Total Hip Arthroplasty for Crowe Type IV Hip Dysplasia: Surgical Techniques and Postoperative Complications.

Total hip arthroplasty (THA) of Crowe type IV developmental dysplasia of the hip (DDH) is challenging. Although traditional (lateral, posterolateral, and posterior) THA approaches have been used with great anatomic success, they damage periarticular muscles, which are already quite weak in type IV DDH. The recently developed direct anterior approach (DAA) can provide an inter-nerve and inter-muscle approach for THA of type IV dysplasia hips. However, femur exposure with the DAA could be difficult during surgery and it is hard to apply femoral shortening osteotomy. THA techniques used for type IV DDH include anatomic hip center techniques (true acetabular reconstruction) and high hip center techniques, wherein an acetabulum is reconstructed above the original one. Although anatomic construction of the hip center is considered "the gold standard" treatment, it is impossible if the anatomical acetabular is too small and shallow. Procedures used to support type IV DDH reduction with anatomic hip center techniques include greater trochanter osteotomy, lesser trochanter osteotomy, and subtrochanteric osteotomy. However, these techniques have yet to be standardized, and it is unclear which is best for type IV DDH. One-state and two-state non-osteotomy reduction techniques have also been introduced to treat type IV DDH. Potential complications of THA performed in patients with type IV DDH include leg length discrepancy (LLD), peri-operative femur fracture, nonunion of the osteotomy site, and nerve injury. It is worth noting that nowadays an increasing number of Crowe type IV DDH patients are more sensitive to postoperative LLD.

Introduction

Developmental dysplasia of the hip (DDH) is a condition characterized by morphological abnormalities of the acetabulum and femur. During its diagnosis, DDH is classified according to dislocation severity, most commonly based on the Crowe rubric, wherein type IV is the most severe of four types1. Due to the pathological anatomical changes that accompany this condition, primary total hip arthroplasty (THA) is complicated and difficult in patients with Crowe type IV (type IV from here forward for simplicity) DDH, especially the hip reduction component of the operation.

In the 1970s, John Charnley introduced the trochanteric osteotomy for complicated primary hip replacement, including in patients with type IV DDH2. Subsequently, additional operation techniques, with and without osteotomy, have been developed to facilitate reduction during THA. Although several such surgical protocols have been reported to yield excellent results, each has drawbacks. Poor bone stock, massive soft tissue release, lengthened legs after surgery, and anatomical abnormalities can put type IV DDH patients at risk of postoperative complications, such as leg length discrepancy (LLD), peri‐operative femur fracture, nonunion of the osteotomy site, and nerve injury1, 3, 4.

The primary aim of this paper was to review THA procedures, including introducing a direct anterior approach (DAA) THA procedure, for use in patients with type IV DDH. Potential reasons for postoperative complications in type IV DDH patients and options for their management are discussed. We conducted a search of the PubMed database with the keyword “dysplasia hip” and a date range of 1 January 2012 to 31 December 2019, which yielded approximately 2400 potentially relevant studies. From the retrieved literature, we excluded studies involving pediatric patients, pelvic osteotomy, and/or low‐grade (i.e. dislocation type) DDH. Ultimately, we included 64 papers related to THA for type IV DDH in this study.

Direct Anterior Approach Total Hip Arthroplasty

Traditional THA approaches, including lateral, posterolateral, and posterior approaches, have been reported to yield excellent results in patients with DDH3, 4, 5, 6. However, these traditional approaches are associated with some degree of muscle injury, with postoperative dislocation rates of up to 16.6%7. Type IV DDH is associated with hip muscle weakness that may put these patients at particular risk of postoperative dislocation8.

In THA, a DAA enables the hip muscles to be accessed through inter‐nerve and inter‐muscle pathways, and has been gaining favor. Compared with other approaches, a DAA has advantages of faster recovery, less pain, and a lower postoperative dislocation rate9, 10. Hence, at least theoretically, a DAA seems to be the most appropriate approach for THA. Oinuma and colleagues described a case series of 12 totally dislocated hips treated by DAA THA with subtrochanteric osteotomy11. For the operations, they placed each patient in a supine position with the operating table adjusted to 15°–20° to put the patient’ s body in hyperextension. To expose the distal femur, which can be difficult in type IV dysplasia if a subtrochanteric osteotomy is needed, they released the posterior hip capsule, piriformis tendon, obturator internus, and the superior and inferior gemelli. The proximal femur was then moved out of the wound and femoral canal reaming was completed. Blunt dissection of the vastus intermedius was completed to enable subtrochanteric osteotomy to be completed. Over a mean follow‐up period of 3.7 years, Oinuma et al. did not observe any occurrences of motor nerve palsy or infection and no revision operations were needed11. This non‐occurrence of postoperative complications was attributed to abductor muscle preservation, which also enabled full weight‐bearing by 1 week postoperatively, compared with 3–16 weeks with traditional approaches. In a study of 50 dysplastic hips subjected to DAA THA and follow‐up MRI 1 year later, Kawasaki and colleagues noted damage to the gluteus minimus, obturator internus, and tensor fasciae latae without damage to the gluteus medius and piriformis12.

Potential drawbacks of DAA THA include risk of nerve dysfunction, intraoperative femoral fracture, wound complications, early femoral failure, and dislocation. Such complications may be avoided by experienced DAA operators; however, the DAA learning curve is steep13, 14, 15, 16.

Traditional Approaches for Total Hip Arthroplasty

Reconstruction of the acetabulum at its original position is now the generally accepted optimal choice. The main anatomic hip center techniques share common elements. On the acetabular side, a femoral head resection is performed, followed by identification of the true acetabulum, which can be found by following the inferior joint capsule17 or by identification relative to the transverse and round ligaments18. After the true acetabulum has been exposed by removal of scar tissue and osteophytes, it can be reamed to the appropriate size and placed in an appropriate cup and liner. Original acetabular reaming commences with a small reamer, taking care to avoid overreaming of the anterior or posterior acetabular column. According to Zhu and Li19, after preoperative mapping, reamers can be held with a 30°–50° abduction and 5°–25° anteversion position and the acetabulum should be reamed postero‐superiorly to maximize cup coverage. Finally, a cup inclination angle of −40° with a 20°–25° anteversion is generally appropriate. After cup insertion, doom screws are inserted to improve cup stability. According to Tikhilov et al., doom screws provide reliable cup stability when there is >65% cup coverage. Additional cup support techniques can be performed if there is <65%–70% cup coverage. The resected femoral head is used for bone autografting7, 19, 20, 21, 22.

On the femur side, the first step is to expose the proximal femur, followed by intramedullary reaming with modular or custom implants (special reaming tools are provided by the manufacturer). If the femoral anteversion is <25°, a monoblock stem can be selected; if a non‐modular stem is recommended, femoral stem anteversion should be adjusted to 15°–20°. Then, a trial stem is inserted into the medullary cavity and reduced as needed. If sufficient stem reduction cannot be achieved after releasing the soft tissues, then osteotomy should be considered. Osteotomy should be planned for preoperatively if the leg will be lengthened by ≥3–4 cm to reduce the risk of sciatic nerve complications. Prior to completing the hip reduction, to facilitate reduction, extensive soft tissue releasing should be completed, including (potentially as needed) release of the adductor, iliotibial tract, gluteus maximus, iliopsoas, rectus femoris, sartorius, piriformis, gracilis, and biceps femoris. All aspects of soft tissue release should be done in accordance with the specific operative conditions and case characteristics. During post‐hip‐reduction leg‐length lengthening, which may be quite extensive in these patients, the hip and knee are kept in flexion to protect the sciatic nerve. Postoperatively, the flexion angles of the joints should be decreased gradually according to the patients’ neurological signs8, 18, 20, 21, 23.

In general, the question of whether the acetabular or femoral side procedures should be completed first is dependent on operator preference. In some cases, the sciatic nerve is separated at the beginning of the operation and then palpated later to confirm preservation of moderate tension. Because type IV dysplasia hips have substantial anteversion of the acetabulum and femur, combined anteversion of the limb under 55° (20°–25° and 15°–20° for the cup and stem, respectively) is used to avoid postoperative dislocation. Following this principle, in a series of 16 type IV dysplasia hip cases, Zhu and colleagues24 set the cup anteversion according to the native acetabular anteversion to enable preferable cup coverage. Following subtrochanteric osteotomy, they rotated the proximal femur backward to maintain appropriate combined anteversion. Preoperatively, the mean (±standard deviation) femur, acetabular, and combined anteversion extents were 57.5° ± 9.6°, 31.0° ± 2.4°, and 88.6° ± 9.4°, respectively. After THA, the mean femur, acetabular, and combined anterversion extents were 17.9° ± 2.9°, 31.2° ± 2.5°, and 49.2° ± 2.6°. No dislocations occurred during 12 months of follow up20, 21, 24, 25. The main complications that occur following application of an anatomic hip center technique are summarized in Table 1.

Table 1

Outcomes and complications of anatomic hip center techniques

Study	Osteotomy form	Patients (hips)	Mean age (years, range)	Mean follow‐up (years, range)	Preoperative function Score	Postoperative function score	Osteotomy Site malunion	Nerve syndrome (temporary/permanent)	Post‐surgery dislocation	Intraoperative fracture	Preoperative LLD (cm, range)	Postoperative LLD (cm, range)	Revision hips
Kose et al. 27	Transverse	15(21)	41.0 (24–56)	5.0 (3–8)	HHS: 36.2 ± 9.8	HHS: 90.8 ± 2.5	0	1/1	2	5	*	*	2
Ozan et al.28	Transverse	25 (25)	51.4 (35–70)	5.1 (2–7)	HHS: 49.5 (25–72)	HHS: 87.1 (74–94)	1	0/0	3	*	3.6 (1.0–5.5)	0.5 (0–1.5)	0
Imarisio et al.29	Transverse	17 (18)	50.0 (33–71)	4.2 (1–10)	HHS: 52 (38–71)	HHS: 89.0 (78–97)	0	1/0	2	1	4.8 (0–7.5)	0.8 (0–4)	0
Zhou et al.14	Transverse	62 (76)	46.5 (19–73)	10.0 (6.6–13.2)	HHS: 38.8 (21–59)	HHS: 86.1(76–98)	1	2/0	3	4	4.3 (2.1–6.5)	1.0 (0.6–1.7)	2
Zarei et al.31	Transverse	48 (52)	41.0 (19–55)	*(1–3)	HHS: 41.70 (32–46)	HHS: 88.1(74–94)	0	2/0	0	0	5.0 (2–7)	1.0 (0–2)	1
Liu et al.32	Transverse	45(52)	40.6 (18–62)	9.8 (8.9–11.8)	HHS: 33.7 ± 4.7	HHS: 89.8 ± 7.1	0	2/0	2	0	4.38 ± 0.75	0.71 ± 0.37	0
Kılıçoğlu et al.33	Oblique	16 (20)	43.4 (27–60)	6.8 (3.7–10.3)	HHS: 50.0(32–69)	HHS: 83 (75–93)	1	0/0	3	3	*	1.0 (0–3)	2
Bianchi et al.34	Oblique	12 (16)	53.2 (34–70)	8.7 (4–13)	HHS: 37.2 (24–58)	HHS: 83.7 (65–97)	1	0/0	3	2	*	*	0
Vicenti et al.35	8 cases Z‐shaped and 9 cases transverse	15 (17)	38.6 (28–68)	7.3 (5.3–11.1)	HHS: 38.3 (32–52)	HHS: 85.6 (69–90)	0	2/0	0	1	4.5 (3.8–7.0)	1.2 (0.9–1.6)	0
Neumann et al.36	Z‐shaped	12 (16)	58 (20–67)	5.0 (3–8)	HHS: 35.9 (20–65)	HHS: 94.3 (82–100)	0	0/0	0	0	3.0 (0–7.0)	8 cases < 1, 1 ≤ 4 cases≤1.5	0
Hasegawa et al.37	Z‐shaped	18 (20)	58.5 (48–72)	10.2 (5–20)	HHS: 56.1 (54–65)	HHS: 84.5 (77–93)	0	2/0	3	0	3.8 (0.5–7.3)	1.4 (−1–5.5)	4
Sonohata et al.38	Double chevron	28 (36)	58.0 (39–77)	7.3 (5–13)	JOA: 48.1 ± 18.1	JOA:83.1 ± 13.7	1	1/0	4	3	*	*	2
Koulouvaris et al.41	Distal transverse	24(24)	45.8(22–69)	4.6(2.3–6.0)	MAP: 9.96 (6–12)	MAP:17.2 (15–18)	1	*	*	*	2.0 (0–4.5)	0.16 (0–0.28)	0
Hartofilakidis et al.45	Greater trochanteric	140 (192)	50.0 (23–77)	* (10–34)	*	*	32	5/3	6	*	*	*	71
Zhao et al.47	Lesser trochanteric	28 (30)	35.3 (17–67)	4.6 (2–11)	MAP: 9.3 (6.1–11.5)	MAP: 15.9(12.1–17.2)	†	2/0	0	3	4.7 (0.7–‐6.2)	0.8 (0.3–1.5)	0
Wu et al.52	None	46(50)	*(38–77)	6.4 (2.2–11.5)	HHS:40.2 (*)	HHS:86.5 (*)	†	0/0	1	0	*	1.3 (0–1.6)	0
Yan et al.50	None	25 (28)	33 (19–58)	*(1–4.2)	*	HHS:87.3 ± 10.6	†	4/0	0	0	4.6 (3.0–6.5)	0.5 (0–1.6)	0
Zhu et al.51	None	74 (82)	55.8 (20–80)	5.1 (2–8)	HHS:42.1 (24–71)	HHS:89.9 (76–100)	†	0/0	1	1	*	0.4 ± 0.5	1
Imbuldeniya et al.49	None	21 (25)	47.0 (23–89)	18.7(15.8–21.8)	HHS: 46 (29–63)	HHS: 90 (73–98)	†	0/0	1	2	*	1.1 (0–1.6)	17

*Never mentioned in original paper. †Impossible for this condition to occur. LLD, leg length discrepancy.

Because it is difficult to reconstruct the hip center at its original position in type IV DDH cases involving a small, shallow true acetabulum, the high hip technique, wherein the acetabulum is reconstructed superior to the anatomic one, may be employed26. Using a high hip center technique in a cohort of 84 patients, Montalti and colleagues obtained mean vertical and horizontal distances from the rotational center of 33 ± 8 mm and 30 ± 5 mm in type III DDH cases and IV DDH cases, respectively27. After 15 years, revision was performed in only 2 of those cases due to aseptic loosening (one cup and one stem)27. Galea et al. obtained mean hip center heights of 21.2 mm and 28.4 mm superior to the inter‐teardrop line (ITL) in a THA study involving 74 non‐dysplastic/Crowe type I hips and 49 type II–IV dysplastic hips, respectively28. After a mean follow‐up period of 13.8 years, the patients treated for type II–IV DDH had a mean Harris hip score of 89.9; none of the patients suffered dislocation, and hip center height was not associated with Harris hip scores or polyethylene wear rate. However, patients with type IV DDH are at increased risk of postoperative dislocation and of needing revision surgery following hip center reconstruction. In a 30‐year follow‐up study of 49 patients with type II DDH, Watts et al. found cup and stem loosening rates of 68% and 29%, respectively, in cases with a reconstructed hip center that was ≥35 mm superior to the ITL, versus 35% and 18%, respectively, in cases with a hip center that was <35 mm superior to ITL29. In a retrospective review of 1079 THA‐treated patients with DDH with a mean follow‐up of 74.3 months, Komiyama et al. found that mean hip center height was significantly greater in dislocation cases (29.7 mm superior to the ITL) than in non‐dislocation cases (24.1 mm superior to the ITL)30.

Osteotomy Techniques

When an acetabular prosthesis is placed in a type IV dysplastic hip, osteotomy is always needed to facilitate reduction while avoiding nerve complications7. Specifically, osteotomy helps to prevent soft tissue contracture and to protect the sciatic nerve by lessening leg lengthening7, 31. Osteotomy techniques used for this purpose include greater trochanter, lesser trochanter, and subtrochanteric osteotomy. Subtrochanteric osteotomy can be performed several ways, including transverse, oblique, double chevron (V‐shaped), step‐cut (Z‐shaped), and sigmoid methods (Fig. 1).

Figure 1

Types of subtrochanteric osteotomy: (A) transverse, (B) oblique, (C) double chervon, (D) step‐cut, and (F) sigmoid.

Transverse osteotomy is the simplest osteotomy technique. It requires only two transverse cuts to the femur below the lesser trochanter and does not require the use of any specialized instruments. Before the first cut, an upright line should be made along the long axis of the femur with an electric knife to serve as a rotational alignment marker. The first transverse cut is 1 cm distal to the lesser trochanter (−10 cm below the tip of greater trochanter). After a trial stem and head have been applied, the proximal femur can be reduced into the acetabulum. The distal femur should be tracked distally with appropriate force, and then the overlapping portion of the femur should be removed by the second transverse cut. After preparation of the distal femur, a femoral component is inserted. With a non‐modular stem, the original excess anteversion of the femur can be restored to a normal range by rotating the two femur fragments. If the reduction is not satisfactory due to insufficient femur removal, a repeat osteotomy can be performed (Fig. 2)17, 18, 32, 33, 34.

Figure 2

Transverse osteotomy procedure: (A) after distal traction, overlapping femur is resected and the femoral anteversion can be adjusted; (B) the removed overlapping femur bone piece is split vertically into two hemi‐cylinder‐shaped halves; and (C) after final insertion of the femoral prosthesis, the two hemi‐cylinder‐shaped halves of the resected overlapping femur piece can be used to support fixation of the osteotomy site.

In oblique osteotomy, the first osteotomy line is made approximately 1 cm below the lesser trochanter, like in transverse osteotomy except that the line is made at an angle (upward or downward lateral). Although some authors have suggested a 45° oblique osteotomy line, to our knowledge, a significant association between line angle and operation outcome has not been established (Fig. 3)35, 36.

Figure 3

Oblique osteotomy procedure. Upward lateral and downward lateral osteotomy lines are introduced with angle “a” between them. It has been recommended that angle “a” should be 45°, although an optimal angle has not been demonstrated empirically.

Double chevron osteotomy can also be performed as a combined double chevron osteotomy, wherein a transverse osteotomy is first completed to shorten the femur and then the proximal and distal fragments are adjusted to an appropriate anteversion. The transverse osteotomy geometry is then remodeled into a double chevron. After a transverse cut of the femur has been made and the length of femur to be removed has been determined, the double chevron osteotomy site can be marked with ink and then proximal and distal chevon osteotomies can be completed with a reciprocating saw. Double chevron osteotomy can be completed with specialized devices as well, such as multi‐holed broaches, femoral cutting slot guides, and guide pins37, 38, 39.

A step‐cut osteotomy can be done alone or in conjunction with a transverse osteotomy. In the latter case, the transverse osteotomy is completed first to shorten the femur, then the step‐cut osteotomy is completed to enhance rotational stability. For the step‐cut osteotomy, the femur is first cut in the transverse axis 2–5 cm below the lesser trochanter. Then, the reduction is completed after a stem is placed in the proximal part of the femur. After traction of the distal femur part, the length of overlap is taken as the overall femur length that should be eliminated, with half of the bone volume to be eliminated being taken from the proximal femoral fragment and half being taken from the distal femoral fragment. If the femoral anteversion needs to be adjusted by osteotomy, the half‐bone‐volume of the distal femoral part is removed while the proximal part is held at the appropriate position (Fig. 4)40, 41, 42.

Figure 4

Step‐cut osteotomy procedure: (A) after distal femur traction, the length of overlap (a) is determined and femoral anteversion is adjusted; (B) mirrored proximal (b1) and distal (b2) femoral fragments are removed, such that a = b1 = b2; and (C) final insertion of femoral prosthesis is performed (c = a = b1 = b2).

For a subtrochanteric osteotomy, the location of cuts may be proximal or distal. With a distal osteotomy, valgus knee deformity can be corrected in the process of femur shortening. However, a distal osteotomy requires a long incision43.

Among the subtrochanteric osteotomy types, transverse osteotomy has generally been favored due to its procedural simplicity, satisfactory clinical outcomes, and relatively high error‐tolerance. Step‐cut and sigmoid osteotomies have been shown to provide greater rotational stability and more bony surface contact to support early bone tissue union than transverse osteotomies31. However, to our knowledge, they have not been shown to lead to superior clinical results. Meanwhile, the corners of a step‐cut osteotomy may be at increased risk of fracture31. In contrast, transverse, oblique, step‐cut, and double chevron osteotomies were found to have statistically similar levels of stability in a biomechanical experiment44. In a meta‐analysis of 37 studies (795 hips), Li and colleagues found that modified osteotomy (oblique, step‐cut, and double‐chevron) techniques were associated with bone union, nerve palsy, dislocation, and revision rates and clinical Harris hip scores that were similar to those obtained with classic transverse osteotomy45.

Trochanteric osteotomy, originally developed from low‐friction arthroplasty2, presents advantages for THA of dysplasic hips, including favorable exposure of the acetabulum and proximal femur and a substantial abductor lever arm after reattachment of the greater trochanter. However, trochanteric osteotomy has been reported to have a relatively low bony union rate (82%) and, thus, conversely, a high nonunion rate (1%–32%)2, 46, 47. Lesser trochanter osteotomy has been used to treat high dislocated dysplasia hips. Although it can result in better bony union than subtrochanter and trochanter osteotomies, it limits the femur length reduction extent that is possible and has been associated with abductor weakness48.

No Osteotomy Total Tip Arthroplasty

Total hip arthroplasty of dislocated dysplasia hips can be completed without osteotomy in a one‐stage or two‐stage protocol. Obviation of the osteotomy has several potential benefits: (i) avoidance of the risk of osteotomy site nonunion; (ii) no femur shortening, which may lead to truly equal‐length legs; and (iii) no need for internal femur fixation.

In two‐stage THA, the first stage involves femoral head resection, soft tissue release, and prosthesis insertion. At the conclusion of the first stage, an external fixator system is constructed with pins and distraction tubes around the hip to pull the femur gradually into a more distal location until the femoral neck is at the level of the anatomic acetabulum. Approximately 2 weeks later, in the second stage, the external fixator system is removed and THA of the affected hip is completed. Two‐stage THA reduces neurovascular damage risk, but the use of pins in the first stage may lead to infection risk and patients need to spend more days in the hospital than with other methods49.

One‐stage THA without osteotomy has been reported to produce excellent long‐term functional results but has been associated with three notable drawbacks: (i) challenging hip reduction; (ii) high sciatic nerve complication risk; and (iii) difficulty achieving appropriate soft tissue release8, 23, 50, 51. Methods that have been used to facilitate hip reduction in single‐stage THA without osteotomy include use of a low femoral‐neck osteotomy line (as low as the lesser trochanter)50, powerful pharmacological muscle relaxation combined with a special reduction position23, and artful usage of a Hohmann retractor51. To our knowledge, the evidence regarding sciatic nerve complication risk in single‐stage THA without osteotomy is inconclusive. Notwithstanding, insufficient soft tissue release during single‐stage THA can lead to unsuccessful reduction, whereas excessive soft tissue release may lead to a high dislocation risk and hip dysfunction postoperatively. To address this soft tissue release challenge, Wu and colleagues recommend releasing of the following muscles, in this order, until sufficient release is achieved: (i) adductor, iliotibial tract, and gluteus maximus; (ii) iliopsoas, rectus femoris, and sartorius; and, finally, (iii) piriformis and hamstrings8. If reduction remains difficult after release of all of these muscles, Wu and colleagues recommend osteotomy8.

Postoperative Complications

Following THA, LLD is a common complication, especially among patients who present with a severe unilateral dislocation. Postoperative functional LLD in patients treated for type IV DDH is affected by many factors, including bony LLD, pelvic tilt, pelvic imbalance development, spinal lateral curve, spinal deformity, and postoperative prosthesis position. Li et al. found an average bony LLD of 3.5 ± 3.0 mm (bony leg length measured from greater trochanter tip to ankle center) in a sample of 78 type IV DDH patients (70 unilateral and 8 bilateral)52. Zhang et al. measured skeletal limb length (from the femoral head tip to the midpoint of the tibial plafond) of 67 unilateral DDH patients (32 Hartofilakidis type II and 35 Hartofilakidis type III) and found that skeletal limb length on the affected side was >5 mm longer than that on the contralateral side in one‐third of the patients53. Meanwhile, Bilgen et al. reported that the acetabular area on the affected side was 11 mm more distal than that of the contralateral side in Crowe type IV DDH patients54. To protect the sciatic nerve, leg length is often sacrificed by ostoetomy in cases of a severely dislocated femoral head and extensive soft tissue contracture. Although any single factor alone may not disrupt postoperative functional LLD, they may have a clinically significant combined influence on LLD.

Leg length discrepancy is a common post‐THA complication and concerns related to LLD can cause anxiety and depression in DDH patients55. Fujimaki et al. found that patient outcomes are compromised when LLD is ≥5 mm after THA56, and Chen et al. noted that a postoperative LLD of ≥10 mm leads to gait asymmetry57. When clinically significant LLD does occur after THA, additional physical therapy should be applied for 6 months. If physical therapy does not correct the problem satisfactorily, then a shoe lift should be considered. In severe cases, a second surgery can be performed. If the contralateral hip is also in need of THA, then the LLD can be solved with the contralateral operation58. Thakral et al. introduced a surgical technique for contralateral leg lengthening to correct LLD59. If contralateral leg lengthening is contraindicated, shortening of the THA leg may be considered60.

Due to the narrow femoral canal, intra‐operative femur fractures can occur in 5.2%–26.8% of THA cases20. These fractures can be treated with wire‐plate internal fixation. If the femoral canal is too narrow to allow insertion of the smallest available stem, then the femur can be split anteriorly and posteriorly for 4–10 cm6.

A challenging reduction process during THA can put patients at increased risk of osteotomy site nonunion (rate range, 2.8%–7.1%)20. Nonunion risk can be mitigated with plate and screw fixation27, 31, an eagle claw hook and cable system,3 or the application of cerclage wires to two longitudinally split halves of resected femur35.

The main causes of nerve injury complications in DDH patients continue to be debated. Eggli et al. have suggested that nerve injury is caused mainly by direct damage during the operation, rather than leg lengthening61. However, excessive limb lengthening is considered by many surgeons to be the main cause of post‐THA nerve injury. If so, limiting the extent of lengthening to no more than 3–4 cm may reduce nerve injury risk. When osteotomy is applied during THA, reported nerve injury rates range from 5% to 11.3%20. However, in most cases, nerve injury symptoms resolve within 6 months. Even among patients who suffered nerve injury following hip reconstruction at the anatomic acetabulum with extensive leg lengthening (>4 cm), with a nerve injury rate of 14.3%, patients’ nerve symptoms recovered quickly51. Methods used to prevent nerve injury include separating the sciatic nerve and applying palpitation to control its tension21, nerve stimulation62, and femur traction with delayed postoperative reduction63.

Conclusion

Despite the characteristic complications associated with the approach, THA by a DAA can produce satisfactory treatment outcomes for type IV DDH. High hip center reconstruction produces satisfactory clinical results in the short term but has been associated with higher long‐term revision and dislocation rates than reported for reconstruction at the anatomical acetabulum. Reconstruction of type IV DDH at the original acetabulum requires femur osteotomy to enable appropriate hip reduction and prevent nerve injury. Greater trochanter osteotomy, the first procedure applied to treat type IV DDH, produces poor union conditions at the osteotomy site. Meanwhile, lesser trochanter osteotomy treatment of type IV DDH has the drawbacks of limited femur length shortening and a high risk of femur head dislocation. A variety of subtrochanteric osteotomy techniques have been applied to THA for type IV DDH, including transverse, oblique, double chevron, step‐cut, and sigmoid methods. All of these subtrochanteric osteotomy techniques can produce excellent clinical results, with transverse osteotomy being appreciated for its simplicity and the other more complicated techniques being appreciated for their ability to provide greater rotational stability than transverse osteotomy. No‐osteotomy THA methods can also provide satisfactory outcomes for type IV DDH but are associated with elevated risk of complications, such as LLD, intra‐operative femur fracture, osteotomy site nonunion, and nerve injury.