THA for DDH: replacement principles and techniques – acetabular side

Introduction

Developmental dysplasia of the hip (DDH) is a condition characterized by a volumetrically deficient and/or improperly oriented acetabulum, causing hip instability, pain, and functional impairment in the young adult patient (1). The condition encompasses a broad spectrum of severity, from mild dysplasia with incongruence to low or high joint dislocation with proximal migration of the femur (2).

This structural anomaly is not limited to the acetabulum; other factors such as coxa valga, abnormal femoral torsion, small femoral head, and soft tissue laxity concur to the instability.

Untreated, DDH can result in progressive cartilage and labral damage and is a well-recognized risk factor for early-onset hip osteoarthritis (OA) and the need for total hip arthroplasty (THA) (3).

In patients under 40 years of age undergoing THA, DDH represents a major underlying cause of end-stage osteoarthritis, accounting for 10% of cases and forming the largest proportion of pediatric hip diseases (18% overall) (4).

THA has been shown to be a safe and effective treatment for young patients with hip OA secondary to DDH (5, 6). However, the procedure is technically more demanding due to the abnormal acetabular and femoral morphology, soft tissue retraction, and previous surgeries and is associated with a higher risk of perioperative complications.

The aim of this paper was to discuss the different acetabular reconstruction techniques in terms of cup position, acetabular coverage, and fixation in DDH, and their impact on joint biomechanics, abductor function, leg length restoration, and femoral reconstruction strategy.

DDH classification

Several classification systems have been developed to characterize dysplastic hips in the adult population. The two most frequently used systems are those of Crowe et al. and Hartofilakidis et al. (7, 8, 9). Both of them are relatively simple to apply, require only a plain anteroposterior (AP) radiograph of the pelvis, and are based on the proximal migration of the femoral head. They are useful for guiding treatment and providing prognostic information.

The Crowe system measures the upper migration of the femoral head based on the distance between the inferomedial femoral head–neck junction and the inter-teardrop line, as a ratio of the femoral head diameter (7). For the ratio calculation, the height of the pelvis may be a substitute for the femoral head diameter since the latter is typically 20% of the height of the pelvis, which is useful in cases when accurate measurement of the diameter of the femoral head may be difficult owing to deformity or suboptimal radiographic technique (Fig. 1). In a normal hip, the inferomedial head–neck junction (IHNJ) should sit within a few millimeters of the inter-teardrop reference line. Dysplasia is classified into one of four classes according to the cephalad migration of the IHNJ in relation to the inter-teardrop reference line (Table 1). The Hartofilakidis classification system segregates adult dysplastic hips into one of three following categories: dysplastic, low dislocation, or high dislocation (9). It is the simplest and most intuitive classification to use (Table 2).

Figure 1.

Landmarks for Crowe classification (yellow dotted line – inter-teardrop line; green arrowed line – pelvic height; blue arrowhead line – femoral head height; pink arrowed line – distance of cephalad migration of the femoral head).

Table 1.

Crowe et al. (7) classification of hip dysplasia.

Crowe classification	Cephalad migration of the IHNJ
Class I	<50% of the diameter of the femoral head (<10% of the height of the pelvis)
Class II	50–75% of the diameter of the femoral head (or 10–15% of the height of the pelvis)
Class III	75–100% of the femoral head diameter (or 15–20% of the pelvic height)
Class IV	>100% of the diameter of the femoral head (or 20% of the height of the pelvis)

IHNJ, inferomedial head–neck junction.

Table 2.

Hartofilakidis et al. (9) classification of hip dysplasia.

Hartofilakidis classification	Definition
Dysplastic	Subluxated but the femoral head is contained in the true acetabulum
Low dislocation	Femoral head articulates with a false acetabulum, which overlaps the true acetabulum
High dislocation	Femoral head articulates with a false acetabulum, which is proximal, is posterior, and has no overlap with the true acetabulum

The intraobserver and interobserver reproducibility and reliability of the Crowe and Hartofilakidis classification systems are excellent, as was found by Yiannakopoulos et al. (10).

Notably, it is now understood that multiple patterns of instability exist, which are not fully evaluated with simple two-dimensional (2D) imaging and classification. Computed tomography (CT) evaluation of the three-dimensional (3D) morphology of the dysplastic acetabulum allows for a more accurate definition and an evolution from vague terms such as ‘borderline dysplasia’. The Ottawa Classification describes three primary patterns of instability or acetabular undercoverage: anterior, posterior, and lateral instability (11). The latter is further subdivided into anterolateral, posterolateral, and global instability.

Acetabular challenges in DDH

Acetabular anatomy

Acetabular and femoral anatomy in dysplastic hips is highly variable, depending on the severity of the dysplasia and whether previous surgery has been performed. A thorough understanding of the individual anatomy is essential for planning the optimal reconstructive strategy and for anticipating the intraoperative challenges associated with the arthroplasty.

The acetabulum typically is underdeveloped, has a reduced volume, and is shallow, oval-shaped, and excessively anteverted, although in 1/6 of the cases, it may be retroverted (12, 13). Moreover, in case of subluxation (Crowe II and III), the anterolateral and the superolateral acetabular rim may be further compromised due to wear from the subluxated femoral head with segmental deficiency (14, 15). As the severity of dysplasia increases, the anterosuperior bone stock progressively decreases. Interestingly, if the patient presents with a dislocated hip, the native acetabulum has a decreased bone density secondary to chronic unloading; however, the superior rim is often less compromised than in cases with subluxated hips (9, 16).

Furthermore, in DDH, the entire pelvic development is affected, characterized by an enlarged acetabular area and underdeveloped iliac and ischiopubic segments; the hemipelvis is tilted anteriorly in the sagittal plan; and there is an increased internal rotation of the innominate bone (17, 18, 19).

Soft tissue contractures develop secondarily and include shortening of the neurovascular structures, hamstrings, hip adductors, and quadriceps, especially in cases of hip dislocation. The hip abductors shorten and insert on the proximal femur with a more horizontal orientation, which can adversely affect postoperative gait and further compromise arthroplasty stability (9, 20).

Should the patient have had previous surgical treatment with a periacetabular osteotomy, acetabular retroversion has been reported in 44% of cases (21). This may lead to anterior impingement during THA and contribute to posterior wall deficiency. Furthermore, during THA after previous periacetabular osteotomy, the acetabular component may be positioned in greater retroversion compared with DDH patients without prior osteotomy (21).

Biomechanics

In DDH, the reduced femoroacetabular contact area and decreased joint congruency lead to increased contact stress and pressure on the lunate surface, instability, premature cartilage, labral damage, and ultimately the development of OA (22, 23).

Subject-specific finite element analyses have shown that the smaller femoroacetabular contact area in dysplastic hips results in a substantially greater load being supported by the labrum compared with normal hips (24). This may lead to labral hypertrophy and a higher incidence of inside-out labral tears (25). In addition, computer simulation studies have shown that hips with DDH demonstrate significantly increased acetabular edge loading in the anterosuperior region, which correlates with the severity of the acetabular deformity (26).

In DDH hips, femoral head coverage is significantly reduced, femoral neck–shaft angles are increased, the hip joint centers are more lateralized, and the abductor muscle moment arms are shorter compared with healthy controls (27). These factors contribute to a chronic biomechanical disadvantage.

In acetabular reconstruction, superolateral displacement of the hip center (2 cm superior and 2 cm lateral) can reduce the abductor muscle moment arm by approximately 28%, a deficit that cannot be compensated for by increasing prosthetic neck length (28). In contrast, a 2-cm superior displacement without lateralization alters the abductor moment arm and force by less than 10%, provided that neck length is increased to compensate for the reduced muscle length (28). To optimize joint biomechanics, lateralization of the acetabular component should therefore be avoided. In cases in which a high hip center (HHC) of rotation reconstruction is needed, normal joint biomechanics are not fully restored and result in increased load across the hip joint and reduced dynamic range of motion (29).

Preoperative planning

During clinical examination, joint range of motion, the presence of prior surgical scars, and muscle strength should be assessed for adequate preoperative planning. The hip abductors should be particularly examined as abductor muscle function may be impaired due to proximal femoral migration, reduced femoral offset, and disuse. Conversely, hip flexion contracture, which is often associated with increased lumbar lordosis, is common and may warrant anterior capsular release or iliopsoas tendon release.

Pelvic obliquity and leg length discrepancy can be evaluated with the patient standing upright by placing blocks under the shorter limb to level the pelvis or by measuring the distance from the anterosuperior iliac spine to the medial malleolus.

Mandatory imaging modalities include a standard AP pelvic radiograph that includes the proximal femur, along with a lateral view of the hip, which will demonstrate the relevant pelvic and proximal femoral morphology. The teardrop is a useful landmark to assess leg length discrepancy and assist with preoperative planning in dysplasia, as well as in cases of severe unilateral DDH with pelvic asymmetry. The full-length standing lower limb radiograph should be used to measure the extra articular leg length discrepancy (difference in the absolute length between the two legs) (30).

Furthermore, a computed tomography (CT) scan with 3D reconstructions allows assessment of acetabular morphology and available bone stock within both the native and false acetabulum while determining acetabular and femoral version.

During preoperative planning, the location of the true acetabulum should be identified. The bone stock at this site must be assessed, and cup templating can be used to evaluate acetabular coverage and the degree of proximal femoral migration. This crucial step will allow the surgeon to plan for an anatomic restoration versus HHC reconstruction.

Templating the acetabulum includes determining the cup level of implantation, orientation, depth, diameter, and the need for supplementary fixation, such as bone grafts or augments (Fig. 2). Because the acetabulum often has reduced AP dimensions and overall volume, the use of a smaller cup with preservation of the integrity of the anterior and posterior columns is recommended; typical diameters in this setting range from 38 to 50 mm (14). It should be noted that the accuracy of prediction for cup size with digital templating is lower in the subset of patients with DDH compared to other hip pathologies, likely due to the difficulty in accurately determining the vertical position of the hip center (30).

Figure 2.

(A) Right hip DDH (Crowe II) in a patient with arthrogryposis. (B) Three-dimensional CT reconstruction demonstrating a hypoplastic anterior acetabular wall, a very small femoral head, and a high-riding greater trochanter. (C) Preoperative digital planning showing an anatomic acetabular reconstruction, planned leg lengthening of 2.5 cm, and the use of a cylindrical femoral stem to optimize femoral version. (D) Postoperative radiograph demonstrating medialization of the acetabular cup in an anatomic position. A subtrochanteric shortening osteotomy was required to achieve hip reduction due to severe soft tissue contractures associated with arthrogryposis. A trochanteric hook plate was added to enhance rotational stability at the osteotomy site.

Finally, the choice of surgical approach is determined by the surgeon’s experience. In less severe cases of DDH, anterior, anterolateral, or posterior approaches may be used. However, in high dislocations with a potential need for femoral shortening osteotomy, the posterior approach may be preferable, with good exposure of the acetabulum and femoral diaphysis. This approach shows the greatest reduction in LLD and allows intraoperative assessment of sciatic nerve tension during the procedure; however, it is associated with an increased dislocation rate (31).

Acetabular management strategies

Cup position – anatomic vs high hip center

Acetabular reconstruction can be performed with the cup in the anatomic acetabular position or in the false acetabulum leading to a HHC of rotation (32, 33). Schutzer and Harris defined a HHC as a hip center positioned at a height above the inter-teardrop line that is twice the normal distance (34).

Anatomic positioning of the acetabular component is generally preferred because this position usually provides better bone stock, optimizes joint biomechanics, reduces acetabular revision rates, and minimizes the risk of leg length discrepancy (Figs 2 and 3) (7, 32, 33).

Figure 3.

(A) Radiograph of a patient with a bilateral Crowe II DDH. (B) Bilateral acetabular reconstruction using cementless cups at an anatomic position.

Intraoperatively, identification of the cotyloid fossa and the remnants of the transverse acetabular ligament is essential for accurate localization and assessment of the bone stock of the true acetabulum (14). Should there be doubts, fluoroscopy can be used to confirm the location of the acetabular fossa, because failure to accurately identify the true acetabulum can result in reaming into the false acetabulum, leading to a high and laterally displaced hip center.

With adequate exposure of the inferior aspect of the acetabulum, reaming is initiated centrally at the level of the true acetabulum with small reamers, avoiding proximal migration during reaming (Fig. 4). The anteroposterior dimension of the acetabulum ultimately determines the appropriate cup size, bear in mind that in this setting, the diameter of the subluxated femoral head is not a reliable predictor. Oversizing the cup should be avoided, as excessive reaming may compromise fixation within the acetabular columns, particularly in the hypoplastic anterior column. It is preferable to remain laterally uncovered than have an anterior overhang, which may lead to psoas tendinopathy.

Figure 4.

(A) Acetabular reaming is performed at the anatomical acetabular location, and the arrow points to the superior limit of the false acetabulum. (B) A 46-mm trial cup is positioned with an acetabular augment to assess coverage and stability, demonstrating lateral overhang of the augment. (C) The same cup is used with an autogenous femoral head bone graft, contoured to fit the defect, providing better coverage than the augment.

In Crowe I hips, the acetabular component should easily be positioned in the anatomic location without the need for additional structural support. In Crowe II and III hips, superolateral bone deficiency may result in substantial undercovering of the acetabular component when placed in the anatomic position. Various techniques to address this issue will be detailed in the section titled ‘Acetabular coverage’. Alternatively, reconstruction using a HHC may be considered.

In DDH Crowe II or III hips, raising the hip center can increase acetabular coverage while requiring less bone removal from the acetabulum. The peak coverage and smaller volume of reamed bone were observed when the vertical center of rotation was positioned 30–35 mm above the inter-teardrop line (35). The superolateral bone deficiency is more pronounced in Crowe III than in Crowe II hips, making acetabular reconstruction at the anatomic position more challenging. In one series, the cemented acetabular component was placed outside the true acetabular region in 26% of Crowe III acetabulae, compared with only 12% in Crowe II hips (36).

In Crowe IV hips, the acetabulum is hypoplastic, but the superior rim is often relatively preserved, which allows for an anatomic reconstruction with a small hemispherical cup (Fig. 5). Nevertheless, the restoration of the hip center to the true acetabulum can be technically challenging due to soft tissue contractures and is associated with an increased risk of nerve injury. In such cases, a femoral shortening osteotomy can be performed to prevent excessive limb lengthening and protect neural structures (37). Alternatively, placing the acetabular component 1–2 cm above the anatomic center, which by definition does not constitute an HHC, can represent a good compromise, achieving better bone coverage while reducing soft tissue tension, the need for a femoral osteotomy, and operative time (Fig. 6).

Figure 5.

(A) Radiograph of a patient with a Crowe IV DDH. (B) Left acetabular reconstruction using cementless cups with medialization and anatomic position. A femoral shortening osteotomy was performed to facilitate reduction and reduce the risk of nerve injury.

Figure 6.

(A) Radiograph of a patient with a bilateral Crowe III DDH and a previous Chiari pelvic osteotomy with a retained screw on the left side. (B) Bilateral acetabular reconstruction using cementless cups with medialization and a high hip center. On the left side, a high-speed burr was used to cut the screw to allow cup medialization.

It must be considered that the proximal placement of the acetabular cup correlates with the presence of a postoperative limp and decreased hip flexion and internal rotation due to anterior bony or implant impingement (38). The long-term effects of these reconstruction strategies on the knee and spine, provided that the leg length is equalized, is unknown.

Acetabular coverage

Slight undercoverage of a cementless cup is acceptable in dysplastic hips. Although no specific threshold of acceptance has been clearly defined, 75–80% of coverage with host bone is generally recommended (39, 40, 41). In this setting, supplementary screw fixation and the use of a highly porous cup enhance primary stability and promote osseointegration.

Medializing the cup improves bone coverage without increasing its inclination angle. A small-diameter drill hole at the fovea can be used to assess the depth of the medial wall and guide the extent of medialization. Notably, reaming through the medial acetabular wall or a controlled fracture with medial protrusion can increase the coverage of the cup (42, 43). Care must be taken to ensure that this medial defect does not compromise cup stability as excessive medialization can decrease the contact area between implant and host bone. Autologous bone graft harvested from the reamers or from the femoral head should be added to promote healing and restore medial bone stock. Medialization of the acetabular component also reduces joint reaction forces and increases the lever arm of the gluteus muscles, and the resulting change in femoral offset due to the cup medialization can be compensated for when preparing the femoral component (44).

After acetabular reaming and medialization, the trial cup is used to assess stability and coverage and to decide whether additional structural support is required (Fig. 3). During trial cup phase, structural autologous bone graft harvested from the femoral head can be contoured to match the acetabular cavity and secured with two or more screws to the superolateral acetabulum (45, 46, 47, 48, 49, 50). The use of augmentation techniques improves superolateral coverage and support, while also restoring bone stock for potential future revision surgery.

Further options to improve acetabular coverage in DDH are to perform a medial wall osteotomy, which allows for further medialization of the acetabular component (51, 52). For this technique to be safely performed, a minimum acetabular floor thickness of 10 mm is recommended before medial wall osteotomy (58). One downside of this technique is that it compromises the medial bone stock, which is a significant concern in the event of failure and in younger patients who are likely to require revision arthroplasty in the future. The medialization of the acetabular component with controlled protrusion is technically less demanding than performing a medial wall osteotomy or shaping a structural autologous graft to address the acetabular defect (42).

Acetabular version

Patients with DDH frequently present with an increased acetabular and femoral anteversion. Due to the underdevelopment of the anterior acetabular wall and increased acetabular anteversion, it is common for the anterior rim of the cup to remain undercovered and attempts to increase anterior coverage by increasing anteversion may lead to anterior instability. To prevent this complication, acetabular component anteversion should be combined with femoral anteversion to optimize joint stability and achieve an impingement-free range of motion.

Conversely, in the subset of patients with previous periacetabular osteotomies, who may present with acetabular retroversion, excessive retroversion must be avoided. In addition, anterior rim trimming may be necessary to reduce the risk of anterior bony impingement during arthroplasty, and structural bone grafting may be required to address posterior wall deficiency (21, 53).

Cup selection

Acetabular fixation – cemented vs cementless cups

Cemented cups used in DDH without bone grafting have demonstrated a high failure rate, especially if the component is positioned outside the true acetabular region (36, 54, 55). The use of a cemented cup combined with structural acetabular bone graft has shown better survivorship, provided that the graft supports less than 40–50% of the socket (56).

Overall, the high failure rate of cemented cups at mid-term follow-up, together with the improved outcomes of cementless porous-coated cups in revision arthroplasty with deficient acetabular bone stock, has encouraged surgeons to favor the latter in the setting of acetabular reconstruction in DDH (34, 55, 57, 58).

Cementless cups are therefore the most commonly used implants for acetabular reconstruction in patients with DDH, often resorting to smaller components supplemented with screw fixation. Achieving primary stability of a cementless cup in a DDH with deficient acetabular bone stock is challenging, but it is crucial for osseointegration.

Trabecular metal cups can also be considered to enhance the primary stability of the reconstruction and promote bone ingrowth (59, 60). However, at a mid-term follow-up of 8.3 years, no significant difference in survivorship was observed between the various porous acetabular components and trabecular metal cups (6).

Metal augments

Porous metal augments can be utilized to enhance primary stability and improve superior coverage of a hemispherical cup, without the risk of graft collapse or reabsorption (61, 62).

If cup medialization is insufficient to provide adequate coverage and the superolateral defect compromises implant stability, with a cup center–edge angle (CEA) of less than 5°, the use of an augment is indicated (62, 63). The cup CEA is defined as the angle between a vertical reference line and a line drawn from the center of the cup to the lateral edge of the acetabulum (63). It must be noted that augments, which are typically designed for revision arthroplasty, may be too large to fit smaller hips or to accommodate smaller acetabular components (Fig. 4) (64).

Reinforcement rings

Reinforcement rings have long been used in DDH THA to improve socket coverage and provide enhanced superior and lateral support (65, 66). In cases of severe dysplasia, they also protect the bone graft in the superolateral acetabular defect, thereby facilitating its integration with the host bone. One of the concerns with these implants is the limited osseointegration, which can compromise long-term fixation.

Table 3 summarizes the acetabular reconstruction strategy in THA according to the Crowe classification.

Table 3.

Acetabular reconstruction strategy according to the Crowe classification.

Crowe	Acetabular cup position	Bone stock and coverage	Cup fixation	Additional considerations
I	True acetabulum; anatomic center of rotation restoration is usually achievable	Adequate; reaming into medial wall; avoid lateralization	Cementless fixation ± screw fixation	Limb length discrepancy minimal
II	True acetabulum preferred; cup placement 1–2 cm above anatomic center	Superolateral deficiency; cup medialization to increase coverage; structural bone graft or augments may be required	Small cup with screws often needed	Assess femoral version
III	True acetabulum; cup placement 1–2 cm above anatomic center acceptable; high hip center if coverage <70% in anatomic center	Markedly deficient superolaterally; cup medialization to increase coverage; structural autograft or augments frequently needed	Small cup with screws; consider highly porous cup	Subtrochanteric shortening osteotomy often necessary when anatomic hip center is chosen; extensive soft tissue release
IV	True acetabulum; cup placement 1–2 cm above anatomic center acceptable; high hip center	Severely deficient; very small native acetabulum structural allograft required for reconstruction above the anatomic center	Small cup with screw; consider highly porous cup	Shortening osteotomy when anatomic hip center is chosen; extensive soft tissue release

Navigation and robotics

Given that conventional freehand techniques rely heavily on surgeon experience and are particularly challenging when anatomical landmarks are distorted or deficient, as in DDH, robotic or navigation-assisted technologies optimize cup position, restoration of the hip center, length correction, and overall joint biomechanics (67). Furthermore, preoperative simulation allows anticipation of impingement and dislocation risks.

Three-dimensional CT-based planning has demonstrated greater accuracy than conventional templating in dysplastic anatomy. Viceconti et al. showed that CT-based planning improves acetabular component sizing accuracy, particularly in anatomically complex hips, highlighting the limitations of two-dimensional assessment (68).

Robotic systems build on this principle by integrating preoperative CT-based planning with intraoperative execution, improving the reproducibility of cup inclination and anteversion. Tsutsui et al. reported improved target orientation and millimetric spatial accuracy with CT-based navigation, while Nakai et al. confirmed reliable three-dimensional reproduction of the planned cup position irrespective of deformity severity (69, 70). These findings are particularly relevant in dysplastic hips, where cup height and medialization directly affect abductor mechanics and limb-length balance.

Importantly, conventional planning often relies on static pelvic reference planes, which may not capture dynamic changes in pelvic tilt. CT-based navigation studies have shown that commonly used reference planes may not fully account for individual pelvic orientation, particularly in dysplastic hips. Incorporating functional pelvic parameters into preoperative planning and intraoperative guidance may therefore be an important step toward more individualized acetabular positioning (71). In that regard, emerging technologies, such as artificial intelligence (AI), patient-specific instrumentation, and 3D planning, have shown promising improvements in prosthesis placement accuracy in dysplastic hips, particularly in patient-specific approaches (72). In addition, 3D-based planning and modeling techniques may facilitate improved anatomical understanding and surgical simulation in complex DDH cases (70).

Despite these promising considerations and outcomes, most available studies remain limited in size. In addition, although improved radiological accuracy has been consistently demonstrated, translating this precision into clinically meaningful outcomes remains uncertain, particularly in DDH-specific populations where soft tissue balance and femoral factors also play a major role. Cost, learning curve, and operative time are also relevant considerations to take into account.

Survivorship

THA in DDH is challenging due to the aforementioned anatomical and biomechanical factors. These, together with the patient’s relative young age, influence postoperative outcomes and implant survivorship.

Variable revision rates for cemented sockets implanted with structural femoral head autografts have been reported in the literature, with some mid-term and long-term studies describing revisions due to graft collapse or acetabular component loosening. Chougle et al. reported a high rate of aseptic loosening of the cemented acetabular component with structural bone grafting, reaching 63% at 20 years (73). Kobayashi et al., on the other hand, used a cemented cup with a bulk femoral head autograft (mean socket coverage by the graft 33%) and reported a mean follow-up of 19 years with no radiographic evidence of cup fixation failure (49).

Abdel et al. utilized uncemented cups with a mean cup coverage by femoral head autografts of 30% and published a 20-year follow-up with 66% survivorship free from acetabular revision; notably, only one of fourteen cup revisions was performed for aseptic loosening (74). When more than 30% of the cup contact area is supported by graft, the risk of failure increases due to graft reabsorption and collapse (49, 50, 75). Smaller implants have the advantage that the relative contribution of the host bone to the cup support increases.

Fahlbusch et al. reported long-term outcomes of THA in patients with DDH with a minimum follow-up of 21 years (76). Overall, implant survivorship was 98% at 10 years and 84% at 20 years. Clinical outcomes were acceptable, with a mean Harris Hip Score (HHS) of 78. As expected, superior results were noted in patients with lower Crowe grades.

Engesæter et al. analyzed survivorship data from 14,403 THAs performed for pediatric hip sequelae using combined Danish, Norwegian, and Swedish arthroplasty registers (77). Unadjusted analysis demonstrated a 10-year survivorship of 94.7% for pediatric hip sequelae compared with 96.6% for primary osteoarthritis. However, after adjustment for age, sex, and fixation method in a Cox regression model, 10-year survivorship was comparable (93.6 vs 93.8%), and no statistically significant difference in overall revision risk was observed.

Jin et al. evaluated the survivorship of THA performed for high dislocation secondary to DDH or prior septic arthritis (78). Failures were predominantly related to the acetabular component (90.9%), often associated with deficient bone stock and technical challenges inherent to high dislocation cases.

Prior pelvic osteotomy has been shown to reduce the 10-year revision-free implant survival rate of THA to 92.0%, compared with 95.4% in patients without previous osteotomy (79). A higher incidence of cup loosening has also been reported; however, this finding may be related to the greater severity of dysplasia typically present in patients who have undergone prior pelvic osteotomies (79). The 15-year cup survivorship was 90% (95% CI: 86–94%) in patients with prior acetabular surgery, compared with 92% (95% CI: 90–94%) in those without previous acetabular procedures (80).

Historically, THA in young patients has been associated with higher revision rates and reduced implant survival. However, more recent studies have reported excellent mid- to long-term outcomes in this patient population, including those with DDH (4). Implant survivorship in patients under 40 years can be excellent, reaching 97% at 10 years, with no differences observed between etiologies, including DDH (4).

These improvements are likely attributable to advances in implant design, modern cementless fixation techniques, and the widespread use of highly cross-linked polyethylene.

Outcomes

Patients with DDH frequently present with significantly worse baseline function prior to surgery than those with primary OA. However, at one year postoperatively, the DDH group demonstrated significantly greater improvements across different outcome measures (OHS, WOMAC, and SF-12) (81).

Patients undergoing THA for OA secondary to DDH were significantly younger than those treated for primary osteoarthritis and had lower rates of severe medical comorbidities (82). However, they demonstrated higher odds of developing postoperative anemia compared with patients with primary OA.

THA outcomes in patients with DDH were compared with those in patients with primary OA, focusing on revisions, dislocations, and failure mechanisms (83). Patients with DDH were significantly more likely to undergo revision surgery, with a 66% higher risk compared with OA patients. Regarding dislocations, DDH patients had a higher risk (OR: 1.78), but this difference was not statistically significant (83). Overall, while revision risk appears significantly increased in DDH, the evidence for higher dislocation rates remains inconclusive.

Amanatullah et al. reported no significant differences in clinical outcomes between patients undergoing THA after periacetabular osteotomy performed with a modern abductor-sparing approach and a matched cohort undergoing THA for DDH without prior osteotomy (21). Furthermore, a previous shelf acetabuloplasty does not negatively affect THA survivorship in DDH patients (84).

In Crowe IV DDH, despite a relatively high complication rate, functional outcomes remain favorable. The mean postoperative HHS was 88.6, representing a mean improvement of 46.8 points. Residual postoperative leg length discrepancy averaged 0.9 cm, corresponding to a mean correction of approximately 3.4–3.9 cm (5).

For THA in Crowe III and IV hips, no significant differences have been found in HHS or major postoperative complications (fracture, infection, or dislocation) among patients treated with different surgical approaches (anterior, anterolateral, or posterior) (31).

Approximately 38% of patients experience persistent, generally mild to moderate, limping after THA for DDH (72, 76). In addition, 16.5% of patients demonstrate a postoperative Trendelenburg sign, reflecting residual abductor dysfunction (76). Despite anatomical acetabular reconstruction in Crowe IV hips, up to 19% of patients may still require assistive devices due to disruption of the abductor mechanism and alterations in overall biomechanics resulting from chronic dislocation (85).

The controversy between anatomic and HHC reconstruction is likely to persist. Current evidence suggests no significant differences in clinical outcomes or revision rates between the two techniques, although the HHC reconstruction is associated with a higher incidence of dislocation, a reduced need for femoral shortening osteotomy, and a lower incidence of neurological complications (Table 4) (86).

Table 4.

Survivorship and outcome of acetabular reconstruction techniques with an anatomic and high hip center.

	Hips, n	Mean FU, months	Crowe grade	Revision of any component	Other findings
Anatomic hip center
Christodoulou et al. (89)	70	103	Hartofilakidis A, B and C	2.9% cup revisions	Neurologic complications: 4.3%; dislocation rate: 2.9%
Watts et al. (90)	70	84	II: 89%; III: 11%	No revisions	Anatomic hip center had a lower incidence of acetabular loosening (0 vs 17%, P = 0.007) and cup revision (0 vs 28%, P = 0.0002); dislocation rate 4%; no femoral osteotomies
Sun et al. (91)	33	121	IV: 33	No revisions	Subtrochanteric shortening osteotomy in all cases; three dislocations; two intraoperative femoral fractures; mean LLD from 3.8 to 0.8 cm
Ors et al. (92)	127	100.6	IV: 127	2.3% cup revisions	Subtrochanteric shortening osteotomy in all cases; dislocations 3.9%; intraoperative femoral cracks 55%
High hip center
Nawabi et al. (93)	27	156	II and III	3,7% (one stem revision)	Cup medialization; no difference in the Kaplan–Meier survivorship compared to anatomic hip center in 23 patients with Crowe I
Momtalti et al. (94)	84	181	III: 44; IV: 40	6% (one cup revision)	Two dislocations and two sciatic nerve lesions; no femoral osteotomies; the average distance between the inter-teardrop line and the head–neck junction was 38 ± 6 mm for Crowe III and 45 ± 7 mm for Crowe IV
Berniunger et al. (95)	61	38	II: 30; III: 25; IV: 6	1.6% (one up revision)	Activity of daily life and gait reduced for group with reconstructions >75 mm above inter-teardrop line; no dislocation, impingement problems or neurologic complications; no femoral osteotomies
Shen et al. (96)	85	106	II: 46; III: 36	2.4%	No differences for HHS, WOMAC score, Trendelenburg sign, and limp when hip center was 25.1 ± 1.6 mm or 33.1 ± 4.8 mm above the inter‐teardrop line; no femoral osteotomies; one revision for dislocation and another for osteolysis

HHS, Harris Hip Score; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index; FU, follow-up; LLD, limb length discrepancy.

Complications

Globally, patients undergoing THA for DDH have a higher overall risk of revision than those treated for primary OA. However, when all grades of dysplasia are considered together, the rates of dislocation, infection, and aseptic loosening may not differ significantly between the groups (83). However, when the analysis is limited to severe cases, particularly Crowe type IV hips, complication rates increase significantly. In a recent systematic review focusing on Crowe IV dysplasia, dislocation rates reached 7.2%, revision surgery 8.7%, intraoperative fractures 10.5%, nerve palsy 5.6%, deep vein thrombosis 3.6%, and deep infection 3.8%. Dysplastic hips have several inherent risk factors for dislocation, including excessive native anteversion, insufficient acetabular coverage, abductor weakness, and the common necessity for smaller acetabular components, which in turn limit femoral head diameter. A dedicated meta-analysis of dislocation risk factors in DDH identified Crowe IV classification (OR: 2.70), higher cup inclination, and femoral head size <28 mm (OR: 5.07) as significant predictors of instability (72, 87).

The choice of acetabular reconstruction strategy also affects the risk of instability and neurological complications (particularly sciatic nerve palsy). Excessive limb lengthening during the reduction of a chronically dislocated femoral head increases the likelihood of traction nerve injury (in Crowe IV hips, nerve palsy rates of around 5–6% have been reported). A systematic comparison between HHC and anatomical reconstruction suggested a higher tendency for dislocation with proximal cup placement, and fewer neurological complications were observed with this cup positioning, probably due to reduced tension on the sciatic nerve (86).

Infection rates in DDH THA seem similar to those documented in other complex primary arthroplasties. Notably, postoperative infection has been identified as an independent risk factor for dislocation, highlighting the interconnected nature of complications in this group (87).

The complication profile of THA in DDH differs from that of OA, with the risk rising as the severity of dysplasia increases, particularly in Crowe IV hips. Complications are closely related to the acetabular reconstruction strategy, cup positioning, limb-length restoration, and implant selection.

Limitations of current literature

Despite the growing body of literature on THA in DDH, several important limitations constrain the interpretation and generalizability of current evidence.

First, most available studies are retrospective case series with relatively small sample sizes. Since high-level evidence remains scarce, and randomized controlled trials are virtually absent, many conclusions rely on heterogeneous observational data, often with inconsistent inclusion criteria and outcome reporting.

A key limitation is the frequent pooling of dysplasia of varying severity within the same cohorts. Outcomes and complication profiles differ substantially between low-grade and high-grade DDH, particularly in Crowe IV hips, yet many studies do not stratify results accordingly. This lack of severity-specific analysis may obscure clinically relevant differences and limit the applicability of findings to complex cases (72, 83).

There is considerable variability in surgical techniques and reconstruction strategies across the literature. Differences in acetabular reconstruction techniques (anatomic versus HHC), bone grafting, and implant selection introduce significant clinical heterogeneity. Furthermore, the definition of anatomic and HHC reconstruction varies substantially across studies. This variability limits comparability between studies and weakens the validity of pooled analyses.

Outcome reporting also lacks standardization. Studies report radiographic parameters, functional scores, or complication rates, often without consistently using validated patient-reported outcome measures. Definitions of complications, such as instability or nerve injury, are not uniform across studies.

Follow-up duration is another important limitation. Many studies report short- to mid-term outcomes, which may underestimate late complications (72). This is particularly relevant in DDH, where patients are typically younger and implant longevity is a critical consideration.

For navigation and robotic-assisted THA, most studies include mixed patient populations, making it difficult to isolate the specific benefits of these technologies in dysplastic hips. Furthermore, the majority of studies focus on radiological accuracy rather than long-term clinical outcomes or revision rates.

Finally, potential publication bias must be considered. Many reports originate from high-volume specialized centers, which may limit generalizability to lower-volume settings and overestimate the reproducibility of favorable outcomes.

Future directions

One of the most promising developments lies in advanced preoperative planning with CT-based three-dimensional reconstruction, offering a more detailed evaluation of acetabular morphology and spatial anatomy in dysplastic hips (70). Future planning strategies should go beyond merely targeting inclination and anteversion and should include impingement risk modeling and spinopelvic balance (88).

Robotic-assisted and navigation-guided THA offer the potential for more consistent restoration of inclination, anteversion, and hip center of rotation. Considering that increased cup inclination and smaller femoral head diameters have been linked to a higher dislocation risk in DDH, technologies that improve positional accuracy may significantly influence stability rates (87).

Conclusion

Acetabular reconstruction in DDH is a complex field that warrants specialized care and evaluation of strategies. The decision between anatomic and HHC reconstruction must take into account the location of the optimal bone stock to achieve primary stability and long-term biological fixation of the cup, the planned leg length restoration, and the extent to which joint biomechanics can be restored. Ideally, the reconstructed center of rotation should be as close as possible to the anatomic position, although a placement 1–2 cm above remains a valid and viable alternative.

In Crowe I dysplasia, placement of an uncemented cup with slight medialization at the anatomic position is usually achievable. In Crowe II and III, a small uncemented or highly porous small cup with slight medialization positioned anatomically or at a mild HHC (avoiding lateralization) has shown good mid-term results. Structural autogenous bone grafts or metal augments can be used to improve component coverage. Cemented cups are also a viable option, provided adequate bone support is available.

Finally, in cases of high dislocation (Crowe IV), a small uncemented cup in the true acetabulum is an option, but femoral shortening osteotomy is usually required. Alternatively, a HHC acetabular reconstruction can be considered, which can avoid the need for femoral osteotomy.

Overall, the surgeon must recognize the complexity of dysplasia, the surgical challenges, and patient expectations in order to thoroughly plan the dysplastic acetabular reconstruction and deliver the best functional outcome possible.

ICMJE Statement of Interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding Statement

This research did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.