Developmental dysplasia of the hip (DDH) is one of the most common diseases causing hip pain in adults and is an important cause of osteoarthritis (OA). Borderline developmental dysplasia of the hip (BDDH) is a condition that falls between a normal hip and adult DDH. In BDDH, the lateral center-edge angle (LCEA) of the acetabulum is usually defined between 18° and 25° or 20° and 25°; however, this definition remains controversial.
Freiman SM et al reported that the prevalence of symptomatic BDDH to be as high as 12.8%, and the risk of OA in individuals with BDDH is 1.4 to 2.0 times that of a healthy population. The goal of hip-preserving treatment is to ameliorate pathological changes and delay progression of OA. Main treatment methods include non-surgical treatment, arthroscopic surgery, and periacetabular osteotomy (PAO). Arthroscopy has been widely used in the treatment of BDDH due to minimal invasiveness, rapid recovery, and high tolerance, accounting for about 13% of the total number of hip arthroscopic surgeries; however, systematic reviews have shown average early failure rates of 14.1% (0%–46.0%) and 11.1% (1.8%–30.0%).[3,4] PAO can reposition acetabular coverage and improve biomechanics and joint stability, but it is invasive and complications include nerve injury, vein thrombosis, osteonecrosis of the femoral head, stress fracture, and heterotopic ossification. The diagnosis and treatment of BDDH remain challenging in the field of sports medicine and hip preservation surgery clinical guidelines, or expert consensus for guidance.
Based on the principles of science, advancement, and practicability, the experts involved in this consensus adopted the Delphi technique using three rounds of questionnaires and the group nomination method. This consensus was developed by reviewing 13 issues of clinical concern related to BDDH, including the definition, diagnosis, non-surgical treatment, arthroscopic risk factors, indications, and contraindications for arthroscopy or PAO, postoperative rehabilitation, and precautions.
Definition of BDDH
The definition of BDDH, the selection of imaging parameters, reference points of the outer edge of the acetabulum, and the range values have been controversial in the field. Imaging parameters used to describe the BDDH definitions include: LCEA, anterior center-edge angle (ACEA), Sharp angle, Tonnis angle, and anterior and posterior wall indices. Wiberg first proposed in 1939 to measure the acetabular bony outer edge LCEA to evaluate the coverage of the acetabulum to the femoral head. In 1990, Ogata proposed to use the sourcil edge instead of the bone edge of the acetabulum to measure LCEA in children and adolescents whose bone and sourcil edge of the acetabulum did not overlap. Studies have shown that the average difference between Wiberg's and Ogata's methods for measuring LCEA is about 4°. From 2019 to 2021, after eliminating duplicate literature, 29 studies were selected from four systematic reviews of BDDH.[3-6] Of these, LCEA was used to define BDDH in 28 studies, and one used LCEA combined with Sharp angle and ACEA; 14 studies reported the LCEA range of 20° to 25°, 10 reported 18° to 25°, and four reported <25°. Additionally, 18% of hip dysplasias showed a change in pelvic tilt of >10° on radiographs from supine to standing.
To unify understanding and promote application, it is recommended that the LCEA (the line connecting the center of the femoral head parallel to the longitudinal axis of the body and the line connecting the center of the femoral head to the bony outer edge of the acetabulum) should be measured on standing (weight-bearing) anteroposterior pelvic radiographs. The reference points of the outer edge of the acetabulum should refer to Wiberg's method, that is, the lateral bony edge of the acetabulum. The LCEA between 20° and 25° is classified as BDDH, while symptomatic BDDH is defined as an angle between 20° and 25° as well as the presence of hip pain and limited joint mobility.
Diagnosis of Symptomatic BDDH
The diagnosis of symptomatic BDDH includes clinical history, main symptoms, and physical and imaging examinations. There are two definitions of “instability” and “microinstability” for hip instability about BDDH. It is recommended that to use the term “hip instability” to describe joint instability in symptomatic BDDH. Clinical history should be expanded to clarify the presence of trauma, performing dance or other athletic sports, and previous diagnosis and treatment. The main symptoms include hip pain, limited mobility, and limp, mostly caused by mechanical injury and/or hip instability. Physical examinations should include general orthopedic examination and specific tests for hip instability, femoroacetabular impingement (FAI), anterior inferior iliac spine (AIIS) impingement, and generalized ligamentous laxity. Imaging examinations should include X-ray, magnetic resonance imaging (MRI), computed tomography scan and 3D reconstruction, and musculoskeletal ultrasound to assess joint stability, osseous structural abnormalities, soft tissue injury, articular cartilage injury, and OA.
Non-Surgical Treatment of Symptomatic BDDH
The purpose of non-surgical treatment is to relieve pain and improve joint function and dynamic stability of joint muscle tissue. Patients with an initial diagnosis of symptomatic BDDH, no obvious joint instability, and no standardized conservative treatment should receive systematic conservative treatment. Patients with symptomatic BDDH with extra-articular disease and complex symptoms should be recommended for conservative treatment. Treatment options include changes to lifestyle and exercise, taking non-steroidal anti-inflammatory drugs and protective cartilage supplements, and enhancing perihip function through physical therapy. The treatment time is 3 to 6 months. Stretching and muscle flexibility exercise could improve the strength and balance of the perihip muscle group, but should be used with caution for BDDH with hip instability.
Surgical Procedure of Symptomatic BDDH
Hip arthroscopy and PAO are currently common surgical procedures for symptomatic BDDH. The selection of optimal treatment for symptomatic BDDH lacks clinical guidelines or expert consensus. There is insufficient evidence to demonstrate that preferred arthroscopy or PAO or arthroscopy combined with PAO produces better clinical outcomes, but the cause of symptoms (mechanical injury and/or hip instability), surgical risk factors, indications, and contraindications should be given priority when formulating surgical plans.[7,8]
Risk Factors of Arthroscopy for Symptomatic BDDH
Age ≥42 years was a risk factor for arthroscopic surgery of BDDH. Obese patients with hip pain were 5.6 times more likely to have a conversion to total hip arthroplasty after arthroscopy. Body mass index (BMI) was positively correlated with preoperative visual analog scale score and negatively correlated with postoperative hip outcome score-sports subscale of BDDH patients. Beighton score ≥4 indicates that the hip joint has a larger range of internal and external rotation, flexion, and abduction, leading to instability. The risk factors for arthroscopy treatment for symptomatic BDDH include: demographic factors (age ≥42 years and BMI ≥30 kg/m2), symptoms and signs (severe pain when standing or walking straight, and abductor fatigue or physical examination showing hip instability), soft tissue structure (ligamentum teres tear ≥50% and joint capsule and surrounding tissue injury) or generalized ligamentous laxity (Beighton score ≥4), osseous structure (Tönnis angle >15°), OA (Tönnis grade 1), local mild cartilage damage, and psychological factors (severe anxiety, depression, or high expectations).
Indications of Arthroscopy for Symptomatic BDDH
Non-surgical treatment of BDDH has no significant improvement in symptoms, and arthroscopy is the preferred treatment for pathological changes within the acetabular labrum as well as articular cartilage injury. The incidence of BDDH combined with Cam-type FAI is 40% to 93%. It is recommended that clinical symptoms and signs should be attributed mainly to acetabular labral injury, FAI, or AIIS impingement, and symptomatic BDDH without significant improvement after conservative treatment, which are indicated for arthroscopy.
Contraindications of Arthroscopy for Symptomatic BDDH
In BDDH patients, excessive femoral anteversion increases the load of static and dynamic stabilizers in front of the joint (iliopsoas, hip extensor, and/or hip external rotation), which aggravates anterior instability and/or posterior impingement. Femoral neck shaft (FNS) angle >140° increases the abnormal shear force of articular cartilage, which is closely related to the degree of cartilage injury of the acetabulum and femoral head and is prone to poor prognosis after arthroscopy. Anyone of the following four items can be regarded as a contraindication for arthroscopic surgery for symptomatic BDDH: (1) insufficient bony coverage of the anterior acetabulum (ACEA <20°); (2) abnormal osseous structure of proximal femur (Shenton line broken or iliofemoral line percentage >22%, femoral anteversion >35° or FNS >140°); (3) OA and/or cartilage damage (Tönnis grade ≥2, joint space ≤2 mm, MRI showing extensive subchondral bone edema or cartilage exudation); and (4) common contraindications for arthroscopy (systemic or local infection, poor physical condition, limited joint movement or stiffness).
Precautions in Arthroscopy for Symptomatic BDDH
Sixty-three percent of BDDH anteroposterior pelvic radiographs showed crossover signs, which could be mistaken for pincer-type FAI, leading to excessive removal of the acetabular rim, resulting in the reduction of acetabular volume. The capsule should undergo complete closure after capsulotomy to avoid iatrogenic instability. Intraoperative precautions for hip arthroscopy include: (1) abnormal bony structure of the acetabular rim should be removed in limited fashion to minimize impact on the bony coverage of the acetabulum; (2) cam deformity with femoral head neck junction and abnormal AIIS at the acetabular side should be adequately decompressed to avoid residual impingement; (3) injured labrum should be repaired as much as possible to avoid resection; (4) capsule tissue should be closed by suturing after incision; and (5) caution regarding iliopsoas tendon release is warranted.
Indications of PAO for Symptomatic BDDH
PAO treatment of symptomatic BDDH remains controversial. Clinical signs and symptoms should be specified to arise mainly from hip instability, including persistent symptomatic instability after arthroscopy, which are indications for PAO. The contraindications for arthroscopy of insufficient bony coverage of the anterior acetabular (ACEA <20°) and abnormal osseous structure of proximal femur (Shenton line broken or iliofemoral line percentage >22%, femoral anteversion >35° or FNS >140°) are indications for PAO.
Contraindications of PAO for Symptomatic BDDH
Any of the following four items can be regarded as a contraindication for PAO treatment of symptomatic BDDH: (1) abductor internal rotation functional position (X-ray shows a poor match between the femoral head and acetabulum); (2) Tönnis grade ≥2; (3) limited joint motion; and (4) contraindications (systemic or local infection, poor basic physical condition).
Precautions in PAO for Symptomatic BDDH
The selection of surgical approach should meet the requirements of clear anatomical structure, less vascular and nerve injury, less intraoperative bleeding, and thorough orthopedics, and be influenced by the experience and learning curve of specialists. The following points should be noted during PAO procedures: protecting the sciatic and femoral nerves, accurately perform extra-articular osteotomy of the sciatic, pubic, and ilium, and accurately rotate the acetabulum to improve the coverage of the acetabulum on the femoral head and effectively fix.
The overall goals of postoperative rehabilitation are to eliminate pain and swelling, restore neuromuscular control, stabilize the lumbar-pelvic-hip complex, improve motor chain function of the hip, trunk, and lower limbs, and ensure a speedy return to normal life, work, or sports. The basic strategy of recommendation should emphasize the concept of fast-track surgery and focus on individual and phased rehabilitation.
Precautions in Postoperative Rehabilitation
The presence or absence of iatrogenic joint instability after operation should be assessed. Physical and manipulative therapy is contraindicated for postoperative hip instability. In addition, the phased rehabilitation strategy is not absolute, and each stage of rehabilitation is based on the previous stage, giving full consideration to individual recovery, and some patients may undergo phased cross-training.
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