Role of Chiari osteotomy in treating degenerative hip arthritis: A review

Abstract

Chiari pelvic osteotomy (CPO) or medial displacement pelvic osteotomy is a surgical procedure of making a congruent shelf above intact hip joint by using the cancellous bone of ilium along with capsular interpositioning to contain the femoral head and bear weight. CPO is usually considered a salvage procedure indicated in patients with dysplastic acetabular sockets as a part of developmental hip dysplasia. It has been widely performed for several decades but since 1990s number of CPO procedures has decreased because of use of other pelvic osteotomies, total hip arthroplasty (THA), ultrasound screening and narrowing indications for this procedure. However, CPO is not a historical procedure and it has viable indications in modern orthopaedic surgery, especially in patients who prefer joint-conservating procedure or in situations when THA is not feasible. Moreover, keeping the native hip as long as possible should be preferred modern orthopaedic approach. The Chiari osteotomy can produce excellent results in patients who have right indications and when other procedures are not suitable. On the other hand, there are several disadvantages of this procedure such as narrowing of the pelvis, shortening of the limb and risk of sciatic nerve palsy. With in-depth analysis of literature, we discuss indications for CPO, surgical technique of CPO, THA conversion rate after CPO, the interval from the CPO to THA and CPO survival rate.

1. Introduction

First Chiari osteotomy was performed by Karl Chiari in 1952 at University Hospital Vienna. He waited 2 years to perform second operation, after which he concluded that operation was successful. In next period of 20 years, he performed 2000 pelvic osteotomies and published several papers with description of surgery in German and other languages. After his demise, Chiari pelvic osteotomy (CPO) was frequently performed at Department of Orthopaedics in Vienna¹ and various institutions across the world. However, CPO has become less frequently performed procedure because of use of other procedures (Salter, triple osteotomies, and total hip arthroplasty (THA) at younger age) and use of ultrasound screening and early treatment of new-born. Also, historically, indications for CPO included coxa magna after Perthes disease, paralytic hip due to cerebral palsy or poliomyelitis and developmental hip dysplasia (DDH). Today, indication is narrowed to symptomatic, incongruent dysplasia, with early degenerative changes predominantly in adolescent and young adults, but it can also be performed in the middle age according to Karami et al.² Moreover, CPO is not an alternative in young adult patients in whom there is acetabular dysplasia and early signs of osteoarthritis (OA), but rather it is the procedure of choice (Fig. 1).³ Also, THA is not always appropriate and feasible in Low and Middle Income Countries (LMIC) due to lack of surgical and financial resources.⁴ Furthermore, even though THA was chosen as operation of the century, there is tendency to preserve the native hip as long as possible because CPO may possibly slow the progression of OA.^1,5 In this review, surgical technique of CPO, THA conversion rate after CPO, the interval from the CPO to THA and CPO survival rate will be discussed.

Fig. 1.

Anteroposterior radiograph of the patient at the age of 13, showing residual acetabular dysplasia with a center-edge angle of 9° and 59% femoral head coverage.¹¹

2. Surgical technique OF CPO

CPO provides stable osseous coverage of the displaced femoral head and reduces the load across the hip by shortening the medial lever arm.⁶ It aims to enlarge acetabulum by medial displacement of distal pelvic fragment, after which the superior fragment of the osteotomy becomes a shelf, with capsule interposed between osteotomy and femoral head. Shortening the medial lever arm reduces the pressure on the femoral head. According to Chiari, the pressure on the femoral head is reduced as much as 20% with 15 mm medialisation.⁷ Chiari osteotomy is usually considered a salvage procedure in cases of hip incongruity, by providing a fibrocartilaginous cover over the femoral head as a result of the metaplasia of the interposed capsule.⁷ Adequate preoperative radiographs including pelvis and both hips are obtained and Wiberg Centre Edge (CE) angle⁸ as well as head sphericity⁹ are measured and Tönnis OA grading¹⁰ is done. CE angle is formed by a line drawn vertically through the centre of femoral head and a line from the centre of femoral head to the outer edge of acetabular roof. Angle greater than 25° is considered normal whereas angle less than 20° indicates hip dysplasia. Head sphericity is preoperatively classified according to Mose circles classification in 3 categories: 1. Regular - spherical with normal head, neck and acetabulum (minimal and maximal radial difference of the femoral head contour is within 2 mm of the Mose circles), 2. Irregular - spherical femoral head with coxa magna, short neck or steep acetabulum (minimal and maximal radial difference of the femoral head contour is within 2–6 mm of the Mose circles), 3. Very irregular - ovoid femoral head contour (minimal and maximal radial difference of the femoral head contour is ≥ 7 mm of the Mose circles). Tonnis classification of hip OA consists with 3 progressive degrees of degenerative changes to the hip such as narrowing of joint space, sclerosis, cysts, deformity of femoral head, avascular necrosis, etc.

In original surgical technique published by Chiari¹² use of a traction table was recommended to facilitate exposure of the operative field and to ease the intraoperative fluoroscopy. Patient is positioned on table with the affected hip slightly abducted and rotated outwards, in that way gluteus medius is relaxed and the surgeon can easily manipulate the femur. Other surgeons also recommend using a traction table or traction devices.¹³ On the other hand, some authors do not recommend using traction table or traction devices because it can result in low-level osteotomy.¹⁴ The most common approach used for procedure is originally described anterior iliofemoral or Smith-Peterson approach. This approach provides excellent and wide exposure of operating field and minimises damage to the surrounding tissue. Other approaches, such as a posterolateral and Ollier lateral U approach to perform a trochanteric osteotomy are also described.¹⁵ There are several advantages to the lateral approaches (opposed to the anterior approach): easy to achieve proper angle of the osteotomy, greater trochanter osteotomy can be performed and displaced distally thus decreasing the risk of Trendelenburg gait. The use of intraoperative fluoroscopy helps in directing the osteotomy and checking adequate displacement. The anterior (Smith-Peterson) approach ensures safe access to the hip joint and ilium. This approach exploits the internervous plane between sartorius muscle (femoral nerve) and tensor fasciae lata muscle (superior gluteal nerve). A small sandbag under the ipsilateral buttock elevates the hemipelvis facilitating the approach. Surgical landmarks for this approach are the anterior superior iliac spine (ASIS) and the iliac crest which are generally easy to palpate. Skin incision starts laterally to the anterior half of iliac crest, proceeding to the ASIS then curving down for 8–10 cm in line with the lateral border of the patella as a general guide. After the superficial surgical dissection, leg is externally rotated to stretch the sartorius muscle and make it more prominent. Interval between the tensor fasciae lata (TFL) and the sartorius is identified by palpating with a finger and opened with a scissors. TFL is separated from the sartorius and retracted laterally. Tensor muscle, gluteus medius and sartorius are dissected at their origin at ASIS and iliac crest (in children cartilage is incised and with raspatory detached from bone allowing muscles to be pulled back). Hohmann retractor or raspatory or similar instrument is then inserted between the capsule and gluteus minimus to protect gluteal vessels and nerves. A blunt Hohmann or similar retractor is placed carefully in the sciatic notch to protect sciatic nerve and iliac vessels. Exposed head of rectus femoris muscle is detached from joint capsule. Carefully identify the curved head of rectus and capsule attachment at the superior aspect of acetabulum, which is essential to select the level of osteotomy. A Gigli saw or an osteotome is used to complete the osteotomy. According to the original technique, the ideal Chiari osteotomy should be immediately above the joint capsule, displaced by 50% of the pelvic width and make an angle of 10° upwards. According to the Jeličić et al.¹⁶ the level of osteotomy has to be less than 10 mm from upper edge of the acetabulum. If it is above that value, then it affects the CPO survival rate. Colton et al.¹⁷ reported that displacing a Chiari osteotomy by more than 50% can cause substantial problems with bone-healing. Placing a bone graft medially on the cut surfaces of the ilium helps to resolve this problem.¹⁸ Position of osteotome or Gigli saw is checked under the fluoroscope. After identifying correct level, osteotomy is started following the capsular insertion in a curved line and ending under anterior inferior iliac spine (AIIS) anteriorly and the sciatic notch posteriorly. During the osteotomy position of osteotome or Gigli saw is repeatedly checked with fluoroscope. Care must be taken not to penetrate the capsule or inadvertently moving osteotomy downwards to avoid injury to vessels in the sciatic notch or medially. Once the osteotomy is completed, medialisation of the hip is performed by releasing the traction and abducting the hip. This manoeuvre is easy if osteotomy is correctly orientated. Adhering to the technical details described above is essential to achieve successful and stable displacement.¹ Fixation is achieved with cortical screws or multiple threaded Steinmann pins or with Kirschner wires. In the original technique, internal fixation with screws or wires is generally considered unnecessary if the osteotomy surfaces are in good contact. It is important that the coverage of femoral head is sufficient. Check the correct displacement and stability of osteotomy under fluoroscope before closing the wound in layers. Blood loss is generally minimal with this technique. In the original method described by Chiari, the patient was placed in a plaster cast in abduction for 3 weeks but with modern techniques of internal fixation hip spica is no longer needed.¹ Postoperatively patients are encouraged to move hip actively and passively as soon as pain allows. They remain non weight bearing on the operated leg for the first 3 weeks and then partial weight bearing for the next 3 weeks with the help of crutches. Patients are allowed full weight bearing after healing of osteotomy (2–4 months postoperatively). X-ray images are obtained postoperatively for measurement of medial displacement (defined as the extent of the medial shift of the distal fragment as a percentage of the width of the innominate bone at the level of osteotomy), CE angle, percentage of femoral head uncoverage and acetabular angle of Sharp (Fig. 2). Also, angle of Chiari which is defined as the angle between line parallel to the inter teardrop line and the osteotomy line is measured (Fig. 3).

Fig. 2.

a) Medial displacement ($\frac{Y}{X}\times 100)$, WA angle and percentage of femoral head uncoverage – extrusion index ($\frac{b}{a}\times 100)$. b) Acetabular angle of Sharp.

Fig. 3.

Radiographic parameters of Chiari osteotomy. Angle of Chiari (α), the angle between the line parallel to the reference line (inter teardrop line) and the osteotomy line.

3. Discussion

Chiari Pelvic Osteotomy (CPO) was originally described for the treatment of degenerative arthritis of hip secondary to developmental dysplasia of hip (DDH) and subsequently it was used in a range of other conditions such as sequalae of Perthe's disease¹⁹ and early stages of primary osteoarthritis with good success.²⁰ However, due to recent advances in the early diagnosis and successful non operative treatment of developmental dysplasia of hip, introduction of acetabular osteotomies that reorientate the acetabulum rather than distort it, and success of modern total hip arthroplasty (THA) with good long-term survival even in young patients, CPO is less frequently used. Yet CPO has a role in preserving the native hip in young arthritic patients who decline THA for the fear of requiring at least one if not two revisions in their lifetime^21,22 or in countries where THA is unaffordable. Jeličić et al.¹⁶ have shown that CPO is a good alternative to THA in young patients (40 yrs or younger) with incongruent hip and early degenerative changes.

CPO survival rate is the subject of several studies. Multiple factors, including age and the degree of osteoarthritis at the time of CPO, level of osteotomy, shape of the femoral head, Wiberg angle post-surgery, and percentage displacement influence the survival of CPO, and the main determinants are age and the degree of osteoarthritis. THA conversion rate can be roughly divided into 2 groups. It is less than 10% in younger patients with lower grades of osteoarthritis, whereas it is approximately 40% in older patients with high degree of osteoarthritis according to Tönnis grading. In study by Kotz et al.²³ a total of 15 hips (9%) had undergone THR, seven (5%) of 134 hips with pre- or early-stage OA and eight (21%) of 39 with advanced OA (p = 0.003). The mean interval between osteotomy and THR was 16.4 years (5.1–24.5). The mean age of 33.2 years (22–48) in patients who underwent THR was higher than that of 28.8 years (9–54) in those who did not, but this difference was not significant (p = 0.062). Age at osteotomy correlated inversely with the interval between the osteotomy and THR (r = −0.563, p = 0.029). This study is aligned with previously mentioned fact that the age at the time of the surgery is inversely correlated with the interval between the osteotomy and THA and that patients with lower degree of osteoarthritis before CPO have better clinical outcome than patients with advanced, higher degree osteoarthritis. Level of osteotomy (≤10 mm, >10 mm) does not affect THA conversion rate,¹⁶ but it seems to influence the interval between CPO and conversion to THA. This interval was 14 years in cases where the level of osteotomy ≤10 mm, whereas in patients with the level of osteotomy >10 mm CPO-THA interval was 8 years but without statistically significant difference between the groups (p-value = 0.06).¹⁶ Majority of authors agree that level of osteotomy higher than 10 mm of upper edge of acetabulum has an influence on CPO survival because the progression of OA was more frequent in hips with an osteotomy level >10 mm (8 of 11 hips) than in those in which the level was correct ≤10 mm (33 of 123 hips, p = 0.002). Also, partial osteonecrosis of the femoral head was present in five of nine hips where osteotomy was at a low level. Furthermore, the mean Harris hip score (HHS) at the last follow-up was significantly higher in 157 hips with an appropriate level at osteotomy (82 points (45–100)) compared with 16 hips where the level was too high or too low (76 points (56–100), p = 0.019).24, 25, 26 Matsuno et al.¹⁴ reported that 84% of 88 hips with an appropriate osteotomy level had a good clinical result at an average of 9.3 years postoperatively. The influence of OA degree on CPO survival rate has also been established. The 20-year survival rates in the pre - or early - stage and advanced group were 96.3% and 84.7%, and the 30-year survival rates were 91.8% and 43.6%, respectively, in study of Kotz et al.²³ Femoral head shape also influences CPO survival but there is no statistically significant difference between groups with different femoral head shapes in CPO-THA interval rate or THA conversion rate.¹⁶ Studies differ about which femoral head shape predicts good CPO outcome. According to some authors, spherical and ovoid shape of the femoral head are favourable parameters for CPO survival, whereas the head with lateral prominence makes the correct upward osteotomy impossible and will cause unacceptable concentration of load and in that way will decrease survival of CPO.^25,27 On the other hand, flat femoral head is favourable parameter in prediction of CPO survival, because the newly formed acetabulum undergoes remodelling after the operation to conform to the shape of the femoral head, making Chiari osteotomy widely indicated in patients with a flat femoral head. Also, when comparing the instability between the acetabulum and the femoral head, there may be many advantages in a flat femoral head for a flat new acetabulum.²⁰ Furthermore, medial displacement and postoperative Wiberg angle also have influence on CPO survival rate. Jeličić et al. showed that there is no statistically significant difference in CPO survival rate between the groups of patients with Wiberg angle higher or lesser than 30° and that there is statistically significant better CPO survival rate in group of patients with medial displacement above 40% (52% CPO survival rate in patients with medial displacement ≤40% and 68% survival rate in patients with medial displacement >40%) but without difference in CPO-THA interval.¹⁶ With no statistically significant difference Ohashi et al.²⁸ concluded that there is a reduction in the percentage of cases with progressive osteoarthritic changes when the CE angle after CPO was 30°–60° or the medial displacement 40%–60%. Regarding the femoral head coverage, Reynolds et al.²⁷ concluded it should be around 80% for good clinical outcome. Unsatisfactory outcome is more frequently (68%) noticed in patients younger than 10 years and less frequently (23%) in patients above the age of 10 ²⁹. This results might be related to the anti-Chiari effect reported by Hosny et al.²⁹ The anti-Chiari effect is described as decentring and cranial movement of femoral head which some authors relate to the growth cartilage injury of the roof of acetabulum, while according to the others it is related to the technical mistake during the Chiari osteotomy (position of the osteotomy being too high).^19,30 Studies have shown that although CPO relieves pain it does little to slow down OA changes.³¹ Finally, although several factors have been identified to influence the outcomes of CPO, it is not clear which of these parameters are important determinants.²⁸ According to Windhager et al.¹ and Ito et al.²⁴ CPO does not stop, but possibly slows down the progression of hip OA. Chiari pelvic osteotomy is rarely indicated in children and young patients with DDH, because other anatomic osteotomies are preferable in this group.

Chiari osteotomy is frequently criticised because of forming substitute acetabulum with hip capsule, but according to Kotz et al.²³ that effect is outweighed by favourable biomechanical properties of medialisation and good clinical outcomes at long-term follow up. CPO doesn't seem to adversely affect the conversion to THA. Hashemi-Nejad et al. ³² concluded that THA in the post-Chiari patients require fewer acetabular augmentation procedures and had shorter operating times, less blood loss, and fewer early complications. Also, CPO may delay the need for THA, may facilitate acetabular reconstruction, and does not seem to compromise the outcome.

The disadvantages of the Chiari Pelvic Osteotomy include narrowing of the pelvis (so bilateral Chiari osteotomy in women may compromise normal vaginal delivery), a minor degree of shortening of the lower limb because of the upward and medial displacement of the inferior segment of the innominate bone, and the risk of sciatic nerve palsy.³¹

4. Conclusion

CPO has a role in preserving the native hip and careful patient selection and meticulous technique are essential for good outcome. It doesn't adversely affect the future conversion to a total hip arthroplasty. It is a great procedure for sparing the native hip and delaying THA, especially in middle/low-income countries which do not have adequate resources for joint replacement surgery.

Declaration of competing interest

None.