The soft tissue envelope surrounding the hip is complex and includes tendons, ligaments, and joint capsule. As the ability for these structures to respond to repetitive stresses and loads depends mostly on their composition, ligamentous laxity has been shown to influence hip biomechanics [69]. Focal laxity in the anterior capsule as a result of repetitive external rotation and/or extension has been suggested to create an instability and thus potentially subject the acetabular labrum to abnormal stresses [70, 71]. Poor abdominal muscle control may fail to stabilize the pelvis during hip range of motion during activity and may also worsen anterior impingement symptoms by affecting dynamic pelvic tilt.

Proximal femoral version will dictate the position of the anterior aspect of the femoral neck in space relative to the femoral shaft. Hence, depending on hip flexion, the greater the femoral anteversion, the later the acetabular rim collision with the anterior femoral head–neck will occur. Femoral retroversion is considered relative when <15° and absolute when <0°, in the axial plane, to the posterior femoral condyles [72, 73]. The recognition of femoral retroversion is capital in understanding the dynamic interaction between the femoral neck and the anterior acetabular rim during flexion–internal rotation activities. For example, in the setting of a large cam-type morphology associated with a focal overcoverage and relative femoral retroversion, it may be more appropriate to consider addressing only the cam lesion [74]. On the other hand, in cases with the same amount of focal overcoverage and femoral retroversion <0°, but without head–neck offset abnormalities, the most appropriate surgical treatment would include a femoral derotation osteotomy [72, 75] (Fig. 11.4). Similarly, an elevated femoral anteversion would be protective or even adaptive [76] to acetabular retroversion. Final decision to perform adjunctive femoral osteotomy should be based on perioperative impingement-free range of motion of the hip.

In Legg–Calvé–Perthes-related deformity, it has been well established that the varus femoral neck, known as coxa vara, will increase the ease of impingement of the femoral head and greater trochanter on the superior anterior acetabular rim [75, 77]. This situation will be made even worse if retroversion is present [7]. Femoral varus defined as a neck–shaft angle of <125° is also common after childhood hip disease treated with varus intertrochanteric osteotomies (ITO) [77], after femoral neck fractures [78], and in patient with global overcoverage [38]. Thus, if the affected Perthes hip abduction is restricted to less than 20°, a proximal femoral osteotomy should be considered [77]. A final decision dictating whether a valgus-producing ITO [79, 80] or a relative femoral neck lengthening (RFNL) [81, 82] is most appropriate warrants evaluation if extra-articular impingement is present and if femoral offset is enough for adequate abductor muscle tension. The valgus ITO is designed to lateralize the femur to restore normal mechanical alignment of the hip joint [83] while facilitating femoroacetabular clearance. The RFNL procedure is intended to address both extra-articular impingement by advancement of the greater trochanter and intra-articular impingement by head–neck offset improvement via osteochondroplasty [84] (Fig. 11.5). In a study on femoral osteotomies in Perthes hips, Novais noted that 20 % of cases required a valgus-producing ITO, while 61 % underwent a RFNL procedure during the open FAI correcting surgery without increasing complication risks [85]. The overall hip comfort and function has been shown to improve postoperatively [85] with only one posttraumatic femoral neck fracture occurring postoperatively [82]. Midterm OA progression has been noted in 36–40 % of cases with a conversion to a total hip replacement in 7–10 % of cases [84, 86, 87]. Albers et al. have subsequently demonstrated, in a series of 41 isolated RFNL procedures for Perthes disease at a minimum of 5 years of follow-up, that the intervention can reduce pain and improve hip abduction and function [84].

The main indication for SDH in pincer-type impingement is to address the acetabular rim resection and manage the resulting labral damage. Secondary intentions would include RFNL procedures and/or concomitant femoral redirection ITO. In cases of global overcoverage, a circumferential access to abnormal acetabular rim is required and is well addressed via SDH. In cases of focal overcoverage, isolated cranial retroversion can be well suited for the SDH for selected rim trimming. In acetabular retroversion, the SDH is indicated if the retroversion index is less than 30 % or concomitantly to an anteverting periacetabular osteotomy in order to address proximal femoral anatomy such as in patients with sequel after Perthes disease.

The patient is positioned in lateral decubitus on the operating table with the operated leg free, disinfected from last ribs to toes, and draped accordingly. A 20 cm skin incision is made in line with the femoral longitudinal axis, centered on the greater trochanter. Subcutaneous fat is approached until proximal fascia lata is opened longitudinally along the anterior border of the gluteus maximus muscle as well as distally, centered on the femur, for the length of the skin incision. In muscular individuals, dissection is carried further anterior from the midpoint lateral and under the fascia lata, to free the hypertrophied gluteus maximus muscle fibers. This plane is further liberated proximally toward the iliac crest, in the interval between gluteus maximus and fascia lata in order to maximize exposure for later. Gluteus maximus muscle is then reclined posteriorly through gluteus medium fascial sheath, to expose the posterior border of the gluteus medius muscle and allow proper identification of piriformis and short external rotators. The posterior border of the proximal vastus lateralis muscle is elevated on a segment of 5 cm. Careful and precise dissection will allow protection of the inferior gluteal artery which runs along the piriformis muscle and tendon and is aiming to anastomose to the ramus profundus originating from the medial femoral circumflex artery [105]. The greater trochanteric osteotomy will leave a few muscle fibers from the most posterior aspect of the gluteus medius attached to the stable trochanter along with the insertion of the piriformis tendon to protect the extension of the gluteal tributaries to the ramus profundus. The osteotomy should be no greater than 1.5 cm deep and parallel to the leg when the knee is flexed at 90° and the hip in 20° internal rotation. The trochanteric osteotomy can be performed with a 6 mm step cut at its center, and with the saw blade excursion going from posterior to anterior, and just a few millimeter shy of breaking through anteriorly in order to obtain a triplanar trochanteric flip osteotomy [119] (Fig. 11.6). This simple modification from the original technique will allow for increased stability of the trochanteric fragment at closure and earlier weight bearing during recovery. This trochanteric osteotomy is elevated anteriorly (with gluteus medius, gluteus minimus, and vastus lateralis attached) to expose anterior capsule once the interval between gluteus minimus and the cranial border of the piriformis tendon is developed. Bringing the hip in slight flexion and external rotation will expose the joint capsule so a Z-shaped capsulotomy can be performed and the femoral head dislocated posterosuperiorly.

Complete dislocation requires section of the ligamentum teres with long curved scissors while taking care of avoiding acetabular or femoral head cartilage damage in the process. A bone hook placed on the femoral calcar may help in mobilizing the femur in external rotation and flexion to place the leg into a sterile bag on the opposite side of the table. Acetabular rim, labrum, and acetabular cartilage is, at this point, fully accessible for surgical treatment [118, 120]. Labral and cartilage integrity is evaluated carefully. In cases of simple labral tears, labral base can be debrided down to bleeding bone for refixation using bone anchors. Suture knots are typically tied on the capsular outer surface of the labrum to avoid direct contact with the femoral cartilage. When overcoverage has been diagnosed, acetabular rim trimming with a curved osteotome and labral refixation has been described (Fig. 11.7). If the labrum attachment to the acetabular rim is intact, a sharp dissection is required to detach labral tissue for subsequent rim trimming. However, if labrum tissue has been damaged or avulsed, the degenerative labral base is debrided before refixation after appropriate rim trimming. When the labrum is severely damaged or ossified, over a given segment or its totality, and its functional integrity compromised, labral reconstruction has been recommended [121] using ligamentum teres autograft [122], iliotibial band autograft [123], or semitendinosus allograft [124]. Acetabular rim trimming should be conducted with attention to avoid over or under resection. Rim trimming would only be indicated if the lunate surface is oversized [67]; otherwise, it would render the weight-bearing surface smaller, thus increasing joint contact pressure or render the hip unstable [125].

Once the acetabular rim has been decompressed and labral lesions addressed, the residual focal acetabular cartilage injury can be addressed by debridement and microfracture techniques. On the femoral side, the lack of head–neck offset can be evaluated using transparent spherical templates to locate exactly where the head becomes out of sphericity and to guide how much osteochondroplasty is required. The zone of resection is delimited, and a sharp curved osteotome is used to initiate the bone resection from proximal to distal at the head–neck junction. Careful resection is dictated to avoid injury to the retinacular vessels on the superolateral femoral neck. Furthermore, over-resection is discouraged since it may lead to a break in the sealing function of the labrum as it rests onto the femoral head during hip flexion [126]. The femoral head cartilage can also be treated for central osteochondral defects [112, 127–129]. Upon finalization of acetabular rim trimming and femoral osteochondroplasty, a perioperative hip examination under direct visualization should confirm impingement-free full range of motion.

Capsular closure is performed loosely and the trigastric trochanteric osteotomy repositioned on the stable trochanter for fixation with two 4.0 or 4.5 mm cortical screws oriented parallel to each other and toward the lesser trochanter. In cases where subsequent trochanteric distal mobilization, RFNL procedure, or femoral reorientation ITO are indicated, the trochanteric osteotomy would be performed flat to avoid the triplanar deformation at reattachment. Since the vastus lateralis can be safely dissected off the femur distally, surgical exposure for ITO is the same as described above with the addition of an extended skin incision. In rare cases of combined periacetabular osteotomy during the same surgical day, Ganz et al. suggest to perform the ischial osteotomy under direct visualization in a dissection window between inferior gemellus and obturator externus/quadratus femoris (Fig. 11.8).

At closure, the posterior aponeurosis of the vastus lateralis is closed. The fascia lata and subcutaneous tissue are meticulously closed. No drains are necessary. Postoperative mobilization is allowed with 25 % weight bearing, while hip flexion >80° is avoided as well as active abduction. Continuous passive motion of the hip from 0 to 70° has been recommended to avoid intra-articular adhesions for at least 48 hrs. Thromboprophylaxis should also be considered. Weight bearing on the operated leg is progressed when greater trochanter shows signs of healing at 6–8 weeks.

The complication rate for the SDH has been evaluated at 9 % in a retrospective multicenter study when SDH was the surgical approach of a multitude of hip FAI morphologies at 1 year of follow-up [110]. This rate was diminished to 4.8 % if heterotopic ossification was excluded. Of 355 SDH, one complete sciatic paralysis partially resolved, nine patients suffered trochanteric nonunion, one deep infection, and two deep vein thrombosis in the calf that resolved with medical therapy [110]. In the original publication by Ganz et al. on 213 patients, two cases of partial neurapraxia and three cases of trochanteric nonunion were reported. Other authors have subsequently published a 1–1.5 % rate of complications [130, 131].

In patients with overcoverage, the critical part of surgery is the acetabular rim trimming. Removal of an excessive amount of acetabular rim will render a deep socket into a dysplastic one. This complication has never been reported following SDH but has been seen after arthroscopic rim trimming that led to postoperative hip dislocation and the LCEA angle <23°[125, 132]. Steppacher et al. identified a higher failure rate of hips with excessive rim trimming (acetabular index >14°, LCEA <22°), osteoarthritis (OA), increased age (>40), or weight (BMI > 30) at the 5-year mark [133]. There are no guidelines for acetabular bone resection. Preoperative planning is key while some have proposed a mathematical rule [ΔLCEA° = 1.8 + (0.64 × Δmm)] dictating that one millimeter of bony resection corresponds to a 2.4° decrease of the LCEA and five millimeters corresponds to 5°[134]. Others have debated the accuracy of this method and proposed an alternative formula [ΔLCEA°= 1.5 – (1.3 × Δmm)] by studying normal cadaveric hips [135]. The clinical validity and applicability of these calculation methods have not been evaluated to date.

When looking at revision FAI surgery, Ross et al. [136] noted that 13/50 patients presenting for recurrent FAI symptoms had a LCEA equal or greater than 40°. Another center reported on 152 hips undergoing revision FAI surgery, of which 3 had an isolated pincer and 74 had combined lesions [137]. Identified risk factors for revision surgery included female gender and younger age. Moreover, increased anteversion (>20°) was present in 30 %, while femoral retroversion (<5°) was present in 13 % in the revision patient cohort [137]. In a series of 93 hips undergoing SDH, undercorrection and persisting pincer impingement (LCEA >32°) was an important predictor of failure [138]. At the latest follow-up at 10 years, 80 % of patients avoided THA and OA progression, while 38 % had a persisting positive impingement sign.

Systematic reviews conclude that early evidence in the treatment of FAI has proven beneficial for hip function and hip pain with clinically good to excellent results in 68–96 % of the cases [139–141]. Current literature is limited concerning such evidence for pincer–type FAI treatment in isolation. Most of the studies reporting on FAI treatment do so by classifying pincer in combination with cam lesions as mixed type or as pincer alone which represent typically 2–4 % of the total cohorts [139, 141]. SDH has shown improved function in 73 % of pediatric and adolescent patients with FAI where 31/71 hips had rim resection and labral reattachment. No femoral head osteonecrosis was observed at the average of 27 months of follow-up despite having 30 % of patient reoperated for hardware removal [142]. In patients with mixed FAI (cam lesion and crossover sign), Hingsammer et al. evaluated the need for acetabular rim trimming during SDH according to intraoperative hip flexion of >100° and 20° of internal rotation at 90° flexion [143]. If this objective was obtained after the femoral osteochondroplasty, no rim trimming was performed. At a short (1.6 years) follow-up time, all patients achieved 90° hip flexion, there was no difference in patient-reported outcome measures, and half of the impingements sign resolved whether the rim trimming was performed or not. This finding supports Larson et al. [52] who reported on a high prevalence of the crossover sign and/or posterior wall sign in asymptomatic hips (37 %) suggesting that these radiological signs are not necessarily pathognomonic for pincer–type impingement. Contemporary research thus encourages a more conservative approach with surgical resections on the acetabular rim in the presence of cranial retroversion.

Anteverting PAO is indicated in overcoverage when the acetabulum would risk diminishing the size of its weight-bearing articular surface if adequate rim trimming is underdone. Hence, a reverse PAO would better serve global overcoverage with short, down-sloping acetabular sourcil or a negative acetabular index. As for focal overcoverage, the anteverting PAO is indicated in acetabular retroversion with a retroversion index of >30 % [144] or if one aims at a correction of at least 10–20° of anteversion [18]. In rare cases of total acetabular retroversion, the anteverting PAO is the only treatment option. If complicated acetabular reorientation revision surgery is required, one may consider the possibility of arterial compromise of the supra-acetabular arcades from previous surgeries and thus opt for a Tönnis-type triple pelvic osteotomy in order to avoid acetabular fragment osteonecrosis [10].

The modern PAO is performed through an abductor-sparing Smith–Peterson approach with the patient positioned supine on a radiolucent operating table [146]. A 5 cm skin incision is made obliquely from the anterior superior iliac spine (ASIS) to laterally over the iliac crest, and a longitudinal distal extension is made over the medial edge of the tensor fascia lata for 10 cm. Careful subcutaneous dissection is warranted to avoid injury to the lateral femoral cutaneous nerve. The sheath of the tensor fascia lata is opened longitudinally and entered in order to retract its muscle fibers laterally (see Fig. 11.9). The aponeurosis of the abdominal muscle, the inguinal ligament, and the sartorius muscle are surgically detached from the anterior third of the iliac crest. After mobilizing the iliacus muscle subperiosteally down the iliac bone, the hip is brought into flexion to relax tension on rectus femoris and iliopsoas muscle.

Deep dissection down the iliac crest to the anterior inferior iliac spine (AIIS) exposes the origin of the rectus tendon and its reflected head. Special attention must be brought to the cauterization of the ascending branches of the lateral femoral circumflex artery as they appear in the intermuscular interval between tensor and rectus femoris. From the AIIS, the rectus femoris is medially retracted in order to free the capsular attachment of the iliocapsularis muscle from lateral to medial. The iliocapsularis can then be mobilized medially to the rectus, en bloc with the iliopsoas/iliacus muscle complex (see Fig. 11.10). The origin of the rectus is only detached when intracapsular work is indicated which is mostly for femoral head–neck offset correction. Peters et al. have described a modification of the surgical approach that avoids the rectus takedown by approaching medial to rectus femoris and lateral to the iliocapsularis/iliopsoas/iliacus down to medial hip capsule [147]. At this point, the anterior ischium is accessible for the placement of a curved osteotome for the ischial osteotome after blunt dissection down into the infra-articular space between psoas and capsule. The superior pubic ramus is also accessible through this window after retraction of the iliopsoas medial to the iliopubic eminence. The preparation of the outer iliac bone can then be conducted by undergoing a subperiosteal dissection between ASIS and AIIS, in line toward the apex of the greater sciatic notch, for a very limited width to allow for saw motion and positioning. Then, medially over the pelvic brim and down the quadrilateral plate but avoiding the greater sciatic notch, a blunt subperiosteal dissection will allow free motion of osteotomes during the retroacetabular osteotomy.

The first osteotomy is usually the inferior ischial cut. This osteotomy can be performed blind by going medially into the lateral obturator foramen or under fluoroscopic guidance with a false profile view of the hemipelvis [146]. One aims at initiating the bone cut at a 1 cm distance inferior to the articulation and going 15–20 mm deep with the osteotome. Care must be taken to avoid a complete ischial bone cut in order to preserve the posterior ischium in full integrity with the posterior column. The second cut will be conducted at the pubic ramus and as close to the acetabulum as feasible and medial to the iliopubic eminence. The bone cut should be performed perpendicular to the longitudinal axis of the ramus to facilitate acetabular fragment motion. Retractors can be introduced in the superior obturator foramen to protect its content from osteotome injury. A sharp osteotome or a Gigli saw can be used for this osteotomy [146] (see Fig. 11.11).

The third osteotomy is the supra-acetabular osteotomy. It can be performed with an oscillating saw under direct vision while assuming proper muscle protection medially and laterally from the iliac bone. The starting point is just below the ASIS and aiming at the apex of the greater sciatic notch but should end 2 cm from the pelvic brim. At this point, the iliac bone osteotomy travels down the quadrilateral plate to become the retroacetabular osteotomy at equal distance from the greater sciatic notch and the acetabulum as visualized on the false profile view under fluoroscopy. Thus allowing the preservation of the pelvic integrity and safeguarding from intra-articular osteotome penetration. At completion, the retroacetabular osteotomy shall meet the ischial osteotomy to free the acetabular fragment. In very hard bone, a high-speed burr may help in cutting through the pelvic brim turn from the iliac osteotomy into the retroacetabular osteotomy.

Once the acetabular fragment is fully osteotomized, it can be manipulated using a Weber clamp on the pubic rami stump and a 5 mm Schanz screw positioned in the iliac bone, 15 mm above the superior articular line. Initial flexion of the fragment is aided with laminar spreaders and the Schanz screw to distract the iliac and retroacetabular osteotomy. Later, traction upward from the table, followed by rocking motion from medial to lateral with the Schanz screw, will free the residual retroacetabular bony attachments. Then, the acetabular fragment is extended and internally rotated to obtain the desired reorientation of the fragment (Fig. 11.12). In order to mobilize the acetabular fragment into position to correct a retroverted socket, a bone wedge may have to be removed from the iliac bone to allow fragment motion proximally.

Before final fixation with bone screws running from the top of the iliac crest down into the fragment, K-wires stabilize the fragment (Fig. 11.13). A careful radiologic assessment is then required to judge the acetabular fragment position. One aims at obtaining a horizontal acetabular sourcil, appropriate anteversion with the disappearance of the crossover sign and the absence of a posterior wall sign. Moreover, overt medialization or lateralization of the femoral head should be avoided. The acetabular coverage should correspond to a LCEA of 23–33°. Upon finalization of acetabular fragment fixation, a perioperative hip exam under direct vision should confirm impingement-free full range of motion. Otherwise, a capsulotomy should be performed and osteochondroplasty undertaken accordingly.