Surgical hip dislocation with relative femoral neck lengthening and retinacular soft-tissue flap for sequela of Legg–Calve–Perthes disease

Objective Correction of post-LCP (Legg–Calve–Perthes) morphology using surgical hip dislocation with retinacular flap and relative femoral neck lengthening for impingent correction reduces the risk of early arthritis and improves the survival of the native hip joint. Indications Typical post-LCP deformity with external and internal hip impingement due to aspherical enlarged femoral head and shortened femoral neck with high riding trochanter major without advanced osteoarthritis (Tönnis classification ≤ 1) in the younger patient (age < 50 years). Contraindications Advanced global osteoarthritis (Tönnis classification ≥ 2). Surgical technique By performing surgical hip dislocation, full access to the hip joint is gained which allows intra-articular corrections like cartilage and labral repair. Relative femoral neck lengthening involves osteotomy and distalization of the greater trochanter with reduction of the base of the femoral neck, while maintaining vascular perfusion of the femoral head by creation of a retinacular soft-tissue flap. Postoperative management Immediate postoperative mobilization on a passive motion device to prevent capsular adhesions. Patients mobilized with partial weight bearing of 15 kg with the use of crutches for at least 8 weeks. Results In all, 81 hips with symptomatic deformity of the femoral head after healed LCP disease were treated with surgical hip dislocation and offset correction between 1997 and 2020. The mean age at operation was 23 years; mean follow-up was 9 years; 11 hips were converted to total hip arthroplasty and 1 patient died 1 year after the operation. The other 67 hips showed no or minor progression of arthrosis. Complications were 2 subluxations due to instability and 1 pseudarthrosis of the lesser trochanter; no hip developed avascular necrosis.


Introductory remarks
Legg-Calve-Perthes (LCP) disease is an aseptic osteonecrosis of the femoral head of the developing hip. The course of the disease can be divided into typical stages according to Waldenström (Infobox; [9,20]). The disease shows an inhomoge-neous appearance. Some patients show only mild deformations and have little or no late effects, some are affected more severely with early development of arthritis, and some patients are limited in their daily life even before developing osteoarthritis due to impaired range of motion of the hip joint. Around 20% Fig. 1 8 Post-Legg-Calve-Perthes (LCP) deformity of the hip. a The typical post-LCPdeformity of the hip includes an aspherical and enlarged head with a shortened femoral neck.This results in a relatively high riding greater and lesser trochanter potentially resulting in extraarticular impingement.b In addition, the aspherical head results in intraarticular impingement.The area of bone resection (dashed area) is close to the nutrient vessel of the femoral head (medial femoral circumflex artery in red). c To elongate the femoral neck with the goal to overcome extraarticular impingement, a retinacular flap is developed to maintain femoral head perfusion.d The greater trochanter is refixated in a distalized position and the femoral neck is reshaped with offset correction in close proximity to the nutrient vessel. (From [17], with kind permission from SAGE Publishing) of patients are affected bilaterally [12]. The altered shape of the proximal femur after LCP disease can cause restricted range of hip motion, femoroacetabular impingement, hip pain, and joint degeneration in young adults [3,5]. The typical post-LCP deformity in the mature hip consists of a mushroom-shaped head, femoral neck shortening and relatively high riding trochanter. Additional acetabular deformities such as hip dysplasia or retroversion are frequent. Functional problems can result due to femoral or acetabular pathomorphology.
Femoral functional problems can result from the intraarticular cam impingement due to the aspherical enlarged femoral head. If the head is too large to slip under the acetabular rim a head-induced pincer impingement with hinged abduction will occur. In addition, functional retrotorsion of the femur with intraarticular impingement can also occur.
Other femoral functional problems are the extraarticular impingement of the greater trochanter with limited external rotation in flexion and abduction or the extraarticular impingement of the lesser trochanter on the ischial tubercle with limited external rotation in extension. Typical acetabular pathologies consist of dysplasia, acetabular retroversion, and incongruity [17]. The choice of which surgical treatments to use depends on the pathomorphology of the individual patient and requires a stepwise treatment pathway [7].
In this article, we will focus on surgical hip dislocation with relative femoral neck lengthening for the correction of the intraand extraarticular impingement and further the development of a retinacular softtissue flap for the maintenance of femoral head perfusion [2,4,8,11].

Surgical principle and objective
The aim of surgical hip dislocation with relative femoral neck lengthening is to correct intra-and extraarticular femoroacetabular impingement. Surgical hip dislocation allows an excellent overview of the complete hip joint and allows for intraoperative dynamic testing to evaluate impingement-free range of motion of the hip. In addition, intraarticular corrections like labral and cartilage repair are possible. The relative femoral neck lengthening allows distalization of the greater trochanter and reduction of its base to elongate the femoral neck (. Fig. 1). This improves range of motion and corrects intra-and extraarticular impingement of the femoral neck or greater trochanter, respectively. Therefore, a retinacular soft-tissue flap has to be developed to secure femoral head perfusion. For this procedure, precise knowledge of the vascular anatomy of the proximal femur is essential to avoid iatrogenic necrosis [10,14]. Other deformities such as the head-induced pincer impingement with hinged abduction can be corrected with an additional head reduction osteotomy [2,16]. The extraarticular impingement of the lesser trochanter can be corrected by distalization.

Advantages
-Surgical hip dislocation [6] provides unrestricted access to the acetabulum and the femoral head including dynamic intraoperative testing of range of motion and impingement. -With development of the retinacular flap, the femoral head perfusion is secured and deformities of the head--neck region close to the retinacular vessels can be corrected [8,11,19].

Patient information
-General surgical risks: (Thrombosis, pulmonary embolism, allergic reactions, injury of cutaneous nerves with numbness/dysesthesia, excessive bleeding with need of blood transfusion, delayed wound healing and infection) -Specific risks of this procedure: j Delayed union or pseudarthrosis of osteotomy of greater trochanter j Intraarticular adhesions j Heterotopic ossifications j Iatrogenic avascular necrosis due to damage of the retinacular vessels

Preoperative work-up
-Detailed clinical and radiological workup is essential to evaluate whether hip-preserving surgery is indicated. As an alternative, total hip arthroplasty (THA) has to be considered in hips with advanced osteoarthritis. -Detailed patient history (e.g., family history, onset and course of disease, symptoms, previous treatment and operations). -Standardized radiographic imaging including an anteroposterior pelvic radiograph and axial view. -Magnetic resonance (MR) arthrography of the hip, preferably with radial reconstruction and intraarticular contrast injection for evaluation of size and location of cam deformity, congruency of the joint, deformity of greater and lesser trochanter with extraarticular impingement and damage to cartilage or labrum [13]. -Axial imaging (computed tomography or magnetic resonance imaging) of hip and knees for evaluation of femoral torsion. -Abduction/internal rotation radiograph for evaluation of congruency or instability of the joint or hinge abduction. -Preoperative templating to define the location of the osteotomy, the type of correction (relative femoral neck lengthening and offset correction or additional femoral head reduction, femoral osteotomy or acetabular osteotomy).

Surgical technique
Surgical hip dislocation . Figs. 2, 3, 4, 5, and 6. To avoid injury to the retinatcular vessels, care has to be taken not to penetrate the fossa piriformis. The trochanteric fragment is mobilized anterior together with the origin of the vastus lateralis and the insertion of the gluteus minimus and medius muscle.a Schematic drawing after removal of the trochanteric fragment. b Intraoperative view after removal of the trochanteric fragment.The capsule is exposed by mobilizing the gluteus minimus from the capsule. (a from [22], with kind permission from Oxford University Press)  with an enlarged, aspherical head and a shortened neck.This results in a relatively high riding greater and lesser trochanter resulting in restricted range of motion and extraarticular impingement.b Following relative femoral neck lengthening, the greater trochanter was distalized, the base of it reduced to elongate the neck, the cam deformity was resected and in addition the lesser trochanter was distalized. Radiograph was performed at the 8-week follow-up. c Radiograph at 1-year following surgery with healed osteotomies, no signs of osteoarthritis or avascular necrosis

Special surgical considerations
Surgical hip dislocation gives an excellent view of the joint to inspect and treat the femoral head, the head-neck junction, acetabulum, damaged cartilage or labrum, and concomitant pathologies to improve joint containment. During surgery, the impingement-free range of motion can be directly evaluated. The retinacular flap allows for correction of the neck while protecting femoral head perfusion. Precise knowledge of the vascular anatomy of the proximal femur is of upmost importance to perform this technically demanding surgery.

Postoperative management
The postoperative protocol includes the use of a continuous passive motion device during the hospital stay, beginning directly postoperatively, to prevent capsular adhesions. After surgery, patients are mobilized with partial weight bearing of 15 kg with the use of crutches for at least 8 weeks. Depending on the performed procedures (head reduction, femoral or acetabular osteotomies) other restrictions may apply. Abduction, adduction as well as flexion more than 90°is restricted to protect the trochanteric osteotomy. Prophylaxis against thrombosis is prescribed until full weight bearing is allowed. Pro-phylaxis for heterotopic ossification is not applied on a regular basis, as this complication does not occur very often. After radiographic confirmation of healing at the 8-week follow-up, stepwise return to full weight bearing is allowed and abductor training is initiated. Usually, return to work is possible 3 months postoperative.

Errors, hazards, complications
-Iatrogenic lesion to the retinacular vessels with damage to vascular perfusion of the femoral head and avascular necrosis of the femoral head -Intraarticular adhesions (hip arthroscopy might be necessary) -Delayed union or pseudarthrosis of the trochanteric osteotomy can necessitate revision surgery -Hinged abduction due to enlarged and aspherical femoral head (additional head reduction osteotomy might be necessary) -Failure to achieve stability and joint containment (additional periacetabular osteotomy might be necessary) -Heterotopic ossifications -Muscular imbalance, change of gait pattern requiring long rehabilitation

Results
In a retrospective case series, we evaluated 81 adult patients with history of LCPD, who underwent surgical hip dislocation with relative femoral neck lengthening and retinacular soft-tissue flap (. Table 1).

Preoperative findings
All 81 hips presented with clinical relevant intra-and/or extraarticular impingement following LCPD. Reduced range of motion and pain were the leading symptoms. Of the 81 hips, 41 had preoperative Tönnis stage 0 and 40 hips had Tönnis stage 1. In addition, 46 of the hips had previous operations, mostly intertrochanteric varisation osteotomies.

Procedures
Between October 1997 and October 2020, 81 hips (79 patients) were treated with surgical hip dislocation and offset correction.
In 71 hips, a retinacular flap with relative femoral neck lengthening was performed. Concomitant procedures were performed in 32 hips for the labrum, in 11 hips with a periacetabular osteotomy, in 6 hips with a valgus osteotomy, and in 4 hips with a head reduction osteotomy. The mean age at operation was 23 ± 9 (6-51) years. Follow-up and evaluation The mean follow-up was 9 ± 7 (range 1-23) years; 11 hips were converted to a total hip arthroplasty (THA) due to progressive arthrosis after a mean 7 ± 4 (range 1-13) years. One patient died 1 year after the operation unrelated to surgery. The remaining 67 hips showed no or minor progression of the arthrosis.

Revision surgery and complications
None of the patients developed avascular necrosis of the femoral head. Complications included two instabilities with consecutive subluxations, and one patient with pseudarthrosis of the lesser trochanter. Of the 2 patients with instabilities, one received a periacetabular osteotomy and the other patient underwent total hip arthroplasty due to advanced osteoarthritis. The patient with the pseudarthrosis of the lesser trochanter had a revision osteosynthesis and healed trochanter at follow-up. In 43 patients, the trochanteric screws had to be removed. One patient died unrelated to the operation.

Conclusions
Our findings confirm earlier studies that surgical hip dislocation with relative femoral neck lengthening and retinacular soft-tissue flap is an effective treatment option for patients with post-Legg-Calve-Perthes (LCP) deformities [1]. The frequency of pseudarthrosis of the greater or lesser trochanter was similar to the frequency in patients with surgical hip dislocation without relative femoral neck lengthening [2]. The percentage of hips that were converted to THA (14%) is slightly higher than in other studies on results after relative femoral neck lengthening (7% in a follow-up of 3 years [2] and 10% in a follow-up of 3.75 years [15]) but seems to match the results of the other studies regarding the longer followup time of 9 years.