIG 5D).

Completion Osteotomy

images  The final osteotomy is a completion osteotomy of the posteroinferomedial corner of quadrilateral plate connecting the anterior and posterior ischial cuts.

images  A 30-degree long-handled chisel is used to connect these two prior osteotomies (TECH FIG 6).

images  A key point: the blade is placed to connect the prior cuts and the osteotome face should not be more than 50 degrees off the quadrilateral plate. This will prevent accidentally aiming anteriorly into the acetabulum.

images

TECH FIG 6  A. Bone model of right pelvis demonstrating the final cut with a bent osteotome to connect the anterior ischial and posterior column osteotomies. B. Intraoperative fluoroscopic false profile view showing proper positioning of the osteotome.

ACETABULAR DISPLACEMENT

images  A 1-inch straight Lambotte chisel is placed into the supraacetabular iliac saw cut to both confirm completion of the lateral cortex osteotomy and protect the cancellous bone above the acetabulum during displacement.

images  The tines of a Weber bone clamp are placed onto the superior ramus portion of the acetabular fragment in such a way as to place its handle anterior and in contact with the Schanz screw (TECH FIG 7A).

images  A lamina spreader is placed into the iliac osteotomy between the posterosuperior intact ilium and the Lambotte chisel anteriorly.

images  While gently opening the lamina spreader, the Schanz screw and Weber clamp are used to mobilize the acetabular fragment. It is important to ascertain whether the posterior and anterior osteotomies are complete; otherwise, the fragment will not freely rotate and the common outcome will be distal and lateral displacement as you hinge on the lateral, intact cortices. These cuts can be inspected with a narrow or broad 30-degree chisel (TECH FIG 7B).

images  Once the fragment is completely free, it may be positioned to obtain the desired correction. As previously noted, the most common deficiency is anterior and lateral. Therefore, the most commonly used maneuvers are to lift the acetabular fragment slightly toward the ceiling, creating an initial displacement, followed by a three-step movement of lateral, distal, and internal rotation.

images When performed properly, the posteroinferior corner of the acetabular fragment should be impacted slightly into the superior intact iliac cut and the prominent superior tip of the acetabular fragment should be roughly in line with the superior intact iliac crest (TECH FIG 7C).

images  The radiographic “teardrop” and its relation to the femoral head after fragment positioning should be elevated and tilted laterally commensurate with the amount of lateral correction.

images

TECH FIG 7  A. Bone model showing placement of Schanz screw (far left) and large bone-holding clamp for manipulation of acetabular fragment. The bone clamp is placed anterior to the Schanz screw. B.Intraoperative fluoroscopic false profile view of right hip. Seen here is displacement of the acetabular fragment with a lamina spreader (top) and use of an angled chisel from medial to lateral to find areas where the osteotomies are not complete. C. Sawbones model showing acetabular fragment placement. The posteroinferior corner of the fragment is impacted into the superior iliac wing and its prominent anterior spike is roughly in line with the intact iliac crest.

images  It is commonly necessary to medialize the acetabular fragment a little once the desired anterolateral coverage is obtained to recreate the proper position of the femoral head in relation to the medial pelvis. This will maintain proper biomechanical position of the femur in relation to the pelvis.

ACETABULAR FIXATION

images  Once the desired acetabular position is obtained, 3/32-inch smooth Kirschner wires (the approximate diameter of a 2.5-mm drill) are placed proximal to distal through the ilium and into the fragment in a divergent pattern.

images  At this point we perform a final fragment position check in the AP and false profile views (TECH FIG 8A,B).

images Importantly, in the false profile view, we check the anterior femoral head coverage in full extension and at 100 degrees of flexion (TECH FIG 8C). In the former view, the sourcil should be roughly horizontal, the femoral head should be well covered, and the line of Shenton should be intact. The false profile view is to confirm that we have neither overcovered the femoral head nor created impingement from a femoral-sided deformity.

images

images

TECH FIG 8  A,B. Intraoperative fluoroscopic AP and false profile of the right hip. Preliminary check of fragment position. It is important to obtain at least one view including the sacrococcygeal joint over and about 2 cm above the pubic symphysis. This aids in confirming proper final positioning of the acetabular fragment. C. Intraoperative fluoroscopic false profile view of the right hip with the hip maximally flexed. This confirms that the surgeon has not overcovered the femoral head, thus creating femoroacetabular impingement. D,E. Intraoperative fluoroscopic AP and false profile views of right hip. The sourcil is now horizontal with adequate-appearing femoral head coverage in both views. The femoral head is medialized appropriately.

images If there is less than 90 degrees of flexion on palpation or radiograph, it may be necessary to either reposition the fragment or address femoral-sided deformity.

images  The Kirschner wires are measured for depth and length and then replaced with either 3.5-mm or 4.5-mm cortical screws.

images  The image intensifier is used to confirm extra-articular placement of all screws (TECH FIG 8D,E).

images  An additional “home run” screw may be placed anterior to posterior from the AIIS posteriorly into the inferior ilium if required for stability (especially in patients who are ligamentously lax or have a neuromuscular condition or poor bone quality). We prefer not to use this screw unless necessary, as it is our practice to remove these screws once bony healing is confirmed for screw head irritation or in case MRI is to be performed at a later point.

images  The anterior iliac prominence of the acetabular fragment is trimmed and used for bone graft.

images  Gelfoam is placed along osteotomy sites to assist with hemostasis.

WOUND CLOSURE

images  All sponges are removed and wounds are irrigated copiously.

images  Suction drains are placed under the iliacus.

images  The ASIS osteotomy (if performed) is reattached either by using a 3.5-mm, partially threaded cancellous screw and washer or by being sewn back with heavy, absorbable suture through thinner wafer.

images  Careful attention is paid to proper, tight closure over the iliac crest. This is accomplished by predrilling holes in the iliac crest to facilitate passage of heavy, absorbable sutures to reattach the abductor, iliacus, and external oblique musculature.

images  The remainder of the wound is closed in layers.

images

POSTOPERATIVE CARE

images Sitting is permitted on postoperative day 2.

images Partial weight bearing is reviewed by a physical therapist once the epidural catheter is removed on postoperative day 2 or 3.

images Weight bearing is progressed from partial to full, typically by 6 to 8 weeks with radiographic healing and return of abductor strength.

images Range of motion is limited to 90 degrees of flexion, 10 degrees from full extension, and 10 degrees of adduction, abduction, and rotation for the first 6 weeks.

images Resistive exercises are avoided for 3 months.

images Patients older than 16 years are given either low-molecular-weight heparin or warfarin for 4 to 6 weeks.

images Nonsteroidal anti-inflammatories are avoided.

OUTCOMES

images Outcomes are generally good to excellent in the appropriately selected patient.

images Hips with minimal arthrosis (more than 2 mm of joint space and no significant subchondral changes) in younger (less than 35 years old) patients have demonstrated significant improvement in Harris hip and Merle D'Aubigne scores that can last at least 20 years.1,3,4,68

images Hips with moderate to advanced arthrosis in older patients can still show significant improvement in symptoms. However, their symptom relief may be shorter-lived, requiring conversion to either a surface replacement or total hip arthroplasty.

COMPLICATIONS

images Sciatic or lateral femoral cutaneous nerve palsy

images Postoperative wound hematoma requiring return to operating room

images Wound infection

images Nonunion of pubic ramus

images Heterotopic ossification

images Vascular injury

images Intra-articular osteotomy

images Malalignment of fragment leading to insufficient correction or overcorrection

REFERENCES

· Clohisy JC, Barrett SE, Gordon JE, et al. Periacetabular osteotomy for the treatment of severe acetabular dysplasia. J Bone Joint Surg Am 2005;87A:254–259.

· Cunnigham T, Jessel R, Zurakowski D, et al. Delayed gadoliniumenhanced magnetic resonance imaging of cartilage to predict early failure of Bernese periacetabular osteotomy for hip dysplasia. J Bone Joint Surg Am 2006;88A:1540–1549.

· Ganz R, Leunig M, Leunig-Ganz K, et al. The etiology of osteoarthritis of the hip: an integrated mechanical concept. Clin Orthop Relat Res 2008;466:264–272.

· Millis MB, Kim YJ. Rationale of osteotomy and related procedures for hip preservation: a review. Clin Orthop Relat Res 2002;405:108–121.

· Murphy SB, Ganz R, Muller M. The prognosis in untreated dysplasia of the hip. J Bone Joint Surg Am 1995;77A:985–989.

· Peters CL, Erickson JA, Hines JL. Early results of the Bernese periacetabular osteotomy: the learning curve at an academic medical center. J Bone Joint Surg Am 2006;88A:1920–1926.

· Steppacher SD, Tannast M, Ganz R, et al. Mean 20-year followup of Bernese periacetabular osteotomy. Clin Orthop Relat Res 2008;466: 1633–1644.

· Trousdale RT, Ekkernkamp A, Ganz R. Periacetabular and intertrochanteric osteotomy for the treatment of osteoarthrosis in dysplastic hips. J Bone Joint Surg Am 1995;77A:74–85.

· Wenger DE, Kendell KR, Miner MR, et al. Acetabular labral tears rarely occur in the absence of bony abnormalities. Clin Orthop Relat Res 2004;426:145–150.



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